Saddle Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Saddle prospect occurs in the divide between Nixon Fork and Soda Creek drainages and about 1.3 miles (2 km) north of Reef Ridge deposit in Section 13, T. 22 S., R. 22 E., of the Kateel River Meridian. Location is precisely known to within 100 feet (30 meters).
Geology: The Saddle prospect is underlain by a continuous sequence of laminated to thinly bedded, light to dark gray dolomite of the Lower to Middle Silurian Paradise Fork Formation (Dutro and Patton, 1982). Host units strike N 80 to 85 West and dip 55 degrees South. The bedded sequence hosting the smithsonite mineralization is underlain on the north and south by dolomitic shale beds of the Middle to Upper Telsitna Formation (Dutro and Patton, 1982). Mineralization occurs in a 10 foot ( 3m) wide by 20 feet (6 m) long Amphipora-bearing horizon of bedded dolomite containing smithsonite, secondary dolomite, ferricrete, and secondary calcite in solution breccia. Host rock age is Silurian, based on Amphipora sp. found in ore zone of Paradise Fork Formation (Blodgett, 1982). The age of the mineralization is unknown. Soil sampling from surface exploration indicates a weak to moderate zinc anomaly extending in an east-west direction for about 1,200 feet (366 m). Three grab samples in the smithsonite-bearing solution breccia zone averaged 15.79 percent zinc with no appreciable lead (Schmidt, 1997).
Workings: The Saddle prospect was discovered by WGM Inc. and Patino Ltd. during exploration for base metasls in the late 1970s. Intermittant exploration work was continued by Pasminco Ltd. until about 1989 (Schmidt, 1997). Soil sampling from surface exploration indicates a weak to moderate zinc anomaly extending in an east-west direction for about 1,200 feet (366 m). Three grab samples in the smithsonite-bearing solution breccia zone average 15.79 percent zinc and no appreciable lead (Schmidt, 1997).
Age: Host rock age is Silurian, based on Amphipora found in ore zone of Paradise Fork Formation (Blodgett, 1982). The age of the mineralization is unknown.
Alteration: Smithsonite and sulfide species altered to ferricrete by groundwater.
Commodities (Major) - Zn; (Minor) - Pb
Development Status: No
Deposit Model: Appalachian zinc (Cox and Singer,1986; model no. 32b) or Mississippi Valley Typ
2 entries listed. 2 valid minerals.
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Anderson, G.M., and Macqueen, R.W., 1988, Mississippi Valley Type lead-zinc deposits, in Roberts, R.G., and Sheahan, P.A., eds., Ore deposit models: Geoscience Canada Reprint Series 3, Ottawa, Canada, p. 79-90. Blodgett, R.B., 1982, Stratigraphy of Reef Ridge project area; WGM Inc., Anchorage, Alaska, Reef Ridge Project area, Block 10, Doyon region: WGM Inc., 34 pages. Dutro, J.T. Jr., and Patton,W.W. Jr., 1982, New Paleozoic formations in the northern Kuskokwim Mountains, west-central Alaska: U.S. Geological Survey Bulletin 1529-H, p. H13-H22. Patton, W.W. Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811, one sheet at 1:250,000 scale. Schmidt, J.M., 1997, Shale-hosted Zn-Pb-Ag and barite deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska, 1997: Economic Geology Monograph 9, p. 35-65.