Orange Hill, Porphyry copper deposit

Porphyry copper deposit in Alaska, United States

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

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

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)