|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||This unnamed occurrence is located at an outcrop on the south side of an unnamed, east-flowing tributary of Tin Creek at an elevation of 2,850 feet (868 m) in the NW1/4 sec. 14, T. 27 N., R. 24 W., of the Seward Meridian. The reporter investigated the occurrence in 1981 at station nos. 81BT428-429.|
The unnamed occurrence is a well exposed sulfide skarn typical of many silver-base metal-bearing skarns in the Farewell Mineral Belt (Bundtzen, Harris, and Gilbert, 1997; Newberry and others, 1997). Host lithologies are mainly a highly folded and sheared, mid-Silurian, argillaceous limestone of the Terra Cotta Mountains Sandstone, a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The metasedimentary rocks are intruded by a N10W-trending, vertically dipping, 20 meter thick, granodiorite dike. Thinner, anastomosing dikes, which occur throughout the limestone, do not appear to alter the limestone (Smith and Albanese, 1985).
Mineralization consists of a 2 meter by 6 meter zone containing disseminated to semi-massive arsenopyrite, chalcopyrite, pyrite, iron-rich sphalerite (marmatite), galena, and pyrite encased in diopside(?)-garnet gangue minerals. The sulfide mineralization is encrusted with a thin but conspicuous malachite rind. The mineralization is parallel to bedding in host limestone, and begins at the contact of a hornblende granodiorite dike. Although mineralization is spatially related to the dike, no thermal alteration of the limestone was identified. Gangue minerals that accompany the sulfides include magnetite, diopside, and garnet.Bundtzen, Kline, and Clough (1982) reported that chip-channel samples contained up to 2.30 percent copper, 0.30 percent lead, 6.20 percent zinc, 110 grams/tonne silver, 500 ppm cadmium, 100 ppm bismuth, and 100 ppm cobalt. Smith and Albanese (1985) reported that one sample from the mineral zone contained 5,890 ppm copper, 229 ppm lead, 6,690 ppm zinc, 74 ppm cadmium, and 37.5 grams/tonne silver.
|Geologic map unit||(-153.674226806388, 62.4333937481718)|
|Mineral deposit model||Low-temperature lead-zinc skarn (Cox and Singer, 1986; model 18c).|
|Mineral deposit model number||18c|
|Age of mineralization||Unknown; thought to be related to the 25 to 30 Ma granodiorite dike swarm in area (Solie and others, 1991; Szumigala, 1987).|
|Alteration of deposit||Extensive diopside(?) replacement.|
|Workings or exploration||The Tin Creek Occurrence was first described by Bundtzen, Kline, and Clough (1982) and later by Smith and Albanese (1985). The former reference reported that chip-channel samples contained up to 2.30 percent copper, 0.30 percent lead, 6.20 percent zinc, 110 grams/tonne silver, 500 ppm cadmium, 100 ppm bismuth, and 100 ppm cobalt. Smith and Albanese (1985) reported that a single grab sample contained 5,890 ppm copper, 229 ppm lead, 6,690 ppm zinc, 74 ppm cadmium, and 37.5 grams/tonne silver.|
|Indication of production||None|
Additional commentsSee Tin Creek-Midway deposit (MG043).
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 geologiy 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.
Newberry and others, 1997.
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.
Solie, D.N., Bundtzen, T.K., and Gilbert, W.G., 1991, K/Ar ages of igneous rocks in the McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 91-23, 7 p., 1 sheet, 1:250,000 scale.
|Reporters||T.K. Bundtzen (Pacific Rim Geological Consulting)|
|Last report date||12/5/1998|