U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Open-File Report 02-125: This report is available as a pdf file. It can be can be opened and read using Adobe Reader. A free copy of Adobe Reader 5.0 can be downloaded at http://www.adobe.com/products/acrobat/readstep.html. The web-ready pdf file was prepared by John Wallis. Dave Frank and Carolyn Donlin also contributed to completion of this on-line version of the report. TITLE: "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" by Andrew C. Knudsen, Mickey E. Gunter, James R. Herring, and Richard I. Grauch, Western U.S. Phosphate Project, 2002. This 38-page report contains a narrative with ten figures and four tables. The study uses powder X-ray diffraction (XRD), with Rietveld quantification software, to quantify and characterize the mineralogy of 83 composite channel samples and 85 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.) CO32- ) 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. The report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ACKNOWLEDGEMENTS: The authors appreciate the help and participation of the Bureau of Land Management, the Forest Service, and staff at the Enoch Valley mine, Monsanto.