New Mineralogical and Geochemical Features of the Ore Ferromanganese Deposits of the Izu-Bonin and Mariana Island Arcs

Some features of the ferromanganese deposits of the Izu-Bonin and Mariana Island arcs tested in the 1st (1977) and 5th (1978) flights of the R/V Volcanologist are considered. Two types of genetic deposits have been identified - hydrogenic and low-temperature hydrothermal. The main ore minerals of hydrogenic ferromanganese deposits are poorly crystallized structures with a low degree of ordering Fe-vernadite and Mn-feroxygite, with a smaller amount of goethite and bernessite. Low-temperature hydrothermal deposits consist either primarily of bernessite, as well as vernadite and goethite, or of hematite, goethite and feroxygite. Hydrogenic ferromanganese deposits of the Izu-Bonin and Mariana Island arcs are characterized by a Mn/Fe ratio of 0.84-1.36, for low-temperature hydrothermal deposits of the Izu-Bonin arc it is 6.13-13.9. It was found that the content of Co, Ni and Cu is significantly higher in the crusts of the Mariana arc compared with the crusts of the Izu-Bonin arc. The contents of the remaining cations of heavy and rare metals - Pb, Cd, Ba, Sr and others - in the crusts of both arcs are close to each other. The content of most rare earth metal cations in the hydrogenic deposits of the Izu-Bonin and Mariana arcs is comparable to each other. Low-temperature hydrothermal ferromanganese deposits of the Izu-Bonin arc differ significantly from hydrogenic deposits with a low (by 1-2 orders of magnitude) content of cations of non-ferrous, heavy and rare metals. The contents of rare earth metal cations in low-temperature hydrothermal samples of the Izu-Bonin arc are low and range from 0.24 (Tm, Lu) to 32.35 mcg/g (Y). Among all rare earth metal cations, Y, Ce, and Nd are present in the largest amounts in these samples.