Seafloor massive sulfide deposits

Deep ocean research submersibles, bathyspheres and remote operated vehicles have visited and taken samples of black smoker chimneys, and it has been long recognised that such chimneys contain appreciable grades of Cu, Pb, Zn, Ag, Au and other trace metals.

SMS deposits are laterally extensive and consist of a central vent mound around the area where the hydrothermal circulation exits, with a wide apron of unconsolidated sulfide silt or ooze which precipitates upon the seafloor.

Mineralization in submarine magmatic-hydrothermal systems is a product of the chemical and thermal exchange between the ocean, the lithosphere, and the magmas emplaced within it.

Mineral associations may vary (1) in different mineralized structures, either syngenetic (namely, passive precipitation in chimneys, mounds and stratiform deposits) or epigenetic (structures that correspond to feeder channels, and replacements of host rocks or pre-existing massive sulfide bodies), or structural zonation, (2) from proximal to distal associations with respect to venting areas within the same stratigraphic horizon, or horizontal zonation, (3) from deep to shallow associations (i.e., stockworks to mounds), or vertical zonation, (4) from early and climactic to late stages of mineralization (dominated by sulfides, and sulfates or oxides, respectively), or temporal zonation, and (5) in various volcano sedimentary contexts, depending essentially on the composition of volcanic rocks and, ultimately, on the tectonomagmatic context.

The most common minerals in ore-bearing associations of volcanogenic massive sulfide deposits (non-metamorphosed or oxidized) and their modern analogues are pyrite, pyrrhotite, chalcopyrite, covellite, sphalerite, galena, tetrahedrite-tennantite, marcasite, realgar, orpiment, proustite-pyrargyrite, wurtzite, stannite (sulfides), Mn oxides, cassiterite, magnetite, hematite (oxides), barite, anhydrite (sulfates), calcite, siderite (carbonates) quartz and native gold, and are differently distributed in the various associations schematized above.