Copper–zinc albite porphyry in the Hersai porphyry copper deposit, East Junggar, China: A transition between late magmatic and hydrothermal porphyry copper deposit

Ore Geology Reviews 61 (2014) 141–156

Contents lists available at ScienceDirect

Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev

Copper–zinc albite porphyry in the Hersai porphyry copper deposit, East Junggar, China: A transition between late magmatic and hydrothermal porphyry copper deposit Xing-Wang Xu a,b,⁎, Qian Mao a, Xian-Hua Li a, Franco M. Pirajno c, Xun Qu d, Gang Deng d, Dai-Zhao Chen a, Bao-Lin Zhang a, Lian-Hui Dong a,d a

Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Xinjiang Research Center for Mineral Resources, Chinese Academy of Sciences, Urumqi 830011, China c The University of Western Australia, Western Australia 6009, Australia d Xinjiang Bureau of Geology and Mineral Resources, Xinjiang, Urumqi 830000, China b

a r t i c l e

i n f o

Article history: Received 28 March 2013 Received in revised form 25 January 2014 Accepted 28 January 2014 Available online 14 February 2014 Keywords: Copper–zinc albite porphyry Sulfide-rich fluids High temperature Disseminated and intergranular Porphyry copper deposit

a b s t r a c t A 418 Ma albite porphyry dike emplaced in a 429 Ma granite pluton in the Hersai porphyry copper deposit (Nom, East Junggar, China) consists of euhedral and pale-orange luminescing albite phenocrysts and groundmass, zircons, blue-violet luminescing apatites and chalcopyrite–sphalerite-rich miarolitic cavities. This dike is characterized by two-domain textures presented by albites and disseminated intergranular miarolitic cavities, and by geochemical features of continental island arc and adakitic intrusions. The miarolitic cavities consist of various minerals that crystallized in the following sequence: epidote, rutile and sphalerite–chalcopyrite solid solution, titanite and K-feldspar; chalcopyrite with pyrite inclusions; and chlorite, zoisite and calcite. The miarolitic cavities exhibit magmatic to hydrothermal internal textures, such as aplitic textures presented by intergrowths of albite, epidote, rutile and sphalerite–chalcopyrite solid solution, zoning and intersertal texture, poikilitic textures, and layered chlorites. The sphalerite contains a high concentration of exsolved chalcopyrite (up to 10 vol.%). The rutiles intergrown with epidotes contain 137 to 528 ppm Zr corresponding to Zr-in-rutile temperatures of 507 to 625 °C, and the rutiles intergrown with sphalerite–chalcopyrite solid solutions have 381 to 420 ppm Zr and Zr-in-rutile temperatures of 585 to 605 °C. Mineralization temperatures of sphalerite–chalcopyrite solid solutions are possible approximately 600 °C. The formation of the chalcopyrite–sphalerite-rich miarolitic cavities is related to interstitial residual sulfide-rich fluids. The copper–zinc albite porphyry may represent a copper–zinc (Cu–Zn) subtype of porphyry copper deposit that formed as a transition between late magmatic and classical hydrothermal porphyry copper deposits. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Porphyry copper deposits supply nearly three-quarters of the world's copper (Sillitoe, 2010). These deposits are characterized by disseminated and vein-, stockwork- and breccia-hosted mineralization associated with porphyritic intrusions (e.g., Berger et al., 2008; Cooke et al., 2005; Cox, 1986; Lowell and Guilbert, 1970; McMillan and Panteleyev, 1980; Rowins, 2000; Seedorff et al., 2005; Singer, 1995) and are typically formed by precipitation of hydrothermal minerals from aqueous solutions at temperatures lower than 500 °C (e.g., Edwards and Atkinson, 1986; ⁎ Corresponding author at: Institute of Geology and Geophysics, Chinese Academy of Sciences, No. 19, Beitucheng Western Road, Chaoyang District, 100029, Beijing, China. Tel.: +86 10 82998198(desk); fax: +86 10 62010846. E-mail address: [email protected] (X.-W. Xu).

http://dx.doi.org/10.1016/j.oregeorev.2014.01.009 0169-1368/© 2014 Elsevier B.V. All rights reserved.

Halter et al., 2002; Hedenquist and Lowenstern, 1994; Kojima and Sugaki, 1985; Rowins, 2000; Seedorff et al., 2005). For a long time, studies have indicated that porphyry ore fluids are magmatic and exsolved from porphyry magmas intruded into the upper crust (e.g., Audétat et al., 2000; Core et al., 2006; Halter et al., 2002; Harris and Golding, 2002; Harris et al., 2003; Hedenquist and Lowenstern, 1994; Hedenquist et al., 1998; Holliday et al., 2002; Lowenstern and Sinclair, 1996; Redmond et al., 2004). The coexistence of silicate-melt and hypersaline liquid-rich inclusions in quartz phenocrysts in some mineralized porphyries (e.g., Harris et al., 2003; Kamenetsky et al., 1999; Lowenstern et al., 1991), and the occurrence of silicate-melt inclusions in quartz veins at Bajo de la Alumbrera (Harris et al., 2003) and vein dikes in many porphyry ore deposits (e.g., Carten et al., 1988; Harris et al., 2004; Heithersay and Walshe, 1995) indicate that certain porphyry ore fluids are transitional from silicate melts to fluids. Most recently, sulfide melts have been proposed

142

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Fig. 1. Regional tectonic setting (a) and geological map (b) of the Nom area, east Junggar (modified after Qu et al., 2009). The rectangle in figures a and b shows the locations of figure b and Fig. 2, respectively. Main mineral deposits in the Nom area: 1 — Hersai porphyry copper–zinc deposit, 2 — Tonghualin porphyry copper deposit (PCD), 3 — Beishan gold deposit, 4 — Nom pyrite deposit, 5 — Baoshan iron deposit, 6 — Livshigou PCD, 7 — Sangnan PCD, 8 — Qiongheba PCD, 9 — Mengxi PCD.

as a key factor in the genesis of some large porphyry copper deposits (e.g., Halter et al., 2002; Keith et al., 1997; Larocque et al., 2000) and mineralization related to sulfide-rich hydrous magmas has been observed in vein-dikes in the Henderson porphyry molybdenum deposit (Carten et al., 1988). However, physical evidence of mineralization of the sulfide melt for porphyry copper deposits is scarce and their genesis is poorly understood. Moreover, molybdenum and gold are usually essential to the economics of porphyry copper deposits (Cooke et al., 2005; Singer et al., 2005), and the relative abundance of copper, molybdenum and gold is used to classify of porphyry copper deposits (Kesler, 1973; Kirkham and Sinclair, 1995; Sillitoe, 1979). Zinc sulfide is not only present in skarn mantos and peripheral veins in certain porphyry copper systems (e.g., Holliday et al., 2002; Jambor and Owens, 1987; Peters et al., 1966; Rusk et al., 2008; Sillitoe, 2010; Sinclair, 2007), but is also present in the late veins as an economic or potential byproduct of some porphyry copper deposits, such as the E veins at Rosario (Masterman et al., 2005), the D veins at El Salvador (Gustafson and Hunt, 1975) and the late stage veins at Chuquicamata (Ossandón et al., 2001). In this study, we report new evidence that a copper–zinc albite porphyry dike bearing disseminated and interstitial chalcopyrite– sphalerite-rich miarolitic cavities in the Hersai porphyry copper deposit (Nom, East Junggar) has distinct magmatic to hydrothermal internal textures, and the disseminated copper–zinc sulfides formed at high temperature over 500 °C. The occurrence of the copper–zinc albite porphyry dike in the Hersai porphyry copper deposit suggests a potential copper–zinc (Cu–Zn) subtype of porphyry copper deposit as a transitional type of mineralization between late magmatic and hydrothermal porphyry copper deposits.

2. Regional geological setting and deposit geology The Hersai porphyry copper deposit is situated near Nom, a border town adjacent to southwestern Mongolia in East Junggar, China. It belongs to the eastern segment of the Paleozoic Yemaquan arc between the Kelameili ophiolite and Armantai ophiolite (Fig. 1a; Dong et al., 2009; Xiao et al., 2009). The Yemaquan magmatic arc is an earlyPaleozoic Andean-type continental arc that was developed into a continental island arc after the intra-arc rifting that began at 432 Ma (Xu et al., 2013), similar to the Japanese and New Zealand volcanic arcs that contain continental crust basement and are located away of a continent (Bailey, 1981). Intrusive bodies in the Nom area are calc-alkaline and exhibit the geochemical signatures of arc rocks (Du et al., 2010; Qu et al., 2009). The rock types include quartz-diorite, granodiorite and granite stocks, and porphyry dikes (Fig. 1b). These intrusions were emplaced between 429 Ma and 405 Ma and are related to the southward subduction of the Palaeo-Asian oceanic plate (Dong et al., 2009; Du et al., 2010; Qu et al., 2009; Xu et al., 2013; Zhang et al., 2010). In the last five years, many porphyry deposits have been discovered in the Nom area, such as those in Hersai, Tonghualin, Mengxi, Livshigou, Sangnan and Qiongheba (Fig. 1b; e.g., Cheng et al., 2010; Guo et al., 2009; Liang et al., 2010). The potential for further discoveries in the Nom area is considered to be high (e.g., Feng et al., 2010; Wang et al., 2006, 2009). The Hersai porphyry copper deposit is hosted by the cupola of a granodiorite stock that includes some granite plutons and albite porphyry dikes and is cut by granodiorite porphyries and dioritic porphyrite dikes (Fig. 2). Granite, granodiorite and granodiorite porphyry yield U–Pb zircon concordia ages of 429.4 ± 6.4 Ma (N1 = 12), 1

age.

The N refers to both the number of ages and number of zircons used to generate the

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

143

Fig. 2. Geological map of the Hersai porphyry copper deposit.

411.1 ± 4.8 Ma (N1 = 12) and 410.5 ± 4.5 Ma (N1 = 13), respectively (Du et al., 2010). The exposed mineralization and alteration are related to granodiorite porphyries. Specifically, zoned alteration is present around the NS-striking granodiorite porphyry and is arranged outward from a potassic core through a phyllic zone to a propylitic zone (Fig. 2). The 400–500-m-wide potassic zone is found in the core of the deposit and contains K-feldspar, magnetite and specularite; some quartz veins are present in the phyllic zone and some calcite veins occur in the outer propylitic zone. Cu mineralization occurs in the potassic and phyllic zones and five ore bodies have been discovered (Cheng et al., 2010). Sulfide minerals occur in disseminated veinlets, altered hornblendes and miarolitic cavities (Fig. 3). Chalcopyrite–pyrite veinlets (Fig. 3a) and sericite–quartz–chalcopyrite veins (Fig. 3e) are present in the sericitized granodiorites, whereas the K-altered granodiorites have some chalcopyrite veins (Fig. 3b). Mineralization of the granodioritic porphyries is characterized by occurrences of chalcopyrite–pyrite– quartz–K-feldspar veins (Fig. 3c), disseminated chalcopyrite in sericitized and chloritized hornblendes (Fig. 3d) and miarolitic cavities (Fig. 3f). These miarolitic cavities commonly consist of quartz at the margin, chalcopyrite in the middle and sericite at the center (Fig. 3f). A proven resource of Cu ore of the Hersai porphyry copper deposit is approximately 25 Mt with a grade of 0.2–0.8% Cu (Cheng et al., 2010). In addition, the Re–Os isochron ages of molybdenites from quartz-sulfide veinlets are approximately 409 ± 12 Ma, making them broadly coeval with the granodiorite porphyry (Du et al., 2010). 3. Location and macroscopic texture of the copper–zinc albite porphyry dike The copper–zinc albite porphyry was discovered in granite by drill hole zk107-1 in the northern area of the Hersai copper deposit at depths

of 82–92.6 m and 112.8–115.4 m (Fig. 4). These two porphyry segments may represent of two branches of a single dike or two separate dikes. The albite porphyry dike is characterized by porphyritic texture and two-domain texture which comprises an albite domain and a miarolitic cavity domain that is disseminated and intergranular (Fig. 5), and has a sharp contact with the granite. Later calcite veins and fractures are occasionally found in the albite porphyry dike and the adjacent granite.

4. Analytical techniques Some representative fresh rock samples from the copper–zinc albite porphyry were investigated by a combination of optical microscope, electron microprobe, secondary ion mass spectrometry (SIMS), Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA–ICP-MS) and geochemical analysis. All analyses were conducted at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). Internal textures and structures of the copper–zinc albite porphyry were analyzed by optical cathodoluminescence (optical-CL) microscopy and backscattered electron (BSE) images produced by an electron microprobe. The optical-CL microscope consists of a LV100 POL with a DS camera DS-Ri1 (Nikon, Japan) and a Reliotron III stage (Relion, USA). The Reliotron III stage has a cold cathode electron gun that bombards the surface of well-polished thin sections with an electron beam in a moderately-high vacuum. Beam voltage and beam current during analysis were 4–8 kV and 0.3–0.5 mA, respectively. The compositions of minerals including phenocryst and groundmass albite, epidote, titanite and chlorite from the three thin sections were analyzed using a CAMECA SX51 electron microprobe at IGGCAS. The accelerating voltage was 21 kV and the sample current was 10 nA. Beam diameters were 5 μm for albite and titanite and 10 μm for epidote and

144

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Fig. 3. Outcrop (a) and hand samples (b and c), photographs and photomicrographs (d, e and f) showing occurrence of ore veinlets and sulfide minerals. (a) Chalcopyrite–pyrite veinlets (CPV) in sericitized granodiorite; (b) veinlet-like chalcopyrite in K-altered granodiorite; (c) sulfide (chalcopyrite + pyrite)–quartz–K-feldspar vein (SQFV) in granodioritic porphyry with disseminated sulfide in altered hornblende (DSAH); (d) disseminated chalcopyrite in sericitized and chloritized hornblende in granodioritic porphyry; (e) sericite–quartz–chalcopyrite vein in granodiorite; (f) miarolitic cavity consisting of quartz at margin, chalcopyrite in middle and sericite at center. Chl: chlorite, CP: chalcopyrite, Q: quartz, Ser: sericite.

chlorite. The counting times were 10 s for all elements. Well defined natural minerals were used as standards. Rutile crystals in thin sections were analyzed in situ using the same CAMECA SX51 electron microprobe at IGGCAS. Acceleration voltage was set at 21 kv, probe current at 100 nA and beam diameter at 3 μm. The counting time for Zr was 100 s with calc. DL of approximately 40 ppm. The matrix correction methods were PRZ (phi-rho-z). A synthetic rutile was analyzed to inspect the zero-Zr and exclude any machine drift before and after the analyses of the sample rutile. The analytical uncertainty for Zr is better than 10%. Homogeneous and unaltered rock samples, including granodiorite porphyry, albite porphyry and granite from drill hole zk107-1 in the Hersai porphyry copper deposit were selected for elemental chemical analyses. Samples were crushed in a tungsten carbide swing mill, sieved, ultrasonically, cleaned several times in deionized water and then ground in an agate mortar. Rock powders (~ 1.2 g) were then

dissolved with Li2B4O7 (6 g) in a TR-1000 S automatic bead fusion furnace at 1100 °C for 10 min. Major element abundances (wt.%) were determined in whole-rock powder pellets by X-ray fluorescence (XRF) using an XRF-1500 sequential spectrometer at the IGGCAS. Analytical uncertainties were 1 to 3% for major elements. Loss on ignition (LOI) was obtained by weighing before and after 1 h of heating at 1100 °C. Zircon grains used in SIMS U–Pb dating and LA–ICPMS traceelement analyses were hand-picked from 150 zircon grains under a binocular microscope from more than 1000 zircon grains, which were separated by conventional heavy liquid and magnetic techniques and mounted in an epoxy resin disc in an array. Zircon SIMS U–Pb dating was conducted on a Cameca IMS 1280 large-radius SIMS with a 30-μm spot, and trace-element analyses were performed on a LA–ICPMS with a 50-μm spot. Detailed descriptions of the instrumentation, analytical methods and calibration procedures have been provided by Li et al. (2009).

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

145

Sr (362–593 ppm), Sr/Y (48.2–68.9), Ba/Nb (32.0–53.3), (La/Yb)N (7.11–12.45), Th/Yb (1.32–2.18) and Ta/Yb (0.30–0.50), and low Rb (16.5–25.77 ppm), Nb (4.17–4.88 ppm), Y (7.5–9.7 ppm), Ta (0.26– 0.38 ppm), Yb (0.73–0.97 ppm) and Ce/Pb (1.07–1.54), enrichment of light rare earth elements (LREE), Ba, K, Pb and Sr, and depletion in Th, Nb, P and Ti (Table 1). 5.2. Composition, microscopic textures and structures of the copper–zinc albite porphyry

Fig. 4. A geological profile A–B (location shown in Fig. 2). The triangle and corresponding label show the location and number of the samples for zircon separation, SIMS U–Pb dating and LA–ICPMS trace element analysis.

5. Analytical results 5.1. Whole rock geochemistry Five copper–zinc albite porphyry samples have similar major and trace element contents: SiO2 (60–63 wt.%), Al2O3 (19.2–19.8 wt.%), Na2O (7.3–7.8 wt.%), K2O (0.9–1.3 wt.%) and CaO (2.1–2.6 wt.%), high

The copper–zinc albite porphyry consists of 1-mm to 1-cm euhedral albite phenocrysts set in a 50- to 300-μm groundmass of euhedral–anhedral albite, apatite, zircon and miarolitic cavities (Fig. 6a). Most albite phenocrysts have typical parallel lamellar twinning and the albite groundmass has interlocking curved grain boundaries. Some albite crystals are altered and replaced by epidote, chlorite, calcite and apatite. The slightly altered albites show sienna luminescence, whereas the unaltered albite crystals are pale orange, and intensively altered albites are gray in the optical-CL images (Fig. 6b). The intensively altered albites are present near an interstitial miarolitic cavity. However, both the unaltered and altered albites have the same color and composition in the BSE images and the twodomain texture comprising an albite domain and a miarolitic cavity domain that is disseminated and intergranular is well preserved (Fig. 6c). The euhedral blue-violet luminescing apatite groundmass is intergrown with albite, and some yellow-green luminescing apatite occurs along intragranular fractures and at the rims of the large blue-violet luminescing apatite crystals (Fig. 6d). The miarolitic cavities comprise 8% of the volume of the copper–zinc albite porphyry cores. Minerals present in the miarolitic cavities include anhydrous (approximately 2 vol.% zircon, 4 vol.% albite, 3 vol.% apatite, 3 vol.% rutile, 2 vol.% titanite, 2 vol.% calcite, and 1 vol.% K-feldspar, quartz and perovskite), hydrous (approximately 28 vol.% epidote, 12 vol.% chlorite and 2 vol.% zoisite), and sulfide (approximately

Fig. 5. Photographs of a specimen of copper–zinc albite porphyry (a) and four scanning images of cubic sections (b, c, d and e). Images b, c, d and e represent a top, a bottom and two side sections, respectively. CV: calcite vein, MC: miarolitic cavity.

146

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Table 1 The concentrations of major and rare elements in the copper–zinc albite porphyry (CZAP), granite, granodiorite (GD) and granodioritic porphyry (GP) in the Hersai copper deposit. Sample

HES2-1

ZK107-1-10

ZK107-1-3

ZK107-1-4

ZK107-1-5

ZK107-1-6

ZK107-1-7

ZK107-1-9

Rock type

GD

GP

CZAP

CZAP

CZAP

CZAP

CZAP

Granite

Location

Ground surface

422 m

85 m

88 m

90 m

113 m

115 m

180 m

66.98 0.3 16.01 3.28 0.09 1.25 3.02 4.43 1.91 0.14 2.76 100.17 18.04 0.98 5.38 56.00 190.80 7.15 4.00 30.10 52.20 16.44 37.13 693.00 8.13 100.70 4.46 2.79 597.00 12.88 24.53 3.04 11.56 2.16 0.66 1.71 0.24 1.41 0.27 0.75 0.12 0.77 0.13 2.94 0.31 0.14 5.91 0.12 1.61 1.15 85.2 4.15 133.9 2.89 2.09 0.40 1.35 11.28 60.23

62.79 0.24 19.48 4.57 0.24 0.88 2.11 7.26 1.06 0.19 1.46 100.28 5.93 0.971 3.27 25.25 52.6 5.196 6.679 100.5 706.00 17.93 17.99 667.3 9.69 78.10 4.31 1.40 138.1 10.268 20.535 2.620 10.679 2.272 0.704 1.591 0.231 1.276 0.234 0.796 0.142 0.974 0.153 2.330 0.292 0.108 14.526 2.046 1.288 1.343 68.897 20.535 1.41 32.0 2.4 1.32 0.30 0.49 7.11

62.13 0.23 19.52 4.47 0.33 0.61 2.58 7.90 1.04 0.18 1.04 100.03 5.8449 0.906 2.338 32.774 42.484 3.189 2.333 806.218 508.027 17.927 16.816 592.833 9.093 73.814 4.883 1.189 247.64 11.31 22.127 2.87 11.45096 2.417 0.738 1.44 0.2338 1.38 0.2432 0.7216 0.118812 0.76 0.13 2.73 0.26 0.1086 14.385 3.041 1.24 1.466 65.197 22.127 1.54 50.7 2.3 1.63 0.34 1.00 10.03

62.14 0.21 19.77 3.17 0.82 0.67 2.56 7.68 0.96 0.10 1.82 99.89 7.63 0.76 2.17 42.90 27.80 2.97 0.01 1104.00 9164.00 15.60 16.50 363.00 7.52 70.90 4.17 1.33 137.00 8.86 18.88 2.13 7.92 1.56 0.52 1.31 0.19 1.13 0.23 0.67 0.11 0.73 0.12 2.06 0.26 0.10 12.68 1.46 1.19 1.10 48.3 1.49 32.9 2.12 1.63 0.36 0.54 8.18 44.36

59.51 0.18 19.23 4.69 0.41 0.91 2.11 7.82 1.28 0.08 3.34 99.55 5.72 0.98 2.48 27.90 64.50 6.62 7.94 50.70 1168.00 17.45 25.77 442.00 8.40 89.80 4.61 1.19 239.00 16.43 30.71 3.64 13.48 2.27 0.73 1.78 0.25 1.38 0.26 0.76 0.12 0.89 0.16 2.66 0.38 0.13 23.71 3.78 1.94 1.37 52.6 1.30 51.8 3.56 2.18 0.43 0.31 12.45 72.86

60.64 0.24 19.64 4.05 0.52 0.71 2.27 7.66 1.10 0.16 1.52 98.50 6.89 1.33 2.20 42.25 59.65 6.93 5.16 140.04 601.61 17.21 21.79 495.67 8.63 74.46 4.69 1.11 249.79 7.92 18.02 2.48 10.30 2.32 0.62 1.62 0.24 1.33 0.25 0.76 0.12 0.74 0.13 2.62 0.37 0.11 16.86 2.03 1.48 1.49 57.416 18.02 1.07 53.3 1.7 2.00 0.50 0.43 7.21

72.21 0.16 14.63 1.91 0.12 0.68 1.45 4.62 2.75 0.08 1.62 100.22 11.06 0.89 3.84 26.80 139.20 3.77 4.68 9.00 55.60 14.69 45.25 332.00 8.16 91.50 5.29 1.62 819.00 9.85 18.88 2.27 8.50 1.64 0.45 1.36 0.20 1.23 0.25 0.74 0.12 0.87 0.15 2.66 0.41 0.20 7.60 0.06 2.06 1.12 40.7 2.48 154.8 1.86 2.37 0.47 0.82 7.63 46.51

SiO2 TiO2 Al2O3 TFe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total Li Be Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Tl Pb Bi Th U Sr/Y Ce/Pb Ba/Nb La/Nb Th/Yb Ta/Yb Sc/Ni (La/Yb)N SumREE

66.42 0.34 16.55 3.68 0.09 1.62 4.35 4.26 1.23 0.14 1.03 99.72 9.14 0.83 6.15 65.00 11.90 6.64 12.39 13.60 45.60 15.49 14.57 622.00 9.43 87.70 3.92 1.73 405.00 8.67 20.13 2.31 8.88 1.86 0.69 1.80 0.27 1.56 0.33 0.95 0.15 0.98 0.16 2.51 0.26 0.08 4.80 0.02 1.23 0.51 66.0 4.19 103.3 2.21 1.26 0.27 0.50 5.96 48.74

Drill hole zk107-1

18 vol.% chalcopyrite, 20 vol.% sphalerite and 3 vol.% pyrite). However, mineral composition varied greatly from one miarolitic cavity to another. Most zircons and the majority of apatites are found in the miarolitic cavities. For details on the nature of miarolitic cavities the reader is referred to Vernon (2004), Harris et al. (2004) and Kirwin (2007). Micro-fractures, including intragranular fractures, shear fractures and ductile shear zones, are well-developed in the copper–zinc albite

porphyry (Fig. 5). Ductile shear zones with a width of 0.2–0.3 mm and a length of 2–5 mm consist of an oblique alignment of albite kink bands and calcite twins and are filled with ore minerals (Fig. 6e). Some tensile intragranular fractures are filled with ore minerals and connected to a miarolitic cavity. Ductile–brittle shear fractures that are generally filled with cryptocrystalline albite cause a 10- to 50-μm dislocation. As a result, some ore minerals are fractured (Fig. 6f). Some later

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

147

Fig. 6. Photomicrographs showing texture and structure of the copper–zinc albite porphyry. (a) porphyritic texture and disseminated distribution of the miarolitic cavities (MC), crossed-nicols; (b) an optical-CL image showing porphyritic texture, alteration of albite and intergranular miarolitic cavity; (c) a BSE image of images a and b showing the two domain texture; (d) an optical-CL image showing intergrowth of blue-violet luminescing apatite, albite and ore minerals; (e) a crossed-nicol image showing a microductile shear zone; (f) equigranular aphanitic between groundmass albite and fine anhedral sphalerite with chalcopyrite dots, and shear fractures filled by albite and cut through sphalerite grains and albite twin bands, crossed-nicols plus episcopic illumination; (g) a crossed-nicol image showing calcite-filling fractures. Ab: albite, Ap: apatite, CP: chalcopyrite, CT: calcite twins, DSZ: ductile shear zone, Epi: epidote, IAA: intensive altered albite, RA: relict albite, SAA: slight altered albite, SAAP: slight altered albite phenocryst, Sc: shear banding, SF: shear fracture, Sp: sphalerite, Ss: schistosity structure.

calcite veinlets are overprinted on the copper–zinc albite porphyry (Fig. 6g). 5.3. Mineral chemistry All the albite crystals, including phenocrysts, groundmass and those from the miarolitic cavities of the copper–zinc albite porphyry, have the same composition with an albite content of more than 97%. However, the albite from the miarolitic cavities is not altered, whereas some albite phenocrysts and groundmass are altered. The epidote and chlorite are rich in iron. The epidotes contain 37.3–38.2 wt.% SiO2, 21.7–23.1 wt.%

CaO, 19.5–22.8 wt.% Al2O3 and 8.5–15.4% wt. FeO, and the chlorites contain 25.2–27 wt.% SiO2, 17–20.6 wt.% Al2O3, 9.1–13.5 wt.% MgO, 21.8– 27.7 wt.% FeO and 3.7–5.7 wt.% MnO. In general, titanite is Al-rich and contains low concentrations of Ca and Ti (31.1–33.1 wt.% TiO2, 30.7– 31.7 wt.% SiO2, 28.1–28.8 wt.% CaO and 4.1–5.5 wt.% Al2O3). Most titanites with platy inclusions of K-feldspar are Al-rich and Ti-poor. Several metasomatic titanites associated with rutile contain 1.2–1.7 wt.% F (Table 2). The Zr content of in-situ rutile, as measured with an electron microprobe, ranges from 137 ppm to 528 ppm (Supplementary Table 1). The measured Zr content of rutile changes very little, with

148

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Table 2 Chemical composition of minerals from the copper–zinc albite porphyry. Mineral

Albite Albite Albite Chlorite Epidote Titanite Titanite, replacing rutile

Location

Phenocryst Groundmass Ore mineral assemblages

Measured grains

13 7 8 12 14 6 5

Major oxide (wt.%) concentrations Na2O

K2O

CaO

Al2O3

SiO2

F

Cr2O3

MgO

MnO

FeO

NiO

TiO2

ZrO2

Total

11.38 11.43 11.47 0.07 0.05 0.03 0.05

0.10 0.12 0.09 0.05 0.01 0.04 0.03

0.42 0.35 0.37 0.13 22.57 28.36 28.54

19.34 19.22 19.27 19.04 21.74 5.31 4.51

67.80 67.91 68.08 25.93 37.69 31.26 31.18

0.01 0.01 0.01 0.00 0.00 0.00 1.42

0.01 0.01 0.01 0.02 0.01 0.01 0.02

0.01 0.01 0.00 12.05 0.10 0.01 0.00

0.01 0.02 0.02 4.31 0.43 0.12 0.08

0.08 0.12 0.17 24.38 12.64 1.12 0.83

0.01 0.00 0.01 0.00 0.01 0.01 0.00

0.02 0.00 0.01 0.06 0.25 32.51 32.39

0.01 0.01 0.01 0.03 0.03 0.00 0.07

99.18 99.20 99.49 86.06 95.53 98.77 99.13

fluctuations of less than 30 ppm. Miarolitic cavities less than 2 mm in diameter yield similar Zr contents (453–489 ppm) in different rutile clusters (Fig. 7a). However, the Zr content of different rutile clusters in some tube-like miarolitic cavities decreases from two ends towards the middle of the tube (Fig. 7b). Rutile intergrown with sphalerite contains 381–420 ppm Zr (Supplementary Table 1).

5.4. Shape, distribution and internal texture of the miarolitic cavities The miarolitic cavities exhibit a variety of monomineralic and polymineralic assemblages with complex shapes. The miarolitic cavities are dispersed and randomly distributed throughout the rock and in veinlets (Fig. 5). Sphalerite crystals less than 50 μm in diameter are embedded between or around subhedral albite crystals, and 50- to 100-μm oblong sphalerites are intergrown with the albite in an equigranular aphanitic groundmass (Fig. 6f). Some miarolitic cavities ranging from 100 μm to 6 mm in diameter are irregular and shaped as pockets, tubes and polygons (Figs. 7a,b, 8). Most miarolitic cavities have sharp

and straight boundaries with their host albite crystals. Some tubeshaped miarolitic cavities connect to form veinlets. Except for a few ore minerals filling intragranular fractures, most miarolitic cavities are intergranular and interstitial (Figs. 6b, 8h). In general, individual minerals are finely crystalline and euhedral. Polymineralic miarolitic cavities exhibit zoning and intersertal texture. Some zircons, albites and apatite crystals are surrounded by radial epidote and rutile (Figs. 7a, 9a). Titanite with platy K-feldspar inclusions occurs between epidote crystals, while some euhedral Kfeldspar crystals are present adjacent to titanites (Fig. 9b). Chlorite clusters are found between or around epidote, rutile and titanite clusters (Figs. 7a, 9a,b). Irregular anhedral calcite and zoisite are distributed around early-formed minerals or mineral aggregates. Earlyformed minerals, including zircon, albite, apatite, epidote, rutile and titanite, are randomly distributed in the miarolitic cavities (Figs. 7a, 9a, b). Euhedral apatite, epidote and chlorite typically form a mosaic texture (Figs. 7a, 9a,c). Coarse euhedral rutiles are intergrown with epidote crystals (Figs. 8a, 9a), whereas fine rutile inclusions in sphalerite or

Fig. 7. BSE images (a, b, c and e) and a CL image (d) showing shape and internal texture of miarolitic cavities (MC). Image a with two locally enlarged images c and d shows zoning and intersertal texture within a polygon-like miarolitic cavity (a), layered chlorite and unidirectional solidification textures (c) and alteration of violet luminescing apatites by green luminescing apatites (d). Image b with a locally enlarged image e shows intergrowths of rutile and epidote within a tube-like OMA (b) and replacement of rutile by titanite (e). The red circles and labels in images a and b show spot location and number of rutile. The blue rectangles in images a and b show locations of images c, d and e, respectively. Ab: albite, Ap: apatite, Calc: calcite, Chl: chlorite, Epi: epidote, Rt: rutile, V: void, Zr: zircon.

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

149

Fig. 8. BSE (a, c, d, e, f and g), polarized microscope (b) and optical-CL images showing the shape, distribution, composition and internal texture of the miarolitic cavities in the copper–zinc albite porphyry. Images a and b show the same pocket-like miarolitic cavity with poikilitic sphalerite–chalcopyrite enclosing albite, epidote, rutile and titanite. The arrows in images a and b indicate the shear sense; image c with a locally enlarged image d shows the shape of chalcopyrite, and the shape, distribution and internal texture of pyrite inclusions in the chalcopyrite crystal; image e and two locally enlarged images f and g present veinlet-like miarolitic cavities (e), curved veinlet-like fractures filled by sphalerite with chalcopyrite dots (f), and enclosure and cutting of epidote by sphalerite with chalcopyrite dots (g); image h shows interstitial miarolitic cavities (MC). White lines in image c represent the grain boundaries of groundmass albite. AA: altered albite, Ab: albite, CP: chalcopyrite, Epi: epidote, IF: intergranular fracture, IGT: intergrowth texture, Prv: perovskite, Py: pyrite, Rt: rutile, SF: shear fracture, Sp: sphalerite, V: void.

intergrowth with sphalerite are anhedral (Fig. 7a,b). Some coarse chlorites associated with voids have an irregular layered texture (Fig. 7c). Most violet luminescing apatites from miarolitic cavities are intensively altered and replaced by green luminescing apatites in optical-CL images (Fig. 7d), whereas few rutiles are replaced by titanite (Fig. 7e). Chalcopyrite and sphalerite in polymineralic miarolitic cavities are anhedral, form irregular polygons with corroded outlines and are characterized by well-developed inclusions of pyrite and exsolution of chalcopyrite, respectively. These features range in size from b 10 μm to ~1 mm. Chalcopyrite contains inclusions of albite, epidote, sphalerite, pyrite and chlorite (Figs. 8c, 9d, e). Some enclosed albite, epidote and sphalerite with chalcopyrite exsolution represent graphic myrmekitic intergrowth texture (Fig. 9d), while some albite and epidote contain fine rounded, chalcopyrite inclusions (Fig. 9e). Subhedral pyrite grains are pervasive, and occasionally arranged along the border of the host chalcopyrite grains (Fig. 8c). Some cubic pyrite grains have a clear empty void in their center and rims (Fig. 8d). A ring-shaped void separates pyrite from the host chalcopyrite (Fig. 8c,d). Chlorite and pyrite grains, generally less than 50 μm, are distributed throughout coarse chalcopyrite grains. Coarse sphalerite grains have inclusions of rutile, titanite, albite and epidote, and exsolution of chalcopyrite (Figs. 8a, 9c,f). Some enclosed anhedral rutiles are intergrown with sphalerite (Fig. 8a). Chalcopyrite exsolution in sphalerite are pervasively developed as sheaths and blebs, and are larger in the center of the host sphalerite grains (Fig. 9f). The maximum observed amount of chalcopyrite in the

sphalerite is 10% by volume. Some epidote grains are cut by veinlets of sphalerite to form a mesh texture (Figs. 8f,g, 9f), whereas several netlike sphalerites with chalcopyrite blades fill the interstices around epidote and albite clusters (Fig. 9c). Most coarse-grained sphalerite crystals with chalcopyrite blebs, as well as chalcopyrite crystals with pyrite blebs, contain albite–epidote aggregates and exhibit poikilitic texture (Figs. 8a, 9a and c–f; Hughes, 1982). Based on observed textures, the crystallization sequence of the minerals in the miarolitic cavities has been defined. Zircon, apatite and albite crystallized first, followed by the crystallization of epidote, rutile and sphalerite with chalcopyrite exsolution, titanite and K-feldspar. Next the formation of chalcopyrite with pyrite inclusions occurred. Finally, chlorite, zoisite and calcite infilled the void spaces.

5.5. Morphology, U–Pb age and trace elements of zircon Euhedral zircon is present as 50- to 200-μm-long, well-developed prisms ({100} and {110}) and pyramids ({101} and {211}) with length-to-width ratios ranging from 1.1 to 2.0 (Fig. 10a). The most frequent population of zircons, which contributes to more than 80% of the grains, contains nearly equal prisms ({100} and {110}) and various pyramids, from predominantly {211} to nearly equal amounts of {101} and {211}. The other zircon crystal population is comprised predominantly of prism {100} or {110}. All of the zircons exhibit coherent internal structures including concentric oscillatory

150

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Fig. 9. BSE images showing the internal texture of the miarolitic cavities. (a) Mosaic texture between or around euhedral epidote, zoning texture presented by albite radial around by epidote and rutile, enclosure of epidote clusters by sphalerite with chalcopyrite exsolution and intergrowth texture between anhedal rutile and sphalerite; (b) intersertal texture denoted by occurrences of K-feldspar, chlorite and calcite between or among epidote and K-feldspar-bearing titanite; (c) mosaic texture between or around euhedral apatite, epidote and chlorite, enclosure of epidote and chlorite clusters by sphalerite with chalcopyrite dot; (d) enclosure of anhedral sphalerite with chalcopyrite dots, albite and epidote clusters with equigranular aphanitic by chalcopyrite with pervasive pyrite and pyrite–chlorite inclusions; (e) enclosure of albite and epidote with round chalcopyrite inclusions by chalcopyrite with pyrite and pyrite–chlorite inclusions; (f) enclosure of albite and epidote clusters by sphalerite with chalcopyrite exsolution and cutting of epidote by sphalerite with chalcopyrite dots. The arrow in image (d) indicates the shear sense. Ab: albite, Ap: apatite, Calc: calcite, Chl: chlorite, CI: chalcopyrite inclusion, CP: chalcopyrite, Epi: epidote, IF: intergranular fracture, Kf: Kfeldspar, Py: pyrite, Rt: rutile, SF: shear fracture, Sp: sphalerite, Ttn: titanite, Zo: zoisite, Zr: zircon.

zoning in cathodoluminescence images and the absence of secondary overprinting (Fig. 10a). SIMS U–Pb dating revealed that zircons from the copper–zinc albite porphyry contain 2–10 ppm Pb, 24–116 ppm U and 8–106 ppm Th. A mean Th/U ratio of 0.45 was obtained, and the concordia age of the material is 418.2 ± 2.9 Ma (MSWD = 1.6). The weighted average 206 Pb/238U age is 418.5 ± 2.9 Ma (MSWD = 0.24) (Fig. 10b; Table 3), indicating that the copper–zinc albite porphyry was formed at 418 Ma as a late dike intruding granite. As with zircons from unaltered granodiorite in southern Hersai and unaltered magmatic zircons from continental crustal rocks (Hoskin, 2005), the zircons have chondrite-normalized REE patterns characterized by a steep positive slope from La to Lu, with a significantly positive Ce anomaly and a relatively small negative Eu anomaly (Fig. 10c; Supplementary Table 2). The zircons have titanium contents of 7.32 to 14.0 ppm (Supplementary Table 2).

6. Discussion 6.1. Nature of the copper–zinc albite porphyry The copper–zinc albite porphyry in the Hersai porphyry copper deposit has geochemical features of adakites, such as high Sr (362–593 ppm) and Sr/Y (48.2–68.9) and low Y (7.5–9.7 ppm) (Defant and Drummond, 1990). The copper–zinc albite porphyries have similar REE and trace element patterns to granites, granodiorites and granodioritic porphyries in the Hersai area (Fig. 11). All of the copper–zinc albite porphyry, granite, granodiorite and granodioritic porphyries from the Hersai area exhibit continental island arc geochemical features. These features include low Rb, Nb, Y, Ta and Yb content, low Ce/Pb values, moderate La/Yb values, high K and U content and Ba/Nb values, depletion in Nb, Pr, P and Ti, enrichment in Pb, K and

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

151

the albite crystals in the albite porphyry dike had been compacted (Hunter, 1996; Irvine, 1982; Wager et al., 1960). The compaction indicates that the copper–zinc albite porphyry dike had gone through crystal accumulation and fractional crystallization, which may cause enrichment of metal and fluid and the formation of copper–zinc porphyry magmas (Xu et al., 2012a). The albite porphyry was overprinted by hydrothermal alteration. A portion of albite phenocrysts and groundmass with pale orange luminescing CL color in the copper–zinc albite porphyry are possibly primarily magmatic, whereas most albites with gray or weak luminescing CL color are altered (Götze, 2012). The green luminescing apatites along fractures, at the rims of blue-violet luminescing apatites (Figs. 6d, 7d) and within altered albites (Fig. 6b) are related to hydrothermal alteration (Bouzari et al., 2011). Evidence that the intensively altered albites are present near an interstitial miarolitic cavity indicates that the overprinted alteration is most likely related to the ore fluids forming the miarolitic cavities. 6.2. Formation temperatures of zircons and rutiles

Fig. 10. Topological (TP), cathodoluminescence (CL) and backscattered electron (BSE) images (a); SIMS U–Pb concordia age plots (b) and chondrite-normalized REE patterns (c) of separated, representative zircon in the copper–zinc albite porphyry (CZAP, sample zk107-1-5). The chondrite-normalized REE patterns of separated zircons in unaltered barren granodiorite in the Hersai porphyry copper deposit are shown in diagram (c). The normalization values were taken from McDonough and Sun (1995). The damage pits in zircon, which are shown in picture (a), were created by laser ablation during the SIMS U– Pb dating process.

U (Fig. 11b; Winter, 2001), plotting in the field of volcanic arc granites (VAG) in the Rb versus Ta + Yb diagram (Fig. 12a; Pearce et al., 1984), in the continental crust field in the Ce/Pb versus Ce diagram (Fig. 12b; Hofmann, 1988), in the field of arc volcanic rocks in the Ba/Nb versus La/Nb diagram (Fig. 12c; Jahn et al., 1999), and in and near the field of continental island arc in La/Yb versus Sc/Ni diagram (Fig. 12d; Bailey, 1981). This finding is consistent with the evidence from the Taheir tectonic window of East Junggar (Xu et al., 2013), that is, the intrusive bodies in the Hersai area were emplaced in the Yemaquan Devonian continental island arc. The occurrence of the blue-violet luminescing apatites (Fig. 6d) indicates that the copper–zinc albite porphyry is an alkaline-like intrusive (Kempe and Götze, 2002; Marshall, 1988). The presence of interlocking curved or serrated grain boundaries between albite phenocrysts and the groundmass or between groundmass albites (Fig. 6a, b) suggests that

Based on the geothermometer of Watson et al. (2006) and Ferry and Watson (2007), coexisting zircon, rutile and quartz in the copper–zinc albite porphyry indicate that the values of αSiO2 and αTiO2 are defined as αSiO2 = αTiO2 = 1, and their Ti-in-zircon and Zr-in-rutile temperatures can be estimated according to the measured Ti contents of zircon and Zr contents of rutile. The estimated results (Supplementary Tables 1 and 2) show that the Ti-in-zircon and Zr-in-rutile temperatures based on the calibrations of Ferry and Watson (2007) are remarkably similar to those derived by Watson et al. (2006). For example, Ti contents of 7.32 to 14.0 ppm in zircon that record 714 to 771 °C using the calibration of Watson et al. (2006) record 717 to 779 °C with the calibration of Ferry and Watson (2007). Similarly, Zr contents of 137 to 528 ppm in rutiles that record 581 to 689 °C based on Watson et al. (2006) record 584 to 691 °C based on Ferry and Watson (2007). However, the calibrations of the Ti-in-zircon and Zr-in-rutile thermometers proposed by Ferry and Watson (2007) are most appropriately considered as referring to P ≈ 1 GPa, and the pressure dependence of the Ti-in-zircon and Zr-in-rutile thermometers is approximately 50 °C/GPa and 80 °C/GPa, respectively. The pressure effect could be significant and should be corrected (Fu et al., 2008). Statistically, porphyries form at a depth between 1 and 6 km, with a modal depth of 2.8 km (Kesler and Wilkinson, 2008; Seedorff et al., 2005), and granite plutons are commonly emplaced in the upper crust at depths of approximately 8–10 km (e.g., Guillot et al., 1995; Jowhar, 2001; Sides, 1980; Tomiya et al., 2010). On the assumption that the average density of the crust is approximately 2800 kg/m3 (Rudnick and Fountain, 1995) and the gravitational acceleration g is approximately 9.8 m/s2, the pressure dependence of the Ti-in-zircon temperatures can be estimated as approximately 78 °C, 74 °C, 67 °C, 62 °C and 58 °C for intrusive bodies emplaced at depths of 1 km, 2.8 km, 6 km, 8 km and 10 km, respectively, and those of the Zr-in-rutile temperature for the same intrusions are approximately 49 °C, 46 °C, 42 °C, 39 °C and 36 °C, respectively. The statistic results (Supplementary Tables 1 and 2) in which pressure dependence was corrected show the following evidence: 1) The Zr content of 137 to 528 ppm of rutiles from the copper–zinc albite porphyry records temperatures of 507 to 614 °C, 511 to 618 °C, and 518 to 625 °C for the emplacement depth of 1 km, 2.8 km and 6 km, respectively. This result indicates that these measured rutiles were formed at temperatures above 500 °C, in the range of 507 to 625 °C. 2) The Zr content of 381 to 420 ppm of rutiles intergrown with sphalerites records 585 to 594 °C, 589 to 598 °C, and 596 to 605 °C for emplacement depths of 1 km, 2.8 km and 6 km, respectively. This shows that these rutiles and coexisting sphalerites were formed at temperatures approximately 600 °C. This conclusion is consistent with the high concentration of exsolved chalcopyrite in sphalerite (up to

152

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Table 3 Zircon SIMS U–Pb analytical results of the copper–zinc albite porphyry. Spot

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19

Pb (ppm)

U (ppm)

Th (ppm)

Th/U

3 4 3 6 3 6 4 3 3 4 10 3 2 9 5 4 7 4

32 53 43 79 40 77 52 43 32 48 116 32 24 109 61 52 83 52

15 18 19 30 19 25 19 17 13 19 106 13 8 74 31 17 51 16

0.47 0.34 0.44 0.38 0.49 0.33 0.37 0.40 0.42 0.39 0.91 0.41 0.33 0.68 0.51 0.32 0.61 0.32

f206 (%)

207

Pb/206Pb

0.13 0.10 0.00 0.10 0.10 0.05 0.00 0.34 0.24 0.22 0.04 0.34 0.00 0.10 0.26 0.05 0.17 0.06

0.0550 0.0565 0.0530 0.0543 0.0546 0.0556 0.0570 0.0536 0.0501 0.0527 0.0556 0.0538 0.0526 0.0550 0.0514 0.0560 0.0552 0.0550

±σ (%)

207

3.9 3.1 3.8 2.1 3.7 3.1 2.9 3.3 4.7 4.1 1.8 4.3 5.9 1.9 2.8 2.4 3.3 2.6

0.5125 0.5223 0.4902 0.5028 0.5012 0.5097 0.5217 0.5020 0.4683 0.4816 0.5117 0.5011 0.4937 0.5149 0.4660 0.5192 0.5080 0.5122

10 vol.%), which suggests that the sphalerite–chalcopyrite solid solutions formed above 600 °C (Kojima and Sugaki, 1984, 1985). 3) The Ti contents of 7.32 to 14.0 ppm in zircons from the copper–zinc albite porphyry record 669 to 730 °C, 691 to 732 °C, and 676 to 737 °C for emplacement depths of 1 km, 2.8 km and 6 km, respectively. This means that these zircons possibly formed at temperatures between 669 °C and 737 °C, which is slightly less than the formation temperatures between 725 °C and 775 °C suggested by their crystal topologies (Pupin, 1980). 4) The Ti contents of 6.18 to 34.86 ppm in zircons from the granodiorite

Fig. 11. REE (after Boynton, 1984) (a) and trace element (after Sun and McDonough, 1989) (b) spider diagrams of intrusive rocks from the Hersai area.

Pb/235U

±σ (%)

206

Pb/238U

4.2 3.5 4.0 2.7 4.0 3.5 3.3 3.6 4.9 4.4 2.4 4.5 6.1 2.4 3.2 2.8 3.6 3.0

0.068 0.067 0.067 0.067 0.067 0.066 0.066 0.068 0.068 0.066 0.067 0.067 0.068 0.068 0.066 0.067 0.067 0.067

±σ (%)

Age (Ma) T207/235

±σ

T206/238

±σ

1.5 1.5 1.5 1.6 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5

420.1 426.7 405.0 413.6 412.5 418.3 426.3 413.1 390.0 399.2 419.6 412.4 407.4 421.7 388.4 424.6 417.1 419.9

14.4 12.2 13.6 9.1 13.6 12.0 11.4 12.5 16.2 14.7 8.1 15.5 20.7 8.3 10.3 9.9 12.6 10.3

421.7 418.0 418.9 419.0 415.4 414.8 414.0 424.0 422.7 413.4 416.3 421.0 424.6 423.1 410.8 419.5 416.6 421.0

6.1 6.1 6.1 6.6 6.0 6.0 6.1 6.2 6.2 6.1 6.1 6.1 6.2 6.1 6.0 6.3 6.1 6.2

in the Hersai area record 664 to 839 °C and 666 to 842 °C for emplacement depths of 8 km and 10 km, respectively. 6.3. Features of ore fluids forming the miarolitic cavities The absence of disseminated miarolitic cavities in the adjacent earlyformed granite indicates that the ore fluids forming the miarolitic cavities were most likely exclusive to the albite porphyry. The presence of a well-preserved dome and the rectangular terminations of wall albites (Figs. 7a, 8h) indicates that corrosion on the wall albites is slight and the cavities for the ore minerals are possibly primary rather than secondary. If the miarolitic cavities were related to late infiltration and injection, they would not be confined to the copper–zinc albite porphyry and should be found in the adjacent granite as well. They should also be interconnected and the wall minerals should be intensively corroded and altered. The zircons formed at temperatures between 669 °C and 737 °C and blue-violet luminescing apatites from the miarolitic cavities are magmatic, whereas the green-luminescing apatites overprinted along the fractures and rims of the blue-violet luminescing apatites are metasomatic and the hydrothermal minerals of the miarolitic cavities are precipitation from ore fluids. The intergrowths of rutile and epidote (Fig. 7b), rutile and sphalerite (Figs. 8a, 9a), and albite and epidote (Fig. 9d, e) exhibit internal nucleation and typical aplitic textures (Harris et al., 2004), implying that the early-formed albite, epidote, rutile and sphalerite of the miarolitic cavities were crystallized from hydrous magmas rather than hydrothermal solutions. This suggestion is supported by the presence of zoning texture exhibited by random zircon, albite and apatite radial round by epidote and rutile (Figs. 7a, 9a), and the absence of epidote overgrowths on the large albite phenocrysts and groundmass along the outer rim of the ore mineral assemblages. The Zr-in-rutile geothermometer shows that this rutile and coexisting epidote were formed at temperatures above 500 °C in the range of 507–625 °C. However, the presence of intersertal texture, defined as chlorite, calcite and zoisite filling between early-formed mineral grains (Fig. 7a), and the occurrence of layered chlorite associated with voids (Fig. 7c) indicate that these chlorites, calcites and zoisites are most likely interstitial precipitated from hydrothermal solutions (Candela and Blevin, 1995). Therefore, ore fluids forming the miarolitic cavities are possible solidifications of a transition between hydrous magmas and hydrothermal solutions. Moreover, the chalcopyrite exsolutions in sphalerite were formed by exsolution from solid solutions (e.g., Craig and Vaughan, 1981;

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

153

Fig. 12. (a) Rb versus Ta + Yb diagram (after Pearce et al., 1984), (b) Ce/Pb versus Ce diagram (after Hofmann, 1988), (c) Ba/Nb versus La/Nb diagram (after Jahn et al., 1999), (d) La/Yb versus Sc/Ni diagram (Bailey, 1981) for intrusive rocks from the Hersai area. AV: arc volcanics, CA: continental crust average, DOIB: Dupal oceanic island basalt, OIA: oceanic island arc, ORG: ocean ridge granites, PM: primitive mantle, syn-COLG: syn-collision granites, VAG: volcanic arc granites, WPG: within plate granites.

Schwartz, 1942) rather than by a metasomatic process (Bortnikov et al., 1991). This is based on the distribution of chalcopyrite in sphalerite, especially in single, oblong sphalerite crystals in equigranular aphanites with groundmass albite (Fig. 6f), in net-like sphalerite-filling interstices around epidote and albite clusters (Fig. 9c), in subhedral sphalerite that is intergrown with epidote and albite enclosed by chalcopyrite with pyrite inclusions (Fig. 9d), and in veinlet-like sphalerite in epidote crystals (Figs. 8f, 9f). The presence of poikilitic sphalerite–chalcopyrite solid solutions containing albite, rutile and epidote (Figs. 8a, 9a,c,f), and the development of veinlet-like fractures filled by sphalerites with chalcopyrite dots indicate that sphalerite–chalcopyrite solid solutions were likely formed by sulfide melts (Hughes, 1982; Xu, 2009; Xu et al., 2004). These sphalerite − chalcopyrite solid solutions intergrown with rutiles were formed at temperatures approximately 600 °C. The veinlet-like fractures filled by sphalerites with chalcopyrite solid solutions are related to hydrofracturing of sphalerite–chalcopyrite melts (Xu, 2009; Xu et al., 2004). Similarly, the occurrence of coarse chalcopyrite with poikilitic texture (Fig. 9d, e) indicates that these coarse chalcopyrites are possibly also crystallized from sulfide melts. The regular distribution of cubic pyrite crystals with a bleb center and the bleb-inclusion-rich rims of chalcopyrite crystals (Fig. 8c, d) implies a specific sequence of events: (1) pyrite inclusions were formed simultaneously with their host chalcopyrite crystals as exsolutions, rather than metasomatic products; (2) pyrite-rich liquids concentrated at the border of chalcopyrite crystals during the exsolution processes; and (3) pyrite-rich liquids contained some vapor in pore

blebs located in and surrounding the cubic pyrite. This finding suggests that the chalcopyrite melts may contain pyrite vapor. The occurrence of round, microscopic chalcopyrite inclusions inside epidote and albite inclusions in chalcopyrite grains (Fig. 9e) indicates that the ore fluids were saturated in chalcopyrite, which crystallized when albite and epidote formed. In summary, the miarolitic cavities in the copper–zinc albite porphyry were most likely formed by sulfide-rich fluids. The ore fluids were possibly trapped in-situ and enclosed by the crystallizing albite crystals on the basis of the following evidence: 1) the absence of disseminated miarolitic cavities in the adjacent early-formed granite and restriction of the miarolitic cavities to the albite porphyry; 2) the presence of well-preserved domes and rectangular terminations of wall albites (Figs. 7a, 8 h), slight corrosion of the wall albites and primary cavities for the miarolitic cavities; and 3) the great variability in mineral composition and the intergranular and interstitial distribution of the miarolitic cavities. The origin of the ore fluids is possibly similar to that of the vapor for the miarolitic cavities in the dacite porphyries from the Bajo de la Alumbrera porphyry Cu–Au deposit (Harris et al., 2004). The remainder was injected into fractures to form veinlets. The alteration of early-crystallized albite and apatite is related to hydrothermal solutions from the enclosed interstitial ore fluids. 6.4. Ore type of the copper–zinc albite porphyry The disseminated distribution of chalcopyrite–sphalerite-rich miarolitic cavities within the porphyritic intrusions indicates that

154

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

the copper–zinc albite porphyry clearly belongs to the broad class of porphyry copper deposits (e.g., Cooke et al., 2005; Cox, 1986; Lowell and Guilbert, 1970; McMillan and Panteleyev, 1980; Singer, 1995). However, some features and origins of the ore minerals are different from the classical hypogene porphyry copper deposits, in which sulfide ore minerals precipitate from hydrothermal solutions at temperatures lower than 500 °C (e.g., Kojima and Sugaki, 1985; Seedorff et al., 2005; Sillitoe, 2010). The ore minerals of the miarolitic cavities in the copper–zinc albite porphyry exhibit some distinct magmatic to hydrothermal internal textures, such as the aplitic texture exhibited by intergrowths of albite, epidote, rutile and sphalerite–chalcopyrite solid solutions, zoning and intersertal textures, veinlet-like sphalerite–chalcopyrite solid solutions, poikilitic textures, and layered chlorites. The epidote and rutile of the miarolitic cavities were formed at high temperatures above 500 °C, in the range of 507–625 °C, whereas the sphalerite–chalcopyrite solid solutions were formed at temperatures approximately 600 °C. The ore fluids are intergranular residual sulfide-rich fluids transitional between hydrous magmas and hydrothermal solutions. In this respect, the copper–zinc albite porphyry is an atypical porphyry copper deposit which is transitional between late magmatic and hydrothermal deposits. The sulfide content of the copper–zinc albite porphyry indicates that ore grades are approximately 0.6% Cu and 1.3% Zn, and metal zinc is essential to the economics of the copper–zinc albite porphyry. According to the definition of the subtypes of porphyry deposits proposed by Kirkham and Sinclair (1995), the copper–zinc albite porphyry could be defined as a new subtype— porphyry copper–zinc deposit. 6.5. Formation mechanism of the copper–zinc albite porphyry The origin of the copper–zinc albite porphyry involved a series of processes: (1) the ore-bearing adakitic magmas derived from the crystallization differentiation of magmas at continental island arc were first transported to a magma chamber at the middle crust (e.g., Richards, 2003; Richards and Kerrich, 2007; Xu et al., 2012a); (2) the ore elements (Cu and Zn) and their carriers (ore fluids, including sulfide melts, aqueous magmatic fluids) were directly concentrated in alkaline magma by fractional crystallization, accumulation and the concentration of Ca–Fe–Mg silicate minerals from adakitic melts in an intermediate magma chamber (e.g., Candela and Holland, 1986; Core et al., 2006; Halter et al., 2005; Hedenquist and Lowenstern, 1994; Kamenetsky et al., 1999; Keith et al., 1997; Larocque et al., 2000; Lowenstern et al., 1991; Mustard et al., 2006; Richards, 2003; Xu et al., 2012a, 2012b); (3) ore-fluid-rich albite porphyry magma formed when ore-fluid-rich Na-silicate melts, containing some albite phenocrysts, were emplaced in the shallow crust (Xu et al., 2009); (4) some of this magma was injected into peripheral fractures to form dikes; and (5) the crystallization of albite crystals from the porphyry magmas caused sulfide-rich fluid droplets to be trapped interstitially in crystals, resulting in the formation of the disseminated sulfide-rich miarolitic cavities and the copper–zinc albite porphyry. These processes are possibly similar to the formation of miarolitic cavities in plutons (e.g., Candela, 1991; Candela and Blevin, 1995; Harris et al., 2004). 7. Conclusions The copper–zinc albite porphyry dike intruded into the granite approximately 418 Ma in the Hersai porphyry copper deposit (Nom, East Junggar, China) is an atypical porphyry copper–zinc deposit characterized by the abundance of disseminated, intergranular, chalcopyrite–sphalerite-rich miarolitic cavities with magmatic to hydrothermal mineral assemblages and internal textures. The ore minerals were formed by residual sulfide-rich fluid droplets that were trapped interstitially within crystals. Evidence of the copper– zinc albite porphyry suggests that the mineralization of porphyry

copper deposits may initially occur at a late magmatic stage or the transition from a magmatic to a hydrothermal stage. Acknowledgments This research was jointly supported by the NSFC (Grant number 41390422 and 41072060), the CAS Knowledge Innovation Project (Grant number kzcx-ew-ly03 and kzcx2-yw-107) and the National 305 project (Grant number 2011BAB06B03-3 and 2006BAB07B01-03). We would like to thank Zengqian Hou, Jun Deng, Ke-Zhang Qin, Guang-Ming Li, Zhao-Chong Zhang, Xin-Ping Cai and Zheng-Fu Guo for the valuable discussions, Qiu-Li Li, Yu-Guang Ma, Xin Yan and Shao-Feng Dong for the assistance with the SIMS, CL, EMP and SEM analyses, and Shi-Jun Du, Yong Zhang and Hong-Fei Lu for the field assistance. This paper has been significantly improved by the thorough and incisive reviews of two anonymous reviewers. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.oregeorev.2014.01.009. References Audétat, A., Günther, D., Heinrich, C.A., 2000. Magmatic-hydrothermal evolution in a fractionating granite: a microchemical study of the Sn–W–F-mineralized Mole Granite, Australia. Geochim. Cosmochim. Acta 64, 3373–3393. Bailey, J.C., 1981. Geochemical criteria for a refined tectonic discrimination of orogenic andesites. Chem. Geol. 32, 139–154. Berger, B.R., Ayuso, R.A., Wynn, J.C., Seal, R.R., 2008. Preliminary model of porphyry copper deposits. U.S. Geological Survey Open-File Report 2008–1321, pp. 1–55. Bortnikov, N.S., Genkin, A.D., Dobrovol'skaya, M.G., Muravitskaya, G.N., Filimonova, A.A., 1991. The nature of chalcopyrite inclusions in sphalerite: exsolution, coprecipitation, or “disease”? Econ. Geol. 86, 1070–1082. Bouzari, F., Hart, C.J.R., Barker, S., Bissig, T., 2011. Porphyry Indicator Minerals (PIMS): a new exploration tool for concealed deposits in south-central British Columbia. Geoscience BC, Report 2011–17, p. 31. Boynton, W.V., 1984. Geochemistry of the rare earth elements. In: Henderson, P. (Ed.), Meteorite Studies, Rare earth element geochemistry. Elsevier, Amsterdam, pp. 63–114. Candela, P.A., 1991. Physics of aqueous phase evolution in plutonic environments. Am. Mineral. 76, 1081–1091. Candela, P.A., Blevin, P.L., 1995. Do some miarolitic granites preserve evidence of magmatic volatile phase permeability? Econ. Geol. 90, 2310–2316. Candela, P.A., Holland, H.D., 1986. A mass transfer model for copper and molybdenum in magmatic hydrothermal systems: the origin of porphyry-type ore deposits. Econ. Geol. 81, 1–19. Carten, R.B., Geraghty, E.P., Walker, B.M., Shannon, J.R., 1988. Cyclic development of igneous features and their relationship to high-temperature hydrothermal features in the Henderson porphyry molybdenum deposit, Colorado. Econ. Geol. 83, 266–296. Cheng, S., Wang, S., Feng, J., Tan, K., Jia, H., Chen, Q., 2010. Geological characteristics and prospecting standards of the Hersai copper deposit, Xinjiang. Xinjiang Geol. 28, 254–259 (in Chinese with English abstract). Cooke, D.R., Hollings, P., Walsh, J.L., 2005. Giant porphyry deposits: characteristics, distribution, and tectonic controls. Econ. Geol. 100, 801–818. Core, D.P., Kesler, S.E., Essene, E.J., 2006. Unusually Cu-rich magmas associated with giant porphyry copper deposits: evidence from Bingham, Utah. Geology 34, 41–44. Cox, D.P., 1986. Descriptive model of porphyry Cu. U.S. Geol. Surv. Bull. 1693, 1–76. Craig, J.R., Vaughan, D.J., 1981. Ore Microscopy and Ore Petrography. John Wiley & Sons, New York (406 pp.). Defant, M.J., Drummond, M.S., 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere. Nature 347, 662–665. Dong, L.H., Xu, X.W., Qu, X., Li, G.M., 2009. Tectonic setting and formation mechanism of the circum-Junggar porphyritic copper deposit belts. Acta Petrol. Sin. 25, 713–737 (in Chinese with English abstract). Du, S.J., Qu, X., Deng, G., Zhang, Y., Cheng, S.L., Lu, H.F., Wu, Q., Xu, X.W., 2010. Chronology and tectonic setting of intrusive bodies and associated porphyry copper deposit in the Hersai area, Eastern Junggar. Acta Petrol. Sin. 26, 2981–2996 (in Chinese with English abstract). Edwards, R., Atkinson, K., 1986. Ore Deposit Geology. Chapman and Hall, London (466 pp.). Feng, J., Xu, S.Q., Zhao, Q., Lan, X., 2010. Metallogenic regularity and prospecting direction of porphyry copper deposits in Xinjiang. Xinjiang Geol. 28, 43–51 (in Chinese with English abstract). Ferry, J.M., Watson, E.B., 2007. New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers. Contrib. Mineral. Petrol. 154, 429–437. Fu, B., Page, F.Z., Cavosie, A.J., Fournelle, J., Kita, N.T., Lackey, J.S., Wilde, S.A., Valley, J.W., 2008. Ti-in-zircon thermometry: applications and limitations. Contrib. Mineral. Petrol. 156, 197–215.

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156 Götze, J., 2012. Application of cathodoluminescence microscopy and spectroscopy in Geosciences. Microsc. Microanal. 18, 1270–1284. Guillot, S., Le Fort, P., Pecher, A., Barman, M.R., Aprahamian, J., 1995. Contact metamorphism and depth of emplacement of the Manaslu granite (central Nepal): implications for Himalayan orogenesis. Tectonophysics 241, 99–119. Guo, L.H., Zhang, R., Liu, Y.L., Xu, F.J., Su, L., 2009. Zircon U–Pb age of Tonghualing intermediate-acid intrusive rocks, Eastern Junggar, Xinjiang. Acta Sci. Nat. Univ. Pekin. 45, 819–824 (in Chinese with English abstract). Gustafson, L.B., Hunt, J.P., 1975. The porphyry copper deposit at El Salvador, Chile. Econ. Geol. 70, 857–912. Halter, W.E., Pettke, T., Heinrich, C.A., 2002. The origin of Cu/Au ratios in porphyry-type ore deposits. Science 296, 1844–1846. Halter, W.E., Heinrich, C.A., Pettke, T., 2005. Magma evolution and the formation of porphyry Cu–Au ore fluids: evidence from silicate and sulfide melt inclusions. Mineral. Deposita 39, 845–863. Harris, A.C., Golding, S.D., 2002. New evidence of magmatic-fluid-related phyllic alteration: implications for the genesis of porphyry Cu deposits. Geology 30, 335–338. Harris, A.C., Kamenetsky, V.S., White, N.C., Achterbergh, E.V., Ryan, C.G., 2003. Melt inclusions in veins: linking magmas and porphyry Cu deposits. Science 302, 2109–2111. Harris, A.C., Kamenetsky, V.S., White, N.C., Steele, D.A., 2004. Volatile phase separation in silicic magmas at Bajo de la Alumbrera porphyry Cu–Au Deposit, NW Argentina. Resour. Geol. 54, 341–356. Hedenquist, J.W., Lowenstern, J.B., 1994. The role of magmas in the formation of hydrothermal ore deposits. Nature 370, 519–527. Hedenquist, J.W., Arribas, A.J., Reynolds, T.J., 1998. Evolution of an intrusion-centered hydrothermal system: far South-east Lepanto porphyry and epithermal Cu–Au deposits, Philippines. Econ. Geol. 93, 373–404. Heithersay, P.S., Walshe, J.L., 1995. Endeavour 26 North: a porphyry copper–gold deposit in the Late Ordovician shoshonitic Goonumbla Volcanic Complex, New South Wales, Australia. Econ. Geol. 90, 1506–1532. Hofmann, A.W., 1988. Chemical differentiation of the Earth: the relationship between mantle, continental crust and oceanic crust. Earth Planet. Sci. Lett. 90, 297–314. Holliday, J.R., Wilson, A.J., Blevin, P.L., Tedder, I.J., Dunham, P.D., Pitzner, M., 2002. Porphyry gold–copper mineralization in the Cadia district, eastern Lachlan Fold Belt, New South Wales, and its relationship to shoshonitic magmatism. Mineral. Deposita 37, 100–116. Hoskin, P.W.O., 2005. Trace-element composition of hydrothermal zircon and the alteration of Hadean zircon from the Jack Hills, Australia. Geochim. Cosmochim. Acta 69, 637–648. Hughes, C.J., 1982. Igneous petrology. Developments in Petrology, 7. Elsevier, Amsterdam (551 pp.). Hunter, R.H., 1996. Texture development in cumulate rocks. In: Cawthorn, R.G. (Ed.), Layered Intrusions. Elsevier, Amsterdam, pp. 77–101. Irvine, T.N., 1982. Terminology for layered intrusions. J. Petrol. 23, 127–162. Jahn, B.M., Wu, F., Lo, C.H., Tsai, C.H., 1999. Crust–mantle interaction induced by deep subduction of the continental crust: geochemical and Sr–Nd isotopic evidence from postcollisional mafic–ultramafic intrusions of the northern Dabie complex, central China. Chem. Geol. 157, 119–146. Jambor, J.L., Owens, D.R., 1987. Vinciennite in the Maggie porphyry copper deposit, British Columbia. Can. Mineral. 25, 227–228. Jowhar, T.N., 2001. Geobarometric constraints on the depth of emplacement of granite from the Ladakh batholith, Northwest Himalaya, India. J. Mineral. Petrol. Sci. 96, 256–264. Kamenetsky, V.S., Wolfe, R.C., Eggins, S.M., Mernagh, T.P., Bastrakov, E., 1999. Volatile exsolution at the Dinkidi Cu–Au porphyry deposit, Philippines: a melt inclusions record of the initial ore-forming process. Geology 30, 691–694. Keith, J.D., Whitney, J.A., Hattori, K., Ballantyne, G.H., Christiansen, E.H., Barr, D.L., Cannan, T.M., Hook, C.J., 1997. The role of magmatic sulfides and mafic alkaline magmas in the Bingham and Tintic mining districts, Utah. J. Petrol. 38, 1679–1690. Kempe, U., Götze, J., 2002. Cathodoluminescence (CL) behaviour and crystal chemistry of apatite from rare-metal deposits. Mineral. Mag. 66, 135–156. Kesler, S.E., 1973. Copper, molybdenum and gold abundances in porphyry copper deposits. Econ. Geol. 68, 106–112. Kesler, S.E., Wilkinson, B.H., 2008. New insight into Earth's mineral endowment: modelbased estimation of global copper resources. Geology 36, 255–258. Kirkham, R.V., Sinclair, W.D., 1995. Porphyry copper, gold, molybdenum, tungsten, tin, silver. In: Eckstrand, O.R., Sinclair, W.D., Thorpe, R.I. (Eds.), Geology of Canadian Mineral Deposit Types. Geological Survey of Canada, Geology of Canada, 8, pp. 421–446. Kirwin, D.J., 2007. Unidirectional solidification textures, miarolitic cavities and orbicules: field evidence for the magmatic to hydrothermal transition. From http://www.cmicapital.com/SEEGF_Docs_server/Kirwin/2-UST-Europe-10%20Sep%202006.pdf. Kojima, S., Sugaki, A., 1984. Phase relations in the central portion of the Cu–Fe–Zn–S system between 800 °C and 500 °C. Mineral. J. 12, 15–28. Kojima, S., Sugaki, A., 1985. Phase relations in the Cu–Fe–Zn–S system between 500 °C and 300 °C under hydrothermal conditions. Econ. Geol. 80, 158–171. Larocque, A.C.L., Stimac, J.A., Keith, J.D., Huminicki, M.A.E., 2000. Evidence for opensystem behavior in immiscible Fe–S–O liquids in silicate magmas: implications for contributions of metals and sulfur to ore-forming fluids. Can. Mineral. 38, 1233–1249. Li, X.H., Liu, Y., Li, Q.L., Guo, C.H., Chamberlain, K.R., 2009. Precise determination of Phanerozoic zircon Pb/Pb age by multi-collector SIMS without external standardization. Geochem. Geophys. Geosyst. 10, Q04010. http://dx.doi.org/10.1029/2009GC002400. Liang, G.L., Xu, X.W., Gao, C.L., Wu, H.P., Zhang, Z.F., Zhao, F.Z., Yan, X.L., Xiao, J.C., 2010. Geological and geophysical characteristics and prognostic analysis of Mengxi porphyry Cu–Mo deposit, Eastern Junggar. Xinjiang Geol. 28, 402–408 (in Chinese with English abstract).

155

Lowell, J.D., Guilbert, J.M., 1970. Lateral and vertical alteration–mineralization zoning in porphyry ore deposits. Econ. Geol. 65, 373–408. Lowenstern, J.B., Sinclair, W.D., 1996. Exsolved magmatic fluid and its role in the formation of comb-layered quartz at the Cretaceous Logtung W–Mo deposit, Yukon Territory, Canada. Trans. R. Soc. Edinb. Earth Sci. 87, 291–303. Lowenstern, J.B., Mahood, G.A., Rivers, M.L., Sutton, S.R., 1991. Evidence for extreme partitioning of copper into a magmatic vapor phase. Science 252, 1405–1408. Marshall, D.J., 1988. Cathodoluminescence of Geological Materials. Unwin Hyman, Boston. Masterman, G.J., Cooke, D.R., Berry, R.F., Walshe, J.L., Lee, A.W., Clark, A.H., 2005. Fluid Chemistry, structural setting, and emplacement history of the Rosario Cu–Mo porphyry and Cu–Ag–Au epithermal veins, Collahuasi District, Northern Chile. Econ. Geol. 100, 835–862. McDonough, W.F., Sun, S.-S., 1995. The composition of the Earth. Chem. Geol. 120, 223–253. McMillan, W.J., Panteleyev, A., 1980. Ore deposit models — 1. Porphyry copper deposits. Geosoc. Can. 7, 52–63. Mustard, R., Ulrich, T., Kamenetsky, V.S., Mernagh, T., 2006. Gold and metal enrichment in natural granitic melts during fractional crystallization. Geology 34, 85–88. Ossandón, C.G., Fréraut, C.R., Gustafson, L.B., Lindsay, D.D., Zentilli, M., 2001. Geology of the Chuquicamata mine—a progress report. Econ. Geol. 96, 249–270. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 25, 956–983. Peters, W.C., James, A.H., Field, C.W., 1966. Geology of the Bingham Canyon porphyry copper deposit, Utah. In: Titley, S.R., Hicks, C.L. (Eds.), Geology of the Porphyry Copper Deposits, Southwestern North America. The University of Arizona Press, Tucson, pp. 165–175. Pupin, J.P., 1980. Zircon and granite petrology. Contrib. Mineral. Petrol. 73, 207–220. Qu, X., Xu, X.W., Liang, G.L., Qu, W.J., Du, S.J., Jiang, N., Wu, H.P., Zhang, Y., Xiao, H., Dong, L.H., 2009. Geological and geochemical characteristics of the Mengxi Cu–Mo deposit and its constraint to tectonic setting of the Qiongheba magmatic arc in east Junggar, Xinjiang. Acta Petrol. Sin. 25, 765–776 (in Chinese with English abstract). Redmond, P.B., Einaudi, M.T., Inan, E.E., Landtwing, M.R., Heinrich, C.A., 2004. Copper deposition by fluid cooling in intrusion-centered systems: new insights from the Bingham porphyry ore deposit, Utah. Geology 32, 217–220. Richards, J.P., 2003. Tectono-magmatic precursors for porphyry Cu-(Mo–Au) deposit formation. Econ. Geol. 98, 1515–1533. Richards, J.P., Kerrich, R., 2007. Adakite-like rocks: their diverse origins and questionable role in metallogenesis. Econ. Geol. 102, 537–576. Rowins, S.M., 2000. Reduced porphyry copper–gold deposits: a new variation on an old theme. Geology 28, 491–494. Rudnick, R.L., Fountain, D.M., 1995. Nature and composition of the continental crust: a lower crustal perspective. Rev. Geophys. 33, 267–309. Rusk, B.G., Reed, M.H., Dilles, J.H., 2008. Fluid inclusion evidence for magmatic-hydrothermal fluid evolution in the porphyry copper–molybdenum deposit at Butte, Montana. Econ. Geol. 103, 307–334. Schwartz, G.M., 1942. Progress in the study of exsolution in ore minerals. Econ. Geol. 37, 345–364. Seedorff, E., Dilles, J.H., Proffett Jr., J.M., Einaudi, M.T., Zurcher, L., Stavast, W.J.A., Johnson, D.A., Barton, M.D., 2005. Porphyry deposits: characteristics and origin of hypogene features. Economic Geology, 100TH Anniversary Volume, pp. 251–298. Sides, J.R., 1980. Emplacement of the Butler Hill Granite, a shallow pluton within the St. Francois Mountains batholith, southeastern Missouri. Geol. Soc. Am. Bull. 91, 535–540. Sillitoe, R.H., 1979. Some thoughts on gold-rich porphyry copper deposits. Mineral. Deposita 14, 161–174. Sillitoe, R.H., 2010. Porphyry copper systems. Econ. Geol. 105, 3–41. Sinclair, W.D., 2007. Porphyry deposits. In: Goodfellow, W.D. (Ed.), Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods. Geological Association of Canada, Mineral Deposits Division, Special Publication, 5, pp. 223–243. Singer, D.A., 1995. World class base and precious metal deposits—a quantitative analysis. Econ. Geol. 90, 88–104. Singer, D.A., Berger, V.I., Menzie, W.D., Berger, B.R., 2005. Porphyry copper deposit density. Econ. Geol. 100, 491–514. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of ocean basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in Ocean BasinsGeol. Soc. Spec. Publ. Lond. 42, 313–345. Tomiya, A., Takahashi, E., Furukawa, N., Suzuk, I.T., 2010. Depth and evolution of a silicic magma chamber: melting experiments on a low-K rhyolite from Usu Volcano, Japan. J. Petrol. 51, 1333–1354. Vernon, R.H., 2004. A Practical Guide to Rock Microstructure. Cambridge University Press (594 pp.). Wager, L.R., Brown, G.M., Wadsworth, B., Snoeck, E., Verelst, W.J., 1960. Types of igneous cumulates. J. Petrol. 1, 73–85. Wang, X.D., Liu, D.Q., Tang, Y.L., Zhou, R.H., 2006. Metallogenic characteristics and perspective evaluation of the porphyry copper in Qiongheba, Yiwu county. Xinjiang Geol. 24, 398–404 (in Chinese with English abstract). Wang, D.H., Li, H.Q., Ying, L.J., Mei, Y.P., Chu, Z.L., 2009. Copper and gold metallogenic epoch and prospecting potential in Qiongheba area of Yiwu County, Xinjiang. Mineral Deposits 28, 73–82 (in Chinese with English abstract). Watson, E.B., Wark, D.A., Thomas, J.B., 2006. Crystallization thermometers for zircon and rutile. Contrib. Mineral. Petrol. 151, 413–433. Winter, J.D., 2001. An Introduction to Igneous and Metamorphic Petrology. Prentice Hall 150–210.

156

X.-W. Xu et al. / Ore Geology Reviews 61 (2014) 141–156

Xiao, W.J., Windley, B.F., Yuan, C., Sun, M., Han, C.M., Lin, S.F., Chen, H.L., Yan, Q.R., Liu, D.Y., Qin, K.Z., Li, J.L., Sun, S., 2009. Paleozoic multiple subduction–accretion processes of the southern Altaids. Am. J. Sci. 309, 221–270. Xu, X.W., 2009. Dendritic microfractures. J. Struct. Geol. 31, 1061. Xu, X.W., Cai, X.P., Zhang, B.L., Wang, J., 2004. Explosive microfractures induced by K-metasomatism. J. Asia Earth Sci. 23, 421–423. Xu, X.W., Jiang, N., Yang, K., Zhang, B.L., Liang, G.H., Mao, Q., Li, J.X., Du, S.J., Ma, Y.G., Zhang, Y., Qin, K.Z., 2009. Accumulated phenocrysts and origin of feldspar porphyry in the Chanho area, western Yunnan, China. Lithos 113, 595–611. Xu, X.W., Wu, Q., Huang, X.F., Liu, J., Zhang, Y., 2012a. Formation mechanism and evolution process of copper-rich porphyry magma. Acta Petrol. Sin. 28, 421–432 (in Chinese with English abstract).

Xu, X.W., Zhang, B.L., Liang, G.H., Qin, K.Z., 2012b. Zoning of mineralization in hypogene porphyry copper deposits: insight from comb microfractures within quartz–chalcopyrite veins in the Hongshan porphyry Cu deposit, western Yunnan, SW China. J. Asian Earth Sci. 56, 218–222. Xu, X.W., Jiang, N., Li, X.H., Yang, Y.H., Mao, Q., Wu, Q., Zhang, Y., Dong, L.H., 2013. Tectonic evolution of the East Junggar terrane: Evidence from the Taheir tectonic window, Xinjiang, China. Gondwana Res. 24, 578–600. http://dx.doi.org/ 10.1016/j.gr.2012.11.007. Zhang, Y., Liang, G.L., Wu, Q.Y., Wu, Q., Zhang, Z.F., Wu, H.P., Qu, X., Xu, X.W., 2010. Gechronology and Hf isotope evidences for early paleozoic magmatism in the Qiongheba area, East Junggar, Xinjiang, China. Acta Petrol. Sin. 25, 2389–2398 (in Chinese with English abstract).