Ibex; Valdez; Valdez Mining Co.; Donahue Mine, Prince William Sound Mining District, Valdez-Cordova Census Area, Alaska, USAi

Regional Level Types
Ibex; Valdez; Valdez Mining Co.; Donahue Mine	Mine
Prince William Sound Mining District	Mining District
Valdez-Cordova Census Area	Census Area
Alaska	State
USA	Country

Location: These mines are on the west side of Valdez Glacier valley, at an elevation of about 2,500 feet in section 6, T. 8 S., R. 5 W., of the Copper River Meridian. The Ibex mine is shown on the USGS Valdez A-6 topographic map (1951; limited revisions, 1980). It is accurately located. This is locality 33 of Cobb and Matson (1972) and locality 25 of Winkler and others (1981 [OFR 80-892-B]).
Geology: Gold-bearing quartz veins cut metaflysch of the Valdez Group at this mine. The principal vein on the Valdez claims strikes N 60 W, dips 75 degrees south, and is 5 to 6 feet thick in outcrop (Brooks, 1912). The vein is commonly 2 to 6 feet thick in underground workings, where it includes as much as 4 feet of ribbon quartz. At one location underground where the main vein was intersected by another, the vein thickness expanded to 10.5 feet (Johnson, 1916). A continuation of the main vein appears to be present on the Ibex claim about one-quarter mile northwest of the Valdez claims. At least 800 feet of workings had been driven in the Valdez adit by 1920 (Brooks, 1922). The 200-foot adit on the Ibex claim lost the vein after the first 100 feet (Brooks, 1912). A 470-foot adit, a shorter adit,and 50-foot winze explore a quartz vein at the Donahue prospect nearby (Hoekzema and others, 1986). Grab and chip samples from the 3- to 10.5-foot-thick Donahue vein contained from less than 0.003 to 0.413 ounce of gold per ton and 0.01 to 0.1 ounce of silver per ton (Hoekzema and others, 1986). 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: At least 800 feet of workings had been driven in the Valdez adit by 1920 (Brooks, 1922). The 200-foot adit on the Ibex claim lost the vein after the first 100 feet (Brooks, 1912). A 470-foot adit, a shorter adit, and 50-foot winze explore a quartz vein at the Donahue prospect nearby (Hoekzema and others, 1986).
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
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	VA140

Other Regions, Features and Areas containing this locality

References