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Threeman Mining Co.

Prospect, Inactive

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Commodities and mineralogy

Main commodities Cu; Zn
Other commodities Ag
Ore minerals chalcopyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale CV
Quadrangle map, 1:63,360-scale D-7
Latitude 60.874
Longitude -146.57
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is at an elevation of about 1600 ft., approximately 0.75 mi. northeast of Copper Mountain. It is in S1/2 sec. 36, T. 11 S., R. 8 W., of the Copper River Meridian. The location is accurate to within 1000 ft. This site is shown as C-82 in Jansons and others (1984).

Geologic setting

Geologic description

The country rocks at this prospect are mafic volcanic rocks and sedimentary rocks of the Tertiary Orca Group (Nelson and others, 1985). The deposit consists of up to foot-thick lenses of chalcopyrite and pyrrhotite
in two-foot- to 15-foot-wide shear zones.
Three chip samples contained 200 ppm to 1% Cu, 145 ppm to 0.89% Zn, and <0.2 to 6 ppm Ag; a grab sample from the dump contained 4.9% Cu, 0.49% Zn, and 50 ppm Ag (Jansons and others, 1984).
Geologic map unit (-146.571997094399, 60.8734526764473)
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.

Production and reserves

Workings or exploration One 41-foot-long adit. Three chip samples contained 200 ppm to 1% Cu, 145 ppm to 0.89% Zn, and <0.2 to 6 ppm Ag; a grab sample from the dump contained 4.9% Cu, 0.49% Zn, and 50 ppm Ag (Jansons and others, 1984).
Indication of production None

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 10307355

References

Crowe, D.E., Nelson, S.W., Brown, P.E., Valley, J.W., and Shanks, W.C., III, 1992, Geology and geochemistry of volcanogenic massive sulfide deposits and related igneous rocks, Prince William Sound region, south-central Alaska: Economic Geology, v. 87, no. 7, p. 1722-1746.
Crowe, D.E., Nelson, S.W., Brown, P.E., Valley, J.W., and Shanks, W.C., III, 1993, Geology and geochemistry of volcanogenic massive sulfide deposits and related igneous rocks, Prince William Sound, south-central Alaska--Reply: Economic Geology, v. 88, p. 1285-1288.
Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000.
Nelson, S.W., Dumoulin, J. A., and Miller, M.L., 1985, Geologic map of the Chugach National Forest, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1645-B, 16 p., 1 sheet, scale 1:250,000.
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
Last report date 6/10/2000