And Associated Ni-PGE Mineralization from Gondpipri Mafic-Ultramafic Complex, Bastar Craton, Central India

Cent. Eur. J. Geosci. • 6(4) • 2014 • 506-517 DOI: 10.2478/s13533-012-0185-9

Central European Journal of Geosciences

Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and genetic significance

Topical issue

M.L. Dora1∗, H. Singh1, A .Kundu2, M.Shareef3, K.R. Randive4, S. Joshi2

1 Geological Survey of India, Shillong, 793003, India 2 Geological Survey of India, Faridabad, India 3 Geological Survey of India, Bangalore, India 4 Dept of Geology, RTM Nagpur University, Nagpur, 440001, India

Received 25 March 2014; accepted 19 June 2014

Abstract: This paper reports the occurrence of Tsumoite (a bismuth telluride) in the Heti Cu-Ni-PGM prospect, Gondpipri mafic-ultramafic complex, Central India. The Gondpipri complex consists of several tectonically dismembered gabbronorite-gabbro- anorthositic gabbro - olivine gabbro -websterite disposed in ~10 km long tonalite-trondhjemite- granodiorite (TTG) and charnockite-enderbite suite of rocks. The mineralization occurs in the sulphide zone hosted by gabbro variants. The host rocks have been deformed and metamorphosed to granulite grade and subjected to various degrees of hydrothermal alteration. The mineralization comprises chalcopyrite, pentlandite, pyrrhotite, cubanite, millerite, and pyrite. In addition to these, occur (1) tsumoite (2) PGM in the form of moncheite, merenskyite, Pd-mellonite, and Pt-Pd-Te-Bi-Fe-S alloy. The present study indicates that the mineralization occurs in two stages related to: (i) magmatic and (ii) hydrothermal remobilization and transport of Cu-rich sulphides, tsumoite and PGM, and their re-deposition in hydrosilicate alteration zones. It is possible that the mineralization at Heti formed at different stages of bismuth activity under variable fS , T, and fTe conditions due to change in total concentration of Te and S and /or cooling. Since the role of S is limited, Te and cooling are important factor influencing mineralogy and composition of tsumoite and associated2 mineralization.2 Mineralization occurs in two different modes of occurrences. The early mineralisation occur as blebs, specks and dissemination of sulphides, viz. pyrrhotite, chalcopyrite, pentlandite and minor pyrite ± PGM, whereas later mineralisation occur as stringers, minor veins of sulphides viz. pyrite, millerite, cubanite, sijenite, tsumoite and ± PGM. Mineral assemblages and textural relationships at Heti has indicated precipitation of tsumoite and associated PGM along fractures and secondary silicates, which confirms their hydrothermal origin. Keywords: Tsumoite • PGM • base metal sulphides • hydrothermal • Gondpipri mafic-ultramafic complex • Bastar craton © Versita sp. z o.o.

∗

506 E-mail: [email protected] M.L. Dora, H. Singh, A .Kundu, M.Shareef, K.R. Randive, S. Joshi

1. Introduction

and mafic igneous suites constitute the bulk of the geology of Bastar carton [26–31]. TTG and granite cover major part Tsumoite, a Bi-telluride, is a relatively rare mineral that of the area along with supracrustal sequences. The high generally occur as a minor or trace component in ore de- grade Archaean gneisses terrain forms the basement of posits in a wide variety of geological setting [1]. It is a the older and younger supracrustals rocks. The granitoids characteristic accessory component of polymetallic gold- are intrusive into the basement gneisses and also into bearing skarns and base metal ore deposits of magmatic, the older supracrustals. Bastar craton has experienced hydrothermal and metamorphogenic type [2–4]. There are many episodes of mafic magmatism during the Precambrian, 7 3 four known bismuth tellurides: hedleyite (Bi Te ), pilsenite which is evident from a variety of Precambrian mafic rocks 4 3 2 3 (Bi Te ), tsumoite (BiTe) and tellurobismuthite (Bi Te )[5]. exposed in all parts of the Bastar craton in the form of dykes These are usually found to be associated with pyrite, chal- and volcanic rocks [25–33]. These intrude all the older copyrite, pyrrhotite, sphalerite, magnetite, arsenopyrite, suites of rocks (basement gneisses, older supracrustals and native bismuth, and native gold. Studies have shown that granitoids) predominantly along NE-SW directions [34]. tellurides of Pt, Pd, Ni, Ag, Pb and Bi occur in Cu–Ni–PGE The major tectonic movements trigger the generation of deposits of either magmatic origin [6–10] or hydrothermal mafic magmas in the mantle and help in the emplacement origin [11] or metamorphic origin [12–14]. Tellurides have of derived magmas at various crustal levels and associated been intensively studied for understanding the ore genesis mineralization. These are emplaced in different tectonic in different deposits of the world [15–20], example- gold settings such as along passive continental margin, back deposits at Kasperske Hory [21]; Zadní Chodov uranium de- arc compressional basin [35, 36] and intracratonic setting posit [22]; Cu-Ni sulphide mineralization at Stare Ransko [37]. deposit of Czech Republic [23]. The Heti Ni-PGE-tsumoite prospect is part of the Gond- In the Indian context, tsumoite (BiTe) has not been re- pipri mafic-ultramafic complex (GMC), which is situated ported so far although there are few known occurrences in the western part of the Bastar craton (WBC), nearly of Ni–Bi tellurides from Singbhum Craton [24]. In this 200 km SE of Nagpur (Figure 1B). It comprises mainly TTG, research, we could be able to characterize the rare oc- quartz diorite, charnockite, metapyroxenite and metagab- currence of tsumoite (Bi-telluride), probably for the first broic rock, which are intruded by younger undeformed time, from the Heti Ni–PGE prospect within the Gond- dolerites (Figure 1B) [38]. These rocks form the base- pipri mafic-ultramafic complex (GMC) in the Bastar craton, ment for the overlying Meso to Neoproterozoic platformal Central India. In this paper, a detailed analysis of the sediments of the Pakhal Supergroup and Gondwana sed- mineralogy and mineral chemistry of tsumoite with refer- iments along the N-S to NNW-SSE trending Godavari ence to the mechanism of tsumoite – basemetal sulphides rift [36]. GMC consists of several tectonically dismem- (BMS)-platinum group of minerals (PGM) crystallization bered gabbro–websterite–olivine gabbro bodies disposed and its petrogenetic significance in understanding the ore in a 10 km long NE-SW trending linear belt within formation processes is presented and discussed. tonalite–trondhjemite–granodiorite (TTG) and charnockite- enderbite (Figure 1B) [39]. The mineralized host rocks 2. Geological Setting are lensoidal occur as lenticular NE-SW trending body, dipping 45° to 55° southerly and is invariably conformable to regional structure of the country rocks (Figure 1B). The gabbroic rock does not show any exposed contact with Heti Cu-Ni-PGE-tsumoite prospect in Gondpipri mafic- the surrounding rocks, but exhibits layering defined by ultramafic complex (GMC) is located towards the western plagioclase laths and tabular pyroxene (Figure 2A). fringe of Bastar craton (WBC). Bastar craton exhibits a 3. Mineralization and mode of occur- complex tectono-magmatic geology surrounded by four crustal block; the Dharwar craton in SW, the Bundelkhand rence craton in NW and the Singbhum craton in NE, separated by almost parallel NW trending Mesoproterozoic Mahanadi (> 500 km) and Godavari (> 700 km) rifts to the NE and SW. It is also bounded by two mobile belts, the Central Ni-PGE-tsumoite mineralization in the Heti area is lo- Indian Tectonic Zone (CITZ) to NW and the Eastern Ghat calized in the sulphide zone within gabbro variants viz., Mobile Belt to SE (Figure 1A) [25]. The Proterozoic Pakhal gabbro-gabbronorite-anorthositic gabbro [39]. Sulphide Supergroup of rocks, Gondwana Supergroup of rocks and minerals noticed from the freshly broken surface of the Deccan traps occur to the west of Bastar Craton. Gneisses, host rock include chalcopyrite, pyrrhotite and pentlandite. granitoid, granulites, supracrustals (older and younger) These sulphides occur in the form of specks, blebs, fine to 507 Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and…

Figure 1. Location of the study area: (A) showing different cratons of Peninsular India and (B) showing geological map of Gondpipri mafic-ultramafic complex, Bastar craton, Central India (modified after Dora et al., 2011).

508 M.L. Dora, H. Singh, A .Kundu, M.Shareef, K.R. Randive, S. Joshi

Figure 2. Field photographs and photomicrographs of the typical sulfide–silicate relationships at Heti Prospect, Gondpipri mafic-ultramafic complex: (A) field photograph showing Plagioclase layering in gabbro; (B) drill core sample showing two different modes of sulphide mineralization; (C) sulphide globules (Slf) surrounded by Opx and Cpx and occur at interface of silicates, transmitted light; (D) plagioclase(Pl) showing deformation features like tapering twin lamellae, kink bent, transmitted light; (E) Recrystallized and remobilized sulphides (Slf) and tsumoite(Tsm) along fractures, reflected light; (F) veinlets of net structure secondary sulphides (Slf) filling fracture of silicates and chlorites (Chl) under reflected light; (G) worm like cubanite (Cbn) exsolved from chalcpoyrite (Ccp) at low temperature hydrothermal fluid, reflected light.

coarse-grained dissemination and stringers (Figure 2B). of oxidation of sulphides due to alteration of pyrhotite Dissemination and specks are associated with mafic rich and pyrite [40]. This is identified due to the presence of portion of gabbro where as stringers and minor veins are cannery yellow colour patches. associated with secondary chlorite alteration. Temporal The exposed mineralization spreads to about 700 m along hierarchy of alteration, deformation and metamorphism the strike and 40–50 m across the strike. Between 2010 could not explain convincingly in the field due to paucity and 2012, six exploratory boreholes have been drilled at of outcrops. At places, host rock shows various degrees 100 m intervals for Ni–Co–PGE exploration. The boreholes 509 Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and…

Figure 3. Bright grain identiﬁed as TePtPdFeS in SEM, located along interface of silicates and BMS. A) EDS spectrum of TeFeS(Bi?) -Unknown phase B) Back-scattered electron image of TeFeS(Bi?)

intersected disseminated to minor stringers of sulphide obliterated particularly along the shear zone and minor mineralisation at various depths, which are conﬁned to faults. Presence of chlorite, epidote and sericite, developed minor shear zone and micro faults. The borehole data after plagioclase and ferromagnesian minerals, indicates reveal that mineralization was remobilized along the minor that the host rock has undergone deuteric alteration and shear zone in the form of thin ﬁlms and veinlets of BMS. hydrothermal metamorphism (Figure 2E). Mineralogically, in subsurface, chalcopyrite, pyrite and The opaque mineral phases are mainly BMS with sub- millerite occur as predominant constituents, whilst on the ordinate Cr–Fe–Ti oxides and accessory tsumoite along surface the major minerals include pyrrhotite, chalcopyrite, with PGM. The oxide phases include magnetite, chrome- and pentlandite. The chemical analyses show medium to magnetite and ilmenite. Many of the PGM in the stud- low Cu + Ni content (maximum up to 5000 ppm with a ied samples are found within sulphides but a few are Cu:Ni ratio < 1) and medium to low PGE values (Pd: 660 located at sulphides–sulphides and sulphide–silicate (am- ppb; Pt: 506 ppb; Rh: 84 ppb; Ir:180 ppb and Ru: 75 ppb) phibole, chlorite) boundaries. The latter could also be in- [41]. terpreted as the result of direct precipitation from sulphide 4. Petrography liquids, where silicates (pyroxene?) within the sulphide magma acted as nucleation surfaces for PGM crystallization. These are now either amphibole or chlorite as a result of metamorphism and subsequent alteration. Tsumoite and Petrographic and SEM study reveal that gabbroic vari- its alloy occur as anhedral grains, hair crack veins and

ants: are the: prominent host rock with mineral assemblage minor stringers within sulphide, as seen under SEM and comprising augite/diopside, hypersthene and plagioclase EPMA (Figure 3). The BMS generally form aggregates 0 49 0 51 (Ab An ) with minor amphibole, biotite and opaque with irregular shape, whereas individual grain shows eu- (Figure 2C). The host rock were recrystallized under high hedral to anhedral forms. The most common BMS phases grade metamorphism. Recrystallized primary silicates show are pyrrhotite, pentlandite and chalcopyrite with minor well developed triple junctions (Figure 2C) with deforma- millerite and violarite. The BMS minerals indicate two tion evidences in plagioclase, such as bent twin lamellae mode of occurrences i.e., early sulphide stage and the and kink bands (Figure 2D). The original mineralogy i.e later mineralisation stage. Minerals of the early stage pyroxene and feldspar and granulite texture have been comprise pyrrhotite, pentlandite and chalcopyrite, occur as 510 M.L. Dora, H. Singh, A .Kundu, M.Shareef, K.R. Randive, S. Joshi

: : : : : Microprobe: analyzes: : of BMS, including: pentalandite: : 36 28 28 95 33 05 59 64 39 38 (Ni , Fe :,S ),: pyrrhotite: (Fe S ), chalcopy- 30 53 33 76 34 23 63 33 23 8 33 73 rite (Fe ,Cu ,S ), millerite (Ni ,Fe ,S ), 37 77 14 26 40 71 violarite (Ni , Fe ,S ) and pyrite, PGM and tsumoite have been carried out. The analytical results are given in Table 1. These results indicate that chal- 2 copyrite is close to the ideal composition i.e., CuFeS . Pyrrhotite is rather homogeneous in composition and con- tains signiﬁcant Ni (ranging from 0.41% to 0.83 wt%) and Co (maximum up to 0.1 wt%). In pentlandite, the Ni content varies from 34.97 to 36.28 wt% and Co from 1.00 to 2.02 wt%. Other associated nickel sulphide is millerite having Ni con-

Figure 4. Ternary plot for Bi tellurides from Heti Ni–PGE prospect, tent varying between 61.79 and 63.33 wt% (Table 1). The Gondpipri mafic-ultramafic complex; published data for pyrite shows high Co concentration (2.46 wt%) with very tsumoite are taken from Libcie, Czech Republic, Metaliferi low Ni content ( 0.01%).The analysis reveals very insignifi- Mts, Romania; Rudohorie Mts, Solovak and Pribam, Cetral Bhomia [3, 18, 62–68]. cant presence of PGE–Bi–Te in the base metal sulphides, which is below the detection limit. Table 1 further indicates that tsumoite has the average Bi:Te ratios of 0.86 and Te contents of 49 wt%. The compositions of Heti tsumoites are compared with data published for other occurrences in the triangular Bi–Te–Si diagram (Figure 4). Figure 4 shows fine and irregular blebs occupying the interstices between that the tsumoite from Heti is part of the tetradymite group either pyroxene and feldspar or oxide minerals or both 4 3 of Bi-tellurides and has ideal composition between Bi Te (Figure 2C). These are mainly emplaced as an immiscible 3 4 and Bi Te . Its composition probably indicates variation of melt after one set of silicate crystallisation. The later stage conditions in the course of crystallization, such as changes comprises pyrite, chalcopyrite, milerite, bornite, cubanite, in the Bi/Te ratio, temperature and/or pressure [43].There sijenite, Tsumoite, PGM, represented by minor veinlets is a gradual variation of the Te/Bi, Te/S and Bi/S values, redistributed along the fracture planes. Effect of prograde which resulted in the precipitation of various Bi-bearing metamorphism was not observed convincingly on sulphides tellurides in the system (Table 1 and Figure 4). The plot- in Heti prospect. However, post metamorphic disturbances ted points of Bi, Te and S in Figure 4 cluster close to the of the mineralisation during hydrothermal chlorite alter- composition of BiTe, indicating the samples from Heti have ation noticed in the form of net and wire mesh texture the ideal composition of tsumoite. (Figure 2F). At places, cubanite exsolved from chalcopy- Moncheite, Pd-moncheite, merenskyite and melonite (?) rite (Figure 2G) indicates a low temperature hydrothermal are thePGM analyzed (Table 1). The results indicate that origin. the PGM from the Heti prospect are at places associated 5. Mineralogy and Chemistry with tsumoite, occurring mostly as subhedral to anhedral grains along the fractures and interface of sulphides with pyroxenes and feldspar (Figure 5). PGM grains are not homogeneous and show variable substitutions of Pt and Quantitative chemical compositions of BMS-PGM- Pd with Bi and Te. tsumoite minerals were determined with a Cameca SX100 6. Discussion electron microanalyzer at GSI, Faridabad using wave- length dispersive method under the following condition: current of 20 kV and 20 nA and electron beam diameter of less than 1 µm. Counting time were 10 seconds on peak Ore forming processes of Ni–PGM–Bi–Te mineralisation in and 5 seconds on background. The data were corrected the Heti area, in the Gondpipri mafic-ultramafic complex, using PAP software [42]. The following natural and syn- reflect the complexity in the evolution of parental magma. thetic samples were used as standards S and Fe- pyrite; Ore genesis processes were probably controlled by magma 2 2 2 Ag and Te-Ag Te; pure metal standards are used for Co, composition, changes in fS , fO and the rate of cooling Ni, Cu, Ru, Pd, Pt, Au, Bi, Cr and Os. S, Ru, Rh, Ag, In, as seen elsewhere [1, 11]. In general, Ni-PGM crystallize Sb, Pb, Bi were analysed using PET; Fe, Co, Ni, Cu, Te, from residual liquid during fractional crystallization of sul- Pt, Ir and Cr were analysed using LIF; As and Os were phide melt [44, 45]. However, in the Heti area the magma analysed using TAP crystals. became enriched in S and Cu, as a result of fractionation 511 Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and… 00 0 0 BMS 000 0 0 0 0.055 0 bldbldbld bld bld bld bld bld 0.23 bld bld bld 100 100 100 100 27/1 40 / 1 . 42 / 1 . 47 / 1 . 0.349 0.068 bld 61.794 0.2620.004 0.046 0.0430.003 0 24.619 0.199 0.01 47.039 0.039 0 0 0.01 0.01 0 0.0160.005 0.07 0.067 0.0020.006 33.391 0.001 0.283 0.0260.09697.76 bld bld0.012 99.997 0.024 98.043 0.022 0.048 100.775 bld 0.001 0.001 39.24357.938 53.041 46.577 34.301 29.932 36.741 1.905 53.92845.706 66.339 33.442 50.127 25.11 51.217 1.525 26M-2 16JU-3 16JU-3 26M-2 pyrrhotite pyrite chalcopyrite millerite 0 0 0 0 0 0 bld bld bld bld bld bld 100 26/1 0.269 96.71 0.213 33.587 33.112 29.667 26.716 48.231 24.807 26M-2 pentalandite 0 0 bld bld 100 0 7.493 4.047 0 0 bld 3.235 1.643 bld bld 100 100 100 100 100 47.420.268 42.084 0.4751.011 45.1822.972 0.746 51.474 0.452 2.411 22.112 0.454 0.182 1.453 0.506 0.422 42.563 2.166 23.782 19.664 0.512 0.201 8.224 0.3314.627 8.355 7.813 3.1640.059 0.335 5.871 0.074 0.343 0.822 3.761 0.288 2.33 0.145 5.722 0.167 49.637 23.561 0.286 4.318 27.942 16.296 0.391 0.0580.016 0.01 bld bld 0.048 bld 0.383 bld 0.046 bld 0.061 0.0390.043 0.127 0.058 0.155 0.215 2.757 0.122 6.96 0.102 0.084 0.05 0.387 0.172 0.214 1.734 0.105 0.144 0.0220.037 0 0 0.12 0 0.435 0 0.085 0 98.675 101.356 101.65 102.446 101.083 98.559 46.016 51.487 51.652 46.713 24.67 37.69 52.93433.307 54.868 27.383 58.538 31.265 54.014 36.341 12.937 7.08 32.176 22.186 26M-2 16JU-3 16JU-3 16JU-3 16JU-3 26M-2 0 0 / 1 . 21 / 1 . 24 / 1 . 3 / 1 . 5 / 1 . 6 / 1 . 23 / 1 . bdl bld 100 0.13 0.15 0.16 5.855 32.15 0.122 0.276 1.511 0.082 1.124 3.531 0.181 8 sumoite Tsumoite Tsumoite Tsumoite Tsumoite Tsumoite alloy Tsumoite alloy 59.817 13.017 61.189 20.081 26M-2 100.697 T TSUMOITE 0 / 1 . bld 100 PGM 0.011 1.993 4.396 8.844 0.262 1.602 1.074 0.025 4.491 2.783 1.083 3.795 1.318 1 moncheite 58.157 21.713 98.511 60.302 14.725 10.997 26M-2 Pd Representative microprobe analyses and chemical composition of tsumoite-PGM and associated BMS from Heti Ni–PGE prospect, Gondpipri mafic-ultramafic complex, Central India (wt.% and at %). no % Set/Point eight % o o otal otal able 1. sample Data W C T Atomic C T Mineral name Ni Cu Te Bi Pt Pd S Fe Ag Ni Cu Te Pd S Fe Ag Bi Pt T

512 M.L. Dora, H. Singh, A .Kundu, M.Shareef, K.R. Randive, S. Joshi

Figure 5. Back-scattered electron images (EPMA) showing diﬀerent textures of BMS, PGM and Tsm from Heti prospect (A) Moncheite (PGM) occurs at the interface of pentalandite (Pen) and silicate, (B) BiTePdPt occur at the interface of silicates (Sil) and pyrrhotite(Po), chalcopyrite(Ccp) (C) anhedral PGM and Tsumoite(Tsm)occur along fracture of pyrite(Py) as well as along secondary silicates (D) Tsumoite(Tsm) penetrates along fracture of pyrite(Py) associated with zircon(Zrn).

and accumulation of Fe-rich silicates, such as olivine and high temperature of 1050 to 1010℃ as shown in the ex- orthopyroxene. The sulphide minerals started crystallisa- perimental work elsewhere by Naldrett. Pyrrhotite and 2 tion due to cooling and increase in fO during uplift. This pentlandite have formed at relatively high temperature fol- type of crystallisation process has been already reported lowed by chalcopyrite and pyrite. PGM shows elongated in mafic ultramafic complex of Gabbro Akarem, Eastern and anhedral grains, emplaced along fractures of pyrrhotite, Desert, Egypt [46]. Textural relationship between BMS and pentlandite and associated with secondary chlorite of rela- coexisting magnetite firmly suggest that sulphide-silicate tively low temperature of formation, where Pt and Pd were liquid immiscibility was mainly induced by the precipi- eventually bonded with Te and Bi in the residual liquid tation of Ti-magnetite, as indicated in Figure 2C. This to form moncheite, Pd moncheite and tsumoite, as shown probably caused sulphur saturation in melt by decreasing by experimental work on PGE and BMS [50]. Tsumoite sulphur solubility and helps concentration of PGE-Te-Au (BiTe) minerals are volumetrically minor in the Heti Ni– in sulphide melt. Similar observations have been made PGE prospect but their presence is useful in unravelling by different researchers in Bushveld complex and Xinjie the reasons for deposition of associated BMS and PGM. layered intrusion in Emeishan LIP, SW China [47, 48]. It There are two generally accepted mechanisms of PGM is widely accepted that PGM exsolve over wide range of -tsumoite crystallization in Cu–Ni–PGE deposits, i.e., by temperature from sulphide melt as it recrystallize from dif- exsolution from monosulphide solid solution (MSS) [7] and ferent sulphides during cooling [9]. Ore petrographic and by direct crystallization from hydrothermal fluids [11]. The EPMA studies showing pseudo-subophitic intergrowth of exsolution of PGM from MSS generally takes place at pyrrhotite and magnetite at places in Heti prospect. This high temperatures > 650°C[7]; however, it can also persist pseudo-subophitic nature suggests co-crystallization at to low temperatures (~100°C) [51]. High temperature, in 513 Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and…

the range of 450° to 200°C, is widely accepted for PGM-Te majority are located at the sulphide–silicate interfaces or crystallization from hydrothermal fluids [1, 52, 53]. exclusively along fractures of secondary silicates (Figure 5). PGM and tsumoite crystallization are mainly controlled The former mode of occurrence suggests an early stage of 2 2 by cooling rate and local changes in fTe –fS [54, 55]. The PGM-Te crystallization from mss and later mode in form of 2 2 variation in the fTe –fS may be due to changes in total veins and stingers (Figure 5) from late stage hydrothermal concentrations of Te and S, a decrease in the oxidation fluids, which are more common at Heti prospect and at 2 state or cooling. Since the variation in fO has minor places, are associated with tsumoite (BiTe) mineralisation. effect on the mineral stability [56] and the solubility of Secondary sulphides- PGM-tsumoite are associated with native Te is temperature dependent [57], bismuth-tellurides chlorite alteration, occur along fracture planes, Cubanite have been crystallized in response to cooling or change also exsolved from chalcopyrite in association with chlorite in total concentration of Te and S (or both factors). In alteration indicate formation temperature of 200°C[59]. the Heti prospect, the role of sulphur concentration was Formation temperature of chlorite around 250°C has been limited as PGM are mainly tellurides. Tellurium activity established by empirical thermometry based on Aliv, Alvi and cooling rate are thus considered the most important and Fe/Fe+Mg ratio of chlorite [60]. Chlorite in associa- factors influencing the mineralogy and composition of the tion with tsumoite suggests their temperature of formation PGM and tsumoite. was around 250°C. Many of the PGM in the studied samples are found within This is also confirmed from the presence of Pd-Pt bis- sulphides but a few are located at sulphides–sulphides and muthotellurides that are considered to be characteristic sulphide–silicate (amphibole, chlorite) boundaries. The of low-temperature hydrothermal mineralization, similar latter could also be interpreted as the result of direct pre- to those of the New Rambler mine, Wyoming [61]; the cipitation from sulphide liquids, where silicates (pyroxene?) Bucko Lake intrusion, Thompson Belt, Manitoba [62]; the within the sulphide magma acted as nucleation surfaces Sudbury area [52], and Eastern Desert, Egypt [1]. The for PGM crystallization. These are now either amphibole PGM-tsumoite association is interpreted as products of or chlorite as a result of metamorphism and subsequent al- precipitation of PGE from hydrothermal solutions of de- teration. It is most likely that amphibolite and greenschist creasing temperature after the peak of metamorphism in facies metamorphism has preferentially redistributed Ni, the GMC. The movement of these solutions were facilitated Cu and S in the rocks, and this can explain by showing along discrete micro-shear and faults but the source of the the non-magmatic sulphide mineral assemblages (cubanite, hydrothermal solutions is not clear. sijenite). In this study, the exsolution of cubanite with 7. Conclusions chalcopyrite (Figure 2G) clearly indicates that the temperature of formation was around 200°C, which is typical of hydrothermal origin of the sulphides. While PGM associated with these sulphides and chlorite are characteristic The Heti Cu–Ni–PGE prospect occurs as lensoidal and of the hydrothermal environment. lenticular gabbroic bodies located in Gondpipri mafic- Two generations of BMS-PGM were observed in the study ultramafic complex, hosted in Precambrian granitoids of area. Early formed euhedral moncheite was probably the Western Bastar Craton. The gabbroic rock have been exsolved from a sulphide-rich liquid during cooling and deformed and recrystallized under granulite metamorphic mainly occur as inclusions in pyrrhotite and pentlandite, conditions. Mineralisation occurs in two different modes as seen in Figures 5A and 5B, while those of last stage of occurrences. The early mineralisation± occur as blebs, remobilised sulphide were possibly formed at chalcopyrite- specks and dissemination of sulphides, viz. pyrrhotite, chal- silicate contacts, as well as along fracture filling BMS and copyrite, pentlandite and minor pyrite PGM, whereas 2 altered silicates under low fS and relatively high values later± mineralisation occur as stringers, minor veins of sul- 2 of fTe (S-free pyrrhotite) (Figures 5C and 5D). Tsumoite phides viz. pyrite, millerite, cubanite, sijenite, tsumoite associated with remobilised sulphides. Low temperature and PGM. hydrothermal solution may be responsible for mobilisa- Pyrrhotite and pentlandite have formed at relatively high tion of Pd, Pt, Bi, Te to form hydrothermal PGM and temperature followed by chalcopyrite and pyrite. The tsumoite along fracture planes of silicates and associated PGM formed at relatively low temperature, where Pt and 2 BMS under conditions of high Bi and high fS as well as Pd were eventually bonded with Te and Bi in the resid- 2 fTe (Figures 5D) [4, 17, 56]. Sulphur was probably trans- ual liquid to form moncheite, Pd moncheite and tsumoite. ported as sulphide or thiosulfate complexes, whereas Te Many of the PGM occur within sulphides but a few are 2 3 2 Te was transported as aqueous H TeO , Te -, and H - com- located at sulphides–sulphides and sulphide–silicate (am- plexes in the hydrothermal fluid [58]. At Heti prospect only phibole, chlorite) boundaries. These could be interpreted few PGM-tsumoite grains are within sulphides and the as the result of direct precipitation from sulphide liquids 514 M.L. Dora, H. Singh, A .Kundu, M.Shareef, K.R. Randive, S. Joshi

of magmatic origin. After high grade metamorphism, the [4] Sejkora J., Litochleb J, Jakub P, Bohuslav B,Tsumoite associated fluid regimes resulted in remobilization and and associated tellurides from the Au deposit Libcice transport of Cu-rich sulphides, Te, PGE. These minerals near Novy Knín, Czech Republic: mineralogy and redeposited and filled along fracture of early sulphides genetic significance, Journal of Geosceince, 2009, 54, under greenschist facies metamorphic conditions and as- 73–82 sociated with chlorite alteration zones. These modes [5] Rybicki M., Preliminary Data On Bismuth Telluride of occurrences suggest hydrothermal type of mineralisa- From Izerskie Garby Zone, Karkonosze-Izera Block, tion. Mineral assemblages and textural relationships of South-Western Poland, Contemporary Trends in Geo- tsumoite-PGM in Heti prospect has indicated that they science, 2011, 1, 63–66 have formed along fractures of BMS and secondary sili- [6] Cabri L.J., Harris D.C., Gait R.I., Michenerite (PdBiTe) 2 2 cates(chlorite) under variable fS , fTe and fBi, which con- redefined and froodite (PdBi2) confirmed from the Sud- firms their hydrothermal origin. The discovery of tsumoite bury area, Canadian Mineralogist, 1973, 11, 903–912 and Ni–PGM mineralisation open a new window for ex- [7] Cabri L.J., Laflamme J.H.G., The mineralogy of the ploration in Bastar craton and indicates the possibility of platinum-group elements from some copper–nickel de- finding these assemblages in high grade belt elsewhere posits of the Sudbury area, Ontario. Economic Geol- in this craton. ogy, 1976, 71, 1159–1195 Acknowledgments [8] Hudson D.R., Platinum-group minerals from the Kam- balda nickel deposits, western Australia, Economic Geology,1986, 81,1218–1225 [9] Garuti G., Rinaldi R., Mineralogy of melonite-group and other tellurides from the Ivrea-Verbano basic com- We are extremely grateful to Dr.S.K.Wadhawan, Director plex, western Italian Alps, Economic Geology,1986, General, Geological Survey of India and Shri. Raghubir 81, 1213–217 Singh, Dy. Director General and HOD, NER, Shillong [10] Barkov A.Y., Laflamme J.H.G., Cabri L.J., Martin for their kind encouragement and granting permission to R.F., Platinum- group minerals from the Welgreen publish this paper. Authors thank to S/Shri.Rajinder Kumar, Ni–Cu–PGE deposit, Yukon, Canada, Canadian Min- Pankaj Jaiswal, Pitamber Pati, A.Srivastava, R.Umarao, eralogist, 2002,40, 651–669 B.K.Sareen, G.K.Kesri, M.Sadique, S.N. Mahapatra and [11] Rowell W.F., Edgar A.D., Platinum-group element min- B.B.Sharma, for their valuable suggestions and discussions. eralization in a hydrothermal Cu–Ni sulfide occur- Authors thank to Dr.L. G. Gwalani, guest editor of the rence, Rathbun Lake, northeastern Ontario, Economic CEJGS for inviting us to submit a paper for a special issue Geology,1986, 81, 1272–1277 entitled “Mafic-ultramafic rocks and alkaline-carbonatitic [12] Helmy H.M., Stumpfl E.F., Kamel O.A., Platinum- magmatism and associated mineralization to be brought group minerals from the metamorphosed Abu Swayel out in honour of Dr. Piero Comin-Chiaramonti”. The Cu–Ni–PGE mineralization, South Eastern Desert, authors are thankful to the anonymous reviewer’s valuable Egypt, Economic Geology, 1995, 90, 2350–2360 comments and suggestions for improving the quality of [13] Gervilla F., Sanchez-Anguita A., Acevedo R.D., Fenoll this manuscript. MLD thanks Miss. Wanba Syiemlieh for Hach-Ali P., Paniagua A., Platinum-group element typing and handling computer work of this MS. sulpharsenides and Pd bismuthotellurides in the meta- References morphosed Ni–Cu deposit at Las Aguilas (Province of San Luis, Argentina), Mineralogical Magazine, 1997, 61, 861–877 [14] Gervilla F., Kojonen K., The platinum-group minerals [1] Helmy H.M., Melonite group minerals and other in the upper section of the Keivitsansarvi Ni–Cu–PGE telluride from three Cu-Ni-PGE prospect, Eastern deposit, northern Finland, CanadianMinalogist, 2002, Desert, Egypt, Ore Geology Review.2005, 26, 305– 40, 377–394 324 [15] ThompsonR. M., The telluride minerals and their oc- [2] Theodore T.G., Orris G.J., Hammarstrom J.M., Bliss currence in Canada, American Mineralogist., 1949, J.D., Gold-bearing skarns, In: U.S. Geol. Sur.Bull- 34,342-382 1930 [16] Gu x., Watanabe M., Hoshino K., Shi bata y., Mineral [3] Zhao Y., Zhang Y., Bi C., Geology of gold-bearing chemistry and associations of Bi–Te(S, Se) minerals skarn deposits in the middle and lower Yangtze River from China, Neu Jb Mineral, Mh, 2001, 289–309 Valley and adjacent regions, Ore Geology Review, [17] Ciobanu C.L., Cook N.J., Spry P.G., Preface special is- 1999, 14, 227–249 sue: telluride and selenides minerals in gold deposits 515 Tsumoite (BiTe) and associated Ni-PGE mineralization from Gondpipri mafic-ultramafic complex, Bastar Craton, Central India: mineralogy and…

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