Metallogenetic mystery of deep sea ferromanganese nodules
ZHOU Huaiyang;State Key Lab of Marine Geology, School of Ocean and Earth Science, Tongji University;
Deep sea manganese nodules are classified into three genetic types: hydrogenetic, diagenetic and mixed, according to their major metal sources. Hydrogenetic manganese nodule, derived from precipitates from sea water column, is generally characterized of smooth surface, Mn/Fe ratio 2, higher concentration of Co and ∑REE, and slower growth rate. In contrast, diagenetic manganese nodule, from pore water in seafloor sediemnts, is of rough surface, Mn/Fe ratio 2, higher concentration of Cu and Ni, and relative faster growth rate. Classification and identification of ferromanganese minerals of manganese nodules have been very difficult and confused as most of or nearly all of them are amorphous and/or poor crystallized. Up to date, it is commonly accepted that major manganese minerals in hydrogenetic and diagenetic nodules are d-MnO_2 and 10?-manganates, respectively. Globally variation of nodule distribution, nodule types, nodule abundance, mineral and chemical composition in nodules is mainly controlled by primary production, carbonate compensate depth and oxygen minimum zone. Although progresses have been largely achieved for the genesis studies of manganese nodules in deep sea by numerous great efforts in last ~100 years, metallogenetic mysteries are still remain to be further explored.