Knowles; Knowles and Backman Property Prospect, Nelchina Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Knowles; Knowles and Backman Property Prospect	Prospect
Nelchina Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: This prospect is on the north side of upper Mill Creek; the claims extended over the ridge to the north into the headwaters of Glacier Creek (Moffit, 1935, plate 1). It is at an elevation of about 4,800 feet in the NE1/4 section 32, T. 6 S., R. 1 W., of the Copper River Meridian. This prospect is probably located to within one-half mile. It is locality 43 of Cobb and Matson (1972) and locality 35 of Winkler and others (1981 [OFR 80-892-B]).
Geology: Gold-bearing, partly oxidized, lenticular quartz veins with arsenopyrite and galena cut metaflysch of the Valdez Group at this prospect; the metaflysch is locally cut by felsic dikes (Moffit, 1935). The veins are as much as 14 inches wide and dip 85 degrees east; they trend northerly, but other sheared quartz masses and veins along faults have different orientations. 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 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: This prospect was explored with open cuts.
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).

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

Other Databases

Link to USGS - Alaska:	VA059

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References