Rat Fork-Base

Prospect, Active

Alternative names

BMP

Commodities and mineralogy

Main commodities Ag; Cu; Pb; Zn
Other commodities Cd; Co; Fe
Ore minerals chalcopyrite; pyrite; pyrrhotite; sphalerite
Gangue minerals clinopyroxene (johannsenite); epidote; garnet

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale B-2
Latitude 62.3189
Longitude -153.8727
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rat Fork-Base prospect is near the base of the cirque that defines the head of the Rat Fork of Sheep Creek. It is at an elevation of 4,175 feet in the NW1/4 sec. 26, T. 26 N., R. 25 W., of the Seward Meridian. An active rock glacier forms the southern boundary of the prospect area. The location is accurate.

Geologic setting

Geologic description

The Rat Fork-Base prospect consists of disseminated sulfides in calc-silicate hornfels and marble adjacent to an extensive, east-trending, granodiorite sill and dike swarm. (The same plutonic complex is exposed at the Rat Fork-Headwall (MG059) prospect. ) At the Rat Fork-Base prospect, the calc-silicate zone, which consists of garnet, epidote, and clinopyroxene in arkosic, metaclastic rocks, has been intruded by several mafic sills that parallel bedding. The plutonic rocks intrude Lower Paleozoic rocks that are part of the Dillinger sub-terrane (Bundtzen, Harris, and Gilbert, 1997).
The zone of disseminated mineralization trends about east, varies from 1 to 10 meters thick , and can be traced along the strike for about 40 meters. The ore minerals include abundant pyrite and pyrrhotite, with minor chalcopyrite and sphalerite. (The mineralization is similar to that at the Rat Fork-Headwall (MG059), Tin Creek North (MG041), Tin Creek Midway (MG043), Smith Lake (MG055), and Bowser Creek Main (MG068) skarn deposits in the Farewell Mineral belt.)
Sometime in the late 1960s or early 1970s, a single hole was drilled by Falconbridge Minerals through their subsidiary St. Eugene Mining Company but there is little record of their activities. Sulfide-bearing, talus samples collected below the drill station contained 0.31 percent copper, 1.85 percent zinc, 6.5 grams of silver per tonne, 158 parts per million (ppm) cobalt, 161 ppm cadmium, and 41.4 percent iron (Smith and Albanese, 1985).
In 2008, this prospect was one of several in a block of claims that covered more than 70 square miles, known collectively as the BMP project (International Tower Hill Mines, Ltd., 2008).
Geologic map unit (-153.874920327896, 62.3182849927557)
Mineral deposit model Lead-zinc (copper) skarn (Cox and Singer, 1986; model 18c).
Mineral deposit model number 18c
Age of mineralization Unknown; possibly 25 to 35 Ma, based on the age of similar dike swarm in the Tin Creek area (Solie and others, 1991).
Alteration of deposit Surface oxidation of massive pyrite and pyrrhotite forms a pronounced ferricrete gossan.

Production and reserves

Workings or exploration Sometime in the late 1960s or early 1970s, a single hole was drilled by Falconbridge Minerals through their subsidiary St. Eugene Mining Company but there is little record of their activities. The prospect was later sampled by the Alaska Division of Geology and Geophysical Surveys. As of 2008, the prospect was within a large block of claims called the BMP project by International Tower Hill MIne, Ltd. (2008).
Indication of production None

References