Bureau of Mines Report of Investigations/1987

Characterization of Ketchem Dome Tin Prospect, East-Central Alaska

By D. C. Dahlin, L. L. Brown, and J. D. Warner

UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9145

Characterization of Ketchem Dome Tin Prospect, East -Central Alaska

By D. C. Dahlin, l. L. Brown, and J. D. Warner

UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary

BUREAU OF MINES David S. Brown, Acting Director Library of Congress Cataloging in Publication Data:

Dahlin, D. C. (David Clifford), 1951- Characterization of Ketchem Dome tin prospect, east·central Alaska.

(Report of investigations; 9145)

Bibliography: p. II .

Supt. of Docs. no.: 128.23: 9145.

I. Tin ores-Alaska-Ketchem Dome. I. Brown, L. L. (Lawrence 1.), 1928 - . II. Warner, J. Dean. III. Title. IV. Series: Report of investigations (Cnited States. Bureau of Mines) ; 9145.

TN23.U43 [QE390.2.T48] 622 s [553,4'53'09798] 87·600264 CONTENTS

Abstract ...... 1

Introduction •.• . .•...... 0 ••••••••••••••••• ~:. ••••••••• c: ••••••• fl •••••••• It...... 2 Location and prospect history...... 3

Geology . .••...•..•...... •...... • • ...... iI • • •• • • • • • • • • • • • • 4 Mineralogy...... 6 Bulk sample...... 6 Tin ~oncentrate • ••• ••••••• <...... 8 Concentration results •••• , •..•.••••..••..•••..•••...•... ,...... 9 Conclusions. . . . . •• .. •. . . . . • . . . • ...... 11 Refel... ences...... 11

ILLUSTRATIONS

1. Location of the Ketchem Dome tin prospect...... 3 2. Generalized outline of a portion of the Circle intrusion showing location

of tin occurrences and proposed regional trend .•..••. 0 • •• • • • • • • • • • • • • • • • • • 4 3. Ketchem Dome prospect with detail of trench...... 5 4. SEM photomicrographs of some of the accessory minerals in the rock matrix.. 7 S. SEM photomicrograph and element distribution maps of the tin concentrate... 8 6. Cassiterite (light) locked with iron and silicate gangue...... 9 7. Procedure used to concentrate the bulk sample...... 10

TABLES

1. Size distribution of the rougher table feed...... 9 2. Table concentration of the Ketchem Dome greisen bulk sample...... 10 3. Size distribution of the rougher table slime tailings...... 10 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT ft foot oz/st troy ounce per short ton in inch pct percent lb pound ppm part per million

)..1m micrometer wt pct weight percent m.y. million years CHARACTERIZATION OF KETCHEM DOME TIN PROSPECT, EAS~CENTRALALASKA

By D. C. Dahlin,l L. L. Brownl and J. D. Warner3

ABSTRACT

The Bureau of Mines investigated the Ketchem Dome tin prospect in east-central Alaska to evaluate the tin resource. The studies included field investigations, mineralogical characterization, and concentration of the tin-bearing minerals. The tin mineralization consists of cassit­ erite (Sn02), which occurs as grains disseminated in a greisen (quartz­ mica) matrixo A bulk sample from the largest and best-developed greisen vein exposed at Ketchem Dome contained 0.51 pct Sn. Concentration of the cassiterite by gravity table methods resulted in a product that con­ tained 56 pct of the tin at a grade of 41.4 pct Sn. The mineraliza­ tion exposed at Ketchem Dome is typical of greisen found in the area and elsewhere in interior Alaska.

'Metallurgist, Albany Research Center, Bureau of Mines, Albany, OR. 2Geologist, Albany Research Center (retired). 3p hysical scientist, Alaska Field Operations Center, Bureau of Mines, Fairbanks, AK (now with NERCO Minerals, Inc., Vancouver, WAle 2

INTRODUCTION

Tin is a relatively scarce element in Australia, Bolivia, Malaysia, Thailand, the Earth's crust, but it is an indis­ and the United Kingdom (~-2)' Lower tin pensable material in many industrial ap­ prices would benefit the United States, plications. It is used as a protective and U.Su consumption is expected to show coating for metals such as tinplate and slower growth between 1986 and 1993. as an alloying element in solders, However, the uncertainty of foreign bronze, babbitt, and other metals. The sources dictates that domestic resources primary end-uses of tin in the United be evaluated for their potential. States are cans and other containers, The Bureau of Mines has a continuing chemicals, machinery, electrical equip­ program for investigating critical and ment, and applications in transportation strategic mineral resources in the United and construction. Tin has strategic im­ States. Warner (6) provided a detailed portance in solders for sophisticated de­ summary of the Bur~au's efforts to iden­ fense electronics equipment and computers tify tin, tantalum, and columbium and in military vehicles, containers, resources in Alaska and presented an parts, and fittings (~).4 extensive list of references. Alaska Although the United States is con­ contains both placer and lode tin sidered to be the world's major consumer occurrences. Historically, most of the of tin and the largest producer of sec­ State's tin production has been from ondary tin, domestic primary tin produc­ placer deposits on the Seward Peninsula, tion is almost entirely from imported but lode deposits account for most of the ore, primarily from Southeast Asia and reserves and resources. The lode occur­ South America (1). Only a small fraction rences can be categorized in five groups, of the U.S. tin requirement is met by do­ as follows: greisen, vein, skarn, pegma­ mestic mines, and domestic reserves are tite, and volcanogenic massive sulfide. small. The Ketchem Dome prospect is a greisen In October 1985, the economics of pro­ occurrence. 5 ducing and marketing tin on the world This report describes a preliminary market dramatically changed. At that evaluation of the tin resource at Ketchem time, the International Tin Council, Dome, an established tin prospect ~Tith formed by major producers and consumers good exposure of the mineralization. The of tin to stabilize supply and prices, study was done because the prospect is ran out of funds to support the price of thought to be typical of similar occur­ tin, and, consequently, the price dropped rences in the area and in other parts of to approximately half its former value interior Alaska. Also, the form, altera­ (3). The lower prices had a significant tion mineralogy, geologic setting, and negative effect on high-cost oper­ the tin head grade indicate that it is ations such as the old, underground mines similar to greisen veins mined elsewhere in Bolivia and the gravel-pump operations in the world. that have accounted for about two-thirds of the production from Malaysia. All 5"Greisen" refers to hydrothermally producers reevaluated their tin mining altered granitic rock composed primarily industries, and mines were closed in of quartz, mica, and topaz. The mica is usually muscovite or chlorite; among the common accessory minerals are tourmaline, 4Underlined numbers in parentheses re­ fluorite, rutile, cassiterite, and fer to items in the list of references at wolframite. the end of this report. 3

LOCATION AND PROSPECT HISTORY

The Ketchem Dome tin prospect is lo­ optioned the property to Houston Oil cated approximately 5 miles southwest of and Minerals Co. (now Tenneco Minerals Circle Hot Springs in the north-central Co. , Lakewood, CO). Geologis ts wi th portion of the Circle (B-2) Quadrangle, Houston Oil and Minerals Co. located tin­ in east-central Alaska (fig. 1). The bearing greisen vein mineralization on a prospect lies 1 mile to the west of, and small ridge extending northeastward from approximately 1,300 ft above, a gravel the northern flank of Ketchem Dome road the leads north to a year-round road (figs. 2-3). The option on the property between Central (90 miles northeast of was subsequently dropped by Houston and Fairbanks on the Steese Highway) and acquired by an individual placer gold Circle Hot Springs. miner from Fairbanks. Bureau geologists The Ketchem Dome area was originally mapped and sampled the Ketchem Dome pros­ staked in 1977 by Resource Associates of pect in 1984. Alaska, Inc., Fairbanks, AK C]), which

r------~------~~+_------_;66°

Circle Hot Springs I Ketchem Dome ------165° tin prospect (fig.3)

o 25 50

Scale, miles

FIGURE 1.-Localion of Ketchem Dome tin prospect. 4

~o Scole, miles

/ \

/ ./ LEGEND / 63 General outline of the Circle pluton X Tin-bearing greisen occurrence or prospect • 3,000 -10,000 ppm Sn In pan concentrate sample • Greater than I pct Sn In sluice concentrate sample -- Proposed regional trend of tin occurrences or prospects --- Gravel road -"'- Creek

FIGURE 2.-Generalized outline of a portion of the Circle intrusion showing location of tin occurrences and proposed regional trend.

GEOLOGY

Tin-bearing greisen vein mineralization granite that grades into a core of dense, near Ketchem Dome cuts a leucocratic black, chlorite- and sericite-altered (light-colored) seriate phase of the Cir granite with traces of limonite after cle Hot Springs biotite granite pluton pyrite and veinlets of quartz. Purple near its contact with hornfelsed sedi­ fluorite occurs on fractures, and topaz mentary rocks of Paleozoic and/or is locally associated with more pervasive Precambrian (?) age (~, figs. 2-3). The alteration. pluton is a deeply eroded composite in­ The largest and best-developed greisen trusion that forms a crudely horseshoe­ vein is exposed in the two northern shaped outcrop pattern that extends ap­ trenches (fig. 3). The vein is 3 ft wide proximately 8 miles to both the northwest and strikes west-northwest for approxi­ and southeast from Ketchem Dome and has mately 20 ft between the two trench been dated at 60.5±1.8 m.y. by the exposures and is then lost in rubble on potassium-argon method (1). One thin both sides of the ridge. Similar greisen section of the leucocratic phase of the vein material was found in float on pluton collected near Ketchem Dome con­ strike of the greisen vein to the east, tained approximately 36 pct quartz, near the gravel road that parallels 33 pct orthoclase, 26 pct plagioclase Ketchem Creek. This suggests that the (oligoclase), and 5 pct biotite. Minor greisen vein may extend eastward at least amounts of accessory muscovite and pos­ 5,000 ft along strike. sibly topaz, as well as fluorite, zircon, The tin mineralization exposed near and opaque minerals were also observed. Ketchem Dome is typical of greisen found Four hand-excavated trenches expose the elsewhere in the Circle Hot Springs plu­ greisen vein near Ketchem Dome (fig. 3). ton and in interior Alaska. The vein at The greisen is mineralogically zoned, Ketchem Dome occurs along a proposed with a selvage of muscovite-altered regional trend of tin occurrences and 5

N

o 3 Approx. scale, ft

a 600 Approx.---' scale, ft Contour interval, 200 ft

LEGEND Quartz-chlorite veins Geologic contact .... Granite altered to ...... Tin - mine ra lized zone chlorite and sericite ... Gianit. altered to sericite Trench

Seriate biotite granite 3ample location

Hornfe Is

FIGURE 3.-Ketchem Dome prospect with detail of trench. 6

prospects that is associated with the plutons. The mineralized veins or faults Ci r cle Hot Springs pluton and extends are invariably 3 ft o r less in width and from Boulder Creek easterly to beyond can usually only be traced along strike

Portage Creek (fig. 2) 0 This trend in­ for a few tens of feet or less. In some cludes both tin lode and placer mineral­ instances, however, several closely ization. Tin lode mine~alization along spaced greisen veins occur in widths the trend and elsewhere in interior Alas ranging from 10 to 100 ft and may be dis­ ka is typically iron- and chlorite-rich continuously traceable in rubble for a nd generallY occurs in veins and along several hundred to several thousand feet faults or shear zones within moderately along strike. deeply eroded composite biotite-granite

MINERALOGY

BULK SAMPLE also contained some small grains of muscovi teo A 120-lb channel sample was collected Selected portions of the hand specimens from the 3-ft-wide greisen vein exposed were cut and encapulated in plastic i n the northeastern trench at Ketchem mounts, and polished surfaces of the Dome (fig. 3). Representative hand spec­ rocks were prepared for scanning electron imens were selected from the bulk sam"­ microscope (SEM) examination and energy" pIe for mineralogical characterization dispersive X-ray analysis (EDXA). Es­ studies. The remainder was crushed and sentially the same mineralogy was deter­ s plit for chemical analysis and physical mined as described above. However, a few concentration tests. The head analysis small grains of cassiterite were dis­ of the bulk sample was, in percent, seminated in both the quartz and the 0.51 Sn, 72.9 Si02 , 9.80 A1203, 7.80 Fe, micas (chlorite and muscovite). The cas .... 2.29 K20, 0.15 total rare-earth oxides, siterite grains in the quartz ranged up 0.02 S, <0.01 Cb, <0.01 Ta, and <0.01 Ce, to about 100 ~m in diameter, while those and, in ounces per short ton: 0.02 Ag, associated with the micas were generally 0.003 Au, <0.0003 Pt, and <0,0003 Pd. much smaller (f rom 1 to 40 )Jm, with most The hand specimens consisted primarily of in the smaller end of the range). approximately equal amounts of quartz and Many of the fine-grained accessory and chlorite with small amounts of a large alteration minerals were examined and number of accessory and alteration min­ chemically analyzed with the SEM. Fig­ erals. The quartz was granular, trans­ ure 4 shows examples of some of the lucent, and moderately fractured, and the accessory minerals in the rock matrix. chlorite occurred as dark green to black Some of the minerals could be named, but agglomerations and streaks. others were unidentifiable because their The fine-grained accessory and altera­ compositions do not correspond to those tion minerals were scattered throughout of any known minerals. These unidenti­ the rock. They were associated with both fied particles may not warrant new miner­ the quartz and the chlorite as inclusions al names, but they are chemically unique. and along grain boundaries and fractures. Minerals found in the polished surfaces Although the sample contained 0.5 pct Sn, of the rock included apatite, barite, no cassiterite was observed in the hand calcium-cerium oxide, cerium-iron phos­ specimens. Iron-oxide minerals and phate, chalcopyrite, chromite, columbium­ stains occurred in small amounts, pri­ tantalum multiple oxides (ferrocolumbite, marily along healed fractures in the kobeite, petschekite, tapiolite, yttro­ r ock, and a few random clots of sericite columbi te, and others), garnet (alman­ were observed. One of the specimens con­ dite), monazite, pyrite, pyrrhotite, tained a small amount of purple fluorite thorite, thorium oxides, thorium phos­ t hat appeared to be preferentially asso­ phate, uranium oxides, yttrium and other ciated with chlorite masses; the speclmen rare-earth oxides, and zircon. (The 7

FIGURE 4.-SEM photomicrographs of some of the accessory minerals in the rock matrix. A, Cassiterite (circled) with feldspar (l ight), muscovite (gray), and quartz (black) (X 250); B, cassiter· ite in quartz (X 400); C, two multiple·oxide minerals that con' tain uranium in quartz (X 500); D, yttrium·cerium phosphate (light) on apatite (light gray) in feldspar (dark gray) and quartz (black) (X 500); E, columbium·tantalum minerals (circled) with feldspar (light), muscovite (bladed gray), and quartz (black) (X 200). 8 order of abundance could not be accur­ 15 quar tz , 4 iron- oxide minerals , 2 8u1- ate1y established because of the small fid2s , and 2 apatite, and trace amounts amounts involved, so the minerals are of garnet, barite, ilmenite, magnetite, listed alphabetically . ) and fluorite. Other t race minerals were present but were not identified. Fig­ TIN CONCENTRATE ure 5 shows an SEM photomiclograph of the tin concentrate with correaponding tin, The tin concentrate prepared from iron, ano silicon distribution maps. the bulk greisen sample consisted of, Bright areas in each map indicate element in percent , 55 cassiterite, 20 chlorite, concentrations .

FIGURE S.-SEM photomicrograph (A) and element distribution maps (8 tin; C iron; 0 silicon) of the lin concentrate (X 120). EDXA of s i x r andomly selected ca ssit­ erite g~ains in a p oli s h ed surface prepared from the concent r ate gave the following results:

Cassite;.:ite Sn02 Cb205 Fe203 A1 20 3 .&:ain

1 •••• • • • • • •••• 98. 2 0. 89 0. 13 O. 79 2 • • ••• • •• ••• • • 97. 1 1. 21 ND 1. 67 3 • • ••••• • ••••• 97. 1 . 57 . 25 2. 09 4 • •••••••••••• 98. 5 ND . 50 1. 00 5 • •••••••••••• 97. 6 1. 4 2 ND . 99 6 • • • • • • ••••••• 97. 3 . 34 . 64 1. l: 1 ND Not detected.

Although one would expect the cassiterite composition to be relatively uniform within a deposit , the graiT's showed a relatively wide range in the amounts of FIGURE S.-Cassiterite (light) locked with iron and silicate substituted or included elements. gangue (X 180). Although liberation was good at 100 mesh, some of the cassiterite was showed cassiterite locked in particles locked with other minerals present in the less than 1 ).lm in size. Figure 6 shows concentrate , SEM images of polished sur­ cassiterite grains intimately locked with face mounts prepar ed f rom the concentrate gangue.

CONCENTRATION RESULTS

A gravity conce ntration test was con­ tailings (those that settled and bande d ducted on che bulk sample of the tin­ on the table) , and slime tailings (those bearing greisen. The sample was stage­ that washed off the table without set­ ground in rod ffiliis to pass 100 mesh, but tling). Recovery of concentrate was elaborate steps were not taken to prevent emphasized over concentrate grade. The overgrinding. The size distribution of rougher concentrate was tabled again in a the ground sample is s hown in table 1. cleaner step to produce the final tin The ground sample was then tabled on a concentrate. Concentrate grade was em­ slime deck of a wet s haking table to pro­ phasized over recovery in the cleaner duce a rougher concentrate, coarse table step. A flowsheet of the test procedure is shown in f i gure 7, and the results of TABLE L .. Size distribut i on the test are shown in table 2. of the roughe i" table feed The cleaner table concentrate contained nearly 56 pct of the tin at a g cade of Size , mesh wt pct Cumulative wt pct 41.4 pct Sn. These values compare favor­ retaine d ably to those obtained from lode deposits Plus 150•• • •• • 27. 9 27.9 in commercial operations . Although 150 by 200 •• •• 15. 4 43.3 placer concentrates may be nea rly pure 200 by 270 . ... 6. 5 49.8 cassiterite (70 to 75 pct Sn), concen­ 270 by 400 •• • • 16.9 66. 7 trates from lode deposits are substan­ 400 by 500 •• • • 6. 8 73. 5 tially lowe r in grade and may contain Minus 500 • •• •• 26. 5 100. 0 only 15 to 20 pct Sn. Recove ries range 10

TABLE 2. - Table concentration of t he Ketchem Dome greisen bulk sample

Product wt pet Sn, pct Analysis Distribution Rougher concentrate: Cleaner concentrate' •• ••• 0. 7 41.4 55 . 9 Cleaner tailings • •••• • ••• 5. 9 1. 63 18 . 5 Rougher coarse tailings • •• • 62 . 6 . 08 9. 6 Rougher slime tailings ••••• 30 . 8 . 27 16 . 0 Composite o r total •• •••• 100. 0 . 52 100. 0 1Additional analyses, in pct . 11.2 Fe , 10. 1 SL 02 , 2. 95 A1 2 0 3 , 1.30 S , 0 ,, 40 F , 0.21 W, 0. 19 total rare-ea rth ox­ ides, 0.06 Cb, 0.05 Ce , <0 . 01 Ta; in oz/s t: 0. 01 Ag , 0. 006 Au, <0.0003 Pt, and <0.0003 Pd.

from 50 to as much as 65 pct in sophisti­ tailings contained 16 p ct o f the tin, and cated operations, but slime losses are a table 3 shows the siz e distributi on. Be­ major problem (~). cause ca ssiterite is a brittle mineral, The cleaner tailings contained an addi­ recovery might als o be imp roved by more tional 18.5 pct of the tin that conceiv­ precise control of the grinding to pre­ ably could be recovered using a more vent excessive fines and/or by treating elaborate flowsheet. The rougher fine the slime tailings on gravity or other equipment more suitable to fine-particle treatment than shaking tables,

TABLE 3. - Size distribution of the r ougher table slime tailings

wt pct less Undersize Size, }lm th2n size

106 •.••••••••••• • ••••••• .••• 100.0 "15 • •••••• •••••••• • •••• • ••• • 98.0 53 ••••• ••••••••••••••••••• • 92.4 38 •••••••• •• ••••••••••••••• 83.5 27 ••••••••••••••••••••••••• 72.5 Rougher s lime tailings 1 9 ••• •••••••••••••••••••••• 57 . 9 1 3 • •••••••••••••••• • ••••••• 44.7 9. 4 • •• •••••••••••••••••• • • 32.9 6. 6 ••• •••• ••• •••••••• •• ••• 20.9 4. 7 1 • ••••••••• •• •••• •••••• 11.7 FIGURE 7.-Procedure used to concentrate the bulk sample. CONCLUSIONS

The Bureau of Mines completed a prelim­ A two-stage gravity concentration test inary evaluation of the tin resource at recovered 56 pct of the tin at a grade of Ketchem Dome in east-central Alaska. Tin 41.!~ pct Sn . These values compare favor­ occurs as cassiterite in greisen mineral- ' ably with results from commercial lode ization that contains a large number of mining operations" Although optimum con­ accessory minerals in small amounts " The ditions and processes were not investi­ greisen at Ketchem Dome is typical of gated, the potential exists for higher greisen f ound elsewhere in the area and concentrate grade and better recovery , in intericr Alaska.

REFERENCES

1. Carlin, J. F., Jr. Tin. Ch. in 1983; available upon request from Mineral Facts and Problems, 1985 Edition. J . D. Warner, BuMines, Fairbanks, AK. BuMines B 675, 1985, pp. 847-858. 8. Foster, H. L., J. Laird, T. E. C. 2. Tinu BuMines Minerals Keith, G. W. Cushing, and W. D. Menzie" Yearbook 1985, v. 1, 12 pp. (preprint). Preliminary Geologic Map of the Circle 3. Spooner, J. Tin--Trial of Errors. Quadrangle, Alaska. U.S. Geol. Surv. Min. Mag., v. 154, 1986, pp. 475-477. OFR 83-170A, 1983, 30 pp. 4. U.S. Bureau of Mines. Minerals 9. Wilson, F. H., and N. Shew. Map and Materials. A Bimonthly Survey. and Tables ShoWing Preliminary Results of Feb. /Mar. 1986, pp. 5-7. Potassium-Argon Age Studies in the Circle 5. Minerals and Materials. A Quadrangle, Alaska, With a Compilation of Bimonthly Survey. Apr./May 1986, p. 18. Previous Dating Work. U.S. Geol. Surv. 6. Warner, J. D. Critical and Strate­ OFR 81-889, 1981, 1 p. gic Minerals in Alaska. Tin, Tantalum, 10 . Aplan, F. F. Ti n. Sec. in SME and Columbium. BuMines IC 9037, 1985, Mineral Processing Handbook, ed. by 19 pp. N. 1. Weiss. Soc. Min. Eng. AIME, 1985, 7. Freeman, L. (Resource Associates pp< 27-10 to 27-14. of Alaska, Inc.). Private communication,

INT.-8U.OF MINES,PGH.,PA. 28613