|Quadrangle map, 1:250,000-scale||VA|
|Quadrangle map, 1:63,360-scale||A-7|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This mine is southeast of and below Johnson Glacier; it is at an elevation of about 2,900 feet seven-tenths of a mile northwest of Smith Mill on Mineral Creek. The USGS Valdez A-7 topographic map (1996) shows this mine marked by adit symbols. However, this map shows the Hercules mine to be located about 2,100 feet farther west, where the Big Four mine (VA128) is actually belived to be located. This record follows Cobb and Matson (1972, locality 22) in placing the Hercules mine at this location.|
Gold-bearing quartz veins cut metaflysch of the Valdez Group at this locality. On the Hercules claim, a quartz vein, from 18 to 30 inches thick, trends N 80 E and dips 70 degrees north, approximately parallel to schistosity (Brooks, 1912). This vein was traced on the surface for about 70 feet and subsequently developed with about 500 feet of underground workings by 1916 (Johnson, 1915; 1918). Minerals identified in this vein include quartz, carbonate, chlorite, gold, pyrite, pyrrhotite, galena, sphalerite, and possibly chalcopyrite (Johnson, 1915). On the Millionaire claim, a quartz vein from 6 to 20 inches thick strikes N 60 W and dips 70 degrees north (Johnson, 1915). This vein was explored with at least two adits; the upper extended 130 feet and included some stoping and the lower extended 450 feet on a weakly mineralized shear zone (Johnson, 1915). Two U.S. Bureau of Mines chip samples from this area contained 11.8 ppm and 1.6 ounces of gold per ton and 4.2 ppm and 0.7 ounce of silver per ton (Jansons and others, 1984). Twenty-five other samples collected in this area contained from less than 0.05 to 1.5 ppm gold (Pickthorn, 1982).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 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||(-146.343955459771, 61.2234817064107)|
|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).|
|Workings or exploration||The Hercules vein was traced on the surface for about 70 feet and subsequently developed with about 500 feet of underground workings by 1916 (Johnson, 1915, 1918). The vein on the Millionaire claim was explored with at least two adits; the upper extended 130 feet and included some stoping, the lower extended 450 feet on a weakly mineralized shear zone (Johnson, 1915).|
|Indication of production||Yes; small|
|Reserve estimates||Jansons and others (1984) gave inferred reserves for this area of 450 tons of material that contains 22.5 ppm of gold and 9.1 ppm of silver.|
|Production notes||The reported production from this area was 269 ounces of gold and 44 ounces of silver (Jansons and others, 1984).|
Cobb, E.H., and Matson, N.A., Jr., 1972, Metallic mineral resources map of the Valdez quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-438, 1 sheet, scale 1:250,000.
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.
Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000.
Johnson, B.L., 1915, Mining on Prince William Sound: U.S. Geological Survey Bulletin 622-E, p. 131-139.
Johnson, B.L., 1918, Mining on Prince William Sound: U.S. Geological Survey Bulletin 662-C, p. 183-192.
Pickthorn, W.J., 1982, Stable isotope and fluid inclusion study of the Port Valdez district, southern Alaska: Los Angeles, University of California at Los Angeles, M.S. thesis, 66 p.
Winkler, G.R., Miller, R.J., MacKevett, E.M., Jr., and Holloway, C.D., 1981, Map and summary table describing mineral deposits in the Valdez quadrangle, southern Alaska: U.S. Geological Survey Open-File Report 80-892-B, 2 sheets, scale l:250,000.
|Reporters||Travis L. Hudson|
|Last report date||12/14/2001|