Lake Cirque

Prospect, Undetermined

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Sn; Zn
Ore minerals chalcopyrite; galena; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale B-1
Latitude 56.4992
Longitude -132.052
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Lake Cirque prospect consists of three areas of mineralization that crop out through patches of ice and snow along a generally north-south trend about 2,000 feet long. The coordinates are at about the center of the mineralization; it is about 0.9 mile north-northwest of Marsha Peak and about 0.4 mile north of the center of section 18, T. 62 S., R. 86 E. The location is accurate. A map of the mineralization is Plate 29 of Still and others (2002).

Geologic setting

Geologic description

The rocks in the prospect area are part of a belt of Mesozoic or Paleozoic sedimentary and volcanic rocks that have been metamorphosed to Tertiary or Cretaceous schist and gneiss. The belt is about 1 1/2 mile wide and strikes northwest (Brew, 1997; George and Wyckoff, 1973). The metamorphic rocks are bounded on the east by a thick, regionally extensive, 60 to 70 Ma tonalite sill and on the west by a 90 Ma granodiorite pluton (Brew, 1997 Still and others, 2002). On the north side of Groundhog Basin,. about a mile to the north-northeast of this prospect, the metamorphic rocks are intruded by a 16.3 Ma biotite 'tin' granite pluton about 1,000 by 2,0000 feet in size. The granite is probably the source of the numerous rhyolite dikes and sills that extend from it and the mineralization in the area (Newberry and Brew, 1989).
The mineralization at this prospect and in the surrounding area was described in detail by Gault and others (1953). The prospect area was included in various claims blocks staked in the 50s and 60s but for most of that time, the area was covered by permanent snow and ice. In 1976, Bunker Hill Mining Company was able to trace the ore beds in Groundhog Basin (PE040) into the cirque around this prospect and drilled two holes in the mineralization. Still and others (2002) better defined the and sampled the mineralization in a year when much of the snow had melted off.
The mineralization at the Lake Cirque prospect is a continuation of the ore beds at the better known Groundhog Basin prospect (PE040) to the north. Still and others (2002) identified three zones of mineralization among the snow banks. The mineralization is similar in all three. It consists of layers of gneiss and/or calc-silicate gneiss that contain tabular to layered masses of chalcopyrite, galena, sphalerite, pyrite, and pyrrhotite. In the eastern zone, five samples taken in a tabular body several feet thick averaged 8.2 parts per million (ppm) silver, 752 ppm copper, 8,374 ppm lead, 5.13 percent zinc and 842 ppm tin. The west zone is about 80 feet long and 3 feet wide; samples averaged 36.9 ppm silver, 2.318 ppm copper, 9,223 ppm zinc, and 3,267 ppm tin. The mineralization at the south zone is in sheared gneiss with vuggy quartz veinlets. Samples across 9 feet of this zone's best mineralization averaged 3 ppm silver, 446 ppm copper, 1.68 percent zinc, and 567 ppm tin. Another area of mineralization originally located by Gault and others (1953) is on the south side of the cirque and consists of irregular bands and lenses of massive and disseminated pyrrhotite, galena, and sphalerite in calc-silicate gneiss and along fractures. The best sample collected in this zone by Still and others (2002) contained 130 ppm silver, 1,057 ppm copper, 1.06 percent led, 2.8 percent zinc, and 757 ppm tin.
Geologic map unit (-132.053681536306, 56.4988659256816)
Mineral deposit model Banded Ag-Cu-Sn-Pb-Zn tabular replacement bodies, veins, and stringers.
Age of mineralization Probably 16.3 Ma based on a genetic tie to a nearby, zinnwaldite 'tin' granite (Newberry and Brew, 1989).
Alteration of deposit None specifically noted.

Production and reserves

Workings or exploration The mineralization in this area was first described by Gault and others (1953). The prospect area was included in various claims blocks staked in the 50s and 60s, but for most of that time the area was covered by snow and ice. In 1976, Bunker Hill Mining Company was able to trace the ore beds in Groundhog Basin (PE040) in to the cirque around this prospect and drilled two holes. Still and others (2002) were able to better define and sample the mineralization in a year when much of the snow had melted and the rocks were better exposed.
Indication of production None
Reserve estimates None.

References