The MINERALOGY, GEOCHEMISTRY AND THE ORIGIN OF LOWER CLASTIC UNIT IN HUSSAINIYAT FORMATION-WESTERN DESERT OF IRAQ
The origin of lower clastic unit in Hussainiyat Formation
A mineralogical and geochemical study has been done on (20) samples of Hussainiyat Formation (L. Jurassic) in western Iraq. Mineralogical analysis of clays by X-ray diffraction (XRD) shows that the predominant clay mineral is Kaolinite and traces of montmorillonite-illite mixed layer with palygorskite are also found. The non- clay minerals are mostly quartz, goethite, hematite and anatase. Heavy minerals were separated from (clastic) samples and studied by both polarized and reflected microscope. These heavy minerals are detected in fewer than 1% quantities. The most common are silicates and oxides. The most common of these mineral grains are zircon, rutile, tourmaline, apatite, staurolite and garnet. For geochemical study by XRF, samples were analyzed for SiO2, Al2O3, TiO2, Fe2O3, MgO, CaO, Na2O, K2O, MnO, P2O5 and L.O.I. Kaolinite of Hussainiyat contains a high concentration of iron which is interbedded with kaolinite as hematite, goethite and limonite. Manganese is associated with kaolinite of Hussainiyat due to its high iron content. The presence of heavy minerals that are resistant to corrosion, such as zircon and anatase indicates that the acidic granite rocks with almost metamorphic rocks were a source of kaolinite.
The present study showed that the kaolinite deposits within Hussainiyat Formation less mature than other clays (montmorillonite-illite mixed layer and palygorskite), because Hussainiyat suffered from less intense chemical weathering, leading to the dissolution of only alkalis and earth alkali metals but not iron. The alumina is still stable with little silica to form kaolinite due to their high resistance.