Abstract

Abstract. The interaction between faults and hydrothermal fluids is studied observing the internal characteristics of the faults in RT deposit. Distribution and petrography of fault-related rocks, grouped in units (studied with optical microscope and XRD) unravel their timing and genesis. Subsequently, nature of pore fluids and evolution of mechanical properties of faults are deduced. Both rock deformation and circulation of fluids in the deposit were conducted through the successive reutilization of the same structures (N30-60E/~90). Initially quartz veins and afterwards fault planes. During the nucleation of faults, phyllic fluids permeated the deposit, adding pyrite (+chalcopyrite) to the fractures and transforming feldspar to illite in the haloes. Subsequently, these faults were sheared by cataclasis, forming black gouges and pyrite breccias. Later on, gouge was cemented by quartz becoming cataclasite. Finally, hydrothermal illite and remaining feldspars were partially converted to kaolinite. Mechanically, the deformation started as semi-plastic hydro-fracturing, but as the temperature decreased, deformation evolved to a brittle regime of fracturing and shearing. Sericitc alteration, by phyllic fluids, weakened the rocks and facilitated the slip on faults. Finally, silicification hardened the faults locking the slip. Later formation of kaolinite may have weakened the rocks, however no deformation is recorded after it.