File:Sulfidic bronzitite (platinum-palladium ore) (Johns-Manville Reef, Stillwater Complex, Neoarchean, 2.71 Ga; Stillwater Mine, Beartooth Mountains, Montana, USA) 5 (30800356293).jpg
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[edit]DescriptionSulfidic bronzitite (platinum-palladium ore) (Johns-Manville Reef, Stillwater Complex, Neoarchean, 2.71 Ga; Stillwater Mine, Beartooth Mountains, Montana, USA) 5 (30800356293).jpg |
Sulfidic bronzitite from the Precambrian of Montana, USA. (field of view ~10.6 cm across) Silvery & brassy = Pt/Pd-rich pyrrhotite & Pt/Pd-rich chalcopyrite Brown = bronzite pyroxene 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). This is a very high grade platinum ore from the Stillwater Mine's J-M Reef. The platinum/palladium-bearing sulfides are here hosted in bronzitite rock, the rarest known host rock in the mine. Bronzitite is a coarsely-crystalline, intrusive igneous rock composed almost entirely of bronzite pyroxene. An alternate name for bronzitite is bronzite pyroxenite. What makes this rock so high grade? It is about 25% intercumulate Pt/Pd-rich sulfides. This rock has an ore grade of about 10 ounces of Pd-Pt per ton of rock (wow!), with a Pd-Pt ratio of ~3.5:1 (= highest grade platinum group metals deposit in the world). This is the rarest host rock & highest-grade type of platinum ore known at the Stillwater Mine. Stratigraphy: Johns-Manville Reef, Lower Banded Series, Stillwater Complex, Neoarchean, 2.71 Ga Locality: small bronzitite lens in the 5300 West 13300 D6 West area of the Stillwater Mine (= western side of the D6 level, ~84' below the 5300' elevation datum & 13,300' west of shaft), Beartooth Mountains, southern Montana, USA |
Date | |
Source | Sulfidic bronzitite (platinum-palladium ore) (Johns-Manville Reef, Stillwater Complex, Neoarchean, 2.71 Ga; Stillwater Mine, Beartooth Mountains, Montana, USA) 5 |
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@N05/30800356293. It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
5 December 2019
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current | 06:16, 5 December 2019 | 3,924 × 2,116 (5.39 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot D10 |
Exposure time | 1/60 sec (0.016666666666667) |
F-number | f/9 |
ISO speed rating | 80 |
Date and time of data generation | 19:46, 12 December 2016 |
Lens focal length | 8.295 mm |
Orientation | Normal |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 20:56, 12 December 2016 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 19:46, 12 December 2016 |
Meaning of each component |
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Image compression mode | 3 |
APEX shutter speed | 5.90625 |
APEX aperture | 6.34375 |
APEX exposure bias | −0.66666666666667 |
Maximum land aperture | 3.34375 APEX (f/3.19) |
Metering mode | Pattern |
Flash | Flash fired, compulsory flash firing, red-eye reduction mode |
Supported Flashpix version | 1 |
Color space | sRGB |
Focal plane X resolution | 16,460.905349794 |
Focal plane Y resolution | 16,483.516483516 |
Focal plane resolution unit | inches |
Sensing method | One-chip color area sensor |
File source | Digital still camera |
Custom image processing | Normal process |
Exposure mode | Manual exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Portrait |
Supported Flashpix version | 1 |
Image width | 3,924 px |
Image height | 2,116 px |
Date metadata was last modified | 15:56, 12 December 2016 |
IIM version | 2 |