Horsfield

Porphyry copper deposit in Alaska, United States

Names and other identifiers

GMRAP ID 12
Tract name Eastern Alaska Range and Wrangell Mountains (003pCu5002)
Site status deposit

Geographic location

Country United States
State or province Alaska
Geographic location -141.218055556, 62.051111111
Geologic map unit -141.218055556, 62.051111111
Nearby data

Geologic information

Deposit type Porphyry copper
Age (Ma) 111Ma
Age determination method K-Ar
Age range 111 ±3.6 Ma (Inferred from age of Klein Creek pluton.)
Age reference Richter, Lanphere, and Matson (1975)
Minerals actinolite, chalcopyrite, kaolinite, magnetite, pyrite, sericite
Associated rocks breccia, monzonite porphyry, andesite, basalt, diorite, granodiorite, quartz monzonite
Tectonic setting continental margin
Stratigraphic age Cretaceous

Commodity and development information

Development status Prospect
Major commodities Cu
Minor commodities Ag, Au, Mo
Tonnage (Mt) 60Mt
Cu grade (%) 0.15%
Contained copper 90,000t
Gold-Moly ratio -9999

Reference information

Comments Pyrite and chalcopyrite occur in quartz veinlets and as disseminations in monzonite and monzonite porphyry of the mid-Cretaceous-age Klein Creek pluton near its contact with Jurassic or Cretaceous siliciclastic rocks; the associated hydrothermal alteration zone extends across this contact. The deposit has a central 200- by 700-meter zone of potassium feldspar, actinolite, and magnetite alteration, and a 800- by 1,500-meter outer zone of unspecified hydrothermal alteration; estimated to contain 60 million tons with an average grade of 0.20 percent copper and very low amounts of molybdenum. Surface exploration and some diamond drilling.
Study area name United States
References U.S. Geological Survey (2014a); Richter, Lanphere, and Matson (1975); Singer and others (2008); Young and others (1997)
Site reference U.S. Geological Survey National Mineral Resource Assessment Team (2002)