Unnamed Occurrences (ARDF - TN004; north of Kanuti Kilolitna River), Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrences (ARDF - TN004; north of Kanuti Kilolitna River)	- not defined -
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: This record represents occurrences of anomalous rock samples in a thousand-foot-long area along the south slope of hill 2360, north of the Kanuti Kilolitna River. The site is at an elevation of 1,200 feet, 0.45 mile east-northeast of the center of section 7, T. 13 N., R. 20 W., of the Fairbanks Meridian. The location is accurate within a thousand feet.
Geology: The Kanuti River region straddles the southeastern boundary of the Yukon-Koyukuk Basin and includes sedimentary and volcanic rocks of the basin sequence as well as metamorphic and plutonic rocks of the adjoining Kokrines-Hodzana Highlands (Patton and Miller, 1970). The Sithylemenkat Pluton, a 170-square mile body of mid-Cretaceous granitic rocks, intrudes metasedimentary rocks on the south side of the Kanuti River. Dikes of pegmatite are locally abundant on the perimeter of the predominantly porphyritic, biotite quartz monzonite pluton. Overlying and intruding the metasedimentary rocks along the northwest flank of the Kokrines-Hodzana Highlands is an ophiolitelike assemblage of Permian to Jurassic, altered pillow basalt, diabase, and gabbro; serpentinized peridotite and dunite; and bedded chert (Patton and Miller, 1970). Six of the ultramafic bodies extend for 65 miles, from Caribou Mountain in the northeast to the upper Melozitna River in the southwest. Numerous smaller bodies also occur in this belt. The ultramafic rocks are crudely layered, tabular bodies dipping gently to steeply northwest. The Holonada body is about 2,500 feet thick. Layering in the Kilolitna body is less well defined, but the width of its outcrops suggests that it is at least as thick. The lower contact of the ultramafic bodies is sharply defined, possibly by a fault, with little evidence of thermal alteration of the underlying rocks. The ultramafic rocks are composed almost entirely of serpentinized peridotite, chiefly harzburgite, and serpentinized dunite. They are cut by veinlets and irregular masses of chalcedony and drusy quartz. Patton and Miller (1970) found one small mass of colloform magnesite in the northern part of the Kilolitna body (in the Bettles quadrangle). In the late 1960s, the U.S. Geological Survey collected composite rock samples at several locations across the Kilolitna and lower Kanuti ultramafic bodies (Patton and Miller, 1970). Nine samples, each weighing approximately 3 pounds, were analyzed. The range of analytical values for these samples was: 2,400 to 3,000 parts per million (ppm) chromium, 1,900 to 2,400 ppm nickel, les than 0.010 ppm platinum, less than 0.005 ppm rhenium, and less than 0.004 ppm to 0.008 ppm palladium. Chromium content ranged as high as 9 percent in selected grab samples of dunite streaked with grains of chrome spinel. The U.S. Bureau of Mines Alaska Field Operation Center investigated chromite deposits and occurrences in Alaska between 1979 and 1984 as part of the Bureau's critical and strategic minerals program (Foley and others, 1985). Several hand-sorted, chromite-rich samples collected in the Kilolitna River area contained an average of 46.7 percent Cr2O3 (Foley and others, 1985). In 1992, The Alaska Division of Geological and Geophysical Surveys (ADGGS) investigated the Kanuti-Kilolitna River area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). Samples of chromite schlieren (station 92MW437) and chromite pods (station 92MW438) in lherzolite contained more than 30,000 ppm chromium, 2,150 ppm nickel, 29 parts per billion (ppb) platinum, and 510 ppm zinc. A sample (station 92MW438) of serpentinized, slickensided gabbro contained 4,700 ppm chromium, 1,800 ppm nickel, 22 ppb platinum, and 30 ppm tin. A pan-concentrate sample collected about one mile west of this site was anomalous inr uranium, chromium, niobium, tin, titanium, zind, and zirconium.
Workings: In the late 1960s, the U.S. Geological Survey collected composite rock samples at several locations across the Kilolitna and lower Kanuti ultramafic bodies (Patton and Miller, 1970). Nine samples, each weighing approximately 3 pounds, were analyzed. The range of analytical values for these samples was: 2,400 to 3,000 parts per million (ppm) chromium, 1,900 to 2,400 ppm nickel, les than 0.010 ppm platinum, less than 0.005 ppm rhenium, and less than 0.004 ppm to 0.008 ppm palladium. Chromium content ranged as high as 9 percent in selected grab samples of dunite streaked with grains of chrome spinel. The U.S. Bureau of Mines Alaska Field Operation Center investigated chromite deposits and occurrences in Alaska between 1979 and 1984 as part of the Bureau's critical and strategic minerals program (Foley and others, 1985). Several hand-sorted, chromite-rich samples collected in the Kilolitna River area contained an average of 46.7 percent Cr2O3 (Foley and others, 1985). In 1992, The Alaska Division of Geological and Geophysical Surveys (ADGGS) investigated the Kanuti-Kilolitna River area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). Samples of chromite schlieren (station 92MW437) and chromite pods (station 92MW438) in lherzolite contained more than 30,000 ppm chromium, 2,150 ppm nickel, 29 parts per billion (ppb) platinum, and 510 ppm zinc. A sample (station 92MW438) of serpentinized, slickensided gabbro contained 4,700 ppm chromium, 1,800 ppm nickel, 22 ppb platinum, and 30 ppm tin. A pan-concentrate sample collected about one mile west of this site was anomalous inr uranium, chromium, niobium, tin, titanium, zind, and zirconium.
Age: Permian to Jurassic, coeval with the presumed age range of the mafic and ultramafic hostrocks.

Commodities (Major) - Cr, Pt; (Minor) - Ni, Pd, Rh, Zn
Development Status: None
Deposit Model: Podiform chromite (Cox and Singer, 1986; model 8a).

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Link to USGS - Alaska:	TN004

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