A Case Study Of The Newcastle Geothermal System Iron County Utah

Past exploration in low- and moderate-temperature systems of the Great Basin shows that the relatively small area associated with fluid upflow and elevated temperatures is often difficult to detect by drilling widely spaced temperature-gradient holes or by other methods. By studying the Newcastle geothermal system, we hoped to develop a basic understanding of the concealed hydrothemlal system as a tool for assessing other geothermal areas of the Great Basin. The emphasis of our work centered on determining (1) the distribution of subsurface heat and the movement of thermal fluid, (2) the location and geometry of bedrock structures that might control fluid movements, (3) the chemical character of the geothermal water, and (4) the geometry of the bedrock beneath the Escalante Desert. Field studies included: (1) drilling and monitoring temperatures in shallow themlal-gradient boreholes, (2) mapping geologic units and performing structural studies in the adjacent mountains, (3) conducting detailed gravity surveys, (4) conducting electrical resistivity and self-potential (SP) surveys, (5) collecting water samples for detennining major ions and light stable isotope analyses, and (6) mapping Quaternary units.

This CD contains a 30-page report and 37-photo appendix of an investigation by the Utah Geological Survey of five recently discovered earth fissures in southwestern Utah. The earth fissues, which likely resulted from aquifer compaction due to ground-water withdrawal, were revealed after floodwater infiltrated into and enlarged the fissures during January 2005. This study discusses the geology and hydrology of the Escalante Valley where the fissures formed, includes maps of the fissure traces, discusses the most probable cause of fissure formation, and presents recommendations for future study. 30 pages + 37 page appendix