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Ore Geology Reviews 36 (2009) 2–24
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Ore Geology Reviews
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Metallogenesis of the Tibetan collisional orogen: A review and introductionto the special issue
Zengqian Hou a,b,⁎, Nigel J. Cook c
a Institute of Geology, CAGS, Beijing 100037, PR Chinab School of Earth and Geographical Sciences, University of Western Australia, W.A., Australiac Natural History Museum, University of Oslo, Boks 1172 Blindern, 0318 Oslo, Norway
⁎ Corresponding author. Institute of Geology, CAGS, BE-mail address: [email protected] (Z. Hou).
0169-1368/$ – see front matter © 2009 Published by Edoi:10.1016/j.oregeorev.2009.05.001
a b s t r a c t
a r t i c l e i n f oArticle history:Received 21 October 2008Received in revised form 7 May 2009Accepted 7 May 2009Available online 18 May 2009
Keywords:GeodynamicsCollisional processMetallogenesisCollision-related depositsTibetan Orogen
Mineral deposits associated with continental collision are abundant in many orogenic systems. However, themetallogenesis of collisional orogens is often poorly understood, due to the lack of systematic studies on thegenetic links between collisional processes and ore formation in collisional orogenic belts. This paper reviewsthe key metallogenic settings and resultant collision-related ore deposits in the Tibetan Orogen, created byIndo-Asian collision starting in the early Cenozoic. The resulting synthesis leads us to propose a newconceptual framework for Tibetan metallogenic systems, which may aid in deciphering relationships amongore types in other comparable collisional belts. This framework includes three principal metallogenic epochsin the Tibetan orogen, and metallogenesis in: (1) a main-collisional convergent setting (∼65–41 Ma); (2) alate-collisional transform structural setting (∼40–26 Ma); and (3) a post-collisional crustal extension setting(∼25–0 Ma), each forming more than three distinct types of ore deposits in the Tibetan orogen.The main-collisional metaollognesis took place in a convergent setting, i.e., a collisional zone, characterized bycollision-related crustal shortening and thickening, associated syn-peak metamorphism and two distinctmagmatic series (Paleocene–Eocene crust-derived low-fO2 granitoids generated by crustal anatexis and Eocenehigh-fO2 granitoids formedbyMASHprocesses at the base of theTibetan crust).Metallogenesis during this periodformed Sn–W–rare metal deposits related to the low-fO2 granitoids, skarn-hosted Cu–Au polymetallic depositsrelated 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 mosteconomically-significant metallogenic province in the orogen. Four significant ore-forming systems arerecognized in the transform zone: porphyry Cu–Mo–Au systems associated with potassic adakitic melts andcontrolledbyCenozoic strike-slip faults; orogenic-typeAu systems related to large-scale left-slipductile 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-slipfaults developed in the Tertiary foreland basin.Post-collisional metallogenesis occurred in a crustal extension setting, characterized by lithospheric mantlethinning or delamination at depth, crustal shortening at a lower structural level and synchronal extension atshallower levels. The resulting ore-forming systems include: (1) porphyry Cu–Mo ore systems related to high-Kadakitic stocks derived from the newly-formed thickened mafic lower-crust; (2) vein-type Sb–Au ore systemscontrolled by the south Tibetan detachment system (STDs) and themetamorphic core complex or thermal domeintruded by lecuogranite intrusions; (3) hydrothermal Pb–Zn–Ag ore systems controlled by the intersections ofN–S-striking normal faults with E–W-trending thrust faults; and (4) spring-type Cs–Au ore systems related togeothermal activity drivenbypartialmeltingof theuppercrust. Associatedoredeposits liemostlywithin themid-Miocene Gangdese tectono-magmatic belt, in which the scavenging role of fluids derived from evolved magmasystems or dewatering of rift basins, andfinally discharging at intersections of the orogen-transverse and -parallelfaults 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 otherorogenic systems, a more complete classification for these collision-related deposits can be proposed.
© 2009 Published by Elsevier B.V.
eijing 100037, PR China.
lsevier B.V.
3Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
1. Introduction
Mountain belts created by continent–continent collision, e.g., theHimalayan–Tibetan Orogen in East Asia (cf. Yin and Harrison, 2000),the Variscan orogen in Western and Central Europe (cf. Seltmann andFaragher, 1994), the Pyrenees (Sibuet et al., 2004) and the QinlingOrogen in China (cf. Zhang et al., 1996), each extending for thousandsof kilometers along the strike, are among the dominant geologicalfeatures of the surface of the Earth. Characteristic metallogenesisrelating to continent–continent collision is widely expressed withinthese orogenic systems. High heat flows, resulting from the collisionalorogeny and associated crustal thickening, translithospheric shearing,and lithospheric mantle thinning, are regarded as the main causes forhydrothermal mineralization in the orogenic belts (Seltmann andFaragher, 1994). However, the metallogeny of collisional orogens isrelatively less well understood compared to that of accretionaryorogens.
The suite of mineral deposits that can be related to collision eventsis quite broad; Sawkins (1984) previously divided them into six majortypes: (1) ophiolite-hostedmetal deposits, (2) Mississippi Valley-type(MVT) Zn–Pb deposits, (3) carbonate-hosted (Irish-type) Pb–Zndeposits, (4) sandstone-hosted (Laisvall-type) Pb(–Zn) deposits, (5)Sn–Wdeposits related to S-type granites, and (6) U deposits related tocollisional granites (cf. Seltmann and Faragher, 1994). These collision-related deposits have been documented to preferentially developed orpreserved in different orogenic belts. Recently, many more collision-related deposits have been found in other orogenic systems. Many areworld class in size and may be unique in their geological features;some do not easily fit into classical deposit models. For example, fiveMesozoic giant porphyry Mo deposits and numerous orogenic-typegold deposits in the Qinling collisional orogenic belt, China, have beenshown to relate to Mesozoic collisional orogenesis (Kerrich et al.,2000; Zhang and Deng, 2001).
A number of collision-related world-class ore belts, includinggiant deposits, occur within the Tibetan collisional orogen (Fig. 1;cf. Hou et al., 2007a; Khin Zaw et al., 2007). These include theHimalayan porphyry Cu belts in Tibet (Hou et al., 2009a-this issue),the Cenozoic Ailaoshan orogenic-type Au belt inwestern Yunnan (Sunet al., 2009-this issue), the carbonatite–alkalic complex-hostedREE belt in western Sichuan (Hou et al., 2009b-this issue), and theTertiary Lanping Zn–Pb–Cu–Ag belt (He et al., 2009-this issue). Somemore unusual ore deposits, including the giant coal seam-hostedLincang Ge deposit (Hu et al., 2009-this issue) and cesium-(gold)deposits within active hot springs and associated silica-sinters, in-cluding the Targejia Cs deposit (Zheng et al., 1995; Li et al., 2006a,b)have also been discovered in the orogen. These new discoveries inChina, as well as previously-reported data for collision-relateddeposits in other orogenic systems, greatly extend our knowledge ofthe metallogenetic character of collisional orogens, and provide asignificant database for further understanding of collisional metallo-geny. Nevertheless, these discoveries also raise a number of importantquestions, including:
1. Why do the different orogens show differing metallogenicfeatures? How is the metallogenesis of these orogenic belts linkedto collisional orogenic processes?
2. Does the metallogenic preferentiality of collision-related depositsrelate to either the tectonic evolution of different orogenic belts orto the degree of their erosion? Which kind of deposits arepreferentiality developed in which stages (i.e., syn-, late- andpost-collisional) of orogenic tectonic evolution?
3. What are the geotectonic environments and controlling factors fordifferent mineralization styles, deposit types, and ore-formingprocesses in the various tectonic stages of collisional orogens?
The key to answering these questions is to establish the geneticlinks between metallogeny and various geodynamic processes in
collisional orogens, by carrying out orogenic-scale syntheses andcomparative studies on typical collisional orogens and relevantmetallogenesis. The Himalayan–Tibetan Orogen is the youngest andmost spectacular of all continent–continent collision orogenic belts(Yin and Harrison, 2000). It can therefore be regarded as the mostoutstanding natural laboratory on Earth for studying collisionalorogens and related metallogenesis due to (1) generally cleargeological relationships, (2) a well understood paleo-boundaryhistory, (3) a variety of marked, indicative geological features, aswell as (4) a variety of Cenozoic, world-class ore belts and giantdeposits with variablemineralization styles and types, formed inwhatare relatively clear geodynamic settings.
In order to increase understanding of themetallogeny of collisionalorogens, a five-year National Basic Research Program (973 Project tothe senior author) “Metallogenesis of the Collisional Orogen in Tibet”was established in 2002 by the Ministry of Science and Technology ofChina. About 100 researchers and students from nine Institutions inChina took part in this project. As a result, great efforts have beenmade to establish genetic links between collisional orogen andmetallogenesis in the Tibetan orogen during the past five years anda wealth of new data and research results were obtained under theframework of the 973 Project.
This special issue of Ore Geology Reviews provides a comprehensiveaccount of key mineral deposits in the Tibetan collisional orogen.Moreover, other economically significant deposits such as Tanjianshan(Zhang et al., 2009-this issue) and Tuolugou (Feng et al., 2009-thisissue), formed in the Mesozoic period, but nevertheless involved inthe Cenozoic collisional orogen and preserved within the TibetanOrogen, are also included in the special issue.
This introductory paper synthesizes the temporal-spatial distribu-tion, mineralization styles, and major types, tectonic controls, andgeodynamic settings of collision-related Cenozoic deposits in theTibetan orogen, on the basis of a synthesized analysis of thetectonomagmatic evolution and lithospheric geodynamic processeswithin the orogen. This synthesis leads us to propose a newconceptual framework for the Tibetan metallogenic systems, as wellas a new classification for collision-related deposits, in which theTibetan examples can be compared with comparable deposits in othercollisional orogenic systems.
2. Tectonic framework of the Tibetan Orogen
The Tibetan orogen, a direct consequence of a collision betweenthe Indian and Asian continents beginning in the early Cenozoic, isbuilt on a complex tectonic collage created by accretion of threeterranes onto the southern margin of the Asian continent since theearly Paleozoic (Fig. 1; Chang and Zheng, 1973; Allègre et al., 1984).These three terranes are, from north to south, the Songpan–Garze,Qiangtang, and Lhasa Terranes. They are separated from one otherby the Jinsha suture (JS) and the Bangong–Nujiang suture (BNS),respectively; both are representative of Paleo-Tethyan oceanrelicts (Yin and Harrison, 2000) (Fig. 1). The Qiangtang terrane ischaracterized by predominantly Precambrian metamorphic rocks andlate Paleozoic shallow marine strata and Jurassic–Cretaceous marinecarbonate rocks interbedded with terrestrial clastics. It has thethinnest crust (50 to 60 km) and the highest mantle temperature onthe Tibetan plateau (McNamara et al., 1995). The Lhasa terrane iscomposed of mid-Proterozoic and early-Cambrian basement andPaleozoic–Mesozoic cover strata consisting of a sequence of Ordovi-cian–Triassic shallow marine clastic sediments. Internal N–S short-ening of at least 180 km is recorded within the Lhasa Terrane dueto Jurassic–Cretaceous collision with the Qiangtang terrane (Murphyet al., 1997). The present crustal thickness (70 to 80 km) is twice thatof normal crust (Molnar et al., 1993) due to the Indo–Asian continentalcollision. From south to north across the terrane, development of theIndus–Yarlung Zangbu suture (IYS) (Xiao and Gao, 1981), the Xigaze
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4 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
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fore-arc basin (Durr, 1996), and the voluminous Andes-type arcgranitoid batholiths (130 to 70Ma; Schärer et al., 1984; Harrison et al.,1999) suggests northward subduction of the Neo-Tethys slab in thelate Cretaceous (Allègre et al., 1984). Emplacement of Paleocene–Eocene syn-collisional magmas along the southern margin of theLhasa terrane (Fig. 1) suggests the subsequent subduction of theIndian continental slab in the Early Tertiary (Hou et al., 2006a).
To the south of the IYS are the Himalayas, consisting of three tectonicblocks, the Tethyan Himalaya (TH), High Himalaya (HH), and LowHimalaya (LH), separated from each other by the north-dipping MainCentral Thrust (MCT) and Main Boundary Thrust (MBT) (Figs. 1 and 2).Both the MCT and MBT appear to sole into a common N-dippingdetachment, the Main Himalayan Thrust (MHT) (Zhao et al., 1993),suggesting that the main part of the Indian continent has been thrustbeneath the Himalayas along the MHT (Fig. 2A). Crustal-scale thrustingwithin the Himalayas was delayed for 20 to 40 Ma following the onset ofthe collision (cf. Yin and Harrison, 2000 and references therein). This hasbeen attributed to the lateral flow and southward extrusion of a hot,ductile Tibetan lower-crust in theMiocene (Nelson et al.,1996; Beaumont
Fig. 2. Fundamental architecture and orogenic style of three collisional orogenic systems. (A)and Harrison, 2000). MBT: main-boundary thrust; MCT: main-central thrust; STDS: South-Tisymmetric-style orogenic system, represented by the Pyrenean orogen (Roure and Banda,Pyrenean units; CPZ: Central axial zone; NPZ: Northern Pyrenean belt; NP.F: Northern Pyrorogenic system such as the Qinling orogenic system (modified from Zhang et al., 1996). I1: tShang-Dan suture; SF2: Mian-Lue suture.
et al., 2001). This flow process resulted in the development of the High-Himalaya (HH) metamorphic block and the South-Tibetan detachmentsystem (STD) (Burg and Chen, 1984; Burchfiel et al., 1992) and associatedMiocene leucogranite intrusions (Le Fort,1981;Harrisonet al.,1997). Fig. 2shows the structural architecture and major units of the Himalayan–Tibetan Orogen and its comparisonwith other orogenic systems.
3. Tectono-magmatic evolution of the collisional orogen
The Tibetan–Himalayan orogen underwent a complex history oftectono-magmatic evolution from continental collision and subse-quent underthrusting in the main-collisional period (65 to 41 Ma),through intra-continental underthrusting and large-scale horizontalblock movements in the late-collisional period (40 to 26 Ma), to E–Wcrustal extension in the post-collisional period (≤25 Ma) (Hou et al.,2006b,c,d). Geological events, stress regimes, and plausible deeplithospheric geodynamic processes for each collisional stage aresummarized in Table 1 and on Fig. 3. The tectono-magmatic evolutionis briefly described in the following sections.
Asymmetric-style orogenic system, represented by the Himalayan–Tibetan orogen (Yinbetan detachment systems; GCT: great reverse thrust; GT: Gangdese thrust. (B) shows a1987; Roure et al., 1989). SPF: Southern Pyrenean foreland thrust zone; SPZ: Southernenean fault; NPF: Northern Pyrenean foreland thrust-fault zone. (C) Composite-stylehrust-folded zone in hinterland; I2: thrust fault zone; II: fore-land thrust-fold zone. SF1:
Table 1Summary 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 25–0 Ma
Tectonics anddeformation
Andean-type arc alongGangdese mountain range
Tethyan Himalayan thrust belt in southTibet; Narrow mountain range inLhasa terrane; Qimen-Tagh thrust systemand early Tertiary basins in central Tibet
Contraction system in central Tibet strike-slip faulting and shearing systems in eastTibet thrusting system and nappe structurein east Tibet
South Tibetan detachment systemNS-striking normal fault systemacross orogen; East-west extension
Magmatism Calc-alkaline arc granitoids(120–70 Ma), intruded alongthe Gangdese arc
Magmatism occurring along the Gangdesearc in Lhasa terrane Linzizong volcanicrocks (65–40 Ma) Muscovite–granites(66–58 Ma) calc–alkaline granitoids(65–41 Ma) Bimodal bimodal granitoidand gabbro (52–47 Ma) mafic intrusions(42–38 Ma)
Magmatism mainly occurring in thetransform zone in east Tibet High-Kcalc–alkaline rocks (40–30 Ma) Potassicpotassic intrusion rocks (40–30 Ma)REE-bearing carbonatite–alkalic complex(40–27 Ma) Cu-bearing stocks (40–32 Ma)Lamprophyre (35–26 Ma)
Magmatism widely occurring in theTibetan plateau ultrapotassic rocks(26–13 Ma) Potassic rocks (25–0 Ma)Cu-bearing adakitic stocks (19–13 Ma)Leucogranites (23–16 Ma)
Stress regime Convergence and continuouscompression
Early: compressional; late: stress relaxation Early: transpressional late: transformto transtensional
Early: lower-crust flow; late:E–W extension
Possible deeplithosphericprocesses
Subduction of the Neo-Tethyan oceanic slab;melting of wedge mantlemetasomatized bysubduction zonecomponents
Indo-Asian impact (70–65 Ma)→ rollingback of subducted Neo-Tethyan oceanicslab→subduction of Indian continentcontinent→breakoff of oceanic slab→flatsubduction of Indian continental-slab(b40 Ma)
Intra-continental subduction or terraneunderthrusting caused by flat subductionof Indian continent in central Tibet;Asthenospheric upwelling in east Tibet
Break-off and delamination of Indiancontinental slab; Asthenosphericupwelling and mantle lithosphericthinning
6 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
3.1. Main-collisional period (65–41 Ma)
Collisional timing: the timing for the onset of India–Asia collisionis constrained at 55 to 50 Ma by many authors, but existing datasuggest that the initial collision may have started as early as theearliest Paleocene (Yin and Harrison, 2000). Some authors suggestthat India–Asia collision began in the western Himalaya at 52 to
Fig. 3. Collisional processes, tectonic deformation, magmatic activities, stress regime in differAsian plates (Lee and Lawver, 1995) are used to compare the three-stage collisional process
55 Ma (DeCelles et al., 2004) and progressed eastwards untilcollision ended by 41 to 50 Ma in the eastern Himalaya (Chemendaet al., 2000). However, this is not supported by the 40Ar/39Ar age (66to 58 Ma) of syn-collisional crust-derived muscovite granitoids nearthe eastern Himalayan syntaxis (Dong et al., 2006a). Based on themost recent data obtained by the 973 Project (Mo et al., 2003; Dinget al., 2003; Wang et al., 2003), the period for the main collision
ent structural units of the Tibetan Orogen. Convergent velocity data between Indian andes in the orogen.
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between Indian and Asian continents is constrained at ∼65 to 41 Ma(cf. Hou et al., 2006b).
Tectonic deformation: tectonic deformation during the period ischaracterized by development of the Tethyan Himalayan thrust belt insouth Tibet, the Gangdese mountain range in the Lhasa terrane, andthree Cenozoic contractional systems in central Tibet (Figs. 1 and 2).The Tethyan Himalayan thrust belt, located between the STD and IYS(Fig. 1), has an estimated amount of shortening of 130 to 140 km andan initial timing of shortening of ∼50Ma (Ratschbacher et al., 1994). Itconsists of fold and imbricate thrusts involving the passive continentalmargin sequence of the Tethyan Himalaya. The Gangdese range,formed by emplacement of Paleocene syn-collisional granitoids, is ahigh but narrowmountain range similar to the present Altipano–Punaplateau in the central Andes (Fielding, 1996). The central Tibetcontractional systems consist of the Shiquanhe–Gaize–Amdo thrustsystem, the Fenghuoshan–Nangqian fold-thrust belt, and the Qimen–Tagh thrust system (Fig. 1), each juxtaposing Mesozoic strata overTertiary strata, and resulting in crustal shortening of more than 80 km(Yin and Harrison, 2000; Spurlin et al., 2005).
Main-collisional magma suite: four principal magma suites havebeen recognized in the Gangdese range: (1) a ∼5 km-thick, sub-horizontal, early-Tertiary Linzizong volcanic succession (LVS); (2)Paleocene syn-collisional granitoids; (3) Eocene gabbros and asso-ciated granitoid intrusions; and (4) basaltic subvolcanic rocks. Theyform a N1,000 km-long, EW-extending tectono-magmatic belt (Fig. 1).The magmatism mainly took place in three epochs, peaking at 65 to58 Ma, 52 to 47 Ma and ∼42 Ma, respectively (Hou et al., 2006a).These events correspond to three drastic variations in the Indo-Asiacontinental rate of convergence (Fig. 3; Lee and Lawver, 1995).
The LVS, with characteristic andesitic–rhyolitic compositions,yields a wide range of 40Ar/39Ar ages, varying from 64.5–60.3 Ma(Dianzhong unit) to 48.7–44.0 Ma (Pana unit) (Mo et al., 2003; Zhouet al., 2004). Geochemically, the suite is calc-alkaline and high-K calc-alkaline with minor shoshonitic character, and shows LREE enrich-
Fig. 4. Sr–Nd isotopic compositions of Cenozoic magmatic r
ment with variable LaN/YbN ratios (7 to 24) and negative Nb, Ta, P, Tianomalies (Mo et al., 2003), suggesting geochemical affinity with arcrocks but involving crustal contamination (Chung et al., 2005; Moet al., 2007).
Paleocene syn-collisional granitoids mainly occur in the Teng-chong area within the eastern Gangdese range (Fig. 1). Available agedata define a long duration (66 to 41 Ma) for the magmatism, whichformed muscovite granites peaking at 66 to 58 Ma and potassic calc-alkaline monzogranite and syenogranites peaking at 65 to 55 Ma,53 Ma, and 42 Ma, respectively (Dong et al., 2006a). The muscovitegranites are small in volume and occur as stocks or sheet-like bodieshosting rare-metal (Rb, Cs, Li, Y, Yb, etc.) mineralization. They havehigh ASI [nAl2O3/(nK2O+nNa2O+nCaO)] values of 1.03 to 2.63 andAl2O3/Ti2O ratios of 127 to 2033, low FeOt/(FeOt+MgO) ratios ofb0.8 and CaO/Na2O ratios of 0.03 to 0.24 (Dong et al., 2006a), similarto the Himalaya-type high-pressure granites (Sylvester, 1998). Theirhigh Rb/Sr (257–404) and Rb/Ba ratios (13–40), negative εNd(t)(−8.8 to −8.9; Fig. 4), and MREE-depleted patterns suggest a clay-rich, plagioclase-poor pelitic source in thickened Tibetan crust(Sylvester, 1998). The calc-alkaline granitoids occur as multi-phaseplutons with associated Sn mineralization (Hou et al., 2006b). Theyare characterized by LREE enrichment (LaN/YbN=9.4–18.5) withdistinct Eu anomalies, relatively low Rb/Sr (1.0–3.6) and Rb/Ba (0.4–2.5) ratios, and high (87Sr/86Sr)i of 0.7116–0.7138 and low εNd(t)of −8.68 to −9.66 (Fig. 4; Dong et al., 2006a), implying a meta-sandstone source in the Tibetan crust (Sylvester, 1998).
Eocene magma suites, consisting of “paired” granitoid and gabbrobodies with radiometric ages between 52 and 41 Ma (Schärer et al.,1984; Jiang et al., 1999; Mo et al., 2005; Dong et al., 2006b), aredeveloped along the southern margin of the Lhasa terrane. Thegranitoids usually host numerous macrogranular mafic enclaves andare associated with intense polymetallic mineralization (Hou et al.,2006b). They are geochemically calc-alkaline, and characterized bypositive εNd(t) values (+2.5 to +3.9), low (87Sr/86Sr)i (Fig. 4) and low
ocks in the Tibetan Orogen. Data sources: see the text.
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δ18O (2.3–4.5‰) (Jiang et al., 1999; Mo et al., 2007), suggestingsignificant involvement of a juvenile mantle component for magmageneration. Associated gabbros are geochemically tholeiitic and calc-alkaline, and show relatively flat REE patterns and variable degrees ofU, Th, Nb, Ta, Zr, Hf, P and Ti depletion. Their positive εNd(t) values(+2.3 to +5.1) and low (87Sr/86Sr)i values (0.703861–0.705072)suggest a significant contribution from the asthenospheirc mantle(Fig. 4; Hou et al., 2006b).
The late Eocene mafic subvolcanic rocks yield 40Ar/39Ar ages of42.0±2.3 Ma (Gao et al., 2006). These are dominantly tholeiiticbasalts and picritic-basalts with high Mg# ratio (molar [Mg/Mg+Fe]=0.60–0.73) and high contents of Cr (118–310 ppm), V (191–257 ppm)and Ni (113 to 117 ppm) (Gao et al., 2006). Flat REE patterns (LaN/YbN=2.26–2.89), distinct negative Ti, Nb, U, Th anomalies and Sr–Ndisotopic signatures (Fig. 4) suggest an asthenospheric mantle magmasource (Gao et al., 2006, 2008; Hou et al., 2006a).
A three-stage model has been proposed for the tectonic–magmaticevolution during the main-collisional period in Tibet (Hou et al.,2006a; Mo et al., 2007). At ∼70–60 Ma, roll-back of a flatly-subductedNeo-Tethyan oceanic-slab (Chung et al., 2005) facilitated the earlydragging down of the attached Indian continental lithosphere andcollision with the Asian continent, leading to initial shortening of theAsian continental crust and associated crustal anatexis. Paleocenegranitoids were generated at 66 to 58 Ma. Subsequently, the thermalstructure of the mantle wedgewas changed, resulting in generation ofearly LVS magmas at 65 to 60 Ma. At ∼60–54 Ma, the slab roll-backmechanism was substituted by deep subduction of the Indiancontinental lithosphere, which most likely caused a sudden decreasein the convergent rate from 170 mm/a (at ∼70–60 Ma) to 105 mm/a(at ∼60–54 Ma; Lee and Lawver, 1995). This resulted in generation ofcrust-derived calc-alkaline granitoids in the eastern Gangdese rangeat 54 to 52 Ma. At ∼53–42 Ma, break-off of the Neo-Tethyan slaboccurred at depth and upwelling of asthenosphere through this“window” triggered partial melting of the lithospheric mantle, in turngenerating numerous small gabbro intrusions (52 to 47 Ma) andtholeiitic subvolcanic rocks (42 Ma) along the Gangdese belt. Anotherdirect consequence of slab break-off was the sudden decrease in rateof convergence from ∼90 mm/a to ∼60 mm/a at ∼40 Ma (Lee andLawver, 1995), as well as stress relaxation of the Lhasa terrane, duringwhich abundant polymetallic mineralization was deposited.
3.2. Late-collisional period (40–26 Ma)
Late-collisional processes are characterized by large-scale relativemovement among the terranes (blocks) and associated potassicmagmatism in a transpressional regime. This mainly took place atthe eastern margin of the Tibetan Plateau (Hou et al., 2007a), atransform structural zone, which had absorbed stress and strainresulting from the Indian–Asian collision (Dewey et al., 1989; Wanget al., 2001).
Tectonic deformation: deformation in east Tibet has beenfacilitated by three possible mechanisms, i.e., southeastern extrusionof the Indochina block (Peltzer and Tapponnier, 1988; Leloup et al.,1995), block rotation (Royden et al., 1997; England andMolnar, 2000),and internal shortening (Wang and Burchfiel, 1997). Three styles ofdeformations in east Tibet are important to the generation of collision-related mineralization in the transform structural setting. The first islarge-scale Cenozoic strike-slip fault systems, striking both E–W andN–S, forming the Gali–Gaoligong fault system, the Mangkang–Lijiangfault belt, which controls the Yulong porphyry Cu belt (Hou et al.,2003a), the Honghe fault system, and the Xianshuihe–Xiaojiang faultsystem, which controls the MD REE belt (Hou et al., 2009b-this issue;Fig.1). These strike-slip faults occurred at ∼40Ma and ceased at 23Ma(Hou et al., 2003a; Liu et al., 2006), and underwent early-stagesinistral and late-stage dextral movements (Tapponnier et al., 1990;Spurlin et al., 2005). The second deformation style is large-scale
shearing, which formed the Red-River Shear Zone (RRSZ) along theHonghe fault system and which is associated with Au mineralization(Fig. 1; Sun et al., 2009-this issue). The third style is the Cenozoic fold-thrust systems formed due to internal shortening, and which formedthe Lanping–Simao foreland fold belt and caused formation of thrust-controlled sediment-hosted Zn–Pb–Cu–Ag deposits (He et al., 2009-this issue).
Late-collisional magmatism: late-collisional magmatism occurswidely across the Qiangtang terrane, and extends for more than2000 km into three provinces: western Qiangtang; eastern Qiangtang;and western Yangtze, from west to east (Chung et al., 2005).Magmatism in the last two provinces was controlled by Cenozoicstrike-slip faulting systems in northeastern and eastern Tibet (Wanget al., 2001; Hou et al., 2003a, 2006b). At least threemagmatic districtsor zones have been recognized in the transform structural setting,from west to east. These include: (1) a potassic intrusive zone withradiometric age of 41 to 27 Ma, hosting Cu–Mo–Au deposits withNNW-strike along strike-slip faults (Zhang and Xie, 1997; Chung et al.,1998; Wang et al., 2001; Hou et al., 2005a, 2006c); (2) a potassic calc-alkaline and shoshonitic lamprophyre district with a surface area of∼50,000 km2 (Guo et al., 2005); and (3) a 270 km-long, NS-tendingzone of REE-bearing carbonatite–alkalic complexes with radiometricages of 40 to 28 Ma (Yuan et al., 1995; Wang et al., 2001; Hou et al.,2006c).
Late-collisional magmatism in the transform structural zone ismainly expressed as small-volume extrusive or intrusive bodies,ranging from mafic to felsic in composition and characterized by highto very high alkali contents (Chung et al., 2005). Shoshonitic andultrapotassic rocks are dominant, with minor potassic calc-alkalinerocks. Mantle-derived carbonatites in western Yangtze (Hou et al.,2006e) are also noted.
Potassic felsic rocks, including Cu-bearing porphyritic monzogra-nites and some felsic volcanic rocks in eastern Tibet, usually have lowcontents of HREE and Y, coupled with high Sr/Y and La/Yb ratios,showing geochemical affinity with adakites (Hou et al., 2003b; Jianget al., 2006). They are, however, characterized by high K2O and MgO,and negative εNd(t) (−0.20 to −4.89; Fig. 4; Deng et al., 1998a,b; Houet al., 2003b), thus distinguishing them from adakites derived frommelting of subducted oceanic slabs (Kay, 1978; Kay et al., 1993; Sternand Kilian, 1996). The associated ultra-potassic barren rocks occa-sionally host mantle xenoliths (Cai, 1992; Zhao et al., 2004), whichalthough having similar Sr–Nd isotopic signatures to the adakiticrocks, yield high contents of Y (N20 ppm) and HREE (Deng et al.,1998a,b; Hou et al., 2005a), suggesting genesis by limited degrees ofmelting of enriched lithosphericmantle (Wang et al., 2001; Zhao et al.,2004).
Oligocene carbonatites in western Yangtze province have low SiO2
(b10.22 wt.%), FeO (b1.20 wt.%), and MgO (b0.73 wt.%) and a widerange of CaO (40.7–55.4 wt.%), and are extremely enriched in LILE (Sr,Ba) and light REE, but relatively depleted in HFSE (Nb, Ta, P, Zr, Hf, Ti)(Hou et al., 2006e), thus suggesting a metasomatized mantle source.However, they also have extremely low εNd(t) (−3.2 to −18.7) andrelatively high (87Sr/86Sr)i (0.706020–0.707923), as well as a widerange of 207Pb/204Pb (15.362–15.679) and 208Pb/204Pb ratios (38.083–39.202) (Hou et al., 2006e, and references therein), distinguishingthem from most carbonatites around the world (e.g., Bell andBlenkinsop, 1987; Harmer and Gittins, 1998). Their Sr–Nd, Sr–Pb andNd–Pb isotopic signatures indicate that the least-contaminatedcarbonatites were probably derived from a transitional sourcebetween enriched mantle I (EMI) and enriched mantle II (EMII)components (Hou et al., 2006e).
Late-collisional tectono-magmatic activities in eastern Tibet havebeen variably attributed to continental subduction (Wang et al., 2001),convective thinning of the mantle lithosphere (Chung et al., 1998),extension along strike-slip faults (Yin et al., 1995), and slab break-off(Miller et al., 1999). However, the relatively short magmatic duration,
9Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
peaking at ∼35Ma, extension over a distance of 2000 km across entireQiangtang, and mantle-derived magmatic association imply that thelate-collisional magmatism is genetically related to deep geodynamicprocesses involving the asthenosphere and the subcontinental mantlelithosphere. It is most likely that the large-scale strike-slip faultsystems formed during the late-collisional period, acting as seafloortransform faults not only promoting large-scale horizontal terranemovements, but also cutting the subcontinental lithosphere, probablytriggered upwelling of the asthenosphere in eastern Tibet (cf. Zhong etal., 2001, and references therein). Upwelling of the asthenosphereprobably supplied enough heat energy to cause partial melting of theenriched mantle source, producing carbonatites (Hou et al., 2006e),potassic lamprophyres (Guo et al., 2005) and associated ultrapotassicrocks (Chung et al., 1998) during the late-collisional period. Input of ajuvenile asthenospheric component into the thickened (N50 km)mafic lower-crust or crust/mantle transitional zone beneath easternTibet most likely generated the late-collisional potassic adakiticmagmas (Hou et al., 2003b).
3.3. Post-collisional period (25 Ma to present)
Tectonic deformation: post-collisional deformation in the Hima-layas is characterized by crustal shortening at deep structural levelsalong the thrust systems, but synchronous extension at shallowstructural level along detachment systems in south Tibet (STD).Corresponding to the continuous underthrusting of the Indiancontinent northwards beneath the Himalaya until ∼22 Ma (Hodgeset al., 1996), lateral flow and southward extrusion of the hot, ductileTibetan lower-crust was regarded to have taken place via channel flow(Beaumont et al., 2001, 2004), leading to development of the STD andthe High-Himalayan metamorphic block in south Tibet (Burg andChen, 1984; Burchfiel et al., 1992).
The deformation event in Tibet is a series of near NS-strikingnormal fault systems across the Tibetan plateau, produced by themid-Miocene east-west crustal extension. They mainly occurred prior to13.5 to 14 Ma (Coleman and Hodges, 1995; Blisniuk et al., 2001).Recent 40Ar/39Ar dating of NS-trending ultra-potassic dykes indicatesthat initial E–Wextension probably took place at approximately 18Ma(Williams et al., 2001, 2004). These normal fault systems usuallycrosscut the EW-trending thrust faults, and constrain the localizationof potassic intrusions hosting porphyry-type Cu mineralization (Houet al., 2003c, 2006d).
Post-collisional magmatism: Here we refer only to a new phase ofmagmatic activity occurring in the Tibetan Orogen from the lateOligocene to the present (Fig. 1). Two distinct stages of magmatismhave been recognized: an earlier event (25 to 13 Ma) in the Lhasaterrane and in southern Tibet; and a more recent event (13 to 0.5 Ma),which is largely restricted to northern Tibet.
The earlier phase in south Tibet forms two roughly parallel granitebelts, i.e., the high Himalayan leucogranite (HHL) and the northernHimalayan granite (NHG). The HHL forms a discontinuous chain ofsills exposed on either side of the STD; its crystallization age of 24–17 Ma constrains timing of the STD (Harrison et al., 1998). Numerousmodels for genesis of the HHL, including melting induced by thermalrelaxation (Le Fort,1975), frictional heating during thrusting (Englandet al., 1992), and decompressional melting (Harris et al., 1993; Guillotand Le Fort, 1995), have been proposed to interpret the invertedmetamorphism, 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(Harrison et al., 1998). It is composed of numerous elliptical plutonsthat intruded the Tethyan Himalayan cover strata and formed 6 to 8discrete structural-thermal domes, which host associated Au–Sbmineralization (Yang et al., 2009b-this issue).
The 23 to 13 Ma magmatic event in the Lhasa terrane forms a1500 km-long potassic igneous belt along the Gangdese batholiths(Turner et al., 1996; Miller et al., 1999; Williams et al., 2001, 2004;
Ding et al., 2003; Hou et al., 2004a; Zhao et al., 2006c). Available agedata define the ultrapotassic magmatism as occurring from 25 to16 Ma (Miller et al., 1999; Ding et al., 2003; Chung et al., 2003;Williams et al., 2004; Zhao et al., 2006c) and the potassic magmatismfollowing at 18–13 Ma (Miller et al., 1999; Chung et al., 2003; Houet al., 2003c, 2004a; Rui et al., 2003). The ultrapotassic rocks havehigh-Mg# (N40), high-K2O (6.0 to 9.2 wt.%) and high-TiO2 (N1 wt.%),and show heterogeneous compositions with SiO2 ranging from 51 to69 wt.%, similar to SiO2-rich lamprophyres (Conticelli and Peccerillo,1992; Gao et al., 2007). They are enriched in LILE and LREE, depletedin HFSE, and yield a much wider range of 87Sr/86Sr (0.7167–0.7463),and εNd(t) values (−9.5 to −16.6; Miller et al., 1999), and show acontinuous trend from the enriched mantle to the Indian continentalbasement (Fig. 4A), suggesting involvement of the Indian continentallithosphere in magma generation (Zhaoet al., 2003, 2006c). Thepotassic rocks, especially the felsic stocks, are usually associated withCu mineralization (Hou et al., 2003c, 2004b; Qu et al., 2007). Chunget al. (2003) and Hou et al. (2004a) identified these rocks as adakitesfrom the active continental collision zone, distinguishing them fromtypical adakites derived from oceanic-slab (Defant and Drummond,1990; Gutscher et al., 2000) by their high K2O content (2.6 to 8.6 wt.%)and shoshonitic character. A wide range of εNd(t) (−6.18 to +5.52),initial 87Sr/86Sr (0.7049 to 0.7079), 207Pb/204Pb (15.502 to 15.626),and 208Pb/204Pb (38.389 to 38.960), and high Mg# values (32–74)suggest a newly-formed, thickened (N60 km) mafic lower-crustsource but also involvement of juvenile mantle components (Houet al., 2004a).
Generation of the post-collisional potassic and ultrapotassicmagmas in Tibet is mainly attributed to convective removal of thelithospheric mantle (Turner et al., 1993; Miller et al., 1999; Williamset al., 2001; Chung et al., 2005), and break-off of the subducted slab(Maheo et al., 2002; Hou et al., 2004a). However, combined action ofearly break-off of the subducted Indian continental slab and localthinning of subcontinental lithospheric mantle due to delamination orthermal erosion at ∼25 Ma (Miller et al., 1999; Williams et al., 2004)may be a plausible mechanism for plateau uplift, crustal extension,and dyke emplacement at ∼18 Ma (Williams et al., 2001), andsubsequent NS-striking normal faulting prior to 13.5 Ma (Colemanand Hodges, 1995; Blisniuk et al., 2001). The thinning of the thickenedlithosphere probably caused further northward underthrusting of thecold Indian mantle lithosphere to reach the Bangong–Nujiang sutureat this time and resulted in subsequent magmatism, ceasing at 13 to10 Ma in the Lhasa terrane due to shut-off of the heat source from theasthenosphere (Williams et al., 2004; Chung et al., 2005).
4. Metallogenesis of the Tibetan collisional orogen
The Tibetan Orogen underwent a multiple tectono-magmaticevolution from main-collisional convergence at 65 to 41 Ma, throughlate-collisional transform (40 to 26 Ma) to post-collisional extension(25Ma until present). Corresponding stress regimes vary from intenseimpact (∼65 to 54Ma), relaxation (∼53 to 41Ma), transpression (∼40to 30 Ma) to transtension (∼30 to 26 Ma), and from N–S compression(N18 Ma) to E–W extension (b18 Ma) (Fig. 3; Hou et al., 2006b,c,d).Each collision stage is usually associated with distinct metallogenicprocesses, which have produced specific mineralized systems anddeposit types (Fig. 5; Table 2).
4.1. Metallogenesis in the main-collisional convergent setting
Tectono-magmatic activity in Tibet during the main-collisionalconvergent setting is characterized by collision-related crustal short-ening and thickening, associated syn-peak metamorphism and twodistinct magmatic series consisting of Paleocene–Eocene crust-derived granitoids and Eocene mantle-derived bimodal-like suites.Ore formation during this period is genetically related to syn-peak
Fig. 5. Metallogenesis of the orogenic belt and major collision-related deposit types in Tibet from the Cretaceous to present.
10 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
metamorphism caused by continental impact, leading to orogenic-type gold deposits, crustal anatexis associated with crustal shorteningand thickening, forming Sn and rare metal deposits, and to crust-mantle interaction for generation of the bimodal-like igneous suite ina stress relaxation regime, resulting in Cu–Au polymetallic miner-alization. Most collisional deposits occur in the Gangdese tectono-magmatic belt in Tibet (Fig. 1; Table 2).
Syn-peak metamorphism and orogenic-type Au deposits: Suchmineralization mainly occurs along the IYS (Fig. 1), and forms apotential mineralized belt in Tibet. Mayum, a lode gold depositrepresentative of those in this belt, is described in detail by Jiang et al.,2009-this issue. The principal features of the Au deposits in the beltare summarized here. They include: (1) the gold belt is located in ornear a translithospheric structural zone, i.e., IYS, and Au mineraliza-tion is associated with syn-collisional metamorphism (∼59 Ma) in amain-collisional convergent setting (Jiang et al., 2009-this issue); (2)most of the deposits were developed in a greenschist-faciesmetamorphic block along the suture, and were associated withsericitization, silicification, carbonatization and argillization; (3) Audeposits are composed of auriferous quartz veins or vein swarms, andorebodies were usually controlled by second-order splays or shearzones genetically related to the IYS (Hou et al., 2006b); and (4) ore-forming fluids were CO2-rich, low-salinity (0.18 to 7.20 wt.% NaClequiv.), NaCl–H2O systems (Jiang et al., 2009-this issue), similar tothose observed in orogenic-type gold deposits worldwide (Goldfarbet al., 1993, 1998; Kerrich et al., 2000).
Many studies have shown that the majority of orogenic-type Aumetallogenic provinces are associated with accretionary orogenicevents and that Au mineralization is typically related to syn- to post-peak metamorphism in orogenic belts (Kerrich and Wyman, 1990;Barley and Groves, 1992; Goldfarb et al., 1993, 1998; Groves et al.,1998). However, the occurrence of numerous Au deposits along theIYS in a collision zone indicates that collisional orogenic event andassociated syn-peak metamorphism in Tibet might also providesuitable conditions for formation of orogenic lode Au deposits.These factors include: (1) translithopsheric structure marked by theIYS, along which a deep plumbing system was probably established(Kerrich et al., 2000); (2) the second- or higher-order splays on bothsides of the IYS (such as ductile–brittle shear zones and thrust faults),filled by a variety of veins and breccias (cf. Groves, 1993); (3) host
mafic-ultramafic volcanic rocks and greywacke, which probablycontributed metals to the ore-forming fluids; (4) metamorphic fluidsfrom dehydration of a subducted slab, located 30 km depth beneaththe IYS (Makovsky et al., 1999); and (5) suitable P–T conditions for Aumineralization, resulting from syn-peak metamorphism (i.e., 170 to340 °C, 1.5 to 2.4 kbar) (Jiang et al., 2009-this issue).
Crustal anatexis and Sn-rare metal deposits: Cenozoic Sn and raremetal (Rb, Cs, Li, Y) mineralization mainly occurs in the Tengchonggranitoid district, eastern Gangdese, and is related to potassicganitoids and muscovite granites, respectively, formed by crustalanatexis during the main-collisional period (Fig. 1; Hou et al., 2007a).In general, these Sn deposits (e.g., the Lailishan) are similar to those inthe Varisican collisional orogen in many aspects, such as temporal-spatial association with S-type granite, greisen-type alteration, andgangue assemblage (Liu et al., 1993). However, their spatial localiza-tion controlled by fault fracture zones, the stratabound and semi-layered character of the Sn orebodies, cassiterite-bearing oresdominated by massive pyrite, colloidal textures in massive sulfideores containing relict pyrite, as well as bimodal inclusion tempera-tures peaking at 180 and 380 °C, all suggest an overprinting ofCenozoic greisen-type Snmineralization over pre-existing (Paleozoic)massive sulfides (Hou et al., 2006b). The rare-metal deposits (e.g.,Baihuanao) are associated with a group of highly-evolved muscovite-bearing granites, featuring Li-bearing albite with greisen-type altera-tion. They mainly occur at intrusive contacts as vein swarms andstockworks, and partially in the interior of the greisenized graniticbodies (Hou et al., 2007a).
The ore-bearing potential of the main-collisional granitic meltsproduced by crustal anatexis is probably controlled by the ratio ofplagioclase to biotite melting in the Tibetan crustal source, becausebreakdown of biotite in the source during melting would provide aneffective mechanism for enrichment of metals (Sn, W) and incompa-tible elements (Rb, Li, Cs, F, B) (Halls, 1994; Seltmann and Faragher,1994). In eastern Gangdese, very high Rb/Sr and Rb/Ba ratios, andMREE-depleted patterns of the muscovite granites with rare-metal(Rb, Cs, Li) mineralization suggest a clay-rich, plagioclase-poor shalesource, whereas an obvious Eu anomaly and high F contents of thepotassic granitoids hosting Sn deposits suggest a high ratio of biotiteto plagioclase melting (Sylvester, 1998). This implies that crustalanatexis caused by frictional heating during the main-collisional
Table2
Him
alay
angian
tan
dlarge-size
dde
posits
intheTibe
tanco
llision
alOroge
n.
Dep
osits
Long
itud
e/latitude
Metallic
commod
.To
nnag
eGrade
Tecton
icsettingan
den
vironm
ent
Hostrock
Metalloge
nic
epoc
hsGen
etic
type
Classification
and
ore-form
ingsystem
Exploitation
status
Datasource
(s)
Mao
niup
ing(1)
101°58
′
28°23′
LREE
1.2MtRE
O2.89
%RE
OHah
astrike
-slip
fault;thetran
sform
structural
zone
Nordm
arkite
with
minor
carbon
atite
Late-collis
iona
lpe
riod
Complex
-relatedRE
EAlkalic
omplex
-relatedRE
Eore-
form
ingsystem
Und
erex
ploitation
Yuan
etal.
(199
5)
Daluc
ao(2
)10
1°57
′
27°12′
LREE
0.76
MtRE
O5.0%
REO
Daluc
aostrike
-slip
fault;thetran
sform
structural
zone
Nordm
arkite
with
minor
carbon
atite
Late-collis
iona
lpe
riod
Complex
-relatedRE
EAlkalic
omplex
-relatedRE
Eore-
form
ingsystem
Und
erex
ploitation
(Yua
net
al.,
1995
;Ya
nget
al.,19
98)
Yulong
(3)
97°44′
31°24′
Cu–Mo
Cu6.5Mt
Cu:0.99
%Mo:0.02
8%Large-scalestrike
-slip
faultbe
lt;the
tran
sform
structural
zone
Mon
zoniticgran
ite;
quartz
mon
zonite;
Triassic
sand
ston
ean
dmud
ston
e
Late-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
-Moore-form
ing
system
No
exploitation
(Tan
gan
dLu
o,19
95;Hou
etal.,20
03a)
Duo
xiason
gduo
(4)
97°55′
31°10′
Cu–Mo
Cu:0.5Mt
Cu:0.38
%Mo:0.04
%Large-scalestrike
-slip
faultbe
lt,the
tran
sform
structural
zone
Alkali-feldsp
argran
ite;
Mon
zoniticgran
ite
Late-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
-Moore-form
ing
system
No
exploitation
(Tan
gan
dLu
o,19
95;Hou
etal.,20
03a)
Malason
gduo
(5)
98°00′
31°00′
Cu–Mo
Cu:1.0Mt
Cu:0.44
%Mo:
0.14
%Large-scalestrike
-slip
faultbe
lt,the
tran
sform
structural
zone
Mon
zoniticgran
ite;
syen
itic
gran
ite
Late-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
–Moore-
form
ingsystem
No
exploitation
(Tan
gan
dLu
o,19
95;Hou
etal.,20
03a)
Fulong
chan
g(6
)99
°14′
26°49′
Cu–Ag–
Pb–Zn
Ag:
∼20
00t
Cu:0.12
12Mt
Ag:
328–
547g/t
Pb:4.2–
7.4%
Cu:0.63
–11.7%
NE-striking
seco
nd-order
faultrelated
tothrust
fault;thefron
tzo
nein
the
western
thrust-n
appe
system
;the
tran
sform
structural
zone
Cretaceo
ustran
sition
alzo
nebe
twee
npo
rous
sand
ston
ean
dlow-
perm
eability
carbon
aceo
usargillite
Late-collis
iona
lpe
riod
Sedimen
t-
hosted
vein-
type
Zn-Pb-
Cu-A
gde
posit
Sedimen
t-ho
sted
Zn-Pb(-Cu
-Ag)
ore-form
ing
system
Und
erex
ploration
(Che
n,20
06;
Heet
al.,
2009
-thisissu
e)
Sansha
n–Yang
zido
ng(7)
99°18′
26°45′–43
′
Zn–Pb
Cu–Ag
Zn+
Pb:N0.
5Mt;Ag:
N30
00t
Cu:∼0.3Mt
Pb:1.27
–33.5%
Zn:1.60
–3.39
%Cu
:0.38
–1.8%
Ag:
16–18
9g/t
Fracture
zone
swithinha
nging-wall
ofHua
chan
gsha
nthrust
fault;thefron
tzo
nein
theea
sternthrust-n
appe
system
;thetran
sform
structural
zone
Upp
erTriassic
dolomitic
limestone
,breccia
limestone
,sand
ston
ean
dco
nglomerate
Late-collis
iona
lpe
riod
Sedimen
t-
hosted
vein-
type
Zn–Pb
–
Cu–Agde
posit
Sedimen
t-ho
sted
Zn–Pb
(–Cu
–Ag)
ore-form
ing
system
Und
erex
ploitation
(Che
n,20
06);
Heet
al.,
2009
-thisissu
e)
Jinding
(8)
99°25′
26°24′
Pb–Zn
Pb:2.64
Mt
Zn:12
.84Mt
Ag:
1722
t
Pb:1.16
–2.42
%Zn
:8.32
–10
.52%
Ag:
12.5–12
.6g/t
Structural
andlitho
lithictrap
anddo
me
intheea
sternthrust-n
appe
system
;the
tran
sform
structural
zone
Tertiary
glutinite,
argilla
ceou
sdo
lomite,
argilla
ceou
ssiltston
e,qu
artz
sand
ston
e,siltston
e
Late-collis
iona
lpe
riod
Sand
ston
e-
hosted
Zn–
Pbde
posit
Sedimen
t-ho
sted
Zn–Pb
(–Cu
–Ag)
ore-form
ing
system
Und
erex
ploitation
(Xue
etal.,
2007
;Heet
al.,
2009
-thisissu
e)
Baiyan
gcha
ng(9
)99
°24′
26°07′
Ag–
Cu–
Pb–Zn
Noda
taAg:
110–
245g/t,
Cu:0.36
–1.61
%Pb
:0.22
–3.24
%Zn
:1.11
%
Thefron
tzo
nein
theea
stern
thrust-n
appe
system
;thetran
sform
structural
zone
Jurassic–Cretaceo
ushigh
-po
rous
limestone
andthe
overlyinglow-porou
scarbon
aceo
usargillite
Late-collis
iona
lpe
riod
Sedimen
t-
hosted
vein-
type
Zn–Pb
–
Cu–Agde
posit
Sedimen
t-ho
sted
Zn–Pb
(–Cu
–Ag)
ore-form
ing
system
Und
erex
ploration
Hou
etal.
(200
7a)
Laow
nagz
hai
(10)
101°27
′
23°54′
Au
Au:
106T
Au:
3.7–
7.7g/t
Red-Rive
rsh
earbe
lt;thetran
sform
structural
zone
Basaltic
lava
,Paleo
zoic
quartz
grey
wacke
andmafi
ctuff
Late-collis
iona
lpe
riod
Oroge
nic-
type
Au
Oroge
nic-type
Auore-form
ing
system
Und
erex
ploitation
Huet
al.
(199
5)
Don
ggua
lin(11)
101°26
′
23°53′
Au
Au:
50T
Au:
5.2g/t
Red-Rive
rsh
earbe
lt;thetran
sform
structural
zone
Paleoz
oicsilic
eous
slate,
meta-qu
artz
sand
ston
e,an
dlamprop
hyre
Late-collis
iona
lpe
riod
Oroge
nic-
type
Au
Oroge
nic-type
Auore-form
ing
system
Und
erex
ploitation
Huet
al.
(199
5)
Jinch
ang(12)
101°45
′
23°30′
Au
Au:
27T
Au:
1–55
.5g/t
Red-Rive
rsh
earbe
lt;thetran
sform
structural
zone
Paleoz
oictuffaceo
ussand
ston
e,siltston
e,an
dba
saltic
rock
s,au
gite
perido
tite
Late-collis
iona
lpe
riod
Oroge
nic-
type
Au
Oroge
nic-type
Auore-form
ing
system
Und
erex
ploitation
(Liu
etal.,
1993
;Hu
etal.,19
95)
Dap
ing(13)
102°59
′
22°51′
Au
Au:
N20
TAu:
1–32
.5g/t
Red-Rive
rsh
earbe
lt;thetran
sform
structural
zone
Diorite,g
ranite
porphy
ry,
lamprop
hyre,siliceou
ssh
ale,
sand
ston
e,lim
estone
Late-collis
iona
lpe
riod
Oroge
nic-
type
Au
Oroge
nic-type
Auore-form
ing
system
Und
erex
ploitation
Huet
al.(19
95)
(con
tinu
edon
next
page)
11Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
Table2(con
tinu
ed)
Dep
osits
Long
itud
e/latitude
Metallic
commod
.To
nnag
eGrade
Tecton
icsettingan
den
vironm
ent
Hostrock
Metalloge
nic
epoc
hsGen
etic
type
Classification
and
ore-form
ingsystem
Exploitation
status
Datasource
(s)
Lailish
an(14)
98°16′
24°55′
SnSn
:42
,600
TSn
:0.63
–1.58
%Sy
n-co
llision
algran
itedistrict;ea
stern
segm
entof
theGan
gdeseco
llision
alzo
neHim
alay
anpo
tassic
gran
ite;
Precam
brianmetam
orph
icba
semen
trock
s
Main-
collision
alpe
riod
Cassiterite-
sulfide
type
SnGranite-related
Sn–W
–U
ore-
form
ingsystem
Und
erex
ploitation
Liuet
al.(19
93)
Yagu
ila(15)
92°40′
30°20′
Pb–Zn
–
CuPb
+Zn
:4Mt
Pb+
Zn:15
%Northernco
ntactzo
nesbe
twee
nEo
cene
gran
ites
andCa
rbon
iferous
limestone
;the
collision
alzo
newithstress
relaxa
tion
Eocene
gran
itewith+
e Nd
value;
Carbon
iferous
limestone
andtuffaceo
usmud
ston
e
Main-
collision
alpe
riod
Skarn-
type
Pb–Zn
–Cu
Skarn-
type
Cu–Au
polymetallic
ore-
form
ingsystem
Und
erex
ploration
Tang
,unp
ubl.
data
Men
gya'a(16)
92°10′
30°20′
Pb–Zn
–
CuPb
+Zn
:N0.
45Mt
Pb+
Zn:8.2%
Northernco
ntactzo
nesbe
twee
nEo
cene
gran
ites
andCa
rbon
iferous
limestone
;the
collision
alzo
newithstress
relaxa
tion
Eocene
gran
itewith+
e Nd
value;
Carbon
iferous
limestone
andtuffaceo
usmud
ston
e
Main-
collision
alpe
riod
Skarn-
type
Pb–Zn
–Cu
Skarn-
type
Cu–Au
polymetallic
ore-
form
ingsystem
Und
erex
ploration
Tang
,unp
ubl.
data
Xiong
cun(17)
88°26′
29°23′
Cu–Au
Cu:0.82
Mt
Au:
113T
Cu:0.45
Au:
0.62
NW
-strikingfaultfracturalz
one;
the
collision
alzo
newithstress
relaxa
tion
Mesoz
oicgran
itoids
and
pyroclasticrock
s,intrud
edby
Eocene
gran
itic
dyke
s
Main-
collision
alpe
riod
Hyb
rid-type
Cu–Au
Skarn-
type
and
hybrid
Cu–Au
polymetallic
ore-
form
ingsystem
Und
erex
ploration
Xuet
al.
(200
9-thisissue)
Jiama(18)
91°40′
29°39′
Cu–Pb
–
ZnCu
:≥5Mt
Cu:1.1%
Pb:3.48
%Zn
:1.04
%Au:
0.5pp
m
Oroge
n-tran
sverse
norm
alfaultan
dits
intersection
withthrust
fault;theco
llision
alzo
newithpo
st-collis
iona
lcrustal
extens
ion
Mid-M
iocene
mon
zogran
ite
Post-collis
iona
lpe
riod
Porphy
ryCu
–Pb
–Zn
Porphy
ry-typ
eCu
–Moore-
form
ingsystem
Und
erex
ploration
Hou
etal.
(200
9a-thisissue)
Qulon
g(19)
91°38′
29°41′
Cu–Mo
Cu:8Mt
Cu:0.45
%Mo:
0.03
–0.06
%Oroge
n-tran
sverse
norm
alfaultan
dits
intersection
withthrust
fault;theco
llision
alzo
newithpo
st-collis
iona
lcrustal
extens
ion
Mid-M
iocene
mon
zogran
ite
andgran
ite
Post-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
–Moore-
form
ingsystem
Und
erex
ploration
Hou
etal.
(200
9a-this
issu
e)Ting
gong
(20)
90°02′
29°35′
Cu–Mo
Cu:N1Mt
Cu:0.5%
Oroge
n-tran
sverse
norm
alfault;the
collision
alzo
newithpo
st-collis
iona
lcrus
tale
xten
sion
Mid-M
iocene
quartz
mon
zogran
ite,
gran
ite
Post-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
–Moore-
form
ingsystem
Und
erex
ploration
Hou
etal.
(200
9a-this
issu
e)Ch
ongjiang
(21)
89°58′
29°37′
Cu–Mo
Cu:1.5Mt
Cu:N0.45
%Oroge
n-tran
sverse
norm
alfault;the
collision
alzo
newithpo
st-collis
iona
lcrus
tale
xten
sion
Mid-M
iocene
mon
zogran
ite
Post-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
–Moore-
form
ingsystem
Und
erex
ploration
Hou
etal.
(200
9a-this
issu
e)Ba
iron
g(2
2)89
°56′
29°37′
Cu–Mo
Cu:N0.5Mt
Cu:0.73
%Oroge
n-tran
sverse
norm
alfault;the
collision
alzo
newithpo
st-collis
iona
lcrus
tale
xten
sion
Mid-M
iocene
mon
zogran
ite
Post-collis
iona
lpe
riod
Porphy
ryCu
–Mo
Porphy
ry-typ
eCu
–Moore-form
ing
system
Und
erex
ploration
Hou
etal.
(200
9a-this
issu
e)Narus
ongd
uo(2
3)88
°48′
29°57′
Pb–Zn
–
Ag
Pb+
Zn:
N0.5Mt
Pb+
Zn:N20
%Oroge
n-tran
sverse
norm
alfaultan
dits
intersection
withthrust
faultin
aco
llision
alzo
ne
Paleoz
oican
dMesoz
oic
clasticsequ
ences
Post-collis
iona
lpe
riod
Vein-
type
Pb–Zn
–Ag
Sedimen
t-ho
sted
Zn–Pb
(–Cu
–Ag)
ore-form
ingsystem
Und
erex
ploration
Men
get
al.
(200
3)
Targejia
(24)
85°44′
29°36′
Cs(–
Au)
Cs:14
,45
9T
Cs:0.10
–0.26
%Mod
ernge
othe
rmal
fieldwithinorog
en-
tran
sverse
rift
zone
s;Co
llision
alzo
newithpo
st-collis
iona
lcrustal
extens
ion
Qua
tern
arysilic
asinters
near
theve
nts
Post-collis
iona
lpe
riod
Sinter
-hosted
Csde
posit
Hot-spring-type
Cs–Auore-form
ing
system
No
exploitation
(Zhe
nget
al.,
1995
;Zh
aoet
al.,20
06a)
Mazha
la(2
5)91
°49′
28°27′
Sb–Au
b10
,000
TSb
Sb:35
,Au:
3.88g/t
STDsan
dtheirintersection
withorog
en-
tran
sverse
norm
alfaults
intheTe
thya
nHim
alay
a
Lower-M
iddleJurassic
clastics
andCe
nozo
icdioritepo
rphy
ryPo
st-collis
iona
lpe
riod
Vein-
type
Sb–Au
Vein-
type
Sb–Auore-
form
ingsystem
Und
erex
ploration
(Nie
etal.,
2005
;Ya
nget
al.,20
09b-this
issu
e)Sh
alag
ang(2
6)89
°54′
28°51′
Sb≥0.1MtSb
Sb:31
.5%
STDsan
dtheirintersection
withorog
en-
tran
sverse
norm
alfaultin
theTe
thya
nHim
alay
a
EarlyCretaceo
usclastics,
silic
eous
rock
,san
dstone
andCe
nozo
icdiorite
Post-collis
iona
lpe
riod
Vein-
type
SbVein-
type
Sb–Auore-
form
ingsystem
Und
erex
ploration
(Nie
etal.,
2005
;Ya
nget
al.,20
09b-this
issu
e)Lang
kazi
(27)
90°22′
29°01′
Au
Noda
taAu:
2.0g/t
Detachm
entfaults
andtheirintersection
withorog
en-trans
verseno
rmal
faultin
theTe
thya
nHim
alay
a
Metam
orph
icco
re-com
plex
andcentral-intrud
edgran
ites
Post-collis
iona
lpe
riod
Vein-
type
Au
Vein-
type
Sb–Auore-
form
ingsystem
Und
erex
ploration
(Nie
etal.,
2005
;Ya
nget
al.,20
09b-this
issu
e)
12 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
13Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
crustal thickening and associated breakdown of large amounts ofbiotite in the source has produced a hydrous, metal-rich, low-fO2 felsicmagmatic system in the collisional zone. Moreover, advancedfractional crystallization in the evolved magma chamber probablyleads to further enrichment of Sn in the low fO2 magma system (cf.Lehmann et al., 2000).
Scavenging and replacement of Sn-rich fluids exsolved fromhighly-fractionated and residual felsic melt along previously-existingsulfide horizons are extremely important for metal concentration andprecipitation. Tin-rich fluids scavenged the metals in the pre-collisional Sn mineralized granites and adjacent strata (Liu et al.,1993) during greisen-type alteration, further concentrating Sn in theore-forming fluid system. Such fluids are believed to have replaced thePaleozoic massive pyrite lenses along sulfide horizons, which wouldhave provided enough sulfur to form stratabound cassiterite-sulfideorebodies in favorable spaces (e.g., at Lailishan).
Crust/mantle interaction and Cu–Au–polymetallic deposits: TheCu–Au–polymetallic mineralization is associated with the Eocenegranitoids coexisting with Eocene gabbro bodies, and formednumerous economically-significant Cu–Au polymetallic deposits,located in both margins of the Gangdese Eocene granitioid batholith(Fig. 1; Table 2). Most deposits are intrinsically associated withintrusive contacts and occur as skarn-hosted lenses and veinlets (Liet al., 2006a,b). Only a few porphyry-type Mo deposits and hybrid Cu–Au deposits (Xu et al., 2009-this issue), associated with Eocene felsicstocks, were locally preserved due to batholith uplift and deep erosion(Fig. 1). Molybdenite Re–Os ages of 40.3 to 56.0 Ma for four skarn-hosted deposits (Hou et al., 2006b) suggest a genetic link with themain-collisional felsic magma systems during the Eocene.
The metallogenic specialization of the Eocene granitoids, character-ized by Cu–Au–Mo–Pb–Zn mineralization, is probably controlled byprocesses that allowed concentration of metals and volatiles in themagmatic system. Eocene granitoids host mafic enclaves, and coexisttemporally and spatially with contemporaneous gabbro intrusions,suggesting a genetic link with the generation of the mantle-derivedmafic melts. Their positive εNd values (+2 to +3) imply a significantcontribution of a juvenile mantle component to the felsic melt. Aplausible interpretation is that main-collisional crustal thickening inTibet hindered the ascent of the mantle-derived mafic magmas, whichwere ponded at the bottom of the Tibetan lower crust and probablyunderwent a MASH (melting of lower-crust, assimilation, magmaticstorage andhomogenization)process (cf. Hildreth andMoorbath,1988).This MASH process yielded an evolved, volatile-rich, high-fO2, metalli-ferous, hybrid intermediate-felsic melt (Richards, 2003; Hou et al.,2006b). Meanwhile, the high oxidation state of the hybrid melt led tosulfur deposition predominantly as sulfate (Carroll and Rutherford,1985),whereas chalcophile elements (Cu, Au etc.) became incompatibleand were retained and concentrated in the evolving high-fO2 meltsystem (Richards et al., 1991; Richards, 1995). Therefore, these high-fO2
hybrid felsicmelts have largepotential for formingeconomicCu–Au–Modeposits, thus distinguishing them from the low-fO2 crust-derivedmeltsthat generated Sn–Wand rare-metal mineralization.
Fig. 6A illustrates generation of the various deposit types in themain-collisional convergent setting and the structural constraintsimposed by a collisional orogen. It is noteworthy that formation ofeconomically-significant metallogenic provinces and ore deposits waspreviously regarded as unlikely in a syn- or main-collisionalgeodynamic regime (Guild, 1972; Marignac and Cuney, 1999), sincecompression and transpression usually results in the migration offluids away from a collisional zone. It is important that thistranspressive or compressive regime might cause syn-peak meta-morphism, which would release CO2-dominated metamorphic fluidsnecessary to form orogenic Au deposits (Fig. 6A; Kerrich et al., 2000).Meanwhile, volatiles driven off the wet sedimentary wedges duringcrustal thickening and overthrusting penetrate the overlying crustalrocks to cause anatexis, which would generate hydrous felsic melts
enriched in metals (Sn, W) and incompatible elements (Rb, Cs, Li, Y),leading to Sn and rare-metal mineralization (Fig. 6A). Moreover, asmentioned above, themain-collisional zone is not always compressiveand transpressive— it may also be extensional due to stress relaxationin the late stage of main collision, probably caused by slab break-off(Fig. 6A). Stress relaxation could allow shallow-level emplacement ofevolved, volatile-rich, metalliferous, hybrid intermediate-felsic meltsderived from a MASH zone, and subsequent development ofmagmatic-hydrothermal Cu–Au–Mo–Pb–Zn ore systems in a collisionzone (Fig. 6A).
4.2. Metallogenesis in late-collisional transform setting
Late-collisional metallogenesis wasmainly developed in a transformstructural setting in eastern Tibet, dominated by Cenozoic strike-slipfaulting, shearing, and thrusting systems (Fig. 1), and formed one of themost economically-significant metallogenic provinces in China. Foursignificantmineralization systems are recognized in the Tibetan Orogen(Fig. 5): porphyry-type Cu–Mo–Au systems controlled by Cenozoicstrike-slip faults; orogenic-type Au systems related to left-slip ductileshearing; REE-systems associated with Himalayan carbonatite–alkalinecomplexes; andPb–Zn–Ag–Cu systemscontrolledbyCenozoic thrustingand subsequent strike-slip faults (Table 2; Fig. 6B).
Porphyry-type Cu–Mo–Au system: late-collisional porphyry Cu–Mo–Au systems form an economically-significant Cu–Au province inSW China, including the world-class Yulong porphyry Cu belt in theQiangtang terrane (Fig. 1; Hou et al., 2003a), as well as the majorYanyuan–Yao'an Au–Cu belt in the Yangtze block (Hou et al., 2006f).Porphyry Cu deposits in the Yulong belt are associated with Cenozoicpotassic felsic stocks, controlled by the NNW-strike strike-slip faultingsystems in eastern Tibet (Hou et al., 2005a). In contrast, the porphyry-type deposits in the Yanyuan–Yao'an Au–Cu belt are associated withpotassic–ultrapotassic syenitic and granitic stocks (Hou et al., 2006f),controlled by the basement faults that were reactivated during theIndo-Asia collision. These Cenozoic strike-slip faults and reactivatedbasement faults probably resulted in maximum magma flux into theupper crust, which constructed and sustained a large-volume, long-lived upper-crustal magma chamber essential for producing a largeore-forming system.
The most recent high-precision bulk-rock 40Ar/39Ar (Chung et al.,1998) and zircon U–Pb dating (Liang et al., 2006) define a relativelyshort duration (43 to 30 Ma) for the magmatic activity that generatedthe host rocks. This activity peaked at 42±1 Ma, 36±1 Ma, and 32±1 Ma (Hou et al., 2003a, 2006f), suggesting episodic recharging ofmultiple felsic magmas into a high-level magma chamber in atransform structural setting. Molybdenite Re–Os dating yieldedthree distinct mineralization epochs (40±0.5 Ma, 36±0.5 Ma, 32±1.0 Ma; Hou et al., 2006f), closely matching but slightly later than theepisodic magmatism in eastern Tibet. This indicates that episodicstress relaxation in a transform setting promoted episodic emplace-ment of stocks and associated exsolution of ore-forming fluids fromfelsic magma chambers.
The main lithologies hosting Cu–Mo–Au orebodies are monzo-granites, quartz monzonites, K-feldspar granites and syenites. Ingeneral, Cu–Mo and Cu–Au mineralization is associated withmonzogranitic and granitic porphyries, whereas Au mineralization isassociated with syenitic porphyries (Hou et al., 2005a; Xu et al., 2007).Most of the host porphyries, except for the syenites that containmantle xenoliths, are shoshonitic and high-K calc-alkaline incomposition (Zhang et al., 1998a,b; Hou et al., 2003a), and showgeochemical affinity with adakites (Hou et al., 2003b; Jiang et al.,2006). The genesis of Cu-bearing felsic magmas has been debated, butmore and more evidence favors genesis via partial melting of athickened (N50 km) mafic lower crust involving a juvenile mantlecomponent from the asthenosphere beneath eastern Tibet (Hou et al.,2004a, 2005b).
Fig. 6. Three-stage tectono-magmatic evolution and resultant typical deposits in the continental collision orogenic system. (A) During the main-collisional period — continentalimpact and slab underthrusting resulted in crustal shortening, thickening, and associated syn-peak metamorphism, which produced crust-derived low-fO2 felsic melts by crustalanatexis and CO2-fluids with metamorphic origin, as well as relevant Sn–W–U and Aumineralization 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 bottomof 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, derivedfrom 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 generatedlecuogranitic 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-crustcreated potassic felsic magmas with porphyry Cu–Momineralization in the collisional zone. The detachment fault systems related to extension and high-level emplacement of felsicmagmas 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 byterrestrial sediments in the foreland basin and in rift basins within the orogenic belt is commonly associated with sandstone-type U deposits.
14 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
The geology and mineralization of typical late-collisional por-phyry-type Cu–Mo, Cu–Au and Au–Cu deposits have been describedby many authors (Rui et al., 1984; Tang and Luo, 1995; Hou et al.,2003a; Xu et al., 2007). These deposits, though occurring in atransform structural setting unrelated to oceanic-slab subduction,show broad similarities with those in arc settings in many aspects,such as mineralization style, alteration zonation, and sulfide associa-tion (see Hou et al., 2003a, and references therein). They are usuallyassociated with steeply dipping, pipe-like multiphase felsic stockswith explosive pipes, and are dominantly composed of pipe-like
veinlet-disseminated orebodies within the stocks, with or without aring-shaped, high-grade Cu–Au zone overlying or surrounding aporphyry-type Cu–Mo orebody (Hou et al., 2003a). Associated hydro-thermal alteration commonly forms a concentric zonation aureole,extending from an inner K-silicate zone outwards through quartz–sericite to an outer propylitic zone (Tang and Luo, 1995; Hou et al.,2003a). A few deposits (e.g., Yulong) occur within the structurally-controlled advanced argillic alteration and display features of high-sulfidation epithermal Cu–Au or Au mineralization which overprintthe earlier porphyry-type alteration and mineralization (Hou et al.,
15Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
2007b). Fluid inclusion and δ18O–δD data indicate that supercriticalfluids which exsolved from a high-level magma chamber underwentsimilar evolution and mineralization processes to those in arc settings(Hou et al., 2007b).
REE-bearing ore systems: REE-bearing ore systems are associatedwith Oligocene carbonatite–alkalic complexes, controlled by Cenozoicstrike-slip fault systems. They comprise a world-class REE metallogenicbelt at the western margin of the Yangtze block involved the easternIndo-Asian collision zone (Fig. 1; Table 2). Total reserves exceed 3 MtLREE (Yuan et al., 1995). The geology and other features of the REEdeposits in this belt are described in detail elsewhere in this special issue(Hou et al., 2009b-this issue). Continuous carbonatitic melt-fluidevolution of the REE mineralization system has been establishedbased on fluid inclusion studies on typical deposits (e.g., Maoniuping;Xie et al., 2009-this issue). A number of significant aspects of theREE oresystems are emphasized in the following paragraphs.
It is widely known that primary REE deposits worldwide mainlyoccur in continental rift zones (cf. Mitchell and Garson, 1981).However, available age data from hydrothermal minerals define aHimalayan metallogenic epoch (40 to 28 Ma) for most REE deposits,identical to the crystallization age of the late-collisional host rocks inthe eastern collisional zone (Yuan et al., 1995; Yang et al., 1998; Pu,2001; Tian, 2005; Tian et al., 2008). The temporal-spatial relationshipof the carbonatite–alkalic complexes and associated REE orebodiessuggests that Cenozoic strike-slip faulting and resultant pull-apartstructures and tensional fissure zones facilitated formation of the REE-bearing magmatic-hydrothermal systems and exsolution of ore-forming fluid from the system in a transform structural setting.
Although almost all primary REE deposits in the world areassociated with carbonatite–alkalic complexes, the host alkali rocksin rift zones are variable in composition from aegirine–augite syeniteand nepheline syenite to ijolite (Hou et al., 2009b-this issue). Incontrast, the host alkaline rocks in the eastern collisional zone arepredominantly nordmarkite with minor aegirine–augite syenite,demonstrating the low alkalinity of the magma system. Hostcarbonatites in rift zones are usually enriched in Nb, Ta, P, Ti, and Feand their generation is related to mantle plume activity (Harmer andGittins, 1998). Collisional zone carbonatites are, in contrast, relativelydepleted in high-field strength elements (Nb, Ta, Zr, Hf, Ti), and werederived from subcontinental lithospheric mantle (Hou et al., 2006e).
The fenitization and vein-type mineralization of the late-colli-sional REE deposits are generally comparable with those in rift zones(cf. Hou et al., 2009b-this issue), but mineralization styles in differentdistricts in the eastern collisional zone range widely from stockwork-stringer to breccia-pipe types, depending on the P–T conditions devel-oped beneath the magmatic-hydrothermal systems. Orebody shapesare also variable from lenticular to pipe-like. Ore types are dominat-ed by pegmatitic, carbonatitic, brecciated, stringer (stockwork), anddisseminated ores; they are composed of barite+fluorite+aegirine–augite+calcite+bastnaesite assemblages (Yang et al., 1998, 2000,2001).
Melt/fluid inclusion studies and stable isotopic data indicate thatthe ore-forming fluids were produced by an immiscible carbonatite–nordmarkite magmatic system in the eastern collisional zone (Liuet al., 2004). The initial ore-forming fluids were high-temperature(600 to 850 °C), high-pressure (N350 MPa) and high-density super-critical fluids, characterized by enrichment in sulfates (BaSO4, K2SO4,and CaSO4), CaCO3 and CaF2 (Xie et al., 2009-this issue). The syntheticstudies led to a possible genetic model for REE mineralization (Houet al., 2009b-this issue). In this model, the hydrothermal systemunderwent a complex evolution from separation of high-T sulfate-bearing NaCl–KCl brine, through fluid boiling resulting in effectivedeposition of REE-fluorocarbonate and sulfate, to subsequent mixingwith low-T meteoric water precipitating minor sulfide assemblages,thus generating a three-phase architecture of REE mineralizationsystems at various structural levels.
Zn–Pb–Cu–Ag ore systems: Cenozoic Zn–Pb–Cu–Ag ore systemsoccurred in the Lanping foreland fold belt within the late-collisionaltransform structural setting, and formed the largest known Ag-bearingbase metal province in east Tibet (Fig. 1). The Lanping fold belt under-wenta complex tectonic evolution involving late Triassic rifting, Jurassic–Cretaceous depression, early Tertiary foreland basin development, andfinally formed part of the Lanping–Simao fold belt (Wang et al., 2001),as a consequence of the eastern Tibetan crust shortening related to theIndo-Asian collision (Wang and Burchfiel, 1997). In the fold belt, twolarge-scale Cenozoic thrust-nappe systems juxtaposed Mesozoic lime-stone and gypsum-bearing clastic strata over the Tertiary strata in theforeland basin, and control the spatial distribution of Cenozoic basemetal deposits (Chen, 2006; He et al., 2009-this issue). Each thrust-nappe systemappears to sole into a commongently-dippingdetachmentzone, which is regarded to have probably provided a significant conduitfor regional fluid flow (Xu and Li, 2003; Hou et al., 2006c).
Based on the mineralization styles, ore types, host rocks andstructural control, at least three major mineralization types have beenrecognized: (1) sandstone-hosted Zn–Pb deposits; (2) carbonated-hosted Zn–Pb–Cu–Ag deposits; and (3) vein-type Cu–Ag polymetallicdeposits (Table 2). He et al. (2009-this issue) describe these thrust-controlled, sediment-hosted Zn–Pb–Cu–Ag deposits, and furtherconstrain the timing of regional mineralization to the Late Eocene–Early Oligocene (∼42 to 30 Ma).
Sandstone-hosted Zn–Pb deposits are represented by the Jindingdeposit, the youngest giant sandstone-hosted Pb–Zn deposit in theworld. Xue et al. (2007) reviewed the geologic,fluid inclusion and stableisotope characteristics of the deposit. New data obtained by the 973Project allowed further aspects of ore genesis to be clarified. Firstly, the3D-dimensional topographic reconstruction indicates that the Jindingdeposit generally has amushroom-like shape and itsmain orebodies aretrapped by a structural dome, mainly occurring as tabular body andlenses in Tertiary porous, gypsum-bearing clastic horizon and overlyingCretaceous sandstone (Xiu et al., 2005). Secondly, three distinct types ofbreccias are recognized at Jinding, i.e., structural, dissolution, andexplosive breccias (Wang et al., 2007). The breccias, created bydissolution of gypsum, are abundant throughout the district. Theirclasts consist of black limestone, silty limestone, and coarse sandstone,whereas the matrix is composed of red-mudstone, siltstone and relicgypsum. These dissolution breccias represent unstable horizons withsignificant lateral extent and display a vertical zoning, showing thecollapse features of a salt-dome during gypsum dissolution. Theexplosive breccias occur as “dyke” or “sill” intruded the gypsum-dissolved breccia horizons. The clasts of the breccia are dominated byblack limestone, the matrix mainly consisting of the oxidized Pb–Znsulfide assemblages. These features suggest intense explosion anddischarge of high-pressure fluids associated with mineralization.Thirdly, three types of bitumen have been observed at Jinding, i.e.,soft, brittle, and dense oil–bitumen (Wang et al., unpubl. data). Theseoccur in fissures within the limestone clasts and matrix, and areassociated with celestine and oxidized sulfide assemblages, implyingthe existence of an old oil–gas trap prior to, or during mineralization.Fourthly, the deposit shows a clear mineralogical zonation, from east towest, varying upwards from celestine+barite, pyrite+marcasite,galena+sphalerite to galena assemblages (Luo et al., 1995), suggestingwestward migration and upwards discharge of the ore-forming fluid(Xue et al., 2007). On the basis of these data, Wang et al. (2007)proposed a two-stage model for the formation of the Jinding deposit, inwhich an early thrust-nappe system led to the structural-salt dome andoil-gas trap, subsequent fluid discharge was directed upwards andexplosion of high-pressure or ultra-high-pressure ore-forming fluids(Chi et al., 2006) caused breakage of the salt-dome and precipitation ofsulfide-sulfate assemblages.
The carbonate-hosted Zn–Pb–Cu–Ag deposits (e.g., the Sanshandeposit) are controlled by an east-dipping thrust fault and associatedsecond-order faults (i.e., strike-slip faults) within the front zone of the
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eastern thrust-nappe system. Orebodies are mainly hosted in Triassiclimestone, and occur as lenses, semi-layered, and irregular bodies,showing open-space filling and stratabound features (He et al., 2009-this issue). Vein-type Cu–Ag polymetallic mineralization mainlyoccurs within second-order fissure zones in the western thrust-nappe system, and shows a metal zonation northeastwards varyingfrom Cu in the root zone (e.g., Jinman) to Cu–Ag or Ag–Cu–Zn–Pb inthe front zone (e.g., Fulongchang) (He et al., 2009-this issue).
Fluid inclusions in all these deposits indicate low temperatures(predominately b200 °C), and high but variable salinities (1.6 to27.7 wt.% NaCl equiv.), suggesting that basinal brines were the mainsource of ore-forming fluids (He et al., 2009-this issue). Similarities inPb isotope composition between ore sulfides and rock units in the foldbelt suggest scavenging from these strata by regional fluids as asignificant mechanism of metal enrichment. Although the depositsshare some similarities with MVT-, SST-, SSC-, and SEDEX-typedeposits, in respect to the lack of any igneous affinity and relationshipwith activities of basinal fluids, they also show a set of unique features.The latter includes: (1) they were formed in a strongly deformedforeland basin within a collision zone, and closely related to regionalthrust-nappe structures; (2) they are fault-controlled, commonlywithout strong preference for type of host rocks; and (3) they containa variety of metals including Zn, Pb, Cu, Ag, and minor Sr, Co, etc. (Heet al., 2009-this issue) suggesting that thrust system-controlled,sediment-hosted Zn–Pb–Cu–Ag deposits are most likely a new sub-type within the family of sediment-hosted base metal deposits.
4.2.1. Orogenic-type Au ore systemOrogenic-type Au mineralization in the Ailaoshan Au belt in west
Yunnan represents a significant Au metallogenic province in theTibetan Orogen (Fig. 1). Hou et al. (2007a) summarized the geologyand mineralization characteristics of the gold belt (Table 2). Sun et al.(2009-this issue) report new research results from the Dapingdeposit, which is typical of the belt. The most important aspectsinvolving genesis of the deposits are emphasized here.
The Ailaoshan Au belt is located in the Paleozoic Jinsha–Ailaoshansuture, marked by Palaeozoic Ailaoshan ophiolite mélanges (Liu et al.,1993), and the belt is structurally controlled by the Red-River ShearZone (RRSZ), which is currently a right-slip fault accommodatingearlier left-slip shear (Leloup et al., 1995; Gilley et al., 2003). Recentage data for potassic–ultrapotassic rocks and lamprophyres along theRRSZ (40 to 33 Ma) suggest initial left-slip shearing started at 40 Mabut continued up to 27 Ma (Liang et al., 2007). Recent high-precision40Ar/39Ar dating yielded a limited mineralization age range of 34 to41 Ma for most of Au deposits (Wang et al., 2005, and referencestherein), demonstrating that this Cenozoic Au mineralization isrelated to large-scale shearing during the late-collisional period.
Almost all the gold deposits formed in the greenschist-faciesmetamorphic mélanges are associated with highly-pyritized, dolomi-tized, and sericitized alteration. The orebodies occur mainly as veins,irregular, lenticular bodies in altered rocks and within intrusivecontact zones (Hu et al., 1995; Li et al., 2000). They appear generallycontrolled by lithologically-brittle structures within the ductile shearzones (Hu et al., 1995). Some Au deposits are associated with Cenozoiclamprophyre and granodiorite stocks which intrude the ophiolitemélange, suggesting a genetic link between Au mineralization andCenozoic mantle-derived magmas (Huang and Wang, 1996). Ore-forming fluids belong to the CO2-rich, low-salinity (6.4–12.6 wt.% NaClequiv.), NaCl–H2O system (Xiong et al., 2006; Sun et al., 2009-thisissue). Their origin has been controversial, and has been attributed to:(1) mixing of magmatic water with meteoric water (Hu et al., 1995);(2) the product of mantle-derived fluids (Hu et al., 1998, 1999); and(3) a mixture of metamorphic and crustal fluids derived from a wetsedimentary wedge (Huang and Wang, 1996). Based on detailedstudies of the Daping Au deposit, Sun et al. (2009-this issue)concluded that the ore-forming fluid was dominantly derived from
granulite facies metamorphism in the lower crust but also involving acontribution from the mantle. Interaction with crustal rocks duringlarge-scale shearing might have played an important role in thegeneration of Au deposits.
Fig. 6B illustrates the Cenozoic ore deposits and their relationshipto major structures and magmatic suites in eastern Tibet, a transformstructural setting. Late-collisional metallogenesis involved translitho-spheric shearing and faulting at a deep structural level and crustalshortening and thrusting at shallow level within a transpressivesetting. A shared deep lithospheric process involving upwelling of theasthenosphere is required to interpret the formation of potassic felsicand carbonatitic magma systems and associated ore-forming mag-matic-hydrothermal systems in a transform structural setting. Thesemagmas, derived from subcontinental lithospheric mantle or thecrust/mantle transitional zone, probably migrated along lower-crustalshears and middle-crustal fault conduits, and were recharged into avoluminous, long-lived magma chamber in the upper crust. Stressrelaxation in a transform structural setting caused release of ore-forming fluids from the magma system, and resulted in precipitationof metals (REE, Cu, Mo, Au) during fluid boiling or phase-separation(Hou et al., 2003a, 2009b-this issue). Deep-level ductile shearing andassociated granulite-phase metamorphism led to generation of CO2-dominated metamorphic fluids, which interacted with the granuliterocks in the lower crust and finally formed the Au orebodies in brittlestructures within upper-crustal ductile shear zones (Sun et al., 2009-this issue). The thrust systems at shallow structural levels causedmigration of crustal fluid toward the foreland basins, during whichmetals were scavenged from the strata and fluids were subsequentlydischarged along fissure structures and strike-slip faults to formstructurally-controlled, sediment-hosted Zn–Pb–Cu–Ag deposits (Heet al., 2009-this issue).
4.3. Metallogenesis in post-collisional extension setting
The post-collisional period is an important metallogenic epoch inthe Tibetan Orogen. Post-collisional metallogenesis is mainly devel-oped in a mid-Miocene crustal extensional setting, characterized byE–W extension, N–S-striking normal faults, EW-striking STDs andpost-collisional potassic–ultrapotassic rocks and leucogranites. Foursignificant mineralization systems have been recognized in theTibetean Orogen: porphyry Cu–Mo systems related to post-collisionalpotassic adakite intrusive rocks; vein-type Sb–Au systems controlledby STD and dome structures, vein-type Pb–Zn–Ag systems controlledby intersections of thrust faults with normal fault; and modern hot-spring-type Cs–Au systems (Figs. 1 and 5; Table 2). All types of theseore-forming systems occur in the mid-Miocene Gangdese tectono-magmatic belt in Tibet (Fig. 1). Moreover, post-collisional crustalextension also resulted in the development of metamorphic corecomplex along the eastern margin of the Tibetan plateau, which isassociated with Au mineralization in the Yangtze block (Hou et al.,2006d).
4.3.1. Porphyry Cu–Mo ore systemPorphyry-type Cu–Mo deposits, the most important deposit type
formed in the post-collisional period, form a world-class porphyry Cubelt within the mid-Miocene Gangdese tectono-magmatic belt (Fig. 1;Qu et al., 2001; Hou et al., 2004a,b, 2006d). Hou et al. (2009a-thisissue) report on the geology and mineralization features of the newly-discovered porphyry Cu belt, while Yang et al. (2009a-this issue)describe in detail the geology and alteration of the giant Qulongdeposit, the largest in the belt. Qu et al. (2009-this issue) have usedcathodoluminescence imaging, combined with SHRIMP U–Pb dating,to provide constraints on the timing of porphyry emplacement in theGangdese belt.
A widely accepted model holds that porphyry-type depositsusually occur in island arcs and continental margin arcs related to
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oceanic-slab subduction (Sillitoe, 1972; Mitchell, 1973). The post-collisional Gangdese porphyry Cu belt (GPCB) in Tibet thus provides anew class of porphyry Cu deposits, apparently unrelated to subduc-tion. These Cu deposits are associated with mid-Miocene felsicmultiple stocks, which intruded Andes-type Gangdese arc batholiths(120 to 70 Ma) and syn-collisional geological units (65 to 52 Ma)within the Lhasa terrane. Individual deposits are controlled by near N–S-striking (i.e., orogen-transverse) normal faults (N13.5 Ma; Blisniuket al., 2001). Available dating defines the timing of felsic magmatismto have been 18 to 13 Ma, peaking at 16±1 Ma (Hou et al., 2004a), atleast ∼50 Ma after subduction-related arc magmatism, but followingthe onset of E–W extension at ∼18 Ma (Williams et al., 2001),exhumation of the Gangdese batholiths at 18 to 21 Ma (Copelandet al., 1987; Harrison et al., 1992) and molasse deposition at 19 to20 Ma (Harrison et al., 1992). Molybdenite Re–Os dating of theseporphyry Cu deposits yielded a range of mineralization ages rangingfrom 14 to 16 Ma (Hou et al., 2003b), suggesting that the regional Cu–Momineralizing event was coeval with emplacement of mid-Miocenefelsic stocks in a post-collisional extension setting.
The host rocks in the GPCB are usually high-K calc-alkaline withminor shoshonites, and show geochemical affinity to adakites (Houet al., 2004a). The genesis of the adakitic host rocks has been debated;their sources have been variably attributed to a thickened lower crust(Chung et al., 2003), a newly-formed mafic lower crust (Hou et al.,2004a) and the subducted Neo-Tethyan slab (Gao et al., 2007). Thegrowing lines of evidence support the hypothesis that they werederived from partial melting of a thickened (N50 km), newly-formedmafic lower crust involving a juvenile mantle component (Hou et al.,2009a-this issue). Heat energy to trigger lower-crustal melting wasprobably provided by either upwelling of asthenospheric mantlethrough a window resulting from break-off of the subducted Indiancontinental slab at ∼25 Ma (Maheo et al., 2002; Williams et al., 2004)or by mantle thinning due to delamination (Chung et al., 2005).
The post-collisional Cu deposits in the GPCB reinforce somegeneralizations about their characteristics (e.g., mineralization style,alteration zoning, metal association, and ore-forming fluids) com-pared to porphyry Cu deposits in arc settings (Hou et al., 2009a-thisissue; Yang et al., 2009a-this issue). However, the formation of bothdeposit classes involved distinct processes for enriching in H2O,metals and S in the metal-bearing magma systems. In arc settings, theH2O in calc-alkaline Cu magmas was derived from dehydration of anenriched mantle wedge (Richards, 2003), metasomatized by thesubduction-slab fluids. In contrast, breakdown of amphibole in lower-crust during melting is regarded as the most significant mechanism inthe formation of hydrous, high-fO2, potassic Cu magmas in acollisional zone (Hou et al., 2005b, 2009a-this issue). Metallic Cuand S in the calc-alkaline magmas in arc setting were usually derivedfrom the subducted oceanic-slab or wedge mantle (Richards, 2003).However, lower-crustal genesis of the host rocks in the Tibetancollisional zone rules out the possibility that S andmetallic Cu enteredthe magmatic system either via mass transfer from the subductedoceanic slab or directly by mantle melting. Early-stage ore sulfidesand their least-altered host rocks yield average δ34S values of−0.08‰and −0.75‰, respectively (Qu et al., 2007), which are typical ofmantle sulfur. This implies that S and Cu were ultimately derived fromjuvenile mantle components in the newly-formed lower-crust ratherthan from ordinary crustal rocks by scavenging of fluids. It is mostlikely that an indirect contribution of chalcophile metals from themantle to the magma system is a key factor in making them fertile forporphyry Cu–Mo deposits.
Calc–alkaline magmas in arc settings usually underwent a MASHprocess at the base of the crust, which yielded evolved, volatile- andmetal-rich, hybrid fertile melts (Richards, 2003, 2005), thus beinginherently capable of forming porphyry Cu deposits. However, theextensional tectonic regime in the post-collisional period would notpermit adakitic magmas to undergo a MASH process like arc magmas,
but instead favors the high-flux magmas to ascend upwards into avoluminous, highly-evolved magma chamber in the upper crust. Theorogen-transverse normal faults and their intersections with pre-existing lineaments and faults provide optimal conditions for focusedflow and emplacement for magmatic-hydrothermal systems, thusplacing constraints on the spatial-temporal localization of Cu-bearingfelsic stocks.
4.3.2. Sb–Au ore systemsThe Cenozoic Sb–Au ore-forming system was developed in the
Tethyan–Himalayan block in south Tibet, and is related to the southTibetan detachment system (STD), created during the post-collisionalperiod. The vein-type Sb–Au deposits within this ore-forming systemconstitute an EW-extending, Sb–Au metallogenic belt with greatpotential in south Tibet (Fig. 1; Table 2). Yang et al. (2009b-this issue)report on the geology and mineralization of the belt; some geneticaspects are summarized below.
The Tethyan–Himalayan block is characterized by gently north-wards-dipping Neogene detachment fault systems, which connectwith the STD to sole into a common gently-dipping detachment zonebeneath this block (Xu et al., 2006). Due to exhumation and erosionrelated to extension, numerous metamorphic core complexes weredeveloped in the block. Their centers were intruded by mid-Mioceneleucogranite intrusions, leading to numerous thermal domes (Chenet al., 1990). The majority of vein-type Sb–Au deposits are distributedaround the thermal domes, and display a concentric zoning outwardsfrom Au and Au–Sb to Sb mineralization (Yang et al., 2009b-thisissue). Almost all orebodies are controlled by EW-trending detach-ment faults and their intersections with N–S-striking normal faults(Fig. 1; Nie et al., 2005). Yang et al. (2009b-this issue) recognizedthree styles of Sb–Au mineralization in southern Tibet: Sb-only, Sb–Au, and Au-only mineralization styles. These deposits generally showcharacteristics of epithermal deposits, but are distinguished fromtypical epithermal Au deposits in arc volcanic settings and orogenic Audeposits associatedwith syn- or post-peakmetamorphism (cf. Kerrichet al., 2000).
Systematic mineralogical zonation from Au and Au–Sb to Sb, and inore-forming fluids from magmatic water-dominated to meteoricwater-dominated fluids (cf. Yang et al., 2009b-this issue), from themetamorphic dome outwards, imply that the mineralization iscontrolled by a hydrothermal convection system driven by leucogra-nitic intrusions. Near the intrusion-centered hydrothermal system, Audeposits, dominated by fine-vein, breccia, and disseminated Au ores,occur in strongly-silicified metaclastic rocks and the fracture zonesaround the metamorphic domes. Far away from the intrusions, agently-dipping (to N) detachment zone not only increased perme-ability of the strata, but also provided an important conduit for fluidflow. Intersections between the detachment zone and N–S-strikingnormal faults probably are sites of discharge for low-temperature (150to 300 °C), low-salinity (1.2 to 5.9wt.% NaCl equiv.) ore-forming fluids,dominated by meteoric water (Yang et al., 2009b-this issue). A muchwider δ34S range (−2.7 to +11‰) for sulfide ores suggests that fluidscavenging of host rocks plays a significant role in the formation of Sb–Au deposits in southern Tibet.
4.3.3. Vein-type Pb–Zn–Ag ore systemVein-type deposits, formed by Pb–Zn–Ag ore-forming systems in
the post-collision period, occur along the northern edge of the mid-Miocene Gangdese porphyry Cu belt, and formed a paired mineralizedbelt in the Lhasa terrane (Fig. 1). The Ag–Pb–Zn mineralization beltwas spatially controlled by the E–W-trending Cuoqin–Pangduo thrustfault zone, formed by shortening of the Lhasa terrane during the late-collisional period (Fig. 1; Ye, 2004). Individual deposits are located atthe intersections of E–W-trending thrust faults and N–S-strikingnormal faults (Hou et al., 2006d). Mineralization ages and styles arevariable along the belt. Mineralization in the eastern segment is
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dominated by vein- and skarn-type mineralization. Molybdenite Re–Os dating yielded an age range of 13 to18Ma for mineralization (Menget al., 2003), identical to that of the Gangdese porphyry Cu deposits(Hou et al., 2003c), demonstrating a genetic link with the mid-Miocene porphyry Cu ore system. In the western segment, miner-alization is dominated by vein-type Ag–Pb–Zn orebodies, controlledby E–W-trending thrust faults, and featuring silicification and weakchloritization and carbonatization of the host strata. K–Ar dating ofhydrothermal mica yields an older age (25 Ma; Meng, unpubl. data),resembling the initial timing of the post-collision event (∼25 Ma).Ores with up to 1 kg/t Ag display disseminated, veinlet, breccia,massive and banded structures. In general, these post-collisional Ag-bearing base metal deposits are comparable with thrust-controlled,sediment-hosted Zn–Pb–Cu–Ag deposits in the Lanping fold belt.Meng et al. (2003) accordingly proposed a similar structural controlmodel for their generation.
Cesium-gold ore systems: An unusual Cs–Au ore system occurs inthe world-class Tibetan–Himalayan active geothermal zone, related tothe post-collisional magmatism or the Tibetan upper-crust partialmelting layer (Hou et al., 2004a; Li et al., 2005). Preliminary surveysshow that the ore-forming systems form two large-sized Cs deposits(Table 2) and numerous small Cs and Cs–Au deposits and occurrences(Zheng et al., 1995). These are mainly located at the intersection sitesbetween N–S-striking rift zone and the IYS, clustering in a hot-springactive fieldwith crustal-derivedHe (Hou et al., 2004b) (Fig.1). Cesiumoccurs as Cs-bearing opal in silica sinters, i.e., geyeseite (Zheng et al.,1995), composed of at least five sedimentary cycles with the earliestage of 0.1 Ma, estimated by the electron spin resonance (ESR) method(Zhao et al., 2006a). The giant Targejia deposit is the largest,containing 14,459 t Cs with the highest grade of 1.3% Cs (Table 2).Cesium-bearing geyeseite has a range of eSr from 85.9 to 112 and ofeNd between −9.7 and −7.6 (Zhao et al., 2006b), close to uppercrustal values, suggesting an upper crust source for the Cs. Hot-springfluids venting in the district contain abnormally high Cs concentra-tions ranging from 3.85 to 4.48 mg/L (Zheng et al., 1995), and displaypositive correlations between Cs with B, Cl, and Rb (Li et al., 2005),suggesting that Cs is sourced within a high-level magma chambersource or upper-crustal partial melting layer. Based on measuredtemperature (74.0–85.5 °C) and the SiO2 contents of hot spring water(Zheng et al., 1995), Li et al. (2005) estimated that a SiO2-satuated, Cs-rich hydrothermal fluid reached at least 250 °C at depth, andprecipitated Cs-bearing opal at about 100 °C.
Fig. 6C depicts post-collisional metallogenesis and the relationshipsbetween different types of deposits and post-collisional structures inTibet. Metallogenesis relates to post-collisional crustal extension andresultant felsic magma systems that were derived from newly-formedlower crust and/or produced by crustal anatexis and crustal fluid flowscontrolled by orogen-parallel deep detachment faults, and/or orogen-transverse normal faulting. Generation of porphyry Cu deposits requiresthe contribution of a juvenile mantle component sourced in the lowercrust to a hydrous, high-fO2, metallic-rich felsic magma system, and isrelated to deep lithospheric process, e.g., slab break-off or delamination(Fig. 6C). The Sb–Au and Cs–Au mineralization requires crustal ex-tension to allow exhumation of metamorphic core-complexes and theformation of rift zones aswell as crust-derivedmagma systems to deriveconvective hydrothermal systems (Fig. 6C).
5. Classification of collision-related deposits and comparison withglobal examples
Global collisional orogen systems, in terms of their orogenicpolarity, principal architecture, and crustal geometry, may bedivided into three major orogenic-styles, i.e., asymmetric, sym-metric, and composite-styles (Fig. 2). Asymmetric orogenic systems,represented by the Himalayan–Tibetan Orogen (Yin and Harrison,2000), are characterized by single-oriented orogenic polarity and
thrust-related crustal overlapping and slidie-detachment at multi-structural levels. At least five structural units have been recognizedacross the orogenic system: foreland basin; foreland thrust zone;collisional suture; main-collisional zone; and hinterland thrust-foldzone (Fig. 2A). Representative of symmetric orogenic systems is thePyrenean Orogen (Choukroune, 1992; Sibuet et al., 2004), which ischaracterized by symmetrical contractional systems and central fan-shaped structures resulting from horizontal compression. Based onregional geology (cf. Choukroune, 1992) and the deep seismicreflection profiles (cf. Roure and Banda, 1987; Roure et al., 1989;Choukorune and ECORS Team, 1989), a complete structural sectionhas been established for the Pyrenean Orogen, in which the forelandthrust zone and the foreland basin were symmetrically developedon both sides of the central axial uplift zone (cf. Sibuet et al., 2004;Fig. 2B). Composite-style orogenic systems are represented bythe Qinling Orogen (Fig. 2C), which first underwent a Paleozoicasymmetric-style orogeny involving collision between the Qinlingterrane and the North China block, and a subsequent Mesozoicsymmetric large-scale orogeny resulting from collision between theNorth China and Yangtze blocks since the Late Triassic (Zhang et al.,1996; Xu et al., 1996). These orogenic systems, each with theirdistinct orogenic styles, underwent different tectono-magmaticevolutions, and thus resulted in different ore-forming systems andresultant deposit types (Table 3).
In an asymmetric orogen, e.g., the three-stage collisional Tibetanorogen, the transform structural setting in the late-collisional period isthe most spectacular of all continental collision orogenic systems.Large-scale translithospheric strike-slip faulting and shearing in thelate-collisional transform setting resulted in generation of potassic,felsic, lamprophyres and carbonatitic magmas, derived from sub-continental lithospheric mantle or/and the crust-mantle transitionalzone (Hou et al., 2006c), and fundamentally controlled the mantle-derived (e.g., Cu, Au, REE) metallogenic provinces (Fig. 6B). Thethrust-nappe systems formed by internal shortening were developedon the foreland basin in the transform setting, and controlled a crust-derived metallic (e.g., Zn, Pb, Ag) metallogenic province, in whichnumerous sediment-hosted Ag-bearing base metal deposits weregenerated by scavenging and discharging of basinal fluids thatmigrated along a deep detachment zone (Fig. 6B).
In symmetric orogens (e.g., the Pyrenees), the fan-shapedstructures (tectonic wedge) probably substituted for the late-collisional transform structures, and absorbed crustal shorteningand adjusted the collision strain (cf. Choukroune, 1992). In the fan-shaped structure zones, volatiles driven off the wet sedimentarywedge during crustal overthrusting not only penetrated the hotoverlying thrust sheet to result in large-scale crustal anatexis (Harriset al., 1986), in turn creating large volume granitic magmas in theforeland thrust and the central axial uplift zones (Fig. 6A), but alsocaused metals (W, Sn, U) and incompatible elements (Rb, Cs, Li, Y) tobecome enriched in the resulting felsic melts (Seltmann and Faragher,1994). These crust-derived, hydrous, low-fO2 felsic systems, whetheroccurring in the main-collisional (e.g., the Tibetan Orogen) or in post-collisional periods (e.g., the Pyrenean Orogen), have great potentialfor ore formation and are documented to have formed abundant Wand U deposits (Fig. 6A, C; Le Roy, 1978; Kelly and Rye, 1979). Insymmetric orogens, the foreland basins were commonly developedoutside the foreland thrust zones (Fig. 2B), and basinal sedimentswere usually not or onlyweakly deformed. These foreland basins, suchas the Cevennes and Ave basins in the Pyrenean orogen, typicallycontain clusters of MVT-type Zn–Pb deposits (Puigdefabregas et al.,1992; Bradley and Leach, 2003) and also sandstone-hosted copperdeposits (Subias et al., 2001). Long-distance lateral migration of fluidsthrough stable permeable aquifers at deep-structural levels wasregarded as a significant mechanism for generating the MVT Zn–Pbdeposits in weakly-deformed sedimentary basins (Sverjensky, 1986;Leach et al., 2005).
Table3
Classification
ofco
llision
-related
depo
sits
andtheirge
olog
icch
aracteristics.
Dep
ositgrou
p(gen
etic
clan
s)Dep
osittype
Tecton
icsetting
Structural
control
Stress
regime
Hostrock
san
dtheirsources
Mineralizationan
dorefluid
Typicalex
amples
Referenc
es
Porphy
ry-typ
eore-form
ing
system
Porphy
ryCu
–
Mode
posit
Late-collis
iona
ltrans
form
structural
zone
;Co
llision
alzo
newithpo
st-
collision
alcrus
tale
xten
sion
Strike
-slip
faultan
dstrike
-slip
pull-ap
artba
sin;
Oroge
n-tran
sverse
faultan
dits
intersection
withthrust
fault
Tran
spressiona
l;tran
sten
sion
alex
tens
iona
l
Mon
zogran
ite;
gran
ite;
mon
ozon
ite,
andgran
odiorite,d
erived
from
athicke
ned,
juve
nile
mafi
clower-crust
orcrus
t-man
tletran
stiona
lzon
e
Fine
d-ve
inan
ddissem
inated
;Ortho
mag
matic
fluids
Yulong
;Qulon
g;Tibe
tanOroge
n(Tan
gan
dLu
o,19
95;Hou
etal.
2003
a,b,
2009
a-this
issu
e)Po
rphy
ryAu–
Cude
posit
Late-collis
iona
ltrans
form
structural
zone
Strike
-slip
fault,reactive
basemen
tfault
Tran
spressiona
l;tran
sten
sion
alAlkalig
ranite,sye
nite,a
ndqu
artz
syen
ite,
derive
dfrom
thelitho
sphe
ric
man
tle
Fine
-veinan
ddissem
inated
;orthom
agmatic
fluids
Beiya,
Yao'an
;Tibe
tanOroge
nXuet
al.(20
07)
Porphy
ryMo
depo
sit
Collision
alzo
newithpo
st-collis
iona
lcrus
tale
xten
sion
;Co
llision
alzo
newith
main-
collision
alstress
relaxa
tion
Oroge
n-tran
sverse
fault;
intersection
withthrust
fault
Tran
sten
sion
alex
tens
iona
lGranite,q
uartzmon
zonite,a
ndmon
zogran
ite,
derive
dfrom
alower-
crus
tbu
tinvo
lvingman
tleco
mpo
nents
Fine
d-ve
inan
ddissem
inated
;orthom
agmatic
fluids
Sharan
g,Tibe
tan
orog
en;Niann
ihu,
Jindu
iche
ng,Q
inlin
gOroge
n
(Zha
ngan
dDen
g,20
01;Hou
etal.
2006
b)
Orogenic-type
Auore-form
ing
system
Shea
rzo
ne-typ
eAude
posit
Late-collis
iona
ltrans
form
structural
zone
withlarge-scalesh
earing
;Co
llision
alzo
nene
arthesu
ture
withsyn-
peak
metam
orph
ism
Duc
tile-brittle
tran
sition
alsitesin
shea
rzo
neTran
spressiona
lco
mpression
alOph
iolitemélan
ges,clasticsequ
ences
andmafi
c-ultram
aficrock
swith
gree
nsch
ist-facies
metam
orph
ism
Metam
orph
icfluids
invo
lvingman
tle
compo
nent
Aila
osha
nAube
lt;
Tibe
tanOroge
n;Jia
ncha
ling,
Qinlin
gOroge
n
(Huet
al.199
5;Zh
ang,
2001
)
Carlin-likeAude
posit
Collision
alzo
nene
arthesu
ture
with
syn-
topo
st-pea
kmetam
orph
ism
Faults
boun
ding
theterran
ene
arthesu
ture
Compression
alLate
Paleoz
oic-Triassic
turbidites
Micro-fi
ned,
and
dissem
inated
;Lo
w-
salin
ityH2Sfluids
Dashu
i,Laerma,
Bagu
amiao;
Qinlin
gOroge
n
(Lia
ndPe
ters,
1998
;Mao
etal.,
2002
)Granite-related
Sn–W
–Uore-
form
ingsystem
Greisen
-typ
eSn
–W
depo
sit
Collision
zone
withcrus
t-de
rive
dlow-
fO2gran
itoids
;Fo
reland
thrust
and
centrala
xial
upliftzo
neswithS-type
gran
itoids
Faultan
dfracturalz
one
Intrus
iveco
ntacts
Compression
alCa
lc-alkalinegran
itoid,
derive
dfrom
crus
tala
natexis
Massive
sulfide
-style,
stoc
kwork-style,
Vein
swarm-style;
orthom
agmatic
fluids
Lailish
an,T
ibetan
Oroge
n;Pa
nasq
ueira,
Pyrene
anOroge
n
(Liu
etal.,19
93;
Hou
etal.,20
07a;
Kelly
andRy
e,19
79)
Greisen
-typ
erare-
metallic
depo
sit
Collision
zone
withcrus
t-de
rive
dlow-fO2gran
itoids
Faultan
dfracturalz
one
Intrus
iveco
ntacts
Compression
alMus
covite
gran
itoid,
derive
dfrom
crus
tala
natexis
Stoc
kwork-style,v
ein
swarm-style;
orthom
agmatic
fluids
Baihua
nao;
Tibe
tan
Oroge
nLiuet
al.(19
93)
Granite-related
Ude
posit
Foreland
thrust
andcentrala
xial
upliftzo
neswithS-type
gran
itoids
Unc
lear
Compression
alHHPgran
ites,d
erived
from
crus
tal
anatex
isVein-
style,
bree
cia-
style;
CO2-richfluids
mixingwithmeteo
ric
water
Margn
acan
dFana
y,Py
rene
anOroge
nLe
Roy(197
8)
Skarn-type
polymetallic
ore-form
ing
system
Skarn(and
hybrid)-type
Cu–Au
Collision
zone
withmain-
collision
almixed
crus
t/man
tle-de
rive
dhigh
-fO2
gran
itoids
Faultan
dfracturalz
one
intrus
iveco
ntacts
Compression
withlate-stage
stress
relaxa
tion
Calc-alkalinegran
ites
derive
dfrom
the
MASH
proc
ess,an
dMesoz
oiccarbon
ate
andclasticform
ations
Skarn-
hosted
,vein-
stoc
kwork
orthom
agmatic
fluids
Chon
gmud
a,Xiong
cun,
Tibe
tan
Oroge
n
Liet
al.(20
06a,b)
Skarn-
type
Pb–Zn
–
Cude
posit
Collision
zone
withmain-
collision
almixed
crus
t/man
tle-de
rive
dhigh
-fO2
gran
itoids
Thrust
faultan
dfracturalz
one
Intrus
iveco
ntacts
Compression
withlate-stage
stress
relaxa
tion
Calc-alkalinegran
ites
derive
dfrom
the
MASH
proc
ess,an
dPa
leoz
oic–
Mesoz
oic
carbon
atean
dclasticform
ations
Skarn-
hosted
,vein-
stoc
kwork
orthom
agmaticfluids
mixed
withmeteo
ric
water
Men
gzho
ng'a,
Yagu
ilaTibe
tan
Oroge
n
Hou
etal.(20
06b)
(con
tinu
edon
next
page)
19Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
Table3(con
tinu
ed)
Dep
ositgrou
p(gen
etic
clan
s)Dep
osittype
Tecton
icsetting
Structural
control
Stress
regime
Hostrock
san
dtheirsources
Mineralizationan
dorefluid
Typicalex
amples
Referenc
es
Alkalicomplex
-relatedRE
Eore-
form
ingsystem
Vein-
type
andbreccia-type
REEde
posits
Late-collis
iona
ltrans
form
structural
zone
withstrike
-slip
faulting
system
andcarbon
atite-alka
lineco
mplex
es
Strike
-slip
faultan
dreactiva
tedba
semen
tfault
Tran
spressiona
l,tran
sten
sion
al,
extens
iona
l
Carbon
atitesill,
alka
lisyen
iteintrus
ion
andwall-rock
sVeinsystem
-style,
brecciapipe
-style
dissem
inated
-style
orthom
agmatic
fluids
Mao
niup
ingDaluc
aoLizh
uang
;Tibe
tan
Oroge
n
(Yua
net
al.,19
95,
Yang
etal.,19
98)
Sedimen
t-ho
sted
Zn–Pb
(–Cu
–Ag)
ore-
form
ingsystem
MVTZn
–Pb
depo
sit
Foreland
basinTh
rust-n
appe
system
Extens
iona
lfau
ltan
dup
liftof
basinmargin
Compression
al;
extens
iona
lUnd
eformed
andwea
kly-de
form
edcarbon
ateform
ation
Ope
n-sp
acefilling
;ba
sina
lbrine
Ave,
Pyrene
anOroge
n(B
radley
andLe
ach,
2003
;Le
achet
al.,
2005
)Sa
ndston
e-
hosted
Pbde
positor
Laisva
ll-type
Foreland
basinTh
rust-n
appe
system
Noob
viou
s,bu
trelatedto
extens
iona
lfau
ltan
dup
liftof
basinmargin
Compression
al;
extens
iona
lSh
allow
marinesand
ston
eDisseminated
Pb;
basina
lbrine
Caledo
nide
orog
en(Seltm
annan
dFaragh
er,199
4;Ihlenet
al.,19
97)
Sand
ston
e-
hosted
Zn–Pb
depo
sitor
Jinding
-typ
e
Tran
sform
structural
zone
withlate-
collision
althrust-n
appe
system
ontheforeland
basin
Structural-litho
logicaltrapan
dsalt-dom
ein
thethrust-n
appe
system
Tran
spressiona
lTe
rrestrial-facies
sand
ston
eStratoid,len
ticu
lar;
basina
lbrine
Jinding
inLanp
ing
basin;
Tibe
tan
Oroge
n
(Xue
etal.,20
07;
Wan
get
al.,20
07)
MVT-lik
eZn
–Pb
–Cu
–Ag
depo
sitor
Irish-
type
Tran
sform
structural
zone
withlate-
collision
althrust-n
appe
system
onthe
foreland
basin
Thrust
faultinthefron
tzon
eof
thethrust-n
appe
system
Tran
spressiona
lSh
allow
marinecarbon
ateform
ation
withminor
terrestrials
ands
tone
Stratoid
and
lenticular;Ba
sina
lbrines
Heish
an,H
uish
anHua
chan
gsha
n,Tibe
tanOroge
n;Irelan
d,Variscan
Oroge
n
(Che
n,20
06;Heet
al.,20
09-thisissu
e;Se
ltman
nan
dFaragh
er,199
4)
Vein-
type
Cu–Ag–
Znde
posit
Tran
sform
structural
zone
withlate-
collision
althrust-n
appe
system
onthe
foreland
basin
Seco
nd-order
faultan
dfissure
zone
sin
thethrust-n
appe
system
Tran
spressiona
lFe
ldsp
athicqu
artz
sand
ston
e,siltston
ean
dcarbon
aceo
ussh
ale
Largeve
inan
dve
insw
arm;Ba
sina
lbrine
sJin
man
,Fulon
gcha
ng,
Baiyan
gping;
Tibe
tan
Oroge
n
(Che
n,20
06;Heet
al.,20
09-thisissu
e)
Vein-type
Sb–
Auore-form
ing
system
Vein-
type
Aude
posit
Detachm
entsystem
withgran
itic
intrus
ionin
theforeland
thrust
zone
;po
st-collis
iona
lexten
sion
setting
Metam
orph
icco
reco
mplex
Intersection
sitesof
detach
men
tfaultan
dorog
en-
tran
sverse
fault
Extens
iona
lGreen
schist-faciesmetam
orph
icrock
sVeins
andlens
esMag
matic
water
with
minor
meteo
ricwater
Lang
kazi;Tibe
tan
Oroge
n(Yan
get
al.,20
06,
2009
a,b-this
issu
e)
Vein-
type
Sbde
posit
Detachm
ents
ystem
intheforeland
thrust
zone
;po
st-collis
iona
lexten
sion
setting
Intersection
sitesof
detach
men
tfaultan
dorog
en-
tran
sverse
fault
Extens
iona
lFine
-san
dstone
andsiltston
eintercalated
withinterm
ediate-mafi
cvo
lcan
ics
Largeve
inan
dve
insw
arm;Meteo
ric
water
Shalag
ang,
Zhax
ikan
g;Tibe
tan
Oroge
n
(Yan
get
al.,20
06,
2009
a,b-this
issu
e)
Spring
-typ
eCs–
Auore-form
ing
system
Sinter-h
ostedCs
depo
sit
Collision
alzo
necu
tby
orog
en-trans
verse
faults
andriftingba
sins
Oroge
n-tran
sverse
faults
and
mod
ernge
othe
rmal
system
Extens
iona
lSilic
asintersan
dminor
calcareo
ussinter
Cs-sinter;
geothe
rmal
system
Dag
ejia;Tibe
tan
Oroge
nZh
enget
al.(19
95)
Spring
-typ
eAude
posit
Collision
alzo
newithQua
tern
ary
v olcan
oes
Extens
iona
lfau
ltsan
dmod
ern
spring
activity
Extens
iona
linterm
ediate-felsicvo
lcan
ics
Vein,
stoc
kwork
geothe
rmal
system
Teng
chon
g;Tibe
tan
Oroge
nHou
etal.(20
06d)
20 Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
21Z. Hou, N.J. Cook / Ore Geology Reviews 36 (2009) 2–24
Porphyry-type Cu–Mo (Cu–Au, Au–Cu, Mo) and orogenic-type Audeposits are most characteristic for asymmetric- and composite-styleorogenic systems. In the Tibetan Orogen, porphyry-type deposits occurin each stage of the continental collision, varying fromMo deposits (e.g.,Sharang) in themain-collisional convergent setting, through Cu–Mo–Audeposits (e.g., Yulong) in the late-collisional transform setting, to Cu–Modeposits (e.g., Qulong) in thepost-collisional, extensional setting (Fig. 6).Host rocks to the Cu–Mo deposits are usually K-rich, and their Cu-bearing magmas are regarded to have been derived from thickened,juvenile mafic lower-crust. The source of theMo-bearingmagmas is notwell constrained; it is most likely that these magmas have undergone aMASH process at the base of the Tibetan crust (Fig. 6A). In the QinlingOrogen, porphyry Mo mineralization formed a world-class Mo metallo-genic province inChina.Mostof the giantModeposits,withmolybdeniteRe–Os ages of 145 to 132 Ma (Li et al., 2003), occur in a post-collisionalcrustal extension setting, and were controlled by orogen-transversefaults (Zhang andDeng, 2001), as in theGPCB inTibet (Fig. 6C). Availablegeochemical and stable isotopic data indicate that the felsic magmaswere derived from the lower crust but also involve mantle components.Molybdenum was extracted from Mo-rich metamorphic basement byascending magmas (Fig. 6C). In symmetric orogens, e.g., the Pyrenees,porphyry-type Cu–Mo deposits, even developed in the axial zone, wereprobably eroded out, due to intense uplift of Paleozoic and pre-Paleozoicmassifs (terrane) (Sibuet et al., 2004).
Although some researchers consider that collisional orogens (e.g.,Alpine and Himalayan Orogens) have limited Au potential (Barley andGroves, 1992), both the Qinling and Tibetan Orogens contain majormetallogenic provinces, located in or near the translithosphericstructures (Li and Peters, 1998; Chen, 2001; Hou et al., 2006b). In theTibetan Orogen, orogenic-type Aumineralization accompanied syn- topost-peak metamorphism during the main-collisional (e.g., Mayum)to late-collisional periods (e.g., Ailaoshan belt). In the Qinling Orogen,there are at least twokinds of Au deposits, i.e., the Carlin-likeAu (Li andPeters, 1998) and shear zone-type Au deposits (Zhang, 2001). Theformer, with radiometric age of 240 to 170 Ma (Mao et al., 2002),mainly occurs as disseminated orebodies in or near Paleozoic suturesand associated brittle-ductile shear zone (Fig. 6A; Li and Peters, 1998;Zhang, 2001). The latter, with radiometric age of 170 to 120 Ma (Chen,2001), mainly occur as Au quartz veins within metamorphic corecomplexes in the hinterland thrust-fold belt (Zhang and Zheng, 2001;Chen, 2001), and formed in a post-collisional extension setting, similarto the Aumineralization related to the STD and the structural domes insouthern Tibet (Fig. 6C; Yang et al., 2009b-this issue).
The variety of deposits related to continental collision mentionedabove indicates that there aremore collision-relateddeposits than thoseincluded in the classification of Sawkins (1984). A new classificationincluding all these newly-discovered collision-related deposits incollisional orogenic systems is therefore necessary. Based on the newinformation from study of the Tibetan Orogen, eight principal groups ofdeposits or ore-forming systems can be defined (Table 3). These are: (1)porphyry-type Cu–Mo; (2) orogenic-type Au; (3) granite-related Sn–W–U; (4) alkali complex-relatedREE; (5) sediment-hosted Zn–Pb(–Cu–Ag); (6) vein-type Sb–Au; (7) skarn-type polymetallic; and (8) hot-spring-type Cs–Au deposits. Table 3 summarizes the tectonic setting,structural controls, deposit types, and major characteristics of each.
Acknowledgments
This study was supported by the National Basic Research Plan 973Project (2002CB41260 to ZQH) from the Ministry of Science and Tech-nology, China, and the Outstanding Youth Foundation (40425014 to ZQH)of NSF of China. The authors thank researchers from the 973 ScientificTeam for their constructive discussions and comments. We are deeplyindebted to two anonymous Ore Geology Reviews referees for theirvaluable comments and suggestions for improvement of the manuscript.Special thanks are due to Khin Zaw for his comments and suggestions.
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