Geology and Alteration of the Raft River Geothermal System, Idaho

Abstract

Alteration zoning in the Raft River geothermal system is similar to other moderate temperature liquid dominated systems. X-ray analyses of cuttings form deep exploration test wells indicate that montmorillonite occurs primarily in the outer portion of the system and that with increasing temperature, montmorilloinite is replaced by chlorite and mixed layer clay. Kaolinite and illite are present throughout the system. A parallel change is recorded in the distribution of zeolites. Clinoptilolite is the dominant zeolite in the low temperature portion of the field. within the higher temperature portions of the field which are characterized by chlorite and mixed layer clay, wairakite/analcime and laumontite are the important zeolites.