ALBERT

Description: Magmatic-hydrothermal systems form a variety of ore deposits at different proximities to upper-crustal hydrous magma chambers, ranging from greisenization in the roof zone of the intrusion, porphyry mineralization at intermediate depths to epithermal vein deposits near the surface. The physical transport processes and chemical precipitation mechanisms vary between deposit types and are often still debated. For this study, we investigate the fluid evolution from proximal to distal settings at the Pirquitas and Chinchillas Mines in NW Argentina and the Sweet Home Mine, Colorado. New results from fluid inclusion and isotopic analyses indicate a contribution of magmatic fluids in the formation of the SnAg Pirquitas Mine, even though no direct association to a magmatic intrusion is visible. Therefore, this deposit may represent a rather distal setting. In contrast, the Ag-Pb-Zn Chinchillas Mine is hosted in volcanic extrusive units and is directly associated to an underlying dacite diatreme. In that respect, this deposit is proximal to a volcanic complex, but due to its shallow emplacement is distal to an inferred magmatic intrusion at depth. The Ag-polymetallic Sweet Home Mine (currently mined for gemmy rhodochrosite) is related to an assumed hidden Mo porphyry, but may be located more proximal to a magmatic intrusion as compared to the other deposits. Performing fluid inclusion analysis, Raman spectroscopy, noble gas isotopic compositions and LA-ICPMS measurements as well as the analysis of stable (H, O, S) and radiogenic (Pb, Sr) isotopic compositions, we aim to reconstruct the evolution and P-T-x properties of the ore-forming fluids in the respective ore deposits. As all studied deposits are characterized by a distinct sulfide mineralization stage, we also investigate whether this stage has formed by mixing of magmatic fluids with variable amounts of externally derived fluids. Furthermore, numerical modelling of the transition from a porphyry to an epithermal environment, considering country rock permeability, fluid pressure distribution, fluid temperatures, and varying locations of the magmatic plume, is used to build a quantitative model for the formation of these types of epithermal deposits.