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Unnamed (near Kohlsaat Peak)

Occurrence in Alaska, United States with commodities Gold, Copper, Molybdenum, Lead, Zinc, Arsenic
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Geologic information

Identification information

Deposit ID 10308443
Record type Site
Current site name Unnamed (near Kohlsaat Peak)

Geographic coordinates

Geographic coordinates: -152.73181, 62.2375 (WGS84)
Relative position Curtin, Karlson, O'Leary, Day, and McDougal (1978) locate this silt sample site approximately one and a quarter mile N20E of Kohlsaat Peak in the southwest quarter of Section 23, T. 25 N., R. 19 W., of the Seward Meridian.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Gold Primary
Copper Primary
Molybdenum Primary
Lead Primary
Zinc Primary
Arsenic Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Chalcopyrite Ore
Galena Ore
Pyrite Ore
Quartz Gangue
Tourmaline Gangue

Alteration

  • (Local) Carbonate, chlorite, sericite, and quartz alteration.

Nearby scientific data

(1) -152.73181, 62.2375
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Comments on the geologic information

  • Geologic Description = Curtin, Karlson, O'Leary, Day, and McDougal, (1978) recorded a silt anomaly with up to 0.75 ppm gold from a stream draining Kohlsaat Peak. In the late 1980s Cominco American Incorporated (unpublished report) collected rock samples of quartz-sericite-chlorite altered intrusive upstream from the published stream silt site that contained values ranging from 2.43 to 7.96 ppm gold from samples with minor arsenopyrite and chalcopyrite. Foley and others (1997) report six rock samples from the Kohlsaat pluton with maximum values of 14 ppb gold, 4 ppb palladium, and 5 ppb platinum. Reiners and others (1996) describe the Kohlsaat pluton as a concentrically zoned body with a biotite-granite-porphyry core that intruded seriate and porphyritic intermediate composition rocks. The latter include olive-, pyroxene-, and biotite-bearing quartz syenite, quartz monzonite, and monzonite. Lamprophyric mafic and ultramafic rocks that range in composition from peridotite to alkali gabbro and monzonite are found as large xenoliths at the northeastern margin of the pluton. The granite-porphyry core is altered to sericite, quartz, carbonate and tourmaline assemblages, with minor enrichments of copper, gold, lead, molybdenum, and zinc. They have postulated that the composite pluton at Kohlsaat formed from depleted mantle melts that were contaminated during several stages of mafic magma generation by crustal components. The Kohlsaat pluton is one of the larger composite plutons (Tcp) in the Yentna region described by Reed and Nelson (1980). These composite plutons form a 65-km-long curvilinear belt from Mt. Estelle in the south to Cascade Creek in the northeast that primarily intrude Mesozoic marine sedimentary rocks (KJs). Anomalous gold, platinum-group elements, copper, chrome, nickel and arsenic are reported from these plutons (Reed and others, 1978; Reed and Nelson, 1980; Nelson and others 1992; Foley and others, 1997). Gold and platinum group element placers have been worked at sites downstream from these bodies (Mertie, 1919; Cobb, 1973). See TL020, TL023, TL052, and TL005.
  • Age = Late Cretaceous/early Tertiary; mineralization is interpreted to be linked to the Kohsaat pluton which has been determined to be 65.6 +/- 1.9 m.y. old by Reed and Lanphere, 1973.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Mining district

District name Yentna

Comments on the workings information

  • Workings / Exploration = Reconnaissance mapping, stream silt and rock sampling by the U.S. Geological Survey (Curtin, Karlson, O'Leary, Day, and McDougal, 1978; Reed and Nelson, 1980) and Cominco American Incorporated in the late 1980s (unpublished report) have been done in this vicinity.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF TL051

Bibliographic references

  • Deposit

    Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1374, 213 p.

  • Deposit

    Reed, B.L., and Elliot, R.L., 1970, Reconnaissance geologic map, analyses of bedrock and stream sediment samples, and an aeromagnetic map of parts of the southern Alaska Range: U.S. Geological Survey Open-file Report 70-271, 24 p., 4 plates, scale 1:250,000.

  • Deposit

    Reed, B. L., and Lanphere, M. A., 1973, Alaska-Aleutian Range batholith-- Geochronology, chemistry, and relation to circum-Pacific plutonism: Geological Society of America Bulletin, v. 84, no. 8, p. 2583-2610.

  • Deposit

    Curtin, G.C., Karlson, R.C., O'Leary, R.M., Day, G.W., and McDanal, S.K., 1978, Geochemical and generalized geologic maps showing the distribution and abundance of gold and silver in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-E, 2 sheets, scale 1:250,000.

  • Deposit

    Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, scale 1:250,000.

  • Deposit

    Reiners, P.W., Nelson, B.K., and Nelson, S.W., 1996, Evidence for multiple mechanisms of crustal contamination of magma from compositionally zoned plutons of the Alaska Range: Journal of Petrology, v. 37, p. 261-292.

  • Deposit

    Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska: Economic Geology, Monograph 9, p. 396-449.

  • Deposit

    Mertie, J.B., Jr., 1919, Platinum-bearing gold placers of the Kahiltna Valley: U.S. Geological Survey Bulletin 692-D, p. 233-264.

Comments on the references

  • Primary Reference = Foley and others, 1997

Reporter information

Type Date Name Affiliation Comment
Reporter 10-AUG-98 Madelyn A. Millholland Millholland & Associates