Oceanic ore-bearing ferrobasalts: Physicochemical conditions of formation

Statistical study of basalts from mid-ocean ridges differing in spreading r ate shows that two main petrochemical groups of basalts, N-MORB and ferroba salts, are zonally distributed along ang across their crest. Ferrobasalts a re all basalts "enriched" in Fe and Ti as compared with N-MORB. Of them, 1 to 5% may have high concentrations of sulfide and sulfide-oxide drop-like o re segregations. Hydrothermal ore-forming systems are spatially conjugate w ith regions of development of ferrobasalts enriched in water and magmatic m inerals. Ferrobasalts with high concentrations of liquation drop-like segre gations that occur in volcanogenic sections of the Earth's crust of the MOR crest are the products of fractionation of basic melts in shallow intrusiv e chambers. Water- and chlorine-enriched ferrobasalt melts may be the produ cts of crystallization differentiation of E-MORB-type basic liquids. Estima tion of the physicochemical and polybaric conditions of fractionation of pe trogenetic components shows that, given magma crystallinity is no more than 0.3, melts of ferrobasalt composition may form under pressures less than 5 kbar in a wide range of varying partial pressures of oxygen during fractio nation of both picritoid and tholeiitic magmas.