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

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

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.