Unnamed (north of Thompson Pass)

Prospect, Probably inactive

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-5
Latitude 61.1472
Longitude -145.7508
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is about 1.9 miles north of Thompson Pass and about one-quarter of a mile northwest of the trans-Alaska oil pipeline. It is at an elevation of about 2,500 feet in the SE1/4 section 22, T. 8 S., R. 3 W., of the Copper River Meridian. This prospect is probably located to within one-half mile. It is locality 91 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

Lode claims were staked and active from 1953 to 1955 on gold deposits at this locality (U.S. Bureau of Mines, 1980; Winkler and others, 1981 [OFR 80-892-B]). These deposits are probably gold-bearing quartz veins similar to others that are widespread 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 (-145.752837287192, 61.1466927777464)
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 Small-scale surface prospecting.
Indication of production Undetermined

References

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.
U.S. Bureau of Mines, 1980, Valdez 1:250,000 quadrangle map overlay showing mineral deposit locations, principal minerals, and number and type of claims: U.S. Bureau of Mines Open-File Report, August 1980.
Reporters Travis L. Hudson
Last report date 12/14/2001