|Quadrangle map, 1:250,000-scale||MG|
|Quadrangle map, 1:63,360-scale||B-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Rat Fork-Headwall prospect is just below the crest of a steep ridge that forms the headwall of a glacial cirque at the head of the Rat Fork of Sheep Creek; it is at an elevation of about about 5,500 feet in the NW1/4 sec. 27, T. 26 N., R. 25 W., of the Seward Meridian. The location is accurate.|
The Rat Fork-Headwall prospect consists of disseminated sulfides and a sulfide vein in calc-silicate skarn in a east-trending, granodiorite dike swarm more than 1.5 kilometers wide (Bundtzen Kline, and Clough, 1982). The dike swarm cuts lower Paleozoic clastic rocks and carbonates of the Dillinger sub-terrane (Bundtzen, Harris, and Gilbert, 1997). The dikes are not dated at this prospect but are similar to dikes that have dated as 25 to 35 Ma at the nearby Tin Creek-Midway prospect (MG043) to the northeast (Solie and others, 1991; Bundtzen, Harris, and Gilbert, 1997).
The calc-silicate skarns, which are composed of garnet, epidote, and clinopyroxene (johannsenite) occur mainly in arenaceous, recrystallized limestone. The sulfide-bearing vein parallels a pervasive joint set which cuts various calc-silicate rocks and limestone (Smith and Albanese, 1985). The sulfide vein trends N85W, dips 85S, varies from 0.5 to 3 meters thick, and can be traced for about 22 meters along strike. The main ore minerals in the vein are pyrite, sphalerite (marmatite), galena, and chalcopyrite. The sulfides locally make up to 45 percent of the vein. Chip samples taken across the vein at three places contained up to 0.56 percent copper, 11.10 percent lead, 14.10 percent zinc, 301 grams of silver per tonne, 3.80 percent arsenic, 0.12 percent cadmium, and 42.40 percent iron (Smith and Albanese, 1985).
The Rat Fork-Headwall prospect is part of a widespread polymetallic mineral belt, the Farewell Mineral belt, that includes the Tin Creek North (MG041), Tin Creek South (MG044), Bowser Creek-Main (MG068), Bowser Creek Northeast (MG067), and Smith Lake (MG055) prospects.In the late 1960s and early 1970s, Falconbridge Minerals through their exploration operator St. Eugene Mining Company, diamond drilled from two stations near the sulfide vein but there is little information on the results of this work. 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||(-153.893120229783, 62.3187846224074)|
|Mineral deposit model||Lead-zinc (copper) skarns (Cox and Singer, 1986; model 18c).|
|Mineral deposit model number||18c|
|Age of mineralization||Inferred to be 25 to 35 Ma, based on K-Ar dating of similar granodiorite dike swarms nearby.|
|Alteration of deposit||Extensive oxidation of pyrite-rich areas to ferricrete gossan.|
|Workings or exploration||In the late 1960s and early 1970s, Falconbridge Minerals through their exploration subsidiary St. Eugene Mining Company, diamond drilled from two stations near the sulfide vein but there is little information on the results of this work. Subsequently, the prospect was examined and sampled by several government agencies. As of 2008, the prospect is within a large block of claims called the BMP project by International Tower Hill MIne, Ltd. (2008).|
|Indication of production||None|
Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000.
Bundtzen, T.K., Kline, J.T., and Clough, J.G., 1982, Preliminary geology of the McGrath B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File report 149, 22 p., 1 sheet, scale 1:40,000.
Cobb, E.H., 1972, Metallic mineral resources map of the McGrath quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-379, 1 sheet, 1:250,000 scale.
Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Iliamna, Lake Clark, Lime Hills, and McGrath quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-485, 101 p.
International Tower Hills Mines, Ltd., 2008, BMP: http://www.ithmines.com/s/BMP.asp (as of April 30, 2008).
Reed, B.L. and Elliott, R.L., 1968, Geochemical anomalies and metalliferous deposits between Windy Fork and Post River, southern Alaska: U.S. Geological Survey Circular 569, 22 pages.
Smith, T.E., and Albanese, M.D., 1985, Preliminary prospect examinations in the McGrath A-2, A-3, and B-2 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 85-54, 19 p.
|Reporters||T.K. Bundtzen (Pacific Rim Geological Consulting); D.J. Grybeck (Port Ludlow, WA)|
|Last report date||6/5/2008|