Chahacteristics of variscan and palaeogene fluid mobilization and ore forming processes in the Velence Mts., Hungary : a comparative fluid inclusion study

The Variscan S-type intrusive granite and Palaeogene intermediate subvolcanic-volcanic environment are characterised by intense mineralization in the Velence Mts. Pegmatite, quartz-molybdenite stockwork, and base-metal-fluorite vein mineralization of granite were formed at 1-2.5 kbar pressure at 300-550 °C, around 300 °C and 150-300 °C, respectively. Occasional immiscibility of carbonic aqueous fluids occurred during molybdenite deposition. Cu-porphyry, copper bearing breccia and high sulphidation type epithermal mineralization related to Palaeogene igneous activity were formed in low-pressure (20-300 bar) boiling hydrothermal system at 350-450 °C and 250-350 °C. In the Variscan granite-related fluid circulation, early (pegmatitic) fluids had low salinities and late vein-forming solutions had higher salinities with enrichment of Ca. This trend is interpreted as incursion of basin (formational) waters into the granite-related hydrothermal system. Hydrothermal circulation at subvolcanic level in the Palaeogene system was characterised by co-existence of high- and low-salinity fluids due to boiling, and fluids in the low temperature epithermal zones had low salinities. Decrease of salinity with temperature is interpreted as dilution of hydrothermal fluids by meteoric water. Fluid inclusion petrography and microthermometry proved that the eastern zones of the granite body were overprinted by the younger hydrothermal event. Fluid inclusion studies may support the establishment of temporal and spatial evolution of fracture systems not only in the granite of the Velence Mts. but other granitoid areas of Hungary