Osmium isotopic constraints on sulphide formation in the epithermal environment of magmatic-hydrothermal mineral deposits

In the magmatic-hydrothermal environment, fluids with similar metal concentrations and sources may yield contrasting mineral assemblages in successive stages of sulphide mineralization. These differences are linked to physico-chemical conditions mineralizing (e.g., T, pH, fS2, fO2) acquired during their interaction country rocks and/or by mixing groundwater. Here, we integrate petrography osmium (Os) isotope (187Os/188Os) geochemistry, discuss novel constraints on magmatic fluid-rock fluid-groundwater that deemed govern deposition systems. We studied pyrite (FeS2) enargite (Cu3AsS4) from porphyry-related polymetallic Cerro de Pasco (14.54–14.41 Ma) Colquijirca (10.83–10.56 epithermal deposits Central Andes, Peru. Sulphide mineralization is genetically associated Miocene magmatism includes breccia replacement bodies carbonate rocks, veins cutting sedimentary rocks. At both deposits, followed paragenesis. Pyrite has a radiogenic initial 187Os/188Os isotopic composition (187Os/188Osi-pyrite or Osi-pyrite = 0.80 1.45). Enargite (I) enclosing filling cracks also (Osi-enargite I 0.56 1.24). Conversely, (II) formed irregular surfaces earlier an unradiogenic II 0.13 0.17). Our data show paragenetic evolution records sharp change within these sulphides. record compositions, indicating hydrothermal However, suggests mantle-like signature ascended parental chambers environment without incorporation crustal Os via This difference be due being altered previous stages, flushed pulses. findings imply ore metals (i.e., Cu, Au) magma-derived, whereas some capture rock lithologies Eifelian black shale study area) Thus, siderophile chalcophile trace element sulphides act as tracer source, degree wall-rock interaction.