Tracking fluid mixing in epithermal deposits – Insights from in-situ ?18O and trace element composition of hydrothermal quartz from the giant Cerro de Pasco polymetallic deposit, Peru

Ore precipitation in mineral deposits formed the upper parts of a porphyry system, at shallow crustal level (< 1.5 km), such as epithermal Au-Ag-(Cu)-(As) and polymetallic is often triggered by fluid cooling and/or mixing between fluids from different sources. Commonly, deposits, two main sources are identified deeply sourced magmatic meteoric water stored surficial aquifer. Oxygen hydrogen isotope compositions gangue alteration minerals using conventional bulk isotopic methods support existence these types. However, analysis provides only limited information on exact mechanisms changing proportions involved fluids. Due to their high spatial resolution, SIMS in-situ oxygen LA-ICP-MS trace element analyses, transects across growth zones single crystals adequate tools dynamics this mixing. In study, analyses were performed 10 selected quartz giant Cerro de Pasco porphyry-related deposit central Peru. The results, combined with previous microthermometric inclusion studies same or equivalent crystals, allow quantifying documenting types that large deposit. ?18Oquartz values range 4‰ 20‰ display variations up 11.5‰ inside cannot be only, nor mainly ascribed temperature changes. Rather, record variable rising moderate-salinity ?18OH2O around 10‰ low-salinity 0 4‰, latter below paleo-water table. Each analyzed also important variation content, Al (43 2098 ppm), Li (0.7 18 Ge (1.1 24ppm) Ti (0.8 ppm). These do not systematically correlate compositions. This suggests content controlled complex interplay composition, temperature, pressure, rate. Application published Ti-in-quartz geothermometers grains which well constrained microthermometry, shows it can lead overestimation underestimation temperatures more than 50 °C. obtained patterns measured along profiles studied less clearly compositions, reveal abrupt changes suggest surface-derived was continuous process. It rather took place through influx multiple short-lived pulses into surface