The O (super 18) content of water in primary fluid inclusions from Providencia, north-central Mexico

The oxygen from inclusions in sphalerite from three different orebodies is 1-3 per mil lighter than value expected for pristine magmatic waters (probably because of exchange between hydrothermal fluid and crystalline granodiorite) but has composition reasonably close to that previously calculated for fluids that deposited calcite and quartz. Oxygen in inclusions in quartz and calcite has exchanged with host during cooling, but less than 45 percent of theoretical exchange at surface temperature has occurred. Carbon in sphalerite has value inferred for Providencia hydrothermal fluid, believed to be juvenile. Only 50 percent of possible exchange has occurred between fluid-inclusion carbon and calcite host. Size of inclusions may influence amount of exchange.