A mineralogical and geochemical investigation of modern aeolian sands near Tonopah, Nevada: Sources and environmental implications

Abstract

The mineralogical and geochemical composition of sands across arid to semi-arid landscapes can be used to evaluate the nature of their source lithologies. Once these characteristics are established, these sands have the potential to be implemented as background reference materials in environmentally-focused studies (e.g., mine waste pollution). Tonopah, Nevada is an economically disadvantaged town with a long history of silver mining. Tonopah and surrounding areas with similar histories are also examples of significantly understudied regions with respect to several environmental concerns.Sands sampled in this study are part of a star-shaped dune system ~15 km north of Tonopah. They are medium-grained and are very well sorted: arithmetic mean grain size from 263 to 335 µm. From Quartz – Feldspar – Lithic (QFL) classification the sands are feldspathic litharenites to weakly litharenitic. Powder X-ray diffraction and polarized light microscopy observations identify quartz, ordered calcian albite, and sanidine as the dominant minerals with rarer calcite, magnesian calcite, and amphibole. Scanning electron microscopy indicates grains have a range of textural maturity, with rhyolitic and basaltic lithic grains present. From bulk elemental chemistry, sands are geochemically akin to that of Earth’s bulk upper continental crust, are quartz-rich, formed in arid to semi-arid climates, and were derived from a felsic igneous province (or provinces).The origin of these sands is further investigated by comparing bulk major elemental signatures to the composition of global, regional, and local dune systems, in addition to local and regional bedrock. Regionally, Tonopah sands are compositionally similar to those of the Mojave Desert dune fields (e.g. Cadiz) and distinct from those of the Algodones and Parker dunes of California and Arizona respectively. Consistent with source inferences for the Cadiz, Danby, and Dale lake sands of the Mojave Desert, Tonopah sands are inferred to be derived from chemically evolved provinces. For Tonopah, derivation from the local, Micoene-aged, andesite-dacite-rhyolite suites is inferred.Through comprehensive characterization of the Tonopah sands a geogenic background composition for the region, and an important reference material for future environmental investigations, has been established.