Alaska Gold Hill

Prospect, Probably inactive

Alternative names

Black Diamond

Commodities and mineralogy

Main commodities Au
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals carbonate minerals; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-7
Latitude 61.13
Longitude -146.5173
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on a bench along the north side of Port Valdez about eight-tenths of a mile west of Camp Bowie; it is at an elevation of about 450 feet in the SE1/4 of section 32, T. 8 S., R. 7 W., of the Copper River Meridian. This prospect is probably located to within one-quarter mile. It is locality 20 of Cobb and Matson (1972) and locality 17 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

Two shear zones, 0.5 inch to 4 feet thick, contain crushed country rock and quartz veinlets in metaflysch of the Valdez Group (Jansons and others, 1984). The mineralized zones are assumed to be gold-bearing (Cobb, 1979 [OFR 79-1241]; Winkler, Miller, and others, 1981). Three adits, one 50 feet long with a 75-foot-long crosscut and 55-foot-long drift, one 120feet long, and one 605 feet long, were present (Johnson, 1919). This deposit is probably similar to other gold-bearing quartz veins cutting metaflysch of the Valdez Group in the southern Valdez quadrangle. Data summarized by Goldfarb and others (1997) show that gold-bearing quartz veins in the Valdez Group commonly contain pyrite, arsenopyrite, carbonate minerals, chlorite, and white mica and formed from water-rich fluids with 5 to 15 mole percent CO2 and significant amounts of CH4, N2, and H2S. The vein-forming fluid salinities were less than 8 percent, vein formation temperatures ranged from 225 to 375 degrees centigrade, and emplacement depths varied from 3 to 10 kilometers. The vein-forming fluids were produced by metamorphic devolatilization reactions. Radiometric dating indicates that the veins formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171), when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Geologic map unit (-146.519332746138, 61.1294771881082)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Radiometric dating indicates that the gold-bearing quartz veins in the Valdez Group formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171), when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Alteration of deposit Country rocks to gold-bearing quartz veins in Valdez Group metaflysch can be variably silicified, carbonitized, and sericitized (Goldfarb and others, 1997).

Production and reserves

Workings or exploration Three adits were driven to explore this deposit: one 50 feet long with a 75-foot-long crosscut and 55-foot-long drift, one 120 feet long, and one 605 feet long (Johnson, 1919).
Indication of production Undetermined
Production notes There is no reported production from this deposit (Jansons and others, 1984).

References

MRDS Number A011461

References

Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Hudson, T.L., 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol. G-1, p. 657-670.
Reporters Travis L. Hudson
Last report date 12/14/2001