BOUGHT WITH THE INCQMB FROM THE '- SAGE ENDOWMENT FUND ■--"^ .- THEGlK^COE, - '•i ' IS9X- A'iSimL \ ' ■ :, iy///./i ^ « Cornell University Library TN 270.C88 Prospecting for minerals; a practical han 3 1924 004 446 187 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004446187 THS "N^Smr X4.&N^I>" SSRIEIS OF PRACTICAL HANDBOOKS FOR THE USE OF PROSPECTORS, EXPLORERS, SETTLERS, COLONISTS, AND ALL INTERESTED IN THE OPENING-UP AND DEVELOP- MENT OF NEW LANDS. EDITED BV GRENVILLE A. J. COLE, M.R.I.A., F.G.S., PROFESSOR OF GEOLOGY IN THE ROYAL COLLEGE OF SCIENCE FOR IRELAND. In Large Grown 8uo, with Illustrations. [NOW READY. VOL. I.— PROSPECTING FOR MINERALS.— By S. Herbert Cox, Assoc.R.S.M., M.Inst. M.M., F.G.S. SHORTLY WILL BE ISSUED. VOL. II.— FOOD SUPPLY. — By Robert Bruce, Agricultural Superintendent to the Roj'al Dublin Society. VOL. III.— BUILDING CONSTRUCTION IN WOOD, STONE, AND CONCRETE.— By Jas. Lyon, M.A., Professor of Engineering in the Royal College of Science for Ireland, sometime Superintendent of the l^ngineering Department in theUniversity of Cambridge; and J. Taylor, A. R. C.S.I. *«* Other Volumes will follow, dealing- with subjects of primary importance in the Examination and Utilisation of I/ANDS which have not as yet been fully developed. G£:rrrrxx I— I EH Oh & A » O £h 14 •a 1 Quartz crystals. j Distinctly crystalline ; some j are volcanic. Some are volcanic. With hornblende, augite, or mica. With homblende.augite, ormica. Finely crystalline. Compact. Mica. X • ■ : • : : : : : Vitreous Matter. : i : : : X X X : : : X X X X X Olivine. : : : X : : i : I X X Quartz. X : X : : X : : : : X : : : : : Magnetite or Tit. Iron. • • J ; X : : : X | I : : : X X Augite. : : : : X : : : X X : : ■ X X X Hornblende. : X X X 1 I X X ■; i X X X • I : Plagioolase.* i 1 X X X : : X X X • • X X X X Orthoclase or Sanidine. X X 1 • 1 X X • 1 I X X i i 1 1 i % |2! Granite Syenite, .... Quartz diorite, Diorite, .... Gabbro, .... ^ ...._. Quartz porphyry (Elvan, &c. Fine grained syenite, . Fine grained diorite, . Dolerite, .. Diabase, Rhyolite, Trachyte, Hornblende-andesite, . Augite-andesite, . Anamesite, . Basalt Pitchstone, . Tachylyte, . Perlite, Obsidian, Pumice, CHAKAOTBK. Hydro- thermal. Trappean (rocks of in- termediate grain). Volcanic. Glassy (usually volcanic). a < O M *■§ 03 43 a 43 i;5 4* ft ® 2 « o s »- gi a> O ■35 ft Id P443 o '00 ^ ft o a :g§ 2 53 1: 8-3 .a o ■a a (B O 00*> . eS .. 00 ^^ " fl> o § eS o 10 PEOSPECTING FOE MINEEALS. Volcanic rocks are those which have reached the surface, either through volcanoes or simple fissures, and have been distributed as lava streams or as volcanic dust, &c. ; they have very marked differences in structure, dependent upon their chemical composition. The trachytes contain a large propor- tion of silica, and are generally of a grey colour ; they consist of hornblende and sanidine, which is a transparent variety of ortho- clase. It must be remembered that in true trachytes no free quartz occurs, and that when quartz crystals are developed, or when there is an excess of silica in the glassy ground, the rock becomes a rhyolite. On the other hand, there is a series of basic volcanic rocks in which the percentage of silica is not high, and these are known collectively as basalts. Basalt consists of augite and magnetite, with a certain quantity of one of the triclinic felspars, and, generally, olivine ; these rocks are named basalt, anamesite, or dolerite, according as they are fine grained, of medium, or distinctly crystalline structure. There is also a series of intermediate rocks between trachytes and basalts, known as andesites, in which the hornblende-andesites consist of hornblende and a triclinic felspar, and are allied to the diorites ; whilst the augite-andesites are very closely allied to the basalts, but contain more silica in their composition. Sedimentaey Rocks. The meclianically formed sedimentary rocks consist of mud, clay, sand, and gravel, together with their corresponding shales, slates, sandstones, and conglomerates, which have been produced by consolidation of the sediments. They are also at times changed, by a process of metamorphism, analogous to what takes place in the formation of granite, to schists, gneiss, or quartzite. The organically formed rocks comprise limestones and coals, the former being produced by the accumulation of the shells of molluscs, &c., which have extracted lime from the water to form their covering ; the latter, by the growth, decay, and submer- gence of trees and plants. Besides these, certain beds, such as gypsum, magnesian limestone, and rock salt, have been pre- cipitated from solution in inland waters, such as the Dead Sea, or Great Salt Lake of Utah. Movements of the Rocks.— These varied rocks which have either, as the sedimentary deposits, been formed under water, or, as the eruptive rocks, intruded through other beds at all times during the geological history of the Earth, have, since their INTRODUCTION AND HINTS ON GEOLOGY. 11 formation, been subjected to numerous changes. Some have been raised from the sea without being tilted to any extent from their original horizontal position ; others have been folded into most fantastic shapes ; and others again have been completely in- verted. In other cases, movements which have taken place since the rocks became solidified have caused fractures, and by the rocks on one side of the crack sliding on those on the other, faults have been produced. Without entering into any of the theories which have been propounded to account for these movements, it may be stated that, even at the present day, great and important movements of the land are continually taking place ; in some parts the land is slowly rising from the sea ; in others, a continued but gradual subsidence is going on. Earthquakes, moreover, produce slight oscillations of the land, and thus a redistribution of the land and sea is in constant progress. There is ample evidence, in the occurrence of fossiliferous rocks which enter into the structure of important mountain ranges, that these oscillations of the land have also occurred in the past, and the varying angles at which the different sedimentary rocks are lying show that in many cases they must have been subjected to a lateral pressure, which has produced the crumpling of the rocks already referred to, and, in some cases, the dislocations or faults which have also been mentioned. Where the rocks have been folded in the form of an arch, they are said to form an anticlinal ; and where they occupy a basin, they are spoken of as forming a synclinal. Widespread folds of the foregoing nature are called ge-anticlinals and geo- synclinals respectively ; and it is interesting to note that in the areas occupied by ge-anticlinals the rocks are generally so much broken and jointed that they offer great facilities for removal by the ordinary denuding agents ; hence it is hardly to be wondered at that ge-anticlinals generally occupy valleys and depressions on the present surface of the earth. Not only is this the case with large structural movements, but the ordinary anticlines and synclines, which are of more local character, are found to exhibit the same peculiarity ; for the synclines generally constitute the hills, while the anticlines occupy the valleys. Geological Observations in the Field. — While it is not necessary for the prospector to make accurate geological surveys of the country on which he is engaged, it is very often of im- portance for him to obtain some idea of its structure ; as upon 12 PROSPECTING FOR MINERALS. this may frequently depend the value, or otherwise, of special areas to which he may be inclined to devote his attention. More especially in stratified deposits, such as coal, is this of importance ; but, even when dealing with lodes, it is frequently useful to study the distribution of the rocks in order to discover what effect those of different nature exert upon the mineral deposits. In examining the surface of a country in which the rocks are of sedimentary origin, it will be found, as a rule, that the beds are inclined at varying angles to the horizon, and in making a geological survey of any special district it is necessary to note the dip and strijke of the rocks at every available point. When any well-marked bed occurs, such, for instance, as a seam of Fig. 1.— Plan. coal or belt of conglomerate or limestone, its line of outcrop should be carefully followed and mapped ; the boundaries of any eruptive rocks should also be clearly delineated on the plan. The strike of a rock is the direction of a horizontal line in any of the beds ; or, in other words, the direction in which a level drive would be put in on the floor of the bed. The dip is a line at right angles to the strike on the plane of the beds, and the angle is to be measured in relation to the horizon. When any particular bed is followed on the surface, it is often found that it does not continue with the same strike for any great distance ; that, in fact, it gradually veers round, as shown at (a) in the sketch, the direction of the dip changing at the same time. By a study of a plan thus made the positions of the anticlines and synclines can be determined, and other lines of elevation can also be noted ; and a section constructed, INTRODUCTION AND HINTS ON GEOLOGY. 15 such as the following, which serves to convey a very fairly accurate conception of the structure of the country. As a matter of fact, the boundaries of rocks are sometimes rather obscure in consequence of the variable movements which have occurred ; but the occurrence of faults and dykes is what makes this tracing of boundaries on the surface most difficult. The Fig. 2.— Section. displacements due to faults may be only an inch or so, or may be several hundred feet ; while in a few exceptional cases, as, for instance, in the fault which crosses Scotland from Dunbar to the Ayrshire coast, the displacement may be as much as two or even three miles. A study of faults is of very great importance, more especially on account of their close association with mineral lodes ; but faults should never be assumed for the purpose of explaining difficulties which are encountered in mapping the surface geology, unless very good evidence of their existence can be found, and until every other means of explanation of the phenomena has been tried and found wanting. 14 CHAPTER II. THE DETERMINATION OF MINERALS. The determination of the more important minerals which may be met with deserves special attention at the outset of the subject, and the present chapter will be devoted to the simpler means of distinguishing them. It is not, however, intended to encroach upon the detailed study of mineralogy, on which sub- ject the many valuable treatises published can be consulted. When minerals occur in a sufficiently pure state, they are generally crystallised more or less perfectly, in certain definite forms— e.g'., pyrites, calcite, and garnet — but many minerals, especially those forming sedimentary rocks, are composed of very minute grains, in which either the crystalline form has been imperfectly developed or the minerals are altogether amorphous — e.g., earthy limestone, coal, and massive pyrites. A few are incapable of crystallisation — e.g., amher and lim.onite. Mineralogy treats only of natural inorganic substances which have the same composition throughout ; but rocks, which may be composed of several minerals, either crystallised or not, some- times exhibit on a large scale regular forms, which must not be considered as due to crystallisation, but to the process of oooling ; or to cooling and drying, and the consequent contrac- tion. Compact basalt, for instance, which has been formed in a molten state, is frequently divided during cooling into more or less regular prisms, which are often six sided ; and some of the extensive beds of gypsum near Paris have, in drying, assumed the form of huge prismatic pillars. There are certain physical properties of minerals which are of importance in their determination, regarding which a few notes will be of interest. Structure. When minerals do not occur either in isolated crystals or in distinct groups, but consist of aggregated crystalline or compact particles, they affect different kinds of structure ; and this struc- THE DETERMINATION OF MINERALS. 15 ture, besides assisting in the determination of minerals, is of economic importance ; for on it depends the value of certain minerals for ornamental purposes. Granular Structure, of which sandstone may be taken as a type, is produced by more or less rounded grains being cemented together. A coarse granular structure is best seen in chrome iron-ore, in which the grains, since they are not cleavable, can be noticed at once. Galena and zinc blende are often more or less granular ; but, since both these minerals cleave readily, the fracture is lamellar when the grain of the ore is coarse. If, however, they are fine grained, these, in common with many other ores- — e.g., copper glance, cinnabar, pyrrhoiine, and, more rarely, enargite and stibnile — exhibit a fine granular structure, and are sometimes so fine grained as to approach more or less perfectly to a compact texture. Saccharoid Structure. — When the mineral is composed of small crystalline grains, showing facets and cleavages, the structure is called saccharoid — e.g., statuary marble and alabaster. Lamellar Structure. — When the crystalline particles are minute and flat, being laid one on the other, the structure is termed scaly — e.g., chlorite ; while a true lamellar or laminar foliated structure, which is best seen in talc and mica, also exists in molybdenite, and more rarely, and in a less perfect manner, in nickel glance. Capillary structure is best illustrated by asbestos, the fibres of which are readily separable ; but a similar structure may be noticed in some specimens of millerite, the fibres being easily separable, but small, brittle, and generally radiating. Only a few other minerals possessing this structure could be mentioned, and an equally small number occur in velvet or tuft-like ex- crescences. Fibrous structure is the term employed to describe those minerals in which the fibres cannot be easily separated, and is generally to be observed in minerals crystallised in a lode perpendicular to the walls of the fissure; but is sometimes developed parallel to the walls, or even in radiating groups. In the first two cases the fibres are straight, as in chrysotile, which forms small veins in serpentine, and is only a variety of ser- pentine itself; and again, in calcite and gypsum, two minerals which sometimes exhibit this structure, but do not ordinarily possess it; both fibrous calcite and fibrous gypsum have been called satirirspar, and are cut as ornaments. The fibrous radiate structure is conspicuous in malachite, wood tin, and some 16 PROSPECTING FOE MINERALS. hcematites ; is ■well marked in stalactites of oalcite, ha/rytes, and calamine, while gothite, spherosiderite, and apatite may also, be mentioned as occurring in radiating fibrous forms. Minerals possessing this radiate structure are often called " concretions," but many concretions consist of concentric layers where there is no sign of crystallisation, and must, therefore, be distinguished from those in which crystallisation exists. Radiate Structure is not only found in minerals formed of minute needle-shaped crystals, but stout prismatic crystals with pyramidal ends are sometimes arranged in radiating groups, as in the case of amethyst quartz when crystallised in vughs or cavities in rocks or lodes. Pyrites also, and azurite, when found in ball* which have crystallised in a semi-liquid mud, exhibit the above structure. When radiating crystals assume a slender prismatic form they diverge from one another, sending their needle-shaped projections in every direction around the centre, like spines on a sea urchin ; pyrolusite, stibnite, and natrolite occur in such forms. Bacillary Structure is the term used to describe those minerals which occur grouped in bundles like sticks — e.g.,Epidote. Dendritic Structure. — Where many crystals are attached one to the other, like beads in a necklace, and especially where these diverge like the branches of a tree, they are called dendritic. Native coj)per, silver, and gold frequently occur in this form, and oxides of iron and manganese are often found in the joints of rocks crystallised in the most beautiful fern-like forms. Concretionary Structure is affected by uncrystallised minerals- which have grown from a centre in concentric layers ; and may also be seen in certain rocks — e.g., basalts, sandstones, &c., in which decomposition has taken place around centres. Where nodules have grown around a centre in mud or loose sand, the form i& spherical or nearly so. Many valuable ores of iron occur in spherical forms; extensive deposits (oolitic iron) formed entirely of small grains occur in the Jurassic system of Europe ; pisolitic ores, in which the grains are the size of a pea, are found in the Tertiary rocks, and similar ores also occur in serpentine. In the Jurassic system, oolitic limestones composed of small perfectly round grains of carbonate of lime occur, and a similar structure is developed in the calcareous sand on the shores of the Great Salt Lake at Utah. The centre of these nodules is sometimes formed of a mineral grain, and very often of a fossil plant, fish, or shell. In slaty rocks the nodules are flattened and irregular in shape, and are sometimes mistaken for fossils. THE DETERMINATION OP MINERALS. 17 Mammillary Structure. — When concretions have been formed at the same time around several centres, which are at regular distances apart, a mammillary structure is induced — e.g., chalcedony, which is very variable in form and size ; different modifications are described as botryoidal (like a bunch of grapes), reniform (kidney-like), &c. Nodules of ironstone with fossil fish occur in the Carbonifer- ous and Permian systems of Europe, and nodules of cement stone in the Cretaceous rock of New Zealand. When deposition takes place around a stick, the concretion has the form of a cylinder, this structure being very common in some bog iron ores ; and eart.hy cobalt ores are found under the same conditions in New Caledonia, where they occur in a decomposed diorite associated with serpentine, and have accumulated around the roots of existing trees. Concretions of manganese ore are also formed in the depths of the sea. Vitreous Structure. — When minerals exhibit no sign of crystallisation they are called amorphous ; and some which do not possess the power of crystallising can be distinguished as having a compact or vitreous structure — e.g., amber. Cleavage. Crystallised minerals have a tendency to split more readily in some directions than in others ; this property is termed cleavage. In some minerals the cleavages are so easy that, in transparent varieties, the planes of cleavage can be seen through the crystals, this being often the case in Iceland-spar, orthoclase, and barytes. In the cube and rhombohedron, in which the faces are all of the same shape, there are three directions of cleavage parallel to the sides — e.g., galena and rpcksalt in the cube, and calcite, dolomite, and siderite in the rhombohedron. These cleavages are very apparent and are good characters for recognition of these minerals. - The most useful instance of cleavage is that which occurs in the diamond, in which there is an easy cleavage parallel to the sides of the octahedron ; advantage is taken of this property in shaping diamonds for cutting. If the blade of a knife is applied in the proper direction, a smart blow will effect the cleavage. In six-sided prisms there is an easy cleavage parallel to the base in some minerals — e.g., beryl or emerald and apatiie. In the rhombic prism there is also frequently an easy cleavage parallel to the base — e.g., topaz and talc. Barytes, which crystal- 2 18 PROSPECTING FOE MINERALS. lises in modified rhombic prisms, has two easy cleavages parallel to the sides of the prism, and one parallel to the base. In the oblique prisms oiorthoclase there are two easy cleavages, one parallel to the base and another at right angles to the first and parallel to the oblique diagonal. They are at right angles to one another, hence the name of the mineral. Cleavage is also a property of certain rocks — e.g., slates — and is most perfectly developed in roofing slates of good quality. In quarrying sandstones advantage is taken of the joints of the rock to divide it into building stones and slabs of different thickness, which have subsequently to be dressed on th(i sides as required ; but these properties of jointing and cleavage in rocks are of quite diff'erent origin from the cleavage of minerals, being due entirely to stress or pressure in various directions after the consolidation of the rooks, and have no relation whatever to the composition of the rocks, whereas, cleavage in minerals is a structural peculiarity, which is constant in certain mineral species. Lustre. The term lustre is employed by mineralogists to describe, with certain adjectives, the brilliancy or gloss of any substance. In describing the lustre, well-known substances are taken as the types, and such terms as adamantine lustre (diamond-like) and vitreous lustre (glassy) are used. When minerals do not possess any lustre at all they are described as " dull." The lugtre of a mineral is quite independent of its colour. The terms usually employed to describe the lustre of minerals are as follows : — 1. Metallic. 5. Resinous. 2. Semi-metallic. 6. Greasy. 3. Adamantine. 7. Nacreous. 4. Vitreous. 8. Silky. These terms are purely arbitrary for, although a plate of polished silver may be taken as the best type of metallic lustre, this is also exhibited by all the metals irrespective of their colour, and by most metallic sulphides, such as pyrites, stibnite, &c.; hence no distinct line can be drawn between those minerals pos- sessing a metallic lustre and those coming under the sub-metallic group, of which diallage and anthracite may be taken as types. The lustre of minerals will frequently vary — (a) As they are more or less impure. (6) As other physical properties vary. THE DETERMINATION OP MINERALS. 19 In illustration of the iirst class of variations, window glass may be taken as the type of vitreous lustre ; but glass can be made to exhibit a lustre approaching that of the diamond, mother of pearl, opal, &c., by the admixture of certain chemical substances. Something approaching an adamantine lustre can be imparted to glass by lead, and the same effect can also be obtained, although with greater intensity, by substituting the rare metal thallium, which is very closely allied to lead in its chemical properties. Very good imitations of the diamond are made in this way, which are sometimes difficult to detect by a superficial examination. The second class of variations may be illustrated by gypsum, which has a vitreous lustre when crystallised, but a silky lustre when fibrous. Many minerals possess a different lustre on different faces ; pyrosmalite, for instance, which crystallises in the form of a six- sided prism, has a semi-metallic lustre on the sides, while the ends are greasy or nacreous. Calcite and gypsum are vitreous on some faces, and nacreous on others ; and the same may be said of celestine, orpiment. and orthoclase. The lustre of minerals may be taken advantage of for the first subdivision in a scheme for recognition ; and for this purpose it is only necessary to divide them into those which have a metallic lustre and those which no not possess this property. Metallic and Semi- Metallic Lustre. — The first term needs no definition ; all metals in the native or pui-e state, and especi- ally the noble metals, exhibit this quality in the highest degree, and are, indeed, so bright when polished that they can reflect images perfectly. Some sulphides have a perfect metallic lustre, and iron pyrites was formerly used by the Indians of South America to make their mirrors. All metallic sulphides have a metallic lustre, with the exception of zinc blende and cinnabar, which are adamantine ; although some black varieties of zinc blende containing much iron might be described as metallic- adamantine ; and hauerite (sulphide of manganese), which has but an imperfect metallic lustre. Without Metallic Lustre. — This group includes a large number of minerals, many of which are of commercial value ; and it will be well at this point to call attention to those which possess an adamantine lustre. Of these, the diamond affords the most perfect type of adamantine lustre, although other well- known minerals can also be considered as good illustrations — e.g., cassiterite when in pure and shining crystals, zircon, and 20 PEOSPKCTING FOR MINERALS. cerussite. It may be well to again reiterate the fact that colour has nothing to do with this property of lustre. Most minerals whose lustre is adamantine are very heavy ;. the diamond is lightest — sp. gr. 3"5 ; then octahedrite, blende, and gothite — sp. gr. about 4. Between 4 and 5 sp. gr. another variety of titanic acid called rutile and also zircon occur ; between 5 and 6 sp. gr. valentinite, cuprite, emholite, pyrargyrite, and proustite are found ; between 6 and 7 sp. gr. crocoisite, cerussite, anglesite, and vmlfenite — all of which are lead minerals ; these and calomel, or chloride of mercury, have an adamantine lustre ; and between 7 and 8 sp. gr. may be noted cassiterite, or oxide of tin ; mimetite, and pyromorphite — both of which are lead minerals ; wolfram, or the tungstate of iron and manganese, and cinnabar. A few of these — e.g., rutile, pyrargyrite, and wolfram — have a metallic adamantine lustre. Out of the twenty minerals mentioned above as possessing an. adamantine lustre, the diamond is the only non-metallie mineral ; the remaining nineteen are metallic, and of these 6 are compounds of lead, 2 ,, „ silver, 2 ,, ,, mercury. The remarkable property possessed by lead of imparting an adamantine lustre to minerals and artificial products is well known, and is taken advantage of in the imitation of precious stones, but the greater the proportion of lead employed, the softer is the glass formed. Colour. The colour of minerals may be due to four different causes \ but in some cases it is difficult to say to which of these groups coloured minerals belong. Group 1. — Those in which the colour of a mineral is that which it would possess when pure, or when artificially formed. Group 2. — Those in which the colour is due to the mixture of substances crystallising in the same form, and replacing one another in the composition of a mineral. Group 3. — Those in which the colour is due to a small quan- tity of colouring matter, dissolved in a mineral, by -which its chemical composition is not greatly affected. Group 4. — Those in which the colour is due to a mechanical mixture of substances, which are not dissolved in the mineral,, but can easily be distinguished on microscopical examination. THE DETEEMISATION OF MINERALS. 21 In this group are included those minerals whose colours are due to mere impregnation. Group 1. — The first group can be illustrated by the following examples : — Black. — Graphite, coal, and black oxide of copper. Blue. — Azurite and lapis lazuli. Green. — Malachite, libethenite, dioptase, atacamite, nickel ■ochre, texasite, and bromargyrite. Yellow. — Sulphur, amber, orpiment, and wulfenite. Orange.— Realgar. Red. — Cuprite, pyrargyrite, cinnabar, red ochre, and red iisematite. Pink. — Erythrine, diallogite, and rhodonite. White or Colourless. — Nearly all the alkaline and earthy minerals when pure — e.g., barytes, gypsum, calcite, meerschaum, ■cryolite, and quartz. It will be seen that nearly all coloured minerals of the first group are metallic, although none are included in the above list whose lustre is metallic ; they are, with few exceptions, anhydrous oxides of the metals, metallic sulphides, antimonides or arsenides. A few minerals possess a metallic lustre and characteristic colour, as follows : — Violet to Copper Red. or Violet Brown. — Erubescite or bornite. Indigo Blue (semi-metallic). — Covelline. Greenish Grey. — Tin pyrites. Brass Yellow.— Millerite and copper pyrites. Copper Red. — Native copper. Light Copper Red. — Nickeline, breithauptite. Reddish Silver White. — Cobaltine. Reddish Brown (due to tarnish ; normal colour on fracture, tin white to steel grey). — Domeykite. Yellowish Brown to Copper Red. — Pyrrhotine. Violet Brown. — Nickel pyrites, sternbergite. Brown Black.— Hauerite. Group 2. — The most common instances of colour due to the interchange of isomorphous substances are those of the carbon- ates of iron (siderite), of manganese {diallogite), of lime (calcite), and of magnesia and lime (dolomite). The two first are coloured, while the other two are colourless or white ; but, since they can replace one another in any proportion, siderife, which is yellowish, 22 PfiOSPECTING FOR MINERALS. and diaUogite, of a fleshy colour, will impart a shade of colour to calcite or dolomite when combined with them. Kerargyrite and hroiaargyrite are also isomorphous ; the first is grey in colour, the second dark green; and mixtures of the two, or chlorobromides of silver termed eTuholite, (fee, are of all shades from grey to dark green, according to the relative pro- portions of chlorine or bromine they contain. Group '6. — Very little seems to be known of those substances, a very small proportion of which at times impart bright colours to minerals. The colour so derived may be described as acci- dental, since the trace of colouring matter does not greatly afiect the chemical composition of the mineral, and in this class may be included all the gems. Diamond, which is colourless when quite pure, is occasionally red or blue, and then attains a fabul- ous value ; but is more frequently yellowish, brown, or black. Corundum is commonly blue (sapphire), red (ruhy), more rarely yellow (oriental topaz), and still more rarely green (oriental emerald) or violet (oriental amethyst). Topaz is colourless, yellow, or light blue. Emerald, beryl, and aqua marine are the same species, but the first is of a rich deep green and the others of a pale bluish-green colour. The colouring matter of the emerald is still uncertain, for, although some analysts are said to have found chromium present, the emerald loses its colour at a red heat, at which temperature oxide of chromium should not be destroyed ; this seems to suggest an organic matter as the colouring agent. Quartz, which in its pure state is colourless, often occurs milky, smoky, or black, more rarely yellowish (citrine quartz), imitating topaz or violet (amethyst). A crystallised variety from Spain is hyacinth red, and a compact variety pink. Amongst minerals other than gems three are most remark- able on account of the different colours they assume, these are fluor-spar, apatite, and rock-salt. Fluor-spar and apatite occur in nearly the same shades of colour, ranging from colourless to white, pink, red, yellow, green, blue, violet, and the intermediate hues. Rock-salt is found colourless, white, red, yellow, and blue. A variety of orthoclase, remarkable for its apple-green colour, is found in Siberia and Colorado. The colouring substance is still unsettled, although stated by some to be copper. It is not always easy, or, indeed, possible, to draw a clear line between the coloured minerals of Groups 2 and 3. If the most notable groups of the silicates be taken — e.g., the hornblende, augite, garnet, epidote, and tourmaline groups — it is found in THE DETERMINATION OP MINERALS. 23 each that, while all the minerals composing the group obey the same laws of crystallisation, and only vary in composition within certain limits, the minerals are white, colourless, or highly coloured, according to the proportion of colouring matter, chiefly oxides of iron, manganese, and chromium, present. In the hornblende group there are white, or nearly white, varieties (asbestos and tremolite), which do not contain iron ; an inter- mediate variety (actinolite), which contains a small quantity of iron, is green ; and a third variety (hornblende), which contains a large proportion of iron, is black, or nearly black. In the augite group there is a variety (diopside) which is generally transparent, colourless, or pale green, and contains only traces of iron ; while two other varieties are nearly black, and contain large proportions of iron and manganese. In the garnet group there is a variety (grossularia) which is white or very pale green, and contains very little iron ; a red variety (almandine), used as a gem, and containing much iron ; a black variety (melanite), also containing much iron ; and a green variety (uwarowite), containing much chromium. In the tourmaline group the substances which impart colour are more difficult to determine precisely. Those containing much iron are brown or black ; the green contains iron and manganese ; the red contains manganese and no iron ; and the colourless contains no iron, and only a trace of manganese. All the colourless and light-coloured red and green varieties also contain lithia. Group 4. — The substance which most frequently colours rocks and minerals mechanically is oxide of iron, imparting a brownish or red colour to earthy-looking minerals and rocks, and it is to this also that the yellowish and reddish colours of some sand- stones and limestones, used for building purposes, is due ; although, in some marbles, the colour is said to be derived from organic matter. The nickel ore of New Caledonia, which consists of silica, magnesia, and oxide of nickel, seems to be, in some varieties at least, only silicate of magnesia impregnated with oxide of nickel. In some mines the silicate of magnesia exists nearly or quite free from nickel, and of a pure white colour, whence it passes through all shades to the richest green. Some specimens under the microscope show the green oxide of nickel disseminated in grains through the white silicate of magnesia. In some cobalt and nickel mines in Germany stalactites of carbonate of lime are coloured pink by a mechanical impreg- nation of arseniate of cobalt. 24 PEOSPECTINQ FOR MINERALS. The silicates and carbonates of zinc are white when pure, but the presence of iron as a mixture often gives them a yellow colour ; and calamine, when blue, is coloured by copper. Hardness. The hardest substance known in nature is the diamond ; all other minerals can be scratched by it. Between this and the softest — e.g., talc and horn-silver — certain minerals have been chosen to form a series called the scale of hardness, which is of great use in the determination of minerals. It need hardly be added that the true hardness of a mineral is that which it exhibits when approximately pure, and is best tested in crystallised varieties. Scale ov Haednbss. 2." Gypsum } Scratched by the nail. 3. Calcite 1 4. Fluor-spar > Scratched by steel of ordinary hardness. 5. Apatite ) 6. Orthoclase — Scratched by well tempered steel — not by window glass. 7. Quartz. 8. Topaz. 9. Corundum. 10. Diamond. In descriptive books of mineralogy the hardness of minerals is always expressed by numbers; thus, chromite H. 5 '5, signifies that this mineral will scratch apatite, but can be scratched by orthoclase. Some precautions are necessary when testing the hardness of any mineral. The scratch should be made on a smooth clear surface and with a sharp edge or angle of the scratching mineral. It often happens, if the mineral experimented upon is the harder, that, instead of a scratch, a line of dust is left on its surface. This should be carefully wiped away, when it will be easily seen that no scratch has been produced on the harder mineral, and that the edge of the other has been blunted. This is what would happen if an attempt were made to scratch topaz with quartz or corundum with topaz. Streak. In testing the hardness of minerals another character of im- portance — viz., the streak or colour of the dust formed when a mineral is either scratched or powdered, may be observed. THE DETERMINATION OF MINERALS. 25 M g 5 < II Galena Stibnite Bismuth- ine ■Sg, to M Bourno- nite Freisle- benite Argentite 1^ Gersdorf- fite Mispickel Smaltine Cobaltine 11 1-IJ3 . §1 :: || ::::::: : 1 s Magnetite Pyrolusite Polybasite Enargite Psilomelane Grey copper Stromeyer- ine Copper glance i 1 ^i : : : : : : : : ^■S ^1 : on i II C5 per Mangan- ite Haematite Tennantite (red grey) ■1 Haematite Pyrargy- rite °"3 8S i J 1 Iron-black, . Dark steel- grey, . Steel-grey, . Light steel- j ^grey, . \ Black lead-1 grey, . J" Lead-grey, . Light lead-l _grey, . j" Tin-white, . Silver -white 1 with red- > dish hue, ) 26 PROSPECTING FOR MINERALS. A few minerals which are malleable — e.g., copper glance and silver glance — ^^as well as the malleable metals themselves, instead of giving a dust when scratched afford a shining streak. The streak, however, of most minerals is of a lighter colour than the mineral itself. A certain number of minerals with metallic or semi-metallic lustre are difficult to distinguish by their mere appearance,- their colour ranging from silver-white to iron-black. For a discrimination of these their streak is frequently of value, and the preceding table will be of service in distinguishing them. Regarding these it may be noted that stibnite frequently has a blackish tarnish, hismuthine and domeykite have a yellowish iride- scent, smaltine has sometimes a greyish iridescent tarnish, while gersdorjfite and occasionally galetia are tarnished grey or greyish black. Polyhasite in small crystals is red by transmitted light and the dust of enargite has a metallic lustre. Among the softest minerals a few are malleable like wax — e.g., ozokerite and horn-silver ; whilst others are composed of particles or lamellae so slightly cohesive that they separate when either touched or rubbed, and soil the fingers more or less readily — e.g., molybdenite, earthy manganese, red and yellow ochres, steatite, graphite, &o. Flexibility and Elasticity. Some minerals can be easily bent without breaking — e.g., talc, m,ica, chlorite, molybdenite, native silver, re or less easily. The least fusible mineral of this group is orthoclase, which fuses only when in small scales or fragments. AH those minerals which in very thin scales can only be rounded on the edges will be considered as infusible, or nearly so. (a) On charcoal with soda, before the blowpipe, yield a metallic bead or powder, non-magnetic. KePaPgypite, &e. (see Silver Ores), yield a bead of silver. Atacamite, Malachite, &e. (see Copper Ores), yield a bead of copper, and colour the flame either blue or green. THE DETERMINATION OP MINERALS. 45 Cerussite, &C. (see Lead Ores), yield a bead of lead. Bismuth Ochre (see Bismuth Ores) yields a bead, which is brittle, but not magnetic. Molybdite (see Molybdenum Ores) Is not reduced to a bead, but can be obtained as a powder by crushing the fused mass and washing. The mineral is earthy and yellow in colour, and the coating becomes blue in the reducing flame, but the colour is transient. (b) On charcoal with soda yield a magnetic mass, but it is sometimes necessary to reduce a considerable quantity before the magnetic properties can be observed. Cobalt Bloom (see Cobalt Ores) and Several arsenlates of iFon and. nickel (see Iron and Nickel Ores) afford a smell of garlic on charcoal before the blowpipe, of which cobalt bloom may be distinguished by the blue coloration it imparts to the borax bead. There are several other minerals which do not afford a smell of garlic, as follows : — Wolfram (see Tungsten) ; as heavy as tin ore. Vivianite < see Iron Ores) ; scratched by the nail and blue in colour. Siderite (see Iron Ores) ; scratched by a knife, buff in colour, and powder effervesces with hot acid. Lepidolite (see Micas) ; scratched by a knife ; colour, white, violet, or pinkish ; scaly before blowpipe ; colours the flame crimson. Earthy Hsematite (see Iron Ores) ; scratched by a knife ; gives a char- acteristic red streak and powder. Rhodonite (see Manganese Ores) ; not scratched by a knife ; generally flesh red, powder rosy white ; with borax gives a violet bead due to man- ganese, and a green mass with nitre and carbonate of soda. Garnets (see Gem Stones) are generally crystallised, and are harder than quartz. N'. B. — There are some other silicates which occasionally give a magnetic glass when fused before the blowpipe — e.g., hornblende, augite, and some other ferruginous minerals, such as black tourmaline and epidote. Among the foregoing minerals lepidolitC and rhodonite will only yield a magnetic mass in rare cases when they contain much iron, so they will also appear in another group. (c) Minerals which yield a coloured powder and on charcoal with soda do not yield a metallic bead or magnetic mass. Ultramarine or Lapis Lazuli (see Gem Stones) is blue, with a bluish- white powder, and can be scratched by a knife. N.B. — A closely allied blue mineral, hauync, answers to this descrip- tion, but is only found in volcanic rooks, and is transparent, while lapis lazuli is opaque. ' . Rhodonite (see Manganese Ores) is not scratched by a knife, is generally flesh-red, and the powder rosy-white, while it exhibits the manganese reactions with borax, &o. Garnet (see Gem Stones); generally red-brown or black in colour ; is not scratched by the knife ; generally crystallised ; and specific gravity about 4. Cassiterite (see Tin Ores) ; red, brown, orange-yellow in colour, or black with a light grey or brown powder ; easily reduced with cyanide of potassium on charcoal to metallic tin. 46 PROSPECTING FOR MINERALS. Epidote (see Gem Stones) occurs crystallised in prisms of a dark pistache green ; colour of powder, grey. (d) Minerals which yield a white powder and on charcoal with soda do not yield a metallic bead or magnetic mass. Boraeite (see Gem stones) occurs crystallised in cubes, &c., and is about as hard as quartz. Tourmaline (see Gem Stones) occurs in prisms. This division includes a great number of minerals which are scratched by quartz, some of which are compounds of lime, baryta, strontia, &c., such as anhydrite, selenite or gypsum, barytes, strontianite, witherite, cryolite, fluor spar, and apatite, none of which, with the exception of fluor spar and apatite, are harder than barytes. It also includes a still greater number of silicates, which all, with few exceptions — e.g., lepldolite and magnCSlte — are harder than barytes, and most of them harder than fluor spar. These two divisions will be considered separately, under insoluble SaltS and silieates, and they may mostly be recognised by their physical characters and the colours they impart to the blowpipe flame. III. Before the blowpipe, infusible ; or fusible with more diffi- culty than ortlioclase, being only rounded on the edges when used in very thin scales. (a) As hard as quartz or harder than quartz. N'.B. — All the gems proper are to be included here, except opal, which is scratched by quartz ; and tourmaline, which, in some varieties, is fusible. Tin ore is sometimes as hard as quartz, and being fusible, with great diffi- culty might be found here. It will be reduced on charcoal with cyanide of potassium. AndalUSite (see Gem Stones) is usually found in stout square prisms ; with nitrate of cobalt on charcoal the powder assumes a blue colour. DiSthene or Cyanite (see Gem stones) also assumes a blue colour with nitrate of cobalt, and usually occurs in flattened prisms which are white or blue in colour. Quartz and the other gems do not assume a blue colour with nitrate of cobalt. (6) Scratched by quartz ; powder or streak coloured. Siderite (see Iron Ores) ; powder light brown ; effervesces with hydro- chloric acid when warmed. Diallog'ite (see Manganese Ores) ; powder reddish-white ; borax bead- violet. Limonite or Brown Haematite (see Iron Ores) ; powder yellowish- brown ; usually kidney shaped, concretionary or stalactitic ; on charcoal with soda forms a magnetic mass. Bog Iron Ore (see Iron Ores) ; powder ochre-yellow ; mineral earthy. On charcoal with soda forms a magnetic mass. Chromite (see Chromium); powder brown; mineral, black with a lustre approaching metallic ; borax beads green. On charcoal with soda forms a magnetic mass. Pitchblende (see Uranium Ores) ; powder olive to brown ; colours bead of miorocosmic salt green when cold. On charcoal with soda does not form a magnetic mass. THE DETERMINATION OP MINERALS. 47 Cassiterite (see Tin Ores) ; powder light grey or brown ; elds metallic tin with cyanide of potassium on charcoal. Chlorite (see Silicates of Magnesia) ; colour of powder greenish ; mineral, green in small scales. N-B. — Highly coloured serpentine will give a very light streak or powder, much lighter than the deep green or brown of the rock, and it will appear practically white compared with the colour of the rock itse)f . Some serpentines and the nickel ores of New Caledonia (silicate of nickel and magnesia) will be doubtful in this case, and therefore have also been included in the next group of the table. The nickel ore is apple-green ; its powder is considerably lighter, but becomes green again when moistened. Among the differently coloured serpentines, those altered by exposure, and exhibiting a rusty colour will give a very light, but still yellowish, streak. (c) Scratched by quartz ; powder or streak white or very pale green. Minerals containing alumina in considerable quantity in powder assume a blue colour with nitrate of cobalt on charcoal. Zinc MineFalS under the same conditions assume a green colour. Some Magnesia Minerals under the same conditions assume a rosy hue. StFOntianite (see Insoluble Salts) effervesces with acid and colours the blowpipe flame crimson. Caleite (see Insoluble Salts) effervesces with acid and colours the blow- pipe flame yellowish-red. Barytocalcite (see Insoluble Salts) effervesces with acid and colours the blowpipe flame first red and then yellowish-green. Dolomite (see Insoluble Salts) effervesces with acid only when heated, and has a characteristic pearly lustre. Apatite, Mica, Cassiterite, Rutile, Serpentine, and Silicate of Nickel do not effervesce with acid and will be found under their respective groups. In illustration of the use of these tables, a crystal of cerussite or carbonate of lead may be taken, and it will be found — 1. It is a mineral without metallic lustre. 2. It is insoluble in water. 3. It does not burn or volatilise. 4. Before the blowpipe it melts more or less easily. 5. On charcoal with soda it yields a metallic bead which is not magnetic. 6. The bead is lead, being malleable and giving a yellow coating on charcoal. The mineral, therefore, belongs to the lead ores, and a reference to the chapter devoted to lead will easily distinguish cerussite from other lead minerals, for it effervesces in powder with hydrochloric acid, especially if warmed. 48 CHAPTER III. BOCK-FORMING MINERALS AND NON-METALLIC MINERALS OF COMMERCIAL VALUE. It is difficult to separate these two different classes of minerals, as some which form extensive rock deposits are commercially valuable ; besides which it is inadvisable for purposes of discrim- ination to treat them separately. Soluble salts are not of common occurrence, although some, like rock salt, occur as beds of great commercial value in sedi- mentary formations ; while others, as natron or carbonate of soda, occur as surface efflorescences in dry countries, such as Egypt, where they have no chance of being dissolved and carried away by rain. The varied uses of rock salt are well known ; its principal application is in the soda industries, but the consump- tion for domestic purposes is also considerable. The most important potash mineral, carnallite (which is a chloride of potash and magnesia), occurs in the upper beds of rock salt at Stassfurt in Germany, and is scarcely known else- where ; while the most important mineral source of nitre is nitratine, or cubic nitre, a nitrate of soda found in Peru and Ohili, the working of which has during late yeai s formed a most important and remunerative industry. In ttie district of Tara- paca, at a height of 3300 feet above the sea, the ground has been for about 40 leagues covered with beds of this salt, which were at places several feet in thickness, and associated with gypsum, common salt, glauber salt, and the remains of recent shells. Sulphate of magnesia or Epsom salt, which is much used in medicine, occurs as an efflorescence in mines, especially where pyrites has undergone decomposition in presence of magnesian rocks. It is also found in caves. Another soluble salt of value is borax, which is found crystal- lised on the basins of dried-up lakes in Thibet and California ; in the latter locality, in the Calico district, some important beds of borate of lime are being worked which are interstratified with shales. EOCK-FOEMING AND NON-METALLIC MINERALS. 49 The soluble metallic salts, such as the sulphates of iron, copper, and zinc, are easily known ; they are found, in mines where iron pyrites, copper pyrites, or zincblende have become oxidised, and frequently occur in solution in the waters of certain mines, rendering them quite unfit for domestic purposes. In Southern Spain, the river called Rio Tinto has been so named on account of the quantity of sulphate of copper held in solution b)"- it. It will be readily understood that waters circulating below the surface of the ground dissolve some of these salts, and when they reach the surface as springs frequently contain a greater or less quantity of them in solution. These mineral springs are classiiied according to the minerals they hold in soliition. Earthy Oaebonates and Sulphates, with Apatite, Fluoe Spae, and Cryolite. In this group are included fifteen minerals, only a few of which are very common — viz., ealcite, gypsum, and magnesite, which are of universal occurrence ; while some of the others are abundant in certain localities. Cryolite is only known from Greenland, but being a valuable mineral it cannot be omitted. Five non-metallic minerals may be considered as lode-forming minerals; the most important of these — viz., quartz — will be subsequently described. The four others are ealcite, barytes, witherite, and fluor spar ; while others— e.t?., apatite— occur less frequently in reefs. Carbonate of lime crystallises in two distinct systems, and the name of ealcite or calc-spar is reserved for those crystals which, while occurring in a great variety of forms, can all be reduced by cleavage to a rhombohedron. Calcite occurs in reefs, and sometimes, especially in limestone countries, accompanies auriferous quartz, and even carries gold itself, us at Gundagai and Tuena in New South Wales, and Gympie in Queensland. It also occurs crystallised in rents and fissures in limestone. Although crystallised calcite occurs in metalliferous veins in many countries— e.^?., Derbyshire and Cumberland in England, and the Hartz in Germany — the largest crystals are found in Iceland, where it is very pure and transparent, and is called Iceland spar. It exhibits the property of double refraction most perfectly, and on that account is used in the construction of some optical instruments. Probably Iceland can boast the largest natural crystals in the world, since specimens of calcite are re- corded from there in single rhombohedrons six yards in length. The other species of carbonate of lime is called aragonite 4 50 PROSPECTING FOE MINEEALS. EARTHY CARBONATES AND SULPHATES, WITH APATITE, ELUOR SPAR, AND CRYOLITE. Minerals. Dolomite, . Magnesite, . Hydromagnesite, Calcite, Aragonite, . Strontianite, Witherite, . Barytooalcite, Anhydrite, . Gypsum, . Celestine, . Barytes, Fluor spar, . Cryolite, . Apatite, . Composition. O fCaMg Mg Mg water Ca Ca Sr Ba 3a Ca Ca Ca water Sr Ba rca r lAlNa Phosphate of Ca with fluoride or chloride of Ca. Hard- ness. Specific Gravity. 3i-4 29 H 2-17 3i-ih 3 3 3^-4 2 -5-2 -8 2-9 3J-4 37 3-4 4-3 4 3-6 3-3i 3 14-2 2-3 3-3i 4 24-3i ^ 4 3-1 24 3 5 3-2 Eemarks. Crystals often curved and saddle shaped ; lustre pearly (pearl spar). In serpentine, not common. Lustre sometimes nacreous on cleav- age faces. If burned gives lime. Prisms, often in groups. Lustre greasy on fracture. Lustre greasy on fracture ; occurs in veins. Needle shaped ; yel- lowish-white. Generally found with gypsum and rook salt. When burned swells up, becomes opaque and forms plaster of Paris. Crystals white, often with a bluish tinge. Very heavy; occurs in veins. Occurs in veins ; phosphorescent when heated. Fusible in candle flame. Lustre greasy on cleavage faces and fracture ; angles and edges often rounded. A!, Aluminium ; Mg, Magnesium ; Sr, Strontium ; Ba, Barium ; Oa, Calcium; 2ia, Sodium. ROCK-FOKMING AND NON-METALLIC MINERALS. 51 because some of the most perfect crystals have been found in Aragon in Spain; it crystallises in prisms. Aragonite forms many of the stalactites in limestone caves, and it also occurs in radiated kidney-shaped masses in cavities in basalt. When recently deposited from lime springs and stratified in beds it forms what is known as calcareous tufa or travertine, but •oalcite also occurs in similar deposits. Before the blowpipe aragonite whitens and falls to pieces, but in other respects resembles calcite. The reason for this behaviour before the blowpipe is explained by the fact that under the influence of heat aragonite is changed to calcite and splits up into a number of small rhombohedrons. Limestone forms extensive sedimentary deposits in beds of all ages, and when subjected to metamorphic action takes a crystal- line form, the pure varieties which are white and fine grained, and are suitable for statuary purposes, being called saccharoid marble. Marbles assume every colour and shade according to the substances which are mixed with them ; in the Devonian and Carboniferous formations, where fossil corals are plentiful, marbles are found which exhibit, on polished sections, the star- like forms of the corals of which they are composed. When a marble consists of broken fragments which have been sub- sequently cemented by an infiltration of carbonate of lime it is ■called a brecciated. marble. Marbles which are pure white or of a characteristic colour will always be valuable, but for a deposit to be properly worked the means of transit must be easy. The stone must be free from quartz veins or fossils transformed into quartz, and be •easily obtained in blocks or slabs of large size, suitable for ■ornamental work. Marble has to be sawn with toothless stone cutters, but softer limestones, which have not been metamor- phosed, can easily be cut with a toothed saw ; these softer lime- stones are called freestones, and are used for building purposes; they usually occur in the later formations, such as the Oolitic limestone of Bath, or the Oamaru stone of New Zealand. Lithograpliic stone is a very compact and fine-grained lime- stone, free from veins and fossils, easily cut into large slabs, and of a light colour. A lithographic stone possessing these qualities is not obtained in many places, and will always com- mand a good price. Limestones are also of value for smelting purposes or for burning for quicklime, and, accordins; as they contain certain proportions of other materials, may be of value for the manu- facture of hydraulic lime or cement. It is not, however, possible 52 PROSPECTING FOE MINERALS. for the prospector to determine these properties in the field, and samples should always be submitted to a chemist, and, if sufficient inducement offers, to cement manufacturers. The next most important mineral of this group is gypsum,, which is extensively used for building purposes. It is a hydrous- sulphate of lime, which loses its water and falls to powder when burnt ; this powder, which is perfectly white when free fromi iron, possesses the property of re-absorbing the water lost, and in a very short time of assuming again the solid state, ex- panding slightly in so doing. It is this last property that- renders plaster of Paris so valuable for obtaining casts. Gypsum occurs in lenticular masses of considerable extent in the fresh-water Tertiary formation at and near Paris. The large arrow-head shaped crystals which are to be seen in all collections of minerals are exceptional in these deposits, the whole mass being in a compact sugar-like state. Gypsum also frequently exists in groups of crystals arranged around a centre,, and is found in isolated crystals in salt lakes, such as occur in South and Western Australia, a small proportion of sulphate of lime being present in the water. It is also found crystallised in clay beds in New South Wales and elsewhere. The in- crustations, which form in boilers on board steamers, are mostly composed of sulphate of lime. Gypsum is occasionally found in mines where decomposition of pyrites has taken place in the presence of calc spar or limestone. Anhydrite, which differs from gypsum by the absence of water, occurs in rocks of various ages, especially in limestone and those which contain gypsum, and is also very common in beds of rook salt ; gypsum is often found to proceed from the decomposition of anhydrite. The fibrous structure and silky appearance of some minerals has already been explained, and reference made to the occurrence of calc spar and gypsum in this state, as well as to their value for ornamental purposes. The fine-grained forms of both these minerals are sometimes called alabaster, but the term is gener- ally applied to gypsum. The two varieties can be readily distinguished, as gypsum can be scratched by the nail, while calcite cannot. Dolomite is carbonate of lime and magnesia, and crystallises^ like calc spar. Dolomitic limestones contain variable proportions of magnesia and lime. Very many limestones are thus, partly or wholly, dolomitic, and some of them burn to very good hydraulic limes. The dolomitic limestone of Ohio, U.S.A. , is of special interest as forming the reservoirs in which the petroleum ROCK-FORMING AND NON-METALLIC MINERALS. 53 of that field is stored, it being argued by geologists that the ■dolomitisation has resulted in innumerable small cavities being left in the limestone, which is thus enabled to act like a sponge. Magnesite is carbonate of magnesia. It is rarely crystallised, occurs in talcose schists, serpentine, and other magnesian rocks, and is used for the manufacture of Epsom salt. Pure white magnesite has been observed to arise from the spontaneous de- composition of the heaps of refuse from shafts on mines ; pebbles are quickly cemented together by it, and timber, old tools, &c., •encrusted. Hydromagnesite, which differs from magnesite by contain- ing water, occurs in earthy masses under similar conditions to magnesite. Barytes and Witherite are respectively sulphate and carbon- ate of baryta, and both occur in veins, sometimes with galena or copper ores, as in Spain. Barytes is sometimes found in veins alone, and is mentioned in association with gold at Mitchell's ■Creek, New South Wales. Both barytes and witberite are used in the preparation of baryta and its salts, but witherite is far the more valuable mineral. It is used in sugar refining, and also in the manafacture of plate glass. Celestine and Strontianite are sulphate and carbonate of strontia, and are used in the preparation of the salts of strontia for red fireworks. Celestine is usually associated with lime- stone, gypsum, rock salt, clay, and sulphur, while strontianite is found with galena and barytes in veins. The strong crimson colour imparted to the flame by these two minerals will always easily identify them. The three minerals yet remaining to be dealt with under this group are apatite, fluor spar, and cryolite, all of great value for different purposes. Apatite is a phosphate of lime with calcium chloride or fluor- ide, and occurs under the following conditions : — 1. In metamorphic strata, where it is supposed to have origin- ated from animal matter {Dana). It thus occurs in the Laurentian rocks of Canada in green crystals of large size, and is also found in Norway under similar conditions. 2. As an accessory mineral in metalliferous veins, especially those of tin, and beautifully crystallised and of various colours in many eruptive rocks. 3. In veins by itself, mostly in limestone, but sometimes in granites and schists; e.g., Spain and France. In these deposits apatite also occurs as concretions, sometimes showing a radiated structure, but of an earthy appearance externally. 54 . PROSPECTING FOR MINERALS. 4. In sedimentary formations where a considerable accumula- tion of fossils has provided the i^hosphate of lime. In these de- posits it occurs in two principal forms, (a) Coprolites, which are excreta of large animals, especially Saurians ; and (b) concre- tions formed at the expense of the same coprolites, together with shells, bones, &c. The richest of these deposits are from Lower Cretaceous to Lower Jurassic in age, but phosphatic deposits are found and worked in sedimentary deposits of all ages. .Phosphate of lime is very valuable as a manure, and the deposits included under Groups 1, 3, and 4 are worked for this^ purpose. Fluor Spar is a lode-forming mineral, sometimes alone, but also associated with other minerals, especially tin ore and galena. In the lead mines of Derbyshire and Cumberland, which are in limestone, it is found in beautiful crystals of con- spicuous colours, and, when obtained in blocks of sufficient size,, is worked into vases and other ornaments. In Derbyshire the- blue and purple varieties are known to the miners as "blue John." The presence of fluor spar in metalliferous veins is a great advantage, as it is a valuable flux for smelting, and when found in veins by itself it is mined for the same purpose. In addition to its value as a flux it is also used for preparing hydrofluoric acid for etching glass. Cryolite also contains fluorine, but combined with aluminium and sodium. It forms very fusible compounds, and is used as a- flux ; but its principal application is for the manufacture of aluminate of soda, and as a source of the metal aluminium. It is also used in America for the manufacture of a white glass which imitates porcelain. The two hardest of these minerals are apatite and fluor spar,, and the heaviest are those containing baryta and strontia. All minerals of this group will answer to one of the following tests : — • 1. Effervesce with acids either hot or cold ; Carbonates. 2. Yield a stain on silver when fused with carbonate of soda and moistened with water ; Stilpliates. 3. Etch glass when treated with sulphuric acid in a platinum or lead dish ; Fluorides. 4. Colour blowpipe-flame dirty green when moistened with sulphuric acid, and with magnesium wire in a closed tube evolve the disagreeable smell of phosphuretted hydrogen; Phospliates. A reference to the characteristics in the table will serve readily to distinguish one from the other by the blowpipe tests already given. rock-forming and non-metallic minerals. 55 Quartz and Opal. Quartz is the most common substance with which the pro- spector has to deal, and it is therefore necessary to explain its characters. It is, chemically, silica or silicic acid, a compound of silicon and oxygen ; and it may be remarked that silicon does not exist in nature, except in combination with oxygen, forming quartz and silicates. In the blast furnace silica is not fused, but is reduced in very small quantities to silicon ; whilst fusible silicates or slags are also formed. It is only by combination with oxides, such as lime, alkalies, metallic oxides, &c., that silica forms fusible sub- stances in the blast furnace or before the blowpipe, and these fusible substances are termed Silicates. The highest temperature which can be produced artificially is obtained by the combustion of hydrogen in oxygen, and this oxyhydrogen flame is employed to, fuse both platinum and quartz, which are only fusible under the same conditions. Gold or silver at such a temperature fuse immediately and volatilise, forming a dense vapour. The Stanhope pocket microscope, which is only about an inch in length, is made with a drop of fused quartz with one face cut ; fused quartz has a specific gravity of 2-2 only. The specific gravity of the quartz in reefs, as well as that which occurs in granite and some of the acidic volcanic rocks, such as rhyolite, ranges from 2'5 to 2-8, pure quartz giving 2-65. The only natural form of silica known which has as low a specific gravity as 2-2 is a mineral called tridymite, which occurs in some of the highly silicated volcanic rocks, such as rhyolite and trachyte, and crystallises in small hexagonal tables, often occurring in groups of three crystals. Its chemical composition is the same as quartz. These observations are of interest, because they show that, notwithstanding the views still held by many practical men, the quartz which forms our reefs and occurs in granite and other eruptive rocks has never been in a state of fusion. Quartz can be produced artificially in microscopic crystals by the aid of superheated water ; while the geysers sufficiently illustrate the solubility of silica in hot water charged with carbonic acid and its deposition therefrom. Quartz is always crystalline, for even in quartz reefs, where the mineral is com- pact, it is confusedly crystalline ; while flint and the chalcedonies are minutely crystalline when seen under the microscope, but probably contain some amorphous opaline matter. Agates, which 56 PROSPECTING FOR MINERALS. are the only varieties of quartz of any value, consist of layers which are alternately crystalline quartz and variegated chalcedony. In opal water is generally present, although Dana calls it unessential, and in the siliceous deposits from geysers the silica is still comhined with water and the specific gravity is lower, ranging between 1'9 and 2 '3. ... Common opals are of frequent occurrence in eruptive rocks and in veins at the contact of serpentine with other beds. Even in sedimentary formations where siliceous concretions of flint are common, hydrous silica is also found, and is then opaque and resembles flint in appearance. The opal which is of value for ornamental purposes, and is sometimes called noble opal, will be dealt with under the head of gems. A substance of some value for industrial purposes, called infusorial earth or tripoli, is also hydrous silica. It is composed of microscopic organisms called diatoms, and is used in the preparation of dynamite and also in making soluble glass. Silicates op Magnesia and their Crystallographic Allies. It is necessary to divide the silicates into groups according to their chemical composition. Those first dealt with are all sili- cates of magnesia, and all are hydrous. When sufficiently pure, meerschaum, talc, and steatite will give before the blowpipe, when moistened with a solution of nitrate of cobalt, a pink mass which is characteristic of magnesia. The first three minerals in the table are sufficiently soft to be scratched by the nail ; but serpentine is harder, approximating in hardness to calcite. None of these minerals, when pure, efiervesce with acid ; but if they contain an admixture of carbonate of lime, which is some- times the case with serpentine and meerschaum, effervescence can be observed. As regards fusibility, they are very refractory, being only fused with difficulty in small fragments and on thin edges. Meerschaum, when pure, is very light ; and, when dry, will float on water. It will be recognised by its property, when dry, of adhering to the tongue, and by its smooth, compact texture. It is generally found in serpentine, in which rock it occurs in nodular masses ; but is also found in limestones of tertiary age. It is a useful substance when found in quantity, and of a snowy- white colour, being used, as everyone knows, for the manufac- ture of pipes. Talc, Steatite, and Soapstone are, mineralogically speaking, ROCK-FORMING AND NON-METALLIC MINERALS. 57 SILICATES OF MAGNESIA AND THEIR CRYSTALLOGRAPHIC ALLIES. Minerals. Principal Components. Hard- ness. Specific Gravity. Colour and Streak. Remarks. Meerschaum, Silica, 2 2-6-3-4 White, Earthy. Gives magnesia. streak pink colour with water slightly shining cobalt solution before blowpipe. Talc, . Do. 1-H 2-7 Green or greyish Pearlyorresinous; greasy ; laminaa flexible, not elastic. When heated, loses col- our and emits light, but does not fuse. Steatite, Do. n 2-7 Grey, green, yellow, &c. Pearly; soapy to touch ; fine splin- ters fusible to white enamel. Serpentine, . Silica, 3-4 2-6 Green, Resinous or waxy. magnesia. yellow- Becomes brown- iron. reddish ish-red when water heated and loses water. Fuses at edges. Chlorite, Silica, H 2-7 Olive- Thin scales, slight- magnesia. green ly flexible, not alumina, elastic; fuses at iron. edges only. water Yields water when heated in glass tube. White mica. Silica, 2-3 3 Silvery Laminae thin, elas- (Muscovite), alumina, potash white tic, nacreous. In- fusible or fuses only on edges to a grey or yellow glass. Black mica Silica, 24 2-9 Brown Laminae thin — : (Biotite), . magnesia. or black lustre nacreous alumina. streak, on cleavage. Be- iron. greenish fore blowpipe potash grey whitens and fuses on thin edges; gives iron bead with borax. Lepidolite, . Silica, 24-4 3 Pink Lustre pearly in alumina. or small scales or manganese, yellow- massive. Before iron, lithia ish blowpipe colours potash flame crimson. 58 PROSPECTING FOR MINERALS. the same mineral, of varying degrees of purity and in different modes of aggregation Talc is the pure crystallised mineral, occurring in transparent laminiB, which can be bent, but are not elastic like mica. The colour of talc is often a light green or pearly-white, its lustre is nacreous or greasy, and it is characteristically soft and soapy to the touch. Steatite or soapstone is a massive variety of talc, and, -when sufficiently homogeneous and free from cracks, it can be sawn into blocks and used as firebricks. Crushed and puri- fied by washing, it is formed into cakes of different colours, and is used by tailors for marking cloth. Talc and its varieties occur associated with serpentine, magnesian limestone, and especially with talc and chloritic schists. Serpentine is found in extensive masses, sometimes forming high mountain ranges ; it also occurs in veins and beds, and is consequently to be considered as a rock of some importance. Its occurrence and distribution are, moreover, of interest, on account of the valuable mineral deposits — e.g., gold, platinum, copper, nickel, and chrome-iron — frequently associated with it, and it is also the principal repository of meerschaum and soap-stone. Chlorites and Micas are remarkable as occurring generally in thin laminse easily separated one from the other, and trans- parent. They are all softer than calc spar, and are not easily fusible. These characters alone would not be sufficient to dis- tinguish them from talc, but the greasy feel of talc will serve to distinguish it easily enough in most cases ; besides which, talc is generally light green, while the most common variety of chlo- rite, which occurs in small grains or scales, is of a deep green colour. The micas are not likely to be mistaken for talc ; the most common varieties are either white or black, and their plates are elastic, while those of talc are not, and mica does not feel soft or greasy. Chlorites are hydrous silicates of magnesia, alumina, and iron, and there are varieties in which the proportions of these bases are different. In some, magnesia predominates, such as the variety called pehnine ; while in the variety called ripidolite, or simply chlorite, alumina is in the larger proportion, and iron in greater quantity than magnesia. They all fuse with difficulty before the blowpipe to a grey or black slag, and when iron is present in sufficient quantity this slag is magnetic. Pennine occurs in serpentine, often associated with other minerals, and ripidolite is the most common variety in chlorite schists, talcose schists, and amphibolites, being often associated with garnet, magnetite, &c. Rocks and minerals of a dark colour, usually green, are fre- EOCK-FOEMING AND NON-METALLIC MINERALS. 59 quently associated with metalliferous deposits, especially those of copper and more rarely gold ; and chlorite is frequently met with in metalliferous districts, not only with the dark or basic rocks but also accompanying tin, which always occurs in light or acidic rocks, such as granite. Micas, especially when found in large plates, are both flex- ible and elastic, and this property renders mica very valuable when it is white and can be obtained in large sheets. It is some- times used instead of window-glass on board ship, for stoves, and for chimneys for lamps. Biotite, or black mica, contains more magnesia than alumina, and is sometimes called piagnesian mica ; it is often present in eruptive rocks, especially some granites. Muscovite, or white mica, on the contrary, contains more alumina than magnesia, and as it also contains potash in small but appreciable quantities it is sometimes called potash mica. Muscovite is an important mineral to the tin miner, since it is always found in that class of granite in which tinstone occurs, and with quartz alone forms the rock called greisen, which is very generally associated with tin. The rock in which large sheets of mica are found is called by some geologists pegmatite, and has the same composition as granite itself, but the crystals are all of larger size. Muscovite also forms an essential part of other light coloured acidic rocks, such as gneiss and mica schist, and is sometimes found in granular limestone and some volcanic rocks, such as trachyte and basalt, but only as an accessory mineral. When found in small scales in sedimentary rocks it has probably been derived from the disintegration of granite, and it occurs under these conditions in many sandstones. Lepidolite, or lithia mica, is a variety of muscovite containing practically no magnesia, and characterised by the presence of lithia, an alfeali which is of value on account of its medicinal pro- perties. Lithia mica will be readily recognised before the blow- pipe, as it imparts a beautiful crimson colour to the flame, especially if powdered and mixed with a little fluor spar. It generally occurs in scaly granular masses in granite and gneiss, and is sometimes associated with limestone and tourmaline. It is very abundant in Bohemia ; but the most plentiful supply of lithia. is derived from a mineral spring in Cornwall ; and it is probable that the lithia in this water is derived from the tin o-ranites of the country. Lithia mica is associated with tin granites in Bohemia, Saxony, and France. There are several magnesian minerals which have received different names, but are really only varieties of serpentine ; 60 PROSPECTING FOR MINERALS. ANHYDROUS SILICATES OF LIME AND ALUMINA WITH THEIR CRYSTALLOGRAPHIC ALLIES. ( Oryntalline Eodc-forming Minerals. ) Principal Hard- Specitic Colour Mineral. Components. ness, Gravity. and Streak. Eemarks. Orthoclase, Silica, alumina, potash 6 2-55 Colourless, white, pink, greenish Fusible to bubbly glass, blowpipe reaction for potash. Albite, Silica, alumina, 6-6i 2-6 White or pale Fusible to bubbly fZ soda glass. t Oligoclase, . Silica, alumina. 6 2-7 White, greyish, Fusible. « ' soda, lime greenish 1 Labradorite, Silioa,alumina, lime, soda 6 2-7 White, grey, yellow, with coloured plays of light More easily fusible, easily attacked by acids. Anorthite, . Silica, alumina, 6 2-7 Colourless, Do. lime white t'Tremolite, . Silica, magne- 5i 3 2 White or pale Fusible with ebul- sia, lime green lition to white n3 glass. S v Actinolite, . Silica, magne- 5-5 J 3-3 Green, streak Fusible to a grey- 1" sia, lime, and greenish- ish glass. little Iron white M Hornblende, Silica, magne- 5i 3-4 Black or deep Fusible to greyish \ sia, lime, iron green or black glass. CDiopside, . Silica, lime, magnesia 5-6 33 Colourless, white-green Fusible to white or greyish glass. Diallage, . Silica, lime. 4 3 3 Grey, greenish, Fusible to a grey (U magnesia brownish or green glass. "So- Hedenberglte, Silica, lime. 3-5 Black or deep Fusible to a black 3 manganese, zinc, iron green magnetic glass. Augite, Silica, lime, manganese. 6 3-4 Black, deep green, gener- Fusible to a black often magnetic . iron, &c. ally opaque glass. "Enstatite, . Silica, magne- 54 3-1 Greyish- white Nearly infusible. o 4A sia or yellowish ■■i Bronzite, . Silica, magnesia 5-6 3-2 Brown, yellow- Nearly infusible. and little iron ish-brown H Hypersthene, Silica, magne-. 5-6 3-3 Greenish or Fusible to a black sia, iron brown-black. magnetic glass. copper - red plays of light WoUastonite, . Silica, lime 5 2-9 White or pale colours Fusible with diffi- culty. EOCK-FORMING AND NON-METALLIC MINERALS. 61 they are generally coloured green by the presence of a little iron or sometimes nickel. They generally occur in serpentine formations, and the deep green varieties are often associated with the silicated nickel ores. Anhydrous Silicates of Lime and Alumina with their Crystallographic Allies. The minerals of this group are all of great importance in forming rocks, especially those of eruptive origin ; but topaz, tourmaline, olivine, epidote, and garnet, which less frequently play an essential part in the constitution of rocks, are included with the gems. All minerals included in this group are anhydrous silicates, and may be subdivided as follows : — 1. Pelspars, including orthoclase,albite,oligoclase,labradorite, and anorthite, which are silicates of alumina and other oxides. 2. Hornblendes, including tremolite, actinolite, and horn- blende, which are silicates of magnesia, lime, and other oxides. 3. Augites, including diopside, diallage, hedenbergite, and augite, which are of similar composition to the hornblendes, with different proportions, however, of the component substances. 4. Enstatite, bronzite and hypersthene ; the first is a sili- cate of magnesia; the last two are silicates of magnesia and iron. It may be well here to refer to the table showing the composi- tion of the eruptive rocks (p. 9). Orthoclase. — If a piece of granite be taken and a variety composed of large crystals chosen, it will be found that, besides the scales of black or white mica, grains of quartz will be easily recognised by their transparency, irregular shape, and hardness; whilst the rest of the rock will be found to consist of a white, greyish, or pink mineral, scarcely transparent, and breaking easily in two directions, on one of the faces of which the mineral exhibits a nacreous lustre. If the facets produced by the frac- ture are large enough it will be seen that the two are at right angles to one another. This mineral is orthoclase, the most common and most important of all the felspars. It is also called potash felspar, and it is this mineral principally which, by its decomposition, forms deposits of kaolin or clay, the potash being dissolved. In some lavas it is stated to form an amorphous paste, whilst some well-formed crystals of orthoclase can also be detected ; and it is also one of the component minerals of gneiss and many crystalline schists. These are all rocks, in the forma- tion of which water, at a considerable temperature and under pressure, has taken a prominent part. 62 PIIOSPECTING FOR MINERALS. If, on the other hand, a specimen of trachyte be taken in ■which large crystals are developed, it will be found that crystals occur, which like orthoclase in granite, have two cleavages at right angles to one another, but a casual examination of these ■crystals will further show that they are transparent and vitreous. This constitutes another variety of orthoclase, known as sani- dine. It characterises rocks, such as trachyte, in the formation of which heat has played an important part, which have, in fact, come to the surface in a state of fusion. Not only is the ortho- clase in these rocks different in physical aspect from that of granite, but, as already pointed out, the quartz is sometimes replaced by tridymite, the specific gravity of which — viz., 2-2 — is that of fused quartz. Orthoclase, as well as the other felspars, is fusible before the blowpipe ; so that a light-coloured granular or compact rock which is fusible in small fragments is most probably composed ■of felspar, and generally orthoclase. Some of the fusible rocks are granular or compact, but still of eruptive origin — e.g., eurite; some are vitreous and compact — e.g., obsidian — a black rock which is also called volcanic glass ; and some are vitreous and porous — e.g., pumice — in which the porous state has been pro- duced by steam evolved in the interior of the molten mass. These are all of volcanic origin, but there are also rocks com- posed of very minute, even microscopic, grains of felspar which are truly sedimentary rooks, and are termed euritines. Ortho- clase is used in the manufacture of porcelain and enamels. Albite is a felspar, resembling orthoclase, in which soda re- places the potash. It is generally white, and occurs in some particular varieties of granite porphyry, diorite, gneiss, crystal- line schists, &c. It is a rare mineral compared with orthoclase as a constituent of rocks, but some granites contain it as an accessory mineral ; and it is also found forming veins in ordinary granite, being frequently the matrix in which the rarer associ- ated minerals, such as beryl, tourmaline, &c., are imbedded. Oligoclase is like albite, but contains a little lime. It generally occurs in laminar masses or crystals in the same rocks in which albite is found ; its colour is generally white, greyish, greenish, or green. This mineral possesses an easier cleavage than the other felspars, and characteristic parallel strise can be seen on the cleavage planes. The varieties of felspar which are used as ornamental stones, and are called sunstone and moon- stone, are pure orthoclase or oligoclase with enclosed flecks of reflecting material. Labradorite, like oligoclase, is rarely found in crystals, but EOCK-FORMING AND NON-METALLIC MINERALS. 63 in. cleavable laminar masses, the cleavage faces being striated. It is grey, white, yello-w, (fee, and on certain faces often exhibits a remarkable play of colours, such as blue, yellow, green, red, fiery, or semi-metallic. In this felspar lime is an important constituent, and there is also a small proportion of soda. It is more easily fusible than the other felspars, except oligoclase, and is in great part soluble in acids. It constitutes an impor- tant element in the basalts, but often occurs in such small crystals that it can scarcely be seen with the naked eye. An iridescent variety is found on the coast of Labrador in large masses, and forms a valuable ornamental stone. Anortliite is a rarer species of felspar. It occurs in small white or colourless crystals resembling albite in shape, is almost entirely a lime felspar, and is easily fusible, although not so easily as labradorite ; it is also attacked by hydrochloric acid. It occurs in granite, gabbro, serpentine, and many volcanic rocks. The hornblende group includes three principal varieties in which the colour varies in proportion to the increasing per- centage of iron present. Tremolite, containing little or no iron, is white ; actinolite, containing a few units per cent, of iron, is green ; and hornblende, containing much iron, is black. They are in consequence sometimes called white, green, and black hornblende. They are all fusible with ebullition before the blowpipe, the first forming a white, the second a grey, and the last a black bead. The most common form in eruptive and metamorphic rocks is hornblende, the black variety, which occurs as a constituent of syenite, diorite, hornblende -andesite, hornblende-schist, &c., generally in the form of flattened prisms. It is also associated with augite in some modern volcanic rocks. Actinolite occurs mostly in hornblende-schists, where it is frequently in the form of slender needle-shaped or flat prisms. These hornblende-bearing rocks, it may be remarked, are often connected with metalliferous deposits. Tremolite is of much less importance as an element of rocks, but is interesting in other respects. It is more rarely found in ■well formed crystals than the two other varieties, but is often in baccillary or radiated fibrous masses, forming the well-known substance called asbestos when pure and in long flexible fila- ments, and mountain leather, ifec, when of inferior quality. In the compact state, when its crystalline structure can hardly be detected, tremolite forms a very tough and valuable sub- stance known as jade or nephrite, which varies in colour from white to green, and is found in China, Mexico, and New 64 PROSPECTING FOR MINERALS. Zealand. The Chinese images are well known ; the hard ones are made from jade, and those which are soft from other min- erals closely allied to steatite. The Mexican and New Zealand jades are well represented in most collections by stone axes, arrow heads, &c. It may be added, to avoid confusion, that one of the minerals used by the Chinese, and known as jade, is not compact tremolite, but a compact variety of white epidote called zoisite. The augite minerals form a nearly parallel group to those of which hornblende is a type, and differ from them principally in the angles of the crystals. The varieties of the augite group are as follows : — • Diopside is a transparent, colourless, or light green mineral which occurs in serpentine and granular limestone, but is com- paratively rare. It is not a rock-forming mineral, but occurs in veins, and is a silicate of lime and magnesia, with, occasionally, traces of oxide of iron. In the blowpipe flame it is fusible to a white or greyish glass. Diallage, which is of greater importance as a rock-forming mineral, is a variety of augite. It occurs as an element of some varieties of serpentine, and in the important rock called gabbro, which often accompanies serpentine. It contains more iron than diopside, besides a little alumina, and is easily fusible before the blowpipe to a grey or green bead. It is found in laminar masses, and has generally a nacreous or semi-metallic lustre on the prin- cipal cleavage face, and in colour is grey, green, or brown. Hedenbergite is a black lamellar variety of augite containing much iron, manganese, and zinc, besides lime, and is fusible to a black magnetic bead. It is found in some cavities and veins in the older formations, and has no importance as a component mineral of rocks. Augite is the best known and most important mineral of this group. It occurs generally in well-formed black crystals, some- times difficult to distinguish from hornblende, but in the prism of augite the angles of the primitive faces are about 87° and 93°, thus approaching a rectangular prism, whilst in hornblende they are about 124° and 56°, the section of the hornblende prism thus forming a more oblique rhomboidal figure than augite. In sufficiently large crystals these angles can also be obtained by cleavage, as the easy cleavages in both groups are parallel to the faces of the prisms. Another character by which crystals of augite may sometimes be distinguished from hornblende is the brilliant lustre of augite compared with the dull lustre of hornblende. ROCK-FOEMING AND NON-METALLIC MINERALS. 65 Augite contains lime, magnesia, iron, &c., and is fusible to a black glass, which is often magnetic. It is common in the vol- canic lavas, where it may be seen in the same specimen as a con- stituent of the paste in microscopic grains, and in well-formed crystals. Enstatite is very closely related to augite, having nearly the same crystalline form, but belongs to the rhombic system. It is a silicate of magnesia, and, except for its associations, would be more properly included in the preceding group. It is practically infusible or fusible with difficulty on the edges of very small scales. It occurs in some andesites and serpentines, and in the rock called Iherzolite. Bronzite is a variety of enstatite, and is isomorphous with it. It occurs in some serpentines, where it has a lamellar structure, and exhibits a nacreous semi-metallic lustre on the face of easy cleavage. Its colour is brown, pale bronze, or greenish-yellow, and it fuses with very great difficulty, like enstatite. Hypersthene is also isomorphous with enstatite, but contains as much oxide of iron as magnesia. It is a dark laminar mineral, characterised by a reddish-brown colour, with a cupreous lustre on the cleavage planes. It is fusible to a black magnetic bead, and helps to form the eruptive rock called hypersthenite. Wollastomte is a silicate of lime, and is a white mineral, rarely crystallised, possessing a nacreous lustre, and occurring ordinarily in lamellar or bacillar masses in granular limestone, granite, or basalt. In some cases it is associated with silver and copper ores, and frequently with garnet. It is fusible with difficulty before the blowpipe. Hydrous Silicates of Lime and Alumina with their Allies. The Zeolites form a highly interesting group of beautifully crystallised minerals, occurring, in the majority of cases, in cavities or fissures in volcanic rocks, but as they are of no economic importance and are seldom found in mineral veins, much space will not be devoted to their description. Zeolites are hydrous silicates of alumina with oth§r oxides, usually alkalies, and their specific gravity ranges from 2-1 to 2-9. The softest is scratched by fluor spar, and scratches calcite ; the hardest is prehnite, with a hardness between orthoclase and quartz. They are usually colourless or white, or of a very pale pink grey or green, as they contain little or no iron. Even in the darkest of all, a brick-red variety of heulandite, the colour is attributed not to iron, but to a mixture of another mineral. 5 o 66 PROSPECTING FOB MINERALS. Prehnite, which is usually pale green, contains a small percentage of protoxide of iron. All zeolites melt and swell up when heated before the blowpipe. HYDROUS SILICATES OF LIME AND ALUMINA WITH THEIR ALLIES. {Zeolites — Crystallised Minerals of Secondary Origin.) Hard- Speeiflc Streak and Minerals. Components, ness. Gravity. Colour. Remarks. Heulandite, . Silica, alu- 3-5-4 2-2 White to Fusible with intu- mina, lime. brick- mescence, soluble water red, streak white in acids without gelatinising. Stilbite Silica, alu- 3-5-4 2-2-2 White to Fuses to white mina, lime, brown enamel. water or red Apophyllite,. Silica, lime, 4-5-5 2 -3-2 -4 White to Exfoliates and fuses potash, grey or to white enamel, water red potash flame. Laumonite, . Silica, alu- 3-5-4 2-2-2-3 White, Gelatinises with mina, lime, greyish. acid. water yellowish Gelatinises with Natrolite, Silica, alu- 5-0-5-5 2-1-2-2 White, acid, fusible in mina, soda. yellowish candle flame. water reddish Thomsonite, . Silica, alu- 5-5 2-3-2-4 White to Fuses very easily mina, lime. brown to white enamel, soda, water gelatinises with acid. Harmotome,. Silica, alu- 4-4-5 2-3-2-5 White or Fuses without in- mina, baryta, grey tumescence, solu- water ble without gela- tinising. Fuses quietly to Analcime, . Silica, alu- 5-5-5 2-2 White, mina, soda. greenish. glass, gelatinises water reddish with acid. Chabazite, . Silica, alu- 4-4-5 2-1-217 White to In rhombohedrons; mina, lime. reddish intumesces and potash, water whitens before blowpipe. Fuses with intu- Prehnite, Silica, alu- 6-6-5 2-8-2-9 Pale mina, lime. green mescence, soluble water in acids without gelatinising. In radiate groups. Some zeolites are found in gneiss — e.g., heulandite, laumonite harmotome or cross stone, and prehnite. Harmotome and ROCK-FORMING AND NON-METALLIC MINERALS. 67 Tieulandite have been found in the silver mines of Andreasberg ; analcime in the amygdaloids at the copper mines of Lake Superior ; and prehnite occurs, not only in the above copper mines, but also, in New South Wales, with orthoclase and copper ores at Eeedy Creek, County Murchison. Prehnite is certainly, of all the zeolites, the most interesting in consequence of its associations. It is further mentioned as occurring in crystalline rocks and especially in diorite and other hornblende rocks, from the decomposition of which mineral it is probably derived. Basalts and lavas containing abundance of zeolites may some- times be utilised in the arts when, in consequence of the quantity of alkalies present, they are so fusible that they may be easily melted and cast into different forms. Chabazite is the most common of the zeolites found in basalts. Basaltic lavas, especially when they are in the state of sand and contain a sufficient proportion of alkalies, are used as puzzuolana in the manufacture of cement. Non-Crystalline Silicates op Alumina. Clays. — The clays are all products of alteration from other minerals, their composition is variable, and they do not crystallise. The true clays are all plastic and refractory to a greater or less degree, and on these properties their value for industrial purposes depend. Pure kaolin is the type of all the clays. Such hard earthy minerals as allophane and halloysite may be termed, by analogy, hard clays, since their composition is gener- ally similar to some of the soft plastic clays ; but they have not yet been used for manufacturing purposes. They are not plastic, but are derived, in some cases at least, from the decomposition of felspathic rocks, and are often found in mineral deposits. The presence of alkalies in clay is objectionable, as it renders them fusible, as also do many other oxides. Iron is not only objectionable on the score of fusibility, but also as a colouring matter. The presence of too large a proportion of water, car- bonic acid, or organic matter causes clay to contract under the action of fire, and the same result will ensue if the clay is par- tially fusible. Contraction may also arise from the mechanical arrangement of the particles, and of two clays having the same chemical composition, both of which contain a certain percentage of free silica, the finer one will contract more than the coarser, in which the particles are preserved from that close contact which is necessary for their ready combination and fusion. The soft clays are divided into kaolin or porcelain clay, 68 PROSPECTING FOR MINERALS. which is nearly pure, and is derived from the decomposition of felspar in pegmatite or granite ,' plastic or pottery clay, not so- pure as kaolin ; and bole, containing a great percentage of oxide of iron. Puller's earth, is a kind of clay used for freeing wool from fatty matters. It is not easily made into a paste with water, and its application is therefore limited to the above pur- pose, for which it is of great value. CHAPTER IV. PRECIOUS STONES AND GEMS. The minerals which are used for ornamental purposes are mostly of considerable hardness, and capable of receiving a high polish. They vary greatly in their chemical composition, but are best divided by their hardness into two groups, viz., those which are harder than quartz, and those which are not harder than quartz. Harder than Quartz. Diamond is pure carbon. Its hardness, specific gravity, ani peculiar lustre, due to its high refractive power, have been, already referred to. It will be readily recognised by the pro- spector who has once seen it in the rough, if simple tests are applied, for diamond will scratch sapphire. The gem prospector should always carry with him some pieces of sapphire, topaz,, and rock crystal, as well as a diamond. In its natural repositories, diamond is not always readily rocognised by its brilliancy, and it is often encrusted with a black coating, or cemented with ironstone ; but its greater weight will cause it to settle to the bottom of a tin dish or- sieve when washed with other non-metallic minerals of the same size ; and, if the dish or sieve be turned over suddenly, the diamonds will remain on the top of the heap, which should be carefully picked over. Dana says (System of Mineralogy, 5th edition) — "The diamond appears generally to occur in regions that afford a laminated granular quartz rock called itacolumite, which pertains to the talcose series, and which in thin slabs is more or less flexible. This rock is found at the mines of Brazil and the Urals, and also- in Georgia and North Carolina, where a few diamonds have been found. It has also been detected in a species of conglomerate PRECIOUS STONES AND GEMS. 69 •composed of rounded siliceous pebbles of quartz, chalcedony, &c., ■cemented by a kind of ferruginous clay." In some of the schistose rocks of Brazil, above alluded to, it is admitted that the diamond exists in sitH, or in the rock in ■which it -was formed ; and M. G-orceix states that these rocks are traversed by veins of quartz with rutile, tetrahedrite, oligiste, and martite, the two last being varieties of hseraatite. In the Transvaal the diamond has been traced to its parent rock, a kind of serpentine, which occurs as huge dykes or necks ■of igneous rock which have come to the surface, but have not apparently overflowed the lip of the vent or crater, and, accord- ing to Mr. Dunn, a geologist at the Cape who has devoted much time to the study of the diamond and gold deposits of this part of the world, these so-called "pans" are local depressions in the flats, and are sometimes as much as three miles in length He also states that when the eruptive rock has been removed the walls of the cavity exhibit horizontal beds of shale, their edges being turned up along the line of contact with the eruptive rocks. The upper beds are, in some instances, formed of grey, pink, or yellow shales with fossil remains (Saurians) ; the lower "beds, from 50 to 150 feet thick, consist of black carbonaceous «hales. So combustible are these shales, that when accidentally ignited they have been known to burn for over eighteen months. In this serpentine diamonds are generally found crystallised in octahedra and some of the allied forms. . In Borneo diamonds are said to occur in a matrix of serpentine, and in New South Wales and at Beechworth, in Victoria, good diamonds, although small, are found in alluvial deposits in great numbers. Some of these deposits have of late years received a good deal of attention, and may eventually prove of considerable value. Diamonds have also been worked in alluvial deposits on the Vaal River in South Africa, at Golconda in India, and other places ; indeed, with the exception of the mines of the Trans- vaal, in which the stones occur in sit4 in serpentine (as already said), all the important diamond fields of the world have been alluvial deposits. The occurrence of diamonds of different colours affords a remarkable illustration of what has been said about the colours of minerals. As pure carbon, diamond is colourless, as also are the microscopic diamonds artificially produced by an electric current ; but in nature the stones are of different colours, which are imparted to them by a very small proportion of foreign matter. The yellow and grey tints decrease the value of the diamond ; '7.0 prospecting: FOE minerals. but red, blue, and green varieties, on the contrary, are so rare, that when diamonds are so coloured their value is considerably greater than if perfectly colourless. Tor instance, the best ' blue diamond known (44 carats) is estimated at double the calculated value of a good colourless diamond of the same size, viz., £30,000. In Borneo a kind of black diamond is found which is very highly prized in consequence of its exceptional lustre and rarity; it is even harder than the ordinary diamond. In Brazil another variety of black diamond, called "bort," which is rough and without lustre, and somewhat resembles the deposit of gas retorts in appearance,' is found in quantity, and is used for diamond drills. It sometimes occurs in masses as much ■as'8 ozs. in weight, and is as hard as the ordinary .'diamond. Octahedrite, a mineral occasionally found with diamond, is mentioned under rutile, and is sometimes so splendent as to be mistaken for diamond itself. Diamond should also be compared iwith white zircon, the lustre of which is also adamantine. The diamond always occurs as a constituent of rocks. or in alluvial deposits and never in lodes. It is principally valued on account of its hardness and high refractive power, being the most valuable ornamental stone. It is also largely used in rock ■boring drills ; and diamond dust is of importance for polishing jpurposes. Corundum (sapphire,, ruby, (fee). — A number of hard stones .of various colours and known by different names belong to this mineral species ; they are all essentially composed of alumina. The most, common of these gems is 6^?.(e corundum or sapphire^ -which is very frequently found associated with alluvial gold in ■Australia. ■ . ' ' Green varieties, called Oriental emeralds, also occur with sapphires, sometimes in considerable numbers, but seldom of a ■good colour, the most common tint being that of water worn 'bottle glass which may be so often ■ seen on the sea shore. .When pure, and of an emerald colour, they are of a great value, both on account of their hardness and rarity. ■; Yellow corundum is called Oriental topaz, and, being harder .than topaz itself while of the same colour,- has a greater value. The violet variety is called Oriental amethyst and is not common. • Red corundum or ruby is next to diamond in value; indeed, a ruby of Z\ carats when perfect is even more valuable than a diamond of the same size. A ruby of 4 to 6 carats in weight is PRECIOUS STONES AND GEMS. 71 a great rarity and is worth forty or fifty times as much as the best sapphire of the same weight. Black corundum is often met with ; like emery (which is only an impure variety containing more iron), it is useful for cutting and polishing stones of less hardness than itself. Emery, which is largely used for polishing purposes and for the manufacture of emery wheels (now so largely used in machinery works), is the coarsest and commonest variety of corundum ; it contains from 10 to 50 per cent, of magnetite and its abrasive power is about half that of sapphire. Most of the emery of commerce comes from Naxos or Asia Minor. It is found in Asia Minor near the surface like a bed of conglomerate resting upon lime- stone, and it is roughly hand picked on the mines. It is mined by blasting, the bore holes being made in the joints of the rock which are frequently filled with calcite ; sometimes also it is worked by firesetting, although this is said to deteriorate the quality. The fine varieties of corundum have been chiefly obtained from alluvial deposits ; they have rarely been traced to their parent rock and have never yet been found in a matrix from which it would pay to extract them, as is the case with the diamond in the Transvaal and the emerald in Peru. In certain parts of New South Wales, corundum is said to occur in basalt with olivine ; in alluvial deposits it is found with other hard stones and with tin, gold, &c. The hardness of this mineral, which is next to diamond, should make it easy always to distinguish ; so far as the sapphire is con- cerned the colour is quite distinctive. Numerous mistakes, however, have been made about the ruby, and it is no uncommon thing for zircon and garnet to be mistaken for it, notwithstand- ing the easy means of discrimination afforded by the respective hardness of the different minerals. Dana says (^System of Mineralogy, 5th edition) — "Corundum is associated with crystalline rocks, as granular limestone, or dolo- mite, gneiss, granite, mica slate, chlorite slate." A species of felspar with oblique cleavages, called anorthite or indianite, is' said to be the gangue of corundum in the Carnatic, India, with garnet, cyanite, and hornblende. At Barsowski in Russia a granular variety of anorthite is said to occur in the auriferous sand as the gangue of the sapphire. Chrysoberyl comes next in hardness to corundum. It is not transparent, but translucent, and exhibits a play of colours' in difierent shades of green, like a cat's-eye ; sometimes a bluish opalescence is to be seen internally. 72 PROSPKCTING FOR MINERALS. In. alluvial deposits it occurs as rolled pebbles, and in the Ural mountains is found in sM, in peculiar star-like groups of crystals, in mica slate associated with beryl and phenakite. Ifc is composed of alumina and glucina. Spinel is an aluminate of magnesia, and includes several varieties, of which the red variety, spinel ruby, is generally meant when spinel is spoken of as a gem. A variety, which contains a fair proportion of iron and is sometimes called black spinel, is referred to under the name of pleonaste as a stone often found with alluvial tin. Spinel rubies generally have a dull bluish tinge, which places them far below the true ruby in point of value ; they can readily be distinguished by their lesser hardness even when in colour they rival the more valuable gem. Green and blue varieties of spinel also occur. The Hue variety is very inferior to the sapphire, even when of very good colour ; and green spinel is more a curiosity than a gem. It occurs in octahedra when not waterworn. Red spinels are sometimes found in alluvial deposits with gold, but they are generally very small ; and they have occasionally been found in sandstone, but were probably derived from igneous rocks.. They are also said to occur imbedded in granular lime- stone and with calcite in serpentine, gneiss, and allied rocks, as also in cavities in volcanic rocks. Topaz is a silicate of alumina with fluorine ; and its hardness is little less than that of spinel ruby. White topaz is common as waterworn pebbles in alluvial deposits associated with gold, and has an easy and characteristic cleavage parallel to the base of the prism. It is sometimes suflBciently brilliant to be valued as a gem, especially when well cut; but it is not to be compared with a well cut diamond. The pale Hue variety is of value for cutting into large stones for brooches ; specimens are occasionally found of several pounds weight. Topaz of a beautiful slierry colour occurs in Brazil. Specimens of this, when heated, become pink, when they are known as burnt topaz. A lighter coloured variety is found in the tin mines of Saxony, and is said to have been found in Tasmania. The yellow varieties are cut as gems ; although not very valuable they have considerable brilliance and look very well. Emerald and Beryl are chemically the same, being composed of silica, alumina, and glucina. The varieties known as heryl are generally opaque or nearly so, and are light green or yellowish in colour. Large crystals, six- PRECIOUS STONES AND GEMS. 73 sided prisms, are commoa in veins of pegmatite traversing granite, and are also found imbedded in quartz. A pale green or light blue transparent variety is known as aquamarine, and is sometimes used as a gem, but has no great value. It is sometimes mistaken for topaz, but is neither so hard nor so heavy ; nor does it, like topaz, become electric by friction. According to lapidaries, emerald is a little softer than beryl, but its rich and characteristic green colour makes it a gem of great value. It is found in mica schists in Siberia and Salzburg ; and in clay slate with concretions containing' Cretaceous fossils in Granada. The emeralds from the last locality are especially noted for their beauty of colour, but the largest crystals have been obtained from Siberia. Some emeralds have been found in a vein traversing granite in New South Wales, and minute specimens in a syenitic gneiss at Dusky Sound, New Zealand. Phenakite differs from emerald in composition by not con- taining alumina nor the traces of green colouring matter. It is generally colourless, but rarely wine yellow, so that it is difficult to distinguish from topaz, their hardness being also the same. Phenakite is, however, lighter and considerably rarer. It occurs in the Ural in mica schists with chrysoberyl and emerald ; and elsewhere, associated with other minerals. Zircon, is a silicate of zirconia. The crystals are of various shades from colourless and transparent, when they are sometimes mistaken for diamonds, to yellowish, green, brown, and red. The smoky white varieties are known a.a jargons, the transparent red varieties as hyacinths, and the grey and brown forms as zircons. This mineral is remarkable for its brilliant lustre, which approaches that of the diamond, but it is not of much value. It has been found in granite and other crystalline rocks, and occasionally in volcanic rocks. Dichroite or Cordierite is a silicate of alumina, iron, and magnesia. It is not commonly used as a gem ; it is of more value as a curiosity, in consequence of its showing two different colours when light is passed through it from different directions, than on account of its real beauty. It has been named dichroite from this property. It exhibits various shades of blue in one direction, and a brownish-yellow or yellowish-grey in a direction at right angles to the first. It is known to jewellers as "sapphire d'eau." It occurs in granite, gneiss, hornblende, chlorite, and talcose schists, and allied rocks, with quartz, orthoclase, albite, tourmaline. 7i PROSPECTING FOR MINERALS. hornblende, andalusite, and, sometimes, beryl. It is also found in volcanic rocks, and is often decomposed. • Tourmaline will be mentioned as a mineral accompanying tin. There is a remarkable instance of its occurrence with gold in the New Mount Morgan mine in Western Australia, where gold is commonly disseminated through the joints of the crystals. It is a boro-silicate of alumina and other oxides, and contains fluorine. ' There are many varieties, but those used as gems are either red, green, or blue. The first is termed ruhellite by mineralogists, or simply tourmaline by jewellers; the green and blue varieties are known as Brazilian emerald and sapphire respectively, and in Brazil they are worn by dignitaries of the church. Tourmaline is usually found in granite, syenite, gneiss, mica schist, chlorite schist, or talcose schist, as also in diorite, dolomite, granular limestone, &c. The most common variety, schorl, \& black. It is easily recognised, as it occurs in long needle-shaped crystals, which become electric when heated. Garnet is also alluded to as a mineral which often accompanies tinstone, or is likely to be mistaken for it ; only those varieties used as gems will be mentioned here. The colour is blood- or cherry-red, passing to various shades of crimson, purple, and reddish-violet on the one hand, and to orange, red, and hyacinth-brown on the other. Unlike other red stones, garnet is not readily cut in faces, and is generally cut as carbuncles or, in other words, with a smooth oval surface. In this form the best qualities display brilliant fire-red flashes of light. The best garnets used as gems belong to the varieties called almandine and pyrope ; they are chiefly obtained from Syria and Bohemia, and are called in the trade " Syrian " and '' Bohemian garnets." Besides the red-coloured pyrope and almandine, there are some other varieties of very diflerent colours. A green garnet, called ouwarowite, is coloured by oxide of chromium ; a black garnet found in crystalline schists is called melanite, and con- tains much iron. Not Harder than Quartz. ■ There are many varieties of quartz which claim some atten- tion as ornamental stones, all of which consist of silica. Rock Crystal occurs crystallised in six-sided prisms with pyramidal ends ; it is perfectly clear and transparent, and is used both for optical instruments and for ornamental purposes. . PRECIOUS STONES AND GEM'S. 75 It is sometimes found in crystals of enormous size, several ■weighing from 8 to 10 owts. having been recorded ; and it is reported that about a century ago a drusy cavity was opened at Zinken from wliich 50 tons of rock crystal were obtained, which realised £60,000. Smoky quartz, or Cairngorm, has a smoky yellow to brown tinge. The colour is probably due to titanic acid, as crystals containing rutile are generally smoky. It is called cairngorm from the locality in Scotland of that name. Citrine quartz, or False Topaz, which is yellow in colour, is easily distinguished from topaz, which it resembles, by the absence of cleavage and the difference in hardness. Amethyst quartz is the most highly valued of the coloured varieties. It may be described as clear and of a purple or violet colour. It is usually found in cavities in volcanic rocks. Chalcedony generally occurs in stalactitio or concretionary masses, and is usually whitish, yellowish, or yellowish-brown, rarely pure white. This variety, in common with those which follow, is transhicent. Agate is a variegated chalcedony alternating with bands of quartz, in which the colours are cloudy or banded, but rather dull and not showing any sharp contrast one with the other. : Onyx differs from agate in being distinctly banded in well- contrasted shades, such as black and white, or brown and white, but most of the black varieties are artificially stained. Sardonjrx is a brownish-red or orange variety of agate. For agate to become an important article of trade it must be found in large quantities, and in rocks so much decomposed that the process of extraction would be an easy one. Agates are mostly found in cavities in volcanic rock, where they have been deposited by water. Carnelian is of a clear blood-red or light-red colour, but this colour is said to be produced in India by burning, it being due to oxide of iron. Chrysoprase is of a beautiful apple-green colour, due to oxide of nickel. In a warm, dry place the colour of chrysoprase is destroyed, but it can be again restored by keeping it damp. Plasma is an olive-green chalcedony. Heliotrope or Bloodstone is plasma traversed by small veins or specks of red jasper. Under the names of moss agate and dendritic agate are in- cluded those varieties in which dendritic crystals of metallic oxides occur, a common mode of crystallisation for oxide of manganese. 76 PROSPECTING FOE MINERALS. Most specimens of petrified wood, when there is no earthy or clayey matter present, are transformed into chalcedony. Cat's Eye is another translucent variety of quartz, but, unlike chalcedony, it is crystalline, but not amorphous. A variety containing fibres of asbestos is sometimes incorrectly called " crocidolite." It is yellowish-green in colour, with golden and green streaks of light, and has a silky appearance, due to the fibres of asbestos. The original fibrous crocidolite is of a fine blue colour. This stone is well known as occurring in the diamond districts of the Transvaal, and is also found in Ger- many, Ceylon, and elsewhere. Opal is silica in an amorphous condition, usually with some water, and includes not only noble opal, but also those common varieties which are of no value. Fossil wood often consists of hydrous silica. The opal used as a precious stone is translucent, and has a beautiful play of different fire-like colours — red, yellow, green, and blue being conspicuous in some varieties ; while in others, one of these colours is prominent, the rest being less distinct. Perfect opals are very valuable, but their value is greatly en- hanced when they are set, since the operation of cutting is very difficult, in consequence of their brittleness. They are usually found in cavities in amygdaloidal rhyolite and some other lavas. Orthoclase, Oligoclase, and Labradorite. — Some varieties of orthoclase and oligoclase contain minute flakes of other material, are iridescent and exhibit a beautiful play of colours. They are called sunstone and moonstone, and are occasionally set in brooches, but are too soft for rings. They are chiefly obtained from India, America, and Ceylon. Iridescent Labradorite, which is chiefly obtained from the coast of Labrador, is sometimes found in blocks of large size and of varying colours — violet, blue, &c. It is used for decorating artistic furniture, and is sometimes cut for pins, ifec. A beautiful variety of orthoclase known as Amazon stone occurs as large green crystals in Siberia and the United States. It would form a pretty ornamental stone, b\it is not transparent. Olivine or Chrysolite, which is also known as peridot, is a silicate of magnesia coloured with a small proportion of iron ; its usual colour is bottle green of various shades. It is not so hard as quartz and but little harder than glass, besides which it is brittle and therefore of very little value. It is an essential constituent of basalt, and occurs in serpentine. In New Zealand and New Caledonia it forms a massive rock, which frequently contains chromite, and has been named duniie. PRECIOUS STONES AND GEMS. IT Epidote is a silicate of alumina and lime, with small propor- tions of iron and water. It occurs crystallised in long prisms of an. olive-green colour in one direction and yellow or brown in another; so that, like cordierite, it is dichroic. It is more a curious than a precious stone; its lustre is vitreous, and it is too dark for orna- mental purposes. It is of common occurrence in many crystalline rocks, especially those which are hornblendic, and in serpentine ; and it often accompanies beds of magnetite and haematite. Eyanite is a silicate of alumina, generally of a light blue colour, but also white, grey, or green. It occurs in long, thin, blade-like crystals imbedded in mica schists and gneiss. It is of no value as a precious stone. Vesuvianite or idocrase is a complex silicate of alumina and other oxides, and is allied to garnet, but crystallises in different forms ; it resembles tinstone, from which, however, it can be easily distinguished by its fusibility. It has a vitreous lustre and a hardness of 6-5, but is of no value as a gem. It is found in volcanic rocks at Vesuvius and in crystalline schists and gneiss in many localities. Andalusite has the same composition as kyanite, but crystal- lises in different forms, besides having, when coloured, a reddish tinge. The variety chiastolite occurs as small white rod-like crystals imbedded in slate, and exhibits the form of a dark cross due to impurities in its sections. It is a little harder than quartz, and its lustre is vitreous. Turquoise is a hydrous phosphate of alumina. It is amor- phous and opaque. The best quality, the Persian turquoise, is of a beautiful sky blue colour. Odontolite, called by jewellers " turquoise of newrock," is fossil bone, coloiired by copper. It is of far inferior quality to the true turquoise, and is easily decomposed ; when the unpolished surface is carefully examined, the structure of bone can be seen. Odontolite occurs chiefly in cave deposits; while true turquoise is found in sandstones,, where it is found in seed-like groups. Ultramarine or Lapis Lazuli. — This beautiful stone is blue ; opaque or semi-translucent ; and is often traversed by veins of pyrites. It is a very complex mineral chemically (if, indeed, it must not be regarded as a rock), consisting of silicate of alumina, with soda, lime, sulphur, chlorine, (fee. So long as the pigment which bears its name was obtained solely from this source, the price of the colour was enormous ; but since it has been manu- factured artificially the price has been greatly reduced, and ultramarine can now be obtained at a fraction of the price formerly paid for it. 78 PROSPECTING FOR MINERALS. Although its ally, hauyne, is crystallised, lapis lazuli occurs in a massive state, being found in crystalline limestone on the banks of the Indus; and in granite, in Persia, China, and Siberia. It is used in mosaic work, and costly vases are made from it ; but it is also worn as a jewel. Boracite. — This mineral, though not a gem, is included here on account of its hardness, which is that of quartz. In the table for the determination of minerals it is placed with tourmaline, which it resembles by containing boron, and also in becoming electric when heated. It contains chlorine, and, mixed with, oxide of copper, will colour the flame azure blue. It is rare, but is found in small white crystals with gypsum and rock salt. COLOURS OF PRECIOUS STONES. Name. -a 1 i % 1 el id 1 i s .2 X X 0) s R X R a X o > R o u X X o 1 X X Diamond, . Corundum, Chrysoberyl, Spinel ruby. Topaz, Emerald, including beryl. Zircon, Cordierite, . Phenakite, . X X X X X R X X X X X X X X X ... u X X X X X R means "rare.' SCALE OF HARDNESS FOR PRECIOUS STONES. 5 Apatite (not a precious stone) ; scratched by steel. 5-5 The hardest glass (imitation gems are still softer), 6 Orthoclase ; scratched by hardened steel, Turquoise; ,, „ ,, 6 '5 Olivine or peridot, .... 7 Quartz, amethyst, cairngorm, \ Tourmaline, 7 '5 Zircon, garnet, . . .J cordierite, 8 Topaz, spinel ruby, emerald, beryl, phenakite. 8 '5 Chrysoberyl. 9 Corundum (sapphire, ruby, oriental emerald, oriental amethyst, oriental topaz), 10 Diamond. Opal. Garnet and varieties. STRATIFIED DEPOSITS. 79 SPECIFIC GRAVITY OF GEMS. Agate, . 2-5 to 2-8 Hauyne, , . 2-4 to 2-5 Amethyst, . . 2-5 „ 2-8 Heliotrope, . 2-5 „ 2'8 Andalusite, . 31 „ 3-2 Kyanite, . ' . 3-5 „ 3-7 Beryl, . . . 2-6 „ 2-8 Labradorite, . 2-68 „ 2-74 Bloodstone, . 2-5 ,, 2-8 , Lapis lazuli, . 2-38 „ 2-42 Boracite, . . 2-9 „ 3-0 Oligoclase, . 2-64 „ 2-68 Cairngorm, . . 2-5 „ 2-8 Olivine, . 3-3 „ 3-5 Carnelian, . . 2-5 „ 2-8 Onyx, . 2-5 „ 2-8 Cat's eye, . . 2-5 „ 2-8 - Opal, . 20 „ 2-2 Chalcedony, . 2-5 „ 2-8 Orthoclase, . 2-53 „ 2-58 Chrysoberyl, . 3-7 „ 3-8 Phenakite, 2-97 Chrysolite, . . 3-3 „ 3-5 Plasma, . 2'5 to 2-8 Chrysoprase, . 2-5 ,, 2-8 Quartz, . 2-5 „ 2-8 Citrine, . 2-5 „ 2-8 Ruby, . 3-9 „ 4-2 Cordierite, . . . 2-5 „ 2-7 Sapphire, . . 3-9 „ 4-2 Corundum, . . 3-9 „ 4-2 Sardonyx, . 2-5 „ 2-8 Crocidolite, . 3-2 „ 3-3 Spinel, . 3-4 „ 4-1 Diamond, . . 3-5 „ 3-6 Topaz, . 34 ,, 3-6 Dichroite, . . 2-5 „ 2-7 Tourmaline, . 3 „ 3-6 Emerald, , . 2-6 „ 2 8 Turquoise, . 2-6 „ 2-8 Epidote, . 3-2 „ 3-5 Vesuvianite, . 3-3 „ 4-0 Garnet, . 3-5 „ 4-3 Zircon, . . 40 „ 4-7 chap: DEE V. STRATIFIED DEPOSITS. Those classes of mineral deposits which come under this head have been formed at the same time as the rocks with which they are interstratified, and, indeed, may be looked upon as rocks themselves. Such substances as slate, marble, and the various building stones, which are quarried ; coal, some deposits of ironstone, rock salt, and gypsum, which are either quarried or mine'd ; and, lastly, rocks which are impregnated, to a greater or less extent, with metallic minerals, come under this group. Regarding those substances which have to be quarried, such as slates and the various building stones, it is not proposed to, enter into any description, while the other two groups require separate treatmentjV because the former (of which coal may be taken as a type) will be worked so that the greatest quantity of material will be removed ; the latter, so that only that portion be taken which will be of a remunerative character. 80 PEOSPECTING FOE MINEEALS. Coal. — It will be of advantage in the first instance to study the manner in which coal has been formed, and thus arrive at some of the principle's which govern its distribution. That coal is of vegetable origin may readily be proved by examining a thin slice of that substance under a microscope, ■when the tissues of plants can be more or less perfectly seen ; but in most cases there are two kinds of structure visible, one the so-called structure of mineral charcoal, resembling charred wood, in which the vegetable tissue cannot be recognised ; and the other, composed of round cell-lite bodies. In recent years it has been shown that, in many cases at all events, the bituminous or volatile matters in coal are due to these round cell-like bodies, and these have been traced to the resinous spores of plants which are allied to the club- mosses of the present day ; but unlike these, which seldom grow to more than a few inches in height, the plants to which these spores belonged grew to a very great height, and the climate and con- ditions generally must have been extremely humid. It is now generally considered that coal seams were formed on the sites where the plants from which they are" derived grew, and, therefore, that the bed of underclay which is frequently found below the coal was the soil upon which these plants grew ; but in some few cases coal seams may have been formed by vast accumulations of drift wood. That most seams of coal were formed in siiH is borne out, however, by the occurrence of roots in this under clay. A careful examination of any section in which seams of coal occur demonstrates the fact that the rocks with which they are chieily associated are alternating beds of shale and sandstone, with occasional beds of fireclay and ironstone. It is not at all unusual to find a thickness of several hundred feet of these rocks, including several seams of coal of varying thickness and quality, some of which could be worked to advantage, while others are not of sufficient value to pay for mining. It is seldom the case that these shales and sandstones contain marine fossils ; remains of plants and occasional fresh-water shells are the only fossils that occur in them, and there can be no doubt that they were deposited under conditions which allowed of the growth of dense forests, of their submergence below fresh- water areas, and of their subsequent elevation when fresh forests grew, which in their turn were altered to coal. Subsequent depressions on a larger scale have in many cases submerged these coal-bearing beds below sea-level, and rocks containing marine fossils are then found overlying the coal-bearing series. STRATIFIED DEPOSITS. 81 It will be perfectly evident that with the mode of formation described the extent of valuable seams of coal is not necessarily coterminous with the shales and sandstones with which they are interstratified. The extent of the coal seams will depend to a great extent upon the local conditions which prevailed at the time of their formation ; and whereas the conditions of soil and climate may have been identical over very wide-spread areas, in which case the coal will be of uniform quality and thickness for great distances, it may equally well prove that these conditions were very local, and consequently that the seams vary much in short distances, thinning and deteriorating in passing from one property to another. It is seldom the case that seams of coal are found in an absolutely horizontal position, and so, if they have any dip at all, they are generally to be found outcropping somewhere or other. These outcrops may be, as in mountainous countries, represented by a cliff, frequently with a hard sandstone forming a scarp, with the softer coal underlying it, as in the accompanying sketch, in which case the coal can ea.sily be tested and meas- ZZ~~~~~—: ured with very little work; :~~ or, as in flat or undulating j,. g^ge^tion. country, where the rocks have been much decomposed, the outcrops may be obscured by surface soil, and then more judgment is necessary in order to decide what work should be done. The following sketch (Fig. 6) will illustrate the conditions alluded to. Where these prevail, some information regarding the strike and dip of the strata and the probability of coal existing can crenerally be gained by an examination of creek beds or any outcrops of rock which exist; after which, a careful examination of the soil will frequently reveal small pieces of coal in it or, possibly, only a black sooty-like smudge in the soil, which will afford some indication of the best places in which to sink small trial holes in search for coal. Surface prospecting is of the greatest value for deposits of this class, and should always be undertaken before any more expen- sive methods of testing the ground are adopted. Having demonstrated the fact that a seam or seams of coal exist on any 6 82 PROSPECTING FOR MINERALS. property, the next point that will have to be considered in form- ing any idea of the extent of these coal seams is, to what move- ments have the rocks been subjected ; what, in fact, are the angles of inclination or dip of the different beds ? Knowing that seams of coal are stratified deposits, or have been formed during z::13!:^_fS C '£ -' S~0. 7 Q^~-_ Fig. 6. — Section. the same geological period as the rocks in which they occur, it will be certain that the coal seams themselves have been sub- jected to the same movements as the rocks, and having once settled the position of a coal seam in a section, any further observations of dip or strike may just as readily be taken in the rocks which crop out at the surface as in the coal seam itself. To illustrate this by a section ; if it is supposed that a coal seam has been found cropping out at the surface in a clifi" as at a (Fig. 7), and dipping in the direction indicated, the thickness of Fig. 7.— Section. the beds to the summit of the cliff can be measured, and then the upper bed traced along the surface towards the dip. Taking advantage of every outcrop of rock which is to be seen, and noting the dip of each, an exact idea can be formed of the course of the coal and the depth at which it will be found at different points. If the dip was uniform, as shown in the section, this would be very simple ; but if, on the other hand, the dip and strike changed at different places, the surface would have to be studied very carefully in order to arrive at these conclusions. In the following plan (Fig. 8) let (a) be a seam of coal, cropping as shown, and (6) a bed overlying it, also cropping at the places marked, and dipping as shown by the arrows. In this case, the STRATIFIED DEPOSITS. 83 main body of coal would lie in the direction indicated by the large arrow, and coal struck along this line could be worked to the rise in three directions. A surface study of the ground may thus be of the greatest value in determining in what direction boring operations can best be carried on, and may frequently save a great expenditure in useless boring, since it is not a very unusual thing for bore- Fig. 8.— Plan. holes to be sunk when the same information could be better obtained by a surface study of the ground. This surface prospecting, however, will not inform us what the thickness of the coal seams may be in any particular area, nor give us any notion of their quality. Having by surface work arrived at a conclusion as to the distribution of the beds, boreholes, situated judiciously so as to prove the thickness and quality of the seams, must be put down and an accurate know- ledge regarding them thus obtained. It is an old and true saying that " a colliery well bored is half won " ; but even boreholes will not give notice at the out- set of all the troubles which may be met with in the workings. There may be small or even large faults which have disturbed the seams, and may thus give rise to a large amount of dead work ; or there may be bands of stone and partings, formed during the 84 PROSPECTING FOR MINERALS. deposition of the coal by streams which carried a certain amount of sediment with them ; or "wash outs" may occur where the- coal has been completely carried away by running water, and its place filled in with sand or gravel ; or the coal may even be cut out by dykes of igneous rock, which have been forced up from below, as at Newcastle and IDawarra in New South Wales. All matters such as these can only be determined in the work- ings, and we must always be prepared to find a fair proportion of such difficulties to contend with and overcome. Surface prospecting and boring can, however, determine the area of the coal-bearing rocks in a certain district, and can demonstrate the existence of workable seams of coal in these deposits; beyond this the prospector can hardly be expected to go. There are always elements of uncertainly in mining, and although coal mining is perhaps the most certain of all, it is not free from disappointments. The quality of coal varies considerably, for while some classes are suitable for steam raising and smelting purposes, others have a much less ex- tended use ; but these characters will be referred to in a later chapter. In working coal it must be borne in mind that everything depends upon local conditions, the thickness of the seams; the presence or absence of bands interstratified with the coal, and the nature of the roof and floor; and it is worth while consider- ing a few points now which bear upon the question. Seams of coal not more than 18 inches thick can be worked to- advantage under special circumstances, but these must all be favourable. The roof and floor must be good ; the inclination of the seam small ; there should be facilities for driving coal- cutting machinery at a cheap rate ; wages should be cheap and the sale price of coal comparatively high ; and, especially, there should be no competition with thicker seams under as favourable conditions in the neighbourhood. Seams are worked up to 50 feet, and even more, in thickness ; but no special advantage exists in woiking a seam over 6 ft. or 7 ft. thick ; as, although more coal can be won in a given area, the expenses of supporting the roof and the difficulties of ventilation militate against cheap working. In the early history of a district the cost of working coal is generally at a minimum and even when wages are high, as, for instance, in the United States, there are many cases where outcrop coal is worked at about 4s. per ton ; while in England, with lower wages, the cost is often 7s. per ton (or even more) when worked from shafts,, with pumping and surface charges to be considered. STRATIFIED DEPOSITS. 85 The presence of bands or layers of shale or stone in a coal seam is sometimes very prejudicial to the working, indeed, at times -will make an otherwise valuable seam useless ; but, in other cases, where the bands are fairly large and separate easily from the coal, the stone from them can be used to build pack walls in the mine and they are no serious inconvenience. Iron Ores. — Deposits of ironstone occur under somewhat similar conditions to coal, but they are much more irregular in their extent. They are frequently found associated with the coal measures, bat quite as often are interstratified with beds in which no coal is present. Most stratified deposits of iron are either carbonate of iron, known as spathic iron ore ; carbonate of iron mixed with some carbonaceous matter, known as hlack hand ironstone; or a hydrous oxide of iron, known as hrown iron ore. There are also deposits of red hsematite, the anhydrous oxide, but these are of rarer occurrence. By far the greater quantity of ironstone mined is brown iron ore, of which the extensive deposits of Bilbao in Spain may be taken as a type. The ores are mined and picked so as to produce as high a percentage of iron as possible, and are sold -on the basis of 50 per cent, iron, so much per unit being paid for each per cent, above this. The prices naturally vary some- what, but from 4d. to 6d. per unit for ores of 50 per cent, and over, delivered in Wales or the North of England, may be taken as about their value. It will be evident that the margin ■of profit in working this ore is slight, and that conditions have to be very favourable to allow of a deposit being worked to advantage. Kock Salt and Gypsum also occur under somewhat similar conditions, but hardly merit any special remarks here, although, of course, the salt industry is enormous. Metallic Ores. — The group of impregnated stratified deposits is well represented on the Continent of Europe by the Banter sandstone, which in parts of Germany is charged with fine grains of galena, the whole rock at times containing about 3 per cent, of lead ; and by the copper slate of Germany in which the impregnated rock yields 2 to 3 per cent, of copper, and is richened at places by veins which traverse it and contain more valuable ores. It is of importance to note that such deposits as the Bunter sandstone and copper slate have afibrded employment to many hundred men for between 200 and 300 years, and so may be looked upon as deposits of very great commercial importance. This also affords another illustration of the fact that very poor 86 PROSPECTING FOR MINEBALS. deposits of this sort will pay ■well to work if the quantity of ore- is sufficient. Gold Deposits.— By far the most important, however, of the- impregnated stratified deposits which have yet been found are the so-called banket beds of the Transvaal. These beds consist of quartz conglomerates which are interstratified with shales. The remarkable feature concerning them is that the pebbles of the conglomerates appear to be imbedded in a matrix of quartz, which must have been deposited from solution around them ; it is in this enclosing quartz that the gold occurs. There are several of these beds lying one above the other and separated by beds of shale. In the neighbourhood of Johannesburg they have been traced and worked for miles along their strike. The most interesting and valuable fact regarding this deposit is the comparatively uniform yield of the stone ; for while, of course, it is not all equally rich, experience has shown that very large areas yield ore which is constantly payable to work, and that by opening the ground on a large scale a constant and steady yield can be maintained. It is difficult to account for the origin of these deposits ; and although many theories have been propounded, it is doubtful whether any of them satisfac- torily explain the occurrence, for it is not easy to understand how the enclosing matrix of quartz can have been formed unless from siliceous springs which also carried gold ; and if this be their source, it is hard to imagine that these springs should have the widespread distribution which would be necessary to explain the phenomena. It is true that some chemical decom- position in inland waters might account for the occurrence, but even this it is hardly possible to investigate at present on the basis of observed facts. Be their origin, however, what it may, it is certain that the deposits are widespread in the Transvaal, and have opened a field for gold mining such as has never been seen elsewhere, and under conditions which have never before been secured. Instead of the uncertainty of reefs, in which rich shoots of gold are suc- ceeded by barren parts, thus preventing one from forming any estimate of value beyond those portions of the reefs or lodes that, can actually be seen, the Transvaal beds have been so developed, as to show their continuity and uniformity in such a manner that they have all the elements of permanence possessed by a coal seam. Their early history, moreover, did not foreshadow the great value they would ultimately acquire ; for it was found that by battery amalgamation only a comparatively small proportion of STRATIFIED DEPOSITS. 87 the gold -was saved, and it is due to the cyanide process for the extraction of gold that the success of the Rand mines is due, while it is equally true that the success of the cyanide process is due to the Eand. In no part of the world has gold mining been carried on upon the extensive scale which is adopted here, and perhaps in no case has capital been so lavishly expended in equipping mines with all the latest improvements, as no expense has been spared when success could be gained by incurring it. At the present time the Band mines are yielding over 200,000 ounces of gold every month, approaching a value of £1,000,000 sterling ; and there appears no reason to anticipate any imme- diate falling off in the yield. No similar deposits to these have yet been found, but the prospector should devote careful attention to testing any similar beds he may meet with. It must be remembered that eminent mining engineers did not attach great importance to these beds when they were first discovered on the Rand, and it is quite possible that similar beds may be found elsewhere. There are certain conglomerates associated with the Carboniferous rocks of New South Wales in which gold has been found ; and in Spain it is stated that auriferous conglomerates exist ; but in neither case have they been developed. There are many other cases in which rocks have become im- pregnated with valuable minerals in the neighbourhood of veins aud dykes, which will be referred to under the heading of Irregular Deposits; but there is one case to which attention should be called at this place, viz., the Belubula deposits near Carcoar in New South Wales. These beds, which crop out close to the Belubula River, rise as a small hill, are regularly stratified, and dip towards the river, as in the following section : — ■ Fig. 9. — Section. In a vertical section of about 90 feet, over 50 feet in thickness is composed of material carrying gold. The auriferous beds are of a fine sandy nature, and are very easily crushed, while the beds with which they are inter- stratified are of a slaty character, and are stated by some 88 PROSPECTING FOR MINERALS. observers to be very fine grained " laccolites ; " the -whole series being considered as of igneous origin. There is, liowever, a very well marked stratification, and the lines of demarcation between the auriferous and non-auriferous beds are well and clearly defined. The auriferous beds are not uniformly rich in gold, but vary in their gold contents from mere traces to nearly 1 oz. per ton. Some thousands of tons have been crushed in a battery, and are rejjorted to have yielded between 5 and 6 dwts. of gold per ton. These beds are somewhat heavily charged with soluble sul- phates, such as alum, sulphate of iron, (fee, which makes it im- possible to recover a fair proportion of the gold by ordinary processes, unless the ores are previously roasted. "Working Expenses. — The most important matter for the prospector to bear in mind as regards the occurrence of impreg- nated minerals in stratified deposits is, that, if it can be shown that these impregnations extend over a considerable area, the conditions of working will be such as to reduce working expenses to a minimum. Under no conditions in lodes can the ore be mined so cheaply ; consequently, if large beds exist it is safe to calculate that, working on a large scale, very low returns will pay. It is true that a large initial expenditure will be necessary to equip the mine on such a scale as will allow a margin of profit upon low grade oi'es, but when this preliminary expense has been incurred the business becomes one of an industrial nature rather than the ordinary mining risk. It is true that very little prospect exists of those sensational returns which sometimes enhance the value of shares in an abnormal manner, but steady profits can be looked for if proper care is exercised in the management. There is yet one point to which attention should be called when considering the working of stratified deposits generally, whether coal, iron, salt, lead, copper, or gold — viz., that the whole success depends in every case upon a most careful attention to detail. It must be accepted as a principle that the profit per ton of ore mined will be small, and that a little laxness in the management here and there will very soon convert a surplus into a deficit. When it is considered that on an output of 1,000 tons a day a halfpenny per ton represents over £600 a year, it will be seen that the most rigid care has to be exercised on small details in order to make this class of mining successful. It is true that this question, perhaps, hardly afiects the prospector ; but still it should be always present in his mind, for he must MINERAL VEINS AND LODES. 89 look ahead and be able to decide whether any property which he secures will bear the investigation it is sure to receive before he can reap any profit from his discovery ; and a thorough knowledge of the conditions which should prevail in subsequent working is the only way in which he can avoid mistakes and an undue expenditure of time and labour in the early history of a mine. CHAPTER VI. MINERAL VEINS AND LODES. Practuring of Bocks. — Bearing in mind the numerous move- ments of elevation or depression to which strata have been subjected since they were originally formed, and the dislocation to which these movements have given rise, it becomes possible to investigate the origin and characters of metalliferous deposit occurring in lodes or fissures in the rocks. It will at once be apparent that when sedimentary strata in an unconsolidated condition are raised from the sea, tilted from one end, or even folded into a number of anticlinal and synclinal curves, they will still be in a sufficiently plastic condition to adapt themselves to any fresh form which they have to assume. This is the reason why the younger sedimentary rocks seldom <5ontain mineral veins unless they have been hardened rapidly by some local cause. On the other hand, where strata have, during the lapse of ages, become consolidated, and changed from mud, sand, or clay, to shale, sandstone, or slate, either in conse- quence of great pressure or chemical action ; or where they have been further subjected to the process of metamorphism and thus assumed the characters of quartzites, schist, or gneiss, it will be evident that any further movements of the rocks must be attended by the formation of cracks or fissures traversing them, because they are no longer sufficiently plastic to accommodate themselves to new forms without breaking. In the present chapter, the manner in which cracks may be formed and the method by which they may be opened to form underground drainage channels will first be considered ; and afterwards some attention devoted to the manner in which the valuable minerals have been brought into the reefs. Any granitic upheaval, or intrusion of other crystalline rock, 90 PROSPECTING FOR MINERALS. tilts the adjacent beds, and, if these are hard, forms a number of cracks or fissures in them, following a direction parallel to the- line of upheaval. These cracks are of two kinds, viz., those which dip or underlay away from the line of elevation, and those which are inclined towards it. Eocks are of very different degrees of hardness, and, when, broken, the line of fracture will vary in angle in the different beds. Prospectors hardly need to be told that this is the case, for they know from their own experience that different classes of rock break very differently when struck with a spalling hammer ; some have a clean straight fracture, others break with curved faces, and others split more readily in one direction than in any other. It is the varying angle of fracture in different classes of rocks which has been the primary cause of the opening of mineral veins or fissure lodes, as will be demonstrated shortly ; but in the meantime the fact is of the greatest importance to be remembered. It is seldom the case that the line of elevation is exactly parallel to the line of strike of the beds, since these have gener- ally, while in a plastic condition, been subjected to certain plications. Hence, in by far the greater number of cases, lodes pass through several different belts of strata ; thus a lode, instead of being represented by a straight line on the surface, follows a sinuous course, which is determined by the characters of the rocks through which it passes. In investigating the history of the formation of lodes it may be assumed that a granitic boss has been forced upwards and has- tilted and fractured the rocks resting upon it ; and after this some settlement of the rocks has again taken place before they assumed a stable condition. These movements are attended with results which may be illustrated by the following diagram : — Granite ' ' Sedimentary Roeiia Fig. 10. -Section. The upheaval forms cracks through the overlying strata from {a) to (b), these cracks dipping away from the line of elevation represented by the granitic boss ; a settling down of the beds MINERAL VEINS AND LODES. 91 results in a sliding of the rocks on the hanging wall side of the- fissure over those on the footwall side of it. It has already been pointed out that the cracks do not traverse the various beds at a uniform angle, and so, when a sliding takes- place of one uneven surface on another, the result will be that certain parts of the lode will remain closed, whilst other parts, are opened. This is illustrated in the following sketch : — Fig. 11.— Section, Underground channels are thus opened which are subse- quently filled with the various minerals of which lodes are formed. The opening of fissures in this manner can easily be demonr strated by drawing an uneven line on a piece of paper, tracing this line and allowing the tracing to move on the original. The result will be seen to be that the steeper parts of the lode are opened, while the flatter portions remain closed. The settling down of the granite boss gives rise to another series of cracks, which underlay towards the line of elevation (as shown in the sketch), and these open in the same manner by the- sliding of the hanging wall on the footwall in the granite area, the sedimentary rocks having by this time come to rest. XiOdes. — These movements are attended by the formation of a number of intersecting lodes in the region of a (Fig. 11), where- the two series of fissures meet; and many secondary lodes might also be formed having a less angle of inclination than the prin- cipal fractures ; also, since these cracks must terminate at some- point or other, cross courses are produced having a direction nearly at right angles to the average strike of the true reefs. These cross courses may be either barren or productive, as the conditions of the country are favourable or not. The ultimate result of these movements is to form a number of underground •92 PEOSPECTING FOE MINEEALS. galleries through which water can circulate freely, and these sub- iterranean waters depobit the various minerals found in lodes. It will be evident from an inspection of the following sections that in a simple fissure the steeper parts of the lode will remain open, the flatter portions being closed; but in those secondary fissures, which junction with the main lodes, the reverse will be the case, because the wedge-shaped block between the two fissures would be but slightly displaced, while the block of country which formed the hanging wall of the main lode Fig. 12.— Section. and the footwall of tlie secondary lode slid on the footwall of the main fissure, opening the flatter portions of the secondary fracture. There are many districts in which the cause of upheaval is not apparent, no boss of granite reaching the surface, and yet the characters of the reefs point to an origin such as described ; but there are many other localities, of which the Gulgong Goldfield, New South Wales, may be cited, where there have been other -agents at work in the formation of reefs. At Gulgong the auriferous lodes are very closely related to dykes of diorite "which penetrate the Silurian slates of the district, and the same may be said regarding many of the lodes of Western Australia. These dykes have clearly had something to do with the origin of the lodes, and have, moreover, determined to a large extent their auriferous character. They intersect the strata at various points and vary greatly in thickness; but where the strata are not penetrated by them the reefs do not appear to be auriferous, while the greater quantity of gold is in leaders traversing the •diorites themselves. In districts which are traversed by dykes, another series of •considerations comes in. These dykes have been formed by the fracture of the strata from some cause or other, and the wedging MINERAL VEINS AND LODES. 93' asunder of the beds by fused rock under great pressure. As- this rock cooled, a number of cracks would be formed from shrinkage, which would not necessai-ily follow any special di- rection. At Gulgong the beds are traversed by a great number of flat-lying leaders, which, in many cases, die out entirely when, they reach the junction of the intrusive rock with the sedimen- tary beds. It is more than probable that reefs which have no connection with these flat leaders, and were formed contempo- raneously with the intrusion of the dykes, will yet be found traversing the adjoining slates. Lodes traverse strata which have been tilted at all angles, but are never continuous throughout their course in one particular bed. This leads us to the consideration of the distribution and extent of the rich parts of lodes. Distribution of Ore in Lodes. — It is apparent that when the angle of underlay of a lode conforms more or less closely tO' the dip of the strata which it intersects, the character of the lode in depth will be more uniform than when it intersects a number of different belts of rock ; because the angle of the line of frac- ture will be uniform over greater areas. Even, however, in cases of this sort, sufficient difierences in the physical con- ditions of the rock will exist to make the fracture more or less irregular, and so there will be portions of the lode which are wider than others. When, on the other hand, the strike of a lode corresponds over long distances with the strike of the strata, but the lode underlays at a steeper angle, and thus intersects a number of different bands in depth, constant changes in value will be found in sinking, but more or less uniformity horizontally ; this con- stitutes the difference between lodes in which the ore occurs in shoots, and those in which it is chiefly found in flats or courses. When a lode which is underlaying at a steep angle also crosses the strike of flat-lying strata, it will intersect a number of different rocks, both along its course, and also in depth ; and the ore will be distributed either in bunches, which have a very limited extension in every direction, or in very flat dipping shoots. As the course of the lode varies so as to more closely assimilate to the strike of the rocks, the horizontal extension of these bunches increases ; while, as the strike of the lode ap- proaches a direction at right angles to the bedding of the strata, the deposits occur in shoots, which dip steeper and steeper in the reefs as their direction more nearly approaches a right-angle- to the bedding of the strata. The following sketch plans are designed to illustrate the- •94 PROSPECTING FOR MINERALS. manner in which shoots of ore dip in lodes under different conditions, but the best idea can be gained by making a model .and cutting sections through it in various directions. T" Plan. ■--^, ^''^-'''^»^ ^* •^<:^^^C>^ ^P^^'^'^^x^ ^,-<^ ^^^ -'i^'^^. ^^^^ -^ >s:^-^>^ ^^"^^^ "" - ^>Sir ^^^v-^^ ^'#^ ".^:^^^ \^ Plan. Pla Fig. 13. — a. Dip of country ; 6, Underlay of lode ; c, Dip of shoots. In the foregoing illustrations, when the dip of the country increases, the shoots of ore more nearly approach the vertical ; and when strata standing on end are intersected by a vertical reef at right angles to the course of the beds the shoots of ore are vertical, and practically occur as pipes or columns of ore. It will be seen, then, that the character of the rook or country exerts a very great influence on the behaviour of lodes and on the distribution of the rich parts ; this has been proved, beyond ■ doubt, to be the case in every district which has been carefully studied. Every prospector is acquainted with the term "kindly ground," which is used to designate those belts of rock which -are favourable for the occurrence of mineral deposits ; but the characters of these belts vary greatly in different districts, and their local characters must be determined in each district which Tve may be called upon to examine. As a general rule, those rocks which are moderately hard appear to be the most favourable for the occurrence of ore, laecause they possess sufficient coherence to remain open when MINERAL VEINS AND LODES. 95 ■they have been fractured, and do not offer too great a resistance to fracture in the first instance. The softer rocks, such as shales, seldom carry valuable deposits ; because the fissures formed are not likely to remain open as channels, but are -quickly filled with fallen matter from the hanging wall. The foregoing remarks give some idea of the manner in which the various lodes have been originally formed by fractures in the rocks, how these cracks have been opened by the action of gravity so as to form underground galleries through which water could circulate freely ; and a study of the lodes themselves furnishes fresh confirmition of the facts that have been stated. It is found in many cases that the walls of lodes have been ■smoothed, polished, and striated by the sliding of one rough irregular surface on the other, and the direction of the striations shows the direction in which this sliding action took place. Where rocks are not sufficiently hard to preserve the striations or " slickensides," a thin clayey partifag or "flucan," separating the lode from its walls, is frequently found, which, it can hardly be doubted, has been formed by the grinding of the rocks. The walls of lodes, for some little distance on either side, are also, in many instances, somewhat shattered by the movement which has taken place ; and, at times, as for instance in the Alburnia mine in New Zealand, this change has been so marked as to give rise to the suppositions that the rock alongside the lode was different to that a short distance away ; and that the bedding of the -country corresponded with the underlay of the lodes themselves, instead of intersecting them at a flat angle as is really the case. A study of reefs will also convince us that they have been deposited by the agency of water, for in many cases the mineral is arranged in a series of bands or zones parallel to either wall. In many cases also the walls have been altered by chemical means, sometimes for great distances from the lodes themselves ; thus, in tin districts, the granite is often decomposed or kaolinised by the action of percolating water ; while, in other localities, the walls are sometimes hardened by silicification of the rocks. No lode has ever been formed by the intrusion of quartz in a fused condition. A very few moments' consideration will con- vince the practical prospector that this is the case, for quartz is one of the most infusible substances known ; so infusible, in fact, that in many of the volcanic rocks, in which free quartz occurs, no doubt can exist that the crystals were formed in the internal laboratories of the earth and floated to the surface in the molten -magma, a fact which is borne out by a microscopic examination •of the rocks, when the lines of flow can be traced around the 96 PROSPECTING FOR MINERALS. crystals. Quartz, then, being of so infusible a nature, ■would,, if it had been intruded in a molten condition, have been suffi- ciently hot to melt the more readily fusible rocks through which it passed, and any theory founded upon the supposition of filling from below by the agency of heat is necessarily wrong, as the- walls of lodes never show any evidence of having been subjected to a heat sufficiently intense to fuse them. Studying lodes, then, as simple fissures, the conclusion is arrived at that the average underlay of a lode does not in any way determine its ore-bearing properties ; but that, even in the same district, lodes may be vertical or lie in an almost horizontal position and yet be equally productive ; but the successive in- clinations of the different parts of lodes are of the greatest im- portance in determining the distribution of the rich parts. As a general rule, the steeper parts of lodes are the richest, although this is not an invariable rule ; the reverse being often the case when hanging wall leaders make junction with a main lode. There are many other points, however, to be considered con- cerning the distribution of the rich parts of lodes. It will be remembered that lodes follow a sinuous course along the surface or along any level in a mine, and so the rich parts will be un- equally distributed along a horizontal line. This irregular distribution also depends upon the different rocks through which the lode passes along its course, and since it is generally found that the richer parts are those in which the lode corre- sponds in direction most nearly to the line of elevation, this distribution of the rich parts in the upper levels of a mine will frequently serve as a guide by which to determine the "kindly country " of any particular district ; and a geological examina- tion of the district will afford data by which it may be inferred in what direction the shoots of ore dip in the lode itself. Observations have hitherto been confined to a single fissure produced by a single upheaval or movement, but single fissures or lodes are of most unusual occurrence, and it is notorious that where they do occur they very seldom contain a sufficient quan- tity of valuable mineral to pay for extraction. As a rule, the force which has produced one vein has also produced a series of others parallel to it ; and it is a noteworthy fact that where the behaviour of one of these has been determined, the behaviour of the others and the distribution of the rich parts can generally be predicted with some precision from a consideration of the- conditions enumerated. In the more known and better opened mining districts, such as Cornwall and Freiberg, it has been shown that several sue-- MINERAL YEINS AND LODES. 97 cessive series of lodes have been formed by tiltings of the strata from different points; and that the lodes following particular courses are generally characterised by special minerals ; but the less known mineral districts have not yet been sufficiently studied to state these facts authoritatively. These upheavals of the strata along different lines have not only opened a series of fresh reefs each time — the younger ones intersecting those which have been previously formed — but in not a few cases, the later movements have re-opened some of the old reefs in an irregular manner, and so some of the accessory deposits have been formed, which are frequently so difficult to account for, but which are met with in lodes from time to time, apparently defying all attempts to explain their origin or to predict their extent. Rich deposits in lodes are also cut off abruptly at places by slides or faults, but the study of these and the means to be adopted for the recovery of lodes will form the matter for a sub- sequent chapter. How IiOd.es were Pilled. — A point has now been reached in the consideration of the subject at which it is necessary to allude to the manner in which lodes or reefs have been filled with their mineral contents. Before stating what is probably the true account of the filling of these cavities, it will be well to glance for a few moments at those theories which have been proposed, and which, for one reason or other, must be rejected as in- adequate to account for observed phenomena. In the early days of geological research there were two schools of geologists, one of which attributed everything possible to igneous origin, or the action of heat ; while the other school sought the aid of water to explain most of the observed facts. It is needless to remark that these extreme views led to a very great number of absurd theories being propounded, both on one side and the other ; but the mode of origin of reefs has remained a matter of dispute after many other points of difference have been settled. It has been held by one school that reefs or lodes are of igneous origin, and have therefore been filled from below the crust of the earth; and, by the other, that they owe their origin to aqueous sigencies, and have been filled from the surface ; but neither of these views can be taken as correct in its entirety. Of course, so long as these two theories were held by opposing parties, it was supposed that if a reef were filled from below, it would necessarily widen as it went down; whereas, if the filling 7 98 PROSPECTING FOR MINERALS. took place from the surface, the width of the reef would gradu- ally diminish until it at last pinched out. It will be seen from the explanation which has already been given concerning the origin of the fissures which have since been filled with difierent minerals, that all true fissure reefs must necessarily thin out and widen a great number of times between their outcrops and that point in depth at which the difficulties of working exceed the value of the mineral, for no true fissure vein has yet been proved to die out entirely in depth. It is stated by many authors that another series of veins, known as " gash veins," does exist ; but their occurrence is of a very doubtful nature. They are variously described as " lenticu- lar cavities," " veins confined to one formation," ifec, without regard to their mode of origin, and so include several classes of deposit which should be otherwise classified. Gash veins, if they do exist, may be regarded as lodes formed by the folding of strata after consolidation ; those occupying the anticlines being necessarily wide towards the surface and narrower as they descend ; whilst those occurring in synclines would widen in depth until the next underlying formation was reached, when they would cut out. It is possible that the saddle reefs of Victoria (which will be described in the chapter on Gold) might belong to this class of deposits, but by far the greater number of the so-called " gash veins " belong to one or other of the irregular deposits to be presently described. When a true lode appears to pinch out, it will inevitably widen again lower down ; and when it is cut off by a slide, it may be found again heaved for a greater or less distance either to the right or left. What the prospector or miner has to decide is whether it is worth his while to spend the time and money necessary to again recover a lode that has been lost. Having from time to time examined numbers of quartz reefs in different parts of the world, it may be safely affirmed that in no case that has come under my notice have the walls of lodes been altered by other means than decomposition or an infiltra- tion of silica, which frequently hardens them ; besides which, quartz, as already pointed out, is far less fusible than most of the rocks through which the reefs pass. A careful examination, moreover, shows that reefs have been opened by the sliding action previously described, the walls being frequently scratched and striated by this movement. When the walls are examined, no signs whatever of fusion having taken place can be seen, but many angular prominences yet remain. In many cases lodes are also found to have a banded structure in lines parallel to the MINERAL VEINS AND I.ODES. 09 walls, the different bands sometimes containing different min- erals, showing that the solutions which deposited these minerals varied from time to time. A consideration of the foregoing phenomena leads to the con- clusion that in every case lodes have been filled directly by crystallisation of minerals from solution, and that the constitu- ents of these minerals have been dissolved from the rocks through which the subterranean water filtered. In some cases they may have been derived in the immediate vicinity of the lodes in which they are found ; and, in others, they have come from some considerable distance, being only deposited when the waters have met with rocks of special composition or other con- ditions have been favourable. In speaking of this subject it will be well to give some familiar instances of the solvent action of water under different conditions. Limestone, for instance, is nearly insoluble in quite pure water ; but when this water has previously dissolved a certain quantity of carbonic acid, which all rain water takes up in falling through the air, it is then capable of dissolving carbonate of lime. All water in limestone districts is " hard," or, in other words, contains carbonate of lime in solution ; and the caves, which are always found in limestone, show the extent to which solution has gone on. Caves, however, not only afford proof that the limestone has been dissolved, but show also how it may again be deposited, the stalactites which hang from the roofs and the stalagmites on the floors having been thus formed. In many cases deposits of calcareous sinter occur on the surface, and some remarkable deposits are found in mines, to which allusion will be subsequently made. The action of carbonic acid is not, however, limited to the solution of carbonates, but has also the power of decomposing many minerals, such as the felspars, in doing which it dissolves the alkalies in the form of carbonate, and sets free silica in a soluble form. Quartz is also soluble in these solutions of alkaline carbonates. The solvent action of water charged with carbonic acid is greatly increased when either the temperature or pressure is augmented, and as soon as the temperature is lowered or pressure decreased the substance held in solution is again deposited. As a proof of the foregoing statement, reference need only be made to the hot-springs of the Rotomahana district, N.Z., where, before the Tarawera eruption which destroyed all the terraces which had been deposited by these springs, all the actions 100 PROSPECTING rOE MINERALS. specified were going on. The water came to the surface charged with carbonic acid, which was given ofi' when it reached the sur- face, the pressure having been diminished, and the silica which - had been dissolved from the rocks through which the water had passed was again deposited as sinter, forming the famous white and pink terraces. The silica held in suspension by tlie water was the cause of the bright pellucid blue colour so charac- teristic of these springs. The sinter consisted entirely of silica, while carbonic acid was evolved in large quantities at the geysers. Sulphuretted hydrogen is not less important in the chemical laboratories of nature. As a gas it issues from springs in many districts, being readily recognised by its unpleasant smell like rotten eggs. This gas has properties which are relied upon for many reactions in analytical research. It precipitates some metals in acid, others in alkaline solutions ; but most of the metals are dissolved in alkaline sulphides. It is essential to remember that in all cases, whether water be charged with carbonic acid or sulphuretted hydrogen, the solvent action is greatly increased by pressure or heat ; and that when the temperature is lowered or the pressure decreased deposition will ensue. This is the principal reason why minerals have been deposited in lodes, for it must be borne in mind that the water circulating in lodes cannot be under the same pressure as it was when in the pores of the rocks, and that as it rises towards the surface the temperature steadily decreases. As an illustration, an extract may be quoted from Mr. G. F. Becker's report on the geology of the Oomstock lode ( U.S. Geo- logical Survey, 1880-81) : — " Baron von Richthofen was of opinion that fluorine and chlorine had played a large part in the ore deposition on the Comstook, and this the writer is not disposed to deny ; but on the other hand, it is plain that most of the phenomena are sufficiently accounted for on the supposition that the agents have been merely solutions of carbonic and hydrosulphuric acids. These reagents will attack the bisilicates and felspars. The- result would be carbonates and sulphides of metals, earths and alkalies, and free quartz ; but quartz and the sulphides of the metals are soluble in solutions of carbonates and sulphides of the earths and alkalies, and the essential constituents of the ore- might, therefore, readily be conveyed to openings in the vein where they would have been deposited on relief of pressure and diminvition of temperature." "An advance boring on the 3,000 feet level of the Yellow MINERAL VEINS AND LODES. 101 Jacket struck a powerful stream of water at 3,065 feet (in the west country) which was heavily charged with hydrogen sul- phide and had a temperature of 170° F., and there is equal evidence of the presence of carbonic acid in the water of the lower levels. A spring on the 2,700 feet level of the Yellow Jacket, which showed a temperature of above 150° F., ■was found to be depositing a sinter largely composed of car- bonates." But it is not necessary to turn to America alone for illustra- "tions of the filling of reefs, for any mining district which has been sufficiently studied will afford subject for reflection. In the Thames Goldfield, New Zealand, for instance, most of the phenomena alluded to are very clearly demonstrated. The country rock consists of numbers of stratified bands of sub- marine volcanic rocks, some of which are hard, green, and undecomposed ; others consist of a softer white rock in which "the felspars have suffered decomposition, and the rock itself is charged with numbers of small crystals of pyrites, especially near the reefs. The rock is also traversed by numerous small black veins, chiefly sulphide of iron and antimony, and it is in these decomposed rocks that the richest deposits of gold are found in the reefs. All miners who are acquainted with the Thames Goldfield will recognise the carbonic acid which has been alluded to in the heavy gas so prevalent below the 400 feet level, and which renders ventilation so difficult. The Big Pump affords an illustration of the quantity of carbonates held in solu- tion under pressure and ready to be deposited when this pres- sure is removed ; and the records of the Pumping Association show that a very heavy expense was incurred in cleaning the columns from the incrustation of carbonates, which, during the ■earlier days of the deep levels, formed with almost unprecedented rapidity. It cannot be said that free sulphuretted hydrogen has been ■detected in this locality, but there is little doubt that it must have existed during the charging of the reefs. It is a well-known fact in all mining districts that the junc- tions of lodes are generally the richest points, always supposing -that the junction takes place in " kindly country ;" the expla- nation of this is simple on the aqueous theory of filling of lodes. Water traversing two different channels of necessity passes through different belts of country, and thus holds different sub- stances in solution. As a case in point, suppose the water in one channel contains carbonates of lime and alkalies in solution, .as well as silica derived from decomposition of felspars ; and 102 PROSPECTING FOR MINERALS. that the other, charged with sulphuretted hydrogen, brought with it sulphide of antimony dissolved in sulphide of lime. The result of these two waters meeting would be that carbonate of lime would be formed, sulphuretted hydrogen set free, and sulphide of antimony deposited, as well as the silica which was formerly held in solution by the carbonic acid. Numbers of such illustrations might be given, but it is not the object of this book to explain all phenomena which occur in lodes, but merely to direct the observations of prospectors into the right channels. It is well known that in every district certain rocks are more "kindly" for one special mineral than for any other. Lime- stone, for instance, is very often the rock in which galena occurs; while gold is frequently closely related to diorite. In such cases the solution carrying the metals may have traversed various rocks flowing sometimes for great distances without meeting with conditions favourable for deposition, and only have met with these conditions when it reached that belt of country which we, in working the mine, designate "kindly ground," where, by an interchange of materials, by chemical action, in fact, deposi- tion ensued, and shoots, bunches, or courses of ore were formed as the case might be. This raises the very interesting question of the origin of gold and other minerals which have accumulated in lodes, and a very close relationship can hardly fail to be traced between the rocks- encasing the lodes and the mineral deposits which occur in them. In connection with this a quotation may be permitted from Mr. R S. Emmons's report on the mining industry of the Leadville district, Colorado, because it very well expresses the views it is desired to enunciate. He says : — " The earlier geologists devoted much speculation to the subject of the origin of metallic minerals in ore deposits, and arrayed themselves on the side respectively of the Neptunists or Plutonists, according- as they believed them to have been brought to their present position by descending or ascending currents, whether gaseous or liquid. As pure theory has been gradually modified by the results of actual investigation, the upholders of the two opposing^ schools have come to concede in this, as in other questions of general bearing on geology, an element of truth even in the views of their opponents. Only extremists maintain that any series of geological phenomena admit of but one explanation, or are due to one universal immediate cause. It is generally agreed that subterranean waters, however deep seated their apparent source, came originally from the surface. It is, more- MINERAL VEINS AND LODES. 103 over, proved that no rocks are absolutely impermeable to water, but as on the earth's surface, so within its solid crust, there is a constant circulation either through capillary pores, where it is not readily visible, or through the larger and more apparent channels formed by joints, cleavage planes, faults, dykes, and , stratification lines, the direction taken by such waters varying with different local conditions. In the case, therefore, of ore deposits, which are derived from aqueous solutions circulating within the earth's crust, a class which is constantly augmented by scientific investigations, the question as to the immediate sources of the metals in solutions from which they were de- posited, whether above or below the present position, is one which must be determined independently in each individual case, and to which no general answer can probably ever be given." A few examples may be mentioned in illustration of the fore- going remarks. At Adelong, N. S. Wales, the reefs traverse a hard, undecomposed syenitic granite, and are undoubtedly true fissure reefs ; but the country rock from the surface to the lowest levels exhibits no appreciable change in its composition, the granite throughout being a hard, solid compact rock. The lodes themselves, however, are not completely filled with quartz, but are really softer channels of country largely composed of chlorite ; and all those parts which were not filled mechanically have since been charged with auriferous quartz by the cir- culating waters. In this case, the deposition of the gold and quartz was probably due to chemical changes induced in these softer channels, and not in any way to the decomposition of the solid granite itself Grenfell, on the other hand, which is also in N. S. Wales, may be taken as a case in point where the rock has exerted a powerful influence on the mineral deposits. The rook in which the richest deposits of gold occurred in the Consols Reef was a dark-coloured porphyrite containing a dark- oreenish mica, while in the lower levels, where the reef ceased to be payable, no mica was to be seen. In this case, the presence of mica in the rock appears to point to the class of ground which possessed the necessary substances for precipitating gold, and shows how necessary it is to trace the extent and boundaries of different classes of rock. Even more marked than this is the case of the Thames, where the shoots of gold can be traced through several different belts of rock with which other beds are interstratified, in which gold does not occur in payable quantities ; and a section ot the Alburnia Mine will illustrate this varying character very well, 104 BROSPECTING FOR MINERALS. those belts marked (a, Fig. 14) being the hard and unproductive country. It is often the case that the charging of reefs is attri- buted to what is known as solfataric action, the final stage of volcanic eruption when only steam and gases are emitted from the craters being called the solfatara stage. Where, as at the Thames, reefs are found traversing volcanic rocks, it is reason- able to suppose this to have been the case. In Mr. Becker's report on the Oomstock lode, which has already been quoted, he shows, in a section from Mount Davidson through the upper Fig. 14.^Section through Alburnia Mine. end of the Sutro tunnel, several belts of country which have been decomposed by solfataric action, although it is worthy of notice that none of these bands approach the Oomstock lode itself, which occurs at the junction of diorite and diabase at its outcrop, but intersects the diorite in depth. In his report on the Mount Morgan gold deposits, Mr. R. L. Jack, Government Geologist for Queensland, attributes the occurrence of gold at that place to deposition from a hot spring. The country in the immediate vicinity appears to be traversed by dykes of rhyolite, and there are considerable deposits of sili- ceous sinter resembling in character the deposits of geysers. It is in association with these siliceous sinter deposits, as well as with brown aud red hsematite ores, which might justly be described as gossan, that the gold occurs. It is perfectly reasonable to believe that deposits of gold may be formed in this manner ; indeed geysers and hot springs generally afford the best illustra- tions of many of the operations going on during the charging of reefs, and in isolated cases, such as Mount Morgan, substances of economic value may well be introduced ; but it must be borne in mind that nearly all lodes which contain iron in any form, notably as iron pyrites, decompose near the surface to form a porous kind of haeimatite which is known to miners as "gossan," and that this gossan will sometimes extend for a depth of 100 feet to 150 feet from the surface before the true ore of the mine is met with. It is very questionable whether the theory of deposition from IRREGULAR DEPOSITS. 105 a hot spring is correct in the case of Mount Morgan, or whether the deposit is simply a lode which has opened to very large dimensions ; later developments appear to point to the deposit being nothing else than a lode. Gossans are due to the oxidation of ores of iron, and all substances in the lode which can be readily oxidised are so changed ; where copper pyrites, for instance, is present it becomes •changed to sulphate of copper, which is carried away in solution, leaving the gossan porous. Noble metals, such as silver and gold, are rarely carried away in solution ; but silver is frequently changed to the condition of chloride. All silver mines afford illustrations of how this action has gone on. Bearing these points in mind, it will be evident that the character of a gossan will seldom afford any index of the true nature of the lode it covers. Generally speaking, lodes which have a good gossan on the surface are valuable in depth for one class of mineral or other ; and a gossan which has a snuffy brown colour and great porosity may generally be looked upon as the best indication. CHAPTER VII. IRREGULAR DEPOSITS. A GREAT number of the repositories in which minerals occur come under one or other of the divisions which are classed as irregular deposits, and, in some cases, they are of very great im- portance. Their irregularity, however, makes the extent of the ore even more uncertain than in lodes, such as have been described in the preceding chapter, and no rules can be enunci- ated which afford any guide as to their distribution. In certain cases huge deposits of ore are found which yield vast quantities of mineral ; in others, a little ore occurs in bunches, always inducing further prospecting, but not always leading to deposits of sufficient extent and value to repay the cost of exploratory workings. These irregular deposits are, in fact, of the most speculative nature, and, while they at times result in the ac- cumulation of large fortunes, they as often, or perhaps more frequently, only lead one to expend money on prospecting which is never repaid. It is unfortunately the case that no one, how- ever experienced, can say with any certainty whether it is judicious to continue prospecting work on a particular deposit or 106 PROSPECTING FOR MINERALS. to abandon it, for, when the ore is poor and of small extent, a few feet driven may completely change the aspect of aiBfairs and render a mine which had no encouraging features one which has a very considerable prospective value. These irregular deposits may be subdivided as follows : — 1. Impregnations. 2. Reticulated veins. 3. Lenticular aggregations. 4. Irregular masses. 5. Contact deposits. 6. Cave deposits. A description of the conditions of each of these will be given in this chapter, with some illustrations of their occurrence. Impregnations. — It will be remembered that in the chapter on stratified deposits some instances have been given of the impregnation of beds by copper, lead, and gold, in which somewhat constant characters prevail over wide areas ; but there are also rocks, frequently of igneous origin, which are impreg- nated with mineral in a most irregular manner, and which, at times, have been worked to considerable advantage. The cause of these impregnations is not always, or indeed often, easy to find, but frequently a joint in the rocks, looking like a wall of a lode (sometimes with a thin vein of quartz, calcite, or barytes) forms an indicator vein, and the impregnated rock lies on one or other side of this indicator, and occasionally the rock is impreg- nated with mineral on both sides of it. The distance to which this impregnation extends from the indicator is very various, and when cross cut may prove to be only a foot or two wide in places and at others to extend for a hundred feet or more. Probably the best illustration that can be found of this class of deposit is in the mines of the Calico District, near Los Angeles, in Southern California, the rock of which district is andesite. The nature of the rock varies a good deal in different parts of the range of hills which rises from the edge of the Mohave Desert ; but they are almost devoid of vegetation, and have weathered in large patches of iron red, pink, and green, thus affording a most curious patchwork appearance when seen from a distance, and one which would inevitably attract attention. These rocks are traversed by veins, such as are described, and are impregnated with chloride of silver in a very irregular manner, biit over a very wide extent. The ore is of a free milling character, and is worked by battery and pan amalgama- tion, the Boss continuous system being adopted. The deposits have been suflS.ciently rich at times to give rise to much litigation IRREGULAR DEPOSITS. 107 between the respective companies which have been working them ; but, taken on an average of the good and bad worked, they have yielded about 10 oz. of silver per ton of ore. In some cases huge chambers, which can only be likened to caves of the largest type, have been excavated, the whole of the rock thus broken having been crushed and the silver extracted ; while in other parts of the mines drives, many hundreds of feet in length, have failed to develop any ore that is of sufficient value to pay for extraction. It will be evident that mines of this class require the most constant care in sampling and assaying, and a rough system of testing whether the rock carries silver is practised in the mines, while regular assays are made day by day of all ore that shows sufficient indications to these rough tests. Very closely related to these are the so-called fahlbands of Kongsberg, Snarum, and Skutterud in Norway, which are regarded as impregnations by von Cotta. They are described by J. A. Phillips as "parallel belts of rock of considerable width and extent impregnated with sulphides of iron, copper, and zinc, and sometimes also with those of lead, cobalt, and silver." The fahlbands of Kongsberg are worked for silver, and are about 1,000 feet thick ; but it is only in a few localities where they are sufficiently rich to pay for working. They are traversed by veins which are unremunerative in the gneiss and schists, but become highly argentiferous in passing through the fahlbands or grey beds, which exert the same influ- ence on the veins traversing them as the ordinary " kindly country" does upon reefs or lodes in general, so that, in reality, these fahlbands hardly deserve to be considered as an inde- pendent class of deposits. The cobalt deposits of Snarum and Skutterud also occur in fahlbands which are sometimes rich enough to pay for working, but these, unlike those of Kongsberg, are not traversed by mineral veins, and so would be more properly considered as impregnations. In Western Australia there are decomposed rocks of consider- able width which carry a little gold, but none have been found up to the present which will repay the cost of working. The occurrence of gold in this country in lodes in which the gangue is not pure quartz, but a ferruginous material containing, how- ever, a large proportion of silica, appears to have led prospectors to think that every decomposed rock met with was of the same nature ; and they have accordingly named these decomposed rocks "lode formation." 108 PEOSPECTING FOR MINEBALS. A considerable amount of work has been expended on these so-called " lode formations " without, however, demonstrating the fact that any of them are payable ; while the lodes them- selves, which these deposits are supposed to resemble, are the richest gold producers yet found in the colony. Reticulated Veins (Stockworks). — In some districts certain belts of rock are traversed by a great number of small veins which intersect the country in all directions, forming a perfect network. Where these veins contain any mineral which is of economic value, the whole of the rock is crushed for the mineral which it contains. Where reticulated veins occur, the country Tock itself is generally impregnated with the mineral as well; and, in some cases, the impregnation has no doubt been brought about by the infiltration of the mineral waters which charged the veins ; while, in other cases, the rock was impregnated first, and the veins derived their mineral from the rock. Deposits of this sort are called Stockworks. Tinstone is frequently found under these conditions both in Cornwall and " intersect at x, and x y will Fig. 23.— Section. be the line of intersection. Schmidt's law may be defined as follows : — If a lode is intersected by a cross-course or fault, and the lode is heaved either to the right or left, then, in order to find in which direc- tion this heave has taken place, it is necessary to know the direction of the line of intersection of the two. This being determined, the course of the lode and cross-course having been shown on a plan, and the line of intersection also indicated, the determina- tion in which direction the heave has taken place is sim- ple. A perpendicular is Fig. 24. — Plan. erected to the cross-course at the point a (Fig. 25) on the side on which the lode is lost, as in the following diagram. The line of intersection is produced to 6, and then on which- ever side of the line a b, the perpendicular a c falls is the direction in which to search for the lost lode. In the case given, a d would be the direction drive. The following show that in some cases the lode will not be heaved at all by the cross-course, Fig. 25. — Plan. while in others it may be in the direction of the greater angle fa d ; and in others in the direction of the lesser angle /oe. in which to diagrams DYNAMICS OF LODES. 121 The distance to be driven in either case can only be found ■when the amount of vertical displacement of the fault is known, and this cannot always be determined. Where accurate plans liode heaved in direction of greater angle. Lode not heaved. Lode heaved in direction of lesser angle. Fig. 26.— Plan. and sections of the geological structure of the country traversed by the fault are available, the exact position of the beds on either side of the fault may be recognised; and, having the ];22 PROSPECTING FOR MINERALS. amount of vertical throw, the heave can easily be determined^ since by setting out the line of intersection in elevation instead of plan, the ratio which exists between the vertical displacement- and the heave can readily be arrived at. Exceptions to Schmidt's Law. — There are a few cases in which Schmidt's law does not apply, but these are chiefly where subsequent movements have taken place, tilting the fault from its original plane to one dipping in the opposite direction. It will be readily seen that in some cases the movements are very complicated and require most careful study before they can be properly understood. The following plan w;ill explain what a complicated network might be produced by the successive action of two faults with their corresponding heaves on a single lode : — \^^^^^^^e ^ Fig. 27.— Plan. The lode ah ode was originally one continuous fissure,, and was first of all heaved by the fault x in the direction of the lesser angle ; subsequently, the country was dislocated by the fault y which heaved both the lode and the original cross- course in the direction of the greater angle, thus giving rise to the somewhat complicated structure apparent in the plan. A study of this plan illustrates very well the comparative dates of the difierent dislocations. It will be evident that in the first case the country was broken by elevation parallel to the once continuous line abcde, and, the fissure being opened in the manner previously described, the channel was filled with ore before the second movement took place. This second move- DYNAMICS OP LODES. 123^ ment was an elevation parallel to the line x, and it will be evident, from the way in which the lode is heaved by it, that the lode and fault x are underlaying in the direction indicated by the arrows on the plan. The underlay of the fault y must also be as indicated, and the elevatioil parallel to the line y must have been the last structural movement which had taken place. Other cases may occur in which a lode is intersected bj' a cross-course which strikes in the same direction as the lode, but underlays in the opposite direction, as below (Fig. 28) ; in cases of this sort there will, of course, be no heave apparent, but the same lode may be brought to the surface several '^Ji- — iQ. ^— ^'*^_*]! —^■-' ' times by parallel faults. "I^^C---'-- "^r" — — - Some districts are tra- ^.1^^^"" \ "jI^^--— " ' versed by a great num- '_. —~^^' — Z."^CI^*--" ^ ber of faults of this sort, - ■■^^~ J^ILl- — •— ^^ ~_ "S" and taking Grenfell, j^'^_ — ^r 3. — "— —'~ New South Wales, as an ^ ^~— — —^Z- illustration, the reefs " "" have been faulted time ^^S- 28.-Sectioii. after time, so that at present the quartz appears to occur in a succession of isolated blocks which are found following a zigzag line through the country from the surface downwards, the blocks seldom having a greater extent than about 200 feet. The lodes in this district occur in a rock which is called por- phyrite, consisting of felspar crystals in a felsitic base ; near the surface, and for some hundreds of feet below it, the rock has been decomposed and changed from its original blue colour to a sort of dirty brown. This rock, although hard to work in the mines (requiring the use of explosives), crumbles away rapidly when exposed to the action of the atmosphere ; it traverses the- country in a north and south direction, the beds on either side of it to the east and west being slates. In these slates several reefs have been found which run parallel to the main line of upheaval ; but in no case have they proved to contain a sufficient quantity of gold to pay for extraction. In the belt of porphyrite, however, some very rich reefs have been found ; but instead of running north and south, as in the slates, they traverse the porphyrite obliquely, coursing north-east and south-west and underlay to the north-west at angles varying from 56° to 65°. As already stated, these reefs have been subjected to numerous- heaves, and these have generally thrown the reef in the direction of the footwall ; so that a vertical section of one of the mines would be much as shown in the adjoining sketch (Fig. 29). 124 PROSPECTING FOE MINEEALS. In all cases where the reefs have been set back in this manner the slides which have dislocated them traverse the country at very flat angles, and the movement, instead of being a sliding or settling down of that part of the country, which is on the hanging wall side of the reef, is represented by the reverse faults which have been previously de- scribed. Hence Schmidt's law would not be applic- able in driving for the recovery of the lost lodes. There has, however, been one exception proved to this rule in the Home- ward Bound Claims, where highly payable stone was traced to a depth of 300 feet from the surface. Several floors, such as described, were met with which heaved the reef into the footwall, sometimes for as great a distance as 25 feet, but at the 300 feet level the reef jumped for a 29.— Section. distance of 9 feet into the hanging wall, and it is worthy of note that the slide which dislocated the reef at this point traversed the country at a steeper angle and, on its underlay, met the underlay of the reef; so that normal conditions super- vened, and the movement which took place was a downward one on the hanging wall side of the slide. Other instances might, of course, be quoted in which Schmidt's law is not applicable for the recovery of lost lodes, but in by far the greater majority of cases the rule is applicable ; the excep- tions are only given with the view of explaining why in certain cases it will lead to incorrect conclusions. 125 CHAPTER IX. ALLUVIAL DEPOSITS. Having alluded to all the different conditions under which minerals occur, either as reefs or stratified deposits, it is now pro- posed to devote a chapter to a description of those repositories of minerals known as alluvial deposits. This subject is of the more importance because, although they are of a less permanent character than reefs, the greater quantity of both tin and gold which has, up to the present time, been won, has been derived from deposits of this sort ; and large areas still exist in which a judicious application of capital on comparatively poor ground will be remunerative. It should be mentioned here that the only minerals of importance which are found in alluvial de- posits are gold, the other precious metals, as well as tinstone and the gems which, from their hardness, and their power of resist- ing chemical change, are preserved in their original state, even when submitted for long periods to the action of the weather. Source of Materials. — It will be evident to all that alluvial deposits have been derived, in the first instance, either from reefs or irregular deposits, such as described, or from rocks which are impregnated with mineral ; and that, in the majority of cases, the tin and gold found in these alluvial deposits have also been derived directly from reefs, although it is probable that the larger nuggets of gold were deposited by chemical or electrical action at the places where they are found. Age of Parent Heefs. — Although at one time these alluvial deposits formed part of parent reefs, and have, by the denuding and transporting action of water, been broken down and rounded, they were in some cases detached from the reefs at a very early period in the history of the earth, and have since been subjected, to the action of water flowing in many different directions ; hence, the discovery of payable alluvial gold may not afford the means of tracing directly the reefs from which this gold was derived. In order to render this quite clear, it is necessary once more to refer to the rocks in which the reefs occur, and the periods- 126 PEOSPECTING FOR MINERALS. during which the fissures were formed that are now filled with mineral deposits. A special history necessarily appertains to each individual district, and it is manifestly impossible to deal in these pages with many instances ; but it will be of interest to mention a few as illustrating the class of investigation that may be adopted by the prospector who will take sufficient trouble to study the reasons for the various facts that he observes. Australian Reefs. — In Victoria the reefs chiefly occur in Upper Cambrian and Lower Silurian rocks ; while in New South Wales they traverse the beds of the Upper Silurian and Devonian systems. During the Devonian period, or at its close, great upheavals took place, granite in many places was brought to the surface and the enclosing rooks were fractured along a number of lines, the direction of which depended upon the lines of upheaval of these granites. The fissures formed were charged with mineral, and from that time the formation of alluvial deposits commenced, the rocks themselves being worn away by the action of running water, and the minerals broken from the reefs concentrated in the river channels of that day. There can be no doubt that such was the case, because at the base of the coal measures of New South Wales there are beds of con- glomerate in which water-worn gold occurs, and sometimes, as at Tallawong, there is sufficient gold present to make these conglomerates worth working. Of course, the gold in these conglomerates must have been derived from reefs which existed before the Carboniferous for- mation (now occupying such a large area in New South Wales) had been deposited ; but, at the same time, there are many reefs in the country which are of much later origin. The Silurian rocks, for instance, are traversed by dykes of diorite, some of which are on such a massive scale as almost to merit the term of bosses, and it has been pointed out by the late Mr. Wilkinson that many of these dykes are very closely associated with the occurrence of gold. Dykes of this rock penetrate not only the coal measures, but also the younger Hawkesbury sandstone, so that it is a difficult point to determine the period of their intrusion or even to say whether they are due to one or a series of eruptions. Be that as it may, however, it is perfectly certain that at some places the reefs are due to the intrusion of rocks of this class, and a study of the alluvial deposits in these districts gives unmistak- able evidence of the fact that the gold was derived direct from the parent reef ALLUVIAL DEPOSITS. 127 A visit to some of these localities, or even an inspection of a map on which the reefs and gold leads are delineated, is con- vincing of the fact that the alluvial deposits have been derived directly from the reefs. The streams in which the alluvial deposits occur cross the belts of country in which the reefs are found, and it is only those parts of the streams which now lie below the line of reef that payable gold has been obtained. This distribution of the gold not only points to the fact that it has been derived directly from the reefs, but also shows conclusively that the drainage system of the country has not been changed since the alluvial deposits began to be formed. But this is not always the case ; for, in other localities, very great changes have ensued since the earliest deposition of the gold-bearing gravels. For instance, it has been pointed out by Mr. Wilkinson that at Biragambil, New South Wales, there is a gully in which payable alluvial deposits occurred that have since been worked out, the gold of which could only have been derived from the auriferous conglomerates of the coal measures ; these conglomerates were denuded and their gold concentrated by a process of natural sluicing. The proof that this is the case is to be found in the fact that above a certain point in the gully, a point at which the coal measures cease, and Silurian slates are met with, no gold has yet been found ; nor are the condi- tions of the slates such as are favourable for the occurrence of reefs. Deep Leads. — There are also some other and most important alluvial drifts in the Gulgong district, which have not been deposited by existing streams, these drifts being known as the deep leads ; they are found at considerable depths below the surface of the ground, and are frequently buried beneath as much as 100 feet of basalt. Similar conditions prevail in Victoria and New England. These gravels were deposited by streams which, flowing during Miocene and older Pliocene times, had a somewhat different course from those which flow at the present day, and their course was suddenly arrested during the middle Pliocene period by streams of molten rock, which, flowing from fissures opened in the surface of the ground, poured down some of the watercourses and dammed back the water in others, up which they flowed until they found their level. The magnitude of this eruption can be appreciated when it is remembered that in the New England district around Armidale the granites and ■other rocks (which had been, since the Devonian period, sub- jected to Ijhe eroding action of water, and had been cut by it 128 PEOSPECTING FOE MINEEALS. into a number of gullies and gorges) were once more levelled off" and converted into a table land, all the irregularities being filled up by this molten rock. It has been suggested by Mr. Norman Taylor that it was in some way due to the effect of this basaltic eruption that the- occurrence of diamond in the older drifts of Gulgong can be traced. There are many interesting places in this neighbour- hood in which there is much difficulty in accounting for the manner in which the gold drifts were brought to their present position. Amongst others the Canadian and Whitehorse claims may be mentioned, in both of which the auriferous gravels now lie at a much lower level than any of the surrounding country, being, in fact, deposited in a depression. It is true that both these deposits, which adjoin one another, are resting on lime- stone and, indeed, are found in cavities in the limestone itself; hence, one is led to the conclusion that the river which deposited this gold very probably had an underground course for some distance, in which case a lead of gold may yet be traced through caves of limestone which mark the former course of the river. These deep leads have since, at times, been again cut through by streams, which have in places even cut gorges through the basalt, and the earlier deposits have been once more concentrated by the action of running water. 'New Zealand Eeefs and Deposits. — In New Zealand the conditions have been very different to those which prevailed on the Australian Continent. It is true that auriferous reefs are found traversing Lower Silurian beds, as in Yiotoria, and Upper Silurian beds, as in New South Wales ; but they also intersect both Upper Devonian and Lower Carboniferous rocks, which in this country consist chiefly of slates, sand- stones, and breccias. The lower Secondary rocks which overlie these beds are not traversed by reefs, so that probably the date of the formation of the reefs was anterior to the deposition of these beds. There is, however, no absolute proof that this is the case, for the earliest known alluvial deposits in New Zealand are those known as the cement work- ings of Cement Town, near Eeefton, which are of Cretaceous age; they belong to the coal measures of the colony, which, as already pointed out, are Cretaceous. All that is known for certain of the period of formation of the reefs is that they were formed after the close of the Carboniferous period, and before the commencement of the Cretaceous period. There is ample evidence in support of this, for alluvial gold, more or less rich, is somewhat widely distributed on the west ALLUVIAL DEPOSITS. 129 coast of the South Island in rocks of Cretaceous age ; while some very rich deposits of recent date are due to a natural concentra- tion of these gravels. As an illustration, the Mangles River, a branch of the Buller River, may be taken, in which some very rich alluvial was worked near the junction. This gold was generally coarse near the lower part of the river ; and a similar class of gold was worked as high as Macgregors on the Tiraumea, at which place the conglomerates of the coal measures cease and the head waters of the Mangles flow through granite and slate. It is a remarkable fact that above this point, although there is still a certain amount of alluvial gold obtained, it is in far less quantity, and is much fiuer than obtained lower down; so that no doubt can exist as to the rocks from which the coarse gold has been derived. Much time has been spent unprofitably by miners in prospecting these Cretaceous coal measures for reefs, it having apparently been overlooked that the gold was probably derived from the conglomerates and simply concentrated, and that the rocks are not such as would be likely to contain reefs. Later again in the geological history of New Zealand, in fact, during the Upper Miocene period, the land stood at a much higher elevation than at present, and continental conditions, with large rivers, prevailed. During this time the course of the rivers was more nearly north and south than now. The Buller River instead of flowing into the sea at Westport, as at present, delivered itself into Golden Bay near Nelson; the Aorere flowed at a higher level and drained to what is now the mouth of the Parapara ; while other large rivers flowed north and south along the west coast, carrying large quantities of shingle with them and depositing thick beds of gravel with small quantities of gold. Remains of these old terrace deposits yet exist ; indeed beds of gravel, frequently over 300 feet thick, occur, which have since been cut through by the fit^?^^S% ,£-S^:S^?5r?55' cross streams now flowing ;5°=1o'2.a°'a Z%o-o"l."i°^'^= irom east to west, and in \ ^ / which most of the rich ?=====^^^ g^ . = alluvial deposits have _ - = been worked. ^= • - - These alluvial deposits ,-,.„„ ™ ,. , , ^, , . arerepresentedinthefol- ''%^'^X^J^t^- lowing section (Jbig. oO), the wash generally being found on blue marly clays of Tertiary age, which are spoken of by miners as "false bottom." Alluvial 9 130 PROSPECTING FOE MINERALS. deposits have also been formed by the denuding action of water on reefs in recent times ; those which occur on the main or slate bottom are of this order. The alluvial deposits of Australia and New Zealand may thus be grouped as follows : — Australia, Carboniferous conglomerates. Mt. Poole ? . Deep leads of Miocene and Pliocene Pleistocene and recent leads on Tertiary bottom. Pleistocene and recent leads on main bottom. Black sand beaches. New Zealand, No parallel. Cements of Cretaceous age. Miocene gravels of West Coast, only suitable for hydraulic sluic- ing. Recent alluvial deposits on false bottom. Becent leads on main bottom. Beach deposits. — (a) Back (6) Black sand beaches. leads. The beach deposits of New Zealand are almost unique in their occurrence, for, although gold occurs to some extent in similar beds in Australia and elsewhere, they have never been of the importance of those in New Zealand. All along the west coast a heavy current sets to the northward, which during heavy southerly gales is yet stronger. Wherever beaches exist which are exposed to this northerly current there are deposits of alluvial gold found near low -water mark, mixed with black sand. These deposits are worked by means of a portable sluicing table, which is wheeled down to the edge of the sea at low ■ water, a flexible hose being rolled down after it. It is found that after every storm the gold in the sand is renewed. Sometimes the men who own these claims have to wait as much as six months for their deposit of gold to be renewed ; but, even under these conditions, they are reported to make good wages at their work. The back leads, which have yielded large quantities of gold, have been formed in the same way, but, since their deposition, have been removed beyond the action of the waves by an elevation of the land. Alluvial Deposits of British. Columbia. — Special attention has been devoted to a description of the Australasian alluvial deposits, because they illustrate nearly every condition which can prevail ; but it may be well to allude to British Columbia as affording an illustration on a gigantic scale and exhibiting features which are perhaps better studied there than elsewhere. This mountainous country affords evidence throughout of the important part glacial action has played in shaping its ranges ALLUVIAL DEPOSITS. 131 a.iid forming its lakes. Moraines of great size are found and, in addition to this, the hills are covered over large areas by a glacial till which is sometimes of very great thickness. The "till" carries gold in greater or less quantities, and has been washed by hydraulic power at places where it has been found to carry sufficient gold to make it remunerative. At the present time a good deal of attention is being devoted to testing these •deposits, and large areas, as yet untouched, will no doubt be worked in the future. But where these deposits of "till" have been cut through by recent streams, the process of resluicing, already described, has concentrated the gold, and some of the richest alluvial drifts have been formed which have yielded most phenomenal returns. Williams Creek, for instance, in the Oarriboo district yielded $20,000,000 in the early days, and many other (although not so rich) deposits have also been worked. The occurrence of rich alluvial deposits under these -conditions has, of course, led to prospecting for reefs in the vicinity, but hitherto without much success. It will be self- evident that this is another instance in which the alluvial gold has travelled for some distance from its parent reef, but that, having been transported for the first part of its journey by ice, it has not been greatly worn, hence an inspection of the gold itself would not give any idea of the distance it had travelled. The following are a few of the conditions which have to be considered in the determination of the value of alluvial deposits. It will be evident that gold may be found under any of the following conditions : — 1. In the beds of rivers ; either with shingle in the stream, or as beaches, or in pockets or ledges on the solid rock. 2. Under a cover of a few feet of shingle or surface soil, which may be stripped by hand. •3. As leads below many feet of cover, in which case the ground has to be worked by means of shafts, and the lead blocked out. 4. As poor deposits scattered through large quantities of gravel, in which case the whole deposit has to be sluiced on a large scale. As regards the two first classes of deposits it is unnecessary to make any further remarks, except to point out that a study -of them, and the peculiarities of the rivers which have deposited them, may serve as a guide in following the leads in the third class of deposits. Gold is deposited by rivers at all points where the current is -checked by any means ; thus, during floods, when the section of 132 PROSPECTING FOB MINERALS. Fig. 31. — Section. a river is as follows (Fig. 31), gold is thrown up on the banks, and small beaches are left when the river falls, which can frequently be worked by such simple methods as cradling ; but leads have been formed in the main course of the river, and fol- low the direction in which the main body of the river- flowed. This being the case, a careful study should be made of everything which causes any change in the direction of a river. The following sketch illustrates this, and gives a fair idea of the manner in which beaches are formed, and the gold renewed in thesr- beaches- from time to time when the river is flooded. The principal current would flow down the centre of the course so- long as no obstructions were encountered; but when any bluff was met,, the direction of the cur- rent would be changed and pass from one side of the stream to the other, to be once more deflected on meeting a bluff on the other side of the river. Not only this, but when a river is cutting its bank on one side, it is continually depositing shingle on the other, the section of the stream beings as in the accompanying sketch (Fig. 33). The auriferous deposits will, therefore, be formed in the slack ■water on the shallow side of the stream, and the leads of gold will follow much straighter lines than the regular course of the stream which deposited them, and, moreover, will not be uniformly rich along the lead. It is evident that where a close idea can be formed of the former direction of the stream which deposited the leads of gold, much information may be gleaned as to the direction which the richer parts of the leads will take ; but unfortunately it is often the case that the surface has been so changed since the deposition. Fig. 32.— Plan. ALLUVIAL DEPOSITS. 133 ■of these deep leads as to make it almost impossible to arrive at satisfactory conclusions. It is only after the leads have been "worked that the former course of the river can be traced. In those deposits, which come under Class 4, no attention Fig. 33,— Section. ■whatever is paid to the distribution of leads of gold ; but the whole body of wash is sluiced away on a face, the profits being ■dependent upon the enormous quantity of material moved. It is chiefly in America that operations of this sort have been carried on, where, on the slopes of the Rocky Mountains, large •claims are worked to treat wash dirt from 100 to 200 feet in thickness, in which, it is stated in official reports, as small a return as 2^d. per cubic yard will pay. In cases of this sort there are, of course, several faces opened up for sluicing, and the quantity of water brought in is enormous, while, necessarily, all other conditions must be of a favourable character to enable these low grade deposits to pay dividends on the capital involved. It will be of interest to call attention to the salient points in any such scheme, in order to afford the prospector the opportunity of gauging the chances of success. Necessarily, the first consideration is the quantity of gold present in the drifts, and the thickness and extent of these drifts themselves. This question should be gauged at the outset by .sinking shafts through the drift, and cradling or hand-sluicing everything that is raised from the shafts. By these means the best idea can be obtained of the average yield of the drifts. When the yield is high, other conditions are of comparatively 134 PROSPECTING FOR MINERALS. little importance; but when low every other feature must be considered in forming an estimate. The quantity of water available must be gauged and the cost estimated of bringing this on to the property ; and seeing that the pressure obtainable is an important point, a careful survey will be required to see at what altitude the water can be brought on to the claim. This survey is of the more importance, because by it the only fair estimate can be made of the cost of the race, the amount and height of flumicg, where it is advisable to use siphons, and a hundred other small points, all of which bear upon the value of the ground. The next most important feature, after the value of the gravel and quantity of water have been determined, is what facilities exist of disposing of tailings, or, in technical terms, " what dump exists." This is of great importance, and involves several considerations. When the deposit to be sluiced is situated high up on ranges above the river level, especially if a stretch of unoccupied ground exists between the claim and the river, no possible difficulty can exist ; but this is not always the case. Difficulties may arise, either from there not being suffi- cient fall, or from farmers or others occupying the lower lying ground and objecting to the tailings being deposited upon their property. This has formed so important a matter in the United States as to necessitate an Act of Congress (known as the Debris Act) restricting owners from depositing tailings, except under arrangement, and compelling them to impound them in settling areas when required, and only to allow the clean water to escape. The difficulty of impounding is not so very serious in the matter of additional cost if a sufficient head of water is avail- able, for by the use of hydraulic elevators the tailings can be raised to 10 or 15 per cent, of the height representing the pressure of water available. When this pressure, however, cannot be obtained the absence of dumping ground will make an otherwise valuable property of no value at all. Even when the tailings can be dealt with by elevators the initial cost of the undertaking is considerably increased if they have to bft employed. Some very extensive operations are conducted at times with the object of recovering the gold in the beds of live rivers, and very often the results achieved are not commensurate with the expenditure. The methods adopted vary a good deal, according to the nature of the river; thus, for instance, on the Molyneux River, in New Zealand, dredging has been very successfully ALLUVIAL DEPOSITS. 135 adopted, bucket dredges being employed, and the material dredged sluiced on the barge. Similar operations are being proposed on the Eraser Eiver in British Columbia. The suc- cess of these operations depends to a very large extent upon the facility with which the dredges can be moored, the dangers from rapid rising of the river, and the manner in which opera- tions are conducted. When other conditions are favourable, very low grade gravel will pay for dredging, but it is difficult — indeed, impossible — to estimate what the yield of a river bed will be, except by means of a dredging plant, so that the ex- pense of a dredge has to be incurred for the purpose of pro- specting. It is true that some idea may be gained by testing the river bed at low water, or even by running out wing dams. Tests are also made by divers, and occasionally by bore holes ; but these can never be relied upon as giving accurate results. Hence some speculation must always attend the first operations in dredging a river. In other cases a river is diverted, and its original bed laid dry ; and in others again, by the construction of crate dams down the centre of the stream, and the deflection of the river to one or other side, one-half of the river bed at a time is rendered available for sluicing operations. Great danger exists in these cases from floods, and it is by no means an un- usual thing for the work of months to be carried away in a night, many promising enterprises having thus been brought to an untimely end. Alluvial deposits, it will be seen, include forms of mining which vary from the most primitive methods of washing with a tin dish, cradling or hand sluicing, to operations which involve the expenditure of large quantities of capital, and tax the energies of the best hydraulic engineers to bring them to a successful issue. 136 CHAPTER X. NOBLE METALS. Gold — Platinum — Osmiuin — Iridium — Palladium — Tellurium. Gold. Distribution. — Gold is more universally disseminated in nature than is generally supposed, although there are only a few fields in the world where it is abundant. Australia has hitherto proved the richest goldfield, California coming next on the list, but South Africa promises to eclipse all other countries in the future. Its general mode of occurrence is, like platinum, in the native state ; but, unlike that rare metal, gold is found in association with many ores, especially sulphides. Gold occurs in actual combination with tellurium only ; there are tellurides of gold, of gold and silver, gold and lead, &c. Mode of Detection.— There is very little difficulty in re- cognising gold, although many curious mistakes are made by men who have had no experience, specks of copper pyrites in quartz and even small yellow flakes of mica being at times taken for the precious metal. Gold, however, remains of the same colour in every light, is metallic, and can be cut with the point of a knife ; whereas, other minerals are brittle ; moreover, it is not affected by acid other than nitro-muriatic acid. Tlie prospector, however, soon gets so well acquainted with its appear- ance as to hardly ever make a mistake ; if the stone be crushed and washed, the gold will be very readily recognised in a tin dish in which, if any doubt exists, it can be amalgamated with a little mercury. Association with Sulphides. — Although gold is almost universally present in iron pyrites, it is not, in most cases at NOBLE METALS. 137 •any rate, in actual combination with sulphur ; but is only dis- seminated through the pyrites in the metallic state, or inter- ■calated in minute scales between the crystalline layers of that mineral. Gold is also found mixed with copper pyrites, galena, zinc blende, mispickel, stibnite, magnetic pyrites, and cinnabar, all of which are sulphides. It is often found in company with native bismuth, magnetic iron, haematite, barytes, apatite, fluor- spar, and siderite ; but its most universal matrix is quartz, although calcite or dolomite more rarely form the gangue. Auriferous Belts. — The most usual mode of occurrence of ^old is in reefs, from which alluvial deposits are derived. In the richest and most celebrated gold-mining districts these reefs ■do not occur singly, but in belts. The reefs in the two most important mining districts of Victoria at Ballarat and Sandhurst, which lie to the south and north of the dividing range respectively, form two well marked mineral belts. In New South Wales there is an important, though not so well marked, belt which extends north and south of Bathurst ; and in California the whole of the Auriferous veins of the Sierra Nevada can be considered as a great auriferous belt. In each of these cases the main trend of the belts is north and 5outh ; but there are many auriferous reefs occurring in them which strike in other directions, especially east and west, or at right angles to the principal veins, and these are called cross- "veins or cross-courses. In Victoria the number of cross reefs is probably not one-tenth of the total number of reefs known, but in New South Wales they are of more frequent occurrence. It is important to study the course of the greater number of reefs in any district, because the dispersion of gold in alluv&Tf^ jnost abundant in regions where the drainage system corresponds with their strike, rivers flowing at right angles across the general •direction of the reefs not having abraded them over so extensive an area. Gold, in Eruptive Bocks. — Auriferous veins occur most frequently either in or associated with eruptive rocks. In Transylvania eruptive rocks of Tertiary age are traversed by veins containing pyrites, gold, and other minerals, sometimes •silver, and sometimes the rare metal tellurium combined with gold, gold and silver, or gold and lead. Other veins which cross the main lodes appear to have exerted a favourable influence on them. The most important eruptive rock in which the precious metal •occurs is the so-called propylite, an altered variety of andesite which occurs in some of the Transylvanian mines, and which is 138 PROSPECTING FOE MINERALS. the enclosing rock of tlie Comstock lode ; the same rock is also found at the Thames in New Zealand. In the Ural Mountains gold also occurs in eruptive rocks. In the district of Berezowsk, in the Southern Urals, crystalline schists have been traversed by dykes of a fine-grained variety of granite, parallel in strike with the direction of the mountain chain. This variety of granite, especially when it is in contact with the lodes, contains iron pyrites altered and decomposed to limonite. At right angles to the dykes innumerable quartz veins occur, from 1 inch to 3 feet wide, containing gold, iron pyrites, &c., but they have not proved very remunerative. Gold also occurs in the same district in quartz veins traversing diorites, serpentines, &c. The auriferous belt of California extends along the lower slopes of the Sierra Nevada, which is formed of granites, flanked by crystalline schists and other rocks up to the Jurassic. It consists of quartz veins striking in the same direction as the beds, and containing numerous metallic sulphides which all carry gold. One of the most remarkable gold veins in California is the great mother lode, which extends for a distance of over 70 miles, with a thickness varying from 6 feet to over 60 feet. In some places it outcrops like an immense white wall, but is not always- remunerative. Bedded Veins. — The Veta Madre in Mexico is a vein coinciding with the strata, and is considered to be a bedded vein, the dip of both the lode and rocks being about 45°. It attains at some places a thickness of 150 yards, and occurs at the junction of clay slates and conglomerates which are supposed to be, the former, of Devonian and, the latter, of Triassic age. The veinstone is amethyst quartz with calcspar, enclosing fragments of the country rock. Gold, silver, and silver glance are the principal ores ; but numerous other minerals occur, including the common sulphides. In cases of this sort where ore deposits, are for a part of their course, regularly interstratified between the beds, it is diificult to avoid using the term "bed" to describe them ; and, indeed, it is quite possible that such deposits may in some cases have been formed as beds in a similar manner to the banket beds of the Transvaal already described. When the term " bedded veins " is employed it must be understood that their formation is attributed to the same origin as that of true veins, and that they have not been formed contemporaneously with the strata in which they are enclosed. NOBLE METALS. IBS' It must be clearly understood that, although auriferous- quartz veins are generally associated with eruptive rocks, perhaps the greater number of reefs traverse sedimentary strata which have also been intersected by dykes. Beefs traversing Sedimentary Beds. — In Victoria, wherfr careful observations have been made and records kept, the auriferous quartz veins which traverse the lower Silurian rocks are considered to be richer than those which occur in the upper Silurian ; those in the lower Silurian also strike more nearly north and south than those in the upper part of the system. Cross reefs striking east and west are comparatively rare. The reefs in New South Wales are generally smaller and richer than those in Victoria. They occur mostly in the upper Silurian and Devonian systems, and cross reefs are more fre- quent than in Victoria. Reefs associated with. Diorite. — In all the Australian Colonies, as in other parts of the world, eruptive rocks are frequent associates of gold-bearing veins ; but in Victoria the mode of occurrence is somewhat peculiar, dykes of diorite sometimes lying alongside auriferous reefs, and in other places intersecting and sometimes heaving them. An interesting instance of this class of deposit occurs at the Wentworth goldfield, near Orange, in New South Wales, where the gold seems to be partly held in solution by mispickel, from which it exudes when heated in the shape of moss- like ex^ crescenoes (Liversidge, Trans. Royal Soc, N.S. W., 1876). According to the late Mr. C. S. Wilkinson, the auriferous deposits occur at the junction of serpentine with a felspathic rock containing hornblende (hornblendic felsite), which in some places passes into diorite. Along this line of junction is what the miners term the "lode," which, at the surface, is a fissure 6 feet or more in width, extending in a direction nearly north-west and south-east for a distance of 50 chains. It is filled with a red sandy ferruginous clay containing hard siliceous accretions of irregular shape, locally termed "clinkers." It- underlays to the north-east at an angle of about 65°, though in some places it is nearly vertical. The hornblendic felsite forms the footwall, and the serpentine the hanging wall. Shoots. — In the felsite at varying distances along the "lode " aje quartz veins from a few inches to 6 feet thick, coming in from the west and abutting against the lode, which they appear to follow down, forming irregular quartz "pipes" or "shoots," which dip diagonally in the lode towards the east. These veins have only been found to contain payable gold when they 140 PROSPECTING FOE MINERALS. junction with the "lode" and form shoots, which are also called " bonanzas." The Wentworth field affords an illustration of the influence exerted by cross veins in determining the dip of shoots of gold in the reefs, but in many other localities, especially where the I'ocks are dipping at moderate angles, and are of different -degrees of hardness, the rich parts of the lode will be deter- mined by the intersection of the lode and a belt of congenial or " kindly " country. It is of the greatest importance to discover the laws which govern the distribution of the rich parts in reefs, and the causes which have influenced the dip of the "pay ■shoots." Although the laws which have been enunciated in the chapter on fissure lodes will not always explain all the peculiarities of a field, they will form the basis on which to work ; and, when considered in conjunction with any local peculiarities which may exist, will generally give valuable 333/'! level Fig. 34.— Section. results. A careful record of the work in a mine, showing, in Addition to the direction of the levels, the distribution of the rich parts worked, and any changes in the rocks, or intersections NOBLE METALS. Ul of veins, will afford most valuable hints as to the direction which future workings should take. These details unfortunately are seldom shown on the plans of mines. Saddle Reefs. — A class of reefs not hitherto described in these pages, which are called "saddle reefs," occur at Sandhurst, Victoria. The foregoing sketch (Fig. 34) gives an idea of their shape, and at the same time suggests that they may have been formed at the intersection of a parallel system of fractures with cross-joints in the rocks ; but it has also been suggested that they are due to foldings of the strata. The richest parts are said to be at the caps of these reefs; the branches (which are called the eastern and western legs respec- tively) being relatively poor, although generally one of these legs will pay to work for some distance down, while the other is barren. Many of these saddles are found one be- low the other, as shown in the sketch, and they are only developed by sinking. It is not in Sandhurst only that reefs of curved shape occur; at Clunes, for instance, there are several saddle reefs. The adjoining section shows the shape of one of them, which seems to be a vein of segregation in the folds of an anticline to the west,, and of a syncline to the east. In the place where this section has been taken, the allu- vial wash is covered by 84 feet of gravel, 142 feet of basalt, and 1 5 feet of sur- face soil (Fig. 3.5). Flat Veins. — In Gipps- land there are some inter- esting veins of segregation which are illustrated by the accompanying sketch. They are called "flat veins," and occur in dykes of diorite porphyry, which, for a certain depth from the surface, are decomposed to clay. The quartz is very rich in; the soft, decomposed matrix, but when the undecomposed rock *eo ff Fig. 35. — Section. Fig. 36.— Section, 142 PROSPECTING FOR MINERALS. is reached in depth, the quartz appears to become poor, or to run out. Gold in Itacolumite. — In Brazil, gold occurs under excep- tional circumstances in beds of metamorphic sandstone, which is sometimes flexible, containing mica, micaceous iron, and other minerals, and forming lenticular masses in a formation which is supposed to belong to the Lower Silurian or Cambrian period. This sandstone, which is called " itacolumite," not only contains ^old, but also diamonds, rutile, tourmaline, &c. The gold is always alloyed with silver and copper, and sometimes with platinum. Gold in Pyrites. — The occurrence of both copper and iron pyrites containing gold at Borsa-bSnya in the northern Car- pathians, at Barraneos, in Portugal (where it is also associated with black oxide and other ores of copper), and some other localities deserves to be mentioned. Gold in Timazite. — At Borsa-bd,nya, besides some trachyte, there is a peculiar labradorite rock, called timazite or horn- blende andesite, whicli traverses both the mica schists and Carpathian sandstone. A whole mountain is formed of this timazite, in which a certain number of veins occur nearly parallel to one another. Copper pyrites and iron pyrites, with little quartz, compose the filling of these lodes, and are both auriferous, and iron pyrites is also disseminated through the timazite. Gold in Transylvania. — At Rodna, Transylvania, gold and silver occur with sulphides in a vein of calcspar and quartz in a contact deposit. The country consists of mica schist, horn- blende schist, granular limestone, and Tertiary deposits, traversed by dykes of andesite. When these come in contact with the limestone the ore deposits occur. Gold in Ifevada. — In the Eureka district, Nevada, a great ore channel extends along the eastern base of Prospect Moun- tain for a distance of 12 miles. This appears to be a contact deposit in beds of limestone, quartzite, shale, (fee. The ore contains gold, silver, and lead, and some of the mines have yielded a considerable return in bullion. Breccia Lode. — Before concluding this branch of the subject there are some exceptional modes of occurrence of gold which should be described. The first of these is at Browns Creek mine near Blayney, New South Wales, described as an immense breccia lode, in which the gold is disseminated in fine particles. The vein stuff is a ferruginous flinty rock, with concretions of ■chalcedony and the country rock is limestone penetrated , by dykes NOBLE METALS. 143 of grey diorite. It has been stated that this deposit shows evidence of segregation or deposition from hot springs which probably accompanied the diorite eruption. Another remarkable deposit which occurs at Belubula, New South Wales, has already been described in the chapter on strati- fied deposits ; but the most remarkable deposit of all is that of Mount Morgan in Queensland of which the following descrip- tion by Mr. R. L. Jack published shortly after its discovery is of interest. The summit of Mount Morgan is composed of what Mr. Jack 1-1-5 5-4 Shining ver. /Products of de- (horn-silver), composition Bromargyrite, Br 57 1-2 6 Yellow- ish- green occurring gen- erally in crusts, J coatings, and lodargyrite, . I 46 ... 1 5-6 Yellow S cauliflower- Rmbolite, . 1 01, Br 66 1-1-5 5-4 Yellow or green like excre- scences, rarely in minute cry- 1 \ stals. 8, Sulphur; Fe, Iron; Cu, Copper; Sb, Antimony; As, Arsenic; 01, Chlorine; Br, Bromine; I, Iodine. The preliminary examination with the blowpipe having deter- mined that a mineral belongs to this group, it is practicable in some cases to decide by simple inspection which o-f the foregoing minerals it is; but in others it is necessary to apply certain tests in order to discriminate between them, and the following notes will be of service : — Ifative Silver is not likely to be mistaken for anything else, its malleability and white characteristic colour being sufficient for its determination. It will be distinguished from platinum by being fusible before the blowpipe, while platinum is not. It might be confounded with one of the native silver amalgams, hnt these are rare. One of these, called "amalgam," contains 150 PROSPECTING FOR MINERALS. about 30 per cent, of silver, is brittle and generally is found either massive or as coatings ; while another, called " arquerite," contains HQ per cent, of silver and is malleable. It often occurs - in crystals, whilst native silver is generally found in strings, branches, or dendritic crystals. Native silver has never been worked in alluvial, and is not likely to be found in this kind of deposit ; although its occurrence is not impossible. Argentite is fairly abundant and, being of great value, is important to recognise. Its surface is usually tarnished, but it may be cut like lead and then appears of a bright lead colour. It is so easily fusible that it will melt if brought near to the flame of a candle. Grey copper, especially when tarnished black, might be mistaken for silver glance as it has the same external appearance, but, in addition to the characters already mentioned, silver glance will not give antimonial fumes, nor the smell of garlic due to arsenic before the blowpipe. There is also a great difierence in weight, the specific gravity of argentite being about 7, whilst that of grey copper is about 5. Some cobalt ores will be distinguished from silver glance in that they are more or less brittle, at least not malleable or sectile; infusible in the flame of a candle; and yield a blue bead with borax before the blowpipe. To distinguish silver glance from copper glance or bournonite the blowpipe reduction assay on charcoal with soda is necessary, as they are both easily sectile and fusible ; the first will give a silver, the second a copper bead. This distinction, however, will be made before the mineral is included in this group. Stromeyerine. — The lustre and colour of cupriferous sulphide of silver are the same as those of bournonite and some grey copper ores ; but these will emit white fumes and a smell of garlic before the blowpipe, while stromeyerine will not. This mineral, however, may be difficult to distinguish on account of the presence of copper, and an assay may be necessary. Stephanite, being brittle, will be easily distinguished from- silver glance, which is sectile. Prom black oxide of copper it will be distinguished by the reduction of the metal on charcoal with carbonate of soda, and from polybasite by the absence o£- arsenic. Pyrargyrite and Proustite, the two ruby-silver ores, will be distinguished from one another by their streak, that of proustite being lighter in colour, and by their difierent be- haviour before the blowpipe ; pyrargyrite yields fumes of antimony, proustite the smell of garlic. They are each, how-^ ever, liable to be confounded with other ores. SILVER AND LEAD. 151 When crystallised they resemble specular iron or haematite, but may be easily distinguished ; for iron ores will not melt before the blowpipe alone, while the silver ores will, and at the same time emit the characteristic fume. Another ready test will be that of hardness, specular iron being scratched with difficulty by a knife, while the silver ores yield easily to it. Specular iron also becomes magnetic on charcoal before the blowpipe. From copper glance they will be distinguished by the colour of the streak, as also from polybasite. "When compact the ruby-silver ores sometimes resemble realgar, cinnabar, and red oxide of copper in appearance, but will be distinguished by the colour of the streak, which is cochineal-red for ruby silver, orange for realgar, scarlet-red for cinnabar, and brown-red for oxide of copper ; the distinction from cinnabar, however, will be doubtful. Before the blowpipe cinnabar entirely disappears, as it is composed of sulphur and mercury, both of which are volatile. Pyrargyrite occurs sometimes of a lead-grey colour, when it resembles silver glance, copper glance, and bournonite ; but the streak will in all cases be sufficient to remove any doubt. Kerargyrite, or horn silver, presents the appearance of wax, and is as readily cut ; so will be easily recognised. The newly- cut face soon tarnishes and becomes greyish-violet on exposure to light. Rubbed on wet iron, zinc, or copper, horn silver yields a coating of silver, and blocks of this mineral sawn through with a steel saw show silver coatings on either face. Bromargyrite is similar in character, but is generally of various shades of green. lodargyrite is often earthy and yellow, and, consequently, resembles some earthy oxides, such as those of lead, bismuth, antimony, and molybdenum ; but these always accompany the metals from the alteration of which they are formed. The blow- pipe test will ascertain the nature of the yellow powder. The study and discrimination of silver ores is very important, for not only are they interesting in consequence of their value, but several compounds in, which silver exists are not easily recognised. As it often happens that a small quantity of a rich silver mineral, disseminated in grains through an ore, is sufficient to make that ore very valuable, it is most desirable for the ])rospector to thoroughly accustom himself to the recognition of such minerals ; as a failure in this respect may result in his missing a valuable discovery. As an illustration, it may be mentioned that small grains of argentiferous mispickel occur disseminated through some galenas, 152 PROSPECTING FOR MINERALS. which are, in consequence, very rich ; and it is also well known that silver chloride in large proportions is often found in an earthy matrix which would generally be disregarded. Such is the case with the rich chlorides of silver scarcely visible in the so-called "pacos" and "colorados" of Peru, and in the gossan at the outcrops of many silver-bearing lodes. Valuing Silver Ores. — Native silver often occurs accom- panying other silver ores, and is sometimes sufficiently abundant to form its most valuable constituent, as at Kongsberg, in Sweden, and in Peru. Argentite or silver glance, which is the sulphide of silver, is perhaps the most important of the ores of this class ; but the antimonial silver ores also occur in consider- able abundance in certain localities, notably in some of the American mines. The chlorides and chlorobromides of silver are also, at times, of importance ; but as they are essentially ores of decomposition, are seldom found at any great depth from the surface. In the gossan of many silver-bearing lodes they are abundant and of great value, and are also at times found disseminated through andesitic and rhyolitic rocks, as in the Calico District of California. A simple, but rough, method is sometimes adopted of testing the value of ores from day to day when chlorides are the minerals chiefly worked — viz., by powdering the ore in the mine, mixing it with a solution of hyposulphite of lime, which dis- solves the chloride, and then adding sodium sulphide, which forms a dark-coloured precipitate if much silver is present. It is evidently impossible to estimate in this way the contents of silver, but it affords a very good test whether the ore is of value or not. Some rich silver ores are very brittle, especially those contain- ing antimony and arsenic, and great care is necessary in the process of taking average samples, or unreliable results will be arrived at. Care is also necessary in working the ores on a large scale to see that all the dust produced is saved for treat- ment, as this is frequently the richest part of the ore. Many silver deposits in America, along the Cordillera (both to the north and south), and in Europe, especially in Transylvania, are connected with some peculiar kinds of eruptive rooks belong- ing to the group of andesites, and spoken of as propylites. This rock occurs at the famous Comstock lode in Nevada, where not less than a dozen varieties of eruptive rocks, andesites, propy- lites, &c., belonging to three different epochs of eruption, form the accompaniment of this rich deposit. A better opportunity could not be selected for again directing the attention of pro- spectors to the important connection which may be observed SILVER AND LEAD. 153 l)etween the eruptive rocks and their metalliferous contents, and to the importance of studying their connection carefully. It may be added that some of these deposits are of very recent -origin, as the rocks of the andesitic family have been chiefly erupted during tertiary times. The silver ores of the second class mentioned at the beginning ■of this chapter are those which occasionally carry silver, and then come under the class of argentiferous ores. These may be -enumerated as follows : — Galena (sulphide of lead). See Lead. BoTirnomte (sulpho-antimonide of lead and copper). See 'Copper. Tetrahedrite (antimonial grey copper). See Copper. Tennantite (arsenical grey copper). See Copper. Mispickel (arsenio-sulphide of iron). Zincblende (sulphide of zinc). See Zinc. The above minerals, when argentiferous, do not give evidence ■of the presence of silver, unless they are submitted to the process •of assay. A very simple test for the presence of silver in ores, however, is mentioned in Charles H. Aaron's Practical Treatise -on Testing and Working Silver Ores, and is as follows: — " The ore should be ground fine, and then a few ounces are mixed with about one-tenth of its weight of salt, and one-twentieth of •copperas. This is placed in an old frying pan, and heated gently so long as a smell of burning sulphur can be noticed, the mass being stirred with a thin bar of iron all the time. After all the sulphur has been driven off, the heat is increased for a few minutes to a light red, and the mass stirred until it swells up and becomes sticky, care being taken not to fuse the ore. The mass is then taken out, and allowed to cool on a rock, and after •a little more salt has been added, and the ore mixed with water to the consistency of mortar, a strip of sheet copper, previously cleaned, is inserted, and left there for ten minutes. The copper is then removed, washed in clean water, and if any silver is present, it will be coated with a white substance, which will be heavier or lighter, according to the richness of the ore, and, if very rich, will appear grey and rough. The frying pan should be smeared with clay or mud, and dried before being used." ' Silver exists in traces, or in larger proportions, in all galenas ; but an assay is the only way to ascertain the percentage, as there is no physical character to distinguish the poor from the rich argentiferous galenas. It has often been stated that galenas with small crystalline facets, like coarse lump sugar, are rich in silver, while those with large cleavages are poor ; but 154 PROSPECTING FOR MINERALS. this character at best is only local, for some galenas with large- cubical cleavages yield as much as 1,500 ozs. of silver per ton^ whilst other fine-grained ores contain 50 ozs. per ton, or even less< Argentiferous grey copper and galena, accompanied by the different arsenical and antimonial silver ores, form the chief characteristic of the silver mines of Saxony and Bohemia. Lead Ores. All ores of lead give a bead of metallic lead when heated on charcoal with soda before the blowpipe. They will be readily distinguished one from the other by the characters given in the following table : — TABLE OF LEAD ORES. Metal Mineral. Composition. per cent. Hard- ness. Specific Gravity. streak. Remarks. Galena, . Sulphide 80 2i 7-6 Lead-grey Metallic lead- grey ; cubical cleavages or granular. Minium (red Oxide 90 2-3 4-6 DuH-yel- Not common, lead), low or bright red found with ga- lena ; orange- yellow to red. Cerussite, Carbonate 77 3-^ 6-4 White or greyish White to grey ; decrepitates and fuses. Anglesite, Sulphate 68 2i-3 6-2 White, grey, or black Not common. Crocoisite, Chromate 64 2i-3 6 Orange yellow Colour red; blackens and f us e s when heated. Pyromorphite, Phosphate and chloride 76 34-4 6-5 White or yellowish Various colours, yellow, red and green ; swells up and changes colour when heated. Mimetite, Arseniate 48 3i 7-2 Light yellow Lustre adaman- tine ; generally covered with a black coating of arsenic ; faces of crystals curved. SILVER AND LEAD. 155> _ Lead mining in Europe is inseparable from silver mining, as. silver is mostly extracted from argentiferous galena; cheap labour and scientific appliances enabling poor ores, containing only 9 or 10 ozs. of silver per ton, to be treated at a profit,, both lead and silver being extracted. In America, where the production of silver is enormous, the proportion of galena mined to silver ores proper is relatively small, and the economic conditions are not so favourable to a large production of lead, a metal of comparatively little- value. Galena. — Galena is found in abundance throughout Australia,, but up to the present time only those ores which are rich in silver have received much attention. The immense deposits of comparatively poor ores, however, of which the best illustration is to be found in the Broken Hill mines, are being worked, and doubtless as time goes on, and still more economical appliances- than those now in use are introduced, still poorer ores will be worked. The most troublesome feature about the Broken Hill ores has been the association of zincblende with the galena, more especially because the silver is associated with each mineral, sa that no process of concentration is of value in enriching the ore. A very ingenious process has been devised by Mr. Ashcrofb for dealing with this class of ore and is now in operation. A brief description of the process may be of interest. The mixed ore, consisting of galena and blende is first roasted so as to desulphurise a portion of the blende, leaving an amount which is determined by circumstances still unaffected. The roasted, ore is then leached with ferric chloride, the zinc being dissolved as chloride, leaving the silver behind and the iron taking the place of the zinc as hydrate. The zinc is subsequently precipi- tated by electricity, an iron anode being employed, and the ferric chloride is thus renewed. The galena, together with the hydrate of iron and what zinc has not been dealt with, is smelted and the silver and lead saved toother in the ordinary way. The process appears to be admirable, as it afifords a smelting mixture which is very easily treated and the original solution of ferric chloride is continually renewed. Galena, or sulphide of lead, is the principal ore of lead, and the permanent ore in depth ; but at the outcrops of lodes several other minerals, mentioned in the table, which are products o£ decomposition, are found. These are the oxidised ores, such as carbonate, sulphate, phosphate, arseniate, and, more rarely^ molybdate and chromate of lead. The combinations of lead 156 PHOSPECTXNG FOB, MINEEALS. ■with chlorine (except as pyromorphite) are very rare, and so also is the oxide. Although carbonate, arseniate, and phosphate of lead are of very frequent occurrence in galena lodes, they are seldom sufficiently abundant to be considered as regular ores, except in the upper workings before the water level is reached, below which galena is to be expected as the permanent ore. As galena is often accompanied by iron and copper pyrites, there is generally a gossan on the back of the lode in which •crystals of carbonate of lead, mostly as white tables or needles, .are found in the vughs and crevices. Carbonate of Iiead. — Carbonate of lead is not only found •crystallised, but also in earthy masses of a yellowish or ochreous ■ colour, and may be readily distinguished by its weight. When ■occurring in this form, it is usually mixed with earthy substances and oxide of iron, but if a specimen is broken carbonate of lead in a pure state will generally be found in the centre, and be recognised by its bright vitreous or adamantine lustre. Lead-antimony Ores. — There are several compounds of lead with antimony, but they are never sufficiently plentiful to be •considered as ores. One of these, jamesonite, contains small proportions of iron, copper, zinc, and bismuth. It occurs in grey fibrous masses or small prisms, and is found in Cornwall .associated with quartz and bournonite. Another of these com- pounds, zinkenite, resembles stibnite and bournonite and occurs lin an antimony mine in the Hartz. Bournonite. — Bournonite, which is spoken of in the chapter on Copper Ores, is a compound of lead, copper, and antimony. It occasionally forms mineral deposits by itself, as, for instance, in Columbia, South America. Lead IiOdes. — The ores most commonly found associated with galena in lodes are zincblende, iron and copper pyrites, and .arsenical iron or mispickel. The matrix or vein stuff generally associated with lead is either quartz, fluor spar, or barytes. Lead ores mostly occur in lodes, while copper occurs most frequently in contact veins ; but lead also occurs in contact veins, and, more rarely, in masses in sedimentary deposits, -especially limestone. The best illustration of regular lodes is to be found in the lead and silver veins of the Hartz, Saxony, and Bohemia, which have an extremely regular structure. A plan of these lodes •shows the veins and cross-veins belonging to different systems ■of fracture and filling, arranged with the regularity of a mosaic. SILVER AND LEAD. 157^ and in the vein itself the ores and their accompanying gangue are arranged with such order and regularity from the -walls to the centre, that the name of "ribbon veins" or "banded veins" has been applied to them. As a rule, the points of the crystals are turned towards the interior of the fissure, and iu con- sequence they are sometimes called " combed veins." The adjoining sketch represents the section of a vein at Przibram, Bohemia, the different numbers referring to the different bands, of ore. Fig. 40. — Section.— 1, Casing or country rock; 2, Flucan ; 3, Quartz;. 4, Iron pyrites ; 5, Calcite ; 6, Quartz and barytes ; 7, Zinc- blende and galena. Lodes of this sort afibrd evidence of very slow deposition from waters carrying the mineral matters in solution. This has allowed the ores and minerals to crystallise beautifully, sections of the veins showing plainly the order in which the various minerals were deposited, the oldest deposits coating the walls of the lodes, the youngest l3eing found at the centre. This banded structure is almost peculiar to lead and silver lodes ; but some deposits of copper, iron, manganese, zinc, &c., are also found in " combed veins." As already stated, lead ores also at times occur as "contact deposits," most of the silver lead mines worked in the centre of Prance, on the boundaries of the granitic region called the central plateau, occurring under - these conditions. 158 PROSPECTING FOE MINEEALS. In the neighbourhood of Pontgibaud the country is composed 'Of granite, mica schists, and gneiss, and the lodes are in granite. Numerous dykes of porphyry crop out at the surface, and the vein stuff is a kind of granite differing but little from the country rock and much decomposed at the surface, involving a heavy expense in timbering. The ore is disseminated through the granitic matrix in veins, strings, or irregular masses, or in fine grains. The galena is generally accompanied by a little zincblende and pyrites, -while grey copper and barytes occasionally occur in some of these contact veins, but are replaced by quartz in depth; -others contain fluor spar. Shoots. — The ore forms chimneys or shoots rarely more than 150 feet to 250 feet in length, but permanent in depth. Other similar deposits occur in the granitic chain of Forez ; most of them in gneiss, but some in granite. One of these in granite is formed of two small leaders, which occasionally join together. The associated minerals are the same — viz., blende and pyrites ; the vein stuff is quartz with a little heavy spar, and the ore occurs under nearly the same conditions as those just described in irregular pockets or shoots. In the same region other contact deposits occur in granite, mountain limestone, or sandstone, sometimes at the contact of porphyry, and have about the same composition as those men- tioned above. CHAPTER XII. QUICKSILVER OR MERCURY. ■Cinnabar or sulphide of mercury is the only regular and valu- able ore of this metal. It is of a bright red to brownish-black colour, is always red in powder, and affords fumes of quicksilver when heated with soda on charcoal. Native mercury and amal- gam also occur, and grey copper or tetrahedrite sometimes contains this metal. Tests for Cinnabar. — Cinnabar is very easily scratched with a knife, affording a deep red streak, and before the blow- pipe it volatilises, giving off a strong odour of burning sulphur ; mixed with dry carbonate of soda and heated over a candle 'flame, in an iron spoon, it gives off vapour of mercury, which may be condensed on a gold coin held half-an-inch above the QUICKSILVER OR MKRCURY. 159 mixture. The surface of the coin appears whitish at first, but "when rubbed between the fingers becomes brilliantly amalga- mated ; with care this test easily detects 1 per cent, of cinnabar in an ore ; the mercury is removed from the gold coin by gentle heating. Blowpipe tests distinguish cinnabar at once from red oxide of iron, and all other red minerals. Wative Mercury in a pure state is rarely found, but occurs -disseminated in liquid globules in cavities in the cinnabar- bearing rocks, especially at or near the surface. It is easily recognised, and a rock suspected to contain metallic mercury may be tested by simply heating it as described above, but without the addition of carbonate of soda. Cinnabar Deposits. — Cinnabar occurs in the Palatinate as lodes, and impregnations which have penetrated from the lodes, in strata of Carboniferous age, and in the eruptive rooks which traverse them — viz., porphyry, melaphyre, and amygdaloid. These deposits are nearly exhausted. At Idria, Austria, cinnabar is found in impregnated beds and stockworks in bituminous shales, dolomitic sandstones, and limestone breccias of Triassic age, dipping 30° to 40°, and covered by Carboniferous sandstones and shales in a reversed 3)osition. This deposit has been worked for nearly 400 years, and is said to become richer as the depth increases. The quicksilver deposits at Almaden, in Spain, have a far remote history, for in the time of Pliny 10,000 lbs. were sent •annually to Kome from these mines. They occur in upper Silurian slates, sometimes interstratified with beds of lime- stone ; but the ordinary slates themselves, which are much contorted, rarely contain cinnabar. The enclosing rock usually •consists of black carbonaceous slates and quartzites alternating with schists and fine-grained sandstones. These bed-like deposits incline, near the surface, at an angle of about 65°, and then dip almost vertically. They consist principally of quartz with either granular or compact cinnabar, which permeates the mass generally, and is concentrated in pockets and bunches; while the clefts and cavities by which the deposit is traversed often contain native mercury. Veins of cinnabar occur in the neighbourhood and also eruptive rocks, diorites, with which the deposit seems to have some relation, showing that the beds are impregnations, probably originating from the veins. The quicksilver-bearing belt of California extends along the coast range for a distance of about 300 miles. The description of some of the deposits would be highly interesting and instruc- 160 PROSPECTING FOR MINERALS. tive, but space will only allow of a rapid glance at their generaB mode of occurrence as described in a report by M. G. Eolland (Ann. des Mines). "These deposits are generally impregnations in the Cretaceous- and Tertiary formations ; they seem to be richer when the beds- are more schistose and transmuted ; they are more or less closely in relation with serpentines which are themselves sometimes impregnated. The cinnabar is mostly found in talcose and clay schists, often decomposed and impregnated with oxide of iron, sometimes in quartzose schists, in sandstones, more(rarely in limestone rocks, limestone breccias, (fee. Native mercury is found in some magnesian rocks near the surface. There are no defined fissures nor veins proper. The cinnabar with quartz, pyrites, and bituminous substances is sometimes disseminated in the rock in fine particles and spots, sometimes forms certain kinds of stockworks or reticulated veins and nests. The parts thus impregnated congregate and form rich zones, the size of" which occasionally reach 80 fathoms, and the percentage 35 per cent., and flat-like veins or lenticular deposits, the strike and dip of which agree with those ot the schists of the country generally. These rich zones without defined limits gradually merge into poor stufi' containing half a unit per cent., or mere traces, and are of no value." Sulphur Bank, one of the principal mines, was originally worked as a sulphur deposit. Sulphur in workable quantities is known to exist in some volcanic countries, and volcanic rocks are abundant at the Californian cinnabar mines. The author previously quoted remarks that a trachytic lava, probably of post-Eocene age (Tertiary) is quarried for the cinnabar with which it is impregnated, and adds : — " Some geyserites (siliceous deposits from geysers) and some modern deposits, calcareous or siliceous, of concretionary form, and produced by old hydrothermal springs, are coloured by cinnabar.. Lastly, there are actually geysers and hot springs which deposit cinnabar." He quotes the Steamboat Springs, Nevada ; the Iceland Geyser ; the Ohaeawai Springs in New Zealand ; and the Solfatara of Puzzuoli, near Naples. At the Steamboat Springs the percentage, though very low, is not so low as to be neglected, and a deposit of cinnabar which is being worked, and is, at the same time, in process of formation, can be seen there. In a very interesting paper published in the Transactions of the Institution of Mining and Metallurgy, vol. iv., Mr. James JVIac- tear says, in speaking of the Mexican deposits, " It would seem. QUICKSILVER OR MERCURY. 161 as if the general line of the Californian deposits was continued through the Mexican mountain ranges, but there seems also to be another line of deposits extending in a direction north-east and south-west." He also says, " It is found that there are very considerable differences to be met with both as regards the character of the quicksilver deposits themselves and the nature of the associated rocks ; but it is abundantly clear that the deposits have in all cases resulted from the action of mineral springs. There can scarcely be a doubt that these were hot springs similar in character to those now in action in California and New Zealand." In Queensland, at Kilkivan, near Gympie, cinnabar occurs in lodes of calcite, and sometimes of calcite and quartz. These have not been worked yet on an industrial scale, so that little can be said of their extent in depth ; but it may be concluded from the few known occurrences in the world that quicksilver is, of all ores, the most likely to impregnate large belts of country. Cinnabar has been found in alluvial deposits in New South Wales, and also at Waipori, in New Zealand ; in the latter place it occurs as rolled fragments in the wash. One of the most interesting localities in New South Wales is on the Cudgegong River, near Rylstone, and has been described by the late Mr. C. S. Wilkinson as follows : — "Perhaps the most important feature connected with the occurrence of the ore is that the solid cinnabar is sometimes seen to gradually merge into, or impregnate, the clay or drift of the deposit in which it is found. This is, then, direct evidence that it has not been drifted by running water, like the water-worn pebbles and other material forming the old tertiary lead ; but that it has probably been de- rived from thermal waters which issued from the underlying Devonian rocks, and permeated the tertiary deposit." Deposits are traced by the occurrence of red grains of cinna- bar in alluvia; these cannot be confounded with red hsematite nor red oxide of copper if the blowpipe is used. As to the appearance of the ore, it is very variable, and it will be useful to quote the varieties of colour it assumes at Idria, and the names by which the different classes are distinguished by the miners there. Stahlerz (steel ore) contains 75 per cent, of mercury, and occurs in a compact or fine granular form. Iiebererz (liver ore) is compact and lustrous, usually forming nests in the stahlerz. Ziegelerz (brick ore) is sandy, granular, and of a bright red colour. 11 162 PROSPECTING FOR MINERALS. In all the above-mentioned deposits, cinnabar is found in connection with rocks impregnated with carbonaceous or bi- tuminous matter, and in every case where deposits have been worked upon an extensive scale, there is evidence of great volcanic disturbances, which have apparently been the cause of the deposition during the solfatara stage of eruption. Annual Produce of Mercury. — The annual output of mer- cury for the world is stated to be about 100,000 flasks of 76'5 lbs. each, and Spain produces about one-half of this. Payable Grades. — To give some idea of the grade of ore that is payable, it may be mentioned that the New Almaden mine paid $257,478 in dividends on mining 22,615 tons of ore yielding 2-02 per cent., and $53,641 on mining 25,584 tons of ore yielding 1-22 per cent, of mercury, but, of course, the condi- tions vary in every different locality. The average price of quicksilver is about £6, 10s. per flask. TABLE OF MERCURY ORES. Mineral. Composition. Hard- ness. Specific Gravity. Streak. Eemarts. Cinnabar, Quicksilver, . Sulphide of Mercury Native 2i 8 13-6 Red Volatile when heated and yields mercury with carbonate of soda. Vol atile when heated. CHAPTER XIII. COPPER. The minerals and ores of copper are generally easy to recognise in consequence of their very conspicuous colours ; they are also the most commonly known, both for the above reason and also on account of their frequent occurrence. General Characters of Copper Ores. — All copper minerals, with carbonate of soda on charcoal, yield before the blowpipe a COPPER. 163 bead of copper, which sometimes contains iron. They impart a green colour to the flame, and colour the borax bead green. In nitric acid they give a green solution, which becomes azure blue when ammonia is added ; and metallic copper will be deposited on iron in a nitric acid solution. Classification of Copper Ores. — They may be subdivided into those ores in which copper is in combination -with sulphur, arsenic, or antimony alone ; and those which are oxidised ; these are classified in the two following tables : — TABLE OF UNOXIDISED COPPER ORES. Uineral. Copper combined Copper per Hard- Specific Streak. Kemarkg. with cent. ness. Gravity. Native copper, ... 2-6-3 8 -4-8 -9 Shining Metallio and duc- tile. Chalcopyrite, . S, Fe 34 3-5-4 4 Greenish- black Yellow, often iri- descent (peacock ore). Purple, crystals Bomite or eru- S, Fe 55 3 5 Black bescite, rare. Tetrahedriteor S, Sb, As, 35-40 3-4 5 Dark Streak dark red ; grey copper, Zn, Fe, Ag, Hg brown or black when rich in zinc mineral ; grey. iTennantite, S, As, Fe 51 4 4-5 Reddish- grey Crystallised or massive. Enargite, S, As, Sb, Fe S 47 3 4-4 Black Rarely crystallised. Covellite, 66 1-5-2 4 Black Indigo blue. ■Redruthite or S 79 2-5-3 5-8 Black Very easily seotile. copperglance, Bonrnonite, . Sb, S, 13 2 5-3 5-8 Dark- ■ Shining conchoidal Pb 41 7. grey fracture Arsenides of As 70-88 3-4 7-8 Before blowpipe copper. yields blackish- grey malleable bead. S, Sn 24-30 4 4-3-4-5 Black Takes silvery polish ; tarnishes on exposure. S, Sulphur; Sb, Antimony; As, Arsenic; Fe, Iron; Zn, Zinc; Pb, Lead; Ag, Silver; Hg, Mercury; Sn, Tin. 164 PROSPECTING POK MINERALS, TABLE OF OXIDISED COPPER ORES. Minerals. Composition. Copper per cent. Hard- ness. Specific Gravity. Colour and Streak. Kern arks. Melaconite, . Oxide 80 3 6-2 Black Usually earthy, soiling the fin- Cnprite, Oxide 88 3-5-4 6 Cochineal- red, streak brown gers. Often covered withmalachite. Chalcanthite, Sulphate, 25 2-5 2-2 Blue Crusts and prisms ; soluble in water. Azurite, . Carbonate 55 3-5-4 3-8 Azureblue Often in radiated crystallised concretions. Malachite, . Carbonate 57-5 3-5-4 4 Emerald green Often mammil- lated and fib- rous. Libethenite, . Phosphate 5.3 4 3-8 Green, streak greenish- yellow Small crystals, surface dark. Atacamite, . Oxychloride 44-5 3-3-5 3-7 Dark olive green Crystallised, fib- rous, or gran- ular. Arseniates of 50-60 3-4 3-5-4-2 Green Sometimes crys- copper. tallised. Chrysooolla, . Silicate 37 2-3 2-2 Green or bluish Crusts and coat- ings. Dioptase, Silicate 40 5 3-3 Emerald Crystallised; green rare. Native copper, in the celebrated copper region of Lake Superior, in North America, forms the regular ore of the mines. It occurs in grains of all sizes, and occasionally in huge masses of over a hundred tons in weight, in beds of conglomerate, alter- nating with trappean rock. Copper Ores.^ — Copper pyrites or chalcopyrite is the most common ore in nearly all the copper deposits of the world, while blue and green carbonates, in crystals, concretions, or impreg- nations are the surface ores formed by the decomposition of copper pyrites and other ores of copper. Copper also occurs combined with sulphur as bornite or COPPER. 165 purple copper ore ; redruthite, or copper glance ; and tetra- hedrite or grey copper. These generally accompany copper pyrites, being more or less abundant, and sometimes become the principal ore in the lode, as, for instance, purple copper in Tuscany, grey copper in Germany, and copper glance in Siberia -and New Zealand. The carbonates are accompanied near the surface by other oxidised ores, such as cuprite or red oxide of copper, melaconite •or black oxide of copper, as well as the phosphates, arseniates, silicates, and oxychloride. Of these, cuprite and melaconite are the most important, and sometimes form the permanent ore of mines to a considerable depth. These oxidised surface ores are usually mixed with hydrous oxide of iron or gossan forming the cap of the lode. To understand the occurrence of gossan in the upper parts of a lode, it must be borne in mind that copper pyrites and purple ore are sulphides of copper and iron The surface waters which percolate through the rocks remove the sulphur and copper as sulphate of copper, leaving the iron in the form of a more or less spongy and honey-combed mass, which i.s called "gossan." It is consequently easy to anticipate from the nature of a gossan if the ore lying below is likely to be a rich compact copper ore, or whether it is mostly composed of iron pyrites carrying little or no copper. In the first instance the large percentage of oopper which has been removed must have leit the iron in a very porous condition ; while in the latter the gossan will generally be more compact. Copper pyrites is not generally found pure immediately below the gossan, but a richer ore, commonly called " black ore," which has no special mineralogical name, is first met with. It is black and earthy, like manganese or black copper ore, but, if broken, nests of copper pyrites will generally be found in the centre, and the ore passes from black to yellow through intermediate shades of bronze. What is called " peacock ore " is only copper pyrites coated with oxide and exhibiting iridescent colours. By leaving a piece of clean yellow copper pyrites in water for some time it will become coated in this way. The easy decomposition of copper ore under the influences of the atmosphere explains why the waters at some copper mines are quite unfit to drink. It is well known that tools abandoned for a time in old workings become covered with a coating of metallic copper, as if they had been left in a bath of sulphate of copper. 166 PROSPECTING FOE MINERALS. Native copper in copper lodes is also a product of decomposi- tion of sulphides, and is often lound as plates, when deposited on the side of a cavity or fissure ; or as ramified crystals, •vrhett deposited in a soft clay. Tests for Copper Ores. — The various copper minerals enumerated in the tables may be distinguished in the following manner, a bead of copper having first been obtained Irom the specimen before the blowpipe : — The Bead op Copper contains Iron, and is therefore ATTRACTED BT THE MaGNET. a. Colour of mineral, gold-yellow ; sometimes iridescent on surface. Copper pyrites. h. Colour, black on surface; fracture shows the colour of copper pyrites in the interior. Black ore. c. Colour, violet or between copper-red and reddish-brown. Brubescite. d. Colour, steel' or lead-grey, or iron-black. Grey Copper, before the blowpipe, yields abundant fumes of antimony. Sulphur is always present, and arsenic is sometimes detected. Tennantite. — Odour of garlic due to arsenic is prominent, and sulphur also present. The Bead of Copper is not attracted by the Magnet. 1. Lustre metallic, semi-metallic, or resinous. a. Colour, indigo blue ; lustre, not quite metallic ; more nearly resinous when crystallised, and resinous or dull when massive. Covelllte or indigo copper. 6. Colour, iron or steel-grey ; lustre, metallic. Redruthite, before blowpipe, ia very fusible, and yields a smell of sul- phur. BournOBite is easily fusible, and emits white fumes due to antimony. Melaconite is infusible. 2. Luiire non-metallic. a. Colour, black ; earthy, soils the fingers. Melaconite. h. Colour, cochineal red ; dust, brown-red. Cuprite. c. Colour, blue ; soluble in water. Chalcanthlte. d. Colour, blue or green ; insoluble in water. Azurite, which is blue, and malachite, green, are fusible, and their powder is soluble in acids with effervescence. Llbethenlte, Atacamite, and Arsenlate of Copper are green, fusible, and soluble in acids without effervescence. Atacamite colours the flame, near the substance, blue, and arseniates of copper emit smell of garlic before the blowpipe. ChrysoeoUa and Dioptase are green, and infusible. COPPER. 167 Chalcopyrite, or copper pyrites, is only to be compared with iron pyrites, which it somewhat closely resembles. It will not be mistaken for gold, although it has the colour of that metal ; nor for stannine, purple copper ore, or variegated copper. Stannine, although sometimes yellowish, has a greenish hue, and copper pyrites is distinguished from iron pyrites by being easily cut by a knife, and crushed to powder with a hammer ; while iron pyrites is much harder, scratches glass easily, and strikes fire with steel. Iron pyrites, in consequence of surface decomposition, sometimes exhibits the variegated colours of the so-called peacock ore, and is likely to be mistaken for it in this state it' not tested with the knife. It is always advisable to examine the colour in a freshly-broken specimen, when the yellow colour of copper pyrites is characteristic. Grey copper, including tennaniite and enargite (which are only varieties) are not so easy to distinguish, their steel grey colour being similar to that of many other minerals. When crystallised they sometimes resemble zincblende, but this last mineral gives a white dust when scratched, and is infusible. More complicated crystals are ' liable to be con- founded, at first glance, with haematite or specular iron, arseni- cal cobalt, and grey cobalt, both of which latter contain arsenic, and with silver glance or argentite. When massive, the analogies with other minerals are still more numerous. Grey copper and its varieties may be mis- taken for magnetic iron, chrome iron, mispickel, gersdorffite, stibnite, the cobalt ores mentioned above, argentite, or red- ruthite. The iron and chrome ores are much harder than grey copper, and are moreover infusible. The nickel and cobalt ores are very heavy, which is sufficient to distinguish them ; besides which, they will be recognised by means of the borax bead. Mispickel is silver white, and when struck with a hammer smells of garlic; while the light-coloured varieties of grey copper, which might, be mistaken for it, do not contain arsenic. Stibnite is fusible when brought near the flame of a candle, and volatile when heated before the blowpipe. Sulphides of copper and argentite are sectile and malleable, while grey copper is brittle ; besides which, the sulphides smell of sulphur when heated before the blowpipe, while grey copper gives white fumes due to antimony. Bournonite, when massive, is also likely to be mistaken for grey copper, and a reduction on charcoal with soda will be necessary to distinguish them, when a bead of lead and copper will be obtained from bournonite. When the prismatic crystals 168 PEOSPECTING FOR MINERALS. of bournonite are longitudinally striated, they resemble stibnite and the prismatic mangaoese oxides, but the manganese ores are infusible, and stibnite volatilises entirely before the blowpipe. A ready test for bournonite is its fracture, which is perfectly conchoidal and shining. The ores of copper, which do not possess a metallic lustre, will be easily distinguished from other minerals of similar appearance by the following characters : — Cuprite, when crystallised, might be mistaken for zincblende or other minerals of the same form, such as magnetite. It will, however, be readily distinguished by its red streak. When lamellar it might be mistaken for red silver ; but this mineral gives abundant antimony fumes before the blowpipe. Cinnabar, which is also red,, will entirely volatilise before the blowpipe ; besides which, the difference in specific gravity is appreciable, that of cinnabar being 8, and of cuprite 6. Cuprite will also give the green flame due to copper. Black Oxide of Copper will be distinguished from black earthy manganese and cobalt wad by the borax bead in the oxidising flame, which is violet with manganese, and deep blue when cobalt is present ; while copper alone gives a bead which is green when hot, and pale blue or greenish-blue when cold. Azurite will be distinguished from lapis lazuli and vivianite, when earthy, by being soluble in acids with effervescence. When crystallised, azurite does not resemble any other mineral. Malachite will also be distinguished from other green minerals, which are numerous, by being soluble with effervescence in acids. The minerals likely to be mistaken for malachite are some arseniates and phosphates of copper and atacamite amongst the copper ores and, amongst other minerals, pyromorphite and copper uranite. These minerals are all green, but of different hues. Pyromorphite will be readily distinguished from copper ores by its high specific gravity ; besides which it is not always green, but often yellowish-green, yellow, or brown. Copper uranite, which crystallises in laminae, exhibits on the larger faces a pearly lustre, and fuses before the blowpipe to a blackish mass. The arseniates and phosphates of copper are soluble in ammonia, and the arseniates give before the blowpipe the characteristic smell of garlic. Atacamite gives the blue fiame characteristic of chloride of copper when brought near the flame of a candle, it not being necessary to previously moisten the mineral with acid. Copper Ore Deposits. — Copper occurs in various kinds of COPPER. 169 rock in lodes of very different age. It is, of course, difficult to determine the age of a lode which occurs in crystalline schists -or sedimentary strata, unless they are overlain by beds which are not traversed by the lode and of which the age is known ; but some copper deposits have been formed in very recent times. Where copper ore occurs in beds or impregnations it does not follow that the ore has in all cases been deposited at the same time as the bed in which it is found. In G-ermany, however, near Mansfeld, there is a typical instance which leaves little doubt that the ore was formed at the time of deposition of the strata or during the Permian period, the formation being known as the "copper slate." The average composition of the ore is constant over a large area, and the rock contains from 2 to 3 per cent, of copper with a small proportion of silver and gold which make it payable to work with cheap labour and fuel. Copper ores occur in true fissure lodes, in crystalline schists and in rocks of all ages, and are also common in eru[)tive rocks, ■especially porphyry, melaphyre, and serpentine ; and in sedi- mentary strata from the Cambrian period to Tertiary times. Copper very frequently occurs in contact deposits ; where this is the case it has been segregated from the eruptive rocks, either diorite, gabbro, or serpentine, and lies either at the junction of one of these rocks with sedimentary strata or at the junction of two eruptive rocks of different ages. A well-known instance of a copper-bearing contact deposit is that of Monte Oatini, in Tuscany, where the rock which carries the copper is serpentine. The ore in deposits of this sort occurs in rounded irregular masses, and the features of the lodes are of a very variable character. It should be borne in mind, especially when exploring a new •country, that copper is frequently associated with rocks of a dark colour, which are very often green ; but it must not be supposed that the colour is imparted by copper, for it is generally due either to some other metal, such as iron, or to the presence •of a green non-metallic mineral, such as chlorite. Serpentines and hornblendic rocks are often associated with copper ores, but green serpentines owe their colour to iron, nickel, or chromium ; and if copper is found disseminated through some of them, it is the exception, and not the rule, unless in the immediate vicinity of ore deposits. On the con- trary, iron and chromium are found in all serpentines, and nickel frequently occurs. Hornblendic rocks are green, grey, or black, according as 170 PBOSPECTING FGE MINERALS. actinolite (which is green) or common hornblende (which is^ black) occur in them. Actinolite is of frequent occurrence in some schists, and black hornblende in diorites, and other dark coloured rooks which are associated with copper ores. Other green minerals enter into the composition of some rocks, especially gabbros, so it may be clearly understood that the green colour of rocks is seldom due to the presence of copper; and although green rocks are frequently associated with copper ores, they are not always to be looked on as indications of the occurrence of deposits of this metal. Near Wallaroo, the most reputed mines of South Australia,, hornblende is of frequent occurrence in the rocks of the country, which are mica and talc schists, the nearest ridge being com- posed of syenite. In New Caledonia the copper region occupies both flanks of a mica schist range in which hornblende is very common, and occurs associated with garnets, chlorite, and white and green micas ; and through these rocks serpentine protrudes at places, especially in the vicinity of the copper deposits. The main deposit which has been worked consisted of several parallel shoots or pipes of ore enveloped in foldings of the schists. Serpentine occurs in several parts of Australia where copper also is known, and also in New Zealand ; but, although serpen- tine is frequently associated with metals, and especially copper, it does not follow that it is always accompanied by such deposits; in fact the serpentines of the Lizard in Cornwall, although in a copper-bearing district, are devoid of copper ores themselves ; besides which, although contact deposits are generally numerous where they occur, they are seldom of great importance, and are very irregular. Australia is wonderfully rich in copper. It is sufficient to mention Wallaroo in South Australia, Peak Downs and Clon- curry in Queensland, Cobar and Nymagee in New South Wales, and Mount Lyell in Tasmania. Copper ores generally occur with quartz as a gangue ; but occasionally some other minerals, such as fluorspar, barytes, and calcite, are found in association with them. The ores of copper, or indeed of any metal, are always associ- ated with other ores in greater or less quantities ; but those veins in which there is the least variety are generally the most valuable, since they are more easily concentrated, and their metallurgical treatment is more simple. Copper ores, especially copper pyrites, grey copper, and mela- conite occasionally contain silver and gold. At Lake S.uperior TIN. 171 native copper often contains nuclei of pure silver enclosed in the mass of copper without being alloyed with it. Iron pyrites sometinies contains copper at the rate of a few units per cent., as in Cornwall and at Huelva in Spain, where some extensive deposits of pyrites are worked for sulphuric acid and yield 1 or 2 per cent, of copper, with a very small proportion of silver and gold, but still sufficient to give a reasonable profit. Poor copper ores or cupriferous tailings,, when in sufficient quantities and when suitable materials are at hand, can be worked very cheaply by one of the many wet processes known. Yellow copper ore is seldom pure copper pyrites, but is gener- ally mixed with more or less iron pyrites; so that an assay is always necessary to determine the value of an ore. It is often the case that a picked specimen of apparently pure chalcopyrite mixed with a small quantity of quartz will yield about 25 per cent, of copper, or even less, instead of over 33 per cent., which it should do theoretically. This low return is not due to the presence of quartz alone, but to an admixture of iron pyrites y and it is seldom the case that a concentrated pyritous ore yields more than 15 per cent, of copper on an average in a large consignment. CHAPTER XIV. Tin — Titanium — Tungsten — Molybdenum. Tin. Cassiterite or oxide of tin is the only ore of this metal, although another mineral, Stannine, containing tin, copper, and sulphur is known. Stannine is not sufficiently abundant, however, to be of much importance, and, although it has been found in lodes of some size in Cornwall, it is sold as an ore of copper and not of tin. Tinstone stands nearly by itself in its mode of occurrence and formation, as a type of a strongly marked class of deposits. It is always associated with granitic rocks, quartz-porphyries, or gneiss, all of which are of analogous composition, being rich in silica, which crystallises as quartz, and being called in consequence "acidic" rocks. Tin lodes are nearly all of great antiquity and 172 PROSPECTING FOR MINERALS. occur only in those of the above-named rocks which are charac- terised by the presence of white mica. It is only in two or three places in the world, notably Tuscany and Elba, that granites of this type have been erupted during recent times, and they contain tin in small quantity, as well as some of the minerals usually associated with it, such as tourmaline, lithia mica, and emerald. Although this fact is of no immediate practical value, it is important, because it shows that there really are laws which govern the distribution of minerals, although tliese are sometimes very obscure ; but by constant observation it is certain that, amongst discoveries of merely scientific interest, laws capable of practical application will occasionally be found. Tinstone is always associated with quartz and rarely occurs in green rocks, unless their colour be due to chlorite ; nor in dark coloured rocks, except where stained red by the decora- position of ferruginous minerals ; neither is it found in lime- stone. Those granites which are characterised by abundance of white mica have, with good reason, been termed " tin granites," and a •coarse-grained rock composed of granular quartz mixed with white mica, and called "greisen," occurs in all the tin fields of the world — e.g., Cornwall, Germany, and. Australia. The minerals most commonly associated with tin — viz., topaz, mica, tourmaline, fluorspar, apatite, and other rarer minerals containing fluorine — seem to show that it was originally contained in the granite as fluoride of tin, and that the associated minerals have been formed at its expense. It is an established fact in the genesis of minerals that fluorine is always accompanied by silicon and boron ; it is therefore natural to find silicates con- taining boric acid, such as tourmaline and axinite, in association with tin. Other minerals which frequently accompany this metal are wolfram, molybdenite, raispickel, garnet, beryl, &c. Tin appears to have been brought to the surface disseminated through the granite in which it occurs ; and has subsequently been concentrated in all the cracks and joints of the rock, forming in many cases a perfect network of veins known as stockworks ; the best known instance of this class of deposit being in the Erzgebirge Range in Saxony. At Zinnwald, the tinstone is concentrated in a number of curious concentric zones, which, for a thickness of about 1 foot, are impregnated with tin, so that the whole of the rock has to be removed for the extrac- tion of the ore. The rocks constituting these zones are greisen impregnated with tinstone and wolfram, and they have been TIN. 173 frequently displaced by vertical and inclined fissures •which reach the surface. The tinstone in these beds appears to have been formed contemporaneously with the greisen in which it occurs, and the greisen itself is probably a granite altered in situ, topaz being formed at the expense of aluminous silicates. The stockwork at Geyer consists of a mass of granite in mica schists, traversed by numerous tin lodes, from which the ores and other minerals have penetrated into the joints of the granite. The same veins extend into the surrounding mica schist, but there they appear to contain less ore. Considerable confusion exists in the use of the term " stockwork," and so the foregoing instances are given in illustration of this class of de- posit, but in the chapter on "Irregular Deposits" the different characters have already been described. The Altenberg deposit consists of a rock called "stockwork porphyry," or "zwitter rock," and is tin-bearing throughout; but the ore is so finely disseminated as to be hardly perceptible, and in such small quantities that often one-third to one-half per cent, only can be produced from it. The rock is a fine- grained greisen, and the term of porphyry is very inappropriate. It merges gradually into the surrounding country, which is com- posed of granite, chloritic granite, porphyry, and quartz por- phyry, no clear line of demarcation existing. The rock is dark coloured, sometimes almost black, and consists of quartz, mica, chlorite, tinstone, (fee, and pyrites is disseminated tiirough it in minute particles ; but the quartz alone can be distinctly recog- nised ; it frequently occurs as grains without crystalline struc- ture. Molybdenite, bismuth glance, copper pyrites, iron pyrites^ fluorspar, topaz, plies equally well to all the similar tables. Iron Pyrites. — All the minerals under this head give a magnetic mass when heated on charcoal before the blowpipe. Every prospector knows the common yellow pyrites to which he refers as "mundic" and not one will mistake it for gold, although some specimens have a beautiful golden colour. The most ready test is its hardness, which enables pyrites to strike fire with steel, giving at the same time a smell of sulphur. There are two species of iron pyrites of the same composition, but crystallising differently. " Pyrite " is the mineralogical name of the species which crystallises in cubes and modifications of the cube ; the name " marcasite " being reserved for the other species which, being of a paler yellow, is often called "white pyrites," but must not be confounded with mispickel, known amongst miners as " white mundic." Marcasite crystallises in prisms, which often affect the form of tables. Both pyrite and marcasite are found in concretions, stalactites, and radiated balls. Their hardness is the same, but the specific gravity of marcasite is less than that of pyrite. They are both readily decomposed, especially when exposed alternately to the sun and rain; this property is sometimes taken advantage of in lixiviation processes for the recovery of gold or preparation of sulphate of iron. Marcasite, however, decomposes with greater facility than pyrite. It is often found replacing the carbonate of lime in fossil shells, and these are difficult to preserve unless covered by a substance which prevents access of air. It is to the decomposition of marcasite and pyrites, and the heat generated during the i)rocess that many of the fires in coal mines and on board ship, said to originate from spontaneous combustion, are due. There is another kind of pyrites which is not of such common occurrence — viz., magnetic pyrites or pyrrhotine. It contains more iron than the common pyrites and is slightly magnetic in its natural state ; its colour is also different, being bronze-yellow. Mispickel, commonly called " white mundic," diffters in composition from the other forms of pyrites by the substi- tution of arsenic for part of the sulphur; its tin-white colour makes it an easy matter to recognise it. Its hardness is not so great as that of ordinary iron pyrites, but it also strikes fire with steel, and then gives a smell of garlic, due to arsenic. It 186 PROSPECTING FOR MINERALS. will be easily distinguished from arsenical cobalt (smaltine) and grey nickel (gersdorffite), -which it resembles, by the borax assay- before the reducing flame of the blowpipe. With smaltine the bead will be blue, and with gersdorffite light green, when cold, if cobalt is absent ; while the borax bead, with mispickel, would give the reaction of iron — viz., bottle green when cold. The bead of nickel and the bead of iron will be best distinguished in th& oxidising flame; when cold, the nickel bead is red, while that of iron is light yellow or colourless. Common iron pyrites occurs as an accessory mineral in all metalliferous veins. It always accompanies gold in the reefs^ when this precious metal is free ; and is generally auriferous itself to a greater or less extent, being seldom free from traces of gold even when free gold does not occur in the district. From an industrial point of view pyrites should be considered as an ore of sulphur, being used in the manufacture of sulphuric- acid, the sulphates, and sometimes sulphur itself In sedimentary rocks pyrites is frequent, especially in fossili- ferous beds, having been deposited in them by the decomposition of organic matter. As a rule, marcasite is the variety found in sedimentary formations which have not been metamorphosed, while pyrites occurs in lodes and metamorphic rocks. It has been said that pyrites is easily decomposed in Nature^ This decomposition takes place in two different ways. In the first, a soluble sulphate of iron is formed with the generation of heat ; this explains in some cases the high temperature of mines and mineral springs. In the second, the sulphur is slowly displaced and hydrous oxide of iron formed ; this explains how it is that at the surface, or in exposed parts of a pyritous deposit,, cubical crystals of limonite frequently occur, which, if broken, are found to contain a nucleus of undecomposed pyrites in thfr centre. Magnetic pyrites often contains from 3 to 10 per cent, of nickel, and is then mined for that metal. Nickeliferous pyrrho- tine occurs in veins in diorite in Italy, and in porphyry in Scotland, at the contact of gabbro with the country rock. Arsenical pyrites is practically an ore of arsenic, but oftert contains gold or silver. It is more frequently associated with tin and copper ores. NICKEL AND COBALT. 187 TABLE OF SULPHURETTED IRON OEKS. Iron Useful Mineral. combined Substance. Hard- Specific Streak. Hemarks. with Per cent. ness. Gravity. Pyrite, Marcasite, . S S54 6-6i 5 Grey Often auriferous. S S54 6-64 4-8 Greyish- Very easily decom- green posed. Pyrrhotine, . S S39 4 4-6 Dark- grey Slightly magnetic ; sometimes nickel- iferous. Mispickel, . S, As A3 43 5-5 61 Black Sometimes aurifer- ous. S, Sulphur ; A», Arsenic. Nickel and Cobalt. The ores of nickel and cobalt are of two classes — viz., those in which the metals are combined with arsenic, sulphur, or both ; and those in which the metals are oxidised. The first class includes all those ores which are mined in Europe, where they exist in veins in granite, gneiss, or schists,. and at the contact of these rocks with diorite, gabbro, » Roasting at a gentle heat. Hexagonal carbonate of lime. A metallic element. Chloride of mercury. See Oeological Table. A coal yielding a large quantity of illuminating gas. Hair-like. 3^ troy grains. Containing fossil carbon. Irregular offshoots of mineral from lodes. Compounds of carbonic acid with a base. Carbonic anhydride CO2. See Geological Table. Conversion to carbon. Chloride of magnesia and potash. A red variety of quartz. Clayey material found between a vein and its walls. Oxide of tin. Oriental cat's eye is chrysoberyl and false cat's eye quartz enclosing fibres of asbestos. A diagonal lode. Irregular deposits of mineral in the caves gener- ally found in limestone. Sulphate of strontia. Auriferous conglomerate. Carbonate of lead. Oxide of antimony. Hydrous silicate of alumina, lime, potash, and soda ; a zeolite. Sulphate of copper. A variety of quartz. Sulphide of copper and iron. GLOSSARY. 219 Chiastolite, Chloanthite, Chlorides, . Ohlorination, Chloeine, Chlorite, c hloeobromides, Chrome Iron, Chromite, . Chromium, . Chbtsobektl, Chetsocolla, Chrysolite, . Chrtsopease, Chrtsotile, . CtXNABAR, . ClTEIN'E, Clay, . Clay Slate, . Cleavage, . Cleavage Planen, Clinometer, . Coal, Cobalt.. Cobalt Bloom, . COBALTIPEEOirS WAD, . cobaltieerous mispickel, cobaltine, Columnar, . Columns (of Ore), Combed Veins, . Combustible, Conchoidal, Concretion, . Congenial, . Conglomerate, . Contact Deposits, Silicate of alumina. Arsenide of nickel. Compounds of chlorine with metals. Conversion of gold into chloride of gold by the action of chlorine. An element. A hydrous silicate of magnesia and alumina. Compounds of chlorine and bromine with metals. A chromate of iron. A metallic element. Aluminate of glucina ; a gem. A hydrous silicate of copper. Silicate of magnesia and iron. An apple-green variety of quartz. Hydrous silicate of magnesia ; a fibrous variety of serpentine. Sulphide of mercury. False topaz ; a yellow variety of quartz. A hydrated silicate of alumina in very finely divided particles. , A slate formed by the induration of clay. The property possessed by certain minerals and rocks of splitting more readily in certain directions than others. The planes along which cleavage takes place. An instrument for measuring angles on a verti- cal wall face, rossilised carbon formed by the carbonisation of vegetable matter. A metallic element, Arseuiate of cobalt. Impure oxide of manganese, containing cobalt. Sulphide and arsenide of iron, containing cobalt. Sulphide and arsenide of cobalt. In the form of columns. Deposits of ore in lodes having a- small lateral, but considerable vertical, extent. See Banded Vtins. Capable of being burned. Shell-like. A nodule formed by the aggregation of mineral matter from without round some centre. « A term applied to rocks in which lodes become ore.-fcearlng. Consolidated gravel. Mineral deposits occurring at the line of junction of two dissimilar rocks. 220 GLOSSAEY. contoktion, . Copper, coppekas, COPPEE Glance, COPPEE NiOKBI,, Copper Pyrites, Copper Slate, copeolites, . cordierite, . Corundum, . Coterminous, Courses (op Ore), covelline, . Cradle, . Crate Dam,. Crateriform, Cretaceous, . Crevioing, . Ceocidolite, Ceocoisite, , Cross Course, Cryolite, Crystallisation, Cube, . Cuprite, Ctanidation, Cyanite, , Dead Work, Decrepitate, Deep Leads, Dboradation, Dehydrated, Dendritic, . Denudation, Crumpling and twisting, A metallic element. ' Sulijhate of iron. Sulphide of copper. Arsenide of nickel. Suliihide of copper and iron. Slate impregnated with copper minerals. Phosphate of lime; petrified excrements of animals. Silicate of alumina, iron, and magnesia ; a gem. Alumina; a gem. Finishing at the same point. Deposits of ore in lodes having a small vertical, but considerable lateral, extent. Sulphide of copper. An apparatus for washing alluvial gold, mounted on rockers. A dam built of crates filled with stones. In the form of a crater. See Geological Table. Searching the crevices in rocks forming the beds of streams in search for gold. A fibrous silicate of iron, soda, and magnesia. Chromate of lead. A vein intersecting another of greater geological age, which it frequently displaces from its original course. Fluoride of alumina and soda. The assumption by matter of a definite geo- metrical form. A solid six-sided figure, of which each of the sides is a square and all the angles right angles. Ped oxide of copper. Conversion of gold into a double cyanide of potassium and gold by the action of cyanide of potassium. A silicate of alumina. Work in unproductive ground. Explosive breaking tip into fragments when heated before the blow-pipe. Alluvial deposits of gold or tinstone buried below a considerable thickness of soil or rock. Wearing away. Deprived of water. Like branches of trees. Stripping by water and other agents. GLOSSARY. 221 Detmtus, Devonian. Diabase, DiALLAGE, DiALLOGITE, Diamond, Diatoms, DiCHROIC, DiCHEOITE, DiOPSIDE, DiOPTASE, DiOKITE, Dip, DiSINTEGKATION, Dislocation, DiSTHENE, dolerite, Dolomite, . Domes, . dometkitb, Dredging, . Drift, . Dkusy, Dry Ores, Ductile, Dump, , D unite, Dyke, . Efflorescence, Elastic, Elaterite, Electrum, Elements, . Elevation, . Elvan, Accumulations from the disintegration of exposed roelv surfaces. See Geological Table. An igneous rock, see p. 9. A silicate of lime and magnesia. Carbonate of manganese. Crystallised carbon ; a gem. Minute plants which are provided with siliceous envelopes. Exhibiting two different colours when light is transmitted in two different directions. Cordierite ; a silicate of alumina, iron, and magnesia. A silicate of lime and magnesia. A silicate of copper. An igneous rock, see j). 9. The angle of inclination of beds or strata measured in relation to a horizontal line. The breaking asunder of solid matter due to chemical or physical forces. The displacement of rocks on either side of a crack. Cyanite ; a silicate of alumina. An igneous rock ; see p. 9. Carbonate of lime and magnesia. Strata which are dipping away in every direction. Arsenide of copper. Raising material from below water by means of a dredge. Loose crumbly aUuwal deposits. Cavities in rocks lined with crystals. Silver ores which do not contain lead. Capable of being drawn into wire. A space below place of delivery where tailings can be deposited. A massive olivine rock in which small grains of chromite are interspersed. A vertical or highly dipping injected sheet of eruptive origin. Crystals or powder formed on the surface of minerals, due to their decomposition. Substances capable of being stretfihed and then resuming their original form. Elastic bitumen ; a hydrocarbon. ' An alloy of silver and g<5ld. Substances which have never been decomposed. A front or side view of anything. An igneous rock, see p. 9. ■222 GLOSSARY. Embolite, Emerald, Emery, Enargite, Enstatite, . Eocene, Epidote, Epsom Salt, Ebodinc, Erubescite, Eruptive, Ertthbine, . lixCRESCENCB, Exfoliate, . Fahlbands, False Bottom, Fault, . Felspars, Ferruginous, Fibrous, Fireclay, Fissures, Fissure Lodes, Flats (op Ore), Flocculent, Floor, . Flucan, Fluor Spar, . Footwall, . fossiliferous, Fossils, Franklinite, Free Milling, Freislebenite, Fullers Earth, Chlorobromide of silver. A silicate of alumina and gluciua ; a gem. An impure variety of corundum. Sulphide, arsenide, and autimonide of copper. A silicate of magnesia and iron. See Geological Table. A hydrous silicate of alumina, iron, and Ume. Hydrous sulphate of magnesia. Gradually wearing away. Bornite ; sulphide of copper and iron. Formed by a. violent breaking out of enclosed matter. Arseniate of cobalt. Grown out of. To peel off in leaves from the outside. Zones of crystalline schists impregnated with metallic sulphides which influence the richness of lodes passing through them. In alluvial mining a stratum on which auriferous beds lie, but which has other bottoms below it. A displacement of the strata accompanied by a fracture of the rock. Anhydrous silicates of alumina and of an alkali or lime. Containing iron. Consisting of fibres which cannot be easily separated. A silicate of alumina that will stand intense heat ; it is almost entirely free from alkalies or lime. Open cracks. A lode occupying what was once a fissure opened by a movement of the rocks. A horizontal ore deposit occupying a bedding plane in the rook. Cloudy, resembling lumps of wooL The bottom of a coal seam. A soft clayey substance, casing. Fluoride of lime. The lower side or boundary of a lode. Rocks containing fossils. The remains of plants or animals accidentally buried in the earth. Oxide of iron, zinc and manganese. Ores which yield their gold or silver to amalga- mation. A sulphide of silver, lead, and antimony. Soft unctuous clays employed in the treatment of woollen goods. GLOSSAllY. 223 Gabbro, Galena, Galmbi, Gansue, Garnets, Garnierite, Gash Veins, Ge-Anticlinal, Gelatinise, Gkological Table, Geo-Stnclinal, . Gersdohpfite, Getsers, Glacial Deposits, Glacier Deposits, Glauber Salt, Glaucodote, Gneiss, gobthite, GrOLD, . Goslarite, . An igneous rook, see p. 9. Sulphide of lead. A silicate of zinc. The matrix in a lode in which ore occurs. Anhydrous silicates of alumina and the earths coloured by oxides of iron, manganese and chromium. A silicate of nickel. Fissures which are confined to particular rocks or beds and which do not extend into adjoining rocks. Dome-shaped bendings, not only- of the strata or formation, but of the earth's crust covered with its strata which may or may not be contorted. Become like jelly. The rocks which constitute the earth's crust are divided according to their relative position and fossil contents as in the following table ; those at the top of the table being the youngest. Post Tertiary — Kecent and Pleistocene. /■pliocene. J Miocene. j Oligooene. V Eocene. ( Cretaceous. ■I Jurassic. (. Triassic. C Permian. I Carboniferous. -! Devonian. Silurian. [Cambrian. Tertiary (Cainozoic), Secondary (Mesozoio), Primary (pt.) (Palaeozoic), Primary (pt.) (Azoic), Archaean. Basin-shaped bendings of the earth's crust, the reverse of ge-antiplinals. An arsenide of nickel- Intermittent boiling springs. Deposits formed by the ice sheets of the glacial period. Deposits formed by existing glaciers or their former extensions. Sulphate of soda. A variety of cobaltine. A stratified granitoid rock in which the minerals are arranged in layers. A hydrous oxide of iron. A metallic element. Sulphate of zinc. ' 224: Gossan, Granite, Gkanulak, . Graphite, Gbeisen, Gbet Coppbe, Geossulaeia, Gtpsum, hematite, . Hallotsite, . Hanging Wall, . Haemotome, Haueeite, . Hausmannite, Hadtne, Heave, .... Hedeneeegite, Helioteope, . Hessite, Heulandite, Homogeneous, hoenblende, „ Andesite, HoEN Silver, HU.MID, . Hyacinth, . Hydraulic Elevator, . Hydraulic Lime,. Hydeocarbons, . Hydeomagnesite, Hydeotheemal, . Hydrous, Hypbrsthenb, Hypersthenitb, Iceland Spab, Idocease, Igneous, GLOSSARY. Hydrated peroxide of iron often quartzose, found capping lodes that contain ferruginous minerals. An igneous rock, see p. 9. In the form of grains. A form of carbon. A granitic rock consisting of mica and quartz. Tetrahedrite ; a complex copper ore ; see p. 163. A green variety of garnet. Hydrous sulphate of lime. Anhydrous oxide of iron. A hard clay. The upper side or boundary of a lode opposite the foot wall. Hydrous silicate of alumina and baryta. Sulphide of manganese. Anhydrous oxide of manganese. Silicate of alumina, soda, and lime, and sulphate of lime. An apparent lateral displacement of a lode pro- duced by a fault. Black variety of augite. Bloodstone ; a dark green variety of quartz with specks or veins of jasper. Telluride of gold. Hydrous silicate of alumina and lime ; a zeolite. Of the same structure throughout. A siUoate of lime, magnesia, and iron. An igneous rock ; see p. 9. Chloride of silver. Warm and moist. A variety of zircon, A machine for raising gravel by means of hydraulic pressure. Lime which has the property of setting under water. Compounds of carbon and hydrogen. Hydrous carbonate of magnesia. Pertaining to hot water, especially with respect to its action in dissolving, re-depositing and otherwise producing mineral changes within the crust of the globe. Containing water regarded as water of crystal- lisation. A silicate of magnesia and iron. A rock formed of labradorite and hypersthene. Crystallised transparent carbonate of lime. A silicate of alumina, lime, and magnesia. Applied to all agencies, operations, and results which appear to be connected with subter- ranean heat. GLOSSARY. 225 Impounding Tailings,. Impekgnation, Indioatob Vein, . Indueated, . Infusorial Earth, In Situ, Intbrsteatified, . Intrusion, . Intumescence, Iodaegteite, Iodine, . Iridescent, . Iridium, Ibidosmine, . Ieon, Ieon Pteites, Isomorphism, Itaoolumitf, Jade, . Jambsonitf, Jabgon, Jet, JiGGEE, . Jurassic, Kaolin, Kauri Gum, . Keraegteite, Kerosene Shale, KiLLAS, . Kindly Ground, . Ktanite, Labbadoeite, IiAOCOLITES, . Enclosing them so that they cannot flow where they are not wanted. Ore disseminated through rook and having no sharply- defined limits. A vein which is not metalliferous itself, but, if followed, leads to ore deposits. Hardened. A aiUceous deposit formed chiefly of fragments of diatoms. In the place where formed. Interbedded with. Forcing through. Swelling when heated. Iodide of silver. A metallic element. Exhibiting a, play of different colours like ;i rainbow. A metallic element. An alloy of iridium and osmium. A metallic element. Sulphide of iron. The property of certain chemical compounds of different composition, but crystallising in the same forms, of replacing one another in minerals. A flexible sandstone. Nephrite ; a silicate of lime, magnesia, and iron. A sulphide of lead and antimony. A variety of zircon. A hard variety of coal, which is cut and polished for ornaments. A machine for the concentration of ores. See Geological Table. A very pure clay. A gum which exudes from the kauri pine in New Zealand, and is frequently found fossilised. Chloride of silver. A shale containing a large proportion of hydro- carbons of high illuminating power. Clay slate. Those rocks in which lodes become productive of mineral of value. See Cyanite. A silicate of lime, alumina, and soda. Lenticular sheets of eruptive rock spread between beds, having an intrusive origin and not occur- ring as an overflow. 15 226 GLOSSARY. Lamellae, Lamina, Lapis Lazuli. Laumontite, Lavas, . Leaders, Leads, . Lenticulab, Lbpidolite, Lheezolite, . LiBETHBNITE, Lignite, Lime, Limestone, LiMONITE, LlNNa)ITE, Lithographic Stone, Live Eivees, Lode, . Lode Fobmation, Magma, Magnesia, . Magnesitb, . Magnetic Pyrites, Magnetite, . MainJBottom, Malachite, , Malleable, . Mammillaet, Manganese, . Manganite, . Marble, Maeoasite, . Martite, Matrix, Meerschaum, Melaconite, Melanite, Melaphyrb, Meeoury, |. In thin sheets. Thin plates or scales. XJltramarine, see p. 77. A silicate of lime and alumina. Rocks which have flowed in a molten state from volcanoes. Small veins carrying mineral which are offshoots from lodes. The auriferous portions of alluvial deposits marking the former course of the stream. ' Lens-like. A lithia mica. A variety of pyroxeue-olivine-rock. Phosphate of copper. A hydrous variety of coal retaining its woody structure. Oxide of calcium, produced by calcining carbon- ate of lime. Rock formed of carbonate of lime. Hydrous oxide of iron. A sulphide of nickel and cobalt. A very fine grained limestone. Rivers which are now running. Any vein that appears likely to produce metallic ore. A term applied in many cases to decomposed rocks with small leaders traversing them. Paste or groundwork of igneous rocks. Oxide of magnesium. Carbonate of magnesia. Pyrrhotine ; a sulphide of iron. Magnetic oxide of iron. Hard rock below alluvial deposits. Green carbonate of copper. Capable of being moulded. In smooth, rounded prominences. A metallic element. Hydrous oxide of manganese. Metamorphic limestone. Radiated pyrites ; rhombic sulphide of iron. A variety of haematite. The rock or mineral containing metallic ores or precious stones. A hydrous silicate of magnesia. Black oxide of copper. A black variety of garnet. An igneous rock. A metallic element. GLOSSARY. 227 Metalupbkous, Mktamokphism, Meteokic Iron, . Micas, . Mica Schist, MlLLEBITE, MiMETITE, Minium, Miocene, MiSPICKEL, Molybdenite, Molybdenum, Moltbdite, . Moonstone, . Moraines, . Mountain Leather, MUNDIC, Muscovite, . Nacreous, . Nagtagite, . Natrolitb, . Natron, Nephrite, Neptunists, . Nickel, . NiCKELINE, . Nickel Ochre, NiCOPTRITE, . Nitrates, Nitratine, . Nodular, Noumeite, . Nucleus, Obsidian, Octahbdrite, Octahedron, Odontolite, . Metal bearing. A term used to express a change in the minera- logical or chemical composition and internal structure of rooks produced by the operation of heat, heated water or vapour, pressure, &c. Iron which has fallen on the earth froin inter- planetary space. Flexible and elastic minerals occurring' in thin plates ; silicates of alumina and potash, mag- nesia, lithia, or iron. A metamorphic rock consisting of a, laminated aggregate of quartz and mica. Sulphide of nickel. Arseniate of lead. Bied lead ; oxide of lead. See Geological Tahle. Sulphide and arsenide of iron. Sulphide of molybdenum. A metallic element. Molybden-ochre ; oxide of molybdenum. A variety of adularia felspar. Deposits formed by glaciers. Impure asbestos. Pyrites ; sulphide of iron. Potash mica. Resembling mother of pearl. Telluiide of gold and lead. Hydrous silicate of alumina and soda ; a zeolite. Carbonate of soda. Jade ; a silicate of lime, magnesia, and iron. Those who ascribe all geological phenomena to the action of water. A metallic element. Arsenide of nickel. An arseniate of nickel. Sulphide of nickel and iron. Compounds of nitric acid with bases. Nitrate of soda. Concretions of rock matter aggregated round a central nucleus. Silicate of nickel. A body about which anything is collected. A volcanic glass. Titanic oxide. An eight-sided figure, each of the sides being an equilateral triangle. False turquoise ; fossil bone coloured by. copper- 228 GLOSSARY. Oligiste, Oligoolase, Olivine, Onyx, . Opal, . Opalescence, Oeganio Compounds, Oeiektal Amethyst, „ Emeeald, „ Topaz, Oepimbnt, . Obthoclase, OUTCEOP, Oxides, . ozokeeite, . Pack Walls, Palladium, . Pan Amalgamation, Paetings, Peacock Oee, Peaely, Pegmatite, Pennine, Pbblitb, Peemian, Pbteipibd, Petholeum, Pbteology, Pbtzite, Phbnakite, Phosphates, Pipes (op Oee), PiSOLITIC Oees, Pitchblende, PiTOHSTONB, . Plagioolasb, Plasma, Plastic, An oxide of iron (haematite). Silicate of alumina, soda and lime; a soda-lime- felspar. Silicate of magnesia and iron. A variety of quartz in alternate layers of white- and brown or white and black. Hydrous silica. Exhibiting a. play of colours like the precious- opal. Compounds containing carbon, generally derived, from animals or plants. A variety of corundum. A sulphide of arsenic. A sihcate o£ alumina and potash ; potash felspar. The appearance on the surface of the ground of a rock, lode, or coal seam. Compounds of oxygen with any element. Mineral wax ; a solid petroleum. Walls built of loose material in mines to support the roof. A metallic element. Amalgamation of silver or gold with mercury by grinding in a pan. Small bands of shale or stone occurring in a coal seam. Copper pyrites which has become tarnished. Kesembliug mother of pearl. Veins of coarsely crystallised granite in granite, A variety of chlorite. A volcanic glass. See Geological Table. Changed to stone. A natural mineral oil. The study of rocks. Tellaride of silver and gold. A silicate of glucina ; a gem. Compounds of phosphoric acid -with a base. An elongated body of ore in limestone, generally" standing nearly vertical. In concretions about the size of a pea. Oxide of uranium. A volcanic glass, see p. 9. Eelspars in which the two principal cleavage planes are not at right angles to one another. A green variety of quartz. Easily moulded. GLOSSARY. 229 Platinihidium, Platinum, P1.E0NASTE, . Plications, Pliocene, Plumbago, . Plujib Bob, . Plutonists, . Poltbasite, . Porcelain Clay, . porphtbite, . porphtby, . Position Blocks, Potash, Precipitate, Prehnite, Prismatic, . Prisms, Productive, . Proptlite, Prospecting, Pboustite, . Psilomelane, Pumice, . Purple of Cassius, Pyrabgtrite, Pyrites, Pyrolusite, . Pybomoephite, Pykope, Pyhosmalite, Pyrehotine, <3uAKRrED, . Quartz, An alloy of platinum and iridium. A metaUic element. A variety of spinel. The smaller foldings of a rock. See Geological Table. Graphite ; carbon. A weight suspended by a string used to determine vertical lines. Those who attempt to explain all geological phenomena by the action of heat. A sulphide of silver, copper, antimony, and arsenic. Kaolin, the purest form of clay. An igneous rock consisting essentially of a true porphyry ground mass containing crystals of plagioclase. Any igneous rook consisting of a ground mass in which conspicuous crystals are embedded. Mining claims which are in a position which will contain a lode if it continues in the direc- tion in which it has been proved in other claims, but which themselves have not yet been proved. Oxide of potassium. A solid substance thrown down in one solution by the addition of another solution. A silicate of alumina and lime. In prisms. Solids whose bases are plane figures, and whose sides are parallelograms. Yielding payable ore. Originally defined as tertiary volcanic rocks consisting of triclinic felspar and hornblende in a fine-grained non-vitreous ground mass. Searching for minerals. A sulphide and arsenide of silver. Manganate of baryta. A vesicular volcanic glass. A purple precipitate formed by adding stannous chloride to chloride of gold. A sulphide and antimonide of silver. Cubic sulphide of iron. Black oxide of manganese. Phosphate of lead. A variety of garnet. A silicate of iron and magnesia. Magnetic pyrites ; sulphide of iron. Worked in the open. Crystallised silica. 230 GliOSSAEY. QUAKTZ DiOBITE, QUABTZITE, . QuAKTZ POEPHTBT, Quicklime, , quioksilvee, Radiating, . Ramified, Realgar, Red Lead, . Rededthitk, Reduction, . Reefs, . Refraction, Repeaotoet, Renifoem, . Resinous, Reticulated Veins, Reveese Faults, Rhodonite, . Rhombic Dodecahedron, Rhombohedeon, . Rhtolite, Ribbon Veins, Rim Rock, RiPIDOLITE, . Rise, Rook Cetstal, Rook Salt, Roof, , rueellite, RUBT, . RUTILE, Sacchaboid, Saddle Reefs, Sal- Ammoniac, Saltpetre, . Sampling, Sandstone, An igneous rock, see p. 9. A metamorphic sandstone. An igneous rock, see p. 9. Oxide of calcium produced by roasting limestone. Mercury ; a metallic element. Diverging from a centre. Branched in many directions. SulpMde of arsenic. Minium ; oxide of lead. Copper glance ; snlphideof copper. Reducing compounds to a metallic state. Lodes, ledges, or veins. Deviation from a direct course ;1 the property' possessed by some minerals of deflecting rays of light. Difficult to treat for the recovery.]of metals. Kidney-like. Resembling resin. Veins traversing rocks in all directions. Faults due to thrust, the hanging wall side of the, fault being forced upwards on the footwall. Silicate of manganese. A twelve-sided figure, each side of which is a rhomb. A six-sided figure, each side of which is a rhomb. An igneous rock, see p. 9. See Banded Veins. Bed rock in alluvial mining which outcrops above' the level at which the auriferous lead occurs. A variety of chlorite. That portion of a bed or coal seam which lies- above a level is said to be "to the rise." A clear colourless variety of quartz. Chloride of sodium. The strata immediately above a coSl seam. A red variety of tourmaline. „ „ corundum. A form of oxide of titanium. Like lump sugar. Quartz reefs occurring in the form of saddles; see p. 141. Chloride of ammonium. Nitrate of potash. Mixing ores so that a portion taken may fairly represent the whole body. Consolidated sand. GLOSSARY. 231 Sanidine, Sapphire, Sabdonyx, Saueians, SCAEP, . soheelite, Schist, . SOHOHL, Sectile, Section, Sediment, Sedimentakt, Segregations, Selenium, Serpentine, . Shale, . Shingle, Shoots, Siderite, Silica, . Silicates, Silurian, Silver, Silver Glanck, Sinter, . Slags, . Slate, . Slickknsides, Slide, Slimes, Sludge Channel, Sluice Box, . Sluicing Table, Smaltinb, Smithsonite, Soapstone, Silicate of alumina and potash ; a slajsy variety of orthoclase. A blue variety of corundum. A variety of quartz. A group of reptiles now extinct. A steep face. Tungstate of Ume. A laminated metamorphic rock. A black variety of tourmaline. Can be cut with a knife. A cut through. A deposit formed by water. Rocks composed of sediment. Aggregations of ores in a cavity having an irregular form but defined limits. An element. Hydrous silicate of magnesia. Consolidated clay. Clean gravel. Deposits of ore in lodes, which have a limited lateral extent but considerable extent in depth ; they generally dip at varying angles between horizontal and vertical. Carbonate of iron. An oxide of silicon. Compounds of silica or silicic acid with a base. See Geological Table. A metallic element. Sulphide of silver. A deposit from hot springs. Fusible silicates formed when ores are smelted and the metals extracted. Indurated clays, sometimes metamorphosed. Smooth, polished, and sometimes striated sur- faces on the walls of lodes produced by friction. A fault or cross course. The very fine grained particles produced by crushing ores, which do not readily sink in water. Tail race for conveying the tailings away after the gold has been extracted from alluvial beds. A wooden trough in which alluvial beds are washed for the recovery of gold or tinstone. A table on wheels used for washing black sand for gold on the coast of New Zealand. Arsenide of cobalt. Carbonate of zinc (Dana). A compact variety of talc. 232 GLOSSARY. Soda, . SoLPATARic Action, Spathic Iron, Sphekosiderite, Spinel, . Stalactites, Stalaomites, Stannine, Steatite, Stephanite, . Steenbebsitb, Stibnitb, Stilbitb, Stockwoeks, Stratification, Streak, . Striated, Strike, . Steometeeine, Strontia, Strontianite, Strontium, . Sulphates, . Sulphides, Sulphur, Sulphuretted Hydrogen, sunstone, Surface Chaegbs, Syenite, Sylvanitb, Syncline, Oxide of sodium. The final stage of volcanic eruption when steam and gases only are emitted from the craters. Carbonate of iron, do. do, Aluminate of magnesia. loiole-like incrustations hanging down from the roof of caves. Similar to stalactites, but formed on the floor of the oaves by the deposition of solid matter held in solution by dropping water. Sulphide of tin and copper. Hydrous silicate of magnesia. Sulphide and antiraonide of silver. Sulphide of silver and iron. Sulphide of antimony. Hydrous silicate of alumina and lime. Rock which is traversed by so many metalli- ferous veins as to render the whole deposit of sufficient value for treatment. The arrangement of sedimentary rocks in beds or strata. The powder of a mineral or the colour-effect pro- duced by scratching it with a knife. Marked with furrows. A horizontal line upon the floor of a bed or foot- wall of a lode. Sulphide of silver and copper. Oxide of strontium. Carbonate of strontia. An element. Compounds of sulphuric acid with a base. Compounds of sulphur with metals. An element. A sulphide of hydrogen. A variety of oligoclase. All expenses incurred on the surface of a mine which have to be charged against the mineral. An igneous rock, see p. 9. Telluride of gold and silver. Strata bent in the form of a trough. Tachylyte, Tailings, Tail Race, Talc, . Tellurium, A volcanic glass. The refuse from a mine after the valuable ore have been extracted. A channel for removing tailings A hydrous silicate of magnesia. A metallic element. GLOSSAEY. 233 Tennan-tite, Tetbahedrite, Thomsonite, Till, TiMAZITE, Tin Dish, . TiK Pyhites, Tinstone, TiTANATES, . Titanic Iron, TiTANlVM, Toad's Eye Tin, Topaz, . tokbanite, Tourmaline, Tbachtte, . Translucent, Transparent, Teappean, . Travertine, . Tremolite, . Triassic, Tbiclinic, Tridtjiite, . Tripoli, Troubles, tungstates, Tungsten, . Ultramarine, Underclay, . Underlay, . Uranium, uwarowite, . A sulphide and arsenide of copper and iron. A complex copper ore, see p. 163. Hydrous silicate of alumina, lime, and soda ; a zeolite. A glacial deposit. Hornblende andesite. A dish used by prospectors for washing gold- bearing materials and extracting the gold. Sulphide of copper and tin. Cassiterite ; oxide of tin. Compounds of titanic acid with a base. Specular iron containing oxide of titanium. A metallic element. A variety of wood tin occurring in small spherical particles embedded in a mass of darker or lighter colour. A silicate of alumina with fluorine ; a gem. A dark brown variety of cannel coal. A silicate of alumina and other oxides, see p. 74. An igneous rock, see p. 9. Transmitting light, but not transparent. Transmitting light perfectly; objects can be seen through a transparent medium. Rocks occurring in dykes and sheets. Material deposited by calcareous springs. A white variety of hornblende. See Geological Table. Crystals having three axes which are not at right angles. Silica — resembling quartz, but occurring in small flat hexagonal tables. A hydrous silica powder composed chiefly of diatoms. Disturbances in a noal seam. Compounds of tungatio acid with a base. A metallic element. Lapis lazuli, see p. 77. The clay forming the floor of many coal seams. The inclination of lodes to the vertical. A metallic element. A chrome garnet. Valentinite, Vesuvianite, "Vitreous, ViVIANlTE, . Volcanic, Oxide of antimony. A silicate of alumina, lime, and magnesia. Glassy. Hydrous phosphate of iron. Ejected from a volcano. 234 GLOSSAEY. Wad, . Wash Outs, Watbk Powek, WiLLEMITE, . Wins Dams, WiTHEKITE, . WOLFKAM, . wollastonitk, Wood Tin, . w0lfenite, . Zeolites, ZiNO, Zinc Blende, ZiNo Bloom, ZlNCITE, ZiNCKENITE, . Zircon, ZOISITE, ZwiTTEK Rook, An impure earthy ore of manganese. Parts of coal seams which have been removed by streams flowing at the time of their formation. The power which is developed by the pressure of water when applied to water wheels, .turbines, &c. Anhydrous silicate of zinc. Dams built from the side of a river with the object of deflecting it from its course. Carbonate of baryta. Tungstate of iron and manganese. A silicate of lime. Tinstone of a brown colour of various shades ; botryoidal and reniform in shape and fibrous in structure. Molybdate of lead. Hydrous silicates of alkalies or alkaline earths with silicates of alumina. A metallic element. Sulphide of zinc. Hydrous carbonate of zinc. Red oxide of zinc. Sulphide of lead and antimony. A silicate of zirconia ; a gem. A non-ferriferous rhombic ally of epidote. A stockwork porphyry at Altenberg. 235 INDEX. ACTINOLITE, 60, 63. Adelong, 103. Agate, 55, 75, 79. Alabandine, 191 . Albite, 60, 62. Albumia Mine, 103. Alluvial deposits — Their mode of occur- rence, 4, 125 ; source of materials, 125 ; age of parent reefs, 125 ; deep leads, 127; New Zealand deposits, 128 J comparative table, 130; British Columbia deposits, 130; conditions under which found, 131 ; considera- tions regarding working, 1.33. Amber, 198, 204. Amethyst quartz, 75, 78, 79. Analcime, 66. Anamesite, 9. Andalusite, 77, 79. Anglesite, 154. Anhydrite, 50, 52. Annabergite, 189. Anorthite, 60, 63. Anthracite, 198. Antimony, 193, 194. Apatite, 50, 53, 78. ApophyUite, 66. Aragonite, 49, 50. Argentite, 149. 150. Arsenic, 193, 194. Asbestos, 63. Aaphaltum, 198. Atacamite, 164. Augite, 60, 64. „ andesite, 9. Australian reefs, 126. Azurite, 164, 168. Banket beds, 86. Barytes, 50, 53. Barytocaloite, 50. Basalt, 9. Beryl, 72, 78, 79. Biotite, 57, 59. Bismuth, 193, 195. ,, ochre, 197i Bismuthine, 197. Bismuthite, 197. Bloodstone, 75, 79. Blowpipe— Characters of minerals, 31 ; lamp or candle, 32 ; use of, 33; oxi- dising and fusing flame,{34 ; reducing flame, 34 ; reagents, 34 ; accessories, 34. Bog oak, 201. Boracite, 78, 79. Borax beads— Colour of, 3b ; with co- balt, 36; with copper, 36; with titanates and tungstates, 36 ; with manganese, 36 ; with nickel, 36 ; with chromium, 37; with uranium, 37; with iron, 37. Bornite, 163. Boumonite, 156, 163, 167. Braunite, 191. Bromargyrite, 149. Bronzdte, 60, 65. Brookite, 177. Brown coal, 198. Cairngorm, 7-5, 78, 79. Calamine, 180. Calaverite, 147. Calcite, 49, 50. Cannel coal, 198, 199, 201. Carbonate of lead, 156. ,, of soda, and nitre— Tests. with, 38. Carbonic acid — Action of, 99. Camelian, 75, 79. Cassiterite, 171, 174, 175, 177. Cat's eye, 76, 79. Cave deposits, 113. Celestine, 50, 53. Cerussite, 154. Cervantite, 195. Chabazite, 66, 67. Chalcanthite, 164. 236 INDEX. Chalcedony, 55, 75, 79. Chalcopyrite, 16,S, 167. Charcoal — Tests on, 37 ; with carbonate of soda, 38. Ohloanthite, 189. Chlorite, 57, 58. Chrome iron, 192. Chromite, 1S2. Chromium, 179, 192. Chrysoberyl, 71, 78, 79. Chrysocolla, 164. Chrysolite, 76, 79. Chrysoprase, 75, 79. Cinnabar, 158, 159. 162. Citrine quartz, 75, 79. Clays, 67. Cleavage of minerals, 17. Coal, 198, 199; origin of, 80; occurrence and prospecting for, 81 ; comparative thickness of, 84 ; bands in, 84. Cobalt, 179, 187. Cobaltiterous mispickel, 189. Cobaltiferous wad, 189. Cobaltine, 189. Colour of minerals, 20 ; table of, 25. Combustible minerals, 198. Contact deposits, 111. Copper, 162, 163 ; in stratified deposits, 85 ; arsenides of, 163 ; arseniates of, 164 ; ores, tests for, 166 ; black oxide of, 168. Copper glance, 163. „ nickel, 189. ,, pyrites, 164, 167. Cordierite, 73, 78, 79. Corundum, 70, 78, 79. Covellite, 163. Crocidolite, 79. Crocoisite, 154. Cryolite, 50, 54. Cuprite, 164, 168. Determination of minerals, 39. Diabase, 9. Diallage, 60, 64. Diallogite, 191. Diamond, 68, 78, 79, 199. Dichroite, 73. Diopside, 60, 64. Dioptase, 164. Diorite, 9. Dolerite, 9 Dolomite, 50, .52. Dynamics of lodes, 114. Elasticity of minerals, 26. Elaterite, 198, 203. Electrum, 146. Embolite, 149. Emerald, 72, 78, 79. Emery, 71. Enargite, 163. Enstatite, 64, 65. Epidote, 77, 79. Erubescite, 163. Erythrine, 189. Fahlbands, 107. False topaz, 75. Faulting of lodes, 114 ; relative age of, 115. Flame— Oxidising and fusing, 34; re- ducing, 34 ; colour of, 35 ; red, 36 ; yellow, 36 ; green, 36 ; blue, 36 ; violet, 36. Flats, 110. Flexibility of minerals, 26. Floors, 109. Fluorspar, 50, 54. Fuller's earth, 68. Fusibility of minerals, 35 ; scale of, 35. Gabbro, 9. Galena, 154, 155 ; in stratified deposits, 85. Galmei, 180. Garnet, 73, 78, 79. Garnierite, 189. Geological— Age of coal, 2 ; age of gold, 3 ; notes in the field, 11. Gersdorffite, 189. Glass tubes— Tests with, 39 Glaucodote, 189. Goethite, 182, 184. Gold, 146 ; in stratified deposits, 86 distribution, 136 ; mode of detection 136 ; association with sulphides, 136 , auriferous belts, 137 ; in eruptive rooks, 137; in bedded veins, 138 in reefs traversing sedimentary beds, 139 ; in reefs associated with diorite 139 ; in shoots, 139 ; in saddle reefs, 141 i in flat veins, 141 ; in itaoolumite 142; in pyrites, 142 ; in timazite, 142 in Transylvania, 142; in Nevada, 142 ; in breccia lodes, 142 ; at Mt Morgan, 143 ; in deep leads, 144. INDEX. 237 Granite, 9. Graphite, 198. Grey copper, 163, 167. Gypsum, 50, 52, 85. H Hardness of minerals, 24 ; scale of, 24. Harmotome, 66. Hauerite, 191. Hausmaonite, 191. Hauyne, 79. Hasmatite, 182, 184. Heaves — Law regulating direction of, 117 ; percentages, 118. Hedenbergite, 60, 64. Heliotrope, 75, 79. Hessite, 147. Heulandite, 66. Hornblende, 60. ,, andesite, 9. Horn silver, 149, 151. Hydromagnesite, 50, 53. Hypersthene, 60, 65. Iceland spar, 49. Impregnations, 106. lodargyrite, 149, 151. Iridosmine, 146. Iron, 179 ; sulphate of, 184 ; ores, mode of occurrence, 85. Iron pyrites, 185, 187. Irregular deposits, 105. ,, masses, 109. Jade, 63. Jet, 201. K Kaolin, 67. Kerargyrite, 149, 151. Kyanite, 77, 79. Labradobitk, 60, 62, 76, 79. Lapis lazuli, 77, 79. Laumontite, 66. Lead-antiraony ores, 156. ,, lodes, 156. ,, ores, 154. Leadville, 102. Lebererz, 161. Lenticular aggregations, 108. Lepidolite, 57, 59. Libethenite, 164. Lignite, 198. Limestone, 51. Limonite, 182, 184. Linnaeite, 189. Lithographic stone, 51. Lustre of minerals, 18. M Magnesite, 50, 53. Magnetic pyrites, 186. Magnetite, 183, 184. Malachite, 164, 168. Malleability of minerals, 26. Manganese, 179, 190. Manganite, 191. Marble, 51. Marcasite, 185, 187. Meerschaum, 56, 57. Melaconite, 164. Mercury, 158, 159, 162. Meteoric iron, 184. Mica, 57, 58, 59. Microcosmic salt — Colours of beads, 37. MUlerite, 189. Mimetite, 1,54. Mineral deposits — Their mode of occurrence, 3 ; conditions to be studied, 5. Minerals with metallic lustre — Easily fusible or volatile, 41; infusible or fusible with more difiBculty than orthoolase, not volatile, 43. Minerals without metallic lustre— Sol- uble in water, 43 ; insoluble in water, 44. Mineral veins and lodes, 89 ; fracturing of rocks, 89 ; distribution of ore in, 93; how filled, 97. Minium, 154. Mispickel, 185, 187. Molybdenite, 177. 178. Molybden-oohre (Molybdite),, 177. Molybdenum, 171, 177, 178. Mountain leather, 63. Mount Morgan, 104. Muscovite, 57, 59. ^38 INDEX. N Nagtagitb, 147. NatroHte, 66. Nephrite, 63. Nickel, 179, 187. Nickeline, 189. Nioopyrite, 189. Nitrate of cobalt — Tests with, 38. Noble metals, 136. Noumeite, 189. Obsidian, 9. Ootahedrite, 177. Oligoclase, 60, 62, 76, 79. Olivine, 76, 78, 79. Onyx, 75, 79. Opal, 55, 76, 78, 79. Oriental amethyst, 70, 78. ,, emerald, 70, 78. ,, topaz, 70, 78. Orpiment, 193, 194. Orthoolase, 60, 61, 76, 78, 79. Ozokerite, 198, 203. Palladium, 146. Peacock ore, 165. Pennine, 58. Perlite 9. Petroleum, 198, 202. Petzite, 147. Phenakite, 73, 78, 79. Pitch blende, 192. Pitchstone, 9. Plasma, 75, 79. Platiniridium, 146. Platinum, 145, 146. Plumbago, 199. Polybasite, 149. Prehnite, 66. Proustite, 149, 150. Psilomelane, 191. Pumice, 9. Pyrargyrite, 149, 150. Pyrolusite, 191. Pyromorphite, 154, 168. Pyrrhotine, 187. Q Quartz, 55, 74, 78, 79. „ diorite, 9. „ porphyry,. 9. Quicksilver, 158, 162. R Realgar, 193, 194. Red lead, 154. Redruthite, 163. Reticulated veins, 108. Rhodonite, 191. Rhyolite, 9. Ripidolite, .58. Rook crystal, 74. Rooks, 7 ; igneous or eruptive, 8; hydro- thermal, 8 ; trappean, 8 ; table of eruptive rooks, 9; volcanic, 10; sedi- mentary, 10 ; movements of , 10 ; strike and dip, 12. Rock salt — Occurrence of, 85. Ruby, 70, 78, 79. Rutile, 177. Sapphige, 70, 78, 79. Sardonyx, 75, 79. Schmidt's law, 119 ; exceptions to, 122. ScheeUte, 177, 178. Segregated veins, 111. Serpentine, 57, 58. Shoots, 158. Siderite, 183, 184. Silver, 149. Silver glance, 149. Silver ores — Valuing, 152. Smaltine, 189. Smell of minerals, 27. Smoky quartz, 75. Soapstone, 56. Soluble salts, 48. Specific gravity of minerals, 27 ; high density liquids, 29 ; diffusion column, 29. Spinel, 72, 78, 79. Stahlerz, 161. Staunine, 165, 177. Steatite, 56, 57. Stephanite, 149, 150. Sternbergite, 149. Stibnite, 195. Stilbite, 66. Stockworks, 108. Stratified deposits, 79 ; coal, 80 ; iron ores, 85 ; rock salt and gypsum, 85 ; metallic impregnations, 85 ; gold in Transvaal, 86; gold in New South Wales, 87 ; working expenses, 88. Streak of minerals, 24 ; table of, 25. Stromeyerine, 149, 150. Stroutianite, 50, 53. , INDEX. 239 Structure of minerals, 14 ; granular, 15 ; sacoharoid, 15 ; lamellar, 15 ; capillary, 15 ; fibrous, 15 ; radiate, 16 ; baciUary, 16 ; dendritic, 16 ; concretionary, 16; mammillary, 17; botryoidal, 17; reniform, 17; vit- reous, 17 : amorphoas, 17. Sulphur, 193, 194. Sulphuretted hydrogen— Action of, 99. Syenite, 9. Sylvanite, 147. T. Tachyltte, 9. Talc, 56, 57. Taste ot minerals, 27. Tellurium, 147. Tennautite, 163. Tetrahedrite, 163. Thames goldfield, 101. Thomsonite, 66. Tin, 171, 177. Tinstone, 171. Titanic iron, 183, 184. Titanium, 171, 176, 177. Topaz, 72, 78, 79. Torbanite, 198. Tourmaline, 74, 78, 79. Trachyte, 9. Transvaal deposits, 86. TremoUte, 60, 63. Tridymite, 55. Tungsten, 171, 177, 178. Turquoise, 77, 78, 79. u. ULTR.4.MAEINE, 77. Uranium, 179, 192. Valentinite, 195. Vesuvianite, 77, 79. Vivianite, 184. w. Wad, 191. Willemite, 180. Witherite, 50, 53. WoKram, 177, 178. WoUastonite, 60, 65. Working expenses, 88 Yellow jacket, 100. z. Zeolites, 65. Ziegelerz, 161. Zinc, 179. Zinoblende, 180. Zinc bloom, 180. Ziucite, 180. Zircon, 7.3, 78, 79. BELL AND BAIN, LIMITED, MINIKKS, UITCHELL SXKBKl', OLASGOW. A SELECTION FROM CHARLES GRIFFIN & CO.'S CATALOGUE OP SCIENTIFIC AND TECHNICAL WORKS MESSRS. CHARLES GRIFFIN ., F.E.S. 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The "New Land" Series for Colonists and Prospectors (See next page). LONDON: CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND. 54 CHARLES OBIFPIN ie GO.'S PUBLICATIONS. The "New Land" Series Practical Hand-Books Fop the Use of Prospectors, Explorers, Settlers, Colonists, and all Interested in the opening' ' up and Development of New Lands. .■. . EDITED BY GEENVILLE A. J. COLE, M.E.I. A., F.G.S., Professor o( Geology in the Royal College of Science for Ireland. In large Crown 8vo, with Illustrations. NOW READY. Vol. L-^PROSPECTING FOR MINERALS. By S. Herbert' Cox, Assoc.R.S.M., M.Inst.M.M., F.G.S. SHORTLY WILL BE ISSUED. Vol. .^2.— FOOD SUPPLY. By Robert Bruce, Agricultural' ' Superintendent to the Royal Dublin Society. • Vol 3.— building CONSTRUCTION m WOOD, STONE, AND CONCRETE. By Jas. Lton, M.'A., Professor of Engineering in the Royal College of Science for Ireland j sometime Superintendent of the Engineering Department in the University of Cambridge; and J. Taylor, A.R.C.S.L \* Other Volumes will follow, dealing with subjects ; of Primary Importance in the Examination and Utilisation of Lands which have not as yet been fully developed. LONDON : CHARLES GRIFFIN & CO., LIMITED,. EXETER STREET, STRAND; PROSPEOTING AND MINING. 55 GRIFFIN'S "NEW L AND" SERIES. Now Readg. With Illustrations. Price 5s. PROSPECTING FOR MINERALS: A PRACTICAL HANDBOOK FoF ProspeetoFs, Explorers, Settlers, and all interested in the Opening up and Development of New Lands, BY S. HERBERT COX, Assoc.R.S.M., M.Inst.M.M., F.G.S, Ac. General Contents.— Introduction and Hints on Geology— The Determina- tion of Minerals : Use of the Blow-pipe, &c. — Eock-forming Minerals and Nou- Metallio Minerals of Commercial Value : Eock Salt, Borax, Marbles, Litho- graphic Stone, Quartz and Opal, &c., &c.— Precious Stones and Gema — Stratified Deposits: Coal and Ores- Mineral Veins and Lodes — Irregular Deposits — Dynamics of Lodes: Faults, &c.— Alluvial Deposits— Noble Metals : Gold, Platinum,' Silver, &c. — Lead — Mercury — Copper — Tin — Zinc— Iron — Nickel, &c.— Sulphur, Antimony, Arsenic, :&c. — Combustible Minerals— Petroleum- General Hints on Prospecting — Glossary — Index. Second Edition. With Illitsirations. Cloth, Sa. 6d. GETTING GOLD: A GOLD-MINING HANDBOOK FOR PRACTICAL MEN. By J. 0. F. JOHNSON, F.G.S., A.I.M.E., Life Member Australasian Mine-Managers' Association, General Contents.— Introductory : Getting Gold— Gold Prospecting (Alluvial and General) — Lode or Eeef Prospecting — The Genesiology of Gold — Auriferous Lodes — Auriferous Drifts — Gold Extraction — Secondary Processes and Lixiviation — Calcination or " Boasting " of Ores — Motor Power and its Transmission— Company Formation and Operations — Rules of Thumb : Mining Appliances and Methods — Selected Data for Mining Men — Australasian Mining Kegulations. " Should prove of the GKEATEST VALUE. Almost every page bristles with sugges- tions." — Finajuiial ^ews. "Practical from beginning to end . . . deals thoroughly with the Prospecting, Sinking, Crushing, and Extraction of gold."— BriJ. Australasian. ■ "Directors and those interested in the formation of companies would do well to pur- chase Mr. Johnson's book." — Miniiuj Journal. " The reader, be he miner or novice, will gain from Mr. Johnson's book a GRIP of the gold industry."- j^/rican Critic. -■"Should be specially commended to all who have any idea of proceeding to the gold fields." — Financial Truth. /" The most striking elements are the numerous ' TIPS ' and USEFUL WRINKLES given." —Stamdard. LONDON: CHARLES GRIFFIN & CO., LIMITED, EXETER STREET. STRAND. 56 CHARLES GRIFFIN '>c. ' General Contents. — Historical Sketch — Blasting Materials — Blasting Pow- dep^Various Powder-mixtures — Gun-cotton — Nitro-glycerine and Dynamite — Other Nitro-compounds — Sprengel's Liquid (acid) Explosives —Other Means of Blasting — Qiialities, Dangers, and Handling of Explosives — Choice of Blasting Materials — ^Apparatus for Measuring Force — Blasting in Fiery Mines — Means cf I^iting Charges — Preparation of Blasts — Bore-holes — Machine-drilling — Chamber MineS; — Charging of Bore-holes — Determination of the Charge — Blasting in Bore- hoies-^Firing — Straw and Fuze Firing — Electrical Firing; — Substitutes for Electrical Firing — Results of Working — Various Blasting Operations^Quarrying — Blasting Masonry, Iron and Wooden Structures — Blasting in earth, under water, of ice, &c. " This admirable work." — Colliery Guardian, "Should prove z vade-mec-uin \.o Mining Engineers and all engaged in practical work. — Iron and Coal Trades Review. LONDON : CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND. CHARLES GRIFFIN " This volume amply realises the expectations formed as to the result of the labours of so eminent an authority. It is remarkable for its originality of con- ception and for the large amount of information which it contains. . . . We recommend every one who desires information not only to consult, but to STUDY this work." — Engineering. " Will at once take front rank as a text-book." — Science and Art. " Prof. Roberts-Austen's book marks an epoch in the history of the teaching of metallurgy in this country." — Industries. LONDON: CHARLES GRIFFIN & CO., LIMITED. EXETER STREET,: STRAND, 64 CHARLES GRIFFIN ^ GO.'S PUBLICATIONS. GEIFPIN'S METALLUBGICAL SERIES. Third Edition. Revised and Enlarged. Handsome Cloth. THE METALLURfiY OF GOLD. T. KIRKE ROSE, D.Sc.Lond., Assoc.R.S.M., Assistant Assayer of the Royal Mint. Revised and partly Re-written. Including the most recent Improve- ments in the Cyanide Process. With Frontispiece and numerous Illustrations. GENERAL CONTENTS. The Fiopeities of Gold and its Alloys. Chemistry of the Compounds of Gold. Mode of Occurrence and Distribution of Gold. Placer Mining. Shallow Deposits. Deep Placer Mining. Quartz Crushing in the Stamp Battery. Amalgamation in the Stamp Battery. Other Forms of Crashing and Amal- gamating Machinery. Concentration in Stamp Mills. Stamp Battery Practice in particular Localities. Chlorination : The Preparation of Ore for Treatment. Chlorination : The Vat Process. Chlorination: The Barrel Process. Chlorination; Practice in particular Mills. The Cyanide Process. Chemistry of the Cyanide Process. Pyritio Smelting. The Refining and Parting of Gold Bullion. The Assay of Gold Ores. The Assay of Gold Bullion. Economic Considerations. Bibliography. " A COMPHEHLNSIVE PEACTlcAL TREATISE on this important subject."— ?7je Times. •*The MOST COMPLETE deicription of the ghlobikation peockss which has yet been pnb- llBhed."— J/miny Journal. " Dr. Rose gained his experience in the Western States of America, but be has secured details of gold-working from all parts of the world, and these should be of gekat seeticb to practical men. . . . The four chapters on Chlorination^ written from the point of "new alike of the practical man and the chemist, teeh with considebationb hitbebto unbxcoq- NisxD, and constitute an addition to the literature of Metallurgy, which will prove to be of classical value." — Nature. ''Adapted for all who are interested in the Gold Mining Industry, being free from tech- nicalities as far as possible, but is more particularly of value to those engaged in the industry — viz., mill-managers, reduction-oificers, &c." — Cape Times. LONDON: CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND. METALLUROICAL WORKS. GRIFFIN'S METALLURGICAL SERIES. THE METALLURGY OF IRON. THOMAS TURNER, Assoc.R.S.M., F.I.O., Director of Technical Instruction to the Staffordshire County Council. In Large 8vo, Handsome Cloth, With Numerous Illustrations (many from Photographs). Price 16s. GENEEAL CONTENTS. Early History of Iron. . Modern History of Iron. The Age of Steel. Chief Iron Ores. Preparation of Iron Ores. The Blast Furnace. The Air used in the Blast Furnace. Beactions of the Blast Furnace. The Fuel used in the Blast Furnace. Slags and Fluxes of Iron Smelting. Properties of Cast Iron. Foundry Practice. Wrought Iron. Indirect Production of Wrought Iron. The Puddling Process. Further Treatment of Wrought Iron. Corrosion of Iron and Steel. " A MOST valuable summary of useful knowledge relating to every method and stage in the manufacture of cast and wrought iron down to the present moment . . . particularly rich in chemical details. . . . An exhaustive and really needed compilation by a most capable and thoroughly up-to-date metallurgical authority." — Bulletin of the American Iron and Steel Association. " This is a drlightful book, giving, as it docs, reliable information on a subject becoming every day more elaborate. . . . The account of the chief iron ores is, like the rest of this work, RICH in detail. . . . Foundry Practice has been made the subject of considerable investigation by the author, and forms an interesting and able chapter." — Colliery Guardian. " Mr. Turner's work comes at an opportune moment and in answer to a real demand. ... a thoroughly useful book, which brings the subject up to DATE. The author has produced an eminently readable book. . . . What- ever he describes, he describes well. . . . There is much in the work that will be of GREAT VALUE to thoBe engaged in the iron industry." — Mining Journal. in preparation. Companion- Volume on THE METALLURGY OF STEEL. By F. "W. HARBORD, Assoc.RS.M., F.I.C. LONDON; CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND. o 66 CHARLES GRIFFIN - M8NTAL Work trebly interesting because intelligible." — Saturday Review. "There is no question that, given the perfect grounding of the Student in his Science, the remaiRder comes afterwards to him in a manner much more simple and easily acquired. The work is an example of the advantages of the Systematic Treatment of a Science otct the fragmentary style so generally followed. By a long way the best of the small Manuals for Students." — Analyst. LABORATORY HANDBOOKS BY A. HUMBOLDT SEXTON, Profeasor of Metallurgy in the G-laegow and West of Scotland Technical College. Sexton's (Prof.) Outlines of Quantitative Analysis. FOR THE USE OF STUDENTS. With Illustrations. Fourth Edition. Crown 8vo, Cloth, 3s. " A COMPACT LABOKATOEY GUIDE for beginners was wanted, and the want ha» been well supplied. ... A good and useful book." — Lancet. Sexton's (Prof.) Outlines of Qualitative Analysis. FOR THE USE OF STUDENTS. With Illustrations. Third Edition. Crown 8vo, Cloth, 3s. 6d. " The work of a thoroughly practical chemist."— iWiisft Medical Journal. 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" Cannot but prove an acquisition to those studying Navigation."— Jfarine Engineer. Practical Mechanics : Applied to the requirements of the Sailor. By Thos. Mackenzie, Master Mariner, F.E.A.S. 3s. 6d. ■ ' Well worth the money exceedingly helpfu i . "—Shipping World. Ocean Meteorology : For Officers of the Merchant Navy. By William Allingham, First Class Honours, Navigation, Science and Art Department. Trigonometry: Eor the Young Sailor, &c. By Rich. C. Buck, of the Thames Nautical Training College, H.M.S. " Worcester." Price 3s. 6d. Practical Algebra. By Rich. C. Buck. [Shortly. A Medical and Surgical Help for Shipmasters. Including First Aid at Sea. By Wm. Johnson Smith, F.R.C.S., Principal Medical Officer, Seaman's Hospital, Greenwich. 6s. "Sound, judicious, keally helpful."— 7 7ic Lancet. The Legal Duties of Shipmasters and Officers. By Benedict Wm. GiNSBURG, M.A., LL.D., Barrister-at-Law. LONDON: CHARLES GRIFFIN & CO., LIMITED, EXETER STREET. STRAND. PRACTICAL MEDICAL HANDBOOKS. GBIPFIN'S "FIRST AID" PUBLICATIONS. ©n Xanb. Third Edition, Rbviskd. Large Crown 8vo. Handsome Cloth, is. A MANUAL OF AMBULANCE. By J. SOOTT RIDDELL, CM., M.B., M.A., ist. -Surgeon, Aberdeen Koyal Infirmary ; Lecturer and Examiner to the , .bulance Association ; Examiner to the St. Andrew's Ambulance Associat. Glasgow, and the St. John Ambulance Association, London. With Numerous Illustrations and Full Page Plates. General Contents. — Outlines of Human Anatomy and Physiology — The Triangular Bandage and its Uses — The EoUer Bandage and its Uses — Fractures — Dislocations and Sprains — Hemorrhage — Wounds — Insensi- bility and Fits — Asphyxia and Drowning- Suffocation— Poisoning — Bums, Frost-bite, and Sunstroke — Kemoval of Foreign Bodies from (a) The Eye ; (6) The Ear; (c)TheKose; {d) The Throat; (e) The Tissues— Ambulance Transport and Stretcher Drill — The After-treatment of Ambulance Patients — Organisation and Management of Ambulance Classes —Appendix : Ex- amination Papers on First Aid. "A CAPITAL BOOK. . . . Tho directions are bhort and clear, and testify to the hand of an able surgeon." — Edin. Med. Journal. " This little volume seems to ua about as good as it couldpossibly be. . . Contains practically every piece of information necessary to render First aid. Should flml Its place in eveet household libhart."— /)oiVy Chronicle. **So ADMIRABLE is tliis work, that it ia difficult to imagine how it could be better," — Colliery Guardian. Ht Sea. Crown 8vo, Extra. Handsome Oloth. 6s A MEDICAL AND SURGICAL HELP FOR SHIPMASTERS AND OFFICERS IN THE MERCHANT NAVY. INCLUDING FIRST AID TO THE INJURED. By WM. JOHNSON SMITH, F.R.C.S., Principal Medical OflBcer, Seamen's Hospital, Greenwich. With Coloured Plates and Numerous Illustrations, *,* The attention of all interested in our Merchant Navy is requeRted to this exceedingly useful and valuable work. It is needless to say that it is the outcome of many years, PKACTiOAL EXPEBiENCB amongst Seamen. '• SOOND, JUDICIOUS, REALLY UKi,vtui.."~The La7n:et. "It would be difficult to find a Medical and Surgical Guide more clear and comprehensive than Mr. Johnson Smith, whose experieoce at the Greenwich Hospital eminently qualifies him for the task. ... A most attractive work. . . . We have read it from cover lo covrr. . . , it gives clearly written advice to Masters and Officers in all medical and surgical matters likely to come before them when remote from the land and without a doctor. . . . We recommend the work to evbrt Shipmaster and OSiQer."— Liverpool Journal of Commerce. LONDON: CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND, A BOOK NO COLONIST isHuuLij Be. wiiriuui. Thirty-Second Kdition. Royal 8vo, Handsome Cloth, 10s. 6d. A DIOTIONAEY OF Doiestic Medicine and Honsehold Surgery, SPENCER THOMSON, M.D, Edin., L.R.C.S., REVISED, AND IN PARI RE-WRITTEN, BY THE AUTHOR, BT JOHN CHARLES STEELE, M D., Late or Shy's Hospital, AND BT GEO. RE ID, M.D., D.RH., Med. Oppioek, Staffs. Codnty Codnoil. With Appendix on the Management of the Sick-room, and many K'ints for the Diet and Comfort of Invalids. In its New Form, Dn. Spencer Thomson's "Dictionaky op Domestic Medicine" fully sustains its reputation as the " Kepresentative Book of the Medical Knowledge and Practice of the i)ay " applied to Domestic Requirements. The most recent Improvemknts in the Treatment oe the Sick — in Appliancks for the Relief of Pain; — and in all matters connected with Sanitation, Hygiene, and the Maintenance of the General Health — will be found in the New Issue in clear and full detail; the experience of the Editors in the Spheres of Private Practice, of Hospital Treatment, and of Sanitary Supervision respectively, combining to render the Dictionary perhaps the most thoroughly practical work of the kind in the English Language. Many new Engravings have been introduced — improved Diagrams of different parts of the Human Body, and Illustrations of the newest Medical, Surgical, and Sanitary Apparatus. *jf* All Directions given in such a form as to he readily and safely followed. FROM THE AUTHOR'S PREFATORY ADDRESS. "Without entering upon that difficult ground which correct professional knowledge and educated, judgment can alone permit to be safely trodden, there is a wide and extensive field for exertion, and for usefulness, open to the unprofessional, in the kindly offices of a true DOSIESTIC MEDICINE, the timel^ help and solace of a simple HOUSEHOLD SUHGrEHY, or, better still, in the watchful care more gener-^ ally known as ' SANITARY PRECAUTION,' which tends rather to preserve health than to cure disease. ' The touch of a gentle hand ' will not be less gentle because guided by knowledge, nor will the safe domestic remedies be less anxiously or carefully administered. Life may be saved, suffering may alwaya be alleviated. Even to the resident in the midst of civilisation, the ' KNOWLEDGE IS POWER,' to do' goodi to the settler and emigrant it is INVALUABLE." " Dr. Thomson has fully succeeded in conveying to the public a vast amount of useful professional knowledge." — Dublin Journal of Medical Scie7ice. " The amount of useful knowledge conveyed in this Work is surprising." — Medical Tirnes and Gazette, " Worth its weight in gold to families and the clergy."— Oxford Herald. LONDON: CHARLES GRIFFIN & punrn m-nrr-r nTn»iir»