Iraqi Bulletin of Geology and Mining

The Iraqi territory is covered mainly by sedimentary rocks, Quaternary sediments and very rare igneous and metamorphic rocks. The sedimentary rocks are represented mainly by carbonates and clastics, with subordinate gypsum, marl and shale. The igneous rocks are represented mainly by gabbros, whereas the metamorphic rocks are represented mainly by serpentines.

In order to compile the lithological map of Iraq, the 89 exposed geological formations and units, and 18 types of Quaternary sediments are classified into 14 lithological units, depending on the main constituent of each geological formation and different types of Quaternary sediments, which appear on the Geological Map of Iraq at scale of 1: 100 000. Each lithological unit is given a certain color depending on its main lithological constituent.

Using GIS techniques, the exposed geological formations and Quaternary sediments that are presented on the Geological Map of Iraq at scale of 1: 1000 000 are assigned to 14 lithological units. However, on the Geological Map of Iraq, many formations are grouped together, age wise, due to scale limitation. This case is found only in the northern and northeastern parts of Iraq, which are mountainous areas, with intensely folded and thrusted strata, besides to the wide age range of the exposed formations, which extends from Precambrian to Pleistocene. In such cases, the lithology of the most predominant geological formation in the group is taken in consideration for assigning the group to a certain lithological unit. Moreover, the coverage area of each lithological unit is determined, also using ArcGIS software.

Thick succession of conglomeratic limestone (about 300 m thick) is exposed on right and left sides of Dokan reservoir and covers more than 40 Km2 of surface area. It called "Dokan Conglomerate" in this study, which is not described and shown on any geological map, previously. The Dokan conglomerate is indurate and weathering resistant, which mostly consists of blocks, boulders and gravels of Qamchuqa Formation, with some clasts of Kometan Formation, and at the upper part rare clasts of Pila Spi Formation can be observed. The conglomerate is folded and in some place has more than 30 degrees, and angularly overlies the Kolosh, Shiranish, Kometan formations with more than 20 degrees difference in dip. In other areas, the conglomerate shows, more or less equal dip with aforementioned formations.
The paleocurrent analysis revealed southwest, south, southeast direction for lower, middle and upper part of the conglomerate. From indicating the origin of the pebbles of the conglomerate, the succession should be younger than Upper Eocene, due to the presence of clasts of Pila Spi Formation (Upper Eocene). For finding the stratigraphic position and relation of the Dokan Conglomerate with other Tertiary unit, the surround areas were inspected. The inspection was concentrated to the south of Dokan area, toward which the paleocurrent is directed. To the southwest of Taq Taq Town, about 40 Km to the south of Dokan town, an equivalent of the conglomerate was found, which nearly consists of similar lithology, but with finer caliber and more rounded pebbles. This conglomerate is very similar to the Bai Hassan (Upper Bakhtiary) Formation, which according to previous studies is exposed in nearby area. Therefore, the Dokan Conglomerate is believed to be the equivalent of Bai Hassan Formation.

Fifteen samples of stream sediments were collected from the Lesser Zab River (LZR), which represent one of three major tributaries of the Tigris River at northeastern Iraq. The sediment samples were subjected to laboratory studies including chemical analyses (using polarized energy dispersive XRF) for major (SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, P2O5, TiO2 and MnO, in weight %) and trace (Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr and Zn in ppm) elements. These results have been used to characterize chemical weathering and transportation in the catchments area, to assess relative mobility of elements during weathering and to understand trace element associations. Correlation coefficients being significant for most of the major elements among themselves which suggests that concentrations of these elements are significantly controlled by Ferro manganese oxides-hydroxides, clay and carbonate mineral abundances during weathering and transported of Lesser Zab river sediments. Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW) and Index of Compositional Variation (ICV) for LZR sediments averages at (46%, 50% and 2.25 respectively), indicating that weathering in the basin is of moderate intensity. Comparison of the chemistry of sediments with the composition of source rocks and average Upper Continental Crust (UCC) suggests significant loss of most major elements from source rocks during weathering, the degree of loss being more for Na2O and K2O. Available results seem to indicate that Sr and Ba are effectively more mobile than other metals, which is thought to be a combined effect of higher solubility of Sr and Ba. Trace elements show higher concentrations in the river sediments and significant positive correlation with themselves (exception Cr) and with Al2O3, Fe2O3 and MnO. These observations suggest that trace element concentrations are also controlled mainly by clay mineral abundances and those of Fe-Mn oxides. Cr shows significant positive correlation with SiO2 which indicates to diffusion of Cr from chromite margin toward the silicate matrix during alteration of chromites and metamorphism, resulted in the development of ferrit-chromite and chlorite. Observed higher Al2O3 concentrations and its strong association with trace elements in LZR sediments would indicate to preponderance of clay minerals over K-bearing minerals such as K-feldspars and micas. Hence, the sediments of the LZR are mainly enriched in clays in comparison with rock forming minerals. Enrichment factor and geo-accumulation index calculated for trace elements in LZR sediments suggest that they are mainly of natural origin and that anthropogenic activities exert little influence on their abundances.

Mineral characterization of samples collected from the upper part of Sargelu Formation at Rania area was carried out using the XRD and XRF techniques. The obtained results from this study show the presence of quartz, in well crystalline structure. The crystalline nature of quartz is studied by description and measurement of crystal axis and the forms of the quartz crystals. The results obtained show that these crystals are trigonal, type: α-quartz, with crystal forms of rhombohedron, trigonal dipyramid, and trigonal prism.
Geochemical analyses for both host rock and quartz crystals carried out using XRF instrument. The host rock is mainly composed of CaO and MgO, indicating dolomitic rocks, while the quartz crystals show the presence of traces of Al, Fe, Mg and Ca oxides accompanying the major component SiO2.

The genesis of this well crystalline α-quartz was related to chemical precipitation from deeper groundwater supersaturated within silica, and the source of silica possibly from dissolution of radiolarians, either within chert layers or in adjacent limestone beds of Sargelu Formation.

Stylolites of the Kometan Formation are genetically studied and classified in this paper. Mineralogy and chemistry of the stylolite-seam residual deposits were investigated. Mass and thickness reduction of the limestone, due to pressure-solution, were estimated by geometric and chemical criteria methods.
Sedimentary stylolites and younger tectonic stylolites were identified, in addition to several mesoscopic, younger reverse and normal faults, and different types and sets of veins with various age relationships relative to the stylolites. Residual deposits of the stylolite seams are composed of quartz, orthoclase, illite and glauconite. Diagenetic cementation by calcite, pyrite and bitumen is abundant, whereas chert and pyrite nodules are common along the stylolite seams. The least mobilized elements during stylolitization are Ti, Al and K, followed by Fe, Si, Cr and U, whereas Ca, Na, Mg, Mn and Ni are mostly mobilized.
Limestone mass reduction due to pressure solution was estimated in the studied section using chemical criteria, by about 5%, whereas limestone thickness shortening was estimated by about 15 cm / one cm stylolite seam thickness using two independent means: (1) geometric methods and (2) chemical and bulk density parameters. The difference in the estimated values is negligible despite the significant variation in the seam thickness and bulk density of the residual deposits as well as the uncertainty of the exact age relationship between the stylolite seams and the segmented cross-cutting veins.

The Penjween serpentinized peridotites occupy parts of the southern Zagros Suture Zone displaying pseudomorphic and non-pseudomorphic micro-textures, in addition to different types of vein serpentine formation. Serpentinization is accompanied by abundant veining marked by generations of vein-filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation. The author have selected a representative set of veins from serpentinized peridotite of Penjween ophiolite from different localities and studied them in detail for their microstructures by coupling optical and scanning electron microscopy (SEM) with Back-Scattered electron (BSE) images. Four main veining episodes (V1 to V4) accompany the serpentinization of the oceanic lithosphere of the Penjween serpentinite peridotites. Serpentine microstructures and mineral composition of veins provide information on the relative rates of crack opening, vein mineral precipitation, the crystallization conditions, and the temporal evolution of alteration. The first episode represents vein generation V1 and is interpreted as tectonically controlled penetration of early seawater-dominated fluid within peridotites, enhancing thermal cracking and mesh texture formation. The second episode marks two subsequent vein types (V2 and V3) formed in a closed, diffusive system and accommodated volume expansion required to reach serpentinization of the protolith (Stage 1). The last vein episode (V4) records instead an open hydrothermal system, where brittle fracturing and advective transfer dominated and enabled the completion of serpentinization (Stage 2). These results show a complete history of alteration, with the crystallization of different types of serpentine recording different tectonic events and modes of hydrothermal alteration of the Tethys oceanic lithosphere.

This research deals with the hydrochemistry of groundwater in western part of Karbala city, which is located in the Mesopotamian plain, 100 Km southwest of Baghdad. The geological formations outcrop in Karbala city are, Injana, Dibdibba and Quaternary sediments. The climate is characterized as being continental, dry, and relatively hot in summer, cold and little rain in winter. The movement of groundwater is toward the center of the city in two directions. Water samples were analyzed to determine the major anions and cations, in addition to the heavy metals measurements that prove the contamination of groundwater by Al and Zn. The type of water in this area was believed to be of chloride and sulphatic and the water classification according to TDS quantity is brackish water. The groundwater is not suitable for any uses except some limited use in agriculture and live stocks.

The ground-penetrating radar survey (GPR) has been conducted to detect some grave markers in a cemetery location. This was done through measuring seven profiles that range in length from (30 – 100) m. The results of only three profiles were found to deserve analysis. It was revealed that external effects were associated with the GPR anomalies in the studied area. Precautions were taken into consideration before the measurements and during the interpretation process. Reflex software was used to distinguish and process the GPR anomalies.
It was found during the excavation process that those anomalies are not related to buried bodies. It is most probably due to the soil condition of the studied area. However, it was a good chance to identify those anomalies, especially; that the excavation was performed instantly in the area.