OLD HOT BRINE MANGANESE DEPOSITS IN A SHALLOW-SEA RIFT BASIN: AN EXAMPLE FROM THE SINIAN MANGANESE DEPOSITS IN THE WULING MOUNTAIN AREA

There are a number of the Late Proterozoic manganese deposits in the Wuling Mountain area, South China. The deposits are confined largely to the sapropel-type carbonaceous shales of the Lower Sinian Datangpo Formation (ca. 700 Ma), and characterized by orientation, zonation and equidistance of their spatial distribution. The genetic model for the deposits may be compared with that for modern ocean-ridge manganese deposits, and their formation tend to be constrained by the factors such as basement nature, Sinian sedimentary cycles, depositional system and palaeotectonic settings of the basin. The mineralization model suggested by the author has offered an alternative explanation for the formation of the foregoing manganese deposits. During Early Siniam, the uplifting of the mantle and rifting of the crust allowed for superficial water to penetrate downwards along the faults or rifts, giving rise to a hot brine convective system. After having emplaced in the shallow-sea basin in the Wuling Mountain area, the ore-bearing hot brine from the hydrothermal system was subjected to biological and chemical processes, thus resulting in the formation of the manganese deposits in the study area.