ABSTRACT
Today’s geothermal systems have long been recognized as the modern analogs of high-crustal level (<2 to 3 km paleodepth) mineral deposits (Lindgren, 1933; White, 1955, 1981), including epithermal deposits (typically <1 to 2 km depth) of gold and silver (Henley and Ellis, 1983; Rowland and Simmons, 2012; Simmons and Browne, 2000) and slightly deeper porphyry-type deposits of copper, gold, and molybdenum (Gustafson et al., 2004; Heinrich et al., 2004; Sillitoe, 2010). Although most active geothermal systems contain some anomalous concentrations of metals, such as gold (Au), silver (Ag), arsenic (As), antimony (Sb), mercury (Hg), and copper (Cu), their concentrations and volumes within the rock reservoir are typically too low to be mined. Chemical analyses of uids of many active geothermal systems disclose very low concentrations at or below limits of detection of economically important metals, such as Au, Ag, and Cu.* Considering that most paleogeothermal systems investigated in the search of economically minable mineral deposits (i.e., ore deposits) also have sub-economic concentrations of select elements, it is not surprising that most active geothermal systems are also not signicantly mineralized. Nonetheless, modern geothermal systems afford opportunities to better understand the processes that form ore deposits, including transport, concentration, and deposition of sought-after elements. Also, mineralized paleogeothermal systems afford the opportunity to better understand uid-rock interaction through the study of a large volume of exposed hydrothermally altered rocks made possible by erosion and/or mining.
