| Paleoclimate, Neoproterozoic Banded Iron Formations (BIFs), and the Absence of BIF-hosted Iron Ore Deposits in the Arabian-Nubian Shield |
| Paper ID : 1085-ISCH |
| Authors |
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Ayman El-Badry Maurice *1, Khalil I Khalil2, Paul D Asimow3 1Geology Department, Faculty of Science, Helwan University 2Geology Department, Faculty of Science, Alexandria University 3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA |
| Abstract |
| Banded iron formations (BIFs) comprise the largest iron resource on Earth, accounting for most global iron production. The Neoproterozoic Rapitan-type BIFs are composed mainly of iron and silica; their origin has been attributed to Snowball or Slushball Earth conditions. In this theory, extensive sea ice cover totally or partly isolated the oceans from the atmosphere and initiated reduced ocean conditions that permitted the buildup of dissolved Fe and Si in ocean water. Upon melting of the sea ice, renewed interaction of oxygenated atmosphere and reduced oceans resulted in oxidation and precipitation of the dissolved iron to produce the original BIF precipitate. BIFs of this type have relatively high silica contents, which limit their grade and use as a source of Fe ore. Fortunately, the dissolution and leaching of silica by meteoric water or hydrothermal solutions can locally convert low-grade BIFs to high-grade Fe ores. Hence, the formation of high-grade BIF-hosted iron ore deposits requires either (a) prolonged periods of high rainfall and areas of high relief to allow rapid drainage and permit extensive dissolution of silica or (b) extensive hydrothermal circulation to leach huge amounts of silica gangue. The Neoproterozoic BIFs of the Arabian-Nubian Shield (ANS) have no genetic relationship with glaciation, indicating that the local climate was not polar during their deposition. Moreover, the ANS BIFs are devoid of high-grade iron ores, which can be attributed to arid and non-tropical local climate and/or limited hydrothermal activity since the stabilization of the ANS at the end of the Neoproterozoic. |
| Keywords |
| Banded Iron Formation, BIF, Neoproterozoic, Snowball Earth, Arabian-Nubian Shield |
| Status: Abstract Accepted (Oral Presentation) |