Geology of the Copper Mountain district

During the 1982 and 1983 field seasons, W. Dan Hausel of the Wyoming State Geological Survey mapped the supracrustal rocks of the Copper Mountain District (Need MrSid Browser Plugin), and Hausel and Karl Albert mapped the accessible mine workings in the historical DePass Copper Mine (see Hausel and others, 1985). Along with mapping these ancient Archean (>2.5 billion year old) rocks, the WSGS made a preliminary reconnaissance study of the mineral resources. Copper Mountain has varied and scattered occurrences of copper, gold, silver, iron , tungsten, beryl, spodumene and uranium.

Copper Mountain is located in central Wyoming within the Wyoming Province (Figure 1) – an Archon that extends north from Wyoming into Canada. The rocks are somewhat characteristic of a high-grade supracrustal belt and consist of layered quartzofeldspathic gneiss, amphibolite, mica schist with some orthoquartzite and banded iron formation. However, lacking the high grade granulite metamorphism characteristic of high grade supracrustal terrains elsewhere in the world, Copper Mountain probably is best described as a supracrustal metasedimentary belt. The Copper Mountain metamorphic complex can be separated into three general rock types: (1) supracrustal rocks (>2.72 Ga), (2) granites (2.64-2.72 Ga), and mafic dikes (1.9-2.2 Ga).

Mineralization includes copper. The principal copper producer in the district was the DePass mine. This property was developed by more than 11,000 feet of mine tunnels and shafts, in a cupriferous mafic dike. Available records show that a minimum of 567,610 pounds of copper were shipped from the mine during the years of 1906, 1917, and 1918, along with gold and silver. Samples collected by the WSGS in the 1982 study showed the mine to still host good mineralization. For example, samples collected by the WSGS contained from 0.7% to 1.97% copper. An early 1918 report indicated that a sample of the ore contained 0.14 opt Au and that gold values were fairly continuous throughout the mine.

Other mineralization includes relatively continuous, but thin, banded iron formations that have been prospected and mined at several locations in the district. Where mined, the target appears to have been copper in the iron formation. Unfortunately, no resource estimates for the iron formation are known, but the resource would probably be in the 10s of millions of tons.

Gold was mined at the Gold Nugget property in the district. This is a vein deposit in muscovite schist. A 1935 report indicated that the ore averaged 0.42 opt Au and ranged from a trace to 2.37 opt Au. Some tungsten was produced nearby in the 1940s. The ore contained between 0.16 to 2.56% WO3.

Several pegmatites occur in the district. These were prospected for feldspar, columbite-tantalite, tourmaline, garnet, petalite, apatite, clevelandite, lepidolite, beryl and aquamarine. Some excellent aquamarine specimens were reportedly recovered from some of these pegmatites.

The district was of interest for uranium in the late 1970s. The uranium is mostly found on the flanks of the belt in the Tepee Trail Formation (Eocene), but some uranium is also reported to occur in propylitically altered fractures in Precambrian granite.

During the Laramide orogeny, the Owl Creek Mountains were thrust to the north, such that Precambrian rocks now overly overturn and folded Paleozoic and Mesozoic rocks. A number of fractures in Precambrian rocks along the northern flank of the district are stained by hydrocarbons which seeped through the thrust sheet from the underlying Phanerozoic rocks.

REPORTS ON COPPER MOUNTAIN PREPARED BY THE WSGS

Lageson, D.R., and Hausel, W.D., editors, 1978, Occurrences of uranium in Precambrian and younger rocks of Wyoming and adjacent areas: Geological Survey of Wyoming Public Information Circular 7, 37 p.

Hausel, W.D., and Holden, G.S., 1978, Mineral resources of the Wind River Basin and adjacent Precambrian uplifts: Wyoming Geological Association 30th Annual Field Conference Guidebook, p. 303-310.

Hausel, W.D., and others, 1979, Wyoming mines and minerals map: Geological Survey of Wyoming Map Series MS-5, scale 1:500,000.

Hausel, W.D., 1981, Reconnaissance report on the Gold Nugget property, Copper Mountain district, Fremont County: Geological Survey of Wyoming unpublished Mineral Report MR81-4, 6 p.

Hausel, W.D., 1983, Economic geology of the Gold Nugget mineralized area, Copper Mountain, Wyoming: Geological Survey of Wyoming unpublished Mineral Report MR83-17, 9 p.

Hausel, W.D., 1983, Reconnaissance and economic geology of the Copper Mountain metamorphic complex, Owl Creek Mountains, Wyoming: American Association of Petroleum Geologists - Energy Minerals Division, Program with Abstracts, p. 13.

Hausel, W.D., and Graff, P.J., 1983, Reconnaissance and economic geology of Wyoming's Copper and Owl Creek Mountains: California Mining Journal, November, p. 26-31.

Hausel, W.D., and Graff, P.J., 1983, Reconnaissance and economic geology of the Copper Mountain metamorphic complex, Owl Creek Mountains, Wyoming: Wyoming Geological Association 34th Annual Field Conference Guidebook, p. 179-184.

Hausel, W.D., Graff, P.J., and Albert, K.G., 1984, Economic geology of the Copper Mountain supracrustal belt, Wyoming [abstract]: Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section Newsletter, 1 p.

Hausel, W.D., Graff, P.J., and Albert, K.G., 1985, Economic geology of the Copper Mountain supracrustal belt, Owl Creek Mountains, Fremont County, Wyoming: Geological Survey of Wyoming Report of Investigations 28, 33 p., 3 plates (scale 1:24,000).

Harris, R.E., and Hausel, W.D., 1986, Wyoming pegmatites in Colorado Pegmatite Symposium: Colorado Chapter, Friends of Mineralogy, May 30th-June 2nd, p. 101-108.

Hausel, W.D., 1986, Minerals and rocks of Wyoming: Geological Survey of Wyoming Bulletin 66, 117 p.

Figure. GEOLOGIC MAP OF COPPER MOUNTAIN, OWL CREEK RANGE (scale 1:24,000)

Copper Mountain.TIF

Figure 1. Generalized map of the Wyoming Province (Archon) showing location of the Copper Mountain belt.

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