File:Sulfidic tremolitite (platinum-palladium ore) Stillwater mine MT.jpg
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[edit]DescriptionSulfidic tremolitite (platinum-palladium ore) Stillwater mine MT.jpg |
Sulfidic tremolitite (field of view ~3.0 cm across) from the Johns-Manville Reef, Lower Banded Series, Stillwater Complex (Neoarchean, 2.71 b.y.) in the Stillwater Mine, Beartooth Mountains, Montana, USA. An exceedingly rare rock in the J-M Reef is tremolitite. Tremolitite is a rock dominated by tremolite (Ca2Mg5Si8O22(OH)2), a whitish amphibole that typically forms needle-like crystals. This was originally a dunite, composed of olivine crystals. Metamorphic alteration has transformed the olivine into tremolite. This rock is from a very localized alteration spot in the J-M Reef. Typically, dunites get altered to serpentinites (serpentine with a little magnetite), and this tremolitite was observed to be in close association with such rocks. This ore sample grades out to ~2.0 ounces of Pd & Pt per ton of rock. The Pd-Pt ratio is about 3:1 (= highest grade platinum group metals deposit in the world). Locality: 41W1500 stope (4100’ elevation above sea level & 1500’ west of shaft), Stillwater Mine, underground & west of the Stillwater River, southwestern Stillwater County, Beartooth Mountains, southern Montana, USA. Southern Montana’s Beartooth Mountains has one of only three platinum mines in North America. There, platinum and palladium are mined from the 2.71 billion-year-old Stillwater Complex, a classic example of an LLI (large, layered igneous province). LLIs are large intrusive bodies that display large-scale and small-scale layering, even including cross bedding, ripples, graded bedding, channelforms, and other sedimentary-like features. The Stillwater started out as a large subsurface mass of slowly cooling magma. As various minerals crystallized, they settled to the bottom of the magma chamber. This resulted in layering. Igneous rocks that formed this way have a cumulate texture. Currents in the still-liquid portions of the magma chamber produced the sedimentary structures mentioned above. Most of the Stillwater displays only large-scale layering. The rocks in the Stillwater are ultramafic & mafic intrusive igneous rocks. Common lithologies include gabbros, norites, harzburgites, anorthosites, troctolites, chromitites, pyroxenites, and dunites. Portions of the Stillwater have been metamorphosed. Olivine is the most commonly altered component, usually metamorphosed to serpentine. The main platinum & palladium occurrence is in the Johns-Manville Reef (J-M Reef), an interval in the lower part of the Lower Banded Series. There, the Pt & Pd occur in intercumulate sulfides, typically pyrrhotite (Fe1-xS) and chalcopyrite (CuFeS2). Platinum ores in the J-M Reef are principally sulfidic anorthosites, but other lithologies also occur. The J-M Reef is the highest grade deposit known for platinum-group elements (PGEs). |
Date | |
Source | Sulfidic tremolitite (platinum-palladium ore) (Johns-Manville Reef, Lower Banded Series, Stillwater Complex, Neoarchean, 2.71 Ga; 41W1500 stope, Stillwater Mine, Beartooth Mountains, southern Montana, USA) |
Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/14828814031. It was reviewed on 5 August 2014 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
5 August 2014
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current | 01:39, 5 August 2014 | 3,008 × 2,000 (3.65 MB) | Tillman (talk | contribs) | Transferred from Flickr via Flickr2commons |
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Orientation | Normal |
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Horizontal resolution | 72 dpi |
Vertical resolution | 72 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 20:23, 4 August 2014 |
Color space | Uncalibrated |
Image width | 3,008 px |
Image height | 2,000 px |
Date and time of digitizing | 16:10, 9 February 2007 |
Date metadata was last modified | 16:23, 4 August 2014 |
IIM version | 2 |