Unnamed (west of West Fork Maclaren River near VABM Little)

Occurrences, Inactive

Commodities and mineralogy

Main commodities Ag; Cu
Other commodities Au; Hg; Pb; Sb; W; Zn
Ore minerals bornite; chalcopyrite; covellite; galena; scheelite; sphalerite; tetrahedrite; tennantite
Gangue minerals calcite; epidote; quartz

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-6
Latitude 63.2178
Longitude -146.815
Nearby scientific data Find additional scientific data near this location
Location and accuracy Numerous occurrences of copper minerals are at elevations of 5,200 to 5,900 feet near VABM Little, about 2 miles west of the West Fork Maclaren River. Most of the occurrences are on the north side of the mountain in the NE1/4 section 5 and NW1/4 section 4, T. 20 S., R. 5 E., Fairbanks Meridian. For this record the location is in the NE1/4 section 5 and is a general location for the occurrences. The site corresponds to locality A27 of Kurtak and others (1992), to locality 9 in figure 4 of Cobb (1979 [OFR 79-238]), and to locality 17 in table 2 of Nokleberg and others (1991).

Geologic setting

Geologic description

The area is underlain by basalt and andesite of the Nikolai Greenstone of Late Triassic age (Nokleberg and others, 1982, 1991). The volcanic rocks are sheared, faulted, and propylitized. Locally, faults are filled with quartz-calcite-epidote veins containing copper- and silver-bearing minerals that include bornite, chalcopyrite, and tetrahedrite and possibly covellite and tennantite. On the basis of metal concentrations found in assay, some of the veins probably contain galena, sphalerite, and scheelite.
The veins typically are discontinuous and narrow, less than 6 inches thick. One vein, however, widens to 2 feet thick and can be traced discontinuously through rubble crop for 250 feet (Kurtak and others, 1992, p. 144). According to assays reported by Kurtak and others (1992), propylitic basalt is weakly cupriferous (311 parts per million [ppm] copper, sample 637). Some of the veins are significantly richer. Representative samples composited from a 30-foot-wide rubble zone assayed 7.68 percent copper and 1.08 ounce silver per ton (sample 1298). Sample 1741 of a tetrahedrite-bearing vein contained 7.43 percent copper and 990 ppm tungsten; possibly this vein contains scheelite. Sample 1266 (1.0-foot-wide) from the vein that can be traced 250 feet assayed 16.9 percent copper and 0.85 ounce silver per ton. Sample 1852 showed that elevated base-metal and trace-element values and gold occur in one quartz-tetrahedrite vein that assayed 1.51 percent copper, 2.12 percent lead, 1.16 percent zinc, also 990 ppm arsenic, 400 parts per billion gold, 330 ppm tungsten, 323 ppm mercury, and 0.67 percent antimony. This vein almost certainly contains galena and sphalerite.
Geologic map unit (-146.817266849932, 63.2173606108238)
Mineral deposit model Basaltic Cu (Cox and Singer, 1986; model 23).
Mineral deposit model number 23
Age of mineralization Probably Cretaceous or early Tertiary (see MH060).
Alteration of deposit The mineralization is associated with quartz-calcite-epidote in propylitized intermediate and mafic volcanic rocks.

Production and reserves

Workings or exploration Mineralization was first reported near VABM Little in the early 1970s (Smith and others, 1973). The area was examined and sampled by the U.S. Bureau of Mines in about 1990; the Bureau collected 15 samples, mostly in rubble crop, during the course of study of the Valdez Creek Mining District (Kurtak and others, 1992).
Indication of production None

Additional comments

The U.S. Bureau of Mines recommended trenching in rubble crop areas to better define the veins, although it was recognized that the veins apparently were narrow and discontinuous (Kurtak and others, 1992).

References

References

Reporters W.T. Ellis (Alaska Earth Science), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (USGS)
Last report date 8/3/2001