Mihaela-Elena CIOACĂ
Geological Institute of Romania, 1 Caransebeş St 012271, Bucharest, Romania, mihaela.cioaca@igr.ro

FLUID EVOLUTION IN THE BOLCANA ORE DEPOSIT, METALIFERI MOUNTAINS (ROMANIA)

Full text

Bolcana is one of the porphyry Cu-Au ore deposits associated with the Neogene metallogenesis from Metaliferi Mountains. This deposit is characterized by the spatial association between the porphyry Cu-Au type mineralization, superimposed on a microdioritic subvolcanic structure and the base metal and gold-silver low sulfidation hydrothermal veins that cross cuts the subvolcano and the surrounded andesitic rocks. Fluid inclusions are found both in the quartz stockwork veins and in the hydrothermal veins. This paper comprises the results of the petrographic and microthermometric study of the fluid inclusions associated with both type mineralizations from Bolcana ore deposit. Fluid inclusions from „porphyry” veins are grouped in six main types, respectively (1) – high salinity type enriched in daughter minerals like halite, sylvite, metallic minerals etc., (2) –vapor-rich type, (3) – two-phase liquid+vapor type, (4) – liquid-rich type and (5) - silicate melt inclusions and (6)- sulfide melt inclusions. These inclusions homogenized at T ≥ 370°C, most of them at T ≥ 580°C. Boiling traces are evidenced. Fluid inclusions associated with hydrothermal veins are predominantly liquid-rich type, trapped at temperatures of around 300° C from low salinity solutions. No evidence of boiling is observed in these veins. Thus, the spatial association between porphyry and hydrothermal veins suggests that both belong to the same magmatic-hydrothermal system and a poliascendent evolution of metallogenesis in the Bolcana structure. Results of fluid inclusions study reveal that fluids responsible for the porphyry Cu-Au mineralization have exclusively magmatic origin, high salinity and were enriched in Cu, Fe, Au metallic compounds. Boiling was implied in metallogenesis. The vein mineralization represents tardive metallogenetic events and was induced by the downing of temperature and salinity, caused by the mix of magmatic and meteoric waters.