Late Neoproterozoic banded iron formation (BIF) in the central Eastern Desert of Egypt: Mineralogical and geochemical implications for the origin of the Gebel El Hadid iron ore deposit

摘要

The banded iron formation (BIF) in the Gebel El Hadid area is part of the Late Neoproterozoic island-arc/ophiolitic assemblage of the central Eastern Desert of Egypt, where it alternates concordantly with low-grade metavolcaniclastics. The BIF units are mainly of oxide facies consisting of iron oxide mesobands with intercalations of quartz-carbonate +/- chlorite +/- magnetite mesobands in the form of layers and pods. Geochemically, the Gebel El Hadid BIF is characterized by heavy REE-enriched NASC-normalized patterns, rarely with a weak positive Eu anomaly. The Neoproterozoic age of the Egyptian BIF suggests that they are of Rapitan type, but their size, petrological and geochemical characteristics suggest that they are of Algoma type having formed before the final collision between major fragments of East and West Gondwana. The nature and composition of the BIF and associated metavolcaniclastics indicate their formation as a result of submarine hydrothermal activity concomitant with arc volcanism. The Gebel El Hadid BIF units were deposited in pulses during periods of quiescent arc activity at ca. 717 +/- 8 Ma (U-Pb age on volcaniclastic zircon). Submarine diagenesis under suboxic conditions produced an early generation of magnetite, hematite and quartz, whereas regional metamorphism led to the formation of coarse-grained and porphyroblastic magnetite and quartz. Post-metamorphic oxidation led to martitization of magnetite, and formation of hematite and specularite. (C) 2015 Elsevier B.V. All rights reserved.