Palygorskite, Chlorite and Illite Minerals in the Dukhan Sabkha Deposits, Qatar

Abstract

The clay samples were studied using X-ray diffraction. The range of the run was between 2°and 40° and the run was 1.2°/min. Electronic Microscope also used in the study by using great magnification range from X20 up to 1000,000 to allow to examination the surfaces of fine grains and to takes photographs with great focus. Chemical analyses also carried out under the SEM, using energy-dispersive X-ray spectrometry to define their dominant elements. From the study, it emerged that the dominant clay minerals in the samples are palygorskite, followed by chlorite and illite. Based on the peak area measurements, the mean percentage of palygorskite in the clay deposits included dolomite and anhydrite is 59% (approximate percentage is 34%-79%). It is 23% for chlorite (approximate percentage is 7%-40%) and 9% for illite (approximate percentage is 4%-13%). After excluded dolomite and anhydrite from the samples, it is 65% for palygorskite (approximate percentage is 47%-85%), 25% for chlorite (approximate percentage is 8%-40%) and 10% for illite (approximate percentage is 6%-15%). Through EDX analyses of the palygorskite needles it was inferred that the P is the dominant element, followed by Si, Mg, Al, Ca, and K. Phosphate nodules of a globular shape (spherulites) in various sizes (1-<2 μ) also occur in most of the clay samples, especially that rich in palygorskite. In some samples, the phosphate nodules were present in small groups connected together as bunches.The main conclusion of this study are:(1) In Dukhan Sabkha, clay-rich deposits are mainly found beside the edges of the Sabkha, especially where the Sabkha is supplied with surface drainage. Later the wind contributes in distribution part of these sediments within the Sabkha. The thickness of clay-rich layers in such as these locations is between 0.5 and 1.5 cm.(2) Palygorskite is mainly authigenic, formed inside the Dukhan Sabkha. This is because the conditions of formation this mineral within the Sabkha are widely available. Part of palygorskite is definitely detrital being, derived from shales of the Lower and Upper Dammam Formation of the Eocene age that exposed on the surface of Qatar. A small proportion of this mineral could also reach to inside Dukhan Sabkha after carried to Qatar as dust by the northern wind or by water currents from the neighboring areas, especially from the eastern part of the Arabian Peninsula.(3) Chlorite and illite minerals are not form locally inside the Dukhan Sabkha; both of them are from pre-existing sedimentary rocks from outside the Sabkha. The main source of these two minerals is a detrital rocks derived from shales of the Tertiary of the Lower Dammam Formation and Rus Formation of Eocene age in addition to Dam Formation of Miocene age in Qatar and part of these minerals may reached to inside the Sabkha from outside Qatar.(4) This work can be used as model for the study the possibility of formation palygorskite within the Sabkhas areas in Qatar and in the Arabian Gulf areas.