Unnamed Occurrences (ARDF - BT011; near Caribou Mountain), Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrences (ARDF - BT011; near Caribou Mountain)	- not defined -
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

See also Upper Kanuti (BT012) and Lower Kanuti (BT014).
Location: This site includes several similar occurrences along the ridge which extends northeast from the summit of Caribou Mountain. The coordinates are of one occurrence approximately at the center of these occurrences; it is near hill 2355 at an elevation of about 2,300 feet, about 0.25 mile south-southwest of the center of section 6, T. 15 N., R. 14 W., of the Fairbanks Meridian. The other occurrences extend to about 0.8 mile northeast and 1.5 miles southwest. The location is accurate.
Geology: This site consists of ten chromite occurrences in Jurassic or older, dunite and pyroxene-peridotite of the Caribou Mountain ultramafic complex (Foley and McDermott, 1983). The chromite occurs as massive chromitite in alternating layers of dunite and pyroxene-peridotite; as wispy concentrations of disseminated chromite in dunite; and as disseminated and massive chromite in dunite. The chromite deposits are small and discontinuous (Foley and McDermott, 1983). Samples of the occurrences contain up to 20% chromium but the mean is less than 2%. Chromium analyses vary erratically as is typical of podiform chromite deposits (Foley and McDermott, 1983). Samples also contain cobalt, copper and nickel values typical of ultramafic rocks, consistent with the apparent absence of sulfide minerals (Foley and McDermott, 1983). The platinum group elements are generally low, although one high-grade chromite sample contains 377 ppb Pd and 1,337 ppb Pt (Foley, 1992). 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 components are mainly interlayered dunite and pyroxene-peridotite, with subordinate gabbro, pyroxenite, serpentinite, and chromitite. Individual layers may 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 or 2% of the rock.
Workings: Only surface sampling and mapping.
Age: The chromite is a normal primary constituent of the ultramafic rocks which are Jurassic or older.
Alteration: Some serpentization of the ultramafics.
Reserves: Foley (1992) estimates that there are 1,800 to 2,200 million tons of chromic oxide in three deposits. Seven other unmeasured or minor chromite occurrences were noted.

Commodities (Major) - Cr; (Minor) - Co, Ni, PGE
Development Status: None
Deposit Model: Podiform chromite (Cox and Singer, 1986; model 8a)

Other Databases

Link to USGS - Alaska:	BT011

Other Regions, Features and Areas containing this locality

References