Mineralizing processes at shallow submarine hydrothermal vents; examples from Mexico

Recent studies on shallow submarine hydrothermal vents (at water depths <200 m below sea level [mbsl]) suggest that their activity could have been responsible for the formation of oxide, sulfide, and precious metal-bearing ores. The boundary between shallow and deep hydrothermal vents has been established at a depth of 200 mbsl, which represents an abrupt change in the environmental parameters and in the structure of the biotic communities. Shallow submarine vents support complex biotic communities, characterized by the coexistence and competition of chemosynthetic and photosynthetic organisms. Some biogeochemical and biomineralizing processes related to chemosynthesis are similar to those described in deep hydrothermal vents and in cold seeps. Frequently, hydrothermal shallow vent water has lower salinity than seawater. This fact, together with the isotopic compositions, is evidence of a meteoric component in vent water. Venting of exsolved gas, evidenced by continuous bubbling, is a striking feature of shallow submarine hydrothermal systems. In most cases, vent gas is rich in CO (sub 2) , but occasionally it can be rich in N (sub 2) , CH (sub 4) , and H (sub 2) S. In Mexico, shallow submarine hydrothermal venting has been studied in Punta Banda and Bahia Concepcion, Baja California Peninsula, and in Punta Mita, Nayarit. The tectonic setting of those hydrothermal systems corresponds to continental margins affected by extension, with high geothermal gradients. These vents do not show obvious links with volcanic activity. Their study has contributed to the understanding of mineralogical and geochemical processes in shallow submarine hydrothermal vents. Those systems could be a potential source of geothermal energy.