Tectonic environments and Fe-Mn Ore formation in the Central and South Atlantic

Fe-Mn ores are widespread in tectonically active zones of the Atlantic. Dir ectly in the rift structures, they are represented by substantially ferrugi nous varieties with minimal contents of minor elements (Cu, Ni, Co, Zn, Ph) against the background of the highly reduced Mn phase. Anomalies in the co mposition of ore crusts can be used as indicators of hydrothermal vents. Of particular interest are intersections of rift segments and transform fract ure zones. There is a regular increase in the Mn content and a correspondin g decrease in the Fe content in ores that are traced from rifts toward faul t zones and further to underwater rises located outside of a spreading ridg e. The Ni and Co contents increase in the same direction against the backgr ound of persistently low contents of Cu, Zn, and Pb usually composing hydro thermal sulfide ores. Ore formation in the South Atlantic is marked by seve ral features, which are less manifested in its central segment: (1) an irre gular pattern of ore deposition that occurred under conditions of the inten se volcanic activity in the triple junction areas; (2) wide distribution of Lower Proterozoic Mn-ore formations in adjacent continents that can serve as an additional source of ore substance; and (3) the occurrence of strong circumoceanic currents that oxidize ore-bearing sediments and stimulate the ir erosion and redeposition. The study of ore genesis in active zones of th e Atlantic made it possible to define the close relationship between the se dimentary Fe-Mn ore formation and tectonic-magmatic processes controlling b oth deposition and destruction (dissolution) of ore formations. The high mo bilit of elements in the oxidizing ore genesis principally changes the unde rstanding of particular Fe-Mn ore sources, deposition environments, and spe cific chemistry of major ore-forming metals-Mn and Fe.