浙江舟山海岸带古木埋藏区铁的微生物成矿作用

以浙江舟山海岸带铁矿石为研究对象,通过对铁矿石及其周围环境背景样品的形态学显微观察、矿物学及地球化学分析,结果显示渗漏水沉淀铁泥中存在大量形貌与Leptothrix ochracea和Gallionella ferruginea中性铁氧化菌极为相似的微生物鞘,该微生物可促进Fe2 的氧化和Fe3 的快速沉淀,并且细胞最终被完全矿化后将永久保存起来.与此相对应的是:在铁矿石内部存在大量的似球形和丝杆状的针铁矿,并且还保留了死亡的铁细菌外鞘,这些特征揭示该铁矿石与微生物历史活动密切相关.将现代渗漏水铁泥中铁细菌的矿化作用和铁矿石中保留的微生物活动记录相对比,为该环境下的铁矿石生物成矿作用及其成因机制提供了良好的佐证.铁矿石的形成与古木堆积密切相关,古木埋藏腐烂过程产生的腐植酸加剧了基岩及其周围土壤中的铁淋滤进入到潮间带,从而为铁矿石形成提供充足的铁来源.该研究有助于更好理解和认识地史时期腐植质及微生物在铁矿床形成中的作用.

Iron Biomineralization and Biometallogenesis in the Ancient-Wood Buried Zone from Coast of Zhoushan Island, Zhejiang Province

In the present study,we describe the formation of iron ores collected in the intertidal zone of the Zhoushan Island in Zhejiang Province in the East China Sea,where ancient-wood layers were buried.Morphological,mineralogical and geochemical analyses were performed on the iron ores and the surrounding geological material.The results show that the iron ores are not only composed of spherical and fibre-like aggregates of goethite,but also contain the dead bacterial sheaths,which present morphological characteristics reminiscent of bacterial activity.Similar present-day biomineralization characteristics were also observed in an iron seepage system near the studied intertidal zone.The presence of Leptothrix-like sheaths and Gallionella-like stalks in the present-day environment promoted the oxidization of Fe2 to Fe3 and the rapid precipitation of biogenic iron oxides around the bacteria.The role of bacteria in mineral formation in the seepage area is believed to represent an analogue mechanism for the formation of the iron ores.It is hypothesized that the degradation of the ancient wood provided humic substances which accelerated the leaching process of iron from the surrounding bedrock and soils,and then created local biogeochemical conditions which led to the biomineralization of the iron ores.The present findings help elucidate the role of bacteria and humic substances in the formation of iron ores in the history time.