Unnamed (south side of the West Fork Robertson River valley)

Occurrence, Active

Commodities and mineralogy

Main commodities Cu; Pb; Zn
Ore minerals chalcopyrite; galena; pyrite; pyrrhotite; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-2
Latitude 63.3092
Longitude -144.7424
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is about 1.8 miles southwest of the mouth of Rock Candy Creek. It is at an elevation of about 4,000 feet in the SE1/4 section 31, T. 18 S., R. 16 E., Fairbanks Meridian. The occurrence is on the moraine of the glacier at the head of the West Fork Robertson River near the junction with a smaller tributary glacier. The location is accurate.

Geologic setting

Geologic description

Two types of massive sulfide mineralization were found on glacial moraine here during geological reconnaissance in 1975. These occurrences contain sparse base metal concentrations. Banded pyrrhotite with approximately 1 percent combined copper, lead, and zinc is in carbonate breccia with siliceous fragments. Pyrrhotite and calcite occur in bands that wrap around the breccia fragments. Farther up the glacier, banded pyrite and quartz-sericite schist with disseminated pyrite are abundant on the moraine on the ice. The rocks contains blueish-white quartz crystals and porphyroblasts as much as one-quarter inch in diameter; the protolith is probably a rhyolitic lapilli tuff. Along the southern side of the glacier, meta-andesite (?) with black chlorite and white tourmaline crystals developed in open spaces (R.A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1976).
This occurrence is in the Jarvis Creek Glacier subterrane of Devonian age (Nokleberg and others, 1992). This subterrane consists of a complex sequence of volcaniclastic metasedimentary rocks, predominantly of intermediate composition. The unit includes felsic and mafic metavolcanic units and metasedimentary rocks, including calcareous schist, dolomite, limestone, siltstone, quartzite, and black carbonaceous schist. The rock units are typically thin bedded, strike northwest, and dip moderately southwest. The schistosity and folds are generally parallel to the regional strike but with local exceptions (R.A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1976). The metamorphosed volcanic and sedimentary rocks have been intruded by several gabbro and mafic sills and dikes and plutons of felsic to intermediate composition (R.A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1976).
Geologic map unit (-144.744643562686, 63.3088146978733)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization Devonian or younger, on the basis of the age of the host rock, which is in the Jarvis Creek Glacier subterrane (Nokleberg and others, 1992).

Production and reserves

Workings or exploration This occurrence has only had limited surface sampling.
Indication of production None

Additional comments

Unpublished data cited is available for viewing by contacting Grayd Resources Inc. in Vancouver, B. C., Canada (www.grayd.com), or Northern Associates Inc. in Fairbanks, Alaska.