Utilization of Geothermal Waters for Mining Processes in the Andes Mountains

Abstract

It is well known that most mines located in the Andes Mountain are limited by the availability of water, and much effort is applied to delivering water supplies from surface, some time using costly water dams, and groundwater sources, as desalted and seawater is also being considered at elevated costs. A large number of geothermal resources have been identified in the vicinity of existing and planned mines, and some of these geothermal systems have been assessed to have potential to provide large volumes (925 l/s) of industrial water. The areas of the Andes Mountain that are marked by geological alteration, including volcanic activity, also host many geothermal systems. Magma emplaced close to the surface (5-7 km depth) can induce a convective regimen in the deep groundwater creating a geothermal reservoir. These systems may have localized upflow zones covering a few km2 located above the heat source, and may also have outflow aquifers that extend as long as 20 km. The fluid which typically circulates through these hydrothermal systems is dilute brine of near-neutral pH, having salinity of one-tenth to one quarter of seawater and some dissolved gases, as well as large energy reserves. These geothermal reservoirs are usually isolated from shallower meteoric ground waters by a deep clay layer (smectitte-illite/smectite) created by thermal alteration within and above the geothermal system. Therefore, geothermal wells are drilled much deeper than most ground water wells and specifically case off shallow ground waters to depths of typically 500 to 1000m. Effectively, these wells tap into aquifers which