Compositional Features and Industrial Assessment of Talcose Rocks of Itagunmodi-Igun Area, Southwestern Nigeria

Talcose rocks from Itagunmodi and Igun areas within the Ilesa Schist Belt, southwestern Nigeria, were studied to determine their compositional affinities and industrial properties. The talcose bodies occurred as lensoid enclaves closely associated with amphibolites and quartz-mica schist. Petrographic and X-ray diffraction-aided mineralogical studies reveal that the talcose rocks are of the talc-chlorite schist variety composed predominantly of talc (average 73.63%), subordinate chlorite (average 16.08%) and accessory lizardite (average 6.5%). Total whole rock characterization of the samples using Lithium Fusion digestion revealed high mean concentrations of SiO2 (57.53%), MgO (24.84%) and Fe2O3 (7.73%) with significant enrichment of Ni, Co and Cr; and low values of Ba, Rb, Sr, V, Cu and Pb. The talc-chlorite schists plotted in the peridotitic komatiite field of the Al2O3-(FeO + TiO2)-MgO diagram. Water Absorption Capacity ranges from 6.25% 8.20%, Loss on Ignition is 4.8% 6.1% while Linear Shrinkage is 1.25% 1.70% and firing colour is brown to dark-brown. The overall compositional features of the talcose rocks of the area, which were hitherto uncharacterized, show their suitability as raw materials for paint, coloured pottery, ceramic insulation, textile, rubber and plastic manufacture with varying beneficiation requirements. Their high trace element content however, makes them unsuitable for use in pharmaceutical and cosmetic applications.


Introduction
Talcose rocks, which are alteration products of mafic and ultramafic rock units, grade metamorphism. The Ilesa schist belt, located in southwest Nigeria, is one of such belts, hosting the Ifewara fault Zone-which divides the belt into two contrasting lithologies composed mainly of schist (of quartz, biotite, garnet and muscovite mineralogy) and gneisses; along with pelitic schists, quartzites and metabasites on the eastern and western halves respectively [3]. Talc, the essential mineral in these rocks, is an important industrial mineral with wide and varied usage. Notable occurrences of talc bodies in southwest Nigeria include Baba Ode [4], Erin Omu [5], Wonu-Apomu [6], Kumaru [7], Oke-Ila [8], Ile Ife, Ikirun and Esa Oke [9]. Talcose, tremolitic, chloritic and anthophyllitic are the four major mineralogical varieties of talc bodies identified in the Southern area [10]. A number of talcose rock occurrences have been studied for their petrology, petrogenesis [9] [11] and industrial features [12]. The talcose rocks of Itagunmodi-Igun area have, however, not been characterized in terms of their compositional properties. This study therefore involves a mineralogical, petrochemical and physical characterization of these rocks in order to elucidate their compositional characteristics and their potential as industrial raw material.
The study area is located west of Ilesa town, within latitudes 7˚30' -7˚35' and longitudes 4˚37' -4˚42' (Figure 1), covering an area of about 81 km 2 . Six representative samples of the outcrops, collected during a geologic mapping on 1:10,000 scale, were prepared for thin section examination under the petrological microscope. Pulverized samples were analysed for elemental composition using

Field Relationship and Petrographic Features
Low to medium-grade metamorphic rocks dominated by quartz-biotite schist, with quartzite and amphibolite occur along with the talcose rocks in the study area ( Figure 2). The study area lies west of the Ifewara Fault Zone (IFZ) [13] [14], within the Ilesa schist belt; in which talc bodies are known to be closely associated with amphibolites, quartzite and pelitic schists [9]. The talcose rocks Figure 1. Location of Itagunmodi-Igun within the Proterozoic Schist Belts of Nigeria (after [15]). occur as discontinuous lensoid enclaves within amphibolites of massive textural variety and quartz-biotite schist in the western and eastern parts of the study area respectively ( Figure 2). This is in line with the assertion that talcose rocks of Nigeria associate closely with mafic and ultramafic rocks [9]. In the western half of the study area, they continue intermittently for a strike length of about 6 km with a north-easterly trend. They were observed occupying low lying areas within the study area, with quartzites and amphibolites forming ridges at the northwestern and central to southern parts of the study area respectively. On outcrop scale, the talcose rocks have a characteristic soapy feel, dirty-white colour and are extremely fine-grained, occurring mostly as poorly exposed outcrops

Discussion
Mineralogical and elemental data of the samples were interpreted to unravel the compositional characteristics, petrogenetic affiliations of the rocks, and physicochemical properties were investigated to determine their suitability as industrial materials.

Mineralogy
Thin section study of the rocks revealed a predominant mosaic of talc aggregates   (Table 2).

Chemistry
Major oxide concentration in the samples analysed include    (Table 4). Loss on Ignition in the analysed samples ranged from 4.80 -6.10 (Table 3).
A comparison of the average major oxide content of the talc-chlorite schist of the study area with talcose rocks from Esie, Oke-Ila, Iseyin and other parts of southwestern Nigeria indicates that silica concentrations are comparatively similar, the magnesia in the talcose rocks of the study area is less than the other areas compared, while it has higher ferric oxide. The alumina content is less than those in talcose rocks of Oke-Ila and Iseyin (  -18  20  10   Chlorite  16  14  17  -16  17  14  15  16  20  22  12  8   Hornblende  12  13 11    Iseyin, while Zn and Co concentrations are less. The relative chemical mobility of Na, Ca and K during secondary alteration processes [9] is visible in strong depletions of oxides of these elements relative to amphibolites and quartz-mica schists having field relationships with the talcose rocks.
The low values of Ba, Sr and Rb are probably due to their chemical instability during secondary alteration processes [9]. Cr and Ni are chemically immobile, even under hydrothermal alteration conditions, and this explains their enrichment in the talcose rocks in the study area. Zr and Sr also have low values in the talcose rocks likely due to the absence of mineralogical phases in the rock to host them.
On the Al 2 O 3 -(FeO + TiO 2 )-MgO plot of [18], the talc-chlorite schist plot in the peridotitic komatiite field ( Figure 6). This assertion is supported by the low concentrations of aluminium and potassium oxides, and the high magnesium content in the rocks ( Table 3). The talcose bodies were therefore, most likely metamorphosed from a komatiite; an ultramafic mantle-derived volcanic rock.
The talcose rocks also plot within the komatiitic field on [19]

Industrial Appraisal
Talc, as an industrial mineral, has found application in the manufacture of various products such as ceramics, cosmetics, rubber, roofing sheets, paper, pharmaceuticals, paint and insecticides [20]. The suitability of talc for industrial application is largely a function of its physico-chemical properties.  (Table 6).
A comparison of industrial properties of talcose rocks of the study area with those of other parts of south western Nigeria indicates that the WAC values for rocks from the study area are lower than those from Wonu-Apomu, Erin-Omu, Journal of Geoscience and Environment Protection other areas are wider than those of the study area, while the LOI are comparable with talcose rocks in Iseyin and Wonu-Apomu (Table 7). Average talc composition in the Itagunmodi-Iguntalc-chlorite schist is comparable to industrial and pharmaceutical grade Luzenac talc deposit in France [21] but significantly higher than the talc composition of Lumphurm [22] and Pitchbury [23] textile-, and rubber-grade talc deposits respectively. Mean chlorite compositions in the Pitchbury, Lumphurm and Itagunmodi-Igun talcose bodies are approximately the same (Table 8).

Journal of Geoscience and Environment Protection
Talc is a versatile industrial mineral useful in the manufacture of paints, cosmetics, pharmaceuticals, detergents and agricultural products. Talc, when used as a cement substitute, has less energy-intensive production requirement than Portland Cement and absorbs far more carbon dioxide as it hardens, thereby leaving a negative carbon footprint.
On the ISO Quality Specification for talc [24], the talcose rocks of the study area fall in Types C and D for wt% talc content (with values ranging from 68% -91%), and Type A for wt% LOI at 1000˚C (with values 4.8% -6.1%).
When fired, the talcose rocks are brown to dark brown in colour, making them suitable as materials for insulation ceramics and in coloured pottery, but not as white wares and enamels as these require a white firing colour and an average of 6% CaO [25] [26]. The maturing temperature of the talc could be improved as a result of the presence of aluminium-rich chlorite, thereby increasing its usability for ceramic manufacture. Also, the absence of iron minerals in the talc schists is advantageous as they are known to cause spotting in ceramics [6].
They will also find use in the manufacture of plastics, textiles, paint, rubber and  (Table 3). However, they areunsuitable for paper manufacture as the requirements include white colour, fine grain, no mica content and very low Fe 2 O 3 and CaO contents [28]. The talc-chlorite schists have high Fe 2 O 3 content and are brown to dark brown in colour post-bleaching. They also do not meet the criteria for refractory materials [29], as their Fe 2 O 3 and SiO 2 contents are too high. To be desirable as raw material for the improvement of the rigidity and stability of rubber at high temperature during polypropylene plastic manufacture, talc raw materials should have low specific gravity, fine particle size distribution, softness and good colour [28]. The talcose rocks of the study area meet most of these criteria and will be useful if well processed. To be used in textile manufacture, talc raw materials are required to be free of hard/gritty particles (e.g. calcite, quartz), smooth, greasy, have good colour and moisture content < 0.3%. Though the talc deposits in the study area are essentially free of gritty particles, are smooth and greasy; its colour may restrict its use to certain textile types/varieties. They should also be properly processed to remove potential impurities like chlorite and hornblende.
Although the talc content in the talc-chlorite schists of the study area are comparable with that of the Luzenac pharmaceutical grade talc deposit [21], due to the elevated concentrations of trace elements (Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V and Zn) in the talcose rock, which far exceed minimum risk levels prescribed by the Agency for Toxic Substances and Diseases Registry ( [30]; Table 9), they are unsuitable as raw materials in the production of pharmaceutical and cosmetic products. They are however useful, if beneficiated, as industrial grade talc raw materials.

Conclusion
Talc