CH4-N2 in the Maldon gold deposit, central Victoria, Australia

Ore Geology Reviews 58 (2014) 225–237

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CH4-N2 in the Maldon gold deposit, central Victoria, Australia Bin Fu a,b,⁎, Terrence P. Mernagh c, Alison M. Fairmaid b, David Phillips b, Mark A. Kendrick b a b c

Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia School of Earth Sciences, The University of Melbourne, Parkville, VIC 3010, Australia Geoscience Australia, PO Box 378, Canberra, ACT 2601, Australia

a r t i c l e

i n f o

Article history: Received 26 July 2013 Received in revised form 7 November 2013 Accepted 21 November 2013 Available online 28 November 2013 Keywords: Fluid inclusions Methane Nitrogen Gold mineralisation Metamorphism Magmatism Central Victoria

a b s t r a c t The Maldon gold deposit in central Victoria has geological, geochronological and fluid chemistry characteristics that distinguish it from typical vein-hosted, ‘orogenic’ gold deposits in this region. The deposit lies within the thermal aureole of the Late Devonian Harcourt Granite and associated granitic dykes that postdate regional metamorphism (~445 Ma) and large gold deposits such as Bendigo. The fluid inclusions are characterised by the presence of non-aqueous (i.e. carbonic) fluids, which exhibit complex freezing and heating behaviour, as well as mixed CO2–low-salinity aqueous fluids (mostly ≤10 wt.% NaCl eq.). Raman analysis indicates that carbonic inclusions can vary from CO2-rich to CH4 + N2-rich. Furthermore, higher-salinity fluid inclusions, containing 20–22 wt.% NaCl eq., occur locally. Overall, fluid inclusions in the K-feldspar zone are much less abundant by volume than those in the cordierite zone probably due to recrystallisation, suggesting limited magmatic fluid input. The Harcourt Granite is a moderately reduced, I-type granite and it is suggested that the ‘retrograde’, reduced fluids (e.g. CH4 + N2-rich), formed within the thermal aureole of the granite and associated dykes during contact metamorphism, are not part of the regional mineralising fluid system, which was dominated by deeply derived CO2–low-salinity aqueous fluids of metamorphic origin. Thus, the Maldon deposit is an ‘orogenic’ gold deposit that was metamorphosed and/or remobilised during the emplacement of post-orogenic intrusions. © 2013 Elsevier B.V. All rights reserved.

1. Introduction It has been long recognised that the transport and precipitation of gold and related components such as sulphur and carbon are controlled by fluid composition (e.g. Ho et al., 1990; Phillips, 1993; Phillips and Evans, 2004; Ridley and Diamond, 2000). Gold mineralisation commonly occurs in low- to high-grade metamorphic rocks from Archean greenstone belts and much younger slate belts or, arguably, is sometimes associated with reduced intrusions (e.g. Goldfarb et al., 2005; Groves et al., 1998; Hart, 2007; Thompson and Newberry, 2000; Thompson et al., 1999) and there has been considerable debate as to whether the mineralising fluids are of metamorphic or magmatic origin (e.g. Phillips, 1993; Phillips and Hughes, 1996; Groves and Phillips, 1987; Goldfarb et al., 2005; Wall, 2005; Phillips and Powell, 2009, 2010; Yardley and Cleverley, in press; Xue et al., 2013). In some cases, where gold veins occur in the roof of a coeval pluton (e.g. Fort Knox, Alaska and Timbarra, Australia), it appears that there is a clear genetic association and that they may be classed as reduced intrusion-related gold systems (RIRGS). The most diagnostic deposit style within the RIRGS classification is intrusion-hosted sheeted arrays of thin, low-sulphide quartz veins with an Au–Bi–Te–W signature (Hart, 2007). RIRGS fluids may differ in composition from those in ‘orogenic’ gold deposits that are low-salinity aqueous, typically 3–7 wt.% ⁎ Corresponding author at: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. E-mail address: [email protected] (B. Fu). 0169-1368/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.oregeorev.2013.11.006

NaCl equiv., mixed with certain amounts of CO2 ± H2S (e.g. Phillips and Powell, 2010). RIRGS in shallow environments typically contain high temperature (N 350 °C), immiscible brine (N30 wt.% NaCl equiv.) and low salinity (b 5 wt.% NaCl equiv.) vapour inclusions that commonly contain CO2. RIRGS in deeper environments contain abundant low-salinity CO2rich, aqueous fluids (b10 wt.% NaCl equiv.), which in some deposits are post-dated by moderate- to high-salinity brines (10–40 wt.% NaCl equiv.) (Baker, 2002; Mernagh et al., 2007). Previous fluid inclusion studies on Australian gold deposits have demonstrated a common association of low-salinity, CO2-bearing or CO2rich (carbonic) fluid inclusions with gold mineralisation (e.g. Mernagh et al., 2007) but the fluid compositions of gold deposits may vary widely. For example, in the Yilgarn Craton of Western Australia, Fan et al. (2000) reported CH 4-rich fluids in gold-rich skarns at the Nevoria deposit and Hagemann and Lüders (2003) reported CH4-bearing fluids in quartz and high-salinity fluids (≤ 24 wt.% NaCl equiv.) in stibnite from the Wiluna gold deposit in Western Australia. Similarly, Polito et al. (2001) reported highsalinity (≤ 42 wt.% NaCl equiv.) fluids in pre-gold, Mo-type quartz veins and CH 4 -rich fluids in syn-gold, quartz-calcite veins at the Junction gold deposit. However, little attention has been paid to fluid inclusions in gold deposits within thermal aureoles of intrusions such as Maldon in central Victoria, Australia. This study focuses on the Maldon gold deposit where N2 + CH4-rich inclusions are abundant and builds on the previously published microthermometric results for fluid inclusions from Victorian gold deposits including Maldon (e.g. Fu et al.,

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2012). We attempt to better characterise the fluid inclusions and further determine the origin of gold-mineralising fluids and the genesis of the Maldon gold deposit and help distinguish, if any, so-called RIRGS from ‘orogenic’ gold deposits worldwide. 2. Geology The western Lachlan Orogen in central Victoria, Australia, is a historically important gold province, having produced approximately 2500 tonnes of gold since the 1850s (Phillips and Hughes, 1996; Phillips et al., 2003; Ramsay et al., 1998). Gold mineralisation occurs throughout the western Lachlan Orogen, which has been sub-divided, from west to east, into the Stawell, Bendigo and Melbourne zones, separated by a series of faults (e.g. Gray and Foster, 1998; VandenBerg et al., 2000; Miller et al., 2006; Fig. 1). The Stawell and Bendigo zones are separate structural entities but have a similar structure and stratigraphy. The Bendigo Zone consists of Cambrian metavolcanic rocks, overlain by quartz-rich turbidites of the Ordovician Castlemaine Supergroup (VandenBerg et al., 2000). This sequence was deformed along north-trending axes prior to intrusion of Late Devonian granites. The Bendigo Zone is bounded to the west by the Avoca Fault Zone and to the east by the Mount William Fault Zone. Both are west-dipping, listric thrust faults carrying Cambrian greenstones in their hanging walls. The Melbourne zone lies to the east of the Bendigo zone and is distinctive in that it contains a conformable marine sedimentary succession (the Murrindindi Supergroup) that extends continuously from the Ordovician to the end of the Early Devonian (VandenBerg et al., 2000). The Maldon gold deposit (56 t Au) shares many similarities to other typical ‘orogenic’ gold deposits, such as Bendigo and Ballarat. All occur

within the Bendigo Zone, and have similar host rock lithologies and structural styles of mineralisation (e.g. Phillips et al., 2003). Mineralisation is hosted by quartz reefs in fracture systems cutting Early Ordovician metasediments. Several deformation events have affected the gold deposit, resulting in a variety of fault and reef structures with associated alteration (Ebsworth et al., 1998). The auriferous reefs occur mainly within high-angle fractures associated with the overturned western limbs of some anticlines, which strike slightly west of north and have steep east-dipping axial planes. Mineralisation occurs in pipe-like shoots and in small cross-cutting fractures. The reefs have a complex history of vein paragenesis, faulting and alteration, which have been attributed to D3–D6 structures (Ebsworth et al., 1998). In contrast to other gold deposits in the region, the Maldon deposit (Fig. 2) is situated in the thermal aureole of the Late Devonian Harcourt Granite. From the Harcourt Granite, the contact metamorphism grades outwards through a K-feldspar zone, a cordierite zone, and a biotite zone (Hughes et al., 1997). Mineralisation occurs as native gold and minor maldonite (Au2Bi) and is accompanied by sericite–chlorite– carbonate alteration. Other ore minerals include pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, molybdenite, scheelite, bismuth, native antimony and stibnite. The sharp truncation of the quartz veining by the granite, the presence of granitic dykes cross-cutting quartz veins, and the abrupt termination of the mineralised high-strain zone at the granite contact indicate intrusion after the main mineralisation event (Phillips and Hughes, 1996). Ciobanu et al. (2010) also argued that mineralisation at Maldon was the product of a single main event involving gold-rich fluids formed during deformation prior to emplacement of the intrusion, with at least two later events of sulphidation of initial Au– Bi ± Te associations producing local-scale reworking and remobilisation of the initial ore. The subsequent events refined the ore, increasing the

Fig. 1. Pre-Permian map of central Victoria, Australia showing major faults, structural zones and seismic sections (Fu et al., 2012; modified after VandenBerg et al., 2000). Abbreviations: MF — Moyston Fault; CF — Coongee Fault; AF — Avoca Fault; MuF — Muckleford Fault; WF — Whitelaw Fault; MWF — Mount William Fault (in the Heathcote Fault Zone); GF — Governor Fault (in the Mount Wellington Fault Zone). SG — Stawell Granite; HG — Harcourt Granite. Gold deposits included in this study: 1. Stawell — Magdala; 2. Maldon; 3. Bendigo; 4. Wattle Gully; 5. Fosterville; 6. Ballarat; 7. Mount Piper; 8. Woods Point; 9. Walhalla.

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Fig. 3. Simplified drill hole logging and sample locations. Minor felsic or mafic dykes are not shown.

Fig. 2. Geological map of the Maldon gold deposit, central Victoria and sample locations, modified after Ebsworth and Krokowski de Vickerod (2002). Early Ordovician sedimentary rocks in the region are Castlemainian (Olc) and Lancefieldian (Oll). Inferred contact metamorphic isograds around the Harcourt Granite include: a K-feldspar (Kfs) zone, a cordierite (Crd) zone and a biotite (Bt) zone (Hughes et al., 1997). Quartz samples were collected from the following drill holes: DDH088 (M05 and M06), Nuggetty Reef in the K-feldspar zone; DDH093 (M09 and M12), Derby Reef in the cordierite zone; DDH120 (M13, M14, M15 and M16) and DDH122 (M18), Eaglehawk Reef in the cordierite zone.

proportion of gold relative to the initial maldonite with no or little additional input of gold and the latest sulphidation event is attributed to ‘retrograde’ fluids in the thermal aureole (Ciobanu et al., 2010). 3. Sample descriptions and analytical methods Both samples M14 and M15, newly collected from DDH120 (380.5 m and 380.7 m), are within an interval that graded 0.94 g/t Au, and are quartz veins in altered/mineralised metapelite in the cordierite zone, i.e., Eaglehawk Reef. Six other quartz specimens of Fu et al. (2012) from three drill holes (DDH088, DDH120 and DDH122) into the Maldon gold deposit were repeated for further detailed petrographic and fluid inclusion analysis: M05 and M06 (DDH088) from Nuggetty Reef in the K-feldspar zone; M12 (DDH093) from Derby Reef and M13 and M16 (DDH120) and M18 (DDH122) from Eaglehawk Reef in the cordierite zone (Figs. 2 and 3). Descriptions of the samples and two others (M02 and M09) from Fu et al. (2012) are summarised in Table 1. All doubly polished, thick sections (200–300 μm) were prepared at the Australian National University, Canberra. Fluid inclusion microthermometric measurements were undertaken using either the

Monash University (Melbourne) Linkam FTIR600 heating/freezing stage or the Geoscience Australia (Canberra) Linkam MDS600 heating/freezing stage. Both heating/freezing stages were calibrated with synthetic fluid inclusions (pure CO2 in a CO2–H2O mixture, and pure H2O). The uncertainty of solid CO2 and ice melting temperatures at and below 20 °C was better than ±0.3 °C, whereas the uncertainty of the H2O homogenisation temperature at the critical point (374 °C) was ±3 °C. Abbreviations of the different types of microthermometric measurements made on fluid inclusions are listed in Table 2. Raman spectra of representative fluid inclusions were recorded on Geoscience Australia's HORIBA Jobin Yvon LabRAM spectrometer equipped with a holographic notch filter, 600 and 1800 g/mm gratings, and a liquid N2 cooled, 2000 × 450 pixel CCD detector. The inclusions were analysed with 514.5 nm laser excitation from a Melles Griot 543 Series argon ion laser, using 5 mW power. A 100× Olympus microscope objective was used to focus the laser beam and collect the scattered light. The focused laser spot on the samples was approximately 1 μm in diameter. Wavenumbers are accurate to ± 1 cm−1 as determined by plasma and neon emission lines. For the analysis of CO2, O2, N2, H2S and CH4 in the vapour phase, spectra were recorded from 1100 to 3200 cm−1 using a single 30 s integration time per spectrum. Raman detection limits (Wopenka and Pasteris, 1987) are estimated to be around 0.1 mol% for CO2, O2 and N2, and 0.03 mol% for H2S and CH4 and errors in the calculated gas ratios are generally less than 1 mol%. A full table of Raman results (mole fractions or mol.%) for gas species (CO2, N2, H2S and CH4) in non-aqueous fluid inclusions or mixed gas– aqueous fluid inclusions is available in Appendix A. 4. Results Fluid inclusions in the Maldon gold deposit are very complex, compared to many other Victorian gold deposits (Fu et al., 2012 and references therein). This is a likely consequence of the intrusion of the Harcourt Granite into a pre-existing ‘orogenic’ gold deposit. It is noted that, when recrystallised, quartz in veins is commonly finegrained and devoid of fluid inclusions (Fig. 4). Therefore, the fluid inclusion studies were restricted to the larger, relict quartz grains, which contained the earlier generations of fluid inclusions. Based on phase associations, microthermometric data and Raman spectroscopic results, the fluid inclusions can be divided into the following four compositional types (Fig. 5): (1) high-salinity fluid inclusions (20–22 wt.% NaCl eq.) (W1), with degree of filling, F = 0.90–0.95;

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Table 1 List of quartz samples from the Maldon gold deposit, central Victoria, Australia. Sample Locality name M02

Grade Sample description (g/t Au)

M05

Dyke related to the Harcourt Granodiorite Not (DDH-57 W1/ca. 292 m) assayed Nuggetty Reef (DDH088/168.3 m) 0.08

M06

Nuggetty Reef (DDH088/173.3 m)

0.09

M09

Derby Reef (DDH093/228.85 m)

0.07

M12 M13

Derby Reef (DDH093/246.8 m) Eaglehawk Reef (DDH120/377.1 m)

0.02 0.04

M14

Eaglehawk Reef (DDH120/380.5 m)

0.94

M15 M16

Eaglehawk Reef (DDH120/380.7 m) Eaglehawk Reef (DDH120/383.25 m)

0.94 0.1

M18

Eaglehawk Reef (DDH122/264.2 m)

0.1

Unaltered feldspar-rich granitic dyke. 70% quartz veins grading to laminated quartz with stylolitic mineralised seams. Moderately phyllosilicate (phlogopite) altered and weakly carbonate (now cordierite) altered fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–10% pyrrhotite & arsenopyrite, 1–2% chalcopyrite, trace to minor sphalerite and a possible trace of visible gold. Massive, milky white quartz with minor phyllosilicate (phlogopite) and chlorite alterated metasediment fragments, common pyrite & a trace of pyrrhotite. Close to the east bounding fault with 10% quartz veining in moderately phyllosilicate (phlogopite)–sericite-silica altered fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–2% pyrrhotite and arsenopyrite and common pyrite. Felsic dyke, alteration not recorded, 1–2% disseminated pyrrhotite and common pyrite 60% laminated to breccia style stylolitic quartz veins in very strongly silicified, strongly phyllosilicate (phlogopite) altered, strongly carbonate (now cordierite) altered and moderately chloritised fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–2% pyrrhotite & pyrite, common arsenopyrite and a trace of chalcopyrite. Close to the east bounding fault with 50% quartz veining in very strongly silicified, strongly phyllosilicate (phlogopite) altered, strongly carbonate (now cordierite) altered and moderately chloritised fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–2% pyrrhotite and arsenopyrite, minor pyrite and a trace of chalcopyrite. Same as above Within the east bounding fault zone, comprising 10% laminated quartz veins in very strongly silicified, strongly phyllosilicate (phlogopite) altered, moderately carbonate (now cordierite) altered and moderately chloritised fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–2% pyrrhotite, common pyrite and traces of chalcopyrite & arsenopyrite. 50% laminated to breccia style stylolitic quartz veins in strongly phyllosilicate (phlogopite) altered, strongly carbonate (now cordierite) altered and moderately chloritised fine grained metasedimentary rocks (hornfelsed, graded turbidite depositional units). 1–2% pyrrhotite & pyrite and traces of chalcopyrite & arsenopyrite.

(2) low (to moderate)-salinity aqueous fluid inclusions (W2) with salinities mostly of ≤10 wt.% NaCl eq. and F = 0.6–0.9; (3) mixed carbonic–low-salinity aqueous fluid inclusions (CW), that is, H2O– CO2 ± CH4 ± N2, F ≤ 0.7; and (4) carbonic fluid inclusions (either CO2-rich or CH4-rich) (C) with variable amounts of N2 (≤52.5 mol%). A solid is occasionally seen in low-salinity aqueous fluid inclusions (W2). It does not dissolve at 300 °C or higher and could not be identified by Raman analysis. There are some factors that need to be taken into consideration with regard to relative chronology for the fluid inclusions. (1) The high-salinity fluid inclusions (W1) occur only in one sample (M06) from the K-feldspar zone at Maldon (Fig. 5a). (2) Only low-salinity aqueous inclusions (W2) are observed in the Harcourt Granite (M02) (Fu et al., 2012). (3) CO2-rich inclusions commonly coexist with mixed carbonic– low-salinity aqueous fluid inclusions (CW) and, to a lesser extent, low-salinity aqueous inclusions (W2) (Fig. 5d). (4) Dark, monophase CH4-N2 inclusions occur in a dyke (M12) as well as metasedimentary rocks in the cordierite zone. They do not coexist with other types of fluid inclusions types (Figs. 5f to h).

inclusions (CW) are believed to have formed earlier than CH4-rich inclusions and high-salinity fluid inclusions (W1). However, the lowsalinity, aqueous–carbonic fluid inclusions that have relatively constant CO2/H2O volume ratios (degree of filling: 0.7–0.8) that occur in the nearby Bendigo deposit (Fu et al., 2012) were not observed in this study. This can be interpreted to suggest that ‘primary’ ‘orogenic’ goldmineralising fluids were not preserved at Maldon after post-trapping changes in early quartz (Fig. 4). Fluid inclusions, especially in the cordierite zone, are commonly irregularly shaped, suggesting that the fluid inclusions have been re-equilibrated by processes such as stretching, leakage, decrepitation and necking-down (Bodnar, 2003 and references therein)

Based on the petrographic texture and the mode of occurrence, both CO2-rich inclusions and mixed carbonic–low-salinity aqueous fluid Table 2 Types of microthermometric measurements made on fluid inclusions and their abbreviations. Measurement

Abbreviations

Initial/first melting temperature of ice or solid CO2 (on warming) Final melting temperature of ice, clathrate or solid CO2 (on warming) Homogenisation temperature of aqueous fluids, CO2 or CH4/N2, to liquid (L) or gas/vapour (G/V) as the final phase transition (on warming) Homogenisation temperature of CH4/N2 before the final melting of solid CO2 (on warming), i.e. solid CO2 is present Temperature of solid CO2 disappearance, i.e. melting or sublimation as the final phase transition (on warming) Heterogeneous temperature of CH4/N2 before CO2 is frozen to be a solid phase (on cooling)

Ti Tm Th Ths Ts Thet

Fig. 4. Microphotograph of doubly polished, thick section in cross-polarized, transmitted light showing early quartz and recrystallised quartz from Nuggetty Reef in the Kfeldspar zone at Maldon (sample M06). Scale bar = 1 mm.

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(Fig. 5). Here, we summarise the microthermometric data for all types of fluid inclusions, including those presented in Fu et al. (2012), that are preserved in the Maldon samples. The highest-salinity fluid inclusions (W1) from the Nuggetty Reef have final ice melting temperatures (Tm, ice) between − 16.4 °C and − 18.6 °C (Fig. 6 and Table 3), indicating salinities of 20 to 22 wt.% NaCl eq. (Potter et al., 1978). These inclusions (W1) have a Ti value lower than the eutectic temperature of the NaCl–H2O system (−21 °C). This implies that other ions possibly Ca2+ must be present. The homogenisation temperatures (Th) vary from 158 °C to 187 °C. For the low-salinity aqueous inclusions (W2), final ice melting temperatures (Tm, ice) vary mostly between −6.6 °C and ~0 °C, indicating typical salinities mostly ≤10 wt.% NaCl eq. (Potter et al., 1978; Fig. 6 and Table 3). Two aqueous inclusions in the cordierite zone have slightly higher Tm, ice values of −11.4 °C and −12.1 °C, corresponding to salinities of ~ 16 wt.% NaCl eq., and slightly higher Th values of 199 °C and 213 °C. Although the initial melting temperature, Ti, is rather difficult to determine, some low-salinity aqueous inclusions (W2) have a Ti value close to or above the eutectic temperature (−20.8 °C) of the NaCl–H2O system. The low-salinity aqueous inclusions (W2) homogenise into the liquid phase between 84 °C and 369 °C (Fig. 6 and Table 3). Low-salinity aqueous inclusions (W2) from the cordierite zone have a much wider range in homogenisation temperature than those in the K-feldspar zone (and the Harcourt Granite itself). This may reflect post-trapping changes or reequilibration of the fluid inclusions. Thus, it is unclear if there is an inferred temperature gradient for the mineralising fluids. The carbonic phase of the mixed carbonic–low-salinity aqueous fluid inclusions (CW) freezes at temperatures between −100 °C and −70 °C and undergoes final melting at temperatures (Tm, CO2 or Ts), from − 71.0 °C to − 57.6 °C. When observed, homogenisation to liquid varied between 6.6 and 23.4 °C, or homogenisation to vapour from 11.0 °C to 18.8 °C. The mixed carbonic–low-salinity aqueous fluid inclusions (CW) exhibit final clathrate melting from 8.3 °C to 11.5 °C, indicating salinities of ≤4.0 wt.% NaCl eq., if the NaCl–H2O–CO2 system is assumed (e.g. Diamond, 1992). Total homogenisation temperatures (Th, total) varied between 177 °C and 329 °C, when homogenisation was into the liquid phase, and 171 °C to 362 °C, when homogenisation was into the CO2-vapour phase (Fig. 6). Carbonic fluid inclusions (C) exhibit very complex freezing/heating behaviour. Based on the classification of van den Kerkhof and Thiéry (2001), five subtypes are observed during the microthermometry heating cycle with the final phase transition being either homogenisation of liquid and gas (H-type) or solid disappearance, that is, melting or sublimation (S-type). The five subtypes are as follows: (Ci) These correspond to the H1-type of van den Kerkhof and Thiéry (2001): L + G → L/G. (Where L = liquid; G = gas; and S = solid). (Cii) Their behaviour during microthermometry corresponds to the H3-type, S + L/G → S + L + G → L + G → L/G, as defined by van den Kerkhof and Thiéry (2001). (Ciii) The carbonic inclusions are H4-type (i.e. S + L + G → S + L/G → S + L + G → L + G → L/G). (Civ) These are characterised by S1-type phase transitions (van den Kerkhof and Thiéry, 2001): S + L/G → L/G. (Cv) These are S2-type (i.e. S + L + G → S + L/G → L/G) carbonic inclusions. Some carbonic [i.e. subtype (Ci)] fluid inclusions show homogenisation into liquid at Th from −110.1 °C to −89.2 °C, and homogenisation into gas phase at Th from −102.7 °C to −80.5 °C, which is higher than the critical point of pure CH4 (i.e. − 82.6 °C). No melting of solid CO2 was observed in these inclusions. A solid phase forms in subtype (Cii) inclusions between − 100 °C and − 70 °C and undergoes final melting at temperatures (Tm, CO2) from −65.6 to −58.5 °C. All these Tm, CO2 values are lower than the triple point of pure CO2 at −56.6 °C, suggesting the presence of other gas

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species such as CH4 and/or N2. Subtype (Cii) inclusions homogenise to liquid from −47.7 °C to 13.5 °C or to gas from −30.0 °C to 13.3 °C, all lower than the critical point of pure CO2 at 31.1 °C. Seven subtype (Ciii) carbonic fluid inclusions are characterised by the following phase transitions: CH4 (±N2) homogenisation into liquid or gas between −105.3 °C and −83.0 °C in the presence of solid CO2; solid CO2 melting between − 80.6 °C and −59.9 °C; and CO2 + CH4 (± N 2 ) homogenisation into liquid or gas between − 51.7 °C and − 33.5 °C (open circles with tied solid lines in Fig. 7). Subtype (Civ) has Ts varying from −75.9 °C to −59.0 °C; no homogenisation behaviour above Ts was observed. Carbonic fluid inclusions of subtype (Cv) have Ths (to liquid or gas) between − 105.1 °C and − 90.5 °C, and T s between − 85.2 °C and −64.9 °C. The measured homogenisation temperatures (Th, i.e. Thet, not Ths), are lower than Ts, and range between −95.5 °C and −78.8 °C (to liquid or gas) (e.g. open circles with tied dash lines in Fig. 7). The new Raman analyses expand on the preliminary data reported by Fu et al. (2012) and confirm that the carbonic fluid inclusions (C) have highly variable ratios of CH4/CO2, from CO2-rich to CH4-rich, with N2 contents up to 52.5 mol%. (Fig. 8). In this diagram, it is clear that subtype Cii inclusions are CO2-rich, whereas subtypes Ciii and Cv are CH4(+N2)rich. Furthermore, the diagram shows that the N2 content increases with increasing CH4/CO2 ratio, especially for the cordierite zone. The origin of the fluid inclusion CO2/CH4/N2 compositional variations is the subject of discussion below. In addition to the fluid phases, one of the carbonic inclusions contains graphite, which was confirmed by Raman analysis. Based on parameters calculated from the Raman spectrum (R2 = 0.064; Fig. 9) and using the empirical calibration of Beyssac et al. (2002), the formation temperature of graphite in the carbonic inclusion is estimated at 613 ± 50 °C. Small amounts of H2S, ≤ 2.2 mol%, are also present in some of the carbonic inclusions from the cordierite zone.

5. Discussion 5.1. Origin of nitrogen and methane Mixed CO2 and low-salinity aqueous fluid inclusions and their origins, either metamorphic or magmatic, have been extensively documented and discussed in the literature (e.g. Phillips and Powell, 2009, 2010; Yardley and Cleverley, in press). Here, we discuss the unique fluid type: N2 + CH4-rich inclusions. N2-rich fluid inclusions are very rare in the Victorian goldfields and have only been reported previously from two other localities: Brunswick and Stawell–Magdala (Fu et al., 2012; Gao and Kwak, 1995). It is known that nitrogen release from ammoniumbearing minerals such as micas influences the oxidation state of coexisting, equilibrated fluids (e.g. Andersen et al., 1993; Shepherd et al., 1991). For instance, ammonium ions, displaced from phyllosilicate minerals during wall-rock alteration, may be oxidized to N2 with concomitant reduction of CO2 to CH4: þ

þ

K þ ðNH4  micaÞ ¼ NH3 þ H þ ðK  micaÞ 8NH3 þ 3CO2 ¼ 4N2 þ 3CH4 þ 6H2 O As a result of these reactions, initially oxidised, CO2-dominated fluids can acquire much lower CO2/CH4 ratios and higher N2/CH4 ratios. There is no direct petrological evidence for mixing of two end-member fluids in Maldon, namely, CO2-rich fluids and CH4 + N2-rich fluids. Moreover, CH4–N2 inclusions are rarely seen in igneous rocks. The presence of primary, biphase CH4 vapour-bearing aqueous fluid inclusions in quartz from the Wattle Gully and Bendigo gold deposits led Cox et al. (1995) and Jia et al. (2000) to suggest that CH4 may result from localised reaction between syn-metamorphic, CO2 — low-salinity aqueous fluids and graphitic or carbonaceous wall-rocks (e.g. slate) during

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deposit (Malmsbury), which may have high salinities, up to ~ 25 wt.% NaCl equivalent (Galpin, 2000). The high-salinity brines can be effective in dissolving base metals relative to gold and they are not related to ‘gold-only’ mineralisation regardless of their magmatic or metamorphic origin. Nevertheless, the unique association of both CH4–N2 and highsalinity fluid inclusions in the Maldon gold deposit and the presence of aqueous fluid inclusions with relatively high homogenisation temperatures (up to 370 °C) and re-equilibration, features that are uncommon elsewhere in Victoria, could be explained by the same reheating event related to emplacement of the Harcourt Granite. Neither CH4 + N2-rich fluids nor high-salinity brines at Maldon are the mineralising fluids as seen in Victorian ‘orogenic’ gold deposits. 5.2. Evolution of the hydrothermal system

Fig. 6. Microthermometric data plotted for aqueous inclusions including mixed CO2/CH4 and aqueous fluid inclusions in the Maldon gold deposit. Thin lines link inclusions formed as a result of phase separation. Data sources: Fu et al. (2012); this study.

regional metamorphism and gold mineralisation. Thus, we propose that N2(+CH4) was produced locally by NH4-bearing phyllosilicate minerals in wall-rock slates (and/or maturation of organic matter in shales) at Maldon during contact metamorphism, with limited involvement of high-temperature magmatic fluids from the post-orogenic Harcourt Granite, which is a moderately reduced, I-type intrusion (P. Blevin, unpublished data). If this is correct, the ‘retrograde’, reduced fluids, formed within the thermal aureole of the granite and associated dykes during contact metamorphism, are not part of the regional mineralising fluid system, which is dominated by mixed CO2 and low-salinity aqueous fluids of deeply derived metamorphic origin. This is consistent with the following observations: (1) CH4 is a minor fluid component in many other Victorian gold deposits (Fu et al., 2012 and references therein); (2) the existing carbon isotopic data for Victorian ‘orogenic’ gold deposits cluster around δ13C of−5‰ (e.g. Bierlein et al., 2004; Cox et al., 1995; Gao and Kwak, 1995; Green et al., 1982; Jia et al., 2001). The δ13C is much heavier than that of organic matter (~– 25‰; Hoefs, 2004), suggesting an abiogenic origin of methane, at a regional scale; (3) muscovite in the Bendigo goldfield has a high nitrogen content (650 to 900 ppm), resulting from ammonium substitution for K+, and a low-δ15N value of 2.8 to 4.5‰, consistent with mineralising fluids derived from metamorphic devolatisation (Jia et al., 2001); and (4) in conjunction with above and the other existing stable isotope (O, S) and lead isotope data (e.g. Andrew et al., 2002; Bierlein et al., 2004; Gray et al., 1991; Jia et al., 2001; Thomas et al., 2011), fluid inclusion halogen and noble gas data suggest the presence of two different sources in the Victorian goldfields, particularly in the Bendigo Zone, which are deeply derived metamorphic fluids and sedimentary rocks, especially organic-rich shales, and the significance of fluid-rock interaction as controls on fluid compositions (Fairmaid et al., 2011; Fu et al., 2012). Overall, the halogen and isotopic compositions of Victorian gold deposits are consistent with derivation of the mineralising fluids from metamorphic devolatisation of basement, sedimentary–volcanic rocks. The origin of the high-salinity fluids (W1) preserved in the Kfeldspar zone at Maldon is uncertain. It is noted that high-salinity brines have rarely been observed in other Victorian gold deposits. The only reported occurrence is aqueous inclusions from the Belltopper Hill

On the basis of field relationships, Ciobanu et al. (2010) suggest that there was a single main gold mineralisation event at Maldon followed by local scale reworking and remobilisation of the initial ore. 40Ar/39Ar dating of mineralisation in central Victoria (see review in Phillips et al., 2012 and references therein) indicates that there are two main episodes of mineralisation at ~445 Ma and ~380–370 Ma. Most of the deposits in the Stawell and Bendigo zones yield ages of ~445 Ma and are associated with the early and most significant gold mineralisation event. Thus, by association, we assume that the main gold mineralisation event at Maldon occurred at ~445 Ma. As discussed above, the fluids associated with ‘orogenic’ gold mineralisation in Victoria are commonly low-salinity, H2O–CO2 (± minor CH4) fluids. 40 Ar/39Ar ages ranging from 375 to 367 Ma have been obtained from intrusive dykes and pegmatitic veins at Maldon (Bierlein et al., 2001; recalculated in Phillips et al., 2012) indicating that this was the age of magmatism. Our data show that fluid inclusions in the K-feldspar zone are much less abundant and have arguably lower homogenisation temperatures than those in the more distal cordierite zone (e.g. Fig. 6), probably due to recrystallisation. The more distal corderite zone is dominated by low-salinity aqueous inclusions (W2) and vapour-rich carbonic inclusions (C) with high concentrations of CH4 and N2. The highly variable density of the carbonic fluid inclusions could result from re-equilibration or post-trapping changes. The presence of graphite in the CH4-rich inclusions indicates either accidental trapping of graphite generated at high temperature during the magmatic intrusion or, less likely, post-trapping changes (i.e. incomplete redox reactions: CH4 + CO2 = C + H2O). The Late Devonian peraluminous granites are widespread across the western Lachlan Fold Belt but not all granites are associated with gold deposits (Fig. 1). Only the Maldon, Mount Piper, Woods Point and Walhalla deposits may arguably have characteristics of RIRGS (Bierlein and McKnight, 2005; Bierlein et al., 2003). All these deposits formed after the main gold event at ~445 Ma (Phillips et al., 2012). The age of mineralisation at these deposits is almost indistinguishable from that of their associated igneous intrusions. However, this does not necessarily indicate that significant gold together with other metals was provided by magmatic fluids although the average gold grade of Maldon reefs within the thermal aureole is approximately double that of those just outside (G. Ebsworth, pers. comm.). The presence of maldonite, molybdenite, scheelite, bismuth, native antimony and stibnite, also indicate that magmatic fluids were involved in the reworking and remobilisation of gold at Maldon. These minerals also occur in RIRGS around the world (Hart, 2007). Therefore, we suggest that the gold in other RIRGS in the western Lachlan Fold Belt may also have been remobilised locally from preexisting ‘orogenic’ gold deposits. By analogy, this may have also been the case for some ‘orogenic’ gold deposits worldwide. They may have been completely overprinted by later magmatic/metamorphic events and are now only evident as RIRGS.

Fig. 5. Microphotographs of fluid inclusions in quartz veins from the Maldon gold deposit, central Victoria. (a) Secondary high-salinity fluid (W1) inclusions (M06); (b and c) primary and pseudo-secondary low-salinity aqueous (W2) inclusions (M15 and M14); (d) coexisting low-salinity aqueous–carbonic (CW) fluid inclusions and CO2-only (Cii) inclusions (M05); (e) low-salinity aqueous–carbonic (CW) fluid inclusions and (f and g) CH4-rich (C) inclusions (M16); and (h) CH4-rich inclusions (M15). Gr: graphite. Scale bars: 50 μm.

232

Table 3 Summary of microthermometric data (°C) for fluid inclusions in selected samples from the Maldon gold deposit, central Victoria, Australia (Fu et al., 2012; this study). Inclusion type (number of fluid inclusions measured)

Tm, CO2 (or Ts)

Th/Ths (CO2–CH4)

Harcourt Granite (M02) Low-salinity aqueous (n = 4)

K-feldspar zone (M05 & M06) High-salinity aqueous (n = 6)

Mixed low-salinity aqueous-CO2 (±CH4 ± N2) (n = 8) CO2 (±CH4 ± N2) (non-Ci-subtypes) (n = 12)

−60.2 to −57.8 (n = 7) −76.7 to −58.5 (n = 11)

CH4 (±CO2 ± N2) (±H2O) (Ci-subtype) (n = 8)

not observed

6.6 to 17.6 (L) (n = 8)

XCO2 (mol.%)

XN2 (mol.%)

XCH4 (mol.%)

XH2S (mol.%)

3.9 to 13.1 (n = 4)

158 to 223 (L) (n = 3)

−18.6 to −16.4 (n = 6) −7.2 to −2.6 (n = 8) −4.1 (n = 1)

19.9 to 21.6 (n = 6) 4.3 to 10.7 (n = 8) 6.6 (n = 1)

158 to 187 (L) (n = 5) 197 to 222 (L) (n = 5) 177 (L) (n = 1); 171 (G) (n = 1)

0.5 to 16.2 (n = 38)

84 to 379 (L) (n = 39); 389 (G) (n = 1) 319 & 329 (L) (n = 2); 259 to 362 (G) (n = 10)

8.4 to 10.2 (n = 6)

84.2 (n = 1)

5.7 (n = 1)

10.0 (n = 1)

0.0 (n = 1)

12.6 to 89.2 (n = 6)

0.0 to 21.2 (n = 6)

10.8 to 71.2 (n = 6)

0.0 (n = 6)

13.1 & 13.3 (n = 2)

17.0 & 21.0 (n = 2)

65.7 & 69.9 (n = 2)

0.0 (n = 2)

−12.1 to −0.3 (n = 38)

mixed low-salinity aqueous-CO2 (±CH4 ± N2) (n = 14)

−71.0 to −57.6 (n = 13)

11.8 & 23.4 (L) (n = 2); 6.1 to 18.8 (G) (n = 4)

CO2 (±CH4 ± N2) (non-Ci-subtypes) (n = 51)

−80.6 to −58.9 (n = 51)

CH4 (±CO2 ± N2) (±H2O) (Ci-subtype) (n = 11)

not observed

−96.6 to 10.3 (L) (n = 14); −103.9 to 13.3 (G) (n = 30)/−102.7 to −83.0 (G) (n = 8) −110.1 (L) (n = 1); −112.0 to −92.1 (G) (n = 17)

salinity Th (Total) (wt.% NaCl eq.)

−9.2 to −2.3 (n = 4)

−92.4 to 11.7 (L) (n = 11)/−92.5 to −89.4 (L) (n = 5) −93.1 to −89.2 (L) (n = 7); −89.7 (G) (n = 1)

Cordierite zone (M09, M12, M13, M14, M15, M16, M18) low-salinity aqueous (n = 40)

Salinity was estimated from Potter et al. (1978).

Tm (clathrate)

−5.4 (L) (n = 1)

7.7 to 11.5 (n = 11)

10.7, 14.3 (n = 2)

14.9 to 87.9 (n = 7)

0.0 to 31.1 (n = 7)

9.1 to 54.0 (n = 7)

0.0 to 1.1 (n = 7)

0.0 to 100.0 (n = 44)

0.0 to 37.7 (n = 44)

0.0 to 100.0 (n = 44)

0.0 to 2.2 (n = 44)

0.0 to 3.0 (n = 10)

0.0 to 52.5 (n = 10)

47.5 & 100.0 (n = 10)

0.0 (n = 10)

299 (G) (n = 1)

B. Fu et al. / Ore Geology Reviews 58 (2014) 225–237

Low-salinity aqueous (n = 8)

Tm, ice

B. Fu et al. / Ore Geology Reviews 58 (2014) 225–237

233

Fig. 9. Raman spectrum for graphite (Gr) in a carbonic fluid inclusion from the Maldon gold deposit, central Victoria. Abbreviations: D1 and D2, first-order bands at 1350 cm−1 and 1620 cm−1; S1, second-order band at 2700 cm−1 (the band at 2900 cm−1, S2, is weak and thus not labelled), after Beyssac et al. (2002).

Fig. 7. Microthermometric data plotted for non-aqueous (CO2-, CH4-rich fluid) inclusions, excluding the S1-type of van den Kerkhof and Thiéry (2001), in the Maldon gold deposit. Carbon dioxide homogenisation temperature (Th, CO2) or CH4 homogenisation temperature (Th, CH4/N2) versus CO2 final melting temperature (Tm, CO2), for CO2-rich and lowsalinity aqueous–carbonic fluid inclusions and CH4-rich inclusions, respectively. Vertical lines link inclusions with two homogenisation events (see text for details). Data sources: Fu et al. (2012); this study.

origin or, less likely, metamorphic origin (released after having been ponded at depth for ~ 70 Ma) with organic-rich sediments during contact metamorphism. Our results support the conclusion that the Maldon deposit is an ‘orogenic’ gold deposit that was metamorphosed and/or remobilised during the emplacement of post-orogenic intrusions (e.g. Hughes et al., 1997). This process has obscured some of the ‘orogenic gold’ textures and fluid characteristics of this deposit and imparted characteristics commonly associated with RIRGS.

6. Conclusions The Maldon gold deposit is situated in the thermal aureole of the moderately reduced, I-type, Late Devonian Harcourt Granite and quartz veins in the pelitic and psammopelitic rocks may have been variably recrystallised during the emplacement of post-orogenic intrusions. The fluids in the Maldon gold deposit are different from those of typical ‘orogenic’ gold deposits as they are CH4 + N2-rich fluids, which exhibit complex freezing and heating behaviour, and minor amounts of high-salinity brines. The presence of graphite in the CH4 + N2-rich inclusions indicates either accidental trapping of the solid phase at high temperature or, less likely, post-trapping changes (i.e. incomplete redox reactions). The methane and nitrogen may have formed locally by interaction of mixed CO 2 and low-salinity aqueous fluids of magmatic

Acknowledgements This work was initially supported by GeoScience Victoria and the Australian Research Council (LP0882157). The authors are indebted to Gregory Ebsworth and Joseph Krokowski de Vickerod (Alliance Resources Ltd, now Octagonal Resources Ltd) for giving access to mine sites/drill cores, providing logging notes for Table 1 and Fig. 3, and for their guidance on deposit geology, as well as to Avi Olshina for providing the geology maps. Thanks are given to G. N. Phillips, G.R. Olivo, P.S. Garofalo, and an anonymous referee for their constructive comments on earlier versions of the manuscript and F. Pirajno for editorial handling. TPM publishes with the permission of the CEO of Geoscience Australia.

Fig. 8. End-member (CO2, CH4, N2) plot of all non-aqueous fluid inclusions in quartz from the K-feldspar (Kfs) zone and the cordierite (Crd) zone in the Maldon gold deposit, central Victoria, analysed by Raman spectroscopy. Data source: Fu et al. (2012) and this study. See text for abbreviations of fluid types or subtypes. uc: Unclassified carbonic fluid inclusions (C-type).

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Appendix A. Microthermometric data and laser Raman results for representative non-aqueous fluid inclusions in quartz from the Maldon gold deposit, central Victoria, Australia.

Sample no.

Inclusion no.

Compositional fluid type or subtype

Th/Ths

Ts/TmCO2

ThCO2

10.8 L 7.3 L 11.3 L

-82.3 L/-91.0 L

-58.7 -59.0 -59.8 -76.7

K-feldspar zone M05 1-3 1-4 1-5 M06 3-7 3-7 (replicate*) 3-6 3-5 3-11 3-12 3-13 n2m_1 n2m_2 n2m_3 n2m_5 n2n_1 n2n_2 n2n_3 n2n_4 n2n_5 n2n_6 n1b_x

Cv Cv Cv Ci Ci C C C C C C C C C C C

-90.1 L -83.3/-92.5 L -92.4 L -90.6 L -90.4 L

-68.4 -76.0 -69.7

Cordierite zone M13 12-1 12-3 12-4 12-2 11-2 11-7 na_1 na_2 na_3 na_4 nb_1 nb_2 nb_3 nc_1 nc_2 nc_3 nc_4 nc_5 nc_6 M14 n2a_1 n2a_2 n2a_3 n2a_4 n2a_5 n2a_6 n2a_7 n2b_1 n2b_2 n2b_3 n2b_5 n2b_6 n2b_7 n2b_8 n2b_9 n2b_10 n2c_1 n2c_2 n2c_3 n2c_4 n2c_5 n2c_6 n2c_7 n2c_8 1e_5 1e_6 1c_3 1c_4 1c_5

Ciii Ciii Ciii Cii Cii Cv C C C C C C C C C C C C C Cii Cii Cii Cii Cii Cii Cii Cv Cv Ci Cv Cv C C C C C C C C C C C C Cii Cii Cii Cii Cii

-83.0 V -88.8 V -93.2 V

-65.2 -65.6 -66.1 -62.9 -60.4 -80.5

-34.4 V -33.5 V -49.3 V -18.1 V 7.1 V

-59.0 -58.8 -59.0 -59.4 -59.5 -60.0 -59.9 -85.2 -85.2

14.8 L 14.2 L 13.8 L 10.3 L 11.3 L 8.0 L 8.4 L

CW Cii Cii Cv

-102.7 V

-92.5/-96.5 V -92.4/-96.1 V -101 V -78.8/-90.5 V -86.5/-102.5 V

-69.6 -64.9

-62.5 -62.7 -63.4 -63.8 -64.2

-11.5 L -15.0 L -6.4 V n.d. V -12.4 V

CO2 (mol %)

N2 (mol %)

CH4 (mol %)

H2S (mol %)

References

84.2 88.5 89.2 11.0 12.6 19.2 13.0 27.9 13.3 13.1 3.1 0.0 12.5 2.9 13.1 13.5 14.0 15.0 13.5 14.8 0.0

5.7 0.0 0.0 15.0 16.1 21.2 19.0 15.8 21.0 17.0 10.3 0.0 14.5 9.7 19.9 18.2 17.6 17.5 17.7 18.9 20.2

10.0 11.5 10.8 74.0 71.2 59.5 68.0 56.4 65.7 69.9 86.6 100.0 72.9 87.5 67.0 68.2 68.5 67.5 68.8 66.3 79.8

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012)

61.1 32.6 29.3 50.4 72.2 15.2 83.3 88.9 87.3 85.9 8.7 7.9 7.3 64.6 74.9 61.4 15.7 76.3 74.8 82.9 80.4 82.8 80.3 81.8 77.4 74.7 4.1 6.1 0.0 12.3 13.3 51.4 30.6 84.2 81.1 83.7 83.3 83.7 70.8 70.5 69.6 75.7 68.2 67.6 61.3 56.1 49.2 49.8

0.0 9.4 10.7 10.6 7.0 30.5 7.8 5.2 5.4 7.5 33.6 30.8 32.9 15.8 0.0 20.2 25.6 10.2 11.3 5.5 6.0 5.3 7.9 4.4 6.1 9.7 32.0 35.9 0.0 32.6 30.9 11.0 22.7 5.0 8.3 4.8 5.9 6.3 7.6 9.0 10.5 7.8 9.8 0.0 5.8 5.6 9.0 12.7

38.9 58.0 60.1 39.0 18.9 54.4 9.0 5.9 7.2 6.6 57.7 61.3 59.8 19.6 25.1 18.5 58.7 13.5 13.8 11.6 13.6 11.9 11.8 13.9 16.5 15.6 63.9 58.1 100.0 55.1 55.8 37.1 46.8 10.8 10.6 11.5 10.8 10.0 21.6 20.5 19.9 16.5 22.0 32.4 32.9 36.1 40.1 36.2

0.0 0.0 0.0 0.0 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.2 1.8 1.3

Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012)

B. Fu et al. / Ore Geology Reviews 58 (2014) 225–237

235

Appendix A (continued) (continued) Sample no.

M15

M16

M18

M12

Inclusion no.

Compositional fluid type or subtype

1c_6 1d_1 1d_2 1b_1 1b_2 1b_3v 1a_3 1a_4 1e_1 (1a_)x1 (1a_)x2 (1a_)x3 (1d_)y1 (1d_)y2 (1d_)y3 za_1 za_2 za_3 za_4 za_5 za_6 zb_1 zb_2 zb_3 1d_1 1d_2 1d_3 1c_1 1c_2 1c_3 1b_3 1b_21 1b_2v 1b_1v 1a_2 1a_1v 1-3 1-4 2-2 2-3 2-5 wa_1 wa_2 wa_3 3-11 3-10 3-7 3-9 3-1 3-2 3-3 2-1 nxa_1 nxa_2 nxa_3 nxa_4 nxa_5 nxb_1 nxb_2 nxb_4 nxb_5 aa ab ac ad ba bb bc c1a c1b c1c c1d c1e

Cii Cii Cii Ciii C CW Cv Cii Cii C C C C C C C C C C C C C C C Cii Cii C Ciii Ciii C Cii C CW CW (+solid) C CW Ci CW Cv CW CW (+solid) C C C Cv Cv Cii Cii Cii Cii Cii Cii C C C C C C C C C CW CW Ci CW Ci Ci Ci CW Cii CW CW C

Th/Ths

-96 V

-96.4(?) V

-100.5 V -104.5 V

Ts/TmCO2

ThCO2

CO2 (mol %)

N2 (mol %)

CH4 (mol %)

H2S (mol %)

-64.0 -59.8 -59.9 -73.1 not observed -58.7 -75.4 -62.8 -62.4

-17.6 V 6.5 V 6.0 V -73.1 V

-62.8 -62.8

ca. -35 V ca. -40.7 V

-62.2 -79.9

-45.8 V -49.2 V

-59.0

7.0 V

not observed not observed not observed -68.9

?V ?V ?V ?V

-59.3 -79.6 -71.0 -59.6

V?

46.1 70.1 71.1 0.0 3.7 87.9 7.4 45.4 58.9 68.2 68.5 71.5 15.7 19.9 0.0 9.7 0.0 0.0 8.1 0.0 11.3 48.4 54.7 50.1 37.5 38.4 36.1 24.2 20.6 18.5 72.4 25.1 81.8 85.3 58.6 61.5 3.9 78.3 6.0 14.9 82.2 38.4 37.6 36.8 16.0 0.0 69.8 48.5 80.2 100.0 100.0 87.5 0.0 0.0 0.0 0.0 0.0 82.6 85.7 85.8 67.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 30.5 0.0 26.5 19.5

7.4 11.8 11.8 28.1 26.2 3.0 31.0 16.6 16.2 0.0 0.0 0.0 31.4 29.0 0.0 36.9 0.0 0.0 30.5 0.0 35.9 22.2 13.6 15.3 28.0 21.8 33.7 21.0 30.1 26.0 10.0 24.8 7.7 0.0 0.0 18.8 35.2 0.0 34.0 31.1 0.0 31.8 31.7 33.4 37.7 0.0 0.0 21.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 14.2 7.1 9.4 6.8 28.9 29.1 38.3 42.4 0.0 0.0 52.5 0.0 2.3 0.0 0.0 1.3

46.0 18.2 17.1 71.9 70.1 9.1 61.6 38.0 24.9 31.8 31.5 28.5 52.9 51.1 100.0 53.4 100.0 100.0 61.4 100.0 52.8 29.5 31.7 34.5 34.5 39.8 30.2 54.8 49.3 55.5 17.6 50.2 9.4 14.7 41.4 19.7 60.9 21.7 60.0 54.0 17.8 29.7 30.7 29.8 46.4 100.0 30.2 30.2 19.8 0.0 0.0 12.5 100.0 100.0 100.0 100.0 100.0 2.1 4.1 2.4 25.6 71.1 70.9 61.7 57.6 100.0 100.0 47.5 100.0 67.3 100.0 73.5 79.3

0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 3.1 2.4 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

14.0 V? ?V -26.5 V -19.5 L

-92.1 V -95.5 V

-88.9 V/-101.9 V -91.2 V/-105.1 V

V? ?L

-78.1 -78.5 -65.2 -65.1 -63.1 -62.1 -62.3 -63.6

-30.0 V -25.4 V -5.2 L -40.7 L -43.2 L -5.5 L

-67.7

-51.3 V

-62.0

?V

-98.5 V -112.0 V ?V -110.0 V -77.5 V

References

Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012)

Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012) Fu et al. (2012)

(continued on next page)

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Appendix A (continued) (continued) Sample no.

Inclusion no.

Compositional fluid type or subtype

c1f c2a c2b c2c c2d c2e

C Ci Ci C Ci Ci

Th/Ths

Ts/TmCO2

-108.5 V -109.0 V -108.8 V -111.7 V

ThCO2

CO2 (mol %) 15.1 0.0 0.0 0.0 0.0 0.0

N2 (mol %) 0.0 51.1 49.0 47.1 47.8 51.3

CH4 (mol %) 84.9 48.9 51.0 52.9 52.2 48.7

H2S (mol %)

References

0.0 0.0 0.0 0.0 0.0 0.0

Note: L (liquid) or G/V (gas or vapour) represents homogenisation phase. See text for different compositional fluid types or subtypes (no data for Civ or S1-type here). All temperatures (°C) were obtained by microthermometry, compositions are given in mol.%. * Analysed after microthermometry.

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