Seacoast; Bunker Hill Prospect, Prince William Sound Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Seacoast; Bunker Hill Prospect	Prospect
Prince William Sound Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is eight-tenths of a mile south-southwest of Mount Shasta and about one-quarter mile north of lower Uno Creek; it is at an elevation of about 2,000 feet in the SE1/4 section 24, T. 8 S., R. 8 W., of the Copper River Meridian. This prospect is probably located to within one-quarter mile. It is locality 14 of Cobb and Matson (1972) and locality 11 of Winkler and others (1981 [OFR 80-892-B]).
Geology: The Seacoast deposit consists of several gold-bearing quartz veins and lenses that cut metaflysch of the Valdez Group (Johnson, 1915). The quartz bodies range from an inch to 11 feet thick, but most are thin. They contain pyrite, galena, free gold, pyrrhotite, chalcopyrite, sphalerite, carbonate, chlorite, limonite, and malachite. Two adits, raises, winzes, and drifts totaling about 725 feet of length explored the Seacoast deposit,although only one test shipment of ore has been reported (Cobb, 1979 [OFR 79-1241]). The Bunker Hill deposit is a 4- to 25-inch-thick quartz vein in Valdez Group metaflysch that has been explored with a 100-foot-long adit (Johnson, 1915). This vein is reported to contain arsenopyrite, galena, pyrite, sphalerite, and limonite in a gangue of quartz, calcite, and chlorite. The U.S. Bureau of Mines collected four chip samples in this area that contained as much as 1.29 ppm gold and 2.0 ppm silver (Jansons and others, 1984). These veins 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 devolatization 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).
Workings: The Seacoast vein was explored by two adits, raises, winzes, and drifts totaling about 725 feet of length (Cobb, 1979 [OFR 79-1241]), although only one test shipment of ore has been reported. The Bunker Hill deposit has been explored with a 100-foot-long adit (Johnson, 1915).
Age: 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: Country rocks to gold-bearing quartz veins in Valdez Group metaflysch can be variably silicified, carbonitized, and sericitized (Goldfarb and others, 1997).
Production: There is no reported production from these deposits (Jansons and others, 1984).

Commodities (Major) - Au; (Minor) - Cu, Pb, Zn
Development Status: Undetermined.
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	VA117

Other Regions, Features and Areas containing this locality

References