Bentonite and smectite-rich shale deposits of Iraq

الملخص EN

Bentonite (senso stricto) is reported in the Mukdadiya Formation (Upper Miocene – Pliocene) in several localities within the Low Folded Zone of Iraq.

The bentonites are beleived to have resulted from the alteration of volcanic ash in a fluvial system (lakes) environment.

The mineralogy is dominated by Ca-montorillonite and quartz.

The major chemical oxides are SiO2, Al2O3, CaO and Fe2O3.

The reserves were estimated by about 1.45 million tons, but the Na-activation processes showed little success and most of the reserves were exhausted in the native sulfur purification process at the Mishraq sulfur mines.

On the other hand, the Late Maastrichtian – Danian phosphatic succession of the Iraqi Western Desert, include 5 to 6 smectite-rich shale beds, arranged in a transgressive cyclic sequences deposited in an open-subtidal reducing marine environment of the Maastrichtian Digma Formation (Safra Beds) and the Paleocene Akashat Formation (Traifawi Member, Danian).

The mineralogy is dominated by smectites, rich in montmorillonite, with subordinate kaolinite, quartz, calcite, apatite, pyrite, palygorskite, chalcedony, opal-CT and organic matter.

The dominant major chemical elements are Si, Al, Fe, Mg, Ti, Ca and P.

Trace elements, normalized to average shale show high anomalies of Cd, Mo, Cr, Zn, V, U and Ni.

The important factors controlling the mineral formation include intense chemical weathering in the source area, normal marine coupled with upwelling currents, precipitation of the authigenic phosphate-shale-silica facies association in a middle to outer system of shallow to deep marine environment within local inner to outer ramp semi-closed basin.

Geochemical indices reflect the chemical weathering of the source rocks, which included metamorphic, felsic with a great influx of mafic rocks, and older sedimentary rocks of the Arabian Shield.

Weathering, under warm and semi-humid climate, generated low lateritic pedogenic soils at the source area.

The reserves were estimated by about 300 million tons in the Digma Formation deposits and about 23 million tons in the Traifawi Member deposits.

The former is being mined for the past 25 years and used mainly as a drilling mud.