Latitude & Longitude (WGS84):
65° 52' 17'' North , 152° 25' 15'' West
Latitude & Longitude (decimal):
Mindat Locality ID:
202072
Long-form identifier:
mindat:1:2:202072:6
Location: This record represents anomalous rock samples of a ten-mile-long ultramafic body on the northwest slopes of the Ray Mountains, stretching from Holonada Creek on the east to the upper reaches of the northeast tributaries of Slokhenjikh Creek on the west. The samples are in T. 12 N., R. 23 W. and T. 13N, R. 22 W., of the Fairbanks Meridian. For this record, the site is Alaska Division of Geological and Geophysical Surveys (ADGGS) sample station 92Ha232 (Solie and others, 1993), the westernmost of the sample localities. It is at an elevation of about 1,950 feet 0.55 mile west of hill 2358, in the northeast quarter of section 18, T. 12 N., R. 23 W. The location is accurate within 500 feet. This site corresponds with the site for Holonada Creek, U.S. Bureau of Land Management MAS number 0020480134.
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). Chromite in serpentinized dunite in the Holonada Complex forms roughly parallel, planar bands up to about 0.5 inch thick that alternate with layers of serpentinite containing abundant disseminated chromite (U.S. Bureau of Mines memo from Albany Research Center to Jim Barker, 1986). The chromite grains are subhedral to euhedral and generally sand size. Polished section examinations show that the individual chromite grains are extensively fractured. The Bureau of Mines Alaska Field Operation Center investigated chromite deposits in Alaska between 1979 and 1984 as part of the Bureau's critical and strategic mineral program (Foley and others, 1985). The Holonada area contained 10 occurrences of disseminated and massive chromite in dunite bedrock and rubble. One occurrence, about 400 feet long and 5 to 15 feet wide in outcrop, contains more than 20 percent chromite (13,000-26,000 tons Cr2O3)). Four other occurrences contain 4 to 8 percent chromite (less than 1,000 tons Cr2O3 each) (Foley and others, 1985). The Bureau collected 12 hand-sorted, chromite-rich, rock samples of the Holonada ultramafic body that contained an average of 33.2% Cr2O3 (Foley and others, 1985). None of the concentrates examined during beneficiation studies contained detectable precious metals (1986 U.S. Bureau of Mines memo from Albany Research Center to Jim Barker). In 1992, the Alaska Division of Geological and Geophysical Surveys (ADGGS) collected 7 samples of chromite, or of chromite in dunite and/or lherzolite, in the Slokhenjikh Creek area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). The samples contained maximum values of 30,000 parts per million (ppm) chromium, 2,313 ppm nickel, 38 parts per billion (ppb) palladium, 23 ppb platinum, 295 ppm zinc, and 23 ppm bismuth. At one site (station 92Ha232), chromite covered a 25 by 300 foot area. Two samples of chalcedony in the ultramafic rocks contained detectable platinum and palladium (respective maximums of 33 ppb and 14 ppb (Solie and others, 1993).
Workings: The Bureau of Mines Alaska Field Operation Center investigated chromite deposits in Alaska between 1979 and 1984 as part of the Bureau's critical and strategic mineral program (Foley and others, 1985). The Holonada area contained 10 occurrences of disseminated and massive chromite in dunite bedrock and rubble. One occurrence, about 400 feet long and 5 to 15 feet wide in outcrop, contains more than 20 percent chromite (13,000-26,000 tons Cr2O3)). Four other occurrences contain 4 to 8 percent chromite (less than 1,000 tons Cr2O3 each) (Foley and others, 1985). The Bureau collected 12 hand-sorted, chromite-rich, rock samples of the Holonada ultramafic body that contained an average of 33.2% Cr2O3 (Foley and others, 1985). None of the concentrates examined during beneficiation studies contained detectable precious metals (1986 U.S. Bureau of Mines memo from Albany Research Center to Jim Barker). In 1992, ADGGS collected 7 samples of chromite, or of chromite in dunite and/or lherzolite, in the Slokhenjikh Creek area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). The samples contained maximum values of 30,000 parts per million (ppm) chromium, 2,313 ppm nickel, 38 parts per billion (ppb) palladium, 23 ppb platinum, 295 ppm zinc, and 23 ppm bismuth. At one site (station 92Ha232), chromite covered a 25 by 300 foot area. Two samples of chalcedony in the ultramafic rocks contained detectable platinum and palladium (respective maximums of 33 ppb and 14 ppb (Solie and others, 1993).
Age: Permian to Jurassic, based on age of host rocks and deposit model.
Commodities (Major) - Cr; (Minor) - Ni, Pd, Pt, Zn
Development Status: None
Deposit Model: Podiform chromite (Cox and Singer, 1986; model 8a).
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2 valid minerals.
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List of minerals arranged by Strunz 10th Edition classification
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References
Foley, J.Y., Barker, J.C., and Brown, L.L., 1985, Critical and strategic minerals investigation in Alaska - chromium: U.S. Bureau of Mines Open-File Report 97-85, 54 p., 1 sheet. Patton, W.W., Jr., and Miller, T.P., 1970, Preliminary geologic investigations in the Kanuti River region, Alaska: U.S. Geological Survey Bulletin 1312-J, p. J1-J10. Solie, D.N., Wiltse, M.A., Harris, E.E., and Roe, J.T., 1993, Land selection unit 34 (Bettles & Tanana quadrangles): References, DGGS sample locations, geochemical and major oxide data: Alaska Division of Geological and Geophysical Surveys Public Data File 93-34, 41 pages, 1 sheet, scale 1:250,000. 
