Kinetics of the Formation and Transformation of Iron Oxides in Hydrothermal Systems

世界上大部分的铁供应来自：(a)前寒武纪带状铁地层（BIFs），由海底热液环境中积累的各种含铁矿物（赤铁矿、磁铁矿、菱铁矿和黄铁矿）组成；(b)由磁铁矿、赤铁矿、菱铁矿和黄铁矿转化而成的富赤铁矿次生铁矿。拟议研究的目标有三个方面：(i)了解海底热液系统（如bif和VMS -火山块状硫化物矿床）中氧化铁（和其他主要含铁矿物）形成和转化的地球化学环境系统和过程；（ii）发展矿物学和地球化学方法，确定含铁矿物的沉积环境；（三）建立铁矿床勘查新模式。这些目标将通过两个系列的实验室研究来实现，探索：(1)含铁和含硅热液与不同成分海水混合过程中含铁矿物和二氧化硅形成的动力学；(2)在250℃以下温度下赤铁矿磁铁矿非氧化还原转化的动力学。(1)局部海水中溶解氧和HCO3-的浓度是决定海底热液矿床等矿物学特征的主要因素；(2)富赤铁矿bif是太古宙海洋和大气含氧的良好证据；(3)富菱铁矿岩体形成于缺氧盆地；(4)赤铁矿向磁铁矿的转化，或磁铁矿向赤铁矿的转化，在许多类型的矿床中不是由氧化还原反应引起的，而是由赤铁矿中简单地添加Fe2+或从磁铁矿中浸出Fe2+引起的：Fe2O3 (hm) + Fe2+ + H2O = Fe3O4 (mt) + 2H+；(4)地壳深部和地表均形成富赤铁矿。

Most of the world's Fe supply comes from: (a) Precambrian banded iron formations (BIFs), which were composed of a variety of iron-bearing minerals (hematite, magnetite, siderite, and pyrite) that accumulated in submarine hydrothermal environments; and (b) hematite-rich secondary iron ores that were transformed from the magnetite, hematite, siderite, and pyrite of BIFs. The goals of the proposed research are three-fold: (i) to understand the systematics of the geochemical environments and processes involved in the formation and transformation of iron oxides (and other major Fe-bearing minerals) in submarine hydrothermal systems (e.g., BIFs and VMS -volcanogenic massive sulfide deposits); (ii) to develop mineralogical and geochemical methods to identify the depositional environments of Fe-bearing minerals; and (iii) to develop a new exploration model for iron ore deposits. These goals will be achieved through two series of laboratory investigations, exploring: (I) the kinetics of the formation of iron-bearing minerals and silica during the mixing of Fe2+- and silica-bearing hydrothermal fluids with seawater of various compositions, and (II) the kinetics of the non-redox transformation of hematite magnetite at temperatures below 250 C. Some of the important hypotheses will be tested in this research, including: (1) the concentrations of dissolved O2 and HCO3- in the local seawater played major roles in determining the iron mineralogy of BIFs and other hydrothermal ore deposits formed on the ocean floor; (2) hematite-rich BIFs are good evidence for the oxygenated oceans and atmosphere during the Archean era; (3) siderite-rich BIFs suggest they formed in anoxic basins; (4) the transformation of hematite to magnetite, or magnetite to hematite, which in many types of ore deposits was not caused by redox reactions, but caused by simple additions of Fe2+ to hematite, or leaching of Fe2+ from magnetite: Fe2O3 (hm) + Fe2+ + H2O = Fe3O4 (mt) + 2H+; (4) hematite-rich iron ores formed in deep crust as well as on the land surface.