Source of ore-forming fluids in El Cobre VHMSdeposit (Cuba): evidence from fluid inclusions and sulfur isotopes

Abstract

The El Cobre deposit, east of Cuba, lies in the intermediate volcanosedimentary sequence of the Sierra Maestra intraoceanic island arc. The structure of the deposit corresponds to that of a volcanogenic-hosted massive sulfide (VHMS) model. It comprises (a) thick stratiform bodies (baryte and anhydrite), (b) three stratabound bodies (formed by silicification and sulfidation of limestones or sulfate strata), (c) stockwork zones, an older anhydrite stockwork and a younger quartz-pyrite stockwork grading downwards to (d) simple veins (quartz with sulfide ores). Pyrite, chalcopyrite and sphalerite are the most abundant sulfides. Fluid inclusions from this deposit have a salinity between 2.3 and 5.7 wt.% NaCl eq., homogenization temperatures range between 177 and 300 °C. Sulfur exhibits a range of δ 14S values from − 1.4 to +7.3 for sulfides and from + 16 to +21 for sulfates. Fluid inclusions and sulfur isotope data at El Cobre deposit indicate that the hydrothermal fluid from which the sulfide precipitated was seawater, modified by reaction with volcanic host rocks during hydrothermal circulation.