Chromitite band in serpentinite (Neoarchean; North Star Mine, Red Lodge Chromite District, Beartooth Mountains, Montana, USA) 3 : 無料・フリー素材/写真
Chromitite band in serpentinite (Neoarchean; North Star Mine, Red Lodge Chromite District, Beartooth Mountains, Montana, USA) 3 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
|---|---|
| 説明 | Chromitite band in serpentinite in the Precambrian of Montana, USA.The Red Lodge Mining District is located near the southeastern termination of the Beartooth Mountains, southwest of the town of Red Lodge in southern Montana, USA. Active mining took place during the 1940s. Most of the old, small mines occur on the high plateaus or just below the eroded plateau edges (for example, along the northwestern margin of Rock Creek Canyon).Mines in the Red Lodge District targeted chromium ores in the form of chromitite rocks hosted in serpentinite. In this area, lenses, or pods, or fault-chopped stratiform bodies of serpentinite occur among high-grade metamorphic rocks such as quartzites, gneisses, migmatites, amphibolites, etc.The rocks in the Beartooth Mountains are very old. They are principally Archean in age (2.5+ billion years old). The chromite-bearing serpentinite bodies of the Red Lodge District were originally chromite-bearing peridotites (dunites) of early Neoarchean age, or older. Granulite-grade to upper amphibolite-grade regional metamorphism at about 2.75 Ga altered the original dunites to serpentinites. The rocks of the area were also altered by greenschist-grade metamorphism between 1.6 to 1.8 billion years ago, during the late Paleoproterozoic.Chromitite is a coarsely-crystalline textured, intrusive igneous rock that is rich in the mineral chromite (FeCr2O4 - iron chromium oxide). The black, granular band seen here is chromitite; the matrix is serpentinite. Serpentinite is a metamorphic rock, the result of low- to high-grade metamorphism of olivine-rich peridotites (dunites) in the presence of water. Serpentinite in this area contains scattered chromite and/or magnetite.Age: Archean (early Neoarchean metamorphism at 2.75 Ga, plus late Paleoproterozoic metamorphism at 1.6 to 1.8 Ga).Locality: old mine rock pile along Hellroaring Road (Forest Service Road 2004), near the eroded edge of Hellroaring Plateau (apparently derived from the nearby North Star Mine, a.k.a. North Star Claim), northwestern side of Rock Creek Canyon, southeast of Hellroaring Lakes & southwest of the town of Red Lodge, Red Lodge Chromite District (Red Lodge Mining District; Hellroaring Mining District), Beartooth Mountains, southern Montana, USA (45° 02' 09.94" North latitude, 109° 26' 48.49" West longitude) |
| 撮影日 | 2013-05-28 00:00:10 |
| 撮影者 | James St. John |
| タグ | |
| 撮影地 |