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（BIF），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）富含赤铁矿的次生铁矿石，由BIF中的磁铁矿、赤铁矿、菱铁矿和黄铁矿转化而来。拟议研究的目标有三个方面：（一）了解海底热液系统中氧化铁（和其他主要含铁矿物）形成和转化所涉及的地球化学环境和过程的系统学（例如，BIFs和VMS -火山成因块状硫化物矿床）;（ii）发展矿物学和地球化学方法，以确定含铁矿物的沉积环境;（iii）发展新的铁矿床勘探模式。这些目标将通过两个系列的实验室研究来实现，探索：（I）在含Fe 2+和二氧化硅的热液流体与各种成分的海水混合期间，含铁矿物和二氧化硅的形成动力学，以及（II）赤铁矿的非氧化还原转化动力学 温度低于250 ℃的磁铁矿。 本研究将对一些重要的假设进行检验，包括：（1）当地海水中溶解O2和HCO 3-的浓度在确定BIFs和其他海底热液矿床的铁矿物学中起着重要作用;（2）富赤铁矿的BIFs是太古代海洋和大气含氧的良好证据;（3）富含菱铁矿的生物IFs表明它们形成于缺氧盆地;（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，这不是由氧化还原反应引起的，而是由Fe 2+向赤铁矿的简单添加或Fe 2+从磁铁矿中的浸出引起的：Fe_2O_3（hm）+Fe_2 + + H_2O = Fe_3O_4（mt）+2 H +;（4）富赤铁矿型铁矿既产于地壳深部，也产于地表。

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.