ASSESSMENT OF SOME CLAY DEPOSITS FROM THE GERCUS FORMATION (MIDDLE EOCENE) FOR BRICK MANUFACTURING IN THE DOKAN AREA, NE IRAQ

The objective of this research is to evaluate the suitability of some clay deposits from the Gercus Formation (Middle Eocene) in the Dokan area, Northeastern Iraq for brick manufacturing. Physical properties of the raw material including grain size analysis and Atterberg limits showed that composed mostly of sand and silt with a minor proportion of clay and classified as muddy sand. According to the plasticity chart, the studied sample plotted on the field of silt and organic clay with low plasticity. The geochemical analysis by X-ray fluorescence revealed that composed of a low percentage of silica and alumina and a high percentage of calcium oxide and magnesium oxide. The mineralogical analysis by X-ray diffraction showed that the studied samples were composed of non-clay minerals (dolomite, quartz, hematite, albite, anatase, and orthoclase) and clay mineral (montmorillonite, kaolinite, and illite). Twelve ceramic briquettes were prepared from the clay sample by semi-dry pressing method and pressed by 200 kg/cm² pressure with 14 – 15 % moisture content and fired at 880, 900, and 920 °C for evaluation tests of linear firing shrinkage, apparent porosity, water absorption, bulk density, efflorescence, and compressive strength. Results of physical and mechanical properties of the studied ceramic briquettes compared with the specification of Iraqi standard (1993) for clay brick manufacture, according to this specification the studied sample was not suitable for brick manufacturing due to a high percentage of water absorption and low compressive strength.


Geological Setting
The research site is situated in the Dokan area; which is located in the central northern part of Iraq, Iraqi Kurdistan Region within Sulaimaniya Governorate.The study area is situated within the High Folded Zone of the Outer Platform of the Arabian Plate (Fouad, 2012).The Gercus Formation is part of the Paleogene sequences in northern Iraq and has been represented by a thick section of the Middle-Late Eocene clastic sediments.A complete section of these rocks forms an outcrop on the northeastern side of the Unstable Folded Zone (Al-Qayim & Al-Shaibani, 1991;Al-Rawi, 1980;Jassim & Goff, 2006).
The Gercus Formation consists of claystone, sandstone, and siltstone all red, with very rare conglomerate lenses (Al-Shiwaily et al., 2011;Kassab, 1972;Van Bellen et al., 1959).The formation exhibits variation in thickness within the ranges of 35 to 150 m.The age of the formation is probably Middle Lower-Middle Eocene (Sissakian & Fouad, 2015).The studied sample was taken from the red clay deposits of the Gercus Formation (Middle Eocene), which cropped out at the Kalka Smaq area (Figure 1).It is located at the intersection of latitude 35°55'21.28''N and longitude 44°54'21.72''E with an elevation reaching 890 m above sea level.The Gercus Formation in the studied area is underlain by the Sinjar Formation (Early Eocene), which is conformable and graditional and the appearance of the first red clay bed represents the contact between them.The overlying formation is the Pilaspi Formation (Late Eocene) with unconformable contact, marked by the presence of a bed of conglomerate.In this research study, the red clay deposits from the lower part of the formation.

MATERIALS AND METHODS
For this study, the sample was taken from the red clay deposits from the lower part of the Gercus Formation at Kalka Smaq from the Dokan area.To study the suitability of this type of clay for brick manufacture first grinding the sample into very small pieces like clay, the material was mixed with about 14 to 15% water to make it moist.Thereafter, the mix formed as rectangular molds using a method where the mixture was partly dry, which is a semi-dry pressing method, and then pressed by 200 Kg/cm² pressure with 8.5*2.45*2.45cm dimensions.The pressed brick samples dried at room temperature and then fired at three different firing temperatures 880 °C, 900 °C, and 920 °C, three briquettes for each firing temperature.Preparing these briquettes was carried out at Aso Brick Factory.Grim (1962) and Dondi et al. (1992) proposed numerous tests for evaluating clay for the brick industry.Many tests performed on the raw material are grain size distribution by sieve and hydrometer (B.S., 1967) and Atterberg limits (liquid limit, plastic limit and plasticity index) (ASTM, 1972), both tests performed at the Sulaimaniya Architecture Laboratory.Geochemical composition of the raw material identified by X-ray fluorescence (XRF) at Mass Cement Factory.Mineralogical composition of the raw material determined by X-ray diffraction (XRD) at Amethyst Lab Co. Mashhad, Iran.Tests conducted on the fired specimens are linear firing shrinkage (ASTM, 1982a), apparent porosity, water absorption, and bulk density (ASTM, 1986).Both tests of compressive strength (ASTM, 1982b) and efflorescence (Iraqi Central Organization for Standardization and Quality Control, 1988) determined the ceramic briquettes at Aso brick Factory.

RESULTS AND DISCUSSION
Results and discussion of the tests done on the sample are listed below:

Grain size analysis
The analysis of grain size characterizes the proportional distribution of sand, silt, and clay present within a specific sample.It is known that decreasing particle size results in greater plasticity and reactivity of the clay (Ryan, 1978).Furthermore, this increase in the fineness of particles increases the silica melt that binds crystals together and then becomes more coherent (Kingery, 1967;Rado, 1969).The results obtained from the analysis of grain size by sieve and hydrometer of the studied sample show that composed mostly of sand (76.65%) and silt (13.94%) portions, with a small quantity of clay (9.41%;Table 1).
The result of the grain size distribution of the studied sample is plotted on the Folk classification triangle (Folk, 1980) to classify the sample, based on the proportion of sand, silt, and clay (Table 1).It revealed that the sample was plotted on a field of muddy sand (Figure 2).Winkler (1954) produced the diagram for evaluating the suitability of clay samples in different ceramic products depending on the ratio of fine particles sized (< 2 μm, 2 -20 μm and > 20μm) (Table 1).According to the Winkler diagram (Figure 3), the studied sample is neither suitable for manufacturing bricks nor roofing tiles.

Atterberg limits
The ceramics industry needs materials that are easy to shape and work without breaking, so having good plasticity is very important (Grim, 1962).The plasticity is affected by the size of the grain and the typology of the clay minerals, the plasticity increases due to the clay minerals, where the layers are weakly bound such as minerals of illite and/or montmorillonite nature (Manfredini & Hanuskova, 2012).Atterberg limits include the plastic limit, liquid limit, and plasticity index for the studied sample, Table 2 shows the results of these tests.The plasticity of clay is evaluated by the plasticity index, which is determined by the difference in moisture content between liquid limit and plastic limit.
The clay workability chart (Bain & Highley, 1979); (Figure 4) was used to evaluate the suitability of the studied sample in different ceramic industries, depending on the plasticity index and plastic limit.According to this chart in Figure ( 4), the studied clay sample is suitable for the brick industry with some treatments.The plasticity chart by Krynine et al. (1957) was used for the classification of the studied sample (Figure 5), which represents the relation between the plasticity index [PI = 0.73 (LL-20)] and liquid limit (LL %).Depending on this chart, the sample is located on the field of silt and organic clay with low plasticity.
According to Budnikov (1964), clay with a plasticity index of less than 10 can be utilized in the ceramic industry.Hence, the studied sample with a plasticity index of less than 10 so can be utilized in the ceramic industry, such as the brick industry.

Geochemical Analysis
The geochemical properties play an important role in the ceramics industry and determining the main oxide content of the raw materials helps in understanding the behavior of the ceramic body during firing by estimating the refractory oxides, flux, and melting temperature (Mahmood & Aqrawi, 2022).In addition, some oxides affect the mechanical and physical characteristics of ceramic products (Shreve & Brink Jr, 1977).Fluxes induce a restricted and regulated quantity of glass formation within ceramic compositions that serve to bond crystalline components together.Fluxes are important in the vitrification of clay bodies by lowering the melting temperatures (Jassim & Goff, 2006).CaO, Na2O, K2O, MgO, and Fe2O3 are common fluxes in clay (Fakhfakh et al., 2007;Rattanachan & Lorprayoon, 2005;Riley, 1951).The result of the geochemical analysis of the raw material from the Gercus Formation is shown in Table 3.It reveals that the raw material is composed basically of silica is about 33.5%.Silica is important in controlling firing shrinkage, which causes densification of the ceramic product (Aqrawi, 2009).Calcium oxide comprises approximately 12.76% of the raw material composition owing to the presence of calcite.This oxide can make the liquid phase form at high temperatures because it acts like a flux (Aqrawi, 2000).It is utilized as one of the techniques for controlling water absorption and firing shrinkage (Das et al., 2005).Furthermore, it provides the densification of the ceramic briquettes at high firing temperatures.Alumina shows a minor amount about 3.28%.Alumina and silica function as refractory oxides within the ceramic industry resulting in increasing water absorption and apparent porosity and decreasing the linear shrinkage, bulk density, and liquid phase (Aqrawi, 2009).The Magnesium oxide (MgO) shows a high proportion about 18.77% owing to the significant presence of dolomite mineral within the raw material.According to (Medhioub et al., 2010), magnesium participates in the structure of clay minerals, and magnesium oxide (MgO) operates as a sintering agent, which encourages the process of vitrification.Iron oxide is about 6.9% being responsible for the reddish color after firing (Faraj, 2014).Moreover, iron oxide with other fluxes can make a higher amount of liquid phase at a lower firing Figure 4: Clay workability chart (Bain & Highley, 1979) and plots of the studied sample.
Figure 5: Plasticity chart by (Krynine et al., 1957) and plots of the results of the studied sample.

Iraqi Bulletin of Geology and Mining
Vol.20, No.1, 2024 p 75 88 temperature which helps to accelerate the vitrification (González et al., 1998;Medhioub et al., 2010).Other oxides of Na2O, K2O, Cl, and SO3 exhibit a minor amount (Table 3).Chloride salt exists as Cl.Na2O and SO3 represent the presence of sodium sulfate salts that cause efflorescence on the surface of bricks.Loss on ignition was determined during firing at 1000 °C and is approximately 21.01 %, the significant quantity of Loss on Ignition (L.O.I) is attributed to the decomposition of carbonate minerals and the release of CO2 gas, in conjunction with the presence of both adsorbed and molecular water on and in the crystal structure of the clay minerals (Hakeem, 2012).

Mineralogical Analysis
The XRD analysis provides information about the mineralogical composition.The XRD analysis shows that the sample chosen from the Gercus Formation consists of non-clay and clay minerals.Non-clay minerals can be described as dolomite, quartz, hematite, albite, anatase, orthoclase, and clay minerals can be described as montmorillonite, kaolinite, and illite (Figure 6).The average percentage of non-clay minerals and clay minerals in the studied sample is shown in Table 4.The high proportion of dolomite mineral during firing causes disintegration that results in a cracking body.Fine grain dolomite mineral acts as a flux mineral that enhances reactions during firing and decreases refractory degree (AL-KASS, 1985) disintegration of carbonate minerals during firing increases the porosity of the ceramic body and water absorption percent, and decreases its density.Quartz has a big role in the ceramic industry that decreases its plasticity, is responsible for decreasing shrinkage, and causes cracking of these ceramic bodies during dryness and firing.It causes viscous silica refractory material in higher temperatures (Rado, 1969).Hematite acts as a flux material and is responsible for the red color of the raw materials.Kaolinite mineral Kaolinite has low drying and firing shrinkage.It's used in ceramic industries to optimize green strength, plasticity, and casting behavior (Ciullo, 1996).So, illite has intermediate drying and firing shrinkage.It contributes to consistency and workability, smooth surface finish, and resistance to shrinkage and cracking in the ceramic industry use (Ciullo, 1996).

Apparent porosity, water absorption, and bulk density
The apparent porosity is the expression of the proportion of the volume of open pore space of the sample to its overall external volume and is expressed as a percentage.So, water absorption represents the percentage of water, absorbed by the porous structures present within ceramic material, the ratio of both is influenced by the grain distribution, grain size, and the degree of pressure utilized throughout the pressing process and molding process (Kingery, 1967).Bulk density is expressed as the ratio weight of the sample to the total volume which represents the volume of the solid material with the volume of any gaps or holes on its surface both opened and closed (Kingery, 1967).The results of the apparent porosity, water absorption, and bulk density tests were conducted on the ceramic specimens fired at 880, 900, and 920 °C shown in Table 5. Figure 7A shows the relationship between apparent porosity and different firing temperatures and illustrates that apparent porosity increases with increasing firing temperatures.Figure 7B shows the relationship between water absorption at different firing temperatures, as well as the results of water absorption, exhibiting a positive correlation with apparent porosity (Table 5).Figure 7C illustrates the relationship between the bulk density and firing temperatures.It demonstrates an inverse relationship between bulk density with apparent porosity and water absorption at all firing temperatures, the reason for the increase in apparent porosity and water absorption and decrease in bulk density is due to the extensive decomposition of CaCO3 which occurred at about 900 °C, which leaves the pores in the ceramic body by releasing CO2.These results are influenced by various factors, such as the composition of the fired materials, their grain size, the temperature employed, and the temporal length of the firing procedure as well as the time of maturation.Figure 7: Relationship of the apparent porosity, water absorption, and bulk density with firing temperatures for the studied ceramic specimens.

Linear Firing Shrinkage
It refers to alterations in linear dimensions of ceramic briquette that have occurred at different firing temperatures.Shrinking in ceramic briquettes is characterized by the fusion of certain grains, consequentially leading to the convergence of the grains; the quantity of melt phase is directly proportional to the number of impurities that serve as flux agents (Aqrawi, 2000).Measuring the linear shrinkage is a vital point to understand the alters that take place during the firing process (Merza, 1997).The percentage of linear shrinkage was subsequently calculated according to ASTM (1982).
Linear shrinkage occurs when water is lost because of chemical and mechanical reasons, but overall clay shrinkage can only occur when a reaction between adjacent grains occurs (Prentice, 1988).Table 6 exhibits the results of the linear shrinkage of ceramic briquettes, and Figure 8A illustrates the change in linear shrinkage at different firing temperatures, linear shrinkage increases from 880 to 900 °C and decreases at 920 °C this is referred to as the liberation of CO2 resulting from carbonate decomposition prevent the convergence of individual grains from each other during this firing temperatures (Al-hakim, 1998; AL-KASS,

C
Assessment of Some Clay Deposits from Gercus Formation (Middle Eocene) for Brick Manufacturing in the Dokan Area, NE Iraq Rezan Q. Faraj 84 1985), this expansion attributed to the bloating ability of clays and forming new mineral phases (Hakeem, 2012).

Compressive strength
It is the essential degree of the load that a sample can withstand without being smashed.The compressive strength of a material is directly correlated with its bulk density while inversely correlated with its apparent porosity, to achieve a high level of compressive strength it is necessary to minimize the open porosity of the material (Kitouni & Harabi, 2011), alternatively, increasing in densification causes an increase in compressive strength, and the densification affected by the maximum firing temperature and concentration of lime that influences the creation of calcium silicate phase, and this phase is very important in densification of the ceramic specimens.According to Khalaf & Issa (2021), the uniform distribution of both grains and pores is responsible for the high compressive strength Table 6 exhibits the results of compressive strength for the ceramic specimens fired at 880, 900, and 920 °C. Figure 8B illustrates the relation between the compressive strength and different firing temperatures.It is noticed that there is an inverse relationship between compressive strength values and firing temperatures this is referred to the high amount of carbonate in the raw material which decomposed at these temperatures leading to decreasing density and increasing the porosity in the studied ceramic briquette.

Efflorescence
Efflorescence refers to the deposition of crystalline salt on the surface of the ceramic body as a consequence of moving the contaminated water through layers of clay deposits, leading to the formation of a white or gray powdery substance on the surface of the ceramic body (Kingery, 1967).The efflorescence test was performed on the ceramic specimens fired at 880, 900, and 920 °C, then boiling the briquettes for 1 hour and followed by allowing them to soak for additional 5 hours according to (Iraqi Central Organization for Standardization and Quality Control, 1988).Efflorescence is determined by comparing the fired briquettes at distinctive levels to None; does not correspond to efflorescence.Light; means that the amount of salt on the surface area is no more than 15% of the complete surface area of the sample.Moderate; means that the amount of salt on the surface area of the briquette is in the range of 15 -50 %, and Dense; the amount of salt on the surface area of the briquettes is more than 50% (Aqrawi, 2009).Table 6 exhibits the results of the efflorescence test for the studied ceramic specimens fired at 880, 900, and 920 °C and shows that the efflorescence test for all specimens is light.

Assessment of the Studied Sample for the Brick manufacturing industry
The results of the above properties were compared with the requirements of Iraqi Standards (1993) as shown in Table 7.According to this specification, the studied ceramic specimens are not suitable for the brick industry due to low compressive strength and high percentage of water absorption.The compressive strength of clay brick is positively associated with the percentage of clay minerals mainly with the concentration of Al, and Si, but the water absorption (term of porosity) is related to carbonate and evaporate minerals (Gypsum).Al-Bassam (2004) stated that the surface area of brick increased with the released CO2 from carbonate and H2O from gypsum after drying which caused to formation of high porosity (voids) on the brick surfaces but the studied samples indicate that have low compressive strength with a high water absorption ratio.

CONCLUSION
The following conclusions have been reached depending on the results of this investigation:  The physical properties of the raw material in terms of grain size distribution by sieve and hydrometer show that it consists mainly of sand and silt with a small amount of clay and the sample is classified as muddy sand.The assessment of the studied sample according to grain size analysis exhibits that the studied sample is neither suitable for the production of bricks nor roofing tiles.
 The results of the physical properties (Atterberg limits) of the studied raw material and the clay workability chart the sample is suitable for the brick industry with some treatment and according to the plasticity chart the sample plotted on the field of silt and organic clay with  The results derived from the geochemical analysis of the sample being investigated indicate that the raw material consists mainly of silica with a high percentage of calcium oxide and magnesium oxide, which means the high content of carbonate minerals such as dolomite in the raw material and the significant quantity of Loss On Ignition (L.O.I) is attributed to the decomposition of carbonate minerals and release of CO2 gas in conjunction with the of both molecular and absorbed water within the crystal structure of the clay minerals.
 The X-ray diffraction illustrates that the studied sample chosen from the Gercus Formation consists of non-clay minerals, such as (dolomite, quartz, hematite, albite, anatase, and orthoclase) and clay minerals like (montmorillonite, kaolinite, and illite).
 The results of the physical characteristics of ceramic briquettes under investigation demonstrate that an increase in firing temperatures leads to a corresponding increase in both apparent porosity and water absorption.Furthermore, there is an inverse relationship between bulk density with apparent porosity and water absorption at all firing temperatures the reason for the increase in apparent porosity and water absorption and decrease in bulk density is due to the extensive decomposition of CaCO3 which occurred at about 900 °C which leaves the pores in the ceramic body by releasing CO2 gas.
 Linear firing shrinkage of the studied ceramic specimens increases from 880 °C to 900 °C and decreases at 920 °C this is referred to as the escaping of CO2 gas due to carbonate disintegration during this firing temperature that prevents the convergence of the grains from each other.
 The compressive strength value of the studied ceramic specimens progressively decreased with increasing the firing temperatures this is referred to the high ratio of carbonate mineral in the raw material which decomposed at these firing temperatures leading to decreasing density and increasing porosity in the studied ceramic specimens.
 The efflorescence tests for the ceramic specimens under investigation which fired at 880, 900, and 920 °C, are slight.
 The results of the physical and mechanical characteristics of the studied ceramic specimens compared with Iraqi Standards (1993) for clay brick manufacture according to this specification the studied ceramic specimens are not suitable for the brick industry due to low compressive strength and high water absorption.

Figure 2 :
Figure 2: Relative distribution of sand, silt and clay proportions of the studied sample(Folk, 1980).

Figure 3 :
Figure 3: Winkler diagram (Winkler, 1954) for the technological classification of bodies for structural clay products and plots of the studied sample.

Iraqi Bulletin of Geology and Mining Vol.20, No.1, 2024 p 75 88Table 1 :
Particle size distribution percentage of the studied clay sample.

Table 3 :
Chemical analysis for the studied sample.

Table 4 :
The average percentage of minerals in the studied sample.

Assessment of Some Clay Deposits from Gercus Formation (Middle Eocene) for Brick Manufacturing in the Dokan Area, NE Iraq Rezan Q. Faraj 82
Figure 6: XRD diffractograms of the studied sample.

Table 5 :
Results of the water absorption, apparent porosity, and Bulk density for the studied ceramic specimens at different firing temperatures.

Table 6 :
Results of linear firing shrinkage, compressive strength, and efflorescence tests for the studied ceramic briquette at different firing temperatures.

Bulletin of Geology and Mining Vol.20, No.1, 2024 p 75 88
Figure 8: Relationship of linear firing shrinkage and compressive strength with different firing temperatures for the studied ceramic specimens.

strength kg/cm² Firing temperature B Assessment of Some Clay Deposits from Gercus Formation (Middle Eocene) for Brick Manufacturing in the Dokan Area, NE Iraq Rezan Q. Faraj low
plasticity.Therefore, the studied sample with a plasticity index of less than 10 can be utilized in the ceramic industry such as the brick industry.