Geology and Genesis of the Major Banded Iron Formation-Hosted High-Grade Iron Ore Deposits of India
Joydip Mukhopadhyay, Jens Gutzmer, N. J. Beukes, Harendra Nath Bhattacharya, 2008. "Geology and Genesis of the Major Banded Iron Formation-Hosted High-Grade Iron Ore Deposits of India", Banded Iron Formation-Related High-Grade Iron Ore, Steffen Hagemann, Carlos Alberto Rosière, Jens Gutzmer, Nicolas J. Beukes
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With a current annual production of about 170 million tons (Mt), India is the sixth largest producer of high-grade iron ore (>60 wt % of Fe) in the world. The greater part of the high-grade iron ores of India (>5 billion tons reserve base) are hosted by voluminous banded iron formations of major Archean greenstone belt successions. Major deposit districts include (1) the Noamundi-Koira Valley of the Singhbhum craton of eastern India, (2) the Bailadila-Dalli-Rajhara deposits of the Bastar craton in central India, (3) the Donimalai-Hospet deposits, as well as (4) the Goa deposits of the Eastern and Western Dharwar cratons, respectively, in southern India. The present investigation was carried out to compile, augment and interpret information on the geologic setting, mineralogy, petrography, and geochemistry of the most important districts. Results reveal that high-grade iron ore deposits in the major Indian ore districts have characteristics that are similar to many other high-grade BIF-hosted iron ore deposits worldwide. Close correspondence exists in particular with iron ore deposits regarded to be of supergene-modified hydrothermal origin, in particular those of the giant Serra dos Carajás district (Brazil). Hard ores rich in hematite and martite in most of the Indian deposits are believed to have formed during early hydrothermal events. Chemical weathering in wet tropical humid-monsoonal climate resulted in extensive supergene modification of these hydrothermally upgraded iron ores and surrounding BIF to soft saprolitic hematite-martite ores, as well as the development of surficial goethitic ores. The proposed genetic model leads to the conclusion that currently known high-grade hard hematite-martite ore deposits in India might persist to greater depth than currently envisaged, and that deposits of soft and friable hematite-martite ore might, at depth, be underlain by high-grade magnetite-rich hard ore or, alternatively, by hydrothermally altered BIF.
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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