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JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.74, July 2009, pp.27-34

Mineralogical Characteristics and Mineral Economics of Kaolinite Deposit of Sawa Area, Chittaurgarh, Rajasthan M. S. SHEKHAWAT and VEENA SHARMA Department of Geology, M. L. Sukhadia University, Udaipur - 313 001 Email: [email protected] Abstract: A large deposit of low-grade kaolinite is occurring within the rocks of Lower Vindhyan Supergroup southwest of Chittaurgarh, Rajasthan. The deposit is being utilised by open-cast, manual to semi-mechanised methods of mining. Kaolinite produced is being marketed without processing. Earlier, nearly 60% of the kaolinite produced from the area was consumed by cement industries, but in recent past, utilisation of low-grade kaolinite has been minimised by cement industries in production of ordinary cement and hence its production has significantly declined. Mineralogical studies reveal that kaolinite is the main clay-mineral and quartz, calcite, iron-oxides and biotite are present as non-clay minerals in clay deposit of the area. Chemical analysis of the kaolinite show that alumina ranges from 15 to 35% while, silica and iron varies from 51 to 78% and 0.25 to 2.50% respectively. Keywords: Kaolinite, China clay, Mineralogy, Mineral Economics, Vindhyan Supergroup, Rajasthan.

INTRODUCTION

A wide variety of clays are known to occur for the use of humanity. Chief amongst them are kaolinite, nacrite, montmorillonite, illite, attapulgite etc. (Wikipedia, 2008; Grim, 1953). Kaolinite (Al2O3 2SiO2 2H2O) is a microcrystalline mineral of kaoline group characterised by its softness, non-swelling nature on addition of water, chemical inertness over wide range of pH (4.5 to 7.0), low conductivity of heat and electricity etc. These properties make it useful for a large number of industries i.e. ceramic, refractory, paper, textile, rubber, paint etc. Kaolinite is generally formed by weathering or hydrothermal alteration of alumina rich older rocks or minerals viz. granite, gneiss, felspar, felspathoids and other silicates (Deer et al. 1971). Rajasthan is one of the leading producers of china clay in the country and accounts for about 20% of the national production. But the deposits are mostly low-grade and hence, per unit realisation is very low as compared to high-grade clay. Kaolinite deposit of the study area is occurring about 15 km southwest of Chittaurgarh (Fig.1) near the village Sawa (24°48'2"N - 24°45'6"N : 74°35'9"E - 74°34'1"E) within the rocks of Vindhyan Supergroup (Prasad, 1984). The deposit is located in flat land and covered with 1 to 4m thick layer of fertile soil (Fig. 2a) mostly used notably for growing opium crop. Two mining leases have been granted by the State Government that are producing about 81,485 tonnes

kaolinite valued at about Rs. 66.43 lakhs per year from the area (Ambash, 2006). It is being quarried by open-cast semimechanised method of mining (Fig. 2b). Three open-cast quarries measuring 850 m x 250 m x 45 m, 475 m x 270 m x 30 m and 80 m x 60 m x 20 m have been developed for production of kaolinite in the area. Field observations and samples for laboratory study were taken from these quarries. Lower Vindhyan rocks of Chittorgarh area have been studied by Coulson (1927), Heron (1936), Prasad (1984) and Srivastava and Gyan Chand (1984) but detailed studies on kaolinite deposit have yet not been carried. Hence, this study was taken up to describe mineralogical characteristics of the kaolinite using X-ray diffraction (XRD), Differential Thermal Analyses (DTA), Petrographic, Scanning Electron Microscopic (SEM) and Chemical Analyses studies. Mineral economics has also been discussed to understand economic importance of the resource. GEOLOGICAL SETTING AND FIELD CHARACTERISTICS

Kaolinite deposit of the study area occurs as a prominent band extending for about 4.5 km in strike length and has 150 to 450 m width (Fig.1). It overlies the Bhagwanpura limestone and is underlain by Sawa grit-sandstone unit belonging to Lower Vindhyan Supergroup (Prasad, 1984).

0016-7622/2009-74-1-27/$ 1.00 © GEOL. SOC. INDIA

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M. S. SHEKHAWAT AND VEENA SHARMA

Fig.1. Location map of the study area southwest of Chittaurgarh, Rajasthan (based on Google Earth, 2008). SS - Sawa sandstone, SG - Sawa grit, K - Kaolinite deposit, L - Laterite band, BL - Bhagwanpura limestone, Q - Kaolinite and laterite quarries, S - Stacks of low-grade kaolinite.

Bhagwanpura limestone is characterised by presence of organo-sedimentary structures resembling stromatolites (Raja Rao and Mahajan, 1965; Srivastava and Gyan Chand, 1984). The contact of Bhagwanpura limestone and kaolinite deposit is marked by occurrence of a prominent laterite band that extends parallel to entire length of kaolinite deposit (Fig. 1). The overlying Sawa grit is exposed as a thin bed and consists mainly of rounded to sub-rounded coarse grained quartz cemented in fine siliceous matrix with small amount of ferruginous material. It gradually merges into a prominent bed of sandstone (Sawa sandstone) which

is also described as orthoquartzite (Srivastava and Gyan Chand, 1984). These litho-units including kaolinite deposit are trending NNE-SSW with gentle easterly dips. The kaolinite deposit is comprised of three different lithological zones. From west to east these are: (i) a zone of laminated kaolinite, (ii) a zone of white to off-white massive kaolinite and (iii) a zone of gritty kaolinite. The laminated kaolinite shows alternate laminations of white and pink, and white and yellow colour (Fig. 2c). Width of individual lamina varies from 1 mm to 2 cm and contrast in colour of these laminations is more clearly observed in wet samples. The JOUR.GEOL.SOC.INDIA, VOL.74, JULY 2009

MINERALOGICAL CHARACTERISTICS OF KAOLINITE DEPOSIT OF SAWA AREA, RAJASTHAN

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white clay having soapy feel to touch and it is considered as good quality clay zone of kaolinite deposit of the area. However, at certain places, few patches of ferruginous nonlaminated and gritty kaolinite have also been observed in working quarries. This high-grade white kaolinite zone gradually merges into a prominent zone of gritty kaolinite that varies from 75 to 150 m in width and makes about 50% of the kaolinite deposit. It is composed mainly of fine grained white clay mixed with sub-rounded to angular, white, semitransparent granular quartz that varies from 1 to 3 mm in size. The grain size as well as proportion of quartz gradually decreases with increasing depth. Due to higher concentration and comparatively larger grain size of quartz, the kaolinite samples of this zone appear loose and friable. MINERALOGICAL CHARACTERISTICS XRD Analyses

Five representative bulk samples of kaolinite collected from two working quarries were prepared for XRD analyses using powder method (Cullity, 1978). The diffractograms were obtained on Phillips PD 1730 diffractometer (ADP10) using Ni-filtered, Cuka radiation at 40 kV and 30 nA at CRDL, Hindustan Zinc Ltd., Debari, Udaipur. XRD data obtained are given in Table 1. The values of d-spacing obtained for these samples were compared with those of different clay minerals from JCPDS cards. XRD data presented in Table 1 show that kaolinite is clay mineral in the bulk samples and other associated non-clay minerals are quartz, biotite, calcite and hematite. DTA Analyses

Fig.2. (a) Field photograph showing topography and longitudinal vertical section of a kaolinite pit of the area. (b) Quarry section showing development of benches in kaolinite. (c) Fine alternate brownish-yellow and white laminations in kaolinite.

kaolinite splits more easily along these laminations. Clayey material is fine grained and apparently there is no grain size variation in these laminations. However, intensity and colour contrast in these laminations gradually decreases from west to east i.e. from contact with laterite band to white kaolinite zone. At several places, joints or planes of weakness at right angle or inclined to the laminations have been observed in quarry sections. The middle kaolinite zone that varies from 20 to 30 m in width is composed mainly of very fine grained JOUR.GEOL.SOC.INDIA, VOL.74, JULY 2009

Differential thermal analysis (DTA) of two clay samples of the area has been carried out at Sophisticated Instrumentation Centre for Applied Research and Testing (SICART), Vallabh Vidyanagar, Gujarat by using DTA analyzer at the heating rate of 20°C/min upto a temperature of 1400°C. Calcined aluminum oxide was used as standard reference material. The DTA curves obtained for the samples (Figs. 3a and b) show that endothermic peaks of an area 2320 mJ and 3402.8 mJ are at 592°C and 578°C respectively. The exothermic peaks with an area of -1825 mJ and -2677 mJ are recorded at 1011°C and 1010°C for these samples. The nature and intensity of endothermic and exothermic curves of both the clay samples indicate that clay mineral of the area is kaolinite having quartz as major impurity (Grim, 1953; Deer et al. 1971; Mackenzie, 1972). Petrographic Study

Several thin sections of kaolinite samples collected from

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M. S. SHEKHAWAT AND VEENA SHARMA Table 1. XRD data of bulk kaolinite samples from Sawa area, Chittaurgarh, Rajasthan SK-1 d(A°)

Int.

7.13 4.25 3.57 3.33 2.49 2.45 2.38 2.33 2.28 2.23 2.12 1.97 1.81 1.54 1.37 1.25 1.20 1.18 1.08

33 16 28 90 2 7 3 3 6 3 4 3 11 8 6 2 2 2 1

SK-2 MI

d(A°)

Int.

K Q K Q K B K K B,Q K,Q K,Q K,B,Q Q K,B,Q B,Q Q Q Q Q

10.03 7.18 4.27 3.58 3.34 2.57 2.50 2.47 2.39 2.34 2.28 2.24 2.13 1.98 1.82 1.78 1.67 1.38 1.37 1.25 1.18 1.09

3 34 17 28 93 2 1 7 2 2 6 3 4 3 10 1 8 3 5 1 1 1

SK-3 MI

d(A°)

Int.

B K Q K K,Q K B,Q K,B K K K,B,Q K,Q Q K,B,Q Q K,B K,B,Q Q B,Q Q Q Q

10.03 7.18 4.48 4.26 3.58 3.34 2.57 2.45 2.37 2.34 2.28 2.24 2.12 1.98 1.81 1.67 1.54 1.48 1.45 1.37 1.25 1.18 1.08

3 26 1 17 23 89 2 6 2 2 5 3 5 3 9 3 8 1 1 6 2 2 1

SK-4 MI

d(A°)

Int.

MI

B K K Q K K,B,Q K K,B,Q K K K,B,Q K,Q Q K,Q Q K,B,Q B,Q K,B B,Q B,Q Q Q Q

10.27 7.02 5.00 4.51 4.26 3.58 3.52 3.35 3.06 2.98 2.70 2.56 2.52 2.46 2.28 2.24 2.13 1.98 1.81 1.67 1.54 1.45 1.38 1.37 1.28 1.25 1.22 1.20 1.18 1.15 1.08

7 10 3 3 51 10 2 230 1 1 6 4 3 24 13 8 16 7 29 7 20 5 9 13 3 5 2 3 7 3 4

B K Q K Q,B,K K,H K K,B,H Q,B,K Q,B,K Q,K Q,K Q,K Q,H Q,B,K Q,B Q,B,K,H Q Q,B Q Q,H Q,H Q Q Q,H Q

MI – Minerals identified, K – Kaolinite, Q – Quartz, B – Biotite, C – Calcite, H - Hematite

the different zones have been prepared and studied under polarising microscope. In most of the sections, the clayey material appears as white to pale-yellow granular aggregates or as amorphous mass (Fig.4a). However, the sections of laminated kaolinite show reddish-brown colour probably due to presence of fine grained impurities of iron-oxides (Fig.4a). The crystallised form of the clay minerals could not be observed even at higher magnification. Iron-oxides are also present as dark-red spherical disseminated grains within the clayey groundmass (Fig.4b). Quartz is present as distinct anhedral grains of variable size. In sections of laminated and massive white clay, grain size of quartz is fairly uniform while in that of gritty kaolinite, a considerable variation in grain size has been observed. Felspar grains appear partly or completely altered into clayey material retaining their original shape. However, a few fresh grains showing poor

twinning have also been observed. Calcite constitutes a considerable part of laminated kaolinite samples. It occurs as aggregate of small subhedral grains forming thin veins mostly along cracks in larger grains of quartz present in clayey material suggesting its secondary origin (Fig.4c). Biotite is present as small flakes with poorly visible one set of cleavages while, muscovite is present rarely as thin long slender flakes. Two samples of massive white clay were also scanned through electron microscope (LEO 430, CAMBRIDGE) at University Department of Geology, Udaipur. They reveal that clay of the study area is poorly crystallised with less distinct hexagonal outline. The edges of the grains are somewhat ragged and irregular, and show poor elongation in one direction (Fig.4d). This type of grain morphology is reflected mostly by kaolinite (Grim, 1953). JOUR.GEOL.SOC.INDIA, VOL.74, JULY 2009


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gritty kaolinite (samples 11, 12 and 13) is exceptionally high in silica and low in alumina. The FeO content is high particularly in samples of laminated kaolinite (samples 5, 6 and 7). The CaO shows abnormally high concentration in samples of white kaolinite (samples 8 and 9). MgO have fairly uniform values except two samples whereas values of K2O are high in kaolinite of marginal zones. MINERAL ECONOMICS

Fig.3. a and b. DTA curves of the kaolinite samples showing endothermic and exothermic peaks.

Chemical Analyses

The major element chemical analyses of 9 kaolinite samples have been carried out by using conventional method at J. K. Cement Ltd., Nimbahera. The analytical data presented in Table 2 show that kaolinite of the area is high in silica and low in alumina (cf. Deer et al. 1971; Jain, 1998) and they have negative correlation. However, among the three kaolinite zones, the massive white kaolinite (samples 8, 9 and 10) contains low silica and high alumina whereas

In India, china clay deposits are occurring in nearly all the states with total estimated reserves of 222 million tonnes (Ambash, 2006) which may also increase on detailed exploration. These deposits are mostly pocket type with thick overburden and fall under the category of low-grade and hence, quarried selectively on small-scale by manual to semimechanised methods of mining. The production data presented in Table 3 show that the states of Gujarat, Kerala and Rajasthan are the major producers of china clay in the country and account for more than 80% of the national production. It has also been observed that per unit realisation of china clay produced from Gujarat and Kerala is about two times more than that from Rajasthan. It is because large quantity of china clay produced in Gujarat and Kerala is being supplied to the consuming industries after suitable processing whereas in Rajasthan, it is being sold without any processing. In Rajasthan china clay is mainly produced from Chittaurgarh and Bhilwara districts. The china clay deposits of these areas contain high amount of ferruginous and gritty impurities. For a long period, from 1985-86 to 1995-1996, Rajasthan was leading producer of china clay in the country (Choudhuri, 1990, 1992, 1994; Sachdeva, 1995; Bose, 1996) which was due to use of large quantity of low-grade unprocessed china clay in production of ordinary cement by cement industries located around Chittaurgarh and other

Table 2. Chemical analyses of kaolinite of Sawa area, Chittaurgarh, Rajasthan Sample No.

SK-5

SK-6

SK-7

SK-8

SK-9

SK-10

SK-11

SK-12

SK-13

SiO2 Al2O3 FeO CaO MgO MnO K2O Na2O LOI Total

69.17 18.90 1.55 0.57 0.79 5.34 3.11 99.43

69.96 20.11 2.03 0.45 0.44 4.19 2.08 99.26

68.17 21.30 2.48 1.19 0.20 0.73 4.09 98.16

51.04 31.98 0.77 7.99 0.01 0.29 5.01 98.09

52.04 32.26 0.78 8.31 0.08 0.51 3.00 97.28

55.96 34.77 0.48 1.19 0.06 1.05 5.01 98.51

76.76 15.46 0.23 0.11 1.05 3.86 2.01 99.48

78.21 15.30 0.36 0.10 0.28 1.46 3.00 98.71

71.53 17.09 0.56 1.90 0.16 1.26 4.02 97.52

SK-5 to SK-7: laminated kaolinite, SK-8 to SK-10: white kaolinite, SK-11 to SK-13: gritty kaolinite JOUR.GEOL.SOC.INDIA, VOL.74, JULY 2009

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Fig.4. Photomicrographs showing (a) cryptocrystalline nature of kaolinite (K) of the area partly stained with ferruginous impurities. (Bar = 0.3 mm), (b) disseminated fine grains of hematite (H) within cryptocrystalline mass of kaolinite (K). (Bar = 0.3 mm), (c) thin veins of calcite (C) along fractures of large quartz grains (Q) present in kaolinite. (Bar = 0.8 mm), (d) SEM photomicrograph showing less distinct hexagonal outlines with ragged and irregular edges of the kaolinite grains.

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Table 3. Production and sale value of kaolinite in India during 2001-02 to 2005-06 (Quantity in tonnes and value in Rs. ‘000) States

2001-02

Andhra Pradesh Chhattisgarh Gujarat Haryana Jharkhand Karnataka Kerala Madhya Pradesh Maharashtra Orissa Rajasthan West Bengal Total Share of Rajasthan

2002-03

2003-04

2004 -05

Quant.

Value

Quant.

Value

Quant.

Value

Quant.

Value

100687 168 112246 22526 40941 15781 230019 24963 420 2825 180366 83817 814759 22.14%

9623 13 23663 2438 27044 10599 674201 1591 43 1558 24235 30157 805165 3.01%

110048 1535 122265 1520 34863 14787 223593 20947 360 3065 206493 83275 822751 25.10%

10349 131 31529 125 31576 10481 748966 1465 44 1855 26499 49212 912232 2.90%

89791 2167 154413 — 45280 13547 257650 25107 60 3177 219450 86242 896884 24.47%

9207 241 35422 — 36214 10659 816994 1864 7 1960 29515 40125 982208 3.00%

53170 2970 226063 — 60685 12372 334111 15522 890 8006 152699 67166 933654 16.35%

4234 309 49146 — 48500 10900 928525 1367 111 2353 15006 30881 1091332 1.37%

2005-06 Quant.

Value

27428 2172 1575 177 393901 69957 — — 70988 61784 10141 9928 335890 1145395 12750 1138 230 14 6505 1994 165214 17415 71942 31451 1096564 1341425 15.07% 1.30%

Source: Das (2004); Ambash (2005, 2006)

parts of the state. In production of ordinary cement it was used as suitable filler for blending the high strength lime kilns due to its fineness, softness and inertness over a wide range of pH. But over the last decade, the cement industries have minimised the use of low-grade china clay in production of ordinary cement and it has resulted in declining of its production in the state. The use of processed china clay has significantly increased in manufacturing of vitrified tiles in ceramic industries. But, china clay of the state could not find its use due to nonprocessing practices. The china clay deposits of Rajasthan are fairly large and have thin cover of alluvial overburden. Hence, these can be easily developed on large-scale to fetch national as well as global market if produced china clay is marketed after suitable processing. The data presented in Table 3 also reflect that the share of Rajasthan in production of kaolinite is about 20% but the value share is only about 3%, therefore value enhancement through beneficiation is suggested. SUMMARY AND CONCLUSIONS

The clay deposit of the area occurs as a prominent band near to the ground surface having a thin soil cover (1 to 4 m) and characterised by presence of lithological zoning. The core is composed mainly of massive white clay where as western and eastern marginal zones are composed of laminated and gritty kaolinite respectively. XRD, DTA, petrographic and SEM studies show that kaolinite is the only clay mineral and quartz, felspar, biotite, muscovite, calcite and hematite are non-clay minerals in JOUR.GEOL.SOC.INDIA, VOL.74, JULY 2009

kaolinite deposit of the area. Kaolinite occurs as fine-grained aggregates with poor crystallinity. Quartz, felspar and hematite are present as subhedral to euhedral grains while, biotite and muscovite found in the form of small flakes. The grain morphology of kaolinite and associated minerals suggests that they have undergone a long transportation from the source area to the basin of their deposition. The mineral assemblages of the kaolinite deposit also indicate that they have been derived from quartzo-felspathic crystalline metamorphic rocks. Thus, it has been concluded that kaolinite is formed by alteration of felspar of widely distributed Banded Gneissic rocks (Heron,1953) reclassified in the region as Mangalwar Complex of Bhilwara Supergroup (Gupta et al. 1997) occurring about 10 km west of the study area. The pink and yellow coloured laminations in kaolinite deposit are due to addition of percolating ferrous and ferric solutions from adjoining older laterite band along fractures or joints. The abnormally high concentration of CaO in the form of thin calcite veins observed in few samples can be explained by addition of carbonate solutions derived from Bhagwanpura limestone of the Lower Vindhyan sequence. The chemical analyses presented in Table 2 show that kaolinite of the area is nearly 10 to 25% higher in silica and depleted by same amount in alumina as compared to good quality kaolinite of the country (cf. Deer et al. 1971; Jain, 1998). The laminated kaolinite does not find any use due to presence of high content of iron-oxide (1.5 to 2.55%) and hence, treated as rejected mineral waste. The gritty-kaolinite that contains very high amount of silica (71 to 78%) and very low amount of alumina (15 to 17%) finds only a limited

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use in ceramic industries due its good whiteness. Thus, it has been concluded that kaolinite of the area should be upgraded by suitable methods of beneficiation for its appropriate and extensive utilisation. Acknowledgements: The authors are greatly indebted to Prof. P. S. Ranawat, Department of Geology, Mohanlal Sukhadia University, Udaipur for his suggestions to improve this manuscript. They are grateful to Dr. R. N. Roy, Senior Manager (Geology) CRDL, HZL, Udaipur and the Director SICART, Vallabh Vidyanagar, Gujarat for providing XRD

and DTA laboratory facilities respectively. The authors are thankful to Shri Sudhir Shrotriya, Dy. General Manager (Geology), J. K. Cement Ltd. Nimbahera for providing chemical analyses of kaolinite samples of the area and useful discussion during the field study. The Head, Department of Geology, M. L. Sukhadia University, Udaipur is gratefully acknowledged for extending other required facilities for completeing this work. The authors are also thankful to Shri B. C. Bhattacharya, Ceramic Engineer, Department of Mines and Geology, Government of Rajasthan, Udaipur for his helpful discussion.

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Geology of the Aravalli Region Southern Rajasthan and Northeastern Gujarat. Mem. Geol. Surv. India, v.123, 262p. HERON, A.M. (1936) The Geology of South-Eastern Mewar. Mem. Geol. Surv. India, v.68(1). HERON, A.M. (1953) The Geology of Central Rajasthan. Mem. Geol. Surv. India, v.79(1), 386p. JAIN, A.K. (1998) Exploration, mining and prospecting/upgrading issues of kaolin (china clay) in India. Proc. Conf. on “Indian Industrial Minerals” held at Udaipur, India, v.1, pp.214-217. MACKENZIE, R.C. (1972) Differential thermal analysis. Academica Press, London, pp.4, 8, 168. PRASAD, B. (1984) Geology, Sedimentation and Palaeogeography of the Vindhyan Supergroup, South-Eastern Rajasthan. Mem. Geol. Surv. India, v.116(1), 107p. RAJA RAO, C.S. and MAHAJAN, V.D. (1965) Notes on stromatolites and probable correlation of the Bhagwanpura limestone, Chittaurgarh district, Rajasthan. Curr. Sci., v.34(3), pp.82-83. SACHDEVA, O.P. (1995) Indian Minerals Year Book, IBM, Nagpur. v.2, Part-I, pp.435-440, Part-II, pp.5, 56-57. S RIVASTAVA , H.B. and G YAN C HAND (1984) Geological and Sedimentological studies of the rocks south of Chittaurgarh, Rajasthan. Rec. Geol. Surv. India, v.114(2), pp.69-75. WEBSITE: http://en.wikipedia.org/wiki/Clay. October 2008.

(Received: 20 October 2008; Revised form accepted: 10 December 2008)

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