Download Electron Microscopic Studies of Ilmenite from the Chhatrapur Coast

Hindawi Publishing Corporation
Journal of Geochemistry
Volume 2014, Article ID 192639, 8 pages
http://dx.doi.org/10.1155/2014/192639
Research Article
Electron Microscopic Studies of Ilmenite from the Chhatrapur
Coast, Odisha, India, and Their Implications in Processing
D. S. Rao1 and D. Sengupta2
1
2
Mineral Processing Department, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, Odisha 751 013, India
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, India
Correspondence should be addressed to D. S. Rao; [email protected]
Received 2 April 2014; Revised 20 June 2014; Accepted 25 June 2014; Published 15 July 2014
Academic Editor: Franco Tassi
Copyright © 2014 D. S. Rao and D. Sengupta. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Ilmenite from the Chhatrapur coast, Odisha, India, was studied using optical microscope, X-ray diffraction, particle size analysis,
and electron microprobe to decipher their micromorphology, texture(s), and elemental composition. The micromorphological
features by electron microscope indicate that weathering processes such as mechanical and chemical, affected the placer heavy
mineral ilmenite. These detrital ilmenites contain TiO2 in the range of 50.25% to 55.41% and FeO 42.72% to 49.99% in addition
to Al2 O3 , MgO, MnO, CaO, Na2 O, Cr2 O3 , NiO, ZnO, ZrO2 , V2 O5 , and HfO2 (0 to 0.034%). Ti/(Ti + Fe) ratio in the ilmenite
varied from 0.413 to 0.5, which indicates the effect of weathering/oxidation confirming microscopic observations. All the results
revealed that these ilmenite grains were derived from the gneissic/granitic, basic and high grade metamorphic rocks, belonging to
the Eastern Ghats Group of the Precambrian complex of coastal Orissa.
1. Introduction
Ilmenite (FeTiO3 ), an important and the most abundant
ore mineral of titanium, occurs in India along the coastal
beach sands of Odisha, Andhra Pradesh, Tamil Nadu, and
Kerala states. One important occurrence in Odisha is in the
coastal stretch over a strike length of 18 kms (covering a
total area of 26 Km2 ) between Gopalpur in the south and
confluence of the Rushikulya river with Bay of Bengal at
Ganjam in the north [1–6]. The Indian Rare Earths Limited
(IREL), a public sector undertaking of the Department
of Atomic Energy, Government of India, is mining and
processing ilmenite along with other heavy minerals like
garnet, monazite, rutile, sillimanite, and zircon from these
sands since 1984, at its Chhatrapur (Matikhalo) plant. Several
researchers have studied the ilmenites from across the world
to assess the provenance from the geochemistry of ilmenites
[7–11]. However, no in depth study has been undertaken
on the variation in the chemical composition from grain
to grain for the Chhatrapur beach placer ilmenites, aside
from some preliminary investigations [12, 13] and the work
on surface microtextures [14]. In view of this, the authors
present here a detailed mineral geochemistry (by EPMA)
for characterizing the ilmenites from the beach sands of
Chhatrapur area, Ganjam district, Odisha. The results have
been interpreted based on the present study for not only
the understanding of the provenance of the ilmenites in this
region but also their effects in processing and/or utilization.
2. Geology of the Area
The coastal area of Odisha (from Gopalpur to the Mahanadi
delta) runs in a NE–SW direction, nearly perpendicular
to the strike of the Eastern Ghats rocks. The Chhatrapur
beach placer deposit (84∘ 54󸀠󸀠 22󸀠 –85∘ 3󸀠󸀠 48󸀠 N Lat.: 19∘ 15󸀠󸀠 –
19∘ 26󸀠󸀠 36󸀠󸀠 E Long) is located in the Ganjam District of Orissa
State on the southeastern sea coast of India. The details of
the location map are described elsewhere [6]. The Orissa
coast, in general, and the Chhatrapur coast, in particular, are
essentially alluvial, devoid of any rocky exposures, and consist
of unsorted fine to medium grained, rounded to subrounded,
and moderate to well sorted sand [15], mixed to varying
degrees with heavy ilmenite, sillimanite, zircon, monazite,
2
3. Materials and Methods
Concentrated ilmenite sample from Chhatrapur coast was
obtained from the Indian Rare Earths Limited Company,
Chhatrapur. The sample was characterized by optical microscopy, X-ray diffraction (XRD), particle size analysis, scanning
electron microscopy (SEM), and electron probe microanalysis (EPMA). The samples were mounted in epoxy resin
(cold mounting) and polished using conventional methods
for optical and electron microscopic studies. The polished
section of ilmenites was then examined and analysed by a
JEOL, Super Probe JXA-8600 model electron microprobe
operating along with a current setting of 2 × 10−8 A, and using
Standard Programme International (SPI) mineral standards
and online ZAF correction procedures. Particle size analysis
of the sample was carried out using laser diffraction analyzer
(CILAS-1180 Particle Size Analyzer, France make).
1800
I
1600
1400
Intensity (counts)
garnet, rutile, and pyroxenes as well as amphiboles and light
(quartz, feldspar) minerals. The coast is characterised by
extensive formation of dunes [4] that have around 20% of the
heavy minerals [2]. These dunes are separated by low-lying
areas and interdunal valleys. Regionally, the area forms a part
of the Precambrian (belonging to the Eastern Ghats) complex
and includes upper Gondwana laterites, Tertiary sediments,
and Quaternary beach placers. The Eastern Ghats mobile belt
is one of the oldest groups of rocks in the Indian Peninsula
[16]. The rocks of this belt are mainly consisting of charnockites, khondalites, granites, granodiorites, and unclassified
granulites. The belt shows a fairly consistent trend (NE–
SW) for over 1000 kms from Prakasam District of Andhra
Pradesh to the southeastern edge of the Talcher coalfield of
Odisha. The Eastern Ghats around Chhatrapur in the Ganjam
District form detached hill ranges that are mainly composed
of charnockite, khondalite group, granites, granodiorites,
and unclassified granulites. The charnockite rocks are silica
rich, with orthopyroxene (hypersthene)-bearing granulitic
composition whereas khondalite is metasedimentary and
contains a variety of minerals such as sillimanite + garnet ±
graphite ± spinel ± cordierite and hypersthene, in addition
to quartz and K-feldspar (orthoclase) [17, 18]. Associated
with these and also included in the khondalite group are
the quartzites/garnetiferous quartzites, liptinites, and calcsilicate rocks. More or less, these Eastern Ghats rock types
form a banded assemblage, metamorphosed under granulite
facies conditions, and are permeated by quartz-feldspar
neosomes [4]. Based on the mode of occurrence of different
lithounits along with their structural analysis Rao et al. [4]
published a stratigraphic succession of the area. This area lies
in a semiarid, subtropical climate. The main drainage system
of this area is the river Rushikulya (that flows southeasterly),
which originates from the highlands of Eastern Ghat group of
rocks and debouches into the sea at Ganjam. Of course, many
streams and streamlets (Bahuda and Ghoda Hoda) which
originate from the nearby coastal hills also join the sea near
by the Chhatrapur deposit. These streams are ephemeral in
nature and are the major suppliers of the sediments to this
region.
Journal of Geochemistry
1200
1000
I
P
800
600
I
P
I
P I
400
P
200
0
10
15
P
I
I
II I P
P
20
25
2𝜃 (deg.)
I
I
P
P I I I
P I
P
P PI
30
35
40
I: ilmenite
P: pseudorutile
Figure 1: X-ray diffraction pattern of the ilmenite sample.
4. Results
4.1. XRD and Particle Size Analysis. The bulk ilmenite sample
was ground to below 45 microns and subjected to X-ray
diffraction. The X-ray diffraction of the ilmenite sample
(Figure 1) indicates predominantly ilmenite (JCPDS number 29-0733) and minor quantities of pseudorutile (JCPDS
number 29-1494). Similar observation was also made by
Sasikumar et al., [19] for the ilmenite of this area. The
variation of particle size and particle size distribution is
shown in Figure 2. The particle size of the sample varied
between 0.04 microns to 600 microns. The particle size of
the sample varies between 100 and 500 microns and 80% of
the ilmenite is around 200 microns. The mean particle size
is 175.14 microns. Ilmenite in this deposit is fine to medium
grained and moderately well sorted to well sorted and shows
unimodal distribution and fine to coarsely skewed. Based on
the particle size and perfection of roundness it can be stated
that the ilmenite from this locality is texturally matured.
4.2. Optical Microscopy. Reflected light microscopic studies
of this ilmenite sample indicate that ilmenite is the major
phase with minor amounts of hematite. The quantity (volume
percentage) of hematite in the sample is too low for which
hematite peaks were not observed in the X-ray diffraction pattern. The ilmenite occurs mostly as subrounded
to subangular grains marked by numerous surface pits,
etch marks/grooves, crescentic pits, and mesh-like patterns.
Sometimes ilmenite contains exsolved laths, streaks, and
irregular bodies of hematite. Similarly, hematite also contains
exsolved bodies of ilmenite which may be laths, fine streaks,
and as patches. Ilmenite-hematite intergrowth also gives rise
to emulsion texture and seriate texture. The alteration of the
grains has occasionally resulted in an amorphous to cryptocrystalline to microcrystalline mass resembling leucoxene
(Figure 3) and pseudorutile. Leucoxene and anatase occur as
patches along the margins and fractures of ilmenite which
is due to alteration of ilmenite. The alteration characteristics
Journal of Geochemistry
3
pits as well as sets of grooves (Figures 5(c) and 6(c)) oriented either in same different directions or in different
directions might have developed by the effects of solution
activity. Undulatory wavy surfaces formed due to solution
effect and removal of blocks were also observed on these
ilmenite grains (Figures 4(c) and 5(d)). The present study
of micromorphological features by electron microscope
establishes the fact that two types of weathering processes
such as mechanical and chemical, affected the placer heavy
mineral ilmenite that operated during their transportation
as well as after deposition.
100
Cumulative value (%)
80
60
40
20
0
−100
100
0
200 300 400 500
Particle size (microns)
600
700
800
Figure 2: Particle size analysis of the ilmenite concentrate sample.
50 𝜇
(d)
(b)
(a)
(c)
Figure 3: Mineralogical and textural features of ilmenite taken
under reflected light. Note the various sizes and shapes of the
ilmenite grains and some of the grains are also fresh while some are
altered. (a) The ilmenite grains from Chhatrapur Deposit showing
the rows of subparallel pits left by leaching out of the hematite
exsolution lamellae. (b) The alteration along grain boundaries (c)
along fractures of ilmenite. (d) Patchy leucoxene is observed by
complete alteration of ilmenite.
of the ilmenite from this area were studied in detail in [4,
20]. Rao et al. [4] concluded that the alteration leads to
enrichment of TiO2 , MgO, Al2 O3 , Cr2 O3 , SiO2 , K2 O, V2 O5 ,
BaO, CaO, and Na2 O with loss of FeO, MnO, and ZnO. They
further advocated that the alteration products could be due
to the exogenic processes that operated on these ilmenites
after their release from the parent rocks of the Eastern Ghats
complex.
4.3. Scanning Electron Microscopy. Micromorphological
studies of ilmenite from the study area by SEM depict the
development of a number of microfeatures on the ilmenite
grains. The ilmenite grains of this area exhibit subrounded
to rounded shape (Figures 4(b), 4(d), and 5(a)) along with
impact “V” marks and deep pits are seen resulting from
mechanical collision and later from solution activity (Figures
4(c), 5(b), and 5(d)). Mechanical features like V-shaped pits
suggest that grains are formed by grain to grain collision in
an aquatic environment [21]. Even the crescentic structures,
4.4. Mineral Chemistry. The mineral chemistry of ilmenite
was determined by EPMA spot analysis. The major and
minor elemental composition analyses of the ilmenite from
this deposit are given in Table 1 along with the structural
formulae and end member compositions. The TiO2 content
of the ilmenite from this deposit varies from 50.25% to
55.411% which is comparatively lower or higher than the
theoretical ilmenite 52.75% [22]. Higher TiO2 may be due
to leaching of other cations. Lower TiO2 could be due to
the presence of hematite exsolved with ilmenite. Sukumaran
and Nambiar [7] reported 50% to 56% of TiO2 from the
ilmenites of Ratnagiri coast of Maharashtra which is well
comparable with the ilmenite of Chhatrapur coast. The minor
variations could be due to the source rock basis. The FeO
content of the ilmenite from this deposit varies from 42.719%
to 49.987%. The large range of FeO in the ilmenite could
be due to hematite exsolved with in ilmenite. Ilmenite from
the Honnavar beach is having 50 to 56.33% TiO2 and 41
to 46.89% FeO [8]. The result presented here is broadly in
agreement with those of Hegde et al. [8]. The MnO content
of ilmenite in this deposit varies from 0.125% to 0.579% while
the MgO content varies from 0.069 to 1.357%. The presence of
significant amounts of manganese and magnesium indicates
that the ilmenite of Chhatrapur constitutes a solid solution
series with pyrophanite and geikielite, respectively [23]. As a
result of these solid solutions, the TiO2 content of the ilmenite
is higher or lower than the ideal value. Significant amounts
of V2 O5 (0.247% to 0.306%), Al2 O3 (0 to 0.087%), Cr2 O3 (0
to 0.089%), NiO (0 to 0.051), ZnO (0 to 0.233%), CaO (0 to
0.061%), and Na2 O (0 to 0.19%) were also detected in these
ilmenite grains. K2 O and SiO2 were analysed but not detected
in any of these grains. However, these grains contain trace
amounts of ZrO2 (0 to 0.036%) and HfO2 (0 to 0.034%) in
their crystal lattice which is reported here for the first time.
5. Discussion and Conclusions
The chemical composition (particularly TiO2 concentration)
of the ilmenites can be compared with that of the igneous
and metamorphic ilmenites to identify the possible source
rocks [10, 11, 24]. The igneous ilmenites show a wide
variation of TiO2 concentrations (42%–52%) whereas the
ilmenite compositions derived from metamorphic sources
have a mean value of about 51% TiO2 . These Chhatrapur ilmenites have titanium dioxide concentration ranging from 50.25% to 55.41% and are well comparable to
4
Journal of Geochemistry
(a)
(b)
(c)
(d)
Figure 4: Micromorphological studies of ilmenite grains from Chhatrapur area: (a) general view of the ilmenite concentrate, (b) rounded
to subrounded grains of ilmenite, and (c and d) rounded to subrounded edges of angular grains of ilmenite with flat surface indicating long
distance transportation of the sediments.
(a)
(b)
(c)
(d)
Figure 5: Micromorphological studies of ilmenite grains from Chhatrapur area: (a) rounded grains being pitted and fractured along a linear
direction which could be due to mechanical collision of grains. (b) Deposition of foreign materials along the fractures as well as grooves of
the ilmenite grains. (c and d) Platy grains having been leached out leaving behind pits/groves.
1
Al2 O3
0.061
FeO
44.368
MgO
0.959
MnO
0.281
CaO
0
Na2 O
0
TiO2
53.708
Cr2 O3
0.041
NiO
0
ZnO
0.164
ZrO2
0
HfO2
0
V2 O5
0.292
Total
99.874
Ti/Ti + Fe
0.483
Based on
6(O)
Al
0.0036
Fe
1.8524
Mg
0.0714
Mn
0.0119
Ca
0
Na
0
Ti
2.0165
Cr
0.0016
Ni
0
Zn
0.006
Zr
0
Hf
0
V
0.0117
Total
3.9751
End member
composition%
Pyrophanite 0.6148
Gaekelite
3.6886
Ilmenite
95.697
6
0.028
45.768
0.17
0.283
0.013
0
53.231
0.048
0
0.049
0
0
0.287
99.877
0.473
6(O)
0.0016
1.9245
0.0127
0.012
0.0007
0
2.0128
0.0019
0
0.0018
0
0
0.0116
3.9796
7
0
46.394
0.512
0.477
0
0.003
51.488
0.033
0
0.038
0.016
0.034
0.284
99.279
0.461
6(O)
0
1.9752
0.0389
0.0206
0
0.0003
1.9713
0.0013
0
0.0014
0.0004
0.0005
0.0116
4.0215
8
0.07
42.719
0.248
0.346
0.061
0.023
55.411
0.025
0
0.041
0
0.033
0.306
99.283
0.500
6(O)
0.0041
1.7695
0.0183
0.0145
0.0032
0.0022
2.0825
0.001
0
0.0015
0
0.0005
0.0122
3.9095
9
0.046
45.329
0.951
0.244
0.019
0.01
52.455
0.025
0.003
0.009
0
0.026
0.287
99.404
0.472
6(O)
0.0027
1.9123
0.0715
0.0104
0.001
0.001
1.99
0.001
0.0001
0.0003
0
0.0004
0.0116
4.0023
10
0.036
45.355
0.225
0.294
0.021
0.056
53.027
0.08
0
0
0.036
0
0.287
99.417
0.474
6(O)
0.0022
1.9142
0.0169
0.0126
0.0011
0.0055
2.0125
0.0033
0
0
0.0009
0
0.0116
3.9808
11
0.008
47.691
0.071
0.579
0.006
0
50.25
0.028
0.028
0.021
0
0
0.273
98.955
0.448
6(O)
0.0005
2.0545
0.0054
0.0253
0.0003
0
1.9466
0.0011
0.0012
0.0008
0
0
0.0113
4.047
12
0.038
49.987
1.254
0.41
0.014
0.05
45.665
0.054
0
0
0
0
0.247
97.719
0.413
6(O)
0.0023
2.2158
0.099
0.0184
0.0008
0.0052
1.8203
0.0023
0
0
0
0
0.0105
4.1746
13
0.031
44.685
0.707
0.286
0.007
0
53.282
0.019
0.023
0.016
0.009
0
0.289
99.354
0.479
6(O)
0.0018
1.8799
0.053
0.0122
0.0004
0
2.0157
0.0008
0.0009
0.0006
0.0002
0
0.0116
3.9771
14
0.028
43.729
1.357
0.125
0
0.004
54.656
0.015
0.034
0.233
0.011
0
0.295
100.49
0.491
6(O)
0.0016
1.8053
0.0999
0.0052
0
0.0004
2.0291
0.0006
0.0013
0.0085
0.0003
0
0.0117
3.9639
15
0.019
45.301
0.554
0.493
0.002
0.012
52.228
0.053
0
0
0.035
0
0.284
98.981
0.471
6(O)
0.0012
1.9236
0.042
0.0212
0.0001
0.0012
1.9943
0.0021
0
0
0.0009
0
0.0116
3.9982
16
0.005
46.781
0.429
0.161
0.005
0.009
52.153
0.036
0.013
0.044
0
0.021
0.286
99.943
0.462
6(O)
0.0003
1.9758
0.0323
0.0069
0.0003
0.0009
1.9808
0.0014
0.0005
0.0017
0
0.0003
0.0116
4.0128
17
0.057
45.387
0.863
0.501
0
0.19
52.683
0.089
0
0
0
0.029
0.276
100.08
0.472
6(O)
0.0034
1.9035
0.0645
0.0213
0
0.0185
1.9868
0.0035
0
0
0
0.0004
0.0111
4.013
18
0.062
44.539
0.729
0.177
0
0.223
53.933
0.017
0
0
0.01
0
0.295
99.985
0.483
6(O)
0.0036
1.8575
0.0054
0.0075
0
0.0215
2.0227
0.0007
0
0
0.0002
0
0.0118
3.9309
19
0.011
45.935
0.069
0.147
0.003
0.026
53.883
0
0
0.031
0.011
0
0.296
100.41
0.475
6(O)
0.0006
1.9188
0.0057
0.0062
0.0002
0.0025
2.024
0
0
0.0011
0.0003
0
0.0118
3.9712
20
0.04
47.109
0.399
0.206
0.013
0.039
51.574
0.048
0.051
0
0.028
0.02
0.279
99.806
0.458
6(O)
0.0024
1.9976
0.0301
0.0088
0.0007
0.0038
1.9666
0.0019
0.0021
0
0.0007
0.0003
0.0114
4.0264
0.438 0.4854 0.4475 0.6156 1.0124 0.8045 0.5215 0.6482 1.2133 0.7886 0.6272 0.2722 1.067 0.3424 1.0707 0.401 0.3211 0.4321
1.431 2.5799 2.5307 0.6515 1.9118 1.0154 3.5854 0.8695 0.259 4.2431 2.7248 5.2293 2.114
1.603 3.2423 0.2898 0.2952 1.478
98.131 96.935 97.022 98.733 97.076 98.18 95.893 98.482 98.528 94.968 96.648 94.499 96.819 98.055 95.687 99.309 99.384 98.09
5
0.087
45.053
0.659
0.205
0
0
53.503
0.023
0
0
0.012
0.003
0.293
99.838
0.478
6(O)
0.0051
1.8862
0.0492
0.0087
0
0
2.0143
0.0009
0
0
0.0003
0
0.0118
3.9765
0.6186
0.7226
98.659
4
0.08
44.638
0.666
0.22
0.018
0
55.094
0.016
0
0
0
0
0.294
101.03
0.488
6(O)
0.0046
1.8373
0.0489
0.0092
0.0009
0
2.0392
0.0006
0
0
0
0
0.0116
3.9523
3
0.036
45.877
0.375
0.202
0
0
53.114
0.043
0
0.008
0.012
0.015
0.286
99.968
0.472
6(O)
0.0021
1.9269
0.0281
0.0086
0
0
2.0061
0.0017
0
0.0003
0.0003
0.0002
0.0115
3.9858
2
0.001
45.242
0.185
0.28
0
0.071
53.741
0.018
0
0
0
0
0.29
99.828
0.478
6(O)
0
1.8978
0.0139
0.0119
0
0.0069
2.0272
0.0007
0
0
0
0
0.0117
3.9701
Table 1: EPMA results (in wt.%) of various ilmenite grains from the Chhatrapur coast.
Journal of Geochemistry
5
6
Journal of Geochemistry
(a)
(b)
(c)
(d)
Figure 6: Micromorphological studies of ilmenite grains from Chhatrapur area. (a) Step like wavy surface feature developed due to solution
effect and removal of blocks. (b) Crescentic structures and pits produced by solution activities. (c) Porous/pitted surface developed by solution
activities. (d) Flaky, porous, and corroded surface developed due to chemical weathering appearing.
the metamorphic ilmenites. The TiO2 concentration of the
present ilmenite suggests that the ilmenites were formed in
a high grade metamorphic environment such as granulite
facies metamorphic rocks. The granulite facies metamorphic rocks include charnockites, khondalites (quartzites/garnetiferous quartzites, quartz-granulites, quartz-garnet-sillimanite-graphite-schist, liptinites, and calc-silicate rocks),
granites, pegmatites, granodiorites, and unclassified granulites. As mentioned earlier the geology of the catchment area
of Rushikulya river and Chhatrapur is dominantly constituted of the Eastern Ghat group of rock types. Hence, the
Eastern Ghat group of rocks appears to be the major source
for the ilmenite. Outcrops of igneous intrusive rocks in the
Eastern Ghat group also suggest that the ilmenites were
formed in a high grade metamorphic environment [25].
The wide ranges of the V2 O5 (0.247% to 0.306%), Cr2 O3
(0 to 0.089%), and NiO (0 to 0.051) content indicates that the
ilmenites from this area represent an admixture of multiple of
source rock types. Elevated abundances of these siderophile
elements in the Chhatrapur ilmenite suggest that basic
rocks like pyroxene granulites along with metasedimentary
rocks like khondalite and charnockite which are present in
abundance in the Eastern Ghats complex of Orissa are also
the source rocks.
The present study on beach sand ilmenite of Chhatrapur
coast is restricted only on a concentrate sample drawn from
IREL, and hence it could be assumed to be a mixture of recent
and older sediments as well as from a near and distant source
based on microscopic, electron microscopic, and available
literature. Mineralogical studies by optical as well as electron
microscope on the ilmenite from this deposit revealed that
these grains heave been subjected to chemical weathering
giving rise to altered rims. Chhatrapur ilmenite has undergone least weathering compared to the ilmenite from beach
sands of Kerala and Tamil Nadu [26]. Sasikumar et al. [27]
have reported that the ilmenite of Chhatrapur coast has 90%
ilmenite and 10% altered ilmenite. Ti/(Ti + Fe) ratio has also
been considered as an important parameter for estimation of
alteration of ilmenites. The common process involved in the
alteration of ilmenite is hydration and conversion of ilmenite
into pseudorutile that has Ti/(Ti + Fe) ratio between 0.5 to 0.6
[8]. This is due to the leaching of iron. The observed ratio of
Ti/(Ti + Fe) for ilmenite of Chhatrapur coast (0.413 to 0.500)
is comparable to that of the ilmenites from the Honnavar
coast [8].
From microscopic as well as from electron microprobe
studies, it can be inferred that the ilmenite from the Chhatrapur coast fall under three different types. These are as follows.
(a) Unaltered ilmenite: ilmenites without any sign of
alteration. They are fresh and compact (Figures 4(b),
4(c), and 5(c)).
(b) Moderately altered ilmenite: ilmenite grains which
show signatures of alteration along grain boundaries
or fracture planes (Figures 3, 5(a), 5(b), and 5(d)).
Journal of Geochemistry
(c) Highly altered ilmenite: ilmenite grain is completely
affected by alteration leading to leucoxene (Figure 3)
and forming porous structure (Figures 6(c) and 6(d))
often associated with foreign materials along the
fractures and grooves (Figures 5(b), 6(b), and 6(c)).
Sasikumar et al., [27] have reported that the ilmenite
of Chhatrapur coast has 90% ilmenite and 10% altered
ilmenite.
From the above studies it can be concluded that the
Eastern Ghats group of rocks consists of khondalite suite of
rocks (consisting of garnetiferous quartz-sillimanite schists,
gneisses, garnetiferous quartzites, quartz granulites, calcsilicate rocks, and quartz- sillimanite-graphite schists), charnockite suite of rocks (tonalitic and granodioritic varieties
in composition as well as pyroxene granulites), and leptynite
besides intrusive granites, pegmatites, quartz veins, and other
metasediments which appears to be the major source of the
Chhatrapur beach placer for the heavy mineral assemblage in
general and ilmenite in particular.
6. Implications in Metallurgical Processing
The Ilmenites are the major heavy mineral of the total
heavy mineral assemblage at Chhatrapur coast. The physical
and chemical properties of the ilmenites vary drastically
with respect to their alteration. Considering the magnetic,
conducting, and density properties used during separation
of heavy minerals one from the other, it is obvious that
the altered as well as unaltered ilmenites behave differently.
Unaltered ilmenite has a higher specific gravity and a better
electrostatic and magnetic response than the iron poorer and
titanium richer altered ilmenite. Coexistence of unalteredaltered ilmenite and presence of leucoxene in the sample need
to be identified and quantified under microscope as they have
direct bearing on separation. Since the degree of weathering
or alteration can be an indicator of its economic value, compositional characterisation by such integrated instrumental
techniques would not only help to adopt better methods
for industrial processing but also facilitate the production of
different grades of synthetic rutile.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
Acknowledgments
The authors are indebted to Indian Rare Earths Limited,
Chhatrapur, Institute Instrumentation Centre of IIT, Roorkee, for providing the sample, and EPMA, respectively.
Thanks are also due for the permission of the Director of
CSIR-IMMT, Bhubaneswar, to publish this paper.
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