Tarasof Point Occurrence, Aleutians Mining District, Aleutians West Census Area, Alaska, USAi

Regional Level Types
Tarasof Point Occurrence	Occurrence
Aleutians Mining District	Mining District
Aleutians West Census Area	Census Area
Alaska	State
USA	Country

The mode of occurrence suggests an epithermal gold vein model should be considered as a possible model for this system.
Location: West side of Anderson Bay, 2 miles (3.2 km) southwest of Tarasof Point. Anomaly no. 20 of Christie (1974). Anderson Bay is the south arm of Makushin Bay.
Geology: The occurrence is defined by multiple color anomalies surrounding breccia pipes emplaced through a pendant(?) of volcanic rocks of the Unalaska Formation (see Drewes and others, 1961) between exposures of diorite plutons. The color anomalies occur in two 1,000 ft (300 m) by 3,000 ft (915 m) areas. Late mineral quartz-feldspar porphyry and crowded feldspar porphyry dikes cut the breccia pipes. The breccia pipes may have originally contained up to 15 to 20 percent sulfides, which are now totally leached. Copper may have been present, as traces of chalcopyrite occur in the adjacent diorite plutons. Alteration and the amount of pyrite appear to decrease abruptly away from areas of breccia. According to Christie (1974), fracturing is very important (in localizing alteration?). Within the breccia pipes, there is intense silicification and peripheral to this, secondary chlorite and epidote are developed. The occurrence is capped by highly altered rocks distinguished by the development of limonite.
Workings: Reconnaissance mapping and multiple soil samples were used to evaluate the color anomaly. Samples showed up to 260 ppm copper, 28 ppm molybdenum, 2.6 ppm silver, and 0.24 ppm gold.
Age: Cenozoic
Alteration: The core of the occurrence shows intense silicification and on the periphery, the development of chlorite and epidote indicate propylitic alteration. Leaching is complete in the area of interest.

Commodities (Major) - Mo, Cu, Ag, Au
Development Status: No
Deposit Model: Copper porphyry, epithermal gold vein

Other Databases

Link to USGS - Alaska:	UN027

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References