4.1. Massive ironstone
The massive ironstone is found as lenses of limited thickness and extension; the thickness ranges from few centimeters up to_4 m, as can well be seen in Chabid Al-Abid and Umm Idaya areas (Fig. 1). The Ga’ara Formation which hosts the ironstone beds is overlain by the sandstones of Rutba/Msa’d Formation in the Chabid Al-Abid at the northern rim, and by the carbonates of Mulussa Formation in Umm Idaya at the southern rim of the Ga’ara Depression. Hematite is the predominant mineral with lesser amounts of goethite. Kaolinite and quartz are the major non-ferruginous minerals in this type of ironstone; secondary calcite occurs as crack filling.