Pork Chop Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Pork Chop prospect is situated near the summit of a southerly spur of the Mystery Mountains about one mile (1.6 km) north of Cottonwood Creek at an elevation of 2,500 feet (762 m) in Section 10, T. 23 S., R. 22 E., of the Kateel River Meridian. Location is accurate to within about 300 feet (91 m).
Geology: The Pork Chop prospect is one of six mineralized zones that occur in a prominent 7 mile (11 km) long, northeast trending belt that crosses the central part of the Mystery Mountains (DiMarchi and others, 1997). This belt is marked by a central core of copper-gold soil anomalies, and a peripheral zone of lead-zinc soil anomalies (DiMarchi and others, 1997). At Pork Chop, porphyry-like mineralization consist of disseminated chalcopyrite and pyrite in intensive altered tourmaline-quartz veins, vein breccias, and shears, all within several small quartz porphyry bodies that intrude Cretaceous Kuskokwim Group flysch. The Cretaceous flysch is thermally altered to biotite hornfels. Malachite is frequently observed in hairline fractures of intrusions. The strongest tourmaline alteration appears to be near the intersection of northeast trending and northwest trending faults. Most of the hydrothermal alteration is restricted to the quartz porphyry and does not invade the country rock (DiMarchi and others, 1997). The Pork Chop prospect is believed to be Late Cretaceous, based on isotopic age of Mystery Mountains plutonic rocks (Moll and others, 1981). Surface samples analyzed by ASA Inc. run as high as 5,000 ppm copper and 1,000 ppb gold. Clautice and others (1993) report values as high as 141 ppm copper, 788 ppb gold, 1,870 ppm arsenic, 14.0 ppm uranium, 2.00 percent zinc, and 441 ppm cadmium from grab samples at the Pork Chop prospect.
Workings: Regional exploration work conducted by WGM Inc. during 1975-to-1978 discovered the Pork Chop, Copenhagen Hill (MD030), and Ursus (MD033) prospects in the Mystery Mountains (Andrews, 1978). Hecla Mining Company explored and sampled the Pork Chop prospect in 1982 (Bell, 1983). From 1988 to 1990, American Copper and Nickel Inc. conducted exploration of the Pork Chop and related prospects in the Mystery Mountains, and flew a detailed airborne geophysical survey of the area. From 1991 to 1997, ASA Inc. continued to explore the Pork Chop and related deposits (DiMarchi and others, 1997). No drilling has taken place at the Pork Chop prospect. Surface samples analyzed by ASA Inc. run as high as 5,000 ppm copper and 1,000 ppb gold. Clautice and others (1993) report values as high as 141 ppm copper, 788 ppb gold, 1,870 ppm arsenic, 14.0 ppm uranium, 2.0 percent zinc, and 441 ppm cadmium from grab samples at the Pork Chop prospect.
Age: The Pork Chop prospect is believed to be Late Cretaceous, based on isotopic age of Mystery Mountains plutonic rocks (Moll and others, 1981).
Alteration: Sericite+quartz+tourmaline+malachite.
Reserves: None.
Commodities (Major) - Au, As, Cu, Zn; (Minor) - Ag, Cd, Sb
Development Status: No
Deposit Model: Porphyry Cu-Au (Cox and Singer, 1986; model no. 22c)
Mineral List
6 entries listed. 5 valid minerals.
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References
Andrews, Tom, 1978, Summary of Progress, Doyon Project, Mystery Mountains (Block 10): Anchorage, Alaska, WGM Inc., 24 p. (Held by Doyon, Limited, Fairbanks, Alaska, as proprietary report 78-42). Bell, J.D., 1983, Mystery Mountains Area, Block 10, Doyon Region, Kuskokwim District: Hecla Mining Company Summary Report, 25 p. Clautice, K.H., Bowman, N.D., Clough, J.G., Gilbert, W.G., Kline, J.T., Smith, T.E., and Blodgett, R.B., 1993, Land selection Unit 8 (Kantishna River, Ruby, and Medfra quadrangles); References, lead isotope, geochemical and major oxide data: Alaska Division of Geological and Geophysical Surveys, 42 p., 1 sheet, scale 1:250,000. DiMarchi, J.J., and Frantz, P.S., 1997, Annual Report for 1997-Doyon Option Lands, Block 10: ASA Inc.-Montague Gold Joint Venture Report, Volume II: Unpublished report, 189 p. (Report held by Doyon, Limited, Fairbanks, Alaska.) Moll, E.J., Silberman, M.L., and Patton, W.W. Jr., 1981, Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-C, 15 p., 2 sheets, scale 1:250,000.
