Mn-Ba-Hg mineralization at shallow submarine hydrothermal vents in Bahía Concepción, Baja California Sur, Mexico
Por:
Canet C., Prol-Ledesma R.M., Proenza J.A., Rubio-Ramos M.A., Forrest M.J., Torres-Vera M.A., Rodríguez-Díaz A.A.
Publicada:
1 ene 2005
Resumen:
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 silica-carbonate fine-layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders. Manganese crusts are made up of barium rich, X-ray-amorphous todorokite-like and romanechite phases, and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment. In the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter-thick iron oxyhydroxide coatings on volcanic cobbles and boulders. These coatings are composed of poorly crystallized six-line ferrihydrite, accompanied by minor cinnabar and fine-grained colloform pyrite. Textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition. The vent precipitates display a significant enrichment of Hg, As and Sb. Arsenic is probably adsorbed onto Mn- and Fe-oxide substrates. The NASC (North American Shale Composite)-normalized REE patterns of the vent precipitates show a pronounced positive Eu anomaly that is probably inherited from the hydrothermal fluid. © 2005 Elsevier B.V. All rights reserved.
Filiaciones:
Canet C.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
Prol-Ledesma R.M.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
Proenza J.A.:
Departament de Cristal Lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Barcelona, Spain
Rubio-Ramos M.A.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
Forrest M.J.:
Moss Landing Marine Labs, Moss Landing, CA, United States
Torres-Vera M.A.:
Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San Jose 2055, 78216 San Luis Potosi, Mexico
Rodríguez-Díaz A.A.:
Facultad de Ingeniería, Universidad Nacional Autónoma de México, 04510 México, D.F., Mexico
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