USING TEMPERATURE PROFILES, ISOTOPIC TRACERS, GROUNDWATER RESIDENCE TIMES, AND AUDIO MAGNETOTELLURIC DATA TO CONSTRAIN FAULT & CRUSTAL PERMEABILITY WITHIN THE SOCORRO GEOTHERMAL SYSTEM, NEW MEXICO

A 335 m deep geothermal exploration well (NMGT2) was completed within fractured crystalline basement rocks proximal to a fault zone at the base of Socorro Peak, 2 km west of the town of Socorro, New Mexico. The well was drilled in a region of high heat flow (490 mW/m² ). Upward vertical head gradients and the curvature of the temperature profile strongly suggest a groundwater up-flow zone. The maximum fluid temperature at the bottom of the borehole was about 42 ^oC. The NaCl fluids collected from the well were brackish, having a total dissolved solids concentration of 1970 ppm. Silica and cation geothermometers suggest maximum fluid temperatures of 60-80 ^oC. The uncorrected ¹⁴C age for groundwater collected from NMGT2 was about 20,000 years. Pre-development hydraulic head maps suggest that groundwater recharge occurs about 20 km to the west, within the Magdalena Mountains. This suggests a lateral flow rate of about 1 m/yr. A published audio magnetotelluric survey carried out in the vicinity of well NMGT2 indicates that the geothermal fluids had an intermediate resistivity of about 70 Ohm-m. Strontium and ³He/⁴He isotopic data argues for deep basement circulation. We used this geochemical and geophysical data to calibrate a cross-sectional hydrothermal model of the Socorro-La Jencia Basin. The goal of the modeling exercise was to assess whether or not isotopic tracer and electromagnetic geophysical data could improve our understanding of crustal and fault permeability and flow patterns.