GEOLOGIC CONTROLS ON GROUNDWATER FLOWPATHS IN THE SPRING MOUNTAINS, NV INFERRED FROM SPRING WATER GEOCHEMISTRY AND 87SR/86SR

We seek to better understand the geologic controls on groundwater flow and geochemical evolution in the Spring Mountains, NV using geochemistry, ⁸⁷Sr/⁸⁶Sr, and variations in flowpath geology. This combination of analyses can provide insights into flowpaths in regions with complex topographic and structural features such as in the Spring Mountains. Understanding groundwater quality and flow in arid regions like the southern Great Basin is important as groundwater springs are commonly the primary source of perennially available fresh water to riparian ecosystems. Furthermore, desert communities often rely on groundwater for their drinking water supply, as surface water is scarce. Recharge in the Spring Mountains contributes to groundwater flow locally as well as regionally to the Death Valley regional groundwater flow system (DVRFS). Groundwater flow in the Spring Mountains is controlled by north to northeast-trending thrust faults, which serve as possible conduits for deep groundwater to discharge at the land-surface.

Variability in groundwater source areas is evident from analysis of spring water geochemistry and ⁸⁷Sr/⁸⁶Sr. Geochemical indicators, including Mg/Ca and ⁸⁷Sr/⁸⁶Sr of spring waters, correlate to three main water types: 1) limestone and dolomite dominated springs emerging in the central Spring Mountains, with ⁸⁷Sr/⁸⁶Sr ranging from 0.708-0.711 and a Mg/Ca between 0.5-1.0; 2) dolomite dominated springs along the Keystone Thrust with Mg/Ca (>1.0) and ⁸⁷Sr/⁸⁶Sr (>0.710); and 3) siliciclastic dominated springs, with sulfate concentrations >0.001 mol/L and ⁸⁷Sr/⁸⁶Sr >0.730. Rocks specimens representing units along potential groundwater flowpaths were also collected and underwent leaching experiments. ⁸⁷Sr/⁸⁶Sr results for leachates are pending and will further constrain spring water source areas and flow paths. Results from this study provide insight into the importance of structural features in controlling groundwater flowpaths as spring geochemistry can be often be predicted by the location of the spring emergence relative to large thrust faults.