Threeman (Standard Copper)

Mine, Inactive

Commodities and mineralogy

Main commodities Cu; Zn
Other commodities Ag; Au; Co
Ore minerals chalcopyrite; cubanite; galena; pyrite; pyrrhotite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale CV
Quadrangle map, 1:63,360-scale D-7
Latitude 60.855
Longitude -146.537
Nearby scientific data Find additional scientific data near this location
Location and accuracy The mine is at an elevation of about 300 feet above the north shore of inner Landlocked Bay, and about 0.25 mile north-northeast of VABM Dick. It is in the S1/2 sec. 6, T. 12 S., R. 7 W., of the Copper River Meridian. The site location is accurate to within 1000 ft. The location corresponds to site C-73 in Jansons and others (1984) and to #14 in Cobb (1972: MF-392).

Geologic setting

Geologic description

The deposit at this mine is in mafic volcanic and sedimentary rocks of the Tertiary Orca Group (Nelson and others, 1985). It consists of two sulfide lenses up to about 6 ft wide and over 300 ft. long in pillow basalt and sedimentary rocks (Mihelich and Wells, 1957). Sulfide minerals include chalcopyrite, cubanite, galena, pyrite, pyrrhotite, and sphalerite.
Chip and grab samples contained 53 parts per million (ppm) to 5.25 percent Cu, 40 ppm to 2.85 percent Zn, <0.02 ppm to 0.10 ppm Au, <1 ppm to 22 ppm Ag, and 5 to 700 ppm Co (Jansons and others, 1984). Sixteen chip samples taken in 1955 contained 0.3 percent to 8.6 percent Cu, 0.05 percent to 0.64 percent Zn, trace to 0.07 oz. Au/ton and trace to 0.78 oz. Ag/ton (Mihelich and Wells, 1957).
A 2014 grab sample contained 0.025 ppm Au, 8.63 ppm Ag, 4.09 percent Cu, and 1.62 percent Zn. A stream sediment sample collect roughly 1000 ft to the northeast contained 0.25 ppm Ag, 330 ppm Cu, and 482 ppm Zn (Angel, 2014).
Geologic map unit (-146.538992541645, 60.8544512702824)
Mineral deposit model Cyprus massive sulfide (Cox and Singer, 1986; model 24a)
Mineral deposit model number 24a
Age of mineralization Probably Tertiary based on the age of the host rocks.
Alteration of deposit Oxidation of copper minerals (Angel, 2014).

Production and reserves

Workings or exploration
There are several thousand feet of workings on three levels. Three adits were caved when visited by this reporter in 1974 and 1986 (also see Sainsbury, 1993). Chip and grab samples contained 53 parts per million (ppm) to 5.25 percent Cu, 40 ppm to 2.85 percent Zn, <0.02 ppm to 0.10 ppm Au, <1 ppm to 22 ppm Ag, and 5 to 700 ppm Co (Jansons and others, 1984). Sixteen chip samples taken in 1955 contained 0.3 percent to 8.6 percent Cu, 0.05 percent to 0.64 percent Zn, trace to 0.07 oz. Au/ton and trace to 0.78 oz. Ag/ton (Mihelich and Wells, 1957).
Field work including sampling was performed in 2014. A 2014 grab sample contained 0.025 ppm Au, 8.63 ppm Ag, 4.09 percent Cu, and 1.62 percent Zn. A stream sediment sample collect roughly 1000 ft to the northeast contained 0.25 ppm Ag, 330 ppm Cu, and 482 ppm Zn (Angel, 2014).
Indication of production Yes; medium
Reserve estimates Inferred reserves of 1,902,000 tons at 1.05 percent Cu (Sainsbury, 1953).
Production notes 1,159,660 lbs. Cu, 101 oz. Au, 5,308 oz. Ag from 6,196.5 tons ore (Mihelich and Wells, 1957).

Additional comments

Nelson and others (1985) interpret the country rocks as accreted ocean crust. Crowe and others (1992; 1993) and Sainsbury (1993) discuss the genesis of the volcanogenic massive sulfide deposits in this area.
Chugach Alaska Corporation, Anchorage, Alaska has control of these lands.

References

MRDS Number 10307359

References

Angel, A.K., 2014 Mineral Assessment of Chugach Alaska Lands, Unpublished Report, 21p. (Report held by Chugach Alaska Corporation, Anchorage, Alaska).
Sainsbury, C.L., 1993, Geology and geochemistry of volcanogenic massive sulfide deposits and related igneous rocks, Prince William Sound, south-central Alaska, A discussion: Economic Geology, v. 88, p. 1284-1285.
Reporters S.W. Nelson, Anchorage, AK; A.K. Angel (Alaska Earth Sciences, Inc.)
Last report date 9/9/2014