STOLM FROM RICHARD D. RLGELP
Potential for Lode Deposits in the Livengood Gold Placer District Eastcentral Alaska
By R. L. Foster
GEOLOGICAL SURVEY CIRCULAR 590
Washington 1968 United States Department of the Interior WALTER J. HICKEL, Seem
Geological Survey William T. Pseora, Dirsctor
first printing 1968 SKond printing 1969
Fm on apPrifu ho U.S. G.okgiit Sumy, W*, D.C. 20242 CONTENTS
Page Page Abstract ------1 Economic geology-Continued lnrroduction ------1 Geochemical investigations ------Geologic environment ------1 Conclusions and recommendations - - - - - Economic geology ------2 References cited------Lode deposits - - - - .. ------2
ILLUSTRATIONS
Page Figure 1. Generalized geologic map and sections of the 1,ivengood district ------2. Map showing distribution of gold lode prospects and productive gold placer deposits- - - 3. Map of Livengood district showing location of stream- and spring-sediment samples and anomalous metal concentrations ------4. Diagrammatic geologic cross sections of the Ruth Creek area (c-C' in fig. I), showing alternative structural interpretations ------
Page Table 1. Semiquantitative spectrographic analyses, and other analyses for gold and mercury, of stream- and spring-sediment samples ------2. Semiquantitative spectrographic analyses and gold analyses from lode prospects - - - - - 3. Semiquantitative spectrographic analyses and gold analyses of rocks ------
Potential for Lode Deposits in the Livengood Gold Placer District East-Central Alaska
By R. 1. Foster
Abstract for gold, by spectrograph for about 30 elements, and The Livengood gold placer district of east-central Alaska con- by a specific atomic-absorption-type instrument for tains small bedrock deposits that probably were the source of the mercurv. Bedrock samoles were analyzed by thesame placer gold. Stream sediments inpartsofthedistrict, particularly and a few sahplesof both rock and stream in the Ruth Creek drainage, are characterized by abnormally high sediment materials were analyzed for go 1d by fire concentrations of gold, arsenic, mercury, antimony, molybdenum, and silver, and Ruth Creek itself is characterized bv. hiehlv-. acid assay check the atomic-absor~tiOn water. The area is complex geologically and is cur by many thrust faulte, some of which have been invaded by serpentinire. Ruth Creek GEOLOGIC ENVIRONMENT and some of the othergeochemically anomalousareasare in upper plate clasric rocks that may be underlain by siliceous carbonates The southern two-thirds of the I.ivengood district rocks beneath thrust faults. The small lode deposits in the upper is underlain chiefly by a metamorphosedclastic facies plate rocks may represent leakage anomalies above economicall1 of sedimentary rocks, the northern one-third, by a significant metal deposits in rocks in or below the thrust faull zones. chert-carbonate facies. These facies are separated by INTRODUCTION an eastward-trending belt of serpentinites(fig. 1). The serpentinites and associated rocks are considered to The Livengood district is in the Yukon-7'anana up- have been emplaced o
ECONOMIC GEOLOGY Geochemical Investigations Lode deposits Geologic studies, I ock analyses, and reconnaissance stream-sediment investigation have revealed a large The small lode gold deposits known in the Liven- polymetallic anomaly n ear Ruth Creek and several good district (fig. 2) are in siliceous graywacke near minor anomalies, including a gold a'nomaly, near Lillian, Olive, and Ruth Creeks, in altered breccias Lucille Creek (fig. 3). on Ruth Creek, and in silica-carbonate rock on Ger- trude Creek and at the Griffin prospect. These deposits The Ruth Creek anomaly (fig. 3, localities 42-47 are spatially related to monzonitic stocks anddikesof inclusive) is characterized by above-background con- centrations of gold, arsenic. mercury, ant i m o n y, probable Tertiary age (fig. 1). Brief descriptions of the deposits follow; the nu m be r s refer to locations molybdenum, silver, and boron in stream sediments (sample Nos. 42-47. table I). Small sulfide veins, shown in figure 2. fracture coatinrs.-, disseminations. and revlacement (1) Gertrude Creek p r o s p e c t.-M a s s i v e, iron- deposits (field Nos. 2-6. table 2)'near .&all mon- stained silica-cqrhnnate rock, which is greenon fresh zonitic stocks and dikes (field Nos. 1-3, table 3) con- surfaces, contains minor amounts of gold (sample tain anomalous concentrations some of these elements, No. 2 1, table 2). which account, at least in part, for their presence in stream sediments down drainage. The anomalous zinc (2) Ruth Creek prospect.-Pyritized, brecciated, iron-stained igneous rock shows replacement by silica concentrations on table 1 (sample Nos. 47, 48) may and carbonate and contais traces of gold (sample Nos. be real but are suspect because the samples were collected downstream from galvanized culverts. 20 and 23-29, table 2). The presence of sulfidized rocks: is also indicated (3) Lillian Creek p r o s p e c t.-Narrow auriferous by acid rnetalliferous water in Ruth Creek. The water arsenopyrite-quartz-scoroditeveins occur in and near -. is red from suspended oxidized iron compounds, al- a limonite-stained dike in altered and contortedgray- though the ground water discharging into Ruth Creek wacke-argillite country rock. Samples from thepros- is clear. The pH determined in the field on four sam- pect contain from 0.5 to 48 ppm gold (sample Nos. I- 1I ples ranged from 3.0 to 5.0; a laboratory deterrnina- and 22, table 2). tion on one sample gave apHofabout 2.75. The chem- (4) Griffin prospect.-Massive, sulfide-bearing, ical composition of the stream water (table onpage 3) green-stained silica-carbonate-talc rock veined by shows that at least some of the water has been in con- quartz contains as much as 3.9pprn (partsper million) tact with various sulfides or sulfosalts other than py - gold (sample Nos. 16-17, table 2). rite. (5) Old Smoky prospect.-Narrow, northwestward- Other anomalous areas in c l u d e those in the Olive trending auriferous arsenopyxite-quartz veins occur Creek drainage, Alder Gulch area, and near I:ucillc in a ferruginous quartzite footwall near the intersec- Creek. A sample from the left t r i b u t a r y of Alder Gulch It is interesting that the geologic setting and geo- (sample No. 40, table 1) contains anomalous amounts chemical suit? of anomalous metals (arsenic, mercury, of lead and mercury, which are attributed tomineral- and antimony in particular) are similar to the setting izatiun along or near the major east-trending fault and suite known to be favorable for the occurrence of inferred to underlie the headwater area of this drain- Carlin-type gold deposits in north-central Nevada age basin (fig. I). (Roberts, 1960, IYhh; flardie, 1900; Er i c k son and others, 1960). However, the significance of these ap- The anomalously high gold content in stream- parent similarities in not known. sediment samples from Fanny Gulch (sample No. 9, table I) and Lucille Creek (Sample No. 20, lab. No. Geophysical investigations and more detailed geo- ACE-419, table 1) suggests gold metallization in the logic studies would he a logical first step in deter- chert-carbonate terrane, whereas the strongly anoma- mining the dip of the faults, but ultimately d r i 1l in g lous gold values in panned concentrates from Lucille would be required. If the information gained from an Creek (sample No. 70, lab. Nos. ACE-486,-488,-490, investigation of the Ruth Creek anomaly indicates eco- table 1) indicate the possible presence of a small gold nomic mineralization associatvd with thrust sheets placer deposit. cut by Tertiary(?) intrusive rocks, then a search for similar geologic environments along the 1-ivengood The significanceof anomalous anlounts of rllanganese trend is suggested. Both the anomalous metalconcen- and antimony in a sample collected in the F an k 1i n r trations in the fault-zonc metasomatites and the silica- Creek drainage (sample No. 23, table I) is unasscssed; carbonate-talc rock s themselves are indicative of these anomalies may be related to the p 1- e s n of c c e hydrothermal activity within and along the postulated mafic i gn cou s rocks and massive chert-carbonate major faults in the vicinity of the monzonitic rocks. strata. The silica-carbonate-talc rocks derived from the CONCLUSIONS ANL3 R ECOXllIENDATlOK?; serpentinitcs are considered favorable hosts. Their low magnetic susceptibility, due to the oxidation of The combination of minor lode :leposits, gcochem- primary and secondary magnetite during hydrothermal ical anomaly, and structural pattern at Ruth Creek alteration, contrasts sharply with that of the serpen- makes this area worthy of further investigation as a tinites. Thus, magnetometer surveys along and on potential exploration targct. Dip of the faults in the strike with highly magnetic serpentinitesmight reveal area is a critical factor. Jf the faults neilr- I.ivcngood the presence of silica-carbonate-talc rocks w h i c h (figs. 1, .4& arc low-angle thrusts dipping south, a could provide additional exploration targets. footwall section of chert-cal-bonate rocks may exist at shallow depth. The siliceous dolomite andcontorted The available data suggest that thc Livengood Creek or fractured chert in such a section arc considered gold placer deposits repressnt a sizeable gold resource favorablc hos~rocks for gold deposition. If the minor which warrants additional economic a p p r a i s a 1. In- lode deposits in the Kuth Creek area represent leak- formation from 640 drill holes in the gravels of the age over a mincralizcd z o 11e, the chert-carbonate Livengood Creek area indicates some 17 million cubic rocks, as well as some of the rocks in thc fault zone ydrds of material with an average recoverable gold \!ould bc logical targets for physical exploration. On content of about 70 cents per cuhic yard (gold at $35 thu ~.)thorhand, if the faults are high-angle reverse per ounce) (C. F. Herbert, written commun., 1966). 0;-srr-]kc-sl~p in nature (fig. 4Q), thcn the favorable I'he 1.ucille Creek gold placer deposit found during i !-J, :.L -carhonntc strata may he huricd at too great a this study also should belnvestigatedfurther, dlthough .i.-pti; to b~!a practicable target. the thick overburden and lack of water might make th~sdeposit uneconomic.
.4nalysin of Kurh Creek wdrer REFERENCES CITED ..\nalyst: I<. n. names; I Rlakc, M. C., Jr., Irwin, W. P., and Coleman, K. G., Constituent Conccn:ration Constituent Concentration 1967, Upsidedown met amor p h i c zonation, blue- I (I)l~tTU (Pr'm) schist facies, along a regional thrust in California Si02 and Oregon: U.S. Geol. Survey Prof. Paper 575-C, A 1 9 P. Cobb, E. H., 1964, Placer gold occurrences in Alaska: Fe (coral) U.S. Geol. Survey hl i n e x a 1 lnv. Resources Map M n MH -38. Zn Erickson, R. I,., VanSicklc, G. H., Nakagawa, H. M., Cu McCarthy, J. H., Jr., and Leong, K. W., 1966, Gold geochemical an0mdly in the Cortez district, h s Nevada: U.S. Gcol. Survey Circ. 534. Ca Foster, R. L., 1907, Tectonic inclusions from a ser- hlg pentinite, east-central Alaska: U.S. Geol. Survey Prof. Paper 375-D, p. D120-D122. Foster, R. L., and Chapman, R. M., 1967, Locations Irwin,W. P., 1964, Late Mesozoic orogenies in the and descriptions of lode prospects in the Livengood ultramafic belts of northwestern California and area, east-central Alaska: U.S. Geol. Survey open- southwestern 0.r egon: U.S. Geol. Survey Prof. file rept., 3 p. Paper, 501-C, 9 p. Foster, R. L., 1968, Descriptions of the Ruth Creek, Roberts, R. J., 1960, Alinement of mining districts Lillian Creek, Olive Creek, Griffin, Sunshine No. in north-central Nevada, & Geological Survey Re- 2, and Old Smoky prospects, Livengood district, search 1960: U.S. Geol. Survey Prof. Paper 400-B, Alaska: U.S. Geol. Survey open-file rept., LO(?) p. p. B17-B19. Hardie, Ry&onS., 1966, Carlin gold mine, Lynn dis- -1966, Metallogenic provinces and mineral belts trict, Nevada: Nevada Bur. Mines Rept., 13, p. 73- in Nevada: Nevada Bur. Mines Rept., 13, p. 47-72. 83. TABLES 1-3 AND FIGURES 1-4 Table 1.--Semiquantitative spectrographic analyses and other analyses for gold --. -. [Looked for but not detected: Bi, Cd, Pt, Pd, Fh, Sc, Sn, Ta, Te. Symbols used: <, less than; detectability. Spectrographic analyses by D. J. Grimes; results are reported to the nearest sorption by A. L. Meier, R. L. Miller, and T. A. Roemer. Mercury analyzed by instrumental are given in percent. pH, field determination; sample 42 includes laboratory determination *- -- Au Au Sample Lab. Field Spectro- Atomic NO. No. No. Ag As graphic Ahsorp- B Ba Be Co Cr Cu Hg La t ion nnn Fb- WFP- 30300
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Au Au Sample Lab. Field Spectro- Atomic No. No. No. Ag As graphic Absorp- B Ba Be Co Cr Cu Hg La tion
51 ACE-082 51 A 200 A --* 30 300 1 15 150 30 .70 20 5 2 526 52 c.5 A A c.02 70 700 1 20 150 50 .85 50 53 090 53 A A A - - - 30 300 h i/~annedconcentrate. - I_nercury of stream- nr~d spr'irig-sediment samples from the Livengood district--Continued Table 2.--Semiquantitative spectrographic analyses and gold C~ovkctl for but not detected: Bi, Cd, Hg? Pt, Fd, Rh, Sc, Sn, Ta, Te, Symbols used:<, less ference; (lo), lower lirnit of detectabllity. Spectrographic analyses by Arnold Farley, Jr., 0.3, 0.2, 0.15, 0.1, and TO on. Gold analyzed by atomic absorption by A. L. Meier, K. L. Yager. Results are given in parts per million except for Mg, Fe, Ca, Ti, which are given Au Sample Lab. Field Spectro- Atomic Fire No. No. No. Ag As graphic absorp- assay B Ba Be Co Cr Cu :-... Sample Description Sample Description Samples 12-15 from Old Smoky prospect. Samples 1-1 1 from Lillian prospcct, 12 ------5-ft chip samplefrom biotitemonzonite-quartzite I ------10-ft chip sample (2-111. interval) along reddish- contact zone; 3 narrow (1-in.) quartz-arseno- brown quartz-arsenopyrite zone, Sample is in pyrite veins are present in quartzite. or near top of brown pyrite-bearing siltstone 13 ------Vein grab sample from No. 12 zone. and below a hanging wall of gray argillite. 14 ------Do. 2 ------Selected samples from No. 1 chip sample zone. 15------Do. 3 ------Selected sample from No. 4 chip sample zone. 4 ------7-ft chip sample (2-in. interval)innarrow(2-in.) Samples 16-17 from Griffin prospect. reddish-brown to yellow-brownquarts- 16----- Adit tailings, grab samples of massivegray car- sulfide(?) vein in gray silty mudstone. - - 5 ------Selected fragments from No. 4 chrp samplezone. bonace which con t a i n s quartz veins and is 6 ------Selected quarrz-arsenopyrite vein matcrialfrom stained green by weathering of disseminated No. 4 chip sample zone. sulfides. 17 ------Do. 7------Do. 8---+--- Grab sample from altered, yellow-brown dike rock. Samples 18-19 from Sunshine No. 2 prospect. 9 ------Selected sulfide mass from inter~orofNo.8dike. 18 ------Crab sample from altered yellow-brown dike. 10 ------5-ft chip sample (2-in. interval) across altered 19 ------Selecred samplefrom yellow-brownfriablemate- dike. rial in lower adit tailings. I]-++--- - Selected material from friable, rcddlsh-brown altered material containing quartz veinlcts, analyses from lode prospects in the Livengood district than;>, greater than; G, greater than 10; A, not detected; --- , not looked for; I, inter- and E. E. Martinez; results are reported to the nearest number in the series 1, 0.7, 0.5, Miller, and T. A. Roemer. Gold analyzed by fire assay by W. D. Goss, L. C, Huff, and T. L. in percent. Field numbers are shown in figure 21 - - . 50 15 300 10 15 50 100 1,000 200 50 20 <200 150 0.2 5 0.1. 0.2 100 15 150 20 10 30 A A 1,500 <20 50 10 A 150 200 A 15 A 70 5 15 7 .7 A A 1,500 <20 50 10 A LOO 300 A 10 A 100 5 15 5 >1 A A 2,000 <20 70 A A 100 300 A I. 200 150 320 3 1 Sample Description Sample Description 20------Grab sample from serpentinite scree. Sample 20 from Kuth Creek bench placer cut. Samples from Ruth Creek prospect-Continued 21 ------Grab samplefrommasslvegreen-stainedquartz- 25 ------Grab sample from light-gray (reddish-brown on carbonate. Sample 21 from Gertrude Creek weathered surface) fine-grained brecciated. prospect. sulfide-bearing sheared igneous rock made up 22------Grab sample from yellow-brown silicic dike rock. of plagioclase, chlorite, and carbonate. Sample 22 from Lillian Creek prospect area. 26 ------Selected sample from light-gray (reddi~h-brown on weathered surface) fine-grained sulfide- Samples 23-29 from Ruth Creek prospect. bearing cataclasite. 27------Selected sample from g r e en i s h-g r a y fine- 23 ------Grab sample from gray (reddish-brown on grained sulfide-bearing cataclasite. weathered surface) medium-grained brecciated 28 ------2.5-ft chip sample (4- to 5-in. interval) in light- s u 1f i d e-b e a r in g igneous rock composed of gray (reddish-brown on weathered surface) plagioclase, chlorite. and carbonate. massive sulfide-bearing carbonate metaso- 24 ------Grab sample from dark-gray (reddish-brown on matite derived from the replacement of igneous weathered surface) fin e-g r a i n ed sulfide- breccia. bearing igneous rock composed of plagioclase. 29 ------Se 1ec t ed sample from light-gray (reddish on chlorite, and carbonate and containing quartz weathered surface) brecciated cataclasite. Table 3.--Semiquantitative spectrographic analyses and old [Looked for but not detected: Au (spectrographic), Bi, Cd, Hg, Pt, Pd, Rh, Ta, Te. Symbols (.5), lower limit of detectability. Spectrographic analyses by Arnold Farley, Jr.; results on. Gold analyzed by atomic absorption by A. L. Meier, R. L. Miller, and T. A. Roemer. cent. Field numbers are shown in figure 23 Au Atomic Sample Lab. Field Ag As absorp- B Ba Be Co Cr Cu La Mo Mn No. No. No. tion Sample Description Sample Description 1-6 ------10-ft chip samples (2-in. interval in bedrock; 7 ------Grab sample from altered sulfide-bearinggray continuous sampling on soft material). Bed- (reddish-brown on weathered surface) igneous rock sample Is ~ulfide-bearinggray to dark- rock with minor c h lo r it e and sericite; ap- gray (dark brown on weathered surface) proximately 70 percent of rock isreplacement altered porphyritic fine-grained larite(?) with carbonate. sericite and limonite rnassesadjacent tofrac- 8--+---- Grab samplefromaltered sulfide-bearingdark- tures; quartz nests and veinlets corn rnon; gray (brown on weathered surface)porphyritic opaque minerals associated withf r a c t u r e s. fine-grained larite(?) with quartz veinlets, quartz nests, and marrix material. Soft mate- quartz nests, minor sericite and carbonate. rial is essentially limonitic igneous rock de- and disseminated opaque minerals. composed in place. analyses by atomic absorption of rocks from the Livengood district used: <, less than; >, greater than; A, not detected; ---,not looked for; I, interference; are reported to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so Results are given in parts per million except for Mg, Fe, Ca, Ti, which are given in per- Sample Description Sarnplc Description 9 ------Grab sample from sulfide-bearing yellowish- 11------Grab sample sulfide-bearing gray (reddish- brow n medium-grained rnonzonitic(7) dike brown on weathered surface)porphyriticfine- rock with secondary limonite, quartz, sericite, grained latite(7) with quartz nests and minor and clinozoisite. carbonate. 10 ------Scree grab sample from dark-gray to dark- 12 ------Grab sample from sulfide-bearing dark gray grayish-brown (brown on weathered surface) (brown on weathered surface) medium-grained porphyritic medium-grained quartz mon- monzonice; limonite stain common, zonite; pseudographic text u r e with quartz 13 ------+ Scree grab sample from brownish-gray (brown enclosing brown-stained K-feldspar and pla- on weathered surface) porphyritic medium- gioclase. grained quartz monzonite with limonite stain. Minor elements (table 3) indicate this rock to be a possible late-stage differentiate. A A' B LEVEL LEVEL EXPLANATION =%' =%' Strike and plunge of Placer workings Dark-green metabasdt (locally sheared) lineation Vein I Flood-plain alluvium Gray siliceous dolomite with interbedded gray and black chert &, Fwil location Surficial deposits, undifferentiated 1 Black and gray banded chert breccia, black marble, vilcaii-clastic and tuffaceous beds J Monmnitic rocks ?- Contact Approximutely located; qwried where doubtful Black and dark-gray to grayish- brown graywacke and argillite Fault Dotied where concealed; bar and ball on Includes alternating arenaceous and argillaceous clas- 1"W downthrom side tic beds of Devonian (?) age south of the Tolonana 0 RiverandeastofClearyCreek FAULT AND UNCONFORMlTY Thrust or reverse fault Dotted where concealed; sawteeth on upper plate or hanging wall side Green fine- to coarse-grained metadiorite (dike :o t A equivalents included in RSP) Vertical Inclined S, = S, Strike and dip of foliation APPROXIMATE MEAN DECLIMITIOH. 1968 + 15 Dark- to light-green serpeninite, peridotite, rneta- I Vertical Inclined basalt, tectonic inclusions, and silica-carbonate-talc Strike and dip of joints metasomatites Figure 1.--Generalized geologic map and sections of the Livengood district. -- EXPLANATION o5 a2 Inactive Active id placer a' Gold lode proapect NfsSRbss. iefifeld ?b81* ~mCtablet d Rock mmple location Nu* isfwld leu& given in table $ .LODE 1. Gertrude Creek prospect 6 3 2. Ruth Creek pmpect r (r 3. Lillian Creek prospect 4. Griffin prospect 5. Old Smoky prospect 6. Sunshine No. 2 prospect PLACER 1. Good Luck (Lucky) Creek 2. Amy Creek 3. Amy Creek (Fanny Gulch) 4. Livengood Creek-Franklin Creek area (includes placer drift mine on benches in Livengood Creek) 5. Gertrude Creek 6. Gertrude Creek (Warwick Gulch) 7. Glenn Gulch 8. Livengood Creek-Myrtle Creek area 9. Ruth Creek area 0. Lillian Creek 1. Olive,Creek -.-. . - 2. Eeter Creek Base from U.S. Geological Survey 1 Livengood IC-4). 1952; Livengood (8-4). 1953; 1 % 0 I 2 MILES IIII I Lrvengcd (C-3). 1954; and Livengood (8-3). 1954 I I CONTOUR INTERVAL I00 FEET ~i~~~~?.--flap showing distribution of gold lode prospects and productive gold placer deposits in the Livengood district. - EXPLANATION Metdimentary strata UNCONFORMITYR[ Metadiori*?) Chert-carbonate faciea Contact ------L SEA Fault LEVEl R8ver.s~or thrust 0 500 1000 FEET Figure 4.--Digrammatic geologic cross sections of the Ruth Creek area, (C--4' in-fig. l), showing alternative structural interpretations. A. Thrust interpretation, with possible min- eralization in: a, silica-carbonate-talc selvage below faulted unconformity; e, brecciated mafic stock; and-c, chert-carbonate footwall complex. B. High-angle reverse or strike-slip fault interpretation with mineralization in: a, silica-carbonate-talc ~elvage;and 2, brec- ciated mafic stock. * U.S. GOVERNMENT PRINTING OFFICE : l86D 0-353-622