X-RAY DIFFRACTION AND ENERGY DISPERSIVE SPECTROSCOPY OF TERLINGUA CREEK AND ALAMITO CREEK SEDIMENTS, TRANS-PECOS REGION, TX

Sediments collected from Terlingua Creek and Alamito Creek were studied in order to create working mineralogical modes for each drainage, respectively. The purpose of creating this mode is to determine a group of possible primary materials that could then be weathered into clay minerals, found in suspended Rio Grande sediments, as secondary products. Using a Scanning Electron Microscope (SEM) to do Energy Dispersive Spectroscopy (EDS) in conjunction with powder X-Ray Diffraction (XRD) an accurate approximation of modal mineralogy for sediment collected in each creek can be determined. The specific lithologies of rock units exposed in the Terlingua Creek and Alamito Creek subbasin watersheds are likely to be the dominant contributors of primary materials. Primary exposed lithologies present in the these subbasin are Cretaceous carbonates, terrigenous sedimentary rocks, and Tertiary volcanics/intrusion. Volcanics and intrusions in the Terlingua Creek and Alamito Creek subbasin are characterized by multiple tuffs, basalts, trachytes, syenites, andesites, rhyolites, alkali gabbros, pyroxenites, nepheline syenites, and calc-silicate skarns. The results of this study find the modal mineralogy of Terlingua Creek sediments to be: 39.3% quartz, 37.3% calcite, 15.2% feldspars, 5.6% pyroxenes, 2.5% clays, and <1% organics. The modal mineralogy of Alamito Creek sediments is found to be: 47.2% zeolites, 31.8% feldspars, 20.1% quartz and other related silica minerals, and 0.88% calcite. The minerals found in Terlingua Creek and Alamito Creek sediments have a direct relationship to the mineralogical compositions of the primary materials in their respective subbasin watersheds as either mechanically weathered grains or as secondary mineral products.