Zimmerman Prospect (near junction of Twin and Pedro Creeks), Fairbanks Mining District, Fairbanks North Star Borough, Alaska, USAi

Regional Level Types
Zimmerman Prospect (near junction of Twin and Pedro Creeks)	Prospect
Fairbanks Mining District	Mining District
Fairbanks North Star Borough	Borough
Alaska	State
USA	Country

Location: Cobb (1972, MF-413), loc. 31; SW1/4NW1/4 sec. 12, T. 2 N., R. 1 E., of the Fairbanks Meridian. This prospect is 1/4 mile northeast of the mouth of Twin Creek. Accuracy is within 1,000 feet.
Geology: Hill (1933) visited the site and the following geologic description is a summary of his observations. Extensive exposures of mineralized quartz diorite and schist occur in a hydraulic cut on the Zimmerman property. Near the southwest or lower end of the cut, a fault zone strikes east and dips 85 N. The fault zone consists of 11 feet of blue clay gouge that contains a large amount of fragmental quartz and silicified schist. Some of the fragments contain arsenopyrite and have a peculiar greenish-yellow stain. A few samples from a 3-foot zone of silicified mineralized schist contained as much as 0.08 ounces of gold per ton. Northeast of the gouge, the rock is quartz diorite. For seven feet above the fault, the diorite is badly crushed, but farther to the northeast, it is less altered, breaks in blocky forms, and is cut by several minor fault fractures that strike from west to N 60 W. Southwest of the main fault, the rock is highly silicified schist with many quartz veinlets and everywhere contains a small amount of finely disseminated arsenopyrite. The rock is bluish gray, hard, and heavier than the nomal quartz-mica schist. For at least 70 feet south of the main fault, this rock is broken and crushed, and there are several well-defined slip planes that vary in strike from N 70 W to west and dip north, all roughly parallel to the main fault. The samples of the altered quartz diorite north of the fault contained neither gold nor silver. The silicified mineralized schist south of the fault carried only a trace of precious metals except for a few samples from a 3-foot zone that contained as much as 0.08 ounces of gold per ton. The gold-bearing samples contained notable sulfides (Hill, 1933, p. 118-119).
Workings: Surface samples were taken from a hydraulic cut (Hill, 1933).
Alteration: The schist in the vicinity of the Zimmerman prospect is silicifed, and some schist fragments carry a peculiar greenish-yellow stain (Hill, 1933).

Commodities (Major) - Au
Development Status: None
Deposit Model: Auriferous, silicified schist.

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Link to USGS - Alaska:	LG070

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References