An Integrated Exploration Approach to the Sishen South Iron Ore Deposit, Northern Cape Province, South Africa, and Its Implication for Developing a Structural and/or Resource Model for These Deposits
Dennis Alchin, Vanessa Lickfold, Pieter J. Mienie, Deon Nel, Marius Strydom, 2008. "An Integrated Exploration Approach to the Sishen South Iron Ore Deposit, Northern Cape Province, South Africa, and Its Implication for Developing a Structural and/or Resource Model for These Deposits", Banded Iron Formation-Related High-Grade Iron Ore, Steffen Hagemann, Carlos Alberto Rosière, Jens Gutzmer, Nicolas J. Beukes
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The high-grade hematite Sishen South iron ore deposit is located due south of Postmasburg on the southern-plunging limb of the Maremane dome in the Northern Cape of South Africa. To develop a structural model that could be used for mineral resource estimation it was crucial to investigate the effects of at least three compressive orogenic episodes and several extensional events on the formation, erosion, and preservation of iron ore on the Maremane dome and surrounding environs. Due to the general paucity of outcrops, much of the work was initially based on the interpretation of ground gravity surveys, Landsat TM images, and surface drill hole information combined with the limited mapping data.
Results indicate that iron ore was preserved from erosion by deep, semicircular, troughlike depressions, formed by the interference of the Kheis orogeny, north-trending F2 synclines, and the Lomanian orogeny east-northeast-trending F3 synclines and half grabens formed adjacent to reactivated west-dipping north-south-striking normal faults. Reactivated faults played a pivotal role at Sishen South; sustaining troughlike depressions in which previously formed iron orebodies could be unaffected by subsequent uplift and erosion.
As part of the ongoing regional exploration, a large area in the Northern Cape province was covered by an airborne gravity gradiometric survey. Interpretation of the survey data combined with the previous information facilitated the construction of geologic sections spaced at 5-km intervals across the entire survey area. The effects of regional deformation on the deposit, combined with an integrated approach for its exploration, culminated with the compilation of a set of consistently interpreted structural cross sections for each orebody at Sishen South, which were incorporated into three-dimensional solid models and used for confident mineral resources estimation. Without this consistent approach, confidence in the mineral resource estimate was suboptimal.
The iron ore deposits of the Northern Cape province of South Africa have previously been considered type examples of ancient supergene deposits and little support has been afforded hydrothermal and/or supergene-modified hydrothermal ore formation processes. Recently, however, some evidence, which is partly discussed in this paper, has been found relating the iron (and manganese) mineralization in this region to structurally controlled hydrothermal fluid flow related to the Kheis orogeny.
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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