Unnamed (on upper Benson Creek)

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu
Ore minerals chalcopyrite; malachite
Gangue minerals iron oxides; quartz

Geographic location

Quadrangle map, 1:250,000-scale SO
Quadrangle map, 1:63,360-scale D-6
Latitude 64.913
Longitude -164.641
Nearby scientific data Find additional scientific data near this location
Location and accuracy This lode prospect is in the headwaters of Benson Creek (SO123) at an elevation of about 1,000 feet. This is locality 6 of Cobb (1972, MF 445; 1978, OF 78-181).

Geologic setting

Geologic description

An adit at this location exposed two, 3- to 5-foot-wide, silica-rich zones in marble that contained chalcopyrite, malachite, and iron oxides (Cathcart, 1922). Mineralization was banded, discontinuous, and appeared to follow layering in the highly folded host rocks. Wimmler (1926, in Asher, 1969, DGGS R18) collected a sample of copper-rich material from what appears to be this locality that assayed 0.04 ounces gold per ton, 0.20 ounces silver per ton, and 1.75 % copper. In places, the contact of the mineralized rocks seems to extend into marble suggesting replacement. This deposit is one of many occurrences of copper mineralization in silica-rich rocks near the regional contact between marble in a lower Paleozoic metasedimentary assemblage and pelitic schist of possible Cambrian or Precambrian age (Till and others, 1986). This type of copper occurrence is present at several localities in the western Solomon quadrangle (Gamble, 1988) and has similarities to several in the Kougarok area of the northeastern Teller quadrangle. In the Teller quadrangle, the Ward mine (TE071) is an example of this type of copper mineral occurrence. The Ward mine has been described as a zone of silicification in marble above a thrust contact with underlying metapelitic schist (Sainsbury and others, 1969; Sainsbury, 1975, p. 90-94). The silica-rich rocks have been metamorphosed and commonly have a laminar fabric. Copper-bearing minerals, mostly malachite but also including azurite and in places chalcopyrite and possibly bornite, are disseminated in the silica-rich rocks. The minor sulfides tend to be along faint laminae and joints (Sainsbury and others, 1969, p. 22). Malachite and azurite also occur in small veins and veinlets in the silica-rich rocks. The summary characterization of this type of Seward Peninsula mineral deposit by Sainsbury (1975, p. 90-94) contains inconsistencies with some descriptions of these deposits. Their origin is uncertain and other possibilities should be considered. One possiblity is that the silica-rich rocks are quartzites and that there is a stratigraphic control to the Ward deposit and similar occurrences elsewhere on Seward Peininsula. Quartzite at the base of the regional carbonate assemblage is recognized elsewhere in the Kougarok Mountain area (Puchner, 1986, p. 1777).
Geologic map unit (-164.643625771168, 64.9122558142947)
Mineral deposit model Copper-bearing mineralization in silica-rich zones at or near base of marble.
Age of mineralization Unknown; if stratigraphic controls are important then it is probably Paleozoic in age.
Alteration of deposit Silicification (?) and oxidation; the development of silica-rich rocks at or near the the base of Paleozoic marble overlying characterizes this type of copper occurrence.

Production and reserves

Workings or exploration A short adit was driven to explore this prospect before 1920.
Indication of production None

References

MRDS Number A012664

References

Puchner, C.C., 1987, Geology, alteration, and mineralization of the Kougarok Sn deposit, Seward Peninsula, Alaska; Discussion reply: Economic Geology, v. 82, p. 2201-2204.
Reporters Travis L. Hudson (Applied Geology)
Last report date 8/19/1999