Tarasof Point

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu; Mo
Ore minerals pyrite
Gangue minerals chlorite; epidote; limonite

Geographic location

Quadrangle map, 1:250,000-scale UN
Quadrangle map, 1:63,360-scale B-3
Latitude 53.6833
Longitude -166.9333
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

Geologic description

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.
Geologic map unit (-166.935174936994, 53.6824446074405)
Mineral deposit model Copper porphyry, epithermal gold vein
Mineral deposit model number 17, 25
Age of mineralization Cenozoic
Alteration of deposit 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.

Production and reserves

Workings or exploration 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.
Indication of production None

Additional comments

The mode of occurrence suggests an epithermal gold vein model should be considered as a possible model for this system.

References

MRDS Number A106021

References

Christie, J.S., 1974, Aleut-Quintana-Duval 1974 joint venture, final report: Unpublished Quintana Minerals Corporation report, 24 p., 3 appendices, 2 maps. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters Damon Bickerstaff, F.H. Wilson
Last report date 3/18/1996