post-collisional sb and au mineralization related to the south tibetan detachment system, himalayan...

Ore Geology Reviews 36 (2009) 194–212

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Post-collisional Sb and Au mineralization related to the South Tibetan detachmentsystem, Himalayan orogen

Zhusen Yang a,⁎, Zengqian Hou b, Xiangjin Meng a, Yingchao Liu a, Hongcai Fei c, Shihong Tian a,Zhenqing Li a, Wei Gao a

a Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, PR Chinab Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, PR Chinac Chinese Academy of Geological Sciences, Beijing, 100037, PR China

⁎ Corresponding author.E-mail address: [email protected] (Z. Yan

0169-1368/$ – see front matter © 2009 Elsevier B.V. Aldoi:10.1016/j.oregeorev.2009.03.005

a b s t r a c t
a r t i c l e i n f o
Article history:Received 8 April 2008Received in revised form 11 March 2009Accepted 11 March 2009Available online 25 March 2009

Keywords:Sb–Au depositFluid inclusionStable isotopeThermal domeSouth Tibetan detachment systemHimalayan orogen

More than 50 Sb–Au deposits and occurrences have recently been found in an E–W-striking structural–thermal dome zone, related to the South Tibetan detachment system (STDS) in the Himalayan orogen. Theyare mainly distributed around the thermal domes intruded by mid-Miocene leucogranite bodies, and show ametallic zoning varying from Au, Sb–Au, to Sb mineralization from the domes outwards. At least threemineralization styles are recognized, i.e., Sb-, Sb–Au-, and Au-styles of deposits, all hosted in the Mesozoic,Tethyan passive continental-margin sequences. The Shalagang-style Sb deposits, controlled by N–S-strikingnormal faults and E–W-striking bedding faults, are usually composed of quartz–stibnite veins with open-space filling structure. Low homogenization temperatures (135–367 °C) and low salinities (0.5–12.6 wt.%NaCl equiv.), as well as highly variable calculated δ18OH2O values (−11.5–12.3‰) and very low δD values(−140 to −166‰), suggest an ore-forming fluid dominated by geothermal or meteoric water. The Mazhala-style Sb–Au deposits were controlled by small-scale bedding faults and their intersections with N–S-strikingnormal faults. They consist of gold-bearing quartz–stibnite veins with minor disseminated ores, and areassociated with silicification, sericitization, chloritization and carbonatization. CO2-rich fluid inclusions inAu-bearing gangue quartz, calculated δ18OH2O values (5.4–11.5‰) and measured δD values (−72 to −119‰)for precipitation of gangue quartz suggest a mixed ore-forming fluid containing both meteoric and magmaticwaters. Langkazi-style Au deposits, controlled by detachment faults and normal faults along the margin ofthe thermal dome, consist of Au-bearing quartz veins and disseminated ores with intensive silicification,chloritization and sericitization. Gangue quartz from Au-bearing quartz veins yielded a limited range ofδ18OH2O values (1.8–8.2‰) and δD values (−52 to −83‰), suggesting an ore-forming fluid dominated bymagmatic water.The genetic links among these deposits, the granite-intruded thermal domes and ore-controlled faultsystems suggest a mid-Miocene metallogenic epoch. The spatial zonation in metallic associations, and thevariation in compositions and sources of ore-forming fluids indicate that these Sb and Au deposits resultedfrom a post-collisional dome-centered geothermal system, driven by mid-Miocene granite magmas related tothe STDS. Rb–Sr and S isotopic data indicate that the scavenging of the convective geothermal fluids throughMesozoic permeable strata play an extremely significant role in concentrating metallic Sb and minor Au, andforming Sb, Sb–Au, and Au deposits in southern Tibet.

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1. Introduction

The processes responsible for the uplift and associated mineraliza-tion in theTibetan–HimalayanOrogencreatedby the Indo–Asia collisionhave become the focus of interest and contention. The South Tibetandetachment system (STDS), a post-collisional structure in the Hima-layan orogen, occurs along a strike of 2000 km within the Himalayanterrane (Burchfiel et al., 1992) (Fig.1A). It was active at the same time as

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compressional deformation at lower structural levels (Burchfiel andRoyden, 1985), and records extrusion of a crustal wedge at theHimalayan topographic front (Hodges and Hurtado, 1998; Wu et al.,1998). The STDS controls emplacement of mid-Miocene leucogranite(Searle et al., 1993); rapid decompression of the footwall due to fastdenudation was regarded to have resulted in crustal anatexis andformation of leucogranite magma (Harris and Massey, 1994).

The STDS is also a significant metallogenic environment, in whichmore than 50 vein-type Sb and Au deposits and occurrences occur alongan E–W-striking structural–thermal dome zone (Fig.1), bounded by theIndus–Yalu suture (IYS)and the STDS, thus forminganE–W-strikingbelt

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Fig. 1. (A) Simplified geological map of the Tethyan Himalaya showing the distribution of antimony and gold deposits, thermal domes, and leucogranites along the South Tibetandetachment system (modified from Pan et al., 2004; Zheng et al., 2004). The numbers of the deposits correspond with Table 1. Abbreviations: THS–Tethyan Himalayan sedimentarysequences; GHM–Greater Himalayan metamorphic rocks; LHM–Lesser Himalayan meta-sedimentary sequences; JS–Jinsha suture; BNS–Bangong–Nujiang suture; IYS–Indus–Yalusuture; STDS–South Tibetan detachment system; MCT–Main Central thrust; MBT–Main Boundary thrust; MFT–Main Frontal thrust. (B) Geological model showing the mechanism ofGreater Himalayan extrusion and South Tibetan detachment system extension (after Xu et al., 2006). Additional abbreviations: MHT–Main Himalayan thrust; GHD–GreaterHimalayan detachment fault; KLD–Kangmar–Lhagoi Kangri detachment fault.

195Z. Yang et al. / Ore Geology Reviews 36 (2009) 194–212

of Sb–Au mineralization in southern Tibet (Fig. 1; Table 1; Nie et al.,2005; Yang et al., 2006; Hou et al., 2006a,b,c,d; Hou and Cook, 2009-thisissue). The genetic link between the STDS and Sb–Aumineralization hasremained poorly understood up until now.

Most of the Sb and Au deposits in southern Tibet are currentlycategorized as medium or small in size due to poor exploration.Preliminary analysis indicates, however, that the belt carries significantpotential for additional discoveries (Yang et al., 2006). The genesis of the

196 Z. Yang et al. / Ore Geology Reviews 36 (2009) 194–212

deposits is controversial. Li et al. (2002) regarded the Shalagang Sbdeposit to have been formed by Miocene magmatic–hydrothermaloverprinting of preexisting products of Mesozoic sedimentary exhala-tion. Nie et al. (2005) suggested that most of the Au and Sb deposits inthe belt are closely related to late-Yanshanian and early-Himalayanalkali-rich igneous rocks. Fu et al. (2005) proposed that the Kangmar–Lhagoi Kangri thermal domes (metamorphic core-complex) in southernTibet are an important factor controlling the spatial and temporaldistribution of Sb–Au mineralization. The lack of consensus reflects, inpart, the fact that only a few of the deposits have been studied to anysignificant extent (fluid inclusion, stable isotope and geochronologicaldata are generally lacking). In addition, only a limited number of oredistricts have been investigated in the kind of detail necessary toconstrain the relationship between deformational processes and Sb–Aumineralization.

This contribution firstly reports detailed data on mineralization,fluid inclusion and stable isotope for some of the Sb–Au deposits. Wealso discuss the post-collisional Sb–Au ore-forming system and itsgeodynamic setting in the Tethyan Himalaya, based on the spatial andtemporal distribution of deposits and major ore-controlling factors.

2. Geological setting

2.1. Regional geology

It is now widely recognized that the Tibetan–Himalayan orogen iscomposed of four E–W-striking terranes or blocks (from north tosouth, the Songpan–Ganze, Qiangtang, Lhasa, and Himalaya terranes;Fig. 1A inset). The Lhasa terrane, bounded by the Bangong–Nujiangsuture to the north and the IYS to the south, consists of Precambrian–Cambrian metamorphic basement and unconformably overlyingDevonian–Upper Cretaceous marine sedimentary sequences (PearceandMei,1988; Yin et al.,1988; Pan et al., 2004). This terrane is believedto have separated fromGondwana during the Permian or Triassic (e.g.,Allégre et al., 1984; Chang et al., 1986), and then drifted northwardsand finally collided with the Qiangtang terrane in the Early Cretaceous(Kapp et al., 2005). The occurrence of Andean-type arc granitoidbatholiths (120–70 Ma; Schärer and Allègre, 1984; Debon et al., 1986;Harris et al., 1988), the Xigaze fore-arc basin, and the IYS (Fig. 1), allsuggest northward subduction of the Neo-Tethyan oceanic lithospherein the Cretaceous (Kapp et al., 2005), and subsequent closure due tothe Indian–Asian continent collision in the early Tertiary (Yin andHarrison, 2000). The IYS, a main boundary between the Indian andAsian continents, can be traced discontinuously for a distance of atleast 3000 km from Myanmar to Afghanistan. The boundary iscurrently damaged by a south-dipping thrust system, i.e., the GreatCounter thrust, composed of at least five south-dipping thrust faultsalong the IYS (Yin and Harrison, 2000).

The Himalayan terrane consists of four lithotectonic units: theTethyan Himalaya, the Greater Himalaya, the Lesser Himalaya, and theSubhimalaya, from north to south. They are separated from one anotherby four north-dipping Cenozoic fault systems, i.e., the STDS, the MainCentral thrust (MCT), the Main Boundary thrust (MBT) and the MainFrontal thrust (MFT), fromnorth to south (Fig.1). The TethyanHimalaya,a significant metallogenic tectonic unit, is bounded by the STDS and theIYS (Fig. 1). It consists of Late-Precambrian to Early-Paleozoic sedimen-tary and meta-sedimentary rocks and thick Permian to Late Cretaceouspassive continental margin sequences (Burchfiel et al., 1992; Garzanti,1999). The sedimentary environment evolved from a basin and slope toan outer-shelf during the Late Cretaceous, followed by a final

Notes to Table 1:The tonnage of antimony deposits in China is classified as large (N100,000 metric tons Sb‘occurrence’ is an unexploited site of mineralization. Mineral abbreviations: Apy–arsenopchalcopyrite, Ct–cassiterite, El–electrum, Ep–epidote, Gn–galena, Li–limonite, Ma–marcasisericite, St–stibnite, Tt–tetrahedrite, Zo–zoisite. Alteration abbreviations: argi.–argillation, csilicification.

transgression–regression cycle and terrestrial deposition during thePaleocene and Eocene. The latter event recorded the narrowing andclosing processes of the Neo-Tethys as a result of the convergencebetween Indian and Asian continents (Williams et al.,1996; Jadoul et al.,1998; Rowley, 1998; Xia et al., 2005). This continental convergence,which started in the Tertiary, resulted in the formation of a forelandthrust–fold belt in the Himalaya, which has an estimated amount ofcrustal shortening of 130–140 km and an initial timing of shortening of~50 Ma (Ratschbacher et al., 1994). The foreland thrust–fold beltconsists of fold and imbricated thrusts involving the passive continentalmargin sequence of the Tethyan Himalaya. The Greater Himalaya,boundedby theMCTand the STDS (Burg and Chen,1984; Burchfiel et al.,1992), is mainly composed of Neoproterozoic metamorphic basementrocks, and is a typical lower-crust unit (Parrish and Hodges, 1996;DeCelles et al., 2000). The crystalline sequence of the Greater Himalayais partially at a lower stratigraphic level than the Lesser Himalaya (Panet al., 2004). This has been attributed to the lateral flow and southwardextrusion of a hot, ductile Tibetan lower-crust in the Miocene (Nelsonet al., 1996; Beaumont et al., 2001).

2.2. South Tibetan detachment system and thermal dome

The South Tibetan detachment system (STDS) is a northward-dipping, low-angle normal-fault system (Fig. 1), which is traceablealong a strike of 2000 km in the Himalaya (Burg and Chen, 1984;Burchfiel et al., 1992; Chen and Liu, 1996). This structure places non-or weakly metamorphosed Tethyan Himalayan strata against GreaterHimalayan amphibolite-facies gneisses and leucogranites (Burg andChen, 1984; Burchfiel et al., 1992; Edwards et al., 1996; Hodges et al.,1996). The basal detachment in the STDS is represented by a gentlynorth-dipping brittle fault, underlain by a sub-parallel myloniticcarapace in the uppermost 500–1000 m of the footwall (Schärer et al.,1986; Hodges, 2000; Wang et al., 2001; Liu et al., 2004b). In mostcases, well-developed shear-sense indicators of the mylonite aregenerally consistent with NE- or NW-directed motion of the hangingwall (e.g., Burchfiel et al., 1992) with a minimum displacementamount of ~35–40 km (Hodges, 2000). The timing of slip on the STDSis well constrained at 21–12Ma by 40Ar–39Ar dating of muscovite fromthe mylonites and by U–Th–Pb dating of accessory minerals fromleucogranites in the STDS footwall (Schärer et al., 1986; Xu, 1990;Noble and Searle, 1995; Edwards and Harrison, 1997; Searle et al.,1997; Hodges et al., 1998; Wu et al., 1998; Murphy and Harrison,1999;Wang et al., 2001; Liu et al., 2004b).

Thermal dome structures, related to the STDS, can be traced for2000 kmalong the central part of the TethyanHimalaya, and constitute adiscontinuous zone of schists and gneisses domes (Fig. 1A). Kangmardome is themost typical of the dome zone; its core consists of deformedaugen orthogneiss with a U–Pb zircon age of 562±4Ma (Schärer et al.,1986), mantled by progressively less metamorphosed Carboniferous–Triassic sedimentary sequences of the Tethyan Himalaya (Burg et al.,1984). Other domes result in outcrop of variably-deformed basementcomplexes, composed of Early Ordovician or Neoproterozoic orthog-neisses and paragneisses (Debon et al., 1986; Gao et al., 1996; Baldwinet al.,1998).Most of the domeswere intrudedbyCenozoic leucogranites(Burg et al., 1984; Debon et al., 1986) with crystallization ages of 17.6–9.5 Ma (Schärer et al., 1986; Harrison et al., 1997). Formation of thesedomes has been attributed to the exhumation bymotion on extensionalstructures (Chen et al., 1990; Lee et al., 2000) that postdates the Tethyanfold–thrust belt. This extensional structuremost likely connectswith thenorthward-extending part of the STDS (Xu et al., 2006).

), medium (10,000–100,000 metric tons Sb) and small (b10,000 metric tons Sb). Anyrite, Au–gold, Ba–barite, Cc–calcite, Chl–chlorite, Ci–cinnabar, Cln–chalcedony, Cp–te, Mi–malachite, Mt–magnetite, Py–pyrite, Q–quartz, Re–realgar, Sp–sphalerite, Srt–arb.–carbonatization, chlo.–chloritization, kaol.–kaolinization, seri.–sericitization, sili.–

Table 1Summary of geology and mineralization of major deposits in Tethyan Himalaya.

No. Depositname

Deposittype

Commodity Tonnage Grade Host rock Host rockage

Orebodymorphology

Mineralassemblage

Alteration References

1 Lulu Q-vein Sb Small 24.2% Sb Shale, siltstone,and sandstone

Early–MiddleJurassic

Vein andlenticularbody

St, Py, Apy, Ci, Q,Srt and Cc

Sili., seri.,carb., andargi.

Tibetan Bureauof Geology andMineral Resources

2 Shalagang Q-vein Sb Middle 31.5% Sb Shale, siltstone,siliceous rock,sandstone andCenozoic diorite

EarlyCretaceous

Vein, bed,lenticularbody andbanded

St, Py, Ci, Re, Apy,Sp, Q, Srt and Cc

Sili., seri.,carb., argi.,and chlo.

Li et al. (2002)Nie et al. (2005)

3 Wuladui Q-vein Sb Middle 2.0% Sb Sandstone, shale,mudstone, limestoneand pyroclastic rocks

LateCretaceous

Vein,lenticularbody andbanded

St, Py, Ci, Re, Apy,Q, Srt and Cc


Nie et al. (2005)

4 Ranba Shearzone

Au Small 1.3 g/tAu

Schist, gneiss, amphiboliteand Cenozoic mylonite,gabbro and diorite

Middle–LateProterozoic

Lenticularbody orbanded

Py, Mt, St, Li, Q, Srtand Chl

Seri., sili.,and chlo.

Nie et al. (2005)

5 Shengna Q-vein Au Small 3.0 g/tAu

Slate, silt–slate, meta-sandstone and Cenozoicdiabase and granite

Early–MiddleTriassic

Lenticularbody andbanded

Py, Li, Au, El, Q, Srtand Cc

Sili., seri.,carb., andchlo.

Nie et al. (2005)

6 Langkazi Q-vein/alteredcataclasite

Au Small 2.0 g/tAu

Slate, phyllite, meta-sandstone and Cenozoicdiorite, gabbro and granite

LateTriassic


Py, Cp, Li, Tt, Ct,Au, El, Q, Chl, Srt,Cc and Zo

Sili., seri.,chlo., andcarb.

Qu et al. (2003)

7 Luren Q-vein Sb Occurrence Shale, siliceous shale andsandstone

LateCretaceous


St, Py, Apy, Q, Srtand Cc


This study

8 Shabao Q-vein Sb Occurrence Slate and meta-sandstone LateTriassic


St, Py, Q, Srt andCc

Sili., seri.,and carb.

Zheng et al.,unpub. data

9 Telie Q-vein Sb Occurrence Slate and meta-sandstone LateTriassic





10 Xiangdala Q-vein Sb Occurrence Slate and meta-sandstone LateTriassic





11 Shama Q-vein/alteredcataclasite

Au Occurrence Slate, phyllite and meta-sandstone

LateTriassic


Py, Li, Au, El, Q, Srtand Cc


This study

12 Xiaba Q-vein Sb Occurrence Shale, siltstone andsandstone


Lenticularbody and vein

St, Py, Ci, Q and Cc Sili., carb.,and argi.

This study

13 Cheqiong–zhuobu

Q-vein Sb Small 4.7% Sb Shale, siltstone, sandstone,marlite and Cenozoicdiabase



St, Py, Apy, Ci, Li,Q and Cc

Sili., carb.,and argi.

Nie et al. (2005)

14 Yongri Q-vein Sb Small 3.6% Sb Shale, sandstone, siltstone,marlite and Cenozoicdiabase, diorite porphyry



St, Py, Apy, Ci, Q,Cc and Cln

Sili., andcarb.

Nie et al. (2005)

15 Rangla Q-vein Sb Small 20.9% Sb Shale, siltstones, marliteand Cenozoic diabase,diorite porphyry



St, Py, Ci, Ba, Qand Cc

Sili., carb.,and argi.

Nie et al. (2005)

16 Zhegu Q-vein Sb–Au Small 43.1% Sb Shale, siltstones, marliteand Cenozoic diorite

LateTriassic

Vein, bed andlenticularbody

St, Py, Apy, Au, El,Q, Srt and Cc

Sili., seri.,chlo., andcarb.

Qu et al. (2003)2.7 g/tAu

Nie et al. (2005)

17 Gudui Q-vein Sb–Au Small 32.5% Sb1.2 g/tAu

Shale, siltstone,sandstone and andesite

EarlyJurassic


Py, St, Au, El, Qand Cc

Sili., carb.,and chlo.

Qu et al. (2003)Nie et al. (2005)

18 Yancang Q-vein Sb–Au Occurrence Shale, siltstone andandesite



Py, St, Au, El, Qand Cc

Sili., carb.,and chlo.

This study

19 Mazhala Q-vein Sb–Au Small 35.0% Sb3.8 g/tAu

Shale, siltstone, andesite,marlite and Cenozoicdiorite porphyry


Band, beddedand lenticularbody

St, Py, Ma, Cp, Ci,Li, Au, El, Q, Cc,Srt, Chl and Ep

Sili., carb.,seri., andchlo.

Nie et al. (2005)

20 Zeri Q-vein Sb Small 22% Sb Siltstone, mudstone,shale and marlite



St,Py, Ma, Au, El,Q, Srt and Cc

Sili., carb.,and kaol.

Nie et al. (2005)

21 Zhaxikang Q-vein Sb–Zn Small 5.6% Sb6.2% Zn1.9% Pb

Black shale, sandstone,limestone and basalt

Middle–LateJurassic


St, Py, Gn, Sp, Apy,Li, Mi, Q, Cc, Srtand Cln

Sili., andcarb.

Nie et al. (2005)

22 Chalapu Q-vein Au Small 3.5 g/tAu

Meta-sandstone,siltstone and slate.

LateTriassic

vein,lenticularbody andbanded

Py, Apy, Au, El, Li,Q, Srt, Cc and Chl

Seri., sili.,and chlo.

Nie et al. (2005)



Discrete leucogranite bodies mainly occur along the STDS, andpartially intrude the thermal domes in the Tethyan Himalaya (Burchfielet al., 1992; Guillot et al., 1993; Hodges et al., 1996). They occur at allscales, ranging from sills and dikes a few cm in width to plutons withdimensions of several hundreds of km (Hodges, 2000). Crosscuttingrelationships indicate that these leucogranites are multiple-stagebodies; discrete bodies can be divided into three groups: muscovite +biotite granites with little or no tourmaline; tourmaline + muscovitegranites; andmuscovite + biotite + tourmaline granites (Hodges et al.,1993; Inger and Harris, 1993; Guillot and Le Fort, 1995). Their traceelement geochemistry supports a genetic model involving fluid-under-saturated (dehydration) melting of Greater Himalayan sequence rocksat high temperatures (≥750 °C) (Harris and Inger, 1992; Harris et al.,1993; Harris and Massey, 1994), due to decompression during theextensional slip of the STDS (Xu et al., 2006). Various geochronologicaldata constrain the duration of leucogranite magmatism at 23–12 Ma(Harrison et al., 1995a,b; Hodges et al., 1996; Edwards and Harrison,1997; Wu et al., 1998; Coleman, 1998; Searle et al., 1999).

2.3. Tectonic evolution of southern Tibet

The tectonic evolution of southern Tibet since the Indo–Asiancollision consists of a three-stage history from the main-collisionalconvergence (65–41 Ma), through late-collisional transform (40–26 Ma) to post-collisional extension (25–0 Ma) (Hou et al., 2006a,b,e;Hou and Cook, 2009-this issue). The main-collisional convergenceresulted in northward subduction of the Indian continental lithospherefollowingmovementof theNeo-Tethyanoceanic-slab beneath theAsiancontinent (Kaneko et al., 2003; Leech et al., 2005), and the formation ofthe Gangdese batholiths in Tibet and the foreland thrust–fold belt inHimalaya (Yin and Harrison, 2000; Hou et al., 2006a,b,e). A low-anglesubduction of the Indian continent beneath Asia during the late-collisional period (Leech et al., 2005; Hou et al., 2006a,e) resulted in thethickening of the crust in southern Tibet (Zhao et al., 1993, 1997), theformation of a south-directed thrust system in the southern Himalaya,and further development of the foreland thrust–fold belt in the TethyanHimalaya. During the post-collisional period, at least three Indian crustwedges were extruded towards the south at the Himalayan topographicfront (Hodges and Hurtado, 1998; Wu et al., 1998), resulting in south-directed thrusting of the Greater Himalaya and north-directed down-slip of the TethyanHimalaya along the STDS (Burchfiel et al.,1992; Chenet al.,1996). Rapid decompression of the footwall due to fast denudationresulted in partial melting of the thickened crust to form leucograniticmagma (Harris and Massey, 1994), which was transported southwardsalong the ductile shear zones of the thrust or detachment systems(Beaumont et al., 2001) to form leucogranite bodies. Denudation of theSTDS, together with compressional diapirism of the leucogranites,caused a prominence of the footwall, resulting in the formation of theTethyan Himalayan thermal dome zone (Fig. 1B) (Xu et al., 2006).

Extensive post-collisional E–W extension in mid-Miocene alsooccurred in southern Tibet (Williams et al., 2001; Hou et al., 2004),and resulted in the formation of numerous N–S-striking normal faultsystems across the Tethyan Himalaya, locally forming rifts, such as theSangri–Cuona andGulu–Yaodong rifts. The timingof these normal faultsin southern Tibet has been constrained at 8–4 Ma (Chen et al., 1996).Controlled by the normal fault systems and zones of rifting, ancient andmodern hydrothermal systems have produced several high-tempera-ture geothermal fields with mantle-derived helium (Hou et al., 2004; Liet al., 2005), such as Kawu and Gudui geothermal fields in the TethyanHimalaya.

3. Antimony and gold mineralization

More than 50 Sb and Au deposits and occurrences with variablecharacteristics have been discovered in the Tethyan Himalaya (Nieet al., 2005). Together, they form a 600 km-long, E–W-striking belt of

Sb–Aumineralization (Fig.1A). Three styles of themineralization havebeen recognized, i.e., Sb-, Sb–Au-, andAu-styles (Yang et al., 2006). Thegeology and characteristics of some of these deposits are summarizedin Table 1. A number of typical deposits are described here.

3.1. Antimony deposits

Antimony deposits occur at a significant distance from the thermaldomes along the STDS in the Tethyan Himalaya (Fig. 1A). This kind ofdeposit is dominated by large quartz–stibnite veins with weakcountry rock alteration, and is controlled by N–S-striking high-anglenormal faults and E–W-striking bedding faults in Mesozoic fine-grained clastic and siliceous rocks (J2–K1). Representative depositsinclude Shalagang and Zhaxikang.

The Shalagang Sb deposit is located in the southwest of the Ranbathermal dome (Fig. 1A), where an E–W-striking anticline occurs as a partof the foreland thrust–fold belt. The core of the anticline, intruded byCenozoic diorite stocks, is composed of fine-clastic rocks, limestone andintercalated intermediate-maficvolcanic rocksbelonging to the lowerpartof Jiapeila Formation (K1); both limbs consist of siliceous rock, sandstoneand limestone of the upper part of same formation (Fig. 2A). Both NW-and NE-striking strike–slip faults cut all Cretaceous stratigraphic units,whereas nearly E–W-striking bedding fault and N–S-striking normal faultcontrol the localization of the Sb orebodies in the district (Fig. 2A).

The Shalagang deposit comprises six ore blocks with an averagegrade of 31.5% Sb. The No.1 ore block is N350 m long, and 1–5 m wide,consisting of four orebodies controlled by an N–S-striking normal fault(Fig. 2A). The orebodies are dominated by quartz–stibnite veins,showing banding and comb structures, typical of open-space filling.Associated alteration, including silicification, carbonatization, chloriti-zation and kaolinization, forms a narrow (1–2mwide) halo envelopingthe orebodies. The No. 9 ore block is 2400 m long, 3–5 m wide, andcontains three main orebodies, which were controlled by nearly E–W-striking bedding fault north-dipped at 20–40° (Fig. 2A). At least threetypes of ores are recognized: quartz–stibnite veinlets; massive stibniteore; and breccia ore. The quartz–stibnite veinlets consist of 1–15 cmwidequartz–stibnite vein swarmsparallel towall-rockbedding.Massivestibnite ore is composed almost entirely of coarse stibnite, whereas thebreccia ore consists of siliceous clasts cemented by hydrothermal quartzand stibnite. The orebodies in No.9 ore block were previously regardedas an early-Cretaceous sedimentary-exhalative product, however,typical open-space filling structure of the quartz–stibnite ores (Fig. 3)suggests that the ores were formed by fluid filling in the fracture spacealong a bedding fault. The ore veinlets of No. 7 ore block cut the dioritestock, indicating that Sb mineralization postdates diorite intrusion.

Oremineral assemblages in Shalagang aremainlycomposedof quartzand stibnite with minor pyrite, arsenopyrite, cinnabar and calcite.Coarse-grained sphalerite occasionally occurs as ore clasts within thequartz–stibnite vein (Fig. 3). According to crosscutting relationship ofveins and mineral relationships, three mineralization stages have beenidentified (fromearly to late): quartz–arsenopyrite stage, quartz–stibnitestage, and calcite stage.

The Zhaxikang Sb–Zn deposit is located at the south of theYelaxiangbo thermal dome (Fig. 1A), where an E–W-striking anticli-noriumwas developed as a part of the foreland thrust–fold belt. The Sb–Zn mineralization occurs at the southern wing of the anticlinorium,composed of shale of theRidang Formation (J1–2), limestoneand shale ofthe Lure Formation (J2), fine sandstone and shale intercalated withbasalt, andesite and tuff of the Zhela Formation (J2–3), and quartzsandstone of the Buweimei Formation (J3), from north to south (Fig. 2Binset). Several modern hot springs occur in and around the mine.

A number of quartz–stibnite veins are hosted in the finesandstone and shale of the Zhela Formation (J2–3), and arecontrolled by N–S-striking normal faults (Fig. 2B). Most veins dipwestwards at 50–70°, except for one that dips east at 80°. The mainorebody (No. 1 orebody) is about 320 m long and 4–5 m wide, and

Fig. 2. Geological maps of the (A) Shalagang, (B) Zhaxikang, (C) Mazhala and (D) Zhegu deposits (modified from Li et al., 2002; Qu et al., 2003). Each deposit is hosted in Mesozoic volcanic–sedimentary sequences, and is controlled by E–W-striking bedding faults (fracture zones), N–S-striking normal faults and their intersections.

199Z.Yang

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Fig. 4. Reflected light photomicrographs showing the mineral assemblages in veins and host rocks in the Mazhala (A–B) and Zhegu (C–D) Sb–Au deposits. (A) Stibnite and gold (Au)filling in the intercrystalline pore between quartz, calcite (cc) and arsenopyrite (apy). (B) Framboidal pyrite in shale host rock. (C) Stibnite filling in the cracks cut the former quartzvein. (D) Pyrite and arsenopyrite disseminated in the host rock of altered diorite.


consists of a Sb-bearing vein system: fine-grained quartz–arseno-pyrite vein with coarse-grained sphalerite clasts near the footwall,light-yellow quartz vein near the hanging wall, and central fine-grained quartz–stibnite–sphalerite veins, all formed by repeatedinfilling during successive mineralization stages. Associated alteration isrelatively weak, consisting of an argillation halo, a few cm in width, andenveloping quartz–calcite veinlets throughout in the district.

The ore at Zhaxikang is mainly composed of quartz, stibnite,sphalerite and arsenopyrite with minor pyrite, chalcopyrite, covellite,calcite and malachite, showing typical structures of open-space filling,such as massive, banded, crustiform, comb, drusy, and cavities, andvarious textures including semi-euhedral, euhedral, enchased, enclosed,and replaced textures (Fig. 3). According to crosscutting relationships ofveins andmineral relationships, threemainmineralization stages can berecognized: quartz–arsenopyrite; quartz–sphalerite–stibnite; and cal-cite–quartz stages (from early to late). The observations that quartz–stibnite veins cut a coarse-grained sphalerite vein, and that coarse-grained sphalerite clasts occur in the quartz–arsenopyrite vein, indicatesthat Zn mineralization preceded Sb mineralization.

3.2. Antimony–gold deposits

The Sb–Au deposits are distributed in the peripheries of the thermaldomes along the STDS in the Tethyan Himalaya (Fig. 1A). This kind of

Fig. 3. Thin-section photomicrographs and outcrop photographs of ores from the Shalagang (A–in the intercrystalline pore between quartz, reflected light. (B) Deformed bands within a stib(D) Semi-euhedral pyrite and arsenopyrite in thehost rockof altered shale, reflected light. (E)Ouof bunchy stibnite coated by quartz, and chalcedony (cln) filling in the drusy cavity of quararsenopyrite, reflected light. (H) Euhedral pyrite within a quartz–calcite–sphalerite vein, reflec

depositmainly occurs as quartz–stibnite veinswithminor disseminatedores, controlled by small-scale E–W- and NW-striking bedding faultsand intra-formational cleavage zones, locally by N–S-striking normalfault. Orebodies aremainly hosted inMesozoicfine-grained clastic rocks(T3–J2) with broad alteration halos. Representative deposits includeMazhala and Zhegu.

The Mazhala Sb–Au deposit is located at the southwest of theYelaxiangbo thermal dome (Fig. 1A), and occurs in the core of a NW-striking anticline, part of the foreland thrust–fold belt (Fig. 2C).The core of the anticline is mainly composed of the Ridang Formation(J1–2), which is surrounded by J2–K1 strata. Due to regional N–Scompression and E–W strike–slip faulting, axial rotation of theanticline took place in a NW–SE-direction. A complex fracture system,resulting from post-collisional crustal extension, was developed in thecore of the anticline, providing significant structural control on theSb–Au mineralization (Fig. 2C).

The Sb–Au mineralization at Mazhala is widely developed within asequence of shale, slate intercalatedwith thin siltstone and andesite (J1–2).Ores are associated with intensive silicification, chloritization, epidotiza-tion, sericitization, carbonatization, argillation and pyritization. However,Sb–Au orebodies appear to only occur sporadically (Fig. 2C), although thisis possibly due to the lowdegree of exploration. Thirty-six small orebodiesare currently known at Mazhala, commonly clustering, with lode,lenticular and strata-like morphology occurring in well-developed

D) and Zhaxikang (E–H) Sb deposits. (A) Stibnitewith arsenopyrite (apy) inclusionsfillingnite grain, reflected light. (C) Sphalerite clasts surrounded by quartz, transmitted light.tcropofquartz–arsenopyrite (qz–apy)vein containing sphalerite (sp)breccias. (F)Outcroptz. (G) Stibnite (st) growing in the intercrystalline pore between quartz, sphalerite andted light.


fracture systems (Fig. 2C). Principal ore types include quartz lodes,veinlets, disseminated, and brecciaed types. The mineral assemblage ismainly quartz + stibnite withminor native gold, arsenopyrite, pyrite andmarcasite. Gangue minerals are calcite, sericite, chlorite and epidote.Native gold occurs mainly as rounded grains in enclaves and inintercrystalline pore zones (Fig. 4).

The Zhegu Sb–Au deposit is located in the west of the Yelaxiangbothermal dome (Fig. 1A), where a series of E–W-striking folds wasdeveloped as a part of the foreland thrust–fold belt. Thedistrict ismostlycovered by Quaternary units; Upper Triassic–Lower Jurassic volcanic–sedimentary strata, consisting of shale, siltstone, thin sandstone,limestone, marl and minor altered andesite, outcrop locally (Fig. 2D).Three fault systems are noted at Zhegu, but only N–S-striking normalfaults and associated breccia zones play an important controlling role onthe localization of the orebodies (Fig. 2D).

The deposit consists of three prospects, Nalu, Youtang and Guoyagou(Fig. 2D). Orebodies occur as veins, veinlets, stringers and lenses hostedwithin T3–J1 clastic sequences. Individual orebodies have various lengthsof 10–70mandwidths of 1–4m, and are usually perpendicular to normalfaults. In the Youtang prospect, three orebodies occur as quartz–stibniteveins and vein swarms along a high-angle zigzag normal fault (Fig. 2D).Two types of ores can be recognized: quartz–stibnite vein and

Fig. 5. Simplified geological map of the Langkazi gold deposit showing

disseminated types. The former ismainly composed of quartz and stibnitewith minor arsenopyrite, native gold, sericite, and calcite (Fig. 4); thelatter mainly consists of quartz, stibnite and sericite with minorarsenopyrite, pyrite, native gold, chlorite and calcite (Fig. 4). Native goldoccurs as rounded grains, 10–30 µm in diameter, within host stibnite andintercrystalline pores.

3.3. Gold deposits

Several gold deposits and occurrences are distributed in theinterior of the thermal domes and surrounding area along the STDS(Fig. 1A). This type of deposit occurs mainly as disseminated bodieswith minor vein-fillings, and is controlled by tensional ductile shearzones, brittle–ductile detachment faults and brittle normal faults (e.g.,Fig. 5). Host rocks are the Pre-Ordovician metamorphic rocks in thecore of the thermal domes; late-Paleozoic epimetamorphic rocksbounded by the detachment faults, and weakly metamorphosedTriassic rocks adjacent to the thermal domes. Associated alterationformed wide alteration haloes enveloping the orebodies. Representa-tive deposits include Langkazi and Chalapu.

The Langkazi Au deposit is located in the eastern part of the Ranbathermal dome (Fig. 1A). Host rocks are mainly quartz–sericite schist,

mineralization controlled by detachment fault and normal faults.


slate, phyllitic slate and meta-sandstone of the Nieru Formation (T3),which is in fault contact with the non-metamorphosed RidangFormation (J1–2) (Fig. 5). As a result of doming, a set of NNW-strikingdetachment faults and NNE- to NE-striking high-angle normal faultswere developed. They crosscut the E–W-striking main-collisionalfolds (Fig. 5). Except for the dome-intruded mid-Miocene granitebody, Cenozoic diorite, gabbro, minette and mafic dykes also occur inthe district.

Gold mineralization at Langkazi is controlled by detachment faultsand high-angle normal faults. Orebodies occur as Au-bearing quartzveins and disseminated lenses in low-grade metamorphic rocks of theNieru Formation (T3), and to a minor extent in Cenozoic magmaticrocks. Although the host rocks were intensively silicified andchloritized, forming a wide alteration halo, only a number of smallorebodies have been discovered, again perhaps due to the low degreeof exploration. Most individual orebodies are 50–170 m long and 0.8–2.7m thick, NE-striking and dipping to NW. Ore types are quartz veins,altered slate, altered dyke, structural breccias and oxidized hematiteores. Ore minerals are pyrite, chalcopyrite, tennantite, cassiterite,native gold, goethite, and lepidocrocite; Gangue minerals are quartz,calcite, siderite, muscovite, zoisite and chlorite.

Fig. 6. Photomicrographs showing the fluid inclusions in quartz. (A) Rounded type I fluid inclliquid ratio of 25%, Zhaxikang. (C) Elongated type II fluid inclusion with CO2 gas and liquid cliquid ratio of 15%, Zhegu. All scale bars are 20 µm.

4. Fluid inclusion data

Fluid inclusions in quartz in quartz–stibnite veins from four deposits(the Shalagang Sb deposit, Zhaxikang Sb–Zn deposit, Mazhala Sb–Audeposit, and Zhegu Sb–Au deposit) were investigated in this study.Microthermometric measurements were performed on doubly-polishedsections using a Linkam heating–freezing stage, with a measuredtemperature range from −198 °C to 600 °C. Accuracy of the measure-ments was ensured by calibrating with the triple point of CO2 (−56.6 °C)and the freezing point (0.0 °C) of pure H2O. The precision of thetemperature measurement is reproducible within 0.2 °C for freezing and2 °C for heating.

4.1. Fluid inclusion petrography

Due to the lower deformation andmetamorphism of these Cenozoicdeposits,mostfluid inclusions showprimary characteristics on the basisof the criteria given by Roedder (1984), and thus have been studied indetail. These fluid inclusions can be divided into twomajor types, basedon the phases at room temperature and paragenetic and textural studiesof the primary fluid inclusions from these deposits.

usionwith gas/liquid ratio of 20%, Shalagang. (B) Elliptoid type I fluid inclusionwith gas/ontent of 80%, Mazhala. (D) Type I fluid inclusions with negative crystal form and gas/

Table 2Microthermometry data of type I fluid inclusions in quartz from Sb and Au deposits inthe Tethyan Himalaya, southern Tibet.

Sample Th (°C) Ti (°C) Salinity Data source

(wt.% NaCl equiv.)

Shalagang Sb depositSLGE-4 148–250 −2.0–−2.4 3.39–3.71 This studySLG-3 181–293 −2.0–−3.4 3.39–5.56 This studySLG-3-1 135–288 −2.1–−4.4 3.55–7.02 This studySLG-3-2 139–280 −2.8–−4.2 4.65–6.74 This studySLG-6 186–367 −0.3–−3.2 0.53–5.26 This studySLG-17 212–297 −2.2–−3.6 3.71–5.86 This studySLG-19 135–352 −0.8–−1.8 1.40–3.06 This studyLS-01 235–246 −2.8–−3.1 4.80–5.26 Qu et al. (2003)LS-06 141–269 −3.0–−8.9 5.11–12.58 Qu et al. (2003)

Zhaxikang Sb–Zn depositZXK-2 167–217 −0.6–−2.0 1.05–3.39 This studyZXK04-1 162–242 −0.8–−1.8 1.40–3.06 This studyZXK04-2 198–268 −0.4–−1.8 0.71–3.06 This studyZXK04-3 178–260 −0.7–−1.2 1.23–2.07 This study

Mazhala Sb–Au depositMZL-1 193–226 −1.7–−2.9 2.90–4.80 This studyMZL-8 185–256 −2.1–−3.4 3.55–5.56 This study

Zhegu Sb–Au depositZG-3 165–223 −1.4–−2.6 2.41–4.34 This studyZG-4 170–217 −2.4–−3.8 4.03–6.16 This studyZC-09 146–236 −0.5–−2.0 1.05–3.55 Qu et al. (2003)ZC-18 228–267 −2.2–−3.6 3.87–6.01 Qu et al. (2003)ZC-20 176–259 Qu et al. (2003)ZC-21 255–306 −1.6–−2.2 2.90–3.87 Qu et al. (2003)ZC-23 165–242 −3.7–−3.9 6.16–6.45 Qu et al. (2003)

Th–homogenization temperature, Ti–ice melting temperature.


Type I (liquid–vapor two-phase) inclusions are dominated by H2O(Fig. 6A, B and D) and are the most abundant type at Shalagang,Zhaxikang and Zhegu, and the second abundant type at Mazhala. Theytypically occur as scattered or isolated inclusions, and are alignedalong growth zones of quartz, and invariably homogenized to theliquid phase. Type I inclusions in quartz from most of the studieddeposits have regular forms including smooth grain, pillar andpolygon, and sometimes may show negative crystal forms (Fig. 6),

Table 3Microthermometry data of type II fluid inclusions in quartz from Mazhala Sb–Au deposit.

Sample Size Gas/liquid ratio Tf Tc TCO2

(μm) (%) (°C) (°C) (°C)

MZL-1 7×13 CO2–65 −59.2 10.6 26.37×11 CO2–40 −59.0 10.4 29.65×14 CO2–55 −59.0 10.5 27.86×11 CO2–80 −59.0 9.9 25.18×15 CO2–85 −59.0 9.9 30.14×6 CO2–85 −59.0 10.2 28.35×8 CO2–95 −59.1 5.6 25.85×11 CO2–45 −59.9 9.9 27.15×13 CO2–50 −59.9 9.9 29.2

MZL-8 15×51 CO2–20 −59.3 10.7 29.425×40 CO2–65 −59.5 10.5 27.714×18 CO2–50 −59.3 10.3 26.75×18 CO2–65 −59.3 10.2 27.318×19 CO2–15 −59.3 10.4 29.410×19 CO2–60 −59.5 10.2 26.612×16 CO2–50 −59.4 10.1 24.69×14 CO2–65 −59.1 10.3 24.4

12×13 CO2–60 −59.1 10.3 26.316×7 CO2–20 −59.1 10.811×28 CO2–50 −59.1 10.3 29.6

Tf–first melting temperature, Tc–CO2 clathration melting temperature, TCO2–CO2 homogenizaVCO2–homogenization to CO2 vapor, L–homogenization to liquid, V–homogenization to vapo

except at Shalagang and Zhaxikang where irregular forms dominateamong type I inclusions. Their size ranges from 3 to 30 µm; vapor/liquid ratio varies from 5 to 35%.

Type II (CO2–liquid) inclusions have three phases, i.e., H2O, gas,and liquid CO2 (Fig. 6C), and the total CO2 content varies from 20 to80%. Type II inclusions vary from 5 to 40 µm in size and usually haveregular forms, although they may also show negative forms. Theseinclusions are the most abundant type at Mazhala. They mainly occurin quartz associated with Au-containing quartz–stibnite veins. CO2

liquid phase in the type II inclusions is mainly homogenized to the gasphase, and some to the liquid phase.

4.2. Microthermometric results

Homogenization temperatures (Th) of fluid inclusions in the fourstudied deposits are summarized in Tables 2 and 3. In the Shalagangdeposit, fluid inclusions in quartz homogenized from135 to 367 °C,withan average Th of 227 °C, while those in the Zhaxikang deposit yielded aTh range from 162 to 268 °C, averaging 209 °C. In Th-frequency diagram(Fig. 7), the distributions of Th for fluid inclusions from the Shalagangand Zhaxikang deposits show a main-peak at 200 °C and 210 °C,respectively. The Th of fluid inclusions in quartz from the Mazhaladeposit range from 185 to 304 °Cwith an average of 249 °C, whereas theTh of inclusions from Zhegu range from 146 to 306 °C, and averaged199 °C. The distribution of Th for inclusions from Mazhala shows threedistinct peaks at 210 °C, 250 °C and 290 °C (Fig. 7), corresponding tothoseof type I inclusions, type II inclusionshomogenized to liquidphase,and type II inclusions homogenized to gas phase, respectively.

Salinity of fluid inclusions was calculated from the final meltingtemperature of ice crystals using the equation of Bodnar (1993). Forfluid inclusions with CO2 clathration, salinity was calculated using theequation of Bozzo et al. (1973). Salinities of fluid inclusions have arelatively narrow range (0.2–12.6 wt.% NaCl equiv.) for all fourdeposits (Tables 2, 3; Fig. 8). It is obvious that these data suggest low-salinity fluids in the mineralization system.

Volatile components of fluid inclusions were analyzed by LaserRaman probe on a number of fluid inclusions from the Shalagang andZhegu deposits to determine the composition of volatile phases. LaserRaman spectroscopic analysis demonstrates the presence of CO2 and N2

gas, but H2O is themost abundant volatile component in the inclusions.At Shalagang, both gas and liquid phases are mainly composed of H2O,

Th Density Salinity

Phase (°C) Phase (g/cm3) (wt.% NaCl equiv.)

LCO2 299 V 0.683LCO2 302 Critical 0.612LCO2 300 V 0.657LCO2 266 V 0.702 0.2LCO2 302 V 0.590 0.2LCO2 0.647LCO2 250 L 0.691 8.13LCO2 304 V 0.67 0.2LCO2 302 0.624 0.2VCO2 250 L 0.316LCO2 0.278LCO2 290 Critical 0.676LCO2 291 Critical 0.666VCO2 251 L 0.316LCO2 292 V 0.678LCO2 291 Critical 0.709LCO2 288 V 0.711LCO2 290 V 0.683

249 LLCO2 299 V 0.612

tion temperature, Th–homogenization temperature, LCO2–homogenization to CO2 liquid,r.

Fig. 7. Histogram of homogenization temperature of fluid inclusions in the gangue quartz. (A) Shalagang. (B) Zhaxikang. (C) Mazhala. (D) Zhegu.

Fig. 8. Diagrams of homogenization temperature (Th) vs. salinity showing (A) salinityunchanged with Th decrease in the Shalagang and Zhaxikang Sb deposits, and(B) salinity increase with Th decrease in the Mazhala and Zhegu Sb–Au deposits.


with a small amount of CO2 in some inclusions. At Zhegu, both gas andliquid phases of inclusions consists of H2O and CO2; N2 is detected in thegas phase of some inclusions. Results indicate that the fluid inclusionsfrom Zhegu contain more CO2 than those from Shalagang.

Type II inclusions in the Mazhala deposit have a first meltingtemperature range from −59.0 to −59.9 °C (Table 3), i.e., lower thanthe triple point temperature of pure CO2 (−56.6 °C), indicating thatthey also contain other gases, such as H2S and CH4 besides CO2. Thetemperature range of CO2 homogenization (24.4–30.1 °C) (Table 3) isalso lower than the critical temperature of pure CO2 (31 °C), indicatingthe presence of some H2S and CH4.

5. Isotope data

Samples analyzed for oxygen, hydrogen and sulfur isotopes werecollected from quartz–stibnite veins, their host rocks and altereddiorite stocks in five deposits (Shalagang, Zhaxikang, Mazhala, Zheguand Langkazi). Bulk-rock samples were prepared by pulverizing handsamples; mineral separates were obtained by handpicking and heavyliquid floating. Analysis was performed in the Institute of MineralResources, CAGS (Beijing), using conventional methods. The precisionof the analysis is reproducible within 0.2, 3 and 0.2‰ for oxygen,hydrogen and sulfur isotopes, respectively.

5.1. Oxygen and hydrogen isotopes

Table 4 summarizes the range of oxygen and hydrogen isotopicvalues in quartz from the five deposits. At Shalagang, four samples ofquartz separated from the quartz–stibnite veins yielded a limited rangeof high δ18O values (21.3–21.7‰), and a narrow range of low δD values(−151 to −166‰), similar to the δD values of modern geothermalwater in southern Tibet (−140‰NδDN−165‰; Zheng et al., 1982).According to the oxygen isotopic exchange equation (Zhang, 1985) andfluid inclusion Th in quartz (203–257 °C), the hydrothermal fluids thatprecipitated quartz in the quartz–stibnite veins would have δ18OH2O

Table 4Hydrogen and oxygen isotope data of quartz from Sb and Au deposits in the TethyanHimalaya, southern Tibet.

Sample Petrography Mineral δ18OV-SMOW δDV-SMOW Th(°C)

δ18OH2Oa

(‰) (‰) (‰)

Shalagang Sb depositSLGE-4 Q–St vein Quartz 21.7 −151 203 9.5SLG-6 Q–St vein Quartz 21.3 −158 208 9.4SLG-17 Q–St vein Quartz 21.6 −166 257 12.3SLG-19 Q–St–Apy vein Quartz 21.5 −160 236 11.2

Zhaxikang Sb–Zn depositZXK-1 Q–St–Sp vein Quartz 5.8 200 −6.6ZXK-2 Q–St vein Quartz 1.3 −140 194 −11.5ZXK-3 Q–St–Sp vein Quartz 12.2 −152 201 −0.2ZXK-5 Q–St–Sp vein Quartz 12.6 200 0.2ZXK-7 Q–St vein Quartz 9.8 −160 200 −2.6ZXK04-1 Q–St vein Quartz 2.1 −152 200 −10.3ZXK04-2 Q–St vein Quartz 2.6 −144 200 −9.8ZXK04-3 Q-vein Quartz 4.0 −154 200 −8.4ZXK06-23 Q–Py vein Quartz 11.9 200 −0.5

Mazhala Sb–Au depositMZL-1 Q–St vein Quartz 19.3 −106 200 6.9MZL-2 Q–St vein Quartz 19.5 −108 253 10.0MZL-2-1 Q–St vein Quartz 17.9 −104 253 8.4MZL-4 Q–St vein Quartz 21.0 −98 247 11.2MZL-4-1 Q–St vein Quartz 21.3 −115 247 11.5MZL-8 Q–St vein Quartz 20.6 −119 200 8.2

Zhegu Sb–Au depositZG-3 Q–St vein Quartz 23.1 −75 193 10.2ZG-3-1 Q–St vein Quartz 23.4 193 10.5ZG-4 Q–St vein Quartz 17.6 −73 203 5.4ZG-4-1 Q–St vein Quartz 23.9 −76 200 11.5ZG-6 Q–St vein Quartz 22.8 −72 200 10.4ZG-8 Q–St vein Quartz 19.3 200 6.9ZG-9 Q–St vein Quartz 21.1 200 8.7

Langkazi Au depositD1-9b Q-vein Quartz 16.5 −67 177 2.4D2-9b Q-vein Quartz 15.3 −52 185 1.8D3-3b Q-vein Quartz 16.0 −58 178 2.0DIV-4b Q-vein Quartz 14.4 −59 199 1.9H1-3b Q-vein Quartz 14.3 −58 211 2.5H1-12b Q-vein Quartz 17.1 −59 220 5.9Y2-1b Q-vein Quartz 15.7 −83 238 5.5TC58b Q-vein Quartz 15.7 −80 301 8.2TC204b Q-vein Quartz 17.4 −60 200 5.0

Th–homogenization temperature, Apy–arsenopyrite, Py–pyrite, Q–quartz, Sp–sphalerite,St–stibnite.

a Calculate using the isotopic exchange equation (Zhang, 1985): δ18Oquartz–δ18OH2O=3.42×106 T−2−2.86.

b Zheng (1999).

Fig. 9. Oxygen and hydrogen isotopic compositions of the ore-forming fluids in the fivedeposits in southern Tibet. The Shalagang and Zhaxikang Sb deposits show geochemicalaffinity with the geothermal water in Tibet, whereas the Langkazi Au deposit shows alarge contribution of magmatic water to the ore-forming fluids. The Mazhala and ZheguSb–Au deposits were resulted from a mixed geothermal fluid with magmatic water.


values from9.4 to 12.3‰ (Table 4). Nine quartz samples fromZhaxikanggave a wide range of δ18O values, varying from 1.3 to 12.6‰, and of δDvaluesbetween−140and−160‰, close to current geothermalwater insouthern Tibet (Zheng et al., 1982). Calculated δ18OH2O values vary from−11.5 to 0.2‰ (Table 4). These data suggest involvement of geothermalwater in formation of the Shalagang-style Sb deposits (Fig. 9).

In the Mazhala Sb–Au deposit, high δ18O values (17.9–21.3‰) andrelatively low δD values (−98 to −119‰) are determined for sixquartz samples (Table 4). Calculated δ18OH2O values are 8.2–11.5‰.Similar O and H isotopic signatures, with high δ18O values rangingfrom 17.6 to 23.9‰ and δD values varying from −72 to −76‰, areobtained from the Zhegu samples (Table 4). Calculated δ18OH2O valuesare between 5.4 and 11.5‰ (Table 4). These data suggest a mixed fluidsource for the Mazhala-style Sb–Au deposits (Fig. 9), involving bothmeteoric and magmatic waters.

Gangue quartz from the Langkazi Au deposit yielded a limitedrange of δ18O values (14.3–17.4‰), and a narrow range of δD values

(−52 to−83‰) (Table 4). Calculated δ18OH2O values range from1.8 to8.2‰, suggesting a fluid dominated by magmatic water (Fig. 9).

5.2. Sulfur isotopes

Sulfur isotopic compositions of stibnite, sphalerite, pyrite,arsenopyrite and galena separated from quartz–stibnite veins,coarse sphalerite veins and host rocks, as well as previously reporteddata for studied deposits in southern Tibet are compiled in Table 5.Two stibnite and nine fine-grained sphalerite and pyrite samplesseparated from quartz–stibnite–sphalerite veins in the Zhaxikangdeposit, yielded δ34S values ranging from 4.5 to 7.1‰, and 8.7 to10.6‰, respectively (Table 5). Six coarse-grained sphalerite, pyriteand galena samples separated from the coarse sphalerite vein andfrom sulfide clasts in the quartz–arsenopyrite–stibnite veins yieldeda range of higher δ34S values (9.9–12.0‰), comparable with nodularpyrite in the Cretaceous strata (δ34S=9.9‰, Li, 2000), suggestingthat the strata may be a potential sulfur source. δ34S values of fine-grained sphalerite in the quartz–stibnite–sphalerite veins aresimilar to the coarse-grained sphalerite in the coarse sphaleriteveins, implying that sulfur in the Sb mineralization may have beenmobilized from preexisting sphalerite in the Cretaceous strata.

Stibnite, pyrite and arsenopyrite from the other four depositsyielded narrow δ34S ranges between−4.3 and 2.1‰ (Table 5), similarto those of sulfides from skarn- and porphyry-type deposits in thecentral Gangdese range (skarn-type: −3.9 to−0.1‰, porphyry-type:−1.7 to 2.1‰; She et al., 2005). Like Zhaxikang, a coarse sphalerite clastin the quartz–stibnite vein from Shalagang yielded a heavy δ34S valueof 10.3‰ (Table 5).

5.3. Rb–Sr isotope data

Rb–Sr isotopes of fluid inclusions in quartz and stibnite from thequartz–stibnite veins in the Shalagang Sb deposit were investigatedusing the laser ablation inductively coupled plasma–mass spectrometry(LA–ICP–MS) in the Institute of Geology and Geophysics, CAS (Beijing).The analysis yielded 87Sr/86Sr ratios varying between 0.708951 and0.718457, and 87Rb/86Sr ratios varying between 0.010441 and 0.331820(Table 6). These fluid inclusions have much lower 87Sr/86Sr ratios thanthose of the S-type granites at Kangmar (0.7725–1.0098) and Gaowu(0.7567 to 0.7704) in southern Tibet (Wang et al., 1981), but distinctlyhigher than the mid-Miocene Gangdese adakitic rocks (0.70435–0.707920; Hou et al., 2004; Qu et al., 2004). The 87Sr/86Sr ratios are

Table 6Rubidium and strontium isotope data of fluid inclusions in quartz and stibnite from theShalagang Sb deposit.

Sample Mineral Rb (µg/g) Sr (µg/g) 87Rb/86Sr 87Sr/86Sr

SLG-4 Quartz 1.9 55.9 0.098832 0.710804SLG-6 Quartz 2.0 52.9 0.110621 0.710267SLG-19 Quartz 3.8 33.5 0.331820 0.718457SLGE-1 Stibnite 3.6 472.5 0.021817 0.710418SLG-1 Stibnite 3.1 359.8 0.025070 0.708951SLG-3 Stibnite 2.5 684.5 0.010441 0.714681SLG-16 Stibnite 7.1 1322.4 0.015540 0.709049

Table 5Sulfur isotope data of sulfides from Sb and Au deposits in the Tethyan Himalaya, southern Tibet.

Sample Petrography Analyzed mineral δ34SV-CDT (‰) Reference

Shalagang Sb depositSLGE-4 Quartz–stibnite vein with sphalerite breccia Stibnite −3.7 This studySLGE-4 Quartz–stibnite vein with sphalerite breccia Sphalerite 10.3 This studySLG-3 Quartz–stibnite vein Stibnite −3.0 This studySLG-6 Quartz–stibnite vein Stibnite −3.9 This studySLG-7 Stibnite vein Stibnite −3.6 This studySLG-9 Slate (K1) Pyrite −2.7 This studySLG-17 Quartz–stibnite vein Stibnite −3.6 This studyS-1 Quartz–stibnite vein Stibnite 2.1 Qu et al. (2003)S-2 Quartz–stibnite vein Stibnite 0.3 Qu et al. (2003)S-9 Quartz–stibnite vein Stibnite −0.1 Qu et al. (2003)S-11 Quartz–stibnite vein Stibnite −1.6 Qu et al. (2003)S-12 Quartz–stibnite vein Stibnite −1.4 Qu et al. (2003)S-13 Quartz–stibnite vein Stibnite −1.7 Qu et al. (2003)S-14 Quartz–stibnite vein Stibnite −1.4 Qu et al. (2003)S-16 Quartz–stibnite vein Stibnite −0.9 Qu et al. (2003)I-3a Quartz–stibnite vein Stibnite −0.3 Li (2000)G9-3 Quartz–stibnite vein Stibnite −1.6 Li (2000)G9-3a Quartz–stibnite vein Stibnite −0.9 Li (2000)VIII-9 Quartz–stibnite vein Stibnite −1.8 Li (2000)I-1b Stibnite vein Stibnite −0.5 Li (2000)G9-3b Stibnite vein Stibnite −1.5 Li (2000)Strata Slate (K1) Pyrite 9.9 Li (2000)

Zhaxikang Sb–Zn depositZXK04-2 Quartz–stibnite vein Stibnite 4.5 This studyZXK-3 Quartz–stibnite–sphalerite vein Stibnite 7.1 This studyZXK-5 Quartz–stibnite–sphalerite vein Sphalerite 9.1 This studyZXK-6 Quartz–arsenopyrite vein with sphalerite breccia Sphalerite 11.1 This studyZXK06-15 Quartz–pyrite vein Pyrite 8.9 This studyZXK06-23 Quartz–pyrite vein Pyrite 8.7 This studyZXK06-21 Pyrite vein Pyrite 10.6 This studyZXK06-25 Coarse sphalerite vein (early) Sphalerite 12.0 This studyZXK06-26 Coarse sphalerite vein (early) Sphalerite 11.4 This studyZXK06-26 Coarse sphalerite vein (early) Pyrite 11.2 This studyZXK1-1 Quartz–stibnite–sphalerite vein Sphalerite 10.2 This studyZXK1-3 Quartz–stibnite–sphalerite vein Sphalerite 10.6 This studyZXK1-4 Quartz–stibnite–sphalerite vein Sphalerite 10.4 This studyZXK1-5 Quartz–stibnite–sphalerite vein Sphalerite 10.4 This studyZXK1-9 Quartz–stibnite–sphalerite vein Sphalerite 9.7 This studyZXK2-3 Coarse sphalerite vein (early) Sphalerite 11.2 This studyZXK2-3 Coarse sphalerite vein (early) Galena 9.9 This study

Mazhala Sb–Au depositMZL-1 Quartz–stibnite vein Stibnite 0.1 This studyMZL-2 Quartz–stibnite vein Stibnite −0.3 This studyMZL-4 Quartz–stibnite vein Stibnite 0.1 This studyMZL-6 Quartz–stibnite vein Stibnite −0.2 This studyMZL-8 Quartz–stibnite vein Stibnite −0.8 This study

Zhegu Sb–Au depositZG-3 Quartz–stibnite vein Stibnite −4.3 This studyZG-3-1 Quartz–stibnite vein Stibnite −3.7 This studyZG-4-1 Quartz–stibnite vein Stibnite −3.6 This studyZG-6 Quartz–stibnite vein Stibnite −3.8 This studyZG-9 Altered diorite Stibnite −4.0 This studyZG-10 Altered diorite Pyrite 0.3 This studyZG-10 Altered diorite Araenopyrite −1.2 This study


similar to those of volcanic and black shales (0.7095–0.7176; Yin andWang, 1998), but slight higher than that of carbonate rocks (0.707443–0.707960; Huang et al., 2004) in southern Tibet.

6. Discussion

6.1. Timing of Sb–Au mineralization

The age of the Sb–Aumineralization in southern Tibet has not beenpreviously determined due to the lack of suitable minerals for dating.The timing of the mineralization can, however, be constrained by


regional and district geological data, especially the tectonics andstructures that control orebodies in the Tethyan Himalaya. At leastthree kinds of faults have been recognized as controlling the spatial–temporal localization of the Sb, Sb–Au and Au deposits. The first is anE–W-striking, low-angle normal fault system, developed along themargin of the thermal dome. It connects southwards with the STDS,appearing to sole into a common N-dipping detachment (cf. Hou andCook, 2009-this issue). The STDS regionally controls the regionaldistribution of the Sb and Sb–Au deposits (Fig. 1), whereas detach-ment faults along the dome control the localization of the Au depositson a local scale (Figs. 1 and 5). The 21–12 Ma age for the formation ofthe STDS (Yin and Harrison, 2000) constrains the Sb, Sb–Au and Aumineralization to the mid-Miocene. The second set of controllingfaults belongs to the N–S-striking normal fault system across theHimalayan–Tibetan orogen (Fig. 1). The intersection sites of thesefaults with the E–W-striking detachment faults control localization ofthese deposits (Figs. 2 and 5). The normal faults, which cut the STDS,are dated at 8–4Ma in the Himalayas (Chen et al., 1996), but formed atN13.5 Ma elsewhere in Tibet (Blisniuk et al., 2001). This implies thatthe minimum age of the mineralization is about 8–4 Ma. The thirdstructural control is represented by the intra-layer fracture zones thatmainly occur in the sedimentary sequences on the limbs of folds,including bedding faults and intra-formational cleavages. These zonesunderwent early-stage compression and late-stage extension in thepost-collisional period, resulting in numerous open-spaces for sulfideprecipitation. Moreover, spatial–temporal relationships and cleargenetic links between these deposits and the granite-intrudedthermal domes also suggest the Sb, Sb–Au, and Au mineralizationtook place in or postdated the period of leucogranite emplacement(17.6–9.5 Ma; Schärer et al., 1986; Harrison et al., 1997).

6.2. Post-collisional epithermal Sb–Au ore-forming systems

The regional distribution of the Sb and Au deposits in southernTibet around the thermal domes and along the STDS suggests that themineralization is related to mid-Miocene extensional structures andassociated magmatism, and occurs in a post-collisional crust exten-sional setting (Hou and Cook, 2009-this issue). Spatially, the Audeposits are always distributed in the interior of the thermal domes,the Sb–Au deposits mostly occur at the peripheries of the domes, andthe Sb deposits are almost always found far away from the domes (Fig.1A). This reflects a metallogenetic zonation from Au, Sb–Au to Sbmineralization from the dome outwards. A vertical zonation is alsonoted, with the Au deposits dominantly hosted in Triassic or olderstrata, the Sb–Au deposits in Upper Triassic to Middle Jurassic strata,and the Sb deposits restricted to Middle Jurassic to Lower Cretaceousstrata. Together, these distinct deposits constitute a post-collisionalSb–Au ore-forming system, controlled by the thermal domes andextensional structures in the Tethyan Himalaya.

Post-collisional Sb–Au ore-forming systems in southern Tibet arecharacterized by low-temperature, low-salinity ore-forming fluids,and shallow structural levels and extensional setting for ore genera-tion. The absence of any daughter-minerals in the observed fluidinclusions in gangue quartz rules out the possibility that orthomag-matic fluids were involved in mineralization. Available microthermo-metric data indicate that the ore-forming fluids for all these depositsacross the region were characterized by low temperatures (135–367 °C) and low salinities (0.2–12.6 wt.% NaCl equiv.) (Fig. 8). The ore-forming fluids are generally similar to the geothermal water insouthern Tibet, but may have also involved some input of magmaticwater resulting from magma chamber degassing, as suggested by theoxygen-hydrogen isotopic data (Fig. 9).

For the Shalagang-style Sb deposits, the range of lower δD values(−140 to −160‰) in fluid inclusions and calculated δ18OH2O values(−11.5 to 0.2‰) at Zhaxikang is veryclose to active geothermalwaters insouthern Tibet (−140‰NδDN−165‰; Zheng et al., 1982), suggesting a

geothermal fluid dominated by meteoric water. The Shalagang Sbdeposit alsoyielded similar δDvalues (−151 to−166‰) forore-formingfluid, but has a rather high calculated δ18OH2O value (9.4–12.3‰). Suchhigh δ18OH2O values may be explained in two possible ways. Oneexplanation is input of metamorphic fluid derived from the thermaldome into the ore-forming fluid system; another is a very low water/rock ratio, resulting in δ18OH2O of the fluid being close to that of thealtered rocks. For the Mazhala-style Sb–Au deposits, calculated δ18OH2O

(6.9–11.5‰) and measured δD values (−98 to −119‰) at Mazhalasuggest a mixed fluid containing both meteoric and magmatic water(Fig. 9). The Zhegu Sb–Au deposit yielded relatively high δD values (Fig.9), suggesting a greater input of magmatic water. The appearance ofCO2-rich fluid inclusions with abundant N2 in both deposits alsosuggests a contribution of magmatic water. However, the low-salinity(0.2–8.1 wt.% NaCl equiv.) and low-Th of fluid inclusions in bothdeposits indicate that this magmatic fluid contribution is generallysmall. For the Langkazi-style Au deposits, they yielded relatively high δDvalues (−52 to −83‰) and δ18OH2O values (1.8–8.2‰) (Fig. 9),resembling typical magmatic water, suggesting that ore-forming fluidswere dominated bymagmatic water with onlyminormeteoric water. Insummary, the spatial distribution of the deposits and the correspondingvariation in compositions of the ore-forming fluids infer a dome-centered geothermal system driven by the mid-Miocene granite body,inwhich the contribution of magmatic water from degassing of magmachamber to ore-forming fluid system gradually decreased from thethermal dome outwards and from the deep hydrothermal systemupwards. This is mirrored in the zonation of mineralization from Au,Sb–Au to Sb.

In the dome-centered geothermal system, the sulfur in the ore-forming fluids near the centre was mainly derived from the magmaticsystem, as suggested by the close-to-0‰ sulfur isotopic compositions ofstibnite and associated sulfides in the Au and some Sb–Au deposits(Table 5). In contrast, the ore-forming fluids far away from the centreprobably obtained sulfur from the Mesozoic strata that the fluids passedthrough.Keyevidence to support thismodel comes fromtheZhaxikangSbdeposit, inwhich stibnite andassociated sulfides (sphalerite andpyrite) inores have δ34S values (4.5–10.6‰), similar to the nodular pyrite (9.9‰) orclose to the coarse-grained sphalerite (9.9–12.0‰) in Cretaceous strata(Table 5). Moreover, the scavenging role of the convective fluids throughMesozoic permeable strata is also extremely significant for concentrationof Sb and minor Au (Hou and Cook, 2009-this issue). This suggestion issupported by the Rb–Sr isotopic data of fluid inclusions in these deposits.For example, fluid inclusions in quartz and stibnite from the Shalagang Sbdeposit yielded very high 87Sr/86Sr ratios (0.708951–0.718457), indicatingthat the 87Sr-rich ore-forming fluid contains large amounts of radiogenicSr. However, these 87Sr/86Sr ratios are much lower than those of thedome-intruded leucogranites (N0.7567), ruling out the possibility of thegranitic melts as source. In contrast, these 87Sr/86Sr values are similar tothose of the Mesozoic volcanic–sedimentary sequences in southern Tibet(0.707443–0.7176; Yin and Wang, 1998; Huang et al., 2004), suggestingthat the convective hydrothermal fluids obtain a large amount of metallicelements (Sb, Sr) from the Tethyan volcanic–sedimentary formation bywater/rock interaction.

6.3. A possible tectonic model for Au–Sb mineralization

The Sb and Au deposits are regionally distributed along the E–W-striking thermal dome zone, related to the STDS, and are locallydistributed around the thermal domes intruded by mid-Miocenegranites, or are clustered at the intersections between N–S-strikingnormal faults and E–W-striking detachment faults. These observationsindicate that the Sb–Au mineralization has a close relationship to themid-Miocene extensional structures and crustal-derived graniticmagma systems formed in a post-collisional crustal extension setting.They are therefore a product of post-collisional tectono-magmaticevolution of the Tethyan Himalaya.


Based onprevious geological and geophysical data on theHimalayanorogen, combined with analysis of tectono-magmatic activity in south-ern Tibet, a three-stage tectonic model for metallogenesis of post-collisional Sb–Au deposits in the Tethyan Himalaya can be proposed.Three significant geological processes resulting in regional Sb–Aumineralization are emphasized here.

(1) Formation of the foreland thrust–fold belt and associated bed-ding faults (40–26Ma): Indo–Asian continental impact along theIYS and subsequent subduction of the Indian continent beneaththe Asian continent resulted in the formation of the Gangdesesyn-collisional magmatic belt in Tibet at 65–41 Ma and theforeland thrust–fold belt in the TethyanHimalaya (Hou and Cook,2009-this issue). The thrust–fold belt consists of fold andimbricated thrusts involving the Mesozoic passive continentalmargin sequence, and has an estimated amount of shortening of~135 km; the timing of shortening was 50–17 Ma (Ratschbacheret al., 1994). Such crustal shortening and associated intensefolding greatly increased the permeability of the Mesozoicstratigraphic units by development of numerous bedding faultsand fracture zones. Crustal shortening also resulted in crustalthickening within the foreland belt, which provided a neces-sary condition for crustal anatexis to form leucogranite melts(Fig. 10A).

(2) Extrusion of lower-crust and formation of the STDS (26–18 Ma): During the early post-collisional stage (26–18 Ma), thenorthern part of the Indian continent has been thrust along theMain Himalayan thrust (MHT), a northward gently-dippingdetachment (Zhao et al., 1993). This crustal-scale thrusting

Fig. 10. Sketch maps of tectonic model illustrating tectonic evolution, relevant ore-forming enthe Tethyan Himalaya. (A) The Indian continent northward subduction with a low-angle durfold belt in southern Tibet. (B) Southward extrusion of the lower-crust to form the Greater H26–18 Ma; the decompression melting along the STDS resulted in generating leucogranite mcentre of the dome at 18–8 Ma, led to a dome-centered geothermal fluid system and associ

within the Himalayas was delayed for 20–40 Myr following theonset of the collision (cf. Yin and Harrison, 2000), which hasbeen attributed to the lateral flow and southward extrusion of ahot, ductile Tibetan lower-crust in the Miocene (Nelson et al.,1996; Beaumont et al., 2001). This flow process resulted in theexhumation of the Greater Himalaya, and north-directeddown-slip of the Tethyan Himalaya along the STDS (Burg andChen, 1984; Burchfiel et al., 1992; Hodges and Hurtado, 1998;Wu et al., 1998). Extensional denudation of the STDS causedthinning of the overlying strata and resultant upraising of thecrust, contributing to formation of the thermal domes (Burch-fiel and Royden, 1985; Burchfiel et al., 1992; Chen et al., 1996;Xu et al., 2006). Rapid decompression due to fast denudation ofthe STDS triggered partial melting of the thickened crust(Harris and Massey, 1994; Nelson et al., 1996; Hochstein andRegenauer-Lieb, 1998; Searle et al., 2003), and allowedleucogranite emplacement along the STDS (Schärer et al.,1986). The STDS provided a significant conduit for long-distance transport and convection of geothermal fluids.

(3) Dome-centered granite intrusion and formation of the geother-mal system (18–8 Ma): Due to break-off of the subducted Indiancontinental slab and/or mantle thinning caused by lithospheredelamination or mantle convection (cf. Hou and Cook, 2009-thisissue), E–W crustal extension occurred during the late post-collisional period (b18 Ma) and resulted in N–S-striking normalfault systems (13.5–8Ma) across the Tibetan–Himalayan orogen.Meanwhile, uprising of the thermal domes (18–14 Ma; Liu et al.,2004a) and emplacement of leucogranite magmas in the centersof the domes (17–10 Ma; Chen et al., 1996; Harrison et al., 1997)

vironments, and dome-centered geothermal system and resultant Sb and Au deposits ining 40–26 Ma, resulting in crustal thickening and the formation of the foreland thrust–imalaya, and the Tethyan Himalayan detachment northwards to form the STDS duringagmas. (C) Uprising of the thermal dome and emplacement of leucogranite body in theated Au, Sb–Au and Sb mineralization from the dome outwards.


led to a dome-centered geothermal fluid systems driven byintrusion, developed along the entire thermal dome zone acrossthe Tethyan Himalaya (Fig. 10C). Near the centre of thegeothermal systems, Au-rich ore-forming fluids, which aredominated by magmatic water resulting from magma chamberdegassing, filled and replaced along the detachment faults andbrittle normal faults to form Au deposits close to the thermaldome. Far away from the centre of the geothermal system, thehydrothermal fluids flowed outwards along the E–W-strikingdetachment faults and scavenged metallic Sb from permeableMesozoic strata. Discharge of the ore-forming fluids andprecipitating of stibnite and other sulfides at the intersectionsof theE–W-striking andN–S-strikingnormal faultsfinally formedthe Sb deposits. In the transitional zone around the centers of thegeothermal system, CO2-rich, Au-bearing fluids dominated bymagmaticwatermixedwith heatedmeteoricwater continuouslyinfiltrating along detachment faults, resulting in precipitation ofsulfides in extensional fracture systems to form the Sb–Audeposits (Fig. 10C).

7. Conclusions

(1) The Tethyan Himalaya in southern Tibet probably underwent acomplex three-stage evolution from the formation of theforeland thrust–fold belt (65–26 Ma) due to Indo–Asiancollision, through southward extrusion of the lower-crust andsynchronal formation of the STDS (26–18 Ma), to uplifting ofthe dome and dome-centered granite intrusions in a crustalextensional setting (18–8 Ma), thus providing a significantmetallogenic setting for generation of numerous Sb and Au oredeposits.

(2) The Sb and Au deposits are mainly distributed around the STDS-related structural–thermal domes intruded by mid-Mioceneleucogranite bodies. They are controlled by E–W-strikingdetachment (and bedding fractural zone) and N–S-strikingnormal faults and their intersections. Thermal doming anddevelopment of extensional fault systems in a post-collisionalcrustal extension setting are important factors for generation ofthe mid-Miocene Sb and Au mineralization.

(3) There are at least three mineralization styles in south Tibet: Sb-,Sb–Au, and Au-styles of deposits. They are all hosted inMesozoicpassive continentalmargin volcano–sedimentary sequences, andshow a metallic zonation varying from Au, Sb–Au, to Sbmineralization from the dome outwards.

(4) Fluid inclusion and oxygen–hydrogen isotopic studies indicatethat the deposits were generated by a dome-centered geother-mal fluid system driven by the leucogranite bodies related tothe STDS. From the centre of the geothermal system outwards,ore-forming fluids vary from magmatic to meteoric water;corresponding mineralization forms a spectrum varying fromAu and Sb–Au to Sb deposits.

(5) Rb–Sr isotopic data of fluid inclusions and sulfur isotopic data ofsulfides indicate that scavenging of convective fluids from thepermeable Mesozoic strata was extremely significant forconcentration of metallic Sb and minor Au to form Sb or Sb–Au deposits outside the dome structures.

Acknowledgements

This study was financially supported by the National BasicResearch Program 973 Project (2002CB41260 to ZQH), the NationalScience and Technology Infrastructure Program (2006BAB01A04 toZSY) and the National Natural Science Foundation (40573024 to XJM)from theMinistry of Science and Technology, China. The authors thankresearchers from the Tibetan Geological Survey and the No.2Geological Team of Tibetan Geological Exploration Bureau for their

logistic and field support. We are deeply indebted to two anonymousOre Geology Reviews referees for their incisive reviews, valuablecomments and suggestions to improve this manuscript. We also thankDrs. Wei Huang and Wan Jiang for their help.

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post-collisional sb and au mineralization related to the south tibetan detachment system, himalayan...

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