39Ar geochronology

Journal of Asian Earth Sciences 41 (2011) 525–536

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Magmatic-hydrothermal evolution of the Cretaceous Duolong gold-rich porphyry copper deposit in the Bangongco metallogenic belt, Tibet: Evidence from U-Pb and 40Ar/39Ar geochronology Jinxiang Li ⇑, Kezhang Qin ⇑, Guangming Li ⇑, Bo Xiao, Junxing Zhao, Lei Chen Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China

a r t i c l e

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Article history: Received 5 May 2010 Received in revised form 25 February 2011 Accepted 2 March 2011 Available online 13 March 2011 Keywords: Gold-rich porphyry copper deposit Zircon U–Pb geochronology 40 Ar/39Ar geochronology Duolong Bangongco metallogenic belt Tibet

a b s t r a c t The Duolong gold-rich porphyry copper deposit was recently discovered and represents a giant prospect (inferred resources of 4–5 Mt fine-Cu with a grade of 0.72% Cu; 30–50 t fine-gold with a grade of 0.23 g/t Au) in the Bangongco metallogenic belt, Tibet. Zircon SHRIMP and LA-ICP-MS U–Pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes, the first at about 121 Ma (Bolong mineralized granodiorite porphyry (BMGP) and barren granodiorite porphyry (BGP)) and the second about 116 Ma (Duobuza mineralized granodiorite porphyry (DMGP)). Moreover, the basaltic andesites also have two episodes at about 118 Ma and 106 Ma, respectively. One andesite yields an U–Pb zircon age of 111.9 ± 1.9 Ma, indicating it formed after the multiple granodiorite porphyries. By contrast, the 40Ar/39Ar age of 115.2 ± 1.1 Ma (hydrothermal K-feldspar vein hosted in DMGP) reveals the close temporal relationship of ore-bearing potassic alteration to the emplacement of the DMGP. The sericite from quartz-sericite vein (hosted in DMGP) yields a 40Ar/39Ar age of 115.2 ± 1.2 Ma. Therefore, the ore-forming magmatic-hydrothermal evolution probably persisted for 6 m.y. Additionally, the zircon U–Pb ages (106– 121 Ma) of the volcanic rocks and the porphyries suggest that the Neo-Tethys Ocean was still subducting northward during the Early Cretaceous. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The Cretaceous Duolong (Duobuza-Bolong, Duobuza is the northeastern ore section; Bolong is the southwestern ore section) gold-rich porphyry copper deposit was recently discovered by the No.5 Geological Team (at the Bureau of Tibetan Geology and Exploration) in 2000, together with the super-large prospect in the Bangongco metallogenic belt (Fig. 1a), Tibet (inferred resources of 4–5 Mt fine-Cu, with a grade of 0.72% Cu; 30–50 t-fine gold, with a grade of 0.23 g/t Au; Li et al., 2008). Due to the discovery of the Duolong deposit, the Bangongco metallogenic belt may be the third porphyry copper belt following the Yulong and Gangdese (Fig. 1a). All of the deposits belong to the Tethyan-Himalaya metallogenic province. Moreover, the porphyry deposits of the Bangongco metallogenic belt are a Cretaceous, Cu–Au mineralization assemblage and formed in a magmatic active arc setting (Li et al., 2008), differing from those of the Yulong and Gangdese. The porphyry deposits of the Yulong and Gangdese metallogenetic belt respectively formed in the Eocene and Miocene, and both of them belong to ⇑ Corresponding authors. Address: Beitucheng West Road 19#, Chaoyang District, Beijing 100029, PR China. Tel.: +86 10 82998187; fax: +86 10 62010846. E-mail addresses: [email protected] (J.-X. Li), [email protected] (K.-Z. Qin), [email protected] (G.-M. Li). 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.03.008

Cu–Mo mineralization assemblage and formed in a post-collision geotectonic setting (Hou et al., 2004, 2007, 2009; Qu et al., 2004, 2007, 2009; Qin et al., 2005, 2006; Liang et al., 2006, 2009). In addition, the Bangongco metallogenic belt is analogous to the Panagyurishte ore district of the Srednogorie zone in Bulgaria, which formed in the Late Cretaceous (Von Quadt et al., 2002, 2005; Tarkian et al., 2003; Kouzmanov et al., 2009) and is present in the western segment of the Tethyan-Himalaya metallogenetic province. The Late Cretaceous Elatsite porphyry deposit (located about 55–60 km east of Sofia, Bulgaria) in the Panagyurishte ore district has a Cu–Au–PGE mineralization assemblage and was formed in an arc setting (Von Quadt et al., 2002, 2005; Tarkian et al., 2003), resembling the Duolong mineralization. However, the study of the Bangongco metallogenic belt is in its initial stage, and preliminary studies have assessed only the geochronology (Qu and Xin, 2006; Li et al., 2008), fluid inclusions (She et al., 2006; Li et al., 2007) and geochemical characteristics of the Duolong deposit (Li et al., 2008). In this paper, we systematically sample the Duobuza and Bolong mineralized granodiorite porphyry, barren granodiorite porphyry, and mafic – intermediate volcanic rocks (Fig. 1b) from the Duolong gold-rich porphyry copper deposit, and present a new work on their formation age using the precise zircon SHRIMP and LA-ICP-MS U–Pb geochronology methods. Also, we date the hydrothermal K-feldspar, biotite and sericite using

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a

b

Fig. 1. The sketch tectonic and location map (a) (after Hou et al., 2004) and generalized geologic map (b) of the Duolong gold-rich porphyry copper deposit (Li et al., 2008).

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Ar/39Ar geochronology. Finally, we discuss the duration of the magmatic-hydrothermal evolution of the Duolong deposit as well as the implications on the metallotectonic setting of the Bangongco metallogenic belt. 2. Geologic setting of the Duolong gold-rich porphyry copper deposit

sequence of littoral facies, with an EW strike and WNW dip of 50–80°. It is composed of arkosic sandstone, siltstone-interbeded siliceous rock, basalt and dacite. The Late Cretaceous Meiriqie group contains basaltic andesite, dacite, volcanic–clastic rocks, andesite porphyry and andesite (Fig. 1b). The Paleogene Kangtuo group is composed of the brown–red clay and sandy gravel. 2.1. Magmatic activity

The Duolong gold-rich porphyry copper deposit is located ca. 100 km northwest of Gerze city, and north of the BangongcoNujiang suture zone (Fig. 1a). It is a typical volcanic type in the porphyry copper deposit classifications (Mcmillan and Panteleyev, 1980), which formed in the Early Cretaceous and the magmatic arc resulted from the Neo-Tethys Ocean subduction (Li et al., 2008). The stratigraphy is mainly made up of the Middle Jurassic Yanshiping and the Late Cretaceous Meiriqie groups (Fig. 1b). The Middle Jurassic Yanshiping group is a clastic-interbeded volcanic

The hypabyssal intrusive rocks are mainly composed by the multiple granodiorite porphyries, which intruded into the Middle Jurassic Yanshiping group (Fig. 1b). These porphyries mostly appear as stock and dyke. Duobuza mineralized granodiorite porphyry (DMGP; Fig. 2A and B) has a kidney shape with a north–south extension of 200 m and an east–west length of 1000 m (Fig. 1b) in the northeastern section of Duolong deposit. This porphyry mainly contains plagioclase, quartz, chloritized

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Fig. 2. Thin section photomicrographs of the main lithologic units in the Duolong gold-rich copper deposit. A. Duobuza mineralized granodiorite porphyry (DMGP) in the Duobuza ore section, which developed potassic and argillic alteration (DbzJ2-1); B. DMGP that developed an intensive argillic alteration with plagioclase altered to sericite, illite-hydromuscovite and kaolinite (DbzTC-6); C. Bolong mineralized granodiorite porphyry (BMGP) in the Bolong ore section, which developed mainly an argillic alteration (DW2-8); D. barren granodiorite porphyry (BGP), and chlorite altered hornblende (Dbz-crp); E. basaltic andesite from the western partition of the Duolong deposit (Nd-1); F. basaltic andesite (Dw2-1); G. basaltic andesite from the central partition of the Duolong deposit (Dbz-183); H. andesite in the northeastern part of the Duolong deposit (DM1). Hb: hornblende, Pl: plagioclase, Chl: chlorite, Q: quartz, IL-Hm: illite-hydromuscovite, Kao: kaolinite; Kf: K-feldspar.

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Table 1 Description of the lithology of the main magmatic rocks from the Duolong gold-rich porphyry copper deposit, Tibet. Sample

Lithology

Texture

DW2-8

Granodiorite porphyry Granodiorite porphyry Granodiorite porphyry Granodiorite porphyry Granodiorite porphyry Granodiorite porphyry Granodiorite porphyry Basaltic andesite Basaltic andesite Basaltic andesite Andesite

Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst Porphyritic phenocryst

Dbzcd p DbzJ21 DbzTC6 Zk00178 Zk00191 Zk001140 Dbz183 Nd-1 DW2-1 DM-1

Mineral composition

texture, (40–45%) texture, (40–50%) texture, (43–50%) texture, (44–55%) texture, (46–55%) texture, (41–50%) texture, (41–48%) texture, (7–9%) texture, (7–11%) texture, (10–13%) texture, (15–25%)

Alteration

Phenocryst

Matrix

Pl (10–15%, 0.6–3 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (25%, rounded shape, 0.5–2.5 mm), chloritized Hb and Bio (5–10%) Pl (15–20%, 0.5–2.5 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (20%, rounded shape, 0.4–2 mm), Hb and Bio (6–10%) Pl (15–20%, 0.5–4 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (20%, rounded shape, 0.5–2 mm), chloritized Hb and Bio (8–10%) Pl (18–25%, 0.5–3 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (20–22%, rounded shape, 0.4–2.5 mm), chloritized Hb and Bio (6–8%) Pl (20–23%, 0.5–4 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (18–22%, rounded shape, 0.6–3 mm), chloritized Hb and Bio (8–10%) Pl (16–20%, 0.5–3.5 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (20–22%, rounded shape, 0.4–3 mm), chloritized Hb and Bio (5–8%) Pl (18–21%, 0.5–4 mm, Carlsbad-Albite compound twin and oscillatory zoning), Q (17–19%, rounded shape, 0.6–3 mm), chloritized Hb and Bio (6–8%) Hb (2–4%), Pl (5%), Py (<1%), 0.3–3 mm

Q, Pl, Kf; 0.1– 0.2 mm Q, Pl, Kf; 0.1– 0.3 mm Q, Pl, Kf; 0.1– 0.2 mm Q, Pl, Kf; 0.1– 0.2 mm Q, Pl, Kf; 0.1– 0.15 mm Q, Pl, Kf; 0.1– 0.2 mm Q, Pl, Kf; 0.1– 0.2 mm Pl (strip shape), Hb; 0.05–0.1 mm Pl, Hb; 0.05– 0.15 mm Pl (strip shape), Hb; 0.05–0.1 mm Pl, Hb, Q; 0.05– 0.1 mm

Hb (1–5%), Pl (6%), Py (<1%), 0.3–2 mm Hb (2–5%), Pl (8%), Py (<1.5%), 0.3–2.5 mm Pl (10–15%), Hb (5–10%); 1–2 mm

Argillicpotassic Weakly potassic Argillicpotassic Argillicpotassic Argillicpotassic Argillicpotassic Argillicpotassic Fresh Fresh Fresh Fresh

Abbreviations: Pl, plagioclase; Q, quartz; Hb, hornblende; Bio, biotite; Kf, K-feldspar.

hornblende and biotite, and shows argillic-potassic alteration assemblages (Table 1). Bolong mineralized granodiorite porphyry (BMGP; Fig. 2C) exposes as an elliptical shape of the width of 200 m and length of 300 m (Fig. 1b) in the southwestern section. This porphyry is similar to the DMGP on the mineral composition (Table 1), and dominantly shows argillic alteration. In addition, the restricted appearance of the barren granodiorite porphyry (BGP, Fig. 2D) occurs in the central section of Duolong deposit. The texture and mineral assemblage are similar to the DMGP and BMGP. But it is weakly altered by the hydrothermal fluid (Table 1). Based on the alteration characteristics, volcanic rocks (Fig. 2) can be divided into pre- or syn-mineralization basaltic andesite, post-mineralization basaltic andesite and andesite. The pre- or syn-mineralization basaltic andesites occur in the northeastern and southwestern section, and show weak and intensive propylitic alteration caused by the mineralized porphyries. The basaltic andesites (Fig. 2E) have porphyritic texture and are mainly composed of plagioclase, hornblende and minor pyroxene (Table 1). The post – mineralization (Fig. 2F and G) basaltic andesites are distributed in the central section of Duolong deposit. The post-mineralization fresh andesite (Fig. 2H) occurs in the northeastern section of Duolong deposit, and mainly contains plagioclase and hornblende (Table 1). Geochemical characteristics show that the porphyries and volcanic rocks have the same arc magma characteristics (Li et al., 2008): a high-K calc-alkaline series, a depletion of HFSE (such as Nb, Ta, Zr and Hf), and an enrichment in large ion lithophile elements (such as Rb and Ba) of basaltic andesite (SiO2 of 49–53%), andesite (SiO2 of 58%) and granodiorite porphyry (SiO2 of 65– 68%; Li et al., 2008).

propylitic alteration zone from the ore-bearing porphyry center outwards and upwards. However, the phyllic alteration is not well developed and quartz–sericite veins occur only locally. 2.2.1. Potassic alteration zone Dispersive K-feldspathization displays a dominant development. The secondary K-feldspar altered mainly the plagioclase phenocryst and the dispersive matrix. The K-feldspar alteration halo also occurred at the edge of quartz–chalcopyrite–magnetite veins (A-type, Gustafson and Hunt, 1975). Additionally, quartz – K-feldspar veinlet occurred. Moreover, secondary biotite replaces hornblende, primary biotite, and other Mg- and Fe-minerals. Quartz–biotite–chalcopyrite veins and biotite veinlets (EB type, Gustafson and Quiroga, 1995) were recognized. Hydrothermal magnetites developed dominantly in the potassic alteration zone, while chalcopyrite coexists closely with magnetite. Petrographic observations suggest that magnetite may be formed at the same time or slightly earlier than the chalcopyrite. Moreover, the potassic alteration zone is mostly developed in the mineralized granodiorite porphyry and at depth of the mineralized body. It was superposed by an intermediate argillic alteration. 2.2.2. Intermediate argillic zone This zone is superposed on the potassic alteration zone. It is characterized mainly by kaolinization and illitization-hydromuscovitation of plagioclase and chloritization of biotite. The quartz– chalcopyrite vein (chalcopyrite present in the center of the vein, with argillic alteration halo; B type, Gustafson and Hunt, 1975), and chalcopyrite veinlets occur in the intermediate argillic alteration zone.

2.2. Hydrothermal alterations At Duolong deposit, a wide range of hydrothermal alteration is developed, comprising mainly albitization, biotitization, K-feldspathization, sericitization, silicification, epidotization, chloritization, illitization, and kaolinization. In addition, these alterations occur in an area of more than 10 km2. The alteration zone can be divided into the potassic alteration, intermediate argillic and

2.2.3. Propylitic zone This zone occurs mainly in the pre-mineralization basaltic andesite (in the Duobuza section). The main alteration minerals contain epidote, chlorite and carbonate. Moreover, the chlorite replaces biotite phenocryst rims, cleavages and centers. The carbonate, quartz, epidote and other minerals fill the amygdalas of the basaltic andesite.

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2.2.4. Phyllic alteration Only quartz–sericite veinlets occur in the local area, consisting with a typical alteration model of the gold-rich porphyry copper deposit (Sillitoe, 2000). 2.3. Mineralization characteristics At present, the Duobuza mineralization (the northeastern ore body of the Duolong copper deposit) occurs in the granodiorite porphyry and within the contact zone of the wall rock of feldspar quartz sandstone from the Middle Jurassic Yanshiping group. Furthermore, it is closely associated with the potassic alteration zone, superposing by the intermediate argillic alteration. Moreover, Duobuza ore body has been controlled with a width (north–south) of about 100–400 m, a length (east–west) of about 1400 m, a 200° (SW) dip and an angle of 65–80°. The mineralization displays a certain degree of vertical variation, which possesses a stockwork of disseminated veinlets in the upper part of the ore body with a gradual transition to sparsely disseminated ore in the lower part, accordingly, a reduced copper content. A preliminary analysis reveals a positive correlation between the gold and copper (Li et al., 2007). The measured amount of the resource is 2.7 Mt fineCu with a grade of 0.94% and 13 t fine Au with a grade of 0.21 g/t in the Duobuza ore body (Li et al., 2008). The Bolong ore section of the Duolong copper deposit is of about 900 m width and of about 1000 m length with a lateral vergence towards the southeast. The estimated copper resources of Bolong ore section are around 2.68 Mt with a mean grade of 0.55%, while the estimated gold resources are around 28 t with a mean grade of 0.24 g/t (Li et al., 2008). The hypogene ore minerals are composed mainly of chalcopyrite and magnetite, followed by pyrite, hematite, rutile, and minor chalcocite, bornite and native gold. In general, hydrothermal magnetite closely coexists with chalcopyrite in the Duolong deposit. The intimate relationship between the copper–gold and hydrothermal magnetite is consistent with the mineralization characteristics of a typical gold-rich porphyry copper deposit (Sillitoe, 2000; Li et al., 2006; Imai and Nagai, 2009). Quartz – molybdenite veins are sparsely present. The amount of chalcopyrite is greater than that of bornite and far more than pyrite. Chalcopyrite occurs mainly as disseminated stockwork veinlets, while bornite occurs mainly as blebs exsolution from chalcopyrite. Furthermore, K-feldspar, albite, quartz, sericite, chlorite, carbonate, illite and gypsum are associated with the hypogene minerals. 3. Analytical methods and results of the zircon U–Pb and 40 Ar/39Ar geochronology 3.1. Zircon U–Pb geochronology 3.1.1. Zircon SHRIMP U–Pb geochronology Based on detailed field work, the DMGP (DbzJ2-1), and BMGP (DW2-8) and basaltic rocks (Nd-1, Dbz-183; Fig. 1b) were sampled for SHRIMP zircon U–Pb geochronology. Zircons were extracted using conventional separation techniques and then handpicked under a binocular microscope. Together with the TEMORA zircon standard (Black et al., 2003), they were mounted in epoxy and polished to expose the cores of the grains. Pictures were taken with reflection and transmission light microscopy and under cathodoluminescence (CL) using a scanning electron microscope. U–Pb dating was performed on the SHRIMP II at the Beijing SHRIMP Center at the Chinese Academy of Geological Sciences. The spot size of the ion beam is between 25 and 30 lm. The SL13 (572 ± 1.2 Ma, U = 238 ppm) and the TEMORA

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(417 ± 1.1 Ma) standards were used in the analyses, as discussed by Black et al. (2003). The ablation spot sites for analysis were selected on the basis of the cathodoluminescence and microscope images. In order to maintain precision, one TEMORA analysis was performed after every three or four spots on the sample zircons during data collection. The ages and concordia diagrams were produced with the SQUID 1.03 (Ludwig, 2001) and ISOPLOT/Ex 2.06 (Ludwig, 1999) programs. The uncertainties for individual analyses (ratios and ages) in tables are quoted at the 1d level, whereas the errors on weighted mean ages are quoted at the 2d level in figures. The zircon SHRIMP U–Pb data are presented in Supplementary Table A1. 3.1.1.1. Mineralized porphyries. The size of the zircon from the Duobuza and Bolong mineralized granodiorite porphyry (DbzJ2-1, DW2-8) changes from 150 to 400 lm. Their Th/U ratios range from 0.45 to 0.9 and are higher than 0.1 (the value of magmatic zircon; Fernando et al., 2003). The CL images indicate that the majority of the zircons have a euhedral crystal form and an obvious oscillatory zone (Fig. 3a and c), which indicates that these zircons have a magmatic origin and that their age can represent the crystallization age of the granodiorite porphyry (Song et al., 2002; Fernando et al., 2003; Samuel and Mark, 2003). The zircon 207Pb/235U–206Pb/238U concordia age of the DMGP (DbzJ2-1) from the northeastern ore section of the Duolong deposit is 116.8 ± 1.7 Ma (n = 12, MSWD = 1.2; Fig. 3b). The zircon 207Pb/235U–206Pb/238U concordia age of the BMGP (DW2-8) from the southwestern ore section is 121.1 ± 1.7 Ma (n = 9, MSWD = 0.8; Fig. 3d). One zircon with the U–Pb age of 115.2 ± 2.7 Ma may be contaminated. 3.1.1.2. Basaltic andesites. The zircon size, which ranges between 100 and 350 lm (Fig. 3e and g), of the basaltic andesite (Nd-1, Dbz-183) is slightly smaller than that of the mineralized granodiorite porphyries. These zircons have a magmatic origin that was identified by their euhedral crystal form, obvious oscillatory zone (Fig. 3e and g), and their Th/U ratios (0.38–1.77) higher than 0.1 (Song et al., 2002; Fernando et al., 2003; Samuel and Mark, 2003). Zircon U–Pb age of basaltic andesite (Dbz-183) show two groups as follows. One group yields a 207Pb/235U–206Pb/238U concordia age (Fig. 3f) of 105.7 ± 1.7 Ma (n = 7, MSWD = 1.0), representing the true crystallization age of basaltic andesite. The other group yields an older 207Pb/235U–206Pb/238U concordia age (Fig. 3f) of 121.5 ± 1.2 Ma (n = 4, MSWD = 1.3), possibly representing the age of inherited zircon. Zircon 207Pb/235U–206Pb/238U concordia age of the basaltic andesite (Nd-1) from the western part of the Duolong deposit (Fig. 3h) is 117.9 ± 1.5 Ma (n = 11, MSWD = 1.1), which indicates the basaltic andesite formed after the BMGP. 3.1.2. Zircon LA-ICP-MS U–Pb geochronology Zircon LA-ICP-MS U–Pb dating of intensive argillic DMGP (DbzTC-6), BGP (Dbz-cdp), basaltic andesite (Nd-1, DW2-1) and andesite (DM-1) was performed. The analyses were conducted on a Neptune MC-ICP-MS equipped with a 193-nm laser at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing, China. During the analyses, a laser repetition rate of 6– 8 Hz at 100 mJ was used. The spot sizes are 40–60 lm. Each spot analysis consisted approximately of 30 s background acquisition and 40 s sample data acquisition. The detailed analytical technique has been described by Yuan et al. (2004) and Xie et al. (2008). 207 Pb/206Pb, 206Pb/238U, 207Pb/235U (235U = 238U/137.88), and 208 Pb/232Th ratios are corrected by the Harvard zircon 91,500 (Wiedenbeck et al., 1995) as the external calibrant. Common Pb contents were evaluated using the method described by Anderson (2002). The age calculations and concordia diagrams were generated using ISOPLOT (ver 3.0) (Ludwig, 2003). The uncertainties

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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig. 3. Cathodoluminescence (CL) images (a, c, e, g) and 207Pb/235U–206Pb/238U concordia plots (b, d, f, h) of SHRIMP U–Pb dating of zircons from DMGP, BMGP and basaltic andesite (Dbz-183, Nd-1) in the Duolong gold-rich porphyry copper deposit, Tibet. Errors are quoted at the 2d level.

for individual analyses (ratios and ages; in tables) are quoted at the 1d level, whereas the errors on concordia and weighted mean ages

are quoted at the 2d level in figures. The zircon LA-ICP-MS U–Pb data are presented in Supplementary Table A2.

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The size of the zircons from the intensive argillic DMGP (DbzTC6), BGP (Dbz-cdp), andesite (DM-1) and basaltic andesite (Nd-1, DW2-1) changes from 150 to 500 lm. CL images indicate that the majority of the zircons have a euhedral crystal form and an obvious oscillatory zone. Their Th/U ratios range from 0.39 to 0.98 and are all higher than 0.1. These zircon characters indicate that they have a magmatic origin (Song et al., 2002; Fernando et al., 2003; Samuel and Mark, 2003). 3.1.2.1. Mineralized and barren porphyries. The zircon Pb/235U–206Pb/238U concordia age of the intensive argillic DMGP (DbzTC-6) is 116.4 ± 2.5 Ma (n = 15, MSWD = 1.1; Fig. 4a), and the weighted mean age is 116.1 ± 1.9 Ma (n = 15, MSWD = 1.5; Fig. 4b). This age is in good concordance with the age of DMGP (DbzJ2-1). The zircon 207Pb/235U–206Pb/238U concordia age of the BGP (Dbz-cdp) is 120.7 ± 1.9 Ma (n = 15, MSWD = 1.0; Fig. 4c), while the weighted mean age is 122.4 ± 1.9 Ma (n = 15, MSWD = 1.4; Fig. 4d), which is concordant within their errors with the crystallization age of the BMGP (DW2-8).

207

3.1.2.2. Basaltic andesites and andesite. The zircon 207Pb/235U–206Pb/238U concordia age of the andesite (DM-1) is 111.9 ± 1.9 Ma (n = 17, MSWD = 0.9; Fig. 4e), and the weighted mean age is 110.9 ± 1.8 Ma (n = 17, MSWD = 1.2; Fig. 4f). The zircon 207 Pb/235U–206Pb/238U concordia age of the basaltic andesite (Nd-1) is 118.1 ± 1.6 Ma (n = 11, MSWD = 0.3; Fig. 4g), while the weighted mean age is 118.5 ± 1.4 Ma (n = 11, MSWD = 0.3; Fig. 4h), which is concordant within their errors with the SHRIMP zircon U–Pb age of the same sample. The zircon 207Pb/235U–206Pb/238U concordia age of the basaltic andesite (DW2-1) is 106.4 ± 1.4 Ma (n = 14, MSWD = 1.1; Fig. 4i), while the weighted mean age is 105.7 ± 1.6 Ma (n = 14, MSWD = 1.5; Fig. 4j), which is concordant within the error range of the SHRIMP zircon U–Pb age of the basaltic andesite (Dbz-183), both north of the mineralized Bolong area. 3.2.

40

Ar/39Ar geochronology

The secondary K-feldspar (Zk001-91), biotite (Zk001-78) and sericite (Zk001-140) were respectively separated for 40Ar/39Ar dating from the depth of 91 m, 78 m, and 140 m belonging to the drill hole No. Zk001 of Duobuza area (Fig. 1b). They all belong to the intermediate argillic alteration superposed on the potassic alteration zone, and hosted in the DMGP. The secondary K-feldspar is separated from the quartz – K-feldspar – chalcopyrite veinlet (width of 6–8 mm). The secondary biotite typically occurs as fine-ragged clots that have replaced the igneous groundmass, and micro-scale chlorite intergrowths occur within it. The secondary sericite is derived from the quartz – sericite – minor pyrite veinlet (width of 6–7 mm). The 40Ar/39Ar step-heating analysis was performed at the Laboratory of Paleomagnetism and Geochronology (SKL-LE) at the Chinese Academy of Sciences, Beijing, on a MM5400 mass spectrometer that operated in static mode. The detailed experimental process has been previously reported (Wang et al., 2004, 2006). The secondary K-feldspar, biotite, sericite and Bern-4 M standards were irradiated in vacuo within a cadmium-coated quartz vial for 47.5 h in position H8 of the reactor at the facility of Beijing Atomic Energy Research Institute (49–2). The Bern-4 M biotite standard age is 18.7 ± 0.1 Ma, recalculating by more appropriate Ga1550 biotite standard age of 98.8 Ma (Renne et al., 1998) than of 97.8 Ma (Baksi et al., 1996). The data were corrected by the system blanks, mass discrimination, interfering Ca, K-derived argon isotopes and the decay of 37Ar and 39Ar. The plateau and isochron ages were calculated using ArArCALC (Koppers, 2002). Plateau ages were defined using the criteria of Dalrymple and

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Lanphere (1971) and Fleck et al. (1977), specifying the presence of at least three contiguous gas fractions that together represent more than 50% of the total 39Ar released from the sample and for which no age difference can be detected between any two fractions at the 95% confidence level. Furthermore, inverse isochron diagrams test the assumption made in the plateau ages where any trapped nonradiogenic Ar has an atmospheric composition (40Ar/36Ar = 295.5). Both the plateau and inverse isochron age uncertainties are given at a 2r confidence level. The age results from the step-heating experiments are presented in Supplementary Table A3. The plateau age of secondary K-feldspar (Zk001-91) from the DMGP is 115.2 ± 1.1 Ma (Fig. 5a), which accounts for about 75% of the released 39Ar. The inverse isochron age is 114.5 ± 1.5 Ma with an elevated (40Ar/36Ar)i ratio of 325.6 ± 5.2 (Fig. 5b). The age spectrum of secondary biotite from the altered granodiorite porphyry (Zk001-78) is highly disturbed. The high apparent age spectrum (Fig. 5c) may be caused by 39Ar recoil due to the presence of minor chlorite (Snee, 2002), which is consistent with the chloritization of biotite along rims and fractures. The age calculations on three steps gives an age of 119.2 ± 1.1 Ma (Fig. 5c), and the inverse isochron age of 119.9 ± 2.3 Ma with the (40Ar/36Ar)i ratio of 154.5 ± 246.7, which deviates from the atmospheric ratio of 295.5 (Fig. 5d). This biotite alteration age is older than zircon U– Pb age of 116.8 ± 1.7 Ma or partly overlapped with it. So, we conclude that this biotite 40Ar/39Ar age do not have any geological significance. The age spectrum of secondary sericite from the Zk001-140 quartz–sericite vein is highly disturbed and L-shaped, and shows excess argon (40Ar) at least in the first three steps. This suggests that excess argon trapped in the sericite could have affected the plateau age. Therefore, the age spectrum of five steps gives an integrated age of 115.2 ± 1.2 Ma, including 32% of the released 39Ar (Fig. 5e). The inverse isochron yields an good age of 115.5 ± 1.5 Ma with the (40Ar/36Ar)i ratio of 290.8 ± 11.7 (Fig. 5f), which is in good concordance within their errors with the integrated age. This indicates that the integrated age of 115.2 ± 1.2 Ma might be reliable.

4. Discussion 4.1. Magmatic-hydrothermal evolution 4.1.1. Magma evolution Zircon U–Pb geochronology of porphyries and volcanic rocks can reveal the complex history of magmatic evolution (Harris et al., 2004; Deckart et al., 2005). At Duolong deposit, Zircon U– Pb age (120.7 ± 1.9 Ma) of the BGP (Dbz-cdp) is concordant within their errors with the crystallization age (121.1 ± 1.7 Ma) of the BMGP (DW2-8). This shows that BMGP (DW2-8) and BGP (Dbzcdp) were nearly simultaneously emplaced at about 121 Ma. Subsequently, the emplacement of DMGP occurred at about 116 Ma. Therefore, these ages show that there may have been at least two episodes of porphyritic intrusions in this deposit, which generally possesses a consistent model of multi-pulse ore-bearing magmatic activities in other porphyry copper deposits (Sillitoe, 2000; Ballard et al., 2001; Maksaev et al., 2004; Deckart et al., 2005). Basaltic andesite (Nd-1) from the western part of the Duolong deposit were erupted between BMGP and DMGP, as evidenced by the SHRIMP zircon U–Pb age of 117.9 ± 1.5 Ma and the LA-ICPMS zircon U–Pb age of 118.1 ± 1.6 Ma. The SHRIMP zircon U–Pb age of the fresh basaltic andesite (Dbz-183) is 105.7 ± 1.7 Ma, which is concordant within their uncertainties with the LA-ICPMS zircon U–Pb age of 106.4 ± 1.4 Ma for the basaltic andesite (DW2-1) in the Bolong ore section. This indicates that they formed

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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

Fig. 4. 207Pb/235U–206Pb/238U concordia (a, c, e, g, i) and weighted mean (b, d, f, h, j) ages of LA-ICP-MS zircon U–Pb dating of DMGP (DbzTC-6), BGP (Dbz-cdp), andesite (DM-1), and basaltic andesite (Nd-1, DW2-1) from Duolong gold-rich porphyry copper deposit in Tibet. Errors are quoted at the 2d level.

clearly later than the mineralized porphyries with an age of 121 and 116 Ma, and are post-mineralization volcanic rocks. In addition, the LA-ICP-MS zircon U–Pb age of the andesite (DM-1) is 111.9 ± 1.9 Ma, which is also significantly later than the formation

age of the mineralized porphyries and the mineralization age. This shows that this andesite is also post-mineralization volcanic rock. In conclusion, the magmatic evolution sequence of the Duolong gold-rich porphyry copper deposit is as follows (Fig. 6): the earliest

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K

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 5. The 40Ar/39Ar ages (a, c, e) and their corresponding inverse isochon ages (b, d, f) of the hydrothermal K-feldspar, biotite, and sericite from the Duolong porphyry copper deposit, Tibet. WMPA: weighted mean plateau age.

BMGP (DW2-8) and BGP (Dbz-cdp) ? basaltic andesite (Nd-1) ? DMGP (DbzJ2-1, DbzTC-6) ? andesite (DM-1) ? basaltic andesite (Dbz-183, DW2-1). The magma composition show an evolution trend from the intermediate-acid to basic. 4.1.2. Duration of magmatic-hydrothermal evolution Estimates of the longevity of igneous-related hydrothermal ore deposits vary significantly among deposits. Short-lived hydrothermal systems ranging from 100,000 to 300,000 yr were confirmed in some porphyry – related deposits (e.g., Far Southeast-Lepanto, Arribas et al., 1995; Round Mountain, Henry et al., 1995; Potrerillos, Marsh et al., 1997). By contrast, long-lived hydrothermal systems can last for several million years and consist of numerous short-lived hydrothermal pulses, such as La Escondida,

Chile (Padilla-Garza et al., 2004), Chuquicamata, Chile (Ballard et al., 2001), El Teniente (Maksaev et al., 2004), Río Blanco (Deckart et al., 2005), and Bajo de la Alumbrera, Argentina (Harris et al., 2008). At Duolong deposit, two episodes of magmatic-hydrothermal activity have been identified. Firstly, the published molybdenite (quartz – molybdenite veins, hosted in the BMGP and wall rock) Re–Os age of 118.0 ± 1.5 Ma (2d, She et al., 2006), indicating the Cu–Au mineralization is closely related to the emplacement of the BMGP (Fig. 6). Secondly, the secondary K-feldspar from the potassic zone yields a good 40Ar/39Ar plateau age of 115.2 ± 1.1 Ma, which overlaps within their uncertainties with the U–Pb age of the DMGP. The 40Ar/39Ar age of 115.2 ± 1.2 Ma for secondary sericite (from quartz–sericite veinlet hosted in the DMGP) is

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Fig. 6. Duration of ore-forming magmatic-hydrothermal evolution in Duolong gold-rich porphyry copper deposit, Tibet.

consistent with the 40Ar/39Ar plateau age of hydrothermal K-feldspar. The Cu–Au mineralization is dominantly associated with potassic alteration assemblages. Therefore, the two 40Ar/39Ar ages consistency suggests that the hypogene Cu–Au mineralization and potassic alteration probably was produced during a short period. These 40Ar/39Ar ages reveal the close temporal relationship with the emplacement of DMGP. Finally, combined with the U– Pb ages of BMGP and DMGP mineralized porphyries, the duration of magmatic-hydrothermal evolution probably persisted for 6 m.y. (Fig. 6). 4.2. Implications for the tectonic setting The Bangongco-Nujiang suture zone is an important plate boundary in the northern part of the Qinghai-Tibet Plateau (Yin and Harrison, 2000), but detailed studies are lacking. The opening and closure time of the Bangongco-Nujiang Neo-Tethys Ocean has been on debate. The latest research results of the 1:25 million regional geological survey show that the Neo-Tethys Ocean formed during the Late Permian – Early Triassic (Ren and Xiao, 2004). Whole-rock Sm-Nd dating of the Shemalagou gabbro in the central section of the Bangongco-Nujiang suture zone indicated that the Neo-Tethys Ocean may have opened in the Early Jurassic (Qiu et al., 2004). Based on the geological phenomena of the Upper Jurassic stratigraphy unconformity on the ophiolite, the NeoTethys Ocean may have closed in the Early Cretaceous (Guo et al., 1991). However, the Duoma pillow basalt and the Tarenben OIB-type basalt of the Late Cretaceous (around 110 Ma) indicate that the Bangongco-Nujiang Ocean had not yet completely demised around 110 Ma (Zhu et al., 2006) and may imply that the closure time of the Neo-Tethys Ocean was later than the previous opinion of Late Jurassic – Early Cretaceous (Huang and Chen, 1987; Yin and Harrison, 2000; Kapp et al., 2003). The boninitic (basaltic andesite and andesite; SiO2 > 53%, MgO > 7% and TiO2 < 0.6; Ti/V ratio of 5–13, Ti/Sc of 40–80) rocks

that form in the forearc of the island arc setting were discovered in the ophiolite melange, which suggests that intra-ocean subduction occurred (Shi et al., 2004). Moreover, the gabbro of the SSZ (Super subduction zone)-type ophiolite yield a zircon SHRIMP U– Pb age of 167.0 ± 1.4 Ma, which indicates the Neo-Tethys Ocean subducted at least during the Middle Jurassic (Shi, 2007). According to a regional tectonic and sedimentary facies analysis, the Neo-Tethys Ocean subducted northward under the Qiangtang block in the Late Jurassic (Huang and Chen, 1987; Kapp et al., 2003). Significantly, the subduction polarity of the Neo-Tethys Ocean has been debated to be as follows: subduction northward during the Late Triassic – Early Cretaceous (Murphy et al., 1997; Kapp et al., 2003; Ding et al., 2003; Zhang et al., 2004; Li et al., 2008) or subduction southward during the Late Jurassic – Early Cretaceous (Pan et al., 1997, 2004; Mo et al., 2005; Zhu et al., 2009). In summary, the opening and closure times of the Bangongco-Nujiang Neo-Tethys Ocean and its evolution process have been a topic of debate. Trace element geochemistry characteristics and tectonic diagrams of volcanic rocks from the Duolong gold-rich porphyry copper deposit confirm that this deposit formed in a continental margin arc setting (Li et al., 2008). The zircon U–Pb ages of the volcanic rocks and the porphyries fall in the range from 106 Ma to 121 Ma, and the Duolong porphyry copper deposit is located north of the Bangongco-Nujiang suture zone. These evidences suggest that the Neo-Tethys Ocean still subducted northward during the Early Cretaceous. And its closure time should be later than 106 Ma. 5. Conclusions Zircon SHRIMP and LA-ICP-MS U–Pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes at Duolong deposit, the first at about 121 Ma (BMGP and BGP) and the second about 116 Ma (DMGP). The 40Ar/39Ar age of 115.2 ± 1.1 Ma (hydrothermal K-feldspar vein hosted in DMGP)

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and 40Ar/39Ar age of 115.2 ± 1.2 Ma (quartz–sericite vein hosted in DMGP) reveals the close temporal relationship with the second porphyritic intrusions. The ore-forming magmatic – hydrothermal evolution probably persisted for 6 m.y. Moreover, the basaltic andesites also have two episodes, the first (about 118 Ma) formed between the two episodes of porphyritic intrusions, and the second (about 106 Ma) and andesite (about 112 Ma) formed after the multiple granodiorite porphyries. Additionally, the zircon U–Pb ages (106–121 Ma) of the volcanic rocks and the porphyries formed in a continent margin arc setting, suggest that the Neo-Tethys Ocean was still subducting northward during the Early Cretaceous. Acknowledgments This article was funded by the Natural Science Foundation Project (40902027, 40672068, 40772066) and the China Postdoctoral Science Foundation (20090450567). We obtained support and help from Mr. Tianping Zhang (a senior geologist) and other geologists in the No.5 Geological Team at the Tibet Bureau of Geology and Exploration. We also obtained specific guidance and assistance from Prof. Quanren Yan concerning the SHRIMP zircon U–Pb dating process at the Beijing SHRIMP Center, Chinese Academy of Geological Sciences; and from Assistant Prof. Liewen Xie and Yueheng Yang concerning the LA-ICP-MS zircon U–Pb dating process; and from Prof. Fei Wang and Huaiyu He concerning the 40Ar/39Ar dating process at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Constructive comments by Bor-ming Jahn, Juhn G. Liou, and Katja Deckart improved the manuscript. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jseaes.2011.03.008. References Anderson, T., 2002. Correction of common lead in U-Pb analyses that do not report 204 Pb. Chemical Geology 192, 59–79. Arribas Jr., A., Hedenquist, J.W., Itaya, T., Okada, T., Concepción, R.A., Garcia, J.S., 1995. Contemporaneous formation of adjacent porphyry and epithermal Cu-Au deposits over 300 ka in northern Luzon, Philippines. Geology 23, 337–340. Baksi, A.K., Archibald, D.A., Farrar, E., 1996. Intercalibration of 40Ar/39Ar dating standards. Chemical Geology 129, 307–324. Ballard, J.R., Palin, J.M., Williams, I.S., Campbell, I.H., 2001. Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by ELA-ICP-MS and SHRIMP. Geology 29, 383–386. Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W., Korsch, R.J., Foudoulis, C., 2003. TEMORA1: a new zircon standard for Phanerozoic U-Pb geochronology. Chemical Geology 200, 155–170. Dalrymple, G.B., Lanphere, M.A., 1971. 40Ar/39Ar technique of K-Ar dating: a comparison with the conventional technique. Earth and Planetary Science Letters 12, 300–308. Deckart, K., Clark, A.H., Aguilar, C., Vargas, R., Bertens, A., Mortensen, J.K., Fanning, M., 2005. Magmatic and hydrothermal chronology of the giant Rio Blanco porphyry copper deposit, central Chile: implications of an integrated U-Pb and 40 Ar/39Ar database. Economic Geology 100, 905–934. Ding, L., Kapp, P., Yin, A., Deng, W.M., Zhong, D.L., 2003. Early Tertiary volcanism in the Qiangtang terrane of central Tibet: evidence for a transition from oceanic to continental subduction. Journal of Petrology 44, 1833–1865. Fernando, C., John, M.H., Paul, W.O.H., Peter, K., 2003. Atlas of zircon textures. Reviews in Mineralogy and Geochemistry 53, 469–500. Fleck, R.J., Sutter, J.F., Elliot, D.H., 1977. Interpretation of discordant 40Ar/39Ar age spectra of Mesozoic tholeiites from Antarctica. Geochimica et Cosmochimica Acta 41, 15–32. Guo, T.Y., Liang, D.Y., Zhang, Y.Z., 1991. Geology of Ngari, Tibet (Xizang). The Chinese University of Geosciences Press. pp. 1–464 (in Chinese with English abstract). Gustafson, L.B., Hunt, J.P., 1975. The porphyry copper deposit at El Salvador, Chile. Economic Geology 70, 857–912. Gustafson, L.B., Quiroga, G.J., 1995. Patterns of mineralization and alteration below the porphyry copper orebody at El Salvador, Chile. Economic Geology 90, 2–16. Harris, A., Dunlap, W., Reiners, P., Allen, C., Cooke, D., White, N., Campbell, I., Golding, S., 2008. Multimillion year thermal history of a porphyry copper deposit: Application of U-Pb, 40Ar/39Ar and (U-Th)/He chronometers, Bajo de la Alumbrera copper-gold deposit, Argentina. Mineralium Deposita 43, 295–314.

535

Harris, A.C., Allen, C.M., Bryan, S.E., Campbell, I.H., Holcombe, R.J., Palin, J.M., 2004. ELA-ICP-MS U-Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu-Au deposit: implications for porphyry-related mineralization. Mineralium Deposita 39, 46–67. Henry, C.D., Elson, H.B., Castor, S.B., 1995. Brief duration of hydrothermal activity at Round Mountain, Nevada, determined from 40Ar/39Ar geochronology. Geological Society American Abstract Program 27, A329. Hou, Z.Q., Xie, Y.L., Xu, W.Y., Li, Y.Q., Zhu, X.K., Khin, Z., Beaudoin, G., Rui, Z.Y., Wei, H.A., Ciren, L., 2007. Yulong deposit, eastern Tibet: a high-sulfidation Cu-Au porphyry copper deposit in the eastern Indo-Asian collision zone. International Geology Review 49, 235–258. Hou, Z.Q., Gao, Y.F., Qu, X.M., Rui, Z.Y., Mo, X.X., 2004. Origin of adakitic intrusives generated during mid-Miocene East–west extension in southern Tibet. Earth and Planetary Science Letters 220, 139–155. Hou, Z.Q., Yang, Z.M., Qu, X.M., Meng, X.J., Li, Z.Q., Beaudoin, G., Rui, Z.Y., Gao, Y.F., Zaw, K., 2009. The Miocene Gangdese porphyry copper belt generated during post-collisional extension in the Tibetan Orogen. Ore Geology Reviews 36, 25– 51. Huang, J.T., Chen, B.W., 1987. Geological evolution of Tethys Sea around China and its Adjacent Areas. Geological Publishing House. pp. 1–78. Imai, A., Nagai, Y., 2009. Fluid inclusion study and opaque mineral assemblage at the deep and shallow part of the Batu Hijau porphyry copper-gold deposit, Sumbawa, Indonesia. Resource Geology 59, 231–243. Kapp, P., Murphy, M.A., Yin, A., Harrison, M.T., Ding, L., Guo, J.H., 2003. Mesozoic and Cenozoic tectonic evolution of the Shiquanhe area of western Tibet. Tectonics 22, 1029. Koppers, A.A.P., 2002. ArArCALC—Software for 40Ar/39Ar age calculations. Computer Geoscience 28, 605–619. Kouzmanov, K., Moritz, R., von Quadt, A., Chiaradia, M., Peytcheva, I., Fontignie, D., Ramboz, C., Bogdanov, K., 2009. Late Cretaceous porphyry Cu and epithermal Cu-Au association in the Southern Panagyurishte District, Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits. Mineralium Deposita 44, 611–646. Li, G.M., Li, J.X., Qin, K.Z., Zhang, T.P., Xiao, B., 2007. High temperature, salinity and strong oxidation ore-forming fluid at Duobuza gold-rich porphyry copper in the Bangonghu tectonic belt, Tibet: evidence from fluid inclusions study. Acta Petrologica Sinica 23, 935–952 (in Chinese with English abstract). Li, J.X., Li, G.M., Qin, K.Z., Xiao, B., 2008. Geochemistry of porphyries and volcanic rocks and ore-forming geochronology of Duobuza gold-rich porphyry copper deposit in Bangonghu belt, Tibet: constraints on metallogenetic tectonic settings. Acta Petrologica Sinica 24, 531–543 (in Chinese with English abstract). Li, J.X., Qin, K.Z., Li, G.M., 2006. The basic characteristics of gold-rich porphyry copper deposits and their ore sources and evolving processes of high oxidation magma and ore-forming fluid. Acta Petrologica Sinica 22, 678–688 (in Chinese with English abstract). Liang, H.Y., Campbell, I.H., Allen, C., Sun, W.D., Liu, C.Q., Yu, H.X., Xie, Y.W., Zhang, Y.Q., 2006. Zircon Ce4+/Ce3+ ratios and ages for Yulong ore-bearing porphyries in eastern Tibet. Mineralium Deposita 41, 152–159. Liang, H.Y., Sun, W.D., Su, W.C., Zartman, R.E., 2009. Porphyry copper-gold mineralization at Yulong, China, promoted by decreasing redox potential during magnetite alteration. Economic Geology 104, 587–596. Ludwig, K.R., 1999. User’s Manual for Isoplot/Ex, Version 2.06: Age Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication, pp: 1–49. Ludwig, K.R., 2001. SQUID 1.02: A User’s Manual. Berkeley Geochronology Center, Special Publication 2, pp: 1–19. Ludwig, K.R., 2003. ISOPLOT 3.0: A Geochronological Toolkit for Microsoft Excel, Berkeley Geochronology Center, Special Publication No. 4. Maksaev, V., Munizaga, F., McWilliams, M., Fanning, M., Marthur, R., Ruiz, J., Zentilli, M., 2004. New chronology for EI Teniente, Chilean Andes, from U-Pb, 40Ar/39Ar, Re-Os, and fission track dating: implications for the evolution of a supergiant porphyry Cu-Mo deposit. Society of Economic Geologists Special Publication 11, 15–54. Marsh, T.M., Einaudi, M.T., McWilliams, M., 1997. 40Ar/39Ar geochronology of Cu-Au and Au-Ag mineralization in the Potrerillos district, Chile. Economic Geology 92, 784–806. McMillan, W.J., Panteleyev, A.J., 1980. Ore deposit models. 1: porphyry copper deposits. Geoscience Canada 7, 52–63. Mo, X.X., Dong, G.C., Zhao, Z.D., Zhou, S., Wang, L.L., Qiu, R.Z., Zhang, F.Q., 2005. Spatial and temporal distribution and characteristics of granitoids in the Gangdese, Tibet and implication for crustal growth and evolution. Geological Journal of China Universities 11, 281–290 (in Chinese with English abstract). Murphy, M.A., Harrison, T.M., Durr, S.B., Chen, Z., Ryerson, F.J., Kidd, W.S.F., Wang, X., Zhou, X., 1997. Significant crustal shortening in south central Tibet prior to the Indo-Asian collision. Geology 25, 719–722. Padilla-Garza, R.A., Titley, S.R., Eastoe, C.J., 2004. Hypogene evolution of the Escondida porphyry copper deposit, Chile. Society of Economic Geologists Special Publication 11, 141–165. Pan, G.T., Chen, Z.L., Li, X.Z., Yang, Y.J., Xu, X.S., Xu, Q., Jiang, X.S., Wu, Y.L., Luo, J.N., Zhu, T.X., Peng, Y.M., 1997. Geological – Tectonic Evolution in the Eastern Tethys. Geological Publishing House. pp: 1–218 (in Chinese with English abstract). Pan, G.T., Wang, L.Q., Zhu, D.C., 2004. Thoughts on some important scientific problems in regional geological survey of the Qinghai-Tibet Plateau. Geological Bulletin of China 23, 12–19 (in Chinese with English abstract). Qin, K.Z., Li, G.M., Zhang, Q., Li, J.X., Miao, Y., Xiao, B., Zhang, T.P., Duo, J., Li, J.G., Lu, Y., 2006. Metallogenetic conditions and possible occurrences for epithermal

536

J. Li et al. / Journal of Asian Earth Sciences 41 (2011) 525–536

gold mineralizations in Gangdese and Bangonghu velts, Tibet—In view of porphyry-epithermal Cu-Au metallogenetic systematics. In: Proceedings of 8th national conference of mineral deposits, China. Geological Publishing House, pp. 666–670 (in Chinese with English abstract). Qin, K.Z., Tosdal, R.M., Li, G.M., Zhang, Q., Li, J.L., 2005. Formation of the Miocene porphyry Cu (-Mo-Au) deposits in the Gangdese arc, southern Tibet, in a transitional tectonic setting. Mineral Deposit Research: Meeting the Challenge 3, 44–47. Qiu, R.Z., Zhou, S., Deng, J.F., Li, J.F., Xiao, Q.H., Cai, Z.Y., 2004. Dating of gabbro in the Shemalagou ophiolite in the western segment of the Bangong Co-Nujiang ophiolite belt, Tibet-with a discussion of the age of the Bangong Co-Nujiang ophiolite belt. Geology in China 31, 262–268 (in Chinese with English abstract). Qu, X.M., Hou, Z.Q., Li, Y.G., 2004. Melt components derived from a subducted slab in late orogenic ore-bearing porphyries in the Gangdese copper belt, southern Tibetan plateau. Lithos 74, 131–148. Qu, X.M., Hou, Z.Q., Zaw, K., Li, Y.G., 2007. Characteristics and genesis of Gangdese porphyry copper deposits in the southern Tibetan Plateau: preliminary geochemical and geochronological results. Ore Geology Reviews 31, 205–223. Qu, X.M., Hou, Z.Q., Zaw, K., Mo, X.X., Xu, W.Y., Xin, H.B., 2009. A large-scale copper ore-forming event accompanying rapid uplift of the southern Tibetan Plateau: Evidence from zircon SHRIMP U-Pb dating and LA ICP-MS analysis. Ore Geology Reviews 36, 52–64. Qu, X.M., Xin, H.B., 2006. Ages and tectonic environment of the Bangong Co porphyry copper belt in western Tibet, China. Geological Bulletin of China 25, 792–799 (in Chinese with English abstract). Ren, J.X., Xiao, L.W., 2004. Lifting the mysterious veil of the tectonics of the QinghaiTibet Plateau by 1:250000 geological mapping. Geological Bulletin of China 23, 1–11. Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., DePaolo, D.J., 1998. Intercalibration of standards, absolute ages and uncertainties in 40Ar/39Ar dating. Chemical Geology 145, 117–152. Samuel, A.B., Mark, D.S., 2003. High-precision U-Pb zircon geochronology and the stratigraphic record. Reviews in Mineralogy and Geochemistry 53, 305–326. She, H.Q., Li, J.W., Feng, C.Y., Ma, D.F., Pan, G.T., Li, G.M., 2006. The high-temperature and hypersaline fluid inclusions and its implications to the metallogenesis in Duolong porphyry copper deposit, Tibet. Acta Geologica Sinica 80, 1434–1447 (in Chinese with English abstract). Shi, R.D., Yang, J.S., Xu, Z.Q., Qi, X.X., 2004. Discovery of the boninite series volcanic rocks in the Bangong Lake ophiolite mélange, Western Tibet and its tectonic implication. Chinese Science Bulletin 12, 1272–1278. Shi, R.D., 2007. SHRIMP dating of the Bangong Lake SSZ-type ophiolite: constraints on the closure time of ocean in the Bangong Lake-Nujiang River, northwestern Tibet. Chinese Science Bulletin 52, 936–941. Sillitoe, R.H., 2000. Gold-rich porphyry copper deposits: descriptive and genetic models and their role in exploration and discovery. In: Hagemann, S.G., Brown, P.E. (Eds.), Gold in 2000. Society of Economic Geologists Reviews in Economic Geology, vol. 13, 315–345.

Snee, L.W., 2002. Argon thermochronology of mineral deposits— a review of analytical methods, formulations, and selected applications. US Geological Survey Bulletin 2194, 1–39. Song, B., Zhang, Y.H., Liu, D.Y., 2002. Introdution to the naissance of SHIRMP and its contribution to isotope geology. Journal of Chinese Mass Spectrometry Society 23, 58–62 (in Chinese with English abstract). Tarkian, M., Hunken, U., Tokmakchieva, M., Bogdanov, K., 2003. Precious-metal distribution and fluid-inclusion petrography of the Elatsite porphyry copper deposit, Bulgaria. Mineralium Deposita 38, 261–281. Von Quadt, A., Moritz, R., Peytcheva, I., Heinrich, C.A., 2005. Geochronology and geodynamics of Late Cretaceous magmatism and Cu-Au mineralization in the Panagyurishte region of the Apuseni-Banat-Timok-Srednogorie belt, Bulgaria. Ore Geology Reviews 27, 95–126. Von Quadt, A., Peytcheva, I., Kamenov, B., Fanger, L., Helnrich, C. A., Frank, M., 2002. The Elatsite porphyry copper deposit in the Panagyurishte ore district, Srednogorie zone, Bulgaria: U-Pb zircon geochronology and isotopegeochemical investigations of magmatism and ore genesis. Timing and Location of Major Ore Deposits in an Evolving Orogen, pp. 119–135. Wang, F., Zhou, X.H., Zhang, L.C., Ying, J.F., Zhang, Y.T., Wu, F.Y., Zhu, R.X., 2006. Late Mesozoic volcanism in the Great Xing’an Range (NE) China: timing and implications for the dynamic setting of NE Asia. Earth and Planetary Science Letters 251, 179–198. Wang, F., Zhu, R.X., Li, Q., He, H.Y., Luo, Q.H., Lu, Q.X., Sang, H.Q., Wang, Y.L., 2004. A differential uplifting of Qinling orogeny belt evidences from 40Ar/39Ar thermochronology of granites. Earth Science Frontiers 11, 445–459 (in Chinese with English abstract). Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Von Quadt, A., Roddick, J.C., Spiegel, W., 1995. Three natural zircon standards for U-Th-Pb, LuHf, trace element and REE analyses. Geostandards Newsletter 19, 1–24. Xie, L.W., Zhang, Y.B., Zhang, H.H., Sun, J.F., Wu, F.Y., 2008. In situ simultaneous determination of trace elements, U-Pb and Lu-Hf isotopes in zircon and baddeleyite. Chinese Science Bulletin 53 (10), 1565–1573. Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan-Tibetan orogen. Annual Reviews of Earth Planet Sciecce 28, 211–280. Yuan, H.L., Gao, S., Liu, X.M., Li, H.M., Gunther, D., Wu, F.Y., 2004. Accurate U-Pb age and trace element determinations of zircon by laser ablation inductively coupled plasma mass spectrometry. Geostandard Newsletter 28, 353–370. Zhang, K.J., Xia, B.D., Wang, G.M., Li, Y.T., Ye, H.F., 2004. Early Cretaceous stratigraphy, depositional environments, sandstone provenance, and tectonic setting of central Tibet, western China. GSA Bulletin 116 (9–10), 1202–1222. Zhu, D.C., Mo, X.X., Niu, Y.L., Zhao, Z.D., Wang, L.Q., Liu, Y.S., Wu, F.Y., 2009. Geochemical investigation of Early Cretaceous igneous rocks along an east– west traverse throughout the central Lhasa Terrane, Tibet. Chemical Geology 268, 298–312. Zhu, D.C., Pan, G.T., Mo, X.X., Wang, L.Q., Zhao, Z.D., Liao, Z.L., Geng, Q.R., Dong, G.C., 2006. Identification for the OIB-type basalts in Central Qinghai-Tibetan Plateau: geochronology, geochemistry and their tectonic setting. Acta Geologica Sinica 80 (9), 1312–1328 (in Chinese with English abstract).