西昆仑玛尔坎苏石炭纪大型锰矿带构造背景与成矿条件

Tectonic Setting and Metallogenetic Conditions of Carboniferous Malkansu Giant Manganese Belt in West Kunlun Orogen

西昆仑北段玛尔坎苏地区探明的大型碳酸锰成矿带,是我国近年最重要的找矿成果之一。该锰矿带构造上属北昆仑晚古生代弧后伸展盆地,其构造动力学背景为古特提斯洋向北俯冲于塔里木地块之下形成的弧盆体系。锰矿体主要发育于晚石炭世喀拉阿特河组含炭泥质灰岩夹薄层灰岩中。矿石中主要金属矿物为菱锰矿(75%~95%),次为软锰矿、硫锰矿及少量黄铁矿等。含锰岩系岩性和岩相学研究表明,玛尔坎苏锰矿带属典型的海相沉积锰矿床,其矿床成因可能与晚古生代半局限盆地沉积和海底热液活动有关。海底热液活动可能为成矿提供了丰富的物质来源。含锰岩系元素和同位素地球化学特征表明,玛尔坎苏锰矿沉淀时的水体环境为常氧条件,而矿层下盘(部分)岩系的岩性及地球化学特征反映其沉积时的水体环境为低氧—贫氧条件。玛尔坎苏锰矿带锰矿石具有负的δ^13C值(-23.3‰^-10.0‰),推测有机质导致的还原作用是该锰矿由原生氧化锰在成岩期转化为菱锰矿和形成富锰矿的重要机制。

The large scale Carboniferous Malkansu manganese carbonate metallogenic belt in west Kunlun orogen is one of the most important prospecting achievement in China.The belt belongs to the back-arc extension basin of north Kunlun in Late Paleozoic.The basin was formed in the subduction of paleo Tethys Ocean beneath the Tarim plate.The Mn orebody is hosted by the marine sedimentary sequence of the Upper Carboniferous Kalaatehe Formation.The ore is composed of rhodochrosite(75%-95%),pyrolusite,alabandite,and pyrite.Based on petrographic and lithologic studies,it is suggested that the Upper Carboniferous Kalaratehe Formation represents sedimentary sequence of back-arc basin.Based on trace elements,C isotopes(δ^13C=-23.3‰--10.0‰),it is suggested that the ore-forming condition of the Carboniferous Malkansu manganese ore body is normoxic.It is speculated that the dissimilatory reduction of manganese oxides in combination with organic matter resulted in the precipitation of manganese carbonates.