广西东平地区碳酸锰矿床Ga含量高异常的发现及成因初探

摘要

Gallium(Ga) is a typical kind of dispersed element extracted from bauxite,sphalerite and coal.Recently,an unusually high content of Ga was discovered in manganese carbonate deposits of the Beisi Formation in Dongping area,Guangxi.The content of Ga is between 5.16 × 10-6 and 82.80 × 10-6,and the average content is 33.76 × 10-6,reaching the industrial grade of Ga.What's more,the average content of Ga in manganese ore beds and surrounding rocks is respectively 46.40 × 10-6 and 19.31 × 10-6,higher than values in most reported manganese ore deposits both in China and abroad.Geochemistry suggests that the manganese carbonate deposits belong to hydrothermal sedimentary genesis.Combined with the latest report about Ga in ferromanganese deposits from the ocean,it is held that the occurrence of Ga was closely associated with manganese-bearing minerals and the source of Ga was related to seafloor hydrothermal activity.Finally,the genetic types of manganese ore deposits were determined by Mn/Fe-Ga and Co-Ga logarithmic coordinate crossplots.%Ga是一种典型的稀有分散元素,主要产于铝土矿、闪锌矿及煤矿之中.最近,在广西东平地区下三叠统北泗组碳酸锰矿床中发现Ga高异常含量,ω(Ga)介于5.16×10-6～ 82.80×10-6之间,平均为33.76×10-6,达到了Ga工业品位标准;锰矿层和围岩中ω(Ga)平均分别为46.40×10-6、19.31×10-6,高于国内外已报道的大部分锰矿床.文中根据北泗组碳酸锰矿床地球化学特征,揭示了该锰矿床为热水沉积;同时,结合现代大洋铁锰沉积有关Ga的最新报道,提出北泗组碳酸锰矿床中Ga的赋存与含锰矿物密切相关,其来源与海底热液活动有关.最后,文中还利用Mn/Fe-Ga、Co-Ga关系图判别了古代铁锰沉积的成因类型.