File:Native copper stockwork in skarn rock (Madison Gold Skarn Deposit, Late Cretaceous, 80 Ma; west of Silver Star, Montana, USA) 5.jpg
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English: Skarn with native copper stockwork from the Cretaceous of Montana, USA. (public display, Montana Bureau of Mines and Geology Mineral Museum, Butte, Montana, USA)
Skarn is a contact metamorphic rock with a crystalline texture. It forms by heating and addition of elements (metasomatism) to country rock in the immediate vicinity of an igneous intrusion (batholith, stock, sill, dike, laccolith). The mineralogy of skarns is highly variable, depending on the chemistries of the host rock and the intruding magma. From museum signage: The Madison Gold Skarn Deposit, [an unusually copper-rich skarn], is located just west of Silver Star, Montana. It is at the intrusive contact between granitic rocks of the Cretaceous Rader Creek Pluton and limestones of the Madison Group. The deposit has been mined off and on since the 1860s, and the nearby Broadway Mine was one of the earliest patented hard-rock claims in Montana. [Seen here is a] sawn slab of metallic copper "stock work veins" in highly altered skarn. The origin of the veins is not clear. They may have once been chalcoite veins, which were later converted to copper. However, it is also possible that the elemental copper precipitated directly in cracks in the skarn rock from acidic groundwater rich in dissolved copper sulfate (like the modern-day Berkeley Pit Lake). Geology: Madison Gold Skarn Deposit, Campanian Stage, Late Cretaceous, 80 Ma Locality: unrecorded/undisclosed mine at the Madison Gold Skarn Deposit, west of the town of Silver Star, southwestern Montana, USA |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/49600448161/ |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/49600448161 (archive). It was reviewed on 2 March 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 12:53, 2 March 2020 | | 3,470 × 2,200 (6.24 MB) | Ser Amantio di Nicolao (talk | contribs) | User created page with UploadWizard |
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