| Keywords |
Basin and Range; Great Basin, geochemistry, groundwater, GIS, arsenic, boron, barium, calcium, chloride, fluoride, iron, bicarbonate, postassium, lithium, manganese, sodium, silica, sulfate |
| Abstract |
Maps of Great Basin groundwater geochemistry show distinctive regional spatial patterns. Factors affecting the concentrations of dissolved constituents include bedrock lithology, location within structural zones, geothermal systems, and surficial playa deposits and salt lakes. In this study, a large geochemical database of ~24,750 Great Basin groundwater samples from springs and wells was compiled from multiple sources. These data were uploaded into a geographic information system (GIS) and used to produce concentration maps for As, B, Ba, Ca, Cl, F, Fe, HCO3, K, Li, Mn, Na, SiO2, and SO4. These maps were then examined to identify geologic factors that might have influenced their concentration, including the presence of geothermal systems. A weights-of-evidence statistical analysis was then performed to assess the correlation between the concentration maps and a set of ?150o C geothermal systems. The results indicate that all 14 constituents correlate to some degree with geothermal systems. Fluorine, boron, arsenic, and silica have the highest spatial correlation. In addition, a subset of the data representing samples with measured temperatures ?20oC was also analyzed; overall correlations were lower, but manganese, arsenic, and silica are still useful indicators. Samples from both the full and the ?20oC datasets were grouped into statistically significant populations. The weights at break points for these groups can be used as a measure of likelihood of a sample having been influenced by geothermal activity. The study shows that (1) regional groundwater geochemical patterns exist in the Great Basin, (2) these patterns can serve as effective geothermal exploration tools, and (3) a set of concentrations derived from the weights-of-evidence analysis may serve as favorability indices indicative of the influence of geothermal activity on hot and cold groundwater samples. |