湘中地区中奥陶统“桃江式”锰矿的成矿作用研究

湘中地区“桃江式”锰矿产于中奥陶统磨刀溪组斜坡相-盆地边缘相沉积之中。发育锰矿层１～２层,锰矿层具有粒序层理、平行层理、斜纹层、水平纹层及角砾状等构造,夹于深水低能的暗色泥岩之中,是一种碳酸盐重力流沉积。其形成受区域构造、岩相古地理、沉积事件及水介质物理化学条件等的影响。其沉积学和地球化学特征显示锰质主要由海底热水补给,是一种热水成矿作用的产物。

Studies of Ore-Forming Process of "Taojiang-type manganese",Middle Ordivician in Central Hunan Province

The "Taojiang-type manganese" is situated at the slope-basin margin factes zone of Modaoxi Formation, Middle Odivician in Central Hunan Province. The manganese-bearing series consists of manganese ore,black carbonaceous mudrock and mass clayrock. The manganese ore bed shows a lot of graded bedding, parallel bedding, small scale cross-bedding, horizontal bedding,braccisted structure and scour mark Structure ......etc.,with ABCE or ABE Bouma sequence,which may berecognized as carbonate gravity flow deposits (turbidite). The formation of manganese ore was affected and controlled by tectonics, sedimentary facies and pelaeogeography, sedimentary geological events and physicochemical condition of medium and so on.There are evidences of sedimentology and geochemistry Showing that the manganese originates from hydrothermal exhalation and extrusion at the spreading sea-noor.The mechanism of manganese ore is divided into two Stugds:first stage is Mn2+ migration in anoxic water;second stage is Mn2+ precipitation and replacing carbonate ooze. The higher content manganese ore is formed to benefit by recrystallization in the fate diasensis sarge of the sedimentary rock.