Identification of a New Blind Geothermal System with Hyperspectral Remote Sensing and Shallow Temperature Measurements at Columbus Salt Marsh, Esmeralda County, Nevada

摘要

Hyperspectral remote sensing-derived mineral maps and follow-up shallow temperature measurements were used to identify a new blind geothermal target in the Columbus Salt Marsh playa, Esmeralda County, Nevada. The hyperspectral survey was conducted with the ProSpecTIR VS2 instrument and consists of 380 km~2 of 4-meter spatial resolution data acquired on October 29, 2008, covering the playa and surrounding hills. Using these data, borate and sulfate evaporite minerals and opal/chalcedony, carbonates and argillic alteration were identified and mapped. Field samples were collected and validated with laboratory spectral measurements and x-ray dif-fractometer analysis. Mineral maps were then used to guide a shallow temperature survey with nearly 100 two-meter-deep measurements.rnThe largest area of sulfate and borate crusts identified with the hyperspectral survey occurs in the southwestern portion of the playa. Directly up the hydrologic gradient from these crusts, the 2-meter survey identified a 4.1 km by 1.7 km area of anomalous shallow temperatures. The shape of this temperature anomaly is elongate in an east-northeast direction parallel to, and along trend with, nearby Quaternary faults, and the down-slope direction of this trend points towards the area of sulfate and borate crusts. A cold spring associated with some of the sulfate and borate crusts yields anomalous geothermometer temperatures (115℃ and 137℃, respectively for the quartz and Mg-corrected Na-K-Ca geothermometers), providing corroboration of a geothermal component to shallow groundwaters in the playa. A geothermal reservoir may exist at depth in the vicinity of, or laterally displaced from, the shallow temperature anomaly, in an area with a fanning strike pattern of Quaternary faults.