Mineralogical and Microchemical Methods for the Characterization of High-Grade Banded Iron Formation-Derived Iron Ore
Brick Ramanaidou, Martin Wells, David Belton, Michael verrall, Chris Ryan, 2008. "Mineralogical and Microchemical Methods for the Characterization of High-Grade Banded Iron Formation-Derived Iron Ore", Banded Iron Formation-Related High-Grade Iron Ore, Steffen Hagemann, Carlos Alberto Rosière, Jens Gutzmer, Nicolas J. Beukes
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A range of techniques has been applied to the mineralogical and microchemical characterization of high-grade iron ore hosted by banded iron formation (BIF), including reflectance spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscope, electron microprobe, and proton induced X-ray emission analysis (PIXE). These tools provide key physicochemical properties of the main ore minerals, such as magnetite, kenomagnetite, maghemite, hematite, and goethite, which in turn determine the grade of the deposit and its economic viability. For instance, current automated HyLogging™ systems, based on reflectance spectroscopy, provide quick and objective measurements of hematite, goethite, and gangue mineralogy on large volume of cores and drill chips. X-ray diffraction used on powders offers a full account of the bulk mineralogy of the sample as well as aluminum substitution in the structure of hematite, goethite, and maghemite. On the other hand, Raman spectroscopy provides in situ iron oxide mineralogy and cation substitution at the thin section scale. In situ microchemical analyses, using scanning electron microscopy, electron microprobe, and PIXE, emphasize the mineralogical relationship and distribution of deleterious elements such as P, Al, and Si that underpins the development of downstream processing methods for assessing upgradability and exploitation of iron ore deposits.
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The spark to put together this volume on banded iron formation (BIF)-related high-grade iron ore was born in 2005 during a steamy night in Carajás where the iron research group from the Universidade Federal Minas Gerais, Vale geologists, Carlos Rosière and Steffen Hagemann, were hotly debating the hypogene alteration genesis for the high-grade, jaspilite-hosted Serra Norte iron ore deposits. A couple of caipirinhas later we decided that the time was opportune to put together a volume that captured the new and innovative research that was being conducted on BIF-related high-grade iron ores throughout the world. We had little problem convincing our South African colleagues Jens Gutzmer and Nic Beukes to join the effort and decided that the 2008 biannual Society of Economic Geologists' (SEG) meeting in South Africa would be the perfect place to present this project through a combined field trip and workshop near Sishen.
The enthusiastic support that we received from the research community, SEG, and industry to put this volume together was generated by the significant increase in exploration activity, and with it the need for more detailed information on what exactly controls the location of high-grade iron orebodies, and renewed research interest around the world in models for the genesis of BIF-related high-grade iron ore, and particularly the relative importance of hypogene and supergene processes in formation of high-grade ore.
This volume concentrates on new research on the characteristics and metallogenesis of BIF-related high-grade iron ores. It contains a state of the art series of papers on established and new iron ore districts and deposits, the different components of the BIF iron mineral system, and how to best explore for this ore type. Although the emphasis of many of the contributions to this volume is on the hypogene aspect of high-grade iron ore formation, it is important to note that most BIF-related iron ore districts have a very pronounced supergene overprint due to deep lateritic weathering. The transformation of many hypogene iron orebodies of reasonable grade and size to the giant deposits exploited today can be related to this geologically recent supergene overprint; most of the past and still much of the present mining of high-grade iron ore relates to soft ore interpreted in most cases to be the direct result of supergene processes. Also mentioned here should be the recent resurgence of a syngenetic model that advocates the formation of chert-free BIF