Author: Ashraf Fahmy Ismael
Publishing Date: 2010
Volume: 25 Issue: 3
Eocene ironstone of Gabal Ghorabi mine area (El Bahariya depression, Egypt), represents an unconformity-bounded condensed succession, exhibiting a lateral facies change towards the equivalent relatively thicker carbonates of the surrounding scarps. It rests unconformably on different horizons of the underlying folded Cenomanian Bahariya Formation and is subdivided into two main shallowing-upward ironstone sequences, separated by an intra-Eocene (paleokarst) unconformity. The lower ironstone sequence comprises four ironstone facies namely: a) lagoonal/tidal flat mud-ironstone facies, b) lagoonal fossiliferous ironstone facies (proximal tempestite), well developed in the southern sector of Gabal Chorabi mine area, c) shallow subtidal-intertidal nummulitic-ooidal-oncoidal ironstone facies, dominated in the southern and central sectors of Gabal Chorabi, and d) Shallow subtidal nummulitic ironstone facies, that dominated in the northern sector. The upper ironstone sequence begins by the deposition of shallow subtidal green mudstone facies as a result of a new marine transgression followed by a peritidal ironstone sequence, which consists of three repeated shallowing-upward cycles. The upper ironstone sequence is intensively lateritized and karstified and iron ore laterite and stratabound karst-related barite are formed. The main valuable minerals founded in the area are haematite and goethite, and the main gangue minerals are quartz, dolomite, apatite and barite.
Key Words: Ironstone; Stratigraphy; Mineralogy; Gabal Ghorabi; El-Bahariya; Egypt.