File:Auriferous greenschist (Homestake Mine, Black Hills, South Dakota, USA) 5.jpg
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| Description |
English: Auriferous greenschist from the Precambrian of South Dakota, USA.
In this specimen, two small masses native gold (Au) are visible near the bottom margin. Many gold ores have invisible gold (= microscopic). The largest gold mine in the Americas was the long-lived Homestake Mine in the town of Lead (pronounced “Leed”), South Dakota, USA. Located in the Lead Window of the northern Black Hills Uplift in western South Dakota, the Homestake Mine produced about 40 million ounces of gold. The gold at Homestake is almost exclusively confined to the Homestake Formation, a Paleoproterozoic (~1.9-2.0 billion years) sedimentary unit that originally consisted of interbedded Mg-rich siderite iron formation and marlstones. The Homestake Formation has been strongly deformed and multiply metamorphosed, with many of the original rocks converted to greenschists (cummingtonite schists). The gold was originally deposited with iron formation sediments by seafloor volcanogenic exahalative processes. Slight metamorphic gold mobilization and tight structural folding resulted in the formation of auriferous greenschist pods along fold axes. Location: Homestake Mine, town of Lead, northern Black Hills, western South Dakota, USA |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/50837175218/ |
| 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@N05/50837175218. It was reviewed on 15 January 2021 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 15:50, 15 January 2021 | | 3,670 × 2,051 (5.45 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/50837175218/ with UploadWizard |
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