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Porphyry copper prospect in Alaska, United States

Names and other identifiers

GMRAP ID 3386
Alternate names Tim's Greisen, Tim's Gossan, TG, TG North
Tract name Yukon-Tanana Upland (003pCu5003)
Site status prospect

Geographic location

Country United States
State or province Alaska
Geographic location -157.5568, 64.1736
Geologic map unit -157.5568, 64.1736
Nearby data

Geologic information

Deposit type Porphyry copper
Age (Ma) 74Ma
Age determination method K-Ar potassium feldspar
Age range 74 ±2.8 Ma (K-Ar potassium feldspar); 72.9 ±2.8 Ma (unknown method)
Age reference Harris (1985); Western Alaska Copper and Gold Co. (2012)
Minerals argentojarosite, beudantite, chalcocite, chalcopyrite, covellite, jarosite, molybdenite, native copper, pyrite, pyrrhotite, sphalerite
Tectonic setting continental margin
Stratigraphic age Late Cretaceous

Commodity and development information

Development status Prospect
Major commodities Ag, Cu, Mo
Minor commodities Pb, W, Zn
Gold-Moly ratio -9999

Reference information

Comments Discovered in early 1980s. Greenschist and amphibolite country rocks are intruded by a large intrusive complex (two lobes with six types of porphyritic intrusive rock and an intrusive microbreccia). Mineralization occurs as (1) veins containing molybdenite, chalcopyrite, pyrite, and pyrrhotite; (2) gossan containing argentojarosite, jarosite, and beudantite; (3) a supergene zone beneath the gossan containing chalcocite, covellite, native copper, and chalcopyrite; and (4) calc-silicate wall rocksnear the intrusive that contain pyrite, chalcopyrite, and sphalerite. Alteration consists of early potassic and propylitic alteration in the microbreccia and earlier porphyritic intrusions, and later sericite-quartz-pyrite alteration throughout theintrusive complex. The deposit also has undergone supergene enrichment. Drilled 7 holes totaling 1,668 m in 1981; drilled two shallow ""Winkie"" holes in 1982; trenches, geologic mapping and geophysical surveys, extensive sediment and soil sampling program.
Study area name United States
References U.S. Geological Survey (2014a); Harris (1985); Western Alaska Copper and Gold Co. (2012)
Site reference U.S. Geological Survey National Mineral Resource Assessment Team (2002)