High-Grade Iron Ore Exploration in an Increasingly Steel-Hungry World: The Past, Current, and Future Role of Exploration Models and Technological Advances
Hilke Dalstra, Marcus Flis, 2008. "High-Grade Iron Ore Exploration in an Increasingly Steel-Hungry World: The Past, Current, and Future Role of Exploration Models and Technological Advances", Banded Iron Formation-Related High-Grade Iron Ore, Steffen Hagemann, Carlos Alberto Rosière, Jens Gutzmer, Nicolas J. Beukes
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Earliest discoveries of iron ore basins worldwide were commonly the result of regional, government-instigated surveys. After initial discovery, exploration for high-grade iron ores within these basins used ore genesis models from a very early stage. These models included syngenetic, hypogene, and supergene concepts. Systematic prospecting using a supergene genetic model with stratigraphic and structural contributions was hugely successful in identifying major resources in the Hamersley province at an early stage, but the use of this model resulted in significant underestimation of the size of some deposits. With detailed drilling and mining of deposits, many features which seemed at odds with a simple supergene origin were discovered, and modified supergene-metamorphic, syngenetic, or hypogene models were proposed. It was the recognition in these models that high-grade hematite ores could occur concealed beneath unmineralized iron formation that initiated a concealed orebody search by Hamersley Iron from 1980 to 1994. The concealed orebody search was modeled on the CSIRO supergene-metamorphic model. This was followed by a dedicated high-grade hematite search following hypogene concepts by the Hamersley Iron Task Force from 1994 to 2001. These programs were successful in identifying semiconcealed high-grade hematite ores, but none led to a major discovery to replace the Mount Tom Price deposit. Before the concealed orebody search and the Task Force, very limited exploration using a syngenetic model had been carried out at Paraburdoo, which resulted in discovery of the largely concealed Lens 2 deposit.
Worldwide, models for the formation of high-grade hematite ores are being refined due to current global exploration activity, which is resulting in greatly improved understanding of the geology of deposits and iron ore provinces. Exploration models are shifting from supergene to hypogene, which has led to deeper drilling and discovery of significant additional resources in some areas. Modern academic and exploration techniques are refining the current ore genesis models and together with the availability of new geophysical methods provide the iron ore exploration geologists with an invaluable set of tools to discover the future, most likely concealed hematite, deposits to satisfy the world's ever-increasing hunger for iron ore.
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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