OB

Prospect, Undetermined

Commodities and mineralogy

Main commodities Au
Ore minerals gold
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale C-7
Latitude 57.6603
Longitude -136.0964
Nearby scientific data Find additional scientific data near this location
Location and accuracy The OB prospect is at sea level on Klag Bay, apparently on or just inside the southwest boundary of the patented claims of the Chichagof Mine (SI093). According to Bittenbender and others (1999, fig. 6), the OB prospect includes both patented and unpatented claims. For this record, the site is plotted 0.4 mile southeast of the center of sec. 36, T. 48 S., R. 57 E. It is location P-72 of Bittenbender and others (1999) and MAS no. 0021140313 (U.S. Bureau of Land Management, 2002). The location probably is accurate within 0.2 mile.

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of this prospect as Cretaceous graywacke and argillite containing sparse, lenticular beds of basalt. The rocks are cut by numerous high-angle, mainly northwest-striking faults. These include the extension of the fault at the Hirst Mine (SI087), which controls the mineralization there and transects the area of this prospect.
Bittenbender and others (1999), citing Still and Weir (1981), describe the prospect as an auriferous quartz vein up to 4 feet thick in graywacke. Samples of the vein contained up to 0.2 ounce of gold per ton. Workings include a 200-foot adit with a winze, and several trenches. There is no record of production, but the extent of the workings suggests some gold may have been produced.
Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler, 1995; Goldfarb, 1997; Goldfarb and others, 1997). ARDF record SI087 provides an overview of the geology of auriferous quartz veins in the Chichagof Mining District.
Geologic map unit (-136.098224398815, 57.6599286416074)
Mineral deposit model Low-sulfide gold-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler and others, 1995; Goldfarb, 1997; Goldfarb and others, 1997).

Production and reserves

Workings or exploration Workings include a 200-foot adit with a winze, and several trenches.
Indication of production Undetermined
Production notes There is no record of production, but the extent of the workings suggests that some gold may have been produced.

Additional comments

The prospect is in West Chichagof-Yakobi Wilderness.

References

References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
Goldfarb, R J., 1997, Metallogenic evolution of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 4-34.
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.
Haeussler, P J., Bradley, D., Goldfarb, R., Snee, L., and Taylor, C., 1995, Link between ridge subduction and gold mineralization in southern Alaska: Geology, v. 23, no. 11, p. 995-998.
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004