Unnamed (Tozitna River, Ray Mountains)

Occurrences, Inactive

Commodities and mineralogy

Main commodities Mn
Other commodities Ag
Ore minerals braunite; hausmannite

Geographic location

Quadrangle map, 1:250,000-scale TN
Quadrangle map, 1:63,360-scale C-2
Latitude 65.6378
Longitude -150.70128
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents occurrences of geochemically anomalous rock samples in a two-square-mile area in the eastern Ray Mountains, on ridges southeast of the Tozitna River. The site is at U.S. Bureau of Mines sample station RM24197 (Barker, 1990), at an elevation of 3,000 feet, in the northwest quarter of section 4, T. 9 N., R. 15 W., of the Fairbanks Meridian. The location is accurate within 1,000 feet. This site closely corresponds with the site for Ray Mountains, U.S. Bureau of Land Management MAS number 0020480132.

Geologic setting

Geologic description

Chapman and others (1982) map the Tozitna River area as Rampart Group, Mississippian to Jurassic sedimentary and mafic volcanic rocks, along with abundant gabbro and sparse ultramafic rocks. Mafic and ultramafic rocks, including locally serpentinized peridotite, gabbro, and pyroxenite, occur approximately one mile northeast of this site. Contacts between the mafic and ultramafic lithologies are well defined, suggesting a zoned ultramafic complex (Barker, 1990). The country rocks at these occurrences are locally hematitic chert and argillite, interlayered with andesite, that are thrust over the mafic and ultramafic rocks (Barker, 1990).
These occurrences consist of the manganese minerals hausmannite and braunite, which were discovered in 1979 during a joint U.S. Bureau of Mines - U.S. Bureau of Land Management mineral resource evaluation (Barker, 1990; Foley, 1992). The site was revisited by the Bureau in 1987 to determine its manganese resource potential.
The deposits consist of lenticular layers of massive manganese minerals intercalated with red and green chert (Barker, 1990). Four occurrences, ranging in thickness from 2 inches to 3.5 feet, were examined. In each case, the mineralized layer is underlain and overlain by hematitic chert that is part of a thick sequence of green andesite. At one location, a 3.5-foot-thick layer can be traced in outcrop and float for about 300 feet, along a strike of S75E. This layer dips 50o into a hillside, and is marked by minor shears or bedding-plane faults. The mineralized rock is black, has a fine-grained, soft, earthy texture, and is noticeably heavy. A grab sample (RM24197) contained 26.2 percent manganese, 1.8 parts per million (ppm) silver, 43 ppm copper, 92 ppm nickel, 30 ppm vanadium, and no detectable gold. A 42-inch-wide channel sample (RM23330) contained 16.1 percent manganese and no detectable gold or silver. X-ray diffraction analyses identified the minerals hausmannite and braunite. Thirty pounds of mineralized material was collected and sent to the U.S. Bureau of Mines Albany Research Laboratory for pyrometallurgical testing, but the results have not been made public.
Geologic map unit (-150.70383838589, 65.6373190974263)
Mineral deposit model Volcanogenic Mn (Cox and Singer, 1986; model 24c).
Mineral deposit model number 24c
Alteration of deposit Hematitization and propylitization.

Production and reserves

Workings or exploration These occurrences of the manganese minerals hausmannite and braunite were discovered in 1979 during a joint U.S. Bureau of Mines - U.S. Bureau of Land Management mineral resource evaluation (Barker, 1990; Foley, 1992). The site was revisited by the Bureau in 1987 to determine its manganese resource potential. A grab sample (RM24197) contained 26.2 percent manganese, 1.8 parts per million (ppm) silver, 43 ppm copper, 92 ppm nickel, 30 ppm vanadium, and no detectable gold. A 42-inch wide channel sample (RM23330) contained 16.1 percent manganese and no detectable gold or silver. Thirty pounds of mineralized material was collected and sent to the U.S. Bureau of Mines Albany Research Laboratory for pyrometallurgical testing, but the results have not been made public.
Indication of production None
Reserve estimates Barker (1990) estimated that the individual manganese deposits would not exceed 50,000 short tons and most would contain considerably less.

References