Colorado; Upper Colorado 1-3 Prospect, Hope District, Kenai Peninsula Borough, Alaska, USA

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Location: The record describes a prospect at an elevation of 2,400 and 2,800 feet in the SW1/4 section 36 of T. 7 N., R. 2 W., and the NW1/4 section 1, T. 6 N., R. 2 W., of the Seward Meridian. It is situated on the south side of Colorado Creek about 2 miles west of the Seward Highway. This is location 23 of Cobb and Richter (1977), location 31 of MacKevett and Holloway (1977), location 45 of Cobb and Tysdal (1980), and location S-259 of Jansons and others (1984). This location is accurate to within a quarter of a mile.
Geology: The deposit consists of auriferous, sulfide-bearing, quartz-calcite veins that heal fractures in the Gilpatrick dike of Eocene age. The veins are as much as 8 inches wide and carry arsenopyrite, pyrite, galena, sphalerite, and gold. Considerable free gold is visible in some of the veins (Martin and others, 1915). The dike ranges from 4 feet to nearly 15 feet wide, strikes N10E, and dips nearly vertically. Its average width is about 5.5 feet (Tuck, 1933). The wall rock is slate (Tuck, 1933) of the Valdez Group of Late Cretaceous age Nelson and others, 1985). The cleavage of the slate is parallel to the strike of the dike.
Workings: Tuck (1933) reported a 20-foot adit at an elevation of 2,200 feet and open cuts at 2,240 and 2,350 feet. Exposures in the adit and open cuts indicate that the quartz-calcite veins and stringers make up about 20 percent of the dike. The workings were accessed from the Seward Highway by a 2-mile trail on the south side of Colorado Creek. At the 20-foot adit, two 5-foot-long channel samples yielded respectively, 0.05 ounce of gold and 0.2 ounce of silver per ton, and 0.01 ounce of gold, 0.2 ounce of silver per ton (Tuck, 1933). The U.S. Bureau of Mines visited the prospect in 1979 and found three adits, two of which were caved, and numerous pits and trenches (Jansons and others, 1984). They collected three grab samples and a chip sample. One grab sample assayed a trace of gold and 0.15 ounces of silver per ton. Two other grab samples and the chip sample assayed a trace of gold and 0.01 ounces of silver per ton (Jansons, 1981).
Age: Eocene or younger; the veins reheal a fractured Eocene dike.

Commodities (Major) - Ag, Au; (Minor) - Pb, Zn
Development Status: None
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

References

Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. Cobb, E.H., and Richter, D.H., 1972, Metallic mineral resources map of the Seward quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-466, 2 sheets, scale 1:250,000. Jansons, Uldis, 1981, 1979 Bureau of Mines sample sites and analytical results for samples collected in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Open File Report 83-81, 229 p. 5 sheets. 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. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Martin, G.C., Johnson, B.L., and Grant, U.S., 1915, Geology and mineral resources of Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 587, 243 p. Tuck, Ralph, 1933, The Moose Pass-Hope district, Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 849-I, p. 469-530. Tysdal, R.G., 1978, Mines, prospects, and occurrences map of the Seward and Blying Sound quadrangles, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-880-A, 2 sheets, scale 1:250,000.

Mineral List

Arsenopyrite Calcite

Galena Gold

Quartz Sphalerite

6 entries listed. 6 valid minerals.