|Quadrangle map, 1:250,000-scale||VA|
|Quadrangle map, 1:63,360-scale||A-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is immediately below the Richardson Highway, about one-half mile west of mile 40. It is at benchmark Elbow (elevation of 1,656 feet) in the NW1/4 section 4, T. 8 S., R.1 W., of the Copper River Meridian. It is locality 42 of Cobb and Matson (1972) and locality 34 of Winkler and others (1981 [OFR 80-892-B]).|
Geologic descriptionGold-bearing quartz veins from 3 to 5 feet thick cut metaflysch of the Valdez Group at this prospect (Moffit, 1935). One vein strikes N 40 E and was followed in an adit for 300 feet. Open cuts and a 150-foot long adit were also used to explore the veins. These veins are 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||(-145.436949821356, 61.2078987235808)|
|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||One vein strikes N 40 E and was followed in an adit for 300 feet. Open cuts and a 150-foot long adit were also used to explore the veins (Moffit, 1935).|
|Indication of production||None|
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.
Moffit, F.H., 1935, Geology of the Tonsina district, Alaska: U.S. Geological Survey Bulletin 866, 38 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|