A.S. Mahjoor, M. Karimi and A. Rastegarlari

A.S. Mahjoor, M. Karimi and A. Rastegarlari, 2009. Mineralogical and Geochemical Characteristics of Clay Deposits from South Abarkouh District of Clay Deposit (Central Iran) and Their Applications. Journal of Applied Sciences, 9: 601-614.

DOI: 10.3923/jas.2009.601.614

URL: https://scialert.net/abstract/?doi=jas.2009.601.614

MATERIALS AND METHODS

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Sampling for this study is made from three active mines at Bikheirkhong plain (Fig. 1). Since sediment sequences in all three mines are almost similar. Sampling at three mines was made from the layers underneath the sandstone’s layers. This sandstone is a proper guide for following up on clay sequences in the region. The thickness of the sandstone layer varies from 60 to 80 m. In a general view, clay sequences can be divided into two entirely distinctive reddish and blackish colors. In fact, the upper 35 to 45 m of clay sequences is reddish, while the lower 25 to 35 m is grayish black. In order to obtain better and more distinctive results, the sampling method was designed in such a way that the samples have appropriate and constant distances from one another and incorporate all the important lithological and apparent changes in the layers. Samples are taken from channels of 0.5x10x0.2 which are 12 m away from each other and parallel to the layers by counting and quartering method, in a vertical profile, from fresh surfaces. Samples are crushed by agate crusher. Clay mineral associations have been studied using X-ray diffraction. X-ray diagrams were obtained using a Phillips PW 1730 diffractometer with CuKa radiations and Ni filter. A tube voltage of 40 kV and a tube current of 25 mA were utilized. Three X-ray diagrams were performed, after air-drying, ethylene-glycol salvation and heating at 490 °C during 2 h. The identification of clay minerals was made according to the position of the (001) series of basal reflections on the three X-ray diagrams (Reynolds, 1980; Moore and Reynolds, 1989) and by comparison with the Powder Diffraction File (JCPDS, 1995). Quantitative mineralogical composition was obtained using the method of Fabbri et al. (1986). Chemical analyses were carried out by a Philips PW 1400 XRF spectrometer, operating with Rh tube at 30 kV and 60 mA.

Fig. 2:	Generalized geological map of study area after (Houshmandzadeh and Soheili, 1990), showing locations of the analyzed samples reported in Table 1 and 2

Quantitative ICPMS analyzes of REE Carried out by Perkin-Elmer ELAN 6000 instrument.

RESULTS AND DISCUSSION

The XRD patterns of all whole-rock samples indicate the predominating presence of, Illite, Quartz and Kaolinite and iron mineral. Peaks were observed, indicating that goethite was incorporated in the clay minerals. Chlorite is present in trace amounts in samples. Identification of secondary minerals was difficult, because their peaks tended to be obscured by the greater peaks of the major minerals kaolinite, illite and quartz. Semi-quantitative analyses, showed differences in bulk mineral compositions between the individual sediments and also in the composition of blackish and reddish series of the sediment (Table 1).

Difference between amount of clay minerals in reddish and blackish series is obvious. For example, the kaolinite content varies from 9 wt.% in FA-1 to 61 wt.% in FA-5 in Fariadoon samples and the average amount of kaolinite differs from 20.8 wt.% in Hozsefid to 33 wt.% in Fariadoon samples. It seems that the samples much richer in quartz being poorer in kaolinite. Samples from same depths in three study locations are close in bulk mineral composition. Samples from reddish series contain high amounts of quartz and illite and minor amount of kaolinite. Samples from Blackish series contain high amounts of kaolinite and quartz and minor amount of illite. 0.5 to 3 cm thick layer intersecting veins of secondary quartz are dispersed in both reddish and blackish series layers. Dispersion and thickness of these veins in reddish series are more abundant and this is the principle reason for the abundance of quartz in reddish series in comparison with blackish series. Almost all the samples consist of small amounts of some secondary minerals such as Gypsum, natroalonite and paragonit. These minerals are the product of interaction between leached sulfuric solutions from upper layers with some clay minerals such as illite in clay reach sediments. Reducing content of these minerals from top to bottom in study profile and the appearance of these minerals in joints and cracks support this interpretation. A sudden reduction in the content of these secondary minerals in the boundary of the reddish and blackish series of clay sediments is obvious. All sediments are, therefore, rich in kaolinite, illite and quartz, which indicate that they are derived mainly from felsic sources.

Geochemistry of the sediments: Table 2 lists the results of the major, trace elements and REE analyses for the Study area sediments compared to the average compositions of the Upper Crust (UC) and the North American Shale Composite (NASC), from Gromet et al., (1984). As expected from weathered rocks, there is a large variation in the major element content for all analyzed samples. For example, the SiO₂ contents range from 48.82 to 70.35 wt.%, the TiO₂ content from 0.99 to 2.5 wt.%, the Al₂O₃ content from 14.94 to 29.2 wt.% and the Fe₂O₃ content ranges from 1.12 to 7.83 wt.%. SiO₂/Al₂O₃ ratios of samples vary from 1.8 to 4.3, which are lower than UC and NASC. The contents of MgO, CaO and MnO are all low. The Na₂O and K₂O contents range from 0.31 to 2.33 wt.% and from 0.93 to 3.01 wt.% respectively. K₂O/Na₂O ratio for the samples are obviously lower than NASC and mostly Higher than UC.

Nesbitt and Young (1982, 1996) and Nesbitt et al. (1996) used the ternary diagrams Al₂O₃-(CaO+Na₂O)-K₂O (the A-CN-K), diagram and Fe₂O₃+MgO-(CaO+Na₂O+K₂O)-Al₂O₃ (the A–CNK-FM), diagram to deduce weathering trends. On both the A-CN-K diagram (Fig. 3b) and the A-CNK-FM diagram (Fig. 3a), all the sediments display an intense weathering history.

Table 1:	Semi-quantitative (wt.%) mineralogical composition of Torab, Hozsefid and Fariadon mines, in South Abarkouh District, analyzed by X-ray diffractometry

Table 2:	Major (wt.%) and trace (ppm) element composition of Torab, Hozsefid, and Fariadone sediments, SADC
Major elements as wt.% and trace elements in ppm. Total Fe as Fe2O3, CIA = [Al2O3/(Al2O3+CaO+Na2O+K2O)]x00 and CIW = [Al2O3/(Al2O3+CaO+Na2O)]x100 in molecular proportions. CaO in both CIA and CIW is CaO in silicate fraction only and was corrected following the McLennan (1993) method. UC = Upper Crust after Taylor and McLennan (1985) and NASC = Average North American Shale after Gromet et al. (1984). Eu/Eu* = Eucn/ [(Smcn )(Gdcn )]

Fig. 3:	(a) Triangular Al2O3-(CaO+Na2O+K2O)-Fe2O3+ MgO plot of sediment samples (after Nesbitt and Young, 1980, 1982, 1996; Nesbitt et al., 1996). (b) Al2O3-(CaO+Na2O)-KO2 plot of sediment samples (after Nesbitt and Young, 1982, 1982, 1996; Nesbitt et al., 1996) and Upper Crust (UC) given by Taylor and McLennan (1985) and North American Shale Composite (NASC) given by Gromet et al. (1984).

The sediments plot in a region clearly suggesting different relative contents in Al₂O₃, CaO, Na₂O and K₂O from those NASC and UC and plot closer to high Al₂O₃ contents, which is suggestive of a relatively high intensity of weathering. Weathering has proceeded to a stage at which significant amounts of the alkali and alkali earth elements were removed from the sediments.

Two chemical weathering indices have been proposed: Chemical Index of Alteration (CIA) (Nesbitt and Young, 1982) and Chemical Index of Weathering (CIW) (Harnois, 1988). Nesbitt and Young (1982) reported a CIA value of nearly 100 for Kaolinite and chlorite and 70 to 75 for average shale’s, whereas Taylor and McLennan (1985) reported a CIA value of 85 to 100 for residual clays. Condie (1993) reported that most post-Archean shale’s show moderate losses of Ca, Na and Sr from source weathering, with CIW values of 80 to 95 and Sr contents of 75 to 200 ppm. In contrast, most Archean shales, show greater losses of all three elements, with CIW of 90 to 98 and Sr contents <100 ppm.

Fig. 4:	Al2O3/SiO2 vs. 100TiO2/Zr diagram for SADC samples (after Garcia et al. (1994)

Fig. 5:	SiO2/Al2O3 vs. K2O/Na2O diagram for SADC

The CIA of the sediments varies between 82 to 95, which is high compared to UC and NASC, but close to that of kaolinite (Table 2). The CIW, which does not include K₂O, ranges between 90 to 96, with Sr contents ranging from 62 to 124 ppm.

The CIA and CIW are both higher than those of average shales, suggesting relatively intense source area weathering. The high CIA and CIW values in the sediments probably reflect the presence of clay minerals and absence of detrital feldspars. High ratio of TiO₂/Zr (0.011-0.022) indicates the maturity of South Abarkouh samples (Ugidos et al., 2003) (Fig. 4). Therefore, the South Abarkouh sediments are more mature than post-Archaean shales such as NASC (Condie et al., 1995) (Fig. 5).

TRACE ELEMENT GEOCHEMISTRY

The behavior of trace elements during sedimentary processes is complex due to factors including weathering, physical sorting, adsorption, provenance, diagenesis and metamorphism (e.g., Nesbitt et al., 1980; Taylor and McLennan, 1985; Wronkiewicz and Condie, 1987; Condie et al., 1995; Manceau et al., 2000; Roddaz et al., 2006). The trace element data show moderate variations compared to NASC and UC (Table 2). All sediments have similar contents in trace elements and are almost enriched in Y, Zr, Nb, Th and U. These elements are associated with heavy minerals, such as zircon, which is resistant to weathering. They are preferentially partitioned into melts during crystallization and anatexis (Feng and Kerrich, 1990; BALning et al., 2004) and as a result, these elements are enriched in felsic rather than mafic rocks. Thorium and U behave differently during weathering, as U, unlike Th, is chemically mobile as U6+ and there is a tendency of the Th/U ratio to be elevated above upper crustal values of 3.5 to 4.0 (McLennan et al., 1993). The sediments show Sc, V, Zn, Ni and Cr, contents similar to, or even above, abundances for NASC. However, they are depleted in Co, Cu, Rb, as well as in Sr and Ba contents. Generally these elements are associated with clay minerals and their low values could be attributed to the low values in parent rocks and the high quartz content in the sediments (Table 1). This is in agreement with studies by Nesbitt et al. (1980), Wronkiewicz and Condie (1987) and BALning et al. (2004), in which these authors conclude that small cations, such as Na, Ca and Sr, are selectively leached and weathered from weathering profiles, whereas cations with relatively large ion radii, such as K, Cs, Rb and Ba, may be fixed by preferential exchange and adsorption on clays. Therefore, in general, weathering conditions were more intense in the source area before sedimentation. Strontium and barium mostly reside in plagioclase and K-feldspar, respectively (Picouet et al., 2002). The fractionation of these two elements can result from the selective weathering of these feldspars. Weathering of plagioclase will decrease the Sr content, because plagioclase is more easily weathered than K-feldspar and Sr is more mobile than Ba. A depletion of Ba could be due to recrystallization of clays and progressive destruction of feldspars. Potassium, Rb and Cs are mainly hosted in micas and K-feldspar (Picouet et al., 2002); thus, alteration of these minerals will dominate the fractionation of these elements. Rubidium has a trend comparable to that of Nb and V and is less mobile than K, whose behavior it otherwise follows. Rubidium with respect to K is preferentially retained in weathered illite (Garrels and Christ, 1965). Nb and V are less mobilized, in agreement with what is known about their behavior during weathering (Middleburg et al., 1988).

RARE-EARTH ELEMENT VARIATIONS

All analyzed sediment samples have similar concentrations of the REEs. Chondrite-normalized patterns are typical for shale in general, with an enrichment of the LREEs.

Samples have pronounced negative Eu anomalies. The Eu anomaly parallels the depletion in Na₂O and CaO, suggesting that it developed at least partially in response to plagioclase weathering, where most of the Eu is hosted. The Eu anomaly in sedimentary rocks is usually interpreted as being inherited from igneous source rocks (McLennan and Taylor, 1991; McLennan et al., 1980; Awwiller, 1994; Compton et al., 2003).

Fig. 6:	Rare earth element plots of (a) Torab, (b) Fariadon and (c) Hozesfid samples normalized to C1 chondrites after Taylor and McLennan (1985)

Figure 6 shows that despite the difference in the absolute abundances, the samples show REE patterns that are similar to NASC, but differ in the HREE content compared to the UC. The chondrite-normalized La/Yb ratio ranges from 6.2 to 10.2, with most sediment having slightly higher values than UC. The relative depletion in the HREEs compared to LREEs may be due to a lower concentration of heavy minerals, for example zircon. The low abundances of Zr in the sediments (Table 2) support this interpretation.

Provenance: The REEs and high field strength elements (HFSE, including Y, Zr, Ti, Nb and Ta), Th, Sc, Hf and Co are the most suitable ones for provenance determination, because of their relatively low mobility during weathering, transport, diagenesis and metamorphism. Ratios of both incompatible and compatible elements are useful for differentiating between felsic and mafic source components. In addition, the REE patterns have been also used to infer sources of sedimentary rocks, since basic rocks contain low LREE/HREE ratios and no Eu anomalies, whereas more silicic rocks usually contain higher LREE/HREE ratios and negative Eu anomalies (Cullers and Graf, 1983). Therefore, the REE patterns of the source rocks may be preserved in sedimentary rocks (Taylor and McLennan, 1985; Wronkiewicz and Condie, 1987, 1989; Condie et al., 1995; Compton et al., 2003). Mineralogical maturity of the sediments indicated by the proportion of compositionally mature alumina-rich minerals such as kaolinite is consistent with having a felsic or reworked sedimentary source (Roddaz et al., 2006; Cullers et al., 1975, 1987). The CIA, which varies from 78 to 95 and the CIW values (90 to 96) point towards a more felsic source and may indicate sediment recycling processes (Nesbitt et al., 1980). Ekosse (2001) suggested the ratio of TiO₂/Al₂O₃ as a province indicator. From Fig. 7, the TiO₂/Al₂O₃ plot indicates provenance of materials from predominantly granite-rhyolite. In discrimination diagram for sedimentary provenance (Roser and Korsch, 1988). The South Abarkouh clay samples plot in felsic igneous and quartzose sedimentary province fields (Fig. 8).

The sediments have fractionated REE patterns, with slightly high ratio of (La/Yb)_cn and a negative Eu anomaly. The LREEs are enriched and HREE pattern are almost flat, with low ratio of (Gd/Yb)_cn, These characteristics indicate that the original source area was felsic and the negative Eu anomaly is regarded as evidence for a differentiated source, similar to granite (McLennan, 1989; McLennan et al., 1993; Taylor and McLennan, 1985, 1995).

Fig. 7:	Position of South Abarkouh district of clay deposits samples on TiO2/Al2O3 binary diagram suggested by Ekosse (2001)

Fig. 8:	Discrimination diagram for Sedimentary provenance of South Abarkouh clay sediments (Roser and Korsch, 1988). DF1 = [56.50 TiO2-10.879 Fe2O3(total)+30.875 MgO-5.404Na2O+ 11.112K2O]/Al2O3-3.89. DF2 = [30.638TiO2-12.541Fe2O3(total)+7.32MgO+12.031Na2O+ 35.402K2O]/Al2O3-6.382

The relative enrichments of incompatible elements (e.g., LREE, Th) over compatible elements (e.g., Sc, Co) in the sediments, indicate relatively felsic average provenance compositions and a relatively severe weathering regime (McLennan et al., 1993; Krogstad et al., 2004). The slight differences among the REE patterns probably do not reflect changes in source area composition, but are likely due to variations in mineral sorting and weathering.

The immobile elements La and Th are more abundant in felsic than in basic rocks, whereas Sc and Co are more concentrated in basic rocks than in felsic rocks (Taylor and McLennan, 1985; Wronkiewicz and Condie, 1987; Condie et al., 1995).

Fig. 9:	(a) Th versus Sc for sediment samples. (b) La versus Sc for sediment samples. Th/Sc = 1 and La/Sc = 3 ratio is that of the upper continental crust (UC)

It has been shown that ratios, such as La/Sc, Th/Sc, Co/Th, Cr/Th and Eu/Eu*, in siliciclastic sediments, can place constraints on the average provenance composition (Cox et al., 1995; Cullers, 1994b, 1995; Cullers et al., 1988; Wronkiewicz and Condie, 1987, 1989, 1990; Condie et al., 1995). Thus, the concentration of these elements and the corresponding elemental ratios in sediments may be useful for provenance determination. The geochemical differences between elements such as Th and La (indicative of a felsic source) and Sc and Cr (indicative of a mafic source) have been exploited to distinguish between felsic and mafic provenance by various authors (McLennan, 1989; McLennan and Taylor, 1991; McLennan et al., 1980; Wronkiewicz and Condie, 1990; Condie et al., 1995; Krogstad et al., 2004). The Th versus Sc and La versus Sc plots (Fig. 9a, b) shows that the sediment data scatter above the Th/Sc = 1 and La/Sc = 3 lines with most samples that have Sc contents below 10 ppm indicating a more felsic component. The Th/Sc and La/Sc values are higher than that of UC. The ratios of Th/Sc range from 1.6 to 2.8 and La/Sc from 2 to 5, suggesting a felsic source of sediments (Weber et al., 1998).

Fig. 10:	Ternary plot of La-Th-Sc for the sediment samples after Cullers (1994a) compared with Upper Crust (data from Taylor and McLennan, 1985) and North American Shale Composite (data from Gromet et al., 1984)

In a La-Th-Sc diagram (Fig. 10), which is used to discriminate felsic and basic provenance of finegrained sediments (Cullers, 1994a, b), the sediment data fall in a region that indicates a predominantly felsic source, but does not exclude an intermediate source or possible mixing between felsic and basic source rocks. The sediment data show a cluster along the La-Th edge, at a position closer to La than to Th indicating that La, Th and Sc have been removed in weathered profiles. The sediments have low contents of Sc, Fe, REE, Th, Hf and Cr (and Co), high La/Sc, Th/Sc, La/Cr, Th/Cr and Ba/Sc ratios, which indicates that they were derived mainly from felsic rocks (Cullers et al., 1987, 1988; Cullers, 1988; Roddaz et al., 2006) rather than from basic rocks. The sediments with a basic component were most likely derived from metasedimentary rocks, such as muscovite-biotite schists. Thus, on the basis of chemical composition, the sediments are derived locally, mainly from highly acidic rocks, with minor contributions from basic rocks.

Application: The chemical data were plotted in a ternary diagram (silica-alumina-other oxides), as used by Fabbri and Fiori (1985) to classify raw materials and industrial ceramic bodies (Fig. 11). This diagram shows ceramic compositional fields and reflects the overall chemical composition of SADC raw materials. In this diagram, some samples plot into the white bodies’ field, but most of the samples do not. Taking into account the ideal composition for an optimum white body product according to the mentioned authors (SiO₂ = 72 wt.%, Al₂O₃ and total oxides = 8 wt.%), samples outside the white bodies field need processing.

Fig. 11:	Triangular diagram of SADC clays: SiO2 = Al2O3 = total oxides are plotted, (data from Fabbri and Fiori, 1985)

Fig. 12:	Ternary diagram SiO2-Al2O3-other oxides of the kaoliniteic materials from the SADC district and comparison with the Chemical composition of commercial kaolins (Ligas et al., 1997) and ball clays (after Fabbri and Fiori, 1985)

From their chemical composition, they could be considered as raw material for use in structural ceramic products (Konta, 1995). From chemical and mineralogical analysis, the studied clay samples are ball clays (Fig. 12 Bergaya et al., 2006).

The mineralogical and chemical composition of the SADC kaolins shows both favorable and adverse aspects for ceramic applications. These materials already use in ceramic industry.

The favorable characteristics are:

•	A simple mineralogical association, mainly represented by kaolinite and illite plus silica phases
•	The prevalence of kaolinite and illite to other minerals
•	The low iron amount, particularly if referred to a clay material, which allows these kaolins to be potentially used in white body production (Murry, 2007)

Nevertheless, the most relevant limitation, which could cause many problems in the ceramic manufacturing, is abundance of silica phases, prevailing on clay minerals, making these materials less plastic to be used as ceramic raw material. Pb in SADC kaolin makes it difficult to be used in both the pharmaceutical and paper industries. For the SADC kaolin to be used in the rubber and plastic industries, metals such as Mn, Fe and Cu should not exceed 5 ppm and soluble salts present is removed. The beneficiation processes may be expensive for any profit to be realized. Further beneficiation tests are needed for it to be considered for other industrial applications such as plaster, crayons, pesticides and insecticides.

CONCLUSION

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We analyzed 15 samples from three locations in South Abarkouh district of clay deposite (SADC), in order to determine their mineralogical and chemical compositions, REE characteristics, provenance and possible applications. XRD analyses show that the sediments are dominated by kaolinite, illite and quartz, with minor, chlorite, albite, gypsum, paragonite, natroalonite and goethite. From the weathering diagrams (Fig. 4, 5), it is possible to infer that the samples underwent a relatively high degree of weathering. Weathering has proceeded to a stage where a major part of the alkali and alkali earth elements were removed. The low CaO contents in sediments indicate their maturity relative to most typical post-Archean shales, such as NASC. The sediments are depleted in Ca, Na and Sr compared to Archean shale compositions (Condie, 1993; Condie et al., 1995). CIW values of around 93 and variations in CIA values from 82 to 95, indicate that the sediments contain residual clays rich in kaolinite (Taylor and McLennan, 1985). The low contents of Sc, Fe, REE, Th, Hf and Cr (and Co), and high La/Sc, Th/Sc, La/Cr, Th/Cr and Ba/Sc ratios in the sediments, all indicate that the sediments were derived from granitic rocks. This also agrees with the general shape of the chondrite-normalized REE patterns (including a negative Eu anomaly). The slight increase in the LREE is probably a source area effect. Mineralogical and geochemical data here reported that the provenance of the sediments was dominated by felsic sources. The basic component in the sediments was most likely derived from metasedimentary rocks, such as muscovite-biotite schists, while the felsic sediments are derivatives of granitoid rocks. We find that, despite intense weathering, which affected the contents of most elements, the REE, Th and Sc remained immobile; this observation can be considered as one of the most important geochemical results of the present study.

Even though all these materials are currently exploited in the production of various ceramic products, most of them are not comparable to commercially marketed European counterparts Nevertheless, the studied samples show interesting features for application in the ceramic sector if well treated, especially considering the high iron oxide content. However, due to the generally high quartz contents they may possess a refractory behavior. These clays have chemical and mineralogical compositions that indicate their useful for brick, ceramic and earthenware production. Further systematic applied testing of the clays has yet to be carried out to determine their physical, mechanical and technological properties.