The effect of grain size on the distribution and fractionation of the major chemical trace and rare earth elements in shale, silt and sand rocks of the Muqdadia formation in north of Iraq

(17) samples were collected from Muqdadia formation from various areas in Erbil governorate and Aqra district north of Iraq, which were represented by the sections (A, B, D, R, W). (10) samples were used in analyzing the element using Plasma–Mass Spectrometry (ICP–MS) Analysis and the Inductive Couple Plasma–Mass Spectrometry (ICP–MS) Analysis for four granule sizes after these granules were separated from each sample. The elements included were Al, Fe, Mg, Ca, Na, K, Ti, P, Rb, Cs, Sr, Ba, Au, Mo, Pb, Cu, Zn, As, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Cr, Ni, Co, Mn, Sc, V, Zr, Hf, Ta, Nb, Th, U, Ga, La, Dy, Ho, Er, Tm, Yb, Lu, Y. The geochemical study revealed that there is no significant variation in the content of the main, trace and rare earth elements in the four sizes of shale, silt, fine sand and coarse sand. Also, it was found that the sizes of silt and fine sand contain the highest portion of the trace elements and the rare earth element. It was also, noticed that the patterns of the rare earth elements in the granule sizes are similar in general with some differences, as these differences were reflected in some changes in the portions of these elements. In general, it was observed that the total content of the rare earth elements in the various sizes is relatively small and this might be due to two main factors; the high decrease by calcite (calcium carbonate) and the free silica (quartz) and the other reason is that the mineral that contain REEs are mostly derived from rock sources (mafic or ultra-mafic), which contain these elements with low concentrations. Patterns of REE in the study samples and the four sizes are similar to the pattern of (PAAS) with slight differences like the presence of LREE and on a lower level in HREE and also the presence of negative anomaly Ce*/Ce in the size of shale, silt, fine sand and coarse sand. Although there are variations in the values of anomaly Eu* /Eu, the values are not far from the acceptable PAAS values and they are, generally, higher than PAAS due to the presence of the mafic and ultra-mafic component in the sediments of the current study. In all the sizes, except the shale size, it was found that ∑ REE varies and increases with the increase of the contents of Al2O3 and Fe2O3. As for the shale size, it was found that the relationship between REE∑, Mn and P2O5 is negative and this is because the shale were sedimented in river environments that don’t permit them to absorb sufficient amounts of REE as is the case with the shale that are sedimented in sea environments where there is a direct contact with the seawater that although contains slight concentrations of REE but they are effective when they are adsorbed on shale particularly when the average sedimentation of the shale is low. But in the current study, the shale is river sediments and the river contains insignificant concentrations of REE and the sediment in the river is faster compared to the sea environment and this case doesn’t permit the shale to adsorb large portions of REE.


Introduction
It is known that transferring and sedimenting the clastic sediments require mechanical sorting and it impact on the chemical construction of the lime sediments is considered an important aspect and might influence the distribution of the old aeration elements and the source rocks ]8,19[.The chemical components are distributed basically inside the group through the mechanical properties of the host minerals.The process, basically, divides Al 2 O 3 (shale minerals) from SiO 2 (quartz and feldspar) from the zirconium.Also, the fractioning divides TiO 2 that exists in the shale minerals and Ti oxides from the zirconium that is present in the zirconium and sorting it with the quartz.However, the variable content of the inactive elements in the clay stone is due to the level of aeration that affects the mother rocks.
Therefore, the chemical structure of the clastic sedimental rocks is considered very important as it reflects the impact of the aforementioned geological elements on the source rocks throughout the time because some elements are transferred quantitatively by the erosion and sediment from the mother rocks into the clastic elements ]29[and these elements include the rare earth elements (REE) as the distribution of these elements is not affected by the sedimental processes ]25,30[ as it was clear that shale and silt which are derived from the granite rocks include concentrations of the rare earth elements (REE) and their patterns and negative irregular sizes that are more similar to the granite source rocks compared to the sizes of the sand and gravel.
Although there is no direct relationship between the abundance of REE and the clay minerals, seral studies like ]12,28,29[ concluded that the total content REE is kept in the part of the siltshale.the rare earth elements are either absorbed on the external surfaces or as exchangeable cataions inside the crystal structure of the shale and silt and this makes them contain a structure of elements that is similar to the rocks of the source.On the contrary, the sand and gravel sizes are rich with quartz and feldspar, which contain low concentrations of rare earth elements (REE) and they always lack the mafic minerals relative to the source rocks and consequently the REE are less in them than the source rocks and the size of the negative anomaly Eu is lower due to the accumulation of the blageocals feldspar ] 21[Consequently, it is important to mention that the important elements in decreasing the rare earth elements (REE) is the carbonate phase and the silica-quartz phase.As for the physical experiment, it is IOP Publishing doi:10.1088/1755-1315/1300/1/0120173 characterized with the demolition and destruction of the rocks and they are many and various like the processes of heating, cooling, freezing and melting... etc. and eventually it prepares the rocks to be more convenient to the processes of the subsequent chemical aeration especially in the wet areas and it is also important in the dry or the very cold areas .The sediments that result from these processes either sediment within the same sedimental basin (intera basinal) or transferred by the various factors like the wind, surface water, glacial, earth gravity (extra basinal).So, the transference and sedimentation of the clastic sediments are connected with the sorting mechanism that affects the chemical structure of the ground sediments ]9, 20[.Several studies demonstrated that, during the aeration processes and the occurrence of sorting, the trace elements components in the very fine sizes that are represented by shale increase [ 42 ] , when he took a series of (sand, silt and shale), he found that elements like (Rb, Cs and Bi) are of high contents in the shale rocks.
In this study, a comparison will be made concerning the distribution of the main trace elements and the rare earth elements in the granular sizes of the clastic sediments that are present in the outcrobe and identifying the extent of the granular size on the distribution of these elements.

The tectonic setting and the geology of the area
One of the most important formations that can explain the size distribution and its impact on elements distribution is Muqdadiya Formation (Formerly Lower Bakhtiar).This formation was first described in Iran by [10].they gave it an ideal section in Agha Jeyari oil field in the south of Iran ]8[and this formation extends to the north of Iraq.This formation was divided into two parts; lower and higher the Bakhtiari [ 9 ] and these names were changed in

Map (1): geological map of Muqdadiya formation [ 3 ]
The first area of the study (Aqra) is located within Aqra fold in Aqra district/ Nineveh governorate and it is about 100 kilometers northeast of Mosul city.It extends within the to the east.According to the classification of it is located within the unstable shelf that is located with the high folded zones.From the other hand, the classification of demonstrates that this area is located with the high folded zone of Forland basin, which is asymmetric fold with two sub-surfaces, its southern extreme is inversed and therefore, it is

Methodology
The field work involves all the rock samples of Muqdadiya Formation (Lower Bakhtiari), five sections, three of which are in Aqra district and the other two are from Erbil governorate.A number of samples were selected from each section to represent the subject of the current study.Three samples were selected from the first section, which are: (1A, 2A and 3A), which is located on the northern wing of Bordarsht structure, five samples from the second section (1B, 2B, 3B, 4B and 5B), which is located on the extension of the first section.
From the other hand, four samples were taken from the third section (1D, D2, D3 and D4), which is located in Gali Zanta, seven samples were taken from the fourth section (1R, 2R, 3R, 4R, 5R, 6R and 7R) which is located on the southern west sinking area of Bermam Dagh fold.
In the modeling process, the field changes that are characterized with the variation of the rocks were taken into consideration.Also, obtaining clean samples that were not subjected to the atmospheric effects were adhered by taking them after digging for 10-20 centimeters.
Sieving was conducted for 10 sand samples by the dry sieving method using the mechanical shaker with various-diameter sieves according to [ 85 ] .Five hundred (500) grams of each sample was taken and sieved to get various sizes (coarse sand, fine sand and silt) according to the requirements of the current study.
The content of the main and trace elements was determined in Acme laboratory in Vancouver,Canada through using the Inductive Couple Plasma-Mass Spectrometry (ICP-MS) Analysis and the Inductive Couple Plasma-Mass Spectrometry (ICP-MS) Analysis.

Results
The geochemical study involved the analysis of the main elements, trace elements, the rare earth elements and studying the rocks contents in terms of the abundance and distribution of the main and trace elements and the variation in their concentrations in the various sections mentioned above and for the various granule sizes (coarse sand, fine sand, silt and shale) based on the geochemical data.When splitting the granular sizes of the samples, it is observed, in general, that silica is concentrated in the coarse sizes that are represented by the coarse and the fine sand.So, the sand contains a larger portion of silica compared to shale .Although the content of silica decreases with the decrease of the granular size [ 1 ] , but the content in the shale content is affected greatly by the presence of the shale minerals and their portions in the sample.
In general, it is observed that the content of Al 2 O 3 increases in the fine sizes.When observing the particles of the sand, it is clear that silt contains the highest percentage of Al 2 O 3 (9.9%)and it is also noticed that the content of Al 2 O 3 in shale (8.8%) is high also compared to the rest of the sizes.Therefore, the increase of aluminum is an indicator of the effect of shale minerals that contain this phase.The content of Al 2 O 3 can be related to CaO as they are negatively correlated as Ca is considered one of the mobile minerals and consequently the aeration processes leads to their depletion [ 84 ] .Also, the content of K 2 O can be related to the content of Al 2 O 3 in the shale size because some shale minerals contain K 2 O in their atomic structure such as the Illite.
As for the minerals, the content of the carbonate is characterized by the CaO content, which, in turn, influences the contents of the main and trace elements in the mineral system of with CaO and this is evident when the content of these oxides in the various granular sizes is observed.For instance, the lowest content of CaO in the coarse sand size (17.356%) and the lowest content of TiO 2 in the same size is (0.415%).As for the trace elements, its effect on their content is variant depending on the relationship of these elements with the rest of the oxides.The lowest content of aluminium oxide is in the coarse sand and the average contents of aluminium oxide in the rest of the sizes are (20.684%,19.761% and 19.792%) in shale, silt and fine sand respectively.
From the other hand, it is observed that the content of Fe 2 O 3 increases with the fine sizes as the highest content of Fe 2 O 3 in shale is 5%, while the content decreases in the coarser sizes (3.21%, 3,84% and 4.32%) in C. F. S. respectively.The increase of MgO content is with the shale size with the mineral content for the shale minerals like the chlorite, smectites and baliogorscite in the shale size.Also, the content of Na 2 O in the granule sizes is dependent on the mineral content especially feldspar plagioclase and the degree of maturity of granular clast for each size and as the degree of maturity of the clasts of silt, coarse sand and fine sand low or medium, then the Na content is higher than the size of the shale.From the other hand there was a variation in the K 2 O content in the different sizes of the granules; (1.41%) in the coarse sand, (1.06%) in the fine sand and (1.32%) in shale.So, it is noticed that the K 2 O content follows the behavior of Al 2 O 3 in the sizes in a good manner and this denotes its presence in the earth clast such as potassium feldspar or the minerals that include the potassium like the biotite and muscovite and the results of their aeration.Also, it is included in the crystal net of the illite and it is adsorbed on the surfaces of the shale minerals.It is noticed that there is an increase in the Titanium oxide content towards the shale.Although this increase is slight, but it is attributed to the low mobility of TiO 2 during the aeration of the source rocks and during the transporting as well.There is a gradual increase in the content of P 2 O 5 towards the fine sizes as its content is (0.08%) in the coarse sand is, (0.09%) in the fine sand, (0.12%) in silt and (0.11%) in shale.The reason behind that increase in these sizes might be due to the presence of phosphorus in the abietite or due to the replacement of the phosphate root for the aluminum and silica in the minerals of the shale.From the data, it is observed that manganese that manganese behavior is very similar to titanium behavior, and the reason might be due to the fact that this element has low mobility and so it is resistant to aeration.The two elements Rb and Cs are similar in the chemical properties due to the similarity of their radii and their electrical charge.When observing the four granule sizes of the coarse sand, fine sand, silt and shale, it is evident that the highest contents of Rb and Cs are in the size of the shale.Moreover, the highest content of Sr is in the size of the fine sand and this is due to the high content of Ca in this size and mainly with the calcite and plagioclase feldspar.
The content of barium is variant in the four granule sizes.The variation is slight as it is (260 ppm) in the coarse sand, (262 ppm) in the fine sand, (299.4 ppm) in silt and (279.14 ppm) in shale.The ionic radius of Ba (1.44A°) and therefore it can replace the potassium and consequently it is present in potassium feldspars and the carbonate minerals, but the geochemical behaviour of Ba in the sediment circle is considered more complicated due to its potential of sedimenting it in the form of barium sulfurite (Barite BaSO 4 ).
From the other hand, when observing the four granules sizes (coarse sand, fine sand, silt and shale), it is clear that the highest contents of Rb and Cs are in the shale size (Cs 2.7 ppm) and (Rb 44.82 ppm) It is observed that the highest content of Sr is in the fine sand size and the reason behind that is due to the high content of Ca in this size and mainly with the calcite or plagioclase feldspar, while, the content of barium is different in the four granule sizes.The difference is slight as it is (260 ppm) in the coarse sand, (262 ppm) in the fine sand, (299.4 ppm) in silt and (279.14 ppm) in shale.
The contents of Y,Ga,Nb,Ta,Zr and Hf increase in the direction of the finer sizes, but it is noticed that the content of U and Th increase in the current study samples with the increase of the granule size.
It is noticed that Cr content increases starting from the shale, silt and fine sand and it remarkably decreases in the coarse sand.As for the increase of its content in the shale, it is due to that the chromium is related basically to the shale minerals and with the ferric hydroxides [ 82 ] .So, it is noticed that there is a gradual increase in Ni content starting from the coarse sand towards the shale, on the contrary of the cobalt that shows a gradual decrease in the direction of the finer sizes (the shale).The reason behind that is that cobalt is more mobile than Ni during the aeration process.The general pattern of the sizes (C, F, S and Sh) is characterized with homogeneity in general and homogeneity in particular with the pattern IOP Publishing doi:10.1088/1755-1315/1300/1/01201724 PAAS and the diagram can be classified into two patterns: the slib, which refers to the light rare earth elements (LREE) and the flat pattern, which represents the heavy rare earth elements (HREE), with the presence of negative anomaly Eu/Eu* that is almost identical in all the study sections and relatively higher than PAAS.This was determined through the equation Eu/Eu*=Eun/(Smn*Gdn)0.5, where n refers to the values that were calibrated in relation to the chondrite and the reason behind the increase and decrease lower than PAAS in the Eu/Eu* is due to the presence of the plagioclase feldspar, which contains Na.It is noticed that the value of Eu in shale is lower than the values in the rest of the granule sizes due to the low content of plagioclase that includes Na compared to the size of the shale.
It is observed that the only difference between the patterns of the current study and PAAS is in the total content of the rare earth elements in the various sizes (77.9 ppm) in the coarse sand, (82.939 ppm) in the fine sand, (84.407 ppm) for silt and (97.37 ppm) for shale and all of these values are ,lower than ƩREE in PAAS (184 ppm.This is mainly due to the effect of reduction caused by the calcite and the silica in sand and shale compared to PAAS and the effect also represents the same reason that the content of REE in the coarse granule in lower than the content in the shale as the total content of REE increases in the fine sizes of clastic sediments [ 842,1249 ] ,but the patterns are extremely similar.

Conclusions:
The current geochemical study showed that the main elements are distributed in the various granule sizes with various concentrations.The reason behind these differences is due to the portions of these mineral that contain these elements and which compose the sizes in addition to the nature of these minerals.It was observed that the shale size is the distinguished one in terms of the content of these elements and this content might be high or low.
The behavior of elements with high ion radius (Cs, Rb, Sr and Ba) depends on the elements that are similar to them in terms of the charge and the radius and consequently depend on the type and content of the main minerals in the granule sizes, but in general, the content is the highest in the sized of silt and shale.For instance, the connection of Rb with K 2 O is positive and strong and might be (0.9) for all the granule sizes.This connection refers that the element exists mainly in the minerals that contain K 2 O and also in the shale minerals.
The element Rb usually exists in the shale mineral that contain the potassium like the feldspar 1300 (2024) 012017 IOP Publishing doi:10.1088/1755-1315/1300/1/01201725 -K, mica minerals and shale minerals and it is also adsorbed on the surface of the shale minerals.The ion radius of Rb (1.49A is higher than the radius of the ion K 1.33 A°, so its cohesion strength with the shale minerals is higher than the cohesion strength of the potassium and also the potassium will occupy a position in the crystal net before the Rubidium and the ratio Rb/K 2 O will increase with the increase of aeration intensity against the mineral phases that contain these mineral elements.So, the highest percentage will be in the shale size (0.0033%) and it decreases with the coarser sizes with values (0.0030, 0.0029 and 0.0028) for silt, fine sand and coarse sand respectively.The behavior of the rubidium is greatly identical to the behavior of the cesium and therefore it is noticed that the content of Cs   The content of the ferromagnetic elements that include (Cr, Co, Ni, V and Sc) varies in the different granule sizes.The highest content of Chromium is in the fine sand and that is due to the presence of chromite mineral in this size with highesr concentrations compared to other sizes.Also, the Cr content in all the sizes in the study samples is higher than its content in UCC.As for Ni, its content increases in favour of the fine sizes (silt and shale), whole the content of Co decreases with the fine sizes and the Co/Ni ration in all the granule sizes of the study is lower than the ration in PAAS.
The highest content of Vanadium is in the shale size as it is adsorbed on the surfaces of the shale minerals or replaces SiO 2 , but the content of Scandium varies in the four sizes according to the different content of the mineral phases that contain it.When comparing the patterns of the rare earth elements, it is clear that they are identical morphologically in the four granular sizes (coarse sand, fine sand, silt and shale) and also identical in general with the pattern of PAAS.Also, the anomalycerium Ce/Ce* is negative in all the sections and granular sizes.The anomaly Eu /Eu* exists in all the sections and granular sizes is higher than the one in PAAS which results from the effect of fractioning the calcite plagioclase feldspar 1300 (2024) 012017 IOP Publishing doi:10.1088/1755-1315/1300/1/01201727 in the source rocks and eventually this high ration refers to the mafic source of the sediments of the current study.
The highest content of the rare earth elements is in the size of shale compared to the rest of the sizes due to the effect of the granular size, but ΣREE is lower than PAAS in all the sizes due to attenuating the effect that occurs by the impact of silica and calcite and also the concentration of the elements that incubate the rare earth element (REE).
shorter and steeper from the northern part [ 42 ] .The second area of the study is located in Erbil governorate to the north east of Iraq and it is located with the southern west sinking part of Bermam Dagh fold and extends between the latitudes (24° 57 0) and (44° 03) east and the longitudes (36°150) and (°36 9 0) to the north.Based on the classification of [ 41 ] , this area is located within the FootHill Zone and Mesopotamian Zone of the Forland basin.Map (2), tectonic map shows the area of the study

Figure ( 9 )
Figure (9): The relationship between K 2 O percentage and Rb ppmThe content of the high ionic potential elements varies from one size to another (Zr,Hf,Nb,Th,U,Ta and Y). for example, the content of Zr and Hf increases towards the finer sizes and the highest content is in the shale size and the lowest content is in the coarse sand and the highest percentage of Zr/Hf in the shale size and the lowest is in the coarse sand and this percentage increases with the increase of silica content SiO 2 .

Figure ( 10 )
Figure (10): The relationship between Zr ppm and Hf ppmThe content of Nb increases in the direction of the finer sizes (shale and silt), while the highest content of Ta is in the coarse sand and the highest content of U and This is in the coarse sand, but the ratio Th/U is much lower than in PAAS.The Ga is strongly connected with Aluminium and the highest ration of Ga/Al is in the coarse sand and the highest content of Y is in the fine sizes represented by the silt and shale.
bottom to the top and the higher part is the one that include more conglomerate and this was the reason behind classifying it into high and low parts ]6[.The rock sequence of the formation is composed of the sand and stone and the fragile sand rock which is easily fragmentize in addition to the shale and silt rocks.The age of this [ 9 ]tion is dated to the Early Pliocene age and its age was determined by the fossil Hippairan[ 9 ]and the lower limit of contact with the Fat'ha formation (the middle Miocene), whereas the higher contact is consistent with Bai Hassan formation and it is identified at the emergence of the first layer of the massive conglomerate.thickness and the sequenced sedimentation of this formation, it plays an important role in the geology of the middle east [ 4 ] , as the wide spread of this formation was observed and it has counterparts inside and outside Iraq.Inside Iraq, its counterpart is the (Dibddibba Formation) which extends into the Kuwaiti lands and outside Iraq it has several counterparts like (Monqoura Formation) in Syria and (Hofuf Formation) in Saudi Arabia and (Selmo Formation) in Turkey [ 2 ] .