Unnamed (west of Anderson Mountain)

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Zn
Ore minerals arsenopyrite; chalcopyrite; enargite; galena; sphalerite
Gangue minerals barite; calcite; chlorite; quartz; sericite; siderite

Geographic location

Quadrangle map, 1:250,000-scale HE
Quadrangle map, 1:63,360-scale D-2
Latitude 63.8
Longitude -147.95
Nearby scientific data Find additional scientific data near this location
Location and accuracy The prospect is located about 0.5 mile west of the summit of Anderson Mountain at an elevation of 4,500 to 5,500 feet. It is in sec. 9, T. 13 S., R. 2 W., of the Fairbanks Meridian. The location is accurate to within one mile. This is locality 12 of Cox and others (1989).

Geologic setting

Geologic description

The prospect is in the Upper Devonian(?) felsic metavolcanic schist and phyllite, often containing relict phenocrysts of quartz, orthoclase, and plagioclase (Wilson and others, 1998). The deposit consists of massive layers of chalcopyrite, galena, sphalerite, enargite, and arsenopyrite in gangue of quartz, sericite, chlorite, calcite, barite, and siderite. The sulfide beds appear to lie on an irregular paleosurface on the footwall, with domal sulfide accumulations at the tops of layers (Nokleberg and others, 1994). The Hines Creek fault, a major structure that is responsible for much structural complexity at Anderson Mountain, is two miles south of the prospect. Numerous high-angle faults displace the sulfide layers, and folding makes tracing the layers a challenge. The discovery drill hole in 1976 intersected a massive sulfide zone that measured 1.7 meters thick and assayed 1.2% copper, 2% lead, 8.5% zinc and 61.4 grams of silver per ton (Schuster, 1998). Surface grab samples reportedly contain 14% combined lead and zinc, 2.5% copper and 274 grams of silver per ton. Nokleberg and others (1994) report copper grades varying from 0.5 to 19%, lead grades up to 5%, up to 22% zinc and up to 170 grams of silver per ton.
Geologic map unit (-147.952313610955, 63.7995593142041)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a)
Mineral deposit model number 28a
Age of mineralization Mineralization was probably syngenetic with the Upper Devonian(?) host rocks.
Alteration of deposit Absence of footwall alteration and stringer mineralization suggests off-vent deposition.

Production and reserves

Workings or exploration Geophysical and geochemical surveys have defined a potential zone of volcanogenic massive sulfide mineralization stretching over a strike length of 1373 meters. There has been about 2500 meters of drilling at the prospect (Robertson, 1998). The discovery drill hole in 1976 intersected a massive sulfide zone that measured 1.7 meters thick and assayed 1.2% copper, 2% lead, 8.5% zinc and 61.4 grams of silver per ton (Schuster, 1998). Surface grab samples reportedly contain 14% combined lead and zinc, 2.5% copper and 274 grams of silver per ton. Nokleberg and others (1994) report copper grades varying from 0.5 to 19%, lead grades up to 5%, up to 22% zinc and up to 170 grams of silver per ton.
Indication of production None

Additional comments

High geochemical values of arsenic, antimony, mercury, and tungsten may be derived from older schist basement. Anderson Mountain is significantly different from prospects in the Totatlanika Schist belt to the north (e.g. HE122) in having higher Cu content.

References

MRDS Number 10307537

References

Nokleberg, W.J., and (seven) others, 1994, Metallogeny and major mineral deposits of Alaska and Metallogenic map of significant metalliferous lode deposits and placer districts of Alaska, in Plafker, G. and Berg, H.C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol.. G1, p. 855-904, Plate 11, scale 1:2,500,000.
Robertson, R., 1998, Grayd hits massive sulphide: The Northern Miner, v. 84, no. 17, p. 3.
Schuster, T., 1998, Grayd advances Alaskan properties: The Northern Miner, v. 84, no. 18, p. 2.
Reporters N. Van Wyck (Stevens Exploration Management Corporation)
Last report date 4/7/2000