Thompson-Ford; Owl Mine, Prince William Sound Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Thompson-Ford; Owl Mine	Mine
Prince William Sound Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: This mine is in the upper Uno Basin about 1.5 miles southeast of Mount Shasta (Pickthorn, 1982, sheet 2); it is at an elevation of about 2,700 feet in the NW1/4 section 29, T. 8 S., R. 7 W., of the Copper River Meridian. This mine is probably located to within one-quarter mile. It is locality 19 of Cobb and Matson (1972) and locality 16 of Winkler and others (1981 [OFR 80-892-B]).
Geology: The Thompson-Ford deposit is a shear zone in metaflysch of the Valdez Group that contains gold-bearing quartz veins as mush as 1.5 feet thick (Johnson, 1915). The quartz veins contain calcite, pyrite, galena, chalcopyrite, and sphalerite. This mineralized zone strikes northwest and dips vertically. It was traced for 115 feet on the surface and developed by about 735 feet of underground workings, including a shaft, adit, crosscuts, and drifts (Johnson, 1915; Jansons and others, 1984). The Owl deposit consists of a shear zone with quartz stringers and lenses as much as 1.5 feet thick that strikes northwest and dips 30 degrees north in metaflysch of the Valdez Group (Johnson, 1915). The quartz also contains calcite, chlorite, limonite, malachite, pyrite, chalcopyrite, galena, and sphalerite. This deposit was explored by about 190 feet of underground workings by 1914 (Johnson, 1915). Ore shipments were made to the Tacoma smelter from the Thompson-Ford deposit, but the production has not been reported (Johnson, 1915; Jansons and others, 1984). Three U.S. Bureau of Mines chip samples from this area contained 0.4 to 0.59 ppm gold and 0.2 ppm silver; five grab samples contained as much as 5.02 ppm gold and as much as 3.1 ppm silver (Jansons and others, 1984). These deposits 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 Owl deposit was explored with about 190 feet of underground workings by 1914 (Johnson, 1915). The Thompson-Ford deposit was traced for a length of 115 feet on the surface and developed by about 735 feet of underground workings, including a shaft, adit, crosscuts, and drifts (Johnson, 1915; Jansons and others, 1984).
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: Ore shipments were made to the Tacoma smelter from the Thompson-Ford deposit but the production has not been reported (Johnson, 1915; Jansons and others, 1984).

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

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Link to USGS - Alaska:	VA116

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References