Fluvial sediments are sourced from the exposed rocks, among these, the crystalline rocks, which are influenced by streams under surface conditions. Other fluvial sediments origins are from soils which pass the mineralogical composition from the source rock and/or alter them, and new mineral faces could form  . Sediments include different grain sizes (i.e. coarse sandstone to colloidal grains). Thus, studying resent sediments offer insight on the physiochemical and environmental regimes in shallow marine and fluvial conditions which are influenced greatly by the changes of earth and human activities   , and therefore, sediments are used, usually, as pollution monitor in different aquatic regimes. On the other hand, colloidal grains are greatly influenced by various parameters and thus hardly to provide accurate analysis results. While fine grain sediments are less influenced and therefore used frequently as chemical and biochemical pollution indicators  .
Moreover, fluvial sediments, in comparison, represent the main heavy metals settling agent in water systems and those heavy metals are not washed out from the system; instead it could be induced within the water and sediments storage by various biological and chemical processes    . Thereafter, heavy metals, of various origins, main source of enrichments in water systems are through rock and soil erosion in fine grain sediments     .
Additionally, tiny size sediments (i.e. clay size) are the main size fraction used by researchers to determine heavy metals concentrations which are related in part to their mobility   . Furthermore, heavy metals are adsorbed on negative charge surfaces such as clay minerals, organic materials and other oxides, within insoluble organic and inorganic bond form, in the aquatic regimes by several human activities   . This study aims to identify clay minerals assemblages and their relationship with the heavy metals distribution and origins within the Lesser Zab river (LZR) sediments.
2. Geological Setting
The regional geology of northern Iraq consists of the Zagros Mountains Range with an NW-SE structural trend in the north-eastern part, and Taurus mountain Range with an E-W structural trend in the north and northwestern parts. The structural framework of Iraq was divided by  into Thrust Zone, Folded Zone and Unfolded Zone (Figure 1).
The LZR and its tributaries traverse the Zagros Suture and the Unstable Shelf tectonic zones of northeastern Iraq. The Zagros Suture Zone which is shared between Iran and Iraq consists dominantly of igneous and metamorphic rocks belonging to Shalair, Penjween-Walash and Qulqula-Khwaqurk Zones  . The unstable shelf is dominated by sedimentary rock formations which are parts of three tectonic zones; Imbricated, high folded and foothill zones. It is important to know the general lithological characteristic of the rock units and formations which form the bed rock of the LZR and its tributaries because of these bed rocks make the source of water and recent sediments.
Figure 1. Location map showing sediment sampling locations in the LZR (after Ali, 2012).
The LZR traverses many tectonic and rock units belonging to the Unstable shelf which were divided by  in to four divisions: Zagros suture zones including (Penjween-Walash zone), imbricated zone (Balambo-Tanjero zone), High folded zone and Foot hill zone (Hamrin-Makhul sub zone). Tectonically, the study area extends from highly Folded Zone of the Foreland Basin into the foreland and related basins, as well as the platform region of the Arabian Plate (Figure 2). According to  the folded zone contains three tectonic zones which are, from west to east: the Mesopotamian zone (Quaternary molasses and buried structures), the Foothill zone (Neogene molasses and long anticlinal structures separated by broad synclines), and High Folded zone (Paleogene molasses and harmonic folded structures). These longitudinal tectonic zones are segmented into blocks bounded by ENE-WSW (shifting to NE-SW) transverse faults with both vertical and horizontal displacement. The transverse blocks have been active, at least, since the late Cretaceous and greatly influenced the sedimentary facies of the Cretaceous and Tertiary sequences  . Structurally, the studied area (Lesser Zab River) lies in the Foothill and high Folded zones of the platform foreland of Iraq as shown in Figure 2  .
The LZR is situated between 360˚00'23.67'' - 350˚41'14.9'' North and 450˚14'29.75'' - 440˚03'35.4'' East. The elevation ranges between 230 and 631 m above sea level. The LZR travels 400 km until its junction with the Tigris River at 35 km southwest Sharqat city and its catchment covers an area of 22,250 km2 (Figure 3)  . The river in the study area passes through many villages, towns and agricultural lands where possible man-made pollution sources could affect its water quality, in addition to the natural pollution causes such as spring waters, erosion and weathering of outcrops, etc.  . River collects its water from
Figure 2. The bar shape illustrates the relationship between type of sediment and the percentages for each type.
Figure 3. X-ray Diffraction pattern showing the main detected minerals of studied bulk sample.
the northeast drainage area. Lesser river is sourced from the Zagros suture zone are in N-NE Iraq and then merge with other rivers in Tigris River to the SW of the area.
3. Material and Methods
Fifteen recent sediment samples were collected from the lesser Zab Main stream (Figure 3) located in the north-eastern of Iraq during April 2009. About 2 - 4 kg of sediments were collected manually from the main stream in contact with running water using a metal bucket of the dimensions 26 × 8 × 3 cm3. Sampling was performed at distance from the river banks to avoid possible contamination from the bank material. Details of the analysis techniques are given in   .
The samples were sun-dried and then ground into fine powder in an agate mortar. The samples were sieved to pass through of 200 µm, and then pressed into thick pellets of 32 mm diameter using wax as blinder. USGS standards, GEOL, GBW 7109 and GBW-7309 sediment equally pressed into pellets in an equivalent manner as the samples, and these used for quality assurance   . Multi-element concentration was determined by using polarized energy dispersive XRF. The PEDXRF analysis was carried out at the Earth Sciences Research and Application Center of Ankara University, TURKEY using Spectro XLAB 2000 PEDXRF spectrometer and following  .
Grain size analysis is carried out to separate sand from the silt and clay using sieve (0.063 mm, 230 meshes) by wet sieving. The silt and clay fractions downward from (230 mesh) sieve were separated using sedimentation tube method according to   . The statistical parameters of the grains were calculated using the equations proposed by  .
Mineralogical characteristics of the samples were determined by using X-ray diffraction analysis, type P analytical Xpert PRO MPD with Ni-filtered and CuK α radiation, for diagnosis and assessment of mineral components as well as identifying the type of clay minerals in the isolated clayey size (<2 μm). Both randomly oriented powder and slide samples were prepared following the procedure described by   . They were scanned over the range from 5˚ to 40˚ 2θ at a scanning speed 2˚ 2 θ/min. The oriented slides were analyzed in various stages (non-treated, treated by Glycol ethylene at 60˚C/2 hr. to distinguish the expandable mineral phases, the slides were heated at 550˚C/2 hr. for chlorite detection). All minerals basal reflection peaks were identified according to ASTM cards  . The semi quantitative determination of the relative amounts of major clay minerals was calculated by using analytical Xpert High Score software depending up on specific reflections and intensity factors.
4. Results and Discussion
4.1. Sediment Grain Size and Mineralogical Analysis
The results of the grain size analysis and textural composition of the studied sediment samples are given in Table 1 and Figure 2, which provide the percentages of the sediments components of sand, silt and clay. The results indicate clearly decrease in the sand percentage from 80% to 1% with an average of 22.7%, while the silt portion was high in all sites (i.e. 12% - 87% with an average
Table 1. Results of the grain size analysis and the common texture of the LZR sediments following Carver, 1971.
of 51.8%). The quantity of clays was relatively less than silt, and ranges between 5% to 48% (25.5% in average), and its percentage declines inversely to the silt portions. According to  classification, most of the studied recent LZR sediments can be classified as clayey silt and silty sand types which compose of 66.67% and 20.0% respectively of the studied samples (Figure 2). This indicates that the fluctuation in the relative variation of the grain size distribution within the studied sediments because of the local contrast in the hydrological conditions, like stream speed, energy of transportation and geological, geomorphological and climatic natures that influenced sediments properties  .
Moreover, XRD patterns of the oriented and non-oriented slides which are obtained under different measurement conditions, as shown in Figure 3 and Figure 4, reveals the existence of clay and non-clay minerals contents. Non-clay minerals are represented by quartz that appeared at the basal reflections 3.34, 4.26, 2.46, 2.28 Å, calcite 3.04 Å, dolomite 2.89 Å and feldspar 3.2 Å; whereas clay minerals includes; kaolinite that appeared at the basal reflections 7.16, 3.57 Å, illite 10, 5 Å, chlorite 14, 7.1, 3.53 Å, palygorskite 10.5, 6.5 Å and smectite 13 - 15 Å (Figure 4).
Clay mineral assemblages consist mainly of palygorskite (32.94% - 40.44%) with an average of (37.20%), kaolinite (22.53% - 26.14%) and illite (21.92% - 26.17%) are in lesser abundance with averages of (24.55% and 24.11%), respectively. Whereas chlorite (14.05% - 23.74%) and smectite (11.89% - 16.57%) are frequently presented in small quantities in all studied sediment samples with averages of 19.07% and 14.15% respectively (Table 2). The recorded clay minerals in the recent LZR sediments are coincided with previous works within older rock units and as suggested by   . This suggests that these sediments are inherited from other source rocks exposed in the catchment drainage basin of LZR. Thus, major transformation was not observed in these sediments except for new formation of palygorskite from the transformation layer of smectite, since the minerals pair exhibit good negative correlation (−0.598) in the LZR sediments.
4.2. Heavy Metal Concentrations in Clay Fractions
The concentrations of heavy metals (i.e. Co, Cr, Cu, Ni, Ba, Pb, Rb, Zn, V and Ga) and major elements (Al2O3, Fe2O3 and MnO) within clay fraction (<2 μm) sediments and their portioning in the Lesser Zab stream are provided in (Table 3) and (Figure 5). Statistical parameters of the data (arithmetic mean, maximum and minimum value, standard deviation and coefficient of variation) were calculated to observe general variability in the LZR sediment chemistry (Table 3). The concentrations of trace elements generally vary by 5% to 27% for the LZR. Coefficient of variation (C.V.) is maximum (20% - 27%) for Co, Rb and Zn, (16% - 20%) for Pb and Cu, (10% - 15%) for Cr and Ga, and is within <10% for other elements (Table 3).
The average contents of Al2O3, Fe2O3 and MnO are about 9.98%, 6.27% and
Figure 4. X-ray Diffraction pattern from clay minerals of studied clay fraction sample. (A) Normal Sample (without treatments); (b) Sample; (c) Heated to 350˚C; (d) Heated to 550˚C.
0.086% respectively; the source of these oxides is mostly clay minerals as well as contributions from silica-rich minerals such as quartz and feldspar.  -  illustrated that the concentrations of Fe2O3 and MnO of the LZR sediments are significantly controlled by ferro manganese oxides-hydroxides, clay and carbonate minerals abundances that are progressively diluted by quartz content.
In addition to the major elements described above, ten trace elements (Co, Cr, Cu, Ni, Ba, Pb, Rb, Zn, V and Ga) analyzed in the in the clay fraction samples collected from LZR sediments (Table 4). The relationship between major and
Table 2. Estimation of clay mineral constituents of LZR sediment samples.
Figure 5. Heavy metal concentrations within the clay size sediments, Lesser Zab River.
heavy metals is listed in Table 4 and shown in Figures 6-8. The distribution of (Co, Ni, Ba, Pb, Rb, Zn and Ga) and somewhat (Cr, V and Cu) shows significant positive correlation among themselves and major (Al2O3, Fe2O3 and MnO)
Table 3. Elements Concentration of LZR Sediments
Table 4. Correlation coefficients for the selected variables; oxides, trace elements and sediments size fractions.
Figure 6. The relationship between Al2O3 and other elements in the studied samples.
oxides in the clay fraction, suggesting that a common mechanism regulates their abundance. Thus, suggest that these element concentrations are controlled mainly by Al-rich phases such as clay mineral abundances and Fe-Mg, Fe-Mn oxides  .
Moreover, Co, Ni and Cu sourced from clay minerals while Zn could be sourced from the ferromagnesian heavy minerals such as amphiboles, pyroxenes etc.  as it is common with LZR and older sediments   .  indicates that Co has moderate mobility controlled mainly by adsorption and co-precipitation with Mn-Fe oxides. Ba and Rb are usually associated with feldspar and biotite  and clay minerals  . In addition, lead (Pb) is generally adsorbed on iron oxide minerals while Rb with feldspar and mica  . Also, copper has intermediate mobility controlled by adsorption of Fe and Mn-oxides and organic matters; it is closely associated with geogenic (lithogenic) materials
Figure 7. The relationship between Fe2O3 and other elements in the studied samples.
and exists in ultrabasic ophiolitic rocks  . Increasing heavy metal concentration in clay fraction of LZR sediments could be related to the adsorption on fine grain sediments. Thus, heavy metals portioning would essentially be influenced by clay content which in turn contributes significantly to the accumulation of heavy metals in the LZR sediments.
4.3. Principal Component Analysis (PCA)-Factor Analysis
PCA is used to determine the interaction between the measured independent properties. The principal component analysis has been widely applied in the interpretation of the geochemical and hydrogeochemical data    . It is one of the multivariate statistical analytical tools used to assess metal behavior in sediments and water  . Also, PCA is an approach to find the most crucial factors that describe the natural influence with eigenvalues ≥ 1.0  . According
Figure 8. The relationship between MnO and other elements in the studied samples.
to  the factor loadings were classified as “excellent”, “very good”, “ good” and “fair”, as the absolute loading values of (>0.71), (0.71 - 0.63), (0.63 - 0.55) and (0.55 - 0.45) respectively. For factor loadings, the loading was defined as excellent and very good and loadings of (<0.63) were considered insignificant, and some of the factors not explained because contain loading fair lower than (0.55). Factor analysis allows us to group the elements with similar distribution.
In this study, three factors have been observed for LZR sediments, and components account for (81.915%) of the total variation in the system, (the first component accounts for 60.119% of the variation, the second 13.616% and the third accounts for only 8.180%) (Table 5, Figure 9). Thus, three components reflect the relation between the measured variables.
The first factor is explained 60.119% of the variation in the system and it is very important because influenced by (Cu, Co, Zn, Rb, Ba, Pb, Ga) and clay fractions. This factor considered fine clay particles factor, which shows the fine
Table 5. Characteristic Rotated (R-Mode) factor loading matrix for all (15) variables from the geochemical composition of LZR sediments.
Figure 9. Principal component factor analysis loading two-dimension plots for sixteen variables.
grains influence on the enrichments of the heavy metals contents. Also, the existence of Fe2O, MnO and Al2O3 in this factor indicated the influence of Fe-Mn oxides-hydroxide phase and clay minerals to enrich the heavy metals contents within the LZR sediments.  illustrated that these element concentrations are controlled mainly by clay mineral abundances and Fe-Mg, Fe-Mn oxides. The second factor has 13.616% of total variance and affected by (Cr, Ni) and silt fractions. This factor considered independent fine minerals particles factor.
While Ni and Cr exist in the solid components of weathering productions  , also substitution of Fe location by Ni in to the Fe-rich (goethite and hematite) minerals  . Also, the most abundant independent mineral is usually chromite which is resistant to the weathering, with heavy minerals (i.e. tourmaline, rutile, hornblende and magnetite)    which can exist in siliciclastic rocks in various grain sizes from sand to clay. Thus, Cr and Ni richness in the silt fraction of LZR sediments represented by the third factor.
Grain size distributions and textural composition indicate that these sediments are mainly characterized as clayey silt and silty sand as texture. This indicates that the fluctuation in the relative variation of the grain size distribution of the study sediments is because of the local contrast in the hydrological conditions such as stream speed, energy of transportation and geological, geomorphological and climatic natures that influenced these sediments properties.
The clay mineral assemblages in the LZR sediments consist mainly of palygorskite, kaolinite, illite, chlorite and smectite, following previous works, which reveals that these sediments were derived from rocks of similar mineralogical and chemical composition and that heavy metals portioning is linked to the tiny grain size amount.
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