- Email: [email protected]
Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India
Ore Geology Reviews 55 (2013) 134–145
Contents lists available at SciVerse ScienceDirect
Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev
Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India Pranjit Hazarika a, Biswajit Mishra a,⁎, Sakthi Saravanan Chinnasamy b, Heinz-Juergen Bernhardt c a b c
Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur 721302, India School of Agricultural Earth and Environmental Sciences, Department of Geology, University of KwaZulu-Natal, Durban 4000, South Africa Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität, Bochum 44801, Germany
a r t i c l e
i n f o
Article history: Received 24 March 2013 Received in revised form 27 May 2013 Accepted 31 May 2013 Available online 7 June 2013 Keywords: Pyrite X-ray imaging Trace elements Invisible gold Kundarkocha
a b s t r a c t Gold mineralization at Kundarkocha, India, is hosted in sheared gray quartz veins that were emplaced in carbonaceous pyritic phyllite. Gold occurs as enclosed grains within sulfides and free grains in quartz. Based on characteristic textural and chemical features, documented by X-ray element imaging, electron probe microanalysis and laser-ablation inductively-coupled plasma mass spectrometry analyses, four pyrite types were identified in carbonaceous phyllites and auriferous veins. Rock-hosted fine-grained syn-sedimentary to early diagenetic pyrite framboids (PyI) have lower contents of Co and As but consistently high gold values. Pyrite of the next generation (PyII) has numerous silicate and rare sulfide inclusions; lower contents of Co and Ni, moderate As values; the highest mean value of invisible gold and maximum concentrations of trace elements such as Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Ta, Th, U and Cr. Pyrite of the third generation (PyIII) shows evidence of overgrowth over PyII, contains both silicate and sulfide inclusions, and are characterized by moderate contents of Co, high Ni and low Au values and higher concentrations of large ion lithophile elements, but lesser amount of high field strength elements. Pyrites of the latest type (PyIV) occur as polycrystalline aggregates that contain inclusions of gold, sulfides and rare silicates, show oscillatory zoning of Co and As and the lowest concentrations of all other trace elements. Successive decrease in contents of majority of trace elements from PyII to PyIV is attributed to fluid-assisted recrystallization during diagenesis and low grade metamorphism. Later generation pyrites (PyII through PyIV) exhibit higher Au contents regardless of their As values, indicating occurrence of invisible gold mostly as nanoparticles, at times reaching up to 500 ppm. Unlike the majority of trace elements that underwent large-scale remobilizations, gold was somehow locked up in pyrite resulting in a rather lean deposit at Kundarkocha. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Pyrite is the most dominant sulfide mineral in the Earth's crust and occurs in varied geological settings, including high grade metamorphic rocks (Craig and Vokes, 1993). In sedimentary systems, pyrite grows as micron-to-nanosize framboids and continues to form well developed cubic crystals as a consequence of recrystallization during diagenesis and metamorphism. Because of its refractory nature, pyrite preserves changes in pertinent fluid chemistry during these subsequent fluidaided geological events. Accordingly, pyrite grains show zoning in terms of presence/absence of silicate inclusions and variation in its reflectivity. Besides optical microscopy, different zones in pyrite can be characterized as fingerprints of changing environments, by a range of micro-beam analyses (Belcher et al., 2004; Craig et al., 1998; Large et al., 2007). Apart from Co, Ni and As, a large number of trace elements may be irregularly distributed in pyrite forming diverse enriched zones
⁎ Corresponding author. Tel.: +91 3222283372; fax: +91 3222255303. E-mail address: [email protected] (B. Mishra). 0169-1368/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.oregeorev.2013.05.006
and their element maps obtained by various micro-beam analytical tools. These maps may reveal information about pyrite growth history and relative time of transport of these elements in the ore fluids (Cook et al., 2009; Craig et al., 1998; Sung et al., 2009; Thomas et al., 2011; Reich et al., 2013). Furthermore, Winderbaum et al. (2012) demonstrated that statistical treatment, involving multivariate regression analyses of laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) data can discriminate different texturally distinct generations of pyrite. Pyrite is a common ore mineral in various orogenic gold deposits. Diverse sources of gold have been proposed for the formation of these deposits. These include: from the (i) mantle (Barley and Groves, 1990), (ii) deep crust (Cline et al., 2005; Kerrich et al., 2005), and (iii) deep-seated magmas (Johnston and Ressel, 2004; Spooner, 1993). One of the characteristic features of many sediment-hosted gold deposits, a sub-group of the generalized orogenic gold deposits, is their striking association with pyritic carbonaceous shales that are generally metamorphosed to greenschist facies. Anomalously high contents of gold and arsenic can be seen from the data of Crocket (1990) and Ketris and Yudovitch (2009) in black carbonaceous
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
shales, compared to other crustal rocks. In recent years, micro-beam analytical studies of pyrite from many sediment-hosted gold deposits reveal elevated levels of invisible gold in the mineral and higher concentration of trace elements such as Ni, As, Pb, Zn, Mo, Te, V and Se (Large et al., 2007, 2009, 2011). While such initial enrichment took place during sedimentary formation of pyrite, gold was released during diagenesis to subsequent low-grade metamorphism (Large et al., 2009). Invisible gold in pyrite can occur by various mechanisms such as substitution (Boyle, 1979; Cook and Chryssouilis, 1990; Johan et al., 1989; Marcoux et al., 1989; Tarnocai et al., 1997; Wu and Delbove, 1989), chemisorption (Fleet and Mumin, 1997), and occurrence as nanoparticles (Ciobanu et al., 2012; Hough et al., 2011; Palenik et al., 2004; Reich et al., 2005, 2006). Gold mineralization occurs in gray quartz veins within carbonaceous phyllites at Kundarkocha in the eastern Indian Shield. The mine is
135
owned by M/s Manmohan Mineral Industries Pvt. Ltd., and constitutes a small deposit with six underground levels developed at 30 m interval from the surface. The average strike length of the lodes is only 70 m. Reserves (and grades) are: proven: 41,500 t (3.3 g/t), possible: 88,000 t (2.04 g/t); and probable: 17,325 t (2.24 g/t), with a cut-off grade of 1 g/t Au. In spite of being a small deposit, the mine has been operational for some time. However, apart from two abstracts (Baidya, 1996; Mishra et al., 2008), there is no other published literature on this deposit. In this communication, we first briefly describe the general geology of the study area, with emphasis on gold mineralization, followed by results of detailed electron probe microanalysis (EPMA), X-ray imaging, quantitative line scan analyses and few LA-ICP-MS analyses of various generations of pyrite from the ore zone. Another important contribution of our study relates to anomalously high concentrations of invisible gold in pyrite.
Fig. 1. Simplified geological map (modified after Saha, 1994) of the Eastern Indian Shield showing the Singhbhum craton, North Singhbhum Mobile Belt and the Chottanagpur Gneissic Complex. Ages of various rock units are shown in the map. (1) (Augé et al., 2003) Gabbro intrusion: U–Pb Zircon age; (2) (Mishra et al., 1999) Older metamorphic group, Older metamorphic tonalite gneiss, Singbhum granite and Mayurbhanj granite: 207Pb–206Pb zircon age; (3) (Mukhopadhyay et al., 2008) Iron Ore Group of rocks: U–Pb zircon age; (4) (Roy et al., 2002a) Dalma lava: whole rock Rb–Sr age; (5) (Roy et al., 2002b) Dhanjori lava: Whole rock Sm–Nd age; (6) (Saha et al., 1988) Singhbhum granite; (7) (Sharma et al., 1994) Older metamorphic group: whole rock Sm–Nd age. The ages are representative of the rock units, not location-specific.
136
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Fig. 2. Lithological map of the area around Kundarkocha modified after Banerjee and Thiagarajan (1965). The mine lease boundary is shown by the polygon WSW of the Kundarkocha village, located on the quartz vein.
2. Geological background The Eastern Indian Shield comprises the Archean Singhbhum Cratonic Block (SCB) to the south, and Proterozoic North Singhbhum Mobile Belt (NSMB) and Chhotanagpur Gneissic complex on the north (Mahadevan, 2002). To the north of SCB, nearer to its boundary with NSMB, lies the ~200 km-long, arcuate Singhbhum shear zone (Fig. 1). The Older metamorphic group (OMG, ~3.3–3.6 Ga; Mishra et al., 1999; Sharma et al., 1994) and the Iron Ore Group (IOG) of greenstone sequences (3.3–3.5 Ga; Mukhopadhyay et al., 2008) constitute the supracrustals of the SCB. The Singhbhum batholith and the Gabbroanorthosites, comprising the younger Baula igneous complex have
been respectively dated, giving ages of 3.1–3.3 Ga (Mishra et al., 1999; Saha et al., 1988) and ~3.1 Ga (Augé et al., 2003). Three phases of Singhbhum Granites, two sub-units of the OMG (older metamorphic group and Older Metamorphic Tonalite Gneiss), two sub-units of the IOG (IOG shale, tuff and phyllite and IOG lava), Singhbhum Group metapelites and quartzites, are all clubbed into one unit each, respectively as the OMG, IOG, and the Singhbhum Group in Fig. 1. The IOG comprises low metamorphic grade argillaceous and arenaceous metasediments along with mafic lavas/tuffs and banded iron formations (BIF) that account for the vast iron ore reserves in the eastern Indian states of Odisha and Jharkhand. Sporadic gold mineralization in diverse rock units has been reported from the eastern Indian
Fig. 3. Underground photographs showing the mode of occurrence of auriferous gray quartz vein with carbonaceous phyllite (a, c); Cr-bearing mica schist and carbonaceous phyllite (b); and later barren milky quartz veins within auriferous quartz vein (c, d).
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Shield. These include: (i) the Kundarkocha-Digarsahi sector within the greenstone-granite block; (ii) the Banduan-Belpahari area in the eastern part of the Singhbhum orogenic Belt; and (iii) the JhaldaJaipur area in the Chhotanagpur Gneissic Complex (Baidya, 1996). Kundarkocha, where a working mine is presently operational, is the most prominent of these. The Kundarkocha deposit is located ~ 45 km south of Jamshedpur in the East Singhbhum district (22°28′N, 86°15′E; Fig. 1). The rocks exposed around Kundarkocha are low grade metasedimentary units such as chlorite-biotite schist, carbonaceous phyllite, Cr-bearing mica schist and talc-chlorite schist. All these rocks are sheared and mylonitized. Measurable fabrics in the pelitic rocks (schists/phyllite) are: (i) axial planar foliation (S1), related to the first phase of tight isoclinal folding (F1); and (ii) S2 foliations, that are almost axial planar to the puckers and large folds (F2), and mylonitic in nature. In addition, granitic rocks occur in the northwestern and southeastern parts of the area. While a gabbroic unit is exposed on the eastern side, young dolerite dykes intrude all lithologies (Fig. 2). Rocks exposed underground
137
are mostly carbonaceous phyllite and Cr-bearing mica schist (Fig. 3a). Besides these, various quartz veins are emplaced (Fig. 3b–d). The gold lodes occur in gray/smoky quartz veins within carbonaceous phyllite (Fig. 3b, c) that are crosscut by later barren milky quartz veins (Fig. 3d). Arsenopyrite geothermometry (Kretschmar and Scott, 1976; Sharp et al., 1985) in the fS2-buffered assemblage of pyrite + pyrrhotite + arsenopyrite yielded a temperature (and fS2) range of 310° (10−10.5) to 380 °C (10−7.8). The deduced temperature range possibly reflects metamorphic conditions of the pyritic ore, which is in accordance with mineralogy of the pelitic rocks (Mishra et al., 2008). 3. Analytical methodology X-ray maps of pyrite were obtained using a Cameca SX-50 Electron Probe Micro Analyzer at Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität, Bochum. Quantitative data on pyrite grains were obtained using the above equipment and using a Cameca SX-100 unit, housed in the Department of Geology & Geophysics, IIT
Fig. 4. Representative photomicrographs documenting various ore mineral associations. Syn-sedimentary to early diagenetic fine grained pyrite (a, b) in carbonaceous phyllite; occurrence of gold with later recrystallized pyrite (PyII) (c, d); inclusions of gold and other sulfides within later hydrothermal pyrite (PyIV) (e, f). All mineral abbreviations are after Kretz (1983).
138
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Kharagpur. Analytical conditions for both instruments were: 25 kV accelerating voltage; and 100 nA beam current. Matrix correction was performed by the program PAP (Pouchou and Pichoir, 1984). The count time for Fe and S was 20 s; for other elements it was 60 s for both background and unknown. The following standards and emission lines were used: FeS2 (Fe-Kα, S-Kα), GaAs (As-Lα), Se (Lα), Co (Kα), Ni (Kα), Cu (Kα), Mo (Lα), Ag (Lα), Te (Lα), Au (Mα). Detection limits (in ppm) are: Fe, 140; S, 155; As, 210; Se, 350; Co, 110; Ni and Cu, 115; Mo, 340; Ag, 400; Te, 220. With the above analytical conditions the detection limit of gold was too high (~700 ppm). Thus, special care was taken for gold analysis. Using the PET crystal at 30 kV accelerating voltage, 150 nA beam current and 500 s count time for both peak and background, another set of analysis was performed for Au, Co and Ni on the same spots. Co and Ni were analyzed to compare the results, following the two above sets of analytical protocol, and were found to vary within 5%. Most importantly, the detection limit for Au could be lowered to about 35 ppm and the relative error on individual measurement was b25%. In spite of attaining such low detection limit for gold, considering the EPMA analytical precision in general, analyses with gold values ≥100 ppm were only considered for interpretation. However, all data are given in Appendices. Selected trace elements were analyzed using Laser AblationInductively Coupled Plasma Mass spectrometry (LA-ICP-MS) at IIT Kharagpur using a Cetac 213 nm Nd YAG laser-ablation system connected to a Varian 820 quadrupole ICP-MS. The ablation was done at 5 Hz pulse frequency, 60 μm spot size and 730 V energy. Analyses were performed in peak hopping mode with each analysis consisting of a 20 s background measurement with the laser turned off, and 40 s peak signal measurement with the laser turned on. Calibration was done using NIST 610 glass and data were reduced using the Glitter© software using Fe or Co as an internal standard. Recent studies (e.g., Glaus et al., 2010; Murakami and Ishihara, 2013; Velásquez et al., 2012) have demonstrated that the effect of matrix mismatch is
minimal and insignificant. Therefore, the use of NIST 610 glass, rather than a matrix-matched sulfide reference material, as an external standard is justified. Typical uncertainties as estimated from repeated analyses of NIST 610 glass are b16% (2σ) for all elements reported. Because of large size of laser spot size, no gold analysis could be performed, as it would yield average values and in reality as discussed later, pyrite grains are intensely zoned with varying gold contents. 4. Ore mineralogy About fifty ore samples, collected from the 2nd, 3rd, and 4th underground levels, were first studied by reflected light microscopy. Three representative samples (KC1, KU14 and KU15) were selected for detailed micro-beam analyses. Pyrite is the most dominant ore mineral, followed by pyrrhotite, sphalerite, chalcopyrite, and arsenopyrite, in decreasing order of abundance. Pyrite occurs both in the carbonaceous phyllite and along with other sulfides and gold in the gray quartz vein. Fine-grained syn-sedimentary to early diagenetic pyrite occurs exclusively as clusters (Fig. 4a, b) in the carbonaceous phyllite. Coarse-grained euhedral and polycrystalline aggregates of later hydrothermal pyrite, containing numerous inclusions of silicates, sulfides and carbonates, occur both in phyllite and auriferous gray quartz veins. Gold mineralization is associated with hydrothermal alteration assemblages that comprise chlorite, muscovite, biotite, albitic plagioclase, K-feldspar, ankerite and gold is mostly associated with sulfides (Fig. 4c–f) and rarely as small specs in gray quartz. Mineral abbreviations are after Kretz (1983). 5. Pyrite texture and trace element chemistry Three forms of pyrite were identified on the basis of textural criteria. These are fine-grained aggregates (possibly recrystallized
Fig. 5. SEM-BSE images of sample# KU14f, illustrating association of PyII and PyIV (a); inclusions of various silicates, sulfides, ankerite and monazite within PyII (b and d); silicate and sulfide within PyIV (c). All mineral abbreviations are after Kretz (1983).
0.04 16.01 87.8 b0.02 0.11 0.01 0.02 b0.01 0.48 b0.05 0.01 nd nd nd 13.86 nd nd b1.39
0.02 7.83 0.58 0.02 0.04 0.01 0.01 nd 0.09 0.07 nd nd nd nd 5.95 nd nd b0.71
nd 54.7 6.35 0.21 0.21 b0.01 0.08 b0.02 0.02 b0.25 b0.01 b0.01 nd 0.01 2.48 b0.03 b0.02 b5.80
139
0.03 3.64 0.31 0.01 0.05 0.01 0.01 nd 0.95 b0.01 nd 0.01 nd nd 1.95 nd nd b0.28
KC1/6 KU14e/4
PyIV PyIV
KU14e/3 KU14d/1
PyIV
framboids), euhedral pyrites with well-preserved grain boundaries and pyrites occurring as polycrystalline aggregates. These pyrites are further chemically classified into four types. Pyrites occurring with euhedral grain boundaries possibly formed by recrystallization during diagenesis or early metamorphic processes. Polycrystalline aggregates of pyrite are interpreted as synchronous with shearing that may have formed by dissolution and re-precipitation in the presence of a metamorphic fluid. The geochemical signature of these pyrites was ascertained by characteristic (i) X-ray element images of Co, Ni, As, (ii) Co to Ni ratio, and (iii) absolute concentrations of trace elements. Microprobe analyses of pyrites are given as appendices in the supplementary data file.
PyIV
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
nd 1962.3 154.5 b3.41 2.02 0.79 3.93 1.08 0.83 b8.83 nd 0.18 0.14 nd 161.1 b1.30 0.64 b247.4 0.01 2.91 0.26 nd 0.01 nd 0.01 nd 0.02 0.01 nd nd nd nd 0.48 nd 0.02 b0.30 nd 115 b3.11 b0.17 6.85 0.07 0.18 b0.04 5.48 1.6 b0.02 b0.02 b0.03 b0.08 169.6 b0.06 0.03 19.5 22.9 882.3 273.4 51.3 6.65 1.28 1.39 0.58 13.49 426 b0.32 0.75 b0.46 2.99 14635 b1.19 1.69 381.8 nd: not detected, values mentioned as ‘b’ refers to the detection limit of corresponding spot for the specific element.
b4.63 450 465 8.03 7.8 0.81 2.14 b0.52 24.5 29.9 0.49 0.70 0.57 48.4 13418.7 0.33 0.26 244.4 18.1 440 291.6 12.17 4.52 1.08 1.94 b0.46 38.3 27.4 0.72 1.32 0.57 22.6 18846.3 0.74 b1.46 b168.6 16.4 451.2 129.3 6.44 3.56 0.45 1.23 0.33 15.92 22.4 b0.24 b0.23 b0.47 9.82 11296.4 b1.21 b1.14 b117.6 nd 62.4 4.16 b0.07 0.10 0.02 0.08 b0.02 0.09 b0.20 nd b0.01 0.01 0.01 1.20 0.01 nd 8.81 b17.5 6476.9 1126.3 13.9 74.7 7.86 11.48 4.10 20.5 b38.9 4.89 11.20 b1.77 5.16 5021.9 nd 1.56 b888.2 48.9 436.7 433.1 29.1 4.67 1.05 3.21 b0.79 21.9 34.9 0.39 b0.63 0.49 18.9 5142.6 2.51 b2.30 b363.1 7.70 565 238.7 6.78 44.7 49.4 b0.91 b0.19 3.20 b8.50 916.7 1765.7 b0.41 1.85 983.3 149.5 4.21 b162.1 179.9 1913.5 988.6 16.91 9.84 12.83 71.5 0.61 5.87 64.1 2.80 3.68 b0.61 1.58 2090.4 25 4.51 1837.4 Li Ti Zn Rb Sr Y Zr Nb Ag Ba La Ce Ta W Pb Th U Cr
146.1 974.8 528 78.9 2.66 0.24 1.34 0.66 7.34 260.9 nd nd nd 2.42 694.4 b0.41 b0.24 741.6
KU14f/2 KU14f/1
PyIV PyIV
KU14f/3 KC1/5
PyIII PyIII
KC1/4 KC1/3
PyIII PyIII
KC1/2 KU14e/1
PyIII
KU14f/4
PyII PyII
KU14e/2 KC1/1
PyII
KU14d/3 KU14d/2
Element
This pyrite type is rather uncommon, is observed in two samples (KC1 and KU14e), and appears to overgrow PyII (Figs. 6 and 8). It is typified by moderate absolute concentrations of Co (363–3410 ppm), high Ni (400–13,670 ppm) and Co to Ni ratios of b 1 (0.04–0.90). The mean Au concentration is 193 ppm with a highest value of 330 ppm (Appendix A3). PyIII contains high concentrations of Ti, Zn, Rb, Sr, Ag, Ba, W and Pb and low concentrations of Y, Zr, Nb, Th, U, La, Ce, Ta (Table 1). It is noteworthy that PyIII has relatively lower concentrations of all trace elements than PyII, excepting Pb, Ag, Ba and W (excluding KC1/5, Table 1). These pyrites contain frequent inclusions of silicates (Fig. 6a) such as chlorite and biotite that might account for the higher concentrations of Ti, Zn, Rb, and Sr. The higher concentrations of Pb and Ag may be due to submicroscopic inclusion of galena. While higher trace element
Analysis#
5.3. Pyrite III
Table 1 LA-ICP-MS trace element spot analysis of pyrite-II, pyrite-III and pyrite-IV (all values reported in ppm).
PyII is the most common type, which can be seen in all the X-ray images (Figs. 6–9). These pyrites are characterized by relatively low contents of Co (350–2020 ppm), Ni (140–2350 ppm), varying Co to Ni ratios (0.42–6.40), and moderate arsenic (1040–6300 ppm). PyII contains numerous inclusions of chlorite, biotite, K-feldspar and albitic plagioclase; minor monazite and ankerite, and rare sulfides such as sphalerite and galena (Fig. 5b). Au has a concentration up to 450 ppm with a mean value of 223 ppm (Appendix A2). PyII has highest concentration of trace elements, which include Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Th, U, and Cr (Table 1). The high Ba, Pb and Zn contents may be attributed to inclusions, as seen as the spike in counts of these elements in LA-ICP-MS analysis. The higher contents of Pb and Ag may be due to presence of micro-inclusions of galena while that of La, Ce, Th and U may be ascribed to monazite inclusions as observed under the SEM (Fig. 5). But, almost flat trends and smooth counts for most of the other trace elements may indicate their presence in the structure or as ubiquitous and regularly-distributed micro-inclusions. Studies carried out by Deditius et al. (2011) reveal that most of the trace element-bearing nanoparticles in pyrite are associated with polycrystalline or distorted regions and some of the nanoparticles are associated with porous zones in pyrite (Reich et al., 2005).
PyII
5.2. Pyrite II
PyII
PyI is the first generation of early diagenetic pyrite, which occurs as very fine-grained aggregates (Fig. 4b) and is possibly recrystallized sedimentary framboidal pyrite. It has a very low Co concentration (mostly below EPMA detection limits), low (b1) Co/Ni ratio and low As content (240–480 ppm). This early pyrite contains a consistently high concentration of gold (180–270 ppm; mean value 218 ppm; Appendix A1). Unfortunately, no ICP-MS analysis of these fine-grained pyrites could be obtained because of large diameter of the laser beam (60 μm), which would have resulted in erroneous quantification of the trace elements.
PyIV
5.1. Pyrite I
140
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
contents can be seen in portions of PyIII with visible inclusions, contents of trace elements decrease without visible surficial inclusions.
6. Discussion 6.1. Gold solubility in pyrite
5.4. Pyrite IV PyIV is the last generation of pyrite, occurring as polycrystalline aggregates that overgrow and replace PyII and PyIII. These pyrites, like PyII, can be seen in all four samples (Figs. 6–9). In general, these are rich in Co (350–22620 ppm) and As (1020–22,120 ppm). Although, the Ni content varies widely (140 to 14,170 ppm), ~80% of the data are b 2000 ppm and only four have values exceeding 10,000 ppm (Appendix A4). However, these broad concentration ranges include a sub-type that shows oscillatory zoning with respect to Co and As. The Co to Ni ratio varies in the ranges 0.07–132 and 0.06–2.31 for Co- and As-rich zones, respectively. Such oscillatory Co/As zoning is strikingly absent in sample# KC1. Inclusions of native Au, chalcopyrite and sphalerite are seen (Figs. 4e, f and 5), although silicate inclusions are rather uncommon. Gold contents show large variation; the highest and mean values are 500 and 203 ppm respectively. Concentrations of all trace elements are low (Table 1) in PyIV excepting Ti, Zn and Pb in one analysis (KU14f/2). PyIV contains inclusions of sulfides and silicates. Sulfides such as chalcopyrite and sphalerite may have precipitated from the mobilized Pb, Zn and Cu during recrystallization of pyrite of earlier generations that were rich in trace elements (Large et al., 2011). Very low concentrations of Pb, Zn, Ag, Rb, Sr, and Y in PyIV, compared to earlier pyrites is interpreted to have formed as a result of coupled dissolution–reprecipitation, during F2 shear deformation thus remobilizing the trace elements (c.f. Chernoff and Barton, 2001; Large et al., 2007, 2011; Layton-Matthews et al., 2008).
In spite of numerous studies, substitution mechanism of Au in arsenian pyrite still remains unclear. Previous studies (Cook and Chryssouilis, 1990) have suggested occurrence of gold in arsenian pyrite as solid solution whereby Au and As replace for Fe and S in the pyrite structure, respectively. Many workers have reported a positive correlation between Au with As in arsenian pyrite (Cook and Chryssouilis, 1990; Large et al., 2009; Simon et al., 1999). XANES analyses demonstrated the occurrence of gold and arsenic as Au1+, Au0 and As1− in arsenian pyrite (Simon et al., 1999). The study of Reich et al. (2005) revealed that the maximum amount of Au as a function of the As content (~0.02 M ratio), that can be incorporated into the pyrite structure is described with an equation CAu = 0.02 × CAs + 4 × 10−5. The line defined by this equation describes the solubility limit of gold in pyrite, in the sense that the points falling below the line are due to substitution and those plotting above are suggested to occur as gold nanoparticles (Auo). Based on negative correlation between Fe and Au1+, substitution of Au for Fe has also been suggested (e.g., Johan et al., 1989; Marcoux et al., 1989; Tarnocai et al., 1997; Wu and Delbove, 1989). Micro-XANES spectroscopic data and SIMS analyses suggest occurrence of Au in two mutually exclusive chemical forms, i.e., chemically bound (Au+) and elemental (Au0) in arsenopyrite (Cabri et al., 2000). Chouinard et al. (2005) have proposed incorporation of gold into the structure of pyrite by coupled substitution of Au3+ with Cu+ (Au3+ + Cu+ = 2Fe2+), which requires unusually oxidizing conditions; an unrealistic proposition for Kundarkocha pyrites, which are associated with carbonaceous phyllites. However, the lack of any correlation between Au and other cations in arsenopyrite has been interpreted as incorporation of Au
Fig. 6. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KC1 (a); X-ray element maps (b–d) of different generations of pyrites. The vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Note the rarity of silicate inclusions and absence of Co rich zone in PyIV.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
141
Fig. 7. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14d (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Polycrystalline aggregates of PyIV rimming PyII display zoning of Co and As.
into lattice defects (Aylmore, 1995) and chemisorption of Au from ore fluids on the As-rich Fe-deficient surface sites of arsenian pyrite (Fleet and Mumin, 1997). The negative correlation between As and S along with lack of any correlation between As and Fe in pyrites from Kundarkocha (Fig. 10a, b) suggests substitution of As for S in the pyrite, wherein arsenic occurs as As1− (Deditius et al., 2008, 2009; Fleet and Mumin, 1997) instead of cationic As (As3+). This observation is in good agreement with the expected reducing condition of the sedimentary environment, containing carbonaceous phyllite. The molar ratio of Au/As in the analyzed pyrites varies from 0.002 to 0.33 (Fig. 10d) in contrast to the maximum molar ratio of ~0.02 inferred by Reich et al. (2005) for solubility limit, which results in points falling both below and above the solubility line. However, a positive correlation is observed between gold and arsenic for those analyses that plot below the solubility limit of gold in pyrite, implying the occurrence of Au as solid solution (Boyle, 1979; Cook and Chryssouilis, 1990; Johan et al., 1989; Winderbaum et al., 2012). Whereas most of the analyses that plot below the solubility limit are from the As-rich zones of PyIV, the earlier generations of pyrites (PyI, PyII, and PyIII) usually plot above the solubility limit (Fig. 10d), excluding few As-rich points of PyII. However, the analyses of Co-rich zones in PyIV, by and large plot above the solubility limit. Our observations, exclusively for As-rich zones in pyrites are in accordance with earlier findings (Cook and Chryssouilis, 1990; Reich et al., 2005) that suggest that solubility of Au in solid solution of pyrite is a function of As. On the other hand, higher gold contents in the As-poor zones imply non-exclusive contribution of As in the context of higher gold concentration in pyrite. This is because of occurrence of gold as nanoparticles and/or its incorporation in the melts involving low
melting point chalcophile elements such as Te and Bi at upper greenschist facies conditions (e.g., Ciobanu et al., 2012; Cook et al., 2009). The presence of most of the points above the Au solubility limit (Fig. 10d) and the lack of any correlation between Au with As or Fe (Fig. 10c, d) may suggest the existence of Au mostly as nanoparticles (Auo) in earlier sedimentary and diagenetic pyrites. Maximum Au values of 280 ppm (PyI), 450 ppm (PyII), 330 ppm (PyIII) and 500 ppm (PyIV), reported in this study, are on the higher side compared to published data on invisible gold contents in sediment-hosted gold deposits (Large et al., 2009). However, Palenik et al. (2004) have reported invisible gold as high as 0.84 wt.% (EPMA data) in thin As rich zones (1–20 μm) of arsenian pyrite (8.1 wt.% As) from Screamer zone of Betze-Post-Screamer deposit in Carlin trend, which is highest ever reported from Carlin type deposits. On the contrary, the later hydrothermal pyrites from Kundarkocha are relatively depleted in As (highest 2.2; average 0.38 wt.%) and coarse-grained (~500 μm). Gold in the later hydrothermal or syn-deformational pyrite (As-rich PyIV) is more likely to be structurally-bound. The hydrothermal solution responsible for precipitation of later generations of pyrite (As-rich PyIV) was possibly undersaturated with respect to Auo as indicated by most of the analyses which plot below the solubility limit defined by the Au versus As plot (Fig. 10d) (e.g., Reich et al., 2005). 6.2. Pyrite growth and remobilization of trace elements The fine-grained framboidal nature of PyI can be explained by rapid nucleation of the mineral at low temperature sedimentary conditions (Butler and Rickard, 2000). Their coarsening to form larger euhedral porphyroblasts was due to (i) recrystallization, as a consequence of
142
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Fig. 8. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14e (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Polycrystalline aggregates of PyIV appear to grow by dissolution–reprecipitation of earlier pyrites with relicts of PyII and PyIII shown by dotted curves/lines. PyIV has patchy zonation of Co and As. See text for discussion.
slower growth with increasing temperature during subsequent diagenesis and low grade metamorphism (Craig et al., 1998; Wagner and Boyce, 2006) resulting in PyII and (ii) overgrowth by later pyrites (Large et al., 2007), as is the case with PyIII and PyIV. PyII is the most common variety amongst all the pyrite types that (i) contains inclusions of silicates and rare sulfides, and (ii) possesses relatively lower contents of Co, Ni (with varying Co to Ni ratios), intermediate As values and maximum Au concentrations of 450 ppm. In addition, these pyrites are characterized by the highest contents of a large number of trace elements, of which presence of some (Ti, Zn, Rb, Sr, Ba and Pb) may be a consequence of visible inclusions, and others may occur in solid solutions or as ubiquitous nanoparticles (Cook et al., 2009; Deditius et al., 2011; Huston et al., 1995; Winderbaum et al., 2012). The third generation pyrite type is rather rare that shows textural indications of overgrowing PyII and contains both silicate and sulfide (galena and sphalerite) inclusions. Moderate concentrations of Co, high Ni contents, Co/Ni >1 and relatively low Au values typify this pyrite type. In general, these pyrites have higher concentrations of large-ion lithophile (and chalcophile) elements, possibly due to presence of surficial inclusions, but lower values of high-field strength elements. The last generation of pyrite occurs as polycrystalline aggregates that seem to have overgrown both PyII and PyIII. These pyrites (i) contain inclusions of Au, chalcopyrite and sphalerite (ii) are Co-, As rich, often showing oscillatory zoning for these two elements, and (iii) have lowest concentration of all other trace elements. Further, barring exceptions, Ni contents are generally low. Although anomalously high gold concentrations of 500 ppm were observed, the mean Au value (203 ppm) is less compared to PyI and PyII and more or less similar to that in PyIII. In general, the fine-grained sedimentary pyrites are enriched in trace elements whereas their recrystallization during hydrothermal activity,
metamorphism and shear deformation results in their expulsion to form other sulfides or they get incorporated into the sulfides as micro-to-nanoinclusions (Deditius et al., 2011; Huston et al., 1995; Large et al., 2009), leading to formation of coarse grained syndeformational pyrites that are depleted in trace elements (e.g., Chernoff and Barton, 2001; Large et al., 2007, 2011; Layton-Matthews et al., 2008). Such decrease in trace element contents has been observed in PyII through PyIV. However, hydrothermal and metamorphic pyrites may be highly enriched in certain trace elements such as Co, Ni and As that occur as solid solution (Craig et al., 1998), as also seen in Kundarkocha pyrites. Studies of earlier workers (e.g., Large et al., 2007, 2009) suggest that early diagenetic pyrite have elevated Au content (0.2–200 ppm), which is remobilized during subsequent recrystallization to form large sediment-hosted deposits such as Sukhoi Log, Bendigo, Carlin and Spanish Mountain. The above authors have observed Au–As-rich rims on later hydrothermal pyrites in Bendigo and Carlin whereas the Ni–Co rims on the hydrothermal pyrites of Sukhoi Log and Spanish Mountain do not have any detectable Au. The Kundarkocha hydrothermal pyrites (PyII through PyIV) exhibit elevated Au contents irrespective of their As contents, implying that the majority of gold occurs as nanoparticles. However, there remains an inconsistency in the Au contents of these later pyrites. Inclusions of native gold and sulfides are present in the later hydrothermal pyrites. The higher Au content in the later pyrite may indicate the inability of the hydrothermal fluid to remobilize gold from the early diagenetic pyrites during recrystallization or later dissolution and reprecipitation. Pyrite may play a significant role for scavenging trace metals in hydrothermal systems thereby monitoring the fluid composition (Reich et al., 2013). Also, the As-rich nature of the later pyrites might be responsible for locking gold in the structure of pyrite.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
143
Fig. 9. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14f (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). PyII is overgrown by PyIV and the latter displays oscillatory zoning of Co and As. Mineral abbreviations used in the figure are after Kretz (1983).
Fig. 10. Bivariate plots showing element correlations in pyrite (a through d); solubility limit of Au in pyrite as a function of As is shown by the solid line in (d). Arsenic and sulfur have a negative correlation (a) implying occurrence of arsenic as As−1; Au has a broad positive correlation for those analyses falling below the solubility limit of Au in pyrite (d). See text for discussion.
144
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
However, the elevated nature of Au in the Co-rich zones of late hydrothermal pyrite (PyIV) remains unclear. 7. Conclusions Based on distinct chemical and textural features, four pyrite types were identified in the carbonaceous phyllite and auriferous veins at Kundarkocha. The pyrite history started with syn-sedimentary to early-diagenetic framboidal types (PyI) that are characterized by low values of Co, As and uniformly high gold contents. Successive generations of pyrites (PyII through PyIV) formed as a consequence of diagenetic–metamorphic recrystallization and later fluid-assisted overgrowths. PyII contains the highest concentrations of trace elements, which decreased in PyIII and PyIV, essentially due to coupled dissolution–reprecipitation. However, the gold content remained the same since the metal was primarily confined in the host pyrites as nanoparticles. Thus, the inefficiency of hydrothermal fluid to remobilize gold from its initial sink, i.e., sedimentary to syn-diagenetic pyrite, for whatever reason, might have resulted in small deposits such as Kundarkocha. Acknowledgments PH thanks the Council of Scientific and Industrial Research, India for the financial assistance in the form of a Research Fellowship. The authors acknowledge the cooperation and help extended during fieldwork by authorities of M/s Manmohan Mineral Industries Pvt. Ltd. SEM-BSE imaging and partial EPMA data were generated by the equipments procured through a DST funding (IR/S4/ESF-08/2005) to the Department of Geology and Geophysics, IIT Kharagpur. Dr. Dewashish Upadhyay is thanked for his help in LA-ICP-MS analyses. Constructive comments from Martin Reich and two anonymous journal reviewers, and editorial assistance from Cristiana Ciobanu and Franco Pirajno helped to improve the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.oregeorev.2013.05.006. References Augé, T., Cocherie, A., Genna, A., Armstrong, R., Guerrot, C., Mukherjee, M.M., Patra, R.N., 2003. Age of the Baula PGE mineralization (Orissa, India) and its implications concerning the Singhbhum Archaean nucleus. Precambrian Res. 121, 85–101. Aylmore, M.G., 1995. Distribution and Agglomeration of Gold in Arsenopyrite and Pyrite. (Ph.D. thesis) Curtin University, Perth. Baidya, T.K., 1996. Prospect for gold in some areas of the Eastern Indian shield. Proc. National Workshop on Exploration and Exploitation of Gold Resources of India, 2–4 December. NGRI, Hyderabad, pp. 165–169. Banerjee, A.K., Thiagarajan, T.A., 1965. Progress report of investigation of gold at Kunderkocha Singhbhum district, Bihar. Bull. Geol. Surv. India Ser. A 38, 106. Barley, M.E., Groves, D.I., 1990. Deciphering the tectonic evolution of Archaean greenstone belts: the importance of contrasting histories to the distribution of mineralization in the Yilgarn Craton, Western Australia. Precambrian Res. 46, 3–20. Belcher, R.W., Rozendaal, A., Przybylowicz, W.J., 2004. Trace element zoning in pyrite determined by PIXE elemental mapping: evidence for varying ore–fluid composition and electrochemical precipitation of gold at the Spitskop deposit, Saldania Belt, South Africa. X-ray Spectrom. 33, 174–180. Boyle, R.W., 1979. The geochemistry of gold and its deposits (together with a chapter on geochemical prospecting for the element). Geol. Surv. Can. Bull. 280. Butler, I.B., Rickard, D., 2000. Framboidal pyrite formation via the oxidation of iron (II) monosulfide by hydrogen sulphide. Geochim. Cosmochim. Acta 64, 2665–2672. Cabri, L.J., Newville, M., Gordon, R.A., Crozier, E.D., Sutton, S.R., McMahon, G., Jiang, D.T., 2000. Chemical speciation of gold in arsenopyrite. Can. Mineral. 38, 1265–1281. Chernoff, C.B., Barton, M.D., 2001. Trace elements in black shale Fe-sulfides during diagenesis and metamorphism. Geological Society of American Annual Meeting, November 5–8. Chouinard, A., Paquette, J., Williams-Jones, E., 2005. Crystallographic controls on trace element incorporation in auriferous pyrite from Pascua epithermal high-sulfidation deposit, Chile-Argentina. Can. Mineral. 43, 951–963.
Ciobanu, C.L., Cook, N.J., Utsunomiya, S., Kogagwa, M., Green, L., Gilbert, S., Wade, B., 2012. Gold-telluride nanoparticles revealed in arsenic-free pyrite. Am. Mineral. 97, 1515–1518. Cline, J.S., Hofstra, A., Muntean, J., Tosdal, D., Hickey, K., 2005. Carlin-type gold deposits in Nevada: critical geologic characteristics and viable models. Economic Geology 100th Anniversary Volume, pp. 451–484. Cook, N.J., Chryssouilis, S.L., 1990. Concentrations of invisible gold in the common sulfides. Can. Mineral. 28, 1–16. Cook, N.J., Ciobanu, C.L., Mao, J., 2009. Textural control on gold distribution in As-free pyrite from the Dongping, Huangtuliang and Hougou gold deposits, North China Craton (Hebei Province, China). Chem. Geol. 261, 101–121. Craig, J.R., Vokes, F.M., 1993. The metamorphism of pyrite and pyretic ores: an overview. Mineral. Mag. 57, 3–18. Craig, J.R., Vokes, F.M., Solberg, T.N., 1998. Pyrite: physical and chemical textures. Miner. Deposita 34, 82–101. Crocket, J.H., 1990. Distribution of gold in the Earth's crust. In: Foster, R.P. (Ed.), Gold Metallogeny and Exploration. Chapman and Hall, London, New York, NY, pp. 1–36. Deditius, A.P., Utsunomiya, S., Renock, D., Ewing, R.C., Ramana, C.V., Becker, U., Kesler, S.E., 2008. A proposed new form of arsenian pyrite: composition, nanostructure and geochemical significance. Geochim. Cosmochim. Acta 72, 2919–2933. Deditius, A.P., Utsunomiya, S., Ewing, R.C., Kesler, S.E., 2009. Nanoscale “liquid” inclusions of As–Fe–S in arsenian pyrite. Am. Mineral. 94, 391–394. 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. Fleet, M.E., Mumin, A.H., 1997. Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis. Am. Mineral. 82, 182–193. Glaus, R., Kaegi, R., Krumeich, F., Günther, D., 2010. Phenomenological studies on structure and elemental composition of nanosecond and femto-second laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochim. Acta B 65, 812–822. Hough, R.M., Noble, R.R.P., Reich, M., 2011. Natural gold nanoparticles. Ore Geol. Rev. 42, 55–61. Huston, D.L., Sie, S.H., Suter, G.F., Cooke, D.C., Both, R.A., 1995. Trace elements in sulfide minerals from eastern Australian volcanic-hosted massive sulfide deposits: Pt. 1. Proton microprobe analyses of pyrite, chalcopyrite and sphalerite. Econ. Geol. 90, 1167–1196. Johan, Z., Marcoux, E., Bonnemaison, M., 1989. Arsenopyrite aurifere: Mode de substitution de Au dans la structure de FeAsS. C. R. Acad. Sci. (Paris) 308, 185–191. Johnston, M.K., Ressel, M.W., 2004. Carlin-type and distal-disseminated Au–Ag deposits: related distal expressions of Eocene intrusive centers in north-central Nevada: society of Economic Geologists Newsletter 59. Controversies on the origin of world-class gold deposits. Part I, carlin-type gold deposits in Nevada. Soc. Econ. Geol. Newsl. 59, 12–14. Kerrich, R., Goldfarb, R.J., Richards, J.P., 2005. Metallogenic provinces in an evolving geodynamic framework. Econ. Geol. 100, 1097–1136. Ketris, M.P., Yudovitch, Y.E., 2009. Estimations of clarkes for carbonaceous bioliths: world averages for trace element contents in black shales and coals. Int. J. Coal Geol. 78, 135–148. Kretschmar, U., Scott, S.D., 1976. Phase relations involving arsenopyrite in the system Fe–As–S and their application. Can. Mineral. 14, 364–386. Kretz, R., 1983. Symbols for rock-forming minerals. Am. Mineral. 68, 277–279. Large, R.R., Maslennikov, V., Robert, F., Danyushevsky, L.V., Chang, Z., 2007. Multistage sedimentary and metamorphic origin of pyrite and gold in the giant Sukhoi Log deposit, Lena gold province, Russia. Econ. Geol. 102, 1233–1267. 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. Layton-Matthews, D., Gemmell, J.B., Large, R.R., Peter, J., 2008. Trace element budget of the Que River shale: exploration implications of hanging-wall modification of sulfide minerals at the Hellyer deposit, Tasmania. 33rd International Geological Congress, Oslo-2008, August 6–14. Mahadevan, T.M., 2002. Geology of Bihar and Jharkhand. Geological Society of India Bangalore (563 pp.). Marcoux, E., Bonnemaison, M., Braux, C., Johan, Z., 1989. Distribution de Au, Sb, As et Fe dans l'arsenopyrite aurifere du Chatelet et de Villeranges. C. R. Acad. Sci. 308, 293–300. Mishra, S., Deomurari, M.P., Wiedenbeck, M., Goswami, J.N., Ray, S., Saha, A.K., 1999. 207 Pb/206Pb zircon ages and the evolution of the Singhbhum Craton, eastern India: an ion microprobe study. Precambrian Res. 93, 139–151. Mishra, B., Saravanan, C.S., Kartikeya, S., 2008. Thermobarometry, trace element zoning and invisible gold in pyrite from the Kunderkocha gold prospect, Eastern India. Abstract, 33rd International Geological Congress, Oslo-2008, August 6–14. 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 the Southern Iron Ore Group, Singhbhum Craton. J. Geol. 116, 449–461. Murakami, H., Ishihara, S., 2013. Trace elements of Indium-bearing sphalerite from tinpolymetallic deposits in Bolivia, China and Japan: a femto-second LA-ICPMS study. Ore Geol. Rev. 53, 223–243. Palenik, C.S., Utsunomiya, S., Reich, M., Kesler, S.E., Wang, L., Ewing, R.C., 2004. “Invisible” gold revealed: direct imaging of gold nanoparticles in a Carlin-type deposit. Am. Mineral. 89, 1359–1366. Pouchou, J.L., Pichoir, F., 1984. A new model for quantitative x-ray microanalysis. I.-Application to the analysis of homogeneous samples. Rech. Aerosp. 3, 167–192. Reich, M., Kesler, S.E., Utsunomiya, S., Palenik, C.S., Chryssoulis, S.L., Ewing, R.C., 2005. Solubility of gold in arsenian pyrite. Geochim. Cosmochim. Acta 69, 2781–2796.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145 Reich, M., Utsunomiya, S., Kesler, S.E., Wang, L.M., Ewing, R.C., Becker, U., 2006. Thermal behaviour of metal nanoparticles in geologic materials. Geology 34, 1033–1036. Reich, M., Deditius, A., Chryssoulis, S., Li, J.W., Ma, C.Q., Parada, M.A., Barra, F., Mittermayr, F., 2013. Pyrite as a record of hydrothermal fluid evolution in a porphyry copper system: a SIMS/EMPA trace element study. Geochim. Cosmochim. Acta 104, 42–62. Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., 2002a. Mid-Proterozoic plume-related thermal event in eastern Indian craton: evidence from trace elements, REE geochemistry and Sr–Nd isotope systematics of basic-ultrabasic intrusives from Dalma volcanic belt. Gondwana Res. 5, 133–146. Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., 2002b. Sm–Nd age and mantle source characteristics of the Dhanjori volcanic rocks, eastern India. Geochem. J. 36, 503–518. Saha, A.K., 1994. Crustal evolution of Singhbhum North Orissa. Geol. Soc. India Mem. 27 (341 pp.). Saha, A.K., Ray, S.L., 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: Geological Society of India Memoir, 8, pp. 13–37. Sharma, M., Basu, A.R., Ray, S.L., 1994. Sm–Nd isotopic and geochemical study of the Archaean Tonalite–Amphibolite association from the eastern Indian Craton. Contrib. Mineral. Petrol. 117, 45–55. Sharp, Z.D., Essene, E.J., Kelly, W.C., 1985. A reexamination of the arsenopyrite geothermometer: pressure considerations and applications to natural assemblages. Can. Mineral. 23, 517–534. Simon, G., Huang, H., Penner-Hahn, J.E., Kesler, S.E., Kao, L.S., 1999. Oxidation state of gold and arsenic in gold-bearing arsenian pyrite. Am. Mineral. 84, 1071–1079.
145
Spooner, E.T.C., 1993. Magmatic sulphide/volatile interaction as a mechanism for producing chalcophile element enriched, Archean Au-quartz, epithermal Au–Ag and Au skarn hydrothermal ore fluids. Ore Geol. Rev. 7, 359–379. Sung, Y.H., Brugger, J., Ciobanu, C.L., Pring, A., Skinner, W., Nugus, M., 2009. Invisible gold in arsenian pyrite and arsenopyrite from a multistage Archaen 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 the Campbell mine, Red Lake greenstone belt, Ontario: evidence for mineralization during the peak of metamorphism. Can. Mineral. 35, 805–815. Thomas, H.V., Large, R.R., Bull, S.W., Maslennikov, V., Berry, R.F., Fraser, R., Froud, S., Moye, R., 2011. Pyrite and pyrrhotite textures and composition in sediments, laminated quartz veins, and reefs at bendigo gold mine, Australia: insights for Ore Genesis. Econ. Geol. 106, 1–31. Velásquez, G., Borisova, A.Y., Salvi, S., Béziat, D., 2012. In situ determination of Au and Cu in natural pyrite by near‐infrared femtosecond laser ablation‐inductively coupled plasma‐quadrupole mass spectrometry: no evidence for matrix effects. Geostand. Geoanal. Res. 36, 315–324. Wagner, T., Boyce, A.J., 2006. Pyrite metamorphism in the Devonian Hunsruck Slate of Germany: insights from laser microprobe sulfur isotope analysis and thermodynamic modelling. Am. J. Sci. 306, 525–552. Winderbaum, L., Ciobanu, C.L., Cook, N.J., Paul, M., Metcalfe, A., Gilbert, S., 2012. Multivariate analysis of an LA-ICP-MS trace element dataset for pyrite. Math. Geosci. 44, 823–842. Wu, X., Delbove, F., 1989. Hydrothermal synthesis of gold-bearing arsenopyrite. Econ. Geol. 84, 2029–2032.
Contents lists available at SciVerse ScienceDirect
Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev
Multi-stage growth and invisible gold distribution in pyrite from the Kundarkocha sediment-hosted gold deposit, eastern India Pranjit Hazarika a, Biswajit Mishra a,⁎, Sakthi Saravanan Chinnasamy b, Heinz-Juergen Bernhardt c a b c
Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur 721302, India School of Agricultural Earth and Environmental Sciences, Department of Geology, University of KwaZulu-Natal, Durban 4000, South Africa Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität, Bochum 44801, Germany
a r t i c l e
i n f o
Article history: Received 24 March 2013 Received in revised form 27 May 2013 Accepted 31 May 2013 Available online 7 June 2013 Keywords: Pyrite X-ray imaging Trace elements Invisible gold Kundarkocha
a b s t r a c t Gold mineralization at Kundarkocha, India, is hosted in sheared gray quartz veins that were emplaced in carbonaceous pyritic phyllite. Gold occurs as enclosed grains within sulfides and free grains in quartz. Based on characteristic textural and chemical features, documented by X-ray element imaging, electron probe microanalysis and laser-ablation inductively-coupled plasma mass spectrometry analyses, four pyrite types were identified in carbonaceous phyllites and auriferous veins. Rock-hosted fine-grained syn-sedimentary to early diagenetic pyrite framboids (PyI) have lower contents of Co and As but consistently high gold values. Pyrite of the next generation (PyII) has numerous silicate and rare sulfide inclusions; lower contents of Co and Ni, moderate As values; the highest mean value of invisible gold and maximum concentrations of trace elements such as Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Ta, Th, U and Cr. Pyrite of the third generation (PyIII) shows evidence of overgrowth over PyII, contains both silicate and sulfide inclusions, and are characterized by moderate contents of Co, high Ni and low Au values and higher concentrations of large ion lithophile elements, but lesser amount of high field strength elements. Pyrites of the latest type (PyIV) occur as polycrystalline aggregates that contain inclusions of gold, sulfides and rare silicates, show oscillatory zoning of Co and As and the lowest concentrations of all other trace elements. Successive decrease in contents of majority of trace elements from PyII to PyIV is attributed to fluid-assisted recrystallization during diagenesis and low grade metamorphism. Later generation pyrites (PyII through PyIV) exhibit higher Au contents regardless of their As values, indicating occurrence of invisible gold mostly as nanoparticles, at times reaching up to 500 ppm. Unlike the majority of trace elements that underwent large-scale remobilizations, gold was somehow locked up in pyrite resulting in a rather lean deposit at Kundarkocha. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Pyrite is the most dominant sulfide mineral in the Earth's crust and occurs in varied geological settings, including high grade metamorphic rocks (Craig and Vokes, 1993). In sedimentary systems, pyrite grows as micron-to-nanosize framboids and continues to form well developed cubic crystals as a consequence of recrystallization during diagenesis and metamorphism. Because of its refractory nature, pyrite preserves changes in pertinent fluid chemistry during these subsequent fluidaided geological events. Accordingly, pyrite grains show zoning in terms of presence/absence of silicate inclusions and variation in its reflectivity. Besides optical microscopy, different zones in pyrite can be characterized as fingerprints of changing environments, by a range of micro-beam analyses (Belcher et al., 2004; Craig et al., 1998; Large et al., 2007). Apart from Co, Ni and As, a large number of trace elements may be irregularly distributed in pyrite forming diverse enriched zones
⁎ Corresponding author. Tel.: +91 3222283372; fax: +91 3222255303. E-mail address: [email protected] (B. Mishra). 0169-1368/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.oregeorev.2013.05.006
and their element maps obtained by various micro-beam analytical tools. These maps may reveal information about pyrite growth history and relative time of transport of these elements in the ore fluids (Cook et al., 2009; Craig et al., 1998; Sung et al., 2009; Thomas et al., 2011; Reich et al., 2013). Furthermore, Winderbaum et al. (2012) demonstrated that statistical treatment, involving multivariate regression analyses of laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) data can discriminate different texturally distinct generations of pyrite. Pyrite is a common ore mineral in various orogenic gold deposits. Diverse sources of gold have been proposed for the formation of these deposits. These include: from the (i) mantle (Barley and Groves, 1990), (ii) deep crust (Cline et al., 2005; Kerrich et al., 2005), and (iii) deep-seated magmas (Johnston and Ressel, 2004; Spooner, 1993). One of the characteristic features of many sediment-hosted gold deposits, a sub-group of the generalized orogenic gold deposits, is their striking association with pyritic carbonaceous shales that are generally metamorphosed to greenschist facies. Anomalously high contents of gold and arsenic can be seen from the data of Crocket (1990) and Ketris and Yudovitch (2009) in black carbonaceous
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
shales, compared to other crustal rocks. In recent years, micro-beam analytical studies of pyrite from many sediment-hosted gold deposits reveal elevated levels of invisible gold in the mineral and higher concentration of trace elements such as Ni, As, Pb, Zn, Mo, Te, V and Se (Large et al., 2007, 2009, 2011). While such initial enrichment took place during sedimentary formation of pyrite, gold was released during diagenesis to subsequent low-grade metamorphism (Large et al., 2009). Invisible gold in pyrite can occur by various mechanisms such as substitution (Boyle, 1979; Cook and Chryssouilis, 1990; Johan et al., 1989; Marcoux et al., 1989; Tarnocai et al., 1997; Wu and Delbove, 1989), chemisorption (Fleet and Mumin, 1997), and occurrence as nanoparticles (Ciobanu et al., 2012; Hough et al., 2011; Palenik et al., 2004; Reich et al., 2005, 2006). Gold mineralization occurs in gray quartz veins within carbonaceous phyllites at Kundarkocha in the eastern Indian Shield. The mine is
135
owned by M/s Manmohan Mineral Industries Pvt. Ltd., and constitutes a small deposit with six underground levels developed at 30 m interval from the surface. The average strike length of the lodes is only 70 m. Reserves (and grades) are: proven: 41,500 t (3.3 g/t), possible: 88,000 t (2.04 g/t); and probable: 17,325 t (2.24 g/t), with a cut-off grade of 1 g/t Au. In spite of being a small deposit, the mine has been operational for some time. However, apart from two abstracts (Baidya, 1996; Mishra et al., 2008), there is no other published literature on this deposit. In this communication, we first briefly describe the general geology of the study area, with emphasis on gold mineralization, followed by results of detailed electron probe microanalysis (EPMA), X-ray imaging, quantitative line scan analyses and few LA-ICP-MS analyses of various generations of pyrite from the ore zone. Another important contribution of our study relates to anomalously high concentrations of invisible gold in pyrite.
Fig. 1. Simplified geological map (modified after Saha, 1994) of the Eastern Indian Shield showing the Singhbhum craton, North Singhbhum Mobile Belt and the Chottanagpur Gneissic Complex. Ages of various rock units are shown in the map. (1) (Augé et al., 2003) Gabbro intrusion: U–Pb Zircon age; (2) (Mishra et al., 1999) Older metamorphic group, Older metamorphic tonalite gneiss, Singbhum granite and Mayurbhanj granite: 207Pb–206Pb zircon age; (3) (Mukhopadhyay et al., 2008) Iron Ore Group of rocks: U–Pb zircon age; (4) (Roy et al., 2002a) Dalma lava: whole rock Rb–Sr age; (5) (Roy et al., 2002b) Dhanjori lava: Whole rock Sm–Nd age; (6) (Saha et al., 1988) Singhbhum granite; (7) (Sharma et al., 1994) Older metamorphic group: whole rock Sm–Nd age. The ages are representative of the rock units, not location-specific.
136
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Fig. 2. Lithological map of the area around Kundarkocha modified after Banerjee and Thiagarajan (1965). The mine lease boundary is shown by the polygon WSW of the Kundarkocha village, located on the quartz vein.
2. Geological background The Eastern Indian Shield comprises the Archean Singhbhum Cratonic Block (SCB) to the south, and Proterozoic North Singhbhum Mobile Belt (NSMB) and Chhotanagpur Gneissic complex on the north (Mahadevan, 2002). To the north of SCB, nearer to its boundary with NSMB, lies the ~200 km-long, arcuate Singhbhum shear zone (Fig. 1). The Older metamorphic group (OMG, ~3.3–3.6 Ga; Mishra et al., 1999; Sharma et al., 1994) and the Iron Ore Group (IOG) of greenstone sequences (3.3–3.5 Ga; Mukhopadhyay et al., 2008) constitute the supracrustals of the SCB. The Singhbhum batholith and the Gabbroanorthosites, comprising the younger Baula igneous complex have
been respectively dated, giving ages of 3.1–3.3 Ga (Mishra et al., 1999; Saha et al., 1988) and ~3.1 Ga (Augé et al., 2003). Three phases of Singhbhum Granites, two sub-units of the OMG (older metamorphic group and Older Metamorphic Tonalite Gneiss), two sub-units of the IOG (IOG shale, tuff and phyllite and IOG lava), Singhbhum Group metapelites and quartzites, are all clubbed into one unit each, respectively as the OMG, IOG, and the Singhbhum Group in Fig. 1. The IOG comprises low metamorphic grade argillaceous and arenaceous metasediments along with mafic lavas/tuffs and banded iron formations (BIF) that account for the vast iron ore reserves in the eastern Indian states of Odisha and Jharkhand. Sporadic gold mineralization in diverse rock units has been reported from the eastern Indian
Fig. 3. Underground photographs showing the mode of occurrence of auriferous gray quartz vein with carbonaceous phyllite (a, c); Cr-bearing mica schist and carbonaceous phyllite (b); and later barren milky quartz veins within auriferous quartz vein (c, d).
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Shield. These include: (i) the Kundarkocha-Digarsahi sector within the greenstone-granite block; (ii) the Banduan-Belpahari area in the eastern part of the Singhbhum orogenic Belt; and (iii) the JhaldaJaipur area in the Chhotanagpur Gneissic Complex (Baidya, 1996). Kundarkocha, where a working mine is presently operational, is the most prominent of these. The Kundarkocha deposit is located ~ 45 km south of Jamshedpur in the East Singhbhum district (22°28′N, 86°15′E; Fig. 1). The rocks exposed around Kundarkocha are low grade metasedimentary units such as chlorite-biotite schist, carbonaceous phyllite, Cr-bearing mica schist and talc-chlorite schist. All these rocks are sheared and mylonitized. Measurable fabrics in the pelitic rocks (schists/phyllite) are: (i) axial planar foliation (S1), related to the first phase of tight isoclinal folding (F1); and (ii) S2 foliations, that are almost axial planar to the puckers and large folds (F2), and mylonitic in nature. In addition, granitic rocks occur in the northwestern and southeastern parts of the area. While a gabbroic unit is exposed on the eastern side, young dolerite dykes intrude all lithologies (Fig. 2). Rocks exposed underground
137
are mostly carbonaceous phyllite and Cr-bearing mica schist (Fig. 3a). Besides these, various quartz veins are emplaced (Fig. 3b–d). The gold lodes occur in gray/smoky quartz veins within carbonaceous phyllite (Fig. 3b, c) that are crosscut by later barren milky quartz veins (Fig. 3d). Arsenopyrite geothermometry (Kretschmar and Scott, 1976; Sharp et al., 1985) in the fS2-buffered assemblage of pyrite + pyrrhotite + arsenopyrite yielded a temperature (and fS2) range of 310° (10−10.5) to 380 °C (10−7.8). The deduced temperature range possibly reflects metamorphic conditions of the pyritic ore, which is in accordance with mineralogy of the pelitic rocks (Mishra et al., 2008). 3. Analytical methodology X-ray maps of pyrite were obtained using a Cameca SX-50 Electron Probe Micro Analyzer at Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität, Bochum. Quantitative data on pyrite grains were obtained using the above equipment and using a Cameca SX-100 unit, housed in the Department of Geology & Geophysics, IIT
Fig. 4. Representative photomicrographs documenting various ore mineral associations. Syn-sedimentary to early diagenetic fine grained pyrite (a, b) in carbonaceous phyllite; occurrence of gold with later recrystallized pyrite (PyII) (c, d); inclusions of gold and other sulfides within later hydrothermal pyrite (PyIV) (e, f). All mineral abbreviations are after Kretz (1983).
138
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Kharagpur. Analytical conditions for both instruments were: 25 kV accelerating voltage; and 100 nA beam current. Matrix correction was performed by the program PAP (Pouchou and Pichoir, 1984). The count time for Fe and S was 20 s; for other elements it was 60 s for both background and unknown. The following standards and emission lines were used: FeS2 (Fe-Kα, S-Kα), GaAs (As-Lα), Se (Lα), Co (Kα), Ni (Kα), Cu (Kα), Mo (Lα), Ag (Lα), Te (Lα), Au (Mα). Detection limits (in ppm) are: Fe, 140; S, 155; As, 210; Se, 350; Co, 110; Ni and Cu, 115; Mo, 340; Ag, 400; Te, 220. With the above analytical conditions the detection limit of gold was too high (~700 ppm). Thus, special care was taken for gold analysis. Using the PET crystal at 30 kV accelerating voltage, 150 nA beam current and 500 s count time for both peak and background, another set of analysis was performed for Au, Co and Ni on the same spots. Co and Ni were analyzed to compare the results, following the two above sets of analytical protocol, and were found to vary within 5%. Most importantly, the detection limit for Au could be lowered to about 35 ppm and the relative error on individual measurement was b25%. In spite of attaining such low detection limit for gold, considering the EPMA analytical precision in general, analyses with gold values ≥100 ppm were only considered for interpretation. However, all data are given in Appendices. Selected trace elements were analyzed using Laser AblationInductively Coupled Plasma Mass spectrometry (LA-ICP-MS) at IIT Kharagpur using a Cetac 213 nm Nd YAG laser-ablation system connected to a Varian 820 quadrupole ICP-MS. The ablation was done at 5 Hz pulse frequency, 60 μm spot size and 730 V energy. Analyses were performed in peak hopping mode with each analysis consisting of a 20 s background measurement with the laser turned off, and 40 s peak signal measurement with the laser turned on. Calibration was done using NIST 610 glass and data were reduced using the Glitter© software using Fe or Co as an internal standard. Recent studies (e.g., Glaus et al., 2010; Murakami and Ishihara, 2013; Velásquez et al., 2012) have demonstrated that the effect of matrix mismatch is
minimal and insignificant. Therefore, the use of NIST 610 glass, rather than a matrix-matched sulfide reference material, as an external standard is justified. Typical uncertainties as estimated from repeated analyses of NIST 610 glass are b16% (2σ) for all elements reported. Because of large size of laser spot size, no gold analysis could be performed, as it would yield average values and in reality as discussed later, pyrite grains are intensely zoned with varying gold contents. 4. Ore mineralogy About fifty ore samples, collected from the 2nd, 3rd, and 4th underground levels, were first studied by reflected light microscopy. Three representative samples (KC1, KU14 and KU15) were selected for detailed micro-beam analyses. Pyrite is the most dominant ore mineral, followed by pyrrhotite, sphalerite, chalcopyrite, and arsenopyrite, in decreasing order of abundance. Pyrite occurs both in the carbonaceous phyllite and along with other sulfides and gold in the gray quartz vein. Fine-grained syn-sedimentary to early diagenetic pyrite occurs exclusively as clusters (Fig. 4a, b) in the carbonaceous phyllite. Coarse-grained euhedral and polycrystalline aggregates of later hydrothermal pyrite, containing numerous inclusions of silicates, sulfides and carbonates, occur both in phyllite and auriferous gray quartz veins. Gold mineralization is associated with hydrothermal alteration assemblages that comprise chlorite, muscovite, biotite, albitic plagioclase, K-feldspar, ankerite and gold is mostly associated with sulfides (Fig. 4c–f) and rarely as small specs in gray quartz. Mineral abbreviations are after Kretz (1983). 5. Pyrite texture and trace element chemistry Three forms of pyrite were identified on the basis of textural criteria. These are fine-grained aggregates (possibly recrystallized
Fig. 5. SEM-BSE images of sample# KU14f, illustrating association of PyII and PyIV (a); inclusions of various silicates, sulfides, ankerite and monazite within PyII (b and d); silicate and sulfide within PyIV (c). All mineral abbreviations are after Kretz (1983).
0.04 16.01 87.8 b0.02 0.11 0.01 0.02 b0.01 0.48 b0.05 0.01 nd nd nd 13.86 nd nd b1.39
0.02 7.83 0.58 0.02 0.04 0.01 0.01 nd 0.09 0.07 nd nd nd nd 5.95 nd nd b0.71
nd 54.7 6.35 0.21 0.21 b0.01 0.08 b0.02 0.02 b0.25 b0.01 b0.01 nd 0.01 2.48 b0.03 b0.02 b5.80
139
0.03 3.64 0.31 0.01 0.05 0.01 0.01 nd 0.95 b0.01 nd 0.01 nd nd 1.95 nd nd b0.28
KC1/6 KU14e/4
PyIV PyIV
KU14e/3 KU14d/1
PyIV
framboids), euhedral pyrites with well-preserved grain boundaries and pyrites occurring as polycrystalline aggregates. These pyrites are further chemically classified into four types. Pyrites occurring with euhedral grain boundaries possibly formed by recrystallization during diagenesis or early metamorphic processes. Polycrystalline aggregates of pyrite are interpreted as synchronous with shearing that may have formed by dissolution and re-precipitation in the presence of a metamorphic fluid. The geochemical signature of these pyrites was ascertained by characteristic (i) X-ray element images of Co, Ni, As, (ii) Co to Ni ratio, and (iii) absolute concentrations of trace elements. Microprobe analyses of pyrites are given as appendices in the supplementary data file.
PyIV
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
nd 1962.3 154.5 b3.41 2.02 0.79 3.93 1.08 0.83 b8.83 nd 0.18 0.14 nd 161.1 b1.30 0.64 b247.4 0.01 2.91 0.26 nd 0.01 nd 0.01 nd 0.02 0.01 nd nd nd nd 0.48 nd 0.02 b0.30 nd 115 b3.11 b0.17 6.85 0.07 0.18 b0.04 5.48 1.6 b0.02 b0.02 b0.03 b0.08 169.6 b0.06 0.03 19.5 22.9 882.3 273.4 51.3 6.65 1.28 1.39 0.58 13.49 426 b0.32 0.75 b0.46 2.99 14635 b1.19 1.69 381.8 nd: not detected, values mentioned as ‘b’ refers to the detection limit of corresponding spot for the specific element.
b4.63 450 465 8.03 7.8 0.81 2.14 b0.52 24.5 29.9 0.49 0.70 0.57 48.4 13418.7 0.33 0.26 244.4 18.1 440 291.6 12.17 4.52 1.08 1.94 b0.46 38.3 27.4 0.72 1.32 0.57 22.6 18846.3 0.74 b1.46 b168.6 16.4 451.2 129.3 6.44 3.56 0.45 1.23 0.33 15.92 22.4 b0.24 b0.23 b0.47 9.82 11296.4 b1.21 b1.14 b117.6 nd 62.4 4.16 b0.07 0.10 0.02 0.08 b0.02 0.09 b0.20 nd b0.01 0.01 0.01 1.20 0.01 nd 8.81 b17.5 6476.9 1126.3 13.9 74.7 7.86 11.48 4.10 20.5 b38.9 4.89 11.20 b1.77 5.16 5021.9 nd 1.56 b888.2 48.9 436.7 433.1 29.1 4.67 1.05 3.21 b0.79 21.9 34.9 0.39 b0.63 0.49 18.9 5142.6 2.51 b2.30 b363.1 7.70 565 238.7 6.78 44.7 49.4 b0.91 b0.19 3.20 b8.50 916.7 1765.7 b0.41 1.85 983.3 149.5 4.21 b162.1 179.9 1913.5 988.6 16.91 9.84 12.83 71.5 0.61 5.87 64.1 2.80 3.68 b0.61 1.58 2090.4 25 4.51 1837.4 Li Ti Zn Rb Sr Y Zr Nb Ag Ba La Ce Ta W Pb Th U Cr
146.1 974.8 528 78.9 2.66 0.24 1.34 0.66 7.34 260.9 nd nd nd 2.42 694.4 b0.41 b0.24 741.6
KU14f/2 KU14f/1
PyIV PyIV
KU14f/3 KC1/5
PyIII PyIII
KC1/4 KC1/3
PyIII PyIII
KC1/2 KU14e/1
PyIII
KU14f/4
PyII PyII
KU14e/2 KC1/1
PyII
KU14d/3 KU14d/2
Element
This pyrite type is rather uncommon, is observed in two samples (KC1 and KU14e), and appears to overgrow PyII (Figs. 6 and 8). It is typified by moderate absolute concentrations of Co (363–3410 ppm), high Ni (400–13,670 ppm) and Co to Ni ratios of b 1 (0.04–0.90). The mean Au concentration is 193 ppm with a highest value of 330 ppm (Appendix A3). PyIII contains high concentrations of Ti, Zn, Rb, Sr, Ag, Ba, W and Pb and low concentrations of Y, Zr, Nb, Th, U, La, Ce, Ta (Table 1). It is noteworthy that PyIII has relatively lower concentrations of all trace elements than PyII, excepting Pb, Ag, Ba and W (excluding KC1/5, Table 1). These pyrites contain frequent inclusions of silicates (Fig. 6a) such as chlorite and biotite that might account for the higher concentrations of Ti, Zn, Rb, and Sr. The higher concentrations of Pb and Ag may be due to submicroscopic inclusion of galena. While higher trace element
Analysis#
5.3. Pyrite III
Table 1 LA-ICP-MS trace element spot analysis of pyrite-II, pyrite-III and pyrite-IV (all values reported in ppm).
PyII is the most common type, which can be seen in all the X-ray images (Figs. 6–9). These pyrites are characterized by relatively low contents of Co (350–2020 ppm), Ni (140–2350 ppm), varying Co to Ni ratios (0.42–6.40), and moderate arsenic (1040–6300 ppm). PyII contains numerous inclusions of chlorite, biotite, K-feldspar and albitic plagioclase; minor monazite and ankerite, and rare sulfides such as sphalerite and galena (Fig. 5b). Au has a concentration up to 450 ppm with a mean value of 223 ppm (Appendix A2). PyII has highest concentration of trace elements, which include Li, Ti, Zn, Rb, Sr, Y, Zr, Nb, La, Ce, Th, U, and Cr (Table 1). The high Ba, Pb and Zn contents may be attributed to inclusions, as seen as the spike in counts of these elements in LA-ICP-MS analysis. The higher contents of Pb and Ag may be due to presence of micro-inclusions of galena while that of La, Ce, Th and U may be ascribed to monazite inclusions as observed under the SEM (Fig. 5). But, almost flat trends and smooth counts for most of the other trace elements may indicate their presence in the structure or as ubiquitous and regularly-distributed micro-inclusions. Studies carried out by Deditius et al. (2011) reveal that most of the trace element-bearing nanoparticles in pyrite are associated with polycrystalline or distorted regions and some of the nanoparticles are associated with porous zones in pyrite (Reich et al., 2005).
PyII
5.2. Pyrite II
PyII
PyI is the first generation of early diagenetic pyrite, which occurs as very fine-grained aggregates (Fig. 4b) and is possibly recrystallized sedimentary framboidal pyrite. It has a very low Co concentration (mostly below EPMA detection limits), low (b1) Co/Ni ratio and low As content (240–480 ppm). This early pyrite contains a consistently high concentration of gold (180–270 ppm; mean value 218 ppm; Appendix A1). Unfortunately, no ICP-MS analysis of these fine-grained pyrites could be obtained because of large diameter of the laser beam (60 μm), which would have resulted in erroneous quantification of the trace elements.
PyIV
5.1. Pyrite I
140
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
contents can be seen in portions of PyIII with visible inclusions, contents of trace elements decrease without visible surficial inclusions.
6. Discussion 6.1. Gold solubility in pyrite
5.4. Pyrite IV PyIV is the last generation of pyrite, occurring as polycrystalline aggregates that overgrow and replace PyII and PyIII. These pyrites, like PyII, can be seen in all four samples (Figs. 6–9). In general, these are rich in Co (350–22620 ppm) and As (1020–22,120 ppm). Although, the Ni content varies widely (140 to 14,170 ppm), ~80% of the data are b 2000 ppm and only four have values exceeding 10,000 ppm (Appendix A4). However, these broad concentration ranges include a sub-type that shows oscillatory zoning with respect to Co and As. The Co to Ni ratio varies in the ranges 0.07–132 and 0.06–2.31 for Co- and As-rich zones, respectively. Such oscillatory Co/As zoning is strikingly absent in sample# KC1. Inclusions of native Au, chalcopyrite and sphalerite are seen (Figs. 4e, f and 5), although silicate inclusions are rather uncommon. Gold contents show large variation; the highest and mean values are 500 and 203 ppm respectively. Concentrations of all trace elements are low (Table 1) in PyIV excepting Ti, Zn and Pb in one analysis (KU14f/2). PyIV contains inclusions of sulfides and silicates. Sulfides such as chalcopyrite and sphalerite may have precipitated from the mobilized Pb, Zn and Cu during recrystallization of pyrite of earlier generations that were rich in trace elements (Large et al., 2011). Very low concentrations of Pb, Zn, Ag, Rb, Sr, and Y in PyIV, compared to earlier pyrites is interpreted to have formed as a result of coupled dissolution–reprecipitation, during F2 shear deformation thus remobilizing the trace elements (c.f. Chernoff and Barton, 2001; Large et al., 2007, 2011; Layton-Matthews et al., 2008).
In spite of numerous studies, substitution mechanism of Au in arsenian pyrite still remains unclear. Previous studies (Cook and Chryssouilis, 1990) have suggested occurrence of gold in arsenian pyrite as solid solution whereby Au and As replace for Fe and S in the pyrite structure, respectively. Many workers have reported a positive correlation between Au with As in arsenian pyrite (Cook and Chryssouilis, 1990; Large et al., 2009; Simon et al., 1999). XANES analyses demonstrated the occurrence of gold and arsenic as Au1+, Au0 and As1− in arsenian pyrite (Simon et al., 1999). The study of Reich et al. (2005) revealed that the maximum amount of Au as a function of the As content (~0.02 M ratio), that can be incorporated into the pyrite structure is described with an equation CAu = 0.02 × CAs + 4 × 10−5. The line defined by this equation describes the solubility limit of gold in pyrite, in the sense that the points falling below the line are due to substitution and those plotting above are suggested to occur as gold nanoparticles (Auo). Based on negative correlation between Fe and Au1+, substitution of Au for Fe has also been suggested (e.g., Johan et al., 1989; Marcoux et al., 1989; Tarnocai et al., 1997; Wu and Delbove, 1989). Micro-XANES spectroscopic data and SIMS analyses suggest occurrence of Au in two mutually exclusive chemical forms, i.e., chemically bound (Au+) and elemental (Au0) in arsenopyrite (Cabri et al., 2000). Chouinard et al. (2005) have proposed incorporation of gold into the structure of pyrite by coupled substitution of Au3+ with Cu+ (Au3+ + Cu+ = 2Fe2+), which requires unusually oxidizing conditions; an unrealistic proposition for Kundarkocha pyrites, which are associated with carbonaceous phyllites. However, the lack of any correlation between Au and other cations in arsenopyrite has been interpreted as incorporation of Au
Fig. 6. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KC1 (a); X-ray element maps (b–d) of different generations of pyrites. The vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Note the rarity of silicate inclusions and absence of Co rich zone in PyIV.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
141
Fig. 7. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14d (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Polycrystalline aggregates of PyIV rimming PyII display zoning of Co and As.
into lattice defects (Aylmore, 1995) and chemisorption of Au from ore fluids on the As-rich Fe-deficient surface sites of arsenian pyrite (Fleet and Mumin, 1997). The negative correlation between As and S along with lack of any correlation between As and Fe in pyrites from Kundarkocha (Fig. 10a, b) suggests substitution of As for S in the pyrite, wherein arsenic occurs as As1− (Deditius et al., 2008, 2009; Fleet and Mumin, 1997) instead of cationic As (As3+). This observation is in good agreement with the expected reducing condition of the sedimentary environment, containing carbonaceous phyllite. The molar ratio of Au/As in the analyzed pyrites varies from 0.002 to 0.33 (Fig. 10d) in contrast to the maximum molar ratio of ~0.02 inferred by Reich et al. (2005) for solubility limit, which results in points falling both below and above the solubility line. However, a positive correlation is observed between gold and arsenic for those analyses that plot below the solubility limit of gold in pyrite, implying the occurrence of Au as solid solution (Boyle, 1979; Cook and Chryssouilis, 1990; Johan et al., 1989; Winderbaum et al., 2012). Whereas most of the analyses that plot below the solubility limit are from the As-rich zones of PyIV, the earlier generations of pyrites (PyI, PyII, and PyIII) usually plot above the solubility limit (Fig. 10d), excluding few As-rich points of PyII. However, the analyses of Co-rich zones in PyIV, by and large plot above the solubility limit. Our observations, exclusively for As-rich zones in pyrites are in accordance with earlier findings (Cook and Chryssouilis, 1990; Reich et al., 2005) that suggest that solubility of Au in solid solution of pyrite is a function of As. On the other hand, higher gold contents in the As-poor zones imply non-exclusive contribution of As in the context of higher gold concentration in pyrite. This is because of occurrence of gold as nanoparticles and/or its incorporation in the melts involving low
melting point chalcophile elements such as Te and Bi at upper greenschist facies conditions (e.g., Ciobanu et al., 2012; Cook et al., 2009). The presence of most of the points above the Au solubility limit (Fig. 10d) and the lack of any correlation between Au with As or Fe (Fig. 10c, d) may suggest the existence of Au mostly as nanoparticles (Auo) in earlier sedimentary and diagenetic pyrites. Maximum Au values of 280 ppm (PyI), 450 ppm (PyII), 330 ppm (PyIII) and 500 ppm (PyIV), reported in this study, are on the higher side compared to published data on invisible gold contents in sediment-hosted gold deposits (Large et al., 2009). However, Palenik et al. (2004) have reported invisible gold as high as 0.84 wt.% (EPMA data) in thin As rich zones (1–20 μm) of arsenian pyrite (8.1 wt.% As) from Screamer zone of Betze-Post-Screamer deposit in Carlin trend, which is highest ever reported from Carlin type deposits. On the contrary, the later hydrothermal pyrites from Kundarkocha are relatively depleted in As (highest 2.2; average 0.38 wt.%) and coarse-grained (~500 μm). Gold in the later hydrothermal or syn-deformational pyrite (As-rich PyIV) is more likely to be structurally-bound. The hydrothermal solution responsible for precipitation of later generations of pyrite (As-rich PyIV) was possibly undersaturated with respect to Auo as indicated by most of the analyses which plot below the solubility limit defined by the Au versus As plot (Fig. 10d) (e.g., Reich et al., 2005). 6.2. Pyrite growth and remobilization of trace elements The fine-grained framboidal nature of PyI can be explained by rapid nucleation of the mineral at low temperature sedimentary conditions (Butler and Rickard, 2000). Their coarsening to form larger euhedral porphyroblasts was due to (i) recrystallization, as a consequence of
142
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
Fig. 8. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14e (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). Polycrystalline aggregates of PyIV appear to grow by dissolution–reprecipitation of earlier pyrites with relicts of PyII and PyIII shown by dotted curves/lines. PyIV has patchy zonation of Co and As. See text for discussion.
slower growth with increasing temperature during subsequent diagenesis and low grade metamorphism (Craig et al., 1998; Wagner and Boyce, 2006) resulting in PyII and (ii) overgrowth by later pyrites (Large et al., 2007), as is the case with PyIII and PyIV. PyII is the most common variety amongst all the pyrite types that (i) contains inclusions of silicates and rare sulfides, and (ii) possesses relatively lower contents of Co, Ni (with varying Co to Ni ratios), intermediate As values and maximum Au concentrations of 450 ppm. In addition, these pyrites are characterized by the highest contents of a large number of trace elements, of which presence of some (Ti, Zn, Rb, Sr, Ba and Pb) may be a consequence of visible inclusions, and others may occur in solid solutions or as ubiquitous nanoparticles (Cook et al., 2009; Deditius et al., 2011; Huston et al., 1995; Winderbaum et al., 2012). The third generation pyrite type is rather rare that shows textural indications of overgrowing PyII and contains both silicate and sulfide (galena and sphalerite) inclusions. Moderate concentrations of Co, high Ni contents, Co/Ni >1 and relatively low Au values typify this pyrite type. In general, these pyrites have higher concentrations of large-ion lithophile (and chalcophile) elements, possibly due to presence of surficial inclusions, but lower values of high-field strength elements. The last generation of pyrite occurs as polycrystalline aggregates that seem to have overgrown both PyII and PyIII. These pyrites (i) contain inclusions of Au, chalcopyrite and sphalerite (ii) are Co-, As rich, often showing oscillatory zoning for these two elements, and (iii) have lowest concentration of all other trace elements. Further, barring exceptions, Ni contents are generally low. Although anomalously high gold concentrations of 500 ppm were observed, the mean Au value (203 ppm) is less compared to PyI and PyII and more or less similar to that in PyIII. In general, the fine-grained sedimentary pyrites are enriched in trace elements whereas their recrystallization during hydrothermal activity,
metamorphism and shear deformation results in their expulsion to form other sulfides or they get incorporated into the sulfides as micro-to-nanoinclusions (Deditius et al., 2011; Huston et al., 1995; Large et al., 2009), leading to formation of coarse grained syndeformational pyrites that are depleted in trace elements (e.g., Chernoff and Barton, 2001; Large et al., 2007, 2011; Layton-Matthews et al., 2008). Such decrease in trace element contents has been observed in PyII through PyIV. However, hydrothermal and metamorphic pyrites may be highly enriched in certain trace elements such as Co, Ni and As that occur as solid solution (Craig et al., 1998), as also seen in Kundarkocha pyrites. Studies of earlier workers (e.g., Large et al., 2007, 2009) suggest that early diagenetic pyrite have elevated Au content (0.2–200 ppm), which is remobilized during subsequent recrystallization to form large sediment-hosted deposits such as Sukhoi Log, Bendigo, Carlin and Spanish Mountain. The above authors have observed Au–As-rich rims on later hydrothermal pyrites in Bendigo and Carlin whereas the Ni–Co rims on the hydrothermal pyrites of Sukhoi Log and Spanish Mountain do not have any detectable Au. The Kundarkocha hydrothermal pyrites (PyII through PyIV) exhibit elevated Au contents irrespective of their As contents, implying that the majority of gold occurs as nanoparticles. However, there remains an inconsistency in the Au contents of these later pyrites. Inclusions of native gold and sulfides are present in the later hydrothermal pyrites. The higher Au content in the later pyrite may indicate the inability of the hydrothermal fluid to remobilize gold from the early diagenetic pyrites during recrystallization or later dissolution and reprecipitation. Pyrite may play a significant role for scavenging trace metals in hydrothermal systems thereby monitoring the fluid composition (Reich et al., 2013). Also, the As-rich nature of the later pyrites might be responsible for locking gold in the structure of pyrite.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
143
Fig. 9. Photomicrograph showing EPMA line scan and ICP-MS laser ablation spots in sample# KU14f (a); X-ray element maps (b–d) of different generations of pyrites, vertical color bars represent relative elemental concentrations from low (bottom) to high (top). PyII is overgrown by PyIV and the latter displays oscillatory zoning of Co and As. Mineral abbreviations used in the figure are after Kretz (1983).
Fig. 10. Bivariate plots showing element correlations in pyrite (a through d); solubility limit of Au in pyrite as a function of As is shown by the solid line in (d). Arsenic and sulfur have a negative correlation (a) implying occurrence of arsenic as As−1; Au has a broad positive correlation for those analyses falling below the solubility limit of Au in pyrite (d). See text for discussion.
144
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145
However, the elevated nature of Au in the Co-rich zones of late hydrothermal pyrite (PyIV) remains unclear. 7. Conclusions Based on distinct chemical and textural features, four pyrite types were identified in the carbonaceous phyllite and auriferous veins at Kundarkocha. The pyrite history started with syn-sedimentary to early-diagenetic framboidal types (PyI) that are characterized by low values of Co, As and uniformly high gold contents. Successive generations of pyrites (PyII through PyIV) formed as a consequence of diagenetic–metamorphic recrystallization and later fluid-assisted overgrowths. PyII contains the highest concentrations of trace elements, which decreased in PyIII and PyIV, essentially due to coupled dissolution–reprecipitation. However, the gold content remained the same since the metal was primarily confined in the host pyrites as nanoparticles. Thus, the inefficiency of hydrothermal fluid to remobilize gold from its initial sink, i.e., sedimentary to syn-diagenetic pyrite, for whatever reason, might have resulted in small deposits such as Kundarkocha. Acknowledgments PH thanks the Council of Scientific and Industrial Research, India for the financial assistance in the form of a Research Fellowship. The authors acknowledge the cooperation and help extended during fieldwork by authorities of M/s Manmohan Mineral Industries Pvt. Ltd. SEM-BSE imaging and partial EPMA data were generated by the equipments procured through a DST funding (IR/S4/ESF-08/2005) to the Department of Geology and Geophysics, IIT Kharagpur. Dr. Dewashish Upadhyay is thanked for his help in LA-ICP-MS analyses. Constructive comments from Martin Reich and two anonymous journal reviewers, and editorial assistance from Cristiana Ciobanu and Franco Pirajno helped to improve the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.oregeorev.2013.05.006. References Augé, T., Cocherie, A., Genna, A., Armstrong, R., Guerrot, C., Mukherjee, M.M., Patra, R.N., 2003. Age of the Baula PGE mineralization (Orissa, India) and its implications concerning the Singhbhum Archaean nucleus. Precambrian Res. 121, 85–101. Aylmore, M.G., 1995. Distribution and Agglomeration of Gold in Arsenopyrite and Pyrite. (Ph.D. thesis) Curtin University, Perth. Baidya, T.K., 1996. Prospect for gold in some areas of the Eastern Indian shield. Proc. National Workshop on Exploration and Exploitation of Gold Resources of India, 2–4 December. NGRI, Hyderabad, pp. 165–169. Banerjee, A.K., Thiagarajan, T.A., 1965. Progress report of investigation of gold at Kunderkocha Singhbhum district, Bihar. Bull. Geol. Surv. India Ser. A 38, 106. Barley, M.E., Groves, D.I., 1990. Deciphering the tectonic evolution of Archaean greenstone belts: the importance of contrasting histories to the distribution of mineralization in the Yilgarn Craton, Western Australia. Precambrian Res. 46, 3–20. Belcher, R.W., Rozendaal, A., Przybylowicz, W.J., 2004. Trace element zoning in pyrite determined by PIXE elemental mapping: evidence for varying ore–fluid composition and electrochemical precipitation of gold at the Spitskop deposit, Saldania Belt, South Africa. X-ray Spectrom. 33, 174–180. Boyle, R.W., 1979. The geochemistry of gold and its deposits (together with a chapter on geochemical prospecting for the element). Geol. Surv. Can. Bull. 280. Butler, I.B., Rickard, D., 2000. Framboidal pyrite formation via the oxidation of iron (II) monosulfide by hydrogen sulphide. Geochim. Cosmochim. Acta 64, 2665–2672. Cabri, L.J., Newville, M., Gordon, R.A., Crozier, E.D., Sutton, S.R., McMahon, G., Jiang, D.T., 2000. Chemical speciation of gold in arsenopyrite. Can. Mineral. 38, 1265–1281. Chernoff, C.B., Barton, M.D., 2001. Trace elements in black shale Fe-sulfides during diagenesis and metamorphism. Geological Society of American Annual Meeting, November 5–8. Chouinard, A., Paquette, J., Williams-Jones, E., 2005. Crystallographic controls on trace element incorporation in auriferous pyrite from Pascua epithermal high-sulfidation deposit, Chile-Argentina. Can. Mineral. 43, 951–963.
Ciobanu, C.L., Cook, N.J., Utsunomiya, S., Kogagwa, M., Green, L., Gilbert, S., Wade, B., 2012. Gold-telluride nanoparticles revealed in arsenic-free pyrite. Am. Mineral. 97, 1515–1518. Cline, J.S., Hofstra, A., Muntean, J., Tosdal, D., Hickey, K., 2005. Carlin-type gold deposits in Nevada: critical geologic characteristics and viable models. Economic Geology 100th Anniversary Volume, pp. 451–484. Cook, N.J., Chryssouilis, S.L., 1990. Concentrations of invisible gold in the common sulfides. Can. Mineral. 28, 1–16. Cook, N.J., Ciobanu, C.L., Mao, J., 2009. Textural control on gold distribution in As-free pyrite from the Dongping, Huangtuliang and Hougou gold deposits, North China Craton (Hebei Province, China). Chem. Geol. 261, 101–121. Craig, J.R., Vokes, F.M., 1993. The metamorphism of pyrite and pyretic ores: an overview. Mineral. Mag. 57, 3–18. Craig, J.R., Vokes, F.M., Solberg, T.N., 1998. Pyrite: physical and chemical textures. Miner. Deposita 34, 82–101. Crocket, J.H., 1990. Distribution of gold in the Earth's crust. In: Foster, R.P. (Ed.), Gold Metallogeny and Exploration. Chapman and Hall, London, New York, NY, pp. 1–36. Deditius, A.P., Utsunomiya, S., Renock, D., Ewing, R.C., Ramana, C.V., Becker, U., Kesler, S.E., 2008. A proposed new form of arsenian pyrite: composition, nanostructure and geochemical significance. Geochim. Cosmochim. Acta 72, 2919–2933. Deditius, A.P., Utsunomiya, S., Ewing, R.C., Kesler, S.E., 2009. Nanoscale “liquid” inclusions of As–Fe–S in arsenian pyrite. Am. Mineral. 94, 391–394. 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. Fleet, M.E., Mumin, A.H., 1997. Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis. Am. Mineral. 82, 182–193. Glaus, R., Kaegi, R., Krumeich, F., Günther, D., 2010. Phenomenological studies on structure and elemental composition of nanosecond and femto-second laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochim. Acta B 65, 812–822. Hough, R.M., Noble, R.R.P., Reich, M., 2011. Natural gold nanoparticles. Ore Geol. Rev. 42, 55–61. Huston, D.L., Sie, S.H., Suter, G.F., Cooke, D.C., Both, R.A., 1995. Trace elements in sulfide minerals from eastern Australian volcanic-hosted massive sulfide deposits: Pt. 1. Proton microprobe analyses of pyrite, chalcopyrite and sphalerite. Econ. Geol. 90, 1167–1196. Johan, Z., Marcoux, E., Bonnemaison, M., 1989. Arsenopyrite aurifere: Mode de substitution de Au dans la structure de FeAsS. C. R. Acad. Sci. (Paris) 308, 185–191. Johnston, M.K., Ressel, M.W., 2004. Carlin-type and distal-disseminated Au–Ag deposits: related distal expressions of Eocene intrusive centers in north-central Nevada: society of Economic Geologists Newsletter 59. Controversies on the origin of world-class gold deposits. Part I, carlin-type gold deposits in Nevada. Soc. Econ. Geol. Newsl. 59, 12–14. Kerrich, R., Goldfarb, R.J., Richards, J.P., 2005. Metallogenic provinces in an evolving geodynamic framework. Econ. Geol. 100, 1097–1136. Ketris, M.P., Yudovitch, Y.E., 2009. Estimations of clarkes for carbonaceous bioliths: world averages for trace element contents in black shales and coals. Int. J. Coal Geol. 78, 135–148. Kretschmar, U., Scott, S.D., 1976. Phase relations involving arsenopyrite in the system Fe–As–S and their application. Can. Mineral. 14, 364–386. Kretz, R., 1983. Symbols for rock-forming minerals. Am. Mineral. 68, 277–279. Large, R.R., Maslennikov, V., Robert, F., Danyushevsky, L.V., Chang, Z., 2007. Multistage sedimentary and metamorphic origin of pyrite and gold in the giant Sukhoi Log deposit, Lena gold province, Russia. Econ. Geol. 102, 1233–1267. 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. Layton-Matthews, D., Gemmell, J.B., Large, R.R., Peter, J., 2008. Trace element budget of the Que River shale: exploration implications of hanging-wall modification of sulfide minerals at the Hellyer deposit, Tasmania. 33rd International Geological Congress, Oslo-2008, August 6–14. Mahadevan, T.M., 2002. Geology of Bihar and Jharkhand. Geological Society of India Bangalore (563 pp.). Marcoux, E., Bonnemaison, M., Braux, C., Johan, Z., 1989. Distribution de Au, Sb, As et Fe dans l'arsenopyrite aurifere du Chatelet et de Villeranges. C. R. Acad. Sci. 308, 293–300. Mishra, S., Deomurari, M.P., Wiedenbeck, M., Goswami, J.N., Ray, S., Saha, A.K., 1999. 207 Pb/206Pb zircon ages and the evolution of the Singhbhum Craton, eastern India: an ion microprobe study. Precambrian Res. 93, 139–151. Mishra, B., Saravanan, C.S., Kartikeya, S., 2008. Thermobarometry, trace element zoning and invisible gold in pyrite from the Kunderkocha gold prospect, Eastern India. Abstract, 33rd International Geological Congress, Oslo-2008, August 6–14. 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 the Southern Iron Ore Group, Singhbhum Craton. J. Geol. 116, 449–461. Murakami, H., Ishihara, S., 2013. Trace elements of Indium-bearing sphalerite from tinpolymetallic deposits in Bolivia, China and Japan: a femto-second LA-ICPMS study. Ore Geol. Rev. 53, 223–243. Palenik, C.S., Utsunomiya, S., Reich, M., Kesler, S.E., Wang, L., Ewing, R.C., 2004. “Invisible” gold revealed: direct imaging of gold nanoparticles in a Carlin-type deposit. Am. Mineral. 89, 1359–1366. Pouchou, J.L., Pichoir, F., 1984. A new model for quantitative x-ray microanalysis. I.-Application to the analysis of homogeneous samples. Rech. Aerosp. 3, 167–192. Reich, M., Kesler, S.E., Utsunomiya, S., Palenik, C.S., Chryssoulis, S.L., Ewing, R.C., 2005. Solubility of gold in arsenian pyrite. Geochim. Cosmochim. Acta 69, 2781–2796.
P. Hazarika et al. / Ore Geology Reviews 55 (2013) 134–145 Reich, M., Utsunomiya, S., Kesler, S.E., Wang, L.M., Ewing, R.C., Becker, U., 2006. Thermal behaviour of metal nanoparticles in geologic materials. Geology 34, 1033–1036. Reich, M., Deditius, A., Chryssoulis, S., Li, J.W., Ma, C.Q., Parada, M.A., Barra, F., Mittermayr, F., 2013. Pyrite as a record of hydrothermal fluid evolution in a porphyry copper system: a SIMS/EMPA trace element study. Geochim. Cosmochim. Acta 104, 42–62. Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., 2002a. Mid-Proterozoic plume-related thermal event in eastern Indian craton: evidence from trace elements, REE geochemistry and Sr–Nd isotope systematics of basic-ultrabasic intrusives from Dalma volcanic belt. Gondwana Res. 5, 133–146. Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., 2002b. Sm–Nd age and mantle source characteristics of the Dhanjori volcanic rocks, eastern India. Geochem. J. 36, 503–518. Saha, A.K., 1994. Crustal evolution of Singhbhum North Orissa. Geol. Soc. India Mem. 27 (341 pp.). Saha, A.K., Ray, S.L., 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: Geological Society of India Memoir, 8, pp. 13–37. Sharma, M., Basu, A.R., Ray, S.L., 1994. Sm–Nd isotopic and geochemical study of the Archaean Tonalite–Amphibolite association from the eastern Indian Craton. Contrib. Mineral. Petrol. 117, 45–55. Sharp, Z.D., Essene, E.J., Kelly, W.C., 1985. A reexamination of the arsenopyrite geothermometer: pressure considerations and applications to natural assemblages. Can. Mineral. 23, 517–534. Simon, G., Huang, H., Penner-Hahn, J.E., Kesler, S.E., Kao, L.S., 1999. Oxidation state of gold and arsenic in gold-bearing arsenian pyrite. Am. Mineral. 84, 1071–1079.
145
Spooner, E.T.C., 1993. Magmatic sulphide/volatile interaction as a mechanism for producing chalcophile element enriched, Archean Au-quartz, epithermal Au–Ag and Au skarn hydrothermal ore fluids. Ore Geol. Rev. 7, 359–379. Sung, Y.H., Brugger, J., Ciobanu, C.L., Pring, A., Skinner, W., Nugus, M., 2009. Invisible gold in arsenian pyrite and arsenopyrite from a multistage Archaen 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 the Campbell mine, Red Lake greenstone belt, Ontario: evidence for mineralization during the peak of metamorphism. Can. Mineral. 35, 805–815. Thomas, H.V., Large, R.R., Bull, S.W., Maslennikov, V., Berry, R.F., Fraser, R., Froud, S., Moye, R., 2011. Pyrite and pyrrhotite textures and composition in sediments, laminated quartz veins, and reefs at bendigo gold mine, Australia: insights for Ore Genesis. Econ. Geol. 106, 1–31. Velásquez, G., Borisova, A.Y., Salvi, S., Béziat, D., 2012. In situ determination of Au and Cu in natural pyrite by near‐infrared femtosecond laser ablation‐inductively coupled plasma‐quadrupole mass spectrometry: no evidence for matrix effects. Geostand. Geoanal. Res. 36, 315–324. Wagner, T., Boyce, A.J., 2006. Pyrite metamorphism in the Devonian Hunsruck Slate of Germany: insights from laser microprobe sulfur isotope analysis and thermodynamic modelling. Am. J. Sci. 306, 525–552. Winderbaum, L., Ciobanu, C.L., Cook, N.J., Paul, M., Metcalfe, A., Gilbert, S., 2012. Multivariate analysis of an LA-ICP-MS trace element dataset for pyrite. Math. Geosci. 44, 823–842. Wu, X., Delbove, F., 1989. Hydrothermal synthesis of gold-bearing arsenopyrite. Econ. Geol. 84, 2029–2032.