Fluid evolution of the Yuchiling porphyry Mo deposit, East Qinling, China

Ore Geology Reviews 48 (2012) 442–459

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Fluid evolution of the Yuchiling porphyry Mo deposit, East Qinling, China Nuo Li a, Thomas Ulrich b, Yan-Jing Chen a,⁎, Tonny B. Thomsen c, Victoria Pease c, Franco Pirajno d a

Key Laboratory of Orogen and Crustal Evolution, Peking University, 5 Yiheyuan Road, Beijing, 100871, China Department of Earth Sciences, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark c Department of Geological Sciences, Stockholm University, SE-10691 Stockholm, Sweden d Centre for Exploration Targeting, School of Earth and Environment, University of Western Australia, 35 Stirling Highway, Crawley WA 6008, Australia b

a r t i c l e

i n f o

Article history: Received 19 January 2012 Received in revised form 23 May 2012 Accepted 13 June 2012 Available online 5 July 2012 Keywords: CO2-rich magmatic fluids LA-ICP-MS Yuchiling Mo deposit East Qinling China

a b s t r a c t The Yuchiling Mo deposit, East Qinling, China, belongs to a typical porphyry Mo system associated with high-K calc-alkaline intrusions. The pure CO2 (PC), CO2-bearing (C), aqueous H2O-NaCl (W), and daughter mineral-bearing (S) fluid inclusions were observed in the hydrothermal quartz. Based on field investigations, petrographic, microthermometric and LA-ICP-MS studies of fluid inclusions, we develop a five-stage fluid evolution model to understand the ore-forming processes of the Yuchiling deposit. The earliest barren quartz ± potassic feldspar veins, developed in intensively potassic alteration, were crystallized from carbonic-dominant fluids at high temperature (>416 °C) and high pressure (>133 MPa). Following the barren quartz ± potassic feldspar veins are quartz-pyrite veins occasionally containing minor K-feldspar and molybdenite, which were formed by immiscible fluids at pressures of 47–159 MPa and temperatures of 360–400 °C. The fluids were characterized by high CO2 contents (approximately 8 mol%) and variable salinities, as well as the highest Mo contents that resulted in the development of quartz-molybdenite veins. The quartz-molybdenite veins, accounting for > 90% Mo in the orebody, were also formed by immiscible fluids with lower salinity and lower CO2 content of 7 mol%, at temperatures of 340–380 °C and pressures of 39–137 MPa, as constrained by fluid inclusion assemblages. After the main Mo-mineralization, the uneconomic Cu-Pb-Zn mineralization occurred, as represented by quartz-polymetallic sulfides veins consisting of pyrite, molybdenite, chalcopyrite, digenite, galena, sphalerite and quartz. The quartz-polymetallic sulfide veins were formed by fluids containing 5 mol% CO2, with minimum pressures of 32–110 MPa and temperatures of 260–300 °C. Finally, the fluids became dilute (5 wt.% NaCl equiv) and CO2-poor, which caused the formation of late barren quartz ± carbonate ± fluorite veins at 140–180 °C and 18–82 MPa. It is clear that the fluids became more dilute, CO2-poor, and less fertile, with decreasing temperature and pressure from quartz-pyrite to late barren veins. Molybdenite and other sulfides can only be observed in the middle three stages, i.e., quartz-pyrite, quartz-molybdenite and quartz-polymetallic sulfide veins. These three kinds of veins are generally hosted in potassic altered rocks with remarkable K-feldspathization, but always partly overprinted by phyllic alteration. The traditional porphyry-style potassic–phyllic–propylitic alteration zoning is not conspicuous at Yuchiling, which may be related to, and characteristic of, the CO2-rich fluids derived from the magmas generated in intercontinental collision orogens. Among the fluid inclusions at Yuchiling, only the C-type contains maximum detectable Mo that gradationally decreases from 73 ppm in quartz-pyrite veins, through 19 ppm in quartz-molybdenite veins, and to 13 ppm in quartz-polymetallic sulfide veins, coinciding well with the decreasing CO2 contents from 8 mol%, through 7 mol%, to 5 mol%, respectively. Hence it is suggested that decreasing CO2 possibly results in decreasing Mo concentration in the fluids, as well as the precipitation of molybdenite from the fluids. This direct relationship might be a common characteristic for other porphyry Mo systems in the world. The Yuchiling Mo deposit represents a new type Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO2-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization. © 2012 Elsevier B.V. All rights reserved.

1. Introduction

⁎ Corresponding author. Tel.: +86 10 6275 7390. E-mail address: [email protected] (Y.-J. Chen). 0169-1368/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2012.06.002

The global molybdenum supply is derived almost exclusively from porphyry-type deposits. The traditional metallogenic theories state that porphyry deposits mainly formed in oceanic subduction-related magmatic arcs, such as the southwestern Pacific islands and Andes

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(Pirajno, 2009; Sillitoe, 1972). The characteristics, genetic models and tectonic settings of these deposits, especially in the Western Cordillera, North America, have been extensively studied and well documented (Carten et al., 1993; Clark, 1972; Mirsa, 2000; Mutschler et al., 1981; Seedorff et al., 2005; Sillitoe, 1980; Westra and Keith, 1981; Woodcock and Hollister, 1978). In the past two decades, geologists realized that intercontinental collision belts are also favorable for the development of porphyry deposits (Chen et al. 2000, 2007 and references therein; Richards, 2009). The East Qinling Mo Belt (EQMB; Fig. 1), central China, contains six giant Mo deposits (each with a reserve of >0.5 Mt Mo) and tens of small (b0.01 Mt Mo), medium (0.01–0.1 Mt Mo) and large (0.1–0.5 Mt Mo) deposits, with total reserve of ~6 Mt Mo metal (Chen et al., 2000, 2009; Li et al., 2007, 2011a, 2011c; Mao et al., 2008), ranking as the most important Mo provinces in the world. The major deposits in EQMB are associated with Mesozoic porphyry or porphyry-skarn systems that are proven to have formed in a post-collisional setting, and thus offer the opportunity to study porphyry Mo deposits formed in post-collision settings. However, these deposits are poorly studied, and rarely known by international geologists; and the question whether porphyry deposits generated in different tectonic settings have similar or contrasting geological and geochemical features remains. The Yuchiling porphyry system is one

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of six giant Mo deposits in EQMB, with a reserve of 0.54 Mt Mo metal, grading 0.057%, and was discovered in 2006. The Mo-containing porphyry intrudes the huge Heyu multistage granite batholith. It displays fairly simple lithologies and mineralogical assemblage, but is well developed with quartz-bearing hydrothermal veins, providing an excellent example to gain insight in the geology and fluid evolution of porphyry Mo deposits in post-collision setting. In this contribution, we present the results obtained from a comprehensive fluid inclusion study including conventional petrography and microthermometry combined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). This allows us to confine the physico-chemical properties that prevailed during the evolution of the ore fluid and discuss the mechanisms of metal transportation and precipitation. We also highlight some of the geological differences from the porphyry deposits formed in subduction-related magmatic arcs. 2. Regional geology The Qinling Orogen is an important part of the Central China Orogen (CCO), which is a composite orogenic belt tectonically sutured the Yangtze and North China cratons (Fig. 1A). It is bounded by the San‐Bao fault to the north and the Longmenshan/Dabashan

Fig. 1. Location and regional geology of the East Qinling Mo belt. (A). Tectonic framework of China, showing the location of Qinling Orogen. (B) Tectonic subdivision of Qinling Orogen, showing the location of East Qinling Mo Belt. (C). Regional geology and location of the Mo deposits in the East Qinling Mo belt, showing the location of the Heyu granite batholith and its associated Yuchiling deposit.

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fault to the south (Fig. 1B). Four tectonic units are recognized, from north to south, named the Huaxiong block (southern margin of the North China Craton), the northern Qinling accretionary belt, the southern Qinling block (or fold belt) and the Songpan foreland fold-and-thrust belt (northern margin of the Yangtze Craton), respectively, with the Luanchuan, Shang‐Dan and Mian‐Lue faults (suture zones) being their boundaries, from north to south (Chen et al., 2004 and references therein). The Luanchuan fault was a northward oceanic subduction zone during 1.85–1.45 Ga and then sutured the Huaxiong block and the northern Qinling accretion belt (Chen et al., 2009). In the Late Paleozoic, the North China continent (North China craton + Huaxiong block + northern Qinling accretionary belt) sutured with the South China continent (Yangtze craton + southern Qinling block) along the Shang‐Dan fault. Also in the Late Paleozoic, as an impact of the opening of the Paleo-Tethys Ocean, the Mian‐Lue ocean opened, which separated the southern Qinling block from the Yangtze Craton and is indicated by the ophiolite slices along the Mian‐Lue fault zone (Meng and Zhang, 2000). Triassic subduction and closing of the Mian‐Lue ocean led to the integration of the Yangtze Craton and southern Qinling–North China continent (Chen et al., 2009; Jiang et al., 2010), followed by a Jurassic–Early Cretaceous intercontinental collisional orogenesis that finally resulted in the formation of the EQMB (Li et al., 2007, 2011b; Mao et al., 2008). The Mo deposits cluster in the northeast parts of the Qinling Orogen (Fig. 1), i.e., the Huaxiong block and the northern Qinling accretionary belt (Fig. 1C). The Yuchiling deposit is located in the Huaxiong block and hosted by the Heyu granite batholith (Fig. 2). Main lithostratigraphic units in the region are the Taihua Supergroup (basement) and the Xiong'er Group (cover). The Taihua Supergroup comprises a suite of amphibolite to granulite facies metamorphic rocks, including graphite schists, marbles, quartzites, banded iron-formations, gneisses and amphibolites (Chen and Zhao, 1997). It is further divided into the Beizi, Dangzehe and Shuidigou Groups, with ages of 3.0–2.55 Ga,

2.5–2.3 Ga and 2.3–2.1 Ga, respectively (Chen and Zhao, 1997). The Xiong'er Group is up to 7600 m thick, and covers an area of more than 60,000 km 2 (Zhao et al., 2009). It includes a wellpreserved unmetamorphosed volcanic sequence that unconformably overlies the metamorphic basement (Taihua Supergroup). The Xiong'er Group consists predominantly of basaltic andesite, andesite and dacite, with minor rhyolite. SHRIMP and LA-ICP-MS zircon U–Pb ages indicate that the eruption of the Xiong'er Group volcanic rocks mainly occurred 1.78 to 1.75 Ga ago (Zhao et al., 2009 and references therein). At the current level of exposure, the Heyu batholith is a concentrically zoned suite consisting of four nested, texturally distinguishable phases, and covers an exposure area of 784 km 2 (Fig. 2, Phase 1 to 4). Phase 1 is a medium grained biotite monzonite yielding zircon U–Pb age of 143.0 ± 1.6 Ma (Li et al., 2011b). Phase 2 occurs as a narrow belt surrounding Phase 1, with zircon U–Pb age of 138.4 ± 1.5 Ma, and is also a medium grained biotite monzonite, but has more and larger sized K-feldspar phenocrysts than Phase 1 (Li et al., 2011b). Phase 3 is dominated by reddish megaporphyritic biotite monzonite aged of 132–135 Ma (zircon U–Pb and biotite 40Ar/ 39Ar ages, Han et al., 2007; Guo et al., 2009), and constitutes the largest portion of the Heyu batholith. Phase 4 is represented by the Mo-associated Yuchiling granite porphyry, which intruded Phase 1 and yielded zircon U–Pb age of 133.6 ± 1.3 Ma (Li et al., 2011b).

3. Deposit geology 3.1. The porphyry and alteration The Yuchiling porphyry consists of medium-grained, reddishcolored biotite monzonite, containing phenocrysts of quartz (2–3%) and K-feldspar (3–5%). The groundmass is composed of plagioclase

Fig. 2. Regional and deposit geology of the Yuchiling porphyry Mo system. (A). Geology of the Heyu granite batholith. (B). Geology of the Yuchiling porphyry Mo deposit. The original maps were provided by Henan Institute of Nonferrous Metal Exploration and updated from our field investigation.

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(25–35%), K-feldspar (30–40%), quartz (20–25%) and biotite (3–5%), and a small quantity of accessory apatite, titanite, zircon and magnetite. The porphyry is intensively altered and mineralized, including an economic orebody defined by Mo contents of > 0.03% (Fig. 3). Potassic alteration, as represented by the mineral assemblage of K-feldspar, quartz and/or magnetite, can be clearly observed in the entire porphyry stock, which results in a pink to reddish color of the porphyry. Different types of hydrothermal veins, regardless of pre-, syn- or post-mineralization, can be hosted in the potassic altered porphyry (Fig. 4). Phyllic alteration, represented by replacement of plagioclase, biotite and K-feldspar by quartz and sericite, can be locally observed and generally overprints potassic alteration. In Mo-bearing quartz veins and their alteration halos, intergrowth of molybdenite and sericite is observed. The propylitic alteration zone that surrounds most of the ore-forming porphyries (e.g., Lowell and Guilbert, 1970) is weak and only locally identified at Yuchiling. 3.2. Veins and mineralization Molybdenite is the only mineral of economic value at Yuchiling, and is hosted by moderately to steeply dipping veinlets, with minor disseminations in the altered granite porphyry. Five kinds of veins can be distinguished from early to late according to their crosscutting relationships, vein mineralogy and morphology, and related wallrock alterations. They are: (1) Early barren veins (Q ± Kfs). They are generally 0.3 to 8 cm thick, composed of quartz only (Fig. 4A) or quartz-potassic feldspar (Fig. 4B), and hosted by potassic altered granite (Fig. 4A). Some of the veins and their wallrocks show overprinting by phyllic alteration (Fig. 4B). These veins are usually cut by later veins or stockworks, such as quartz-molybdenite veins (Fig. 4I), supporting a pre-ore timing.

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(2) Quartz-pyrite veins (Q-Py ± Kfs). They are 0.5 to 2.5 cm thick, including two mineral assemblages of quartz-pyrite (Fig. 4C) and quartz-pyrite-K feldspar (Fig. 4J), and occasionally contain minor molybdenite, sericite and fluorite. Pyrite is characteristic of euhedral to sub-euhedral crystals with sizes of 0.6 to 5 mm, and borders the vein walls (Fig. 4C) or grows as free-standing crystals (Fig. 4J). They generally are located in potassic altered rocks, and can be cut by quartz-molybdenite veins (Fig. 4J), also indicating a pre-ore feature. (3) Quartz-molybdenite veins (Q-Mo± Py). They are 0.5 to 6 cm thick veins composed of quartz and molybdenite, with or without minor pyrite, as well as sericite and fluorite, and account for more than 90% of the Mo metal reserve. They tend to have fairly straight walls, and are associated with potassic ± phyllic alterations. Molybdenite occurs as fine-grained (b3 mm) crystals in discontinuous streaks, or aggregate flakes with a rosette texture along veinlet walls (Fig. 4D), or as disseminations throughout the vein quartz. Pyrite, if present, is generally disseminated in the veins, and is encompassed by molybdenite. Sericite is present as aggregate clusters (typically 0.1 to 0.5 mm wide) and intergrows with molybdenite. As indicated by the crosscutting relationships, the quartz-molybdenite veins invariably postdate early barren veins and quartz-pyrite veins (Fig. 4I, J), but predate quartz-polymetallic sulfide veins and late barren veins (Fig. 4K, L). (4) Quartz-polymetallic sulfide veins (Q-PM). These veins are characterized by abundant polymetallic sulfides, including pyrite, molybdenite, chalcopyrite, digenite, galena and sphalerite, and gangue minerals such as quartz, sericite, fluorite and calcite (Fig. 4E). In the veins, pyrite occurs as sub-euhedral crystals, usually replaced by molybdenite, chalcopyrite, digenite and sphalerite along borders or fissures (Fig. 4E), and is the earliest phase of the sulfides. Intergrowth of molybdenite and sericite can be observed along vein walls. Such veins are generally hosted by potassic altered zones overprinted by sericitization. (5) Late barren veins (Q±Cc±Fl). They include quartz (chalcedony) only, quartz-calcite and quartz-fluorite veins (Fig. 4F, G, H, L) hosted in potassically (Fig. 4F, H, L) or phyllically altered rocks (Fig. 4G), and cut the veins mentioned above (Fig. 4L). They are 0.2 to 3 cm thick, and typically show comb or drusy structure. Sometimes, fluorite in different colors can be zoned in an individual vein, with green crystals on the wall, and the purple and brown in the center of the vein. A selvage of sericite, chlorite and occasional pyrite can be recognized (Fig. 4H). 4. Analytical methods 4.1. Fluid inclusion sampling Samples used for fluid inclusion study were collected from drill core ZK0009 as well as the exploration tunnels No. 481 and No. 527, with emphasis on vein types and alterations. 65 thick sections (300 μm) were used for petrographical fluid inclusion studies, 21 of them were further analyzed by microthermometry and laser Raman spectroscopy, and 10 of these by LA-ICP-MS. Detailed features of the samples used in this study are given in Appendix A. 4.2. Microthermometry

Fig. 3. Cross section along A–A′ and B–B′ in Fig. 2B, showing the shape of orebody.

Microthermometry was carried out on a Linkam THMSG600 Heating-Freezing Systems attached to a Leitz microscope at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Thermocouples were calibrated at − 56.6 °C, 0.0 °C and + 374.1 °C using synthetic fluid inclusions supplied by FLUID INC. The heating/ freezing rate is generally 0.2 to 5 °C/min, but reduced to b0.2 °C/min near the phase transformation. The precision of temperature measurements is 3 °C in the range of −180 °C to −120 °C, ±0.5 °C to ±2 °C

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Fig. 4. Five-stage veins and their associated alterations. (A). Early barren quartz vein in potassic altered granite porphyry. (B). Early barren vein in sericitic altered granite porphyry, with K-feldspar distributed along the vein walls. (C). Quartz-pyrite vein in potassic altered porphyry, with pyrite distributed symmetrically along walls of the vein. (D). Quartz-molybdenite vein in potassic altered porphyry, where a rosettes of coarse-grained molybdenite locate along vein walls. (E). Quartz-polymetallic sulfide vein in potassic alteration, consisting mainly of quartz, pyrite, molybdenite and chalcopyrite. (F). Late barren quartz vein in potassic alteration. (G). Late barren quartz vein in phyllic (sericite + quartz) alteration. (H). Late barren quartz-fluorite vein in potassic altered porphyry. (I). Early barren veins and potassic alteration cut by quartz-molybdneite vein. (J). Potassic alteration cut by quartz-pyrite-potassic feldspar vein, and then both cut by quartz-molybdenite vein. (K). Quartz-molybdenite vein cut by quartz-polymetallic sulfide vein, both veins cutting potassic alteration overprinted by phyllic alteration. (L). Quartz-molybdenite veins cut by a late barren quartz-carbonate vein. Abbreviation: Clc = calcite; Cpy = chalcopyrite; Fl = fluorite; Kfs = K-feldspar; Mo = molybdneite; Py = pyrite; Qz = quartz; Ser = sericite; EBV = early barren vein; Q-Py = quartz-pyrite vein; Q-Mo = quartz-molybdenite vein; Q-PM = quartz-polymetallic sulfide vein; LBV = Late barren vein.

in the range of −120 to −60 °C, ±0.2 °C in the range of −60 °C to+ 100 °C, and ±2 °C for temperatures above + 100 °C. Ice-melting temperatures were observed at a heating rate of less than 0.1 °C/min, and homogenization temperatures at a rate of ≤1 °C/min. Homogenization of halite-bearing fluid inclusions was obtained on only one assemblage per sample chip to avoid stretching of fluid inclusions due to repeated heating. Heating cycles of about 5 °C were used to determine the homogenization temperature of bubble and halite in halite-bearing fluid inclusions. Heating cycles also constrained the melting temperature of clathrate to within ±0.2 °C in most CO2-bearing inclusions.

4.3. Laser Raman microspectroscopy Vapor and liquid compositions of individual fluid inclusions were analyzed using the RM-1000 laser Raman microspectrometer at Key Laboratory of Orogen and Crustal Evolution, Peking University. The excitation wavelength was the 514.5 nm line of an Ar + ion laser operating at 25 mW. The spectra were recorded with counting time

of 10 s, and ranged from 400 to 4000 cm −1, 1 accumulation, and the spectral resolution was ±1 cm −1. 4.4. LA-ICP-MS In situ LA-ICP-MS analyses were carried out at the Department of Geological Sciences, Stockholm University. The entire content of inclusions was ablated by the straight ablation technique as outlined in Pettke (2008), using a 213 nm Nd: YAG laser system and a Thermo-Scientific Xseries 2 quadrupole ICP-MS. The instrument was tuned following the strategy of Pettke (2006), and an energy density of 9–9.6 J/cm 2 on the sample and a laser pulse frequency of 10 Hz were used. Helium was used as carrier gas, and mixed with the nebulizer argon gas prior to the entry to the ICP. Detailed operating conditions and data acquisition parameters are listed in Appendix B. Total acquisition time for single analysis was max. 2 min, including 10 s laser warm up, 30 s gas blank measurement followed by 45 s laser ablation (signal) and 15 s washout of the ablation cell. Data were acquired from single spot analysis of 20, 30 or 40 μm in

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size. To avoid fractionation resulting from different beam sizes, the same beam size were used for the standard analyses as for the fluid inclusion analyses in the concentration calculations. Analyses were acquired in a bracketing sequence, measuring the NIST glass standard SRM-610 as external standardization at the beginning and end of fluid inclusion analyses. For quantitative determinations, the concentration of sodium ( 23Na) in the fluid was used as the internal standard (e.g. Günther et al., 1998). Na concentrations were derived from microthermometric NaCl equivalent values, corrected for potential contributions of KCl, CaCl2, FeCl2, MnCl2, ZnCl2 and CuCl2.

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during heating and cooling. Four types of inclusions, designated as W, PC, C and S, are identified. 5.1.1. PC-type (pure CO2 inclusion) They are CO2-only inclusions, containing liquid CO2 or liquid CO2 + vapor CO2 at room temperature (Fig. 5A). The inclusions are generally 8 to 16 μm in diameter and rounded isometric or negative crystal in shape. PC-type inclusions account for >80% of the total inclusions in early barren veins, but become much less abundant in quartz-pyrite and quartz-molybdenite veins; and no PC-type inclusion can be observed in quartz-polymetallic sulfide veins and late barren veins.

4.5. Fluid inclusion references Salinities of aqueous fluid inclusions, expressed as wt.% NaCl equiv, were estimated using the data of Bodnar (1994) for the NaCl-H2O system. Salinities of halite daughter mineral-bearing inclusions were estimated using the data and methodology of Bodnar and Vityk (1994). For inclusions that homogenize by halite dissolution, this method may underestimate salinity by up to 3 wt.% NaCl equiv (Bodnar and Vityk, 1994). Salinities of CO2-bearing inclusions were estimated using the equations of Collins (1979). Data processing of LA-ICP-MS analysis was carried out using the software SILLS Vers. 1.1.0 (Guillong et al., 2008), and results are reported in Appendix C. Limits of detection (LOD) were calculated for each element using the three standard deviation criteria (Longerich et al., 1996), and are reported in Appendix D. 5. Fluid inclusion petrography and microthermometry Fluid inclusions in five types of veins were studied for petrography, microthermometry and LA-ICP-MS measurements. These studies focused on fluid inclusion assemblages, i.e., closely associated groups of inclusions with visually identical phase ratios and similar shape (Goldstein and Reynolds, 1994). 5.1. Fluid inclusion types Fluid inclusions types are identified based on their compositions, phases (L-V-S) at room temperature, and phase transitions observed

5.1.2. C-type (CO2-H2O inclusion) They consist of two (liquid H2O+CO2-rich supercritical fluid) or three phases (liquid H2O+liquid CO2 +vapor CO2) at room temperature, with carbonic phases (liquid CO2 +vapor CO2) occupying 5–95% of total volume (Fig. 5B, C). They are generally 6 to 24 μm in diameter, and have rounded isometric, elliptic or negative crystal shapes. In early barren veins, minor C-type inclusions can be distinguished as primary, while most of them occur in well-defined secondary trials cutting the entire quartz crystals, which is indicative of a later stage of entrapment. In quartz-pyrite and quartz-molybdenite veins, C-type inclusions with variable CO2 content (5–90%) are mainly present in clusters and scattered throughout the sample. In quartz-polymetallic sulfide veins, minor C-type inclusions are present, and their CO2 content is generally low (5–30%). In late barren veins, no C-type inclusions was observed. 5.1.3. S-type (solid- or daughter mineral-bearing inclusion) These inclusions contain daughter crystals, and show rounded isometric or negative crystal shapes with the longest dimensions ranging from 7 to 16 μm. The vapor bubble can either be CO2 (Fig. 5D) or H2O (Fig. 5E). S-type inclusions can be divided into two subtypes in terms of halite presence or absence. SH-subtype inclusions contain halite, irrespective of whether they contain other kinds of daughter minerals or not (Fig. 5D, E); while SM-subtype inclusions contain no halite but opaque/transparent daughter minerals which do not melt during heating (Fig. 5E). Opaque daughter minerals are usually chalcopyrite (opaque, triangular) and hematite (red, platy), and transparent minerals can be Ca-bearing, which is further supported by LA-ICP-MS data (see below). S-type inclusions are present as primary

Fig. 5. Fluid inclusion types at Yuchiling. (A). PC-type inclusion composed of vapor CO2 and liquid CO2. (B). C-type inclusion with high carbonic (vapor CO2 + liquid CO2) content. (C) C-type inclusion with low carbonic (vapor CO2 + liquid CO2) content. (D). SH-type inclusion with a halite crystal plus vapor CO2, liquid CO2 and liquid H2O. (E). Polyphase SH-type inclusion with halite, sylvite, hematite and opaque daughter minerals. (F). W-type inclusion composed of vapor H2O and liquid H2O. Abbreviation: H = halite; Op = opaque daughter mineral; LCO2 = liquid CO2; LH2O = liquid H2O; VCO2 = vapor CO2; VH2O = vapor H2O.

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inclusions in sulfide-bearing veins, but hardly exceed 5% of the total inclusion population. In the same veins, the molybdenite-coexistent quartz crystals often contain more abundant and larger S-type inclusions, compared to quartz that is not coexisting with molybdenite. 5.1.4. W-type (aqueous inclusion) Most W-type inclusions show two visible phases at room temperature, i.e. liquid H2O and vapor H2O, and occur as irregular-shaped to rounded, 4 to 25 μm in size (Fig. 5F). In general, the vapors have filling degrees of 5 to 40 vol.%. Rare inclusions occur as single phases and are occupied by vapor H2O only. In early barren veins and quartz-pyrite veins, W-type inclusions mainly occur as secondary trails along healed fractures, and their abundance is limited (b 10%). In quartz-molybdenite and quartz-polymetallic sulfide veins, however, most of them are densely scattered or grouped in clusters in individual quartz grains, and thus, are considered to be primary. In late barren veins the W-type inclusions are the only type of inclusions observed. 5.2. Occurrence and temporal relationship of fluid inclusions The relative timing of fluid entrapment can be inferred from the distribution of fluid inclusion assemblages in veins of different paragenetic stages (Ulrich and Heinrich, 2001; Ulrich et al., 2002) and from crosscutting relationships between individual inclusion trials (Ulrich et al., 2002). In this study, the distribution of inclusions in various veins was studied in an attempt to delineate the relationship between fluids, vein formation, and ore deposition. The relative abundance of inclusions was visually estimated for each type of inclusions in a total of 21 samples, and shown in Appendix A, along with the vein and alteration types. In early barren veins, the PC-, and C-type inclusions are often randomly distributed or occur as clusters and are thus regarded as primary. PC-type inclusions are predominant in early barren veins, and constitute more than 90% of total primary inclusion populations. Rare W- (3% to 6%) and C-type (4% to 7%) inclusions constitute the remaining 10%. Well-defined secondary trails containing C-, S- and W-types of inclusions are observed to cut the whole quartz crystals, which is indicative of a later stage of entrapment. In quartz-pyrite veins, PC-type inclusions are less frequent, while C-type inclusions become predominant (b10% to >90%). S- and W-type inclusions can be observed, but their abundance is limited (each type 8%). Quartz-molybdenite veins are dominated by C-type inclusions with low CO2 content (5–30%), followed by W-, PC- and S-types inclusions. In quartz-molybdenite veins overprinted by intense sericitization, however, W-type inclusions constitute more than 70% of all inclusions. S-type inclusions in these veins are rare (b5%). In quartz-polymetallic sulfide veins, W-type fluid inclusions are prevalent and the number of all the other fluid inclusion types decrease. Minor C-type inclusions with low CO2 content (5–30%) still exist, though their abundance is generally b 10%. The late barren veins contain only W-type inclusions. 5.3. Microthermometric results A total number of 682 inclusions from 87 assemblages were analyzed by microthermometry (Fig. 6), and the results are reported in Table 1. PC-type inclusions contain only liquid CO2 or liquid CO2 + vapor CO2 at room temperature, but a vapor bubble occurs during cooling runs. These inclusions yield melting temperatures for solid CO2 from − 60.4 °C to −56.6 °C, indicating a possible presence of small contents of other gases such as CH4 or N2, although they were not directly detected by laser Raman spectroscopy analysis (see below). The homogenization temperatures of CO2 to the liquid phase show a large variation from 8.3 °C to 31.0 °C (Table 1, Fig. 6).

C-type inclusions display melting of CO2 solid at temperatures between −80.5 °C and −56.6 °C, with most between −57.5 °C and −56.6 °C. The temperatures are in part lower than the triple point for pure CO2 (−56.6 °C), indicating the presence of a subordinate amount of other gases. These were, however, not detected by laser Raman spectroscopic analysis (see below). Melting of CO2 clathrate occurs at temperatures between 1.1 °C and 9.5 °C, with most between 6 and 9 °C (Fig. 6). This indicates a salinity range of 1.0 to 14.3 wt.% NaCl equiv, clustering 3–7 wt.% NaCl equiv (Fig. 6). Three different modes of partial homogenization of CO2, viz. to liquid, to vapor and by critical behavior, can be observed within a fluid inclusion assemblage. About 63% of the analyzed C-type inclusions show partial homogenization to liquid at temperatures of 14.1–30.9 °C, followed by 31% to vapor at 26.5– 30.9 °C, and 6% by the critical behavior at 31.0 °C (Fig. 7). Most of the inclusions show partial homogenization temperatures ranging from 29 to 31 °C (Fig. 7). Total homogenization temperatures exhibit a wide range from 170 to 449 °C, with four peaks in the modes of 180–210 °C, 240– 320 °C, 330–350 °C and 360–420 °C, respectively (Fig. 6), possibly corresponding to the formation of the earlier four of the five stage veins. In S-type inclusions, all the SH-subtype inclusions show consistent microthermometric behavior, i.e., halite dissolution after vapor bubble disappearance. The liquid–vapor homogenization by vapor bubble disappearance is observed at temperatures clustering 112–375 °C, and then the halite dissolution occurs at temperatures from 188 °C to 457 °C, corresponding to salinities from 31.2 to 54.1 wt.% NaCl equiv. (Table 1, Fig. 6), except for those containing other daughter minerals other than halite. In Fig. 8, the totally homogenized SH-subtype inclusions align along the halite saturation curve. During heating to 600 °C, neither the transparent nor opaque daughter minerals dissolve in the SM subtype, and thus, we can only get liquid– vapor homogenization data for the SM-subtype inclusions. In SMsubtype inclusions with a CO2 bubble, CO2 solid dissolved at temperatures between −59.7 °C and −56.7 °C, while CO2 clathrate dissolved at temperatures between 7.4 °C and 9.5 °C. Liquid–vapor homogenization in these inclusions occurs at temperatures of 286 to 385 °C. In SM-subtype inclusions with a H2O bubble, ice-melting temperatures range from −4.9 to −2.4 °C. Liquid–vapor homogenization in these inclusions occurs at temperatures between 151 °C and 322 °C. W-type inclusions yield first ice-melting temperatures from −37 °C to −23 °C with a small mode at −30 °C to −25 °C, which are below the eutectic temperature of −21.2 °C and −22.9 °C determined for the H2O-NaCl and H2O-NaCl-KCl systems, respectively (Hall et al., 1988). This indicates the presence of other ions in addition to Na + and K+, which is further verified as Li and B by LA-ICP-MS analyses (see Appendix C). Despite this, we regard the fluids as H2O-NaCl-KCl systems in salinity estimation, due to shortage of study of fluids containing Li and B, and the limited concentrations of Li and B in the fluids compared with Na and K. Final ice melting temperatures in W-type inclusions range from −12.2 °C to −0.1 °C, with most falling into the range of −5 to −3 °C (Fig. 6). These measurements constrain a salinity range of 0.2 to 16.2 wt.% NaCl equiv., with the majority between 5.0 and 8.0 wt.% NaCl equiv. (Fig. 8). Total homogenization to the liquid phase is observed at temperatures between 109 °C and 383 °C, with two modes of 280–340 °C and 130–190 °C, respectively (Fig. 6). 6. Fluid composition 6.1. CO2 content of fluid inclusions CO2 molar fractions (XCO2) and densities for individual inclusions were calculated using the program FLINCOR of Brown (1989) and the equations of Brown and Lamb (1989). The results are listed in Table 1. As indicated by both microthermometric data and Laser Raman analysis, the PC-type inclusions contain only CO2, but no clathrate is

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Fig. 6. Histograms showing melting temperatures of clathrate, halite and ice for C, S- and W-types inclusions and homogenization temperatures for PC-, C-,S-, and W-types inclusions.

observed during cooling. Thus, they can be assumed as pure CO2 end-member with XCO2 of 1. Estimated densities from different assemblages show a fairly wide interval from 0.52 to 0.87 g/cm 3. Three parameters are needed to estimate XCO2 in C-type inclusions, including: (1) the melting temperatures of clathrate (Tm, clath), (2) partial homogenization temperature (Th, CO2) and mode, and (3) estimated volume fraction of CO2. Precise estimation of carbonic volume fraction is difficult because of variable shapes and orientations of fluid inclusions, and the errors associated with phase volume estimates can be up to 20% (Anderson and Bodnar, 1993; Roedder, 1984), which have a large effect on density calculations, and a smaller effect on the fluid composition. The obtained XCO2 values in C-type inclusions vary from 0.01 to 0.93, and densities from 0.46 to 1.01 g/cm3 (Table 1).

As stated above, the vapor phase of S-type inclusions can be dominated by either CO2 or H2O; and the inclusions can be viewed as H2O-CO2-NaCl system (e.g. Bowers and Helgeson, 1983; Brown and Lamb, 1989). Unfortunately, no experimental data are available for halite-saturated H2O-CO2-NaCl systems. Considering that the volume percentage of vapor bubbles in S-type inclusions are generally b10%, we herein estimate their density using experimental data of the H2O-NaCl system. The densities of SH-subtype inclusions are estimated between 1.11 g/cm3 and 1.26 g/cm3 (commonly from 1.24 g/cm3 to 1.26 g/cm3), being the highest of all the inclusion types found in this study. As for SM-subtype inclusions with CO2 vapor bubble, the estimated XCO2 values range from 0.01 to 0.36, with densities from 0.71 to

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Table 1 Microthermometric data for different types of inclusions. Fluid inclusion

Vein

TmCO2 (°C)

PC type

Total EBV Q-Py Q-Mo Q-PM Total EBV Q-Py Q-Mo Q-PM Total EBV Q-Py Q-Mo Q-PM Total EBV Q-Py Q-Mo Total EBV Q-Py Q-Mo Q-PM LBV

−60.4 −57.2 −60.4 −56.7 −56.8 −80.5 −58.5 −80.5 −65.8 −57.5

C type

SH subtype

SM subtype

W type

Tmice (°C)

to −56.6 to −56.6 to −56.6 to −56.6 to −56.6 to −56.6 to −56.6 to −56.6 to −56.6 to −56.6

−59.7 to −56.7

−59.7 to −56.7

−4.9 to −2.4

−4.9 to −2.4 −12.2 to −0.1 −6.8 to −0.3 −12.2 to −0.4 −9.4 to −0.1 −8.8 to −0.2 −4.9 to −0.8

Tmclath (°C)

ThCO2 (°C)

1.1–9.5 2.6–8.7 4.3–8.8 3.3–9.5 1.1–9.4

8.3–31.0 9.5–28.7 30.8–31.0 16.2–28.7 8.3–18.3 17.9–31.0 21.0–31.0 23.0–31.0 17.9–31.0 24.2–30.8

7.4–9.5

7.4–9.5

28.8–31.0

28.8–31.0

ThL-V (°C)

112–375 312–375 162–316 126–289 112–123 151–385 154–319 243–309 151–385

TmS (°C)

188–457 390–399 206–457 188–446 203–251

Th~tal (°C)

170–449 170–416 206–449 219–430 195–343 188–457 390–399 206–457 188–446 203–251 151–385 154–319 243–309 151–385 109–383 217–337 205–430 151–378 168–258 109–223

XCO2 1 1 1 1 1 0.01–0.93 0.03–0.76 0.01–0.78 0.01–0.93 0.04–0.86 0 0 0 0 0 0 0 0.01–0.36 0 0 0 0 0 0

Salinity (wt.%)

Density (g/cm3)

1.0–14.3 2.6–12.4 2.4–10.0 1.0–8.7 1.2–14.3 31.2–54.1 46.4–47.3 32.1–54.1 31.2–52.8 32.0–34.7 1.0–7.7

0.52–0.87 0.64–0.87 0.52–0.54 0.64–0.81 0.79–0.87 0.46–1.01 0.60–1.00 0.46–1.01 0.57–0.95 0.62–0.95 1.11–1.26 1.11–1.13 1.19–1.26 1.22–1.26 1.23–1.24 0.71–0.95

1.0–7.7 0.2–16.2 0.5–10.2 0.7–16.2 0.2–13.3 0.4–12.6 1.4–7.7

0.71–0.95 0.57–0.99 0.75–0.98 0.69–0.98 0.57–0.98 0.80–0.99 0.94–0.98

TmCO2 = melting temperature of CO2; Tmice = final melting temperature of ice; Tmclath = final melting temperature of CO2-H2O clathrate; ThCO2 = partial homogenization temperature of CO2; ThL-V = homogenization temperature of liquid–vapor phase for S-type inclusions; TmS = final dissolution temperature of halite daughter crystal; Thtotal = total homogenization temperature; XCO2 = molar fraction of CO2.

0.95 g/cm 3 (Table 1). The densities of SM-subtype inclusions with H2O vapor bubble are between 0.90 and 0.96 g/cm 3 (Table 1).

6.2. Cationic composition of fluid inclusions 102 individual inclusions were analyzed using LA-ICP-MS system (Appendix C). Table 2 lists the element concentration for different fluid inclusion types. The small sizes of C-type inclusions in early barren veins and the lack of useable Na signals for concentration quantification for PC-type inclusions precluded quantitative results for these samples. All the other inclusions measured contain major proportions of Na, K, Ca and Fe, and variable amounts of Li, B, Ti, V, Mn, Cu, Zn, As, Rb, Sr, Nb, Mo, Ag, Sb, Cs, Ba and W. Additional Ta, Th, U, Re and Os were also analyzed, but concentrations were typically below the limit of detection.

Fig. 7. Histograms showing partial homogenization of C-type inclusions to liquid, vapor or by critical behavior.

Fig. 8. (A) Homogenization temperature versus salinity of individual fluid inclusions. Note the alignment of SH-type inclusions along the halite saturation curve, indicating the homogenization by halite dissolution. (B) Enlargement of those for W- and C-type inclusions in Figure A, wide variations of salinities possibly suggesting fluid immiscibility.

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Table 2 The range/average of element contents in various types of fluid inclusions (in ppm). Type

C-type

SH-subtype

SM-subtype

Veins

Q-Py

Q-Mo

Q-PM

Q-Py

Q-Mo

Q-PM

W-type LBV

Li B Na K Ca Ti V Mn Fe Cu Zn As Rb Sr Nb Mo Ag Sb Cs Ba W

210–1234/540 36–1508/286 7974–37,569/19599 546–12,199/3507 587–16,204/5269 62–1631/417 7–29/16 7–984/206 147–5320/1319 19–1635/333 6–374/99 15–94/38 17–457/112 5–562/37 1–9/3 3–73/20 1–14/5 1–4/2 10–199/50 1–567/62 1–11/3

248* 277–635/387 8110–18,716/13202 1532–4848/2816 1918–11,101/5315 399–1018/715 33–43/38 74–371/201 822–3345/1913 50–9566/1482 12–726/228 16–29/23 76–151/105 5–617/108 1–4/2 5–19/13 10–30/20 1–3/2 13–78/38 7–10/8 1–3/2

187–685/409 134–592/272 4794–17,670/10450 592–8738/2837 2553–14,699/7967 81–3792/717 8–92/35 8–466/126 11–3601/1948 45–7369/1980 17–202/96 9–30/22 17–179/86 7–363/59 2–9/4 3–14/10 1–9/4 1–11/3 12–64/32 2–14/6 1–26/9

1096–2261/1768 306–1782/969 79,541–139,217 /117822 23,023–113,641/66580 33,457–45,621/40362 1094–1808/1414 bLOD 9438–22,635/13423 13,155–55,150/37055 262–4223/1477 1782–7186/4018 bLOD 522–3667/1661 218–964/546 bLOD bLOD 27–47/38 1–5/4 485–2534/1293 113–647/294 11–67/25

bLOD bLOD 28,738* 20,895* 162,934* 3866* 2195* bLOD 8950* bLOD 1158* 336* bLOD 54* bLOD bLOD bLOD 12* bLOD 281* bLOD

bLOD bLOD 17,429–45,469/31449 6488–27,856/17172 21,909–56,579/39244 453* bLOD 231–1115/673 1585–166,925/84255 18,862–20,384/19623 208–376/292 261* 229–309/269 33–163/97 bLOD bLOD 21–37/29 2–11/6 55–125/90 22–36/29 14–22/18

203–1494/794 101–1788/853 15,281–35,371/26094 765–3930/1737 bLOD 184–429/306 bLOD 29–67/52 537* 92–523/307 43–216/129 62–461/190 27–285/130 4–512/124 3–3/3 bLOD bLOD 1–27/14 27–310/162 bLOD 2–5/3

“*” marks the value obtained from only one inclusion. Abbreviation: Q-Py, quartz-pyrite; Q-Mo, quartz-molybdenite; Q-PM, quartz-polymetallic sulifide; LBV, late barren veins. LOD, limit of detection.

Mo was found only in C-type inclusions. They display variable Mo concentrations of up to 73 ppm (Table 2, Appendix C). Elements such as Cu, Ti, Zn, Sr and Ba are variable by two orders of magnitudes. SH-subtype inclusions have high concentrations of Mn, Ti, Fe, Cu and Zn (Table 2, Appendix C). One SM-type inclusion with a transparent daughter mineral has unusually high Ca content (162934 ppm), indicating that the daughter mineral is possibly Ca-bearing. The SM-subtype inclusions with opaque daughter minerals have high Fe (up to 166925 ppm) and Cu (up to 20384 ppm) concentrations, suggesting that the opaque mineral is hematite and/or chalcopyrite (Table 2, Appendix C). Mo, Ag Ca and V in the W-type inclusions are below detection limits. The W-type inclusions have the highest B (up to 1788 ppm) concentrations, compared to other inclusion types. They also have very high concentrations of Li, Rb, Sr and Cs (Table 2, Appendix C). 7. Discussion 7.1. Fluid immiscibility and pressure–temperature conditions According to Diamond (1994), if the inclusions were formed in the immiscible two-phase field, the trapping pressures can be approximated from end-member inclusions trapped nearest the solvus. At Yuchiling, fluid immiscibility is evidenced according to the criteria outlined by Roedder (1984). In quartz-pyrite veins (Fig. 9A) and quartz-molybdenite veins (Fig. 9B), C-type inclusions with variable CO2 content are trapped as primary clusters, and thus, interpreted as contemporaneous trapping. They exhibit the same homogenization temperatures, and homogenize to the vapor and liquid phases, respectively. Such fluid immiscibility is considered to be intensive and prevalent during the formation of quartz-pyrite and quartz-molybdenite veins. Accordingly, these inclusions have been selected to estimate trapping pressures based on their end-member low and high XCO2 values, and isochores have been calculated using the FLINCOR program (Brown, 1989) and the equations provided by Bowers and Helgeson (1983). The homogenization temperatures of these inclusions are taken as trapping temperature based on the evidences of fluid immiscibility. Pressure–temperature conditions at which the inclusions formed

Fig. 9. Fluid immiscibility in quartz-pyrite veins (A) and quartz-molybdenite veins (B). Digits next to the inclusions represent their homogenization temperatures, and the homogenization mode include to vapor (V) and to liquid (L). The inclusions show heterogeneous homogenization, with some homogenizing to vapor while others to liquid.

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Fig. 10. Pressure–temperature conditions for different types of veins. (A) Minimum trapping pressure for early barren veins based on isochors of PC-type inclusions and the highest homogenization temperatures of secondary C-type inclusions. (B) Trapping pressures for inclusions from quartz-pyrite veins based on intersections (shaded area) between isochors constructed with the minimum and maximum densities of immiscible C-type inclusions, and minimum and maximum homogenization temperatures. (C) Trapping pressures for quartz-molybdenite veins based on intersections (shaded area) between isochors constructed with the minimum and maximum densities of immiscible C-type inclusions, and minimum and maximum homogenization temperatures. (D) Minimum trapping pressures for quartz-polymetallic sulfide veins based on isochors of C-type inclusions and their homogenization temperatures. (E) Corrected temperatures for late barren veins supposing trapping pressure of 20–32 MPa.

fall along the path defined by the isochores for the inclusions. Fig. 10 shows representative isochores for C-type inclusions trapped in quartz-pyrite and quartz-molybdenite veins. The estimated trapping pressure is 47–159 MPa at temperatures of 360–400 °C for quartzpyrite veins (Fig. 10B), and 39–137 MPa at temperatures of 340–380 °C for quartz-molybdenite veins (Fig. 10C), respectively. In early barren veins, primary inclusions are small, and dominated by PC-type inclusions, which homogenize before 30.9 °C. The small sizes and the low content of H2O in CV-type inclusions preclude precise temperature estimation due to decrepitation before total homogenization. Thus, no homogenization temperatures can be obtained directly. Using the highest homogenization temperature (416 °C) for secondary C-type inclusions as a reasonable lower limit, the isochors of the PC-type inclusions indicate a pressure range from 133 to 220 MPa at temperatures higher than 416 °C (Fig. 10A). In quartz-polymetallic sulfide veins and late barren veins, fluid inclusion assemblages supporting fluid immiscibility have not been observed, and independent temperatures have not been obtained. This precludes exact estimation of trapping conditions. However, minimum trapping pressure estimates are available by constructing isochors and assuming measured homogenization temperatures as minimum trapping temperatures (Brown and Hagemann 1995; Roedder and Bodnar 1980). In quartz-polymetallic sulfide veins, isochors from C-type fluid inclusions indicate minimum pressures of 32–110 MPa at homogenization temperatures of 260–300 °C (Fig. 10D). In late barren veins, the minimum pressure of 18–82 MPa at homogenization temperature of 140–180 °C can be obtained (Fig. 10E). Importantly, the pressure estimation above is consistent with the conclusion by Bowers and Helgeson (1983) that a H2O-CO2 fluid with a salinity of 6 wt.% NaCl equiv will form an immiscible brine, and a low-salinity, CO2-bearing vapor at low pressure (b 100 MPa); whereas at pressures of >100 MPa, immiscible behavior forms low-salinity CO2-H2O mixtures lacking brines.

7.2. P–T–X evolution and vein formation The most likely initial fluid at Yuchiling is recorded by numerous assemblages of single-phase PC-type inclusions, followed by minor C-type inclusions in early barren veins. The fluid was possibly hot (>416 °C), compositionally carbonic-dominated, locally trapped at high pressure (>133 MPa), and magmatic in origin (Zhou, 2010). This is consistent with the expected behavior of CO2 and H2O in felsic liquid-melt system, whereby the earliest exsolved fluid from magmas is usually CO2-dominated, and the majority of CO2 will be degassed before H2O (Chen and Wang, 2011; Giggenbach, 1997; Lowenstern, 2001). Interaction of this initial fluid with wallrocks induced precipitation of quartz and K-feldspar in early barren veins, and caused widespread potassic alteration. Formation of early barren veins sealed the fracture systems and lowered the permeability, and hence, led to a renewed pressure increase in the porphyry system (e.g., Fournier, 1999). Immiscible C-type inclusion assemblages in the quartz-pyrite veins have yield trapping pressures of 47–159 MPa at temperatures of 360–400 °C (Fig. 11). This large pressure fluctuation reflects the dynamics of the early high-temperature regime, resulting in repeated hydrofracturing and sealing in many porphyry systems (Klemm et al., 2007; Rusk et al., 2008; Ulrich et al., 2002), which is likely recorded by the veinlets at Yuchiling. Fluid salinities at that time changed from 2.6 to 12.4 wt.% NaCl equiv., and the CO2 contents was ca. 8 mol%. At this stage, Mo in fluids was enriched, which is indicated by the highest Mo contents in the fluid inclusions in quartz-pyrite veins, compared to the other kind veins (Table 2). Subsequent fluid immiscibility and repeated hydrofracturing and sealing occurred during the formation of the quartz-molybdenite veins at temperatures of 340–380 °C and pressures of 39–137 MPa (Fig. 11). The deposition of molybdenite is associated with a drop in Mo concentrations in the fluid. The related fluid inclusions have lower salinities (av. 4.5 wt.% NaCl equiv) and lower CO2 contents (av. 7 mol%), compared to the quartz-pyrite veins.

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formation of Mo deposits. However, based on microthermometric and LA-ICP-MS studies of fluid inclusions in the Butte Mo deposit, Rusk et al. (2008) concluded that fluid immiscibility was not an important factor in the precipitation of molybdenite. Thus, further comparative studies of barren and mineralized intrusions with emphasis on fluid evolution will help evaluating the hypothesis and understanding the linkage between fluid composition and Mo mineralization. 7.4. The role of CO2 in Mo mineralization

Fig. 11. Pressure–temperature evolution for fluids from the Yuchiling deposit. Abbreviation: EBV=early barren vein; Q-Py=quartz-pyrite vein; Q-Mo=quartz-molybdenite vein; Q-PM=quartz-polymetallic sulfide vein; LBV=Late barren vein.

After the formation of quartz-molybdenite veins, the pressure, temperature and salinity of the fluid-system decreased further, which are estimated 32–110 MPa, 260–300 °C, and ca. 5 wt.% NaCl equiv, respectively. The CO2/H2O ratios of the fluids also decreased significantly, as indicated by the dominance of W-type inclusions and the decreasing amount of C-type inclusions containing only 5 mol% CO2. This fluid P–T–X change caused the formation of quartz-polymetallic sulfide veinlets (Fig. 11), containing pyrite, chalcopyrite, molybdenite, galena and sphalerite, associated with phyllic alteration including sericitization, chloritization, epidotization and silicification. During the formation of late barren veins, the fluids became cooler (140–180 °C) at lower pressure (18–82 MPa) (Fig. 11), and more dilute, with salinity of ca. 5 wt.% NaCl equiv. The fluids also became CO2-poor, as indicated by both the absence of C-type inclusion and the CO2-absence in the prevailed W-type inclusions. 7.3. Mo contents in fluids and Mo mineralization In the 102 analyzed fluid inclusions (Appendix C), 16 have detectable Mo, and 86 have not (Mo detection limit is between 1 and 45 ppm, mostly between 1 and 25 ppm, Appendix D). The 16 results range from 3 to 73 ppm (Table 2, Appendix C), and averaged 17 ppm. It is striking that the fluids forming the Yuchiling giant Mo deposit show such low Mo concentration. In a comparative study of barren and mineralized intrusions, Audétat et al. (2008) noted that Mo is not particularly abundant in the fluid associated with Mo mineralization, as exemplified by the Butte porphyry Mo deposit (USA) whose Mo contents in fluid inclusions are not detectable (Rusk et al., 2004). By contrast, some intrusions with little or no Mo mineralization have high Mo contents. For instance, fluid inclusions from two barren intrusions, i.e. Baveno and Mount Malosa, have Mo concentrations as high as 80 ppm; brine inclusions from the barren Rito del Medio pluton contain 20 to 760 ppm Mo; and two brine inclusions in quartz phenocrysts from granitoids in Capitan Mountains contain 1100 ppm Mo (Audétat et al., 2008). These data demonstrate that the mineralization potential of a given intrusions is not totally controlled by the Mo contents in the fluids exsolved from magmas; and fluid composition and evolution may be crucial for Mo mineralization, either promoting molybdenite precipitation from a low-Mo fluids (such as the Yuchiling and Butte deposits), or impeding Mo concentrations in a high-Mo system (such as plutons at Rito del Medio and Capitan Mountains). Audétat et al. (2008) put forward a hypothesis that fluid immiscibility and associated condensation of brine played a critical role in the

As shown in Table 2 and addressed above, among the fluid inclusions at Yuchiling only the C-type contain detectable Mo. Moreover, the highest Mo concentration in C-type inclusions decrease from 73 ppm in quartz-pyrite veins, through to 19 ppm in quartz-molybdenite veins, and to 13 ppm in quartz-polymetallic sulfide veins, which coincides with the decreasing CO2 contents from quartz-pyrite veins, through quartz-molybdenite veins, to quartz-polymetallic sulfide veins. Hence we propose that decreasing CO2 possibly results in decreasing Mo concentration in the fluids. As a matter of fact, aqueous-carbonic inclusions are ubiquitous in porphyry Mo deposits such as Jinduicheng (Yang et al., 2009), Tangjiaping (Chen and Wang, 2011), Trout Lake (Linnen and Williams-Jones, 1990), Questa (Klemm et al., 2008), and MAX deposits (Lawley et al., 2010); but are limited in porphyry Cu deposits (Cline and Bodnar, 1991; Hedenquist and Lowenstern, 1994; Nash, 1976). In some porphyry Cu-Mo deposit, a close association of Mo mineralization with CO2-bearing inclusions is also obvious, as exemplified by Butte deposit (Rusk et al., 2008). This implies that CO2 might play an important role in Mo mineralization. 7.5. A new type porphyry Mo-mineralization? The western Cordillera, extending from British Columbia (Canada) and southeastern Alaska southward through the western United States to Mexico, hosts a number of large porphyry Mo deposits. Carten et al. (1993) classified these porphyry Mo deposits into two types: (1) high-grade, rift-related, fluorine-rich deposits associated with alkalicalcic intrusions (e.g. Climax and Henderson, Colorado), i.e., Climaxtype; and (2) low-grade, subduction-related, fluorine-poor deposits associated with calc-alkaline intrusions (e.g. Endako), i.e., Endako-type. Selby et al. (2000) found that the Climax-type deposits contain abundant coexisting S-type (30 to 65 wt.% NaCl equiv.), vapor-rich and liquid-rich W-type (1–20 wt.% NaCl equiv.) and C-type inclusions, with Thtotal values between 300 and 450 °C. In contrast, in the Endako-type deposits, the low-salinity (1–10 wt.% NaCl equiv.) W- and C-type inclusions coexist with less abundant S-type (30–60 wt.% NaCl equiv.) inclusions, with Thtotal values clustering 250–450 °C. Compared to the Mo deposits of the above-mentioned two types, the Yuchiling porphyry Mo system is also unique for the observation of a large number of PC- and C-type inclusions in the minerals formed in earlier stages (Table 3). This unusual high CO2 concentration of the fluids may hint a much earlier fluid exsolution, considering the lower solubility of CO2 (than H2O and Cl) in the melt. The S-type inclusions at Yuchiling consistently homogenize by halite dissolution, but do not contain detectable Mo, contrasting the phase separation-induced Mo enrichment in the S-type fluid inclusions in Climax-type deposits (e.g. the Questa Mo deposit, Klemm et al., 2008). Cline and Vanko (1995) and Selby et al. (2000) independently reported that saline fluids do not coexist with vapor-rich W-type inclusions in Questa and Endako Mo deposits. They considered that the fluids were exsolved directly from the crystallizing melt. Their conclusion is based on the observation that saline inclusions are the paragenetically earliest type, which is not the case at Yuchiling. Instead, the interpretation of brine exsolution during a period of high pressure following an initially fracturing event (early barren veins), as suggested by Becker et al. (2008),

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N. Li et al. / Ore Geology Reviews 48 (2012) 442–459

Table 3 Comparison between different types of porphyry Mo systems.

Intrusion

Mineralization

Characteristics

Yuchiling

Climax-type

Endako-type

Type of intrusion Intrusive phases

Stock Multiple intrusions of granites

Stock Multiple intrusions of granites

Cogenetic rock type Style of mineralization

Biotite granite poprhyry Stockwork veinlets, very minor disseminations Quaquversal 0.06% Pyrite, chalcopyrite, sphalerite, galena, wolframite, fluorite, sericite, K-feldspar

Granite porphyry Stockwork veinlets, very minor disseminations Inverted cup 0.30% to 0.45% Pyrite, wolframite (huebnerite), cassiterite, stannite,bismuth sulfosalts, chalcopyrite (rare), fluorite, topaz, sericite Potassic alteration, propylitic alteration, high-silica core and greisen common Aqueous, brine, with or without CO2-H2O By vapor disappearance or halite dissolution

Stock or batholith Composite intrusions of diorite to quartz monzonite Quartz monzonite porphyry Stockwork veinlets, very minor disseminations Inverted cup, tabular 0.10% to 0.20% Pyrite, scheelite, tin minerals (rare), bimuth sulfosalts, chalcopyrite (minor), fluorite, sericite Potassic alteration, propylitic alteration, with no high-silica zone and greisen Aqueous, CO2-H2O, with or without brine By vapor disappearance or halite dissolution 0 to 0.22 Low salinity liquid with moderate to low CO2; or saline fluids 250 °C to 450 °C

Orebody shape Average ore grade Ore-associated minerals

Alteration

Hydrothermal alteration

Fluids

Inclusion type

Tectonic setting Example

Brine homogenization mode

Intense potassic alteration, weak sericitization and propylitic alteration Pure CO2, CO2-H2O, aqueous, with limited brine inclusions By halite dissolution

CO2 content Original phase

0.03 to 1 CO2-rich Vapor

Temperature Collision-related

100 °C to 450 °C Rift-related Jinduicheng (Yang et al., 2009), Nannihu (Yang et al., 2012b), Donggou (Yang et al., 2011), Tangjiaping (Chen and Wang, 2011), Qian'echong (Yang et al., 2012a)

is more appropriate, considering the fluid inclusion petrogenesis and element partition pattern. The Yuchiling deposit is located in a continental collision orogen, and was formed by granitic magmatism associated with continental collision, which differs from the Climax- and Endako-types in their tectonic settings. The high contents of alkalis, incompatible elements and fluorine in the causative intrusion suggest an affinity with Climax-type deposits, whereas the much lower Mo grade is more similar to the Endako-type (Table 3). At Yuchiling deposit, strong potassic alteration is widely observed, but phyllic and propylitic alterations, which are extensively developed at both Climax- and Endako-type deposits are quite weak. Therefore, we propose that the Yuchiling deposit may represent a new type of Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO2-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization, but weak phyllic and propylitic alterations. It is pointed out that these features are shared by all the Mesozoic porphyry Mo systems in the EQMB and Dabie Shan, such as the deposits at Jinduicheng (Yang et al., 2009), Nannihu (Yang et al., 2012b), Donggou (Yang et al., 2011), Qianechong (Yang et al., 2012a), Tangjiaping (Chen and Wang, 2011) and Leimengou (Mao et al., 2008). 8. Concluding remarks The Yuchiling porphyry Mo deposit in the East Qinling Mo belt is associated with the high K calc-alkaline intrusion formed in intercontinental collision orogenesis between the Yangtze and North China cratons. The mineral system is characterized by intense potassic alteration, which is locally overprinted by phyllic alteration. The mineral system developed in five-stage as represented by the following vein types, from early to late, the early barren quartz ±potassic feldspar veins (1), the quartz-pyrite±K-feldspar veins (2), the quartz-molybdenite±pyrite veins (3), the quartz-polymetallic sulfide veins (4), and the late barren quartz ±carbonate±fluorite veins (5).

Low salinity liquid with moderate to low CO2, or saline fluids 300 °C to 450 °C Subduction-related Climax (Hall et al., 1974), Henderson (Seedorff and Einaudi, 2004a,b); Questa (Cline and Bodnar, 1994; Klemm et al., 2008)

MAX (Lawley et al., 2010; Linnen and Williams-Jones, 1990); Endako (Bloom, 1981; Selby et al., 2000)

The ore-forming fluids are rich in CO2. The temperatures and pressures of the fluids decreased gradually, from >416 °C and pressure of >133 MPa for early barren veins, through 360–400 °C and 47– 159 MPa for quartz-pyrite veins, 340–380 °C and 39–137 MPa for the quartz-molybdenite veins, 260–300 °C and 32–110 MPa for quartzpolymetallic sulfide veins, and to 140–180 °C and 18–82 MPa for late barren veins. LA-ICPMS analysis shows that, among the fluid inclusions at Yuchiling, only the C-type contains detectable Mo. The highest Mo contents gradational decrease from 73 ppm in quartz-pyrite veins, through to 19 ppm in quartz-molybdenite veins, and to 13 ppm in quartz-polymetallic sulfide veins, coinciding well with the decreasing CO2 contents from 8 mol%, through 7 mol%, to 5 mol%, respectively. Hence decreasing CO2 content resulted in decreasing Mo concentration in the fluids, as well as the precipitation of molybdenite from the fluids. This may help understanding why the CO2-bearing fluid inclusions have been observed in most of the porphyry Mo systems in the world. The Yuchiling deposit differs from the Climax- and Endako-type porphyry Mo deposits, and may represent a new type of Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO2-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization, and weak phyllic and propylitic alterations.

Acknowledgment Drs. Hui Zhang, Haizhu Hu, Zhiyong Ni and Wen Zhang helped in the field investigation. The research was granted by the National Basic Research Program (No. 2006CB403500) and the National Natural Science Foundation of China (Nos. 40730421, 41072061 and 40425006). Comments and suggestions from two reviewers and Prof. NJ Cook greatly improved the quality of the paper.

N. Li et al. / Ore Geology Reviews 48 (2012) 442–459

455

Appendix A. Summary description of samples, veins, and fluid inclusions

Vein type

Sample no.

Vein minerals

Width (cm)

Alteration/mineralization

Measurement

EBV

ZK009-179 ZK009-313 ZK009-445 481-002B1 481-002B2 ZK009-188 ZK009-342 ZK009-469 ZK009-489 481-003B 481-008B1 481-009 527-001 527-002A ZK009-203 ZK009-255 ZK009-341 481-003A 527-015 481-018A1 481-018A2

Qz, Qz Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz, Qz

1.2 1.5 4.0 0.6 0.7 1.5 2.0 2.0 2.0 3.5 0.5 0.5 0.6 0.9 5.0 0.8 2.8 3.5 3.0 1.2 0.5

Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense Intense

MT, MT, MT, MT, MT, MT, MT, MT, MT, MT, MT, MT, MT MT, MT MT MT MT MT, MT, MT,

Q-Py

Q-Mo

Q-PM LBV

Kf Kf, Mt Py, Fl Py, Mo Py Py Py, Mo, Ser Py, Mo, Ser, Fl Mo, Py, Fl Mo, Ser, Fl Mo, Py, Ser Mo, Ser Mo, Py Mo Mo Mo, Py, Fl Mo, Py, Cp, Sp, Gn Mo, Py, Cp, Gn, Ser Fl

po, weak chl/Py po and ser, weak cc/Py po, weak chl/Py po and weak ser/Py po and weak ser/Py po/Py po, weak chl/Py, Mo po, weak chl, fl and ep/ Py, Mo po, moderate ser and kao/Py, Mo, Cp po, moderate ser and kao, weak cc and chl/Py, Mo po, weak ser, fl, ep and chl/Py, Mo, Cp, Mt po, weak bi, ser, fl, ep and chl/Py, Mo, Cp po and ser, and weak fl, ep and chl/Py po, moderate ser and kao, weak cc and chl/Py, Mo po, weak chl and fl/Py, Mo po, weak ser and chl/Py, Cp, Mo po, ser and cc/Py, Mo po, ser/Py po/Py po, weak ser, ep/Py po, weak ser/Py

LR LR LR LA, LR LA LA LA LR LA LR LR LA LR

Primary fluid inclusion PW

PC

C

5% 3% 5%

90% 90% 88% 3% 5% 75% 80% 2% 90% 2% 3% 1% 2% 1% 35% 1% 1%

5% 7% 7% 95% 90% 20% 13% 95% 8% 95% 90% 95% 3% 90% 55% 94% 25% 10% 73%

LA, LR LA LA

W

2% 3% 3% 5% 3% 2% 3% 5% 3% 90% 3% 6% 3% 70% 90% 25% 100% 100%

S

2% 2% 2%

2% 1% 5% 1% 3% 2% 4% 2%

Vein type: EBV = early barren vein; Q-Py = quartz-pyrite vein; Q-Mo = quartz-molybdenite vein; Q-PM = quartz-polymetal vein; LBV = late barren vein. Minerals: Cc = calcite; Cp = chalcopyrite; Gn = galena; Kf = K-feldspar; Mo = molybdenite; Mt = magnetite; Py = pyrite; Qz = quartz; Sp = sphalerite Hydrothermal alteration: cc = carbonation; chl = chloritization; ep = epidotization; fl = fluoritization; kao = kaolinization; po = potassic alteration; ser = sericitization. Measurement: MT = microthermometry; LA = LA-ICPMS, LR = laser Raman.

Appendix B. LA-ICP-MS operating and data acquisition parameters

Laser system

ESI/New Wave Research UP213 solid state Nd:YAG laser with aperture imaging

Laser wavelength Laser mode Nominal pulse width Repetition rate Spot sizes (diameter) Incident pulse energy Energy density on sample Ablation cell volume (Supercell) Ablation cell gas flow rate Focus

213 nm Q-switched 4 ns 10 Hz 20, 30, 40 um ~0.5 mJ per pulse (at 80 μm beam size) ~9 to 9.6 J/cm2 (homogenized energy distribution, flat beam) ~8 cm3 230–270 ml/min He Fixed at sample surface

ICP-MS

Thermo-Scientific Xseries-2 quadrupole

Cones Detector type Detector mode Detector vacuum Argon gas flow rates Plasma Auxiliary Nebulizer RF power Quadrupole settling time Oxide production rate Robust plasma conditions

Ni, high sensitivity skimmer cones (Xs) Single-collector discrete dynode electron multiplier Dual (cross-calibrated pulse counting and analogue modes) 10−7 mbar (during analysis) 13.0 L/min 0.70 L/min 0.90 L/min 1450 kV 1.5 (min), 15 ms (max) Tuned to ≤1% ThO (248ThO/232Th) Tuned to sensitivity of 238U–232Th

Data acquisition parameters Scanning mode Acquisition mode Isotopes measured (dwell time in brackets) in standard resolution mode (except Na – high resolution mode)

Analysis duration

Peak jumping, 1 point per peak Time resolved analysis 7 Li (10), 11B (10), 23Na (10), 29Si (10), 42Ca (10), 47Ti (10), 51V (10), 55Mn (10), 57Fe (10), 65 Cu (20), 66Zn (10), 75As (10), 77ArCl (10), 82Se (10), 83Kr (1), 85Rb (10), 88Sr (10), 93Nb (20), 95 Mo (10), 107Ag (10), 121Sb (20), 133Cs (10), 138Ba (10), 181Ta (10), 182W (10), 208Pb (10), 209 Bi (20), 232Th (10), 238U (10) 10 s. laser warmup, 30 s. blank, 45 s. ablation, 15 s. washout

Data processing Software External standard matrix Internal standard element

SILLS (vers. 1.1.0) NIST SRM-610 glass 23 Na based on NaCl wt.% equivalent, as determined by microthermometry

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Appendix C. LA-ICPMS concentration data (in ppm) for fluid inclusion

Type Vein C

C

C

Sample

002B1-10-2 002B1-10-3 002B1-10-4 002B1-1-1 002B1-1-2 002B1-1-5 002B1-1-5-2 002B1-1-6 002B1-2-2 002B1-3-1 002B1-3-3 002B1-3-5 002B1-8-1 002B1-8-2 002B1-8-9 002B2-2-1 002B2-2-2 002B2-2-5 002B2-4-4 002B2-4-5 002B2-8-10 002B2-8-10-2 002B2-8-11 002B2-8-13-1 002B2-8-13-2 002B2-8-5 002B2-8-6 002B2-8-7 002B2-8-9 002B2-A-1 188-11-1 188-11-11 188-11-13 188-11-2 188-11-3 188-11-4 188-11-6 188-11-9 188-5-1 188-5-12 188-5-2 188-5-3 188-5-5 188-5-7 342-1-4 342-1-7 489-1-2 489-2-6 489-2-7 489-4-4 Q-Mo 009-4-8 009-2-1 009-9-2 009-4-5 009-4-6 009-4-7 009-3-3 009-3-3 -2 009-5-1 009-7-2 009-7-3 009-4-1 Q-PM 015-1-1 015-1-2 015-1-4 015-2-10 015-2-015 015-2-3 015-2-4 015-2-7 015-2-8 015-4-1 015-4-2 015-4-3

Li

B

Na

Q-Py

36

304 204 1508 371 1234

195 604

389 365 154

106 55 75 597 203 307 87

334 557

210 248

170 87

471 199 128 277 635

316 320

153 384

145 382

261 310

685 187

134 307

29878 13024 8864 31621 24699 34416 30746 30964 13366 34493 13406 12221 29529 24619 17079 17738 33522 33172 22962 20405 12774 13783 13336 26469 26900 23935 31305 20054 13591 23329 12932 11068 11329 10497 12901 13833 10354 16633 9973 9975 11638 12184 27562 7974 37569 24890 16011 11901 13577 14937 18716 15654 17153 16794 14530 13627 8840 8398 8110 13343 11423 11832 9089 6893 6984 5564 9254 9641 11897 11803 10871 16397 17670 10650

K

Ca

3675 952 12199 3660 1980 5730 6871 3082 951 546 3045

Ti

V

Mn

Fe

587

Cu

Zn

147

6 891

83 20

189

354

2584 2550 4848 2209 2895 4938 3215 8738 1013 2774 3522 3418 3163 2668 1614 1523

Rb 72 17 242 208

23

9 12 457

Sr

Nb Mo

166

18

92 114

12 13 26

7

7

1635 334

85 44

165 13

147

65 56

9

14

47

2769

62

15 86

301

28 509 270 2154

11632

82 77

12 29

105 1631

854

1918 1018 399 881 3979 3742

83 23 77 154 984 765 59 715 64 126 302

530 19 86 86 165 36

122 76 78

18 42 53 291 374 86 78

110 258

1533

33 88 371 307

1951 3345 822

43

9825 3792

69 69 18 78 104 33 50 127 110 71 69 33 93 146 138 346 124

92 32 43 15

51 50 9566 117

24 12 120 42

241 1303 94 2984 51

336 726 199 367

2924 3601

362 6243 7369 375 2196

202 186 124 99

29 16

6742

123 242

2553 4619

81 654

26

696

33 17

633

8

127 8

430

26

5 8 30 19 13 47 41 6 11 6 12

8

46

2

108 47

42 2

567

1 2

1

2

2 2

1

3

14 10 11 32 50 12 13 21 9 55 42 7

5 617 76 25

2

13

2

1 1

8

73 35 4

1 1 1 2

2 4

20 16 22 46 23 50 72 10 11 27 12 30 25 50 45 27 37 19 40 76 93 199 42 115 106 48

34 13

5 30

0

1 5 3 1 14 11 2 2 1 4

1

44 5

55 1 1

6

3

2

7 10

1 1 3

16 82 39 122 147 23 95 151

76 25

24 265

34 12

110 3

5

74 87 106 107 278

487

17 32

25

29

5836 11101 611 669

387 63 30 21

227 730 1424

149 113 1

32 95

24

309 217 184

37

40 36

12

562

764 502

307

3321

41

717

14

2 1

29

19

34

15 277

4720 4013

65 84

70

4

19 40 38

W

12 13 15

87

360 522

4 5 1 9

27 6418 2767

Ba

64 25 185

20

104 3368 16204

Ag Sb Cs

32 32 36

36

1582

10443 1332 1549 1448 2454 1813 4606 1532 2568 3458 2353

94

5320

760 5519 5145 3078 10122 5805 5914 1509 1159 2551 1164 1061 2795 1260 3810 5677 3771 1351 5549 2477 910 895 2645 2187 4124 1227 1004 846 3158 4091 4458 9036 3087

As

102

10 64 44 12 33 60 17 73

20 10 81 43 51 20 363 85 236

1

19 4

10 3

1 1 1

5 1 2 2

1 2 4 3 6

78 49 27 28 33 54 28 23 45 12 43 58 16 39 22 33 20 36 48

1 2

3 5 4 4 22 10 2

1 5 3 5

1

N. Li et al. / Ore Geology Reviews 48 (2012) 442–459

457

Appendix C (continued) Type Vein C

SH

SM

W

Sample

Q-PM 015-4-4 015-4-5 015-5-1 015-5-3 015-5-9 015-7-1 015-7-3 015-7-5 Q-Py 188-6-1 188-6-5 188-6-2 188-6-3 188-6-4 Q-Mo 002A-1 Q-PM 015-OP 015-1-3 015-1-4 LBV 018A1-2-3 018A1-5-1 018A1-5-1-1 018A1-2-10 018A1-7-4 018A2-7-1 018A2-1O-2 018A2-1O-7 018A2-8-1 018A2-8-2 018A2-8-3

Li

B

592

2178 1782 1394 2261 306 1537 1096 393

383

101

1190 203

591 251 1207 305 259 1187 830 1029 1454 1494 1788 1023

Na

K

Ca

13485 592 10658 3671 8644 1994 2837 12687 1573 13709 13217 4794 926 14493 5084 14699 79541 107608 45621 139217 54781 123897 33850 33457 137900 23023 108555 113641 42009 28738 20895 162934 17429 27856 56579 25639 6488 21909 45469 8609 15281 1173 20242 3930 25143 1139 25831 765 26858 1774 27718 1444 24684 2354 24356 1318 35371 26979 34570

Ti

V

Mn

Fe

99 466 33 51 24

241 1074 350 15

Cu 1502 3015

11 579

92

1808 1094 1341 3866 2195 453

22635 11713 13872 9458 9438

31773 48245 55150 36953 13155 8950 1115 166925 253 1585 231 29 62

184

537

429

67

Zn

As

Rb

Sr

Nb Mo

45 9 17 13 1989 143 14 4581 134 95 15 1372 73 179 36 125 22 95 25 1423 46 30 7 835 73 700 5755 2241 842 2901 927 341 4223 2464 947 365 262 1782 522 218 723 7186 3667 964 1158 336 54 261 161 20384 208 229 33 18862 376 309 70 32 4 523 216 461 285 44 62 115 90 27 4 112 162 25 114 6 36 43 130 135 393 92 182 173 512 125

Ag Sb Cs 3

13 14

9 7 11 1 3 1

9 2

45 47 34 27

5 5 5 1 12 11 37 2 21 3

27

3 1 3

Ba

W

13 14 18 51 64

4

6 26 14 13 3

40 22 1535 1200 710 485 2534

11 20 67 11 16

647 144 190 113 375 281 125 36 55 109 22 32 132 102 5 27 209 71 152 310 278 300 172

1

14 22 3

5 2

Note: blanks means values below the limit of detection. Type abbreviation: C, C-type; SH, SH-subtype; SM, SM-subtype; W, W-type.

Appendix D. Limit of Detection (LOD) for LA-ICP-MS fluid inclusion analysis (in ppm)

Type

Vein

Sample

Li

B

Na

K

Ca

Ti

C-type

Q-Py

002B1-10-2 002B1-10-3 002B1-10-4 002B1-1-1 002B1-1-2 002B1-1-5 002B1-1-5-2 002B1-1-6 002B1-2-2 002B1-3-1 002B1-3-3 002B1-3-5 002B1-8-1 002B1-8-2 002B1-8-9 002B2-2-1 002B2-2-2 002B2-2-5 002B2-4-4 002B2-4-5 002B2-8-10 002B2-8-10-2 002B2-8-11 002B2-8-13-1 002B2-8-13-2 002B2-8-5 002B2-8-6 002B2-8-7 002B2-8-9 002B2-A-1 188-11-1 188-11-11 188-11-13 188-11-2 188-11-3 188-11-4 188-11-6 188-11-9 188-5-1

566 61 1354 1725 432 206 409 1557 287 372 595 1130 242 1899 643 485 135 785 267 883 586 268 432 457 257 682 339 1914 119 119 68 146 322 233 750 290 153 262 184

295 30 660 863 215 99 196 744 155 207 301 558 130 946 272 198 55 308 112 365 244 112 176 209 117 287 140 872 50 68 29 67 123 98 321 113 62 109 84

843 91 2014 2607 651 309 615 2354 429 554 890 1688 354 2782 938 649 181 1050 361 1189 789 360 580 619 348 920 457 2597 160 164 109 234 496 374 1221 452 238 423 303

533 57 1273 1671 416 197 392 1494 274 352 563 1066 226 1753 591 413 114 662 234 768 537 245 393 406 228 613 305 1813 108 109 58 125 265 198 642 243 129 225 168

3879 408 9013 11634 2855 1386 2755 10397 1970 2488 3970 7585 1704 12665 4218 2996 825 4822 1706 5544 3796 1729 2856 3170 1780 4478 2203 13248 780 854 1167 2469 5138 3964 12948 4677 2473 4485 3117

245 26 554 647 176 92 183 637 123 175 246 464 104 750 248 197 50 307 106 359 245 111 182 193 108 275 120 791 49 54 33 69 144 103 397 115 67 121 79

V 12 1.3 28 44 10 4.8 10 34 6.6 8.2 13 25 5.1 42 14 10 2.7 16 5.9 19 13 6.1 9.3 10 5.8 14 7.1 39 2.3 2.7 4.5 10 21 15 50 19 10 17 12

Mn 27 2.8 60 81 20 9.5 19 71 13 18 27 52 11 92 29 20 5.8 34 12 38 26 12 20 21 12 30 15 95 5.3 5.8 3.9 8.3 17 13 44 16 8.6 15 11

Fe

Cu

Zn

As

1142 35 31 26 118 3.9 3.1 3.2 2578 88 78 75 3459 106 83 77 879 27 22 20 427 14 10 10 848 27 21 20 3125 96 81 83 577 19 17 15 715 24 18 22 1167 40 38 31 2348 67 49 61 481 15 11 15 3782 121 122 108 1208 40 35 30 850 29 20 24 232 7.7 6.3 7.2 1403 42 32 38 470 16 11 13 1552 49 37 45 1010 36 31 33 461 17 14 15 711 27 22 21 805 28 18 23 452 16 10 13 1174 41 34 34 590 21 17 17 3521 106 110 93 208 7.0 6.0 5.6 213 7.0 5.7 6.2 164 5.2 3.7 3.9 353 10 7.5 9.3 720 22 17 19 566 17 12 12 1869 54 41 43 673 21 20 14 343 10 10 9.1 640 19 18 15 416 13 10 12

Rb

Sr

Nb Mo

Ag

Sb

Cs

Ba

W

62 6.6 149 191 48 22 45 171 31 40 64 123 26 205 70 48 13 76 26 87 59 27 42 47 27 68 33 195 12 12 7.4 16 33 25 81 31 16 28 20

9.1 1.0 21 29 6.9 3.1 6.1 25 4.8 5.6 10 19 4.0 34 10 7.1 2.0 12 4.1 13 9.5 4.3 6.9 8.1 4.5 11 5.2 32 1.8 1.9 1.1 2.3 4.8 3.7 11 4.2 2.3 4.3 2.8

2.2 0.1 2.9 4.3 1.1 0.3 0.7 3.1 0.5 1.1 1.2 2.6 0.5 4.7 1.5 1.0 0.2 2.0 0.3 1.5 1.1 0.5 1.1 0.8 0.4 1.7 0.7 4.3 0.2 0.2 0.2 0.4 1.0 0.7 2.3 0.8 0.5 0.6 0.3

5.6 0.5 12 16 4.2 1.9 3.7 13 2.7 3.0 6.6 10.5 2.3 17 5.4 3.5 1.0 4.5 2.1 7.9 4.7 2.2 2.8 5.6 3.2 4.4 3.0 20 1.0 1.3 0.3 0.7 1.5 1.6 4.5 1.5 0.8 1.5 0.7

1.0 0.1 1.9 4.1 0.9 0.4 0.7 3.5 0.4 0.8 1.1 2.1 0.5 4.0 1.3 0.7 0.3 2.1 0.5 1.5 1.1 0.5 0.6 1.1 0.6 2.0 0.3 2.0 0.2 0.3 0.2 0.3 0.7 0.5 2.0 0.6 0.3 0.7 0.4

19 2.1 47 62 15 7.1 14 54 9.8 13 20 39 8.2 65 23 15 4.0 23.0 8.0 27 18 8.1 13 15 8.5 21 10 60 3.6 3.9 2.0 4.4 9.5 7.0 23 8.7 4.6 8.0 5.5

7.6 0.7 18 22 5.7 2.7 5.4 19 3.6 4.8 8.6 15 3.2 25 8.4 5.1 1.6 8.6 3.4 11 7.5 3.4 5.5 6.1 3.4 8.6 4.2 25 1.4 1.4 0.7 1.7 3.8 2.8 8.4 3.1 1.7 3.2 2.1

1.2 0.1 3.4 5.5 0.9 0.5 1.1 2.9 0.6 1.0 1.5 2.8 0.4 5.6 1.8 1.7 0.2 2.3 0.6 1.6 1.6 0.7 0.9 1.1 0.6 1.6 1.3 5.8 0.3 0.3 0.2 0.3 0.7 0.6 2.3 0.8 0.3 0.6 0.4

13 1.2 33 14 9.0 4.5 9.0 32 5.2 8.5 11 21 4.4 25 15 9.0 2.7 12 4.9 18 9.9 4.5 7.1 9.2 5.1 13 4.7 36 2.4 2.4 1.0 2.9 5.4 3.4 14 4.1 3.1 5.9 3.2

(continued on next page)

458

N. Li et al. / Ore Geology Reviews 48 (2012) 442–459

Appendix AppendixDC (continued) (continued) Type

Vein

Sample

Li

B

Na

K

Ca

Ti

V

Mn

Fe

Cu

Zn

As

Rb

Sr

Nb Mo

C-type

Q-Py

C-type

Q-Mo

C-type

Q-PM

SH-subtype

Q-Py

188-5-12 188-5-2 188-5-3 188-5-5 188-5-7 342-1-4 342-1-7 489-1-2 489-2-6 489-2-7 489-4-4 009-4-8 009-2-1 009-9-2 009-4-5 009-4-6 009-4-7 009-3-3 009-3-3-2 009-5-1 009-7-2 009-7-3 009-4-1 015-1-1 015-1-2 015-1-4 015-2-10 015-2-015 015-2-3 015-2-4 015-2-7 015-2-8 015-4-1 015-4-2 015-4-3 015-4-4 015-4-5 015-5-1 015-5-3 015-5-9 015-7-1 015-7-3 015-7-5 188-6-1 188-6-5 188-6-2 188-6-3 188-6-4 002A-1 015-OP 015-1-3 015-1-4 018A1-2-3 018A1-5-1 018A1-5-1-1 018A1-2-10 018A1-7-4 018A2-7-1 018A2-10-2 018A2-10-7 018A2-8-1 018A2-8-2 018A2-8-3

55 163 134 197 226 2011 1038 143 332 96 655 232 168 698 821 569 520 423 608 429 348 818 509 146 322 392 988 132 364 214 267 235 184 150 480 132 385 240 223 277 1698 393 416 1719 1669 723 1153 476 1818 2209 507 2209 160 637 389 108 844 261 930 680 788 992 1622

24 74 58 86 103 709 355 45 103 33 352 112 141 320 435 296 255 208 299 265 232 499 329 64 140 156 351 49 133 77 97 85 125 94 289 76 218 184 130 157 743 156 160 736 715 270 458 189 885 900 274 900 65 261 160 39 308 81 300 209 235 320 481

87 267 219 322 366 3404 1777 295 816 247 1406 321 248 969 1128 782 717 583 840 613 506 1159 700 233 515 625 1584 212 585 344 428 376 289 236 758 205 607 380 351 438 2702 627 666 2636 2559 1103 1772 731 3042 3516 802 3516 316 1097 671 201 1565 483 1669 1256 1419 1856 2899

47 146 119 173 201 1891 992 160 454 140 1034 217 169 662 766 529 485 381 548 419 333 796 492 126 275 329 847 112 315 185 229 201 187 149 476 129 380 241 221 275 1443 326 343 1461 1418 593 952 393 1646 1860 504 1860 170 652 399 109 866 260 903 670 770 992 1545

902 2725 2241 3253 3745 32525 17058 2652 6878 2054 5917 1558 1277 4606 5510 3758 3532 2853 4113 3198 2517 5530 3642 2325 5140 6273 15777 2103 5863 3453 4308 3749 1304 1041 3336 893 2605 1730 1495 1867 27076 6366 6653 27278 26481 11326 18305 7554 31122 35581 3497 35581 2993 10479 6404 1835 14448 4485 15382 11620 13152 17374 26328

24 66 60 86 104 782 454 69 267 74 377 94 82 271 331 243 201 192 278 190 153 319 237 65 129 177 368 57 155 79 91 91 82 68 218 56 188 111 97 119 754 173 173 794 771 320 486 200 805 957 231 957 80 274 166 52 392 124 454 351 325 488 713

3.6 11 9.0 14 15 120 64 9.4 28 8.4 15 5.7 4.1 14 16 13 11 9.4 14 10 7.8 19 12 8.9 21 26 61 8.3 22 14 17 15 4.3 3.3 11 3.0 9.4 5.9 5.2 6.8 108 26 28 111 107 47 76 31 121 140 11 140 10 40 24 6.8 50 18 57 43 47 65 95

3.1 9.3 7.4 11 13 124 63 10 29 8.6 33 11 9.0 32 39 26 24 20 29 22 17 41 27 8.4 18 22 55 7.2 20 11 15 13 9.2 7.1 23 6.1 18 12 10 13 102 22 23 98 95 40 64 26 109 124 23 124 12 42 26 7.0 56 17 59 44 49 66 103

124 373 300 436 529 4832 2548 448 1209 381 1856 396 318 1176 1419 993 882 787 1133 796 637 1446 918 310 659 826 2022 283 749 445 564 498 376 311 930 269 705 477 430 540 3638 861 906 3884 3770 1643 2494 1029 4207 4579 971 4579 473 1631 997 291 2276 705 2365 1795 1978 2621 4162

4.0 11 9.3 14 15 143 75 13 38 12 74 14 11 43 45 32 30 26 38 26 21 51 28 10 21 26 61 8.6 24 14 18 15 17 14 46 12 37 23 22 26 115 26 30 115 111 48 78 32 122 148 50 148 12 46 28 7.9 65 22 71 53 62 75 119

3.6 10 7.7 13 13 112 58 10 26 7.9 48 11 7.5 37 37 34 23 19 27 19 15 48 27 7.9 20 23 47 7.4 19 14 17 14 13 10 31 6.8 22 14 13 15 101 22 26 116 113 43 69 28 89 118 29 118 11 32 20 5.5 48 12 38 36 46 57 61

3.3 11 8.0 12 13 148 74 13 31 8.7 44 15 14 42 53 39 35 26 37 31 25 59 39 11 23 25 76 8.3 28 16 20 15 12 10 28 7.8 20 19 11 14 117 26 25 99 96 47 64 27 144 162 26 162 14 59 36 8.6 67 18 68 53 54 76 114

5.8 18 14 21 24 244 127 22 64 20 92 23 18 71 81 56 51 43 62 46 36 82 50 15 32 41 101 14 37 22 27 24 21 17 53 15 43 27 25 31 174 41 43 180 174 74 120 50 192 226 57 226 22 78 48 14 112 35 120 90 100 134 200

0.8 2.2 1.8 2.9 3.3 28 17 3.1 10 3.1 12 3.9 2.6 11 12 9.2 8.0 6.8 10 7.6 5.7 12 8.0 1.9 4.1 5.1 11 1.7 3.9 2.4 3.0 2.9 2.7 2.4 7.7 2.0 6.2 3.5 3.4 4.2 22 5.2 6.0 26 25 11 17 7.1 24 31 8.2 31 2.6 11 6.7 1.9 16 4.8 16 14 13 16 29

0.1 0.4 0.3 0.5 0.7 3.9 3.4 0.6 1.2 0.6 2.0 0.5 0.4 1.5 1.8 0.6 0.9 0.7 1.1 1.4 0.7 1.8 1.0 0.4 1.0 1.1 3.7 0.3 1.3 0.7 0.9 0.6 0.6 0.5 2.0 0.4 0.9 1.0 0.7 0.8 3.9 1.1 1.3 3.5 3.3 2.0 3.4 1.4 5.4 5.2 1.7 5.2 0.8 1.9 1.2 0.3 1.4 1.1 1.3 2.9 2.9 1.4 3.2

SM-subtype Q-Mo Q-PM

W-type

LBV

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Ag

1.0 0.3 3.2 0.7 2.5 0.5 4.7 0.6 4.5 1.4 45 12 24 5.6 3.7 1.2 8.0 2.1 3.4 0.7 21 8.6 4.8 1.9 2.3 1.4 8.9 5.9 13 6.0 11 3.9 9.2 4.3 10 4.4 15 6.4 7.0 3.7 6.7 3.1 17 7.4 9.8 3.8 2.3 0.8 5.0 1.8 7.3 1.8 19 4.3 2.3 0.7 8.5 1.9 3.4 0.6 4.4 1.4 3.8 1.3 5.3 1.7 3.0 1.5 8.8 4.6 3.1 1.2 8.7 3.9 4.8 2.9 4.6 1.8 6.0 2.6 38 8.7 5.8 2.4 10 2.4 32 9.4 31 9.1 13 4.5 25 4.7 10 1.9 20 9.4 39 8.4 10 5.4 39 8.4 4.5 0.5 12 3.9 7.0 2.4 3.1 0.6 27 2.4 6.3 1.5 18 5.8 13 4.1 21 4.1 21 3.8 26 8.7

Sb

Cs

Ba

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0.1 0.4 0.3 0.4 0.5 5.8 2.5 0.5 1.4 0.4 1.5 0.5 0.5 1.6 1.5 1.6 0.9 1.0 1.5 1.4 0.9 2.1 0.7 0.4 0.8 1.0 2.8 0.3 0.9 0.7 0.8 0.7 0.9 0.6 1.5 0.5 1.5 1.0 0.8 1.1 4.1 1.0 1.0 3.7 3.6 1.5 2.1 0.9 5.3 5.2 1.6 5.2 0.7 3.1 1.9 0.3 3.0 0.7 2.0 2.5 2.6 2.9 4.2

1.6 4.8 3.9 5.7 6.7 66 35 5.9 18 5.5 30 7.0 5.2 22 25 18 16 14 19 15 11 24 15 4.1 9.2 11 28 3.8 10 6.0 7.4 6.5 6.5 5.4 17 4.8 14 8.4 8.1 10 50 11 12 51 49 21 34 14 53 62 19 62 5.9 21 13 3.9 31 9.5 33 25 28 36 55

0.6 1.8 1.5 2.1 2.6 21 11 2.1 6.0 1.8 10 2.7 2.1 8.4 9.2 6.3 7.0 5.1 7.4 5.6 4.3 11 6.2 1.4 3.1 3.6 9.4 1.4 3.0 2.0 2.6 2.3 2.4 1.9 5.5 1.8 4.7 3.1 2.7 3.4 16 4.1 4.6 19 18.8 8.0 13 5.4 19 22 6.3 22 2.1 6.9 4.2 1.3 10 3.5 12 8.0 9.3 13 20

0.2 0.3 0.3 0.5 0.5 3.4 1.9 0.5 1.3 0.4 3.8 0.4 0.4 2.3 1.4 1.5 1.1 1.3 1.9 1.2 0.8 2.5 1.4 0.3 0.9 1.8 2.6 0.3 1.2 0.4 0.6 0.5 0.5 0.3 1.8 0.5 1.0 0.7 0.6 0.7 4.7 0.9 0.9 4.1 3.9 1.6 2.8 1.2 5.3 5.7 1.3 5.7 0.6 1.4 0.9 0.3 3.2 1.2 3.0 2.0 2.3 3.0 6.9

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