Nellis Air Force Range Research Articles

Deciphering groundwater flow systems in Oasis Valley, Nevada, using trace element chemistry, multivariate statistics, and Geographical Information System

The origin of groundwater discharging via evapotranspiration and from springs within Oasis Valley, Nevada, is of concern owing to the close proximity of the Nevada Test Site (NTS) and the possible contamination of groundwater as a result of underground nuclear testing. Principal components analysis, cluster analysis, and population partitioning, along with a Geographical Information System, were used to decipher groundwater flow patterns in Oasis Valley, Nevada. These multivariate statistical techniques were applied to the trace element chemistry of groundwater samples collected from 26 springs and wells within Oasis Valley, the NTS, and the Nellis Air Force Range. The results of all statistical analyses showed similar geographical trends in the trace element chemistry of the groundwaters included in this study. Differences are observed between the groundwaters from the NTS and those of Oasis Valley based on the concentrations of the elements Li, Ge, Mo, Rb, Ba, U, and Ru. A concentration gradient is observed from lower concentrations in the NTS to increasing concentrations toward Oasis Valley suggesting groundwater flow in an overall southwestward direction from the NTS. Also, a different trace element signature is observed for the waters collected in the northern and western region of Oasis Valley, suggesting another source of groundwater to this area.

Stream sediment exploration for gold and silver in Nevada — application of an old prospecting method using modern analytical techniques

The Nevada Bureau of Mines and Geology has completed a mineral resource assessment of the Nellis Air Force Range (NAFR), an area of about 12,000 km 2 in southern Nevada that has essentially been withdrawn from mineral entry since the early 1940s. The NAFR is mainly underlain by Proterozoic and Paleozoic miogeoclinal rocks, Tertiary volcanic rocks, and Quaternary continental deposits. It contains all or part of 36 historic mining districts, about 18 of which are precious metals districts with known but minor gold and silver production. Most of the precious metals mineralization is hosted by Tertiary volcanic rocks and includes both low-sulfidation and high-sulfidation deposit types. Assessment of potential for metallic mineral deposits in the NAFR was carried out using background rock sampling, stream sediment sampling, and remote sensing, followed by examination and sampling of historic mining districts and alteration areas. Silt and float chip sampling were selected as the most efficient methods following a pilot stream sediment sampling study in regional mining districts that also included panned concentrate analyses. Threshold values for anomalous samples were determined from background rock samples. Float chip samples, which consist of small fragments of visibly mineralized and altered rock (generally limonitized and silicified) collected from stream sediment sampling sites, were determined to be the most effective in the differentiation of favorable areas for gold and silver deposits. Ag, As, and Au were present in anomalous amounts in dry stream beds draining more than most of the areas that were determined to have high potential on the basis of subsequent rock sampling. Hg, Mo, and Te were also found to be effective precious metal pathfinders in many cases. Silt sampling was clearly less effective. Ag, As, and Au appear to be the best indicators of potential in silt samples. On the basis of this work, combined silt and float chip sampling is recommended for gold and silver exploration in Tertiary volcanic rocks.

An ecoregional context for natural resources management: A case study at nellis air force range, Nevada

AbstractThis article describes recent developments undertaken by the Air Force, working in cooperation with The Nature Conservancy, to implement ecosystem management at the three million acre Nellis Air Force Range, Nevada (NAFR). The principal focus of those efforts included holding a dialogue facilitated by the Keystone Center which examined long‐range natural resources management strategies for NAFR, the development and presentation of a biodiversity conservation course for military land managers, and the formation of an ecosystem assessment process to establish a scientific foundation for cooperative stewardship within the northeastern portion of the Mojave Desert Ecoregion.