From rocks to ore

Metal enrichment to ore grade is the ultimate outgrowth of large-scale and long-term fractionation processes of the thermally driven and unique water- cooled geological evolution of the Earth. Silicic magmatism along convergen t margins is the most important lithospheric fractionation process for the formation of the continental crust and porphyry/intrusion-related ore depos its. Reconnaissance microanalysis of melt inclusions from Central Andean po rphyry systems refines a metallogenic model for copper-gold and tin porphyr y mineralization. Magmatic mixing and early exsolution of a fluid phase are important ingredients for porphyry Cu-Au systems in association with silic ic rocks df moderate levels of fractionation (such as diorites and monzonit es), whereas extended magmatic fractionation with late-stage fluid evolutio n characterize lithophile-element-enriched tin porphyry systems.