Title: Fractionation of Cu and Mo isotopes caused by vapor-liquid partitioning, evidence from the Dahutang W-Cu-Mo ore field
Abstract: Geochemistry, Geophysics, GeosystemsVolume 17, Issue 5 p. 1725-1739 Research ArticleFree Access Fractionation of Cu and Mo isotopes caused by vapor-liquid partitioning, evidence from the Dahutang W-Cu-Mo ore field Junming Yao, Junming Yao Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorRyan Mathur, Corresponding Author Ryan Mathur Department of Geology, Juniata College, Huntingdon, Pennsylvania, USACorrespondence to: R. Mathur, [email protected] for more papers by this authorWeidong Sun, Weidong Sun Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorWeile Song, Weile Song Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorHuayong Chen, Huayong Chen Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorLaurence Mutti, Laurence Mutti Department of Geology, Juniata College, Huntingdon, Pennsylvania, USASearch for more papers by this authorXinkui Xiang, Xinkui Xiang No. 916 Geological Team, Jiangxi Bureau of Geology, Mineral Resources, Exploration and Development, Jiujiang, ChinaSearch for more papers by this authorXiaohong Luo, Xiaohong Luo Northwestern Geological Team, Jiangxi Bureau of Geology, Mineral Resources, Exploration and Development, Jiujiang, ChinaSearch for more papers by this author Junming Yao, Junming Yao Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorRyan Mathur, Corresponding Author Ryan Mathur Department of Geology, Juniata College, Huntingdon, Pennsylvania, USACorrespondence to: R. Mathur, [email protected] for more papers by this authorWeidong Sun, Weidong Sun Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorWeile Song, Weile Song Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorHuayong Chen, Huayong Chen Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, ChinaSearch for more papers by this authorLaurence Mutti, Laurence Mutti Department of Geology, Juniata College, Huntingdon, Pennsylvania, USASearch for more papers by this authorXinkui Xiang, Xinkui Xiang No. 916 Geological Team, Jiangxi Bureau of Geology, Mineral Resources, Exploration and Development, Jiujiang, ChinaSearch for more papers by this authorXiaohong Luo, Xiaohong Luo Northwestern Geological Team, Jiangxi Bureau of Geology, Mineral Resources, Exploration and Development, Jiujiang, ChinaSearch for more papers by this author First published: 22 April 2016 https://doi.org/10.1002/2016GC006328Citations: 28AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract The study presents δ65Cu and δ97Mo isotope values from cogenetic chalcopyrite and molybdenite found in veins and breccias of the Dahutang W-Cu-Mo ore field in China. The samples span a 3–4 km range. Both isotopes show a significant degree of fractionation. Cu isotope values in the chalcopyrite range from −0.31‰ to +1.48‰, and Mo isotope values in the molybdenite range from −0.03‰ to +1.06‰. For the cogenetic sulfide veined samples, a negative slope relationship exists between δ65Cu and δ97Mo values, which suggest a similar fluid history. Rayleigh distillation models the vein samples' change in isotope values. The breccia samples do not fall on the trend, thus indicating a different source mineralization event. Measured fluid inclusion and δD and δ18O data from cogenetic quartz indicate changes in temperature, and mixing of fluids do not appear to cause the isotopic shifts measure. Related equilibrium processes associated with the partitioning of metal between the vapor-fluid in the hydrothermal system could be the probable cause for the relationship seen between the two isotope systems. Key Points: Negative relationship between Cu and Mo isotope values from chalcopyrite and molybdenite from a skarn Cause of fractionation related to vapor liquid partitioning during cooling of hydrothermal fluid Cu and Mo isotope values from ores relate ore process over large distances 1 Introduction The increasing interest in transition metal isotope geochemistry has led to the measurement of significant isotopic variations of Fe, Ni, Cu, Zn and Mo in sulfide from different mineral deposits [Graham et al., 2004; Rouxel et al., 2004; Johnson et al., 2005; Mason et al., 2005; Asael et al., 2007; Hannah et al., 2007; Kelley et al., 2009; Palacios et al., 2011; Zhou et al., 2014]. A diverse set of hypotheses have been presented to explain isotope values in ores derived from high-temperature geochemical reactions. In general, two hypotheses regarding the interpretation of the transition metal isotopic data from high-temperature mineralization exist: (1) the physiochemical nature of the fluids evolve during the mineralization process which cause isotopic changes in the minerals of the system, (2) the addition/subtraction of different metal sources leads to mixing before which causes isotopic changes in the minerals of the system. The processes that could operate during these two scenarios include equilibrium fractionation, diffusion, changes in temperature, changes in redox, changes in pH, heterogeneity metal source, and mixing of isotopic reservoirs. Both Cu and Mo isotopes have demonstrated significant isotopic variations in sulfide and oxide minerals which provide information about the origin of the ore deposit. Stable Cu isotopes are known to undergo large fractionation in low-temperature deposits where δ65Cu varies on the order of 10‰ [Maréchal et al., 1999; Zhu et al., 2000; Asael et al., 2007; Ikehata et al., 2008; Asael et al., 2009; Weinstein et al., 2011] while the variations in δ65Cu of ∼2.5‰ in high-temperature (hypogene) deposits [Larson et al., 2003; Graham et al., 2004; Rouxel et al., 2004; Markl et al., 2006; Asael et al., 2007; Maher and Larson, 2007; Ikehata et al., 2008; Fernandez and Borrok, 2009; Mathur et al., 2009; Li et al., 2010]. Mo isotope composition of the molybdenites from the hydrothermal deposits varies over ∼2.5‰ [Wieser and de Laeter, 2003; Pietruszka et al., 2006; Hannah et al., 2007; Malinovsky et al., 2007; Mathur et al., 2010b; Greber et al., 2011]. Proposed interpretations of the observed Cu and Mo isotopic changes are complex because an overlap in the isotopic composition of ores and multiple source rocks exists and the isotopic composition of ores within deposits' varies. Therefore, isotope compositions in ores do not clearly fingerprint metal sources [Zhu et al., 2000; Larson et al., 2003; Graham et al., 2004; Maher and Larson, 2007; Li et al., 2010; Mathur et al., 2010a]. However, systematic studies of all deposit types and their isotopic relationships are clearly needed to address the ability of transition metals to indicate specific metal sources. The well-studied Dahutang W-Cu-Mo ore field is an ideal place to analyze the high- temperature variation of Cu and Mo isotopes because the size (Figure 1) of the mineral occurrence and the availability of clearly cogenetic chalcopyrite and molybdenite. The system spans several kilometers and possesses two distinct mineralization types [vein and breccia) to compare. Thus, the combined transition metal isotope approach allows for comparison/contrast of isotope values (and processes that lead to variations) of two distinct mineralization events over a significant geographic area. Figure 1Open in figure viewerPowerPoint (a) Large scale geologic and location map of the Jiuling pluton in southern China map (after Wang et al. [2013]). (b) Detailed geological map of Dahutang W-Cu-Mo ore field, with the Shiweidong, Dalingshang and Shimensi drill core locations. (c) Cross section with sample location and isotope values measured at each spot on the cross section, in order to project all data, drill core were aligned to the line of cross section. To isolate specific causes for Cu and Mo isotope variations in the sulfide minerals, fluid inclusion data and δ18Oquartz and δDfluid inclusion isotope values from cogenetic quartz are presented. The fluid inclusion data permit comparison to see the influence of temperature changes in the fluids and the δD and δ18O isotope data allow for identifying mixing of fluids (and potentially different metal sources if relationships exist with the Cu and Mo isotopes). With this approach, we hypothesize that the vapor-liquid transitions during the evolution of the hydrothermal system at Dahutang caused fractionation of copper and molybdenum isotopes in sulfide minerals. 2 Geology Background and Samples Description The Dahutang W-Cu-Mo ore field is located in the northwestern Jiangxi province, southeast China. The ore field is hosted in the middle part of the Jiangnan Orogen, situated along the southeastern margin of the Yangtze Craton (Figure 1). The oldest rocks in the deposit are gray-green to dark gray phyllite and slate of the Neoproterozoic Shuangqiaoshan Group, intercalated with meta-sandstone characterized by rhythmic turbiditic (flysch) banding. These rocks were intruded by the Jiuling Neoproterozoic biotite granodiorite [Li et al., 2003; Wang et al., 2013]. All of these units were subsequently intruded by Cretaceous granite plutons, which are genetically related to at least some stages of mineralization at Dahutang [Huang and Jiang, 2012, 2013, 2014; Mao et al., 2015]. The granites consist of porphyritic biotite granite, biotite granite and muscovite granite, and granite porphyry dykes. The Dahutang ore field consists of four deposits, the Shiweidong deposit, the Dalingshang deposit, the Shimensi deposit and the Xianguoshan deposit (Figures 1b and 1c). All the deposits have a similar paragenesis and contain veinlet-disseminated, wolframite-sheelite quartz vein and hydrothermal breccia-hosted ore styles. Chalcopyrite (CuFeS2) usually occurs as anhedral granular aggregations, from 2 to 4 mm, in the quartz veins and veinlet stockwork in the greisenized biotite granitoids. Chalcopyrite is intergrown with bornite and molybdenite (MoS2) in the quartz veins and bornite, sphalerite and pyrite in the alteration wall-rocks (Figure 2c). Molybdenite is mainly hexagonal, scaly, enhedral-subhedral single crystals with diameters ranging from 1 to 3 mm that are intergrown within chalcopyrite in the quartz veins (Figures 2b, 2d, and 2e). The ores also occur as matrix cement in breccia which cross cut the main quartz veins and veinlets. Figure 2Open in figure viewerPowerPoint (a) Wolframite crystals replaced by chalcopyrite, molybdenite and scheelite aggregations in the quartz vein, DH-96; (b) quartz veined ore with tabular wolframite and cogenetic chalcopyrite and molybdenite, DH-12; (c) fine-grained anhedral chalcopyrite, molybdenite and bornite in veinlet-disseminated veins, DH-101; (d) Blocky chalcopyrite and molybdenite aggregations in the quartz vein DH-164; (e) Quartz veined ore with intergrown/cogenetic chalcopyrite and molybdenite, DH-183; (f) the micrographs of congenetic chalcopyrite and molybdenite, DH-96. Mineral abbreviations: Bn = bornite, Ccp = chalcopyrite, Mo = molybdenite, Qtz = quartz, Sch = scheelite, Wol = wolframite. The samples of the present study originate from drill core locations and tunnels from the Shiweidong deposit, the Dalingshang deposit, the Shimensi deposit and the Xianguoshan deposit (Figure 1b and 1c). We investigated fourteen samples (Figure 1c, six from Shiweidong, four from Dalingshang, three from Shimensi and one from Xianguoshan) from veinlet-disseminated and quartz veined ores with chalcopyrite-molybdenite sulfides assemblages. Eight samples were collected from drill core and six samples from tunnels (Figure 1c). Veinlet-disseminated vein samples mainly contain fine-grained anhedral chalcopyrite, molybdenite, scheelite and minor wolframite (Figure 2c). Quartz vein samples comprise of blocky chalcopyrite, molybdenite and thick tabular wolframite crystals replaced by scheelite aggregations (Figures 2a–2e). Figure 2f show the micrographs of congenetic chalcopyrite and molybdenite. Two breccia-hosted ores samples from Shimensi which host cogenetic molybdenite and chalcopyrite were analyzed. 3 Methods All samples were wrapped in paper and crushed. Samples of sulfide were separated from the rubble that clearly had coexisting molybdenite and chalcopyrite (Figure 2). The sulfide phases were further crushed to a mineral powder (<500 micron). Over 0.2 grams of mineral powder for each sample were used for analysis. X-ray diffraction was used to confirm mineralogy of the samples and techniques for diffraction are found [Mathur et al., 2005]. Isotopic variation within the same sample (technique used here) has been documented for transition metal isotope systems in sulfide minerals [Rouxel et al., 2004; Mason et al., 2005; Greber et al., 2011]. To minimize this effect, larger sample quantities (0.2g) were separated and powdered in an attempt to homogenize the measured isotope value. Thus, each sample most likely represents an averaged value. Approximately 0.05g of mineral powder for each sample was dissolved with 4ml of ultrapure aquaregia in 15ml Teflon beakers. The Teflon beakers were sealed with Teflon tape and heated to 120–140°C for 12 h. A small aliquot (0.05ml) of the solution was dried and prepared for ion exchange chromatography for the molybdenite samples. We used the chromatographic separation outlined by Pietruszka et al. [2006]. No chromatography was employed for the chalcopyrite samples as multiple studies demonstrated the robustness of this approach [Zhu et al., 2000; Larson et al., 2003; Mathur et al., 2005; Maher et al., 2011]. Cu and Mo isotope ratios were measured on an Isoprobe multicollector ICP-MS at the University of Arizona. Solutions were diluted in ultrapure 2% nitric acid for analysis at 200 ppb Cu and 150 ppb Mo. Intensities of the samples were kept to within 10% of the standard intensities of the samples for Mo and 30% for Cu. It has been demonstrated in Mathur et al. [2009] that the variation of the Cu standard with regards to the sample can vary >50% and still yield the same isotope ratio. As reported in Pietruszka et al. [2006], matching the intensities of the standards and samples is mandatory for consistent results for Mo. Data are presented in the traditional per mil unit and mass bias was controlled by sample-standard bracketing described in Mathur et al. [2010a] for Mo and Mathur et al. [2009] for Cu. In house standards for Mo (sample TTMo8 in Mathur et al. [2010a]) and Cu (1838 USA cent in Mathur et al. [2009]) were interleaved throughout the analytical sessions and overlapped previously reported values with δ97Mo= 0.12‰ ±0.08 (2σ, n=3) and δ65Cu= 0.02‰ ±0.12 (2σ, n=5) (Table 1). Table 1. A Comparison of the Cu and Mo Isotope Compositions of Various Materials Measured on Different Instruments to Show Laboratory Cross Calibrationa Sample PSU n 2σ UA n 2σ WSU n 2σ ASU n 2σ 1838 penny 0.00 6 0.05 −0.05 14 0.09 0.03 3 0.06 n.a. Morenci cpy 0.46 2 0.10 0.55 4 0.12 0.52 2 0.10 n.a. TtMo-8 n.a. 0.12 3 0.08 0.15 4 0.05 0.15 2 0.1 a The 1838 penny and Morenci cpy are copper samples and TtMo-8 is a molybdenite sample (presented in Mathur et al. [2010a]). Initials are PSU= Pennsylvania State University, UA= University of Arizona, WSU= Washington State University, ASU= Arizona State University. At the time of measurement, no international Mo standard was available; this is why the samples were measured in three different labs (University of Arizona, Arizona State University and Washington State University) with slightly different in house and analytical standards. The variations of the Mo isotope standards were analyzed by [Wen et al., 2010] in which the NIST isotope standard 3134 fell within ±0.2‰ of 5 different ICP-MS concentration standards used in previous Mo isotope studies. Thus, the standard reference point for the data presented in most papers is most likely identical. We obtained NIST 3134 (in 2014) and found that the ICP-MS standard used in this paper and [Mathur et al., 2010a; Shafiei et al., 2015] is δ97Mo= −0.28‰± 0.07 (2σd, n=9) in comparison to the NIST 3134. In 2015, we obtained Roch-Mo2 (in 2015) and found that it is δ97Mo= −0.21‰ ± 0.08 (2σd, n=4) in comparison to the NIST 3134. All of these values fall within the reported ranges presented in Goldberg et al. [2013]. The variation demonstrates that the ICP-MS standard used here is isotopically identical to the Roch-Mo2 standard at Arizona State University because TT Mo8 yielded the same value in both labs. With regards to copper, we have several in house standards composed of different sample matrix for comparison. A sample of chalcopyrite was analyzed at three different locations (Pennsylvania State University, Washington State University, University of Arizona). Table 1 contains a summary of the in house standards measured for both Mo and Cu on different mass spectrometers. Errors for the isotope ratios are reported as the variation of the standard deviation over the analytical session with the Mo standard deviation varying 0.09‰ (2σ, n=32) and Cu standard deviation varying 0.12 ‰ (2σ, n=154). Each sample was analyzed in duplicate on different days throughout the analytical session and the reported value is an average value of the two measurements. The error between the measurements was less than the reported variation of the standard during the analytical session. Fluid inclusion temperatures were measured on two samples that encompass the range of isotope fractionation recorded. Microthermometry was conducted on a Linkam THMS 600 heating-freezing stage in the Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences and the description of the methods is in Han et al. [2014]. To ensure that the quartz analyzed is cogenetic with the sulfides, cathodoluminescence (CL) of the mineralized veins was observed on a scanning electron microscope at Juniata College. As seen in Figures 3a and 3b, only areas without cross-cutting/stockwork like textures in the quartz + cogenetic sulfide were chosen for fluid inclusion analysis (Figures 3c–3f). This strategy confirms petrographic evidence that the fluids in the quartz inclusions were similar to the fluids precipitating the sulfide mineralization. Figure 3Open in figure viewerPowerPoint (a) Cathodoluminescence of the mineralized veins from sample DH-96 with yellow areas highlighting locations of fluid inclusions measured; (b) Cathodoluminescence of the mineralized veins from sample DH-101 with yellow areas highlighting locations of fluid inclusions measured. Note the stockwork quartz veins illuminated in the images and the measured fluid inclusions near sulfide boundaries and not near stockwork; (c) Photomicrographs showing quartz intergrown with cogenetic chalcopyrite and molybdenite, Reflected light (200×), DH-96; (d) Photomicrographs of fluid inclusions in the quartz within Figure 3c (200×), DH-96; (e) Photomicrographs showing quartz intergrown with chalcopyrite, Reflected light (200×); (f) Fluid inclusions photomicrographs in the quartz within Figure 3e (200×), DH-101. The hydrogen and oxygen isotopes were analyzed in the Stable Isotope Laboratory of Mineral Resources Institute, Chinese Academy of Geological Sciences, using the Finnigan MAT253 mass spectrometer. Seven quartz samples from chalcopyrite and molybdenite veins were analyzed. Oxygen was liberated from quartz by a reaction with BrF5 [Clayton and Mayeda, 1963] and converted to CO2 on a platinum-coated carbon rod for oxygen isotope analysis. The water of the fluid inclusions in quartz was released by heating the samples to above 500°C by means of an induction furnace, and then reacted with zinc powder at 410°C to generate hydrogen [Friedman, 1953] for isotope analysis. The results are reported in per mil relative to V-SMOW standards, with analytical uncertainty (2σ) of ±2‰ for δD and ±0.2‰ for δ18O. The δ18Owater values of ore-forming fluids from quartz were calculated using the equation 1000lnαquartz–H2O = 3.38 × 106 T−2−3.40 [Clayton et al., 1972] solved at 350°C as indicated by the fluid inclusion data. 4 Results The transition metal isotope values range from −0.03‰ to +1.06‰ for δ97Mo and −0.31‰ to +1.48‰ for δ65Cu (Table 2). δ97Mo and δ65Cu span a range within previously reported values for skarn, porphyry copper, and polymetallic vein systems by Hannah et al. [2007], Maher and Larson [2007], Mathur et al. [2009], Mathur et al. [2010a], Greber et al. [2011], and Greber et al. [2014]. There is no significant correlation between elevation and the Cu and Mo isotope ratios. On the average the breccia samples have lower δ65Cu and δ97Mo isotope (average δ65Cu= −0.40‰; average δ97Mo=0.29‰) in comparison to the vein samples (average δ65Cu= 0.54‰; average δ97Mo=0.49‰). Table 2. Cu and Mo Isotopic Compositions of Chalcopyrite and Molybdenite From Dahutanga Sample Elevation (m) Mineral Assemblage δ65Cu δ97Mo δ18Owater‰ δDwater‰ DH-12 1170 cpy, mo and wf in quartz veins 0.47 0.27 7.39 −79 DH-19 1147 cpy and mo in quartz veins 0.47 0.22 DH-20 1147 massive cpy, mo and wf in quartz veins −0.3 0.78 7.79 −78 DH-49 1097 cpy and mo in quartz veins −0.1 0.96 7.59 −80 DH-96 1141 cpy, wf and massive mo in quartz veins −0.3 1.06 7.69 −78 DH-101 1514 disseminated, massive cpy and mo in quartz veins 1.21 −0 7.79 DH-110 1406 disseminated, massive cpy and mo in quartz veins 0.73 0.47 DH-115 1232 disseminated, massive cpy and mo in quartz veins 0.59 0.25 DH-117 1056 disseminated, massive cpy and mo in quartz veins 0.48 0.24 DH-164 1458 massive cpy and mo in quartz veins 0.56 0.73 DH-183 1301 massive cpy and mo in quartz veins 0.93 0.41 DH-324 518 massive cpy and mo in quartz veins 1.48 −0.01 DH-207 <969 massive cpy and mo in quartz veins 0.81 0.28 7.19 −68 DH-209 <969 massive cpy and mo in quartz veins 0.29 0.74 6.59 −74 DH-251 <933 massive cpy and mo in breccia ores −0.7 0.53 DH-252 <933 massive cpy and mo in breccia ores −0.1 0.05 a Reported mass of samples are cpy=chalcopyrite, mo= molybdenite and wf=wolframite. The δ18Owater values of ore-forming fluids from quartz were calculated using the equation 1000lnαquartz–H2O = 3.38 × 106 T−2−3.40 [Clayton et al., 1972] solved at 350 degrees as indicated by the fluid inclusion data. Analytical uncertainty (1σ) of ±1‰ for δD and ±0.1‰ for δ18O. Figure 4 shows of the Mo and Cu isotope composition for the coexisting sulfide mineral phases in the veins. A simple linear relationship exists (r2>0.7) with a negative slope for the two isotopes. The two breccia samples lie below and parallel this trend. Figure 4Open in figure viewerPowerPoint A plot of the Mo versus Cu isotope composition for the coexisting sulfide mineral phases in the veins (circles) and breccia (triangles). The trend line could be interpreted as a simple binary mixing trend with equal starting and proportioning concentrations of each element. Through petrographic observation on the mineralized veins, several types of fluid inclusions were recognized. In the contribution, we only focus on the fluid inclusions in the quartz which cogenetic with chalcopyrite and molybdenite (Figures 3c–3f). The primary fluid inclusions in the quartz are mainly two-phase aqueous fluid inclusion and minor three-phase fluid inclusions containing a solid crystal (Figure 3f). Fluid inclusion results for the two samples were as follows (Figures 3c and 3d), DH-96 had one area with 50 inclusions that ranged from 344 to 350°C and DH-101 had one area with 2 inclusions that ranged from 340 to 344°C. Both samples possessed many small inclusions that did not have observable bubbles for analysis. Since the two samples display the greatest range of Cu and Mo isotope fractionation and no significant difference in fluid inclusion temperature, no relationship exists between the fluid inclusion temperature and Cu and Mo isotope compositions. Figure 5 plots the fluid δ18Owater and δDwater values versus δ65Cu and δ97Mo values. The δ18O values measured and calculated for water all cluster in the magmatic δ18O isotope values defined by Taylor [1968, 1997] and Sheppard et al. [1971] and show complicated relationships with δ65Cu and δ97Mo values (Figures 5a and 5b). The δ18Owater values have a strong negative correlation (r2=0.70) with δ65Cu from chalcopyrite for 5 of the samples that have a range of δ18Owater from +7.1‰ to +7.69‰. Two samples with δ18Owater at 7.79‰ and 6.59‰ do not fit this trend (Figure 5b). The δD values display a greater range of values and also do not have obvious trends with the δ65Cu and δ97Mo values. No strong correlation exists (r2<0.3) among these two variables (Figures 5c and 5d). Figure 5Open in figure viewerPowerPoint Plots δ65Cu and δ97Mo versus δD and δ18Owater. (a) Plot of δ97Mo versus δ18Owater. where no statistically meaningful relationship exists. (b) Plot of δ65Cu versus δ18Owater. displays strong negative correlation for five samples (r2=0.7). (c, d) δ65Cu and δ97Mo versus δD where no statistically meaningful relationship exists. 5 Discussion The trend displayed by the Cu and Mo isotope values indicates that the ore forming process for the veined mineralization event is similar for the four deposits. The trend provides a means to relate the mineralization event over a large area (∼5 km) and confirms the synchronous relationship of mineralization as seen with the Re-Os results [Feng et al., 2012; Mao et al., 2013; Xiang et al., 2013]. In contrast, the breccia samples do not lie on the trend, and most likely indicate a different metal source since none of the breccia samples have isotope ratios near the veined samples trend. Field relationships show that the breccias cross-cut veined mineralization and clearly are associated with a younger event. The transition metal isotope data provided here augment the field relationships and suggest a completely different source and mineralization history for the breccias. Two possible geochemical models could explain the negative relationship between Cu and Mo isotope composition of the veined samples (Figure 4). First, equilibrium fractionation associated with changes of temperatures or other physicochemical properties of the mineralizing fluid could cause the systematic changes in the isotope compositions of the precipitated metals in sulfides. This type of fractionation is discussed and modeled with simple open system Rayleigh distillation models. The second model that could lead to this trend is geochemical mixing of juvenile waters derived from the magma and fluids from surrounding host rocks. In order to decipher which one of the hypotheses is more likely; fluid inclusion and δ18O and δD isotope data from coexisting quartz are provided and discussed. 5.1 Rayleigh Distillation Model Used to Explain Cu and Mo Isotope Trend Multiple studies have shown the Cu isotope composition of chalcopyrites and Mo isotope composition of molybdenites vary significantly throughout a mineral deposit that formed at high temperatures [Asael et al., 2007; Hannah et al., 2007; Maher and Larson, 2007; Li et al., 2009, 2010; Mirnejad et al., 2010; Mathur et al., 2010a, 2010b; Greber et al., 2011; Mathur et al., 2013; Greber et al., 2014]. The trend seen between the Cu and Mo isotope compositions of the paired coexisting minerals (Figure 4) further demonstrates that the both isotopes fractionate at high temperature. The trend also suggests a similar process acted during mineralization of the veins over the approximate 3 kilometer span of the hydrothermal system. The process that led to the relationship is not easily determined with the transition metal isotope data alone. To date, two general approaches were employed to explain the transition metal isotope values of chalcopyrite and molybdenite. The first approach involves theoretical calculations which model bond energies and vibrational frequencies of the elements at high-temperature present in different metal complexes [Bigeleisen and Mayer, 1947; Urey, 1947; Tossell, 2005; Seo et al., 2007] to predict potential fractionation factors of metals. The second involves experimental work that mimics natural systems analyzed as seen in [Maher et al., 2011; Pękala et al., 2011] for Cu isotopes and [Fujii et al., 2006; Schauble, 2008] for Mo isotopes. In each of the approaches, defining exact processes that lead to changes in the isotope composition of the fluid and precipitating mineral vary. Several studies on copper [Seo et al. 2007, Fujii et al., 2013, 2014; Sherman, 2013] demonstrated with theoretical data that the temperature variations, combined with Cu complexing with different ligands, could