Sulfur isotope geochemistry of the submarine hydrothermal coastal vents of Punta Mita, Mexico

Coastal hydrothermal submarine vents occur near Punta Mita (Mexico) through a seafloor fissure hosted by basaltic rocks and partially covered by recent sediments. Hydrothermal venting produces calcareous tufa mounds, with minor sulfides, barite and apatite. Pyrite is the most abundant sulfide mineral that precipitates around the submarine hot springs. It occurs as framboids, euhedral crystals, thin botryoidal coatings interbedded with calcite, and as replacement of detrital magnetite gains. Vent fluids have temperature below 100 degreesC, and methane is abundant. Sulfur isotopic composition of pyrite predominantly has 534, 13 values from - 10.7 parts per thousand to + 4.9 parts per thousand suggesting that the source of sulfur is microbially reduced sulfate seawater. (C) 2003 Elsevier Science B.V. All rights reserved.