CHARACTERISTICS OF BASIN AND RANGE GEOTHERMAL SYSTEMS WITH FLUID TEMPERATURES OF 150 degree TO 200 degree C.

Six geothermal reservoirs with fluid temperatures over 200 degree C and ten geothermal systems with measured fluid temperatures of 150-200 degree have been discovered in the northern Basin and Range Province of the USA. A comparison of these high - and moderate-temperature systems shows considerable overlap in geographical distribution, geology, and physical properties. Ability to distinguish between moderate- and high-temperature systems using fluid chemistry has been limited by often inaccurate estimates based on shallow samples and by a bias in the NaKCa geothermometer which, in this province, over-estimates fluid temperatures at economic drilling depths for both shallow and deep samples. The best indications of a possible high-temperature reservoir near a moderate-temperature well appear to be silica base temperatures above 210 degree C for deep fluid entries and a high-temperature gradient in the bottom of the well.