Serpentinite-hosted talc–magnesite deposits of Wadi Barramiya area, Eastern Desert, Egypt: Characteristics, petrogenesis and evolution

Abstract

Enormous quantities of practically untapped talc–magnesite rocks are distributed in the Wadi Barramiya area in intimate spatial and genetic association with the ophiolitic serpentinites. These deposits are an important potential source of magnesia, which is used in a broad spectrum of strategic industries. Barramiya ophiolitic serpentinites represent obducted oceanic slices onto island-arc successions. They occur as elongated mountainous ranges in the form of anticlinal–synclinal sheets demarcating the general ENE-WSW brittle–ductile shear zones of the area. The serpentinite-hosted talc–magnesite deposits of Barramiya area are located: (a) along major faults that cut the serpentinite slices, or (b) at thrust contacts between obducted serpentinites and other mélange components (more siliceous country rocks of island-arc affinity). The latter were regionally metamorphosed at greenschist up to middle amphibolite facies conditions. The talc–magnesite rocks represent in situ fissure-fed metasomatic products of serpentinite precursors via extensive rock–fluid interactions. The main fluids involved in the transformation processes of serpentinites to talc–magnesite were SiO2aqueous solutions and CO2. The deposits located along the fault systems cutting the serpentinite-host are magnesite-rich, whereas those located at the contacts between serpentinites and the more siliceous country rocks are typically talc-rich. Based on the proportional distribution of talc and magnesite in conjunction with other accessories, the rocks have been distinguished into assemblages. Their characteristics, petrogenesis and evolution from serpentinite precursors are elaborated in the light of their petrography, XRD, EDAX, and XRF data. Constraints on the conditions of their formation include temperature of about 490°C and a maximum XCO2 of about 0.13. New mapping was undertaken for the area using remote sensing and GIS techniques. Accordingly, the Barramiya talc–carbonate rocks were more precisely mapped as separate layers and their reserve estimation was accomplished.