Barite Concretions in Wadi Halfa Oolitic Ironstone Formation, North Sudan

Abstract

During our examination of the outcrops of the sedimentary formations in northern Sudan, we found discoidal-shape grains of the heavy mineral, barite in a sandstone of the Wadi Halfa Oolitic Ironstone Formation, which was recorded by all the earlier workers as a reworked sandstone. Petrography-wise, the framework of the sandstone consists of very angular to angular quartz grains, in which monocrystalline grains dominate over polycrystalline grains. Barite is the main cementing material of this sandstone, which occurs as concretions. Barite concretions indicate that more of the original porosity has been destroyed by cementation rather than by compaction processes with the inter-granular porosity being reduced mainly due to cementation. The origin of these concretions, as a cementing material in the sandstone, is ascribed to the reaction of Ba with some soluble sulfate to form the extremely insoluble heavy barite that appears as rounded concretions. The sulfur of the sulfate may be from the hydrothermal fluids related to submarine volcanism and/or biogeochemical processes. The deposition of these concretions might have taken place not long after the formation of the sandstone. The source of the barium, however, remains an unsolved problem. Further work is needed to interpret the origin and occurrence of these concretions along the region of Wadi Halfa.