Latitude: 63°10'48"N
Longitude: 147°13'48"W
Location: The map site of this prospect is at an elevation of about 4,100 feet on the west side of Eldorado Creek, about 0.4 mile south of Black Creek. It is in the SE1/4 of sec. 18, T. 20 S., R. 3 E., of the Fairbanks Meridian. The prospect is shown as site 21 in Smith, 1981.
Geology: The Black Creek prospect explores one of several mineral deposits in a belt south of Valdez Creek. The Valdez Creek area is underlain by pre-Upper Triassic pelitic clastic rocks, minor tuff, limestone lenses, and conglomerate. The rocks apparently vary abruptly in regional metamorphosed grade, from prehnite-pumpellyite through greenschist and amphibolite, to granulite. These rocks are intruded by Upper Jurassic alkali gabbro and by dioritic intrusions of Late Cretaceous and Early Tertiary age (Smith, 1981). The bedding and foliation of the strata strike about N 75 E and dip steeply northwest. Strike-slip faults having a similar orientation are also present, particularly on the south side of Valdez Creek (Smith, 1981). On the north side of the creek, a northwest-dipping thrust fault in part explains an apparent 'telescoping' of the metamorphic rocks. The Black Creek deposit apparently consists of sulfide-bearing, locally auriferous quartz veins in sheared, brecciated, and altered sedimentary and dioritic intrusive rocks. The sulfide minerals include arsenopyrite, pyrite, and pyrrhotite. Recurrent movement along faults, pulses of hydrothermal alteration, and recurrent injection of quartz veins has produced complex geology in the prospect area (Smith, 1981). The prospect area is rust stained in the vicinity of the adit due to the oxidation of iron sulfide minerals. There is a gold and arsenic geochemical anomaly around the prospect area. Smith (1981) mapped an old adit consisting of about 200 feet of underground workings. He reported argillite, metagraywacke and dioritic intrusive rock, all displaying varying degrees of shearing, quartz veining, and brecciation. Samples on ten foot intervals contained gold values as high as 120 parts per million. Underground development which terminated in 1998, did not find gold values of economic interest. No drilling has been done.
Workings: One adit and short drifts totaling 220 feet in length. Samples of this adit contained 4 ppm to 86 ppm gold (Smith, 1981). There is another adit and a small mill on the property.
Age: Late Cretaceous or Early Tertiary, because the quartz veins cut dioritic intrusions that are probably that age.
Alteration: Pyritization; silicification; and local iron staining.
Commodities (Major) - Au
Development Status: None
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1987; model 36a)
References
Ross, C.P., 1933, The Valdez Creek mining district, Alaska: U.S. Geological Survey Bulletin 849-E, p. 289-333. Smith, T.E., 1970, Gold resource potential of the Denali bench gravels, Valdez Creek mining district, Alaska, in Geological Survey research 1970: U.S. Geological Survey Professional Paper 700-D, p. D146-D152. Smith, T.E., 1981, Geology of the Clearwater Mountains, southcentral Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 60, 72 p., 3 sheets, scale 1:63,360. Tuck, Ralph, 1938, The Valdez Creek mining district, Alaska, in 1936: U.S. Geological Survey Bulletin 897-B, p. 109-131.
Mineral List
6 entries listed. 6 valid minerals.
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