Structural controls on the talc mineralization at El Nasr mining company concession, Wadi Allaqi district, South Eastern Desert, Egypt: Insights from remote sensing, field investigation and geological traverses

The current work is an integrated study utilizing remote sensing and field-structural data to better understanding of the origin, structural framework and tectonic evolution of the talc ore exploited by El Nasr Mining Company at its concession in Wadi Allaqi district, South Eastern Desert, Egypt. Exploring the best sites in the environs of the currently working mine for future working is also one of the important objectives of the study as well. Processing of Landsat- 8, ASTER and Sentinel- 2 images resulted in mapping of a large elongated NW-oriented and NE-dipping zone of talc-bearing highly-sheared metaultramafics and talc carbonate schists enclosing variably-sized masses of amphibolites and surrounded by highly-sheared metavolcanics and metavolcaniclastics which are tectonically intermingled. Such zone is structurally representing a part of (the hanging wall) of a major left-lateral transpressive zone. The present working talc mine is utterly located along a large lense of highly-sheared metaultramafics (trending N30°-40°W and dipping 55°–78° NE) which is extended northwestward to include the ‘‘Nawal Game’’ mine but outside the concession. However, the rest of talc carbonate zone reveals that the origin of talc was related to the alteration or metasomatic processes that are working intensively upon the mafic metavolcanic rocks. Several promising talc sites distributed within the previously mentioned talc zone are documented and checked for further evaluation and preparation of core-sample study (core-sample locations and core-directions are measured) to extend the concession area and mining activities to the approved sites in near future. The remote sensing-based mapping supported by field-structural work indicated that the investigated area (as a whole) represents a tectonic belt oriented NW-SE and dipping steeply to NE and building up of highly sheared and altered ophiolitic mélange rocks intruded in places by metagabbro-diorite and heavily dissected by mafic dykes and quartz veins following the main directions of thrust/shear which are exclusively major NW-SE and minor NE-SW tectonic trends. The study area was practicing three deformation phases where the most important is D₂ which was producing the NW-trending foliation with NW and SE plunging lineations. During such phase the earlier D1 thrusts were reactivated forming transpressive faults and highly-dipping to subvertical shear zones associated with the alteration/metasomatism of mélange rocks producing talc pockets, lenses and elongated zones of talc-carbonate schists. It is worth mentioning that the talc ore is not recorded along the younger NE- to ENE- tectonic trends (D₃ deformation) indicating that the talc was predominantly related to D₁ and D₂ tectonic events. The structural and tectonic setting of the investigated area can be considered in terms of the tectonic evolution of the greater Wadi Allaqi district (Allaqi suture). The Allaqi suture is a part of the Allaqi-Heiani-Sol Hamid-Onib-Yanbo suture, which juxtaposes the Eastern Desert terrane (Gerf or Aswan terrane) to the north with the Gabgaba-Gebeit terranes to the south. The N30°-40°W trending shearing and the hydrothermal alteration controlling the talc mineralization in the study area is chiefly attributed to the main transpressive tectonic event along the Allaqi suture which ascribed suturing to oblique collision between the aforementioned tectonic terranes.