In this paper, we described the petrographical characters of the Mn-bearing rock types outcropping in the Kalakhuta, Ghatia, Gararia, Itala, Wagaicha, Tambesara and Talwara villages of Banswara district. The Mn associated rocks in the study area are phyllite, schist, quartzite and limestone. The mineral assemblage in phyllite formed under greenschist facies metamorphism. Petrographic studies of various phyllite samples also reveal that porphyroblasts of biotite sat in the fine-grained micaceous matrix (Biotite, muscovite, chlorite) along with quartz, opaque and ore minerals. Petrographic studies of schist reveal its formation under prograde metamorphism. Mineral assemblages observed in schist are typical of greenschist to lower amphibolite facies. The various schist samples at places show clusters made up of perfect rhombshaped garnets which suggest the increase in the grade of metamorphism. The quartzites are disposed conformably with the phyllites, and are at times brecciated and re-cemented by secondary chert and manganese. These Mn-bearing quartzites are with sutured/serrated and straight grain boundaries. The quartzite samples are fully composed of quartz showing undulose extinction with subordinate feldspar, micas and carbonatic materials. The petrographic characteristics explain that mostly limestones are the dolomitic composition but some ferruginous varieties are also noticed at places. The purer variety of limestone consists of calcite, dolomite and some magnetite but tremolite, quartz and some minute flakes of biotite also occur in impure variety.
Banswara district is situated in the southern-most part of Rajasthan. The area is very much renowned by its Bhukia gold deposits. Due to gold, very little attention has been paid towards the other interesting lithological evolutions in the area. The geology of the study area was earlier surveyed by various workers like [
The regional geology of Banswara district comprises Deccan traps, Aravallis and Pre-Aravalli banded gneissic complex [
The Aravalli Supergroup exposed in northwestern India and its basement
Group | Formation | Lithology |
---|---|---|
Champaner Group | Lambia Formation | Metasubgraywacke, meta-conglomerate, gneiss |
~~~~~~~~~~~~~~UNCONFORMITY~~~~~~~~~~~~~~ | ||
Wagidora Formation forformationFormFormation | Metasubgraywacke, mica-schist, pebble and quartzite | |
Lunavada group | Phyllite, Felspathised-mica schist | |
Kalinjara Formation | Quartzite | |
Dolomite | ||
Petromict-meta-conglomerate | ||
Manganiferous phyllite | ||
~~~~~~~~~~~~~~UNCONFORMITY~~~~~~~~~~~~~~ | ||
Synorogenic granite &gneiss |
commonly referred as the ‘‘Banded Gneissic Complex”. The Aravalli Supergroup (2500 to 3300 Ma) overlies the Archaean basement of gneisses and granites (Banded gneissic complex) with a profound unconformity [
The Mn-bearing rocks of study area belongs to Kalinjara formation of Lunavada group which is an important constituent of the southern parts of Aravalli mountain belt (SAMB), lies under Aravalli Supergroup (
The Lunavada Group has been subdivided into the Kalinjara, Wagidora, Bhawanpura, Chandanwara, Bhukia and Kadana Formations [
The Kalinjara formation comprises dominantly phyllite, feldspathic mica- schist, meta-subgreywacke, quartzite, dolomite and manganiferous phyllite as shown in
Besides the collected samples, fifteen fresh and unweathered rock samples were selected for petrographic studies under transmitted light (Olympus BX51) and X-ray diffraction analysis of samples by Xpert Pro Panalytical. Modal Analysis was carried out for rock types to estimate the approximate percentage of various minerals by using Gazzi-Dickinson method.
The phyllite is the dominant rock types of Banswara manganese ores belt. The rocks of the argillaceous composition are represented by phyllites [
The rock is composed of fine-grained muscovite and chlorite as abundant minerals associated with enough amount of quartz. The garnet, magnetite, hematite, feldspar and opaque are accessory minerals. Muscovite laths showing non- pleochroic with moderate relief and low birefringence. At some places, chlorite grains are coalesced with each other indicating that they have suffered directed pressure under metamorphism. Chlorite shows its characteristic greenish pleochroism with low relief. The quartz grains are xenoblastic and show undulose extinction with the encrustation of manganese ores. Garnet crystals are in perfect rhombohedral shaped with several encrustation of opaque minerals (
This rock shows the dominance of muscovite flakes along with chlorite. Quartz layers are sandwiched between muscovite and dark opaque mineral layer (
The rock is rich in perfect lapidoblastic biotite grains set in the fine-grained micaceous matrix (
also composed of xenoblastic medium grained quartz and uniformly cleaved muscovite flakes. The accessory minerals are feldspar, tourmaline and opaque ore minerals.
The rock is fine to medium grained, essentially composed of muscovite and chlorite as dominant mineral, with quartz, biotite, garnet, feldspar and opaques as accessory minerals. The chlorite mineral clearly showing its diagnostic green to brownish color with low relief in plane polarized light. Most of the chlorite occurs in lens-shaped form. The biotite alteration in chlorite clearly noticed in the lower part of section (
In all rock samples, Mn ores associated with encrustation or in inclusion occur in various minerals. Beside this, Mn ores deposited along the boundaries of various minerals grains. Petrographic studies revealing mineral assemblages of different samples are listed in (
Type of Sediment | Metamorphic equivalent | Mineral Assembladge |
---|---|---|
Pelites | Siliceous Phyllite | Muscovite + Chlorite + Quartz + Garnet + Opaque |
Pelites | Manganiferous phyllite | Muscovite + Chlorite + Quartz ± Biotite + Opaque |
Pelites | Muscovite phyllite: | Muscovite + Chlorite + Quartz ± Biotite + Garnet + Opaque |
Pelites | Chlorite-Biotite phyllite: | Chlorite + Biotite + Muscovite + Quartz + Opaque |
The mica schist and phyllite are predominant rocks in the study area and form about 70% of the rocks of this belt, where only the top portion of this formation is mineralized [
Garnetiferous-mica schist is medium-grained, showing clusters of garnet crystals and consists mainly of muscovite as a dominant mineral with quartz, biotite, chlorite, feldspar and opaque as accessory minerals. The microfolded manganese ores bands also occur (
The encrustation of opaques within quartz, garnet and other minerals are common. Garnet is generally abundant constituents of this group of rocks. The garnet crystals are of perfect rhombohedral in shape (
Quartz-mica schist is composed of medium to coarse-grained quartz, and muscovite as essential minerals. The muscovite shows well developed schistose texture. The lamellaes of muscovite shows moderate relief with perfect one set cleavage. Under cross polar muscovite shows high birefringence. The quartz grains are
Type of Sediment | Metamorphic equivalent | Mineral Assembladge |
---|---|---|
Pelites | Garnetiferous-micaschist | Garnet + Muscovite + Chlorite ± Biotite + Quartz + Opaque. |
Pelites | Quartz-micaschist | Quartz + Muscovite + Chlorite ± Biotite + Garnet + Opaque |
Pelites | Muscovite-chloriteschist | Muscovite + Chlorite ± Biotite + Quartz + Opaque. |
arranged parallel to muscovite and biotite lapidoblasts. The quartz grains show undulose extinction. The accessory minerals are biotite, chlorite, alkali feldspar, garnet and opaque minerals. The garnet rims are present with the encrustation of opaques in various minerals (
Muscovite-chlorite schist is composed of dominant mineral as muscovite and chlorite with quartz, biotite, feldspar and opaques as accessory minerals. The muscovite and chlorite flakes uniformly oriented with the deposition of dark color minerals along with their boundaries (
Mn ore deposited along the minerals boundaries and in embedded form. And two theta position of various minerals has given in (Figures 5(16)-(18)).
The limestone samples were collected from Talwara village. Besides these deposits, there are numerous minor occurrences of limestones between Kalinjra and Pali Chhoti localities in Banswara district. Some of the limestone beds are effectively exposed in the west of Talwara and striking NNW-SSW.
The limestone is thick bedded and crystalline. The bedding of limestones is in conformity with phyllites and quartzites. Various irregular joints, fissures, cavernous pockets are characteristic features of limestone in Talwara. The manganese ores are distributed very irregularly in the limestone.
The petrographic studies reveal that mostly limestones are dolomitic in composition [
Type of Sediment | Rock Type | Mineral Assembladge |
---|---|---|
Calcareous | Limestone | Calcite + Dolomite + Magnetite + Quartz + Chert + Opaque. Calcite + Dolomite + Quartz + Hematite + Opaque. Calcite + Dolomite + Tremolite + Biotite + Quartz + Opaque. |
chert, flint and iron-bearing minerals like hematite. Due to impurities, the colour of limestone changes from white to redbrick and greyish. The two-theta position of various minerals has given in (
The quartzite outcrop extends over miles within the area from Gararia to Ratimauri with roughly NW-SE direction and contains thin bands of manganese ore. The quartzites are disposed conformably with the phyllite and are at times brecciated and later re-cemented by secondary chert and manganese [
The different rock samples are composed predominantly of quartz with subordinate mica, feldspar, opaques and impurities of hematite (
near Talwara village shows undulatory extinction and contain fractured filled with sericite. Quartz crystal shows straight grain boundaries with sharp extinction. According to [
Type of Sediment | Metamorphic equivalent | Mineral Assembladge |
---|---|---|
Psamite | Quartzite | Quartz + Plagioclase + Orthoclase + Sericite + + Calcite + Opaque. Quartz + Orthoclase + Sericite Calcite + Opaque. Quartz + Plagioclase + Orthoclase + Hematite + Muscovite Opaque. Quartz + Microcline + Muscovite + opaque |
Petrographic studies and modal analysis (
Mineral | Mn phyllite | Siliceous phyllite | Chlorite biotite phyllite | Garnetiferous mica schist | Quartz mica schist | Muscovite chlorite schist | Limestone | Quartzite |
---|---|---|---|---|---|---|---|---|
Qtz | 22 | 39 | 24 | 23 | 39 | 21 | 5 | 80 |
Mus | 31 | 31 | 12 | 34 | 28 | 41 | 1 | 2 |
Bio | 3 | 4 | 29 | 3 | 5 | 2 | 1 | 1 |
Chl | 14 | 7 | 22 | 7 | 7 | 20 | × | 1 |
Feld | 2 | 2 | 1 | 3 | 4 | 1 | × | 4 |
Gt | 3 | 2 | 3 | 21 | 4 | 4 | × | × |
Op | 20 | 15 | 9 | 8 | 11 | 9 | 9 | 8 |
Mg | 2 | × | × | × | × | × | 3 | × |
He | 3 | × | × | × | × | × | 2 | 2 |
Fa | × | × | × | 1 | 1 | 2 | 0 | × |
Ca | × | × | × | × | × | × | 56 | 2 |
Do | × | × | × | × | × | × | 22 | × |
Total | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
Legend?Minerals in (%) Mus = Muscovite, Qtz = Quartz, Bio = Biotite, Chl = Chlorite, Gt = Garnet, Op = Opaque, Feld = Feldspar, Mg = Magnetite, He = Hematite Ca = Calcite, Do = Dolomite, × = None.
day rock types viz, phyllite, schist and quartzite. As the rocks of the study area have undergone metamorphism up to lower amphibolite facies, the deformation took place at relatively low temperature. The phyllite and schist samples mineral assemblages fall in greenschist to lower amphibolite facies and formed by prograde metamorphism of Aravalli metasediments. Quartzite is non-foliated and both medium to coarse grained (Granoblastic). The quartzites disposed conformably with phyllite and narrowly brecciated with re-cemented by secondary chert and manganese. The calcareous rock shows dolomitic composition with some impure ferruginous varieties. Thin sections studies suggest manganese ores in phyllite and schist rocks deposited along the mineral boundaries and the foliation plane. They are also found in form of dark colour patches in some thin sections. In garnet and quartz, manganese is found in both ways as inclusion or encrustation over them. In limestone manganese mineralisation in sporadic forms etc. In quartzite, manganese ores associated in form of patches and encrustation as well.
The authors are grateful to Prof. Abu Talib, Chairman Department of Geology, AMU Aligarh, Mr Syed Mujtaba, Superintendent Geologist, Geological Survey of India, Faridabad for XRD and their valuable guidance providing research facilities. Anonymous reviewer for suggesting necessary corrections in the manuscript. Mohd Shaif is grateful to UGC for financial support in the form of a fellowship (MANF).
Shaif, M., Siddiquie, F.N. and Mukhopadhyay, S. (2017) Petrographic Characteristics of Manganese Bearing Rocks of Banswara Manganese Ores Belt, District Banswara, Rajasthan (India). Open Journal of Geology, 7, 1047-1062. https://doi.org/10.4236/ojg.2017.77070