Download Geology and petrography of ochres and white clay deposits in

Geoarchaeology and Archaeomineralogy (Eds. R. I. Kostov, B. Gaydarska, M. Gurova). 2008.
Proceedings of the International Conference, 29-30 October 2008 Sofia, Publishing House “St. Ivan Rilski”, Sofia, 147-152.
GEOLOGY AND PETROGRAPHY OF OCHRES AND WHITE CLAY DEPOSITS IN
RAJASTHAN STATE, INDIA
Giovanni Cavallo1, Manoj Pandit2
1University
2University
of Applied Sciences, South Switzerland, DACD, LTS PO Box 12 6952 Canobbio, Switzerland; [email protected]
of Rajasthan, Dept. of Geology, 302004 Jaipur, India; [email protected]
ABSTRACT. Rajasthan State in NW India is the leading producer of ochres used in paint, cement, rubber, glass, linoleum, plastic industries and
foundries, lacquers and also for imparting colour to paper and cement. The main mines are located in Bhilwara, Chittaurgarh and Udaipur districts,
in the Precambrian Aravalli Delhi Fold Belt (ADBF, also known as Aravalli Mountain region). The NE-trending Aravalli Mountains that run for more
than 750 km in NW India represent the most prominent tectonomorphic feature in this region. It marks the Western boundary of the Bundelkhand
craton that occurs to the East while in the South the continuity of ADFB is lost under the vast Deccan volcanics of much younger age. Geological
evolution of this terrain includes an Archean basement over which green schist- to amphibolite-facies metasedimentary sequences of Palaeo- to
Mesoproterozoic (Aravalli Supergroup) and Meso- to Neoproterozoic (Delhi Supergroup) volcano-sedimentary sequences were deposited. The
petrographic approach on the materials collected in these areas, inherited by the micromorphology of the soils, is correlated to the geology. Texture
and co-exixting mineral characteristics have been used to infer original minerals and host rocks. Minerals non-usable as pigments (quartz, feldspar,
etc.) have also been discriminated.
also been described as mineral resources in all the reference
literature, such as Krishnaswamy (1988). Rajasthan State in
the NW of India is one of the most important localities in the
production and export of ochre and clay pigments. Here ochre
deposits and mines are located at various places, however, the
notable occurrences are in Bikaner, Chtittaurgarh, Jaisalmer,
Jhunijhunun, Jodhpur, Nagaur and Udaipur districts.
Introduction
Clay pigments and, more in general, earthy pigments (Hradil
et al., 2003) have been widely used from ancient times to date
for decorating bodies, caves, religious temples and
architectural surfaces, both walls and stones (Delamare et al.,
2000). The use of these materials is primarily related to their
easy availability in all the countries and in varied geological
contexts being products of weathering of a variety of host
rocks. As reported in the ancient treatises, these raw materials
were used mixed with inorganic and/or organic binding medium
depending upon the tradition of the pictorial techniques and the
specific purpose.
We have recently initiated a detailed geological,
mineralogical and geochemical investigation of the ochre
deposits of Rajasthan in order to understand the composition
of the raw material and the process of transformation of some
selective minerals as earthy pigments. This paper presents
some preliminary results on geological and petrographic
characteristics of some ochre and white clay occurring in the
Precambrian terrain (Fig. 1) of central and SE Rajasthan
(Bhilwara, Chittaurgarh and Udaipur districts).
Despite such a wide application spectrum, not much is
known about their origin, chemical and mineralogical
composition and physical properties. This impedes the work of
specialists in the field of conservation and restoration of
cultural heritage especially in terms of choosing the best
proxies for original pigments. A number of substandard and
synthetic materials available in the market are being used,
however, they contain impurities especially sulphates which
are detrimental to the historical artworks. The process and
technique of preparing the final pigment from the raw material
is also misunderstood sometimes.
Geology of the ochre and clay deposits
Bhilwara district
Precambrian rocks in the Bhilwara district include a
significant Archean (Sandmata Complex, Hidoli Group, Berach
Granite, etc.) and a subordinate Proterozoic component
(Aravalli Supergroup, Delhi Supergroup and Vimdhyan
Supergroup). The oldest rocks in this region have been
described as the Bhilwara Supergroup which is predominantly
Archean in age with an early Proterozoic component (Gupta et
al., 1997). This group includes the Sand Mata Complex
(medium to high grade migmatites, gneisses, granulites etc.),
Hindoli Group (low-grade metagraywacke, phyllite and tuff) and
India has a long tradition, historical and cultural background
in the use of ochres and clay pigments in the art work. This is
well documented in the ancient and medieval literature
(Bhattacharya, 1976; Seth, 2006) and also continues even in
the present times as part of the culture. The pigments have
147
Mangalwar Complex (migmatites, calc-silicate rocks, schist,
amphibolite, quartzite etc.). The Berach Granite and
presumably time equivalent Jahazpur Granites represent the
end Archean magmatism in this area. The basement rocks in
the Bhilwara sector define tectonic contacts on either side, with
the Aravalli and Delhi metasediments in the West while the
Great Boundary Fault juxtaposes these rocks and the
sediments of Vindhyan Supergroup in the East.
which corresponds to the predominant tectonic direction in the
ADFB. On the basis of geological considerations the ochre
deposits in the Bhilwara district seem to be genetically
associated with the Late Archean Hindoli Group and can be
further discriminated into two settings within the Hindoli Group
metasediments and along its contact with the Proterozoic
Jahazpur Group. A solitary deposit (BI 02) is located within
dolomite and biotite schist terrain of Mangalwar Complex close
to the contact with Berach Granite. Such a lithological control is
clearly seen in the predominant calcareous mineralogy of this
deposit.
The ochre deposits and operating mining sites are located to
the ENE of Bhilwara town and show a geological cum tectonic
control. The deposits are located in a NE-trending linear belt
Fig. 1. Precambrian geological map of
Rajasthan (modified after Heron, 1953;
Gupta et al., 1997)
148
Chittaurgarh district
District Chittaurgarh, which is located to the south of
Bhilwara, also shares a common geological history with the
latter. The rocks of Bhilwara Supergroup (migmatites,
gneisses, dolomites, schists) form a peneplained basement in
this area. The Berach Granite, exposed in patches, represents
a late Archean intrusive phase into the Migmatitic gneisses of
the Mangalwar Complex. The rocks of Vindhyan Supergroup
(alternating bands of sandstone, shale and limestone) exposed
in the eastern part of the region occurs stratigraphically above
the basement with an angular unconformity between the two.
In the southeastern part of the district all the Proterozoic rocks
have been covered by Late Cretaceous – Early Eocene (~65
Ma) basaltic flows known as Deccan Traps.
Table 1
Description and location of ochre and white clay deposits
N
Description and location
BI04
Yellow ochres and white clay (Itawa Tahsil, Kotri
village)
BI06
Rock (c) yellow ochre (b), reddish horizon (a)
(Mine BS Mandora)
BI07
Pebbles mixed with red ferruginous material
(near Joralia village)
BI15
Red material (near Manoharpura and Hansed Ka
Kheda villages)
CH03 Red (a) and yellow (b) ochre (mine Banasti II,
Sawa)
CH04 Red (a), yellow (c) ochre and white clay (b)
(mine Banasti IV, near Sawa)
CH05 White sandy clay (a,b) (mine Banasti I, Sawa)
CH07 Lens of yellow Ochre (as CH05)
CH08 Red ochre (as CH05)
CH09 Red ochre (a) and yellow ochre plus white clay
(near Barada village)
CH10 White sandy clay (Kantharia village)
CH13 Red material (a), contact red material - bauxite
(b), Bauxite and clay (c) (Senwar)
CH14 Yellow ochre (a) and white clay (b) (Senwar)
CH15 Red ochre (Senwar)
UD01 Red ochre (a – bottom; b – middle part; c – top)
(Iswal)
This is one of the major ochre and white clay producing
areas in SE Rajasthan where extensive deposits are located
within the Proterozoic Lower Vindhyan rocks (Suket Shale).
The deposits are clustered in a small area south of
Chittaurgarh town and occur close to the boundary between
Nimbahera Limestone and Suket Shale representing the topmost units of the Lower Vindhyan sequence. The two other
occurrences are located to the north and southeast of
Chittaurgarh town. Both these sites are within the Lower
Vindhyan terrain, the former along the boundary between
Binota Shale and Bari Shale sandstone (no exposures of host
rock are seen, however, and the deposits show a complete
alteration). The latter deposit is located along the contact
between Suket Shale (Lr. Vindhyan) and Kaimur sandstone
(Up. Vindhyan).
Petrography
Bhilwara district
Sample BI04 (a: bottom, yellow material; b: middle (white
clay, yellow and traces of red material; c: top, white clay). The
yellow Ochre sample (BI04a-b) contains metamorphic quartz
both as individual crystals and in polycrystalline aggregates
while yellow Fe-oxihydroxides are seen disposed along parallel
planes. Quartz grains are about 40 µm in size. Sericite and
biotite are also present. Samples BI04a and Bi04b show the
preservation of the original microstructure and texture which
can be correlated to a biotite schist (Fig. 2) and to a quartzfeldspar rock (Fig. 3). Biotite appears to be the main
contributor for Fe-oxihydroxides; opaque minerals (magnetite)
are also related to the process of biotite decomposition. The
clay minerals (sericite) can be linked to the feldspar alteration.
Udaipur district
Udaipur district has been hailed as the type area for the
Aravalli Supergroup which shows best development in the
Udaipur valley. In addition, there are a number of outcrops of
the BGC gneisses and granites to the east and southeast while
a tectonized contact with the younger Delhi Supergroup is
seen towards the western part of the district. The westernmost
part of the district shows NE-trending linear ridges of 967 Ma
old Sendra – Ambaji granites and host calc-silicate rocks of
Kumbhalgarh Group (Delhi Supergroup). The oldest dated
rocks (3.3 Ga old TTG gneisses) from NW Indian terrain are
located to the southeast of Udaipur city.
The now abandoned red ochre quarry at Iswal (to the
northwest of Udaipur city) has been one of the major producers
of red ochre in the past. The quarry, which exposes a 15 m
thick section of red ochre, has presently been filled up as a
part of a new road development project in the region. However,
it was possible to take samples from the southern face of the
quarry. The ochre deposits are located within the
chlorite/phyllite/tuff (Bari Lake Group), the uppermost formation
of Lower Aravali, and quartzites of the Jharol Group (lower part
of the Upper Aravalli). The deposits are located along the
transition from shallow (Lower Aravalli) to deep sea facies
(Upper Aravalli) depositional conditions.
Materials and methods
The samples collected in the Bhilwara (BI), Chittaurgarh (CH)
and Udaipur (UD) districts are listed in Table 1. All the samples
have been analyzed by means of an optical microscope both in
transmitted and incident light.
Fig. 2. Microstructure of the sample BI04a showing the characters of the
original biotite schist rock (PPL)
149
Sample Bl15 includes secondary calcite and clay minerals in
a red matrix and can be traced to a felsic rock (biotite gneiss)
as the source (Fig. 4).
Fig. 3. Microstructure of the sample BI04b showing the characters of the
original quartz-feldspar rock (XPOL)
The fabric of the sample BI04c does not exhibit any layering,
excepted for metamorphic quartz (individual crystals and
polycrystalline aggregates). The high interference colour of the
very fine grain minerals is in accordance with clay minerals
(kaolinite group). In some cases polycrystalline quartz
aggregates exhibit effects of mechanical stresses which have
completely obliterated the original structure of the quartz.
Petrographic observations allow the identification of quartz as
relict phase while the entire section can be described as an insitu profile.
Fig. 4. Microstructure of the sample BI15 showing the characters of a
biotite gneiss (PPL)
Chittaurgarh district
Sample CH03 (from the bottom to the top. a: red material; b:
yellow Ochres). The sample CH03a shows the presence of red
oxides and abundance of probable gibbsite Al(OH)3 crystals
(Fig. 5) causing the matrix to be isotropic. Traces of yellow
Ochre are observed.
Sample BI06 (from the bottom to the top. c: host rock 10 cm
thick; b: lens of yellow ochre; a: reddish horizon). Sample
BI06c seems to be a product of complete alteration of granite
and shows a characteristic mineralogy comprising destroyed
and secondary calcite (calc-silicate rock). Sample BI06b shows
a close association of quartz (∅med=250 µm), Feoxihydroxides and clay minerals; accessory phases include
muscovite and amphibole. No layering has been observed.
The sample does not show any features of layering.
Mineralogical and petrographic characteristics suggest
quartzite to be the original rock which has altered to form an
ochre deposit. The sample BI06a shows development of red
oxides (non in-situ alteration) and secondary calcite in pores.
Quartz occurs in accessory quantity while clay minerals occur
as interstitial filling.
Sample BI07 includes metamorphic quartz (∅med=1 mm) and
presence of fractures which have also acted as channel ways
for passage of solutions. Besides, calcite also occurs both as
fracture filling around oxides as well as clusters of few mm size
grains. The most likely original rock seems to be granite
gneiss. Some pebbles of quartzite are present which show recrystallized mosaic of quartz grains with typical dihedral angles
close to 120°, triple point junction. Ochraceous material is both
spread around and as round particles, the former ranging in
size between 10 and 100 µm. The particles are sometimes
elliptical in shape with major axis 800 µm and minor axis 400
µm. Muscovite, marble fragments, alteration product of
feldspars as secondary epidote, metamorphic quartz filled with
secondary calcite are also present (BI07a). Pebbles of
quartzite mixed with red oxides, sometimes with radial
structures; traces of muscovite are also seen. The sample
BI07b seems to be a part of lateritic horizon.
Fig. 5. Gibbsite occurring as randomly orientated crystals (PPL)
Sample CH03b: yellow Fe-oxides (limonitic material?) and
associated clay minerals are seen. Quartz (∅=10-20 µm),
altered feldspars (∅=150 µm) are also present while clay
minerals form prominent fractures fills.
Sample CH04 (from the bottom to the top. c: yellow Ochre; b:
white clay; a: red Ochre). Sample CH04c is a yellow ochre
which shows a high abundance of clay minerals and
subordinate quantity of fine grained quartz (∅=20 µm).
Muscovite is in traces. In the sample CH04b white clay and
quartz fragments ∅=40 µm are present; large fragments of
altered feldspars are also present. The sample CH04a
comprises mainly altered plagioclases which can be
recognized by the grain boundaries, grain shapes and textural
relationship. The sample contains significant amount of opaque
150
minerals (Fe-Ti oxides). These features indicate a mafic source
which can most likely be the Deccan basalt as confirmed by a
relict basaltic/doleritic texture.
and very fine grained clay minerals. Some traces of quartz and
muscovite are also seen. Closely associated red oxide, fine
clay minerals and large grains of altered calcite (fragments of
marble) suggest a calc-silicate rock as possible source.
Sample CH13c shows predominant clay minerals and red
oxide along with some relict feldspar grains and accessory
zircon.
Sample CH05 comprises abundant clay minerals mixed with
coarse-size quartz and pebbles of granitic rocks (∅=1.0-2.0
mm); the latter show altered feldspars and quartz. At places
the relicts of the host rock are seen as individual quartz
fragments within fine clay matrix. Some fine crystals of sphene
and zircon are also seen which further confirm a granitic
source (CH05a). The sample CH 05b (from the top of the
profile) is also similar to CH05a.
Sample CH14 (from the bottom to the top. a: white clay; b:
yellow Ochre). Sample CH14a is a mix of clay minerals and
yellow Ochres with quartz grains of variable size (∅=20-200
µm); traces of opaque minerals are also present. A large grain
showing growth of secondary quartz around Fe-oxihydroxides
nuclei can also be seen. Sample CH14b consists of clay
minerals and angular to sub-angular quartz fragments (∅=20600 µm) as well as quartz in veins and traces of Fe-oxides.
Some relict plagioclases and secondary quartz vein can be
seen.
Sample CH07 is a yellow ochre which includes fine bands of
clay minerals (imparting a layered appearance) and randomly
oriented individual fine grained quartz (∅=10 µm).
Sample CH08 also includes altered plagioclase and Feoxides. Although the plagioclase grains have been completely
altered the original grain boundaries are still preserved. The
still preserved igneous texture of porphyritic basalt and
absence of quartz can be traced to a basaltic source (Fig. 6).
The sources of released iron are magnetite and pyroxenes.
Sample CH15 includes predominant iron oxides, completely
altered plagioclases (sericite), which still retains the shape and
textural relationships seen as a relict basaltic texture (Fig. 7).
The iron oxides were derived from Fe-Ti oxides and augite
present in the basalt.
Fig. 6. Altered plagioclases showing still preserved porphyritic basalt
texture (PPL)
Fig. 7. Altered plagioclases in a well preserved texture of basaltic rock
(PPL)
Sample CH09 (a: red material; b: yellow and white). Samples
from the site CH09 show sub-rounded altered feldspars of
variable size set in a matrix of iron oxide (CH09a). Yellow
limonitic material is seen mixed with secondary calcite
(microsparitic) and sparitic calcite forms veins. Micritic calcite is
also present. Quartz (∅=50-100 µm) is present as accessory
mineral. Traces of clay minerals; some fragments of original
rock (marble) are still present (CH09b) and allow the
identification of impure marble as the source rock.
Udaipur district
Sample UD01 (a, bottom; b, middle part; c top). Sample
UD01a includes a red coloured matrix where the Fe-oxides are
generally in the form of rounded globules; the nuclei of these
globules are generally represented by opaque minerals.
Alteration of plagioclase into clay is quite evident which
suggests that the original rock must have been volcanic in
origin as abundant altered euhedral plagioclases are relict
phases associated with red oxides (UD01b); secondary calcite
fills cracks and micro-cracks. Red matrix (Fe-oxides) is the
most prevalent constituent along with feldspars and traces of
quartz (UD01c).
Sample CH10 includes clay minerals and coarse grained
quartz along with secondary calcite in veins. The feldspars are
completely altered and form the matrix. Secondary calcite
veins also have inclusions of quartz fragments. The
mineralogical and textural attributes indicate a quartz-feldspatic
source rock.
Discussion
The samples collected at Bhilwara show a close association
between yellow ochres (FeOOH) and clay minerals (BI04a-bc). The yellow ochres seem to be the alteration products of
biotite and the clay minerals (white clay, probably kaolinite)
from the alteration of the feldspars. The alteration of biotite into
Sample CH13 (from the bottom to the top. a: red ochre; b:
contact between red ochre/bauxite, c: bauxite). Sample CH13a
behaves almost as an opaque rock due to abundant oxides
151
of the original rock are sometimes very well preserved. In
many cases the reconstruction of the entire profile could be
possible and the deposits can be described as an in-situ
alteration profile.
FeOOH is clearly seen (Fig. 8). The relict microstructures are
typical of schists (biotite schists) as well as metamorphic
quartz-feldspar rock (granite gneiss). For these samples the
original characters of the host rocks are well preserved. The
upper part of the succession is dominated by white clay
minerals where the original character of the host rock has been
completely obliterated. The lithological and geological setting
of this area also supports the petrographic observations. The
samples BI06 is mainly dominated by white clay minerals; the
geological profile (from the bottom to the top) includes a
probably calc-silicate rock and quartzite. The samples BI07
show the character of a lateritic horizon where fragments of
marble and quartzite are seen mixed with red iron oxides. The
sample BI15 shows the character of an altered schist; the
matrix is dominated by opaque red minerals.
The common character in the Bhilwara and Chittaurgarh
districts is the association between white clays and yellow
ochres; this is controlled by the geology where feldspar
alteration is responsible for clay formation (very likely kaolinite)
and biotite alteration for yellow ochres (very likely goethite).
Another common characteristic is the association of altered
plagioclases to red oxides. In these cases the original rocks
are volcanic (basalts in Chittaurgarh district and tuffs in
Udaipur).
Further studies would include mineralogical and chemical
analyses that will be carried out to identify the phases non
detectable under microscope and for a better understanding of
the amorphous phases occurring in the samples.
Acknowledgements. We thank Rajiv Rahi of the University of
Rajasthan, Dept. of Geology, for his cooperation and assistance
during field work. We are thankful to the Rajasthan State Mines and
Geology Department for providing help and guidance during field work
and in particular to Mr. Labana for his active help during field work in
Bhilwara district. The smiles, bright eyes, and colorful dresses of the
people working in the mines will eternally remain engraved in our
memories. We acknowledge the financial assistance received from
Rector’s Conference of the Swiss Universities of Applied Sciences
represented by the General Secretary Office (KFH) – grant number P0710-04.
Fig. 8. Incipient alteration of biotite into FeOOH (XPOL)
References
The main characteristic in the samples from Chittaurgarh
include complete or almost complete alteration of plagioclases
reflecting an original basaltic rock as the source. The source of
iron in these samples can be traced to breakdown of iron
bearing minerals such as magnetite and pyroxenes.
Bhattacharya, A. K. 1976. Technique of Indian Painting.
Bhattacharsee Publ. for Saraswart Library, Calcutta, 30 p.
Delamare, F., B. Guineau. 2000. Colors. The Story of Dyes
and Pigments. Harry N. Abrams, Inc., Publ., 13-29.
Gupta, P., Y. K. Arora, R. K. Mathur, P. B. Prashad, T. N.
Sahai, S. B. Sharma. 1997. Lithostratigraphic Map of the
Aravalli Region, Southern Rajasthan and Northeastern
Gujarat. Geological Survey of India Publication, Jaipur.
Heron, A. M. 1953. Geology of Central Rajputana. – Geol.
Survey of India Memoir, 79, 1-389.
Hradil, D., T. Grygar, J. Hradilova, P. Bezdicka. 2003. Clay and
iron oxide pigments in the history of painting. – Applied
Clay Science, 22, 223-236.
Krishnaswamy, S. 1988. India’s Mineral Resources. Oxford &
IBH Publishing, New Delhi-Bombay-Calcutta, 366-374.
Seth, M. 2006. Indian Painting. The Great Mural Tradition.
Harpin Publishing (for India), Harry N. Abrams, New York,
390-397.
Although the samples from Udaipur are limited to a single
face of abandoned mine, the same situation seems likely for
the samples collected at Iswal, Udaipur district where the
original character of volcanic rock (tuffs) is recognizable.
Conclusions
Ochres and clays are not generally studied throughout
optical microscopy; the use of petrographic examination allows
to reveal many distinctive characters of the deposits otherwise
non detectable by means of ancillary techniques such as XRD,
XRF, ICP-MS and SEM/EDS.
The samples studied show a strong connection between the
host rocks and the deposits; the microstructure and the texture
152