A STATISTICAL ANALYSIS OF THE DISTRIBUTION OF SELENIUM IN THE PERMIAN PHOSPHORIA FORMATION, SOUTHEASTERN IDAHO

The Permian Phosphoria Formation in the western United States is of importance economically and interest scientifically. Along with the economic significance, however, there have come important environmental concerns relating to the presence of naturally-occurring Se and other trace elements, which, when mobilized by mining operations can become pollutants. This project combines mineralogical and geochemical work done on the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, exploring the statistical relationships between Se and mineralogical and chemical data for a group of 475 samples. Samples were collected from nine measured stratigraphic sections, including pairs of less- and more-weathered sections from four active mines, plus an additional least-weathered deep core.

The statistical analyses include evaluation of descriptive statistics and correlation matrices, as well as factor analysis to gain a better understanding of the latent factors that may be affecting Se residency. These analyses produced results showing the expected chemical associations such as correlations to sulfide minerals and organic carbon, as well as the importance of weathering on the mobility of Se. Also, less expected results such as the correlation between Se- and ore-producing carbonate-fluorapatite rich strata are shown. Finally, this work provides a data set of statistical relationships that can be considered in development of geochemical models to better understand trace element residency in the Phosphoria Formation.