Mineralogical characterization of strata of the Meade Peak phosphatic shale member of the Permian Phosphoria Formation; channel and individual rock samples of measured section J and their relationship to measured sections A and B, central part of Rasmussen Ridge, Caribou County, Idaho

Knudsen, A. C.; Gunter, M. E.; Herring, J. R.; Grauch, R. I.

Abstract:

The Permian Phosphoria Formation of southeastern Idaho hosts one of the largest phosphate deposits in the world. Despite the economic significance of this Formation, the fine-grained nature of the phosphorite has discouraged detailed mineralogical characterization and quantification studies. Recently, selenium and other potentially toxic trace elements in mine wastes have drawn increased attention to this formation, and motivated additional study. This study uses powder X-ray diffraction (XRD), with Rietveld quantification software, to quantify and characterize the mineralogy of composite channel samples and individual samples collected from the stratigraphic sections measured by the U.S. Geological Survey in the Meade Peak Member of the Permian Phosphoria Formation at the Enoch Valley mine on Rasmussen Ridge, approximately 15 miles northeast of Soda Springs, Idaho. These samples are from the deep, least-weathered drill core, section J, and channel samples from the less-weathered section B and more-weathered section A. Sections A and B were collected from benches exposed by mining. The dominant minerals present in these samples are carbonate-fluorapatite, which is the ore mineral, quartz, muscovite, albite, orthoclase, the ammonium feldspar buddingtonite (NH4AlSi3O8), dolomite, and calcite. Because of their potential for hosting trace elements such as Se, the presence of minor pyrite and sphalerite is also noteworthy. The variable degree of exposure that sections have undergone and their close proximity to each other allows for consideration of the effects of weathering on the mineralogy of the rocks. While much of the mineralogy is similar between all three sections, the carbonate minerals decrease with increased weathering. Analysis of the carbonate content in the carbonate-fluorapatite by Rietveld refinement shows relatively low carbonate content (2 ? 3% (wt.) CO3 2- ) in the apatite structure relative to global phosphorites. Further analysis and interpretation of these data, and similar data from other mine sites, will be released in a later publication.

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USGS Numbered Series

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32369

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Knudsen, A. C.; Gunter, M. E.; Herring, J. R.; Grauch, R. I.

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ENGLISH

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38 p.

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Open-File Report

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OFR

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2002-125

Citation Search Results Text:

Mineralogical characterization of strata of the Meade Peak phosphatic shale member of the Permian Phosphoria Formation; channel and individual rock samples of measured section J and their relationship to measured sections A and B, central part of Rasmussen Ridge, Caribou County, Idaho; 2002; OFR; 2002-125; Knudsen, A. C.; Gunter, M. E.; Herring, J. R.; Grauch, R. I.