Inside-corner Related Submarine Hydrothermal Mineralization At14.0°S, South Mid-Atlantic Ridge

The14.0°S hydrothermal field at South Mid-Atlantic Ridge (SMAR) is anhydrothermal field firstly found by Chinese scientists locating at the inside-cornerhigh of ridge-transform fault intersection SMAR. To understand the hydrothermalactivities further and the associated ore-forming regularities of polymetallic sulfidesunder the inside-corner high environment from a slow-spreading ridge, detailed studyof mineralogy and geochemistry on both rocks and hydrothermal products from thesurface of the14.0°S hydrothermal field have been carried out. Meanwhile, acomprehensive study on the hydrothermal mineralization was made with thecombination of seafloor observation and geophysical data. Innovative results andconclusions in this research are as follows:1. The SMAR14.0°S off-axis inside-corner high contains the near-axis volcanichigh and the abaxis oceanic core complex (OCC) high. While14.0°S hydrothermalvent field was located at the near-axis high, rather than the OCC structure, indicatingthat magmatic activities have conclusive effect on its development. This is the mostdistinctive feature from other hydrothermal vent fields at inside-corner high fromNorth mid-Atlantic ridge.2. The sulfide ores in14.0°S field are dominated by Pyrite-Marcasite-Amorphoussilica assemblages, several ores are enriched in chalcopyrite, but lack of zinc sulfideslike sphalerite/wurtzite etc. At least three stages of seafloor hydrothermal activitieswere identified in this field. The first and third stages were associated with amorphoussilica precipitations, while the second stage was associated with high temperaturesulfide precipitation. Multi-stages of hydrothermal activities are believed to becorrelated with the thermal cracking events of the deep rock bodies.3. The oceanic crust at14.0°S hydrothermal vent field suffered from strongtectonic cracking events, leading to the large3-dimensional spatial range ofhydrothermal release area. Hydrothermal upwellings are mainly diffusive flows andthe formed mound-stockwork complex thus shows weak vertical zonation. Comparingthe hydrothermal site1with that on the slop (site2), the former release area has a better seafloor permeability.4. The high temperature rock bodies due to the crystallization of the magmaticintrusions deep in the oceanic crust supplies the main heat source for the14.0°Shydrothermal field. While the ore-forming fluids and material is originated fromseawater and mafic wall-rock, respectively. We suggested that the overlaiddetachment fault under the volcanic highs and the high-angle normal faults in thehighs are probably two controlling-ore structures.