I TN295 III No. 9105 To ">' ,V ^^c,^' 0^ -o /./^X^>^^^'^^'^ -^ .^ ^0^ o • . .*''^. ^'S.'^Py^ "v^Py^ X'^Py*^ "v^*V^''' X'^'^V^ X-^- .0 ^ •" A.* .. "^ „-^^\'"" <> *' .. 1^ » A 9^ -..,^.^ \."f.^^,^'^ %-^^\o^^ \^'f>J\^^ ^ -!^R-.^^ '^^^ v^^- . ^°^i'^'> .//^iX ^°^^^'> y^-^iX ^^*' -^^ ,*1°^ ' \<^^ » » » • A Oritl-iBin* ortot - fin btoring Protptctttf ortat - lln in4ieot(4 by cburn drilling an4 proiptct thofi ' J Columblum-baarlng ragollth I 2 V Hot Spring! Oonp Scalp, milti Figure 3. — Totty tin belt, Alaslca. In 1956, the Bureau, in an attempt to locate lode sources of the placer minerals, trenched on upper Idaho Gulch and identified two bodies of radioactive ferruginous regolith (figs. 2-3). Subsequent detailed sampling and diamond drilling defined two northwest-dipping, north- east-striking lenses of material containing trace amounts of columbium, phosphorus, and zirconium, among other metals, but no uranium, which was the principal interest of its study. The results of the lode investigations on Idaho Gulch were never published, but are partially incorpo- rated in this report. In 1984, as part of a current Bureau project to investigate critical and strategic minerals in Alaska, Southworth {12) reanalyzed concentrates from channel samples of tailings collected in 1956 by Thomas, for columbium. Southworth found that most samples con- tained between 0.2 pet and 4.5 pet Cb with higher values generally in gravels from the vicinity of Deep Creek, Miller Gulch, and Idaho Gulch. Using placer reserve figures from Thomas (9) and Wayland (8), Southworth calculated an inferred reserve of 100,000 lb Cb20-, within the Tofty placer deposits. BEDROCK GEOLOGY OF THE TOFTY AREA Bedrock outcrops in the Tofty area are rare; most geologic observations have been limited to now- inaccessible drift-mine exposures and sparse road cuts or inferred from placer cobble lithologies. In general, however, much of the area is underlain by a succession of graywacke, quartzite, siltstone, shale, slate, slaty argil- lite, and polymictic comglomerate that has been inter- preted as being a portion of a Mesozoic-age flysch basin that extends approximately 150 miles northeastward from the Tanana River to north of Livengood (13-16). These rocks exhibit local low grade (zeolite facies) metamorph- ism and severe deformation (17). Roadcut and trench exposures near Tofty and on Idaho Gulch show that bedding strikes east-northeast and dips moderately to steeply northwest; however, small hand-specimen to outcrop scale isoclinal folds are locally common. Minor amounts of serpentinized and chloritized ultramafic and mafic rock with locally associated graphi- tic slaty to schistose rock are exposed along the northwest margin of the flysch basin (13). These rocks may have either been tectonically emplaced or partially intruded within the basal flysch unit. Alternatively, some of the ultramafic, mafic, and metasedimentary rocks may under- lie the flysch and be exposed in erosional windows. Magnetite-apatite bearing limestone, similar to that identified on upper Idaho Gulch in this report, is described by Wayland on Harter Gulch (8). The relationship of this rock to other units is unknown; carbonate rocks are not reported elsewhere within the flysch belt. The Mesozoic flysch is cut by two intrusions in the Tofty area. A biotite granite pluton with local felsic segregations and associated tourmaline crops out on Hot Springs Dome, southeast of Tofty, and a monzonite and quartz-monozonite composite pluton crops out on Rough- top Mountain, northeast of Tofty (fig. 3). The intrusion on Roughtop Mountain shows a Late Cretaceous radiometric age of 92 ± 10 million yr, the intrusion on Hot Springs Dome has an early Tertiary radiometric are of 62 ± 3 million yr (13). NATURE AND EXTENT OF PRESENT INVESTIGATIONS During this investigation, data from nine trenches and nine diamond drill holes compiled by the Bureau in 1956 were reevaluated. The reevaluation comprised reanalyses of available samples, selective reexcavation of the trenches, and relogging of available core. Information resulting from the 1956 investigation is presented and acknowledged where appropriate. Figure 4 shows loca- tions of trenches and drill holes and mapped extent of the regolith. Modified 1956 drill logs and geologic cross sections constructed from drill data are presented in appendix A. Additional methods used during this study include selective sampling of the 1956 trenches; optical, radiomet- ric, scanning electron microscope (SEM), microprobe, and X-ray diffraction (XRD) studies of mineral compositions; and magnetic, radiometric, and soil sampling surveys over a 500- by 1,900-ft grid area (outlined on figure 4). no 200 1 1 1 T-l « > LEGEND Tronch and dump Scala.fMt Contour Innrvol 20 (Mt / 1 1 Ragollth / •0-S DKXTKXKl drill hoi* / Figure 4.— Locations of trenches and drill holes and mapped extent of the regolith. GEOLOGY OF THE REGOLITH Two bodies of iron-rich regolith were identified on upper Idaho Gulch by Bureau trenching in 1956. Subsequent drilling indicated the regolith forms conform- able lenses within the N 60° E trending wallrock units. The lenses grade downward into, and apparently have been derived by chemical weathering of dolomitic marble (figs. A-1 — A-6). In plan view, both lenses are irregular in shape, varying in thickness from 3 to 80 ft. The northwestern lens is partially exposed by trenching over a strike length of 620 ft and dips approximately 50° to the northwest (fig. A-6). The southeastern lens is partially exposed over about 350 ft of strike length and dips between 40° and 50° northwest (figs. A-1— A-4). In 1956, both lenses were mapped as pinching out to the southwest, but open ended to the northeast (fig. 4). Cross sections in figures A-1 through A-5 show that the southeastern regolith lens ranges in thickness from 17 to 28 ft, averaging 23 ft at trench T-8, and persists downdip for between 100 and 250 ft. The regohth, where intersected approximately 100 ft downdip in drill holes D-9, D-1, and D-6, has true thicknesses of 12, 16, and 23 ft, respectively. The increase in drill-intersected thicknesses suggests that the southeastern regolith lens may be thicker and extend deeper northeast of the trenches and diamond drill holes. The northwestern regolith lens is approximately 31 ft thick at trench T-6 but is of unknown thickness at distances less than 200 ft downdip (fig. A-6). Where intersected at 200 ft downdip in drill hole D-3, the northwestern regolith lens consists of thin, discontinuous zones in dolomitic marble. The footwall of the regolith grades into marble at distances of as little as 50 ft downdip in some drill holes; the regolith is generally absent at distances greater than 200 ft downdip (figs. A-3 and A-6). Because both the hanging wall and footwall were only observed in drill hole D-3, the attitude and shape of the marble body is unknown. The marble consists of coarse, granular ankeritic (composition determined by XRD analysis) dolomite and calcite with up to 10 pet disseminated and banded rounded magnetite and euhdral to rounded pyrite grains and up to 5 pet disseminated rounded apatite crystals. In this rock, pyrite commonly replaces magnetite. Minor amounts of biotite, some of which is partially replaced by chlorite, are also present and a trace amount of zircon occurs. Drilling and trenching indicate the regolith and marble occur within a succession of probable intermediate grade (greenschist facies) metasedimentary and metaig- neous(?) rocks consisting of variable amounts of quartz, muscovite, sericite, chlorite, and graphite and locally minor amounts of talc, serpentine, dolomite, calcite, magnetite, or pyrite. Lack of outcrop and poor core recovery from drilling preclude detailed correlations between the various rock types. In general, however, the footwalls and lower few feet of the hanging walls of both regolith lenses consist of calcareous chlorite-sericite ± talc ± quartz phyllite and schist and the section of hanging wall beginning a few feet above each lens consists of siliceous muscovite-graphite schist (cross sections A-2, A-3, and A-5 through A-7, appendix A). The footwall of the regolith lens in drill hole D-7 consists of a nonfoliated chlorite-sericite-quartz rock that may represent a meta- morphosed mafic igneous rock. MINERALOGY AND PETROGRAPHY OF THE REGOLITH Most of the regolith consists of a moderate amount of pebble- to cobble-size rock fragments in a dark chocolate brown to brownish orange earthy matrix composed largely of sooty and specular hematite, exotic limonite, small fragments of limonitic boxworks after pyrite, goethite, and hematitic magnetite. The most common rock type consists of a dark red spongelike matrix of siliceous hematite with up to 40 pet rounded to angular 0.5- to 2-mm apatite grains and trace amounts of euhedral zircon crystals. Cross-cutting vein- lets of goethite and chalcedony and patches of limonitic boxworks after pyrite are also common. This hematite- rich rock grades into a less common, more siliceous rock consisting of up to 40 pet euhedral to broken subhedral and finer rounded apatite and irregularly shaped hemati- tic magnetite grains with minor euhedral to angular zircon crystals or fragments in a matrix of iron-stained finely crystalline quartz. Rounded grains of carbonate, chert, and chlorite schist (?) also occur as inclusions in this rock. Other rocks found in the regolith include massive vuggy goethite and yellowish-orange porous limonite within which are rounded fragments of kaolinitized phyllite(?) and veinlets of goethite, hematite, quartz, chalcedony, carbonate, and apatite. Near its wallroek contacts, the regolith is more yellow-orange in color and is composed mostly of limonitic clay. Secondary(?) apatite occurs as bluish gray to white botryoidal masses along fractures in fragments of earthy, porous limonite in these areas. An apple-green clay containing a chromiferous member of the montmorilli- nite-beidellite series and possible traces of anatase' is associated with limonitic kaolinite in the footwall of the southeastern regolith lens in trench T-8. Geochemical, radiometric, optical microscope, micro- probe, and SEM examination of the minus 20-mesh fraction of concentrates panned from regolith samples** indicate the regolith also contains trace to minor amounts of apatite, zircon, monazite, xenotime, brewsterite(?), columbium-bearing rutile, which may locally alter to ilmenorutile, and the columbium minerals aeschynite and columbite. Results of analyses of concentrate samples are presented in table 1, and ranges of mineral content in samples are listed in table 2. Apatite occurs as fine bluish-white grains with a composition (determined by XRD analysis) intermediate between the hydroxyl "Identification of anatase and clay minerals in 1956 by H. D. Hess, formerly of the Bureau of Mines, Albany, OR. "A test procedure for characterization of the Tofty regolith concentrates is described in appendix B. Table 1. — Results of analyses' of samples of pan-concentrated regolith, parts per million Sample^ Cb Sn Ta Ce La Nd Y Description 5 9 15 30 5,700 9,000 100 300 <50 <50 <50 <50 <100 100 <100 <100 1,000 1,000 ND ND 400 400 ND 200 <500 <500 ND ND <10 20 <10 ND Heaping pan reduced to 10.6 g. Heaping pan reduced to 29.4 g. Heaping pan reduced to 20.4 g. 2 heaping pans reduced to 34.7 g. ND Not detected. 'Cb, Sn, and Ta analyses by X-ray fluorescence; Ce, La, Nd, and Y analyses by emission spectrography (other rare-earth elements not detected). Analyses by the Bureau's Reno Research Center, Reno, NV. ^Samples are numbered clockwise starting with trench T-2. Gaps between sample numbers listed here correspond to samples listed in tables 3 and 4. Figure 5. — Scanning electron microscope photomicrograph (A) and columbium X-ray scan (B) of cotumbium-rlch portion of regolith concentrate. Table 2. — Estimated ranges for mineral content in minus 20-mesh fraction of samples of pan-concentrated regolith,' weight percent Mineral Goethite 30-40 Quartz 11-16 Aeschynite 7-9 Magnetite 8-10 Rutile (Cb-bearing) 4-6 Zircon 6-15 Fe-Mg silicates 1-5 Tr Trace. 'Samples 5. 9, 15, and 30. Mineral Feldspar 1-4 Monazite 2-4 Columbite 2-4 Xenotime Tr Brewsterite (?) Tr Apatite Tr Rock fragments Tr (Ca5(P04)30H) and fluor (Ca5(P04).sF) endmembers of the apatite solid solution series. Although apatite is locally abundant in the regolith, its relatively low specific gravity makes it a rare constituent of the concentrates. Zircon occurs as 0.1- to 0.5-mm, clear euhedral and yellowish subhedral bipyramidal crystals or crystal fragments with poorly developed prism faces. Microanalysis indicates monazite to be of the high-cerium and high-lanthanum and low-yttrium and low-thorium variety and locally intergrown with columbite. An SEM photomicrograph and columbium X-ray scan of the columbium-bearing portion of a regolith concen- trate is shown in figure 5. Aeschynite occurs as dark reddish brown to black, approximately 0.1-mm angular, flattened prismatic orthorhombic crystals with a general composition, based on four analyses, of (Cao ^.-i-o.iu Feo.os- Figure 6. — Scanning electron microscope photomicrograph of broken aeschynite grain from regolith concentrate. 0.46 Ceoo4-n.27 Mno.0.0.3 Bao-o.os Tho.0.14 Ago.0.14* 'Cbo.53-Q.90 Ti(), 10-0.47 '-iOfi- Aeschynite is the bright phase in figure 5A with the less intense columbium signals in figure 5B; a closeup of the aeschynite is shown in figure 6. Columbite is also a bright phase in figure 5A, but has the more intense columbite signals in figure 5B. The columbite is the high-iron, low-manganese variety and has a composi- tion of (Feo.9 Mno.o9 Cao.oi) (Cbo.95 Tio.o5)206- REGOLITH SAMPLING METHODS AND RESULTS In 1984, samples of regolith and specimens of rocks were collected from trenches on upper Idaho Gulch for geochemical analyses. The wider trenches, T-5 and T-8, were mapped and sampled in detail (figs. 7-8). Vegetation cover and sloughing of trench walls prevented detailed mapping and sampling of other trenches; only a few samples were collected from trenches T-2, T-3, and T-4 (fig. 9). LEGEND Hemotiiic regoliih I I Limonjtic regolith r . 1 undifferentioied melosedimentory rocks Geologic conioct; hochured where grodotionol cm Trench C5i6 "'Solith lomple pit # 14 Rock specimen O 15 Concenirote sample Figure 7. — Locations of samples collected in trench T-5. Regolith samples were collected from 3- to 4-ft-deep pits (figs. 7-9). One pit was excavated in each of trenches T-2, T-3, and T-4 and a series of pits were dug in each of trenches T-5 and T-8. A vertical channel sample and a bottom sample were collected from each pit. Regolith samples and rock specimens were crushed, split, pulverized, and analyzed by the Bureau's Reno (NV) Research Center. Regolith samples were analyzed for columbium, phosphate (P20,-,l, zirconium, and zinc by X-ray fluorescence (XRF), tin by atomic absorption (AA), and 42 elements plus rare-earth elements by emission spectrography. Results and methods of analyses are presented in tables 3 and 4 and appendix C. Owing to the sensitivity of the analytical techniques used, some variations exist among the results presented for some individual samples. Samples of regolith collected from pits in trenches T-2, T-3, T-4, T-5, and T-8 contain <50 to 1,200 ppm Cb, 0.14 to 21.4 pet P2O5, <100 to 900 ppm Zr, 200 to 1,200 ppm Zn, and not detected to 900 ppm La (table 3). Low columbium values in samples from the pit in trench T-3 are likely not representative of regolith as their yellow- white color suggests that sloughed bank material was included in the samples. Regolith samples also contain 0.07 to >6 pet Ba, 7 to >10 pet Fe, 0.3 to >10 pet Mn, 3 to 4,000 ppm Sr, 2,000 to 20,000 ppm Ti, 50 to 6,000 ppm Cr, and 100 to 3,000 ppm Ni (appendix C). Relatively higher values of columbium, phosphate, zirconium, lanthanum, and strontium are restricted to samples from pits excavated in the red-brown LEGEND Hematitic regolith Limonitic regolith Undifferentiated meto- sedimentary rocks ^,„. Geologic contoct; hochured where grodotionol C .' .' ^ Trench and dump C2> 22 Regolith sample pit Rock specimen 31 v30 Concentrate sample 25 I 50 J Scole, feet Figure 8. — Locations of samples collected in trench T-8. T-2 / / LEGEND Undifferentiated regolith Undifferentioted metosedi- mentary rockt Geologic contaci Trench and dump Regolith sample pit Rock specimen Concentrate sample Dump sample Figure 9.— Locations of samples collected in trenches T-2, T-3, and T-4. Table 3. — Results of XRF analyses^ of regolith samples, in parts per million except as noted Sample Cb La^ P^Os^ Zr Zn Sample type and/or description TRENCH T-2 1 2- 3" <50 1.000 1,200 NA NA NA 0.19 1.95 2.03 300 800 800 NA NA NA 3-ft channel of dump, material is well mixed and silty. From bottom of pit, hematitic regolith. 3.5-ft vertical channel in sample 2 pit. TRENCH T-3 6" 7" 8 72 <50 <50 NA NA NA NA NA 0.14 NA NA 300 NA NA NA From bottom of pit, includes sloughed bank material, 3-ft vertical channel in sample 6 pit. 3-ft-long, 10-in-deep channel of dump. TRENCH T-4 11 300 600 500 200 400 200 0.82 11.7 7.3 400 700 900 400 600 300 4.5-ft-long, 1-ft-deep channel of dump. From bottom of pit, hematitic regolith. Bulk sample A^ collected from this pit. 3.5-ft vertical channel in sample 12 pit. 12" 13 TRENCH T-5 16 <50 ND 0.17 <100 500 17 <50 ND .26 200 400 18 1,000 900 7.1 900 300 19 700 400 .5 800 300 20 100 ND .8 300 300 TRENCH T-8 22 300 ND 9.0 700 400 23 400 • ND 8.1 700 400 24 500 ND 112 200 600 25 700 200 1 .68 400 500 26 1,000 400 10.4 800 300 27 700 200 10.4 700 400 28 <50 NA .26 300 200 29 <50 NA 94 <100 250 32 300 ND 90 100 1,200 33 400 40 2.60 500 900 34 800 90 1.92 500 1,100 35 900 90 1.79 700 1,100 36 300 400 21 .4 900 300 37 300 200 20.4 900 300 38 <50 ND .79 200 200 39 100 ND 1 .47 200 300 40 58 ND 69 200 400 41 100 ND 1.06 300 500 NA Not analyzed ND Not detected. 'Performed by the Bureau's Reno Research Center, Reno. NV; Sn analyzed by AA, but not detected. ^No other rare-earth elements detected in samples, except sample 36 contains 40 ppm Y Analyses by em; ^Percent. "Samples 2, 3,6,7, and 1 2 also contain 2.083, 2.445, 0.05, 0.06, and 1 07 ppm Au and 1 .431 . 1 .528, 1 6, 4 Ag values at or below detection limit. Au and Ag determined by inductively coupled plasma analyses. ^Head analysis of 0.093 pet Cb. ^Head analysis of 0. 1 20 Cb. From bottom of pit, limonitic regolith. 4-ft vertical channel in sample 16 pit. From bottom of pit, hematitic regolith. Bulk sample B^ collected from this pit. 4-ft vertical channel in sample 18 pit. Sample of clay from adjacent to footwall of limonitic regolith. From bottom of pit, hematitic regolith. 4-ft vertical channel in sample 22 pit. From bottom of pit, hematitic regolith. 3-ft vertical channel in sample 24 pit. From bottom of pit, hematitic regolith. 3-ft vertical channel in sample 26 pit. 1.5-ft channel of limonitic clay-rich regolith. Composite of top 1 ft of sample 28 pit. From bottom of pit, hematitic regolith. 3-ft vertical channel in sample 32 pit. From bottom of pit, hematitic regolith. 3.5-ft vertical channel in sample 34 pit. From bottom of pit, hematitic regolith. 2.5-ft vertical channel in sample 36 pit. From bottom of pit in graphite phyllite. Channel in limonitic clay-rich regolith above sample 38. From bottom of pit. 2.5-ft vertical channel in sample 40 pit. ssion spectrography, Reno Research Center. 0, and 'iO.3 ppm Ag, respectively. All other Au and 10 Table 4. — Results of analyses,' in parts per million, and descriptions of rock specimens Sample Cb Sn Ta Au Ag Ce La Y Description 4 <100 <50 <100 <0.007 <0.3 ND ND ND 10 pet rounded to angular apatite grains within matrix of siliceous iron oxides. Cut by chalcedony veinlets. 10 200 <50 <100 .016 .370 ND ND -10 Grab from dump. Mostly red-brown earthy hematite 14 <100 <50 <100 <,007 <.3 ND ND <10 Orange, limonite-rich clay. Grab sample. 21 1,200 <50 <100 <.007 <.3 ND 400 20 Earthy, hematitic matrix cut by chalcedony veinlets. Representative of rocks in trench T-5. 31 200 <50 <100 <.007 <.3 ND 200 -10 4 pet rounded weathered apatite in a dark red earthy hematitic matrix cut by veinlets of goethite. 42 <100 <50 <100 <.007 <.3 ND 90 20 Dark, angular maroon-colored patches in a punky limonitic matrix. Disseminated magnetite blebs also present. 43 300 <50 <100 <.007 <.3 2,000 900 20 Rounded quartz grains in a weathered limonitic matrix. Cut by veinlets of quartz, carbonate, and secondary apatite. 44 200 <50 <100 <.007 <.3 ND 40 40 Dark-red to orange siliceous iron oxide matrix cut by some veinlets of drusy quartz. 45 700 <50 <100 NA NA ND 200 20 Blebs of limonile and magnetite in an iron-stained siliceous matrix. 46 400 <5 NA 0.007 0.3 <500 90 40 40 pet euhedral to angular subhedral and finer rounded apatite, irregular to rounded magnetite, and minor euhedral zircon in an iron-stained siliceous matrix. 47 200 <5 NA <,007 <.3 <500 90 40 Rounded apatite and hematite-magnetite grains, minor angular zircon crystals, and rare fragments of chert or schist (?) in a matnx of coarse recrystallized quartz and Iron oxides. 48 200 <5 NA .020 894 <500 200 40 Massive fine exotic limonite with rounded 3- to 7-mm fragments of clay after phyllite (?), cut by veinlets of goethite. 49 87 <5 NA <.007 <.3 <500 ND 40 5 pet rounded apatite grains in a punky siliceous hematite matrix cut by veinlets of goethite. 50 <50 9.1 NA <.007 <.3 <500 ND 40 Massive vuggy goethite. NA Not analyzed, ND Not detected. 'Cb and Ta analyses by XRF; Sn by AA (5-ppm detection limit) or XRF (50-ppm detection limit): Au and Ag analyses by inductively coupled plasma analyses. Rare-earth analyses by emission spectrography — only Ce, La, and Y detected except sample 42 also contained 1,000 ppm Nd. Analyses by the Bureau's Reno Research Center, Reno, NV. hematitic regolith whereas a small number of high values of zinc, titanium, barium, chromium, and nickel are present in samples collected from both the hematitic regolith and yellow-orange limonitic regolith. Rock specimen sample locations are also shown in figures 7, 8, and 9. Because specimens were generally collected from float, analyses are interpreted to be representative only of the specimen and not the deposit grade. Ten of fourteen specimens contained between 200 and 1,200 ppm Cb with traces of cerium, lanthanum, yttrium, or silver; three samples contained traces of gold and one sample contained detectable concentrations of tin; no tantalum was detected (table 4). The highest co- lumbium concentration (1,200 ppm) was found in a specimen of earthy hematite cut by chalcedony veinlets. Results of analyses for columbium in channel samples collected in 1956 from trench T-8 are presented in table 5 and sample locations are shown in figure 10. The analyses are in good agreement with those from samples collected from pits in 1984 and generally range between 300 and 700 ppm Cb with one value of 200 ppm and one of 1,000 ppm. Results of columbium analyses in 1956 of sludge samples of regolith from drill holes are presented in table 6. Similar to results of analyses of samples from trenches, between 0,01 and 0.10 pet Cb was detected in all samples. Results of analyses of three composite samples of marble from drill hole D-4 are presented in table 7. Between 257 and 731 ppm Cb as well as elevated concentrations of phosphate, lanthanum, zirconium, and cerium are present in the samples. These columbium concentrations are very similar to those found in samples of regolith. Unfortunately, no other drill core containing marble is available for analyses. Table 5. — Results of XRF analyses' for columbium in channel samples collected from trench T-8 in 1956 Cb, Channel Cb, Channel Sample ppm length, ft Sample ppm length, ft 51 300 8.8 61^ . 700 6.3 52 600 9.5 62 . 400 7.3 53 400 7.0 63 . 300 10.4 54 300 9.3 64 . 300 6.9 55 200 10.0 65 . 300 9.95 56 400 7.4 66 . 400 9.80 57 . 300 7.4 67 . 300 13.00 58 400 5.8 68 . 700 8.80 59 300 7.5 69 400 7.60 60^ 1,000 6.3 'Performed by Bureau's Reno Research Center, Reno, NV, in 1984. ^Analysis by unspecified chemical techniques in 1956. Table 6.— Results of 1956 emission spectrograph ic (S) and chemical (C) analyses' for columbium in sludge samples of regolith Drill hole Interval, ft Cb, pet S C n-1 133.2-138.1 138.1-143.3 6.8- 19.3 70.0- 89.4 0.01-0.10 .01- .10 .01- .10 .01- .10 <0.1 D-7 <.1 <.1 n-Q NA NA Not analyzed. 'Analyses performed by Bureau's Reno Research Center, Reno, NV. Table 7.— Results of analyses' of composite samples of marble from drill hole D-4, parts per million except as noted Sample Interval, ft PaOs^ Cb La Zr Y Ce 70 71 72 174-196 196-225 225-245 1.32 1.86 2.74 257 731 416 327 219 927 653 190 277 21 21 26 529 373 1472 'P2O5 analyzed by emission spectrography, other elements by XRF; performed by Bondar-Clegg, Lakewood, CO. ^Percent. 11 LEGEND C. ; ; j^ Trench and dunnp I 53 Channel sample 25 50 Scale, feet Figure 10. — Locations of 1956 channel samples in trench T-8. INTERPRETATION The average grade of the hematitic regolith on upper Idaho Gulch is probably between 0.04 and 0.07 pet Cb. Channel samples from trench T-8 contain from 200 to 1,000 ppm Cb. The weighted average of those values is 0.04 pet Cb over 160 ft comprising six channel samples with lengths varying from 19.9 to 39.2 ft. Sixteen of eighteen samples collected from pits in the hematite-rich portions of the regolith contain between 300 and 1.200 ppm Cb and average approximately 725 ppm Cb; 12 of these samples contain columbium in excess of or equal to 500 ppm. Spectrographic and chemical analyses per- formed in 1956 also show between 0.01 and 0.10 pet Cb in drill hole sludge samples of regolith. Columbium values similar to those in the hematitic regolith samples are also present in samples of marble. In contrast, five of nine samples collected from pits in clay-rich limonitic regolith contain less than 50 ppm Cb and the remaining four samples contain from 50 to 100 ppm Cb. The presence of columbium and the mineralogic similarities between rock specimens and regolith suggest that the specimens are essentially undecomposed or silicified equivalents of the regolith. Many of these rocks fit the description of "boulders of cellular iron-stained apatite-rich material" at Magnet Cove, AR, which is a well-studied, columbium-bearing carbonatite deposit (18, p. 43). At Magnet Cove, rocks with mineralogy and fabric similar to those in the regolith on Idaho Gulch grade downward into a magnetite-apatite-perovskite-bearing marble that contains approximately 300 to 400 ppm Cb. These values are very similar to those found in the marble on Idaho Gulch (table 7). 12 MAGNETIC, RADIOMETRIC, AND SOIL SAMPLE SURVEYS ON UPPER IDAHO GULCH METHODS AND RESULTS Magnetic, radiometric, and soil sample surveys were conducted over the area known, or projected, to overlie ferruginous regolith on upper Idaho Gulch (fig. 4). Magnetic and radiometric measurements were taken at 25-ft intervals on 17 northwest-trending 500- to 900-ft- long lines spaced 100 to 200 ft apart. Soil samples were collected at 25-ft intervals on seven 500-ft-long lines spaced 200 ft apart. Survey lines are oriented N 30 W, perpendicular to the trend of the regolith lenses. Figures 11, 12, and 13 are contour maps showing the results of the three surveys. Results are also tabulated in appendix D. The magnetic survey was performed using a Geomet- ries UniMag 11, model G-846 portable proton magnetometer. ' Measurements were corrected for diurnal variations with time-variation graphs constructed from repeated measurements at a single station. All measure- ments were taken facing N 30 W, perpendicular to the strike of the regolith lenses. High concentrations of magnetite in the regolith produce strong positive magnetic responses. At intensities above 56,600 gammas, two 1,200-ft-long, N 60 E-trending areas, which merge to the southwest, are defined (fig. 11 ). Magnetic profiles are generally asymmetric, with steep positive slopes to the southeast and gentle negative slopes to the northwest. Peak magnetic intensities are offset to the northwest of the regolith, correlating with the northerly dip of the lenses. Total-count gamma-ray radiation was measured using a Scintrex model G15-5 gamma-ray spectrometer. Measurements were taken at hip level over 10-s intervals. Trace amounts of radioactive minerals, including zircon, monazite, apatite, and aeschynite, in the regolith produce radiation measurements between 100 and 250 cps in trenched areas (fig. 12). Two larger irregularly shaped northeast-trending and six other smaller areas with higher radiation values were delineated. Soil samples were collected at depths of 2.5 to 3.0 ft with a hand auger. Approximately 0.5 lb of sample material was placed in a paper envelope, dried, and screened to minus 80 mesh. Samples were analyzed by the Bureau's Reno (NV) Research Center for columbium, P2O5, and zinc by X-ray fluorescence. Most soil samples consisted of gray-brown, clay-rich silt, but some also contained limonite and rock fragments and were yellow-orange to red. Organic contents of ^Reference to specific products does not imply endorsement by the Bureau of Mines. samples ranged widely, but generally were low. Much of the soil in the surveyed area is windblown silt without a developed profile, however some of the samples containing rock chips or hematite staining may contain residual material derived from bedrock. Drilling and a test pit at the midpoint of soil sample line 10,000 NE show that the silt ranges from 3 to 9 ft and averages approximately 5 ft in thickness. The presence of rare bedrock outcrops near Idaho Gulch suggests that the silt cover thickens away from the gulch. The large concentrations of apatite in the regolith are reflected by soil samples with anomalously high P2O5 concentrations. P2O5 soil values above a threshold of 0.3 pet define two 25- to 125-ft-wide anomalous areas that are coincident with and extend beyond the known extent of the regolith (fig. 13). In contrast to P2O5 concentrations, anomalously large columbium or zinc concentrations were limited to samples that were collected either from trenched areas or that contained iron-stained material derived from buried regolith. Five of seven detected columbium values occur within samples collected from regolith exposed in tren- ches; the other two samples were noteworthy for their orange-red color. Zinc values above 240 ppm also are limited to samples collected from trenched areas or that contain iron-staining derived from regolith. INTERPRETATION The magnetic, radiometric, and soil sample surveys produced complementary results indicating that the two regolith lenses extend along strike for approximately 1,200 ft. The two lenses may join to the southwest. Asymmetric magnetic responses offset from the surface expression of the regolith suggest a moderate to steep northwest dip of the two lenses. Comparison of the data indicates that soil P2O5 concentrations define the area underlain by regolith better than does radiation, but neither defines the extent of the regolith as well as its magnetic signature. Higher radioactivity is generally restricted to exposed portions of the regolith. It is likely that away from the trenched areas and Idaho Gulch, all three surveys were seriously hindered in detecting the regolith by the greater thicknesses of silt cover. There is good probability that the lenses may continue undetected along strike, especially to the northeast. \ 13 3N006II \ / 3N00ei I 3N00ZI I BNooeo 3N0080I 3N0(U0I 3N 00901 S" 3N00C0I 3N00ZOI o 3 a o n a Q. 3 c o n 0) XI V >. > 3 W 0) c O) ra E ■o M a> cc I 3 v 3N00S6 3N0096 14 \ \ \ BNOOeil A» 3N0OZI I Ida ho Gulc h / 8-, i-i 3N00III £ o 3 C5 o 3N000I 1 £ € •^ w 0) Q. 3N0060I Q. 3 C O a S^ 3N0090I n T3 » >• > 3 W 3Noatoi c £ 3N 00901 5 >. > «rf 3N00S0I !^ o ■^ ■o 10 ^ >> 3N00M)I ra h- cb E E 3N00E0I n ^tf c 3 O u 3N0OZ0I ^ a o ^ 3N0OI0I 1 ^ 0) w 3 O) 3N0000I U. SNooee 3N0096 \ 3N005II \ 15 / 3N00£I 1 3N00ZII U 3 o o 3N00I II 2 a. 3N000I 1 a. 3 C O 3N0060I m 3N0O80I ■D 3 (0 3N00Z0I c o 3N 00901 c w c o 3N00S0I 3N00K)I (0 c a> o c o u o: a. 3N00E0I ■o c n 3N00Z0I d c N E 3 2 3N00I0I E 3 O u 1 3N00C0I 1 CO T- s 3 o> 8-:- 16 COLUMBIUM RESOURCES Approximately 340.000 lb of indicated and inferred columbium resources are present within the known and inferred extent of the regolith lenses on uper Idaho Gulch. According to standard guidelines, set by Bureau of Mines and U.S. Geological Survey il9), this columbium compris- es approximately 30,000 lb of indicated and approximate- ly 310,000 lb of inferred resources. The indicated resource comprises that portion of the southeastern regolith lens exposed in trench T-8 and intersected in drill holes D-1. D-2, D-3, D-6, D-7, and D-8. Drill hole intersections show that this lens decreases from an average thickness of 23 ft at the surface to an approximate average of 17 ft at 100 ft downdip. Given the 6.900 ft- surface area and 40" north dip of the hematitic regolith in trench T-8. and assuming that the average thickness decreases by 50 pet at 150 ft downdip. the volume of hematitic regolith represented by that exposed in trench T-8 is approximately 500,000 ft". At a measured' tonnage factor of 23.5 ft st and a minimum grade of 0.07 pet Cb," a minimum of approximately 30,000 lb of indicated resource is present. The inferred columbium resource comprises the remaining known or projected regolith. The average '"Tonnage factor determined on dried, compacted material: all analyses are also on a dry basis. "The average grade was determined previously in the text to be between 0.04 and 0.07 pet Cb. Head analyses of 0.12 and 0.093 pet Cb on two 200-lb samples of the regolith suggest the higher value may be more accurate. apparent thickness, as measured in trenches, over the remaining 2,200 ft of strike length is approximately 50 ft. Subtracting 40 pet of this to account for an approximate average amount of unmineralized limonitic regolith, and given an approximately 45° northerly dip of the regolith lenses, the average true thickness is 22 ft. Assuming a weathering pattern similar to that in trench T-8 where the regolith decreases in thickness by 50 pet at 150 ft downdip, then the volume of inferred hematitic regolith is approximately 5.25 million ft'. At a tonnage factor of 23.5 and a grade of 0.07 pet Cb, a minimum of approximately 310,000 lb of inferred columbium resource is present. The regolith also contains zirconium and P2O5 resources. Seven of eight 1984 channel samples collected in pits contain 700 to 900 ppm Zr (table 3). At an average concentration of approximately 0.07 pet Zr and a total regolith tonnage of approximately 245,000 st, an inferred zirconium resource is approximately 340,000 lb. P2O5 values in the same eight samples range from 0.5 to 20.4 pet. The average of these values is 6.5 pet P2O5; discounting the high and low values, the average is 5.2 pet FoO.T. At a concentration of 5 pet P2O5 and a total regolith tonnage of 245,000 st, an inferred P2O5 resource is approximately 12,250 st. Good potential also exists for large additional resources of columbium in the dolomitie marble under- lying the regolith. At an average grade similar to that of the regolith, the marble may contain several times the identified resource. BENEFICIATiON OF COLUMBIUM FROM THE REGOLITH Two large bulk samples of regolith, each weighing approximately 200 lb, were collected from trenches on upper Idaho Gulch for columbium beneficiation studies. Sample A was collected from trench T-4 from the same pit as samples 12 and 13 and had a head analysis of 0.09 pet Cb. Sample B was collected from trench T-5 from the same pit as samples 18 and 19 and had a head analysis of 0.12 pet Cb. Figure 14 illustrates the procedure used to beneficiate the two samples. The samples were screened and ground in stages to pass 65 mesh and then tabled on a slime deck to produce a rougher concentrate, coarse tailings (those that settled and banded on the deck), and fine tailings (those that washed off the deck without settling). The rougher coarse tailings were screened and reground in stages to pass 150 mesh and then re tabled in a scavenger step. A scavenger concentrate, coarse tailings, and fine tailings were produced. The rougher and scavenger concentrates were combined and scrubbed at 50 pet solids for 10 min in a 1:2 volume HCI-H2O solution (13 pet HCl by weight) to remove iron oxide staining from the mineral surfaces. The scrubbed concentrate was washed and decanted four times and then treated by magnetic separation. A hand magnet was used to remove magnetite and other highly magnetic material. The remainder was slurred and pumped through a high-intensity wet magne- tic separator with a grooved-plate configuration at eight power settings. The magnetic field strength varied from approximately 500 G with the hand magnet to about 9,500 G at the maximum power setting. Screening Sample 1 and grinding (minus 65 mesh) \ Rougher tabling r- Concentrate Screening Coarse tailings 1 and grinding (minus 1 50 mesh) ~1 Fine tailings 1 Scavenger tabling 1 Concentrate Coarse tailings "1 Fine tailings ~^ Acid scrubbing Cone 1 entrate i : separation 1 Decant tailings Magneti Magnet 1 c fractions 1 Nonmagneti cs Figure 14.— Flow diagram of columbium beneficiation proce- dure. Tables 8 and 9 show the results of beneficiation of samples A and B. A calculated composite concentrate from sample A contained 57 pet of the columbium at a grade of 0.86 pet Cb. A calculated composite concentrate from sample B contained 53 pet of the columbium at a grade of Table 8. — Gravity and magnetic concentration of sample A 17 „ , Analysis, pel Product wt pet Cb Zr Rougher and seavenger concentrates: Magnetics: With hand magnet' 0.4 0.06 0.03 At 700 G 1 .09 .04 At 1,500 G 3 .42 .09 At 2,200 G .3 1.06 .13 At 4,000 G 1.6 1.06 .17 At6,200G 1.0 - 1.01 .33 At 7,600 G 4 1.10 .27 At 8,700 G 8 1.12 .67 At 9,500 G 4 1.15 .26 Nonmagneties at 9,500 G 1.9 42 1 39 Weight loss from acid scrubbing 2.9 NA NA Subtotal Rougher table fine tailings Scavenger table coarse tailings Seavenger table fine tailings Composite or total 100.0 .10 .05 Calculated composite concentrate^ 6.7 .86 .60 NA Not analyzed. NAp Not applicable. 'Additional analysis: 63.6 pet Fe, ^Mathematical combination of magnetics at 1.500. 2,200, 4,000. 6.200, 7,600 9,500 G. Distribution, pet Sr Cb Zr Sr 0.03 0.3 0.2 <0.1 .09 .1 -;.1 <.1 .15 1.2 .6 .1 .25 3.3 .7 .1 .47 17.3 5.2 1.3 .73 10.4 6.3 1.2 .64 4.3 2.0 .4 .98 8.7 9,8 1.3 .70 4.2 1.8 .4 1 99 7.8 48.1 6.1 NA NAp NAp NAp 10.1 NA NA NA 57.6 74.7 10.9 47.5 .04 .02 .39 18.7 17.5 30.2 27.3 .06 .01 .97 162 50 43.3 15.1 .05 .01 .63 7.5 2.8 15.6 .61 1.00 100.0 57.2 100.0 74.5 100.0 10.9 8.700. and 9.500 G. and nonmagneties at Table 9. — Gravity and magnetic concentration of sample B □ , . . . Analysis, pet Product wt pet 1 -— Cb Zr Rougher and scavenger concentrates: Magnetics: With hand magnet' 0.3 02 -0 01 At 700 G 1 .11 ,02 At 1.500 G .2 .65 04 At 2,200 G 6 1.03 .05 At 4,000 G .7 1.16 07 At 6,200 G 1.8 1.07 .09 At 7,600 G 6 1.07 08 At 8,700 G .9 1,06 11 At 9,500 G 5 1.05 .11 Nonmagneties at 9,500 G 1.5 .65 .34 Weight loss from acid scrubbing 2.3 NA NA Subtotal Rougher table fine tailings Scavenger table coarse tailings 32.9 Scavenger table fine tailings Composite or total 100.0 12 .03 Calculated composite concentrate^ 6.8 .97 .14 NA Not analyzed. NAp Not applicable. 'Additional analysis: 62,0 pet Fe. ^Mathematical" combination of magnetics at 1,500, 2.200. 4,000 6 200 7 600 9,500 G. Distribution, pet Sr Cb .17 .22 100.0 53.3 Zr 100.0 32.9 Sr 0.01 0.1 ^-0.1 ^0.1 .02 .2 ■..1 ■-.1 .04 1.2 .3 .1 .09 4.7 1.0 .3 .11 7.0 1.7 .5 .15 15.8 5.6 1.6 .15 5.2 1.7 .5 .20 7.8 3.5 1.1 .18 3.9 1.7 .5 .52 7.7 17.4 4,5 NA NAp NAp NAp 9.5 NA NA NA 53.6 32.9 9.1 45.1 .05 .02 .11 18,3 31.4 29.*4 32.9 .08 .02 ,24 21.1 22.9 46.7 12.5 .07 03 .20 7.0 12.8 14.8 100.0 9.1 8.700. and 9.500 G, and nonmagneties at 0.97 pet Cb. In each case the grade could be improved to 1.1 pet Cb with a sacrifice of 9 pet in recovery. The concentrates also contained zirconium and strontium. The calculated composite concentrate from sample A contained 74.5 pet of the zirconium and nearly 11 pet of the strontium with grades of 0.60 pet and 1.00 pet, respectively. The concentrate from sample B con- tained nearly 33 pet of the zirconium and 9 pet of the strontium with grades of 0.14 pet and 0.22 pet, respective- ly. 18 DISCUSSION ORIGIN OF THE REGOLITH The ferruginous regolith on upper Idaho Gulch is derived from chemical weathering of the underlying dolomitic marble. Most of the constituents of the regolith, including apatite, zircon, and a mixed assemblage of iron oxide minerals, are also found downdip in the less weathered marble. Columbium minerals and monazite have not been found in the marble; however, analyses show the marble contains trace amounts of columbium, cerium, and P2O5. The origin of the marble is not as clear. Beds of limestone, dolomite, or marble are unknown elsewhere within the extensive Mesozoic flysch belt (17). The marble and possibly associated metasedimentary wall rocks could be older than the flysch and correlative to a unit of Paleozoic-age limestone, dolomite, argillite, phyllite, metachert, and quartz-mica and chlorite schist that is exposed west of Tofty near the Yukon River {17). Near Tofty, this material could either occur as fault-bounded slivers intercalated within the flysch, or underlie the flysch and be exposed in an erosional window. Significant- ly, apatite, which is characteristic of the marble on upper Idaho Gulch, has not been identified in the Paleozoic-age carbonate rocks west of Tofty. Alternatively, the marble and regolith on upper Idaho Gulch may represent a carbonatite and its residual weathering product. Calcite, ankeritic dolomite, biotite, fluorapatite, monazite, xenotime, magnetite, pyrite, ana- tase, hematite, zircon, columbium-bearing rutile, ilmeno- rutile, columbite, and aeschynite are present in the regolith and/or marble. This mineralogy closely resembles that of the apatite-magnetite variety of carbonatite as described by Pecora <20). Similarly, the trace element composition of the marble and/or regolith closely resem- bles that of carbonatites (table 10). Particularly close agreement for level of concentration of trace elements exists for barium, titanium, and P2O5. Magnetite and P2O5 and to a lesser extent, co- lumbium and zirconium, are concentrated in the regolith to levels above those in the parent marble (table 10). This upgraded material is directly comparable to upgraded concentrations of magnetite, P2O5, columbium, and zirconium in residual soils overlying the Sukula carbona- tite complex in southeastern Uganda (21), in "apatite- francolite regolith" overlying the Sokli carbonatite com- plex in Finland (22), and elsewhere (23). The overall interpreted regional geologic setting and the rock assemblages found on upper Idaho Gulch are not overwhelmingly similar to those of classic carbonatite occurrences (20, 24). In particular, no alkalic igneous rocks or alkali-rich alteration halo have been identified in the Tofty area. However, it is possible that the marble intruded along the structurally complex northwestern margin of the flysch basin and that any associated alkalic rocks or alteration halo either remain hidden beneath the extensive silt cover or have not yet been exposed by erosion. Alternatively, poorly exposed and preserved occurrences of serpentinized rock in the vicinity of upper Idaho Gulch may represent metamorphosed mafic alkalic rocks. The grade and tonnage of the identified columbium resource on upper Idaho Gulch is considerably lower than that in exploitable columbium-bearing carbonatites worldwide. However, uneconomic columbium grades similar to or lower than those on upper Idaho Gulch have been identified in carbonatites elsewhere. Specifically, at Magnet Cove, AR, only 6 of 21 samples of the carbonatite exposure in Kinsey Quarry contained detectable co- lumbium with concentration ranging between 0.01 and 0.07 pet (18). Additionally, it should be noted that the extent of the marble that underlies the regolith on upper Idaho Gulch is unknown, and that only three samples of marble have been analyzed. Therefore there is a possibil- ity for yet undiscovered, possibly higher grade columbium resources in the Tofty area. SOURCES OF PLACER MINERALS The bedrock source of the tin belt placer minerals is unknown. Wayland (8) outlines two hypotheses to explain possible origins. One suggests the northeast alignment of placer deposits reflects the trend of an ancient stream channel that has been reworked by younger streams. In this hypothesis, the placer minerals would have been derived from a source outside of the tin belt. The other hypothesis proposes that the placer constituents were derived from sources within the tin belt and that the placer deposits were formed from virtual in-place weath- ering. Wayland concludes that the second theory probably best explains the origin of the cassiterite, but that "the monazite, aeschynite, apatite, and zircon can be accounted for under either hypothesis" (8, p. 403). This investigation shows that a source for some of the placer minerals lies within the tin belt, northwest of the existing placer deposits. High concentrations of radioac- tive minerals and columbium in placer gravels on Idaho Gulch likely result from erosion of ferruginous regolith on upper Idaho Gulch. High concentration of radioactive minerals and columbium in tailings piles on Miller and Deep Creeks and the reported presence of apatite- and magnetite-bearing dolomite on Harter Gulch (8) likewise suggest additional lode sources in the headwaters of those creeks. Table 10. — Trace-element abundances and variations in reported (20) carbonatite deposits and marble and regolith on upper Idaho Gulch, percent Trace Reported . . . , , □ „„, .1,2 element carbonatite ^^'^^^ "^9°"'^ e^/nt c^ZTl ^^arb,e- RegoNth^ Ce^ 02 - '' 06 -0 24 0-0 20 Zr 0.001-0 02 0.02-0 065 -0.09 Ba 05 -10.0 NA 5->6 Ti 10 -3.0 NA 2 - 2.0 Sr 50-2.0 NA - 40 Cb 001- .5 025- 073 - 12 PjOs 10 -6.0 132-2.74 .14-21.4 NA Not analyzed 'Only 3 samples collected (see table 6) ^See tables 2 and 3 'Includes all rare-earth elements. 19 SUMMARY AND CONCLUSIONS Two parallel N 60 E trending, northwest-dipping lenses of slightly radioactive iron-rich regolith were identified on upper Idaho Gulch in 1956 and investigated in 1984 by the Bureau of Mines. The regolith contains major amounts of magnetic and nonmagnetic iron oxide minerals, abundant apatite and zircon, moderate amounts of pyrite, monazite, and columbium-bearing rutile. The regolith also contains trace amounts of xenotime and the columbium minerals aeschynite, columbite, and ilmeno- rutile. Trace to major concentrations of barium, strontium, lanthanum, cerium, yttrium, silver, and titanium have also been identified. Each lens has a strike length of approximately 1,200 ft and persists for 200 to 250 ft downdip where unweathered magnetite-pyrite-apatite- zircon-bearing dolomitic marble has been encountered in drill core. High columbium and generally higher zirconium and P2O5 concentrations are restricted to a central, hematite- rich, red-brown portion of the regolith lenses. These mineralized zones have an average thickness of approx- imately 22 ft, probably decrease in thickness by 50 pet 150 ft downdip, and have average columbium grades between 0.04 pet and 0.07 pet. Given these dimensions and at a grade of 0.07 pet Cb, the regolith lenses on upper Idaho Gulch contain approximately 340,000 lb of columbium resources. Approximately 30,000 lb of this resource is indicated whereas 310,000 lb is inferred. Large additional columbium resources are probably present in the dolo- mitic marble. The regolith also contains inferred re- sources of approximately 340,000 lb of zirconium and 12,250 st of P2O5. Calculated composite concentrates from two large samples of regolith contained 53 and 57 pet of the columbium at grades of 0.97 and 0.86 pet Cb, respectively. In each case the grade could be improved to 1.1 pet Cb with a sacrifice of 9 pet recovery. The unweathered source of the regolith, a dolomitic marble, could be of either igneous or sedimentary origin. Its mineralogy and trace-element geochemistry and the similarity of the regolith to descriptions of other co- lumbium-enriched regoliths suggest the marble is a carbonatite. However, the lack of associated alkalic igneous rocks or alkali-rich alteration halo and the stratiform nature of the regolith can be interpreted as evidence for sedimentary origin of the marble. The marble and regolith are a lode source for some of the minerals of the Tofty placer deposits. Similar bedrock geology or placer mineralogy suggests that additional lode sources may exist in the headwaters of Miller Gulch, Deep Creek, and Harter Gulch. REFERENCES 1. Morgan, J. D. Strategic and Critical Materials. Pres. at AIME All-Institute Sess., Strategic and Critical Miner, and Foreign Policy, Las Vegas, NV, Feb. 27, 1980, 20 pp.; available from J. D. Warner, BuMines, Fairbanks, AK. 2. Cunningham, L. D. Columbium. Ch. in Mineral Facts and Problems, 1985 Edition. BuMines B 675, 1985, pp. 185-196. 3. Wahrhaftig, C. Physiographic Divisions of Alaska. U.S. Geol. Surv. Prof. Pap. 482, 1965, 52 pp. 4. Eakin, H. M. A Geologic Reconnaissance of a Part of the Rampart Quadrangle, Alaska. U.S. Geol. Surv. Bull. 535, 1913, 38 pp. 5. Mining in the Hot Springs District. U.S. Geol. Surv. Bull. 622-G, 1915, pp. 239-245. 6. Mertie, J. B., Jr. Mineral Deposits of the Rampart and Hot Springs Districts, Alaska. U.S. Geol. Surv. Bull. 844-D, 1934, pp. 163-226. 7. Thorne, R. L., and W. S. Wright. Sampling Methods and Results at the Sullivan Creek Tin Placer Deposits, Manley Hot Springs, Tofty, Alaska. BuMines RI 4346, 1948, 8 pp. 8. Wayland, R. G. Tofty Tin Belt, Manley Hot Springs District, Alaska. U.S. Geol. Surv. Bull. 1058-1, 1961, pp. 363-414. 9. Thomas, B. I. Tin-Bearing Placer Deposits Near Tofty, Hot Springs District, Central Alaska. BuMines RI 5373, 1957, 56 pp. 10. Waters, A. E., Jr. Placer Concentrates of the Rampart and Hot Springs Districts. U.S. Geol. Surv. Bull. 844-D, 1934, p. 241. 11. Moxham, R. M. Reconnaissance for Radioactive Deposits in the Manley Hot Springs-Rampart District, East-Central Alaska, 1948. U.S. Geol. Surv. Circ. 317, 1954, 6 pp. 12. Southworth, D. D. Columbium in the Gold- and Tin- Bearing Placer Deposits Near Tofty, Alaska. BuMines OFR 174-84, 1984, 25 pp. 13. Chapman, R. M., W. Yeend, W. P. Brosge, and H. N. Reiser. Reconnaissance Geologic Map of the Tanana Quadrangle, Alaska. U.S. Geol. Surv. Open File Rep. 82-734, 1982, 20 pp. 14. Chapman, R. M., F. R. Weber, and B. Taber. Preliminary Geologic Map of the Livengood Quadrangle, Alaska. U.S. Geol. Surv. Open File Rep. 71-66 (483), 1971, 2 sheets. 15. 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., 83-170A, 1983, 32 pp. 16. Jones, D. L., N. J. Silberling, R. M. Chapman, and P. Coney. New Ages of Radiolarian Chert From the Rampart District, East-Central Alaska. U.S. Geol. Surv. Circ. 868, 1984, pp. 39-73. 17. Chapman, R. M. (U.S. Geological Survey). Private com- munication, 1985; available upon request from J. D. Warner, BuMines, Fairbanks, AK. 18. Fryklund, V. C, Jr., R. S. Harner, and E. P. Kaiser. Niobium (Columbium) and Titanium at Magnet Cove and Potash Sulphur Springs, Arkansas. U.S. Geol. Surv. Bull. 1015-B, 1954, pp. 23-57. 19. U.S. Bureau of Mines and the U.S. Geological Survey. Principles of a Resource/Reserve Classification for Minerals. U.S. Geol. Surv. Circ. 831, 1980, 5 pp. 20. Pecora, W. T. Carbonatites: A Review. Geol. Soc. America Bull. v. 67, 1956, pp. 1537-1556. 21. Reedman, J. H. Resources of Phosphate, Niobium, Iron, and Other Elements in Residual Soils Over the Sukulu Carbonatite Complex, Southeastern Uganda. Econ. Geol., v. 79, 1984, pp. 716-724. 22. Vartiainen, H., and H. Paarma. Geological Characteristics of the Sokli Carbonatite Complex, Finland. Econ. Geol., v. 74, 1979, pp. 1296-1306. 23. Deans, T. Economic Mineralogy of African Carbonatites. Ch. in Carbonatites, ed. by O. F. Tuttle and J. Gittens. Wiley, 1966, pp. 385-416. 24. Parker, R. L., and J. W. Adams. Niobium (Columbium) and Tantalum. Paper in United States Mineral Resources, ed. by D. A. Brobst and W. P. Pratt. U.S. Geol. Surv. Prof Pap. 820, 1973, pp. 443-454. 20 APPENDIX A.— MODIFIED 1956 DRILL CORE LOGS AND GEOLOGIC CROSS SECTIONS CONSTRUCTED FROM DRILL CORE DATA Tables A-1 through A-9 are logs of diamond drill holes D-1 through D-9. Geologic cross sections through drill holes D-1 through D-9 and trench T-8 are presented in figures A-1 through A-6. Table A-1. — Log of diamond drill hole 0-1, Idaho Gulch Bearing Inclination ... Collar elevation S 14 E 45 852 Depth ft . . Size: NX. to 15.5 ft; BX, 15.5 to 119.5 ft; AX, 119.5 to 194.0 ft. 194.0 Interval, ft Recovery, ft Description 0.0 to 9.8 9.8 to 39 7 39.7 to 56.6 56.6 to 126.5 126.5 to 132 2 132.2 to 143.3 143.3 to 162.8 162.8 to 194.0 0.70 5.15 .30 2.45 .35 10.70 6.85 Muscovite-quartz schist, weathered with limonite on fractures. Dark quartz-muscovite schist with up to l-in-wide quartz veins and limonite on fractures. White quartzose phyllite with partings of muscovite phyllite and quartz veins. Black graphite-muscovite schist, minor pyrite and quartz veins. Black phyllite with limonite on fractures. Limonite (regolith) Gray to light-green calcareous quartz-chlorite-sericite phyllite. Dark-gray argillite and chloritic schist, limonite after pyrite and on fractures. Table A-2.— Log of diamond drill hole D-2, Idaho Gulch Bearing S 1 5- E Depth ft . . 179.4 Inclination -68 30' Size; NX. to 14.5 ft; BX. 14 5 to 59.3 ft; AX, 59.3 to 179.4 ft. Collar elevation ft . . 52 Interval, ft Recovery, ft Description 0.0 to 3.0 0.00 Silt with fragments of phyllite. 3.0 to 14.5 1.5 Muscovite-quartz schist, weathered with limonite on fractures. 14.5 to 38 C) Dark quartz-muscovite schist with local quartz veinlets. 38 to 105 16.88 White to gray quartzose muscovite phyllite grading downward to thinly laminated quartz and muscovite schist with minor pyrite and muscovite-graphite phyllite. 105 to 179.4 21.34 Muscovite-graphite pyllite grades downward into graphite-muscovite schist, and then, to graphitic argillite, Pyrite disseminated throughout. 'Included with recovery from 38- to 105-ft interval. Table A-3. — Log of diamond drill hole D-3, Idaho Gulch Inclination -90° Depth 278.0 Collar elevation ft . . 835.2 Size: BX, to 18.9 ft; AX, 18.9 to 206.2 ft; EX, 206.2 to 278.0 ft. Interval, ft Recovery, ft Description 0.0 to 9.0 0.0 Frozen silt. 9.0 to 58.0 ,99 Gray phyllite with limonite on fractures. 58.0 to 60.0 .98 Quartz with limonite after pyrite. 60.0 to 190.7 8.80 Interlaminated dark-gray to black quartz and muscovite-graphite schists, thin bands of quartz, some with pyrite. 190.7 to 192.0 .45 Calcareous chlorite-sericite schist with limonite after pyrite and calcite veinlets. 192.0 to 193.3 VO Granular limonite (regolith). 193.3 to 264.7 (^) Dolomitic marble, weathered, yellow color with abundant quartz and magnetite grains, limonite after pyrite, and veinlets of limonite, calcite-dolomite, and apatite. 264.7 to 278.0 38.97 Quartz-chlorite-sericite schist with disseminated magnetite and pyrite 'Rock type identified from coarse cuttings in sludge. ^Included with 264.7- to 278.0-ft interval. Table A-4. — Log of diamond drill hole D-4, Idaho Gulch inclination -90° Size: NX, to 20.0 ft; BX, 20.0 to 50.4 ft; AX, 50.4 to 184,7 ft; EX, 184.7 Collar elevation ft . . 81 1 to 259.8 ft Depth ft . . 259.8 Interval, ft Recovery, ft Description 0.0 to 5,0 '0.0 Frozen silt. 5.0 to 40.0 '.0 Black phyllite. 40.0 to 50.4 .25 Kaolinized phyllite. 50.4 to 65.4 .43 Siliceous light gray phyllite with pyrite. 65.4 to 75.4 .48 Decomposed Phyllite. 75.4 to 1 35.4 10.71 Gray to black phyllite with thin quartz seams. 135.4 to 174.1 15.86 Slightly calcareous quartz-chlorite-muscovite ± (talc-serpentine) phyllite with quartz along foliation. 174.1 to 191 .0 ('^) Unweathered moderately coarsely crystalline dolomitic marble with disseminated magnetite, pyrite and pyrrhotite, and rare quartz veins, 191 ,0 to 259.8 16.36 Limonite-stained calcareous dolomite marble with disseminated magnetite. More altered intervals include 225 to 228 ft and 232 to 245 ft, 'Rock type identified from coarse cuttings in sludge. ^Included with 191.0- to 259.8-ft intervals. 21 Table A-5.— Log of diamond drill hole D-5, Idaho Gulch Inclination -90 Size: NX. to 45.7 ft; BX. 45.7 to 75.4 ft; AX, 75.4 to 95.4 ft; EX, 95.4 to Collar elevation ft.. 801 155 1ft. Deptfi ft-- 155.1 Interval, ft Recove ry, ft Description 0.0 to 5.0 '0.0 Frozen silt, granular dolomite, and limonite. 5 to 10,0 ■15 Phyllite, quartz, and granular limonite 10 to 27.9 8,84 Weathered, granular rock with coarse dolomite grains in a fine limonitic matnx. Contains fragments of chloritic material, magnetite, limonite after pyrite, pyrite, limonite on fractures, and quartz veins. 27.9 to 65.4 20.39 Coarse dolomitic marble with disseminated magnetite, pyrite, and trace pyrrhotite. fwlinor hematite after magnetite and local limonite on fractures. Chloritic at base. 65.4 to 80.4 3.85 Gray calcareous phyllite 80.4 to 155.1 101 Black phyllite with quartz veinlets. 'Rock type identified from coarse cuttings in sludge. Table A-6.— Log of diamond drill hole D-6, Idaho Gulch Inclination -90" Depth ft., 134.6 Collar elevation ft.. 827 Size: NX, to 5.0 ft; BX. 5.0 to 45.0 ft; AX, 45.0 to 134.6 ft. Interval, ft Recovery, ft Description 0.0 to 5.0 0.0 Frozen silt and schist fragments, 5,0 to 18,0 17 Frozen, fractured arid aliered muscovite-graphite phyllite, 18,0 to 25,0 .78 Fractured and weathered muscovite phyllite, minor quartz veins and limonite. 25,0 to 61 ,0 .30 Frozen granular limonite, some magnetite (regolith). 61 .0 to 70 (') Weathered and fractured limonitic marble, locally chlorite- and sericite-rich with dissem- inated magnetite, hematite, and limonite after pyrite and veinlets of limonite and caicite. 70.0 to 74.4 (') Porous limonite with caicite veinlets. 74.4 to 75.0 (') Kaolinitic schist, 75.0 to 95.4 24.9 Interfoliated muscovite = chlorite i sericite schists with minor limonite after pyrite and on fractures, 95.4 to 1 10.4 5.68 Chlorite-quartz-calcite schist. 110.4 to 134.6 6.00 Interfoliated dolomitic limestone and pyritic graphite schist. 'Included with 75.0- to 95.4-ft interval. Table A-7. — Log of diamond drill hole D-7, Idaho Gulch Inclination -90" Depth ft . . Collar elevation ft . , 832 Size: BX, to 44.3 ft. Interval, ft Recovery, ft Description 0.0 to 14.3 (') Dark, goethite-limonite hematite-bearing regolith. nonmagnetic, 14.3 to 19.3 3.71 Orange earthy limonitic regolith with fragments of chloritic phyllite, 19.3 to 19.8 ,5 Kaolinitic clay with a few fragments of metallic goethite, 19.8 to 43.3 16.55 Nonfoliated. chlonte-sericite-quartz phyllite with segregations of chlorite-serpentine. 'Included with 14.3- to 19.3-ft interval. 44.3 Table A-8. — Log of diamond drill hole D-8, Idaho Gulch Inclination -90 Depth ft Collar elevation ft , , 836 Size: NX, to 5,0 ft: BX, 5,0 to 50,3 ft 50,3 Interval, ft Recovery, ft Description 0.0 to 5.0 (') Earthy, limonitic magnetic regolith. Nonmagnetic limonitic regolith Chlorite-talc-sericite-(serpentine) schist, locally calcareous and altered to kaolinite and limonite 5.0 to 13.8 . 2 64 13.8 to 50.3 . 4 95 'Included with 5.0- to 13.8-0 interval. Table A-9.— Log of diamond drill hole D-9, Idaho Gulch Inclination -90° Depth ft . Collar elevation ft 851 Size: BX, to 30.3 ft; AX, 30.3 to 143.9 ft Interval, ft Recovery, ft Description 0.0 to 45.3 3.08 Dark-gray to blue-colored weathered and fractured phyllite; locally limonitic. 45.3 to 50.3 1 .85 Chloritic schist. 50.3 to 74.3 2,60 Dark-gray to blue-colored decomposed phyllite with iron-stained quartz, 74.3 to 89,4 1.63 Frozen granular limonite (regolith), 89.4 to 93,7 1.85 Dark-gray calcareous schist. 93.7 to 109.6 .70 Chlorite schist, slightly calcareous, with thin quartz seams that contain pyrite. 109.6 to 110.4 '.0 Talc schist 110.4 to 112.8 '.0 Granular limonite. 112.8 to 143.9 5^0 Gray, slightly calcareous schist. 'Rock type identified from coarse cuttings in sludge. 143.9 22 Eliv,ft 690 800 750 700 D-l D-2 Depth 194 ft Dapth 179.4 ft Figure A-1. — Geologic section through drill holes D-1 and D-2 and trench T-8. NW Dtpfh 44 3 ft Figure A-3. — Geologic section through drill hole D-7 and trench T-8. SE Eltv.ft 800 Figure A-2. — Geologic section through drill holes D-3 and D-6 and trench T-8. i^ LEGEND Quartz - muscovite phyllite end scttist Muscovitic quartzlte end schist Graphite -muscovite phyllite, dotted where siliceous x'\''>''^ Chlorite-sericitei quartz ttalc± serpentine phyllite and schist Nonfoliated chloritic rock ra Regoiith ^3 Oolomitic marble y Geologic contoct, dashed where approximate, dotted where inferred 60 J_ 120 _J Scale, feet 23 Depth 259.8 ft Figure A-4. — Geologic section tlirough drill hole D-8 and Figure A-6. — Geologic section through drill holes D-4 and trench T-8. D-5 and trench T-6. Depth 143.9 ft Figure A-5.— Geologic section through drill hole D-9 and trench T-8. i^ :i^ ^ LEGEND Quartz -muscovite phyllite and schist Muscovitic quartzite and schist Graphite -muscovite phyllite, dotted where si liceous Chlorite-sericite± quartz ttalc± serpentine phyllite and schist Nonfoliafed chloritic rock Regollth ^3 Dolomitic morble ./ Geologic contocf, dashed where approximate, dotted where inferred 60 I Scale, feet 120 _J 24 APPENDIX B.— TEST PROCEDURE FOR CHARACTERIZATION OF TOFTY REGOLITH CONCENTRATES 5, 9, 15, AND 30 Planned concentrate samples were acid leached in a 1:1 HCl solution to remove excess iron oxide. The material was then screened at 20 mesh. The plus 20-mesh fraction was optically, radiometrically, and spectroscopically ex- amined and was found to contain no properties character- istic of the suspected columbium-bearing minerals. The remaining minus 20-mesh fraction of each sample was run through a laboratory-model isodynamic magnetic separ- ator at 0-, 0.1-, 0.2-, 0.3-, 0.4-, 0.5-, 0.6-, 1.0-, and 1.7-A settings to isolate minerals of similar magnetic suscepti- bilities. These fractions were examined optically, radiometrically, and spectroscopically to determine possi- ble concentrations of columbium-bearing minerals. The fractions determined to contain the highest concentration of columbium were prepared in polished grain mounts for scanning electron microscope (SEM) and microprobe studies. Aeschynite was positively identified by SEM methods and found to be well concentrated in the 0.7-A magnetic fraction. Columbite was also identified and found concentrated in the 0.5-A magnetic fraction. Columbium-bearing rutile (possibly altered in part to ilmenorutile) was also concentrated in the 0.5-A fraction. Table B-1 summarizes the results of the analyses. Table B-1. — Mineralogical analyses of magnetic^ fractions of samples representative of the regolith concentrates selected for SEM studies, weight percent Magnetic fraction A 0.3 0.4 0.5 0.7 Magnetite 35 ND ND ND Goethite 35 60 ND ND Miscellaneous silicates 20 25 15 10 Columbite 6 6 20 ND Monazite 4 4 ND ND Aeschynite ND 2 5 70 Rutile ND ND ND 10 Zircon ND ND 60 10 Other ND ND ND ND ND Not detected. 'Separated on a laboratory-model isodynamic magnetic separator. 1.0 ND ND 25 ND ND 45 10 15 5 25 APPENDIX C— RESULTS OF EMISSION SPECTROGRAPHIC ANALYSES^ REGOLITH SAMPLES OF Sample 11 12 13 16 17 18 19 20 22 23 24 25 26 CONCENTRATION, ppm Ag <70 5 >3 Oi >5 >6 >3 ] >6 ol i OS 09 >2 Ba .6 >6 .8 07 .2 7 .5 1 .1 .08 .2 .1 .5 Ca <.5 3 1 .4 .7 3 <.6 <.4 <.6 <.7 <.3 <.4 4 Fe 10 10 10 8 9 10 10 10 >10 >10 >10 10 10 K 10 579 10 747697 10 7 Mg .4 .3 .3 1 1 .9 .4 .4 <.05 <.01 .2 .2 .2 Mn >4 >5 >4 >2 >2 >6 >5 >4 >10 >10 >3 >9 >10 Na <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 P <1 3 <2 <.7 <.7 <.7 <1 <.8 <.7 <.7 <.9 <1 2 SI >10 5 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 >10 'Analyses by Bureaus Reno Research Center, Reno, NV 26 RESULTS OF EMISSION SPECTROGRAPHIC ANALYSES' OF REGOLITH SAMPLES— Continued Sample 27 28 32 33 Ag <300 <30 <80 <300 As <800 <100 <200 <800 Au <40 <20 <20 <40 B <90 <50 <50 <100 Be 1 4 8 <3 Bi <200 <600 <100 <2,000 Cb 300 <200 <300 <200 Cd <5 <5 <5 -5 Co 100 <20 200 90 Cr 400 100 6.000 600 Cu 6 100 30 20 Ga 30 <10 20 <9 La 300 <100 <100 <100 Li <20 <20 <20 <20 Mo <1 <1 <1 <1 Ni 400 100 3,000 1,000 Pb <20 <20 <60 <20 Pd <1 <1 <1 -1 Pt <100 <6 <300 <100 Sb <2,000 <600 <3,000 <3,000 So <4 <4 <9 <4 Sn <20 <80 <300 <200 Sr 400 20 100 80 Ta <200 <200 <300 <200 Te <400 <400 1 ,000 -^400 Ti 7,000 10.000 3,000 10,000 V 500 400 400 500 Y <9 <9 <9 -9 Zn <1 <30 200 40 Zr 2,000 40 90 200 AJ i >6 ^ ,3 Ba .3 .1 .3 .4 Ca <.6 1 <.4 <.8 Fe 10 7 10 10 K 6 10 8 9 Mg .2 1 .4 .3 Mn >10 .3 >4 >8 Na <.3 2 <.3 <.3 P <2 <.7 <2 <1 Si >10 >10 >10 >10 'Analyses by Bureau's Reno Research Center, Reno, NV. 34 35 36 37 38 39 40 41 CONCENTRATION, ppm <70 <800 <50 <100 <3 <200 800 •-5 100 200 40 20 300 <20 <1 800 <20 <1 <100 <' 3.000 ■4 <200 50 -200 -400 10.000 600 -9 - 60 400 5 90 ■100 - 300 5 ■ 200 1,000 5 400 300 100 70 300 • 20 ■ 1 2.000 60 - 1 ■ 300 3.000 20 800 70 200 900 20,000 1.000 9 • 20 4,000 ■ 40 ■ 90 ' 50 -100 4 ■ 100 200 • 5 60 200 20 '-10 <100 <20 •1 400 '30 - 1 '70 ■3,000 ■-4 ■ 200 1,000 ■ 300 ■ 600 10,000 600 • 9 ■ 40 90 - 70 '90 '20 '200 8 ■ 700 • 70 ■ 5 80 500 50 'JO ■;100 '20 ■-1 600 <70 ■:1 '90 '.4.000 ■A 600 2.000 100 900 10,000 800 ■ 9 • 20 100 • 40 100 ■ 20 100 7 100 ■ 100 • 5 ' 10 50 40 ■-8 '-100 ';20 ■1 200 30 -.1 ■ 20 ■-600 ■ 4 100 8 200 400 6,000 200 9 80 '30 '50 -^100 20 • 70 6 '100 ';100 ' 5 ' 10 200 50 <2 '-100 '20 <1 400 • 20 --1 ■30 '^600 -.4 ';100 60 -^200 400 6,000 100 '9 80 30 200 ; 1 ,000 <20 100 4 -^100 ■'100 <5 100 200 100 60 300 80 <1 200 100 •-1 ■;20 ';700 <5 <300 100 <200 <400 7,000 700 •-10 --2 200 100 <90 <20 100 9 <100 <200 <5 70 100 100 40 <300 70 <1 400 --80 <1 <6 ;2,000 <5 <300 100 <200 '-900 6.000 400 -9 200 100 CONCENTRATION, pet 0.8 .1 -.2 -10 9 .2 :-5 <.3 <1 '10 10 4 '7 <2 -10 0.7 .2 •10 -10 7 .5 -5 '..3 6 3 -10 -10 <1 .2 .9 8 -10 1 .7 <.3 10 1 >2 <.3 <.7 -10 >7 1 <.1 9 >10 .4 >3 <.3 <.7 >10 >6 .6 .7 >10 10 .4 >2 <.3 <.7 >10 27 APPENDIX D.- -RESULTS OF MAGNETIC,' RADIOMETRIC,' AND SOIL SAMPLE' SURVEYS station Magnetic intensity, gammas Radioactivity, cps Cb, ppm P3O5. pet Zn. ppm Station Magnetic intensity, gammas Radioactivity, cps Cb. ppm P2O5. pet Zn. ppm LINE 9,600 NE LINE 10,000 NE 9,500 SE . 572 73 NS NS NS 9,500 SE 518 80 NS NS NS 9,525 SE 524 72 NS NS NS 9.525 SE 541 87 NS NS NS 9,550 SE 507 73 NS NS NS 9.550 SE 536 97 NS NS NS 9,575 SE 521 72 NS NS NS 9.575 SE 536 106 NS NS NS 9,600 SE 522 68 NS NS NS 9.600 SE . 569 93 NS NS NS 9,625 SE . 520 76 NS NS NS 9.625 SE 580 83 NS NS NS 9,650 SE . 520 76 NS NS NS 9.650 SE . 597 85 NS NS NS 9,675 SE 514 76 NS NS NS 9.675 SE 605 79 NS NS NS 9,700 SE 510 83 NS NS NS 9.700 SE 653 86 NS NS NS 9,725 SE 515 74 NS NS NS 9.725 SE 674 86 NS NS NS 9,750 SE 531 73 NS NS NS 9.750 SE 692 86 NS NS NS 9.775 SE 526 72 NS NS NS 9.775 SE 702 95 NS NS NS 9,800 SE 523 67 NS NS NS 9.800 SE 689 110 NS NS NS 9,825 SE 520 66 NS NS NS 9.825 SE 658 93 NS NS NS 9,850 SE 520 66 NS NS NS 9.850 SE 602 113 NS NS NS 9,875 SE 508 70 NS NS NS 9.875 SE 524 102 NS NS NS 9,900 SE 504 70 NS NS NS 9.900 SE 586 114 NS NS NS 9,925 SE 465 78 NS NS NS 9.925 SE 537 103 NS NS NS 9,950 SE 514 71 NS NS NS 9.950 SE . 536 87 NS NS NS 9,975 SE 515 76 NS NS NS 9.975 SE 524 94 NS NS NS 10,000 SE 530 71 NS LINE 9.800 NE NS NS 10.000 SE 444 96 NS NS NS LINE 10,200 NE 9,500 SE 526 75 NS NS NS 9.500 SE 602 91 ^;50 014 170 9,525 SE 522 70 NS NS NS 9.525 SE 600 90 <50 .12 190 9,550 SE 526 72 NS NS NS 9.550 SE . 595 89 <50 .18 210 9,575 SE 522 72 NS NS NS 9.575 SE 607 87 <50 .16 200 9,600 SE 530 71 NS NS NS 9.600 SE 620 88 <50 .15 180 9,625 SE 528 84 NS NS NS 9.625 SE 630 95 <50 .13 190 9,650 SE 530 72 NS NS NS 9.650 SE . 641 96 <50 .12 190 9.675 SE 545 74 NS NS NS 9.675 SE 641 88 <50 .12 180 9,700 SE 521 70 NS NS NS 9.700 SE 661 95 <50 .10 200 9,725 SE 530 75 NS NS NS 9.725 SE 672 90 <50 10 180 9,750 SE 535 75 NS NS NS 9.750 SE 661 89 NS NS NS 9,775 SE 529 72 NS NS NS 9.775 SE 643 85 ■ 50 .10 180 9,800 SE 539 72 NS NS NS 9.800 SE 627 88 -50 .12 200 9,825 SE 523 78 NS NS NS 9.825 SE . 616 93 <50 .11 190 9,850 SE 527 77 NS NS NS 9.850 SE 610 88 <50 .14 180 9.875 SE 540 78 NS NS NS 9.875 SE 583 94 <50 .36 210 9,900 SE 524 82 NS NS NS 9,900 SE 557 93 <50 .10 170 9,925 SE 520 87 NS NS NS 9,925 SE 537 111 <50 .29 220 9,950 SE 520 88 NS NS NS 9,950 SE . 553 109 <50 .11 170 9,975 SE 524 81 NS NS NS 9,975 SE 523 102 <50 .13 180 10.000 SE 526 83 NS LINE 10.000 NE NS NS 10.000 SE 508 83 • 50 .17 190 LINE 10,300 NE 9,500 SE 566 86 <50 0.35 270 9.500 SE 632 96 NS NS NS 9,525 SE 559 87 <50 .16 190 9,525 SE 611 101 NS NS NS 9,550 SE 536 84 <50 .18 230 9.550 SE . 622 102 NS NS NS 9,575 SE 531 81 <50 .13 200 9.575 SE 630 108 NS NS NS 9,600 SE 562 88 <50 .23 180 9.600 SE 685 116 NS NS NS 9,625 SE 565 92 <50 .16 190 9.625 SE 694 124 NS NS NS 9,650 SE 447 107 <50 .23 190 9.650 SE 868 115 NS NS NS 9.675 SE 578 106 <50 .16 200 9.675 SE 636 117 NS NS NS 9,700 SE 685 100 <50 .12 170 9.700 SE 576 86 NS NS NS 9,725 SE 605 91 <50 .16 190 9.725 SE 586 99 NS NS NS 9.750 SE 648 89 <50 .17 190 9.750 SE 569 96 NS NS NS 9,775 SE 895 87 <50 .20 200 9.775 SE 545 114 NS NS NS 9,800 SE 645 89 <50 .11 190 9.800 SE 544 190 NS NS NS 9,825 SE 538 91 <50 .26 210 9,825 SE 626 204 NS NS NS 9.850 SE 512 89 <50 .12 170 9,850 SE 816 214 NS NS NS 9.875 SE 494 92 <50 .14 200 9,875 SE 527 220 NS NS NS 9,900 SE 519 97 <50 .12 190 9.900 SE 518 147 NS NS NS 9,925 SE 525 99 <50 .20 220 9,925 SE 519 134 NS NS NS 9,950 SE 546 102 <50 .16 200 9,950 SE 511 110 NS NS NS 9,975 SE 551 97 <50 .14 200 9,975 SE 489 93 NS NS NS 10,000 SE 540 86 <50 .15 220 10,000 SE 501 92 NS NS NS NS No sample, NR No reading. 'Total-field magnetic intensity, all readings have a base of 56,000 gammas. ^otal-count gamma-ray radiation. ^Soil sample analyses by XRF by Bureau's Reno Research Center, Reno, NV. 28 RESULTS OF MAGNETIC,' RADIOMETRIC,^ AND SOIL SAMPLE^ SURVEYS— Continued Station Magnetic intensity. Radioactivity. Cb, P2O5, 2n, Station Magnetic intensity, Radioactivity, Cb. P2O5, Zn, gammas ops ppm pet ppm gammas cps ppm pet ppm LINE 10,400 NE LINE 10,700 NE 9,500 SE 580 86 <50 0.19 180 9,500 SE 540 73 NS NS NS 9,525 SE 571 88 <50 16 190 9,525 SE 537 75 NS NS NS 9,550 SE . 581 92 <50 13 180 9,550 SE 527 78 NS NS NS 9,575 SE 576 92 <50 13 190 9,575 SE 521 73 NS NS NS 9,600 SE 645 96 <50 13 190 9,600 SE 508 74 NS NS NS 9,625 SE . 738 113 <50 77 210 9,625 SE . 507 70 NS NS NS 9,650 SE . 1081 109 <50 32 220 9,650 SE . 498 81 NS NS NS 9,675 SE . 887 174 NS NS NS 9,675 SE . 545 79 NS NS NS 9,700 SE . 576 149 250 5.40 460 9,700 SE 548 78 NS NS NS 9,725 SE 545 112 <50 .29 180 9.725 SE 535 73 NS NS NS 9,750 SE 397 105 <50 .28 230 9,750 SE 543 81 NS NS NS 9.775 SE 504 98 <50 .17 170 9,775 SE 576 86 NS NS NS 9,800 SE 548 98 <50 .20 200 9,800 SE 694 84 NS NS NS 9,825 SE . 560 106 <50 .13 170 9,825 SE . 900 63 NS NS NS 9,850 SE 582 133 <50 .26 210 9.850 SE 951 71 NS NS NS 9,875 SE 602 167 <50 56 330 9,875 SE 712 62 NS NS NS 9,900 SE 560 250 180 2.60 1160 9,900 SE 548 60 NS NS NS 9.925 SE 507 179 <50 ,52 280 9,925 SE 521 63 NS NS NS 9,950 SE 510 189 70 ,89 320 9,950 SE 519 63 NS NS NS 9,975 SE . 511 124 <50 .31 290 9,975 SE 530 63 NS NS NS 10,000 SE 532 100 <50 LINE 10,500 NE .20 200 10,000 SE 507 61 NS NS NS LINE 10,800 NE 9,500 SE 582 94 NS NS NS 9,500 SE 567 78 NS NS NS 9.525 SE 551 91 NS NS NS 9.525 SE , 568 81 NS NS NS 9.550 SE 539 86 NS NS NS 9.550 SE 592 79 NS NS NS 9.575 SE 636 81 NS NS NS 9,575 SE 633 75 NS NS NS 9,600 SE 624 87 NS NS NS 9,600 SE 662 73 NS NS NS 9.625 SE 659 103 NS NS NS 9,625 SE 600 82 NS NS NS 9.650 SE . 677 108 NS NS NS 9,650 SE . 557 104 NS NS NS 9,675 SE . 608 159 NS NS NS 9,675 SE . 545 101 NS NS NS 9.700 SE . 587 112 NS NS NS 9.700 SE , 544 88 NS NS NS 9,725 SE . 586 107 NS NS NS 9,725 SE . 532 65 NS NS NS 9,750 SE 595 90 NS NS NS 9.750 SE 564 62 NS NS NS 9,775 SE . 594 87 NS NS NS 9.775 SE . 594 87 NS NS NS 9,800 SE . 585 90 NS NS NS 9,800 SE 643 71 NS NS NS 9,825 SE . 593 98 NS NS NS 9,825 SE 764 60 NS NS NS 9,850 SE . 591 174 NS NS NS 9,850 SE 701 57 NS NS NS 9,875 SE 631 208 NS NS NS 9,875 SE 655 NR NS NS NS 9.900 SE 591 196 NS NS NS 9,900 SE 591 66 NS NS NS 9,925 SE 601 188 NS NS NS 9,925 SE 594 63 NS NS NS 9,950 SE 545 165 NS NS NS 9,950 SE 567 61 NS NS NS 9,975 SE . 527 139 NS NS NS 9,975 SE 568 62 NS NS NS 10,000 SE 521 100 NS LINE 10,600 NE NS NS 10,000 SE 544 62 NS NS NS LINE 10,900 NE 9,500 SE 541 86 <50 0.18 200 9,500 SE 555 83 <50 0.26 210 9,525 SE 547 101 <50 17 200 9,525 SE 559 90 <50 .13 190 9,550 SE 553 102 <50 .22 200 9,550 SE 577 88 <50 .13 200 9,575 SE 592 90 <50 .21 220 9,575 SE 651 84 <50 .14 200 9,600 SE 715 92 <50 16 190 9,600 SE 735 85 <50 .13 190 9,625 SE 954 99 <50 .28 210 9,625 SE 909 79 <50 .25 200 9,650 SE 1159 127 <50 5.10 480 9,650 SE 962 84 <50 .15 180 9,675 SE . 722 142 480 1.85 290 9,675 SE 589 84 <50 .17 180 9,700 SE 593 98 270 .26 220 9,700 SE , 572 89 <50 .15 180 9,725 SE . 540 97 <50 .17 200 9,725 SE 581 87 <50 .10 180 9,750 SE 555 99 <.50 .22 230 9,750 SE 557 114 <50 .23 220 9,775 SE . 568 98 <50 .20 170 9,775 SE 574 117 <50 .39 390 9,800 SE . 586 87 <50 .22 190 9,800 SE 587 90 <50 .20 210 9,825 SE . 612 83 <50 .16 160 9,825 SE 608 81 . <50 .14 160 9,850 SE . 671 95 <50 .26 250 9,850 SE , 607 79 <50 .19 180 9.875 SE . 558 86 <50 .25 250 9,875 SE 588 72 <50 .13 180 9,900 SE . 560 77 <50 .36 170 9,900 SE 736 82 <50 .25 280 9,925 SE . 556 81 <50 .21 180 9,925 SE 724 86 340 2.43 390 9,950 SE . 553 76 <50 .25 200 9,950 SE 566 140 <50 1.05 220 9,975 SE . 543 83 <50 .24 230 9,975 SE 546 91 100 21 260 10,000 SE 563 83 <50 18 190 10,000 SE 549 85 <50 .38 230 NS No sample, NR No reading 'Total-field magnetic intensity, all readings have a base of 56,000 gammas. ^otal-count gamma-ray radiation ^Soil sample analyses by XRF by Bureau's Reno Research Center, Reno, NV. RESULTS OF MAGNETIC,' RADIOMETRIC,^ AND SOIL SAMPLE^ SURVEYS— Continued 29 Station Magnetic intensity, gammas Radioactivity. Cb. P2O.. Zn. Station Magnetic intensity. Radioactivity, Cb. P205, Zn, cps ppm pet ppm gammas cps ppm pet ppm LINE 11.000 NE LINE 11,300 NE 9.500 SE . 558 82 NS NS NS 9.500 SE 523 70 <50 0,17 200 9.525 SE . . 554 82 NS NS NS 9.525 SE 524 66 <-50 .16 190 9.550 SE . . 577 89 NS NS NS 9.550 SE 516 75 <50 .15 190 9.575 SE . 575 93 NS NS NS 9.575 SE 521 70 <50 .19 190 9.600 SE 646 86 NS NS NS 9.600 SE 525 69 <50 .16 200 9.625 SE 700 97 NS NS NS 9.625 SE 528 70 <50 .15 200 9.650 SE 802 95 NS NS NS 9.650 SE 540 68 <50 .21 220 9.675 SE . . 614 87 NS NS NS 9.675 SE . 536 65 <50 .14 220 9,700 SE . 571 79 NS NS NS 9.700 SE 540 71 <50 .13 180 9.725 SE . 556 80 NS NS NS 9.725 SE 551 77 <50 .14 180 9.750 SE 545 76 NS NS NS 9.750 SE 519 65 <50 .15 210 9.775 SE 563 76 NS NS NS 9.775 SE 528 77 <50 .12 190 9.800 SE 569 79 NS NS NS 9.800 SE 530 76 <50 .13 200 9.825 SE , 577 74 NS NS NS 9.825 SE 526 76 <50 .15 200 9.850 SE . 592 80 NS NS NS 9.850 SE . 535 83 -.50 .11 190 9.875 SE . 623 81 NS NS NS 9.875 SE 540 87 <50 .20 200 9.900 SE . 687 82 NS NS NS 9.900 SE 535 81 <50 .14 200 9.925 SE 775 83 NS NS NS 9.925 SE 527 66 <50 .14 190 9.950 SE 784 79 NS NS NS 9.950 SE 525 75 <50 .16 180 9.975 SE . , 802 79 NS NS NS 9.975 SE 516 82 <50 .17 200 10.000 SE 549 78 NS NS NS 10.000 SE 549 81 <50 .16 200 10.025 SE 544 75 NS NS NS 10.025 SE 531 73 -50 -18 190 LINE 11.100 Nb 10.050 SE 10.075 SE 532 538 74 76 <50 <50 .16 .16 190 9.500 SE . , 523 83 <50 0.17 200 190 9.525 SE , 507 93 <50 ,20 200 10.100 SE 528 88 <50 .17 190 9.550 SE , 506 85 <50 ,14 200 10,125 SE 527 81 <50 .20 190 9,575 SE 520 90 <50 .15 180 10,150 SE 556 85 <50 .13 190 9,600 SE , 536 85 <50 .10 190 10.175 SE 565 76 <50 -15 200 9.625 SE 562 87 <50 .19 240 10.200 SE 545 76 -50 -14 180 9,650 SE . 562 624 84 85 <50 <50 .15 .12 190 180 LINE 11.500 NE 9,675 SE 9.500 SE 540 69 NS NS NS 9,700 SE . . 771 82 <50 .11 190 9.525 SE 528 69 NS NS NS 9.725 SE . . 946 86 <50 .15 190 9.550 SE 533 69 NS NS NS 9.750 SE 660 85 <50 .18 190 9.575 SE 528 77 NS NS NS 9.775 SE . , 585 78 <50 .15 200 9.600 SE . 519 77 NS NS NS 9.800 SE . 566 82 <50 .14 210 9.625 SE 520 82 NS NS NS 9.825 SE 580 86 <50 .10 200 9.650 SE 519 84 NS NS NS 9.850 SE . , 573 87 <50 .12 200 9.675 SE 522 81 NS NS NS 9.875 SE , , 580 82 <50 .17 210 9.700 SE 530 82 NS NS NS 9.900 SE . . 611 88 <50 -15 200 9.725 SE 541 74 NS NS NS 9.925 SE , 594 86 <50 .20 200 9.750 SE 533 79 NS NS NS 9.950 SE . 613 84 <50 .14 190 9.775 SE 537 85 NS NS NS 9.975 SE . . 599 82 <50 .17 190 9.800 SE 532 85 NS NS NS 10,000 SE 600 75 <50 .21 190 9.825 SE . 530 84 NS NS NS 10,025 SE 595 NR <50 .18 180 9.850 SE . 514 85 NS NS NS 10,050 SE 551 NR NS NS NS 9.875 SE . 511 80 NS NS NS 10.075 SE 530 NR NS NS NS 9.900 SE . 512 82 NS NS NS 10.100 SE 539 NR NS NS NS 9.925 SE 9.950 SE 502 506 77 77 NS NS NS NS NS NS LINE 11,200 Nt 9.975 SE 10.000 SE 510 511 76 75 NS NS NS NS NS 9,500 SE . . 547 84 NS NS NS NS 9,525 SE . . 550 81 NS NS NS 9,550 SE . . 536 90 NS NS NS 10.025 SE 533 81 NS NS NS 9,575 SE .. 530 88 NS NS NS 10.050 SE 527 81 NS NS NS 9,600 SE . . 543 • 92 NS NS NS 10.075 SE 521 79 NS NS NS 9,625 SE 557 85 NS NS NS 10.100 SE 521 81 NS NS NS 9,650 SE . 600 82 NS NS NS 10,125 SE 514 87 NS NS NS 10.150 SE 531 88 NS NS NS 9,675 SE .. 650 80 NS NS NS 10.175 SE 535 80 NS NS NS 9.700 SE . . 808 82 NS NS NS 9,725 SE . . 625 87 NS NS NS 10.200 SE 532 81 NS NS NS 9.750 SE . 498 92 NS NS NS 10.225 SE 532 85 NS NS NS 9.775 SE , . 506 77 NS NS NS 10.250 SE 539 81 NS NS NS 9,800 SE . 508 78 NS NS NS 10.275 SE 531 79 NS NS NS 9,825 SE . . 515 70 NS NS NS 10.300 SE 535 78 NS NS NS 10.325 SE 531 82 NS NS NS 9.850 SE . . 529 79 NS NS NS 10,350 SE 530 64 NS NS NS 9.875 SE . . 528 82 NS NS NS 9.900 SE . . 543 82 NS NS NS 10.375 SE 531 69 NS NS NS 9.925 SE . . 540 88 NS NS NS 10.400 SE 535 72 NS NS NS 9.950 SE . . 544 87 NS NS NS 9.975 SE . . 522 82 NS NS NS NS No ; sample. NR No reading. 10.000 SE 518 76 NS NS NS 'Total-fiel d magnetic intensity, all readi ngs have a base of 56.000 gammas ^otal-coL jnt gamma- ray radiation. 10.025 SE 527 78 NS NS NS ^Soll sam pie analyses by XRF by Bureau s Reno Research Center, Reno, 10,050 SE 527 77 NS NS NS 10,075 SE 527 78 NS NS NS 10,100 SE 526 75 NS NS NS 10.125 SE 10,150 SE 519 522 77 80 NS NS NS NS NS NS 848^/ IGO 10,175 SE 522 75 NS NS NS 10.200 SE 521 81 NS NS NS ^U.S. Government Printir a Office : 1986 -168 -198/50998 NV. / 5°x. ^-./ ' * : °'^o V*'" -^ 4 o^ 1? ^ ."b' "J?^ <^ o >-^°^ ,^' "e. ;* ^' ^ .^^' "^. \/i / V 0^ ,< '- '^bv^ a5^ *^ %.^v if' %> .^ , o • O , *o. %f. .!b' "^ CONG' ,RESS : l^ : .■■,^:^ ;iii?(::!