Magmatic-hydrothermal processes forming epithermal Sn-Ag ore deposits in NW Argentina
The Puna Plateau in NW Argentina hosts a variety of economic Sn-Ag and Ag deposits which are believed to be analogues to the polymetallic epithermal deposits of the southern Bolivian Sn belt. However, while the Bolivian deposits have a clear association to Miocene magmatism, a direct connection to magmatic intrusions is lacking for the Argentinian deposits so far. Recent studies of fluid inclusions hosted in quartz and ore minerals from the giant Pirquitas deposit have revealed compelling evidence that the hydrothermal system was characterized by mixing of magmatic fluids and meteoric water. In the follow-up PhD project, we will extend fluid inclusion studies to new deep wells in the area of the Pirquitas deposit and to the Cinchillas deposit, which is also located in the Puna Plateau but has a different style of Ag mineralization. The PhD candidate will perform geochemical studies of Pb and S isotopic compositions and fluid inclusions in ore and gangue minerals (microthermometry, Raman spectroscopy, LA-ICPMS, noble gas isotopes). In addition, the candidate will use numerical modelling to resolve the magmatic-hydrothermal transition from an inferred porphyry system at depth to the epithermal regime at shallower levels, using the constraints obtained from data of the Pirquitas system.
Magmatic and hydrothermal processes in the Andean Cu-Au and Sn-Ag ore belts of NW Argentina
The Cenozoic central Andes host orogen-parallel belts of magmatic-related ore deposits with contrasting metal associations (Fe, Cu-Au, vs. polymetallic, Sn-Ag). This project will investigate the role of magmas vs. hydrothermal fluids in metal transport and metallogenesis. There a close linkages to projects G3.5 and G4.1. Besides the potential role of magma processes (differentiation, fluid saturation), other important factors to be studied are the roles of local basement composition and deformation for the metal enrichment, transport, and deposition (faults and shear zones – link to project 10). Both belts are located in an E-W region of 70-km width, and the mineralization and magmatism belong to the main metallogenic epoch in the S central Andes (12-15 Ma), so the geodynamic scenario can be considered invariable. We hypothesize that the different metal associations are controlled by different magma compositions, which depend on source characteristics in addition to the conditions of magma genesis and differentiation, especially oxygen fugacity and volatile contents. To test the roles of magma composition and hydrothermal fluids, the PhD candidate will combine standard geochemistry and petrology of ore and wall rocks with fluid-inclusion studies, melt inclusions and ore minerals with SIMS ion probe analysis, Raman spectroscopy, LA-ICPMS, IR microthermometry, and stable gas isotopes.