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Coastal submarine hydrothermal venting occurs on the west shore of the fault-bounded bay of Bahía Concepción, along a stretch of about 700 m of rocky shoreline. Diffuse hydrothermal seepage of water and continuous gas bubbling (mainly CO₂ and N₂) take place through the sediment-covered seafloor at shallow depth (5 to 15 m). In addition, at about 500 m SE, a cluster of hot springs occurs within the intertidal zone. The temperature and pH of the hydrothermal fluids varies from 72 to 87 °C and 5.95 to 6.02 in the submarine diffuse venting area and reaches 62 °C and pH of 6.68 in the intertidal hot springs. Mn–Ba–Hg mineralization is presently forming as a result of the hydrothermal venting. At the intertidal hot springs, moss-like crusts of manganese oxides and structureless detrital aggregates cemented by opal-A, barite and calcite occur around the main discharge conduits. These aggregates are overlaid by …