Jim Creek Occurrence, Anchorage Mining District, Matanuska-Susitna Borough, Alaska, USAi

Regional Level Types
Jim Creek Occurrence	Occurrence
Anchorage Mining District	Mining District
Matanuska-Susitna Borough	Borough
Alaska	State
USA	Country

Location: Prospect is located 1.5 mile downstream from the headwaters of Jim Creek at a point roughly 1,500 ft north of the creek . Location accurate within 1 mile. Locality 45 of Cobb (1972), and locality 34 of MacKevett and Holloway (1977).
Geology: Heavily silicified greenstone is cut by a vein that averages 1 ft thick. The vein strikes N 80 W, and is approximately vertical. The vein is composed of 40 percent chalcopyrite, 40 percent pyrrhotite, 15 percent sphalerite, and 5 percent calcite; and assays show 15.08 percent Cu, 2.95 percent Zn, 1.75 oz/ton Ag, and trace Au. The greenstone on both sides of the sulfide vein has been replaced by quartz and calcite, and cut by very thin arsenopyrite veins. Assays of replaced wall rock show 0.41 oz/ton Ag and 0.04 percent Cu. An alaskite dike runs approximately 500 ft upslope the sulfide vein prospect and slate outcrops 50 ft downhill from prospect (Landes, 1927).
Workings: The vein is composed of 40 percent chalcopyrite, 40 percent pyrrhotite, 15 percent sphalerite, and 5 percent calcite; and assays show 15.08 percent Cu, 2.95 percent Zn, 1.75 oz/ton Ag, and trace amounts of Au. Assays of replaced wall rock show 0.41 oz/ton Ag and 0.04 percent Cu (Landes, 1927).
Age: Mesozoic or younger
Alteration: Calcite and quartz replacement of greenstone at periphery of sulfide vein.

Commodities (Major) - Ag, Cu, Zn; (Minor) - Au
Development Status: None
Deposit Model: Polymetallic vein (Cox and Singer, 1986; model 22c)

Other Databases

Link to USGS - Alaska:	AN087

Other Regions, Features and Areas containing this locality

References