File:Auriferous greenschist, Homestake Mine SD.jpg
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| Description |
Auriferous greenschist (8.5 cm across) from the Homestake Mine, town of Lead, northern Black Hills, western South Dakota, USA. Two small masses of native gold (Au) are visible near the bottom margin. 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 & multiply metamorphosed, and many of the original rocks were converted to greenschists (cummingtonite schists). The gold has been interpreted as having been originally deposited with the iron formation sediments by seafloor volcanogenic exahalative processes. Slight metamorphic gold mobilization and tight structural folding has resulted in the formation of auriferous greenschist pods along fold axes. |
| Date | |
| Source | Auriferous greenschist, Homestake Mine, town of Lead, northern Black Hills, western South Dakota 1 |
| Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/14550326129. It was reviewed on 1 August 2014 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 20:23, 1 August 2014 | 1,500 × 614 (217 KB) | Tillman (talk | contribs) | Transferred from Flickr via Flickr2commons |
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