Reconnaissance guidelines for gold exploration in Central Alaska

Journal ofGeochemwal Exploratton, 47 ( 1993 ) 89-108 Elsevier S o e n c e Pubhshers B V , Amsterdam

89

Reconnaissance guidelines for gold exploration in Central Alaska T h o m a s D. L i g h t a, Stanton H Moll b, Scott W. Ble a and Gregory K Lee c aU S Geologwal Survey, 4200 UnzversttyDr, Anchorage, AK 99508, USA bTGS Technology, Inc, 4230 Umverstty Dr , Anchorage, AK 99508, USA cU S Geologwal Survey, P 0 Box 25046, Denver Federal Center, Denver, CO 80225, USA (Received 11 October 1991, accepted after revision 11 June 1992)

ABSTRACT Light, T D , Moll, S H , Ble, S W and Lee, G K , 1993 Reconnaissance guldehnes for gold exploration in Central Alaska In F W Dlckson and L C Hsu (E&tors), Geochemical Exploration 1991 J Geochem Explor, 47 89-108 Distribution of more than 300 gold-bearing samples from the Llvengood (Tolovana) and parts of the Falrbanks and Rampart mining districts in central Alaska, USA, indicate that the concentration of gold in placers is spatlaUy related both to structural features and to Late Cretaceous and (or) Tertiary felslc plutons The regional consistency of these spatial relationships Is demonstrated by proximity analysis using a Geographic Information System (GIS), and suggests a genetic association between faults, felslc plutons, and gold occurrences The local presence of gold within several of the plutons Indicates that these are the source of some of the gold In addition, some gold occurs proximal to faults where plutons are not present, suggesting that some of the gold was also derived from the country rock We envision a model whereby weakly mlnerahzed solutions, thermally driven by latent plutonlc heat, were enriched by circulation through clastlc units that may have had a naturally elevated gold background The resultant enriched solutions were channeled and reconcentrated along or adjacent to large-scale fault systems Future exploration to define Individual target areas should be directed toward areas where Late Cretaceous and (or) Tertiary felsic plutons occur near major faults

INTRODUCTION

The Llvengood quadrangle encompasses the Llvengood (Tolovana) mining district and parts of the Falrbanks and Rampart mining districts (Fig 1 ). Placer gold was &scovered in the Rampart mining &strict m 1882, and has been mined intermittently in several localities within the Llvengood quadrangle from about 1910 to the present. Although placer gold has been mined extensively in the Llvengood quadrangle, the lode source (s) of much of the gold Correspondence to T D Light, U S Geological Survey, 4200 Umverslty D r , Anchorage, AK 99508, USA

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RECONNAISSANCEGUIDELINES FOR GOLD EXPLORATION IN CENTRAL ALASKA

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has remained a mystery. This study presents the results of geological and geochemical investigations to evaluate factors controlhng the distribution of gold in the quadrangle The Llvengood quadrangle comprises approximately 16,000 sq km (6,000 sq ml) from 65 ° to 66 ° north latitude and from 147 ° to 150 ° west longitude and lies mostly within the Yukon-Tanana Upland (Wahrhaftlg, 1965 ) The Llvengood quadrangle is underlain by a northeasterly trending sequence of Proterozolc, Paleozoic, and Mesozoic metased~mentary and sedimentary rocks, locally intruded by Cretaceous and Tertiary granitic rocks that presently form topographic highs (Fig 2 ). The major faults in the area are strikeslip splays of the Tmtlna fault zone, and northwest verging thrust faults (Chapman et al., 1971 ) The Tolovana mining district, which includes the Llvengood area in the center of the quadrangle, produced more than 14,000 kg (380,000 oz) of gold (Cobb, 1964), and mining activity has continued to the present Small lode gold occurrences m the Tolovana district have been described in sihceous graywacke, in altered breccias, and in sihceous carbonate closely associated with monzonitic stocks and dikes (Foster, 1968 ) The area designated as the Llvengood mining district (Fig 1 ) encompasses only that area of the previously defined Tolovana mining district (Ransome and Kerns, 1954) where gold deposits occur In the vicinity of Livengood townslte The Fairbanks mining district produced more than 285,000 kg (7,500,000 oz) of gold (Cobb, 1964). The northern part of the district lies in the southeast corner of the Llvengood quadrangle. Numerous placer deposlts occur in stream valleys draining the FaIrbanks schist unit, which consists chiefly of quartzite and quartz-mica schist The source of most of the gold in the southeastern Llvengood quadrangle is thought to be either the Cleary sequence, a distinctive 120-m-thick section of probable volcanogenlc beds that occur within the Fairbanks schist unit (Zf) (Robinson et al, 1982 ), or gold-bearing felslc porphyries such as the Fort Knox stock (Holhster, 1991 ), which lies 1 km south of the Llvengood quadrangle The eastern part of the Rampart mining district includes the Sawtooth Mountains in the west-central portion of the Livengood quadrangle Gold recovery from that p o m o n of the Rampart district within the Llvengood quadrangle IS not known, but some production has been reported from numerous small deposits (Mertie, 1934). Exploration with some minor production at several of these placer operations has continued intermittently to the present SAMPLING AND ANALYTICAL TECHNIQUES

In 1985 the U S. Geological Survey initiated multldlsclphnary reconnaissance Investigations of the mineral resources of the White Mountains National RecreaUon Area in the eastern part of the Livengood quadrangle, Alaska

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EXPLANATION

94

T D LIGHT

(Weber et al, 1988 ). These studies were subsequently extended to cover the Llvengood l 250,000-scale quadrangle as part of the Alaska Mineral Resource Assessment Program (AMRAP) During the AMRAP studies we collected 1846 rock, 1038 stream-sediment, and 575 heavy-mineral concentrate samples as part of a reconnaissance geochemical survey of the Llvengood quadrangle All samples were analyzed by semlquantltative emission spectrography, and selected rock and stream-sediment samples were analyzed by atomic absorption spectrophotometry (Arbogast et al, 1991 ) Analyses were done by USGS personnel at the USGS laboratories in Denver, Colorado, USA We compiled all available data for gold-bearing samples previously reported (Albanese, 1982a,b, 1983, Allegro, 1984; Arbogast et al, 199 l, Cathrail et al., 1987, 1988, 1989; Chapman and Weber, 1972, Eaklns, 1974, McDanal et al, 1988; Sutley et al, 1987) A total of 420 samples from the Llvengood quadrangle contained detectable gold, and were used as the data base for this study We have not tried to equate gold values for data determined by different analytical techmques Because of the variety of analyhcal techniques reported in the literature, we have indicated only those areas where gold was found to be present above the determination limits of the respective analytical methods. A more detailed discussion of the specific analytical techtuques for individual samples, the analytical data, and the data sources are reported by Light et al ( 1993 ) The locations for gold-bearing rock, stream° sediment, and heavy-mineral concentrate samples are shown on Fig 2 SPATIAL ANALYSIS

Whether the plutons or the country rock were the source of the gold has long been, and remains, a point of controversy. Although the source of the gold in the Livengood, Falrbanks, and Rampart districts has not been well defined, the close spatial association with felslc igneous intrusions was recognized early (Mertie, 1934) In the Fairbanks district, rock units with h~gh background gold values, especially the Cleary sequence, have been postulated as the sources of much of the gold (Robinson et al, 1982) Recent exploration at the Fort Knox deposit in the Falrbanks district, 1 km south of the Llvengood quadrangle, revealed disseminated gold in a felslc pluton (Holhster, 1991 ) Conversely, some of the felslc plutons in the Llvengood quadrangle, such as the Tolovana Hot Springs Dome plutons, have no apparent assocmt~on with gold. The distribution of gold indicates that not all the plutons are mineralized, but that specific plutons are the source of at least some of the gold It is hkely that both sources, rock units with elevated gold backgrounds and some individual plutons, played an important role in the distribution of gold m the three districts. Gold mobilized and reconcentrated in hydrothermal systems driven by latent plutonlc heat around felslc intrusions would more effectively traverse

RECONNAISSANCE GUIDELINES FOR GOLD EXPLORATION IN CENTRAL ALASKA

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rocks of highest permeablhty, such as those m major fault zones, which would be exposed to the greatest volume of fluids and would thereby concentrate the most gold Dehneatlon of these areas would define the optimal exploration targets To evaluate the spatial relationship of the gold-bearing samples with the plutons and the faults, we examined the distribution of gold-bearing samples with respect to faults or plutons separately, and with respect to both faults and plutons combined. To determine ff there was a distinction between thrust faults and high angle (normal or lateral ) faults we examined these structures separately We used a Geographic Information System (GIS) to evaluate the hypothesis that the proximity of both faults and plutons was a controlling factor in the localization of gold. A technique that uses buffer zones around such features is known as proximity analysis Buffering is a conceptually simple procedure that allows an area to be defined within a given distance of a specified feature (a pluton or a fault) We created buffer zones ranging from 1 to 5 km around both plutons and faults. Because the gold ~s disseminated within the pluton at the Fort Knox deposit, the areas of the plutons were included within the pluton buffer zones To analyze the effect of differences m the ages of plutons the buffer areas around Cretaceous plutons and Tertmry plutons were analyzed separately Similarly, to analyze the effect of differences in fault type, the buffer zones around thrust faults and high-angle faults (including normal, reverse, and lateral faults) were analyzed separately We also used the GIS to remove the extensive Quaternary cover from the geologic map and create a generahzed bedrock map of the quadrangle (Fig 2) This bedrock map was used as the base map for defining the buffer zones around the plutons and the faults In defining the extent of buffer zones, we reasoned that the zone of influence should be larger around plutons than adjacent to faults because circulating hydrothermal fluids would be driven outward from the plutons Conversely, fluid migrat|on toward faults would create a more restricted area of concentration adjacent to faults. In addltmn, the density of faults in the Llvengood quadrangle is such that a buffer zone of greater than about 4 km around faults covers such a large area that any relationship to the gold d~stribution becomes obscured. For example, a 5 km buffer around faults encompasses about 75% of the total area of the quadrangle A l-kilometer buffer around Tertmry plutons (Fig. 3 ) indicates a positive correlation with the distribution of gold-beanng samples in the central and southern Llvengood district The Vault pluton (TKp) crops out in the Fairbanks mining district and is the most likely source of gold found in heavymineral concentrate samples peripheral to the pluton Gold was also found m several heavy-mineral concentrate samples peripheral to the Cache Mountain pluton, north of the Fairbanks d~strict Gold is conspicuously absent from samples in and around the Tolovana Hot Springs Dome and the northeast-

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trending stnng of small plutons cropping out to the south of the Llvengood district. The 5-km buffer around Tertiary plutons (Fig 4) Includes nearly all the gold-bearing samples in the Llvengood district. This larger buffer appears to be more effective in outlining the potential gold distribution associated with the plutons. Although thoroughly sampled, the lack of gold in samples within both the 1-km and 5-km buffer zones around Cache Mountain and the Tolovana Hot Springs D o m e Indicate that these systems are either barren of gold or else did not develop hydrothermal circulation systems for concentrating gold in sufficient quantities to be of economic interest The 1-kilometer buffer around Cretaceous plutons correlates well with goldbearing samples in the Falrbanks district. The l-lolometer buffer around Cretaceous plutons indicates a positive correlation with gold-bearing rock samples in the southern part of the Sawtooth Mountains (Fig. 5 ). Numerous small dikes or sills of possible Cretaceous age that occur throughout the Sawtooth Mountains may be the source of gold in this area. These units are mostly rubble covered and discontinuous, so their areal extent is unknown. The 5-kalometer buffer around Cretaceous plutons encompasses nearly all the gold-bearing samples in the Rampart district and most of the samples in the Fairbanks district (Fig. 6). Gilmore D o m e lies 8 km southeast of Pedro Dome (Robinson et al., 1990), 1 k m south of the Livengood quadrangle Gilmore dome has an age of 91 Ma (Blum, 1982), and this is assumed to be the age of the gold-bearing Fort Knox pluton (Holhster, 1991 ). Some of the goldbeanng samples in the southeastern Livengood quadrangle that lie outside the Pedro D o m e buffer zone fall within the Gilmore Dome buffer zone The 1-kilometer buffer around thrust faults (Fig. 7 ) indicates a fairly strong correlation with gold bearing samples in the Llvengood and Rampart districts, and a slight correlation in the Fairbanks district. The proximity of thrust faults corresponds with the location of a previously unexplained gold-bearing rock sample from the Wllber Creek unit (Ksu) in the southwest portion of the quadrangle The l-kalometer buffer around high-angle faults (Fig. 8 ) has a much lower association with gold-bearing samples than the 1-1olometer buffer around thrust faults. However, a relationship may exist between the locations of goldbearing samples and high-angle faults in the area just south of L v e n g o o d townslte, in the middle of the quadrangle, and in the southern Sawtooth Mountains, on the western edge of the quadrangle. Numerous gold-beanng heavy-mineral concentrate samples in the Fairbanks district in the southeastern corner of the Llvengood quadrangle do not appear to be related to plutons or faults The occurrence of gold-bearing samples along the north side of the Chatanlka River was attributed to the inferred presence ,of Cleary sequence rocks, coincident with an area in which aeromagnetlc, geochemical, and metamorphic evidence suggests the presence of

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buried plutons extending southwestward from exposures in the Circle quadrangle to the east (Light et al, 1987 ) The numerous gold-bearing heavy-mineral concentrate samples m this area may be related to the spatial proximity of both the Cleary sequence and the Inferred buried plutons D E T E R M I N A T I O N O F T A R G E T AREAS

In the Llvengood quadrangle many of the gold-bearing samples are spatlally related both to faults and to Cretaceous and Tertiary felslc plutons Although some gold-bearing samples do not have a clear relationship to either plutons or faults, the close spatial association of most gold-bearing samples with them suggests a genetic relationship If so, this association could be used to define primary target areas for future gold exploration A much higher correlation of gold-bearing samples exists w~th thrust faults than with high-angle faults Therefore, it is appropriate to maintain the dxstlnCtlOn between fault types m examining the buffer zones and defining potential target zones Because of the possibility of a local correlation, such as m the Llvengood district, the high-angle faults should not be ignored, but should be given a lower level of priority in defining exploration targets We assumed that circulating fluids in hydrothermal systems would occupy zones extending outward from the plutons and that metals would be mobihzed within these zones Ground water migration through country rocks would leach metals and carry them toward the faults This relative movement of metals would create a much larger area of influence around the plutons than around the faults Therefore, in depicting zones of influence around plutons and faults, buffer zones of 5 km are defined around plutons and 1 km are defined around faults. These buffer zones best illustrate the spatial association of these features w~th the gold-beanng samples The consistent relationships between plutons, faults, and gold occurrences in all three mining distncts makes it possible to define exploration targets based on the overlap of the buffer zones for faults and plutons We used a GIS to illustrate the coincidence of areas that meet the criteria of being both within the 1-kilometer fault buffer and within the 5-kilometer pluton buffer (Fig 9) The overlap of these combined buffer zones Illustrates several distinct relationships with respect to the gold-bearing localities in the quadrangle Not surprisingly, the best correlations are those close to the areas of the major gold producing districts in the quadrangle The most striking relationship occurs in the center of the quadrangle where buffer zones for several faults near Llvengood lie within the buffer zone defined around several small plutons in the area There is also a strongly indicated association in the southeast comer of the quadrangle where the buffer zones for the Vault pluton (TKp) and the Pedro Dome plutons (Kp) are coincident with or in close proximity to the buffer zone around the thrust fault at the base of the

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qg 9 Target areas for gold explorauon mdlcated by the overlap of buffer zones around plutons and faults Tertiary plutons are indicated by lorth-south hne pattern, Cretaceous plutons are indicated by northeast-southwest hne pattern, high-angle faults are md~cated by e a s t - west me pattern, thrust faults are md~cated by northwest-southeast hne pattern Numbered areas refer to areas d~scussed m text 1 - - Sawtooth ¢lountalns, 2 - - Raven Creek Hdl, 3 - - Cascaden Ridge, 4 - - Brooks Creek, 5 - - Llvengood, 6 - - East Llvengood, 7 - - Cache Mountain, 8 - ?hatamka See Fig 2 for explanaUon o f geologic base Geology modified after Weber et al ( 1 9 9 2 )

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RECONNAISSANCEGUIDELINES FOR GOLD EXPLORATION 1N CENTRAL ALASKA

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Chatamka u m t (Pzc) Another area of coincident buffer zones occurs m the Sawtooth Mountains m the west-central portion of the quadrangle where the intersections between the numerous thrust faults overlap the buffers for the Cretaceous plutons. Several target areas are ldenUfied on Fig. 9 by the overlap of buffer zones around both plutons and faults The mare target areas ldenUfied by the proximity analysis are: ( 1 ) The Sawtooth Mountains, comprising numerous thrust faults and the Cretaceous quartz monzomte plutons and dikes of the Sawtooth Mountains (2) The Raven Creek Hill area, to the north of the Sawtooth Mountains, defined by high-angle faults in close proximity to Cretaceous alaslote. (3) The Cascaden Ridge area, where the buffer zone for the monzomte of the Cascaden Ridge pluton overlaps northeast trending thrust faults. (4) The Brooks Creek area, a small area of overlap between a northeast trending high-angle fault and the Cascaden Ridge pluton (5) The Llvengood-Tolovana area where northeast trending thrust faults and a north trending high-angle fault are both within the buffer zone of Cretaceous or Tertiary granmc plutons (6) The East Tolovana area, a small area of overlap between the buffer zones around an east-trending thrust fault and a granmc pluton to the south. (7) The Cache Mountain area, which comprises several zones of overlap between the buffer zones around the gramtlc Cache Mountain pluton and both thrust and high-angle faults (8) The Chatamka area, consisting of the overlap between buffers around the Tertiary gramte at Pedro D o m e and the Cretaceous or Tert|ary gramte of the Vault pluton w~th the thrust fault at the base of the Chatamka allochthon (Pzc). It should be noted that the area around the Tolovana Hot Springs pluton (Tp, 30 Km east of the Sawtooth Mountains) where no coincident relationships exist between fault and pluton buffers does not have any gold occurrences. Similarly, the buffer zone around the Cache Mountain pluton (Tp) has some overlap w~th buffer zones around faults. Gold has been observed in a few samples peripheral to Cache Mountain and outside the 5-km buffer The Cache Mountain pluton is a highly evolved peralummous granite with some assocmted gre~sen mmerahzat~on, and scattered gold occurrences m local stream drainages have been attributed to the Cache Mountain pluton (Light et al, 1987 ). However, the lack of alteration m the contact zone around the pluton suggests that the intrus|on was too dry to develop an extensive hydrothermal system The best exploration target m the Cache Mountain v~cmlty may be near the faults surrounding the pluton, rather than within the pluton Several groups of gold-beanng samples occur outside the buffer areas defined around plutons and faults Two of these areas are indicated by numerous heavy-mineral concentrate samples m the northern part of the Fmrbanks mining d~strlct, and, as prewously d~scussed, may be related to the presence of referred buried plutons Two similar areas occur to the north and west of

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Llvengood townslte In the area north of Llvengood, two rock samples and several heavy-mineral concentrates occur close to or within the 1-km proximity o f a thrust fault. The signature o f trace elements within samples of gold from the area to the north of Llvengood are similar to those near the Livengood dome and suggest that there m a y be a buried pluton in the area (John Cathrall, USGS, personal c o m m u n i c a t i o n ) In the area west of Llvengood, several gold-bearing rock samples and heavy-mineral concentrate samples were collected outside the defined buffer zones No gold s~gnature data are available for samples in this area, but the multiple gold occurrences suggest the possibility o f a nearby buried pluton. Both o f these areas would become potential exploration targets if the presence of the inferred buried felsic plutons can be confirmed Several isolated unexplained gold occurrences are in the area o f Mlssisslppian to Tnasslc (?) volcanic and sedimentary rocks in the northwest part o f the quadrangle. We speculate that these occurrences may be related to dikes or perhaps to locally high background concentrations near mafic rocks. Evidence is lacking to support the hypothesis o f gold associated with felslc plutons in this part o f the quadrangle CONCLUSIONS Proximity analysis illustrating the spatial and possibly genetic relationship o f geologic and structural features with mineral occurrences can be useful for interpreting the reconnaissance geochemical data and for defining targets for further exploration The association of plutons and faults with previously known gold occurrences in the Llvengood quadrangle was Illustrated using a GIS data presentation. This assocmtlon has been extrapolated to define exploration targets based on the intersection o f buffer zones around plutons and faults at the defined proximity Application o f this technique will be useful throughout central Alaska, and m other areas with similar geologac environments, as a tool for focusing exploration from the regional to the target level

REFERENCES Albanese, M D, 1982a Geochemicalreconnaissanceof the northern Falrbanks D-1 and southern LlvengoodA-l quadrangles, Alaska, summary of data on stream-sediment,pan-concentrate, and rock samples AlaskaDlv of Geol and Geophys Surv Open-Fde Rep 164, 23 pp Mbanese, M D, 1982b Geochemicalreconnaissanceof the northern Falrbanks D-2 and southern LlvengoodA-2 quadrangles, Alaska, summary of data on stream-sediment,pan-concentrate, and rock samples AlaskaDlv of Geol and Geophys Surv Open-Fde Rep 165.23 pp Albanese, M D, 1983 Geochemical reconnaissance of the Llvengood B-3, B-4, C-3, and C-4 quadrangles, Alaska, summary of data on stream-sediment,pan-concentrate,and rock samples AlaskaDlv of Geol and Geophys Surv Rep of Investlgat~ons83-1, 55 pp Allegro, G L, 1984 Geology of the Old Smoky Prospect, Llvengood C-4 quadrangle, Alaska Alaska Dlv of Geol and Geophys Surv Rep of Investigations84-1, 10 pp

RECONNAISSANCE GUIDELINES FOR GOLD EXPLORATION IN CENTRAL ALASKA

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Arbogast, B F , Lee, G K and Light, T D , 1991 Analytical results and sample locality map of stream-sediment and heavy-mineral concentrate samples from the Livengood 1 ° × 3 ~ quadrangle, Alaska U S Geol Surv Open File Rep 91-23-A (paper copy), 91-23-B (diskette), 121 pp Blum, J D , 1982 Petrology, geochemistry, and isotope geochronology of the Gilmore dome and Pedro dome plutons, Fairbanks mining district Unpublished M S thesis, Unlv Alaska, 107 PP Cathrall, J B, Antweiler, J C and Mosier, E L , 1987 Occurrence of platinum in gold samples from the Tolovana and Rampart mining districts, Llvengood quadrangle, Alaska U S Geol Surv Open-File Rep 87-330, 12 pp Cathrall, J B, McDanal, S K , VanTrump, G , Mosler, E L and Trlpp, R B, 1988 Analytical results, geochemical signatures, mineralogical data, and sample Iocahty map of lode gold, placer gold, and heavy-mineral concentrates from the Tolovana mining district, Llvengood quadrangle, Alaska U S Geol Surv Open-File Rep 88-578, 32 pp Cathrall, J B, Antweller, J C , VanTrump, G and Mosler, E L , 1989 Gold analytical results and gold signatures from the Falrbanks mining district, Falrbanks and Llvengood quadrangles, Alaska U S Geol Surv Open-File Rep 89-490, 32 pp Chapman, R M and Weber, F R , 1972 Geochemical analyses of bedrock and stream sediment samples from the Llvengood quadrangle, Alaska U S Geol Surv Open-File Rep 72-67, scale 1 250,000, 2 sheets Chapman, R M , Weber, F R and Taber, B, 1971 Preliminary geologic map of the L~vengood quadrangle, Alaska U S Geol Surv Open-File Rep 71-66, scale 1 250,000, 2 sheets Cobb, E H , 1964 Placer gold occurrences in Alaska U S Geol Surv Mineral Resources Map MR-38, scale 1 2,500,000, 1 sheet Eakins, G R , 1974 Prehmlnary investigations, Llvengood mining district, ~daska Alaska DI~ of Geol and Geophy Surv Open-File Rep 40, 16 pp Foster, R L , 1968 Potential for lode deposits in the Livengood gold placer district, east-central Alaska U S Geol Surv Circular 590, 18 pp Holhster, V F , 1991 Origin of placer gold m the Fairbanks, Alaska, Area, a newly proposed lode source Econ Geol, 86 402-405 Light, T D , Ble, S W and Lee, G K , 1993 Distribution of gold m the Livengood quadrangle U S Geol Surv Miscell Field Studies Map, scale 1 250,000, in press L~ght, T D , Cady, J W , Weber, F R , McCammon, R B and Rinehart, C D , 1987 Sources of placer gold m the southern part of the White Mountains Recreation Area, East-Central Alaska In T D Hamilton and J P Galloway (Editors), Geologic Studies in Alaska by the U S Geol Surv during 1986 U S Geol Surv Circular 998, pp 67-69 McDanal, S K , Cathrall, J B, Mosier, E L , Antweller, J C and Tripp, R B, 1988 Analytical results, geochemical signatures, mineralogical data, and sample locality map of placer gold and heavy-mineral concentrates from the Manley Hot Springs, Tofty, Eureka, and Rampart mining distracts, Tanana and Llvengood quadrangles, Alaska U S Geol Surv Open-Fde Rep 88-443, 54 pp Mertle, J B, J r , 1934 Mineral deposits of the Rampart and Hot Springs districts U S Geol Surv Bull 844-D, pp 163-246 Ransome, A L and Kerns, W H , 1954 Names and definitions of regions, districts, and subdlstrlcts in Alaska U S Bur of Mines Information Circular 7679, 91 pp Robinson, M S, Smith, T E and Bundtzen, T K , 1982 Cleary sequence of the Fairbanks mining district - - Primary stratigraphlc control of lode gold/antimony mineralization ( a b s ) Geol Soc Amer Abstr Prog, 14(4) 228 Robinson, M S , Smith, T E and Metz, P A , 1990 Bedrock geology of the Fairbanks mining district Alaska Dlv of Geol and Geophys Surv Prof Rep 106, scale 1 63,360 Sutley, S J , Ryder, J L , Light, T D and Weber, F R , 1987 Analytical results and sample local-

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lty map of rock samples from the White Mountains, National Recreation area, Llvengood and Circle quadrangles, east-central Alaska U S Geol Sur Open-File Rep 87-284. 61 pp Wahrhaftlg, C, 1965 Physiographic divisions of Alaska U S Geol Surv Prof Paper 482, 52 PP Weber, F R, McCammon, R B, Rinehart. C D, Light, T D and Wheeler, K L, 1988 Geology and mineral resources of the White Mountains National Recreation Area, East-central Alaska U S Geol Surv Open-Fde Rep 88-284, 234 pp Weber, F R, Wheeler, K L, Dover, J H, Rinehart, C D, Blodgett, R B, Cady, J W, Karl S M, McCammon, R B and Mlyaoka, R, 1992 Geologic map of the Llvengood quadrangle, Alaska U S Geol Surv Mlscell Fwld Studies Map, scale 1 250,000