Valdez Bonanza

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-6
Latitude 61.1901
Longitude -146.2302
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on a saddle on the ridge west of the Second Bench of Valdez Glacier; it is at an elevation of about 4,000 feet in the center of the W1/2 section 12, T. 8 S., R. 6 W., of the Copper River Meridian. This prospect is probably located to within one-quarter mile. It is locality 32 of Cobb and Matson (1972).

Geologic setting

Geologic description

A gold-bearing quartz vein, 2 to 5 feet thick in outcrop, cuts metaflysch of the Valdez Group (Brooks, 1912) at this prospect. This vein can be traced on the surface for 50 feet, but it pinches out in a 100-foot-long adit. The vein is semi-parallel to cleavage in the metaflysch; the footwall is marked by slickensides that continue after the vein pinches out.
This vein is probably 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 (-146.232252244252, 61.1895829410183)
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 This vein is exposed in a cliff and can be traced on the surface for 50 feet; it pinches out in a 100-foot-long adit (Brooks, 1912).
Indication of production Undetermined

References

MRDS Number A011474

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