Hg contents of soils in geothermal areas in the western U.S. were measured and a three-fold distribution was observed: peak, aureole and background. Peak values (up to several 100 ppm Hg) occur in fumaroles of vapour-dominated systems, around hot springs, and in zones overlying steeply dipping, hot-water aquifers. Aureoic values (up to several 100 ppb Hg) are found in zones surrounding the peak areas and delineate areas with shallow geothermal convection. Background values vary between 7 and 40 ppb Hg (geometric mean). Usually, Hg is present in a form that can be easily re-volatilized and released to the atmosphere. Altered areas related to fossil hydrothermal systems can be distinguished from alteration related to active systems by their Hg contents. In the rare cases of Hg enrichments as cinnabar or as traces in other sulphides (pyrite, sphalerite) the Hg is not easily released from its host phase, and distinction between active and fossil systems is not possible. Hg anomaly patterns yield information on the presence as well as the geometry of shallow geothermal circulation patterns. In conjunction with structural geologic data, Hg patterns can be helpful in defining reservoir boundaries and can aid in the selection of drill site location.
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Geotechnical Engineering and Engineering Geology