桃江式锰矿的热水沉积特征

CHARACTERISTICS OF TAOJIANG-TYPE HYDROTHERMAL SEDIMENTARY MANGANESE DEPOSITS

晋宁运动以后的湘中盆地,从早震旦世的陆内拉张阶段,一直沿续到中奥陶世的磨刀溪期。该盆地有火山活动形成的黄长玄武岩、凝灰岩、凝灰熔岩和火山碎屑岩,属具有高地热场的被动大陆边缘盆地。在中奥陶世沿江南古陆中段南缘沉积了黑色碳质页岩、粘土岩、碳酸锰和含锰灰岩。锰矿在沉积特征上具有热水沉积的牛眼状分布结构和由稀粗转变为细密的条纹-条带状构造及喷发角砾岩等特征。矿物成分、矿石的常量、微量、稀土元素、碳同位素、硫同位素和氧同位素均表现出热水沉积的特点。桃江式低磷优质锰矿床系海底热水沉积而形成。

The Taojiang manganese deposit has the following hydrothermal sedimentary and geochemi-cal characteristics. The manganese deposit occurs in a passive continental-margin basin in a high geothermal field. It has a 'ox eye-like' structure both in lithofacies and in manganese content in a single ore body. The ore structures are mainly laminated-banded and massive. The ores are principally composited of Mn-carbonate minerals and authigenic quartz. In addition, there are syngenetic barite, celestine and pyrite, which are common components of typical hydrothermal deposits. Nine samples of manganese ores fall in the hydrothermal field of the diagram of Fe-Mn-(Cu+Ni+Co) × 10. The REE distribution pattern of the ores is similar to that in Fiji. δ13C values of carbonate minerals in the ores are - 1. 7‰ to -9. 3‰; δ34S values of pyrite are -8. 2‰ to -19. 5‰. According to the δ18O values of the manganese ores, the ores were formed at 50-117℃.