Unnamed (near Kohlsaat Peak)

Site Name

Primary: Unnamed (near Kohlsaat Peak)

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Commodity

Primary: Molybdenum
Primary: Zinc
Primary: Copper
Primary: Gold
Primary: Lead
Secondary: Arsenic

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Location

State: Alaska
District: Yentna

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Occurrence
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Not available

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Carbonate, chlorite, sericite, and quartz alteration.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Pyrite
Ore: Galena
Ore: Chalcopyrite
Ore: Arsenopyrite
Gangue: Tourmaline
Gangue: Quartz

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Comments

Comment (Workings): 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Karlson, O'Leary, Day, and McDougal, 1978; Reed and Nelson, 1980) and Cominco American Incorporated in the late 1980s (unpublished report) have been done in this vicinity.

Comment (Geology): 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 In the late 1980s Cominco American Incorporated (unpublished report) collected rock samples of quartz-sericite-chlorite altered intrusive upstream from the published stream silt site that contained values ranging from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.

Comment (Geology): 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.

Comment (Reference): Primary Reference = Foley and others, 1997

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References

Reference (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.

Reference (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.

Reference (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.

Reference (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.

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

Reference (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.

Reference (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.

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

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These ten states contributed the most to the gold production that built the West from 1848 through the 1930s. The Top Ten Gold Producing States.