Unnamed (near lower Kanuti River)

Occurrences, Inactive

Commodities and mineralogy

Main commodities Cr
Other commodities Co; Ni; PGE
Ore minerals chromite

Geographic location

Quadrangle map, 1:250,000-scale BT
Quadrangle map, 1:63,360-scale B-2
Latitude 66.2802
Longitude -150.8769
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site includes fourteen similar mineral occurrences that form a northwest-trending belt about 7 miles long. The coordinates are at the northeast end of the belt at the best exposed of these deposits which is about 0.6 mile north-northwest of hill 2190 and about 9 miles southwest of Caribou Mountain. This locality is at an elevation of about 1,900 feet, in the SE1/4 section 24, T. 17 N., R. 16 W. of the Fairbanks Meridian. Similar mineralization also occurs in three other areas to the southwest .

Geologic setting

Geologic description

Fourteen occurrences of podiform chromite occur within the lower Kanuti ultramafic body (Foley and McDermott, 1983). The best exposure of this mineralization is an 80-ft. long, 5-ft.-thick interval up to 4 inches thick composed of layers of disseminated to coalescent chromite, alternating with barren dunite. A number of other occurrences in the area are poorly exposed or exposed only as rubble. They consist of local concentrations of wispy, disseminated chromite in serpentinized dunite; pods of massive chromitite in rubble; discontinuous lenses of chromitite; and massive and coalescent chromite. Samples contain from 0.2 to 23.5 percent chromium over 1-foot intervals, and 8.5 percent chromium over a 5-foot interval (Foley and McDermott, 1983). The average chromium chromium content of the samples is less than 2 percent. The cobalt, copper, and nickel content of these samples show little enrichment above what is typical for ultramafic rocks (Foley and McDermott, 1983). One concentrated sample of chromite from the area contains 340 ppb platinum.
The ultramafic, mafic volcanic and intrusive rocks, and associated chert in this area are thought to represent a dismembered ophiolite assemblage (Foley and McDermott, 1983). The mafic-ultramafic rocks at these occurrences are similar to those at Caribou Mountain (BT011). They consist principally of interlayered dunite and pyroxene-peridotite, with subordinate gabbro, pyroxenite, serpentinite, and chromitite. Individual layers range from tens to thousands of feet thick. The richest chromite deposits are in the dunite. Although chromite is ubiquitous in the dunite and pyroxene-peridotite, it seldom exceeds 1 to 2 percent of the rock.
Geologic map unit (-150.879532552621, 66.2797323984519)
Mineral deposit model Podiform chromite (Cox and Singer, 1986; model 8a).
Mineral deposit model number 8a
Alteration of deposit Some serpentinization of the ultramafics.

Production and reserves

Workings or exploration The U.S. Bureau of Mines carried out surface sampling and some beneficiation studies (Foley and McDermott, 1983). One of their sample locations was from a pit on claims located in 1975 by the Oil Development Co. of Texas.
Indication of production None
Reserve estimates Foley and McDermott (1983) estimated that 6 to 7 million tons of chromic oxide are present in one 80-ft.-long x 5-ft.-thick exposure of banded and disseminated chromite. Thirteen additional occurrences are minor or unmeasured.

Additional comments

See also: Caribou Mountain (BT011); upper Kanuti River (BT012).

References