Mitchell; Ketchumstuk Prospect, Fortymile District, Southeast Fairbanks Borough, Alaska, USA

The Mitchell prospect is located within Doyon, Ltd. selected or conveyed land. For more information contact Doyon, Ltd., Fairbanks, Alaska.
Location: The Mitchell prospect is located on a hill about 1.5 miles south of Kechumstuk Creek, about 8 miles south of Mount Veta, and about 0.4 mile north of hill 4545. The coordinates are the location of trenches at the Mitchell prospect, in section 27, T. 27 N., R. 12 E., of the Copper River Meridian. The location is accurate. The Mitchell prospect is locality 10 of Cobb (1972 [MF-393]) and locality 39 of Eberlein and others (1977). The Mitchell prospect is located within Doyon, Ltd. selected or conveyed land.
Geology: The rocks in the vicinity of the Mitchell prospect are Paleozoic quartz-mica schist and greenstone that have been intruded by Mesozoic or Tertiary granitic rocks, and the Mount Veta syenite of Jurassic age (Foster, 1976). The Mitchell prospect is a skarn that is hosted in a marble-rich section of a schist roof pendant associated with an extensive area of granitic rocks (Saunders, 1962 [PE 60-11]). The roof pendant is about 5,000 feet long and 500 to 1,000 feet wide; it is probably underlain at shallow depth by intrusive rocks, including hornblende granodiorite (WGM Inc., 1998 [DLR 98-10]). Other carbonate-bearing schist in roof pendants crops out west of the Mitchell prospect. Granodiorite adjacent to the Mitchell prospect skarn is foliated, suggesting a Late Triassic or Early Jurassic age for the intrusion and skarn mineralization (Newberry and others, 1996). Several other prospects are associated with the Mount Veta intrusive complex, including Little Enchilada (EA103), East Eva (EA098), Eva Creek (EA099), Oscar (EA096), Oscar West (EA097), unnamed (north of Fish Creek) (EA062), Molly Creek (EA100), and Little Whiteman Creek (EA060). The Mitchell prospect is a gold-rich copper skarn (Newberry, 1995). The primary ore mineral is bornite; chalcopyrite, covellite, magnetite, sphalerite, galena, and tetrahedrite are also present (WGM Inc., 1998 [DLR 98-10]). Gangue minerals include quartz, garnet, diopside, calcite, and epidote. Trenches at the prospect have boulders as much as 40 centimeters in diameter that contain massive sphalerite, bornite, tetrahedrite, covellite, and malachite. A 5-foot-wide, east-northeast-striking vein of quartz, bornite, and chalcopyrite is exposed in one of the trenches (Saunders, 1962 [PE 60-11]). In some areas the ore is banded on a 3- to 5-millimeter scale with alternating layers of calc-silicates and chalcopyrite and bornite (WGM Inc., 1998 [DLR 98-10]). Malachite is present on some fracture surfaces and also as earthy masses. Soils at the Mitchell prospect contain as much as 4.4 percent zinc, 2,400 ppm lead, 3000 ppm copper, and 21 ppm silver (Dashevsky and others, 1986). The anomalies are at least partially open in all directions (WGM Inc., 1998 [DLR 98-10]). Magnetic highs are spatially associated with the soil anomalies near the trenches and at the northeast corner of the soil grid. A high-grade rock sample contains 230 ppb gold, 8 ppb platinum, 7 ppb palladium, 1.2 ppm tellurium, 150 ppm silver, 3.4 percent copper, 625 ppm lead, 3,100 ppm zinc, 21 ppm molybdenum, 2,830 ppm bismuth, 48 ppm arsenic, 5.9 ppm antimony, 34 ppm tin, and 10 ppm tungsten (Newberry, 1995). A sample of greenish, garnet skarn with disseminated to semimassive bornite contains 1,020 ppb gold, 8.5 ppm tellurium, 230 ppm silver, 6.5 percent copper, 178 ppm lead, 208 ppm zinc, greater than 2,000 ppm bismuth, 53 ppm arsenic, 5.6 ppm antimony, and 36 ppm tin (Burleigh and Lear, 1994). Additional geochemical analyses of several rock and mineralized samples from the Mitchell prospect are reported in Saunders (1962 [PE 60-11]), Foster and Clark (1970), Burleigh and Lear (1994), and WGM Inc. (1998 [DLR 98-10]). Newberry (1995) gives microprobe compositions for pyroxene, garnet, and epidote; lead and sulfur isotopic data; and rare-earth-element abundances from the Mitchell prospect. The Mitchell prospect was discovered in the early 1900's and a little work was done in 1911 (Porter, 1912). The prospect was trenched and examined by Bear Creek Mining Co. in the early 1960's, and these trenches and pits were mapped by Saunders (1962 [PE 60-11]). In 1976, WGM Inc. did reconnaissance mapping in the Mitchell prospect area and conducted stream-sediment sampling, geologic mapping, and soil sampling in 1977 (Dashevsky and others, 1986). In 1997, WGM Inc. surveyed the trenches and collected rock samples at the prospect (WGM Inc., 1998 [DLR 98-10]).
Workings: The Mitchell prospect was discovered in the early 1900's, and a little work was done in 1911 (Porter, 1912). The prospect was trenched and examined by Bear Creek Mining Co. in the early 1960's, and these trenches and pits were mapped by Saunders (1962 [PE 60-11]). In 1976, WGM Inc. did reconnaissance mapping in the Mitchell prospect area and conducted stream-sediment sampling, geologic mapping, and soil sampling in 1977 (Dashevsky and others, 1986). In 1997, WGM Inc. surveyed the trenches and collected rock samples at the prospect (WGM Inc., 1998 [DLR 98-10]).
Age: Granodiorite adjacent to the Mitchell prospect skarn is foliated, suggesting a Late Triassic or Early Jurassic age for the intrusion and skarn mineralization (Newberry and others, 1996).
Alteration: The Mitchell prospect is a gold-rich copper skarn (Newberry, 1995).

Commodities (Major) - Ag, Au, Cu, Zn; (Minor) - Bi, Mo, Pb, Sn
Development Status: None
Deposit Model: Cu skarn (Cox and Singer, 1986; model 18b).

Mineral List

16 entries listed. 14 valid minerals.

References