Geology and geochronology of the Pinaya mineral district: Magmatism and porphyry-style mineralization in the southern extension of the Andahuaylas-Yauri belt, Southern Peru

The Pinaya district hosts porphyry Cu-Au mineralization in the Pinaya deposit and other mineralized centers. Cu-Au mineralization is contained in quartz stockworks with chalcopyrite and bornite associated with potassic alteration in early to intermineral daci-andesitic dikes and irregular intrusions emplaced within terrigenous facies of the Puno Group. Prograde, garnet-skarn formed in adjacent, carbonate-bearing host rocks, likely simultaneously with the potassic alteration of the productive intrusions. Both potassic and skarn associations were overprinted by progressive hydrolytic phases of sericite-clay and dickite-dominated weak and fracturecontrolled advanced argillic alteration. The first was predominantly pyritic, but the second introduced localized chalcocite, digenite, and covellite in addition to pyrite in a high to very high-sulfidation environment. A later, porphyry-centered event of intermediate-sulfidation mineralization formed proximal quartz-adularia containing nominal amounts of precious metals and distal polymetallic veins. Supergene alteration and mineralization produced an irregular profile with mixed oxide-sulfides and supergene chalcocite. The age of the porphyry-related magmatism is bracketed by two U-Pb (zircon) dates of -28 Ma on early and intermineral porphyry phases. This age and the associated trace-element signature of the host intrusions (Sr, V, Sc) not only indicate that Pinaya was emplaced late in the evolution of the larger Andahuaylas-Yauri porphyryskarn metallogenic belt, but also confirms that it can be confidently extended for -60 km to the south. It is proposed here that porphyry Cu-Au mineralization at Pinaya was emplaced at the transition from the flat-slab subduction that characterized the evolution of the Andahuaylas-Yauri batholith and related metallogeny to normal-slab subduction at 28 Ma.