Geochemical study of laterites of the Jamnagar district, Gujarat, India: Implications on parent rock, mineralogy and tectonics

Journal of Asian Earth Sciences 42 (2011) 1271–1287

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Geochemical study of laterites of the Jamnagar district, Gujarat, India: Implications on parent rock, mineralogy and tectonics R.R. Meshram a,b, K.R. Randive a,⇑ a b

P.G. Department of Geology, R.T.M. Nagpur University, Nagpur (MH) 440 001, India A.M.S.E. Wing, Southern Region, Geological Survey of India, Bandlaguda, Hyderabad 500 068, India

a r t i c l e

i n f o

Article history: Received 9 December 2009 Received in revised form 27 April 2011 Accepted 19 July 2011 Available online 6 August 2011 Keywords: Laterite Bauxite Geochemistry Palaeotectonics Flood basaltic province Aluminous laterite Deccan traps

a b s t r a c t The laterite deposits occur in a linear stretch along the northern Arabian Sea coast in the Jamnagar and Porbandar districts of, Gujarat state, India. These deposits are characterised by presence of gibbsite, kaoline, calcite, quartz, anatase, natroalunite, goethite and hematite, and relicts of mafic minerals and plagioclase. On the basis of petro-mineralogy and geochemistry, these deposits are grouped as aluminous laterites (Fe2O3 – 1.45–3.84%, Av. 3.13, Al2O3 – 39.31–57.24, Av. 45.80) and laterites (Fe2O3 – 9.84– 32.21, Av. 25.13%, Al2O3 – 34.74–49.59, Av. 41.27). The major, trace and REE characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic/andesitic composition, and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation. The correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements. The Jamnagar laterite deposits occur as capping over the Deccan Trap basaltic lava flows and pyroclasic deposits. Lateritisation prevailed during Palaeocene age when India was separated from the Seychelles and passing over the equator. During this time climate, morphology and drainage conditions were favourable for lateritisation that result in the formation of Jamnagar and other laterite deposits within the Deccan Province. Flood basaltic provinces of Deccan, Columbia, North Australia and Hawaii appear good location for hosting laterite deposits due to their wide areal extent, small geological time span and uniform chemical composition. However, comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate, morphology and drainage are equally important factors for facilitating lateritisation. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The major and trace element geochemistry has become an indispensible tool to investigate various aspects of laterite/bauxite formation such as parent rock composition, diagenetic and epigenetic processes related to bauxitisation, environmental condition (Eh–pH, drainage, climate), mineralogical changes in parent rock (Mordberg, 1993; MacLean et al., 1997; Esmaily et al., 2009). There are many publications that address the trace element geochemistry of bauxites, most of these though devoted to identifying peculiarities of element distribution and behaviour in profiles of particular deposits or bauxite districts (e.g. Bardossy and Aleva, 1990; Mordberg, 1996; Calagari and Abedini, 2007). Many others record mineralogical influence on the distribution of trace elements such as gallium (Chowdhury et al., 1965), titanium (Paul, 1969), zirconium, scandium, yttrium (Mordberg and Spratt,

⇑ Corresponding author. E-mail address: [email protected] (K.R. Randive). 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.07.014

1998), cerium and other REEs (Gonzalez Lopez et al., 2005; Esmaily et al., 2009) and an array of multiple trace elements including U, Th, Zr and Nb (Mordberg, 1996). It is generally agreed that dissolution of the minerals (which is related to the Eh–pH, solubility, water, climate), and entrapment of their constituents in the crystallising or precipitating phase under surfacial conditions govern the distribution of trace elements in laterites. External influences such as, solutions percolating through the overlying sediments or brought from fractures/faults in structurally disturbed area; precipitation of groundwater if the deposits are low-lying; or evaporates if the deposit was near the sea coast during geological past; may also sometimes contribute trace elements, although such influences could be accounted for only when their source is traceable. The residence, migration and redistribution of these elements from minerals of parent rock to present day laterites form an important topic of study. The Jamnagar laterite deposits (Lat 21°450 –22°170 Long 69°150 – 69°230 ) in Gujarat, India, provide an interesting location for the geochemical investigation of laterites for the reasons mentioned below:

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(a) Spatiotemporal location of the deposition sandwiched between Late Cretaceous–Eocene basaltic magmatism and Miocene sedimentary formation. (b) Occurrence of extrusive, especially, pyroclastic facies of the Deccan Trap Magamtism in and around bauxite deposits (Sahasrabudhe, 1978). (c) Location in the tectonically active area throughout their geological age (Burke and Dewey, 1973; Sychanthavong and Patel, 1987; Biswas, 1987). (d) Occurrence of economically high-grade aluminium deposits (Bhatt, 1996). Besides, this study also provides an opportunity to understand the implications of lateritisation process on palaeotectonics.

2. Geology The Saurashtra region of Gujarat (Fig. 1) is composed of Mesozoic and Cainozoic rocks. The Mesozoic rocks are divided into two formations, the older Dhrangadhra Formation and the younger Wadhawan Formation of the lower Cretaceous age. The Deccan lava flows cover large areas in the Saurashtra region and vary in thickness from few hundreds to thousands of metres and overlie 100–4000 m thick Mesozoic sediments and underlie Tertiary rocks, comprised of marine and fluviomarine strata (Biswas, 1983; Merh, 1995). These Tertiary rocks are divided into lower Gaj formation, middle Piram beds and upper Dwarka Formation. Laterites are sandwiched between the lower Deccan Traps and upper Tertiary rocks.

Fig. 1. Geological map of the Jamnagar laterite deposits. Key map of India shows location of Gujarat, enlarged part shows Saurashtra region and study area, lines AA0 and BB0 are shows position of the geological cross sections (C. S.). Vertical scale is highly exaggerated in comparison to the lateral scale; especially the inset along BB0 Profile is much more exaggerated to show the laterite deposits. Sample locations: (1) AST-1 & AST-2; (2) VR-1, VR-2 & VR-3; (3) MWS-1 & MWS-2; (4) KTR-1 & KTR-2; (5) LM-1 & LM-2; (6) STR-1, STR-2, STR-3 & STR-4.

R.R. Meshram, K.R. Randive / Journal of Asian Earth Sciences 42 (2011) 1271–1287

The laterite deposits of Jamnagar district, occur in the form of linear discontinuous outcrops stretching along NE–SW direction between Gulf of Kutch in the north and Arabian Sea coast in the south for a distance of about 52 km. The width of the lateritic outcrop varies between 1 and 6 km, covering around 200 km2 area (Fig. 1). The laterite capping rises to a height of 30–60 m above mean sea level, variable thickness, but rarely exceeding 7.5 m. Profiles exposed in the mine sections typically contains soil, younger sediments, laterite and host rock (Fig. 2A). These outcrops are sandwiched between older lava flows and younger Gaj sediments (Sahasrabudhe, 1978; Jayaram and Majumdar, 1979; Biswas, 1983, 1987; IBM, 1993; Merh, 1995). The laterite occurring in the Jamnagar district varies greatly in colour (pink to grey/brown to red, depending upon Al and Fe percentages) as well as texture (massive, pisolitic, and clayey). The lithomarge zone (Saprolite) displays creamy white, yellow and red (ochreous) colours. Pisolites are most commonly observed in the reworked ferruginous bauxite zones (Kalsotra et al., 1986). Oolites (<2 mm), pisolites (2–20 mm) and concretions (>20 mm) are sparsely distributed within laterites and sometimes occur segregated within the homogenous aluminous matrix. These are nucleated by

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gibbsite or goethite and surrounded by concentric rings. The rings occur mostly in light grey and brownish shades and could result from the difference in enrichment of ferruginous material (Fig. 2B). On the basis of their mode of occurrence, the bauxite deposits of Jamnagar district are broadly divided into two groups, (i) bouldary/nodular and (ii) massive blanket type (Sahasrabudhe, 1978). The bouldary or noduler bauxite occurs as hard, compact, greyish or pinkish boulders and nodules which are embedded in a clayey matrix. The size and concentration of boulders are variable. The deposits are lensoid or bun-shaped with a convex upper surface. The mineralised horizon is bouldary with ellipsoidal and irregular blocks which form as an aggregate of smaller nodules (Fig. 2C). The thickness of this zone is nearly 4 m. Though there is a lateral repetition of lenses, connected with thin necks, vertical repetition is not seen. The material in these lenses is highly heterogeneous and varies in composition from low grade laterite to high grade, alumina-rich ore (Bhatt, 1996; Meshram, 2009). The massive blanket type of deposit is more ferruginous than the bouldary type. The ore is hard, compact and massive, and overlies a clay horizon. The massive type shows red, brown and pink colours and has a mottled appearance (Bhatt, 1996).

Fig. 2. Field photographs and thin section photomicrographs of Jamnagar laterites, (A) laterite profile showing various zones distinguished by different colours. The numbers on photograph indicates 1 – soil, 2 – limestone, 3 – yellow and purple clay, 4 – laterite, (B) hand specimen showing a composite pisolite having rings of different colours in brecciated textured bauxite, (C) grey pebble of gibbsite in the pink aluminous laterite at the contact of blunt head of the hammer. Other smaller nodules are also present, (D) photomicrograph showing colloform texture in bauxite, (E) the multicoloured oolite of iron oxides in the laterites, (F) relict plagioclase feldspar (white laths) encircled by opaque minerals (figure D–F are photomicrographs).

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3. Definition and nomenclature Valeton (1972) used the term ‘laterite’ to designate Fe–Al rich deposits of Jamnagar district, Gujarat. However, Sahasrabudhe (1978) used term ‘bauxite’ for these deposits and coined a term ‘Jamnagar Bauxite Belt’ to refer the linearly disposed outcrops in Jamnagar and adjoining Porbandar districts of Gujarat (Fig. 1). Many other workers indiscriminately used either of these terms, which created some confusion (see Jayaram and Majumdar, 1979; Biswas, 1983; IBM, 1993; Merh, 1995; Bhatt, 1996). Indeed, there are Al-rich and Fe-rich concentrations within these outcrops, which is clearly demonstrated in their respective chemical analyses. The following discussion is aimed at addressing this issue so as to provide appropriate nomenclature while referring to the Jamnagar deposits. Laterites and bauxites are the rocks enriched in iron and aluminium respectively. They can be ores of these metals, but also are mined for concentrations of Ni, Au, Nb and P (Freyssinet et al., 2005; Retallack, 2010). Bauxite is an assemblage of oxides and hydroxides mainly of aluminium along with iron and titanium. The preponderant aluminium minerals represent more than half of the rocks by weight. Bardossy (1982) classified bauxites as: lateritic bauxite (formed in situ by weathering in hot tropical climate) and karst bauxites (formed in place, transported or trapped within limestone rocks). Some recent classifications (e.g. Bogatyrev and Zhukov, 2009) group them into: lateritic bauxites (residual or in situ), sedimentary bauxites (proximal redepostion of bauxites on hillsides, proluvial, colluvial and alluvial), and karstic bauxites (characterised by localisation on the karstified surface of limestones). Laterites on the other hand, are products of intense meteoric alteration, and are composed of a mineral assemblage that

may contain goethite, hematite, aluminium hydroxide, kaolinite, and quartz. The SiO2/(Al2O3 + Fe2O3) ratio, compared to that of parent rock, should be such that the lateritic formation does not contain more silica than retained in the residual quartz and that needed for formation of kaolinite (Schellmann, 1981, 1986). Petrographic and chemical nature of laterites vary according to their age, nature of the climate, and the sequence of palaeoclimates that have controlled their development (Tardy, 1997). The Jamnagar deposits occur extensively over the lava flows and pyroclastic deposits of the Deccan Trap basaltic magmatism, and not over the Gaj limestones. On the basis of their mineralogy and geochemical attributes they may be called as lateritic bauxites as per Bardossy (1982) and Bardossy and Aleva (1990). However, at some places (e.g. Virpur and Lamba), the deposits may also be called as laterites (see Schellmann, op cit). However, Tardy (1997) suggested that the soft or indurated aluminous accumulations called bauxites, as well as the ferruginous cuirasses and all the other alumino-ferruginous and ferrialuminous accumulations intermediate between two principle types (i.e. laterires and bauxites) are lateritic formations. Valeton (1972) in his study of the Gujarat deposits stated that all laterites of the high-level plateaus are identical with the Al laterites in Gujarat, which in vertical and lateral facies changes from fersiallites in central parts of the plateaus to allites along valley slopes. He proposed three groups: (1) laterites rich in Fe and Si (in central parts of the plateaus), (2) aluminous laterites (on valley edges with good drainage), and (3) siliceous facies of laterites (on the edges of flat fossil sources with slow rates of drainage). The Jamnagar deposits fall in the second group, and represent the aluminous laterites and not the bauxite. We therefore prefer to use following terms for the Jamnagar deposits (a) laterite for the

Table 1 The field and petrographic characteristics of the studied localities of the Jamnagar laterite deposits. Sr. no.

Locality

Field characteristics

Petrography

1

Mewasa (22°170 : 71°050 )

In the Mewasa area laterite is brecciated or fragmentary. Fragments vary in size, shape and composition. These fragments are dispersed in a fluidised media occupying matrix. Gibbsite occurs as: (i) fine grained (with yellowish tinge), (ii) dark brown (with other opaque minerals), (iii) forming colloform banding (Fig. 2a) and (iv) spongy textured (Fig. 2b)

2

Asota (22°160 : 69°230 )

3

Virpur (22°150 : 69°200 )

4

Mahadevia (22°110 : 69°230 )

5

Satapar (21°570 : 69°150 )

6

Lamba (21°540 : 69°190 )

Village Mewasa is located about 5 km south of Virpur facing the Gulf of Kutch. The terrain comprises undulating plains with low lying plateaux and hills. High grade pockets of laterite are located on the northern and eastern hill slopes of Karamkund, at about 1.6 km NE of Mewasa. The fawn grey, saffron and pinkish bauxite occur in pockets below vermicular laterite and followed at depth by kaolinitic clay. The laterite is pisolitic, concretionary and bouldary with an average thickness of 1.2 m This area is a flat terrain with few low lying mounds, and plateaux exposing Gaj limestone. Laterite horizons are present on EW trending ridge towards SW of Mota Asota. The fawn grey to pinkish brown, soft and friable ore body occurs below the pink clay horizon, average thickness being 1.5 m. Economic grade of the ore body is variable Virpur is located WSW of Mota Asota facing Gulf of Kachchh. The concretionary and vermicular laterite occur as capping on the hill tops while saffron to grey, massive and concretionary or brecciated ore occur as pockets along the lower slopes. The average thickness of bauxite is 3 m, of which the lower 1.5 m portion constitutes high grade ore. Below the laterite horizon, light pink, off-white and violet lithomarge clay is present Mahadevia is situated about 6.5 km SW of Mewasa. A prominent N–S trending 2.4 km long laterite ridge is located towards SE of Mahadevia. The deposits are bun shaped, fawn grey to greyish green, bouldary and concretionary in nature. The fine, splintery and scaly gypsum bearing greenish black clay overlie laterite. An extensive elongated outcrop of aluminous laterite is located towards 1 km NE of Navadara village amidst peneplained and low lying humps of Gaj limestone. The aluminous laterite outcrop is 1.5 to about 3 m thick, grey to cream coloured, hard and compact. In the northern part, aluminous laterite containing patches of emery grade, whitish, greyish (fawn grey to cement grey) and brownish ore are present Lamba is located 8.5 km southeast of Navadara on Bhatia–Porbandar road. Ore deposits are associated with a series of undulating humps and low lying hillocks, which are exposed discontinuously for over 7 km in

The laterite is chiefly composed of gibbsite, which is irregular and traversed by micro-veins of calcite and Al–Fe–Ti oxides. Gibbsite is often rimmed by brownish-yellow limonite, opaque crystals of hematite (Fig. 2c) and small needles of rutile/anatase Aluminous laterite varies in colour from earthy white, yellow to brownish dull, whereas laterites occur in shades of brown, earthy and red. These are composed of abundant oolites and relict minerals (Fig. 2d). Laterite occasionally form pebble like structures, for which they were described as ‘bauxite conglomerate’

Laterite is comprised of yellowish brown gibbsite, which showing liesengang banding (Fig. 2e). These bands vary in colour between yellowish white and dark. Irregular patches of relict minerals are rimmed by dark brown bands. Oolites of variable size are sparsely present. In the Satapar area, laterites mostly occurs in three textures namely, (i) tabular to prismatic coarse bauxite, (ii) smaller oolitic (Fig. 2f), and (iii) larger pisolitic. The coarse laterite is yellow to brown in colour and shows brecciation. Oolites vary in shape from subrounded to elongated (elliptical) and forms chain like structures Laterite varies in colour between yellow–brown-deep red–black. The thin sections show presence of, (i) abundant ferruginous oolites, (ii) goethite–limonite and hematite, (iii) relicts of plagioclase feldspar, and

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Fig. 3. Various textures and structures exhibited by the Jamnagar laterites: (a) colloform banding structure in the laterite from Mewasa area, (b) spongy texture exhibited by the laterite from Mewasa area, (c) the gibbsite crystals separated by iron-rich opaque material imparting brecciated structure to the bauxite of Asota area, (d) relict texture seen in the laterite from Virpur area, (e) the lisengang banding structure seen in the laterite of Mahadevia area, and, (f) oolitic texture observed in the laterite from Satapar area.

formation characterised by presence of gibbsite, hematite, goethite, ilmenite and anatase; Fe2O3 – 9.84–32.21 Av. 25.13%, Al2O3 – 34.74–49.59, Av. 41.27; occurring in localities Virpur and Lamba, and (b) aluminous laterite for the formations characterised by presence of gibbsite, kaolinite, calcite and quartz; Fe2O3 – 1.45–3.84%, Av. 3.13, Al2O3 – 39.31–57.24, Av. 45.80; occurring in localities Asota, Mewasa, Mahadevia and Satapar. 4. Sampling and analytical techniques Six localities were selected from north to south along the Jamnagar laterite outcrops, where rich deposits are located and working mines are also present. These localities include: Asota (22°160 ; 69°230 ), Mahadeia (22°110 ; 69°170 ), Mewasa (22°170 ;

69°180 ), Virpur (22°150 ; 69°200 ), Lamba (21°540 ; 69°190 ), and Satapar (21°570 ; 69°150 ). Samples were collected at the above sites in order to analyse the mineralised portions of the district. Among the samples collected, 15 whole ore samples including Asota (2), Mahadevia/Kataria (2), Mewasa (2), Virpur (3), Lamba (2) and Satapar (4), were selected for mineralogical and geochemical study (Fig. 1). Mineralogical studies of the laterites were carried out using Nikon 50i POL Microscope at the Department of Geology, RTM Nagpur University and X-ray diffraction analysis was carried out at the Petrology, Petrochemistry and Ore-Dressing division of AMSE Wing, Geological Survey of India, Bangalore. The analysis was carried out using PANalytical X’Pert PRO XRD System. The DTA and TGA was obtained using PERKIN ELMER DIAMOND TGDTA

Table 2 X-ray diffraction analyses of the laterite deposits of Jamnagar area. Sr. no

Locality

Sample no.

XRD based mineralogy (in order of their decreasing abundances)

1 2 3 4 5 6

Asota Mahadevia (Kotharia) Mewasa Virpur Lamba Satapar

AST-1 and AST-2 KTR-1 and KTR-2 MWS-1 and MWS-2 VR-1, VR-2 and VR-3 LMA-1 and LMA-2 STR-1, STR-2, STR-3 and STR-4

Gibbsite, Gibbsite, Gibbsite, Gibbsite, Gibbsite, Gibbsite,

kaolinite calcite and quartz kaolinite, calcite and anatase kaolinite, calcite, quartz and natroalunite kaolinite, goethite and natroalunite hematite and anatase kaolinite, calcite and anatase

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equipment at Visvesvaraya National Institute of Technology (V.N.I.T.), Nagpur. The powdered samples were heated to 850– 900 °C at the standardised heating rate of 10 °C/min, and the thermograms were recorded automatically by the instrument. The SEM–EDX data were obtained using JEOL JED-2300 Analysis Station instrument at 20 kV accelerating voltage and 1 nA probe current intensity at V.N.I.T., Nagpur. Electron Probe Micro Analyses (EPMA) were carried out using JA-8600 MX Superprobe (WDS) at

the Mineral Physics Division, Geological Survey of India, Hyderabad, at an accelerating voltage of 15 kV and probe current of 1  108 amp. The whole ore XRF analysis for major and some minor elements were carried out at PPOD Laboratory, AMSE Wing, Geological Survey of India, Bangalore using X’UNIQUE II (PHILIPS) X-ray Spectrometry System. The trace element and REE analyses were obtained using Perkin Elmer Sciex ELAN DRC II ICP-MS system with

A

B

C

D

E

F

G

H

Fig. 4. SEM images showing: (a) elongated crystal of gibbsite with the flower like aggregates of hydrated alumina (1200), (b) spongy textured bauxite (1300), (c) crystalline (platy) structure shown by gibbsite (2700), (d) crystalline aggregate of hematite (1100), (e) ilmenite microcrystal within a microcavity (6000), (f) a calcite crystal surrounded by gibbsite (1600), (g) microcryst of hydrated iron ore (3000), and (h) a microcrystal of hematite containing light coloured material which is less iron rich (2700).

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the reference standard BX-N at the National Geophysical Research Institute, Hyderabad, following procedure of Balaram and Rao (2003). The overall precision for ICP-MS analysis was found to be better than 10% RSD. 5. Mineralogy and petrography The chief mineralogical constituent of the aluminous laterites is gibbsite, which is commonly traversed by secondary calcite veins. Gibbsite possesses irregular outline and often shows colloform banding (Fig. 2D). The colour of bands varies between yellowish white and dark brown, even cherry red to black, suggesting harmonic precipitation of the aluminium, iron and titanium oxides. Relict minerals such as plagioclase and mafic minerals are common. The aluminous laterite occurring in the Mewasa area shows brecciated or fragmentary nature. These fragments are composed of gibbsite, which occurs in various forms such as fine-grained (showing yellowish tinge), dark brown (accentuated by opaque minerals), banded, and spongy. The abundance of reddish brown hematite and goethite characterise laterites. Microscopic study reveals conspicuous presence of: (i) ferruginous oolites, (ii) goethite–limonite and hematite (Fig. 2E), (iii) relict minerals such as plagioclase feldspar, and highly altered mafic minerals, and (iv) fragmented aluminous hydroxides within the ferruginous matrix. Major portion of the ore body is composed of hematite followed by limonite–goethite and gibbsite. Gibbsite is mostly confined to the lighter portion of the rock and also occurs

fragmented within the hematite. Ferruginised portion preserves relicts of plagioclase feldspar (Fig. 2F). The fragmented gibbsite is occasionally bordered by ferruginous material thereby imparting mesh like structure. Detailed description of field and petrographic characteristics of the Jamnagar laterites are locality wise given in Table 1 and Fig. 3. Selected mineral phases from laterites and aluminous laterites are discussed below. Gibbsite is the chief mineral constituent of the Jamnagar laterites. The presence of gibbsite is confirmed by the XRD analysis (Table 2) as well as SEM–EDX images. It shows microtextures such as elongated crystals with flower like aggregates, spongy, and crystalline platy habits (Fig. 4a–c). The heat flow data shows peak values in the range of 284.83–292.67 °C; whereas weight loss calculated from thermo-gravimetric curves ranges from 11.56% to 23.99% due to presence of volatile components and hydroxyl ions. EPMA analyses confirm the presence of gibbsite in both laterites and aluminous laterites (Table 3). Kaolinite presence in minor quantities is confirmed by XRD analysis in most of the localities barring Virpur and Lamba. Further confirmation is provided by the endothermic peaks between 485 °C and 498 °C; and the weight loss of 1.62–3.87%. An EPMA analysis of kaolinite is given in Table 3. Hematite is present in the laterites of Virpur and Lamba. SEM–EDX images record presence of hematite. Fig. 4d shows crystal aggregates of hematite, whereas in Fig. 4e a dark crystal of hematite with light coloured less ferruginous spots is observed. Relative concentration of iron is confirmed by EPMA analysis. Goethite is also common to the laterites. XRD data shows presence of goethite. Except

Table 3 Representative analyses of minerals occurring in the laterite deposits of Jamnagar: (1) aluminous laterite from Kataria, (2) laterite from Lamba, (3) calcite from satapar, (4) Anatase from Lamba, (5) magnetite from Lamba, (6) kaolinite from Asota, and (7) hematite from Lamba. Sr. no.

1

2

3

4

5

6

7

SiO2 TiO2 Al2O3 Cr2O3 FeOT MnO MgO CaO Na2O K2O NiO

0.04 0.01 71.55 0.00 0.05 0.00 0.00 0.00 0.02 0.01 0.00

1.56 3.17 67.68 0.12 2.11 0.00 0.03 0.16 0.02 0.00 0.01

0.00 0.00 0.00 0.00 0.01 0.00 0.47 57.71 0.00 0.00 0.00

0.29 89.47 3.51 0.16 0.67 0.00 0.00 0.09 0.05 0.02 0.05

1.12 1.07 2.21 0.07 76.73 0.44 0.01 0.14 0.23 0.00 0.04

25.83 1.60 28.92 0.09 5.61 0.00 0.26 0.23 1.13 0.92 0.00

0.45 2.31 9.58 0.45 65.34 0.31 0.13 0.18 0.10 0.00 0.80

Total Inference

71.67 Gibbsite

74.81 Gibbsite

58.19 Calcite

94.33 Anatase

82.04 Magnetite

64.59 Kaolinite

78.93 Hematite

Table 4 Major element analysis of Jamnagar laterites.

SiO2 TiO2 Al2O3 Fe2O3T MnO MgO CaO Na2O K2O P2O5 S Cr2O3 NiO BaO LOI Total

AST-1

AST-2

VR-1

VR-2

VR-3

MWS-1

MWS-2

KTR-1

KTR-2

LMA-1

LMA-2

STR-1

STR-2

STR-3

STR-4

9.02 3.32 48.32 3.55 0.02 Bld 5.18 0.95 0.07 0.15 0.73 Bld 0.01 0.03 28.64 99.99

18.45 3.54 40.69 2.49 0.02 Bld 7.99 0.73 0.39 0.19 0.66 0.01 0.02 0.03 24.76 99.98

1.2 2.96 37.21 21.55 0.05 0.29 0.91 2.69 0.03 1.01 0.59 0.06 0.02 0.03 31.39 99.99

4.04 5.92 43.49 13.81 0.03 0.47 0.6 1.61 0.15 0.21 0.37 0.04 0.01 0 29.24 99.99

3.7 4.15 49.59 9.84 0.06 0.45 0.6 1.01 0.04 0.16 0.58 0.01 0.01 0.02 29.76 99.98

1.81 4.83 57.24 2.78 0.03 0.43 0.75 1.65 Bld 0.12 0.63 0.03 0.01 0.01 29.66 99.98

8.51 3.63 48.85 3.84 0.02 Bld 4.72 1.25 0.07 0.17 0.58 0.04 0.01 0.03 28.27 99.99

6.89 3.19 42.53 2.51 0.02 Bld 12.37 0.6 0.09 0.09 0.86 Bld 0.01 0.03 30.8 99.99

27.98 3.28 39.31 2.55 Bld 0.02 4.81 0.87 0.2 0.11 0.81 Bld 0.02 0.03 19.99 99.98

1.06 4.12 41.34 25.22 0.04 0.37 0.62 0.84 Bld 0.16 0.67 0.02 Bld 0.02 25.51 99.99

1.19 3.36 34.74 32.21 0.05 0.37 0.48 0.21 Bld 0.11 0.84 0.04 Bld 0.02 26.36 99.98

2.24 5.04 52.96 1.8 0.01 Bld 3.47 0.85 Bld 0.16 1.12 Bld 0.01 0.01 32.31 99.98

10.44 4.58 42.48 1.45 0.01 Bld 10.54 0.68 0.08 0.12 Bld Bld 0.01 0.01 29.59 99.99

7.82 5.33 44.27 1.56 0.01 Bld 8 1.95 0.07 0.11 0.9 Bld 0.01 0.01 29.95 99.99

8.4 4.38 41.3 1.77 0.01 Bld 11.81 0.82 0.12 0.13 0.93 Bld 0.01 0.01 30.29 99.98

Total Fe represented as Fe2O3. Bld - below limit of detection.

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one exothermic peak of 375 °C in the Lamba area, thermionic curves do not depict peaks for goethite. The SEM–EDX image (Fig. 4f), however, show the hydrated iron oxide. Ilmenite presence is observed in the SEM–EDX image Fig. 4g, and by the EDX data. Anatase is recorded in minor quantities in the X-ray diffractograms of Virpur and Lamba, but not in the aluminous laterites. EPMA analysis confirms its presence (Table 3). Calcite is observed in minor amounts in 30

the aluminous laterite. The SEM–EDX confirms presence of calcite Fig. 4h, which is surrounded by gibbsite. Quartz occurs only in traces within aluminous laterites, not in the laterites. The thermal analyses do not record presence of free silica due to its very low content. Natroalunite is recorded in minor quantities within laterite (Mewasa) and aluminous laterite (Virpur). An endothermic peak at 885 °C confirms presence of this mineral.

A

B

40 30 20

LOI

SiO2

20

10 10 0

0

Slope= -5.558E-01 Int= 5.411E01 r=-.99 r'=-.98

C

D

40

15

30

10

20

5

10

0

Fe2O3T

CaO

20

0 Slope= -3.432E-01 Int= 3.404E01 r=-.99 r'=-.9

E

F

2

6 5 4 3

1

TiO2

Na2O

3

2 1

0 70

80

90

100 70

CIA

80

90

100

0

CIA

Fig. 5. Variation of major oxides against Chemical Index of Alteration (CIA) for the Jamnagar laterites (See text for discussion). Open circles: aluminous laterites, filled circles: laterites. Symbols are common for all diagrams except Figs. 9 and 10.

Fig. 6. The Al2O3–SiO2–Fe2 OT3 triangular diagram showing classification of bauxite (after Boulange et al., 1996).

Fig. 7. The Al2O3–SiO2–Fe2 OT3 triangular diagram showing degree of lateritisation (after Schellman, 1986).

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vidual locality (Table 4), thus SiO2 shows consistently low values for the laterites of Lamba and Virpur areas (1.06–4.04), whereas a wide range is recorded for the aluminous laterites of Asota, Mahadevia/Kotharia and Satapar areas (1.81–27.98). The total iron (Fe2O3) shows variation between laterite (9.84–32.21), and aluminous laterite (1.45–3.84), whereas TiO2 (laterites – 2.96–5.92; aluminous laterites – 3.19–5.33), Al2O3 (laterites – 34.74–49.59; aluminous laterites – 39.31–57.24); and Na2O (laterites – 0.21–2.69; aluminous laterites – 0.60–1.95) do not show significant variation. Chemical weathering strongly affects the mineralogy and major elements geochemistry of the bed rocks. The degree of weathering can be evaluated by quantitative measures using whole rock chemical analysis such as Chemical Index of Alteration (CIA) defined by Nesbitt and Young (1982),

CIA ¼ 100  Al2 O3 =Al2 O3 þ CaO þ Na2 O þ K2 O

Fig. 8. Geochemical paths of dismantlement according to Beauvais (1991) indicating various trends followed during the process of bauxitisation depending upon whether quartz is present or absent in the soft microganular matrix, here the shaded portion shows data of ferruginous cuirasses (Tardy, 1997). The Jamnagar laterite samples are resulted due to destruction of kaolinite and strong deferruginisation.

6. Geochemistry 6.1. Major elements geochemistry There is a considerable range of major elements composition among the different localities and among samples within an indi-

This index may serve as a reasonable factor against which variation in different oxides and elements can be plotted. The observed variations (Fig. 5) indicate that: (i) the laterites plot towards the higher values of CIA (>90) whereas the aluminous laterites shows the lower values (75–90); (ii) a cluster of laterites is formed when silica is plotted against CIA (Fig. 5A). Similar cluster is also observed for the values of Loss on Ignition (LOI) against CIA (Fig. 5B); (iii) the best correlation however observed for CaO against CIA, where a strong correlation (r = 0.98 and r0 = 0.97) is seen for the aluminous laterites (Fig. 5C); (iv) CIA plotted against total iron content shows good discrimination between laterites and aluminous laterites (Fig. 5D); (v) in case of Na2O there is a strong correlation (r = 0.99 and r0 = 0.99) within the laterite, whereas no such correlation is observed for aluminous laterite (Fig. 5E); (vi) several other elements such as TiO2, P2O5, MgO, MnO, S, BaO and NiO that do not show any appreciable correlation (e.g. Fig. 5F).

Table 5 Trace element analysis of Jamnagar laterites.

Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

AST-1

AST-2

VR-1

VR-2

VR-3

MWS-1

MWS-2

KTR-1

KTR-2

LMA-1

LMA-2

STR-1

STR-2

STR-3

STR-4

21.0 225.4 338.6 15.5 52.7 38.2 94.5 62.3 6.7 506.1 23.0 726.4 37.3 0.7 82.3 65.7 117.7 17.3 72.3 16.1 4.8 11.0 1.7 8.3 1.4 2.2 0.4 2.2 0.3 19.3 3.0 62.4 16.6 10.8

32.3 278.3 768.2 9.2 88.2 45.2 113.3 90.9 23.6 919.5 22.2 1077.8 57.2 2.6 176.5 89.3 182.2 22.8 86.1 16.3 4.0 10.3 1.5 7.7 1.3 3.0 0.4 2.7 0.4 28.8 4.6 101.3 32.0 12.7

30.9 360.9 719.7 7.9 23.7 30.6 118.4 100.4 1.2 368.7 14.9 1595.0 86.9 0.1 44.6 38.9 71.3 6.5 21.0 3.2 0.7 2.5 0.4 2.6 0.6 1.6 0.3 1.9 0.3 40.8 6.4 81.3 33.8 8.6

42.2 1090.9 664.2 7.4 53.3 126.7 142.5 95.4 4.1 858.3 19.6 1048.5 74.8 0.3 82.9 101.4 103.0 21.9 82.4 13.4 3.5 8.5 1.2 6.1 1.1 2.5 0.3 2.1 0.3 26.7 5.3 57.7 18.3 6.1

35.1 635.1 530.8 18.4 51.1 67.9 130.7 85.6 3.3 654.4 18.3 911.7 57.8 0.3 54.3 48.9 50.4 9.2 33.4 5.9 1.6 4.4 0.8 4.3 0.9 2.1 0.3 2.1 0.3 23.7 4.3 56.8 18.5 9.2

70.8 638.5 637.1 40.5 134.9 95.3 105.3 72.0 1.4 7269.1 32.9 548.3 21.4 0.0 156.9 8.2 18.3 3.1 23.6 9.0 2.5 7.5 1.3 7.1 1.3 2.8 0.4 2.1 0.3 14.1 1.8 39.0 7.2 70154.0

26.4 303.8 833.9 7.9 58.5 36.7 96.8 77.3 7.2 667.6 20.0 810.5 42.3 0.8 72.7 47.0 98.2 10.4 40.1 7.5 1.6 5.1 0.8 4.3 0.8 2.1 0.3 1.7 0.3 22.0 3.6 61.9 16.4 5.7

12.9 320.1 430.1 8.1 44.2 30.1 93.1 61.6 6.7 331.2 10.6 766.3 38.7 0.7 54.0 39.9 77.8 7.8 24.3 3.4 0.7 2.8 0.4 2.1 0.5 1.2 0.2 1.2 0.2 20.2 3.2 59.5 18.0 5.4

24.4 345.4 430.2 6.6 161.3 57.4 106.7 56.6 14.5 691.3 10.4 844.5 41.6 1.5 95.7 47.3 99.5 11.7 40.5 6.0 1.2 3.9 0.6 2.8 0.5 1.4 0.2 1.4 0.2 22.8 3.3 28.4 19.0 5042.0

20.6 592.3 439.8 2.9 15.3 43.6 116.9 79.4 0.7 87.4 8.8 1013.6 84.6 0.0 25.0 23.3 36.9 3.8 12.3 1.8 0.4 1.5 0.2 1.6 0.3 1.0 0.2 1.3 0.2 25.5 6.2 43.5 18.7 5.9

19.9 502.9 365.5 4.0 23.1 48.5 90.8 58.5 0.7 52.5 6.6 704.3 59.1 0.0 20.6 15.6 25.2 2.7 9.0 1.4 0.3 1.1 0.2 1.1 0.3 0.8 0.1 1.0 0.2 17.7 4.2 41.9 12.9 3.4

21.8 522.1 544.9 11.9 58.1 33.3 154.0 92.7 3.9 897.3 18.6 818.7 65.3 0.3 69.4 32.8 32.7 6.6 25.5 5.6 1.5 4.3 0.8 5.2 1.1 2.6 0.4 2.7 0.4 19.8 4.5 18.7 13.5 7.5

28.1 451.0 730.2 5.1 42.6 24.2 127.2 101.3 11.1 463.5 26.4 1126.0 85.8 1.3 60.5 47.7 69.7 9.8 37.7 7.4 1.7 5.3 0.9 5.8 1.1 2.8 0.4 2.7 0.4 29.6 6.7 56.0 23.5 8.0

28.1 462.9 683.1 8.1 36.1 25.9 148.2 108.2 9.5 415.8 22.5 1200.0 101.1 1.3 74.5 53.1 82.7 10.4 38.0 6.9 1.6 5.1 0.9 5.1 1.1 2.7 0.4 2.7 0.4 30.3 7.3 72.2 22.1 8.0

33.4 468.2 640.9 19.3 46.0 23.7 127.4 103.7 12.3 563.7 30.5 1049.3 85.3 1.4 71.2 47.3 78.0 10.3 39.6 7.3 1.8 5.9 1.0 6.4 1.3 3.0 0.5 3.2 0.5 26.8 6.3 53.3 19.9 7.6

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Fig. 9. The chondrite normalised trace elements spidergrams for the laterite samples from different localities of the Jamnagar area (Sun, 1980). Abbreviations indicates localities such as AST – Asota, KTR – Kataria, MWS – Mewasa, VR – Virpur, LMA – Lamba, and STR – Satapar.

Fig. 10. The chondrite normalised rare earth elements spidergrams for the laterite samples from various localities of the Jamnagar area (Nakamura, 1974). Abbreviations as in Fig. 9.

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The triangular variation diagrams using Al2O3–SiO2–Fe2 OT3 are commonly used to show the degree of lateritisation, mineral control and bauxite classification. In this diagram (Fig. 6), majority of the aluminous laterites plot in the bauxite field, whereas laterites fall in the ferruginous bauxite field of Boulange et al. (1996), implying that the classification of Jamnagar laterites into laterites and aluminous laterites holds well. Fig. 7 after Schellman (1986) brings forth the lateritisation process prevalent in the area. The overall trend shows increased degree of lateritisation. Geochemical paths of dismantlement (Beauvais, 1991; Tardy, 1997) shows various trends followed during the process of bauxitisation (Fig. 8), implying that the Jamnagar laterites have resulted due to destruction of kaolinite and strong deferruginisation. 6.2. Trace elements geochemistry The distribution and behaviour of trace elements (Table 5) in bauxites is controlled by factors like: (i) composition of the parent rocks, (ii) physicochemical conditions of bauxite formation, (iii) mineral species of the bed rocks, (iv) chemical properties of elements such as solubility, pH of hydroxide precipitation and possibility of complex formation, (v) diagenetic, epigenetic and recent transformation of bauxites (Mordberg, 1996). MacLean et al. (1997) proposed the use of immobile elements suitable to trace the source of aluminium to a particular rock type or unit. He also indicated that some chemical elements especially Zr, Ti and Cr are strongly immobile during weathering and diagenesis of laterite. Liaghat et al. (2003) reiterated importance of trace elements and opined that study of such elements in bauxite allows inferring their parent rock composition. It was however observed during present study that the trace elements including REE do not show direct correlation with Al2O3, TiO2 or standard indices such as Chemical Index of Alteration (CIA), Mineralogical Index of Alteration (MIA) and fractionation index viz., 100 Al2O3/Fe2 OT3 + Al2O3. Some of the major and trace elements which are normally very mobile under surficial conditions such as K, Na, Sr, La, Mg and Pb, do not show preferred affinity for either laterites or aluminous laterites, whereas, the less mobile elements such as Nb, Th, Zr, Mo, Ga, and Cr show some indirect correlation. The chondrite normalised trace element spidergrams (Sun, 1980) were plotted for the Jamnagar laterite samples (Fig. 9). Majority of the samples show depletion peaks for K, Ba, Sr and Nb, and peaks of enrichment for Zr, Th and U. These enrichment and depletion are apparently related to the availability or unavailability of related carrier mineral phases in the source rock, e.g. Kfeldspar (K+ and Ba+), plagioclase (Sr2+, Eu2+), carbonate (P4+, V5+, Ce4+), garnet (HREE3+), apatite (LREE3+), zircon (Ga4+, Zr4+, Hf4+, Nb4+, Ta4+, Th4+), anatase/rutile/ilmenite (Ti4+, Fe3+ and REE). The Asota samples show strong negative K, Ce and Sr anomalies and positive Gd, U, Nd and Zr anomalies. One of the samples from Mewasa shows very strong positive Sr anomaly, whereas the Lamba samples show complete absence of K and negative Sr and positive Nd anomalies. The Satapar samples show positive Zr anomaly. The generalised trace element pattern of the laterites of Jamnagar is shown in Fig. 11A. The chondrite normalised REE spidergrams (Nakamura, 1974) of the Jamnagar laterites are reported in Fig. 10, the general features observable indicate that: (a) All the samples show LREE enriched and HREE depleted pattern (b) Almost all the samples show pronounced negative Ce anomaly, weak negative Eu and Er anomalies. (c) In case of laterites the curve becomes flat after Eu, whereas for aluminous laterites the curves are gently sloping after Eu.

Rock/Chondrites

Sun (1980)

1000

A

100

10

1

Rb Ba Th U Nb Ta K La Ce Sr Nd Sm Zr Ti Gd Y

Rock/Chondrites

REEs-Nakamura, 1974

1000

B 100

10

1

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 11. Trace elements spidergrams showing the generalised (average) composition of the Jamnagar bauxites (a) trace elements spider (Sun, 1980) and (b) rare Earth Elements (Nakamura, 1974). Symbols open circles: aluminous bauxites, filled circles: ferruginous bauxites, plus sign: average upper continental crust (after Taylor and McLennan, 1981).

(d) The concentration of La ranges between 101.42 ppm and 8.16 ppm, average value 63.08 ppm. Similarly, the concentration of Lu ranges between 0.48 ppm and 0.16, with the average value of 0.34. Fig. 11B shows the generalised REE curves for the Jamnagar laterites. 7. Discussion 7.1. Parent rock composition Hallberg (1984) opined that Zr/Ti ratio can supply information about the chemical nature of parent rock. Floyd and Winchester (1978) used Zr/TiO2 against Nb/Y ratios to model the parent rock compositions of the laterites, particularly when the parent rock is an extrusive igneous rock. When the Jamnagar laterites were plotted in Zr/Ti diagram (Fig. 12), majority of the data plot in the ‘‘andesite’’ field. Similarly, the data plotted in Nb/Y–Zr/TiO2 discrimination diagram occupy ‘‘trachyte’’ and ‘‘trachyandesite’’ fields (Fig. 13). The ternary Zr–Ga–Cr trace element diagram of Calagari and Abedini (2007), in which the data of Jamnagar laterites plots in the Field III, also indicates that the parent rock may be intermediate igneous in composition (Fig. 14). Celik (1999) studied the minamite and alunite occurrences formed from volcanic emanations in Turkey and opined that the alunites were observed mainly in altered dacitic volcanic rocks. He proposed the probable parent rocks on the basis of mineral

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2000

Zr ppm

1500

1000

500

0

1

2

3

4

Ti Wt% Fig. 12. The diagram showing the possible parent rocks of the Jamnagar bauxite belt on the basis of Zr/Ti ratio (after Hallberg, 1984).

1

the remnants of ashes in some of the laterites (Sahasrabudhe, 1978; IBM, 1993; Meshram, 2009) reiterating that the parent rock composition predicted above holds good. The laterite samples invariably contain gibbsite as their more abundant mineral followed by hematite ± goethite ± anatase. However in case of ferruginous cuirassement or ferricrete (Alexander and Cady, 1962), the major mineral constituents, in order of importance, are hematite, kaolinite, goethite, quartz and gibbsite; of these first two are essential and other three are facultative (Tardy, 1997). The association hematite + kaolinite represents dehydrated or poorly hydrated minerals which are dismantled and replaced by hydrated goethite + gibbsite, since the hydration enables transformation of kaolinite + hematite mixture to aluminous goethite. The cuirasses on quartz rich rocks are less ferruginous and rich in kaolinite + hematite; whereas those on quartz-poor rocks are more ferruginous, richer in goethite and poorer in kaolinite + hematite (Tardy, 1997). Presence of gibbsite + kaolinite ± quartz in the aluminous laterites and gibbsite ± hematite ± goethite in laterites therefore indicates that the laterites of Jamnagar area were hydrated, but their parent rock composition (such as quartz-rich and quartz-poor) was relatively different. 7.2. Mineralogical influences on trace elements distribution

Zr/TiO2

.1

.01

.001 .01

.1

1

10

Nb/Y Fig. 13. The diagram showing possible parent rocks for the Jamnagar deposits on the basis of Zr/TiO2–Nb/Y ratios (after Floyd and Winchester, 1978).

Fig. 14. Ternary plot for the concentration of Ga, Zr and Cr in samples of Jamnagar laterites (after Calagari and Abedini, 2007). A–D (star) depicts the concentration values of Zr, Cr and Ga in ultrabasic, basic, intermediate, and acidic igneous rocks respectively. The numbers I–IV represents the area of influence of ultramafic, mafic, intermediate (or argillaceous), and acidic precursor rocks respectively. The samples (open and filled circles) imply intermediate parent rocks.

assemblages such as alunite–quartz (andesite), alunite–quartz– kaolinite (dacite), quartz–kaolinite–natroalunite (dacite). The assemblage of natroalunite–kaolinite–goethite in the laterites of Jamnagar may well be considered to represent the altered volcanic rocks such as andesite and dacite. The bauxite capping in the study area are essentially over the basaltic country unlike the adjoining Saurashtra and Kachchh regions where the capping are also observed over Gaj sediments and the supratrappean beds (Type II and Type III of Sahasrabudhe, 1978). Moreover, there are field evidences such as unusual tuffaceous appearance of the bauxite and

In parent rocks, trace elements are distributed between rock forming and accessory minerals. The rock forming minerals may dissolve during bauxitic weathering, whereas accessory minerals are often resistant to weathering. The distribution between these two groups determines the weathering characteristics of elements (Bardossy and Aleva, 1990; Mordberg, 1996). The mineralogical influence is such that even very mobile elements can be concentrated in bauxite profiles, if the host minerals have not been dissolved (e.g. Boski and Herbosch, 1990; Mordberg et al., 1995). Fig. 11 A gives the generalised pattern of trace element distribution of the Jamnagar laterites. The patterns shows strong negative K anomaly which is apparently related to paucity of potassic mineral in the source rock. Similarly, a smaller negative Sr anomaly probably indicates absence or non-dissolution of calcium rich primary mineral. In this context, the presence of relicts of plagioclase in the Jamnagar laterites provides reasonable explanation for considering incomplete leaching and relative impoverishment of Sr and Eu. Zirconium is generally considered to be relatively immobile element during weathering due to its chemical properties and high resistance of its most common carrier mineral zircon (Mordberg and Spratt, 1998), strong positive anomaly of Zr therefore indicates its enrichment in the source area. However, in the pyroclastic rocks zirconium may not be expected in exceedingly higher amount. Fig. 11B gives the generalised pattern of REE distribution in the Jamnagar laterites. However, the nature of REE distribution during mineralogical reactions associated with weathering is very poorly understood (Mac Lenan, 1989). Several studies have suggested that REE are mobile during weathering but there is little agreement regarding the overall magnitude or their potential for fractionation (Boulange and Colin, 1994). The Jamnagar laterites are LREE enriched – HREE depleted, showing negative Ce and Eu anomalies. There are several possible explanations for the behaviour of REE under weathering environments such as following: (a) REE could be mobilised during intense chemical weathering under warm and humid conditions and the HREE are preferentially transported in solution (Balashov et al., 1964). (b) REE may not be at all mobile during weathering environment (Ronov et al., 1967; Duddy, 1980), especially depending upon pH conditions (Appelo and Postma, 1993; Johannesson et al., 1996).

R.R. Meshram, K.R. Randive / Journal of Asian Earth Sciences 42 (2011) 1271–1287 Table 6 Correlation table for selected tetravalent elements of the Jamnagar laterites.

Ga Zr Nb Hf Ta Pb Th Ti

Ga

Zr

Nb

Hf

Ta

Pb

Th

Ti

1.00 0.73 0.79 0.70 0.80 0.37 0.50 0.56

1.00 0.80 0.99 0.82 0.56 0.87 0.02

1.00 0.75 0.99 0.23 0.52 0.37

1.00 0.78 0.60 0.90 0.04

1.00 0.30 0.58 0.32

1.00 0.76 0.23

1.00 0.29

1.00

(c) The REE may get accumulated within iron crusts containing goethite (Steinberg and Courtois, 1976; Kunhel, 1987; Mongelli, 1997). (d) Weathering may result in the formation of authegenic clay minerals and REE may easily get adsorbed at the surface of clay minerals such as smectite and kaolinite (Roaldset, 1973; Aagard, 1974; Decarreau et al., 1979; Laufer et al., 1984). (e) REE distribution is greatly influenced by the presence or absence of certain minerals in the source rock, such as phases of the bastnasite group (Nesbitt, 1979; Boulange and Colin, 1994; Mameli et al., 2007). It is known that high REE concentration is due to presence of primary minerals such as sphene, apatite and zircon, whereas

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low to moderate REE concentrations are due to presence of quartz, feldspars and biotites in the parent rock (Gromet and Silver, 1983; Mariano, 1989). Moreover, strong partitioning of REEs by the oxides of Ti-Nb (Gonzalez Lopez et al., 2005; Esmaily et al., 2009); ferric hydroxides (Kunhel, 1987; Mongelli, 1997); and REE–carbonate complexes (Johannesson et al., 1996; Mameli et al., 2007), is also well documented. Cerium exists naturally in two forms, viz. Ce3+ and Ce4+, with the latter having higher ionic potential than the other REEs and consequently the lowest mobility (Esmaily et al., 2009). The lower ionic potential of LREEs relative to HREEs means that they were leached from the source and got concentrated in the laterites. The high ionic potential of Ce4+ suggest that its behaviour was similar to the HREEs. The positive Ce anomaly is commonly attributed to the leaching of apatite, sphene and zircons; however the latter is a remarkably resistant mineral under the weathering conditions. Therefore, the negative Ce anomaly is owing to the ability of Ce4+ to get accommodated in the zircon structure because of the similar oxidation state and comparable ionic radii of Zr [4+, 0.84(VIII) Å ] and Ce [4+, 0.97(VIII) Å] (Murali et al., 1983; Hintor and Upton, 1991, ionic radii after Shannon, 1976). The negative Ce anomaly in the Jamnagar bauxites may also indicate that the zircon may not be present in the source rock in significant amount. This observation therefore leads the way to consider the geochemical affinity of Zr4+ with the relatively immobile tetravalent ions such as Ga4+, Hf4+, Ta4+, Th4+, Pb4+, and possibly Ce4+ (not separated from Ce3+ therefore not correlated in table),

Fig. 15. Position of India and possible location of Jamnagar laterite deposits (indicated by circle) during the Palaeocene times (modified after Sychanthavong and Patel, 1987). The fracture zones indicate Pre-Palaeocene structures in the Indian Ocean, whereas the area beyond limit of Indian Subcontinent indicate wet climate suitable for laterite formation. The dotted area indicate humid climate with lesser rainfall, the stripped areas indicate semi-arid, and blank area within India indicate arid climatic conditions.

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Table 7 Comparison of various flood basaltic provinces of the world, their age, areal extent and laterite deposits. Sr. no.

Name of the flood basaltic province

Location

Age

Aerial extent

Copper Mine River Group Keweenawan Province

Mackenzie Large Igneous Province in the NW territories of Canada

Mesoproterozoic

1,70,000 km2

Lake Superior on the Canadian–American Boarder

Proterozoic

100,000 km

3

North Australian Province

Early Cambrian

400,000 km2

4 5

Emeishan Traps Siberian Province

Presence indicated Not known on CFB

North Mountain Province

Permian Late Permian to Early Jurassic Triassic

250,000 km2 1500,000 km2

6

4000 km (diameter)

Not known

7

Triassic

3000 km2

8

Wranglia flood basaltic province Karoo Province

North Australia between the Kimberley region and Queensland boarder. Main continuous outcrop in East Kimberley, Victoria River and Daly River basin: together called Antrim Plateau Volcanics Sichuan Province, SW China Enisei and Lena Rivers, Russia. Most of the continental flood basalts occur within the Tungaska Basin SW Nova Scotia, Canada, stretching from Brier Island to Cape Slit, Annapolis Valley to Bay of Fundy. A gigantic flood basaltic igneous complex along east coast of United States, Europe, NW Africa and South America with a diameter of 4000 km SW Yukon, extending from Vancouver island to central Alaska

9

Parana Basin Province

1 2

10 11 12 13

Ontong Java Plateau Caribbean flood basaltic province Deccan Trap basaltic province North Atlantic Tertiary Province

Laterite deposits

2

Economic deposits not known Economic deposits not known Economic deposits are present

Not known 2

Barotseland in Zambia, Suurberg in eastern Cape, Etekanda in Namibia, Antonio Enes in Mozambique, Lesotho and Nuanetsi– Lebombo Mostly located in Brazil, but also traced in Uruguay, Paraguay and Argentina North of Solomon Islands, Manihiki Plateau and Hikurangi Plateau Large Oceanic Plateau covering Costa Rica, etc.

Late Triassic to Early Jurassic

3000,000 km

Not known

Late Jurassic to Early Cretaceous Cretaceous Late Cretaceous

120,000 km2

Not known

Western and central India and southern Pakistan

Late Cretaceous to Late Eocene Palaeocene to Eocene

500,000 km2

Eocene to Miocene

750,000 Sq, km ?

14

Ethiopian Province

Subdivided into six main subprovinces: the Hebridean, northern Ireland, UK; the Facroe Islands, East Greenland; Baffin Bay, West Greenland; Rockall Plateau and Voring Plateau off NW Norway Highlands of Ethiopia and Yemen, Aiba Formation.

15

Eastern China Province

Eastern China

16

Columbia River Province

17 18

Chilcotin Province Hawaii flood basaltic province

Washington, Oregon and Idaho in NW USA. This group has been divided into four main formations: Imnaha basalt, Grande Ronde basalt, Wanapum basalt and Columbia River basalt Garibaldi Volcanic Belt, British Columbia, Canada Hawaii Islands

2

2000,000 km ?

143,750 km2

? Economic deposits are present Economics deposits are present Economic deposits are present Not known

Eocene to Middle Pleistocene Miocene

Not known

163,700 km2

Economic deposits are present

Miocene to Pliocene Pleistocene

50,000 Sq, km 10,432 km2

Not known Economic deposits are present

Data compiled from Valeton (1972), Lassiter et al. (1995), Garner (1996), Taylor (2006) and Deng et al. (2009).

which show strong correlation among them (Table 6). It is likely that these elements are concentrated as hydrolysates by the in situ weathering of parent rock. Mason and Moore (1991) predicted that the tetravalent elements including Ti4+ may be concentrated in bauxite, the factor of enrichment being four to five times as compared to their parent material. The lower correlation coefficients of Ti4+ with the other tetravalent elements could be due to (i) incomplete leaching of the minerals in parent rocks such as plagioclase, clinpyroxene, zircon, and apatite and (ii) presence of other influencing mineral phases, like anatase and ilmenite, which are present in the laterites and aluminous laterites of the Jamnagar deposits. Chowdhury et al. (1965) have observed harmonic correlation of tetravalent Ga4+ with Al3+, Fe3+ and Ti4+ in several laterite– bauxite deposits in India including Gujarat, which is not seen in the Jamnagar deposits due to influence of bed rock mineralogy as discussed above. 7.3. Implications on the palaeotectonics Bardossy’s (1973) stimulating discussion on the process of bauxite formation in relation to plate tectonics has brought new insight into bauxite research. The palaeo-climate, environment, morphology and drainage conditions that are required for formation of bauxite and laterite deposits were provided by the drifting continents over certain latitudes. Such discussion not only correctly predicted the positioning of the bauxite–laterite provinces

with respect to their palaeolatitudes and palaeo-pole positioning; but also helped the proponents of Continental Drift to substantiate their own hypothesis (e.g. Taling and Runcorn, 1973). Indian context of this hypothesis is discussed in detail by Sychanthavong and Patel (1987), who provided valuable information on palaeopositioning and drifting of Indian Subcontinent since Mesozoic. We discuss it further in relation to the Jamanagar laterite deposits. The deposits of Jamnagar are bounded by a narrow zone between the Deccan Traps and Tertiary Sediments. The fragmented nodules of bauxites are found in the Tertiary sediments, which mean that their age is Pre-Tertiary. Considering Miocene age of the Gaj sediments and Cretaceous age of Deccan Trap magmatism, Palaeocene to Eocene age is a reasonable estimate for the laterite deposits of Jamnagar. It is well known that lateritisation is a process of chemical weathering of rocks, essentially in a tropical climate comprising of alternation of very hot summers and heavy rainfall during the monsoon season (see for e.g. McFarlene, 1976). This type of tropical climate is strictly restricted to the equatorial zone with the exception of topographically controlled areas. According to Sant (1999) the time events shaping morphology of the Saurashtra and Lower Narmada Valley area have occurred around 58 ± 2 Ma, 42 ± 2 Ma, 32 ± 2 Ma. 21 ± 2 Ma and 14 ± 2 Ma among these, first two events record the bauxitisation process. In case of Jamnagar laterite deposits, the first event, i.e. 58 ± 2 Ma was most probably the lateritisation event for the reasons discussed below.

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Sychanthavong and Patel (1987) opined that the age of the Tertiary bauxites of India decreases from north to south from Jammu & Kahsmir, Rajasthan, Gujarat, Madhya Pradesh, Maharashtra, Karnataka and southern Indian states. They attributed this to the drifting and anticlockwise rotation of the Indian plate. The matured bauxite profiles in south as compared to north India is due to more residence time of south India at the equator and vice versa. This study along with those of Frakes and Kempe (1972) and Bardossy (1973) sheds light on the process of lateritisation vis-a-vis drifting of continents. Fig. 15 shows possible location of the Jamnagar area during Palaeocene. The major tectonic event prevailed during this time was the drifting of Seychelles from greater India and development of extensional fractures along which magmas were emplaced. There was an upliftment of the Cambay basin, whereas western continental margin remained stable (Balasubramanyan and Snelling, 1981; Pandey, 1986). In the Jamnagar laterite deposits there are no younger sedimentary rocks underlying laterites, indicating that this area was not submerged since the outpouring of the Deccan basalts (Sychanthavong and Patel, 1987). The area therefore had thick lushgreen vegetation thronging on the heavy rainfall during monsoon and hot climate during summer, which was conducive for lateritisation. The post Deccan Trap landscape is considered to be the ‘zero surface’ (Sant, 1999); the minimum elevation of this surface was considered to be 1000 m in the Saurashtra Peninsula. The flat rolling surface of the Deccan Province had westerly slope and the response of river channels over this surface was moderate to low due to presence of thick vegetation facilitating chemical weathering of the bedrocks. Thus, the drainage, morphology, vegetation, and climate were all favourable for lateritisation during Palaeocene times in this area.

7.4. Lateritisation and flood basaltic provinces Flood basaltic provinces are the large accumulation of basaltic lava flows having remarkably uniform chemical composition and erupted within short time span. Many of the continental flood basalts are associated with early stages of continental breakup and rifting (White and Mckenzie, 1995; Duncan and Richards, 1991). Due to their wide areal extent and stupendous volumes, the flood basaltic provinces are good parent rocks to host large laterite deposits. The Deccan Trap basaltic province is one such area where widespread lateritisation is observed. Several economic deposits are present in Gujarat, Maharashtra and Madhya Pradesh (Sahasrabudhe, 1978; IBM, 1993). Economically viable deposits of laterites are also associated with Columbia River Province in the states of Oregon, Washington and Idaho (Allen, 1948). Examples of laterite deposits associated with flood basalts come from North Australian, Caribbean, North Atlantic and Hawaii flood basaltic provinces (Valeton, 1972 and references therein; Sak et al., 2004; Taylore and Eggleton, 2008; Bogatyrev and Zhukov, 2009). Deng et al. (2009) indicated possibility of presence of laterite deposits in the Emeishan Traps. Nevertheless, there are several other flood basaltic provinces, where laterite deposits are not known, Table 7 lists major flood basaltic provinces and laterite deposits. It is observed that: (a) some of the large basaltic provinces remarkably lack laterite deposits over the basalts (e.g. Siberian, Karoo, Parana); (b) lateritisation process prevailed unequivocally over continental (e.g. Deccan, Columbia) as well as ocean (e.g. Hawaii, Ontong Java) areas; and (c) age of the basaltic province do not have much role in governing the lateritisation process, since older (e.g. North Australian) as well as younger (e.g. Hawaiian) provinces host laterite deposits. It is therefore apparent that it is not just size or age of the parent rock, but the palaeopositioning of the flood basaltic

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provinces, their palaeoclimate, palaeodrainage and palaeoslope are the governing factors for lateritisation. 8. Conclusions On the whole the field geology, mineralogy, petrography, and geochemical characteristics of the Jamnagar laterite deposits appear to indicate: (a) the parent rocks of Jamnagar laterites would have been pyroclastic igneous rocks of trachytic or andesitic composition, (b) the observed variations in the trace and rare earth elements are likely to be due to several factors, most important being, (i) incomplete leaching of minerals from the parent rocks, (ii) presence of other influencing mineral phases that can accommodate several trace elements having similar geochemical properties, and (iii) the geochemical affinity of elements such as Ga4+, Hf4+, Zr4+, Nb4+ Ta4+, Th4+, Pb4+, and Ce4+, which might have been concentrated as the hydrolysates, (c) Jamnagar laterite deposits were developed over the Deccan Trap basaltic rocks during Palaeocene times when Indian Plate was passing over the equator, the morphology, drainage and climatic conditions were favourable for formation of laterites during this time, (d) Flood basaltic provinces are potentially good parent rocks for hosting laterite deposits, however, the palaeopositioning of these provinces along with paeoclimate, palaeomorphology and palaeodrainage are the governing factors for lateritisation.

Acknowledgements We gratefully acknowledge Deputy Director General and HOD, AMSE Wing, Geological Survey of India, Bangalore for providing necessary facilities for geochemical analysis of bauxite samples. We thank Prof. T.C. Devaraju, two anonymous reviewers of JAES, handling editor L. Jennifer and Editor in Chief Bor-Jahn Ming, whose comments immensely helped for the improvement of the original version of paper. The authors are thankful to Mr. Parijat Roy, Mr. Nandu Kanoje, Mr. S.T. Narhari and Mrs. Savita Gaidhane for the help and support rendered during various stages of the work. KRR thanks Mr. Govindrao and Mrs. Maya Manapure for encouragement and support, and especially Chetana for her patience and tolerance during preparation of this paper. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jseaes.2011.07.014. References Aagard, P., 1974. Rare earth elements adsorption on clay minerals. Bulletin du Groupe Francais des Argiles 26, 193–199. Alexander, L.T., Cady, J.G., 1962. Genesis and Hardening of Laterite in Soils. Technical Bulletin of the United States Department of Agriculture, vol. 1282, 90 pp. Allen, V.T., 1948. Formation of bauxite from basaltic rocks of Oregon. Economic Geology XLIII (8), 619–624. Appelo, C.A.J., Postma, D., 1993. Geochemistry, Groundwater and Pollution. Balkema, Rotterdam, 536 pp. Balaram, V., Rao, T.G., 2003. Rapid determination of REEs and other trace elements in geological samples by microwave acid digestion and ICP-MS. Atomic Spectroscopy 24, 206–211. Balashov, Y.A., Ronov, A.B., Migdisov, A.A., Turanskaya, N.V., 1964. The effects of climate and facies environment on the fractionation of rare earths during sedimentation. Geochemistry International 1, 951–969.

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