SB

Occurrence, Probably inactive

Commodities and mineralogy

Main commodities Pb; Zn
Other commodities Ag; Au; Cu
Ore minerals chalcopyrite; galena; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2909
Longitude -144.0868
Nearby scientific data Find additional scientific data near this location
Location and accuracy The SB occurrence is approximately a mile upstream from the mouth of a small north-flowing tributary of the Robertson River in the SW1/4 section 33, T. 18 N., R. 7 E., Copper River Meridian. The occurrence is approximately located at an elevation of about 3,000 feet where massive sulfide boulders are exposed in landslides, mostly on the east side of the creek.

Geologic setting

Geologic description

The SB massive sulfide occurrence is a somewhat enigmatic occurrence that consists of numerous banded, pyrite-rich massive sulfide boulders as much as 15 feet in diameter. This occurrence is about 2.5 miles downstream from the DW-LP massive sulfide zone in an area of thick overburden. The boulders are concentrated in an area approximately 1,400 feet north-south by 500 to 800 feet east-west (J.K. Muntzert and others, unpublished Resource Associates of Alaska, Inc. report, 1977).
The SB boulders were systematically sampled in 1977. The average of 10 samples is 0.26 percent copper, 1.03 percent lead, 4.4 percent zinc, and 1.39 ounces of silver per ton; the samples were not analyzed for gold (J.K. Muntzert and others, unpublished Resource Associates of Alaska, Inc. report, 1977). Sampling by American Copper and Nickel Company in 1994 gave similar values of base metals and silver, but the modern assay techniques indicated the presence of gold. Samples averaged 0.4 percent copper, 1.7 percent lead, 4.5 percent zinc, 63 parts per million (ppm) silver, and 1.7 ppm gold (Dashevsky and others, 2003).
Considerable geophysical, geochemical, and geological work was done in the 1970s to locate the source of the sulfide boulders. The current hypothesis is that these sulfide boulders are glacial erratics from the DW-LP massive sulfide horizon that were rafted down the creek valley on ice (E. Hunter, unpublished data, 1998).
The rocks around the SB occurrence are part of the Tushtena Pass unit; it consists of medium- to coarse-grained, calcareous, quartz-sericite-chlorite-schist, with local carbonate interbeds. Tushtena Pass rocks are typically green to gray, foliated, schistose to blocky, laminated to medium-bedded, quartz-eye bearing, quartz-rich lithologies with subordinate muscovite, sericite, and chlorite.
Geologic map unit (-144.089052621717, 63.2905260080421)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization Devonian, on the basis of the age of the host rocks.

Production and reserves

Workings or exploration Surface samples of boulders were taken in 1977 and 1994 (J.K. Muntzert and others, unpublished Resource Associates of Alaska, Inc. report, 1977; Dashevsky and others, 2003). Considerable geophysical, geochemical, and geological work was done in the 1970s to locate the source of the sulfide boulders. The current hypothesis is that these sulfide boulders are glacial erratics from the DW-LP massive sulfide horizon that were rafted down the creek valley on ice (E. Hunter, unpublished data, 1998).
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.

References