Unnamed (near Purple Lake)

Occurrence, Undetermined

Commodities and mineralogy

Main commodities Au; Mo
Ore minerals magnetite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale A-5
Latitude 55.107
Longitude -131.489
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents two occurrences: one is on the north shore of Purple Lake about 1.2 miles east-northeast of the head of the trail to the lake from Tamgas Harbor; the other is at an elevation of about 1600 feet on the crest of the east ridge of Purple Mountain, about 1.2 miles from the peak. The occurrences are in section 13, T. 78 S., R. 92 E., of the Copper River Meridian. The map site is at the approximate midpoint between these occurrences. The site corresponds to loc. 43a, b in Karl (1992). The location is accurate within 0.1 mile.

Geologic setting

Geologic description

The country rock at this site is Silurian trondhjemite (Berg, 1972 [I 684]; Berg and others, 1988). The trondhjemite, which locally is sheared, sericitized, and permeated with hydrothermal hematite, was regionally metamorphosed to greenschist grade in Late Cretaceous time.
The occurrences are in sheared, hydrothermally altered trondhjemite, and consist of disseminated pyrite, and of pyrite-magnetite veins associated with a 300-foot-wide shear zone. A sample of rusty, altered, granitic rock contained 0.14 ppm Au; a sample of a pyrite-magnetite vein contained 15 ppm Mo (Karl, 1992, loc. 43a, b).
Geologic map unit (-131.490678246957, 55.106658589759)
Mineral deposit model Disseminated sulfide and magnetite mineralization of undetermined origin.
Age of mineralization Probably Late Cretaceous or younger.
Alteration of deposit Trondhjemite is sericitized and locally permeated with hydrothermal hematite.

Production and reserves

Workings or exploration A sample of rusty, altered, granitic rock contained 0.14 ppm Au; and a sample of a pyrite-magnetite vein contained 15 ppm Mo (Karl, 1992, loc. 43a, b).
Indication of production None

References