SB Occurrence, Tok Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
SB Occurrence	Occurrence
Tok Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Unpublished data cited is available for viewing by contacting Grayd Resources Inc. in Vancouver, B. C., Canada (www.grayd.com), or Northern Associates Inc. in Fairbanks,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.
Location: 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.
Geology: 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concentrated in an area approximately 1,400 feet north-south by 500 to 800 feet east-west (J.K. Muntzert and others, unpublished Resource Associates of Alaska, Inc. report, 1977).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4.4 percent zinc, and 1.39 ounces of silver per ton; the samples were not analyzed for gold (J.K. Muntzert and others, unpublished Resource Associates of Alaska, Inc. report, 1977).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 1970's 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are glacial erratics from the DW-LP massive sulfide horizon that were rafted down the creek valley on ice (E. Hunter, unpublished data, 1998).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.
Workings: Surface samples of boulders were taken in i977 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 1970's 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).
Age: Devonian, on the basis of the age of the host rocks.

Commodities (Major) - Pb, Zn; (Minor) - Ag, Au, Cu
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model

Other Databases

Link to USGS - Alaska:	MH329

Other Regions, Features and Areas containing this locality

References