Blue Ribbon

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Au
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals carbonate minerals; chlorite; quartz; white mica

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-7
Latitude 61.2084
Longitude -146.2645
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is located on the south side of a west-trending glacier lobe, about one-quarter mile east of elevation 4030; it is at an elevation of about 3,800 feet in the NW1/4 section 2, T. 8 S., R. 6 W., of the Copper River Meridian. This prospect is probably located to within one-quarter mile. It is locality 31 of Cobb and Matson (1972) and locality 24 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

A gold-bearing quartz vein, from a few inches to 8 inches thick and that locally including ribbon quartz zones as much as 8 inches thick, cuts metaflysch of the Valdez Group at this prospect (Brooks, 1912). The vein strikes east-west, parallel to the foliation in the host rocks. It has been traced over a distance of 1,000 feet along strike, an exceptionally long distance for quartz veins in the area. This vein is 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 (-146.266553410433, 61.2078824131311)
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).

Production and reserves

Workings or exploration This vein was probably explored with small trenches and open cuts.
Indication of production None

References