MANGANESE ORE RIFT BASIN METALLOGENIC SYSTEM AND MASSIVE METALLOGENESIS

Neoproterozoic Nanhua rift basin in south China (Level-I), was formed by re-tension process happened between Yangtze Block and South China Block at ~780Ma, under the background of breakup of Rodinia super-continent. Nanhua rift basin (at the early stage of Nanhua period, ~725Ma) further broke-up into two secondary rift basins, Wuling basin and Xuefeng basin (Level-II), and was accompanied with massive metallogenesis (~660Ma), which results in the formation of a new type of manganese ore, ancient natural gas seep sedimentary type manganese ore. This is the one which was formed in special rift basin metallogenic system, a uniform system made up of internal sub-system (crust-mantle ductile shear zone structures, inorganic and mantle derived gas/liquid vs manganese, volcanic activities) and shallow sub-system (series of synsedimentary faults and their controlling graben basins; ancient natural gas seep and manganese ore sedimentary metallogenesis happened at the center of the basin). Those synsedimentary faults, act not only as channels where manganese and ancient natural gas rise through, but also the linking between internal sub-system and shallow sub-system. Manganese ore metallogenic belt across Guizhou-Hunan-Chongqing border area of south China, including three level-III graben basins, two level-III horsts and at least 16 level-IV graben basins, was formed under the control of Wuling secondary rift basin manganese ore metallogenic system. Level-III graben basin is responsible for the formation of manganese ore metallogenesis sub-belt, whereas level-IV graben basin is responsible for forming large to super-large scale manganese ore. Ancient natural gas seep sedimentary manganese ore has three characteristic features, 1) seep sedimentary structure (i.e. diapiric structure, bubbles filled with asphalt, soft sedimentary deformation textures and seep pipe structures), 2) negative value of carbon isotope (δ¹³C, -7‰~-10‰, PDB), 3) abnormally high positive value of sulfur isotope (δ³⁴S, 50‰~67‰, respectively). Central facies, transitional facies and marginal facies could be observed along synsedimentary faults-controlled seep holes, which are long and narrow banding shaped.