Petrology, Geochemistry And Mineralogy Of Alaskan Type Ultramafic-Mafic Intrusive Complexes: A Case Study Around Mikbi-Zayatit District, South Eastern Desert, Egypt

Abstract

The present work deals with the field geology, petrography, geochemistry and mineralogy of Wadi Zayatit and Wadi Mikbi ultramafic-mafic intrusive complex, South Eastern Desert, Egypt. Based on the current geological maps, field observations, structural relationships, and previous works; the rocks that exposed in the study regions are dunites, peridotites, and gabbro. These rocks characterized by coarse-grained, dark greyish to whitish grey color, massive with lustric features and slightly deformed with low to moderate relief. The commonest of the accessory constituents is an oxide ore mineral of some kinds, the most frequent one is chromite, ilmenite, titano-magnetite and magnesio-ferrite. The petrographic descriptions of each rock unit of the studied layered ultramafic-mafic intrusion are recognized; dunites, serpentinized peridotites, and olivine gabbro. Petrographically, opaque minerals are found as coarse-grained, euhedral crystals dispersed throughout the mineral constituents and represented by titani-ferous magnetite and chromite. Titano-magnetite has high FeO and low TiO2. The Fe2O3 and TiO2 show increase with decrease in silica content (SiO2). These rock units have high contents of Ni (9767 ppm), Cr (7861ppm), and Co (1525 ppm). The clino-pyroxene and bulk-rock chemistry indicates strongly crystallization from orogenic hydrous tholeiitic to calc-alkaline magmatic affinity. These inferences suggest that their primary magma was derived from partial melting of a mantle wedge source that has suffered metasomatism in a subduction zone setting. Ore microscopy, XRD technique, and EDX microchemical analysis of representative mineralized samples of ultramafic-mafic intrusive complex identified chromite, ilmenite, titano-magnetite, magnesio-ferrite and clinochlore.