Microthermometry and Raman spectroscopy of fluid inclusions from El Vapor gold mineralizations, Colombia

摘要： Epigenetic El Vapor gold mineralization is hosted by the Segovia batholith and sedimentary rocks at both sides of El Nús fault, in the eastern flank of the Colombian Andes central cordillera. Gold mineralization is composed by continuous and discontinuous sigmoidal and stockwork veins and veinlets from a few centimeters to two meters of thickness and by hydrothermal breccias. Ore mineralogy includes Pyrite + Galena + Sphalerite + Chalcopyrite + Pyrrhotite + Proustite - Pyrargyrite. Gold occurs as inclusions within pyrite, between quartz crystals and filling fractures within pyrite at a late stage of mineralization. The fluid inclusions in quartz veins occur as clusters of primary inclusions or in alignments of secondary and pseudo-secondary inclusions. Based on petrography and Raman spectroscopy, four types of fluid inclusions could be recognized: (1) Type I are primary biphasic, liquid-rich, with CO2(v) + N2(v) + CH4(v) + KCl(AQ) + NaCl(AQ) + H2O(L), (2) Type II are primary or pseudo-secondary, multi-volatile presenting CO2(V) + CO2(L) + N2(V) + CH4(V) + KCl(AQ) + NaCl(AQ) + H2O(L), (3) Type III are secondary, two-phase, liquid-rich inclusions, composed of H2O(v) + H2O(L) + KCl(AQ) + NaCl(AQ) and have two different times of formation (IIIA and IIIB), (4) Type IV are very rare, three-phasic, secondary inclusions and composed of S + H2O(V) + H2O(L) + KCl(AQ) + NaCl(AQ). The microthermometric and spectroscopic analysis of fluid inclusions indicates that the fluid associated with the first event of mineralization identified in El Vapor have low to moderate salinities (3.5-9.2 wt% NaCl equiv.), with trapping temperatures between 214°C and 350°C and pressures between 0.5kbar and 2.9kbar. Due to the nonexistence of fluid inclusions with variable degree of filling with opposite homogenization and because of the variations of salinity in a restricted homogenization temperatures range, it is proposed an isothermal fluid mixture process, which together with fO2 changes, generated by fluid reaction with the carbonaceous shales of the Segovia sedimentary rocks, could influence the process of gold deposition. Hydrothermal fluids from El Vapor were near neutral and reduced; simlar features have been found in orogenic deposits hosted by turbidite sequences around the world.