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MRD-03 Recent developments on marine mineral deposits
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Drilling of shallow water hydrothermal systems in the Aeolian Arc, Italy: The role of magmatic volatiles
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Sven Petersen, Leibniz-Institute of Marine Sciences, IFM-GEOMAR (Germany)
Thomas Monecke, University of Ottawa (Canada)
Mark Hannington, University of Ottawa (Canada)
Nico Augustin, Leibniz-Institute of Marine Sciences, IFM-GEOMAR (Germany)
Klas Lackschewitz, Leibniz-Institute of Marine Sciences, IFM-GEOMAR (Germany)
Arnaldo A. de Benedetti, Universita degli Studi Roma Tre (Italy)
Guido Giordano, Universita degli Studi Roma Tre (Italy)
Alessandra Esposito, Istituto Nationale di Geofisica e Vulcanologia (Italy)
Bruce Gemmell, CODES, ARC Centre of Excellence in Ore Deposits (Australia)
Harold Gibson, Laurentian University (Canada)
Reinhard Kleeberg, TU Bergakademie Freiberg (Germany)
Katie Perrin, Neptune Minerals (Australia)
Robina Sharpe, Neptune Minerals (Australia)
Marc Peters, University Munester (Germany)
Kirstie Simpson, University of British Columbia (Canada)
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Shallow hydrothermal venting is a widespread phenomenon associated with submarine arc volcanism. In August 2007, shallow drilling was conducted for the first time at two localities in the Aeolian island arc to study the third dimension of hydrothermal systems precipitating polymetallic sulfides at shallow water depth. A lander-type drilling device (Rockdrill I of the British Geological Survey) was deployed from the German R/V Meteor permitting drilling to a maximum penetration of 5 m.
Eleven holes were successfully drilled into the sediment-covered sulfide mineralization at the Palinuro volcanic complex (∼650 m water depth). The mineralized zone remained open in all directions and at depth because all drill holes ended in sulfide mineralization. Up to 4.8 m of massive sulfides/sulfates were recovered from a single drill hole. Metal enrichment at the top of the mineralization was observed with polymetallic (Zn, Pb, Ag) sulfides overlying massive and dense pyritic sulfides. The massive sulfide mineralization at Palinuro contains a number of unusual sulfide minerals including enargite, tennantite, luzonite, covellite, and Ag-sulfosalts. Native sulfur, forming late veins, was an abundant component in all drill holes. In analogy to epithermal deposits forming on land, the occurrence of these unusual minerals suggests a high-sulfidation state of the hydrothermal fluids. The acidic and oxidizing character of the mineralizing fluids is probably related to the presence of magmatic volatiles, presumably derived from a degassing magma chamber at depth. This is also supported by preliminary sulfur isotope data on native sulfur and sulfide separates. The isotope ratios show substantial variation at the surface (-26 to -5‰), but a narrow range between -5 to 0‰ at depth. These variations could be explained by the mixing of magmatic sulfur with a biogenic component derived from the host sediments.
Extensive drilling was also conducted at the submerged portion of the Panarea volcanic complex (∼60-90 m water depth) in areas where circular depressions (<50 m diameter) have previously been reported. Video seafloor mapping suggests that these depressions formed in response to submarine gas explosions and/or collapse following intense gas venting. Drilling yielded up to 3 m of massive anhydrite±gypsum with minor sulfides. The massive sulfates are interpreted to form a seal at the interface between cold seawater and upwelling magmatic-hydrothermal fluids.
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