Modern hot springs in the southern volcanic Cordillera of Peru and their relationship to Neogene epithermal precious-metal deposits

Modern hot springs associated with surface precipitates and acid alteration exist in several areas of the Southern Volcanic Cordillera of Peru. The hot springs are related to continental geothermal systems, which formed important epithermal precious-metal deposits during the Cenozoic. There are several high-temperature geothermal fields in the areas studied, with reservoir temperatures up to 190°C and siliceous sinter deposits that indicate favourable conditions for possible epithermal mineralisation at depth. To evaluate whether the modern geothermal systems are capable of forming epithermal deposits, as were ancient ones during the Cenozoic, the siliceous sinter deposits have been compared with those of geothermal systems in other areas, interpreted as modern examples of epithermal mineralisation. Also, the oxygen and hydrogen isotope composition of hot-spring waters has been compared with those of other geothermal systems and fluids of epithermal deposits in North and South America. The data suggest that the Cenozoic epithermal precious-metal deposits were formed by deeper and longer-term geothermal systems than those existing today. Also, the estimated reservoir temperatures of the geothermal systems in southern Peru are low compared to systems elsewhere which show evidence of subsurface epithermal mineralisation. It is therefore possible that the current formation of economic epithermal deposits, even beneath higher-temperature geothermal fields in the Southern Volcanic Cordillera of Peru, is rather restricted.