Metallogenesis of the Tibetan Collisional Orogen: a Review and Introduction to the Special Issue

Ore Geology Reviews 36 (2009) 2–24

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Metallogenesis of the Tibetan collisional orogen: A review and introduction to the special issue

Zengqian Hou a,b,⁎, Nigel J. Cook c a Institute of Geology, CAGS, Beijing 100037, PR China b School of Earth and Geographical Sciences, University of Western Australia, W.A., Australia c Natural History Museum, University of Oslo, Boks 1172 Blindern, 0318 Oslo, Norway article info abstract

Article history: Mineral deposits associated with continental collision are abundant in many orogenic systems. However, the Received 21 October 2008 metallogenesis of collisional orogens is often poorly understood, due to the lack of systematic studies on the Received in revised form 7 May 2009 genetic links between collisional processes and ore formation in collisional orogenic belts. This paper reviews Accepted 7 May 2009 the key metallogenic settings and resultant collision-related ore deposits in the Tibetan Orogen, created by Available online 18 May 2009 Indo-Asian collision starting in the early Cenozoic. The resulting synthesis leads us to propose a new conceptual framework for Tibetan metallogenic systems, which may aid in deciphering relationships among Keywords: Geodynamics ore types in other comparable collisional belts. This framework includes three principal metallogenic epochs Collisional process in the Tibetan orogen, and metallogenesis in: (1) a main-collisional convergent setting (∼65–41 Ma); (2) a Metallogenesis late-collisional transform structural setting (∼40–26 Ma); and (3) a post-collisional crustal extension setting Collision-related deposits (∼25–0 Ma), each forming more than three distinct types of ore deposits in the Tibetan orogen. Tibetan Orogen The main-collisional metaollognesis took place in a convergent setting, i.e., a collisional zone, characterized by collision-related crustal shortening and thickening, associated syn-peak metamorphism and two distinct

magmatic series (Paleocene–Eocene crust-derived low-fO2 granitoids generated by crustal anatexis and Eocene

high-fO2 granitoids formed by MASH processes at the base of the Tibetan crust). Metallogenesis during this period

formed Sn–W–rare metal deposits related to the low-fO2 granitoids, skarn-hosted Cu–Au polymetallic deposits related to high-fO2 granitoids, and orogenic-type Au deposits formed by CO2-dominant metamorphic fluids. Late-collisional metallogenesis occurred mainly in a transform structural setting dominated by Cenozoic strike- slip faulting, shearing, thrust systems, and associated potassic magmatism in eastern Tibet, and formed the most economically-significant metallogenic province in the orogen. Four significant ore-forming systems are recognized in the transform zone: porphyry Cu–Mo–Au systems associated with potassic adakitic melts and controlled by Cenozoic strike-slip faults; orogenic-type Au systems related to large-scale left-slip ductile shearing; REE-bearing systems associated with lithospheric mantle-derived carbonatite–alkalic complexes; and Zn–Pb– Cu–Ag systems related to basinal brines and controlled by Cenozoic thrust structures and subsequent strike-slip faults developed in the Tertiary foreland basin. Post-collisional metallogenesis occurred in a crustal extension setting, characterized by lithospheric mantle thinning or delamination at depth, crustal shortening at a lower structural level and synchronal extension at shallower levels. The resulting ore-forming systems include: (1) porphyry Cu–Mo ore systems related to high-K adakitic stocks derived from the newly-formed thickened mafic lower-crust; (2) vein-type Sb–Au ore systems controlled by the south Tibetan detachment system (STDs) and the metamorphic core complex or thermal dome intruded by lecuogranite intrusions; (3) hydrothermal Pb–Zn–Agoresystemscontrolledbytheintersectionsof N–S-striking normal faults with E–W-trending thrust faults; and (4) spring-type Cs–Au ore systems related to geothermal activity driven by partial melting of the upper crust. Associated ore deposits lie mostly within the mid- Miocene Gangdese tectono-magmatic belt, in which the scavenging role of fluids derived from evolved magma systems or dewatering of rift basins, and finally discharging at intersections of the orogen-transverse and -parallel faults are extremely important for formation of the low-temperature hydrothermal deposits. Based on the synthesis of deposits in the Tibetan orogen and comparison with the metallogenesis of other orogenic systems, a more complete classification for these collision-related deposits can be proposed. © 2009 Published by Elsevier B.V.

⁎ Corresponding author. Institute of Geology, CAGS, Beijing 100037, PR China. E-mail address: [email protected] (Z. Hou).

1. Introduction collisional orogens, by carrying out orogenic-scale syntheses and comparative studies on typical collisional orogens and relevant Mountain belts created by continent–continent collision, e.g., the metallogenesis. The Himalayan–Tibetan Orogen is the youngest and Himalayan–Tibetan Orogen in East Asia (cf. Yin and Harrison, 2000), most spectacular of all continent–continent collision orogenic belts the Variscan orogen in Western and Central Europe (cf. Seltmann and (Yin and Harrison, 2000). It can therefore be regarded as the most Faragher, 1994), the Pyrenees (Sibuet et al., 2004) and the Qinling outstanding natural laboratory on Earth for studying collisional Orogen in China (cf. Zhang et al., 1996), each extending for thousands orogens and related metallogenesis due to (1) generally clear of kilometers along the strike, are among the dominant geological geological relationships, (2) a well understood paleo-boundary features of the surface of the Earth. Characteristic metallogenesis history, (3) a variety of marked, indicative geological features, as relating to continent–continent collision is widely expressed within well as (4) a variety of Cenozoic, world-class ore belts and giant these orogenic systems. High heat flows, resulting from the collisional deposits with variable mineralization styles and types, formed in what orogeny and associated crustal thickening, translithospheric shearing, are relatively clear geodynamic settings. and lithospheric mantle thinning, are regarded as the main causes for In order to increase understanding of the metallogeny of collisional hydrothermal mineralization in the orogenic belts (Seltmann and orogens, a five-year National Basic Research Program (973 Project to Faragher, 1994). However, the metallogeny of collisional orogens is the senior author) “Metallogenesis of the Collisional Orogen in Tibet” relatively less well understood compared to that of accretionary was established in 2002 by the Ministry of Science and Technology of orogens. China. About 100 researchers and students from nine Institutions in The suite of mineral deposits that can be related to collision events China took part in this project. As a result, great efforts have been is quite broad; Sawkins (1984) previously divided them into six major made to establish genetic links between collisional orogen and types: (1) ophiolite-hosted metal deposits, (2) Mississippi Valley-type metallogenesis in the Tibetan orogen during the past five years and (MVT) Zn–Pb deposits, (3) carbonate-hosted (Irish-type) Pb–Zn a wealth of new data and research results were obtained under the deposits, (4) sandstone-hosted (Laisvall-type) Pb(–Zn) deposits, (5) framework of the 973 Project. Sn–W deposits related to S-type granites, and (6) U deposits related to This special issue of Ore Geology Reviews provides a comprehensive collisional granites (cf. Seltmann and Faragher, 1994). These collision- account of key mineral deposits in the Tibetan collisional orogen. related deposits have been documented to preferentially developed or Moreover, other economically significant deposits such as Tanjianshan preserved in different orogenic belts. Recently, many more collision- (Zhang et al., 2009-this issue) and Tuolugou (Feng et al., 2009-this related deposits have been found in other orogenic systems. Many are issue), formed in the Mesozoic period, but nevertheless involved in world class in size and may be unique in their geological features; the Cenozoic collisional orogen and preserved within the Tibetan some do not easily fit into classical deposit models. For example, five Orogen, are also included in the special issue. Mesozoic giant porphyry Mo deposits and numerous orogenic-type This introductory paper synthesizes the temporal-spatial distribu- gold deposits in the Qinling collisional orogenic belt, China, have been tion, mineralization styles, and major types, tectonic controls, and shown to relate to Mesozoic collisional orogenesis (Kerrich et al., geodynamic settings of collision-related Cenozoic deposits in the 2000; Zhang and Deng, 2001). Tibetan orogen, on the basis of a synthesized analysis of the A number of collision-related world-class ore belts, including tectonomagmatic evolution and lithospheric geodynamic processes giant deposits, occur within the Tibetan collisional orogen (Fig. 1; within the orogen. This synthesis leads us to propose a new cf. Hou et al., 2007a; Khin Zaw et al., 2007). These include the conceptual framework for the Tibetan metallogenic systems, as well Himalayan porphyry Cu belts in Tibet (Hou et al., 2009a-this issue), as a new classification for collision-related deposits, in which the the Cenozoic Ailaoshan orogenic-type Au belt in western Yunnan (Sun Tibetan examples can be compared with comparable deposits in other et al., 2009-this issue), the carbonatite–alkalic complex-hosted collisional orogenic systems. REE belt in western Sichuan (Hou et al., 2009b-this issue), and the Tertiary Lanping Zn–Pb–Cu–Ag belt (He et al., 2009-this issue). Some 2. Tectonic framework of the Tibetan Orogen more unusual ore deposits, including the giant coal seam-hosted Lincang Ge deposit (Hu et al., 2009-this issue) and cesium-(gold) The Tibetan orogen, a direct consequence of a collision between deposits within active hot springs and associated silica-sinters, in- the Indian and Asian continents beginning in the early Cenozoic, is cluding the Targejia Cs deposit (Zheng et al., 1995; Li et al., 2006a,b) built on a complex tectonic collage created by accretion of three have also been discovered in the orogen. These new discoveries in terranes onto the southern margin of the Asian continent since the China, as well as previously-reported data for collision-related early Paleozoic (Fig. 1; Chang and Zheng, 1973; Allègre et al., 1984). deposits in other orogenic systems, greatly extend our knowledge of These three terranes are, from north to south, the Songpan–Garze, the metallogenetic character of collisional orogens, and provide a Qiangtang, and Lhasa Terranes. They are separated from one other significant database for further understanding of collisional metallo- by the Jinsha suture (JS) and the Bangong–Nujiang suture (BNS), geny. Nevertheless, these discoveries also raise a number of important respectively; both are representative of Paleo-Tethyan ocean questions, including: relicts (Yin and Harrison, 2000)(Fig. 1). The Qiangtang terrane is characterized by predominantly Precambrian metamorphic rocks and 1. Why do the different orogens show differing metallogenic late Paleozoic shallow marine strata and Jurassic–Cretaceous marine features? How is the metallogenesis of these orogenic belts linked carbonate rocks interbedded with terrestrial clastics. It has the to collisional orogenic processes? thinnest crust (50 to 60 km) and the highest mantle temperature on 2. Does the metallogenic preferentiality of collision-related deposits the Tibetan plateau (McNamara et al., 1995). The Lhasa terrane is relate to either the tectonic evolution of different orogenic belts or composed of mid-Proterozoic and early-Cambrian basement and to the degree of their erosion? Which kind of deposits are Paleozoic–Mesozoic cover strata consisting of a sequence of Ordovi- preferentiality developed in which stages (i.e., syn-, late- and cian–Triassic shallow marine clastic sediments. Internal N–S short- post-collisional) of orogenic tectonic evolution? ening of at least 180 km is recorded within the Lhasa Terrane due 3. What are the geotectonic environments and controlling factors for to Jurassic–Cretaceous collision with the Qiangtang terrane (Murphy different mineralization styles, deposit types, and ore-forming et al., 1997). The present crustal thickness (70 to 80 km) is twice that processes in the various tectonic stages of collisional orogens? of normal crust (Molnar et al.,1993) due to the Indo–Asian continental The key to answering these questions is to establish the genetic collision. From south to north across the terrane, development of the links between metallogeny and various geodynamic processes in Indus–Yarlung Zangbu suture (IYS) (Xiao and Gao, 1981), the Xigaze 4 .Hu ..Co r elg eiw 6(09 2 (2009) 36 Reviews Geology Ore / Cook N.J. Hou, Z. – 24

Fig. 1. Simplified geological map of the Tibetan Orogen (Yin and Harrison, 2000), illustrating tectonic framework and spatial distribution of the Cenozoic ore deposits. Deposit numbers refer to deposits in Table 2. Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 5 fore-arc basin (Durr, 1996), and the voluminous Andes-type arc et al., 2001). This flow process resulted in the development of the High- granitoid batholiths (130 to 70 Ma; Schärer et al., 1984; Harrison et al., Himalaya (HH) metamorphic block and the South-Tibetan detachment 1999) suggests northward subduction of the Neo-Tethys slab in the system (STD) (Burg and Chen, 1984; Burchfiel et al., 1992) and associated late Cretaceous (Allègre et al., 1984). Emplacement of Paleocene– Miocene leucogranite intrusions (Le Fort,1981; Harrison et al.,1997). Fig. 2 Eocene syn-collisional magmas along the southern margin of the shows the structural architecture and major units of the Himalayan– Lhasa terrane (Fig. 1) suggests the subsequent subduction of the Tibetan Orogen and its comparison with other orogenic systems. Indian continental slab in the Early Tertiary (Hou et al., 2006a). To the south of the IYS are the Himalayas, consisting of three tectonic 3. Tectono-magmatic evolution of the collisional orogen blocks, the Tethyan Himalaya (TH), High Himalaya (HH), and Low Himalaya (LH), separated from each other by the north-dipping Main The Tibetan–Himalayan orogen underwent a complex history of Central Thrust (MCT) and Main Boundary Thrust (MBT) (Figs. 1 and 2). tectono-magmatic evolution from continental collision and subse- Both the MCT and MBT appear to sole into a common N-dipping quent underthrusting in the main-collisional period (65 to 41 Ma), detachment, the Main Himalayan Thrust (MHT) (Zhao et al., 1993), through intra-continental underthrusting and large-scale horizontal suggesting that the main part of the Indian continent has been thrust block movements in the late-collisional period (40 to 26 Ma), to E–W beneath the Himalayas along the MHT (Fig. 2A). Crustal-scale thrusting crustal extension in the post-collisional period (≤25 Ma) (Hou et al., within the Himalayas was delayed for 20 to 40 Ma following the onset of 2006b,c,d). Geological events, stress regimes, and plausible deep the collision (cf. Yin and Harrison, 2000 and references therein). This has lithospheric geodynamic processes for each collisional stage are been attributed to the lateral flow and southward extrusion of a hot, summarized in Table 1 and on Fig. 3. The tectono-magmatic evolution ductile Tibetan lower-crust in the Miocene (Nelson et al., 1996; Beaumont is briefly described in the following sections.

Fig. 2. Fundamental architecture and orogenic style of three collisional orogenic systems. (A) Asymmetric-style orogenic system, represented by the Himalayan–Tibetan orogen (Yin and Harrison, 2000). MBT: main-boundary thrust; MCT: main-central thrust; STDS: South-Tibetan detachment systems; GCT: great reverse thrust; GT: Gangdese thrust. (B) shows a symmetric-style orogenic system, represented by the Pyrenean orogen (Roure and Banda, 1987; Roure et al., 1989). SPF: Southern Pyrenean foreland thrust zone; SPZ: Southern Pyrenean units; CPZ: Central axial zone; NPZ: Northern Pyrenean belt; NP.F: Northern Pyrenean fault; NPF: Northern Pyrenean foreland thrust-fault zone. (C) Composite-style orogenic system such as the Qinling orogenic system (modiﬁed from Zhang et al., 1996). I1: thrust-folded zone in hinterland; I2: thrust fault zone; II: fore-land thrust-fold zone. SF1:

Shang-Dan suture; SF2: Mian-Lue suture. 6 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24

Table 1 Summary of the tectono-magmatic events in different evolution stages (main-, late- and post-collisional) of the Tibetan Orogen.

Period Pre-collision Main-collision Late-collision Post-collision Timing 120–70 Ma 65–41 Ma 40–26 Ma 25–0Ma Tectonics and Andean-type arc along Tethyan Himalayan thrust belt in south Contraction system in central Tibet strike- South Tibetan detachment system deformation Gangdese mountain range Tibet; Narrow mountain range in slip faulting and shearing systems in east NS-striking normal fault system Lhasa terrane; Qimen-Tagh thrust system Tibet thrusting system and nappe structure across orogen; East-west extension and early Tertiary basins in central Tibet in east Tibet Magmatism Calc-alkaline arc granitoids Magmatism occurring along the Gangdese Magmatism mainly occurring in the Magmatism widely occurring in the (120–70 Ma), intruded along arc in Lhasa terrane Linzizong volcanic transform zone in east Tibet High-K Tibetan plateau ultrapotassic rocks the Gangdese arc rocks (65–40 Ma) Muscovite–granites calc–alkaline rocks (40–30 Ma) Potassic (26–13 Ma) Potassic rocks (25–0 Ma) (66–58 Ma) calc–alkaline granitoids potassic intrusion rocks (40–30 Ma) Cu-bearing adakitic stocks (19–13 Ma) (65–41 Ma) Bimodal bimodal granitoid REE-bearing carbonatite–alkalic complex Leucogranites (23–16 Ma) and gabbro (52–47 Ma) mafic intrusions (40–27 Ma) Cu-bearing stocks (40–32 Ma) (42–38 Ma) Lamprophyre (35–26 Ma) Stress regime Convergence and continuous Early: compressional; late: stress relaxation Early: transpressional late: transform Early: lower-crust flow; late: compression to transtensional E–W extension Possible deep Subduction of the Neo- Indo-Asian impact (70–65 Ma)→rolling Intra-continental subduction or terrane Break-off and delamination of Indian lithospheric Tethyan oceanic slab; back of subducted Neo-Tethyan oceanic underthrusting caused by flat subduction continental slab; Asthenospheric processes melting of wedge mantle slab→subduction of Indian continent of Indian continent in central Tibet; upwelling and mantle lithospheric metasomatized by continent→breakoff of oceanic slab→flat Asthenospheric upwelling in east Tibet thinning subduction zone subduction of Indian continental-slab components (b40 Ma)

3.1. Main-collisional period (65–41 Ma) 55 Ma (DeCelles et al., 2004) and progressed eastwards until collision ended by 41 to 50 Ma in the eastern Himalaya (Chemenda Collisional timing: the timing for the onset of India–Asia collision et al., 2000). However, this is not supported by the 40Ar/39Ar age (66 is constrained at 55 to 50 Ma by many authors, but existing data to 58 Ma) of syn-collisional crust-derived muscovite granitoids near suggest that the initial collision may have started as early as the the eastern Himalayan syntaxis (Dong et al., 2006a). Based on the earliest Paleocene (Yin and Harrison, 2000). Some authors suggest most recent data obtained by the 973 Project (Mo et al., 2003; Ding that India–Asia collision began in the western Himalaya at 52 to et al., 2003; Wang et al., 2003), the period for the main collision

Fig. 3. Collisional processes, tectonic deformation, magmatic activities, stress regime in different structural units of the Tibetan Orogen. Convergent velocity data between Indian and Asian plates (Lee and Lawver, 1995) are used to compare the three-stage collisional processes in the orogen. Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 7

between Indian and Asian continents is constrained at ∼65 to 41 Ma ment with variable LaN/YbN ratios (7 to 24) and negative Nb, Ta, P, Ti (cf. Hou et al., 2006b). anomalies (Mo et al., 2003), suggesting geochemical afﬁnity with arc Tectonic deformation: tectonic deformation during the period is rocks but involving crustal contamination (Chung et al., 2005; Mo characterized by development of the Tethyan Himalayan thrust belt in et al., 2007). south Tibet, the Gangdese mountain range in the Lhasa terrane, and Paleocene syn-collisional granitoids mainly occur in the Teng- three Cenozoic contractional systems in central Tibet (Figs. 1 and 2). chong area within the eastern Gangdese range (Fig. 1). Available age The Tethyan Himalayan thrust belt, located between the STD and IYS data deﬁne a long duration (66 to 41 Ma) for the magmatism, which (Fig. 1), has an estimated amount of shortening of 130 to 140 km and formed muscovite granites peaking at 66 to 58 Ma and potassic calc- an initial timing of shortening of ∼50 Ma (Ratschbacher et al., 1994). It alkaline monzogranite and syenogranites peaking at 65 to 55 Ma, consists of fold and imbricate thrusts involving the passive continental 53 Ma, and 42 Ma, respectively (Dong et al., 2006a). The muscovite margin sequence of the Tethyan Himalaya. The Gangdese range, granites are small in volume and occur as stocks or sheet-like bodies formed by emplacement of Paleocene syn-collisional granitoids, is a hosting rare-metal (Rb, Cs, Li, Y, Yb, etc.) mineralization. They have high but narrow mountain range similar to the present Altipano–Puna high ASI [nAl2O3/(nK2O+nNa2O+nCaO)] values of 1.03 to 2.63 and plateau in the central Andes (Fielding, 1996). The central Tibet Al2O3/Ti2O ratios of 127 to 2033, low FeOt/(FeOt +MgO) ratios of contractional systems consist of the Shiquanhe–Gaize–Amdo thrust b0.8 and CaO/Na2O ratios of 0.03 to 0.24 (Dong et al., 2006a), similar system, the Fenghuoshan–Nangqian fold-thrust belt, and the Qimen– to the Himalaya-type high-pressure granites (Sylvester, 1998). Their

Tagh thrust system (Fig. 1), each juxtaposing Mesozoic strata over high Rb/Sr (257–404) and Rb/Ba ratios (13–40), negative εNd(t) Tertiary strata, and resulting in crustal shortening of more than 80 km (−8.8 to −8.9; Fig. 4), and MREE-depleted patterns suggest a clay- (Yin and Harrison, 2000; Spurlin et al., 2005). rich, plagioclase-poor pelitic source in thickened Tibetan crust Main-collisional magma suite: four principal magma suites have (Sylvester, 1998). The calc-alkaline granitoids occur as multi-phase been recognized in the Gangdese range: (1) a ∼5 km-thick, sub- plutons with associated Sn mineralization (Hou et al., 2006b). They horizontal, early-Tertiary Linzizong volcanic succession (LVS); (2) are characterized by LREE enrichment (LaN/YbN =9.4–18.5) with Paleocene syn-collisional granitoids; (3) Eocene gabbros and asso- distinct Eu anomalies, relatively low Rb/Sr (1.0–3.6) and Rb/Ba (0.4– 87 86 ciated granitoid intrusions; and (4) basaltic subvolcanic rocks. They 2.5) ratios, and high ( Sr/ Sr)i of 0.7116–0.7138 and low εNd(t) form a N1,000 km-long, EW-extending tectono-magmatic belt (Fig. 1). of −8.68 to −9.66 (Fig. 4; Dong et al., 2006a), implying a meta- The magmatism mainly took place in three epochs, peaking at 65 to sandstone source in the Tibetan crust (Sylvester, 1998). 58 Ma, 52 to 47 Ma and ∼42 Ma, respectively (Hou et al., 2006a). Eocene magma suites, consisting of “paired” granitoid and gabbro These events correspond to three drastic variations in the Indo-Asia bodies with radiometric ages between 52 and 41 Ma (Schärer et al., continental rate of convergence (Fig. 3; Lee and Lawver, 1995). 1984; Jiang et al., 1999; Mo et al., 2005; Dong et al., 2006b), are The LVS, with characteristic andesitic–rhyolitic compositions, developed along the southern margin of the Lhasa terrane. The yields a wide range of 40Ar/39Ar ages, varying from 64.5–60.3 Ma granitoids usually host numerous macrogranular maﬁc enclaves and (Dianzhong unit) to 48.7–44.0 Ma (Pana unit) (Mo et al., 2003; Zhou are associated with intense polymetallic mineralization (Hou et al., et al., 2004). Geochemically, the suite is calc-alkaline and high-K calc- 2006b). They are geochemically calc-alkaline, and characterized by 87 86 alkaline with minor shoshonitic character, and shows LREE enrich- positive εNd(t) values (+2.5 to +3.9), low ( Sr/ Sr)i (Fig. 4) and low

Fig. 4. Sr–Nd isotopic compositions of Cenozoic magmatic rocks in the Tibetan Orogen. Data sources: see the text. 8 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24

δ18O (2.3–4.5‰)(Jiang et al., 1999; Mo et al., 2007), suggesting shearing, which formed the Red-River Shear Zone (RRSZ) along the signiﬁcant involvement of a juvenile mantle component for magma Honghe fault system and which is associated with Au mineralization generation. Associated gabbros are geochemically tholeiitic and calc- (Fig. 1; Sun et al., 2009-this issue). The third style is the Cenozoic fold- alkaline, and show relatively ﬂat REE patterns and variable degrees of thrust systems formed due to internal shortening, and which formed

U, Th, Nb, Ta, Zr, Hf, P and Ti depletion. Their positive εNd(t) values the Lanping–Simao foreland fold belt and caused formation of thrust- 87 86 (+2.3 to +5.1) and low ( Sr/ Sr)i values (0.703861–0.705072) controlled sediment-hosted Zn–Pb–Cu–Ag deposits (He et al., 2009- suggest a significant contribution from the asthenospheirc mantle this issue). (Fig. 4; Hou et al., 2006b). Late-collisional magmatism: late-collisional magmatism occurs The late Eocene mafic subvolcanic rocks yield 40Ar/39Ar ages of widely across the Qiangtang terrane, and extends for more than 42.0±2.3 Ma (Gao et al., 2006). These are dominantly tholeiitic 2000 km into three provinces: western Qiangtang; eastern Qiangtang; basalts and picritic-basalts with high Mg# ratio (molar [Mg/Mg+ Fe] = and western Yangtze, from west to east (Chung et al., 2005). 0.60–0.73) and high contents of Cr (118–310 ppm), V (191–257 ppm) Magmatism in the last two provinces was controlled by Cenozoic and Ni (113 to 117 ppm) (Gao et al., 2006). Flat REE patterns (LaN/ strike-slip faulting systems in northeastern and eastern Tibet (Wang YbN = 2.26–2.89), distinct negative Ti, Nb, U, Th anomalies and Sr–Nd et al., 2001; Hou et al., 2003a, 2006b). At least three magmatic districts isotopic signatures (Fig. 4) suggest an asthenospheric mantle magma or zones have been recognized in the transform structural setting, source (Gao et al., 2006, 2008; Hou et al., 2006a). from west to east. These include: (1) a potassic intrusive zone with A three-stage model has been proposed for the tectonic–magmatic radiometric age of 41 to 27 Ma, hosting Cu–Mo–Au deposits with evolution during the main-collisional period in Tibet (Hou et al., NNW-strike along strike-slip faults (Zhang and Xie, 1997; Chung et al., 2006a; Mo et al., 2007). At ∼70–60 Ma, roll-back of a flatly-subducted 1998; Wang et al., 2001; Hou et al., 2005a, 2006c); (2) a potassic calc- Neo-Tethyan oceanic-slab (Chung et al., 2005) facilitated the early alkaline and shoshonitic lamprophyre district with a surface area of dragging down of the attached Indian continental lithosphere and ∼50,000 km2 (Guo et al., 2005); and (3) a 270 km-long, NS-tending collision with the Asian continent, leading to initial shortening of the zone of REE-bearing carbonatite–alkalic complexes with radiometric Asian continental crust and associated crustal anatexis. Paleocene agesof40to28Ma(Yuan et al., 1995; Wang et al., 2001; Hou et al., granitoids were generated at 66 to 58 Ma. Subsequently, the thermal 2006c). structure of the mantle wedge was changed, resulting in generation of Late-collisional magmatism in the transform structural zone is early LVS magmas at 65 to 60 Ma. At ∼60–54 Ma, the slab roll-back mainly expressed as small-volume extrusive or intrusive bodies, mechanism was substituted by deep subduction of the Indian ranging from mafic to felsic in composition and characterized by high continental lithosphere, which most likely caused a sudden decrease to very high alkali contents (Chung et al., 2005). Shoshonitic and in the convergent rate from 170 mm/a (at ∼70–60 Ma) to 105 mm/a ultrapotassic rocks are dominant, with minor potassic calc-alkaline (at ∼60–54 Ma; Lee and Lawver, 1995). This resulted in generation of rocks. Mantle-derived carbonatites in western Yangtze (Hou et al., crust-derived calc-alkaline granitoids in the eastern Gangdese range 2006e) are also noted. at 54 to 52 Ma. At ∼53–42 Ma, break-off of the Neo-Tethyan slab Potassic felsic rocks, including Cu-bearing porphyritic monzogra- occurred at depth and upwelling of asthenosphere through this nites and some felsic volcanic rocks in eastern Tibet, usually have low “window” triggered partial melting of the lithospheric mantle, in turn contents of HREE and Y, coupled with high Sr/Y and La/Yb ratios, generating numerous small gabbro intrusions (52 to 47 Ma) and showing geochemical affinity with adakites (Hou et al., 2003b; Jiang tholeiitic subvolcanic rocks (42 Ma) along the Gangdese belt. Another et al., 2006). They are, however, characterized by high K2O and MgO, direct consequence of slab break-off was the sudden decrease in rate and negative εNd(t) (−0.20 to −4.89; Fig. 4; Deng et al., 1998a,b; Hou of convergence from ∼90 mm/a to ∼60 mm/a at ∼40 Ma (Lee and et al., 2003b), thus distinguishing them from adakites derived from Lawver, 1995), as well as stress relaxation of the Lhasa terrane, during melting of subducted oceanic slabs (Kay, 1978; Kay et al., 1993; Stern which abundant polymetallic mineralization was deposited. and Kilian, 1996). The associated ultra-potassic barren rocks occa- sionally host mantle xenoliths (Cai, 1992; Zhao et al., 2004), which 3.2. Late-collisional period (40–26 Ma) although having similar Sr–Nd isotopic signatures to the adakitic rocks, yield high contents of Y (N20 ppm) and HREE (Deng et al., Late-collisional processes are characterized by large-scale relative 1998a,b; Hou et al., 2005a), suggesting genesis by limited degrees of movement among the terranes (blocks) and associated potassic melting of enriched lithospheric mantle (Wang et al., 2001; Zhao et al., magmatism in a transpressional regime. This mainly took place at 2004). the eastern margin of the Tibetan Plateau (Hou et al., 2007a), a Oligocene carbonatites in western Yangtze province have low SiO2 transform structural zone, which had absorbed stress and strain (b10.22 wt.%), FeO (b1.20 wt.%), and MgO (b0.73 wt.%) and a wide resulting from the Indian–Asian collision (Dewey et al., 1989; Wang range of CaO (40.7–55.4 wt.%), and are extremely enriched in LILE (Sr, et al., 2001). Ba) and light REE, but relatively depleted in HFSE (Nb, Ta, P, Zr, Hf, Ti) Tectonic deformation: deformation in east Tibet has been (Hou et al., 2006e), thus suggesting a metasomatized mantle source. facilitated by three possible mechanisms, i.e., southeastern extrusion However, they also have extremely low εNd(t) (−3.2 to −18.7) and 87 86 of the Indochina block (Peltzer and Tapponnier, 1988; Leloup et al., relatively high ( Sr/ Sr)i (0.706020–0.707923), as well as a wide 1995), block rotation (Royden et al., 1997; England and Molnar, 2000), range of 207Pb/204Pb (15.362–15.679) and 208Pb/204Pb ratios (38.083– and internal shortening (Wang and Burchfiel, 1997). Three styles of 39.202) (Hou et al., 2006e, and references therein), distinguishing deformations in east Tibet are important to the generation of collision- them from most carbonatites around the world (e.g., Bell and related mineralization in the transform structural setting. The first is Blenkinsop, 1987; Harmer and Gittins, 1998). Their Sr–Nd, Sr–Pb and large-scale Cenozoic strike-slip fault systems, striking both E–W and Nd–Pb isotopic signatures indicate that the least-contaminated N–S, forming the Gali–Gaoligong fault system, the Mangkang–Lijiang carbonatites were probably derived from a transitional source fault belt, which controls the Yulong porphyry Cu belt (Hou et al., between enriched mantle I (EMI) and enriched mantle II (EMII) 2003a), the Honghe fault system, and the Xianshuihe–Xiaojiang fault components (Hou et al., 2006e). system, which controls the MD REE belt (Hou et al., 2009b-this issue; Late-collisional tectono-magmatic activities in eastern Tibet have Fig.1). These strike-slip faults occurred at ∼40 Ma and ceased at 23 Ma been variably attributed to continental subduction (Wang et al., 2001), (Hou et al., 2003a; Liu et al., 2006), and underwent early-stage convective thinning of the mantle lithosphere (Chung et al., 1998), sinistral and late-stage dextral movements (Tapponnier et al., 1990; extension along strike-slip faults (Yin et al., 1995), and slab break-off Spurlin et al., 2005). The second deformation style is large-scale (Miller et al., 1999). However, the relatively short magmatic duration, Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 9 peaking at ∼35 Ma, extension over a distance of 2000 km across entire Ding et al., 2003; Hou et al., 2004a; Zhao et al., 2006c). Available age Qiangtang, and mantle-derived magmatic association imply that the data define the ultrapotassic magmatism as occurring from 25 to late-collisional magmatism is genetically related to deep geodynamic 16 Ma (Miller et al., 1999; Ding et al., 2003; Chung et al., 2003; processes involving the asthenosphere and the subcontinental mantle Williams et al., 2004; Zhao et al., 2006c) and the potassic magmatism lithosphere. It is most likely that the large-scale strike-slip fault following at 18–13 Ma (Miller et al., 1999; Chung et al., 2003; Hou systems formed during the late-collisional period, acting as seafloor et al., 2003c, 2004a; Rui et al., 2003). The ultrapotassic rocks have # transform faults not only promoting large-scale horizontal terrane high-Mg (N40), high-K2O (6.0 to 9.2 wt.%) and high-TiO2 (N1 wt.%), movements, but also cutting the subcontinental lithosphere, probably and show heterogeneous compositions with SiO2 ranging from 51 to triggered upwelling of the asthenosphere in eastern Tibet (cf. Zhong et 69 wt.%, similar to SiO2-rich lamprophyres (Conticelli and Peccerillo, al., 2001, and references therein). Upwelling of the asthenosphere 1992; Gao et al., 2007). They are enriched in LILE and LREE, depleted probably supplied enough heat energy to cause partial melting of the in HFSE, and yield a much wider range of 87Sr/86Sr (0.7167–0.7463), enriched mantle source, producing carbonatites (Hou et al., 2006e), and εNd(t) values (−9.5 to −16.6; Miller et al., 1999), and show a potassic lamprophyres (Guo et al., 2005) and associated ultrapotassic continuous trend from the enriched mantle to the Indian continental rocks (Chung et al., 1998) during the late-collisional period. Input of a basement (Fig. 4A), suggesting involvement of the Indian continental juvenile asthenospheric component into the thickened (N50 km) lithosphere in magma generation (Zhaoet al., 2003, 2006c). The mafic lower-crust or crust/mantle transitional zone beneath eastern potassic rocks, especially the felsic stocks, are usually associated with Tibet most likely generated the late-collisional potassic adakitic Cu mineralization (Hou et al., 2003c, 2004b; Qu et al., 2007). Chung magmas (Hou et al., 2003b). et al. (2003) and Hou et al. (2004a) identified these rocks as adakites from the active continental collision zone, distinguishing them from 3.3. Post-collisional period (25 Ma to present) typical adakites derived from oceanic-slab (Defant and Drummond,

1990; Gutscher et al., 2000) by their high K2O content (2.6 to 8.6 wt.%) Tectonic deformation: post-collisional deformation in the Hima- and shoshonitic character. A wide range of εNd(t) (−6.18 to +5.52), layas is characterized by crustal shortening at deep structural levels initial 87Sr/86Sr (0.7049 to 0.7079), 207Pb/204Pb (15.502 to 15.626), along the thrust systems, but synchronous extension at shallow and 208Pb/204Pb (38.389 to 38.960), and high Mg# values (32–74) structural level along detachment systems in south Tibet (STD). suggest a newly-formed, thickened (N60 km) mafic lower-crust Corresponding to the continuous underthrusting of the Indian source but also involvement of juvenile mantle components (Hou continent northwards beneath the Himalaya until ∼22 Ma (Hodges et al., 2004a). et al., 1996), lateral flow and southward extrusion of the hot, ductile Generation of the post-collisional potassic and ultrapotassic Tibetan lower-crust was regarded to have taken place via channel flow magmas in Tibet is mainly attributed to convective removal of the (Beaumont et al., 2001, 2004), leading to development of the STD and lithospheric mantle (Turner et al., 1993; Miller et al., 1999; Williams the High-Himalayan metamorphic block in south Tibet (Burg and et al., 2001; Chung et al., 2005), and break-off of the subducted slab Chen, 1984; Burchfiel et al., 1992). (Maheo et al., 2002; Hou et al., 2004a). However, combined action of The deformation event in Tibet is a series of near NS-striking early break-off of the subducted Indian continental slab and local normal fault systems across the Tibetan plateau, produced by the mid- thinning of subcontinental lithospheric mantle due to delamination or Miocene east-west crustal extension. They mainly occurred prior to thermal erosion at ∼25 Ma (Miller et al., 1999; Williams et al., 2004) 13.5 to 14 Ma (Coleman and Hodges, 1995; Blisniuk et al., 2001). may be a plausible mechanism for plateau uplift, crustal extension, Recent 40Ar/39Ar dating of NS-trending ultra-potassic dykes indicates and dyke emplacement at ∼18 Ma (Williams et al., 2001), and that initial E–W extension probably took place at approximately 18 Ma subsequent NS-striking normal faulting prior to 13.5 Ma (Coleman (Williams et al., 2001, 2004). These normal fault systems usually and Hodges, 1995; Blisniuk et al., 2001). The thinning of the thickened crosscut the EW-trending thrust faults, and constrain the localization lithosphere probably caused further northward underthrusting of the of potassic intrusions hosting porphyry-type Cu mineralization (Hou cold Indian mantle lithosphere to reach the Bangong–Nujiang suture et al., 2003c, 2006d). at this time and resulted in subsequent magmatism, ceasing at 13 to Post-collisional magmatism: Here we refer only to a new phase of 10 Ma in the Lhasa terrane due to shut-off of the heat source from the magmatic activity occurring in the Tibetan Orogen from the late asthenosphere (Williams et al., 2004; Chung et al., 2005). Oligocene to the present (Fig. 1). Two distinct stages of magmatism have been recognized: an earlier event (25 to 13 Ma) in the Lhasa 4. Metallogenesis of the Tibetan collisional orogen terrane and in southern Tibet; and a more recent event (13 to 0.5 Ma), which is largely restricted to northern Tibet. The Tibetan Orogen underwent a multiple tectono-magmatic The earlier phase in south Tibet forms two roughly parallel granite evolution from main-collisional convergence at 65 to 41 Ma, through belts, i.e., the high Himalayan leucogranite (HHL) and the northern late-collisional transform (40 to 26 Ma) to post-collisional extension Himalayan granite (NHG). The HHL forms a discontinuous chain of (25 Ma until present). Corresponding stress regimes vary from intense sills exposed on either side of the STD; its crystallization age of 24– impact (∼65 to 54 Ma), relaxation (∼53 to 41 Ma), transpression (∼40 17 Ma constrains timing of the STD (Harrison et al., 1998). Numerous to 30 Ma) to transtension (∼30 to 26 Ma), and from N–S compression models for genesis of the HHL, including melting induced by thermal (N18 Ma) to E–W extension (b18 Ma) (Fig. 3; Hou et al., 2006b,c,d). relaxation (Le Fort, 1975), frictional heating during thrusting (England Each collision stage is usually associated with distinct metallogenic et al., 1992), and decompressional melting (Harris et al., 1993; Guillot processes, which have produced specific mineralized systems and and Le Fort, 1995), have been proposed to interpret the inverted deposit types (Fig. 5; Table 2). metamorphism, crustal anatexis and related faulting in south Tibet. The NHG, 80 km north of the HHL, yields an age range of 17.6 to 9.5 Ma 4.1. Metallogenesis in the main-collisional convergent setting (Harrison et al., 1998). It is composed of numerous elliptical plutons that intruded the Tethyan Himalayan cover strata and formed 6 to 8 Tectono-magmatic activity in Tibet during the main-collisional discrete structural-thermal domes, which host associated Au–Sb convergent setting is characterized by collision-related crustal short- mineralization (Yang et al., 2009b-this issue). ening and thickening, associated syn-peak metamorphism and two The 23 to 13 Ma magmatic event in the Lhasa terrane forms a distinct magmatic series consisting of Paleocene–Eocene crust- 1500 km-long potassic igneous belt along the Gangdese batholiths derived granitoids and Eocene mantle-derived bimodal-like suites. (Turner et al., 1996; Miller et al., 1999; Williams et al., 2001, 2004; Ore formation during this period is genetically related to syn-peak 10 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24

Fig. 5. Metallogenesis of the orogenic belt and major collision-related deposit types in Tibet from the Cretaceous to present.

metamorphism caused by continental impact, leading to orogenic- mafic-ultramafic volcanic rocks and greywacke, which probably type gold deposits, crustal anatexis associated with crustal shortening contributed metals to the ore-forming fluids; (4) metamorphic fluids and thickening, forming Sn and rare metal deposits, and to crust- from dehydration of a subducted slab, located 30 km depth beneath mantle interaction for generation of the bimodal-like igneous suite in the IYS (Makovsky et al., 1999); and (5) suitable P–T conditions for Au a stress relaxation regime, resulting in Cu–Au polymetallic miner- mineralization, resulting from syn-peak metamorphism (i.e., 170 to alization. Most collisional deposits occur in the Gangdese tectono- 340 °C, 1.5 to 2.4 kbar) (Jiang et al., 2009-this issue). magmatic belt in Tibet (Fig. 1; Table 2). Crustal anatexis and Sn-rare metal deposits: Cenozoic Sn and rare Syn-peak metamorphism and orogenic-type Au deposits: Such metal (Rb, Cs, Li, Y) mineralization mainly occurs in the Tengchong mineralization mainly occurs along the IYS (Fig. 1), and forms a granitoid district, eastern Gangdese, and is related to potassic potential mineralized belt in Tibet. Mayum, a lode gold deposit ganitoids and muscovite granites, respectively, formed by crustal representative of those in this belt, is described in detail by Jiang et al., anatexis during the main-collisional period (Fig. 1; Hou et al., 2007a). 2009-this issue. The principal features of the Au deposits in the belt In general, these Sn deposits (e.g., the Lailishan) are similar to those in are summarized here. They include: (1) the gold belt is located in or the Varisican collisional orogen in many aspects, such as temporal- near a translithospheric structural zone, i.e., IYS, and Au mineraliza- spatial association with S-type granite, greisen-type alteration, and tion is associated with syn-collisional metamorphism (∼59 Ma) in a gangue assemblage (Liu et al., 1993). However, their spatial localiza- main-collisional convergent setting (Jiang et al., 2009-this issue); (2) tion controlled by fault fracture zones, the stratabound and semi- most of the deposits were developed in a greenschist-facies layered character of the Sn orebodies, cassiterite-bearing ores metamorphic block along the suture, and were associated with dominated by massive pyrite, colloidal textures in massive sulfide sericitization, silicification, carbonatization and argillization; (3) Au ores containing relict pyrite, as well as bimodal inclusion tempera- deposits are composed of auriferous quartz veins or vein swarms, and tures peaking at 180 and 380 °C, all suggest an overprinting of orebodies were usually controlled by second-order splays or shear Cenozoic greisen-type Sn mineralization over pre-existing (Paleozoic) zones genetically related to the IYS (Hou et al., 2006b); and (4) ore- massive sulfides (Hou et al., 2006b). The rare-metal deposits (e.g., forming fluids were CO2-rich, low-salinity (0.18 to 7.20 wt.% NaCl Baihuanao) are associated with a group of highly-evolved muscovite- equiv.), NaCl–H2O systems (Jiang et al., 2009-this issue), similar to bearing granites, featuring Li-bearing albite with greisen-type altera- those observed in orogenic-type gold deposits worldwide (Goldfarb tion. They mainly occur at intrusive contacts as vein swarms and et al., 1993, 1998; Kerrich et al., 2000). stockworks, and partially in the interior of the greisenized granitic Many studies have shown that the majority of orogenic-type Au bodies (Hou et al., 2007a). metallogenic provinces are associated with accretionary orogenic The ore-bearing potential of the main-collisional granitic melts events and that Au mineralization is typically related to syn- to post- produced by crustal anatexis is probably controlled by the ratio of peak metamorphism in orogenic belts (Kerrich and Wyman, 1990; plagioclase to biotite melting in the Tibetan crustal source, because Barley and Groves, 1992; Goldfarb et al., 1993, 1998; Groves et al., breakdown of biotite in the source during melting would provide an 1998). However, the occurrence of numerous Au deposits along the effective mechanism for enrichment of metals (Sn, W) and incompa- IYS in a collision zone indicates that collisional orogenic event and tible elements (Rb, Li, Cs, F, B) (Halls, 1994; Seltmann and Faragher, associated syn-peak metamorphism in Tibet might also provide 1994). In eastern Gangdese, very high Rb/Sr and Rb/Ba ratios, and suitable conditions for formation of orogenic lode Au deposits. MREE-depleted patterns of the muscovite granites with rare-metal These factors include: (1) translithopsheric structure marked by the (Rb, Cs, Li) mineralization suggest a clay-rich, plagioclase-poor shale IYS, along which a deep plumbing system was probably established source, whereas an obvious Eu anomaly and high F contents of the (Kerrich et al., 2000); (2) the second- or higher-order splays on both potassic granitoids hosting Sn deposits suggest a high ratio of biotite sides of the IYS (such as ductile–brittle shear zones and thrust faults), to plagioclase melting (Sylvester, 1998). This implies that crustal filled by a variety of veins and breccias (cf. Groves, 1993); (3) host anatexis caused by frictional heating during the main-collisional Table 2 Himalayan giant and large-sized deposits in the Tibetan collisional Orogen.

Deposits Longitude/ Metallic Tonnage Grade Tectonic setting and environment Host rock Metallogenic Genetic type Classiﬁcation and Exploitation Data source latitude commod. epochs ore-forming system status (s) Maoniuping (1) 101°58′ LREE 1.2 Mt REO 2.89% REO Haha strike-slip fault; the transform Nordmarkite with Late-collisional Complex - Alkali complex- Under Yuan et al. 28°23′ structural zone minor carbonatite period related REE related REE ore- exploitation (1995) forming system Dalucao (2) 101°57′ LREE 0.76 Mt REO 5.0% REO Dalucao strike-slip fault; the transform Nordmarkite with Late-collisional Complex - Alkali complex- Under (Yuan et al., 27°12′ structural zone minor carbonatite period related REE related REE ore- exploitation 1995; Yang forming system et al., 1998) Yulong (3) 97°44′ Cu–Mo Cu 6.5 Mt Cu: 0.99% Large-scale strike-slip fault belt; the Monzonitic granite; Late-collisional Porphyry Porphyry-type Cu- No (Tang and Luo, 31°24′ Mo:0.028% transform structural zone quartz monzonite; period Cu–Mo Mo ore-forming exploitation 1995; Hou Triassic sandstone system et al., 2003a) and mudstone Duoxiasongduo 97°55′ Cu–Mo Cu: 0.5 Mt Cu: 0.38% Large-scale strike-slip fault belt, the Alkali-feldspar granite; Late-collisional Porphyry Porphyry-type Cu- No (Tang and Luo, (4) 31°10′ Mo:0.04% transform structural zone Monzonitic granite period Cu–Mo Mo ore-forming exploitation 1995; Hou 2 (2009) 36 Reviews Geology Ore / Cook N.J. Hou, Z. system et al., 2003a) Malasongduo 98°00′ Cu–Mo Cu: 1.0 Mt Cu: 0.44% Large-scale strike-slip fault belt, the Monzonitic granite; Late-collisional Porphyry Porphyry-type No (Tang and Luo, (5) 31°00′ Mo: 0.14% transform structural zone syenitic granite period Cu–Mo Cu–Mo ore- exploitation 1995; Hou forming system et al., 2003a) Fulongchang 99°14′ Cu–Ag– Ag: ∼2000 t Ag: 328–547 g/t NE-striking second-order fault related Cretaceous transitional Late-collisional Sediment - Sediment-hosted Under (Chen, 2006; (6) 26°49′ Pb–Zn Cu: 0.12 12 Mt Pb: 4.2–7.4% to thrust fault; the front zone in the zone between porous period hosted vein- Zn-Pb (-Cu-Ag) exploration He et al., Cu: 0.63–11.7% western thrust-nappe system; the sandstone and low- type Zn-Pb- ore-forming 2009-this issue) transform structural zone permeability Cu -Ag deposit system carbonaceous argillite Sanshan– 99°18′ Zn–Pb Zn+Pb: N0. Pb: 1.27–3 3.5% Fracture zones within hanging-wall Upper Triassic dolomitic Late-collisional Sediment - Sediment-hosted Under (Chen, 2006); Yangzidong (7) 26°45′–43′ Cu–Ag 5 Mt; Ag: N3000 t Zn: 1.60–3.39% of Huachangshan thrust fault; the front limestone, breccia limestone, period hosted vein- Zn–Pb (–Cu–Ag) exploitation He et al., Cu: ∼0.3 Mt Cu: 0.38–1.8% zone in the eastern thrust-nappe system; sandstone and conglomerate type Zn–Pb– ore-forming 2009-this issue) Ag: 16–189 g/t the transform structural zone Cu–Ag deposit system Jinding (8) 99°25′ Pb–Zn Pb: 2.64 Mt Pb: 1.16–2.42% Structural and litholithic trap and dome Tertiary glutinite, argillaceous Late-collisional Sandstone - Sediment-hosted Under (Xue et al., 26°24′ Zn: 12.84 Mt Zn: 8.32–10.52% in the eastern thrust-nappe system; the dolomite, argillaceous period hosted Zn– Zn–Pb (–Cu–Ag) exploitation 2007; He et al., Ag: 1722 t Ag: 12.5–12.6 g/t transform structural zone siltstone, quartz sandstone, Pb deposit ore-forming 2009-this issue) siltstone system Baiyangchang 99°24′ Ag–Cu– No data Ag: 110–245 g/t, The front zone in the eastern Jurassic–Cretaceous high- Late-collisional Sediment - Sediment-hosted Under Hou et al. – (9) 26°07′ Pb–Zn Cu: 0.36–1.61% thrust-nappe system; the transform porous limestone and the period hosted vein- Zn–Pb (–Cu–Ag) exploration (2007a) 24 Pb: 0.22–3.24% structural zone overlying low-porous type Zn–Pb– ore-forming Zn: 1.11% carbonaceous argillite Cu–Ag deposit system Laownagzhai 101°27′ Au Au: 106 T Au: 3.7–7.7 g/t Red-River shear belt; the transform Basaltic lava, Paleozoic quartz Late-collisional Orogenic- Orogenic-type Under Hu et al. (10) 23°54′ structural zone greywacke and maﬁctuff period type Au Au ore-forming exploitation (1995) system Donggualin 101°26′ Au Au: 50 T Au: 5.2 g/t Red-River shear belt; the transform Paleozoic siliceous slate, Late-collisional Orogenic - Orogenic-type Under Hu et al. (11) 23°53′ structural zone meta-quartz sandstone, period type Au Au ore-forming exploitation (1995) and lamprophyre system Jinchang (12) 101°45′ Au Au: 27 T Au: 1–55.5 g/t Red-River shear belt; the transform Paleozoic tuffaceous Late-collisional Orogenic- Orogenic-type Under (Liu et al., 23°30′ structural zone sandstone, siltstone, period type Au Au ore-forming exploitation 1993; Hu and basaltic rocks, augite system et al., 1995) peridotite Daping (13) 102°59′ Au Au: N20 T Au: 1–32.5 g/t Red-River shear belt; the transform Diorite, granite porphyry, Late-collisional Orogenic - Orogenic-type Under Hu et al. (1995) 22°51′ structural zone lamprophyre, siliceous shale, period type Au Au ore-forming exploitation sandstone, limestone system

(continued on next page) 11 12

Table 2 (continued) Deposits Longitude/ Metallic Tonnage Grade Tectonic setting and environment Host rock Metallogenic Genetic type Classiﬁcation and Exploitation Data source latitude commod. epochs ore-forming system status (s) Lailishan (14) 98°16′ Sn Sn: 42 Sn: 0.63–1.58% Syn-collisional granite district; eastern Himalayan potassic granite; Main-collisional Cassiterite- Granite-related Under Liu et al. (1993) 24°55′ ,600 T segment of the Gangdese collisional zone Precambrian metamorphic period sulﬁde type Sn Sn–W–Uore- exploitation basement rocks forming system Yaguila (15) 92°40′ Pb–Zn– Pb+Zn: Pb+Zn: 15% Northern contact zones between Eocene Eocene granite with+eNd Main-collisional Skarn-type Skarn-type Cu–Au Under Tang, unpubl. 30°20′ Cu 4Mt granites and Carboniferous limestone; the value; Carboniferous period Pb–Zn–Cu polymetallic ore- exploration data collisional zone with stress relaxation limestone and tuffaceous forming system mudstone Mengya'a (16) 92°10′ Pb–Zn– Pb+Zn: N 0. Pb+Zn: 8.2% Northern contact zones between Eocene Eocene granite with+eNd Main-collisional Skarn-type Skarn-type Cu–Au Under Tang, unpubl. 30°20′ Cu 45 Mt granites and Carboniferous limestone; the value; Carboniferous period Pb–Zn–Cu polymetallic ore- exploration data collisional zone with stress relaxation limestone and tuffaceous forming system mudstone Xiongcun (17) 88°26′ Cu–Au Cu: 0.82 Mt Cu: 0.45 NW-striking fault fractural zone; the Mesozoic granitoids and Main-collisional Hybrid-type Skarn-type and Under Xu et al. ′ – – 29°23 Au: 113 T Au: 0.62 collisional zone with stress relaxation pyroclastic rocks, intruded period Cu Au hybrid Cu Au exploration (2009-this issue) 2 (2009) 36 Reviews Geology Ore / Cook N.J. Hou, Z. by Eocene granitic dykes polymetallic ore- forming system Jiama (18) 91°40′ Cu–Pb– Cu: ≥5Mt Cu:1.1% Orogen-transverse normal fault and its Mid-Miocene monzogranite Post-collisional Porphyry Porphyry-type Under Hou et al. 29°39′ Zn Pb: 3.48% intersection with thrust fault; the collisional period Cu–Pb–Zn Cu–Mo ore- exploration (2009a-this issue) Zn: 1.04% zone with post-collisional crustal extension forming system Au: 0.5 ppm Qulong (19) 91°38′ Cu–Mo Cu: 8 Mt Cu: 0.45% Orogen-transverse normal fault and its Mid-Miocene monzogranite Post-collisional Porphyry Porphyry-type Under Hou et al. 29°41′ Mo: 0.03–0.06% intersection with thrust fault; the collisional and granite period Cu–Mo Cu–Mo ore- exploration (2009a-this zone with post-collisional crustal extension forming system issue) Tinggong (20) 90°02′ Cu–Mo Cu: N1 Mt Cu: 0.5% Orogen-transverse normal fault; the Mid-Miocene quartz Post-collisional Porphyry Porphyry-type Under Hou et al. 29°35′ collisional zone with post-collisional monzogranite, granite period Cu–Mo Cu–Mo ore- exploration (2009a-this crustal extension forming system issue) Chongjiang 89°58′ Cu–Mo Cu: 1.5 Mt Cu: N0.45% Orogen-transverse normal fault; the Mid-Miocene monzogranite Post-collisional Porphyry Porphyry-type Under Hou et al. (21) 29°37′ collisional zone with post-collisional period Cu–Mo Cu–Mo ore- exploration (2009a-this crustal extension forming system issue) Bairong (22) 89°56′ Cu–Mo Cu: N0.5 Mt Cu: 0.73% Orogen-transverse normal fault; the Mid-Miocene monzogranite Post-collisional Porphyry Porphyry-type Under Hou et al. 29°37′ collisional zone with post-collisional period Cu–Mo Cu–Mo ore-forming exploration (2009a-this crustal extension system issue)

Narusongduo 88°48′ Pb–Zn– Pb+Zn: Pb+Zn: N20% Orogen-transverse normal fault and its Paleozoic and Mesozoic Post-collisional Vein-type Sediment-hosted Under Meng et al. – 24 (23) 29°57′ Ag N0.5 Mt intersection with thrust fault in a clastic sequences period Pb–Zn–Ag Zn–Pb (–Cu–Ag) exploration (2003) collisional zone ore-forming system Targejia (24) 85°44′ Cs(–Au) Cs: 14, Cs: 0.10–0.26% Modern geothermal field within orogen- Quaternary silica sinters Post-collisional Sinter -hosted Hot-spring-type No (Zheng et al., 29°36′ 459 T transverse rift zones; Collisional zone near the vents period Cs deposit Cs–Au ore-forming exploitation 1995; Zhao with post-collisional crustal extension system et al., 2006a) Mazhala (25) 91°49′ Sb–Au b10,000 T Sb Sb: 35, STDs and their intersection with orogen- Lower-Middle Jurassic clastics Post-collisional Vein-type Vein-type Sb–Au ore- Under (Nie et al., 28°27′ Au: 3.8 8 g/t transverse normal faults in the Tethyan and Cenozoic diorite porphyry period Sb–Au forming system exploration 2005; Yang Himalaya et al., 2009b-this issue) Shalagang (26) 89°54′ Sb ≥0.1 Mt Sb Sb: 31.5% STDs and their intersection with orogen- Early Cretaceous clastics, Post-collisional Vein-type Sb Vein-type Sb–Au ore- Under (Nie et al., 28°51′ transverse normal fault in the Tethyan siliceous rock, sandstone period forming system exploration 2005; Yang Himalaya and Cenozoic diorite et al., 2009b-this issue) Langkazi (27) 90°22′ Au No data Au: 2.0 g/t Detachment faults and their intersection Metamorphic core-complex Post-collisional Vein-type Au Vein-type Sb–Au ore- Under (Nie et al., 29°01′ with orogen-transverse normal fault in and central-intruded granites period forming system exploration 2005; Yang the Tethyan Himalaya et al., 2009b-this issue) Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 13 crustal thickening and associated breakdown of large amounts of enriched in metals (Sn, W) and incompatible elements (Rb, Cs, Li, Y), biotite in the source has produced a hydrous, metal-rich, low-fO2 felsic leading to Sn and rare-metal mineralization (Fig. 6A). Moreover, as magmatic system in the collisional zone. Moreover, advanced mentioned above, the main-collisional zone is not always compressive fractional crystallization in the evolved magma chamber probably and transpressive — it may also be extensional due to stress relaxation leads to further enrichment of Sn in the low fO2 magma system (cf. in the late stage of main collision, probably caused by slab break-off Lehmann et al., 2000). (Fig. 6A). Stress relaxation could allow shallow-level emplacement of Scavenging and replacement of Sn-rich fluids exsolved from evolved, volatile-rich, metalliferous, hybrid intermediate-felsic melts highly-fractionated and residual felsic melt along previously-existing derived from a MASH zone, and subsequent development of sulfide horizons are extremely important for metal concentration and magmatic-hydrothermal Cu–Au–Mo–Pb–Zn ore systems in a collision precipitation. Tin-rich fluids scavenged the metals in the pre- zone (Fig. 6A). collisional Sn mineralized granites and adjacent strata (Liu et al., 1993) during greisen-type alteration, further concentrating Sn in the 4.2. Metallogenesis in late-collisional transform setting ore-forming fluid system. Such fluids are believed to have replaced the Paleozoic massive pyrite lenses along sulfide horizons, which would Late-collisional metallogenesis was mainly developed in a transform have provided enough sulfur to form stratabound cassiterite-sulfide structural setting in eastern Tibet, dominated by Cenozoic strike-slip orebodies in favorable spaces (e.g., at Lailishan). faulting, shearing, and thrusting systems (Fig. 1), and formed one of the Crust/mantle interaction and Cu–Au–polymetallic deposits: The most economically-significant metallogenic provinces in China. Four Cu–Au–polymetallic mineralization is associated with the Eocene significant mineralization systems are recognized in the Tibetan Orogen granitoids coexisting with Eocene gabbro bodies, and formed (Fig. 5): porphyry-type Cu–Mo–Au systems controlled by Cenozoic numerous economically-significant Cu–Au polymetallic deposits, strike-slip faults; orogenic-type Au systems related to left-slip ductile located in both margins of the Gangdese Eocene granitioid batholith shearing; REE-systems associated with Himalayan carbonatite–alkaline (Fig. 1; Table 2). Most deposits are intrinsically associated with complexes; and Pb–Zn–Ag–Cu systems controlled by Cenozoic thrusting intrusive contacts and occur as skarn-hosted lenses and veinlets (Li and subsequent strike-slip faults (Table 2; Fig. 6B). et al., 2006a,b). Only a few porphyry-type Mo deposits and hybrid Cu– Porphyry-type Cu–Mo–Au system: late-collisional porphyry Cu– Au deposits (Xu et al., 2009-this issue), associated with Eocene felsic Mo–Au systems form an economically-significant Cu–Au province in stocks, were locally preserved due to batholith uplift and deep erosion SW China, including the world-class Yulong porphyry Cu belt in the (Fig. 1). Molybdenite Re–Os ages of 40.3 to 56.0 Ma for four skarn- Qiangtang terrane (Fig. 1; Hou et al., 2003a), as well as the major hosted deposits (Hou et al., 2006b) suggest a genetic link with the Yanyuan–Yao'an Au–Cu belt in the Yangtze block (Hou et al., 2006f). main-collisional felsic magma systems during the Eocene. Porphyry Cu deposits in the Yulong belt are associated with Cenozoic The metallogenic specialization of the Eocene granitoids, character- potassic felsic stocks, controlled by the NNW-strike strike-slip faulting ized by Cu–Au–Mo–Pb–Zn mineralization, is probably controlled by systems in eastern Tibet (Hou et al., 2005a). In contrast, the porphyry- processes that allowed concentration of metals and volatiles in the type deposits in the Yanyuan–Yao'an Au–Cu belt are associated with magmatic system. Eocene granitoids host mafic enclaves, and coexist potassic–ultrapotassic syenitic and granitic stocks (Hou et al., 2006f), temporally and spatially with contemporaneous gabbro intrusions, controlled by the basement faults that were reactivated during the suggesting a genetic link with the generation of the mantle-derived Indo-Asia collision. These Cenozoic strike-slip faults and reactivated mafic melts. Their positive εNd values (+2 to +3) imply a significant basement faults probably resulted in maximum magma flux into the contribution of a juvenile mantle component to the felsic melt. A upper crust, which constructed and sustained a large-volume, long- plausible interpretation is that main-collisional crustal thickening in lived upper-crustal magma chamber essential for producing a large Tibet hindered the ascent of the mantle-derived mafic magmas, which ore-forming system. were ponded at the bottom of the Tibetan lower crust and probably The most recent high-precision bulk-rock 40Ar/39Ar (Chung et al., underwent a MASH (melting of lower-crust, assimilation, magmatic 1998) and zircon U–Pb dating (Liang et al., 2006)define a relatively storage and homogenization) process (cf. Hildreth and Moorbath,1988). short duration (43 to 30 Ma) for the magmatic activity that generated

This MASH process yielded an evolved, volatile-rich, high-fO2, metalli- the host rocks. This activity peaked at 42±1 Ma, 36±1 Ma, and 32± ferous, hybrid intermediate-felsic melt (Richards, 2003; Hou et al., 1Ma(Hou et al., 2003a, 2006f), suggesting episodic recharging of 2006b). Meanwhile, the high oxidation state of the hybrid melt led to multiple felsic magmas into a high-level magma chamber in a sulfur deposition predominantly as sulfate (Carroll and Rutherford, transform structural setting. Molybdenite Re–Os dating yielded 1985), whereas chalcophile elements (Cu, Au etc.) became incompatible three distinct mineralization epochs (40±0.5 Ma, 36±0.5 Ma, 32± and were retained and concentrated in the evolving high-fO2 melt 1.0 Ma; Hou et al., 2006f), closely matching but slightly later than the system (Richards et al., 1991; Richards, 1995). Therefore, these high-fO2 episodic magmatism in eastern Tibet. This indicates that episodic hybrid felsic melts have large potential for forming economic Cu–Au–Mo stress relaxation in a transform setting promoted episodic emplace- deposits, thus distinguishing them from the low-fO2 crust-derived melts ment of stocks and associated exsolution of ore-forming fluids from that generated Sn–W and rare-metal mineralization. felsic magma chambers. Fig. 6A illustrates generation of the various deposit types in the The main lithologies hosting Cu–Mo–Au orebodies are monzo- main-collisional convergent setting and the structural constraints granites, quartz monzonites, K-feldspar granites and syenites. In imposed by a collisional orogen. It is noteworthy that formation of general, Cu–Mo and Cu–Au mineralization is associated with economically-significant metallogenic provinces and ore deposits was monzogranitic and granitic porphyries, whereas Au mineralization is previously regarded as unlikely in a syn- or main-collisional associated with syenitic porphyries (Hou et al., 2005a; Xu et al., 2007). geodynamic regime (Guild, 1972; Marignac and Cuney, 1999), since Most of the host porphyries, except for the syenites that contain compression and transpression usually results in the migration of mantle xenoliths, are shoshonitic and high-K calc-alkaline in fluids away from a collisional zone. It is important that this composition (Zhang et al., 1998a,b; Hou et al., 2003a), and show transpressive or compressive regime might cause syn-peak meta- geochemical affinity with adakites (Hou et al., 2003b; Jiang et al., morphism, which would release CO2-dominated metamorphic fluids 2006). The genesis of Cu-bearing felsic magmas has been debated, but necessary to form orogenic Au deposits (Fig. 6A; Kerrich et al., 2000). more and more evidence favors genesis via partial melting of a Meanwhile, volatiles driven off the wet sedimentary wedges during thickened (N50 km) mafic lower crust involving a juvenile mantle crustal thickening and overthrusting penetrate the overlying crustal component from the asthenosphere beneath eastern Tibet (Hou et al., rocks to cause anatexis, which would generate hydrous felsic melts 2004a, 2005b). 14 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24

Fig. 6. Three-stage tectono-magmatic evolution and resultant typical deposits in the continental collision orogenic system. (A) During the main-collisional period — continental impact and slab underthrusting resulted in crustal shortening, thickening, and associated syn-peak metamorphism, which produced crust-derived low-fO2 felsic melts by crustal anatexis and CO2-ﬂuids with metamorphic origin, as well as relevant Sn–W–U and Au mineralization in a collisional or central axial zone and in the foreland basin. Subsequent break- off of the subducted slab triggered upwelling of the asthenosphere, mantle/crust melting and stress relaxation, creating hydrous, high-fO2 felsic melts, a MASH process at the bottom of the lower-crust and formation of magmatic-hydrothermal polymetallic systems as well as MVT deposits in the foreland. (B) Late-collisional period — transform structural setting, characterized by large-scale strike-slip faulting, shearing and thrusting, was developed in the edges of the orogenic belt, to absorb and adjust strain and stress caused by collision. Translithospheric mega-shearing probably triggered upwelling of the asthenosphere, which resulted in potassic felsic, lamophyric and carbonatite-alkalic magma systems, derived from lithospheric mantle and crust-mantle transitional zone, and relevant magmatic-hydrothermal systems to form porphyry Cu–Mo–Au and complex-hosted REE deposits. Thrust- nappe systems at shallow structural levels controlled sediment-hosted base metallic deposits formed by long-distance migration of basinal brines. (C) Post-collisional period — lithospheric delamination, thinning at depth and crustal extension at shallow levels caused intense melting of the thickened crust. Anatexis of the middle-upper crust generated lecuogranitic magmas and associated Sn–W–U mineralization in the central axial zone and Au mineralization in the foreland. Melting of a thickened, newly-formed lower-crust created potassic felsic magmas with porphyry Cu–Mo mineralization in the collisional zone. The detachment fault systems related to extension and high-level emplacement of felsic magmas commonly drive convective geothermal systems and associated Au, Au–Sb, Sb, and Cs mineralization in the rift zone and in the exhumed core complex or domes. Inﬁll by terrestrial sediments in the foreland basin and in rift basins within the orogenic belt is commonly associated with sandstone-type U deposits.

The geology and mineralization of typical late-collisional por- veinlet-disseminated orebodies within the stocks, with or without a phyry-type Cu–Mo, Cu–Au and Au–Cu deposits have been described ring-shaped, high-grade Cu–Au zone overlying or surrounding a by many authors (Rui et al., 1984; Tang and Luo, 1995; Hou et al., porphyry-type Cu–Mo orebody (Hou et al., 2003a). Associated hydro- 2003a; Xu et al., 2007). These deposits, though occurring in a thermal alteration commonly forms a concentric zonation aureole, transform structural setting unrelated to oceanic-slab subduction, extending from an inner K-silicate zone outwards through quartz– show broad similarities with those in arc settings in many aspects, sericite to an outer propylitic zone (Tang and Luo, 1995; Hou et al., such as mineralization style, alteration zonation, and sulﬁde associa- 2003a). A few deposits (e.g., Yulong) occur within the structurally- tion (see Hou et al., 2003a, and references therein). They are usually controlled advanced argillic alteration and display features of high- associated with steeply dipping, pipe-like multiphase felsic stocks sulﬁdation epithermal Cu–Au or Au mineralization which overprint with explosive pipes, and are dominantly composed of pipe-like the earlier porphyry-type alteration and mineralization (Hou et al., Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 15

2007b). Fluid inclusion and δ18O–δD data indicate that supercritical Zn–Pb–Cu–Ag ore systems: Cenozoic Zn–Pb–Cu–Ag ore systems fluids which exsolved from a high-level magma chamber underwent occurred in the Lanping foreland fold belt within the late-collisional similar evolution and mineralization processes to those in arc settings transform structural setting, and formed the largest known Ag-bearing (Hou et al., 2007b). basemetalprovinceineastTibet(Fig. 1). The Lanping fold belt under- REE-bearing ore systems: REE-bearing ore systems are associated went a complex tectonic evolution involving late Triassic rifting, Jurassic– with Oligocene carbonatite–alkalic complexes, controlled by Cenozoic Cretaceous depression, early Tertiary foreland basin development, and strike-slip fault systems. They comprise a world-class REE metallogenic finally formed part of the Lanping–Simao fold belt (Wang et al., 2001), belt at the western margin of the Yangtze block involved the eastern as a consequence of the eastern Tibetan crust shortening related to the Indo-Asian collision zone (Fig. 1; Table 2). Total reserves exceed 3 Mt Indo-Asian collision (Wang and Burchfiel, 1997). In the fold belt, two LREE (Yuan et al., 1995). The geology and other features of the REE large-scale Cenozoic thrust-nappe systems juxtaposed Mesozoic lime- deposits in this belt are described in detail elsewhere in this special issue stone and gypsum-bearing clastic strata over the Tertiary strata in the (Hou et al., 2009b-this issue). Continuous carbonatitic melt-fluid foreland basin, and control the spatial distribution of Cenozoic base evolution of the REE mineralization system has been established metal deposits (Chen, 2006; He et al., 2009-this issue). Each thrust- based on fluid inclusion studies on typical deposits (e.g., Maoniuping; nappe system appears to sole into a common gently-dipping detachment Xie et al., 2009-this issue). A number of significant aspects of the REE ore zone, which is regarded to have probably provided a significant conduit systems are emphasized in the following paragraphs. for regional fluid flow (Xu and Li, 2003; Hou et al., 2006c). It is widely known that primary REE deposits worldwide mainly Based on the mineralization styles, ore types, host rocks and occur in continental rift zones (cf. Mitchell and Garson, 1981). structural control, at least three major mineralization types have been However, available age data from hydrothermal minerals define a recognized: (1) sandstone-hosted Zn–Pb deposits; (2) carbonated- Himalayan metallogenic epoch (40 to 28 Ma) for most REE deposits, hosted Zn–Pb–Cu–Ag deposits; and (3) vein-type Cu–Ag polymetallic identical to the crystallization age of the late-collisional host rocks in deposits (Table 2). He et al. (2009-this issue) describe these thrust- the eastern collisional zone (Yuan et al., 1995; Yang et al., 1998; Pu, controlled, sediment-hosted Zn–Pb–Cu–Ag deposits, and further 2001; Tian, 2005; Tian et al., 2008). The temporal-spatial relationship constrain the timing of regional mineralization to the Late Eocene– of the carbonatite–alkalic complexes and associated REE orebodies Early Oligocene (∼42 to 30 Ma). suggests that Cenozoic strike-slip faulting and resultant pull-apart Sandstone-hosted Zn–Pb deposits are represented by the Jinding structures and tensional fissure zones facilitated formation of the REE- deposit, the youngest giant sandstone-hosted Pb–Zn deposit in the bearing magmatic-hydrothermal systems and exsolution of ore- world. Xue et al. (2007) reviewed the geologic, fluid inclusion and stable forming fluid from the system in a transform structural setting. isotope characteristics of the deposit. New data obtained by the 973 Although almost all primary REE deposits in the world are Project allowed further aspects of ore genesis to be clarified. Firstly, the associated with carbonatite–alkalic complexes, the host alkali rocks 3D-dimensional topographic reconstruction indicates that the Jinding in rift zones are variable in composition from aegirine–augite syenite deposit generally has a mushroom-like shape and its main orebodies are and nepheline syenite to ijolite (Hou et al., 2009b-this issue). In trapped by a structural dome, mainly occurring as tabular body and contrast, the host alkaline rocks in the eastern collisional zone are lenses in Tertiary porous, gypsum-bearing clastic horizon and overlying predominantly nordmarkite with minor aegirine–augite syenite, Cretaceous sandstone (Xiu et al., 2005). Secondly, three distinct types of demonstrating the low alkalinity of the magma system. Host breccias are recognized at Jinding, i.e., structural, dissolution, and carbonatites in rift zones are usually enriched in Nb, Ta, P, Ti, and Fe explosive breccias (Wang et al., 2007). The breccias, created by and their generation is related to mantle plume activity (Harmer and dissolution of gypsum, are abundant throughout the district. Their Gittins, 1998). Collisional zone carbonatites are, in contrast, relatively clasts consist of black limestone, silty limestone, and coarse sandstone, depleted in high-field strength elements (Nb, Ta, Zr, Hf, Ti), and were whereas the matrix is composed of red-mudstone, siltstone and relic derived from subcontinental lithospheric mantle (Hou et al., 2006e). gypsum. These dissolution breccias represent unstable horizons with The fenitization and vein-type mineralization of the late-colli- significant lateral extent and display a vertical zoning, showing the sional REE deposits are generally comparable with those in rift zones collapse features of a salt-dome during gypsum dissolution. The (cf. Hou et al., 2009b-this issue), but mineralization styles in different explosive breccias occur as “dyke” or “sill” intruded the gypsum- districts in the eastern collisional zone range widely from stockwork- dissolved breccia horizons. The clasts of the breccia are dominated by stringer to breccia-pipe types, depending on the P–T conditions devel- black limestone, the matrix mainly consisting of the oxidized Pb–Zn oped beneath the magmatic-hydrothermal systems. Orebody shapes sulfide assemblages. These features suggest intense explosion and are also variable from lenticular to pipe-like. Ore types are dominat- discharge of high-pressure fluids associated with mineralization. ed by pegmatitic, carbonatitic, brecciated, stringer (stockwork), and Thirdly, three types of bitumen have been observed at Jinding, i.e., disseminated ores; they are composed of barite+ fluorite+aegirine– soft, brittle, and dense oil–bitumen (Wang et al., unpubl. data). These augite+calcite+bastnaesite assemblages (Yang et al., 1998, 2000, occur in fissures within the limestone clasts and matrix, and are 2001). associated with celestine and oxidized sulfide assemblages, implying Melt/fluid inclusion studies and stable isotopic data indicate that the existence of an old oil–gas trap prior to, or during mineralization. the ore-forming fluids were produced by an immiscible carbonatite– Fourthly, the deposit shows a clear mineralogical zonation, from east to nordmarkite magmatic system in the eastern collisional zone (Liu west, varying upwards from celestine+barite, pyrite+marcasite, et al., 2004). The initial ore-forming fluids were high-temperature galena+sphalerite to galena assemblages (Luo et al., 1995), suggesting (600 to 850 °C), high-pressure (N350 MPa) and high-density super- westward migration and upwards discharge of the ore-forming fluid critical fluids, characterized by enrichment in sulfates (BaSO4,K2SO4, (Xue et al., 2007). On the basis of these data, Wang et al. (2007) and CaSO4), CaCO3 and CaF2 (Xie et al., 2009-this issue). The synthetic proposed a two-stage model for the formation of the Jinding deposit, in studies led to a possible genetic model for REE mineralization (Hou which an early thrust-nappe system led to the structural-salt dome and et al., 2009b-this issue). In this model, the hydrothermal system oil-gas trap, subsequent fluid discharge was directed upwards and underwent a complex evolution from separation of high-T sulfate- explosion of high-pressure or ultra-high-pressure ore-forming fluids bearing NaCl–KCl brine, through fluid boiling resulting in effective (Chi et al., 2006) caused breakage of the salt-dome and precipitation of deposition of REE-fluorocarbonate and sulfate, to subsequent mixing sulfide-sulfate assemblages. with low-T meteoric water precipitating minor sulfide assemblages, The carbonate-hosted Zn–Pb–Cu–Ag deposits (e.g., the Sanshan thus generating a three-phase architecture of REE mineralization deposit) are controlled by an east-dipping thrust fault and associated systems at various structural levels. second-order faults (i.e., strike-slip faults) within the front zone of the 16 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 eastern thrust-nappe system. Orebodies are mainly hosted in Triassic granulite facies metamorphism in the lower crust but also involving a limestone, and occur as lenses, semi-layered, and irregular bodies, contribution from the mantle. Interaction with crustal rocks during showing open-space filling and stratabound features (He et al., 2009- large-scale shearing might have played an important role in the this issue). Vein-type Cu–Ag polymetallic mineralization mainly generation of Au deposits. occurs within second-order fissure zones in the western thrust- Fig. 6B illustrates the Cenozoic ore deposits and their relationship nappe system, and shows a metal zonation northeastwards varying to major structures and magmatic suites in eastern Tibet, a transform from Cu in the root zone (e.g., Jinman) to Cu–Ag or Ag–Cu–Zn–Pb in structural setting. Late-collisional metallogenesis involved translitho- the front zone (e.g., Fulongchang) (He et al., 2009-this issue). spheric shearing and faulting at a deep structural level and crustal Fluid inclusions in all these deposits indicate low temperatures shortening and thrusting at shallow level within a transpressive (predominately b200 °C), and high but variable salinities (1.6 to setting. A shared deep lithospheric process involving upwelling of the 27.7 wt.% NaCl equiv.), suggesting that basinal brines were the main asthenosphere is required to interpret the formation of potassic felsic source of ore-forming fluids (He et al., 2009-this issue). Similarities in and carbonatitic magma systems and associated ore-forming mag- Pb isotope composition between ore sulfides and rock units in the fold matic-hydrothermal systems in a transform structural setting. These belt suggest scavenging from these strata by regional fluids as a magmas, derived from subcontinental lithospheric mantle or the significant mechanism of metal enrichment. Although the deposits crust/mantle transitional zone, probably migrated along lower-crustal share some similarities with MVT-, SST-, SSC-, and SEDEX-type shears and middle-crustal fault conduits, and were recharged into a deposits, in respect to the lack of any igneous affinity and relationship voluminous, long-lived magma chamber in the upper crust. Stress with activities of basinal fluids, they also show a set of unique features. relaxation in a transform structural setting caused release of ore- The latter includes: (1) they were formed in a strongly deformed forming fluids from the magma system, and resulted in precipitation foreland basin within a collision zone, and closely related to regional of metals (REE, Cu, Mo, Au) during fluid boiling or phase-separation thrust-nappe structures; (2) they are fault-controlled, commonly (Hou et al., 2003a, 2009b-this issue). Deep-level ductile shearing and without strong preference for type of host rocks; and (3) they contain associated granulite-phase metamorphism led to generation of CO2- a variety of metals including Zn, Pb, Cu, Ag, and minor Sr, Co, etc. (He dominated metamorphic fluids, which interacted with the granulite et al., 2009-this issue) suggesting that thrust system-controlled, rocks in the lower crust and finally formed the Au orebodies in brittle sediment-hosted Zn–Pb–Cu–Ag deposits are most likely a new sub- structures within upper-crustal ductile shear zones (Sun et al., 2009- type within the family of sediment-hosted base metal deposits. this issue). The thrust systems at shallow structural levels caused migration of crustal fluid toward the foreland basins, during which 4.2.1. Orogenic-type Au ore system metals were scavenged from the strata and fluids were subsequently Orogenic-type Au mineralization in the Ailaoshan Au belt in west discharged along fissure structures and strike-slip faults to form Yunnan represents a significant Au metallogenic province in the structurally-controlled, sediment-hosted Zn–Pb–Cu–Ag deposits (He Tibetan Orogen (Fig. 1). Hou et al. (2007a) summarized the geology et al., 2009-this issue). and mineralization characteristics of the gold belt (Table 2). Sun et al. (2009-this issue) report new research results from the Daping 4.3. Metallogenesis in post-collisional extension setting deposit, which is typical of the belt. The most important aspects involving genesis of the deposits are emphasized here. The post-collisional period is an important metallogenic epoch in The Ailaoshan Au belt is located in the Paleozoic Jinsha–Ailaoshan the Tibetan Orogen. Post-collisional metallogenesis is mainly devel- suture, marked by Palaeozoic Ailaoshan ophiolite mélanges (Liu et al., oped in a mid-Miocene crustal extensional setting, characterized by 1993), and the belt is structurally controlled by the Red-River Shear E–W extension, N–S-striking normal faults, EW-striking STDs and Zone (RRSZ), which is currently a right-slip fault accommodating post-collisional potassic–ultrapotassic rocks and leucogranites. Four earlier left-slip shear (Leloup et al., 1995; Gilley et al., 2003). Recent significant mineralization systems have been recognized in the age data for potassic–ultrapotassic rocks and lamprophyres along the Tibetean Orogen: porphyry Cu–Mo systems related to post-collisional RRSZ (40 to 33 Ma) suggest initial left-slip shearing started at 40 Ma potassic adakite intrusive rocks; vein-type Sb–Au systems controlled but continued up to 27 Ma (Liang et al., 2007). Recent high-precision by STD and dome structures, vein-type Pb–Zn–Ag systems controlled 40Ar/39Ar dating yielded a limited mineralization age range of 34 to by intersections of thrust faults with normal fault; and modern hot- 41 Ma for most of Au deposits (Wang et al., 2005, and references spring-type Cs–Au systems (Figs. 1 and 5; Table 2). All types of these therein), demonstrating that this Cenozoic Au mineralization is ore-forming systems occur in the mid-Miocene Gangdese tectono- related to large-scale shearing during the late-collisional period. magmatic belt in Tibet (Fig. 1). Moreover, post-collisional crustal Almost all the gold deposits formed in the greenschist-facies extension also resulted in the development of metamorphic core metamorphic mélanges are associated with highly-pyritized, dolomi- complex along the eastern margin of the Tibetan plateau, which is tized, and sericitized alteration. The orebodies occur mainly as veins, associated with Au mineralization in the Yangtze block (Hou et al., irregular, lenticular bodies in altered rocks and within intrusive 2006d). contact zones (Hu et al., 1995; Li et al., 2000). They appear generally controlled by lithologically-brittle structures within the ductile shear 4.3.1. Porphyry Cu–Mo ore system zones (Hu et al., 1995). Some Au deposits are associated with Cenozoic Porphyry-type Cu–Mo deposits, the most important deposit type lamprophyre and granodiorite stocks which intrude the ophiolite formed in the post-collisional period, form a world-class porphyry Cu mélange, suggesting a genetic link between Au mineralization and belt within the mid-Miocene Gangdese tectono-magmatic belt (Fig. 1; Cenozoic mantle-derived magmas (Huang and Wang, 1996). Ore- Qu et al., 2001; Hou et al., 2004a,b, 2006d). Hou et al. (2009a-this forming fluids belong to the CO2-rich, low-salinity (6.4–12.6 wt.% NaCl issue) report on the geology and mineralization features of the newly- equiv.), NaCl–H2O system (Xiong et al., 2006; Sun et al., 2009-this discovered porphyry Cu belt, while Yang et al. (2009a-this issue) issue). Their origin has been controversial, and has been attributed to: describe in detail the geology and alteration of the giant Qulong (1) mixing of magmatic water with meteoric water (Hu et al., 1995); deposit, the largest in the belt. Qu et al. (2009-this issue) have used (2) the product of mantle-derived fluids (Hu et al., 1998, 1999); and cathodoluminescence imaging, combined with SHRIMP U–Pb dating, (3) a mixture of metamorphic and crustal fluids derived from a wet to provide constraints on the timing of porphyry emplacement in the sedimentary wedge (Huang and Wang, 1996). Based on detailed Gangdese belt. studies of the Daping Au deposit, Sun et al. (2009-this issue) A widely accepted model holds that porphyry-type deposits concluded that the ore-forming fluid was dominantly derived from usually occur in island arcs and continental margin arcs related to Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 17 oceanic-slab subduction (Sillitoe, 1972; Mitchell, 1973). The post- but instead favors the high-flux magmas to ascend upwards into a collisional Gangdese porphyry Cu belt (GPCB) in Tibet thus provides a voluminous, highly-evolved magma chamber in the upper crust. The new class of porphyry Cu deposits, apparently unrelated to subduc- orogen-transverse normal faults and their intersections with pre- tion. These Cu deposits are associated with mid-Miocene felsic existing lineaments and faults provide optimal conditions for focused multiple stocks, which intruded Andes-type Gangdese arc batholiths flow and emplacement for magmatic-hydrothermal systems, thus (120 to 70 Ma) and syn-collisional geological units (65 to 52 Ma) placing constraints on the spatial-temporal localization of Cu-bearing within the Lhasa terrane. Individual deposits are controlled by near N– felsic stocks. S-striking (i.e., orogen-transverse) normal faults (N13.5 Ma; Blisniuk et al., 2001). Available dating defines the timing of felsic magmatism 4.3.2. Sb–Au ore systems to have been 18 to 13 Ma, peaking at 16±1 Ma (Hou et al., 2004a), at The Cenozoic Sb–Au ore-forming system was developed in the least ∼50 Ma after subduction-related arc magmatism, but following Tethyan–Himalayan block in south Tibet, and is related to the south the onset of E–W extension at ∼18 Ma (Williams et al., 2001), Tibetan detachment system (STD), created during the post-collisional exhumation of the Gangdese batholiths at 18 to 21 Ma (Copeland period. The vein-type Sb–Au deposits within this ore-forming system et al., 1987; Harrison et al., 1992) and molasse deposition at 19 to constitute an EW-extending, Sb–Au metallogenic belt with great 20 Ma (Harrison et al., 1992). Molybdenite Re–Os dating of these potential in south Tibet (Fig. 1; Table 2). Yang et al. (2009b-this issue) porphyry Cu deposits yielded a range of mineralization ages ranging report on the geology and mineralization of the belt; some genetic from 14 to 16 Ma (Hou et al., 2003b), suggesting that the regional Cu– aspects are summarized below. Mo mineralizing event was coeval with emplacement of mid-Miocene The Tethyan–Himalayan block is characterized by gently north- felsic stocks in a post-collisional extension setting. wards-dipping Neogene detachment fault systems, which connect The host rocks in the GPCB are usually high-K calc-alkaline with with the STD to sole into a common gently-dipping detachment zone minor shoshonites, and show geochemical affinity to adakites (Hou beneath this block (Xu et al., 2006). Due to exhumation and erosion et al., 2004a). The genesis of the adakitic host rocks has been debated; related to extension, numerous metamorphic core complexes were their sources have been variably attributed to a thickened lower crust developed in the block. Their centers were intruded by mid-Miocene (Chung et al., 2003), a newly-formed mafic lower crust (Hou et al., leucogranite intrusions, leading to numerous thermal domes (Chen 2004a) and the subducted Neo-Tethyan slab (Gao et al., 2007). The et al., 1990). The majority of vein-type Sb–Au deposits are distributed growing lines of evidence support the hypothesis that they were around the thermal domes, and display a concentric zoning outwards derived from partial melting of a thickened (N50 km), newly-formed from Au and Au–Sb to Sb mineralization (Yang et al., 2009b-this mafic lower crust involving a juvenile mantle component (Hou et al., issue). Almost all orebodies are controlled by EW-trending detach- 2009a-this issue). Heat energy to trigger lower-crustal melting was ment faults and their intersections with N–S-striking normal faults probably provided by either upwelling of asthenospheric mantle (Fig. 1; Nie et al., 2005). Yang et al. (2009b-this issue) recognized through a window resulting from break-off of the subducted Indian three styles of Sb–Au mineralization in southern Tibet: Sb-only, Sb– continental slab at ∼25 Ma (Maheo et al., 2002; Williams et al., 2004) Au, and Au-only mineralization styles. These deposits generally show or by mantle thinning due to delamination (Chung et al., 2005). characteristics of epithermal deposits, but are distinguished from The post-collisional Cu deposits in the GPCB reinforce some typical epithermal Au deposits in arc volcanic settings and orogenic Au generalizations about their characteristics (e.g., mineralization style, deposits associated with syn- or post-peak metamorphism (cf. Kerrich alteration zoning, metal association, and ore-forming fluids) com- et al., 2000). pared to porphyry Cu deposits in arc settings (Hou et al., 2009a-this Systematic mineralogical zonation from Au and Au–Sb to Sb, and in issue; Yang et al., 2009a-this issue). However, the formation of both ore-forming fluids from magmatic water-dominated to meteoric deposit classes involved distinct processes for enriching in H2O, water-dominated fluids (cf. Yang et al., 2009b-this issue), from the metals and S in the metal-bearing magma systems. In arc settings, the metamorphic dome outwards, imply that the mineralization is

H2O in calc-alkaline Cu magmas was derived from dehydration of an controlled by a hydrothermal convection system driven by leucogra- enriched mantle wedge (Richards, 2003), metasomatized by the nitic intrusions. Near the intrusion-centered hydrothermal system, Au subduction-slab fluids. In contrast, breakdown of amphibole in lower- deposits, dominated by fine-vein, breccia, and disseminated Au ores, crust during melting is regarded as the most significant mechanism in occur in strongly-silicified metaclastic rocks and the fracture zones the formation of hydrous, high-fO2, potassic Cu magmas in a around the metamorphic domes. Far away from the intrusions, a collisional zone (Hou et al., 2005b, 2009a-this issue). Metallic Cu gently-dipping (to N) detachment zone not only increased perme- and S in the calc-alkaline magmas in arc setting were usually derived ability of the strata, but also provided an important conduit for fluid from the subducted oceanic-slab or wedge mantle (Richards, 2003). flow. Intersections between the detachment zone and N–S-striking However, lower-crustal genesis of the host rocks in the Tibetan normal faults probably are sites of discharge for low-temperature (150 collisional zone rules out the possibility that S and metallic Cu entered to 300 °C), low-salinity (1.2 to 5.9 wt.% NaCl equiv.) ore-forming fluids, the magmatic system either via mass transfer from the subducted dominated by meteoric water (Yang et al., 2009b-this issue). A much oceanic slab or directly by mantle melting. Early-stage ore sulfides wider δ34S range (−2.7 to +11‰) for sulfide ores suggests that fluid and their least-altered host rocks yield average δ34S values of −0.08‰ scavenging of host rocks plays a significant role in the formation of Sb– and −0.75‰, respectively (Qu et al., 2007), which are typical of Au deposits in southern Tibet. mantle sulfur. This implies that S and Cu were ultimately derived from juvenile mantle components in the newly-formed lower-crust rather 4.3.3. Vein-type Pb–Zn–Ag ore system than from ordinary crustal rocks by scavenging of fluids. It is most Vein-type deposits, formed by Pb–Zn–Ag ore-forming systems in likely that an indirect contribution of chalcophile metals from the the post-collision period, occur along the northern edge of the mid- mantle to the magma system is a key factor in making them fertile for Miocene Gangdese porphyry Cu belt, and formed a paired mineralized porphyry Cu–Mo deposits. belt in the Lhasa terrane (Fig. 1). The Ag–Pb–Zn mineralization belt Calc–alkaline magmas in arc settings usually underwent a MASH was spatially controlled by the E–W-trending Cuoqin–Pangduo thrust process at the base of the crust, which yielded evolved, volatile- and fault zone, formed by shortening of the Lhasa terrane during the late- metal-rich, hybrid fertile melts (Richards, 2003, 2005), thus being collisional period (Fig. 1; Ye, 2004). Individual deposits are located at inherently capable of forming porphyry Cu deposits. However, the the intersections of E–W-trending thrust faults and N–S-striking extensional tectonic regime in the post-collisional period would not normal faults (Hou et al., 2006d). Mineralization ages and styles are permit adakitic magmas to undergo a MASH process like arc magmas, variable along the belt. Mineralization in the eastern segment is 18 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 dominated by vein- and skarn-type mineralization. Molybdenite Re– thrust-related crustal overlapping and slidie-detachment at multi- Os dating yielded an age range of 13 to18 Ma for mineralization (Meng structural levels. At least five structural units have been recognized et al., 2003), identical to that of the Gangdese porphyry Cu deposits across the orogenic system: foreland basin; foreland thrust zone; (Hou et al., 2003c), demonstrating a genetic link with the mid- collisional suture; main-collisional zone; and hinterland thrust-fold Miocene porphyry Cu ore system. In the western segment, miner- zone (Fig. 2A). Representative of symmetric orogenic systems is the alization is dominated by vein-type Ag–Pb–Zn orebodies, controlled Pyrenean Orogen (Choukroune, 1992; Sibuet et al., 2004), which is by E–W-trending thrust faults, and featuring silicification and weak characterized by symmetrical contractional systems and central fan- chloritization and carbonatization of the host strata. K–Ar dating of shaped structures resulting from horizontal compression. Based on hydrothermal mica yields an older age (25 Ma; Meng, unpubl. data), regional geology (cf. Choukroune, 1992) and the deep seismic resembling the initial timing of the post-collision event (∼25 Ma). reflection profiles (cf. Roure and Banda, 1987; Roure et al., 1989; Ores with up to 1 kg/t Ag display disseminated, veinlet, breccia, Choukorune and ECORS Team, 1989), a complete structural section massive and banded structures. In general, these post-collisional Ag- has been established for the Pyrenean Orogen, in which the foreland bearing base metal deposits are comparable with thrust-controlled, thrust zone and the foreland basin were symmetrically developed sediment-hosted Zn–Pb–Cu–Ag deposits in the Lanping fold belt. on both sides of the central axial uplift zone (cf. Sibuet et al., 2004; Meng et al. (2003) accordingly proposed a similar structural control Fig. 2B). Composite-style orogenic systems are represented by model for their generation. the Qinling Orogen (Fig. 2C), which first underwent a Paleozoic Cesium-gold ore systems: An unusual Cs–Au ore system occurs in asymmetric-style orogeny involving collision between the Qinling the world-class Tibetan–Himalayan active geothermal zone, related to terrane and the North China block, and a subsequent Mesozoic the post-collisional magmatism or the Tibetan upper-crust partial symmetric large-scale orogeny resulting from collision between the melting layer (Hou et al., 2004a; Li et al., 2005). Preliminary surveys North China and Yangtze blocks since the Late Triassic (Zhang et al., show that the ore-forming systems form two large-sized Cs deposits 1996; Xu et al., 1996). These orogenic systems, each with their (Table 2) and numerous small Cs and Cs–Au deposits and occurrences distinct orogenic styles, underwent different tectono-magmatic (Zheng et al., 1995). These are mainly located at the intersection sites evolutions, and thus resulted in different ore-forming systems and between N–S-striking rift zone and the IYS, clustering in a hot-spring resultant deposit types (Table 3). active field with crustal-derived He (Hou et al., 2004b)(Fig.1). Cesium In an asymmetric orogen, e.g., the three-stage collisional Tibetan occurs as Cs-bearing opal in silica sinters, i.e., geyeseite (Zheng et al., orogen, the transform structural setting in the late-collisional period is 1995), composed of at least five sedimentary cycles with the earliest the most spectacular of all continental collision orogenic systems. age of 0.1 Ma, estimated by the electron spin resonance (ESR) method Large-scale translithospheric strike-slip faulting and shearing in the (Zhao et al., 2006a). The giant Targejia deposit is the largest, late-collisional transform setting resulted in generation of potassic, containing 14,459 t Cs with the highest grade of 1.3% Cs (Table 2). felsic, lamprophyres and carbonatitic magmas, derived from sub-

Cesium-bearing geyeseite has a range of eSr from 85.9 to 112 and of continental lithospheric mantle or/and the crust-mantle transitional eNd between −9.7 and −7.6 (Zhao et al., 2006b), close to upper zone (Hou et al., 2006c), and fundamentally controlled the mantle- crustal values, suggesting an upper crust source for the Cs. Hot-spring derived (e.g., Cu, Au, REE) metallogenic provinces (Fig. 6B). The fluids venting in the district contain abnormally high Cs concentra- thrust-nappe systems formed by internal shortening were developed tions ranging from 3.85 to 4.48 mg/L (Zheng et al., 1995), and display on the foreland basin in the transform setting, and controlled a crust- positive correlations between Cs with B, Cl, and Rb (Li et al., 2005), derived metallic (e.g., Zn, Pb, Ag) metallogenic province, in which suggesting that Cs is sourced within a high-level magma chamber numerous sediment-hosted Ag-bearing base metal deposits were source or upper-crustal partial melting layer. Based on measured generated by scavenging and discharging of basinal fluids that temperature (74.0–85.5 °C) and the SiO2 contents of hot spring water migrated along a deep detachment zone (Fig. 6B). (Zheng et al., 1995), Li et al. (2005) estimated that a SiO2-satuated, Cs- In symmetric orogens (e.g., the Pyrenees), the fan-shaped rich hydrothermal fluid reached at least 250 °C at depth, and structures (tectonic wedge) probably substituted for the late- precipitated Cs-bearing opal at about 100 °C. collisional transform structures, and absorbed crustal shortening Fig. 6C depicts post-collisional metallogenesis and the relationships and adjusted the collision strain (cf. Choukroune, 1992). In the fan- between different types of deposits and post-collisional structures in shaped structure zones, volatiles driven off the wet sedimentary Tibet. Metallogenesis relates to post-collisional crustal extension and wedge during crustal overthrusting not only penetrated the hot resultant felsic magma systems that were derived from newly-formed overlying thrust sheet to result in large-scale crustal anatexis (Harris lower crust and/or produced by crustal anatexis and crustal fluid flows et al., 1986), in turn creating large volume granitic magmas in the controlled by orogen-parallel deep detachment faults, and/or orogen- foreland thrust and the central axial uplift zones (Fig. 6A), but also transverse normal faulting. Generation of porphyry Cu deposits requires caused metals (W, Sn, U) and incompatible elements (Rb, Cs, Li, Y) to the contribution of a juvenile mantle component sourced in the lower become enriched in the resulting felsic melts (Seltmann and Faragher, crust to a hydrous, high-fO2, metallic-rich felsic magma system, and is 1994). These crust-derived, hydrous, low-fO2 felsic systems, whether related to deep lithospheric process, e.g., slab break-off or delamination occurring in the main-collisional (e.g., the Tibetan Orogen) or in post- (Fig. 6C). The Sb–Au and Cs–Au mineralization requires crustal ex- collisional periods (e.g., the Pyrenean Orogen), have great potential tension to allow exhumation of metamorphic core-complexes and the for ore formation and are documented to have formed abundant W formation of rift zones as well as crust-derived magma systems to derive and U deposits (Fig. 6A, C; Le Roy, 1978; Kelly and Rye, 1979). In convective hydrothermal systems (Fig. 6C). symmetric orogens, the foreland basins were commonly developed outside the foreland thrust zones (Fig. 2B), and basinal sediments 5. Classification of collision-related deposits and comparison with were usually not or only weakly deformed. These foreland basins, such global examples as the Cevennes and Ave basins in the Pyrenean orogen, typically contain clusters of MVT-type Zn–Pb deposits (Puigdefabregas et al., Global collisional orogen systems, in terms of their orogenic 1992; Bradley and Leach, 2003) and also sandstone-hosted copper polarity, principal architecture, and crustal geometry, may be deposits (Subias et al., 2001). Long-distance lateral migration of fluids divided into three major orogenic-styles, i.e., asymmetric, sym- through stable permeable aquifers at deep-structural levels was metric, and composite-styles (Fig. 2). Asymmetric orogenic systems, regarded as a significant mechanism for generating the MVT Zn–Pb represented by the Himalayan–Tibetan Orogen (Yin and Harrison, deposits in weakly-deformed sedimentary basins (Sverjensky, 1986; 2000), are characterized by single-oriented orogenic polarity and Leach et al., 2005). Table 3 Classification of collision-related deposits and their geologic characteristics.

Deposit group Deposit type Tectonic setting Structural control Stress regime Host rocks and their sources Mineralization and Typical examples References (genetic clans) ore fluid Porphyry-type Porphyry Cu– Late-collisional transform structural Strike-slip fault and strike-slip Transpressional; Monzogranite; granite; monozonite, Fined-vein and Yulong; Qulong; (Tang and Luo, ore-forming Mo deposit zone; Collisional zone with post- pull-apart basin; Orogen- transtensional and granodiorite, derived from a disseminated; Tibetan Orogen 1995; Hou et al. system collisional crustal extension transverse fault and its extensional thickened, juvenile mafic lower-crust or Orthomagmatic fluids 2003a,b, 2009a- intersection with thrust fault crust-mantle transtional zone this issue) Porphyry Au– Late-collisional transform Strike-slip fault, reactive Transpressional; Alkali granite, syenite, and quartz Fine-vein and Beiya, Yao'an; Xu et al. (2007) Cu deposit structural zone basement fault transtensional syenite, derived from the lithospheric disseminated; Tibetan Orogen

mantle orthomagmatic fluids 2 (2009) 36 Reviews Geology Ore / Cook N.J. Hou, Z. Porphyry Mo Collisional zone with post-collisional Orogen-transverse fault; Transtensional Granite, quartz monzonite, and Fined-vein and Sharang, Tibetan (Zhang and Deng, deposit crustal extension; Collisional zone with intersection with thrust fault extensional monzogranite, derived from a lower- disseminated; orogen; Niannihu, 2001; Hou et al. main-collisional stress relaxation crust but involving mantle components orthomagmatic fluids Jinduicheng, Qinling 2006b) Orogen Orogenic-type Shear zone-type Late-collisional transform structural zone Ductile-brittle transitional Transpressional Ophiolite mélanges, clastic sequences Metamorphic fluids Ailaoshan Au belt; (Hu et al. 1995; Au ore-forming Au deposit with large-scale shearing; Collisional sites in shear zone compressional and mafic-ultramafic rocks with involving mantle Tibetan Orogen; Zhang, 2001) system zone near the suture with syn-peak greenschist-facies metamorphism component Jianchaling, Qinling metamorphism Orogen Carlin-like Au deposit Collisional zone near the suture with Faults bounding the terrane Compressional Late Paleozoic-Triassic turbidites Micro-fined, and Dashui, Laerma, (Li and Peters, syn- to post-peak metamorphism near the suture disseminated; Low- Baguamiao; Qinling 1998; Mao et al., salinity H2S fluids Orogen 2002) Granite-related Greisen-type Collision zone with crust-derived low- Fault and fractural zone Compressional Calc-alkaline granitoid, derived from Massive sulfide-style, Lailishan, Tibetan (Liu et al., 1993; Sn–W–Uore- Sn–W deposit fO2 granitoids; Foreland thrust and Intrusive contacts crustal anatexis stockwork-style, Vein Orogen; Panasqueira, Hou et al., 2007a; forming system central axial uplift zones with S-type swarm-style; Pyrenean Orogen Kelly and Rye, granitoids orthomagmatic fluids 1979) Greisen-type rare- Collision zone with crust-derived Fault and fractural zone Compressional Muscovite granitoid, derived from Stockwork -style, vein Baihuanao; Tibetan Liu et al. (1993) metallic deposit low-fO2 granitoids Intrusive contacts crustal anatexis swarm-style; Orogen orthomagmatic fluids –

Granite-related U deposit Foreland thrust and central axial Unclear Compressional HHP granites, derived from crustal Vein-style, breecia- Margnac and Fanay, Le Roy (1978) 24 uplift zones with S-type granitoids anatexis style; CO2-rich fluids Pyrenean Orogen mixing with meteoric water Skarn-type Skarn (and Collision zone with main-collisional Fault and fractural zone Compression Calc-alkaline granites derived from the Skarn-hosted, vein- Chongmuda, Li et al. (2006a,b) polymetallic hybrid)-type mixed crust/mantle-derived high-fO2 intrusive contacts with late-stage MASH process, and Mesozoic carbonate stockwork Xiongcun, Tibetan ore-forming Cu–Au granitoids stress relaxation and clastic formations orthomagmatic fluids Orogen system Skarn-type Pb–Zn– Collision zone with main-collisional Thrust fault and fractural zone Compression Calc-alkaline granites derived from the Skarn-hosted, vein- Mengzhong'a, Hou et al. (2006b) Cu deposit mixed crust/mantle-derived high-fO2 Intrusive contacts with late-stage MASH process, and Paleozoic–Mesozoic stockwork Yaguila Tibetan granitoids stress relaxation carbonate and clastic formations orthomagmatic fluids Orogen mixed with meteoric water

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Table 3 (continued) Deposit group Deposit type Tectonic setting Structural control Stress regime Host rocks and their sources Mineralization and Typical examples References (genetic clans) ore fluid Alkali complex - Vein-type and breccia-type Late-collisional transform structural Strike-slip fault and Transpressional, Carbonatite sill, alkali syenite intrusion Vein system-style, Maoniuping Dalucao (Yuan et al., 1995, related REE ore- REE deposits zone with strike-slip faulting system reactivated basement fault transtensional, and wall-rocks breccia pipe-style Lizhuang; Tibetan Yang et al., 1998) forming system and carbonatite-alkaline complexes extensional disseminated-style Orogen orthomagmatic fluids Sediment- MVT Zn–Pb deposit Foreland basin Thrust-nappe system Extensional fault and uplift of Compressional; Undeformed and weakly-deformed Open-space filling; Ave, Pyrenean (Bradley and Leach,

hosted Zn–Pb basin margin extensional carbonate formation basinal brine Orogen 2003; Leach etal., 2 (2009) 36 Reviews Geology Ore / Cook N.J. Hou, Z. (–Cu–Ag) ore- 2005) forming system Sandstone - Foreland basin Thrust-nappe system No obvious, but related to Compressional; Shallow marine sandstone Disseminated Pb; Caledonide orogen (Seltmann and hosted Pb deposit or extensional fault and uplift of extensional basinal brine Faragher, 1994; Laisvall-type basin margin Ihlen et al., 1997) Sandstone - Transform structural zone with late- Structural-lithological trap and Transpressional Terrestrial-facies sandstone Stratoid, lenticular; Jinding in Lanping (Xue et al., 2007; hosted Zn–Pb deposit or collisional thrust-nappe system on salt-dome in the thrust-nappe basinal brine basin; Tibetan Wang et al., 2007) Jinding-type the foreland basin system Orogen MVT-like Zn–Pb–Cu–Ag Transform structural zone with late- Thrust fault in the front zone of Transpressional Shallow marine carbonate formation Stratoid and Heishan, Huishan (Chen, 2006; He et deposit or Irish-type collisional thrust-nappe system on the the thrust-nappe system with minor terrestrial sandstone lenticular; Basinal Huachangshan, al., 2009-this issue; foreland basin brines Tibetan Orogen; Seltmann and Ireland, Variscan Faragher, 1994) Orogen Vein-type Cu–Ag–Zn Transform structural zone with late- Second-order fault and ﬁssure Transpressional Feldspathic quartz sandstone, siltstone Large vein and vein Jinman, Fulongchang, (Chen, 2006; He et deposit collisional thrust-nappe system on the zones in the thrust-nappe and carbonaceous shale swarm; Basinal brines Baiyangping; Tibetan al., 2009-this issue) foreland basin system Orogen Vein-type Sb– Vein-type Au deposit Detachment system with granitic Metamorphic core complex Extensional Greenschist-facies metamorphic rocks Veins and lenses Langkazi; Tibetan (Yang et al., 2006, Au ore-forming intrusion in the foreland thrust zone; Intersection sites of Magmatic water with Orogen 2009a,b-this issue) system post-collisional extension setting detachment fault and orogen- minor meteoric water –

transverse fault 24 Vein-type Sb deposit Detachment system in the foreland thrust Intersection sites of Extensional Fine-sandstone and siltstone Large vein and vein Shalagang, (Yang et al., 2006, zone; post-collisional extension setting detachment fault and orogen- intercalated with intermediate- maﬁc swarm; Meteoric Zhaxikang; Tibetan 2009a,b-this issue) transverse fault volcanics water Orogen Spring-type Cs– Sinter-hosted Cs deposit Collisional zone cut by orogen-transverse Orogen-transverse faults and Extensional Silica sinters and minor calcareous Cs-sinter; geothermal Dagejia; Tibetan Zheng et al. (1995) Au ore-forming faults and rifting basins modern geothermal system sinter system Orogen system Spring-type Au deposit Collisional zone with Quaternary Extensional faults and modern Extensional intermediate-felsic volcanics Vein, stockwork Tengchong; Tibetan Hou et al. (2006d) volcanoes spring activity geothermal system Orogen Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24 21

Porphyry-type Cu–Mo (Cu–Au, Au–Cu, Mo) and orogenic-type Au References deposits are most characteristic for asymmetric- and composite-style orogenic systems. In the Tibetan Orogen, porphyry-type deposits occur Allègre, C.J., Courtillot, V., Tapponnier, P., Hirn, A., Mattauer, M., Coulon, C., Jaeger, J.J., Achache, J., Scharer, U., Marcoux, J., Burg, J.P., Girardeau, J., Armijo, R., Gariepy, C., in each stage of the continental collision, varying from Mo deposits (e.g., Gopel, C., Li, T., Xiao, X.C., Chang, C.-F., 1984. Structure and evolution of the Sharang) in the main-collisional convergent setting, through Cu–Mo–Au Himalaya–Tibet orogenic belt. Nature 307, 17–22. deposits (e.g., Yulong) in the late-collisional transform setting, to Cu–Mo Barley, M.E., Groves, D.I., 1992. Supercontinental cycles and the distribution of metal deposits through time. Geology 20, 291–294. deposits (e.g., Qulong) in the post-collisional, extensional setting (Fig. 6). Beaumont, C., Jamieson, R.A., Nguyen, M.H., Lee, B., 2001. Himalayan tectonics explained Host rocks to the Cu–Mo deposits are usually K-rich, and their Cu- by extrusion of a low-viscosity crustal channel coupled to focused surface bearing magmas are regarded to have been derived from thickened, denudation. Nature 414, 738–742. fl juvenile mafic lower-crust. The source of the Mo-bearing magmas is not Beaumont, C., Jamieson, R.A., Nguyen, M.H., Medvedev, S., 2004. Crustal channel ows: 1. Numerical models with applications to the tectonics of the Himalayan–Tibetan well constrained; it is most likely that these magmas have undergone a orogen. Journal of Geophysical Research 109, B06406. doi:10:1029/2003JB002809. MASH process at the base of the Tibetan crust (Fig. 6A). In the Qinling Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic composition of east African carbonatites: – Orogen, porphyry Mo mineralization formed a world-class Mo metallo- implications for mantle heterogeneity. Geology 15, 99 102. Blisniuk, P.M., Hacker, B., Glodny, J., Ratschbacher, L., Bill, S., Wu, Z-H., McWilliams, M.O., genic province in China. Most of the giant Mo deposits, with molybdenite Calvert, A., 2001. Normal faulting in central Tibet since at least 13.5 Myr ago. Nature Re–Os ages of 145 to 132 Ma (Li et al., 2003), occur in a post-collisional 412, 628–632. crustal extension setting, and were controlled by orogen-transverse Bradley, D.C., Leach, D.L., 2003. Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands. Mineralium Deposita 38, 652–667. faults (Zhang and Deng, 2001), as in the GPCB in Tibet (Fig. 6C). Available Burchfiel, B.C., Chen, Z., Hodges, K.V., Liu, Y., Royden, L.H., Deng, C., Xu, J., 1992. 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