Fail:Specularite (high-grade iron ore) (Soudan Iron-Formation, Neoarchean, ~2.69 Ga; Soudan Mine, Soudan, Minnesota, USA) 11 (18411244103).jpg
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Specularite from the Precambrian of Minnesota, USA. The Soudan Iron-Formation is a Neoarchean-aged banded iron formation (BIF) unit in the Vermilion Greenstone Belt of northeastern Minnesota, USA. Stratigraphically, the Soudan is considered to be the middle member of the Ely Greenstone. Metamorphosed pillow basalt successions occur above and below the iron-rich interval: - upper member of the Ely Greenstone - Soudan Iron-Formation member - lower member of the Ely Greenstone Radiometric dating of Ely Greenstone rocks (see Jahn & Murthy, 1975) indicates that the Soudan Iron-Formation is about 2.69 billion years old. The Soudan Iron-Formation was deposited in a deep-water environment and is closely associated with several types of volcanic rocks formed in an ancient island arc setting. As such, the unit is classified as an Algoma-type iron-formation. Superior-type iron-formations were deposited in relatively shallow water, continental shelf settings. The Soudan Iron-Formation is exposed in & around the town of Soudan, Minnesota at roadcuts, glacially-eroded outcrop knobs, surface mines, and underground mines. The best exposures are at Soudan Underground Mine State Park. The Soudan Mine targeted high-grade iron ore (specularite) for many decades and closed in the early 1960s. The site is now accessible to the public and underground tours are offered. Observed iron-rich lithologies in the Soudan Iron-Formation include specularite, jaspilite BIF, and magnetite BIF. The rock shown above is specularite, which is a high-grade iron ore and the mining target at the Soudan Mine. Specularite is a finely-crystalline to coarsely-crystalline metamorphic rock dominated by silvery-gray specular hematite (Fe2O3 - iron oxide). "Specular" means "mirror" - it refers to the shiny, intensely lustrous appearance of each specular hematite crystal flake. Specularite occurs as small to large, irregular-shaped masses within the jaspilite facies of the Soudan Iron-Formation. Studies have shown that the specularite formed by metamorphic alteration of jaspilite (= quartz-rich, banded iron formation), resulting in the leaching away of quartz/silica. The reddish coloration is a thin, scattered, surficial coating of hematite dust. Stratigraphy: Soudan Iron-Formation member, Ely Greenstone, Vermilion Greenstone Belt, Neoarchean, ~2.69 Ga Locality: Soudan Mine, Soudan Underground Mine State Park, Soudan, northeastern Minnesota, USA Reference cited: Jahn & Murthy (1975) - Rb-Sr ages of the Archean rocks from the Vermilion District, northeastern Minnesota. Geochimica et Cosmochimica Acta 39: 1679-1689. |
| A̱tuk | |
| A̱tyin | Specularite (high-grade iron ore) (Soudan Iron-Formation, Neoarchean, ~2.69 Ga; Soudan Mine, Soudan, Minnesota, USA) 11 |
| A̱tyulyuut | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://flickr.com/photos/47445767@N05/18411244103. It was reviewed on 19 Zwat A̱natat 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| A̱tuk/Jen | A̱gban ghwughwu | Shi-a̱ka̱ta̱m | A̱tyunta̱m | A̱di̱dam | |
|---|---|---|---|---|---|
| mi̱ di̱ yong huni | 20:48, 19 Zwat A̱natat 2015 | | 4,000 × 3,000 (4.4 MB) | Natuur12 | Transferred from Flickr via Flickr2Commons |
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