Characterization of the Atalla talc-carbonate rocks, central Eastern Desert, Egypt.

Citation

Abou El Maaty MA, Taman ZI & Wahab WA (2012) Characterization of the Atalla talc-carbonate rocks, central Eastern Desert, Egypt.. Egyptian Journal of Geology, 56 (1), pp. 67-83.

Abstract
The Atalla talc-carbonate mass is one of several talc occurrences in central Eastern Desert of Egypt. Talc-carbonates are genetically and spatially associated with serpentinite in sequences of ophiolitic mélange. These talc-carbonate raw materials could serve as a possible natural magnesia source for industrial applications. Discrimination and mapping of the Atalla talc-carbonates are necessary steps to understand these raw materials in the area. Through the applying of remote sensing techniques, different ophiolitic components of the studied area were successfully distinguished from each others. Thus, the studied talc-carbonate masses were reasonably separated using TEM band ratio images. Petrographical, XRD and XRF analyses were applied in studying these talc-carbonates. Talc-carbonate rocks were distinguished into two main assemblages, namely; talc-carbonate A (TCA: magnesite + talc, other phases are minor) and talc-carbonate B (TCB: talc ± magnesite ± serpentine ± dolomite). TCA variety is considered to be the most promising assemblage to be used in the refractories applications. This assemblage was further subdivided into two categories, depending on the relative abundances of talc and magnesite, into TCA1 (magnesite >= talc) and TCA2 (talc > magnesite). The mineralogical study revealed that the talc-carbonate masses are generally formed at the expense of serpentinites as a result of carbon dioxide metasomatism along fault planes and fractures. These serpentinites represent obducted oceanic slices onto island-arc assemblages and were originated from harzburgite protolith via hydration. Mantle peridotite (harzburgite) protolith is advocated for the serpentinite/talc-carbonates on the basis of the recorded bastite, the proportions of SiO2 and Fe*/ (Fe*+Mg) of the talc-carbonate samples and the presence of antigorite - talc assemblage. The metamorphic conditions could tentatively be assumed for the studied talc-carbonate assemblages (antigorite - talc - magnesite): temperature of about 490°C and a maximum XCO2 of about 0.13.

Keywords
Talc-carbonates; Ophiolits; Serpentinites; Wadi Atalla; Petrogenesis

Journal
Egyptian Journal of Geology: Volume 56, Issue 1