Journal of Global Resources
Volume 6 (01)August 2019-January 2020
Page 89-95
UGC–CARE Listed Journal in Group D
ISSN: 2395-3160 (Print), 2455-2445 (Online)

14
PETROGRAPHIC CHARACTERISTICS OF HOST AND ASSOCIATED ROCKS IN THE PbZn DEPOSIT OF RAMPURA-AGUCHA AREA, BHILWARA BELT (RAJASTHAN) INDIA
Rajiullah Khan1, Mohd Shaif2, F.N. Siddiquie3 and Masood Ahmed4
Research Scholar, 2Assistant Professor, 3Professor, 4Independent Scholar
Department of Geology, Aligarh Muslim University, Aligarh (UP), India
Email: rajiullahkhan17@gmail.com, msaif125@gmail.com, fnaseem2000@yahoo.com
1

Abstract: The present study is to confine the Rampura-Agucha area, Bhilwara district,Rajasthan, which occurs in Bhilwara Super group at the contact with Banded Gneissic
Complex. The Bhilwara belt is a thick pile of metasedimentary rocks in the eastern part ofAravalli-Delhi belt that consists dominant litho-units viz: graphite–sillimanite–garnet schist,
garnet–biotite–sillimanite gneisses with garnet-bearing leucosomes as well as amphibolites,
pegmatites and some scattered calc-silicates while the Pb-Zn ore deposit mainly occurs withingraphite-biotite-sillimanite schist. The mineralogical assemblages of host rocks explain thatthey are formed under the high grade of metamorphism, primarily upper amphibolite to
granulite facies condition. These Pb-Zn bearing ore are intimately associated with schist. The
inclusions of quartz are common in garnets, while ore minerals also contain the inclusion ofquartz and feldspar. The highly fractured grains of garnet, hornblende and pyroxene due todeformation, and pressure are observed in these host rocks while the contact between thequartz grains is of suture type in the calc-silicate rock.
Key words: Pb-Zn, Bhilwara Super group, Petrography, Rocks and Minerals
Introduction
The Pb-Zn deposits of the Rampura-Agucha area occur within Mesoproterozoic metasedimentary rocks belonging to the Bhilwara supracrustal belt of Aravalli-Delhi orogen in the
Bhilwara district of Rajasthan state (Deb & Sarkar, 1990), which is located about 220 km to the
SW of the state capital, Jaipur. The area is very much renowned due to its largest Pb-Zn
deposits, where the ore body is extending over a strike length of about 1.55 km with on averagewidth of 60 m while at places the maximum width goes up to 100 m. The rough estimation of
Pb-Zn ore reserve is around 63.65 million tonnes with an average content of 13.38 percent Zn,
1.9 percent Pb and 9.58 percent Fe (Gandhi et al., 1984). The Pb-Zn bearing rocks
encountered in the present study area are metamorphosed to mainly upper amphibolite to
granulite facies, estimated by Ranawat et al. (1988), Deb & Sarkar (1990). Several pioneer
workers Gandhi et al. (1984), Ranawat et al. (1988), Ranawat & Sharma (1990) and Sharma &Singh (1990) are continuously involved in the study of these ores and its associated rocks.
Recently, Chattopadhyay (2017), mentioned that a large scale of remobilization of ore duringmetamorphism is evidenced mainly in the cleavage and fracture of the associated silicates.
Finally, the present authors did the petrographic studies of the rocks to understand the petromineralogical associations in the study area. However, such type of study always provides
relevant information over mineralogy, textural properties, P-T conditions and paragenetic
history of rocks, which formed the base for depth studies of the area.
Geology of the Study Area
The regional geology of south-eastern Rajasthan is shown by the Banded Gneissic Complex(BGC), Aravalli Supergroup and Delhi Super group (Heron, 1953). The pre-Aravalli group was
renamed as Bhilwara Super group, representing the Bhilwara geological cycle of Archean age,
however, there is a controversy regarding the separate status of Bhilwara Super group.
According to Raja Rao (1976), Bhilwara Super group is older than the Aravalli but Roy et al.
(1981), Naha & Halyburton (1974 & 1977) and Naha & Roy (1983), stress that there is a
striking similarity in the structures of the Bhilwara Super group and the Aravalli rocks. The PbZn deposits of Rampura-Agucha area are located close to the Delwara lineament (Gupta et al.,1980) between the Mangalwar complex and the Sandmata complex that form a part of Bhilwara
Super group/Banded Gneissic Complex. Geologically, the study area comprises an89assemblage of pelitic rocks that constitutes the graphite-biotite-sillimanite schist and garnetbiotite-sillimanite gneiss. These pelitic rocks constitute the most dominant lithologic unit
exposed in the study area along with garnet-bearing leucosomes, calc-silicate gneisses,
amphibolites and pegmatites (Gandhi et al., 1984; Mishra & Bernhardt, 2009). The host rocks
in the study area show NE-SW strike with a steep dip in hanging wall side (750-800SE) andmoderate dip in the footwall side (600-650SE). The general strike of the ore zone is parallel tothe enclosing rocks (NE-SW) while the dip of the ore zone is varying along the strike. The rocksof the Rampura-Agucha area are metamorphosed sedimentary enclaves with an unknown
stratigraphic contact with the Archean basement (Sinha-Roy, 1989). According to Deb andSehgal (1997), the sequence of litho-units is seen from eastern hanging wall to western footwallof Rampura-Agucha Pb-Zn ore deposits are as follows:

Garnet-biotite-sillimanite gneiss (GBSG) with intermittent bands of amphibolites andcalc-silicate rocks, intruded by aplite and pegmatite; Graphite-mica-sillimanite schist (ore body);
 GBSG with lenses of amphibolites, quartzo-feldspathic bands and calc-silicate rocks
intruded by pegmatite/aplites veins;
 Granite-gneiss; Severely mylonitized GBSG;
 Banded and augen gneiss.
The rocks in the area have been subjected to polyphase deformation and metamorphosed up
to high grade with zones of mylonite (HZL, 1992). According to Ray (1982), the area around the
Rampura-Agucha ore deposits has suffered three-phase of deformation namelyi.
An initial isoclinal folding with a variable plunge and axial plane that produced WNWESE trending folds;
ii.
Subsequent isoclinal folding which folded the S1 axial plane about a NE-SW axis;iii.
A weak, local phase of upright, steeply plunging fold.
Figure 01: Simplified geological map of Rampura-Agucha Ore body and Surrounding
Rocks (Simplified after Holler & Gandhi, 1995)

Sampling and Analytical Methods
The author visited the Rampura-Agucha mines and its surrounding area, Bhilwara District,Rajasthan. Due to the scanty and non- availability of rock exposures in the study area, samples
of different rocks types were collected from the Rampura-Agucha mine, small stone queries
and available rock exposures along the Mansi River. About 40 samples of all rock types werecollected from a different location, from each collected samples, few thin sections wereprepared by following Grundmann & Scholz (2015). Thin sections studied in transmitted light90

under the petrological microscope and powdered the five selected samples to 200 mesh size ingrinding mill (for XRD analysis) was carried out in the Department of Geology, AMU., Aligarh.
The powdered rock samples were analyzed in the Department of Mechanical Engineering,
AMU, Aligarh. The XRD pattern was recorded from 50 to 900 with a step size of 0.050 /sec,
using nickel filtered Cu Kα radiations. The data was interpreted and plotted by X'pert High
Score Plus and Origin Pro 8.5, respectively.
PETROGRAPHY
Graphite-biotite-sillimanite Schist
It is the main rock type that hosts the mineralization of the ore. In the field, it shows a very
sharp contact with other surrounding rocks and within these rock units, there are few bands ofcalc-silicates which are barren of ore mineralization except for sporadic specks of pyrite(Gandhi et al., 1984). Megascopically, it is coarse-grained and shows well-developed
schistosity and also contains pink color garnet porphyroblasts. The lead and zinc ore areassociated with graphite-biotite-sillimanite schist mostly in laminated form. Under the
microscope, it chiefly consists of quartz, biotite and sillimanite with a considerable amount ofgraphite as well as potash feldspar, garnet and opaque minerals. The accessory minerals areapatite and tourmaline. The graphite mineral occurs as a subhedral fragments along withfeldspar, biotite, and quartz (Fig.3.e). On the other hand, sillimanite is associated with biotite
and garnet along well developed foliation. Deformation in the twin planes of plagioclase
commonly observed in the thin section (Fig.3.f). Quartz and biotite are common inclusion in thegarnet formed the poikiloblastic texture. Quartz grains are xenoblastic and show undulose
extinction. Biotite flakes uniformly cleaved with preferred orientation results in the formation of
the schistosity. Generally, garnet grains are fractured and occur same time with biotite andsillimanite. The 2θ position of different minerals in the graphite-biotite-sillimanite schist of thestudy area has given in figure 2.A.
Garnet-biotite-sillimanite Gneiss
It is the prevailing lithology within and around the mine. It represents a metasedimentary
sequence of shale and slate. Megascopically, these rocks are medium to coarse grained,showing gneissose structure. They are foliated and contain the leucocratic bands of quartz andfeldspar with insignificant amount of tourmaline alternating with melanocratic layers rich inbiotite and garnet. It is very heterogeneous and shows a well-developed augen structure inwhich fine grained minerals wrapped around the garnet porphyroblasts. Garnet and feldspar
porphyroblasts are ranged from few mm to 100 mm in size and set in a gneissic to schistosegroundmass (Gandhi et al., 1984; Ranawat & Sharma, 1990; Sharma & Singh, 1990). Under
the thin section studies, gneiss samples are medium to coarse grained and consist of quartz,
microcline, plagioclase, sillimanite, garnet, and accessory minerals, including zircon, apatite,
tourmaline and magnetite. Garnet grains are highly shattered and show the inclusions of quartz(Fig.3.h). These inclusions are limited to the central part of the garnet porphyroblasts while theouter side is generally lacking any such inclusions. The dominant garnet composition isalmandine (Holler, Touret, & Stumpfl, 1996). Garnet and feldspar occur as a porphyroblast
while sillimanite grains occur as needles and form clusters. Biotite occurs as a tabular
aggregate with traces of sericite. The 2θ position of biotite, graphite, quartz and sillimanite in
the garnet-biotite-sillimanite gneiss has given in figure 2.B.
Calc-silicate RockThe samples of calc-silicate rocks are collected from the Rampura-Agucha open cast mine andMansi River. It is the minor component of the lithological assemblages and occurs as irregularbands within the gneiss. It is hard and compact, consequently resistant to weathering, forming
prominent boulder outcrops. In hand specimens, these rocks are fine to medium grained types
with frequent garnet porphyroblasts of various sizes.

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Figure 02. (A) 2θ Position of biotite, galena, microcline, quartz and sphalerite in Schist; (B) 2θ
Position of biotite, graphite, quartz and sillimanite in Gneiss; (C) 2θ Position of anorthite,enstatite, labradorite and quartz in Calc- silicate; (D) 2θ Position of actinolite, andesine,
hornblende, labradorite and quartz in Amphibolite; (E) 2θ Position of biotite, plagioclase andquartz in pegmatite, Bhilwara belt, Rajasthan.
(A)

(B)

(D)

(C)

(E)

Figure 03: Representative Transmitted Light Microphotograph of Different Rock Units92

(a) Showing coarse grained quartz (Qtz), biotite (Bt) and garnet (Grt) in Pegmatite, near Bhopalpura village, (b)Showing highly recrystallized quartz grains (suture contact) in calc-silicate at Rampura-Agucha open cast mines,
Bhilwara belt, (c) Showing the large hornblende (Hbl) and clinopyroxene (Cpx) crystal breaking down to an
aggregate of small crystals (mortar texture) in amphibolite at stone quarry near Amartiya road, (d) Amphibolite,
showing hornblende with plagioclase (lamellar twinning), microcline (Mic), quartz and biotite, stone quarry nearAmartiya road, Bhilwara belt, Rajathan.

Fine laminations of a millimeter-scale and compositional variations are also seen in thisrock. Microscopically, various samples of calc-silicate rock have been taken for petrographic
studies which show the presence of diopside, plagioclase and garnet with minor quartz, kfeldspar and rare hornblende as principal constituents, and scapolite, zoisite, titanite andsphene occur as accessory minerals. Plagioclase occurs as tabular and sub-idioblastic grains
while microcline grains are xenoblastic to sub-idioblastic grains. Quartz grains are highly
crystallized, showing the suture contact (Fig.3.b). The 2θ positions of different minerals in calcsilicate rock shown in figure 2.C.
Amphibolite
Amphibolite samples are collected from stone quarry near Amartiya road and Rampura-Agucha
mines. Amphibolites in the study area show an inter-fingering relationship with the calc-silicate
rocks and occur as bands of different width in the garnet-biotite-sillimanite gneiss. Two types ofamphibolite have seen in the study area (i) schistose amphibolite and (ii) granoblastic
amphibolite. They are generally medium to coarse grained in nature. Out of both varieties,
schistose amphibolites occur as enclaves, while granoblastic amphibolites show intrusive
nature with country rocks. Megascopically, it appears dark green to black color, and are
generally medium to coarse grained rocks.
Figure 3. (e) Fine grained garnet-biotite-sillimanite schist showing orientation of quartz and micaceous
minerals, Rampura-Agucha open cast mines, (f) Garnet-biotite-sillimanite schist, showing the plagioclasewith deformation twins, Rampura-Agucha open cast mines, (g) GBSG, showing garnet, microcline (crosshatched twinning) and angular shaped quartz at Mansi river, (h) GBSG, showing inclusions of quartz andbiotite in garnet, Mansi river, Bhilwara belt, Rajasthan.

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It shows a granoblastic to loosely foliated texture. Garnet grains in the amphibolite of
the study area occur as a porphyroblast. Microscopically, it is composed of essentiallyhornblende, plagioclase and garnet along with diopside, biotite and quartz. Pyroxene andhornblende crystals are breaking down to an aggregate of small crystals forming the mortar
texture (3.c). Pyroxene grains are riddled with inclusions of quartz and hornblende, while thehornblende grains are relatively free from the inclusions. Hornblende is showing perfect two set
cleavages while both plagioclase and microcline are showing their characteristic properties i.e.,lamellar and cross-hatched twinning respectively (Fig.3.d). Triple junctions are clearly seen in
the hornblende grain (Fig.3.c), indicating the dynamic recrystallization. According to Roy(2000), amphibolite of the study area to be para-amphibolite formed by high-grade
metamorphic facies of impure dolomitic limestone. X-ray diffraction pattern of different minerals
in amphibolite has given in fig.2.D.
Pegmatite
In the study area, the pegmatite samples are collected from Rampura-Agucha mines.
Pegmatites are common in the study area with individual pegmatite components may be up to
40 meters in thickness locally (Gandhi et al., 1984). Thin veins of pegmatite are seen as
intrusive in the garnet-biotite-sillimanite gneiss, amphibolites and calc-silicate rocks. In hand
specimens study, It is coarse grained rocks. Garnet grains of different sizes are also present in
the pegmatite. Microscopically, pegmatites consist of mainly coarse grained quartz, plagioclase
and biotite with a minor percentage of garnet (Fig. 3.a). Quartz occurs as a xenoblastic grain,
while biotite found as elongated grains. Quartz and feldspar form a graphic intergrowth texture.
The 2θ position of biotite, plagioclase and quartz in pegmatite is shown in figure 2.E.
Mineral Assemblages
Based on petrographic and X-ray diffraction studies of various rock types in the study area, thefollowings mineralogical assemblages are identified and listed in table1.
Table 01: Mineral Assemblage in the Host and Associated Rocks of the Study Area#

Rock types

1

Graphite-biotite-sillimanite-schist

2

Garnet-biotite-sillimanite gneiss3

Calc-silicate rock4

Amphibolite

5

Pegmatite

Mineral assemblages
Quartz, biotite, sillimanite, graphite, microcline, garnet,
apatite, tourmaline and opaque minerals
Quartz, microcline, plagioclase, sillimanite, garnet, zircon,
apatite, tourmaline and magnetite
Diopside, microcline, anorthite, labradorite, quartz,
enstatite, sillimanite, garnet, scapolite, zoisite, titanite andspheneHornblende, actinolite, plagioclase (andesine, labradorite),garnet, diopside, biotite and quartz
Quartz, plagioclase, biotite, tourmaline and garnet

Conclusion
The Pb-Zn deposits of the Rampura-Agucha area occur within meso-proterozoic metasedimentary rocks belonging to the Bhilwara supracrustal belt and consist of pelitic rocks that
constitute the graphite-biotite-sillimanite schist, garnet-biotite-sillimanite gneisses along with
calc-silicate, amphibolite and pegmatite. On the basis of petrographical investigations, itappears that regional metamorphism has played an important role in metamorphism of pelitic
rocks up to upper amphibolite to granulite facies, which are the prominent host rocks of
Rampura-Agucha Pb-Zn deposit. The textures observed in the rocks under investigation reveal
the pre-tectonic crystallization of mineral grains as well as the multiphase of deformation. Thin
section studies and X-ray diffraction patterns of different rock types in the area suggest the PbZn ores are found in schist and deposited along the mineral grain boundaries and generally,
found as dark color patches in thin sections.
Acknowledgments
The author is grateful to Prof. Syed Ahmed Ali, Chairman, Department of Geology, AMU,
Aligarh, and Dr. S. A. Rashid, Associate Professor, Department of Geology, AMU, for thelaboratory work. Mr. Bingi Murli, AGM, Rampura-Agucha mine, his cooperation in fieldassistance is appreciated. The author is grateful to CSIR-JRF for financial support.
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