Study of the mechanisms of mineral deposition at sea-floor by biological and mineralogical experiments

1.微生物介导重金属在海水中的沉积实验研究了微生物介导重金属沉积的机理。在日本津轻海峡青函海底隧道导井中采集的细菌粘液显示出强烈的锰氧化作用。将含有重金属（Mn、Ni、Co、Cr等）的人工海水等分试样并取少量细菌粘液在25℃下培养，分析金属浓度随时间的变化。实验结果表明，海水中的Mn在加入细菌粘液后开始迅速下降，然后在4天后完全消失。溶液中除Mn以外的重金属也随时间而减少，但每种金属的减少方式不同。这些结果表明，某些海洋细菌不仅催化锰的氧化，而且还加速除锰以外的重金属的沉淀。这一事实表明，细菌活动可能在海底重金属沉积中发挥重要作用。通过对太平洋和波罗的海锰结核的分析，证实了这一假设.为了研究硫化物在海底的沉积机理，利用热液反应器对海水与火山岩的相互作用进行了实验研究。实验结果表明，海水中的硫酸盐还原可使重金属（Pb、Zn、Cu、Fe）迅速溶解，硫化物沉淀。这些结果不仅对认识硫化物成矿机理，而且对研究地下岩石作为CO_2和核泥库的长期稳定性具有重要意义。

1. Microbially-mediated metal deposition in seawaterThe mechanism of heavy-metal deposition mediated by microorganisms was studied experimentally. The bacterial slime collected at the pilot shaft of the Seikan Undersea Tunnel under the Tsugaru Straits of Japan shows strong manganese-oxidation effect. An aliquot of artificial seawater containing heavy metals (Mn, Ni, Co, Cr etc.) and a small amount of the bacterial slime were incubated at 25℃ and the changes of metal concentrations with time were analyzed. The results of the experiments showed that Mn in seawater began to decrease rapidly by addition of the bacterial slime and then disappeared completely after four days. The heavy metals other than Mn in the solution were also decreased with time, but the manners of the reduction differ in each metal. These results indicate that some kinds of marine bacteria not only catalyze manganese-oxidation but also accelerate precipitation of heavy metals other than manganese. This fact suggests that bacterial activity may play an important role on the deposition of heavy metals on the seafloor. The manganese nodules from Pacific Ocean and those from Baltic Sea were analyzed to confirm this hypothesis.2. Metal deposition by water-rock interaction at the ocean floorIn order to investigate the mechanisms of sulfide deposition at the ocean floor, seawater and volcanic rocks were interacted by using a hydrothermal reactor. The experiments showed that heavy metals (Pb, Zn, Cu and Fe) were dissolved quickly and sulfide precipitated by reducing sulfate in seawater. These results are applicable not only to understand the mechanism of sulfide mineralization but also to study the long-time stability of underground rocks as CO_2 and nuclear sludge reservoir.