Comparison of deep-sea sulfides located symmetrically east and west of the Mid-Atlantic Ridge rift valley: uniqueness or regularity?
Babaeva S. F., Sukhanova A. A., Hein J. R., Andrew S. I.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2017. V. 146. N 6. P. 18-42
There are currently known to be over two hundred oceanic seafloor massive sulfide (SMS) occurrences. The most outstanding in size, and about a quarter of the global number, occur along the Mid-Atlantic Ridge (MAR). The most prospective ore fields are located in the North Atlantic active zone of the MAR that has a slow spreading rate. For the first time, two potential ore fields were found that are symmetrically located in water depth and distance to the rift valley. These fields are mirror images of each other. The Jubileynoye field 20°09’ N 45°44’ W, discovered in 2012, is located on the west side, and the Zenith-Victoria field 20°08’ N 45°37’ W, discovered in 2008, is localized east of the rift valley. SMS from both fields show mainly three mineral types: pyrite, chalcopyrite, and marcasite. The only difference is the occurrence of sphalerite-type SMS and vein and disseminated mineralization in the Jubileynoye field. Geochemically the two fields are identical and characterized by the following geochemical types: Fe-S; Cu-Fe with Cu < 5 %; Cu-Fe with Cu > 5 %; Zn-Fe. Here we present the mineral and geochemical characteristics of the Jubileynoye and Zenith-Victoria sulfides, mineral evolution, and comparisons of the two deposits. Geochemical and mineral associations and relationships show zoning and stages of mineralization are described. The structure of the ridge segment, symmetrical localization of the Jubileynoye and Zenith-Victoria vent fields, the sequence of formation of minerals (paragenesis) and the ages suggest a single source for the SMS at both fields. We suggest that this segment of the MAR has a single deep zone of melt generation, serving as a heat source for the formation of the hydrothermal systems of both fields. The faults on both sides of the valley may be the conduits for the supply of metals and the formation of these two SMS fields.
Key words: seafloor massive sulfides, hydrothermal fields, Middle-Atlantic Ridge, zonation of mineralization.