Orange Hill

Porphyry copper deposit in Alaska, United States

Names and other identifiers

GMRAP ID 8
Tract name Eastern Alaska Range and Wrangell Mountains (003pCu5002)
Site status deposit

Geographic location

Country United States
State or province Alaska
Geographic location -142.8449, 62.204
Geologic map unit -142.8449, 62.204
Nearby data

Geologic information

Deposit type Porphyry copper
Age (Ma) 105Ma
Age determination method K-Ar
Age range 114 ±3.4 to 105 ±4.0Ma (Inferred from age of Nabesna pluton.)
Age reference Richter, Lanphere, and Matson (1975)
Minerals anhydrite, biotite, bornite, chalcopyrite, chlorite, epidote, kaolinite, magnetite, molybdenite, pyrite, sericite
Associated rocks quartz feldspar porphyry, trondhjemite, basalt, granodiorite, limestone, mudstone, quartz diorite, siltstone, volcaniclastics
Tectonic setting continental margin
Stratigraphic age Early Cretaceous

Commodity and development information

Development status Prospect
Major commodities Ag, Au, Cu, Mo
Tonnage (Mt) 320Mt
Cu grade (%) 0.35%
Mo grade (%) 0.02%
Contained copper 1,100,000t
Gold-Moly ratio -9999

Reference information

Comments The average grade of the unoxidized mineralization is estimated to be 0.35 percent copper and 0.02 percent molybdenum. Gold values range up to 0.04 ounce per ton and probably average about 0.005 ounce per ton. A central 400- by 2,000-meter altered zone contains abundant biotite, quartz veinlets, minor K-feldspar, chlorite, and sericite; it is cut by late anhydrite veins. An outer 1,000- by 3,000-m altered zone contains chlorite, minor sericite, and anhydrite. First discovered and staked as early as 1902 for its possible gold content; by 1940, 18 mining claims had been patented; extensively explored by open cuts, shafts, short adits, and much diamond drilling; underground workings total only 250 to 300 ft and most were reported be caved by 1944.
Study area name United States
References U.S. Geological Survey (2014a); Mendenhall and Schrader (1903); Richter, Lanphere, and Matson (1975); Nokleberg and others (1987); Richter, Singer and Cox (1975); Young and others (1997); Singer and others (2008)
Site reference U.S. Geological Survey National Mineral Resource Assessment Team (2002)