广西宜州石炭纪龙头锰矿床锶同位素组成与地质意义

Strontium isotope compositions of the Carboniferous Longtou manganese deposit in the Yizhou area, Guangxi and Their geological significances

广西宜州是石炭纪沉积型锰矿较为发育的地区。本文以区内具有代表性的龙头锰矿床作为研究对象,系统开展了锶同位素组成研究。锰矿石^(87)Sr/^(86)Sr比值为0.708172~0.708213,平均0.708200,围岩^(87)Sr/^(86)Sr比值为0.708181~0.708248,平均0.708214,反映锰矿成矿物质可能具有多元混合的特征。结合岩相学研究,认为海底热液活动和陆源风化作用共同控制锰矿成矿。龙头锰矿床从Ⅰ矿层到Ⅳ矿层的矿石和围岩^(87)Sr/^(86)Sr比值呈现逐渐降低的趋势,认为可能与古大陆风化作用及对锰矿有重要控制作用的龙头式台沟阶段演化有关。

The Yizhou area of Guangxi Province is an important area in which many Carboniferous sedimentary manganese deposits are relatively developed. In this paper, the representative Longtou manganese deposit in the Yizhou area has been taken as the research object to systematically study the strontium isotope composition. The ^(87)Sr/^(86)Sr ratios of manganese ores range from 0.708172 to 0.708213, with an average of 0.708200. The ^(87)Sr/^(86)Sr ratios of wallrocks range from 0.708181 to 0.708248, with an average of 0.708214.These reflect that the ore-forming materials of manganese ores may have the characteristics of multivariate mixing. Combined with petrographic studies, it is considered that the submarine hydrothermal activity and continental weathering had jointly controlled the manganese ore mineralization. Meanwhile, the ^(87)Sr/^(86)Sr ratios of ores and wallrocks from the I, to II, III, to IV ore-layers of the Longtou manganese deposit are gradually decreased, inferring that this characteristics could be related to the continental weathering and the Longtou platform trench evolution which played an important controlling role in the manganese mineralization.