Silver Gem

Mine, Probably inactive

Alternative names

I.X.L.
Shoup Bay Mining Co.
Spanish

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Pb; Sb; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite; stibnite
Gangue minerals calcite; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-7
Latitude 61.1382
Longitude -146.6232
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is on the ridge between McAllister and Palmer Creeks, on the west side of Shoup Bay; it is at an elevation of about 600 feet on the northeast side of the ridge in the NW1/4 section 35, T. 8 S., R. 8 W., of the Copper River Meridian. This mine is probably located to within one-quarter mile. It is locality 11 of Cobb and Matson (1972) and locality 8 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

Shear zones that contain crushed and brecciated country rock and gold-bearing quartz bodies from a few inches to a few feet wide cut metaflysch of the Valdez Group on these claims (Brooks, 1912). In places the breccia is cemented by quartz and pyrite. At least locally, the shear zones include galena, arsenopyrite, sphalerite, and stibnite. There is at least a 500-foot-long adit on the Silver Gem deposit (Johnson, 1915).
These mineralized zones are 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 (-146.62523624921, 61.1376761619502)
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 There was at least a 500-foot-long adit on the Silver Gem deposit (Johnson, 1915).
Indication of production Yes; small
Production notes Ore shipments are reported from the Silver Gem deposit to a custom mill in Valdez (Johnson, 1915).

References