/\ • '^ *.,■•• .(j,^ 5°^ .S^n 5°^ ,^0*v ^ » o « o - .0 -^ 'fit <^ * 6 « - .V .-i^^ ^'\!^a^*. ^^^ .^"^ ^'* "^o^ ■?^ V^ ,^L'^ '^^ ..^ »'^l^'". ^^ c'T /^* ^..♦^ o^ -"^o «5'^"-. • ■8.* -^ • .^ ... J.^ 0* \.''.-- v-^ %'^^-0** V--f.^-'A* %'^^-.0«* \.''f.^.'A* *^^-?? V M O x^-y V^^V x^^V V»V V^^V" v^^-, '.-^flj."- y^jR^-X .'•".-^k."- ./%^^'\ c^.j^i.^ >\c,:^/^ Bureau of Mines Information Clrcular/1 988 Tin Occurrences Near Rocky Mountain (Lime Peai(), East- Central Alasica By J. Dean Warner, D. C. Dahlin, and L. L. Brown UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 9180 Tin Occurrences Near Rocky Mountain (Lime Peak), East- Central Alaska By J. Dean Warner, D. C. Dahlin, and L. L. Brown UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Model, Secretary BUREAU OF MINES David S. Brown, Acting Director (\ h Library of Congress Cataloging-in-Publication Data Warner, J. Dean. Tin occurrences near Rocky Mountain (Lime Peak), east-central Alaska. (Information circular/Bureau of mines ; 9180) Bibliography: p. 13-14 Supt. of Docs, no.: I 28.27 1. Tin ores -Alaska -Lime Peak. I. Dahlin, D.C. (David Clifford), 1951- II. Brown, L.L. (Lawrence L.), 1928- III. Title. IV. Series: Information circular (United States. Bureau of Mines) ; 9180 TN295.U4 [QE390.2.T48] 622 s [553.4'53'097986] 87-600146 CONTENTS Page Abstract 1 Surficial geology of the North Fork Preacher Introduction 2 Creek 9 Acknowledgments 2 Sampling and analyses 11 Location and land status 2 Placer tin resources 12 Physiography 3 Summary and conclusions 13 Previous work 3 References 13 Regional geology 3 Appendix A. -Description of igneous rocks mapped Lode investigations 3 near Lime Peak 15 Geology of the Lime Peak pluton 3 Appendix B.- Description of greisen occurrences Lode (greisen) occurrences 4 sampled near Lime Peak 17 Geochemical sampling and analyses 7 Appendix C. - Results of analyses of rock samples col- Bulk sampling and analyses 8 lected from the Lime Peak area 19 Beneficiation 8 Appendix D. - Results of analyses and calculated tin Lode tin resources 9 grades of placer samples collected along North Placer investigations 9 Preacher Creek 24 ILLUSTRATIONS 1. Location map 2 2. Tectonostratigraphic map of the Yukon-Tanana physiographic province with inset map showing the Lime Peak pluton and the North Fork of Preacher Creek 4 3. Geologic and sample location map of Lime Peak area 5 4. Geologic and sample location map of Bedrock Creek area 6 5. View looking southeast showing main branch and east and west forks of Bedrock Creek 7 6. Paragenesis of alteration and mineralization at Lime Peak 7 7. SEM micrograph and X-ray element map showing cassiterite in a chlorite matrix 8 8. Photograph looking northeast (downstream) along the headwaters of the North Fork of Preacher Creek from a position near the center of section 10 10 9. Surficial geologic and sample location map for the North Fork of Preacher Creek 10 10. Flow diagram depicting laboratory sample reduction and examination method 11 11. Variation of tin grade along the North Fork of Preacher Creek 12 B-1. Results of fluid inclusion analyses 17 B-2. SEM micrograph of crystals of columbium-bearing rutile in a chlorite and quartz matrix 18 TABLES 1. Head analyses of bulk samples of greisen collected at Lime Peak 8 2. Metallurgical balance for tabling composite bulk sample 9 3. Metallurgical balance for tabling and flotation of sample 99 9 4. Swell factors calculated from gravel samples 11 5. Placer sample concentrate mineralogy and relative amounts of minerals 12 6. Analysis and relative tin concentrations of panned concentrate samples 13 A-1. Composition of Lime Peak pluton samples 15 C-1. Results of quantitative geochemical analyses of rock samples 19 C-2. Results of semiquantitative emission spectrographic analyses of rock samples 22 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT °C degree Celsius mg milligram cm centimeter mg/pan milligram per pan cm^ cubic centimeter mi^ square mile ft foot MMlb million pounds ft^ square foot MMst million short tons ft^ cubic foot m.y. million years g gram mm millimeter gal gallon ^m micrometer in inch pet percent lb pound ppm part per million Ib/st pound per short ton wt pet weight percent Ib/yd^ pound per cubic yard yd3 cubic yard TIN OCCURRENCES NEAR ROCKY MOUNTAIN (LIME PEAK), EAST-CENTRAL ALASKA By J. Dean Warner/ D. C. Dahlin,^ and L. L Brown^ ABSTRACT In 1984 and 1985, as part of its critical and strategic minerals studies, the Bureau of Mines investigated lode and placer tin occurrences near Rocky Mountain (Lime Peak), in east-central Alaska. The lode occurrences consist of mineralogically complex, generally fault-controlled veins, and contain an average of approximately 0.05 pet Sn, as cassiterite. Beneficiation testing of two bulk samples of the vein material produced con- centrates containing 65 and 59 pet of the total tin values at grades of 0.35 and 13.9 pet, respectively. Although as much as 30 million short tons (MMst) of mineralized rock con- taining up to 20 MMlb Sn may be present, the grade of these occurrences is too low to be considered economic at this time. Trace amounts of cassiterite were also identified in surface samples of glacial out- wash gravels collected along North Fork Preacher Creek, which partially drains the area of tin lode deposits near Lime Peak. Low tin grades in the samples do not account for the former erosion of a large volume of lode tin mineralization from near Lime Peak; higher tin grades may be present in gravels closer to bedrock. ^ Geologist, Alaska Field Operations Center, Bureau of Mines, Fairbanks, AK. 2 Metallurgist, Bureau of Mines, Albany Research Center, Albany, OR. ' Geologist, Albany Research Center. .•WTW^HBP INTRODUCTION The Bureau of Mines has intermittently investigated lode occurrences of tin and other metals in the Lime Peak (Rocky Mountain*) area since 1977. These investigations have been conducted as part of the Bureau's Alaskan critical and strategic minerals study, the goal of which is to identify reserves or resources of certain critical and strategic minerals that could be developed in times of prolonged na- tional shortage. The investigations have also been partially motivated by the Federal Bureau of Land Management's need for mineral data in the Steese and White Mountains National Conservation and Recreation areas. Results of Bureau reconnaissance investigations in the Lime Peak area prior to 1984 are presented in Bureau ol Mines Open File Report 31-85 (1).^ That report identifies an area of tin lode mineralization on the southeastern flank of the Lime Peak summit warranting further study and recom- mends that North Fork Preacher Creek be investigated for placer tin. This report presents results of detailed investigations of the lode and placer tin occurrences identified in reference 1. Numerous occurrences of sub-ore-grade lode tin mineraliza- tion as well as low-grade concentrations of placer tin were located. Although the lode occurrences contain relatively large tonnages of resources, the tin grades are too low to be considered economic at this time. ACKNOWLEDGMENTS This report has benefited from geologic and geochemical data donated to the Bureau by Mapco Minerals. Florence Weber, geologist, U.S. Geological Survey, assisted field investigations in 1977 and 1985 and provided the inter- pretation of glacial geology present in this report. David Menzie, geologist, U.S. Geological Survey, provided logistical assistance to a portion of the fieldwork in 1984. LOCATION AND LAND STATUS Lime Peak is located in the Circle (C-6) quadrangle, Alaska, approximately 58 miles northeast of Fairbanks, in the White Mountains (fig. 1). The study area straddles the boundary between the White Mountains National Recrea- tion Area to the west and the Steese National Conservation ■* Although Rocky Mountain is the newly assigned name, the name Lime Peak is retained in this report because it is more widely known. Area to the east. Both areas are administered by the Federal Bureau of Land Management, as authorized in 1980 by the Alaska National Interest Lands Conservation Act (Public Law 96-487), and are currently (1987) closed to mineral entry. ■' Italic numbers in parentheses refer to items in the list of references preceding the appendixes at the end of this report. 148" _J 146" I Sleeit Notional Coniervotion Arao (northern portion) /^ -' Figure 1.— Location map. PHYSIOGRAPHY The White Mountains comprise the northwestern por- tion of the Yukon-Tanana physiographic division (2). Over much of its area, this province is characterized by a deeply eroded terrain of moderate relief with tundra- or mixed spruce- and birch-covered, gently rounded slopes and relatively flat ridgelines. Near Lime Peak, however, and elsewhere in areas with elevations above approximately 2,500 ft, steep rubble-covered unvegetated hillsides are characteristic. In areas of higher elevation that are underlain by granitic rocks, rock spires (tors) are common. Most of the Yukon-Tanana region has escaped the effects of continental glaciation; however, broad U-shaped valleys in many of the more elevated areas of the White Mountains fit- test to former valley glaciation. PREVIOUS WORK Intrusive rock was initially mapped in the Lime Peak area by Prindle (3), in 1913. Most recently, in 1983, the area was geologically mapped by Foster {4.). In 1981, Wilson ob- tained a potassium-argon age of 56.7 ± 0.95 m.y. on biotite from the Lime Peak pluton (5). The Lime Peak pluton was first publicly recognized as tin bearing by Barker, in 1978, who found anomalously high concentrations of tin, columbium, lead, tungsten, zinc, uranium, and yttrium in heavy mineral concentrates panned from streams draining the pluton (6). Subsequent investiga- tions summarized by Burton in 1984, identified two major geochemically anomalous drainage areas near the Lime Peak pluton and numerous occurrences of tin-bearing veins (1). Burton recommended a more detailed investigation of mineralized zones in the Lime Peak summit area and poten- tial placer tin occurrences in the North Fork Preacher Creek area. In 1983, Menzie identified the Lime Peak area as permissive to the occurrence of tin deposits (7). Several mineral exploration companies have in- vestigated the Lime Peak area for deposits of tin, uranium, tungsten, and other metals. Most notably, following an air- borne radiometric survey in 1978, Mapco Minerals Co. located a large claim block just south of the Lime Peak sum- mit. Mapco drilled one shallow diamond drill hole, but ap- parently did not encounter significant mineralization. REGIONAL GEOLOGY The Lime Peak pluton is one of five early Tertiary- and/or Late Cretaceous-age plutons exposed in the White Mountains (4). The composition of these intrusions is similar to that of known tin-bearing intrusions elsewhere in the world; tin mineralization similar to that associated with the Lime Peak pluton has been identified in one other pluton in the White Mountain area. The intrusions are composite biotite granites; however, minor to major amounts of muscovite, hornblende, and tourmaline are locally present and rock compositions include quartz monzonite {1, 4, 8). These plutons intrude a diverse assemblage of variably metamorphosed and deformed upper Precambrian- to mid- dle Paleozoic-age sedimentary and mafic volcanic rocks that have been partially imbricated along northeast-trending thrust faults (fig. 2). Northwest of Lime Peak, the rocks consist of sequences of early Paleozonic shales and cherts and middle Paleozoic mafic volcanic and clastic and calcareous sedimentary rocks that comprise the Livengood, White Mountains, and Kandik River tectonostratigraphic terranes of Churkin {9). Southeast of Lime Peak, on the other hand, the rocks consists of variably metamorphosed lower Paleozoic-age quartzites and shales and comprise the Beaver and Yukon Crystalline terranes. The boundary be- tween the latter two terranes has been variably interpreted as gradational or thrust faulted {10). LODE INVESTIGATIONS In 1984, an 8-mi2 area located near the southeastern flank of the Lime Peak summit, and outlined on figure 2, was mapped and sampled in detail (figs. 3-4). The area con- tains numerous occurrences on tin lode mineralization and is centered around an east-flowing stream that forks near its headwaters. This stream and its forks are referred to as Bedrock Creek and the east fork and west fork of Bedrock Creek, respectively, in this report (fig. 5). GEOLOGY OF THE LIME PEAK PLUTON Because intrusions associated with tin mineralization worldwide are known to display specific geologic attributes (for instance, see Taylor {11) or Hudson {12)), considerable effort was made to document the geology of the Lime Peak pluton. The following paragraphs briefly summarize the results of geologic mapping near Lime Peak (fig. 3); more detailed descriptions of the pluton and its various phases are presented in appendix A. In general, the geology of the Lime Peak pluton is comparable to that of many tin- mineralized plutons worldwide. The Lime Peak pluton is a composite intrusion that out- crops over approzimately 30 mi^ and is elongate to the northeast, parallel to the regional structural grain (fig. 2). The intrusion is exposed over 2,500 vertical ft with abun- dant rubble above 3,500-ft elevation and exhibits a sharp and steeply southeast-dipping and northeast-trending con- tact with metasedimentary rocks to the southeast (i). The lack of roof pendants or other country rock xenoliths, the relatively coarse-grained nature of most of the intrusive rocks, and the steep intrusive rock-country rock contacts K "w" L YT While Mountain lerrane. Ordlvlcean mafic volcanic rocks grading Into Silurian and Devonian I Imeatone Llvengood terrene, early Paleozoic allele and cherts overlain by Devonlen claatlc rocks Beaver terrene, Cambrian quartzlte and shale Yukon Crystalline terrene, Paleozolc(7) and/or Precambrlan composite melemorphic terrene composed mostly ol sedlmentery rocks with continental origins Alluvium Contact High-angle fault, dashed where approximate Thrust fault, dashed where presence uncertain Lime Peak pluton on >:/ her C^iti ■" r : J y See figure 9 ■■\ •k ■ ■ .\ \:?) 20 40 _J I Scale, miles Figure 2.— Tectonostratigraphic map of the Yui 5 y j ""4 \ /- ./\*-l ^'^= Q. (0 E c .2 w u o o. E (0 (A ■o c o o » o I 0) 3 r- J^Y mixed oxide minerals Chlorite Cb-bearing rutile Kaollnite Fe oxides Mn oxides Pb oxides (cerrusite?) Malachite and chrysocolia Ca-Fe-U Mineral Older. .Stage 1. .Stage 2. Younger 'These minerals are common inclusions in chlorite and iron-rich muscovite, but iikeiy represent residual minerals that originated as inclusions In blotlte. Figure 6.— Paragenesis of alteration and mineralization at Lime Peak. Vertical line represents time at which faulting was initiated. Solid line represents ubiquitous minerals; broken line represents occasional or Inferred presence. Table 1.— Head analyses of bulk samples of greisen collected at Lime Peak, percent Sample Cu F Fe Pb S Sn W Zn 32 . 0.02 0.42 19.2 0.13 0.02 0.04 <0.01 0.21 89 . .04 .59 6.9 .06 .02 <.02 <.01 .07 98 . .01 .27 16.7 .04 .57 .03 <.01 .10 99 . .07 .63 20.9 .38 3.95 .18 <.01 .26 Figure 7.— SEM micrograpli {A) and tin X-ray element map (B) showing cassiterite (white) in a chlorite (gray) matrix. the samples in the ridge area also contain elevated concen- trations of arsenic, copper, lead, silver, or zinc; however, there is no apparent correlation between concentrations of tin and other metals. In contrast, elevated concentrations of beryllium, col- umbium, gold, and tungsten are generally confined to greisen sampled in the upper forks of Bedrock Creek. Most of the higher concentrations of beryllium and tungsten were found in samples containing the paragenetically older (stage 1) mineral assemblages; higher concentrations of tin were found in samples containing the younger (stage 2) assemblages. The average tin content of samples of stage 2 greisen is 475 ppm. The weighted average of all channel or continuous chip samples of stage 2 greisen is also 475 ppm Sn over an average width of approximately 2 ft. The average tin con- centration of samples collected on the northwest-trending ridge north of Bedrock Creek is 735 ppm. BULK SAMPLING AND ANALYSES Four bulk samples of greisen, each weighing 100 to 200 lb, were collected at Lime Peak for mineralogical and metallurgical characterization. Sample locations are shown on figures 3 and 4 and head analyses are summarized in table 1. Sample 32 is from a 4.5-ft-long channel across two stage 2 greisen veins, 1.7 and 0.7 ft wide. These two veins are part of an up to 100-ft-wide zone of greisen veins that can be traced for 6,000 ft along strike. Sample 89 is a grab sample from a 12- to 15-ft-wide rubble train of massive stage 2 greisen that can be traced for 100 ft and inferred for 1,000 ft along the strike. Sample 98 is from a 3-ft-wide chan- nel across a stage 2 greisen vein that consists of quartz- chlorite and massive chlorite greisen with traces of pyrite and fluorite. Sample 99 is from a channel across a 1.0-ft- wide stage 2 greisen vein consisting of a 0.6-ft-wide core of limonite- and manganese-stained dense, black massive chlorite, a 0.1-ft-wide hanging wall of massive pyrite altered to clay, and a 0.5-ft-wide footwall of progressively less chlorite-altered granite. This greisen vein pinches and swells over at least a 300-ft strike length. Its maximum width of 5.0 ft is at sample site 98. BENEFICIATION Beneficiation tests were conducted on four bulk samples at the Bureau's Albany (OR) Research Center. In the first test, a composite sample with a calculated head analysis of 0.06 pet Sn was prepared from equal weights of the four samples. The composite was stage ground in rod mills to pass 100 mesh, but elaborate steps were not taken to pre- vent overgrinding. The sample was then tabled on a slime deck of a wet shaking table to produce a concentrate, coarse table tailings (those that settled and banded on the table), and fine table tailings (those that washed off the table without settling). A distinct band of sulfides with minor cassiterite formed in the heavy concentrate fraction. The metallurgical balance for this test is shown in table 2. The concentrate contained 65 pet of the tin at a grade of 0.35 pet Sn. Although recovery of concentrate was emphasized over grade, nearly 35 pet of the tin was lost to the tailings. Microscopic examination of the coarse tailings showed that most of the cassiterite was liberated and, based on chemical analyses, the tin content of the two tailings products was low (0.02 pet Sn). However, the tailings represent 90 pet of the low-grade sample weight and, thus, tin losses in those fractions are relatively high. Recovery may be improved by more precise control of the grinding to prevent excessive fines and/or by regrinding the coarse tailings and retreating them with the rougher fine tailings on equipment more suitable to fine-particle treatment than shaking tables. In the second test, a split of sample 99, which had a head analysis of 0.18 pet Sn (table 1), was stage ground to minus 100 mesh and tabled, as described previously, to produce a rougher concentrate, coarse tailings, and fine tailings. As in the first test, good recovery of the heavy, sulfide-rich frac- tion was emphasized. The rougher table concentrate was then treated in a bulk flotation step to produce a sulfide con- centrate float product and a nonfloat tin concentrate. A rougher flotation step was done with 0.1 Ib/st potassium amyl xanthate as the collector at natural pH of 5.1. The froth was very heavily laden with sulfide minerals. A Table 2.— Metallurgical balance for tabling composite bulk sample' Minus 100-mesh wt Analyses, pet Distribution, pet product pet Sn S Sn S Concrete^ 9.8 0.35 8.68 65.4 69.9 Coarse tailings 45.9 .02 .31 17.3 11.6 Fine tailings 44.3 .02 .51 17.3 18.5 Composite or total . . . 100.0 .05 1.22 100.0 100.0 'Caleulated eomposite head analysis, percent; 0.04 Cu, 0.48 F, 0.15 Pb 1.14 S, 0.06 Sn, 0.16 Zn. 'Additional analyses, percent: 0.07 Cu, 1.56 F, 0.46 Pb, 0.40 Zn. Table 3.— Metallurgical balance for tabling and flotation of sample 99 Minus 100-mesh wt Analyses, pet Distribution, pet product pet Sn S Sn S Rougher table concentrate 12.6 1.05 21.3 93.7 70.5 Sulfide flotation concentrate' 6.5 .25 40.3 11.3 68.7 Nonfloat tin concentrate' 6.1 1.91 1.10 82.4 1.8 Cleaner table concentrate' .6 13.9 NA 58.8 NAp Cleaner table tailings" . . 5.5 .60 NA 23.6 NAp Rougher table coarse tailings 39.4 .01 .71 2.8 7.3 Rougher table fine tailings 48.0 .01 1.76 3.5 22.2 Composite or total . . . 100.0 .14 3.81 100.0 100.0 NA Not analyzed. NAp Not applicable. Additional analyses, percent: '0.15 Cu, 42.9 Fe, 0.67 Pb, 0.85 Zn. '2.91 F. M.10 F. "4.93 F. scavenger flotation step with 0.01 Ib/st collector produced a very small amount of additional float material that was com- bined with the rougher float product for analysis. The nonfloat tin concentrate was then retabled in a cleaner step to further concentrate the tin. The metallurgical balance for the test is shown in table 3. The cleaner table concentrate contained 59 pet of the tin at a grade of 13.9 pet Sn. As in the first test, tin recovery was relatively low in the concentrate, but for different reasons. The cleaner table tailings contained an additional 24 pet of the tin at a grade of 0.60 pet Sn, and it could be recycled to improve recovery. The sulfide flotation concentrate contained 11 pet of the tin, some of which conceivably could be cleaned from the sulfide concentrate and recovered in the cleaner table operation. More elaborate flowsheets and optimum conditions were not investigated. LODE TIN RESOURCES Although the Lime Peak area apparently contains tin- mineralized greisen occurrences that are distributed over an area in excess of 8 mi^, the grade of these occurrences is too low and irregular to allow for adequate definition of in-place tin resources. An estimate of total contained metal, however, may be made by summing all of the mapped lengths and inferred extensions of greisen occurrences, and by assuming they continue for one-half their length at depth and are mineralized over an average width of 2 ft. At an average grade of approximately 0.05 pet Sn and an estimated tonnage factor of 11, this calculation suggests that approximately 5 MMst of rock containing 5 MMlb Sn is present. A slightly higher estimate of 6 to 7 MMlb Sn may be made by assuming the greisen occurrences located on the ridge north of Bedrock Creek have a slightly higher average grade of approximately 0.07 pet Sn. This calculation assumes greisen occurrences are con- fined to a single 2-ft-wide vein. Clearly, as mentioned previously, this is not always the case. For example, the northwest-trending greisen zone in the southern portion of section 3, north of Bedrock Creek and including sample sites 13 through 18, appears to be partially mineralized over a width of 50 ft along its 3,000-ft strike length. Assuming this zone continues for 1,500 ft at depth and is mineralized over 40 pet of its width for an average grade of 0.03 pet Sn (ap- proximately equal to 0.4 x 0.07 pet Sn), this zone may con- tain approximately 20 MMst of rock containing 12 MMlb Sn. Similarly, if the greisen zone extending northwest from sec- tion 3 to section 4, located along the same ridge and exten- ding between sample sites 27 and 40, is assumed to be mineralized over 40 pet of its 20-ft width and is 3,000 ft long and extends to a depth of 1,500 ft, approximately 8 MMst of rock containing 5 MMlb Sn may be present. Therefore, the resources for the area mapped may be on the order of 30 MMst of rock containing 20 MMlb Sn. Beneficiation testing suggests that approximately 60 pet, or 12 MMlb, of this tin could be readily concentrated. It cannot be overemphasized, however, that this resource is too low grade to be considered economic at the present time. PLACER INVESTIGATIONS In 1985, gravels located along the upper portions of North Fork Preacher Creek were investigated for tin- bearing placer deposits. The headwaters of the North Fork partially drain the tin greisen occurrences located near Lime Peak that were discussed in previous sections of this report. Numerous large samples of surface gravels were col- lected and gravel types were mapped. Because samples were collected from surface exposures, the grade of tin in deeper gravels cannot be directly assessed but comparison with placer tin deposits elsewhere in Alaska suggests grade will increase. SURFICIAL GEOLOGY OF NORTH FORK PREACHER CREEK From headwaters located 2 miles southeast of Lime Peak, North Fork Preacher Creek flows northeast toward the lowlands of the Yukon Flats (fig. 2). In its lower course, beyond approximately 5 miles from the headwaters, the creek is mature with a gradient of 1 vertical ft for every 130 to > 600 horizontal ft. In this area, the creek consists of a shallow meandering stream surrounded by a broad alluvial plain containing abundant oxbow lakes. For much of its lower course, the creek also occupies a generally asym- metric (to either the northwest or southeast) valley with relatively steep slopes and a flat trough. Within 5 miles of its headquarters, the North Fork is a juvenile stream with a gradient of 1 vertical ft for every 100 to < 50 horizontal ft. In this area, it has stretches of broad braided stream interspersed with short lengths of poorly developed meandering stream. In its upper course the creek also occupies and has partially incised the trough of a broad, generally U-shaped valley (fig. 8). The upper reaches of North Fork Preacher Creek show evidence of having been affected by at least two periods of 10 Figure 8.— Photograph looking northeast (downstream) along the headwaters of the North Fork of Preacher Creek from a position near the center of section 10. valley glaciation (fig. 9). The older glacier extended at least 5 miles northeastward along the North Fork to a down- valley limit approximately coincident to the northeastern contact between the Lime Peak pluton and neighboring metasedimentary rocks. The position of the terminal moraine of this glacier is indicated by the last of a train of large subangular granite lag boulders that were plucked from an outcrop approximately 3 miles farther up the valley in the central portion of section 35 (fig. 9). A possible rem- nant of lateral moraine from the older glaciation is located near the lag boulder source at the left limit of the creek in the south-central portion of section 35 (fig. 9). An outwash plain extends from the terminus of the older glacier at least another 5 miles farther down the creek (fig. 9). These outwash gravels are locally overlain by 10 to 15 ft of organic material that has crept off the valley's frozen southern slope. Elsewhere along the southern slope, the outwash gravels are also overlain by alluvial fan gravels. Outwash terraces located 3 to 5 ft above the present creek level are common along this stretch of North Fork Preacher Creek, especially where recent stream erosion during flooding has removed overlying organic material. The out- wash gravels are moderately well sorted and locally crudely stratified with rounded clasts that are generally less than 0.5 ft in diameter within a clayey matrix containing only minor amounts of grus. These gravels may contain more abundant fine intrusive phase and tourmaline-bearing cob- bles than other gravels of the area. The retreat of the older and the possible advance of a younger glacier caused the development of a relatively younger outwash plain in the headquarter portion of North Fork Preacher Creek. This plain extends from near the headwaters of North Fork Preacher Creek to the southern terminus of the older glacier (fig. 9). In places along its left limit, the plain truncates alluvial fan and till gravels but elsewhere, on its right limit, it is overlain by alluvial fan gravels. This suggests that the valley is presently cutting to the northwest. The outwash is somewhat variable, ranging from loose- ly packed and poorly sorted grus-rich, to dense, well-sorted clay-rich gravels. Cobbles tend to be subangular to subrounded and moderately coarse, averaging about 0.4 ft in diameter, and are dominantly of intrusive origin. Inci- pient podzolic soil development on these gravels is marked RSE R6E R7E TION 1 ,^L«g boulders.. -^ Lag boulder eource, ^W/ ^ :-^ DD« ,^pM^' BB.CC^^Jp Z ^^^,^ j^^ 1 1 LEGEND "* ) Terminus ol older glaciation ^ Terminus of younger glaciation ^^^„^ Older outwasl) ^^^^ Younger outwash <^ Alluvial fan 9 Z Placer concentrate sample O H Pen concentrate sample .-^-'i^'** Outline of Lime Peak pluton 1 1 \ 1 1 1 TtN Scale. mile Bott odoptad from u S 6 S I 63,360 Circle (C-6 ond C-9) quodronglti Figure 9.— Surficial geologic and sample location map for the North Fork of Preacher Creek. 11 in places by a loose and weathered grus-rich horizon that overlies a thin clay layer, which, in turn, overlies manganese- and iron-stained gravel. The outwash plain gravels grade into unstratified, coarse, grus-rich colluvium along both slopes. SAMPLING AND ANALYSES Twenty-three gravel samples were collected on or near North Fork Preacher Creek (fig. 9). Samples were mostly collected from gravel exposures in cutbanks, a few, however, were also collected from gravel bars. Samples were excavated by hand and loose volumes were measured in 5-gal buckets. Where possible, in-place volumes were also measured. Most samples were subsequently screened to minus 3/8 in and panned to a rough concentrate. A few larger samples were also concentrated with a Keene model HMJ-1 hydromatic jig,^ and two samples were concentrated with a 4-ft-long backpack-style sluice box. In all cases, the rough concentrate was further panned in the field to an ap- proximately pint-size volume. Figure 10 is a flow diagram illustrating how the samples were reduced in the laboratory. Concentrates were screened to minus 16 mesh, further pan concentrated to a standardized volume, examined for mineralogy, and weighed. The samples were then analyzed for tin, colum- ^Reference to specific products does not imply endorsement by the Bureau of Mines. bium, tantalum, yttrium, and cerium by x-ray fluorescence (XRF) and for tungsten using a colorimetric technique. Splits of samples with tin concentrations greater than 2 pet were subsequently assayed for tin. Descriptions, loose volumes, concentrate weights, analytical results, and calculated tin grades of placer samples collected along North Fork Preacher Creek are tabulated in appendix D. Sample volumes range from less than 0.1 to 1.0 yd^ and average approximately 0.2 yd^. The two larger 1-yd^ samples were concentrated with the hydromatic jig. Measured in-place volumes of four samples ranged between 2 and 35 pet smaller than the loose volumes (table 4). Smaller pan concentrate samples were collected from drainages feeding North Fork Preacher Creek in order to help pinpoint potential sources of the placer minerals (fig. 9). Samples were shoveled from gravels located either at the center of the active channel on smaller creeks or from the leading edge of gravel bars on larger streams. Samples were concentrated with a 14-in diameter pan that was heap filled. Concentrates were further reduced, inspected, and Table 4.— Swell factors' calculated from gravel samples Sample Gravel type Volume ft' _ Swell fac- Loose 1 n-place tor, pet F R S V Older outwash • Recent outwash . . . . ■ Alluvial fan .Glacial till 10.4 5.5 6.24 5.46 9.4 5.4 5.4 4.0 10 2 15 35 'Determined by dividing loose volume by in-place volume and subtrac- ting 1. Panned field sample (Plus 16 mesh) Wet screen (16 mesh) (Minus 16 mesh) Binocular microscopic examination Tails Pan to standard volume (10 cm') Optical and ultraviolet light examination of heavy fraction X-ray diffraction of minerals Weigh samples Shipment for preparation and analyses Figure 10.— Flow diagram depicting laboratory sample reduction and examination method. 12 weighed in the laboratory and subsequently analyzed by the same method used on the larger placer samples. The heaviest fraction^ of the placer concentrate samples are composed of variable amounts of cassiterite, magnetite, zircon, monazite, xenotime, topaz, tourmaline (schorl), scheelite, garnet, pyrite (or limonite), columbium-bearing rutile, and chalcopyrite (table 5). Except for magnetite, all of the minerals occur in grains smaller than 1 mm in diameter; magnetite occurs in up to 0.5-cm-wide rounded pebbles. Cassiterite generally occurs as subrounded to subangular, light to dark brown anhedral crystals. However, in sample W, some of the cassiterite occurs as subhedral to euhedral crystals with minor amounts of at- tached greisen. Placer concentrate samples collected along North Fork Preacher Creek contain between 2,100 ppm and 7.25 pet Sn, with grades ranging from 0.002 to 0.04 Ib/yd^ Sn (appendix D). Tin grades of outwash gravel samples systematically decrease downstream as an inverse function of the square of the distance from maximums located both in the Bedrock Creek area and near where North Fork Preacher Creek crosses the northeastern intrusive contact (fig. 11). Concen- trations of tungsten, columbium, tantalum, cerium, and yttrium also decrease downstream of the intrusive contact. Table 6 shows the results of analyses of panned concen- trate samples collected from North Fork Preacher Creek and from streams draining into it. Samples collected by Bur- ton (1) also are included. Relative tin concentrations of the samples have been converted to weight per pan volume calculations, as described by Barker (U), in order to facilitate comparing the results. Only one of the samples 'Approximately greater than a specific gravity of 3.5. Table 5.— Placer sample concentrate mineralogy^ and relative amounts of minerals Sample^ W Q P O N L K I E Beryl NO NO R? NO NO NO NO NO NO Cassiterite A C A M?C A C C A Chalcopyrite NO NO R NO NO R NO NO NO Garnet T? M NO NO NO NO NO NO NO Magnetite . M A C NOG C A C A Monazite A A A M A C C C C Pyrite or limonite . . NO NO R NO NO R T T NO Topaz M M M T M T? NO M NO Tourmaline M M C NO M T NO T? NO Scheelite M M R T M T NOT T Wolframite T? NO NO NO NO NO NO NO NO Xenotime M C M NOM M NOM M Zircon C A C M A A M C A A Abundant. C Common. M Minor. T Trace. R Rare. NO None observed. ? Identification uncertain. 'Determined by optical and X-ray diffraction methods. ^Samples listed according to location on North Fork Preacher Creek, starting near the headwaters. (BB) contained significantly greater than 10 mg/pan Sn, which is the threshold value for anomalous tin concentra- tions determined by Burton (1) for this area. Sample BB was collected from residual material overlying greisen adjacent to Bedrock Creek (fig. 9). PLACER TIN RESOURCES The distribution of placer sample tin grades along North Fork Preacher Creek (see figure 11) clearly indicates that most of the tin in North Fork Preacher Creek is derived from two sources. One of these sources is located near the northeastern intrusive contact where it is crossed by North 0.042 T T T r TRENDS T" >% \ UJ Q < CC o .040- .010- .008- .006- .004- .002- sw A Sample DD N \ A These samples ^ consisted of very ^, loose gravels and are likely not representative ^A KEY NE SAMPLES n Older outwQsh A Younger outwosh O Recent streom olluvium A Alluvial fan grovels Unknown gravel type Till \Tin concentrations in older outwash samp U T C .-3 \ pies Tin concentrations in younger outwash samples, queried where uncertoin Col I u V i um Position of granite contact- T A« »-?—?— ,° Sample A -r- 10 8 DISTANCE ALONG THE NORTH FORK OF PREACHER CREEK, miles Figure 11.— Variation of tin grade along the North Fork of Preacher Creek. 13 Table 6.— Analysis and relative tin concentrations of panned concentrate samples Analysis, ppm Sn cone Weight, Sample Cb Ce Sn Ta W Y g mQ/pan' G 16 66 9 <3 9 9 15.7 0.14 H 16 315 110 3 10 28 19.24 2.11 M 17 320 340 3 20 36 20.07 6.82 P 500 NA 5,000 NA 5,000 NA 2.17 10.85 AA= <70 NA <100 NA <200 NA 6.40 <.64 BB' 94 4,600 8,700 16 855 250 17.37 16.0 CC I 3,400 2,000 36 58 400 19.24 2.5 I Interference because of Zr. NA Not analyzed. 'Calculated as decribed by Barker {14) using the formula: (ppm value) [1,000 (weight in grams)] mg/pan = ^^^^^^ ^From Burton (1). 'Represents concentrate from approximately 9 gal of residual material lying directly on bedrock. Milligram-per-pan value adjusted accordingly. 'Represents concentrate from approximately 15 gal of colluvium near bedrock. Milligram-per-pan value adjusted accordingly. Fork Preacher Creek and is coincident to a hypothesized glacial terminal moraine (compare figures 9 and 11). The second source of tin lies near the headquarters of North Fork Preacher Creek in the Bedrock Creek area. Analytical results, however, show low metal grades that do not in- dicate a significant placer tin resource under present economic conditions. Probable large volumes of former low-grade lode tin mineralization, eroded from sources near Bedrock Creek, are not accounted for by the low placer tin grades found during this investigation. Cassiterite identified in both placer and greisen samples, however, is very fine grained and may be dispersed over a very large area. Additionally, much of the fine cassiterite within the gravels likely has been concentrated at or near bedrock, so the low grades reported from surface gravel samples do not conclusively in- dicate a low potential for placer tin deposits. SUMMARY AND CONCLUSIONS The intrusion at Lime Peak is one of several plutons that underlie the White Mountains highland area north of Fairbanks, AK. These plutons generally intrude a sequence of clastic and carbonate metasedimentary rocks. The geology of the Lime Peak pluton is comparable to that of many tin-mineralized plutons worldwide. Numerous occurrences of tin-mineralized greisen are associated with the Lime Peak pluton in the Bedrock Creek area southeast of the Lime Peak summit. The greisen is composed of complex mineralization-alteration assemblages that can be roughly subdivided into two stages based on their paragenetic relationship to faulting. Cassiterite mineralization is related to the younger of the two assemblages, whereas tungsten is associated with the older event. The average tin grade of 170 samples of greisen from the Lime Peak study area is approximately 0.05 pet; 30 samples from the ridge north of Bedrock Creek define a smaller area, with an average tin grade of approximately 0.07 pet. Beneficiation testing of two bulk greisen samples produced concentrates containing 65 and 59 pet of the total tin values at grades of 0.35 and 13.9 pet, respectively. The lack of outcrops makes determination of mineral- ized widths difficult; however, the size of rubble boulders, together with the width of occurrences that could be chan- nel sampled, suggests that greisen veins are mineralized over an average width of approximately 2.0 ft. Individual occurrences can rarely be continuously traced for more than a few tens of feet; however, discontinous exposures and rub- ble distribution suggest several greisen veins may comprise zones up to 100 ft wide that can be traced for up to several thousand feet along strike. The grade of the greisen occurrences is too low and variable to allow adequate definition of tin resources. An estimate of total contained metal, however, suggests the area has a resource potential of 20 MMlb Sn. Beneficiation testing suggests that approximately 60 pet, or 12 MMlb, of the tin could be readily concentrated. This, however, is con- tained in rock that is too low grade to be considered economic at the present time. Outwash gravels along North Fork Preacher Creek con- tain a diverse suite of fine-grained heavy minerals, including cassiterite; however, analytical results of surface samples show very low metal concentrations that do not indicate a significant resource. Two sources of cassiterite are defined by the distribution of tin grades in gravels. One source is greisen mineralization in the Bedrock Creek area, the other is located on North Fork Preacher Creek where it crosses the northeastern intrusive contact. Low tin grade in surface gravel samples do not account for the former erosion of a large volume of tin-mineralized material from the Bedrock Creek area and suggest that higher grades may be present in gravels closer to bedrock. REFERENCES 1. Burton, P. J., J. D. Warner, and J. C. Barker. Reconnaissance Investigation of Tin Occurrences at Rocky Mountain (Lime Peak), East-Central Alaska. BuMines OFR 31-85, 1984, 44 pp. 2. Wahrhaftig, C. Physiographic Divisions of Alaska. U.S. Geo!. Surv. Prof. Pap. 482, 1965, 52 pp. 3. Prindle, L. M. A Geologic Reconnaissance of the Fairbanks Quadrangle, Alaska. U.S. Geol. Surv. Bull. 525, 1913, 220 pp. 4. Foster, H. L., J. Laird, T. E. Keith, G. W. Gushing, and W. D. Menzie. Preliminary Geologic Map of the Circle Quadrangle, Alaska. U.S. Geol. Surv. Open File Rep. OF 83-170-A, 1983, 32 pp.; 1 oversize sheet; scale, 1:250,000. 5. Wilson, F. H., and N. Shew. Map and Tables Showmg Preliminary Results of Potassium-Argon Age Studies in the Circle Quadrangle, Alaska, With a Compilation of Previous Dating Work. U.S. Geol. Surv. Open file Rep. OF 81-889, 1981; 1 oversize sheet; scale, 1:250,000. 6. Barker, J. C. Mineral Deposits of the Tanana- Yukon Uplands. A Summary Report. BuMines OFR 88-78, 1978, 26 pp. 7. Menzie, W. D., H. L. Foster, R. B. Tripp, and W. E. Yeend. Mineral Resource Assessment of the Circle Quadrangle, Alaska. U.S. Geol. Surv. Open File Rep. OF 83-170-B, 1983, 61 pp.; 1 over- size sheet; scale, 1:250,000. 8. Chapman, R. M., F. R. Weber, and B. Taber. Preliminary Geologic Map of the Livengood Quadrangle, Alaska. U.S. Geol. Surv. Open File Rep. OF 71-66, 1971, 2 sheets; scale 1:250,000. 9. Churkin, M., Jr., H. L. Foster, R. M. Chapman, and F. R. 14 Weber. Terranes and Suture Zones in East Central Alaska. J. Geophys. Res., v. 87, 1982, pp. 3718-3730. 10. Foster, H. L., F. R. Weber, R. B. Forbes, and E. E. Brabb. Re^onai Geology of the Yukon-Tanana Upland, Alaska. Paper in Arctic Geology, ed. by M. G. Pitcher. Mem. Am. Assoc. Pet. Geol., 19. 1973, pp. 388-395. 11. Taylor, R. G. Geology of Tin Deposits. Elsevier (New York) 1979, 543 pp. 12. Hudson, T., and J. G. Arth. Tin Granites of Seward Pennin- sula, Alaska. Geol. Soc. America Bull, v. 94, 1983, pp. 768-790. 13. Gary, M., R. McAfee, Jr., and C. L. Wolf (eds.). Glossary of Geology. Am. Geol. Inst., Washington, DC, 1974, p. 313. 14. Barker, J. C. Reconnaissance of Tin and Tungsten in Heavy Mineral Panned Concentrates Along the Trans-Alaskan Pipeline Corridor, North of Livengood, Interior Alaska. BuMines OFR 59-83, 1983, 24 pp. 15. Carmichael, I. S. E., F. J. Turner, and J. Verhoogan. Igneous Petrology. McGraw-Hill (San Francisco), 1974, 737 pp. 16. Irvine, T. N., and W. R. A. Baragar. A Guide to the Chemical Classification of the Common Volcanic Rocks. Can. J. Earth Sci., v. 8, 1971, p. 523-548. 17. Nockolds, S. R. Average Chemical Compositions of Some Ig- neous Rocks. Geol. Soc. America Bull., v. 65, 1954, pp. 91-108. 18. Thorton, C. P., and 0. F. Tuttle. Chemistry of Igneous Rocks- 1, Differentiation Index. Am. J. Sci., v. 258, 1960, pp. 664-684. 19. Rose, A. W., H. E. Hawkes, and J. S. Webb. Geochemistry in Mineral Exploration. Academic (San Francisco), 1979, 657 pp. 20. Deer, W. A., R. A. Howde, and J. Zussman. An Introduction to the Rock-Forming Minerals. Longman Group Ltd., London, 1966, 528 pp. 15 APPENDIX A.— DESCRIPTION OF IGNEOUS ROCKS MAPPED NEAR LIME PEAK Two major plutonic phases and numerous dikes of analyzed samples of this phase have differentiation indexes* various compositions were mapped near Lime Peak (figure of 92, indicating a high degree of fractionation, and two of 3, main text). Descriptions of each rock type follow. the samples contain minor amounts of normative corum- A coarse-grained intrusive phase (Tgc) underlies most dum. Trace element analyses indicate this phase is relatively of the higher elevations of the Lime Peak area and forms enriched in boron, beryllium, fluorine, lithium, tin, uranium, tors along ridges. This unit comprises medium- to coarse- and thorium compared to the average granite as compiled grained seriate to porphyritic biotite granite and contains by Rose (19) (table A-1). modal compositions between 30 and 38 pet quartz, 40 and 45 The second most abundant lithology, a relatively finer pet orthoclase, 14 and 20 pet plagioclase, and 3 and 7 pet grained, porphyritic granite (Tgp), underlies much of biotite. Trace to minor amounts of fluorite and black tour- Bedrock Creek and the surrounding hillsides. This unit is maline fill miarolitie cavities in this rock, and zircon and characterized by a variable texture, but is most commonly other high-refractive index minerals are common inclusions porphyritic with a hypidiomorphic seriate groundmass and in biotite. Plagioclase, quartz, and biotite typically form a phenocrysts of anhedral orthoclase and quartz. Fine- granular groundmass within which are larger anhedral grained to moderately coarse grained equigranular varieties twinned orthoclase crystals. of this unit are also locally present. Major-oxide analyses of four samples of the coarse- Samples of this rock contain modal compositions between grained granite indicate subaluminous^ (isy to 40 and 50 pet quartz, 29 and 34 pet orthoclase, 10 and 20 pet metaluminous^ (15) and subalkaline (16) compositions that plagioclase, 3 to 7 pet biotite, and 1 to 3 pet museovite, as are generally comparable to that of average biotite alkali well as trace to minor amounts of tourmaline, fluorite, granite reported by Noekolds (17) (table A-1). All four topaz, zircon, monazite, and xenotime. Quartz typically shows undulose to polyerystalline extinction and orthoclase ■Molecular porportion of AI2O3 is approximately equal to that of the sum of commonly has micrographic intergrowths of plagioclase as Na.OandK.O,butislessthanthesumofCaO,NaAandK.O ^ jj j j especially near phenocryst margins, ^Italic numbers m parentheses refer to items m the list of references . , '. . ^ -^ , . . '^ \. .^^ preceeding this appendix. microgranophyric mtergrowths with quartz. Muscovite ex- ^Molecular proportion of AI2O3 exceeds that of the sum of NazO and K2O, but is less than the sum of CaO, Na20, and K2O. ""Sum of normative quartz, orthoclase, and albite (IH). Table A-1— Composition of Lime Peak pluton samples Rock type Tgc Tgp Tgm Tr p^^ b^q /^^ gran- Sample' 10 19 54 21218 58 63 89 102 104 20730 50 (17) ite (79) MAJOR OXIDE ANALYSES,' wt pet SiOj 74.00 74.50 75.50 75.00 75.70 77.30 77.00 77.40 76.50 74.00 71.50 75.01 NAp AljOj 12.70 12.30 12.30 12.30 12.40 12.10 12.30 12.40 12.20 13.60 14.80 13.16 NAp FeA 2.50 2.20 .26 2.15 .18 .27 .43 .12 .22 1.20 .90 .94 NAp PeO NA NA 1.94 NA 1.52 1.83 1.37 1.68 1.58 NA NA .88 NAp MgO 15 .10 .19 .05 .04 .09 .05 .03 .03 ND ND .24 NAp CaO 85 .80 .76 .85 .67 .86 .45 .68 .80 .50 .70 .56 NAp NajO 2.70 2.70 1.90 3.00 2.10 2.10 2.00 2.20 2.10 4.40 5.80 3.48 NAp KjO 5.70 5.80 4.60 5.50 4.50 4.60 4.90 4.20 4.40 4.80 4.40 5.01 NAp TiO^ 15 .10 .18 .05 .05 .05 .09 .03 .04 ND ND .11 NAp PjOs 04 .03 .08 .03 .08 .08 .06 .07 .06 .04 .02 .07 NAp LOI .75 .76 NA .51 NA NA NA NA NA .58 .54 .54 NAp Total 99.54 99.29 97.71 99.44 97.24 99.35 98.65 98.81 97.93 99.12 98.66 99.90 NAp NORMATIVE MINERAL COMPOSITION,' wt pet Albite 23.16 23.20 16.45 25.67 18.27 17.89 17.15 18.84 18.14 37.78 50.02 29.48 NAp Anorthlte 4.00 3.83 3.32 3.89 2.88 3.77 1.87 2.95 3.65 2.25 1.38 2.06 NAp Apatite 09 .07 .19 .07 .19 .19 .14 .16 .14 .08 .05 .26 NAp Corundum 65 .20 3.08 ND 3.13 2.31 3.70 3.20 2.73 .36 ND 1.16 NAp Diopside ND ND ND .13 ND ND ND ND ND ND ND ND NAp Enstatite 38 .25 3.61 .06 2.74 3.18 2.17 3.05 2.77 1.22 ND .60 NAp Hematite ND .61 ND .46 ND ND ND ND ND 1.22 .92 ND NAp llmenite 29 .19 .35 .10 .10 .23 .17 .06 .08 ND ND .32 NAp Magnetite 2.06 1.47 .39 1.60 .27 .39 .63 .18 .33 ND ND 1.36 NAp Orthoclase 34.12 34.81 27.82 32.87 27.35 27.36 29.35 25.12 26.55 28.78 26.50 29.64 NAp Quartz 35.00 35.36 44.80 35.13 45.08 44.68 45.46 46.44 45.59 29.51 20.30 34.07 NAp Wollastanite ND ND ND ND ND ND ND ND ND ND .85 ND NAp CONCENTRATION,' ppm B 100 100 100 200 100 200 100 100 100 200 100 NAp 10 Ba 200 <200 600 70 90 200 100 200 20 <20 <200 NAp 840 Be 10 7 40 30 70 30 30 10 20 20 40 NAp 3 Cb <50 <50 <50 c50 <50 51 <50 57 <50 <50 80 NAp 20 F 980 1,500 1,800 570 3,900 2,900 1,200 5,700 4,800 930 1700 NAp 810 LI 50 44 37 100 61 27.5 64 97 53 NA 25 NAp 40 Rb 210 270 390 240 480 420 370 590 510 NA 330 NAp 276 Sn 7 7 <5 <5 <5 <5 <5 <5 7 NA 48 Nap 3.0 Sr 3 3 46 <10 <10 20.8 <10 <10 <10 <10 <10 Nap 100 Ta <100 <100 <100 <100 <100 100 <100 <100 <100 <100 <100 NAp 3.5 Th 70 60 75 60 70 85 55 75 75 40 35 NAp 20 U 5.3 7.8 4.3 7.8 11 8.5 6.6 14 14 4.8 12.0 NAp 3.9 W <5 <5 <5 <5 8 6 <5 6 <5 NA <5 NAp 1.5 Zr <30 30 200 <30 550 210 170 92 120 <30 <30 NAp 175 Rock types: Tgc Coarse-grained granite. Tgp Porphyritic granite. Tgm Muscovite granite. Tr Rhyollte. BAG Biotite alkali granite. NA Not analyzed. ND Not detected. NAp Not applicable. 'Sequentially numbered generally from northeast to southwest on figure 3 of main text. Samples with 5-dlglt numbers were collected from outside the area shown in figure 3. Sample 21218 Is from near the pluton's southern contact in the southeast quarter of T 9 N, R 4 E; sample 20730 is from a small tongue of granite that extends south from the pluton In the south-central portion of T 9 N, R 4 E (see Burton (/) for location). 'Normalized to 100 pet. 'Ba, Cb, and Ta determined by XRF; B by emission spectrography; W, U, and F by specific chemical methods; Th by radiometric techniques; Zr and Be by ICP methods; and Rd, Sr, LI, and Sn by AA. 16 hibits anomalously high mid-third-order birefringence colors and clear to pale-green pleochroism indicative of a high-iron composition (20), and occurs both in patches associated with biotite and disseminated in the matrix. Topaz occurs as subhedral to anhedral crystals within the groundmass and is interpreted as primary. Major-oxide compositions of five samples of the por- phyritic granite (Tgp) indicate subalkalic and markedly peraluminous compositions with relatively lower total- alkali, AI2O3, Ti02, and MgO concentrations than those of the coarse-grained granite (Tgc). Differentiation indexes of samples of the porphyritic granite, ranging between 89 and 91, are also somewhat less than those of the coarse-grained granite. In contrast, however, the porphyritic granite is relatively enriched in Si02 and P2O5 and has greater than 2 pet normative corundum. The porphyritic granite is also enriched in uranium, thorium, rubidium, fluorine, and possibly columbium, beryllium, zirconium, and tungsten, and contains higher uranium-to-thorium and rubidium-to- strontium ratios relative to samples of the coarse-grained granite and to an average granite composition. Dikes of porphyritic rhyolite, andesite, and 1am- prophyre are also common in the Bedrock Creek area. These dikes range from a few feet to several tens of feet wide, and typically trend northwest, cutting the two more abundant intrusive phases. The rhyolite is composed of subequal amounts of subhedral to euhedral quartz, or- thoclase, and albitic plagioclase and minor irregularly shaped biotite phenocrysts in a fine matrix of quartz, or- thoclase, and muscovite (1). Phenocrysts make up 60 pet of this rock, and fluorite occurs rarely in miarolitic cavities. Major oxide analyses of one sample (50) of the rhyolite in- dicate a peraluminous and alkalic composition with a dif- ferentiation index of 96 (table A-1). One andesite dike was mapped in the east fork of Bedrock Creek, and andesite rub- ble is common on the south flank of the Lime Peak summit. The andesite is dark green to gray and commonly contains phenocrysts of plagioclase feldspar. Two lamprophyre dikes were also mapped in the east fork of Bedrock Creek; this rock is dark green to black and contains no obvious phenocrysts. Neither the andesite nor lamprophyre were ex- amined optically or analyzed for major oxide composition. The major oxide composition of a sample (20730) of medium-grained equigranular muscovite granite (Tgm) from the southern portion of the Lime Peak pluton is in- cluded in table A-1. Although this rock is not present in the area of detailed mapping, its analysis is included for com- parative purposes. Analysis indicates a metaluminous and sodium-enriched subalkalic composition with a differentia- tion index of 96. This rock appears to be the most evolved plutonic phase of the Lime Peak pluton. Where observed in one thin section, the muscovite granite was composed of ap- proximately 40 pet quartz, 30 pet plagioclase, 25 pet ortho- elase, 4 pet muscovite, and variable but generally minor amounts of fluorite, topaz, and blue tourmaline. Tourmaline and fluorite fill miarolitic cavities, and plagioclase occurs as euhedral laths surrounded by anhedral quartz, orthoelase, and topaz, and subhedral muscovite crystals. The muscovite is similar to muscovite in samples of the porphyritic granite. 17 APPENDIX B.— DESCRIPTION OF GREISEN OCCURRENCES SAMPLED NEAR LIME PEAK Approximately 30 different minerals have been iden- tified in greisen samples collected near Lime Peak. These minerals and their paragenetic relationships are listed in figure 6 of the main text. Based on their paragenetic rela- tionship to faulting, two alternation-mineralization stages appear to be represented. Each of these stages is discussed in the following. The paragenetically older (stage 1) mineral assemblage is best exposed, and is largely confined to the East Fork of Bedrock Creek area (fig. 4). Samples containing similar alteration minerals, however, have also been found on the hillside north of Bedrock Creek. This greisen assemblage is relatively barren of tin. Stage 1 may actually represent several separate or paragenetically overlapping mineral suites; however, all of the vein sets are cut by faults or frac- tures associated with later stage 2 alteration. Most characteristically, stage 1 veins sets trend west- northwest and comprise 3- to > 25-ft-wide zones containing three to six thin veins per foot (fig. 4). Locally, however, veins may obtain thickness of up to 0.5 ft or may crisscross in a stockwork fashion (sample 47). The veins may also be very irregular and poddy (sample 119). Stage 1 veins are typically composed of relatively coarse grained muscovite, quartz, and topaz with lesser purple fluorite, molybdenite, and a columbium-tungsten-iron mineral, tentatively identified as wolframoixiolite (fig. 6). The muscovite is quite distinctive and contains anomalously high third-order birefringence colors, and clear to pale green pleochroism similar to that found in the porphyritic and muscovite granites, and similarly indicates a high-iron content^ (20).^ In places along- Bedrock Creek, especially near sample site 126, the muscovite-nch veins parallel up to 1-in-wide veins of quartz, albite, green fluorite, and green 'Microprobe analysis indicates the green muscovite has a general composi- tion of K[(Fe)2Al]lAl3 30io(OH)2. ^Italic numbers in parentheses refer to items in the list of references preceding appendix A. 300 350 400 450 500 550 600 15 ^ n = 50 10 - - 5 - y 1 r n muscovite. The two vein sets may be contemporaneous; however, in a thin section of sample 126, the quartz-albite vein was observed to be cut by a more typical stage 1 veinlet of quartz and topaz. Analysis of fluid inclusions^ in quartz and topaz of the stage 1 vein set indicates a wide range of homogenization and decrepitation temperatures, with homogenization to either a liquid or a vapor (fig. B-1). These results suggest the fluid was boiling at the time that these minerals were precipitated. Corresponding last melting temperature measurements cluster near -25° C, but range as high as -6° C, indicating a range of salinities between 10 and 43 equivalent wt pet NaCl. The paragenetically younger (stage 2) alteration- mineralization assemblage at Lime Peak consists dominant- ly of quartz, chlorite, and sericite, with locally abundant topaz, fluorite, tourmaline, and pyrite. The pyrite locally contains inclusions of bismuth minerals, (bismuthinite and native bismuth). In addition, sphalerite, galena, chalcopyrite, cassiterite (see figure 7), columbium-bearing rutile (fig. B-2), and other fine-grained accessory minerals are sometimes present. Most of these minerals occur as ran- dom clots, small veins, and scattered grains, usually within the chlorite matrix. Late-stage alteration minerals include iron, manganese, and lead oxide minerals, kaolinite, an unidentified calcium-iron-uranium mineral, and malachite and chrysocolla (fig. 6). Sericite in the stage 2 assemblage is distinguished from muscovite of the stage 1 assemblage by its fine-grained nature, lack of pleochroism, and relatively lower birefringence colors, and is probably of the low-iron variety {20). Tourmaline exhibits anomalous purple to blue pleochroism. Chlorite has a light green to yellow pleochroism and exhibits high first-order birefrigence colors indicative of a high-iron, low-silica composition (16).'* 'Analyses by S. Masterman, graduate student, University of Alaska. ■•Microprobe analyses indicate a composition of approximately (F'eo.87Alo.,3)4(Alo.4.Si,,,,),0,„(OH)3. 1 1 n = 31 n 1 1 1 r 1 1 1 1 1 1 1 1 KEY LH Homogenize to o liquid B Homogenize to a gas C Decrepitate H CO, -rich inclusions 1 r n = 26 n II n 1 1 n 1 1 1 1 m 150 200 250 300 350 HOMOGENIZATION TEMPERATURE. » C -5 -10 -15 -20 LAST MELTING TEMPERATURE, Figure B-1.— Results of fluid inclusion analyses; (A) stage 1 vein and (B) stage 2 vein. 18 Figure B-2.— SEM micrograph of crystals of columbium- bearing rutile (white) in a chlorite (gray) and quartz (black) matrix. Where most pervasively developed, the younger (stage 2) greisen assemblage consists of a mass of chlorite and quartz intergrown with, and partially replacing, sericite, topaz, fluorite, and tourmaline. These minerals may be developed around a central open-space-filling veinlet of similar composition. Locally, for example at sample site 89, the wallrocic is so thoroughly recrystallized that vugs lined with quartz, chlorite, and fluorite are present. Pervasive greisen alteration is progressively developed from a less altered, porphyritic-appearing rock containing partially replaced relict anhedral quartz grains in a matrix-of fine- grained quartz, chlorite, sericite, fluorite, and tourmaline. Chlorite and sericite replace biotite and feldspars; chlorite replaces sericite as the alteration progresses. In many altered specimens or outcrops, the alteration zoning is asymmetric. Where the zoning is asymmetric, the most pervasively altered rock, which comprises massive, penetratively deformed chlorite and angular quartz fragments, is truncated by a planar slickensided surface and undoubtedly represents gouge adjacent to a fault. The abun- dance of greisen-altered float with slickensided surfaces in- dicates that much of the paragenetically younger (stage 2) greisen is localized along faults. Analysis of fluid inclusions in quartz from a vein within the quartz-chlorite greisen indicates a relatively narrow range of homogenization temperatures, with an average value of 220° C (fig. B-1). In contrast, corresponding last melting temperature measurements exhibit a wide range of values from 0° to -24° C. The range in last melting temperatures suggests that this greisen assemblage was deposited under a wide range of salinities corresponding to to 40 equivalent wt pet NaCl. 19 APPENDIX C— RESULTS OF ANALYSES OF ROCK SAMPLES COLLECTED FROM THE LIME PEAK AREA Table C-1.— Results of quantitative geochemlcal analyses' of rock samples Sample^ Type Length' or area Analyses, ppm Ag Au Sn U W CbjOs Field description' .G NAp . .Ch 2 ft .. .G 150 ft^ .G NAp . .C 3 ft .. 6 G >0.5 ft 7 G 125 ft^ . 8 G 300 ft^ , 9 G 300 ft^ , 11 G 300 ft' . 12 13 14 15 16 17 18 20 21 22 23 24 25» 26 27 28 29 30 31 33 38 39 40 41 42 43 44 46 47 48 49« 50 51 52 53 55 56 57 59 60 61 62 64 65 .NAp .C 5 ft . .G ........60 ft' .4 ft . .NAp .60 ft .G 100 ft . .G NAp .. .G <0.8 ft .G 200 ft . -G 30 ft' .. .G 60 ft' .. .G NAp .. .G 1 ft . .G NAp .C 20 ft .G 20 ft .G 60 ft' 34 C 35 G 36 C 37 C .30 ft' .NAp .NAp .NAp .NAp .NAp .G 30 ft .G 50 ft .5 ft .C 0.4 ft .NAp .3 ft .NAp .NAp .NAp .NAp .NAp .G NAp . .G 20 ft' . .G 25 ft' . .G NAp . .G 900 ft' .G 60 ft' . .C NAp . .0 4 ft .. .C 10 ft . .NAp .1 ft .NAp ■ NAp LD =0.3 ^8 2.9 LD LD LD LD 310 300 1,010 280 1.0 LD 380 5.0 LD 1,100 1.5 4.1 2.8 2.0 LD LD LD LD 730 200 220 950 1.1 LD 300 28 6 LD 5.9 LD LD 8.5 8 100 12 16 66 14 36 LD 8.8 12 LD 18 6 LD 12 LD LD 9.4 LD LD 25 LD LD 7.6 LD 1.6 LD 120 10 LD LD 4.1 LD 340 19 LD LD 1.6 LD 310 11 LD LD '.8 LD 1,200 14 LD LD ^4 LD 430 19 LD LD 1.0 LD 860 16 6 LD LD LD 130 8.5 LD LD =0.6 '0.007 370 17 LD LD 1.7 LD 230 30 10 LD 2.4 LD 210 33 12 69 ^4 LD 480 37 10 LD. 36.4 ND 99 NA 16 LD NA NA 170 NA 6 LD 1.9 .025 850 22 14 LD 1.4 LD 730 17 LD LD ^8 .024 670 15 8 LD 1.5 =.007 940 27 8 LD 3.10 LD 1,000 31 6 LD 10.8 LD 200 42 200 LD 17.5 .016 35 <.5 20 LD 17.8 LD 800 18 60 LD LD .019 600 14 12 LD LD LD 530 20 20 LD 2.1 LD 100 9.8 32 LD 5.1 LD 400 8.7 6 LD 20.6 LD 3,800 36 LD LD 1.4 LD 120 8.5 10 LD LD LD 300 NA LD 68 LD =.007 1,030 9.4 12 LD 2 LD 620 15 6 LD 2.1 =.009 54 13 LD 79 1.3 LD 10.4 15 160 LD LD .038 6 11 14 LD 6.3 LD 660 22 16 LD NA NA 120 30 6 LD 2 LD 220 6.9 8 LD LD LD 280 15 6 LD 1.5 =.007 220 15 12 LD LD .045 200 19 LD LD 8.5 LD 150 51 LD LD LD LD 2,700 14 10 LD LD LD 490 16 10 LD .5 LD 210 17 8 LD 1.6 LD 180 6 LD LD LD 210 13 32 LD 3.5 LD 240 19 900 56 10 19 20 NA NA 120 NA 30 15 See explanatory notes at end of table. Mn-stalned coarse granite. Chlorite grelsen. Chlorlte-quartz grelsen. Quartz-chlorlte-serlcite-fluorlte grelsen. Chlorlte-quartz llmonltic grelsen boulder. Chlorite-quartz-muscovlte-fluorlte- tourmallne-chalco-pyrlte grelsen. Chlorite grelsen. Do. Do. Chlorite-sericlte-quartz-fluorlte-topaz- pyrlte-chalcopyrite grelsen. Grelsen boulder with open-space- filling quartz-muscovlte-fluorlte- topaz vein. Open spaces are filled with chlorite. Chlorite-altered coarse granite. Chlorite-altered granite and quartz veins. Massive chlorite grelsen. Massive limonitlc chlorite grelsen. Massive chlorite and chlorite- altered granite. Limonitlc quartz-chlorite grelsen. Chlorite-altered granite. Serlcite-quartz-chlorite-pyrite-fluorite- greisen. Chlorlte-quartz greisen. Quartz-chlorite Mn-stalned greisen. Do. ^ Chalcopyrite-pyrite-arsenopyrite- bearlng limonitlc greisen. Fluorite-bearlng greisen. Mn-stalned quartz-chlorite greisen. Chlorlte-quartz-sericite grelsen zone. Quartz-chlorite grelsen. Quartz-chlorite and massive chlorite greisen. Cnlorite-quartz greisen. Quartz-chlorite-sericite-fluorite greisen. Quartz-chlorite-fluorite greisen. Do. Chlorite-sericite-quartz greisen. Chlorite-sericlte-quartz altered granite. Chlorite greisen. Chlorite-sericite-altered granite and massive chlorite grelsen. Do. Chlorite-serlclte altered granite. Muscovite-sericite-topaz greisen. Massive chlorite greisen. Chlorite grelsen. Quartz-green fluorite pegmatite. Stockwork quartz-muscovite-topaz- fluorite veins with trace molyb- denite. Stockwork quartz-fluorite-chlorite- velns. Limonitlc pyrite-chalcopyrite-bearing chlorite grelsen. Biotite-tourmaline pegmatite. Chlorite-sericite-quartz greisen. Sericite-chlorite-quartz greisen. Mn-stalned quartz-chlorite greisen. Chlorite grelsen. Do. Chlorlte-quartz greisen. Quartz-chlorite greisen. Quartz-chlorite altered zone along fault. Pervasively chlorite-altered granite. Quartz-chlorite altered granite adjacent to fault. Quartz-sericile-py rite-tourmaline- altered granite cut by quartz- tourmaline-sericite veins. Dense chlorite greisen. 20 Table C-1.— Results of quantitative geochemical analyses' of rock samples— Continued Sample' Type Length' or area Analyses, ppm Ag Au Sn U W CbjOs NA NA 79 NA 80 22 NA NA 220 NA 8 17 NA NA 210 NA 8 LD NA NA 62 NA 4 LD NA NA 595 NA 5 LD =0.5 LD 15.1 7.5 LD LD LD LD 120 1.7 LD LD 6.6 LD 300 8.3 LD LD LD =0.009 510 12 10 LD ^4 LD 750 7.3 12 LD 2.9 =.012 100 11 LD LD 9.2 =.008 210 33 10 <50 3.8 .011 1,050 17 6 52 \7 LD 170 13 6 LD '.9 =.007 12.6 13 6 62 1.1 LD 580 27 24 LD ^8 .125 5 85 LD LD 1.1 LD 190 13 8 LD LD .021 100 28 LD 77 LD LD LD 8.1 LD LD LD LD 7.9 =.8 LD LD ^3 .007 3,400 60 6 LD LD =.010 250 11 6 52 LD LD 270 17 LD LD LD LD 24.9 9.3 LD LD LD =.007 530 20 LD LD LD LD 230 60 LD 62 LD LD =.009 36 5.7 6 LD 1.2 =.008 810 32 6 LD =.3 LD 250 7.8 LD LD 5.4 LD 1,090 17 LD LD =.7 LD 380 20 LD LD 5.4 .092 520 24 6 58 1.2 .219 460 35 LD 54 5.2 .284 330 26 LD 52 ^8 .080 1,110 28 LD LD 1.2 LD 350 30 LD 60 2.8 =.008 500 23 LD LD 1.6 =.011 380 41 6 72 4.1 =.010 68 26 6 LD 9.1 LD 270 19 LD 78 16.6 =.013 200 93 LD LD 1.8 =.007 58 22 14 63 1.7 LD 210 20 LD 110 6.8 =.007 280 25 LD 93 LD LD 39 22 LD LD =.3 .032 120 17 1,000 100 LD .067 11.7 22 3,200 80 LD =.008 53 12 20 140 *0.6 =.007 150 22 24 200 8.6 LD 870 19 LD 70 6.6 =.008 210 30 LD 160 1.8 =.007 340 12 20 110 4.6 LD 1,060 17 10 140 LD =.008 87 12 6 LD , 205.8 .100 1,050 8.9 ND LD NA NA 590 NA LD LD 23.4 LD 660 16 LD LD 9.4 =.010 670 18 6 LD 91.1 LD 3,700 44 14 LD LD LD 17 8.3 6 LD Field description" 66 . 67 . 68 . 69 . 70 . 71 . 72 . 73 . 74 . 75 . 76 . 77 . 78 . 79 . 80 . 81 . 82 . 83 . 84 . 85 . 86 . 87 . 88 . 91 . 92 . 93 . 94 . 95 . 96 . 97 . 100 101 103 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 .C 5 ft . .C 5 ft . .C 7 ft . .C 7 ft . .C 2.5 ft .C .. .G .. .G .. .G .. .G .. .G .. .G 1,000 ft .4 ft .NAp .NAp .NAp .NAp .NAp 30 ft' G 30 ft' . G NAp . G NAp . G NAp . G 100 ft' G 150 ft' G NAp . G NAp . C NAp . G NAp . .G 5,000 ft' .G NAp ... .G 800 ft' .. .G 1,000 ft' .0 6 ft . .Ch 2 ft . .Ch 0.5 ft ■ Ch .Ch .Ch .Ch .Ch .0.8 ... .2.5 ... .1 ft .. .3 ft .. , . 2 f t . . .G »0.4 ft .Ch 6 ft .. .Ch 2 ft .. .Ch 2.5 ft . .Ch 0.7 ft . .Ch C .3 ft .NAp . C »0.4 ft .C .C ■ Ch ."12 ft .10 ft. . ..0.3 ft . .Ch 0.5 ft .G . .Ch .Ch .... .G .Ch .Ch .NAp .3 ft . .0.8 ft .NAp .0.5 ft .3 ft . .Ch 1 ft . .C 0.4 ft .H . .H . .Ch .1 ft .1 ft .4 ft .C "25 ft .Ch 0.7 ft . .Ch .2 ft .Ch 0.2 ft .Ch 3.5 ft -C 16 ft .C 0.3 ft .C 0.3 ft LD LD 7.6 6.7 LD LD LD LD LD 11.4 67 16 11 60 28 LD LD LD LD 270 14 LD LD LD LD 300 11 280 LD Dense chlorite greisen. Do. Do. Do. Do. Mn-stained, chlorite-altered granite. Chlorite-pyroxene skarn. Chlorite-altered granite. Quartz-chlorite greisen. Do. Mn-stained chlorite greisen. Quartz-chlorite greisen. Quartz-chlorlte-fluorite greisen. Do. Quartz-chlorite greisen. Do. Do. Do. Do. Incipiently chlorite-altered granite. Do. Massive chlorite greisen. Vuggy quartz-chlorite greisen with open space filled with fluorite. Quartz-chlorite greisen. Do. Do. Quartz-chlorite fluorite greisen. Mn-stained, chlorite-altered granite. Quartz-chlorite greisen. Moderately developed chlorite greisen. Quartz-chlorite-green fluorite greisen. Quartz-chlorite greisen. Do. Do. Do. Do. Do. Do. Do. Do. Do. Topaz-muscovite greisen. Quartz-chlorite greisen. Do. Do. Do. Quartz-topaz vein with topaz- muscovite-fluorite-altered selvage. Topaz-muscovite-fluorite greisen. Zone of thin muscovite-topaz(?) quartz veins. Topaz-muscovite-fluorite greisen. Muscovite-rich greisen adjacent to fault. Minor quartz-chlorite-greisen zone. Quartz-chlorite greisen cut by thin muscovite-quartz veins. Chlorite greisen with chlorite altera- tion selvage. Quartz-albite-fluorite vein with selvage of muscovite-topaz- altered feldspar. Quartz-chalcopyrite-chlorite vein. Do. Quartz-chlorite-chalcopyrite greisen zone. Quartz-chlorite greisen. Chlorite greisen with pyritic center of vein. Zone of 12 chlorite veinlets and 1.2-ft-wide quartz-albite-chlorite- biotite vein. Quartz-albite-chlorite-biotite vein from sample 132. Quartz-chlorite-biotite(?) veinlet zone. Zone of 50 quartz-chlorite-biotite(?) veinlets and 1.3-ft-wide quartz- chlorite greisen vein. Quartz-chlorite greisen vein from sample 135. Do. See explanatory notes at end of table. 21 Table C-1.— Results of quantitative geochemical analyses' of rock samples— Continued Sample' Type Length^ or area Analyses, ppm _Afl_ Au Sn U W CbjOs Field description'' 138 139 140 141 142 143 144 147 148 149 151 152 153 154 155 156 157 '158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 .G NAp . C 21 ft .Ch 0.9 ft .Ch .C . .Ch .Ch .4 ft 145 G NAp 146 Ch 0.5 ft .Ch 0.3 ft .H NAp .H NAp .Ch 0.5 ft .Ch 0.3 ft .G NAp .Ch 0.3 ft .C 15 ft .C 0.2 ft .G . .G . .Ch .Ch .Ch .NAp .NAp .1 ft . .0.1 ft .0.4 ft .Ch 0.1 ft -Ch 1.8 ft .Ch 0.2 ft .Ch 7 ft . .C 0.2 ft . Ch 25 ft .C 0.3 ft .G NAp .C 0.3 ft .C 0.1 ft .G NAp .C 0.9 ft .C 0.9 ft .C 0.2 ft .C 0.6 ft .G NAp .Ch 1 ft . .C 0.1 ft .C 0.1 ft .C 0.2 ft .C 0.2 ft .C 0.3 ft 1.5 LD 920 66 LD LD LD 15 LD 0.164 LD 20 LD LD 75 15 LD LD 7.6 15 LD LD 140 22 LD .017 230 16 1.6 LD 110 16 LD LD 77 17 1.2 .007 100 22 1.1 LD 10.7 18 1 .064 8.9 14 2.6 LD 91 24 0.8 LD 340 22 LD 0.015 260 15 ^6 LD 1,150 23 LD LD 96 19 1.6 LD 9.9 37 1.2 LD 17.5 22 3.9 '.007 35 22 8.0 LD 70 34 6.9 LD 25 28 10.4 ^008 67 23 19.2 .009 7,100 24 22.5 LD 230 41 2.5 .033 2,600 22 4.5 LD 46 33 4.6 LD 14.2 24 LD LD 15.1 24 3.1 LD LD 22 LD 56 19 '.3 LD 49 21 LD 21.7 19 2.0 LD 49 16 ^6 LD 22.7 19 7.3 LD 940 37 1.6 LD 33 27 3.2 LD 460 22 1.4 LD 22.7 22 7.9 '0.007 140 33 9.5 '.009 500 50 LD 77 20 3.5 LD 250 25 5.2 LD 200 39 21.2 LD 720 50 80 LD 20 56 400 LD 60 LD 14 LD 8 LD 280 LD 200 LD 32 LD LD LD LD LD LD LD LD 78 12 LD 8 LD 6 LD LD LD LD LD 10 LD 50 LD LD 200 LD LD LD LD 240 110 ND LD 12 95 LD 77 LD LD 200 87 6 LD 80 160 78 LD 200 LD 160 73 16 LD LD 53 LD 53 LD 100 60 LD LD LD ND LD LD LD LD 6 LD 10 LD Muscovite-chlorite-fluorite-altered granite. 1 grain calcite observed. Zone of >75 quartz-chlorite veins and veinlets. Quartz-chlorite greisen with 2 quartz veinlets. Zone of approximately 25 quartz- chlorite veins and veinlets. Zone of quartz-chlorite-veinlets. Quartz-chlorite greisen fault zone. Quartz-chlorite-tourmaline-pyrite greisein vein. Composite of several diffuse quartz- chlorite greisen zones In area. Quartz-chlorite greisen with central quartz vein. Quartz-chlorite greisen. Quartz-chlorite veinlets. Do. Quartz-chlorite greisen. Quartz-chlorite veinlet zone. Quartz-chlorite veinlets. Quartz-chlorite greisen fault zone. Quartz-chlorite veinlet zone. Quartz-chlorite greisen fault zone. Do. Do. Do. Do. Do. Quartz-chlorite veinlets. Green fluorite vein with quartz- chlorite greisen selvages. Quartz-chlorite greisen fault zone. Quartz-chlorite greisen vein zone. Quartz-chlorite greisenized fault zone. Quartz-chlorite veinlet zone. Iron- and manganese-stained greisen vein. Quartz-chlorite veinlets with minor molybdenite. Quartz-chlorite greisenized fault zone. Do. Do. Coarse chlorite(?) greisen. Quartz-chlorite greisenized fault. Do. Do. Composite of quartz-chlorite greisen material from 25 ft of exposures along creek. Quartz-chlorite greisen Do. Do. Do. Do. Do. LD NA NAp ND Less than detection limit. Not analyzed. Not applicable. Not determined because of interterence Sample types: C Chip Ch Channel G Grab H High grade 'Sn, Ta, and Cb (CbjOj) determined by XRF (Ta not detected); splits of samples with 50 ppm analyzed by AA; W by colorimetry; Th and U by radiometric techniques, and Ag and Au by fire assay-ICP. 'Gaps in sample numbers correspond to samples listed in table 1 of main text or table A-1 of Appendix A. ^True thicl200 100 200 20 2 <100 100 200 20 3 90 2,000 40 10 4 <200 200 50 200 5 <300 200 60 30 6 <600 100 70 10 7 <500 <60 <20 10 8 <90 100 30 20 9 <400 <100 <20 10 II <500 90 <20 10 12 <700 200 30 10 13 <700 <70 30 10 14 <90 100 100 10 15 <90 <40 50 10 16 <90 100 60 70 17 <70 100 50 20 18 <200 100 <20 20 20 <90 <60 300 10 21 <90 90 50 20 22 <90 <40 <20 20 23 <100 100 <20 30 24 <200 100 40 40 25 20,000 <60 <20 20 26 <90 <80 40 10 27 <300 500 90 30 28 <100 90 70 400 29 <200 100 40 50 30 <200 100 70 50 31 <90 <30 80 10 33 <90 90 <20 20 34 <300 <60 <20 20 35 <400 <50 <20 20 36 <600 600 <20 30 37 <200 100 30 20 38 <90 200 100 30 39 <90 <80 60 20 40 <400 <80 <20 20 41 <90 100 70 20 43 <300 clOO <20 40 44 <100 <80 <20 20 45 <90 80 40 10 46 <500 <30 200 6 47 <90 100 50 4 48 <200 100 <20 8 49 <90 <80 <20 700 50 < 90 < 30 20 300 51 <100 100 60 20 52 < 200 200 < 20 20 53 <500 <40 30 8 55 <100 <40 <20 10 56 400 <50 90 10 57 < 200 400 200 80 59 <90 90 50 20 60 < 200 200 40 90 61 <400 <60 100 40 62 <90 100 <20 2C 64 <200 800 60 100 71 <90 <70 300 20 72 <500 <40 2,000 6 73 <700 90 100 40 74 <100 600 90 30 75 <400 <80 <20 60 76 <300 <30 70 30 77 <200 <40 <20 20 78 <500 <70 <20 20 79 <200 100 90 20 80 <200 <60 60 20 81 <300 900 20 10 82 400 90 200 100 83 <90 100 80 10 84 400 90 100 60 85 300 < 70 90 7 86 400 80 20 30 87 <600 <100 20 20 88 <90 <90 50 40 91 <200 <30 200 20 92 300 <70 <20 20 93 <200 <30 40 10 94 500 100 400 50 95 400 <80 700 60 96 <90 90 90 20 97 <90 90 50 100 See explanatory notes at end of table. 70 40 10 30 20 30 <8 10 <3 20 <5 20 <6 10 <5 20 <8 40 20 <5 20 20 30 20 30 20 <7 20 <3 30 10 30 50 30 <3 <3 <6 30 20 20 30 40 20 70 20 20 70 30 20 20 70 10 30 <8 20 70 30 10 30 40 40 60 70 <7 <4 <3 20 30 80 90 20 20 40 <6 <6 400 800 10 10 200 <6 90 20 90 90 20 10 300 <6 100 <6 200 30 2,000 <7 40 10 <6 10 <6 30 10 9 <6 800 <6 <6 10 10 <6 <6 10 20 <6 10 80 <6 700 30 30 <6 800 20 <6 10 <6 <6 100 <6 400 20 80 80 10 50 <6 <6 <6 <7 8 <6 40 40 <6 <6 40 <4 <3 <10 <9 <20 <20 <20 <40 <2 <50 <2 <60 <30 <40 <30 <10 <30 <6 <3 6 <8 30 <5 2,000 9 20 10 <6 <7 20 30 <10 20 300 <10 <6 200 <6 10 300 <5 <7 <30 <10 <40 <2 <10 <2 <90 <10 <30 <6 10 <7 <4 <30 <10 10 <5 <7 <20 <9 <8 10 <6 <7 9 <30 <40 <30 <6 <3 <4 <6 <3 <9 <6 <2 10 <2 <10 10 <100 <90 40 <20 2,000 100 <60 800 300 400 200 200 200 <30 <700 <900 <1,000 < 1,000 < 1,000 <800 < 1,000 < 1,000 < 1,000 <800 500 < 1,000 500 <800 60 < 1,000 100 <900 300 < 2,000 300 90 600 2,000 <70 < 1,000 < 2,000 <900 <800 < 2,000 100 < 1,000 500 < 1,000 3.000 <600 20 <600 200 <600 80 < 2,000 300 < 1,000 800 < 1,000 400 < 1,000 3,000 < 1,000 4,000 < 2,000 700 < 2,000 <30 < 2,000 100 < 1,000 500 < 1,000 200 <40 400 <20 <30 200 2,000 <70 <40 <50 <60 300 <30 200 <70 <40 400 400 <60 <60 <900 < 1,000 < 1,000 < 2,000 < 1,000 < 1.000 <600 <600 <600 < 1,000 < 1,000 < 2,000 < 2,000 <600 < 1,000 < 2,000 <600 1,000 <600 <600 < 20 < 1 ,000 <40 <600 1,000 <30 100 <60 <40 < 1,000 < 1,000 < 1.000 < 1,000 < 8,000 300 < 2,000 200 < 2,000 <70 <600 200 <800 <30 < 1,000 20 <7 <5 <2 100 500 200 <20 <20 <20 5,000 1,000 <20 <20 <20 90 <60 300 <80 <600 <800 < 1,000 <900 <600 <600 < 2,000 < 1,000 < 1,000 <600 < 1,000 <80 <600 < 2,000 <900 1,000 400 700 600 600 800 1,000 700 2,000 400 800 600 500 400 1,000 800 500 1,000 800 900 600 900 700 400 700 1,000 1,000 1,000 600 600 1,000 600 1,000 700 400 700 2,000 40 30 2,000 2,000 900 1,000 200 2,000 400 700 700 400 700 500 200 700 300 800 200 700 3,000 2,000 200 200 2,000 800 1,000 500 1,000 100 50 2,000 4,000 800 1,000 3,000 700 300 600 900 <30 60 <30 <30 <30 30 70 <30 <30 <30 40 80 100 90 <30 <30 40 <30 30 300 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 70 ,30 <30 <30 <30 <30 <30 <30 100 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 50 <30 <30 <30 <30 <30 60 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 <30 60 <30 700 <30 7 700 <30 7 900 <30 7 800 40 8 1,000 <30 6 10 7 8 10 7 9 2 3 3 10 9 7 7 7 7 6 6 10 0.07 .06 .06 .1 .1 .05 .06 .08 .03 .1 .09 .06 .03 .02 .04 .03 .04 .02 .01 .07 .09 .09 .1 .06 .08 >.08 >.09 >.04 >.1 >.2 >.09 >.04 >.06 >.06 >.08 >.08 .002 >.2 >.2 >.3 >.06 >.04 >.09 >.04 >.04 .03 >.06 >.05 >.2 >.09 >.1 >.3 7.05 < 0.003 .03 >.2 .03 .02 >.09 >.08 .02 >.04 >.04 .006 .03 .09 <.005 >.06 .02 .008 >.05 .02 .03 >.07 <.002 >.09 >.04 0.05 >4 .2 >1 .1 >2 .03 >3 .1 >2 .1 .03 .1 .09 .08 >2 >4 >2 >5 .6 .1 >4 .07 <2 .1 >4 .2 >2 .2 >4 .1 .2 .2 .3 .1 .03 .2 .2 .07 .1 .2 .1 .07 .1 .2 .2 .004 .1 .08 .02 .03 ND .005 .008 .2 .2 .2 .003 .06 .03 .03 .1 .02 .08 .05 .05 .05 0.09 .9 .1 .06 .06 .1 .2 .02 .04 .1 .1 .08 .1 01 .08 .08 .2 .4 .1 .1 .2 .7 .3 .03 .05 >2 >3 >3 >2 >3 >5 >4 >3 >4 >4 >2 >4 >2 >2 >2 >6 >3 >4 >7 >2 3 4 >3 >2 6 >3 7 4 >5 >5 >3 .f >2 >4 >2 >2 >2 >2 >2 >3 3 <0.04 .1 <.04 .05 .03 <.05 <.03 <.04 <.3 <.03 .06 .08 >4 .05 .04 .07 >2 <.08 .07 .04 >7 .1 .04 .04 >2 .05 .09 .1 >3 .07 .09 .08 >2 >3 >2 <.07 <.03 <.06 <.03 <.03 <.03 <.04 <.03 <.03 <.06 <.03 <.05 .07 <.07 <.03 <.03 <.03 <.03 <.05 <.09 <.06 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.03 <.04 <.03 <.05 <.03 <.03 <.04 <.03 <.03 <.03 <.03 <.03 <0.05 .3 <.06 <.04 <.03 <.03 <.03 <.04 <.04 <.03 <.03 <.03 .09 <.03 <.03 <.03 <.03 <.05 <.03 <.03 <.03 <.03 <.05 <.03 <.03 23 Table C-2.— Results of semiquantitative emission spectrographic analyses' of rock samples— Continued Sam- ppm^ pet pie As B Ba Be Cr Cu Ni Pb Sb Zn Zr Fe Li Mg Mn Ti 100 ... 101 ... 103 ... 105 .. . 106 ... <400 <200 <200 <90 <90 <60 200 100 <80 90 50 80 70 40 30 10 30 30 100 30 <6 60 20 10 30 <6 9 <6 <6 30 <2 <10 <3 <7 <6 300 100 2,000 <60 200 < 1,000 <900 <700 <600 < 1,000 500 200 900 800 500 <30 <30 <30 <30 <30 7 7 6 5 7 >.06 .03 .02 >.04 .02 .05 .02 .02 .01 .01 >4 >2 >3 .9 >2 <.03 <.03 <.03 <.03 <.03 107 .. . 108 ... 109 ... 110 ... 111 ... <90 <90 400 <100 400 90 <80 100 90 <80 <20 30 100 100 30 10 30 60 200 30 30 30 70 30 6 <6 <6 <6 <6 <6 10 <7 <10 <6 <9 <70 100 200 100 200 <600 < 1,000 < 1,000 < 1,000 < 1,000 800 700 500 800 2,000 <30 <30 <30 <30 <30 6 6 6 7 8 >.07 .03 >.1 >.1 >.05 .01 .009 .03 .05 .02 >2 >2 >2 >3 >2 <.03 <.03 <.03 <.03 <.03 112 ... 113 ... 114 ... 115 ... 116 ... <100 400 300 <200 <200 <80 <30 <70 100 <30 40 200 60 100 100 30 > 1,000 70 50 20 50 30 20 40 <7 <6 70 c6 <6 40 <2 <30 <4 <3 <20 1,000 5,000 400 500 2,000 <900 <900 <900 <900 < 1,000 2,000 3,000 2,000 800 2,000 <30 <30 <30 <30 <30 5 7 8 7 7 .02 .02 >.2 >.1 .02 .03 .03 .03 .01 .02 >3 >4 >3 >3 >5 <.03 <.03 <.03 <.03 <.03 117 ... 118 ... 119 ... 120 .. . 121 ... 200 <100 300 <200 <200 <50 90 <50 100 <200 30 40 <20 50 30 10 8 < 2,000 10 > 3,000 20 80 30 60 <3 <6 <6 <6 40 200 <5 <8 <8 9 <80 <20 <40 <20 60 2,000 <600 <800 1,000 <600 < 2,000 600 200 400 60 5,000 <30 40 <30 <30 <30 6 7 8 4 10 >.05 >.3 >.5 >.2 >.09 .02 .01 .03 .02 <.005 .5 .4 .4 .2 >10 <.03 <.03 <.03 <.03 <.03 122 ... 123 ... 124 ... 125 .. . 126 .. . <200 <90 600 400 <90 100 1,000 100 <80 <80 100 20 100 200 30 30 30 20 10 10 50 60 50 50 20 200 200 <6 40 <6 <9 <7 30 40 <3 300 <40 <50 1,000 <80 < 1,000 <600 800 1,000 <600 700 300 200 1,000 700 <30 <30 <30 <30 <30 7 3 5 6 4 >.1 .01 >.09 .04 .04 .1 .04 .03 .04 02 >?. 2 .3 7 .8 <.03 <.03 <.03 <.03 <.03 127 ... 128 .. . 129 .. . 130 .. . 131 ... <90 <200 <90 <200 <90 <30 <30 <60 100 <30 <20 50 20 50 40 <1 5 20 20 5 <3 30 10 50 10 70,000 80,000 2,000 70 200 50 <8 <20 <20 <20 6,000 9,000 4,000 500 3,000 <600 < 1,000 < 3,000 <600 < 1,000 3,000 2,000 1,000 700 400 <30 <30 <30 <30 <30 8 9 8 6 9 <.002 .01 >.08 >.1 >.05 .007 .04 .05 .05 .2 >2 >3 >6 >3 >5 <.03 >.04 <.03 <.03 <.03 132 ... 133 .. . 134 .. . 135 .. . 136 .. . <200 400 400 300 300 200 200 200 200 200 50 60 80 60 50 30 200 100 70 50 40 90 60 50 60 10 40 40 <6 60 10 20 10 10 20 <40 100 <80 <50 100 <600 <600 <600 <600 <600 80 40 20 70 300 <30 <30 <30 <30 <30 3 4 4 3 6 >.2 >.3 >.1 >.1 >.3 .07 .05 .05 .05 .06 .1 .1 .1 .1 .9 <.03 <.03 <.04 <.03 <.03 137 ... 138 .. . 139 .. . 140 .. . 141 ... <90 6,000 300 <100 <90 200 <100 400 500 100 <20 40 50 <20 <20 6 40 20 10 20 40 20 90 90 30 20 70 <6 <6 <6 10 20 9 10 8 <20 100 <50 <20 <20 <600 <600 <600 <600 <600 100 1,000 90 70 70 <30 <30 <30 <30 <30 5 6 3 5 4 >0.4 >.3 >.1 >.2 >.3 0.05 .03 .02 .02 .007 0.6 .6 .1 .2 .2 <0.03 <.03 <.03 <.03 <.03 142 .. . 143 ... 144 .. . 145 .. . 146 ... <200 <200 <200 <90 <100 100 300 2,000 500 100 <20 <20 <20 <20 100 20 100 30 400 50 40 50 20 60 50 <6 30 <6 40 <6 7 20 9 40 10 <20 <60 <20 <50 <30 <600 <600 <600 < 1,000 <600 20 200 100 200 100 <30 <30 <30 <30 <30 3 6 4 6 5 >.09 >.1 >.2 >.1 >.3 .004 .03 .002 .04 .1 .08 .7 .2 .9 .5 <.03 <.03 <.03 <.03 <.05 147 ... 148 ... 149 ... 151 ... 152 .. . 400 500 600 4,000 700 <70 100 100 9,000 100 40 40 80 50 60 100 70 20 > 3,000 30 20 60 20 <3 30 <6 <6 <6 30 40 <4 10 40 <2 20 <60 80 <70 <20 300 <900 <600 2,000 <600 3,000 9,000 300 40 <1 200 <30 <30 <30 <30 <30 8 4 3 .002 4 >.06 >.03 .02 <.002 >.5 .04 .02 .01 .002 .02 >2 2 .2 ND .4 <.03 <.03 <.03 <.03 <.03 153 .. . 154 ... 155 .. . 156 ... 157 .. . 500 <200 400 300 300 100 100 100 90 <80 20 <20 70 100 <20 20 20 20 30 9 50 10 20 <5 20 10 20 <6 7 <6 20 50 20 70 30 <40 200 <30 90 <20 1,000 7,000 3,000 6,000 3,000 50 700 200 500 500 <30 <30 <30 <30 <30 3 5 4 5 4 >.5 >.03 >.3 >.09 .008 .01 .02 .03 .04 .007 .2 <2 .5 >2 .3 <.03 <.03 <.03 <.03 <.03 158 .. . 159 .. . 160 .. . 161 ... 162 .. . 300 400 300 300 300 100 100 100 100 90 <20 100 30 <20 <20 20 600 20 200 20 10 20 30 20 20 <6 30 40 100 <6 40 60 40 70 40 200 800 2,000 1,000 100 5,000 7,000 3,000 7,000 5,000 400 900 2,000 3,000 400 <30 <30 <30 <30 <30 5 6 5 6 5 >.08 >.94 .03 >.06 >.2 .007 .02 .03 >.03 .01 .6 >2 >3 >2 .5 <.03 <.03 <.03 <.03 <.03 163 ... 164 ... 165 .. . 166 ... 167 ... <90 300 300 300 400 <100 90 100 <70 90 20 30 20 80 50 100 50 30 10 10 <8 20 20 20 30 100 <6 20 50 <6 30 30 20 20 20 6,000 90 60 1,000 <20 5,000 2,000 3,000 1,000 1,000 4,000 300 800 400 70 <30 <30 <30 <30 <30 6 5 4 4 3 >.05 >.2 .01 .006 >.1 .02 .009 .02 .009 .003 >7 .6 .4 .9 .08 <.03 <.03 <.03 <.03 <.03 168 ... 169 .. . 170 .. . 171 ... 172 .. . 300 400 300 400 400 <80 100 <80 90 80 <20 <20 <20 60 60 8 40 10 8 90 20 50 20 50 30 10 <6 <6 <6 <6 20 20 20 20 50 1,000 <20 <20 <20 <50 300 <600 < 1,000 1,000 2,000 300 20 100 200 200 <30 <30 <30 <30 <30 3 4 4 4 5 <.002 >.2 >.3 >.2 >.1 .002 .003 .005 .02 .05 .3 .09 .1 .1 .2 <.03 <.03 <.03 <.03 <.03 173 .. . 174 .. . 175 .. . 176 .. . 177 .. . 400 <100 400 300 400 <60 <30 <70 <70 <50 60 80 40 50 200 <3 10 c 1C 200 60 <3 40 40 20 <6 200 <6 <6 <6 40 100 60 20 20 300 300 <40 <20 1,000 <700 < 3,000 2,000 900 <600 500 1,000 500 200 1,000 <30 <30 <30 <30 <30 4 10 6 4 3 >.1 >.3 >.08 >.2 <.004 .03 .1 .05 .02 .02 .6 >7 .5 .1 .5 <.03 <.03 <.03 <.03 <.03 178 .. . 179 .. . 180 ... 181 ... 182 .. . 183 ... 400 <100 <200 <200 <90 90 <80 100 90 100 <70 <60 200 30 40 <20 <20 100 10 10 100 20 10 8 50 40 50 30 10 10 40 30 90 100 10 70 40 20 20 10 <2 <20 1,000 200 200 <60 500 900 1,000 <600 <600 <600 <700 <800 1,000 800 600 100 1,000 800 <30 <30 <30 <30 <30 <30 6 5 6 4 5 8 >.04 >.09 >.2 >.2 >.04 >.09 .04 .02 .06 .07 .02 .07 .7 >2 >3 .2 >2 >3 <.03 <.03 <.03 <.03 <.03 <.04 ND Not detected. 'Au, Cd, Co, Ga, Mo, P, Pd, Pt, Sc, Ta, 'Originally reported In percent V, and Y sought but not detected. NOTE.— No data available for samples 65 through 70, other gaps in sample numbers correspond to samples listed in table 1 of the main text or table A-1 of appendix A. 24 APPENDIX D.— RESULTS OF ANALYSES AND CALCULATED TIN GRADES OF PLACER SAMPLES COLLECTED ALONG NORTH FORK PREACHER CREEK Analysis, ppm Ta Sample Cb Ce Sn A 69 3,500 5,400 B 68 3,100 5,100 C 76 3,900 6,700 D 110 6,200 14,000 E 150 9,700 16,000 F 110 7,000 11,600 I 150 > 10,000 ^2.67 J 120 6,200 20,000 K 150 > 10,000 V.25 L I > 10,000 ^6.54 N I > 10,000 9,800 O 16 445 750 P I > 10,000 10,000 Q 120 8,700 14,000 R I 9,800 6,300 S I > 10,000 2,900 U 180 NA '1.75 V I > 10,000 7,800 W 135 9,600 M.87 X 67 3,300 8,300 Y I 8,100 2,100 Z I 915 400 DD NAp NAp M.80 NAp W Weight, Volume, Sn grade, g yd' Ib/yd^ Remarks 7 340 310 20.24 0.375 0.0006 8 430 300 18.63 .247 .0008 LD 520 355 20.45 .175 .0017 12 945 530 16.25 .225 .0022 14 1,395 '750 17.81 .225 .0028 23 900 625 19.81 .384 0013 37 1,350 '1,000 19.39 1.00 .0011 33 1,125 510 18.99 ^50 .0017 50 > 2,000 885 19.39 1.00 .0031 42 > 2,000 1,135 20.49 .388 .0076 24 >1,170 1,265 16.97 .150 .0024 LD 25 67 19.03 .150 .0002 26 > 2,000 1,150 18.68 .188 .0022 11 11 34 LD 1,550 1,530 540 1,470 '750 1,270 3,055 NA 18.65 12.24 25.8 16.39 .125 .175 .200 .180 .0046 .0014 .0004 .0050 20 1,395 2,310 18.62 .175 .0016 23 > 2,000 600 20.59 .213 .0094 9 1,800 225 19.63 .200 .0019 10 1,125 1,320 18.27 .150 .0006 9 50 '200 29.7 .050 .0003 Ap NAp NAp 29.70 .080 .0400 10-ft-high cutbank in older out- wash. Possibly slumped, older out- wash. 5-ft-high cutbank, older out- wash(?), or possibly recent stream channel. 5 ft of gravels beneath approx. 15 ft of muck, older outwash. 3 ft of gravels beneath approx. 15 ft of muck, older outwash. 3-ft-high cutbank In older out- wash. 3-ft-high cutbank in recent gravels. Concentrated with jig- 3-ft-cutbank in recent stream gravel bar. Concentrated with jig- 3-ft-high cutbank in older(?) outwash. Sampling of tailings indicate this sample prob- ably only represents 62 pet recovery. Concentrated with jig- 12-ft-high exposure of gravels, probably remnant of older outwash. Either older outwash or recent stream gravels. Gravel bar in recent active stream gravels. 3-ft-high cutbank in more recent outwash. Do. Do. Cutbank in fan gravels. Recent gravels concentrated with 5-ft long sluice box. Lateral moraine(?), 10-ft-high- cutbank (older than recent outwash). 5-ft-high cutbank in more recent outwash. Probably a poor sample. 2-ft-high cutbank in more recent outwash. Probably a poor sample. Base of 1 5-ft-high cutbank in recent outwash gravels(?). Probably large dilution from colluvium. 2-ft cutbank in alluvial fan(?) gravel. Small alluvial (outwash?) gravel bench. Sample concen- trated with 5-ft-long sluice box. I Not detected because of interference with Zr. 'Interference noted because of Zr. 'Percent. 'Approximate only. LD Less than detection limit. NA Not analyzed. NAp Not applicable. U.S. GOVERNMENT PRINTING OFFICE: 1988 — 547-000/80,012 INT.-BU.OF MINES,PGH.,PA. 28695 /V «7 O C U.S. Department of the Interior Bureau of Mines— Prod, and Distr. Cochrans Mill Road P.O. Box 18070 Pittsburgh. Pa. 15236 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. S300 I I Do not wish to receive this material, please remove from your mailing list. I I Address change. 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