O18 CONTENT OF WATER IN PRIMARY FLUID INCLUSIONS FROM PROVIDENCIA NORTH-CENTRAL MEXICO

The water of eight samples of primary fluid inclusions in calcite, quartz, and sphalerite was analyzed for δ O 18 by the technique of O'Neil and Epstein (7). The δ O 18 of inclusions in sphalerite from three different ore bodies ranged from 6.2 to 5.8% relative to SMOW. These values are lighter than the 7-9% believed to be typical of pristine magmatic waters and have probably resulted from isotopic exchange between the hydro-thermal fluids and the crystalline granodiorite through which the fluids passed after they left a magmatic source. The 6.2-5.8%0 values are in reasonable agreement with the previously calculated δ O 18 of 6.0-7.9% for the hydrothermal fluids that deposited calcite and quartz at Providencia. The δ O 18 of water in inclusions in quartz and in calcite indicate that the inclusions have exchanged O 18 with their host during cooling of the ore deposit but that less than 45 percent of the exchange that is theoretically possible at surface temperatures has occurred. The δC 13 of CO 2 in inclusions in sphalerite and calcite was -7.0 and -11.0%, respectively, relative to PDB. The sphalerite value is consistent with the value previously inferred for the δC 13 of the hydrothermal fluid and is believed to be typical of juvenile CO 2. The calcite value reflects about 50 per cent of the possible exchange that could occur between inclusion C02 and the host at surface temperatures.