Carbonate Hosted Intermetallic Compounds in Paleoproterozoic Salumber Ghatol Metallogenic Belt, Aravalli Craton, Rajasthan, India

J. Earth Syst. Sci. (2020) 129:137 Ó Indian Academy of Sciences

https://doi.org/10.1007/s12040-020-01410-3 (0123456789().,-volV)(0123456789().,-volV)

Carbonate hosted intermetallic compounds in Paleoproterozoic Salumber Ghatol metallogenic belt, Aravalli Craton, Rajasthan, India

1, 1 2 SURESH CHANDER *, AUSAF RAZA ,SANTANU BHATTACHARJEE 1 and SANJAY DAS 1Geological Survey of India, Jaipur 302 004, India. 2Geological Survey of India, Hyderabad 560 068, India. *Corresponding author. e-mail: [email protected]

MS received 19 September 2019; revised 9 March 2020; accepted 21 March 2020

Carbonate hosted intermetallic compound in the Umarvaniyan area is localized within the intensively sheared (mylonitised) dolomite in a NW–SE shear zone (*15 km), belongs to Salumber Ghatol metallogenic belt, in Debari Group of Aravalli Craton, Rajasthan, India. It is characterized by extensive siliciBcation and ferruginisation with hematite, goethite, magnetite and native gold specks. The intermetallic compound within the dolomite is composed of varying proportion of Cu–Zn–Ni–Os–Fe which has been detected by electron probe microanalysis (EPMA) study. The EMPA (WDS) results of the intermetallic compounds also reveal occurrences of intermetallic compounds of Cu–Zn–Ni–Os–Fe and native Au. The occurrence of these non-separable compounds is probably because these metals were formed at very high temperatures and in reducing condition during the evolving shear with low oxygen and low sulfur fugacity. The fast cooling eAect thereafter probably made the geochemical environment least conducive for reaction between Cu/Zn/Ni and sulphur or oxygen. Keywords. Salumber Ghatol metallogenic belt; intermetallic compound; monazite.

1. Introduction belts are Paleoproterozoic Aravalli Fold Belt (AFB) and Mesoproterozoic Delhi Fold Belt (DFB) deposited The period between 1.9 and 1.5 Ga remained most over 3.3–2.5 Ga old (Gopalan et al. 1990; Roy and fertile and documented worldwide in respect of min- Kroner€ 1996) heterogeneous Archaean terrain known eralization (Corriveau 2007). At *1.7 Ga, high level of as Banded Gneissic Complex (BGC) (Bgure 1). These CO2 content in the atmosphere permitted the depo- belts host a number of economically viable base metal sition of thick dolomite sequences (Evans 1997). These and gold deposits. The ages of these deposits hovers sequences host a number of significant base metal between 1100 and 1800 Ma (Deb et al. 1989). sulphide ore bodies such as Pb–Zn–AgandCudeposit Rajpura–Dariba, Zawar, Rampura–Agucha deposits in Mount Isa, Australia and Pb–Zn–Ag deposit in are rich lead-zinc resources in AFB. Volcanogenic Zawar, India. The period between 2000 and 1800 Ma is massive sulphide deposits of Danva–Basant- also characterized by a global orogeny (Windley 1995). garh–Pipela and also the well-known Khetri copper The Aravalli Craton in northwest India comprises two deposits belong to DFB. Salumber Ghatol metallo- prominent volcano-sedimentary fold belts. These fold genic belt (hereinafter; SGMB) lies in south-eastern 137 Page 2 of 10 J. Earth Syst. Sci. (2020) 129:137

Figure 1. Regional geological map of Salumber Ghatol metallogenic belt, Udaipur District, Rajasthan. part of AFB hosts Bhukia and Dugocha Cu–Au which shows anomalous values of Zn associated with deposits and Chari Cu deposit of economic impor- nickel (table 1). The petrological studies of these tance. The Bhukia gold prospect host gold and asso- samples, however, did not show presence of neither ciated alloys in sulphides (Golani et al. 1999). U–Pb Zn sulphides nor Zn carbonates. This prompted to zircon ages of albite-rich rocks from Bhukia ranges analyse these samples by EPMA which helped in between 1740 and 1820 Ma (Deb 2008). The lithounits identifying presence of tiny grains (\10 microns) of SGMB are dolomite/ferruginous dolomite and car- of intermetallic compounds of Cu–Zn–Ni–Os–Fe and bon phyllite belongs to Jagpura Formation of Debari native Au (Bgure 2). Group. In the present study samples were collected The present paper reports, for the Brst time, from these dolomitic rocks of the Jagpura Formation the occurrence of intermetallic compounds from J. Earth Syst. Sci. (2020) 129:137 Page 3 of 10 137

Table 1. Metal concentration in bed rock samples from Supergroup and Meso-proterozoic Delhi Super- Umarvaniyan Prospect, SGMB (all values are in ppm). group of rocks. The Aravalli and Delhi fold Sample Lithology Cu Pb Zn Ni Co belts were formed by rifting in which volcanic sediments were deposited in two different peri- 1 FD Ferruginous dolomite 90 8 450 30 15 ods (Sinha Roy and Malhotra 1989). Basin was 2 FD Ferruginous dolomite 80 7 600 40 20 closed due to the lithospheric subduction and 3 FD Ferruginous dolomite 85 9 600 45 30 4 FD Ferruginous dolomite 70 7 285 30 15 were folded and deformed. Thus, the Aravalli 5 FD Ferruginous dolomite 60 7 945 50 15 and Delhi fold belts dominantly represent 6 FD Ferruginous dolomite 105 15 990 70 25 volcano-sedimentary sequences. The Aravalli 7 FD Ferruginous dolomite 120 20 615 110 30 Supergroup is represented by two contrasting 8 FD Ferruginous dolomite 240 9 1600 130 30 litho facies association; sand–shale–carbonate 1 SD SiliciBed dolomite 140 10 110 60 30 assemblage of near shore shelf facies and thick 2 SD SiliciBed dolomite 175 30 1400 255 85 sequence of carbonate free shales facies 3 SD SiliciBed dolomite 85 15 3300 570 95 interbedded with thin beds of arenites inter- 4 SD SiliciBed dolomite 115 30 2600 440 145 preted as deep sea facies (Roy and Paliwal 5 FD SiliciBed dolomite 250 20 4200 830 125 1981). Geochronological studies of Sastry et al. 1 FD SiliciBed dolomite 15 4 40 10 40 (1984) and Sastry (1992)inferredanageof 2 FD SiliciBed dolomite 75 8 2000 655 85 2.5–2.0 Ga for Paleoproterozoic rocks of Ara- 3 FD SiliciBed dolomite 30 7 185 50 40 4/10 SiliciBed dolomite 100 8 350 115 100 valli Supergroup. Wiedenbeck et al. (1996)cal- 5/10 SiliciBed dolomite 95 5 480 65 75 culated the age of Aravalli sedimentation as 6/10 SiliciBed dolomite 60 5 170 20 40 2.55 Ga. At *2.0 Ga, the formation of the 7/10 SiliciBed dolomite 140 10 2200 960 130 Aravalli basin foundered by a phase of tecton- 8/10 SiliciBed dolomite 335 20 930 500 145 ism and crustal deformation (Sinha-Roy et al. 9/10 SiliciBed dolomite 20 50 120 10 40 1998). 10/10 SiliciBed dolomite 1200 10 45 50 60 The Debari Group of the Aravalli Supergroup comprises of Mukandpura and Jagpura forma- tions. The litho units exposed within these for- Salumber–Ghatol metallogenic belt (SGMB) occur- mations are coarse clastics, syn-sedimentary basic ring along southern margin of the Aravalli Craton. volcanics and associated pyroclastics, and car- This belt hosts a cluster of Cu–Au deposits in calcitic bonate representing shelf-facies environment. The and dolomitic rocks belonging to Debari Group of the Debari Group also host volcano-sedimentary Paleo-mesoproterozoic Aravalli Supergroup. The sequence of SGMB (Gupta et al. 1981, 1997), EPMA examination carried out during the course of which occur 130 km ESE of Udaipur district, present study helped in identifying the presence of Rajasthan. The Salumber–Ghatol metallogenic tiny grains (\10 microns) of intermetallic compounds belt (SGMB) forms a part of eastern margin of of Cu–Zn–Ni–Os–FeandnativeAu(Bgure 2). The Debari Group of the Aravalli fold belt extend authors have described metal association and draw about 70 km from Salumber in the northwest to meaningful interpretations regarding surface dis- Ghatol in the southeast, exposing meta-sedimen- persion pattern, probable source, spatial correla- taries of Aravalli Supergroup (Grover and Verma tion and age of mobilization within the host rock of 1993; Golani et al. 1999; Chander and Sisodia intermetallic compounds of Cu–Zn–Ni–Os–Fe and 2003). Two distinct carbonate sequences exposed native Au, using Beld investigations, petrography in this metallogenic belt have been classiBed as and EPMA studies. However, the main aim is to older (a) phyllite/carbonaceous phyllite rich and identify and describe the metal association. This (b) dolomite and calcite-marble rich Mukundpura new Bnd may open a new vista for research Formation which are co-folded with younger car- on intermetallic compounds mineralization in bonate and quartz chlorite schist rich Jagpura India. Formation rocks of Debari Group of AFB. The litho units of SGMB are dolomite/ferruginous 2. Geological setting dolomite and carbon phyllite belonging to Jagpura Formation of Debari Group. This dolomite/fer- In the western part of the Indian shield banded ruginised dolomite is Bne grained and bluish/grey gneissic complex (BGC, 3300–2500 Ma) serves as in colour and is ferruginised along the NW–SE the basement for the Paleoproterozoic Aravalli shear zone. 137 Page 4 of 10 J. Earth Syst. Sci. (2020) 129:137

Figure 2. (a) BSE image showing grain of Cu–Zn–Ni–Os–Fe intermetallic compound along with wavelength-dispersive X-ray spectroscopy graph and (b) BSE image showing grain of native gold (Au) along with wavelength-dispersive X-ray spectroscopy graph.

2.1 Dolomite/siliciBed, ferruginous and phyllitic dolomite

The rock is Bne grained, schistose, phyllitic, laminated; bluish and greyish in colour. It shows banded and schistose texture. Main constituents present are carbonate, muscovite, quartz, ferruginous and argillaceous matrix material. The rock is having alternate bands of ferruginous/argillaceous and carbonates ranging in width from *0.1 to 2 mm. Carbonate grains are of Bne size (micrite), xenomorphic and contain Bne sprinkling of ferruginous dusty material. Ferruginous material in darker bands is massive, light yellow brown coloured and Figure 3. Field photograph of the ferruginised dolomite with limonitic (Bgure 3). Angular fragments of quartz extreme ferruginization. J. Earth Syst. Sci. (2020) 129:137 Page 5 of 10 137 and Cakes of muscovite are present in this material. 4. EPMA analysis The mineral constituents are essentially Cattened. Some carbonate bands show pinch and swell struc- The microprobe studies were carried out at GSI, ture and some of them traverse right across the SR Hyderabad to identify mineral phases con- primary carbonate–iron bands. There are thin zones tributing zinc, nickel and copper. A number of with Bnely granulated constituent minerals that monazite grains were detected during the analysis. represent shear planes. These shear planes are often The analyses were carried out using CAMECA SX occupied by quartz–muscovite veinlets. Besides these 100 having Bve spectrometers and LaB 6 source. Bne-grained minerals, the rock also possesses coarse The column conditions were 20 kV/100 nA. The grained, eyed shaped quartz grains and anhedral lines and standards used for monazite analyses and coarsely crystalline opaque magnetite. A quartz vein crystals are YAG for Y La/TAP, apatite for P Ka/ consisting of oriented quartz grains is seen traversing TAP, albite for Al Ka/TAP, orthoclase for SiKa/ right across the schistosity of the rock. TAP, apatite for Ca Ka/PET, La glass for La Lb/LIF, Ce glass for Ce La/LIF, Pr glass for Pr Lb/LIF, Nd glass for Nd La/LIF, Sm glass for Sm 2.2 Carbon phyllite with/without calcareous Lb/LIF, Gd glass for Gd Lb/LIF, Pyromorphite and ferruginous component for Pb Ma/LPET, U glass for U Mb/LPET, Th Fine grained, dark grey to yellowish grey rock with glass for ThMa/LPET and Hematite for Fe Ka/ leucocratic patches contain occasional alternate LIF with 0 beam size. Overlap corrections were dark and light bands. The darker bands are pro- performed wherever it is necessitated. Matrix fusely impregnated with well-oriented Bne-grained eAects are eliminated using X-Phi method pro- opaque material of carbonaceous nature, whereas posed by Merlet (1992, 1994). Age Quant software light colour bands have less opaques with more is used for determining the age which is cross- quartz and sericite. Ferruginous argillic bands checked by manual calculation. contain very Bne size fragments of carbonates and Cakes of muscovite. Secondary veins consist of (i) coarse carbonate grains, (ii) medium size 5. Petrography and mineral chemistry quartz–muscovite grains, and (iii) coarse chlorite– quartz clusters. The veins are randomly oriented Petrographic studies of the dolomite/ferruginous and carbonate veins are brecciate. In some of the dolomite under transmitted light indicate presence sections, xenomorphic carbonate grains having of carbonate minerals mainly dolomite and ferroan ferruginous matrix with incipient banding. dolomite with minor amounts of calcite. The carbonate layers display non-clastic sedimentary texture, i.e., grains of sparite ranging in size from 0.8 3. Methodology to 1.2 mm are conspicuously noticed. However, few carbonate grains are of Bner \0.025 mm in size Samples were collected from the different parts of (micrite), and contain Bne ferruginous dusty the dolomite/ferruginous dolomite. The fresh sam- material. Ferruginous material in darker bands is ples were collected and crushed, sieved, coned and massive, light yellow brown coloured and limonitic. quartered, then analysed for major oxides and trace Angular fragments of quartz and Cakes of mus- elements at chemical laboratory of Geological Sur- covite are noticed as intraclasts. The presence of vey of India (NABL accredited). Major and trace delta and sigma porphyroclasts within this elements were analyzed, using Panalytical Axios dolomite/ferruginous dolomite deBnes brecciation model X-ray Cuorescence (XRF) spectrometers and and extensive mylonitisation (Bgure 4a–d). This by AAS for the quantitative determination of dolomite also contains hematite, specularite, mag- chemical elements using the absorption of optical netite goethite and limonite. The vug/open spaces radiation (light) by free atoms in the gaseous state. are Blled up by secondary Fe-oxides and/or For XRF analysis the rock powder was ground to hydroxides shown in Bgure 4(e). In some of larger –200 mesh size, pressed with binder Perspex in 5% euhedra of magnetite, progressive alteration is Acetone at 20 Ton P and pressed to form pellets. The observed from border to core forming a zoned instrument is calibrated with suitable standards and texture. The oxide mineral, magnetite shows high the sample pellets were then run against standards degree of alteration and complete transformation thus calibrated. to hematite/goethite. Ore microscopic studies 137 Page 6 of 10 J. Earth Syst. Sci. (2020) 129:137

Figure 4. Photomicrograph of (a) a sheared dolomite displaying tailed quartz porphyroclast, (b) a sheared dolomite displaying sigma porphyroclast of quartz, (c) dolomitic calcite vein within mylonite, (d) Sparite crystal as porphyroblast within dolomite, and (e) stock work feeder zone Blled in by Fe vein.

under reCected light indicate the presence of sulphide phases. Veins of pyrite aggregates are hematite and magnetite as oxide phases, colloform present with small inclusions of pyrrhotite. goethite and lepidocrosite as hydroxide phases, The EMPA (WDS) results of the intermetallic while pyrite, chalcopyrite and pyrrhotite are the compounds reveal occurrences of intermetallic J. Earth Syst. Sci. (2020) 129:137 Page 7 of 10 137

Mag

Mnz

Figure 5. (a) Monazite grains occurring along with magnetite and calcite. (b) BSE image of monazite (Mnz) grain occurring as discrete grain associated with magnetite (Mag). compounds of Cu–Zn–Ni–Os–Fe and native Au (Bgure 2a and b). Scanning under EBSD mode helped in identifying tiny grains (up to 20 microns) of Cu–Fe–Ni–Zn, Zn–Ni–Os–Cu–Fe and Os–Zn–Ni–Co intermetallic compounds which have been shown count data (Bgure 2a). These associations make up most of the ore mainly occurs as oxides and hydroxides. The proportion of Cu–Zn–Ni–Co–Os and Fe varies from grain to grain. Native grains of gold (Bgure 2b), associated with hydrated iron-oxide phase have been recorded. A number of monazite grains were also identiBed (Bgure 5a). EPMA dating was carried out for two sets of monazite. The monazite grains were quan- tiBed in order to know the timing of mineralization. Figure 6. Probability density plot of monazite ages. The monazite grains occurring along with the magnetite and calcite in the mineralized dolomite represent a distinct phase, while it is also noticed that a few monazite grains are associated with a 6. Geochemistry and petrogenesis later phase of oxides that traverse the Brst phase (Bgure 5b). Two clusters of data representing two 6.1 Major oxides events of mineralization have been recorded (Bgure 6). The Brst cluster gives an age of 1674+29 Samples of the dolomite/ferruginous dolomite were Ma which is almost synchronous with the major analysed for major oxides (table 3). Total of seven base metal-gold mineralization event in Aravalli samples were analysed for major oxides using XRF fold belt (Deb 2008) and pertains to the discrete analysis and 10 samples were analysed for trace monazite crystals and represents the Brst episode elements using ASS (table 1). These dolomite rocks of mineralization event, whereas the other cluster show SiO2 from 15.78 to 51.79 wt.%, Fe2O3: around 1272+31 Ma represents a subsequent event 2.63–52.80 wt.%, MgO: 0.71–6.41 wt.% and CaO: or a remobilized phase of mineralization. Range of 1.56–42.17 wt.%. On the basis of these major oxide REE contents analysed in monazite grains by values, the samples are differentiated into siliceous EPMA (table 2) are Ce2O3: 27.31–30.86%, La2O3: dolomite and ferruginised dolomite (table 3). The 14.96–16.14%, Nd2O3: 11.31–12.98% and Y2O3: ferruginised dolomite shows high values of Fe2O3 0.70–1.16%. and low values of CaO. 137 Page 8 of 10 J. Earth Syst. Sci. (2020) 129:137

Table 2. EPMA analysis and U-Pb dating of monazite grains, Umarvaniyan Prospect, SGMB.

First episode of mineralization Second episode of mineralization Dataset/point 1/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1 10/1

SiO2 0.634 0.424 0.519 1.704 2.703 0.301 0.636 1.072 0.551

P2O5 29.981 29.415 29.083 29.369 28.566 28.831 28.375 29.177 29.745

Y2O3 1.033 0.701 0.778 0.75 0.757 1.297 1.267 1.136 1.159

La2O3 15.236 15.251 15.383 15.619 15.894 14.965 14.986 15.839 16.146 Ce2O3 30.315 30.198 30.312 30.764 30.862 30.263 30.717 30.682 30.811

Pr2O3 2.681 2.818 2.832 2.952 3.071 3.054 2.815 2.756 2.825

Nd2O3 13.791 13.987 13.428 13.442 12.669 12.985 12.406 13.318 13.437 SmO 1.748 1.564 1.6 1.644 1.585 1.921 1.687 1.479 1.449 PbO 0.082 0.064 0.061 0.054 0.058 0.066 0.072 0.063 0.063

UO2 0.012 0 0 0 0 0 0.01 0 0

ThO2 1.003 1.197 0.875 0.936 0.927 1.314 1.234 1.198 1.178

Yb2O3 0.057 0.003 0.001 0.067 0.021 0.003 0.052 0.054 0.007 Dy2O3 0.25 0.152 0.243 0.225 0.245 0.357 0.414 0.245 0.366

Ho2O3 0.472 0.394 0.397 0.423 0.443 0.534 0.498 0.447 0.516

Er2O3 0.106 0.025 0.02 0.044 0.054 0.061 0.045 0.078 0.045

Tm2O3 0.204 0.17 0.186 0.166 0.186 0.182 0.215 0.115 0.164 FeO 1.088 1.795 0.608 0.712 0.739 0.887 0.929 0.445 0.366 EuO 0.651 0.746 0.724 0.777 0.79 0.765 0.772 0.676 0.637

Lu2O3 0.039 0.026 0.061 0.007 0.003 0.037 0.022 0.025 0.004

Gd2O3 0.997 0.703 1.083 0.848 0.841 1.238 1.018 0.814 1.069 Tb2O3 0.018 0.048 0.012 0.007 0.194 0.077 0.067 0.018 0.067 Total 99.52 98.796 98.23 99.512 99.716 98.062 97.259 98.704 99.534 Age (Ma) 1781 ± 37 1563 ± 20 1618 ± 41 1687 ± 20 1723 ± 31 1174 ± 30 1304 ± 31 1286 ± 31 1326 ± 32

Table 3. Major oxide analysis of the dolomite/ferruginised dolomite.

Sample name SiO2 Al2O3 Fe2O3 MnO CaO MgO Na2OK2O TiO2 P2O5 Ferruginised dolomite UM-1 16.85 4.96 52.80 0.13 9.11 0.71 0.16 1.19 0.61 0.01 Ferruginised dolomite UM-3 48.65 11.39 19.25 0.18 5.99 4.97 2.77 0.23 1.59 0.18 Ferruginised dolomite UM-4 39.83 11.51 22.21 0.16 6.84 6.41 1.17 0.17 2.24 0.23 Ferruginised dolomite UM-5 50.11 14.36 16.12 0.10 1.56 5.96 1.11 0.20 0.95 0.06 SiliciBed dolomite UM-6 17.55 4.09 7.44 0.68 35.63 4.33 0.12 0.21 0.21 0.06 SiliciBed dolomite UM-7 51.79 17.07 6.01 0.04 7.13 1.71 0.19 5.24 0.65 0.06 SiliciBed dolomite UM-2 15.78 2.50 2.63 0.24 42.17 2.15 0.19 0.68 0.09 0.12

6.2 Trace elements Zn (R2 = 0.704) and Co (R2=0.639). The siliciBed dolomite thus shows greater concentration of all A total of 10 samples were analysed for trace the basemetal/alloys than the ferruginous/altered element analysis using AAS (table 1). Cu, Co, and dolomite. This indicates the probability that Ni show sympathetic mutual spatial association, the base metals are concentrated by siliciBed whereas Zn shows lesser degrees of spatial asso- hydrothermal solution and not by secondary ciation with the former metals. Co, Cu, Ni and to surface alteration. lesser extent Zn shows in arcuate pattern anomaly in the central part of the area. Pb shows least spatial correlation with other base metal descri- 7. Discussion bed. However, this metal is abnormally concentrated in NNE part of the area. Binary plots of Zn Ore mineralization at Umarvaniyan in the Salum- vs. Ni and Ni vs.Co(Bgure 7) show that in ber–Ghatol belt is conBned to a linear zone of multiply Umarvaniyan, Ni has positive relationship with deformed rocks occurring at the contact between J. Earth Syst. Sci. (2020) 129:137 Page 9 of 10 137

Figure 7. (a) Binary plot of Zn vs. Ni and (b)Nivs. Co showing sympathetic relation.

carbonate dominated Debari Group and granite/ elements). Fe and Ni being siderophile show common gneisses/feldspathic schist dominated Banswara For- association. But in the study area Fe, Ni, Cu, Zn are mation of Udaipur Group. It has been suggested that intimately associated and form non-separable com- the mineral deposits of Aravalli Supergroup in the pounds. This is probably because, these metals formed Salumber–Ghatol belt represents sedimentary car- at very high temperatures and in reducing condition bonate-hosted Cu–Au deposits belonging to the wider during the evolving shear zone. Melting temperatures class of Proterozoic iron–ore–copper–gold type of these metals are also similar. Where melting point of (IOCG-like) mineral deposits which were formed by Cu–Zn association is between 900 and 940°C, for the Cuids derived from a sub-crustal source (Faree- Cu–Zn–Ni it is slightly higher, i.e., 1125°C. Fast duddin et al. 2012).TheoresofIOCGtypedepositsare upwelling and cooling of solutions, thereafter probably commonly associated with volcanic and/or intrusive made the geochemical environment least conducive for rocks, and their close relationship with shear zones is reaction between Cu/Zn/Ni and sulphur or oxygen. typical for this type of mineralization (Williams 2005). However, presence of sulphur in that reducing envi- Ore genesis in IOCG deposits may involve both ronment is being supported by the presence of pyrite metamorphic- and magmatic-hydrothermal Cuids and phyrrotite, even in small proportions. Sarkar (Hazarika et al. 2019). The basal part of Aravalli (2000) has distinguished two time slots of mineraliza- Supergroup of rocks is characterized by the presence of tion during Aravalli fold belt is considered to be taken volcanic sequence comprising basalt, high Mg basalt place at *1800–1700 Ma (Deb et al. 1989). The and felsic rocks (Sinha Roy and Malhotra 1989; 1272+31 Ma age of monazite as reported in the present Ahmad and Rajamani 1991; Bose and Sharma 1992; paper, appears to be the time of latest episode of Raza and Khan 1993; Shekhawat et al. 2007). There- mylonitisation wherein alloys are stabilized or the fore, the most obvious source for metals may be the mineralization may belong to the second slot as pro- associated basal Aravalli volcanic rocks. It appears posed by Sarkar (2000). However, detailed petrologi- that during the initial stage of Aravalli sedimentation, cal, isotopical and geochronological data are required zinc and iron were co-precipitated under favourable to conBrm these suggestions. conditions (Gupta et al. 1997) and nickel contributed by high Mg-basalts. During the subsequent tectono- metamorphic event, these metals were released from Acknowledgements the host rock and got re-emplaced along the favourable structural locales and combined with oxygen in S-poor, The authors are thankful to the Deputy Director oxidised mineralising Cuid system (Baker 1998). The General and HoD, Geological Survey of India, intermetallic compounds are believed to be formed in a Western Region, Jaipur for permission to publish strongly reducing environment with absent oxygen this paper. We are indebted to the then Deputy and low sulfur activities (Liu et al. 2008). Cu and Zn Director General, and the then Director, Petrology, have almost similar atomic radius and atomic weight Geological Survey of India, Southern Region, and therefore, behave in similar ways (chalcophile Hyderabad for support and permission to carry out 137 Page 10 of 10 J. Earth Syst. Sci. (2020) 129:137

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