Preliminary Mineralogical Characterization of Weathered and Less-Weathered Strata of the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation: Measured Sections C and D, Dry Valley, Caribou County, Idaho.

摘要

The Permian Phosphoria Formation of southeastern Idaho is one of the largest phosphate producing deposits in the world. Despite the economic significance of this Formation, the finegrained nature of this phosphorite deposit has discouraged detailed mineralogical characterization and quantification studies. Recently Se and other potentially hazardous trace elements in mine wastes have drawn increased attention to this formation, and motivated more extensive study. Part of this effort has focused on a more detailed geological, including a mineralogical, characterization of the area. Past research identified the major minerals in the Formation, including carbonatefluorapatite, quartz, and dolomite, and a variety of sheet silicates and feldspars. Minor phases such as pyrite and sphalerite have also been identified in the deposit and may be sources of Se. This study used powder X-ray diffraction, with Rietveld quantification software to quantify and characterize the mineralogy of the 83 samples collected from two stratigraphic sections measured by the U.S. Geological Survey at the Dry Valley mine in the Meade Peak Member of the Phosphoria Formation. Analyses show extensive variability of carbonate substitution in the fluorapatite structure, determined by measuring the apatite a-cell dimension, as well as patterns of correlation between mineralogy and the stratigraphy.