Processos hidrotermais em carste hipogênico silicificado – dissoluções de sílica na gruta Cristal – nordeste brasileiro.

Abstract

The present document is about a master dissertation, where is presented all the development activities during the research. The silicification of carbonate and siliciclastic sediments can occur several times throughout diagenetic evolution, together with dolomitization and dissolution processes, related to the action of hydrothermal fluids. These processes can directly affect porosity and permeability, fundamental factors in the reservoir quality classification. This study presents the effects of silicification and hydrothermal processes from Cristal Cave, Caboclo Formation, São Francisco Craton, and their direct relationship with karstification. Diagenetic and hydrothermal evolution analyses are made based on the stratigraphic profile, divided into two sections: zone I (low karstification process zone) and zone II (high karstification process zone), according to the fracture influence in the lithologies. The hydrothermal processes identified are cementation filling with microcrystalline quartz and recrystallized dolomite, pore-filling by euhedral quartz crystals, and chalcedony, the occurrence of typical minerals of hydrothermal paragenesis such as barite, quartz with wavy extinction, zoned dolomite, and pyrite. Processes that are also associated with hydrothermalism are fractures filled with iron oxide, veins composed of blocky dolomite, quartz, chalcedony, and hydraulic breccia. In the two karstification zones, there are secondary vugular porosity and fracture, with moldic porosity only in the high karstification zone.