Geochemistry of solid materials from two US geothermal systems and its application to exploration. Final: volume 77-14

Abstract

Initial development of geochemical techniques for exploration and exploitation of geothermal systems is described. The techniques are based on analysis of solid materials. Distribution of Cu, Mo, Pb, Zn, Ag, As, Sb, Co, Ni, Mn, Fe, Bi, B, Te, In, Sn, and W are determined and evaluated for several sample types in a hot water system (Roosevelt Hot Springs, Utah) and a vapor dominated system (Geysers, California). The sample types analyzed are magnetic fractions, whole rock samples, and two different heavy liquid separates derived from cuttings composites from geothermal wells and shallow rotary drill holes. The results show that multi-element geochemical zoning is developed at both a relatively small scale of over hundreds of feet around individual steam entries (SEs) and hot water entries (HWEs) in geothermal wells, and at a larger scale of over thousands of feet both vertically and laterally in geothermal systems. Zoning is surprisingly similar for both hot-water and vapor-dominated systems. Trace elements which display the most consistent and useful zoning characteristics are As, Sb, Pb, Zn, Mn, B, and W. Optimum delineation of the zoning is provided by +3.3 heavy liquid (HL) samples compared to the other sample types evaluated. Utilization of +3.3 samples maximizes detection of hydrothermal trace elements and markedly reduces or eliminates chemical signatures specifically related to rock type.