Late Hercynian polymetallic vein-type base-metal mineralization in the Iberian Pyrite Belt: fluid-inclusion and stable-isotope geochemistry (S?O?H?Cl) (original) (raw)

2003, Mineralium Deposita

Late Variscan vein-type mineralization in the Iberian Pyrite Belt, related to the rejuvenation of preexisting fractures during late Variscan extensional tectonism, comprises pyrite-chalcopyrite, quartz-galenasphalerite, quartz-stibnite-arsenopyrite, quartz-pyrite, quartz-cassiterite-scheelite, fluorite-galena-sphaleritechalcopyrite, and quartz-manganese oxide mineral assemblages. Studies of fluid inclusions in quartz, stibnite, and barite as well as the sulfur isotopic compositions of stibnite, galena, and barite from three occurrences in the central part of the Iberian Pyrite Belt reveal compelling evidence for there having been different sources of sulfur and depositional conditions. Quartz-stibnite mineralization formed at temperatures of about 200°C from fluids which had undergone twophase separation during ascent. Antimony and sulfide are most probably derived by alteration of a deeper lying, volcanic-hosted massive sulfide mineralization, as indicated by d 34 S signatures from)1.45 to)2.74&. Subcritical phase separation of the fluid caused extreme fractionation of chlorine isotopes (d 37 Cl between)1.8 and 3.2&), which correlates with a fractionation of the Cl/Br ratios. The source of another high-salinity fluid trapped in inclusions in late-stage quartz from quartz-stibnite veins remains unclear. By contrast, quartz-galena veins derived sulfide (and metals?) by alteration of a sedimentary source, most likely shalehosted massive sulfides. The d 34 S values in galena from the two study sites vary between)15.42 and)19.04&. Barite which is associated with galena has significantly different d 34 S values ()0.2 to 6.44&) and is assumed to have formed by mixing of the ascending fluids with meteoric water. Keywords Pyrite Belt AE Vein mineralization AE Fluid inclusions AE Infrared microscopy AE Chlorine isotopes