| Abstract |
The U.S. Department of Energyís Office of Geothermal Technology has obtained, from Unocal Geothermal Indonesia, 1.1 km of continuous core from a 1995 research corehole, Awi 1-2, drilled into the large, high-temperature, Awibengkok geothermal system in West Java. The core will be the nucleus of a collaborative research effort designed to expand our knowledge of composite volcanic-hosted (ìandesiticî) hydrothermal systems, which provide an increasingly large share of the worldís geothermal power. Awibengkok, an ideal representative for these systems, is hosted principally by Quaternary-age, intermediate- to felsic-composition volcanic rocks. The research corehole penetrated the shallowest portion of the Awibengkok system, where these young volcanics are pervasively propylitized as well as locally silicified and adularized beneath a clay-rich caprock. Thermal-fluid flow appears to occur and to have occurred along faults, fractures, and open, mineralized veins and hydrothermal breccias. Porosity has been enhanced by hydrothermal dissolution. Complementing the core for this research effort is an extensive Unocal data set comprising wireline logs; fluid and rock chemical and mineralogic analyses; physical-property measurements; and full-color digital imagery. With the core, this information, and an elite research team, the project is certain to furnish fundamental new scientific insight into the origin, evolution, and configuration of andesitic systems anywhere on Earth. In turn, this new understanding should help US. geothermal companies find and develop such systems with greater ease and reduced expenditure. |