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 N?os 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 (2) Type II are primary or pseudosecondary, multi-volatile presenting (3) Type III are secondary, two-phase, liquid-rich inclusions, composed of and have two different times of formation (IIIA and IIIB), (4) Type IV are very rare, three-phasic, secondary inclusions and composed of S 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; similar features have been found in orogenic deposits hosted by turbidite sequences around the world.