MAJOR-SOLUTE OBSERVATIONS OF GEOTHERMAL SALINIZATION OF THE JEMEZ WATERSHED, NEW MEXICO

The Jemez Watershed (JW) is set in north-central New Mexico within the Jemez Mountains, which overlies the intersection between the Rio Grande Rift and the Jemez Lineament. A prominent feature of the JW is the Valles Caldera, housing a world-class, high-temperature, liquid-dominated geothermal system (≤ 300 ^oC). Such highly mineralized geothermal systems usually have a significant environmental and hydrogeological footprint. Geologic and geochemical evidence suggests that the JW is influenced by the Valles Caldera geothermal system (VC). In the form of thermal springs, multiple outflow expressions, namely Jemez Springs Hot Springs and Soda Dam Springs, of the VC surround the main tributary (Jemez River or JR) of the JW. Furthermore, just southeast of the VC Ring Fracture Zone, headwaters of Sulphur Creek mixing with intra-caldera, acid-sulfate springs contribute to the JW further downstream.

Recent Fall 2017 sampling during low-flow (~23-26 cfs) conditions reflects impairments of VC geofluids on JW water quality. There is bulk salinization (net ~500 ppm increase in total dissolved solids) of JR waters from just above Soda Dam Springs to San Ysidro Bridge. Upstream JW acidification (from pH 6.2 to 1.61) and trace metal salinization ([Al]: 0.03-21ppm & [Fe]: 0-10ppm) occur in the Sulphur Creek subbasin, and similar downstream influences (from pH 7 to 4.7; [Al]: 0.01-1.5ppm) are observed in Redondo Creek, a JW tributary. We display these geochemical effects spatially and through multivariate statistics (principal component analysis). A tentative binary Cl/Br mixing model reveals bulk salinized waters contain 19-30% geothermal spring/seepage contributions; this mixing model is not applicable to acidified waters, as Cl and Br lose conservative behavior under pH of 2.

These observations set up the upcoming stages of this study, which will employ more geochemical tracers (trace metals, rare earth elements, radiogenic isotopes, etc.). This research aims to ultimately obtain a greater understanding of continental geothermics, in hopes of serving as an analog to environmental assessments of other hydrothermal systems.