Frog Prospect, Koyukuk Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Frog Prospect	Prospect
Koyukuk Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: The Frog prospect is located about 5 miles south-southeast of the west end of Ernie Lake, and about 5 miles west of upper Mettenpherg Creek. The prospect is at an elevation of about 1,160 meters, just northeast of the top of hill 1222 in the NE1/4 section 28, T. 29 N., R. 24 W., of the Fairbanks Meridian. The prospect is the site of samples 218, 219, and 220 in Dillon and others (1981 [AOF 133B]). There are several smaller occurrences about a mile to the southeast and west. The location is accurate.
Geology: The Frog prospect consists of stratiform sphalerite, galena and pyrite in Devonian, Skajit Limestone, and pyrite and minor base metals in siliceous schists within and underlying the carbonate rocks (Kurtak and others, 2002). The principal mineralization consists of disseminated to semi-massive sphalerite-galena-pyrite layers, typically in gray to white, thin-bedded, calcarenite, but also in micaceous interbeds. Individual layers are lensoidal, and only continue 10 feet or less along strike. The lenses average 2 to 3 inches thick, although some are as much as a foot thick. Light brown sphalerite is typically the most abundant sulfide mineral. Although the sulfide layers are distributed sporadically through several hundred feet of the sedimentary section, the main mineralized horizon is a 10- to 35-foot-thick zone in which there is a concentration of sulfide layers. This horizon can be traced for about 350 to 400 feet along strike. Selected samples contain up to 30% zinc, 7% lead, and 1 ounces of silver per ton. But samples across widths of 5 feet or more typically contain less than 2 or 3% zinc and lead; these values do not persist along strike. Dillon and others (1981 [AOF 133B]) collected three samples in the main ore horizon of quartzite, schist, and conglomerate with arsenopyrite(?), pyrite, sphalerite, and galena; the samples contain up to 100 ppm silver, 1% lead, 4% zinc, and 10 ppm antimony. Narrow, 0.2- to 2-inch veins of sphalerite and galena may result from remobilization of the stratiform sulfides into cleavages and fractures. Scattered occurrences of massive to disseminated pyrite and minor sphalerite and galena that are stratigraphically below the main ore horizon extend for up to a mile west. These are 3- to 12-inch-thick, discontinuous stratiform layers in calcareous quartz-muscovite schist. The layers are near the contact of the overlying Skajit Limestone. Approximately 0.8 to 1 mile southeast of the main mineral showing, scattered clots of chalcopyrite and disseminated pyrite and chalcopyrite occur along bedding planes in gray to white, thin-bedded, massive to laminated quartzite. This siliceous unit is 10 to 15 feet thick and is a member of the Skajit Limestone that is stratigraphically above the principal mineralized horizon. This area also contains a small, isolated, chalcocite-bearing quartz segregations in chlorite schist. Ninety-eight mining claims were located from 1976 to 1978; subsequent exploration includes geologic mapping, surface rock and soil sampling, geophysical surveys, and 7 diamond drill holes (Kurtak and others, 2002).
Workings: Ninety-eight mining claims were located from 1976 to 1978; subsequent exploration includes geologic mapping, surface rock and soil sampling, geophysical surveys, and 7 diamond drill holes (Kurtak and others, 2002).
Alteration: Local oxidation with development of limonite and hydrozincite.

Commodities (Major) - Ag, Pb, Zn; (Minor) - Cu
Development Status: No
Deposit Model: Stratiform lead-zinc deposit

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Link to USGS - Alaska:	WI044

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References