Constraints of mineralogical characterization of gold ore: Implication for genesis, controls and evolution of gold from Kundarkocha gold deposit, eastern India

Journal of Asian Earth Sciences 97 (2015) 136–149

Contents lists available at ScienceDirect

Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes

Constraints of mineralogical characterization of gold ore: Implication for genesis, controls and evolution of gold from Kundarkocha gold deposit, eastern India P. R. Sahoo, A. S. Venkatesh ⇑ Department of Applied Geology, Indian School of Mines, Dhanbad 826004, India

a r t i c l e

i n f o

Article history: Received 24 September 2013 Received in revised form 29 September 2014 Accepted 30 September 2014 Available online 12 October 2014 Keywords: Lattice-bound gold Sulfur fugacity Graphitic schist Kundarkocha Singhbhum–Orissa Iron Ore Craton Eastern India

a b s t r a c t Gold mineralization in Kundarkocha gold deposit occurs in the eastern Indian Craton that is hosted by sheared quartz–carbonate–sulfide veins emplaced within the graphitic schist, carbonaceous phyllite and talc–chlorite–serpentine schist belongs to Gorumahisani–Badampahar schist belt of Iron Ore Group. Gold mineralization exhibits both lithological and structural controls in the study area, albeit the stratigraphic control is more ubiquitously observed. Detailed mineralogical characterization coupled with electron probe microanalysis of the sulfide phases reveal the occurrences of gold in three distinct forms (i) as lattice-bound form within sulfides especially enriched in arsenopyrite, loellingite, pyrite, pyrrhotite and chalcopyrite in decreasing order of abundance; (ii) as micro inclusions or nano-scale gold inclusions within pyrite and arsenopyrite especially along the growth zones and micro-fractures as substrates and (iii) as free milling nugget gold grains either along the grain boundaries of sulfides or within the host rocks. Three generations of pyrite (Py-I, Py-II and Py-III) and arsenopyrite (Asp-I, Asp-II, Asp-III) have been identified based on textural, morphological characteristics and mineral chemistry. The lattice-bound gold content in pyrite and arsenopyrite varies from 600 to 2700 ppm and 900 to 3600 ppm respectively and increase in concentration of such refractory gold is seen in the order of chalcopyrite > pyrrhotite > pyrite > loellingite/arsenopyrite. The evolutionary stages of different forms of gold include remobilization of the lattice-bound grains in pyrite and arsenopyrite (Py-I and Asp-I) and re-concentration along the zoned-pyrite and arsenopyrite (Py-II and Asp-II) and ultimately as native gold/nuggets surrounding the sulfides as well as within the main mineralized zone. Lattice-bound gold distribution could have resulted due to metamorphic devolatilization reactions which are further aided by the influx of hydrothermal fluids. These reactions along with additional input of hydrothermal fluid paved the way for expulsion of lattice-bound gold from sulfides to concentrate as nuggets/main lode within shear fractures channelizing the fluid flow. Thermometry results of the arsenopyrite–pyrite–pyrrhotite assemblage yielded a temperature range from 375 to 390 °C which is the ideal condition for gold precipitation. Native silver, gersdorffite and arsenian-ullmannite are being reported for the first time from this deposit indicating the complexity and wide variety of mineral phases associated with gold implying magmatic-hydrothermal input of the source fluid. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Gold deposits, irrespective of their types and genetic variants are invariably associated with sulfides (Phillips and Groves, 1983; Groves et al., 1998; Large et al., 2009; Sung et al., 2009; Deol et al., 2012; Su et al., 2012). Hence detailed studies and characterization of sulfides associated with gold mineralization gives ⇑ Corresponding author. E-mail address: [email protected] (A.S. Venkatesh). http://dx.doi.org/10.1016/j.jseaes.2014.09.040 1367-9120/Ó 2014 Elsevier Ltd. All rights reserved.

some definite clues for understanding the genesis and depositional history of gold. Keeping this view in mind, detailed mineralogical and chemical characterization of sulfides which include the lattice-bound gold distribution in pyrite and arsenopyrite of several generations has been taken up to decipher the genetic constraints and metallogenetic evolution of Kundarkocha gold deposit of Singhbhum orogenic belt in eastern India. Besides free milling gold, refractory gold i.e. the gold present in the lattices of the sulfide minerals has been reported by several earlier workers. Occurrence of invisible gold has been reported from some of the gold deposits

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

from India (Mishra et al., 2001; Saha and Venkatesh, 2002; Deol et al., 2012; Hazarika et al., 2013) and elsewhere (Morey et al., 2008; Large et al., 2009, 2011; Sung et al., 2009; Su et al., 2012; Deditius et al., 2014; Zhang et al., 2014), the mechanism behind the evolution of free gold from the refractory form has not been adequately addressed from the Indian gold occurrences. This article focuses the mechanism of re-mobilization, re-equilibration and re-constitution of lattice-bound gold within the sulfides to re-concentration as free gold during metamorphism and hydrothermal fluid activity. Detailed ore microscopic studies of the samples collected from Kundarkocha, reveal the occurrence of gold as three distinct forms and has a very close relationship with pyrite, arsenopyrite, loellingite and pyrrhotite. Three generations of pyrite and arsenopyrite were detected which shows distinct variation in distribution of lattice-bound gold content. The type-I pyrite and arsenopyrite bears the maximum content of lattice-bound invisible gold and are deformed. They do not carry any gold substrates. The type-II pyrite and arsenopyrite exhibit growth zoning and inclusions of gold occur within the cracks and fractures as well as the zoned region of these minerals. As compared to the stage-1 sulfides, the lattice-bound gold content in type-II is less because of the removal of the lattice-bound gold by fluid activity. The presence of native gold itself occurs in two forms: as inclusions or substrates adsorbed on the sulfides or as individual entity. Phase equilibria conditions on loellingite–arsenopyrite thermometry and sulfur fugacity conditions have been discussed with implication of evolutionary phases related to gold mineralization along with lithological and structural controls on the gold mineralization. Besides, loellingite, native silver, gersdorffite and arsenian-ullmannite are being reported for the first time from the deposit suggesting the complex nature of ore mineralization and environment of deposition of associated gold.

2. Geological overview The Singhbhum–Orissa Iron Ore Craton is one of the promising areas in terms of occurrence of gold mineralization especially within the meta-volcano-sedimentary belts of the Archean Iron Ore Group (Ghose, 1996; Baidya, 1996; Sahoo et al., 2010; Hazarika et al., 2013). The Singhbhum crustal province consisting of south eastern part of Jharkhand and north of Orissa, occupies an area of approximately 50,000 km2. The Singhbhum crustal province can be recognized in two distinct regions: the northern younger, Singhbhum Group (Sarkar and Saha, 1962) or North Singhbhum Mobile Belt (Bhattacharya and Mahapatra, 2008) or Singhbhum Mobile Belt (Misra, 2006) and the southern older, Iron Ore Group province (Sarkar and Saha, 1962), also known as Archean granite–greenstone terrain or Singhbhum Granite Craton (Sengupta et al., 1996; Mukhopadhyay, 2001; Acharyya et al., 2010a, 2010b). The Singhbhum–Orissa Iron Ore Craton is the oldest Archean nucleus of eastern India out of which major part is occupied by Singhbhum Granitic Batholithic Complex (Mahadevan, 2002). The central oval shaped Archean nucleus of this province is known as Singhbhum–Orissa-Iron-Ore-Craton (Saha, 1994) or Singhbhum Orissa Craton (Misra, 2006); (Fig. 1). These two provinces are separated by a sheared zone, known as Singhbhum Shear Zone; extending over a strike length of more than 160 km (Saha, 1994; Mukhopadhyay, 2001). The Iron Ore Group forms an important supracrustal suite of the Eastern Indian Craton which occurs in three basins: (1) Gorumahisani–Badampahar basin in the east (Study area); (2) Noamundi– Jamda–Koira Basin in the west and (3) Tomka–Daitari basin in the south (Fig. 1). Based on the field relations, Saha et al. (1988) proposed that the Iron Ore Group to be between 3100 and

137

3300 Ma. Mukhopadhyay et al. (2008), based on a zircon U–Pb date for the dacitic lava within the Iron Ore Group assigned an age of 3506 ± 2.3 Ma from the southern part of the Craton (Mondal, 2009). The Precambrian Iron Ore Group largely contains BIF in addition to the other meta-volcano-sedimentary rocks (3.1– 3.3 Ga, Sarkar et al., 1969), forming a significant portion of the Singhbhum–North Orissa Craton of eastern Indian shield represented in basinal areas. The northerly plunging asymmetric synclinorium Iron Ore Group rocks predominantly comprises of BIF and low-grade meta-sediments including BIF, phyllites, tuffaceous shales, quartz arenite, argillite, ferruginous quartzite, dolomite, mafic and ultramafic volcanic rocks (Saha, 1994). The Archean Kundarkocha gold deposit is located 45 km south of Jamshedpur in the East Singhbhum which falls under the Gorumahisani–Badampahar schist belt. Gorumahisani–Badampahar schist belt forms the easternmost meta-volcano-sedimentary sequence of the Iron Ore Group exposing greenschist to lower amphibolite facies metamorphic rocks (Figs. 1 and 2). The rocks exposed around Kundarkocha are meta-sedimentary units such as chlorite–biotite schist, carbonaceous phyllite, graphitic schist and talc–chlorite–serpentine schist along with veins and veinlets of carbonates like calcite and ankerite besides quartz veins (Fig. 3). The sequence is intruded by gabbro, ultramafic sills and dolerites. Rocks of the Iron Ore Group in the study area exhibits NW–SE structural trend and registered deformational elements. Foliations of different generations show a near constant dip of 45–65° towards the NE (Fig. 2). Structural analysis of Kundarkocha area displays complex deformation patterns exhibiting at least three phases of deformations (Baidya, 1996; Ghosh and Mukhopadhyay, 2008). However, two phases are clearly observed around the mine site whereas the third one is regional in nature. The general trend of the area is NE–SW and towards the northern part, it deviates and truncates towards N–NNW (Fig. 1). Mineralized quartz veins run parallel to the regional foliation trends showing a similar trend with that of carbonate bearing host rocks and the ultramafic intrusive also follow the strike of foliation which are exposed as sills. The gold mineralization exhibits both lithological and structural controls generally following the regional foliation planes with a near stratiform and strata-bound appearance. The area is traversed by multiple sets of lineaments (Pal et al., 2006) and at places localized shearing along with drag folds are also observed. All these macro and micro-scale structural features localized the Au mineralization forming the ore-shoots.

3. Nature and controls of mineralization From the field relationships and detailed petrographic studies, the gold mineralization is found to be controlled by both lithological and structural parameters. Gold mineralization in Kundarkocha area occurs within the carbon phyllite, graphitic and talc–chlorite–serpentine schist as well as the auriferous quartz– carbonate veins emplaced along the small scale shear fractures and dilatant zones. This zone stretches about 2.5 km in length trending N–S to NE–SW and with variable widths. This shear zone is of brittle-ductile in nature as evidenced by the presence of rotation of porphyroclast, brecciation of carbon phyllite and graphitic schist as well as the sulfide phases (Fig. 3c). The quartz–sulfide– carbonate veins criss-crossing these rocks and also occur as parallel to sub-parallel zones within the planar (shear planes and foliations) surfaces. The small scale shear zone is mainly located within chlorite–serpentine schist and carbonaceous phyllites/ schist (Fig. 3b–e). The fracture planes act as zones of low-pressure gradients and this probably controls the migration of fluid and channelizes the fluid flow. Thus, the ore bearing fluids have deposited metals along these fracture arrays both within and adjacent to

138

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

Fig. 1. Geological map of the Singhbhum–North Orissa Craton showing the study area (Kundarkocha gold deposit) within the eastern iron ore basin i.e., Gorumahisani– Badampahar schist belt (modified after Saha, 1994 and Bhattacharya et al., 2006).

the shear zones mainly in the zone having feeble displacement (Fig. 3a). In the study area the shear fractures can be characterized by certain specific lithotypes and small-scale microstructures like rotational geometry of quartz porphyroclast and brecciation of the lithotypes like carbon-phyllite and graphitic schist, which are the indicators of brittle-ductile shear zone (Fig. 3f). These litho types and microstructures comprise breccia, flattened and stretched quartz grains, kinking and bending of cleavage, en echelon features, ribbon structure in quartz grains and S, M, Z patterns of folding (Fig. 3d and e). Primarily gold production comes from the array of blue/smoky quartz veins transecting the carbonaceous phyllites/graphitic schists in the study area. As reported by Geological Survey of India (GSI), the extension of the veins in the dip direction is more as compared to the strike direction and the mineralized veins were traced for about 200 m of the strike length. Underground exploratory work by Mineral Exploration Corporation Limited revealed a number of auriferous gold veins at different working level in the developed mine. The extension of the veins in the dip direction is more than the strike continuity of the ore body (Banerjee and Thiagarajan, 1965; Sahoo, 2012). The occurrences of small pockets of ore body as revealed by the old workings in the adjoining areas could be the

detached extension of the main mineralized zone. Total geological reserve calculated is around 63,600 tonnes for two lodes; each having its strike length of 250 m up to the depth of 120 m and average thickness of 0.8 m (Mineral Exploration Corporation Limited unpublished report). In the Kundarkocha underground mine, all the working levels are developed at a vertical interval of 30 m beyond the first level.

4. Analytical techniques About forty ore samples, collected from different working levels of the Kundarkocha underground mine, have been carefully studied using reflected light microscopy and representative samples were studied using Electron Probe Micro Analyzer (EPMA). Analyses of the sulfide minerals were carried out on carbon coated and mounted 1-in. diameter epoxy polished stubs. Mineral chemical analyses of the mineralized and non-mineralized samples were conducted using CAMECA SX 100 Electron Probe Micro Analyzer at Institute Instrumentation Centre, Indian Institute of Technology Roorkee, India. A probe current of 25 nA at an accelerating voltage of 20 kV and a beam diameter of 1 lm are used with 5 s counting time. Both line and point analyses on the samples were performed

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

139

Fig. 2. Geological map of Kundarkocha area showing the mineralized quartz lodes (modified after Banerjee and Thiagarajan, 1965).

Fig. 3. Field photographs showing (a) thin mineralized quartz veinlets within the carbon phyllite; (b) native gold and gold bearing sulfide zone along the interface boundary between smoky quartz and carbon phyllite; (c) graphitic schist rock along the ductile shear zone; (d) mineralized chlorite–fuchsite schist exposed in the underground mine; (e) mineralized blue quartz vein along the S2 foliation of the chlorite schist; (f) smoky quartz veins intruded into the ultrabasic rock unit. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

to know the zonal variation of elemental concentration/elemental contouring in sulfides. Standardization is conducted against natural standards using ZAF corrections after Philbert (1963). 5. Ore mineralogy The principal opaque minerals found in the quartz–carbonate– sulfide veins along with schistose rocks and mafic intrusives are pyrite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, pentland-

ite, gersdorffite, rare galena, loellingite and native gold. Gangue minerals include quartz, chlorite, sericite, calcite + ankerite, hornblende and epidote. Detailed petrographic studies of the ore samples reveals pyrite as the most dominant mineral, followed by pyrrhotite, arsenopyrite, chalcopyrite and sphalerite in decreasing order of abundance within the litho units (Figs. 4 and 5). Besides these, very minor amounts of pentlandite (as flames within pyrrhotite), loellingite (FeAs2), native silver, hematite, gersdorffite (NiAsS) and arsenian-ullmannite {Ni(As, Sb)S} are also present in

140

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

Fig. 4. Photomicrographs showing different modes of occurrences and types of pyrite in the host rocks (a and b); native gold in quartz and gold inclusion in the perforated pyrite (c and d) and deformed and perforated early formed pyrite and associated pyrrhotite, galena and chalcopyrite (e and f).

the deposit. Pyrite occurs in the carbonaceous phyllite and along with other sulfides and gold in the blue/smoky quartz veins. Gold mineralization is associated with hydrothermal alteration assemblages that comprise of chlorite, sericite, serpentine, graphite along with native sheaths of gold occurs across a wide variety of rocks in the study area that include the ubiquitous quartz–carbonate veins and with sulfides, stratified carbonaceous phyllite, slate, graphitic schist and the altered mafic/ultramafic rocks. Some arsenopyrite and pyrite mineral phases show growth zoning (Figs. 4 and 5) that invariably contains refractory lattice-bound gold (Table 1). The auriferous quartz–carbonate–sulfide veins, carbonaceous phyllite/slate, graphitic schist contains substantial amounts of gold which is being mined. Presence of substantial amounts of refractory gold in pyrrhotite, arsenopyrite–loellingite, pyrite, chalcopyrite assemblages is also noted. Out of the many sulfide assemblages, predominantly, loellingite, arsenopyrite, pyrite and pyrrhotite possess higher values of lattice-bound gold. 6. Types of gold bearing pyrite and arsenopyrite mineral phases Pyrite is the most abundant sulfidic phase with a size variation from 0.01 mm to 5 mm and occurs mostly as euhedral to subhedral cubes and pyritohedrons of different generations (Fig. 4a–e). Pyrite grains occur virtually in all the lithotypes of this gold deposit. Based on the difference in morphology, textures and lattice-bound gold distribution, they have been classified into three types. This is

the principal mineral with which gold is intimately associated; therefore it can be used as suitable indicator mineral for gold exploration in the study area. Arsenopyrite is seen as well developed idiomorphic crystals with characteristic rhomb shaped grains which are at times deformed in association with pyrite and pyrrhotite (Figs. 4 and 5). In carbonaceous phyllite and talc–chlorite, the rhombic arsenopyrite grains are larger in size and coexist with pyrrhotite. In quartz–sulfide–carbonate veins, the size of the rhomb decreases and is embedded by pyrrhotite. Based on the morphological difference, textural features and presence/absence of invisible gold distribution, the arsenopyrite and pyrite mineral phases have been classified into three types (Figs. 4–6). 6.1. Type I pyrite Py-I is the most abundant phase. Pyrite grains are highly fractured and sheared and mostly found within the carbon-phyllites, graphitic schist and quartz veinlets within this assemblage (Fig. 4a, e and f). Pyrite I is porous and commonly possesses silicate inclusions and occur as isolated or associated with the pyrrhotite. Lattice-bound Au concentration varies from 1600 to 2700 ppm which is relatively higher than the other types of pyrite grains and As content is relatively higher (0.22–0.33%). Ni content varies from 1100 to 4000 ppm suggesting high possibility of contribution from ultramafic units (Table 1) as evidenced from the host lithopackage assemblage associate with the deposit.

141

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

Fig. 5. Photomicrographs showing invisible gold bearing zoned and perforated pyrite (a–c); different stages of arsenopyrite (d and e) and gersdorffite in association with chalcopyrite (f).

Table 1 EPMA data showing distribution of elemental variation including high incidence of gold values within sulfides from Kundarkocha (Asp-Arsenopyrite; Py-Pyrite; Po-Pyrrhotite; CpyChalcopyrite). Ore minerals

S (wt%)

Au (ppm)

Fe (wt%)

Co (ppm)

Ni (wt%)

As (wt%)

Sb (wt%)

Cu (wt%)

Zn (ppm)

Te (ppm)

Asp I Asp I Asp II Asp II Asp III Asp III Py I Py I Py II Py II Py III Py III Po Po Po Po Cpy Cpy Arsenian Ullmannite Arsenian Ullmannite Gersdorffite Gersdorffite

21.7 22.1 21.9 21.3 22.0 21.9 54.0 54.0 55.1 55.1 52.8 52.8 39.7 40.0 39.0 41.0 36.1 36.1 15.5 15.4 17.3 17.4

3600 1600 1300 1200 900 1200 2700 2100 1300 1500 700 900 2400 2600 2200 2300 2000 1100 – – – –

34.2 35.1 34.0 34.1 35.1 35.2 46.0 46.1 45.0 45.0 47.1 46.9 59.1 59.2 60.1 58.1 30.0 30.0 0.2 – 0.6 0.9

– 1000 – – 1300 1000 – 2000 – – – – – 1200 – 1200 – – – – – –

0.1 – – – – – 0.3 0.1 0.4 0.4 – – 0.2 0.2 0.3 0.8 – – 31.7 32.5 38.1 37.0

43.9 43.4 44.8 44.8 43.4 43.4 – 0.2 – 0.1 – – – – 0.1 – – – 7.2 5.8 39.0 38.8

– 0.5 – – 0.5 0.5 – – 0.1 – 0.2 – – – – 0.6 – – 47.3 47.8 5.3 5.6

– – – – – – – 0.1 – – – – – – – – 33.9 34.9 – – 0.6 0.9

– – – – – – – – – – – – – – 600 – – 900 – – – –

– 2200 3300 3100 2000 2000 – – – – – – – – – – – – – – – –

142

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

Fig. 6. BSE image showing micro-scale gold inclusions/substrates within the zoned and perforated pyrite (a and b); loellingite occurring at the core of a deformed arsenopyrite (c); substrates of gold within the arsenic rich core of a zoned arsenopyrite (d); variation in arsenic content exhibited by different grey shades and gold inclusions within the zoned and perforated arsenopyrite (e) and distribution of micro inclusions of gold within the arsenic rich core of a zoned arsenopyrite (f).

6.2. Type-II pyrite This variety has limited distribution and occurs as isolated grains having larger sizes. The pyrite grains are perfectly euhedral in form and are not affected by any deformational features exhibiting growth zoning with silicate inclusions (Figs. 4d, 5a and b). Gold inclusions ranging from 2 lm to 50 lm size are seen within the zoned portions and micro-cracks of the pyrite grains (Fig. 6a and b). The lattice-bound gold content is much lower than the Py-I and with a marked decrease in As content is noticed in this type of pyrite, suggesting the relationship of As and Au in pyrite from earlier to later pyritic phases. These pyrite grains are common in the interface zones of the carbon-phyllite, graphitized schist ad chlorite schist. 6.3. Type-III pyrite This type of pyrite grains are typically euhedral and cubic in nature without any evidence of deformation (Fig. 4b) and are mostly associated with pyrrhotite and chalcopyrite. In majority of the samples, they are embedded by pyrrhotite grains. EPMA data from this

type of pyrite yield much lesser distribution of lattice-bound gold with no trace of arsenic content with gold concentration varies from 600 to 900 ppm (Table 1). 6.4. Type-I arsenopyrite The Asp-I grains are euhedral and deformed in nature which share mutual boundaries with pyrite and pyrrhotite (Fig. 5d). Deformational fabric is evident in this type of arsenopyrite grains resulting shattering and displacement of the rhombohedra (Fig. 6c). In carbonaceous phyllite and talc–chlorite schist, the rhombic arsenopyrite grains are larger in size and coexist with pyrrhotite. In the quartz–sulfide veins, the sizes of the rhombs decrease and are embedded by pyrrhotite. The invisible gold varies from 2700 to 3600 ppm and Ni varies between 1000 and 1200 ppm. 6.5. Type-II arsenopyrite Type-II arsenopyrite show very well developed growth zoning with a loellingite core (Figs. 6d–f and 7). In this study, the presence

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

143

Fig. 7. EPMA elemental mapping on arsenopyrite and pyrrhotite showing the relationships of Fe, As, S and Au distribution and lattice-bound/invisible gold distribution within the zoned arsenopyrite. Figure also clearly demarcates the occurrence of sulfur deficient loellingite within the core of zoned arsenopyrite containing refractory grains of gold particles.

of loellingite is being reported for the first time from this deposit and it is commonly found along the core of the arsenopyrite grains (Fig. 6c). Micro inclusions of gold particles are clearly seen as EPMA–BSE image within the zoned arsenopyrite–loellingite assemblage. Some cracks developed within the zoned arsenopyrite which are filled with silicate gangue minerals and have elongated/ deformed forms suggesting that the arsenopyrite was deposited prior to metamorphic and deformational episodes. The arsenopyrite-II is associated with sphalerite along with pyrite-II and pyrrhotite to a lesser extent. The invisible gold in type-II arsenopyrite varies from 1900 to 2200 ppm which contains high amount of Te (2000–3300 ppm) along with high values of Ni and Co (Table 1).

6.6. Type-III arsenopyrite The arsenopyrite-III grains are very well developed exhibiting finer idiomorphic crystals with characteristic rhombs without any zoning (Fig. 5e). The invisible gold in type II arsenopyrite varies from 900 to 1300 ppm with higher concentration of Sb (4800– 5000 ppm) and 1000 –1300 ppm Co (Table 1).

7. Discussion The presence of both lattice-bound gold and native gold along with nano-scale inclusions of gold within sulfide minerals envisages complicated evolution of gold mineralization (Deditius et al., 2011). These forms are spatially and genetically different from each other and might have formed at various stages, possibly evolved from compositionally contrasting mineralizing fluid in phases. Several workers have proposed various theories for considering the mechanism of gold precipitation within sulfides. In substitutional mechanism, Au might occupy the As sites owing to the similarity in radii of these elements when bonded covalently (Boyle, 1979). Cook and Chryssoulis (1990) suggested that the As substitution in pyrite leads to (AsS)3 anion pairs and the charge may be balanced by the substitution of Fe2+ by Au3+, Sb3+ or As3+. The replacement of Fe sites by Au has been proposed by Arehart et al. (1993) and suggested coupled substitution mechanism of Au for Fe, As for S or 1Au + 1As for 2Fe for gold bearing arsenianpyrite. Tossell et al. (1981) suggested that the Co and Ni-bearing mineral analogues of arsenopyrite, namely CoAsS (cobaltite) and NiAsS (gersdorffite), adopt the pyrite structure and the Sb-bearing

144

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

Co and Ni arsenopyrite analogues such as CoSbS and NiSbS (ullmannite) could also adopt the pyrite structure. Besides loellingite (FeAs2), some complex mineral assemblages like pentlandite (as flames within pyrrhotite), native silver, gersdorffite (NiAsS) and arsenian-ullmannite {Ni(As, Sb)S} are also present in the deposit (Fig. 5f), which may explain the complexity of the mineral phases associated with gold. Based on the studies from Campbell Mine, Ontario, Tarnocai et al. (1997) suggested that the Au enrichment has taken place with relative depletion of Fe, which could possibly imply that Au substitute Fe rather than As in the sulfide minerals. Constant (As + S)atomic ratio (66 at.%) and an increase in the (As/S)atomic ratios within the Au-rich rims/zones is suggestive of Fe substitution by Au rather than As substitution (Figs. 6–8). The substitution

mechanism of Au in arsenopyrite, pyrrhotite and pyrite is very similar and wider variation in numbers of S and As neighbours could result in a wider range of isomer shift from 197Au Mossbauer results (Friedl et al., 1995). Mishra et al. (2001) have proposed that Au3+ substituted Fe3+ for gold precipitation as invisible gold from a central Indian gold prospect. Saha and Venkatesh (2002) suggested a similar mechanism for the precipitation of invisible gold within sulfides from Hutti–Maski gold deposit of south India. Based on these observations, it is highly possible that Au substitutes the Fe sites within the sulfides from the study area as it occurs in a wide variety of sulfide mineral phases including loellingite. This is based on the fact that the lattice-bound gold is not only restricted within arsenopyrite but is also present in other sulfides containing Fe cations (for example, high Au value in pyrite, pyrrhotite and chalcopyrite, Table 1). Analytical data show wide variability in the content of lattice-bound gold in arsenopyrite, pyrite pyrrhotite and chalcopyrite. This may be due to the fluctuating physiochemical conditions for deposition of gold depending on the activity and fugacity of sulfur and redox condition. Hence co-precipitation of Au with arsenopyrite is a surface phenomenon rather than equilibrium between fluid and the interior of the precipitating arsenopyrite crystal (Genkin et al., 1998). The fluctuating physiochemical conditions are further supported by the observation of the variability in As/S ratio in arsenopyrite (Fig. 8), which implies oscillating sulfur activity and temperature (Barton, 1970). The sulfur fugacity, log f (S2) value derived from pyrite-pyrrhotite-arsenopyrite assemblage ranges from 9.7 to 7.5 and corroborates the fluctuation of sulfur activity resulting loellingite formation at the core of the arsenopyrite grains. The precipitation of lattice-bound gold in arsenopyrite, loellingite and pyrite by a plausible (Fe, Au)+3 = (AsS)3 substitution mechanism may have facilitated by rapid, non-equilibrium conditions involving pressure decreases and wall-rock reactions predominantly sulfidation and carbonatization (Ashley et al., 2000) as observed in the study area. 7.1. Zoned pyrite and arsenopyrite and their bearing on Au mineralization

Fig. 8. (a) Atomic% of S vs atomic% of As in arsenopyrite showing negative correlation and (b) positive but weak correlation of Au at.% vs As/S at.% suggest the gold enrichment in the higher arsenic concentration zone (core region and in loellingite) and low concentration of arsenic at the peripheral regions; (c) Fe at.% vs Au at.% showing positive correlation suggest the substitution of Fe by Au.

In the study area, the lattice-bound gold content distribution varies in a wide variety of sulfides, the maximum being in arsenopyrite (3600 ppm); followed by pyrrhotite (3300 ppm), then in pyrite (2300 ppm) and in chalcopyrite (1900 ppm) as shown in Table 1. Even within the same mineral, large variation has been observed suggesting heterogeneous distribution of gold. The refractory gold content of the loellingite which forms the core of the zoned arsenopyrite is higher than the concentration within the surrounding arsenopyrite regions (Figs. 6 and 8). The occurrence of micro to nano-scale gold inclusions along the arsenopyrite–loellingite interface could be explained as an initial phase that has been incorporated as invisible gold within loellingite, then locally exsolved during retrogression of loellingite to arsenopyrite and finally by formation of rich ore shoots containing high gold values (nuggets). These observations suggest that the gold was scavenged from the loellingite during the retrogression to arsenopyrite and deposited within the cracks and interface zones between loellingite and arsenopyrite in the form of nano-scale inclusions (Fig. 6). These sulfides are present along the shear fractures that are strongly controlled by the effect of shearing and thus the primary gold could have co-precipitated with arsenopyrite and pyrite as a solid solution in sulfide and sulfarsenide minerals (Mumin et al., 1994). Abraitis et al. (2004) indicated that solid solution between pyrite and the Co- and Ni-bearing mineral phases are partly responsible for As incorporation in the pyrite lattice. The lattice-bound gold content in the zoned pyrite and arsenopyrite (type II forms) is relatively much lower than the un-zoned members. In the zoned varieties, nano-scale inclusions or

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

substrates of gold within the cracks of the zoned arsenopyrite and pyrite have been observed. The relation between the lattice-bound gold and inclusions of gold can be interpreted as the expulsion from the lattices of the type-I arsenopyrite and pyrite and simultaneous precipitation of nano-scale gold inclusions which could have resulted during the metamorphic and deformational episodes. 7.2. Geothermometry and sulfur fugacity 7.2.1. Loellingite–arsenopyrite and arsenopyrite + pyrite + pyrrhotite thermometry The temperature–composition estimates from the arsenopyrite–loellingite mineral assemblage indicates that the formation of minerals have taken place at 550–600 °C (Figs. 9 and 10). However, there may be some limitations of applicability of these thermometry results as increase in pressure will decrease the arsenic content of arsenopyrite coexisting with loellingite and will increase the upper stability of arsenopyrite coexisting with pyrite by approximately at 14 °C/kbar (Sharp et al., 1985). Arsenopyrite compositions in the f (S2) buffered assemblage (arsenopyrite + pyrite + pyrrhotite) yields temperature range of 375–390 °C at log f (S2) = 9.7 to 7.5 (Kretschmar and Scott, 1976; Sharp et al., 1985). Binary temperature composition plots show

145

arsenopyrite composition as a function of temperature and equilibrium mineral assemblage (Figs. 9 and 10). The overall temperature of formation, fugacity and mineral assemblage suggest a mesothermal depositional condition like many typical Archean greenstonehosted orogenic lode gold deposit. Further, it is surmised that sub-microscopic gold is incorporated into the crystal lattices of arsenopyrite and pyrite at greenschist to lower amphibolite-facies temperatures (Mikhlin et al., 2011), that is progressively expelled as inclusions and as fracture fillings as native gold in sulfides, and ultimately into the thick silicate/carbonate zone, as recrystallization proceeds through mesothermal gold window temperature/pressure conditions, predominantly during deformation and burial. Thus, the reconstitution mechanism of refractory gold holds valid for Kundarkocha gold deposit. 7.3. Evolution of gold mineralization 7.3.1. Lattice-bound gold in pyrite and arsenopyrite Presence of lattice-bound gold has been noticed in arsenopyrite and pyrite phases, and relatively lesser in pyrrhotite from Kundarkocha gold deposit of Gorumahisani–Badampahar schist belt. The lattice-bound gold content in pyrite and arsenopyrite varies from 600 to 2700 ppm and 900 to 3600 ppm respectively and

Fig. 9. Binary temperature composition plot showing arsenopyrite composition in the f (S2) buffered arsenopyrite + pyrite + pyrrhotite assemblage (Fields are after Kretschmar and Scott, 1976).

146

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

phases may be explained by electrochemical accumulation or chemisorption process (Cabri et al., 1989, 2000). The process might have played a vital role as a depositional mechanism for gold on the sulfide surfaces or within the cracks and fractures of the sulfide grains or at the sulfide grain boundaries. In chemisorption process, the gold is precipitated simultaneously or along with pre-existing sulfide minerals by half cell reactions (Jean and Bancroft, 1985; Starling et al., 1989):

AuðHSÞ2 þ e ! Au0 þ 2HS

Fig. 10. Binary diagram showing the fugacity range at a temperature range of 375– 390 °C for the coexisting arsenopyrite–pyrite–pyrrhotite assemblage from Kundarkocha gold mine (Fields are after Sharp et al., 1985).

increase in the concentration of such refractory gold is seen from chalcopyrite > pyrrhotite > pyrite > loellingite and arsenopyrite. The gold deposition has taken place in three forms: as invisible, as substrates and as final stage native gold/nuggets. Various mechanisms have been proposed by many earlier workers (Boyle, 1979; Arehart et al., 1993; Cardile et al., 1993; Fleet et al., 1993; Mumin et al., 1994; Tarnocai et al., 1997; Genkin et al., 1998; Mishra et al., 2001; Saha and Venkatesh, 2002; Chouinard et al., 2005; Paktunc et al., 2006; Morey et al., 2008; Deol et al., 2012; Hazarika et al., 2013) for the precipitation of invisible gold. The most plausible mechanism proposed at this schist belt appears to be the replacement of Fe+3 sites by Au+3 based on textural assemblages, mineralogical and mineral–chemical composition and element–element correlation patterns (Fig. 8). There is a marked variation in the refractory content of these sulfides formed at different stages. Type-I pyrite and arsenopyrite contain the maximum concentration of lattice-bound gold (1600–2700 ppm in Py-I and 2700– 3600 ppm in Asp-I), whereas the type-II pyrite and arsenopyrite contain considerably lower invisible Au content and are very often zoned in nature. The type-III pyrite and arsenopyrite contain very less amount of lattice-bound gold (600–900 ppm in Py-III and 900–1300 ppm in Asp-III). From these observations, it is clear that during evolution from type I to type III pyrite and arsenopyrite, lose or expel considerable amounts of lattice-bound gold from their lattices mostly owing to changes in the metamorphism and hydrothermal processes, whose, possible mechanism is schematically depicted in Fig. 11. 7.3.2. Reconstitution of lattice-bound refractory gold Type II pyrite and arsenopyrite contain lesser amounts of lattice-bound gold compared to type I variety and ubiquitously nano-scale inclusions are seen along the zoned portions and micro cracks. Expulsion of lattice-bound gold within the sulfides is followed by reconstitution leading to the formation of nano to micro-scale inclusions of gold underlying stage-wise generation. The mechanism of different forms of gold occurrences within the sulfides and the inter-granular spaces within silicate–carbonate

ð1Þ

In the electrochemical accumulation, visible and refractory gold is preferentially accumulated on the individual domains of sulfide surfaces that act as cathodes i.e., p-type conductors (for e.g., arsenopyrite/pyrite after doping As in pyrite and in n–p junctions (Moller and Kerstein, 1994). Micro-scale gold might have been precipitated on p-type arsenopyrite as a result of sulfidation of loellingite (n-type); (Moller and Kerstein, 1994; Deol et al., 2012). An alternative explanation given by Neumayer et al. (1993) suggests that the formation of gold is situated at loellingite–arsenopyrite boundaries. The mechanism of gold precipitation may be explained by the introduction of lattice-bound gold along with loellingite and is locally exsolved during the retrogression of loellingite to arsenopyrite based on the EPMA data. Hence, it is evident that the latticebound gold concentration is more in the core regions (loellingite) of the zoned arsenopyrite than along the peripheral zones (Fig. 6d–f). Nano-scale gold could have been precipitated predominantly on arsenopyrite (both in type-I and type- II varieties) as a result of sulfidation of loellingite. Sulfidation can be considered as a dominant process for the gold deposition (Neall and Phillips, 1987; McCuaig and Kerrich, 1998; Phillips and Powell, 2010). The process involves in the consumption of H2S and S from the gold-sulfide complexes while reacting with the wall-rocks (Phillips and Groves, 1983). Thus the loss of sulfur destabilizes the gold complexes. The Fe–Mg rich host rock composition greatly facilitates the breakdown of the Fe–Mg-bearing silicates (e.g., chlorite, actinolite, epidote and serpentine as seen from the study area) to form pyrite and in turn leading to the destabilization of gold complexes in solution (Neall and Phillips, 1987; Bohlke, 1989), as explained in the following equation:

Fe6 Si4 O10 ðOHÞ8 þ 6HAuðHSÞ2 þ 1:5O2 ¼ 6 Au þ 6FeS2 þ 4SiO2 þ 13 H2 O

ð2Þ

Chlorite þ Au  S complex þ O2 ¼ Au þ pyrite þ quartz þ H2 O ð3Þ +3

In the Kundarkocha gold belt, the substitution of Fe by Au+3 within the sulfidic sites, adsorption-reduction and wall-rock sulfidation and phase immiscibility may be the plausible mechanisms for the refractory gold, microscopic substrates and rich nuggets respectively (Figs. 7 and 8). 7.3.3. Deposition of native gold The third stage of gold deposition (i.e. the native gold) is perhaps responsible for the formation of economically viable gold deposit in the study area. Elsewhere in other deposits, Au values locally range as high as 1000–4900 ppm within arsenopyrite and pyrite (Fleet et al., 1993; Mishra et al., 2001; Saha and Venkatesh, 2002). At Kundarkocha, these high Au values in sulfide minerals are sufficient enough to form a viable deposit. It can be interpreted that the dominant phases of the gold deposition according to the gold budget has been precipitated as refractory form within sulfides in the very early stage. Thus, remobilization and redistribution of the lattice-bound gold is the primary mechanism for the deposition of native gold along with the further input of gold from hydrothermal influx resulted from deformational and

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

147

Fig. 11. Sequential formation mechanism of rich nuggets from invisible gold in sulfides by remobilization, redistribution and concentration (after Mumin et al., 1994; Saha and Venkatesh, 2002).

metamorphic changes. The majority of the invisible gold migrates first towards the fractures and voids within the sulfides (during reconstitution), then to the grain boundaries and ultimately migrates out of the host sulfides whereas some of them within the sulfides may represent a remnant phase (Fig. 11). The post depositional remobilization, reconstitution and concentration depends on various factors such as hydrothermal fluid influx, physiochemical conditions (Eh, pH, activity of ions), host minerals (grain size, refractory nature), deformation, metamorphism and fluid-rock interaction (Tomkins and Mavrogenes, 2001; Deol et al., 2012). The deposition of native gold (including visible inclusions within sulfides) is probably due to the adsorption mechanism because at higher temperature and low oxygen fugacity, the heavier minerals are concentrated to the sulfide interfaces (Jean and Bancroft, 1985, 1986; Hyland and Bancroft, 1989; Knipe et al., 1992). The higher sulfur fugacity values obtained from the pyrite-pyrrhotite-arsenopyrite assemblages from study area ranges from 9.7 to 7.5 that could have provided the necessary conditions for the precipitation of gold. Experimentally, it has been demonstrated that chloride complexes of Au+3 and Au+1 adsorb by pyrite pyrrhotite and sphalerite, thio-Au+1 complexes by amorphous As2S3 (Seward, 1973; Jean and Bancroft, 1985; Renders and Seward, 1989), or by electrochemical accumulation of gold on arsenopyrite and pyrite (Moller and Kerstein, 1994). A common feature has been found at Kundarkocha gold deposit that gold is localized along loellingite–arsenopyrite boundary interface within the zoned-arsenopyrite (Fig. 6). Gold is initially introduced as lattice-bound gold within loellingite, then locally exsolved during retrogression of loellingite to arsenopyrite. The formation of rich ore shoots containing high gold values (nuggets) could have formed due to further remobilization and concentration during the late stage of native gold deposition.

8. Conclusions Gold mineralization at Kundarkocha is associated with the quartz–carbonate–sulfide veins emplaced within a variety of meta-volcano-sedimentary package including the carbonaceous phyllite, graphitic schist, talc–chlorite–serpentine schist along with gabbroic intrusion. The mineralization is controlled by the localized shearing that could have acted as a conduit for the mobilization of hydrothermal fluid. Because of the pervasive nature and reducing behavior of the carbon-phyllite and graphitic schist, these

litho-units might have played key role in the concentration of gold mineralization. On the basis of texture, morphology and chemistry of sulfide phases, three types of pyrite and arsenopyrite mineral phases have been established from the Kundarkocha gold deposit. Each type has a differential genetic relationship with the gold partitioning. The type I pyrite and arsenopyrite have highest lattice-bound gold contents and are deformed. The type II pyrite and arsenopyrite are frequently zoned in nature, perforated and bears the nano-scale gold inclusions because of the expulsion from the lattices of the type I sulfides and followed by simultaneous deposition along the zoned portions and the micro cracks. The type III pyrite and arsenopyrite are the youngest ones and bear very low lattice-bound gold contents and are least affected by deformational features with perfect grain boundaries. Hence sequential evolution of free milling gold from the lattice-bound gold trapped in the earlier sulfides, through expulsion and reconstitution during metamorphism and hydrothermal episodes, is established in the Kundarkocha gold deposit. It may be further suggested that the dominant phase of the gold deposition according to the available gold budget could have been precipitated as refractory form within arsenopyrite–loellingite assemblage in the early stages. Thus, remobilization and redistribution of the lattice gold is the primary mechanism for the deposition of rich lodes aided by further input of gold from hydrothermal influx resulted from deformational and metamorphic changes in the meta-volcano-sedimentary sequence of Kundarkocha. It is also observed that consistent distribution of gold occurs in pyrite whereas in arsenopyrite, the variation of lattice-bound gold is higher as compared to the pyrite grains suggesting relatively effective scavenging of lattice-bound gold from arsenopyrite/loellingite assemblage. Pyrrhotite also contains substantial latticebound gold content and it is presumed that the gold deposition could have been taken place at a relatively higher temperature. Presence of gersdorffite and arsenian-ullmannite has a strong indication of magmatic-hydrothermal activity in the area. The wide range of temperature of formation for the sulfides from 375 to 600 °C, as derived from the pyrite–arsenopyrite–pyrrhotite and arsenopyrite–loellingite thermometry reflects the prograde and retrograde metamorphic changes at Kundarkocha, which was responsible for the precipitation of native gold from the refractory gold stage. The precipitation of refractory gold in arsenopyrite, loellingite and pyrite may have facilitated by rapid, non-equilibrium conditions involving pressure decreases and wall-rock reactions, sulfidation and carbonatization as observed in the study area. The

148

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149

primary gold could have co-precipitated along with arsenopyrite/ loellingite and pyrite as solid solution in sulfide and sulfarsenide mineral assemblages. Micro to nano scale gold localization at loellingite–arsenopyrite boundary interface within the zoned arsenopyrite suggests that gold is initially introduced as lattice-bound gold within loellingite, then locally exsolved during retrogression of loellingite to arsenopyrite and the formation of rich ore shoots containing high gold values (nuggets), may be due to further remobilization and concentration during the late stage of native gold deposition. A three stage evolution process has been advocated for the gold deposition commencing from (a) initial co-precipitated of latticebound gold within arsenopyrite, loellingite and pyrite as a solid solution followed by, (b) expulsion, remobilization and reconstitution of lattice-bound gold due to destabilization of gold-sulfide complexes. At this stage, most of the gold content occurs as substrates within the zoned portions and perforated pyrite and arsenopyrite phases and (c) finally expulsion of the native gold from the sulfide systems to get precipitated along the grain boundaries or within the quartz–carbonate veins.

Acknowledgements The authors would like to thank the authorities of M/S Manmohan Mineral Industries Pvt. Ltd. for giving access to the mine, permission to collect samples and providing necessary facilities. We are thankful to Dr. K.L. Pruseth for the electron probe analysis at Indian Institute of Technology, Roorkee. P.R. Sahoo is thankful to ISM for the Ph. D fellowship. The authors are also thankful to the Director, ISM for the facilities. Thanks are due to Prof. Neil Phillips, Prof. Ryan Mathur and anonymous reviewers for their critical reviews and constructive suggestions. We are grateful to Prof Bor-ming Jahn and Prof J.G. Liou for their editorial comments to improve the ms.

References Abraitis, P.K., Pattrick, R.A.D., Vaughan, D.J., 2004. Variations in the compositional, textural and electrical properties of natural pyrite: a review. Int. J. Miner. Process. 74, 41–59. Acharyya, S.K., Gupta, A., Orihashi, Y., 2010a. New U–Pb zircon ages from Paleo– Mesoarchean TTG gneisses of the Singhbhum Craton, eastern India. Geochem. J. 44, 81–88. Acharyya, S.K., Gupta, A., Orihashi, Y., 2010b. Neoarchean–Paleoproterozoic stratigraphy of the Dhanjori basin, Singhbhum Craton, Eastern India: and recording of a few U–Pb zircon dates from its basal part. J. Asian Earth Sci. 39, 527–536. Arehart, G.B., Chryssoulis, S.L., Kesler, S.E., 1993. Gold and arsenic in iron sulfides from sediment hosted disseminated gold deposits: implications for depositional processes. Econ. Geol. 88, 171–185. Ashley, P.M., Creagh, C.J., Ryan, C.G., 2000. Invisible gold in ore and mineral concentrates from the Hillgrove gold–antimony deposits, NSW, Australia. Miner. Deposita 35, 285–301. Baidya, T.K., 1996. Prospects of gold in some areas of the Eastern Indian Shield. National workshop on exploration of gold resources of India, held at National Geophysical Research Institute, Hyderabad from 2nd to 4th December, pp. 165– 169. Banerjee, A.K., Thiagarajan, T.A., 1965. Progress report of investigation of gold at Kundarkocha Singhbhum district, Bihar. Bull. Geol. Survey India Ser. A 38, 106. Barton Jr., P.B., 1970. Sulfide Petrology: Mineralogical Society of America Special Paper 3, 187–198. Bhattacharya, H.N., Chakraborty, I., Ghosh, K.K., 2006. Geochemistry of some banded iron formations of the Archean supracrustals, Jharkhand-Orissa region, India. J. Earth Syst. Sci. 116, 245–259. Bhattacharya, H.N., Mahapatra, S., 2008. Evolution of the proterozoic rift margin sediments-North Singhbhum Mobile Belt. Precambr. Res. 162, 302–316. Bohlke, J.K., 1989. Comparison of metasomatic reactions between a common CO2rich vein fluid and diverse wall rocks: intensive variables, mass transfers and Au mineralization at Alleghany, California. Econ. Geol. 84, 291–327. Boyle, R.W., 1979. The geochemistry of gold and its deposits. Geol. Survey Canada Bull. 280, 584. Cabri, L.J., Chryssoulis, S.L., de Villiers, J.P.R., Laflamme, J.H.G., Buseck, P.R., 1989. The nature of ‘‘invisible’’ gold in arsenopyrite. Can. Mineral. 27, 353–362.

Cabri, L.J., Newville, M., Gordon, R.A., Crozier, E.D., Sutton, S.R., McMahon, G., Jiang, D., 2000. Chemical speciation of gold in arsenopyrite. Can. Mineral. 38, 1265– 1281. Cardile, C.M., Cashion, J.D., McGrath, A.C., Renders, P.J., Seward, T.M., 1993. 197Au Mossbauer study of Au2S and gold adsorbed onto As2S3 and Sb2S3 substrates. Geochim. Cosmochim. Acta 57, 2481–2486. Chouinard, A., Paquette, J., Williams-Jones, A.E., 2005. Crystallographic controls on trace-element incorporation in auriferous pyrite from the Pascua epithermal high-sulfidation deposit, Chile–Argentina. Can. Mineral. 43, 951–963. Cook, N.J., Chryssoulis, S.L., 1990. Concentrations of ‘‘invisible gold’’ in the common sulfides. Can. Mineral. 28, 1–16. Deditius, A.P., Utsunomiya, S., Reich, M., Kesler, S.E., Ewing, R.C., Hough, R., Walshe, J., 2011. Trace metal nanoparticles in pyrite. Ore Geol. Rev. 42, 32–46. Deditius, A.P., Reich, M., Kesler, S.E., Utsunomiya, S., Chryssoulis, S.L., Walshe, J., Ewing, R.C., 2014. The coupled geochemistry of Au and As in pyrite from hydrothermal ore deposits. Geochim. Cosmochim. Acta 140, 644–670. Deol, S., Deb, M., Large, Ross R., Gilbert, S., 2012. LA–ICPMS and EPMA studies of pyrite, arsenopyrite and loellingite from the Bhukia-Jagpura gold prospect, southern Rajasthan, India: implications for ore genesis and gold remobilization. Chem. Geol. 326–327, 72–87. Fleet, M.E., Chryssoulis, S.L., MacLean, P.J., Davidson, R., Weisener, C.G., 1993. Arsenian pyrite from gold deposits; Au and As distribution investigated by SIMS and EMP, and color staining and surface oxidation by XPS and LIMS. Can. Mineral. 31, 1–17. Friedl, J., Wagner, F.E., Wang, N., 1995. On the chemical state of combined gold in sulfide ores: conclusions from Mossbauer source experiments. Neues Jahrb. Mineral. Abh. 169, 279–290. Genkin, A.D., Bortnikov, N.S., Cabri, L.J., Wagner, F.E., Stanley, C.J., Safonov, Y.G., McMahon, G., Freidl, J., Kerzin, A.L., Gamyanin, G.N., 1998. A multidisciplinary study of invisible gold in arsenopyrite from four deposits in Siberia, Russian federation. Econ. Geol. 93, 463–487. Ghose, N.C., 1996. Gold occurrences and its potentiality in Bihar. National workshop on exploration of gold resources of India held at National Geophysical Research Institute, Hyderabad from 2nd to 4th December, 1996: Conference volume 214– 227. Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit. Ore Geol. Rev. 13, 7–27. Hazarika, P., Mishra, B., Chinnasamy, S.S., Bernhardt, H.J., 2013. Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India. Ore Geol. Rev. 55, 134–145. Hyland, M.M., Bancroft, G.M., 1989. An XPS study of gold deposition at low temperatures on sulfide minerals; reducing agent. Geochim. Cosmochim. Acta 53, 367–372. Jean, G.E., Bancroft, G.M., 1985. An XPS and SEM study of gold deposition at low temperatures on sulfide minerals: concentration of gold by adsorption– reduction. Geochim. Cosmochim. Acta 49, 979–987. Jean, G.E., Bancroft, G.M., 1986. Heavy metal adsorption by sulfide mineral surfaces. Geochim. Cosmochim. Acta 50, 1455–1463. Knipe, S.W., Foster, R.P., Stanley, C.J., 1992. Role of sulfide surfaces in adsorption of precious metals from hydrothermal fluids. Inst. Min. Metall. Trans., Sec. B, Appl. Earth Sci. 101, B83–B88. Kretschmar, U., Scott, S.D., 1976. Phase relations involving arsenopyrite in the system Fe–As–S and their application. Can. Mineral. 14, 364–386. Large, R.R., Danyushevsky, L.V., Hollit, C., Maslennikov, V., Meffre, S., Gilbert, S., Bull, S., Scott, R., Emsbo, P., Thomas, H., Foster, J., 2009. Gold and trace element zonation in pyrite using a laser imaging technique: implications for the timing of gold in orogenic and carlin-style sediment-hosted deposits. Econ. Geol. 104, 635–668. Large, R.R., Bull, S.W., Maslennikov, V.V., 2011. A carbonaceous sedimentary source rock model for Carlin-type and orogenic gold deposits. Econ. Geol. 106, 331– 358. Mahadevan, T.M., 2002. Geology of Bihar and Jharkhand: geological society of India, Bangalore, p. 563. McCuaig, T.C., Kerrich, R., 1998. P-T-t-deformation-fluid characteristics of lode gold deposits: evidence from alteration systematics. Ore Geol. Rev. 12, 381–453. Mikhlin, Y., Romanchenko, A., Likhatski, M., Karacharov, A., Erenburg, S., Trubina, S., 2011. Understanding the initial stages of precious metals precipitation: nanoscale metallic and sulfidic species of gold and silver on pyrite surfaces. Ore Geol. Rev. 42, 47–54. Mishra, T., Jose, B., Deepa, K.K., Sreehari, S.M.S., Venkatesh, A.S., 2001. Auriferous mineralization in the Sakoli Group, Central India, with particular reference to sulfide-bound gold. Tran. IMM, Sec. B, Appl. Earth Sci. 110, B103–B109. Misra, S., 2006. Precambrian chronostratigraphic growth of Singhbhum–Orissa craton, Eastern Indian shield: an alternative model. J. Geol. Soc. India 67, 356– 378. Moller, P., Kerstein, G., 1994. Electrochemical accumulation of visible gold on pyrite and arsenopyrite surfaces. Miner. Deposita 29, 404–413. Mondal, S.K., 2009. Chromite and PGE deposits of Mesoarchean ultramafic–mafic suites within the greenstone belt of Singhbhum Craton, India: implications for mantle heterogeneity and tectonic setting. J. Geol. Soc. India 73, 36–51. Morey, A.A., Tomkins, A.G., Bierlein, F.P., Weinberg, R.F., Davidson, G.J., 2008. Bimodal distribution of gold in pyrite and arsenopyrite: examples from the Archean Boorara and Bardoc shear systems, Yilgarn Craton, Western Australia. Econ. Geol. 103, 599–614.

P.R. Sahoo, A.S. Venkatesh / Journal of Asian Earth Sciences 97 (2015) 136–149 Mukhopadhyay, D., 2001. The Archean Nucleus of Singhbhum: the present state of knowledge. Gondwana Res. 4, 307–318. Mukhopadhyay, J., Beukes, N.J., Armstrong, R.A., Zimmermann, U., Ghosh, G., Medda, R.A., 2008. Dating the oldest greenstone in India: a 3.51 Ga precise U–Pb SHRIMP zircon age for dacitic lava of southern Iron Ore Group, Singhbhum Craton. J. Geol. 116, 449–461. Mumin, A.H., Fleet, M.E., Chryssoulis, S.L., 1994. Gold mineralization in As-rich mesothermal gold ores of the Bogosu–Prestea mining district of the Ashanti Gold Belt, Ghana: remobilization of ‘‘invisible’’ gold. Miner. Deposita 29, 445–460. Neall, F.B., Phillips, G.N., 1987. Fluid-wallrock interaction around Archean hydrothermal gold deposits: a thermodynamic model. Econ. Geol. 82, 1679– 1694. Neumayer, P., Cabri, L.J., Groves, D.I., Mikucki, E.J., Jackman, J.A., 1993. The mineralogical distribution of gold and relative timing of gold mineralization in two Archean settings of high metamorphic grade in Australia. Can. Mineral. 31, 711–725. Paktunc, D., Kingston, D., Pratt, A., McMullen, J., 2006. Distribution of gold in pyrite and in products of its transformation resulting from roasting of refractory gold ore. Can. Mineral. 44, 213–227. Pal, S.K., Majumdar, T.J., Bhattacharya, A.K., 2006. Extraction of linear and anomalous features using ERS SAR data over Singhbhum Shear Zone, Jharkhand using fast Fourier transform. Int. J. Remote Sens. 27, 4513–4528. Philbert, J., 1963. X-Ray Optics and X-Ray Micro Analysis. Academic Press, New York, p. 329. Phillips, G.N., Groves, D.I., 1983. The nature of Archaean gold-bearing fluids as deduced from gold deposits of Western Australia. J. Geol. Soc. Aust. 30, 25–39. Phillips, G.N., Powell, R., 2010. Formation of gold deposits: a metamorphic devolatilization model. J. Metamorph. Geol. 28, 689–718. Renders, P.J., Seward, T.M., 1989. The adsorption of thio gold (I) complexes by amorphous As2S3 and Sb2S3 at 25 and 90 °C. Geochim. Cosmochim. Acta 53, 255–267. Saha, A.K., 1994. Crustal evolution of Singhbhum–North Orissa, Eastern India. Memoir 27, Geological Society of India, Bangalore, p. 341. Saha, A.K., Ray, S.I., Sarkar, S.N., 1988. Early history of the Earth: evidence from the eastern Indian shield. In: Mukhopadhyay, D. (Ed.), Precambrian of the eastern Indian shield. Journal of the Geological Society of India, vol. 8, pp. 13–37. Saha, I., Venkatesh, A.S., 2002. Invisible Gold within sulfides from Archean Hutti– Maski schist belt, Southern India. J. Asian Earth Sci. 20, 449–457. Sahoo, P.R., 2012. Metallogenetic aspects of gold mineralization in and around Kundarkocha area of the Singhbhum Orogenic belt, eastern India. Unpublished Ph. D thesis submitted to Indian School of Mines, Dhanbad, p. 247.

149

Sahoo, P.R., Prasad, J., Prakasam, M., Singh, S., Venkatesh, A.S., 2010. Orogenic gold mineralization in and around Kundarkocha, east Singhbhum, Jharkhand. J. Indian Acad. Geosci. 52, 11–18. Sarkar, S.N., Saha, A.K., 1962. A revision of the Precambrian stratigraphy and tectonics of Singhbhum and adjacent region. Quaternary J. Geol. Mineral. Metall. Soc. India 34, 97–136. Sarkar, S.N., Saha, A.K., Miller, J.A., 1969. Geochronology of the Precambrian rocks of Singhbhum and adjacent region, Eastern India. Geological Magazine 106, 13–45. Sengupta, S., Corfu, E., McNutt, R.H., Paul, D.K., 1996. Mesoarchaean crustal history of the eastern Indian Craton: Sm–Nd and U–Pb isotopic evidence. Precambr. Res. 77, 17–22. Seward, T.M., 1973. Thio-complexes of gold and the transport of gold in the hydrothermal ore solution. Geochim. Cosmochim. Acta 53, 269–278. Sharp, Z.D., Essene, E.J., Kelly, W.C., 1985. A re-examination of the arsenopyrite geothermometer: pressure considerations and applications to natural assemblages. Can. Mineral. 23, 517–534. Starling, A., Gillgan, J.M., Carter, A.H.C., Saunders, R.A., 1989. High temperature hydrothermal precipitation of precious metals on the surface of pyrite. Nature 340, 298–300. Su, W., Zhang, H., Hu, R., Xi Ge, X., Xia, B., Chen, Y., Zhu, C., 2012. Mineralogy and geochemistry of gold-bearing arsenian pyrite from the Shuiyindong Carlin-type gold deposit, Guizhou, China: implications for gold depositional processes. Miner. Deposita 47, 653–662. Sung, Y.H., Brugger, J., Ciobanu, C.L., Ping, A., Skinner, W., Nugus, M., 2009. Invisible gold in arsenian pyrite and arsenopyrite from a multistage Achaean gold deposit: Sunrise Dam, Eastern Goldfields Province, Western Australia. Miner. Deposita 44, 765–791. Tarnocai, C.A., Hattori, K., Cabri, L.J., 1997. ‘‘Invisible’’ gold in sulfides from Campbell mine, Red Lake greenstone belt, Ontario: evidence for mineralization during peak metamorphism. Can. Mineral. 35, 805–815. Tomkins, A.G., Mavrogenes, J.A., 2001. Redistribution of gold within arsenopyrite and Loellingite during pro- and retrograde metamorphism: application to timing of mineralization. Econ. Geol. 96, 525–534. Tossell, J.A., Vaughan, D.J., Burdett, J.K., 1981. Pyrite, marcasite, and arsenopyritetype minerals: crystal chemical and structural principles. Phys. Chem. Miner. 7, 177–184. Zhang, J., Deng, J., Chen, Hua.-yong., Yang, Li-qiang, Cooke, D., Danyushevsky, L., Gong, Qing-jie, 2014. LA–ICP–MS trace element analysis of pyrite from the Chang’an gold deposit, Sanjiang region, China: implication for ore-forming process. Gondwana Res. 26, 557–575.