Gold Xinjiang

ARTICLE

Zongyao Rui Richard J. Goldfarb Yumin QiuTaihe Zhou Renyi Chen Franco Pirajno Grace Yun

Paleozoicearly Mesozoic gold deposits of theXinjiang Autonomous Region, northwestern China

Received: 23 February 2000 /Accepted: 10 October 2001 / Published online: 15 January 2002 Springer-Verlag 2002

Abstract The late Paleozoicearly Mesozoic tectonicevolution of Xinjiang Autonomous Region, northwest-ern China provided a favorable geological setting for theformation of lode gold deposits along the sutures be-tween a number of the major Eastern Asia cratonic

blocks. These sutures are now represented by the AltayShan, Tian Shan, and Kunlun Shan ranges, with theformer two separated by the Junggar basin and the lattertwo by the immense Tarim basin. In northernmostXinjiang, nal growth of the Altaid orogen, southwardfrom the Angara craton, is now recorded in the remotemid- to late Paleozoic Altay Shan. Accreted Early toMiddle Devonian oceanic rock sequences contain typi-cally small, precious-metal bearing FeCuZn VMSdeposits (e.g. Ashele). Orogenic gold deposits are wide-spread along the major Irtysh (e.g. Duyolanasayi, Saidi,Taerde, Kabenbulake, Akexike, Shaerbulake) andTuergenHongshanzui (e.g. Hongshanzui) fault systems,as well as in structurally displaced terrane slivers of thewestern Junggar (e.g. Hatu) and eastern Junggar areas.Geological and geochronological constraints indicate agenerally Late Carboniferous to Early Permian episodeof gold deposition, which was coeval with the nalstages of Altaid magmatism and large-scale, right-lateraltranslation along older terrane-bounding faults. TheTian Shan, an exceptionally gold-rich mountain range tothe west in the Central Asian republics, is only beginningto be recognized for its gold potential in Xinjiang. In thiseasternmost part to the range, northerly- and southerly-directed subduction/accretion of early to mid-Paleozoicand mid- to late Paleozoic oceanic terranes, respectively,to the Precambrian Yili block (central Tian Shan) wasassociated with 400 to 250 Ma arc magmatism andCarboniferous through Early Permian gold-forminghydrothermal events. The more signicant resulting de-posits in the terranes of the southern Tian Shan includethe Sawayaerdun orogenic deposit along the Kyrgyzstanborder and the epithermal and replacement deposits ofthe Kanggurtag belt to the east in the Chol Tagh range.Gold deposits of approximately the same age in the Yiliblock include the Axi hot springs/epithermal depositnear the Kazakhstan border and a series of small oro-genic gold deposits south of Urumqi (e.g. Wangfeng).Gold-rich porphyry copper deposits (e.g. Tuwu) deneimportant new exploration targets in the northern TianShan of Xinjiang. The northern foothills of the Kunlun

Mineralium Deposita (2002) 37: 393418DOI 10.1007/s00126-001-0243-6

Z. RuiInstitute of Mineral Deposits,Chinese Academy of Geological Sciences,26 Baiwanzhuang Road, Beijing 100037, P.R. China

R.J. Goldfarb (&)US Geological Survey, MS 964, Box 25046,Denver Federal Center, Denver, CO 80225, USAE-mail: [email protected]

R.J. GoldfarbCentre for Global Metallogeny,Dept. of Geology and Geophysics,University of Western Australia, Crawley, WA 6009, Australia

Y. QiuCentre for Global Metallogeny,Dept. of Geology and Geophysics,University of Western Australia, Crawley, WA 6009, Australia

T. ZhouGreat Central Mines Limited andCentaur Mining and Exploration Limited,210 Kings Way, South Melbourne, Victoria 3205, Australia

R. ChenGeological Survey of China,Ministry of Land and Natural Resources,Beijing 100812, P.R. China

F. PirajnoGeological Survey of Western Australia,100 Plain Street, East Perth, Western Australia 6004, Australia

G. YunCentre for Global Metallogeny,Dept. of Geology and Geophysics,University of Western Australia, Crawley, WA 6009, Australia

Present address: Y. QiuSino Mining Ltd., 7th Floor, Sea Plaza,3A Xi Xin St., Xian 710004, P.R. China

Present address: Taihe ZhouSino-QZ Group, P.O. Box 2424,Mt. Waverley, Victoria, 3149 Australia

Shan of southern Xinjiang host scattered, small placergold deposits. Sources for the gold have not been iden-tied, but are hypothesized to be orogenic gold veinsbeneath the iceelds to the south. They are predicted tohave formed in the Tianshuihai terrane during its earlyMesozoic accretion to the amalgamated TarimQai-damKunlun cratonic block.

Keywords Altay Shan China Gold Tian Shan Xinjiang

Introduction

In recent years, the Chinese government has beenmaking great eorts to develop the economy of west-ernmost China, which includes a general policy to ac-celerate mineral exploration. Much of this work hasbeen focused in the Xinjiang Autonomous Region, a1.66-million km2 area that comprises the northwesternpart of China (Fig. 1). For example, since 1986, the 305

Project jointly supported by the Chinese Ministry ofSciences and Technology, the former Ministry of Geol-ogy and Mineral Resources (now the Ministry of Landand Mineral Resources), the Chinese Academy of Sci-ences, and the Xinjiang Uigar Autonomous Region hasincluded studies on geotectonics, petrology, mineraldeposits, isotope geology, geochemistry, and geophysicsof Xinjiang.

Geological observations indicate that XinjiangAutonomous Region is an extremely promising areafrom a minerals exploration standpoint, with numer-ous, recently-recognized gold deposits and prospects(Table 1). The northern mountain ranges in the region,the Altay Shan and Tian Shan, represent easterncontinuations of eastwest-trending Paleozoic orogenicbelts, which contain signicant gold resources within

Fig. 1. Location of the Xinjiang Autonomous Region in north-western China and surrounding provinces and countries. Theprovince is dominated by two large basins (the Tarim and Junggar)that are separated by three high-relief mountain ranges (AltayShan, Tian Shan, and Kunlun Shan)

394

Table1.SummaryofgoldresourcesandgeologyofmajorgolddepositsintheXinjiangAutonomousRegion,northwestern

China.Almostallofthegolddepositswereform

edduring

Carboniferousto

PermianorogeniceventswithintheAltayShanandTianShan.Deposittypesaredominatedbyorogenicgolddeposits,butsignicantepithermalsystem

sarealso

present

Region

Deposit

Type

Reserve

(tAu)

Geologically

inferred

re-

source(tAu)

Grade

(g/tAu)

Hostrock

Associated

major

structure

Depositage

AltayShan

Aketishikan

Orogenic

5.1

10

4Devonianphylliteandslate

TuergenHongshanzui

faultsystem

Carboniferous(?)

Hongshanzui

Orogenic

0.51.7

Neoprot.to

Ordovicianphyllite

TuergenHongshanzui

faultsystem

Carboniferous(?)

Duolanasayi

Orogenic

5.3

30

8.3

Devonianphyllite,graywacke,

andcarbonate

Irtysh

faultsystem

LateCarboniferous

EarlyPermian

Saidu

Orogenic

Devonianphyllite,graywacke,

andsiltstone

Irtysh

faultsystem

LateCarboniferous

EarlyPermian

Ashele

VMS

11

Devonianmacvolcanicrocks

Irtysh

faultsystem

EarlyMidDevonian

Akexike

Orogenic

2>5

7EarlyCarboniferousyschand

mac/interm

ediatevolcanicrocks

Irtysh

faultsystem

Carboniferous

Permian(?)

Shaerbuliak

Orogenic

210


mac/interm

ediatevolcanicrocks

Irtysh

faultsystem

LateCarboniferous

Kelasayi

Orogenic

510


mac/interm

ediatevolcanicrocks

Irtysh

faultsystem

Carboniferous

Permian(?)

Tasite

Orogenic

13

5EarlyCarboniferousysch

andshearedgranite

Aermantaifaultsystem

Carboniferous(?)

Buerkesidai

Orogenic

37


interm

ediateto

macdikes

Aermantaifaultsystem

Carboniferous(?)

Kelatongke

Magmatic

NiCu

0.15

LateCarboniferousnoritein

macultramaccomplex

Irtysh

faultsystem

LateCarboniferous

Western

Junggar

QiqiuI(Hatu

district)

Orogenic

13.5

23

7.5

EarlyCarboniferousbasalt

Dalabutefaultsystem

LateCarboniferous

SaertuohaiI

Orogenic

4.26.9

EarlyCarboniferousysch

Dalabutefaultsystem

LateCarboniferous

Baogutu

Orogenic

47

6.5

Mid-Carboniferoustu,some

oreinhornfelsnearLate

Carboniferousgranodiorite

Dalabutefaultsystem

LateCarboniferous

Akesai

CuAuskarn

13

8EarlyCarboniferouslimestone

Wenquanfault

Carboniferous(?)

Eastern

Junggar

Qingshui

Orogenic

0.3

27.3

EarlyCarboniferoustuand

graywacke

Kelameilifaultsystem

Carboniferous

Permian(?)

Nanmingshui

Orogenic

0.2

6.1

EarlyCarboniferousmac

volcanicsandgraywacke


Carboniferous

Permian(?)

Jinshan

Orogenic

1.4

32.2

EarlyCarboniferousmac

volcanicsandgraywacke


Carboniferous

Permian(?)

Adake

Orogenic

0.4

25

MidDevonianvolcaniclastics


Carboniferous

Permian(?)

Jinshangou

Epithermal

0.7

531.2

EarlyCarboniferousandesite

andrhyolite

EarlyCarboniferous

Danjiadi-Su-

angfengshanEpithermal

1.05.0

EarlyCarboniferousfelsicto

interm

ediatevolcanicand

hypabyssalrocks

EarlyCarboniferous(?)

395

the Central Asian republics. In Kazakhstan, the AltayShan host the 13.4 million ounces (Moz) Au Vas-ilkovskoye deposit and the 8 Moz Au Bakyrchikdeposit, as well as other large Caledonian (earlyPaleozoic) deposits such as Zholymbet, Stepnyak,Aksu, and Bestyube. In Uzbekistan and Kyrgyzstan,the Tian Shan contain giant Variscan (late Paleozoic)orebodies at Muruntau (170 Moz Au), Kalmakyr,(90 Moz Au), Charmitan (>10 Moz Au), and Kumtor(18 Moz Au), with the latter only 60 km from theXinjiang border (Fig. 1).

Geological setting of Xinjiang

Xinjiang is situated with the south-central part of the Eurasianplate, immediately north of the Himalayan collisional zone andTibetan plateau. The physiography of Xinjiang is dominated bythree rugged eastwest- to northwest-trending mountain rangesseparating large intracontinental foreland basins to the present-dayIndiaAsia convergence. From north to south, these features in-clude the Altay Shan, Junggar/Turpan basins, Tian Shan, Tarimbasin, and Kunlun Shan (Fig. 1). Elevations range from 8,611 m atQogir Peak on the west side of the Tarim basin and the 7,439 mPobedy Peak in the Tian Shan, to 154 m below sea level at AidingLake in the Turpan basin.

The region consists of several independent Precambrian conti-nental blocks that underwent a complex history of dispersion andreconvergence to Eurasia during the Paleozoic. These include (I)the composited Yili block (or DjezkazganKirzig unit of Sengorand Natalin 1996, and also KazakhstanNorth Tian Shan massifof Sokolov 1998) now exposed in the central Tian Shan; (II) theTarim block that forms a long-lived basin underlying much ofsouthern Xinjiang; and (III) parts of the Qaidam block extendinginto southeastern Xinjiang beneath the Qaidam basin (Fig. 1).Paleozoic accretionary complexes and extensional basins dene thesutures between the various blocks. These include terranes of theextensive Altaid orogenic system accreted onto the south side ofthe Angara craton underlying eastern Russia, those added to boththe north and south sides of the Yili block, and those that collidedin the Paleozoic and Mesozoic onto the south side of the Tarimblock. Permian extensional tectonics formed deep basins within theAltaid orogenic complex, evolving between the present-day Altayand Tian Shan. Broad-scale deformation has eected much ofXinjiang during the last 250 million years, with northward-directedcollisions reecting closure of the Paleo-Tethys and Neo-TethysOceans, and the present collision with India.

Tarim basin

The Tarim basin covers about one-third of the land area ofXinjiang (Fig. 1) and is Chinas largest inland basin. The basin isgenerally recognized to overly the Tarim block, one of the threemajor cratonic blocks of China, as Precambrian basement is ex-posed along much of its periphery (Zhang et al. 1984; Coleman1989). The most extensive exposures occur in the northeasternTarim basin in the Kuruktagh region (Allen et al. 1992). In addi-tion, a massive magnetic anomaly extending for 1,000 km acrossthe middle of the Tarim basin at latitude 40 provides evidence ofPrecambrian crystalline rocks generally under 615 km of youngsedimentary cover and a thin Paleozoic sequence. However, mag-netic basement in the center of the basin, termed the central Tarimuplift, is estimated at depths of 48 km or less. The consistent LateProterozoic and early Paleozoic stratigraphy from both the northand south margins of the Tarim basin has been used as an argu-ment that the Tarim was a single coherent cratonic block since theEarly Proterozoic (Li et al. 1996). The Tarim has been character-T

able1.(Contd.)

Region

Deposit

Type

Reserve

(tAu)

Geologically

inferred

re-

source(tAu)

Grade

(g/tAu)

Hostrock

Associated

major

structure

Depositage

Eastern

TianShan

Xitan

Epithermal

(high

suldation)

6.4

5.010

Permian(?)andesite

Yamansu

fault

Permian

Kanggurtag

Replacement

10

20

7EarlyCarboniferous

volcaniclastics

Yamansu

fault

LatePermian

Dadonggou

?EarlyCarboniferous

volcaniclastics

Yamansu

fault

Permian(?)

Matoutan

Replacement

20?

10

EarlyCarboniferous

volcaniclastics

Yamansu

fault

LatePermian(?)

XifengshanII

Orogenic(?)

EarlyPermiangranitoid

Tuwu

Porphyry

90

0.16

Mid-Carboniferousgranitoid

Kanggurfault

Mid-Carboniferous

Western

TianShan

Wangfeng

Orogenic

3.1

8.09.0

Silurian-EarlyCarboniferous

granitoids

NorthTianShan

faultsystem

EarlyPermian

Dashankou

Orogenic

12

LateSilurianEarly

Devonianne-grained

clastics

Uncertain

Axi

Epithermal

50

70

5.8


andbasalt

Carboniferous

Yierm

and

Hotsprings


andbasalt

Carboniferous

Sawayaerdun

Orogenic

100

300

3.05.0

LateSilurianslateandphyllite

PermianTriassic(?)

Bulong

Orogenic

44

LateDevoniangraywacke

andsiltstone

Uncertain

396

ized by a complex multi-stage basin evolution throughout the entirePhanerozoic (Li et al. 1996).

The oldest ages on rocks in the Tarim block of 32633046 Mawere obtained by UPb dating of zircons from gneisses and am-phibolites in the northeastern Tarim basin. Other nearby igneousand metamorphic rocks, as well as those elsewhere around thebasin margin, have dates that span the Early Proterozoic (Li et al.1996; Matte et al. 1996). Late Proterozoic rifting along the northernand southern margin of the Tarim block (Gilder et al. 1991; Li et al.1996) led to passive margin sedimentation through the Cambrianand Ordovician. The onset of mid-Paleozoic orogenic events alongboth margins of the Tarim, continuing into the Mesozoic on thesouth, resulted in deposition of as much as 12 km of terrestrialsedimentary rocks during initial formation of the Tarim basin.Rapid Neogene to Quaternary uplift within the Tian Shan andKunlun Shan has been responsible for the extensive sedimentationwithin the Tarim foredeep during the last 20 million years.

Tian Shan

The Tian Shan range (Fig. 2) is located to the north of the Tarimbasin with several peaks exceeding 5,000 m in elevation. Theeastern part of this >2,500-km-long mountain belt trends eastwest in a 300-km-wide zone across the center of Xinjiang; it con-tinues westward from China for another 1,000 km throughKyrgyzstan and Uzbekistan. In China, the range is often dividedinto the southern and northern Tian Shan provinces, which sur-round a Precambrian nucleus commonly termed the Yili block orcentral Tian Shan province. The Chinese Tian Shan can be con-sidered as having formed the south-central part of the Altaidorogenic zone, an extensive series of Paleozoic subductionaccre-

tion complexes added to the Eurasia continent between the Tarimblock and Angara (Siberia) craton (Sengor and Natalin 1996).

The southern Tian Shan province is composed of early Paleo-zoic passive margin sequences, which are continuous onto thenorthern margin of the Tarim Precambrian block. These marinesedimentary rocks and associated metavolcanic rocks suggest anoceanic basin existed along that margin in Ordovician and Siluriantimes (Carroll et al. 1995). The presence of mid-Silurian throughEarly Carboniferous turbidite-dominant sequences indicates thatthere was a shift to an active continental margin during the mid-Paleozoic. Associated mid-Paleozoic volcanic rocks are referred toas part of the AqishanYamansu arc. It is possible that, during theDevonianCarboniferous, an ocean basin was being subductednorthward ahead of the Tarim block and beneath the central TianShan (Shi et al. 1994; Carroll et al. 1995). Alternatively, a south-ward-dipping subduction zone may have developed beneath thenorthern margin of the Tarim micro-continent (Graham 1995). It is

Fig. 2. Generalized geologic map of the Tian Shan region incentral Xinjiang after Allen et al. (1992, 1993), Shi et al. (1994), andCarroll et al. (1995). Two Paleozoic sequences of allochthonousterranes (northern and southern Tian Shan provinces) wereamalgamated, partly around the Precambrian Yili block, duringa complex series of Devonian to Early Permian arc/terranecollisions. Resulting orogenic (e.g. Wangfeng, Dadonggou, Yuan-baoshan, Sawayaerdun, Xifengshan, Dashankou, Bulong), replace-ment (Kanggurtag, Matoutan) and epithermal (e.g. Xitan, Axi)lode gold deposits are recognized throughout the length of the300-km-wide orogen that cuts Xinjiang, and signicant potentialexists for the discovery of additional gold resources in this orogen.The TuwuYundong deposit is a recently discovered gold-richcopper porphyry deposit

397

clear that, however, no matter what the polarity of the subduction,the Tarim and Yili blocks were amalgamated in the Late Devo-nianEarly Carboniferous. Relatively younger dates on deforma-tion along the western side of the suture may indicate an oblique,diachronous collision that continued until the end of the Paleozoic(Chen et al. 1999).

The 500-m-wide QinbulakQawabulak fault of Allen et al.(1992; also referred to as the Nikolaev line, Central Kazakhstanfault or the NuratauAtbashi megashear zone in the Central Asianrepublics to the west) is the site of the Late DevonianEarly Car-boniferous suture between the Tarim block-southern Tian Shanprovince and the Yili block (Gao et al. 1998; Fig. 2). It can betraced as far to the west as the Aral Sea (Allen et al. 1995) and isoften part of an 8-km-wide HPLT assemblage of thrust sheets(Gao et al. 1999). The giant gold deposits of Central Asia, imme-diately west of Xinjiang, are all within about 100 km of the suture,and except for Kumtor, lie within the southern Tian Shan province.The Yili block is perhaps the easternmost part of the so-calledKazakhstanKyrgyzstan assemblage, a series of small Precambrianfragments that may have joined together in the early Paleozoic(Zonenshain et al. 1990). Alternatively, Shi et al. (1994) claim thatthe Yili block is a fragment of the Tarim craton that rifted away inthe Early Cambrian and then re-collided with the craton later in thePaleozoic. The block pinches out at about longitude 89 and thesuture to the east of this point is directly between the northern andsouthern Tian Shan provinces. (We refer to the area in centralXinjiang east of this longitude as the eastern Tian Shan and that tothe west as the western Tian Shan within later sections of thispaper.) Migmatitic basement in one area within the Xinjiang partof the Yili block has been dated at 14001300 Ma (Allen et al.1992). Ultramac rocks, interpreted by some workers as ophiolites,follow the suture and may have been emplaced during obductionassociated with Yili-Tarim block collision. CarboniferousEarlyPermian carbonate platform facies cover rocks exposed along thesuture suggest a late Paleozoic extensional basin formed subsequentto collision (Carroll et al. 1995; Sokolov 1998).

The North Tian Shan fault represents a Late CarboniferousEarly Permian suture, where rocks of what are now the northernTian Shan province were subducted below and accreted onto theYili block (Allen et al. 1993; Gao et al. 1998). The accreted rocks tothe north of the fault are mainly Devonian to mid-Carboniferouscalc-alkaline volcanic rocks and ysch (the Bogda/Turpan terraneof Coleman 1989 or the Kanggur and Bogda arcs of Pirajno et al.1997), which were separated from the Yili microcontinent by theNorth Tian Shan sea (Carroll et al. 1995). To the east, where theYili block is pinched out, south of the Turpan basin, the NorthTian Shan (or Kanggur) fault separates the northern and southernTian Shan provinces. As in the southern Tian Shan province, ul-tramac rocks along the north side of this suture zone are hy-pothesized to represent obducted oceanic crust. Simultaneously,and to the north of the accreting arcs, the Turkestan (or Junggar)Ocean closed between these arcs that had been added to the Yiliblock and the more northerly terranes of the Altaid assemblagethat had been simultaneously accreting to the Angara craton(Carroll et al. 1990).

Variscan calc-alkaline granite and granodiorite bodies, spreadin age between 400250 Ma, now outcrop over much of the Yiliblock (Hopson et al. 1989; Allen et al. 1992). They reect a hugeand still poorly understood magmatic arc derived from orogenicevents on both sides of the Yili block. Within the central TianShan along the southern margin of Kazakhstan, on the north sideof Issyk-Kul Lake and about 150 km north of the Xinjiangborder, the 100 km2 Talgarskii complex was intruded at 365349 Ma. This complex consists of riebeckite and hastingsitegranites, and alkaline leucogranites (Kogarko et al. 1994). If theabsolute dates are correct, they indicate a region of local exten-sion during the Late DevonianEarly Carboniferous collisionalevent. Subsequent to the amalgamation of the Tian Shan belt,Late Permian through Early Triassic extension in both fore-arcregions (perhaps really a back-arc extension beneath the Tarimduring the latter southerly subduction) appear to be marked byalkaline magmatism within both the southern and northern Tian

Shan. Many of these are a part of Colemans (1989) A-typegranites of central Asia, a group that obviously also erroneouslylumps in much of the subduction-related magmatism. Coleman(1989) argues that isotopic data from these alkaline rocks indicateno Precambrian basement and magma generation from under-plated oceanic crust.

Altay Shan

The Altay Shan form the remote northern border of Xinjiang,separating China from Kazakhstan on the northwest, Russia onthe north, and Mongolia along the northeast (Fig. 3). Highestelevations include 4,374 m Youyifeng Mt., forming a boundarypoint between ChinaRussiaMongolia, and 4,362 m Menghehai-han Mt., which is located about 100 km east of Qinghe in adjacentMongolia. These mountains in China consist of mainly latestProterozoic through Carboniferous turbidites with lesser cherts,basalts, and gabbros. Many of these latter igneous rocks occur aspieces of dismembered ophiolites emplaced within mid-Paleozoicmetasedimentary rocks, commonly in association with blueschistfacies metamorphism. The sedimentary-rock dominant sequencesrepresent a massive series of Altaid accretionary complexes (orterranes in some terminology) added to the Angara cratonthroughout the Paleozoic (Sengor et al. 1993). The ages of thesedimentary rocks generally get younger to the southwest, reect-ing the outward growth of the so-called Altay/Sayan orogen,although Carboniferous and Permian strike-slip events havetranslated some sequences of older rocks outboard of morerecently accreted sequences (Sengor et al. 1993). The major Irtyshshear zone (Fig. 3) separates, what have been termed, the northernGorny Altay unit from the southern Kalba Narym sector of theSurgut unit (Sengor et al. 1993; Allen et al. 1995). The southernmargin of the Surgut unit, dened by the Gornostaev (or Aer-mantai) shear zone, is mainly unexposed because it is overlain byPermian and younger rocks of the Junggar basin. These unitsare possibly similar to the superterrane terminology commonlyused in Cordilleran tectonics; that is, large allochthonous blockswith some amalgamation of dierent lithostratigraphic units priorto accretion.

As with the Tian Shan, Variscan magmatism is also widespreadthroughout the Altay Shan. In northern China, such arc magma-tism is found throughout the Altay Shan, but seems most volu-minous along the China/Mongolia border within the olderPaleozoic terranes. Most of the calc-alkaline magmatism is prob-ably the result of Early Carboniferous oblique subduction. LateCarboniferous to Early Permian post-orogenic right lateral dis-placement along many terrane sutures, such as the Irtysh andGornostaev faults, followed by a latest Paleozoic reversal of shearsense, have complicated recognition of the original continentalmargin (Sengor et al. 1993). Magmatism mainly changed to morealkaline in composition during these transtensional events. Vari-scan alkaline magmatism north of the Irtysh fault is known for itsassociation with some of the worlds largest pegmatite-type raremetal (Li, Be, Nb, Ta, Y, Rb, Cs, Zr, and Hf) deposits, some ofwhich contain gem-grade beryl, within the 450-km-long TalitskyMongolian Altai belt (Kremenetsky 1996). The magmatic orescontinue along a northwest trend across adjacent easternKazakhstan, where they dene the KalbaNarym metallogeniczone (Malchenko and Ermolov 1996). Regional metamorphicgrade is reported to show a transition from greenschist in thesoutheastern Altay to amphibolite and higher grade facies in the

Fig. 3. Generalized geologic map of the Altay Shan region innorthernmost Xinjiang showing the location of the most importantlode and placer gold deposits. Northwest-trending regional faultsystems, mainly separating a complex system of latest Proterozoicto Carboniferous marine sedimentary and volcanic rock-dominatedaccreted terranes of the Altaid orogen, provide a rst-order controlon localization of the lode deposits. Generalized after Chen et al.(1985)

c

398

northwest (Yang et al. 1992), although some of this could reect abroader contact metamorphism associated with the abundance ofmagmatism in the northwest. These metamorphosed rocks areoverlain by unmetamorphosed Permian strata and give whole rockradiogenic dates of 308267 Ma (Yang et al. 1992), indicative of acessation of tectonothermal events by late Early Permian.

Permian basins

A series of large basins, the Alakol, Junggar, and Turpan basins,extend across northern Xinjiang (and western Kazakhstan) be-tween the Tian Shan and Altay Shan (Fig. 1). The commonly oil-bearing Permian to Cenozoic basinal strata are as thick as 15 kmalong the southern margin of the Junggar basin (Clayton et al.1997). The basement to these basins is still debatable (Gao et al.1998), but many workers now indicate that it likely consists ofPaleozoic accretionary complexes and magmatic arcs similar tothose of the southern Altay Shan and northern Tian Shan (Allenet al. 1995; Allen and Vincent 1997). The basins are widely viewedas Late Permian to perhaps Early Triassic extensional features(Allen et al. 1995), although it has also been argued that they didnot form until the Jurassic (Hendrix et al. 1992). A Late Permianorigin would temporally overlap with regional sinistral shear mo-tion of the Eastern European craton relative to the Angara craton,and the onset of a brief Late Paleozoic episode of alkalic magma-tism throughout the northern part of central Asia. The Permianand younger cover rocks overlie the zone marking Late Carbonif-erous closure of the Turkestan Ocean and the suturing between thetwo subduction zones of opposite polarity.

Southern Xinjiang

The geologic history along the southern side of the Tarim block isfairly well understood to the west, but Cenozoic strike-slip eventsand presence of the Qaidam block and associated accretionaryprisms make for a very dicult understanding of the regional ge-ology of southeasternmost Xinjiang. The southern boundary of theTarim block is recognized by the Kudi suture in the southwest,which is also referred to as the Kunlun or Tamkaral fault (Fig. 4).The fault zone separates the 2261 Ma metamorphic rocks of theTarim block from the 1760 Ma metamorphic rocks of the Kunlunterrane. It formed during the Silurian as the Tarim block was un-derthrust beneath the Kunlun terrane. Syn- to post-collisionalCaledonian calc-alkaline magmatism occurred along both sides ofthe fault and is dated between about 460 and 380 Ma (Dewey et al.1988; Matte et al. 1996). Cenozoic strike-slip along the major andreactivated crustal-scale Altyn TaghKarakash fault system hasdisplaced part of the Archean and Proterozoic Kunlun terrane andadjoining rocks of the southern Tarim block, along with the Cal-edonian arc, hundreds of kilometers to the east to form the EastKunlun Shan of southeastern Xinjiang (Zhou and Graham 1996).The Qaidam basin along the northern side of the East KunlunShan, often termed the Qaidam block, is most probably a piece ofthe Tarim block that was oset by the Cenozoic IndiaAsia colli-sion.

To the south of the Tarim basin, Paleo-Tethyan oceanic crustwas thrust northwards underneath the amalgamated TarimQai-dam block and Kunlun terrane. This led to the successive accretionof the Tianshuihai and Qiangtang terranes (or northern Tibetblock) in the Late TriassicEarly Jurassic, Lhasa terrane in the LateJurassic, the KohistanDras arc in the Late Cretaceous, and Indiaby the early Tertiary. Only the former of these Tethysides accre-tionary complexes (see Sengor and Natalin 1996) lies withinXinjiang. The greenschist facies Permo-Triassic ysch of theTianshuihai terrane was subducted below and accreted to thesouthern margin of the Kunlun block along the Altyn Tagh faultzone (Matte et al. 1996), a structure marking the northernboundary of the Tibetan plateau (Fig. 4). The crustal-scale suturenow is located along some of the high peaks of the Kunlun Rangethat rise above the Tibetan plateau and, in the Cenozoic, has been

reactivated as a major sinistral strike-slip system. Anatectic granitesare scattered along both sides of the suture and their absolute datesrange between 210 and 180 Ma (Matte et al. 1996). By about180 Ma, unmetamorphosed Carboniferous to Permian Tethyanrocks of the Qiangtang terrane, the southernmost rocks exposed inXinjiang, collided with the southern margin of the Tianshuihaiterrane along what is now the GozhaLongmu Co fault zone(Matte et al. 1996).

In the southeastern corner of the Xinjiang province, a few ad-ditional signicant tectonic units surround the oset East KunlunShan/Qaidam basin (Fig. 4). The Altyn Tagh Shan are located onthe north side of the Qaidam block and along the southeasterncorner of the Tarim basin. Paleozoic ysch and island arc rocksindicate that the Altyn Tagh Shan were originally part of the TianShanBei ShanQilian Shan Paleozoic orogenic belt that cutsacross much of central China (Zhou and Dean 1996). Right lateraloset along the northeastern extension of the Altyn TaghKarak-ash fault system has displaced a part of the belt. The SongpanGanzi terrane, south of the East Kunlun Shan/Qaidam block, is anearly Mesozoic ysch sequence that denes a large sea trappedbetween the colliding cratonic blocks of China (Sengor et al. 1993).It may continue to the west as rocks dened as those of theTianshuihai terrane and, if so, then if forms the entire backstop foraccretion of the Qiangtang terrane.

Gold deposits of the Altay Shan

Most gold deposits discovered to date in Xinjiang are inthe accreted terranes of the Altay Shan, associated witha complex series of northeasterly-dipping thrust sheets.Both granitoids and gold deposits in the Altay Shan areultimately associated with collisional orogenesis alongthe southern side of the Angara craton, which underliesthe countries to the north. Dong (2000) suggests that theorogenic gold deposits and prospects of the Altay Shancluster into eight belts, which are localized by the mainNW-trending ductile fault zones and lower-order crossstructures. Our observations favor a more irregularpattern for the larger deposits (Fig. 3), although thespatial association with these faults is generally well-supported. The below descriptions are based upon theexisting literature, extensive eld work in Xinjiang bythe lead author, and eld visits by two authors (R.G.and F.P.) to some of the deposits.

Northern Altay Shan

The lesser mineralized northern Altay area consists of abasement of Precambrian schists and then Late Prote-rozoic to Ordovician accretionary sequences, locallyoverlain by rift-related, mid-Paleozoic volcanic and ne-grained clastic basinal rocks. These rocks make up muchof the high elevations of the Altay Shan. A zone of high-angle faults that cuts through the area, collectivelyknown as the Gorny Altay unit (Sengor et al. 1993),trends WNW and includes the TuergenHongshanzuifault zone (Fig. 3). Extensive uplift has exposed base-ment rocks and roots of the Late Devonian to PermianHalongQinghe (or QingheAltay) magmatic arc. Thearc is poorly understood, with a wide range of Paleozoic

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absolute dates (Wang et al. 1993), but the dominantcalc-alkaline granitoids typically appear to young fromthe northwest to the southeast, although many areprobably Early Carboniferous in age.

Lode ores in the northern Altay have historicallybeen mined in neighboring Kazakhstan, including the8 Moz Bakyrchik orogenic gold deposit hosted by mid-Carboniferous metasedimentary rocks (Sokolov 1998).Most of the northernmost Altay gold resources in ad-jacent Xinjiang are in placer accumulations of theNuoerte region (e.g. Ayousai, Hongdun, Laojinggou,Xinjinggou, and Akelsala), occurring within the steepand remote parts of the mountain range. These placersoccur along many of the streams draining the south sideof the HalongQinghe arc, which eventually ow intothe large Irtysh River. Their presence suggests signicantlode gold potential within the large, mainly Early Car-boniferous, calc-alkaline intrusive complex. Recently,also a few orogenic gold deposits have been discoveredhosted in metasedimentary rocks of the northern AltayShan region, although no large lodes have yet been

found that are clearly spatially associated with thegranitoids.

The most signicant of the northern Altay orogenicgold deposits are those of a remote and relatively un-studied gold belt, which stretches for 200 km along apart of the 500-km-long, NW-trending and near-verticalTuergenHongshanzui fault. The fault generally sepa-rates what have been mapped as Early Devonian sedi-mentary and volcanic basinal rocks to the north fromProterozoic and early Paleozoic accretionary complexesto the south. It is implied by OHara et al. (1997) thatsome of the vein host rocks are metamorphosed toamphibolite and higher grades. The fact that the olderrocks are located outward (relative to the Angaracraton) of the younger units reects the complex latePaleozoic strike-slip events along older suture zones inthe Altay belt, as described by Sengor et al. (1993).

Typically, 3- to 10-km-wide mineralized zones arelocalized where NNW- or NE-trending faults intersectthe more regional TuergenHongshanzui system. Manyof these are the probable sources for above describedplacer deposits. Among the larger deposits, the Aketi-shikan deposit (10 t Au resource) is hosted in the basinalstrata, whereas the Hongshanzui deposit is hosted byolder greenschist facies metasedimentary rocks of theNeoproterozoic to Ordovician Habahe Formation. Goldat the Aketishikan deposit occurs as inclusions withinpyrite and arsenopyrite grains within suldized sedi-mentary and volcanic rocks. At the Hongshanzuideposit, which lacks a reported gold resource, mineral-ization occurs along a NW-tending, ductilebrittle shear.

Fig. 4. Geological and tectonic features of the Kunlun Shan,southern Xinjiang (modied after Yin et al. 1998). The region isdened by the northernmost terranes accreted to the Tarim cratonin early Mesozoic, prior to Cenozoic IndiaAsia collision andresulting continent-scale strike-slip motion. Poorly documented,but widespread orogenic gold deposits and resulting placers occuralong much of the length of the northern Tibet block, havingformed as terranes of this block were deformed against the TarimblockQaidam blockKunlun terrane Triassic continental marginbackstop

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The gold, commonly located within sulde grains, oc-curs in quartz veins and breccias, in stockwork net-works, and is disseminated in wall rock. In the vicinity ofthe Laojinggou placers, poorly-documented quartzveins, stockworks, and breccias are reported to occur inzones as long as 3 km and as wide as 1 km that cutgranitoids of the HalongQinghe arc (Tan et al. 1994;Liu et al. 1996). There are no reliable age data for any ofthe gold occurrences, which probably formed sometimeduring Paleozoic deformation, perhaps around the timeof the Early Carboniferous calc-alkaline magmatism orduring slightly later strike-slip. The fact that the ores arenot found in the unmetamorphosed Late Permian rockssuggests veining is older than about 260 Ma.

The possibility that some of the gold deposits in thenorthern Altay Shan are older, perhaps early to mid-Paleozoic in age, also can not be discounted. Theabundance of gold occurrences continues to the north-east across the border into the Mongolian Altai. TheseAuSbW prospects are concentrated within a few tensof kilometers of the China border and show a strongspatial association with Caledonian granite and gran-odiorite (Kempe and Belyatsky 2000). Hence, orogenicgold deposits in the Altay Shan may range in age overmuch of the Paleozoic, with such ages progressivelyyounging to the southwest and, thus, correlative withoutward growth of the orogen.

Southern Altay Shan

The NW-striking, NE-dipping Irtysh fault zone (Fig. 3)separates the Gorny Altay and Surgut units, both Pa-leozoic accretionary wedges, within the lower elevationsof the southern Altay region. Much of the fault zone ismarked by the northwesterly-owing Irtysh River andan extensive belt of ultramac bodies. In places, my-lonitic zones reach 3 km in width (Sengor et al. 1993).Ductile deformation along the fault zone ceased by ca.270 Ma (Travin et al. 1998). Orogenic gold, gold-bear-ing magmatic NiCu deposits and gold-rich volcano-genic massive sulde (VMS) type deposits occur in thearea, with the former being the most widespread.

The orogenic lode gold deposits are mainly distrib-uted along the length of the Irtysh fault zone (Fig. 3),likely indicating an important rst-order control forhydrothermal uid migration. Most of the importantdeposits occur on second-order faults within about 510 km of the main fault strand. Those deposits to thenorthwest along the structure, including Duolanasayi,Saidu, Taerde, and Kabenbulake, cut felsic to interme-diate granitoids, ysch, and volcaniclastic rocks. Thelargest of these, Duolanasayi (Fig. 5), is actually madeup of a number of mineralized bodies that occur along a20-km-long by 10-km-wide zone between the Maerkak-uli and Habahe second-order faults near the Kazakhstanborder. The lodes cut Middle Devonian graywacke,phyllite, and carbonate near hornfels associated with aseries of ca. 290 Ma tonalites (Li et al. 1998). In places,

granodiorite and plagiogranite dikes, some of which cutand are, thus, younger than the tonalite, occur as thefootwall or hanging wall to orebodies. Both the veinsand older parallel dikes are localized along the lime-stone/clastic rock contacts (Fig. 5). The gold occursboth in quartz veins and disseminated within adjacentigneous and metasedimentary country rocks. In additionto a typical orogenic gold quartzpyritesericitecarbonatechlorite alteration assemblage, skarn-likecalc-silicate phases occasionally occur where lodes cutlimestones. Li et al. (1998) report a series of RbSr dateson uid inclusion waters from quartz veins at theDuonalasayi and Saidu deposits of between 269 and305 Ma. Although the meaning of such data may bequestionable, it does hint at a late Paleozoic ore-formingepisode in the southern Altaids that is coeval with re-gional right-lateral shearing events. This is further sup-ported by three KAr dates of ca. 317295 Ma from theSaidu deposit (Cheng and Rui 1997).

In the same area, along the Irtysh fault zone and onlya few tens of kilometers from the Kazakhstan border, anumber of small VMS deposits are hosted in the Early toMiddle Devonian Ashele Formation (Wang et al. 1998;Wang 1999) of the Gorny Altay unit. The FeCuZn-bearing suldes occur as laminations, massive bodies,and stockwork systems between the bimodal, submarinefootwall spilitic rocks and hanging wall quartzkerato-phyric tu. The approximately 1 million tonne resourceat the Ashele deposit (Fig. 3) grades about 2% com-bined Cu + Zn, along with signicant precious metalgrades of 55 g/t Ag and 1 g/t Au. Locally, higher pre-cious metal grades correlate with areas of black ore,composed of massive galenasphaleritechalcopyritebarite (Wang 1999). As with many of the orogenic golddeposits in the Altay Shan, published absolute dates formineralization are quite variable, ranging from about373 to 255 Ma (Li et al. 1998). A cluster of SmNd andRbSr dates on volcanic rocks and massive sulde orescluster near 360 Ma and are interpreted as the mostprobable age for seaoor hydrothermal activity. This isrelatively close in time to the widely accepted Early toMiddle Devonian lithostratigraphy reported for theAshele Formation.

Although the present gold resource at the Asheledeposit is only about 30,000 oz, the Devonian rocksnorth of the Irtysh fault present a favorable target forfuture discovery of large gold-bearing VMS deposits.The belt of precious metal-bearing FeCuZn depositscontinues to the northwest into adjacent Kazakhstan,where it includes the Nikolaevskoe, Belousovskoe,Chekmar, and Snegirikhinskoe deposits (Malchenkoand Ermolov 1996). Deposits of FeCuAu also con-tinue to the southeast for more than 300 km from theAshele deposit, where the Qiaoxiahala deposit occurswithin an ophiolite sequence along the northern side ofthe Irtysh fault zone. Gold enrichments are recognizedin chalcopyrite and bornite within massive magnetitebeds within the Middle Devonian Beitashan Formation(Wang et al. 1999). The presence, however, of a

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dominantly oxidized hypogene iron phase in a Phan-erozoic age deposit and adjacent skarn mineralogysuggest that the Qiaoxiahala deposit might rather be amagmatic gold system, rather than a part of the belt ofVMS occurrences.

Along the southern side of the southeastern part ofthe Irtysh fault zone, the Akexike, Shaerbulake, andKelasayi orogenic gold deposits occur within EarlyCarboniferous ysch and mac to intermediate volcanicrocks of the Surgut unit. Mineralization styles are sim-ilar to those farther northwest along the structure, andinclude veins, breccias, and disseminated ores. At Sha-erbulake, the orebodies are hosted by the ysch, whereasat the Akexike deposit they mainly occur along basalt/tu contacts. In both cases, ductile shearing within an-ticlinal structures is suggestive of saddle reef zones,which are well-known common hosts for orogenic golddeposits in areas such as the Victorian goldelds ofsoutheastern Australia and the Meguma terrane ofeastern Canada. There are no large granitoids in thispart of the Surgut unit, although dikes of various com-positions are widespread. A 292.17.3 Ma RbSr date

on a felsic dike at the Shaerbulake deposit overlaps aPbPb date from there on arsenopyrite of304.17.4 Ma, which is assumed to be the age of golddeposition (Li et al. 1998).

A few orogenic gold deposits in the Surgut unit occur50100 km west of Wulonggu Lake to the north of alarge fault zone (Manrak fault of Allen et al. 1995),which might be a part of the westerly continuation of thecomplex Aermantai fault system (Fig. 3). Known as theSawuer district, the deposits are associated with a smallarea of Devonian and Carboniferous ysch, surroundedby extensive areas of Permian and younger strata. Mostof the deposits are described as occurring within theEarly Carboniferous Heishantou Formation. The oresshow a spatial association to many of the small Variscangranitoids that are described as both calc-alkaline andalkaline, and RbSr dates on these rocks range between329 and 314 Ma (He et al. 1994). Quartz veins at theTasite deposit, discovered more than 50 years ago andrecently having produced about 15,000 oz Au, arehosted in brittle fault zones near the margins of asheared, K-feldspar-rich granite. In contrast, at the

Fig. 5a, b. Geology of theDuolanasayi orogenic gold de-posit, southern Altay Shan.a Regional geology surroundingthe Duolanasayi gold deposit.The deposit occurs in MiddleDevonian clastic rocks, andalong their contacts with lime-stone units, within a few hun-dred meters of hornfelsassociated with 290 Ma tona-lites. b Detailed geology of themain orebodies at the Duol-anasayi deposit showing asso-ciation of gold ores with clastic-carbonate rocks contacts

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Buerkesidai deposit, gold-bearing stockworks occurboth in carbonaceous ysch and intermediate to macporphyritic dikes.

Potential nickelcoppercobalt resources, grading0.74% Ni and 0.3% Cu and with precious metal en-richments, occur at the Kelatongke deposit, about100 km west of Qinghe (Fig. 3). Early Carboniferousmetasedimentary rocks are intruded by a NW-trendingbelt of Late Carboniferous macultramac complexes(Li et al. 1998) that parallel the nearby Irtysh fault. Themagmatic Ni- and Cu-bearing sulde minerals occurdisseminated in biotitehornblende olivine norite inthe lower parts of the complexes. Sulde-rich zones alsoaverage 7.6 g/t Ag and 0.15 g/t Au. These gabbroic-dominant igneous complexes apparently continue intoadjacent Kazakhstan, where they include the Au-and PGE-enriched Checkek deposit (Malchenko andErmolov 1996).

Gold deposits of the western Junggar area

The western Junggar area is characterized by mainlyDevonian to Early Carboniferous metasedimentaryrocks, oceanic basalts, often emplaced in ophiolitic se-quences, and some melange (Shen et al. 1996). The area(Fig. 6) is exposed above the Permian Junggar basinto the east and Alakol basin, in adjacent Kazakhstan, tothe west. Although rock types and ages are similar tothose of the northern Altaids, lithologies and major faultzones trend NESW across the western Junggar areaand are almost orthogonal to those of the Altaids. Thisis likely the consequence of counterclockwise rotation ofpart of the vast Altaid accretionary complex during left-lateral, strike-slip events and basin formation in the LatePermian (Allen et al. 1995). Limited geochronology,discussed below, suggests that this tectonism roughlycorrelates with the time of lode gold formation. It also isthe approximate time of change in northern Xinjiangfrom calc-alkaline to alkaline magmatism. Jin andZhang (1993), using a variety of dating methods, de-scribed a group of 322305 Ma I-type granodiorites andone of 281245 Ma S-type syenites and alkali granitesthat seem to overlap the transitional period within thewestern Junggar region.

More than 300 gold deposits and occurrences arerecognized in the western Junggar area (Shen et al.1996), with the most signicant of these along thenorthern side of the NE-trending Dalabute fault zone(Fig. 6) and a total resource of at least 2.5 Moz Au.Unknown amounts of gold have been mined from oro-genic gold vein deposits since the Ming Dynasty of themiddle 1300s and extensive amounts of placer miningoccurred during the Ching dynasty in the early 1800s inthe Hatu district. Many of the historic and present-daylode deposits are clustered in a 70-km-long by 20-km-wide corridor, between the Dalabute and more northerlyAnqi and Hatu rst-order faults, and extending fromthe Hatu (Qiqiu #1 and #2 deposits) to Saertuohai

districts (Fig. 7). The regional structures are thought tohave formed in the Early Carboniferous as NW-trendingthrust zones (Allen and Vincent 1997), parallel to theIrtysh and other major faults, within the outwardly-growing Altaid accretionary prism (Fig. 3). The EarlyCarboniferous lower greenschist facies rocks that hostore in the districts north of the Dalabute fault are part ofthe Tailegula Formation (Shen et al. 1996; Fan et al.1998), a series of coeval intercalated metasedimentaryand metavolcanic lithologies within part of the late Pa-leozoic accreted margin. Steeply-dipping, gold-bearingveins and adjacent auriferous alteration halos occuralong subsidiary faults to the two main faults, and thesestrike both northeast and in a more discordant NSdirection (Shen et al. 1996).

The more important orebodies of the Hatu district,forming the 1 Moz Au Qiqiu #1 deposit, are locatedalong the northern side of the Anqi shear zone, within aca. 330 Ma tholeiitic basalt. The complex osetting ofmany of the orebodies, including 7 km of post-Permianstrike-slip between the smaller metasedimentary rock-hosted Qiqiu #2 deposit and the Qiqiu #1 deposit(Fig. 7), indicates a signicant amount of post-ore de-formation (Shen et al. 1996). The large Akebasitaobatholith, an alkalic complex with contradictory UPbages of 256 Ma (Jin and Zhang 1993) and RbSr datesof 298285 Ma (Li et al. 1998), is located about 6 kmsouthwest of the district. In addition, mac and graniteporphyry dikes are widespread within the Hatu golddistrict, and it is uncertain as to whether these are es-sentially coeval with the alkalic complex and/or are partof the earlier (ca. 320300 Ma) Variscan calc-alkalineepisode of magmatism. Two such large, older calc-alkaline bodies, of granodiorite and quartz dioritecomposition, occur immediately north of the Hatu fault.

We interpret the occurrences in the Hatu district toclearly be structurally controlled orogenic gold deposits(e.g. Groves et al. 1998), although some workers havedescribed these as volcanic-related epithermal gold de-posits (e.g. Shen et al. 1996; Buckman 2001). Individualquartz veins are generally 100 m along strike and 0.55 m in width, but, locally, are as large as 380 m by 20 m.In the Qiqiu #1 deposit, the large gold resource is hostedin 27 quartz veins and altered metabasalt host rocks,with grades ranging between 5 and 10 g/t Au, althoughlocal pockets of much higher grade are common, typi-cally with abundant visible gold. Gold grains in the veinsin the hanging wall of the Anqi fault are variable in size,but may occur as particles more than 1 mm in diameterwithin the quartz. The deposit has been mined from the1,434-m level down to the 934-m level, with recovery ofabout 10,00015,000 oz/t Au per year and about250,000 oz mined to date. Gold:silver ratios are typically21:1, and As, Cu, Sb, and W enrichments are commonfor most ore zones (Fan et al. 1998). Pyrite and lesserarsenopyrite are the dominant sulde minerals withinand adjacent to the veins, with carbonate, sericite, andchlorite also common in altered wall rocks. The lowergrade (45 g/t Au) Qiqiu #2 deposit is not being mined

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Fig.6.Generalizedgeologicmapofthewestern

Junggarareashowingthelocationofthemostimportantlodegolddeposits,whichareconcentratedintheHatuSaertuohaibelt.The

areaandstructureswithinithavelikelybeenrotatedcounterclockwisefrompositionsoriginallywithintheAltayShan.GeneralizedafterChen

etal.(1985)

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and the carbonaceous, volcaniclastic metasedimentaryrock-hosted ores contain a total resource of 150,000 ozAu in the footwall of the Anqi fault. Rubidiumstron-tium dates on unspecied material from two quartz veinsin the Hatu district are 290288 Ma, suggesting thatveining was slightly younger than adjacent calc-alkalinemagmatism and perhaps simultaneous with the morealkalic episode.

A few dierences characterize some of the other golddeposits in the western Junngar area, although it is likelythat all ores are part of a single, generally coeval hy-drothermal episode. Many of the gold occurrences in theSaertuohai district (Fig. 7), about 60 km northeast ofthe Hatu district, occur in shears within NE- to NNE-striking macultramac ophiolitic slivers along thenorth side of the Dalabute fault. This reects a chemi-cally favorable trap for veining adjacent to a major rst-order structure and provides for a gold-forming scenariovery similar to that in the California Mother Lode dis-

tricts (Bohlke 1989). A talcmagnesitequartz alterationassemblage characterizes altered wall rocks within theSaertuohai district, with vein sulde phases dominatedby pyrite chalcopyrite.

In the Baogutu district, to the south of the Dalabutefault and 40 km southwest of Kelamayi (Fig. 5), tua-ceous conglomerate of the mid-Carboniferous BaogutuGroup hosts gold ores within a few kilometers of a seriesof small ca. 320300 Ma hypabyssal granodiorite stocks(Shen et al. 1996). Many veins cut hornfels zones sur-rounding the stocks, where relatively competent rockswere preferentially hydrofractured during uid owevents. The veins are characterized by common pyrite,arsenopyrite, and stibnite/berthierite. The occasionalpresence of native bismuth and native antimony is atypi-cal of orogenic type gold deposits, perhaps being indica-tive of an overprinting low-temperature post-ore event.The common occurrence of scoradite in many of themineralized outcrops is consistent with supergene events.

Fig. 7. Detailed geology of theHatuSaertuohai gold belt inwestern Junggar. Orogenic golddeposits, known since the1300s, are spatially associatedwith the HatuDalabute faultsystems. Geology generalizedfrom Shen et al. (1996), Allenand Vincent (1997), Chen(1997), Fan et al. (1998), andPirajno (unpublished eldnotes)

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Gold deposits of the eastern Junggar area

The eastern Junggar area (Fig. 8) is underlain by theeasternmost exposures of the Late Devonian to LateCarboniferous volcanic arc and volcanogenic deep ma-rine sedimentary rocks that also characterized much ofthe Altay Shan. Similar age rocks occur on both sides ofthe WNW-trending, N-dipping, 10- to 20-km-wide,Kelameili fault zone. The zone separates the so-calledSurgut unit to the north and JunggaroBalkhagh unit tothe south (Sengor et al. 1993). The fault itself probablyoriginally represented a thrusted suture between dierentPaleozoic blocks of the Altaid sequence, brought to-gether during the Late Carboniferous to Early Permian

closure of the Junggar Ocean (Carroll et al. 1995). Syn-to post-kinematic, felsic to intermediate granitoids arescattered on both sides of the fault, and chromite-bear-ing ultramac bodies occur along the fault zone. Thesebodies generally are poorly studied, although a variety ofgranitoids are characterized by KAr and RbSr datesranging between about 360 and 230 Ma (Chen 1997).Sinistral shear movement was dominant along the faultin the Late Permian, with associated extension leading toformation of the Junggar and Turpan basins.

Many small lode gold deposits, and a few placer golddeposits, stretch along mainly the northeastern side ofthe Kelameili fault for about 400 km (Fig. 8). Most ofthese are small (

Whereas none of these deposits have been dated, it isalmost certain that they are of late Paleozoic age, beingformed at about the same time as the larger gold de-posits to the northwest in the Altay Shan.

In the relative shallowly-exposed Early Carbonifer-ous andesite of the Batamayineishan Formation, about60 km southwest of the fault zone and along thenorthern side of the Bogda Shan, approximately150,000 oz Au are recognized at the Jinshangou deposit.In contrast to the deposits near the fault zone, Jin-shangou is a typical epithermal gold deposit locatedwithin a group of ve calderas distributed along theintersection of two regional fault systems. Commongangue phases include alunite, kaolinite, barite, anduorite, all typical of epithermal ores, as well as themore universally common quartz, albite, sericite, andcalcite.

In the same formation, near the Mongolian borderand 60 km northeast of the Kelameili fault zone, theDanjiadiSuangfengshan (or Twin Peaks) goldsilverprospect (Fig. 8) comprises 12 mineralized bodiesassociated with felsic to intermediate volcanic and sub-volcanic bodies. They are again hosted by caldera-related structures, are enriched in mercury and copper,and locally contain as much as 125 g/t Ag. The deposit,presently being mined, is associated with Carboniferousandesite and rhyolite near a contact with Permian basinll and along the margin of the Turpan basin. The low-suldation deposit is associated with volcanic domefeatures and it also is characterized by widespreadauriferous breccias (Wang et al. 2001).

Gold deposits of the Tian Shan

Most gold deposits recognized in the Tian Shan (Fig. 2)occur within the eastern Tian Shan (e.g. Xitan, Kang-gurtag, Yuanbaoshan, Dadonggou, and Xifengshan II),located to the south of the Turpan basin and in an aridbarren range termed the Chol Tagh, and have beensuggested to continue to the east into the JinwoziMazhuangshan gold district of adjacent Gansu prov-ince. This eastwest-trending Kanggurtag gold belt(Fig. 9), with epithermal deposits and replacement styledeposits, both probably of magmatic anities and EarlyPermian age, is located south of the North Tian Shanfault (also called Kanggur or TuokexunGuozigou faultin places) within rocks of the AqishanYamansu arc.The arc consists of volcanic rocks of the Early Carbo-niferous Aqishan and Yamansu Formations, and gray-wackes of the mid-Carboniferous Kushui Formation,which are separated by the generally poorly-denedYamansu (or Kushui) fault (existing data are toocontradictory to distinguish these three units on Fig. 9).The North Tian Shan fault separates this arc from thoseof the Kanggur arc to the north, and represents a LateCarboniferous to Early Permian suture (Ji et al. 1994).Ma et al. (1997) indicate thrusting within the arcsequence, during subduction from the north of the

Paleo-Tianshan Ocean, until the end of the Carbonifer-ous, which was followed by a translational regime alongrst-order faults in the Permian. Alternatively, this maysimply be the consequences of oblique TarimYili col-lision throughout the late Paleozoic (Chen et al. 1999).Either way, the deposits in the Kanggurtag gold beltmight be located along second-order faults representingdilational zones that were opened between the eastwest-trending, crustal scale North Tian Shan fault andKuluketag (also called the Middle Tian Shan,Shaquanzi, or South Kushui) fault. The latter is locatedabout 75 km to the south of the former, and separatesclastic units from volcanic units within the southernTian Shan province, which suggests it too is a likelyterrane boundary. To the north of the North Tian Shanfault, the recently discovered Tuwu and Yandong por-phyry copper deposits also contain a signicant goldresource.

Despite signicant gold resources in the Tian Shan tothe west of Xinjiang, numerous gold systems have notyet been recognized in the western Tian Shan of Xinjiangitself. The few important deposits discovered to dateinclude Wangfeng and Axi in the Yili block, andSawayaerdun in the southern Tian Shan province; noimportant deposits are recognized in the northern TianShan province. Although characterized by exceptionalrelief, the arid conditions in especially the eastern TianShan have hindered formation of major placer golddeposits. Only a few small placer deposits are located inhigh altitude streams near Wangfeng (e.g. Hongkeng,Tiangeer, and Houxia).

Eastern Tian Shan

Epithermal gold deposits

The Xitan (or Shiyingtan) deposit, which denes thewesternmost part of the Kanggurtag gold belt, is char-acterized by features common to many epithermal veindeposits. The ore is hosted in what is probably aPermian andesite, often brecciated, that overlies a morewidespread Carboniferous andesitic and dacitic volcanicarc terrane. A co-magmatic granite porphyry lies be-neath the host andesite and also outcrops 300 m to thesoutheast of the deposit. Although only 2 km south ofthe Yamansu ductile shear zone, the volcanic host rocksshow only brittle features and are unmetamorphosed.The gold veins occur along what is hypothesized as thenorthwestern margin of a large caldera with a well-de-veloped ring dike system (Pirajno et al. 1997). They werediscovered in 1989 during a regional geochemical survey.The total resource is about 200,000 oz Au, of whichabout 30,00035,000 oz have been recovered since 1993from 510 g/t rock and a large amount of the resource isawaiting processing in a large stockpile of 15 g/t ma-terial. Silver has also been recovered, but no other dataare available other than the fact that the ores average 1:1

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Ag:Au. Mining was originally by open pit and is nowunderground.

Eighteen quartz veins have been identied on thesurface and four of these are being mined (#1, 3, 4, and5). The largest vein (#3) averages 20 m in width, is 150-m-long and continues for 100-m-down-dip. The gold-bearing veins consist of cryptocrystalline and chalce-donic quartz, miarolitic uorite, and platy calcite, arecommonly crustiform, and contain low salinity, aqueousuid inclusions that mainly homogenize between150200 C (Feng et al. 2000). Metallic phases are veryrare with pyrite being the most common sulde mineraland comprising much less than 1% of the gold-bearingveins. It appears more common in the altered andesitethan within the veins themselves. Trace amounts ofarsenopyrite, chalcopyrite, copper oxides, and silversulfosalts and selenides are also recognized in the veins.Alteration around the veinlets is zoned from an area of

silicachloritepyrophyllite, through an area of pyritesericite, and to an outer aureole of chloritecarbonate.Gold grades are highest where local structures intersectand where the Permian(?) andesite is highly brecciated.In the #3 vein at Xitan, gold grades progressivelydecrease from 10 g/t near the surface to 6 g/t at about100 m depth.

Many of the features of the hydrothermal system ledPirajno et al. (1997) to rst classify it as a high-sulda-tion epithermal system. Published absolute dates areimprecise, with reported UPb and RbSr dates on ex-trusive rocks and tonalite at the Xitan deposit rangingbetween 293 and 234 Ma, and RbSr isochron ages forbreccias and veinlets spread between 288 and 244 Ma(Li et al. 1998). Measured d18O quartz values rangingbetween 4.7 and -8.5 per mil (Feng et al. 2000) areconsistent with a predominantly meteoric water com-ponent to the ore-forming uids.

Fig. 9. Geology and distribu-tion of epithermal and orogenicgold deposits within the Kang-gurtag gold belt, eastern TianShan. The Xitan epithermaldeposit, and Kanggurtag,Matoutan, Yuanbaoshan, andDadonggou replacement(?)deposits are hosted by a com-plexly mixed group ofCarboniferous marine sedimen-tary and volcanic rocks. Figuregeneralized from Pirajno et al.(1997)

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Granitoid-related(?) FeCuAu replacement deposits

Other important gold deposits in the Kanggurtag goldbelt appear to be more deeply-formed iron- and copper-rich, perhaps granitoid-related gold deposits that appearmainly as massive replacement bodies in the low meta-morphic grade (probably prehnitepumpellyite) EarlyCarboniferous volcaniclastic rocks of the YamansuFormation. The best studied of these is the Kanggurtagdeposit (also called the Kangguer or #6 Kanggurtagdeposit; Fig. 10), located about 60 km east of Xitan,which has an approximate 300,000 oz Au resource,about half of which has been mined to date. The depositwas discovered in 1989 during regional mapping andgeochemical studies. Pirajno et al. (1997) suggest thatreported sulde zoning at the deposit is consistent with alow suldation epithermal deposit, although much of themineralization style appears like that of a deeper, man-to-type deposit. The Matoutan deposit (also called the#8 Kanggurtag deposit or perhaps the Yaobashan de-posit), located 5 km east of the Kanggurtag deposit, hassimilar looking FeCuAu-rich ore and the mining op-eration appears to be more than double that in size ofKanggurtag. Access to the Matoutan deposit, as well therelease of any geologic and resource data, has beenlimited by the local community at the mine site. How-ever, it is likely that the combined resource of the twodeposits, which are probably part of one large mineral-izing system, exceeds 1 Moz Au.

The Kanggurtag deposit occurs as a series of occur-rences within a 10 5-km area both along and south ofthe Yamansu fault. The mineralized zones are about5 km southeast of a large Variscan tonalite stock, and anumber of small granite dikes are reported within 1 kmof many of the ore zones. Most of the ore at the Kang-gurtag deposit is localized along three, NE- to E-striking,steeply N-dipping ductile shear zones within this area.The largest single zone of continuous mineralizationwithin the volcanic and subvolcanic rocks of the AqishanFormation is about 200 m along strike, averages 2 m inwidth, and continues down-dip for >400 m. An un-mineralized 15-m-wide brittleductile shear zone runsalong the length of the footwall of the mineralized zone.

Termed the #2 orebody, the large ore zone exhibits areplacement style mineralization that contains most ofthe gold resource. The ore consists of massive pyrite,chalcopyrite, and magnetite, with lesser sphalerite, ga-lena, silver sulfosalts, and barite. Hypogene gypsum isalso present. Gold:silver ratios average 1:5, and the oreis zoned from gold-rich near the top (1,100-m level) tomore copper-rich at depth (600-m level). Highest goldgrades often correlate with the volume of magnetite, andaverage gold grades decrease from about 9 g/t at thenear surface to 56 g/t at depths of 200 m. Locally,metal concentrations reach 5% Pb, 10% Cu, and 10%Zn. A ve-stage paragenesis stresses three early stages ofgold, pyrite, and magnetite, followed by barren basemetal and carbonate-rich hydrothermal events (Ji et al.1994; Li et al. 1998).

Quartz veins at Kanggurtag dened a much smallerpart of the resource, occurring in a discontinuous belt forabout 1 km in length, 500 m north of the #2 orebody.Termed the #1 orebody, the quartz vein-hosted ore wasmined out in 1995. The low-suldation epithermalquartz veins contain chlorite, sericite, carbonate, andbarite gangue, with pyrite and arsenopyrite as the mainsulde mineral phases (i.e., 525% of the vein volume).

The area surrounding the Kanggurtag and Matoutandeposits appears highly prospective for the discovery ofadditional lode gold deposits. Weathered fragments ofquartz vein material are scattered over an area of per-haps 20 by 2 km, from just west of Kanggurtag to alarge saline lake east of Matoutan. Much of the quartzlooks barren of metals, is often chalcedonic or waxy, butnonetheless indicates the presence of an extensive hy-drothermal system. Late Paleozoic marble outcrops inthe eastern part of the area and suggests an additionalpotential for FeCuAu skarn deposits.

Numerous RbSr dates bracket volcanoclastic hostrock deposition to between ca. 300 and 280 Ma, and aUPb date on the nearby tonalite is 275 Ma (Li et al.1998). The RbSr method was also used to suggest thatore formation occurred near the end of this magmaticepisode and/or some 2030 million years later duringLate Permian (Li et al. 1998). Stable isotope measure-ments range between 11.3 and 17.7 per mil for d18O ofore-bearing quartz (stages not specied), 53 to 61 permil for dD of uid inclusion waters in the quartz, and0.9 to +3.3 per mil for d34S of suldes from the veins.These data can not distinguish between a magmatic ormetamorphic uid and sulfur source, but they do pro-vide little support for signicant meteoric water withinthe hydrothermal systems at Kanggurtag.

Along the same shear system and 25 km east of theKanggurtag deposit, the Dadonggou occurrence (Fig. 9)was discovered about 10 years ago. The geological set-ting and host rocks are the same as at Kanggurtag, butthe strike of the shear system is NWW at the Dadong-gou occurrence. Granodiorite and plagiogranite dykes,as long as 3 km and as wide as 100 m, parallel the mainYamansu fault and the auriferous shear system. Synki-nematic, concordant quartz veins are widespread, com-monly 10- to 20-m-long and 20- to 30-cm-wide, but theyare barren. A later stage of slightly discordant quartz K-feldspar and albite veins, contains 510% suldeminerals, dominantly pyrite, and averages about 12 g/tAu.

The Kanggurtag gold belt is often shown to continuefar to the east along the Tian Shan, where a monzog-ranite pluton hosts the Xifengshan II gold occurrence.The relatively undeformed quartz veins contain gold,pyrite, and chalcopyrite. Li et al. (1998) claim a RbSrage of 284 Ma for the host granitoid and 272 Ma age formineralization (RbSr on uid inclusions in quartz)at the Xifengshan II occurrence. If reliable, these datasuggest a relatively consistent Permian age forgold deposition across the eastern Tian Shan withinXinjiang.

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Fig. 10. Local geology of theKanggurtag gold deposit, east-ern Tian Shan, in a plan viewand b cross section. Althoughshowing many characteristics ofan orogenic gold deposit,reported downward zoningfrom Au-, to AuCu-, and thento PbZn-rich veins is moreconsistent with many epither-mal deposits

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The deposits along the western edge of adjacentGansu province, including the Jinwozi (or Gold Nest;Fig. 2) and 210 deposits, are often also described as apart of the Kanggurtag gold belt (e.g. Pirajno et al.1997). However, these gold deposits are hosted byDevonian metasedimentary rocks and Permo-Triassicplutons of the Bei Shan, located to the east of theRuoqiangXingxingxia fault, which marks the eastern-most edge of the Tian Shan. The plutons, which are cutby widespread gold-bearing quartz veins, have Pb zircondates as young as 241 Ma (Ji et al. 1994; Ji and Xue1996), requiring veining to be post-Permian. The BeiShan is likely a part of the Qilian Shan, which was right-laterally oset sometime in the Mesozoic and/or Ceno-zoic (Zhou and Graham 1996). Gold deposits within thewesternmost part of the Qilian Shan are Triassic in age(Mao et al. 2000), and we suggest that these deposits inthe Bei Shan may be an oset part of this gold provinceand unrelated to ores of the Kanggurtag gold belt.

Gold-bearing porphyry deposits

A series of porphyry copper deposits, some gold-bear-ing, were discovered in 1993 during regional mapping inthe northeastern Tian Shan and are located about 80 kmsouthwest of the town of Hami (Fig. 2). They are pres-ently being drilled and studied by the No. 1 GeologicalTeam of the Xinjiang Bureau of Geology and MineralResources. The deposits are located about 13 km northof the North Tian Shan (or Kanggur fault) and arehosted by intrusions into the Early to mid-Carbonifer-ous intermediate to mac volcaniclastic rocks of theKanggur arc. The No. 1 Geological Team reports theintrusive rocks to be of Permian age, whereas a con-icting RbSr whole rock date of 370 Ma on the Tuwudeposit host intrusion (Rui, unpublished data) wouldsuggest the country rocks must also be older than theiroften accepted Carboniferous age. The most reliable ageestimate is probably a new ReOs isochron date of322.72.5 Ma for seven molybdenite samples from thedeposit (Du et al. 2001).

Initial reports by the No. 1 Geological Team indicatethat the Tuwu porphyry deposit contains about 3 mil-lion tons of copper at a cuto grade of 0.2% Cu. Inaddition, the deposit is estimated to contain 3 millionozof Au at an average grade of 0.16 g/t, and also sig-nicant amounts of silver. Stockwork-hosted and dis-seminated sulde minerals, in the porphyritic andgranod- ioritic host intrusion, are mainly pyrite andchalcopyrite, with lesser bornite. Biotite is closely asso-ciated with the main ore zones, but K-feldspar is absent.Surrounding alteration zones are dominated by massivesilicication, outward to a quartzsericite zone, thensericitekaolinite, and nally an epidote-rich outer halo.Other deposits in this porphyry copper belt, includingChihu, Tuwu East, Yandong, and Linglong, are evenless well-studied. Gold grades of 0.11 g/t are reportedfor Yandong, where chalcopyritemagnetitebiotite-rich

ore zones are hosted by a subvolcanic diorite. Smallepithermal gold veins are also reported to be widespreadthroughout this region of the eastern Tian Shan.

Western Tian Shan

Orogenic gold deposits

The Wangfeng deposit (Fig. 2), and adjacent smallerprospects (e.g. Saridala, Nalongxiaer, and Babagesayi),are located slightly more than 100 km southwest of thecity of Urumqi. These small orogenic gold occurrencesare restricted to the NW-striking Bingdaban orShenglidaban mylonitized shear zone, which separatesProterozoic to Ordovician, and perhaps Silurian,orthogneiss, schist, and marble from mainly EarlyCarboniferous granitoids, within the northern part ofthe Yili block (or central Tian Shan). The shear zoneparallels, and is only 35 km south of, the deep-crustalNorth Tian Shan fault zone (locally called theHongwuyueqiao fault) and thus may be a related strandof this major suture zone.

The Wangfeng deposit was discovered in 1988 andmining began in 1998 on two of nineteen recognizedorebodies, each comprised of numerous quartz veins andveinlets in the hanging wall of the Bingdaban fault.Presently, an 80,000 oz Au resource is being mined fromthe northwest-striking and near vertical #12 ore zone.The zone consists of two distinct and parallel, 0.6- to0.8-m-wide and 1,300-m-long orebodies that are about10 m apart. To date, less than 1,000 oz Au have beenrecovered. The orebodies appear as silicied, ductileshear zones, with typically 12% pyrite and pyrrhotite(?)in the gold-bearing veinlets. Although the average goldgrade is 5 g/t, there is a strong zonation from 18 g/t nearthe top of #12 down to 1.4 g/t at the lowest levels of theorebodies.

Dates on the intrusive host rocks range from a UPbzircon date on biotite granite of 437 Ma to a RbSr dateof 310 Ma on mylonitized plagiogranite, whereas a RbSr date on unspecied material (uid inclusion waters?)from an auriferous vein was calculated at 277 Ma (Li etal. 1998). The questionable date on the ore materialwould suggest a roughly similar time to gold mineral-ization in the eastern Tian Shan. The signicance of thehost rock dates are uncertain; they might reect a broadSilurian through Permian magmatic evolution in thecentral Tian Shan, as suggested by Allen et al. (1992).Geochemical studies (Chen et al. 2000) suggest miner-alization may have formed at

southeast-trending brittleductile shear zone, which isexposed over a length of almost 2 km and a width of300 m in the mine area. The auriferous quartz containsminor pyrite, with common sericite and ankerite inore-hosting, altered Late Silurian to Early Devonianmetamorphosed clastic rocks. Average grades fromvarious orebodies range between 13 g/t Au, but locallyreach multiple ounces. No important intrusions arelocated in the vicinity of the Dashankou deposit,although Variscan bodies are recognized regionally(Jingwen Mao 2001, personal communication).

The Sawayaerdun gold deposit (Fig. 11), along theChinaKyrgyzstan border, is the largest recognizedorogenic gold deposit in Xinjiang, with >3 Moz of goldand a geologically inferred resource of at least 10 MozAu. This deposit within the eastern Kokshaal area of thesouthern Tian Shan province is hosted by Late Silurianslates and carbonaceous phyllites. The mid-Paleozoicrocks are part of a complex sequence of allochthonousslices, with thrusting having occurred during Variscancollisions (Biske and Shilov 1998).

Gold mineralization at Sawayaerdun is localizedover a 70-km-long by 50- to 600-m-wide zone betweentwo regional faults, perhaps sutures between a series ofaccreted oceanic terranes. In this belt of highly tect-onized metasedimentary rock, economic gold grades of35 g/t most commonly occur as widespread dissemi-nations. Quartz, sericite, siderite, calcite, and chloriteare commonly associated with the gold. Pyrite, pyr-rhotite, and arsenopyrite are the main ore-associatedsuldes, with less common stibnite, chalcopyrite, gale-na, sphalerite, and marcasite. Except for a few smallmac dikes, no igneous rocks have been recognized inthis gold-rich zone. Fluid inclusions mainly homogenizeat two modes of 155220 and 260290 C, and containabundant CO2 and signicant CH4 and N2 (Ye et al.1999). Fluid inclusion waters from ore-related gangueat the Sawayaerdun deposit have dD values of 59 to84 per mil, and d34S data for sulde minerals rangebetween about 3 and +1 per mil. Many of thesefeatures, including a probable Permo-Triassic age offormation, led Ye et al. (1999) to suggest that thedeposit is very similar to the immense Muruntaudeposit, located farther to the west in the southern TianShan province.

On the Kyrgyzstan side of the border, where a con-tinuation of the ores bodies within Early and MiddleDevonian phyllite is known as the Savoyardy deposit,there is a zoning of mineralized veins (United Nations1998). A central zone of arsenopyrite-rich quartz veinsgrades 6.5 g/t Au and is reported to also contain about10% Pb. Surrounding polymetallic veins average 4.5%Sb, 4.5% Pb, and 41.5 g/t Ag. This suggests a district-wide metallogeny similar to that in areas such as CoeurdAlene (Idaho, USA), Keno Hill (Yukon, Canada), andCobar (NSW, Australia), where adjacent gold- and base-metal-rich epigenetic veins may reect metal leachingfrom a variety of geochemically-distinct metasedimen-tary units.

A few hundred kilometers northeast of the Sawy-aerdun deposit, the Bulong deposit is hosted by LateDevonian clastic rocks. A series of parallel quartz veinscontains gold in minor pyrite, with associated chlorite,sericite, and carbonate minerals in altered wall rock.Mining of these veins began in the mid-1990s. Late-stage, barren quartzbarite veins are also extensivewithin the Bulong deposit. Fluid inclusions from thegold-bearing quartz are CO2-rich (Jingwen Mao 2001,personal communication).

Epithermal gold deposits

The 1.6 Moz Au Axi deposit is the most importantepithermal gold deposit in Xinjiang. It is located about80 km north of Yining and less than 100 km from theKazakhstan border (Fig. 2). The deposit was discoveredduring regional mapping in 1988 and has producedabout 250,000 oz Au and an unspecied amount of sil-ver since mining began in 1995. Mining is presently byopen pit, but future underground development is plan-ned. The Axi deposit occurs in an Early Carboniferousvolcanic eld that is located in the cover sequence to theYili block, which is dominated by Proterozoic carbonatesequences and OrdovicianSilurian clastic and carbon-ate rocks. The closest known Variscan granitoid to Axi

Fig. 11. Local geology of the still poorly studied Sawyaerdundeposit near the ChinaKyrgyzstan border. A geologically inferredresource of >10 Moz Au occurs in quartz veins hosted by LateSilurian slates and carbonaceous phyllites

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is 15 km to the northeast, although rare synvolcanicdikes occur in the deposit area. Many other small goldand leadzinc vein occurrences are also associated withthe volcanic system, although only the small Tawobiekedeposit is also being mined.

The Axi deposit is hosted by Early Carboniferousporphyritic andesite of the Dahalajunshan Formation(Fig. 12) to the south of the North Tian Shan fault.These host rocks represent part of the late Paleozoic arcsuperimposed on the Precambrian Yili block duringcollision of the Kunggar arc (or North Tian Shan arc)from the north (Gao et al. 1998). Volcanic pipe-likefeatures are associated with NW- to N-trending base-ment faults (Wang and Wang 1995). Liu et al. (1996)indicate an association of the Axi deposit with volcanicring structures. The deposit is divided into a northernand southern part, each of which is about 500-m-long.The auriferous quartz in the northern part is commonlychalcedonic, sinter-like, and laminated, often showing avariety of colors among the laminations that reectsignicant dierences in trace element chemistry. Muchof the northern orebody is jasperoidal and there is somebrecciation. The quartz and metals were likely precipi-tated at very shallow levels and, in part, in a hot springs

environment. The nearby Yiermand gold occurrence isalso suggested to have formed in a hot springs envi-ronment within rocks of the Dahalajunshan Formation(Zhai et al. 1999). The southern orebody at Axi is morediuse, with extensive silicication and stockworking,rather than discreet veins. Brecciation is much moreextensive.

Fine-grained pyrite is the most common suldemineral in the Axi deposit. Arsenopyrite and scoraditeare also common minor constituents of the ores. Liuet al. (1996) also note the occurrence of rare, ne-grained tetrahedrite, chalcopyrite, and galena, and seri-cite, siderite, and calcite, along with silica, are the maingangue phases. Propylitic, argillic, and phyllic alterationzones surround the orebodies. The deposit averages5.7 g/t Au, with slightly higher grades in the north partand local concentrations of 150 g/t Au, and exhibits aAu:Ag ratio of 1:2. Ore uids were low salinity and oreformation temperatures between 135 and 200 C (Liuet al. 1996).

An auriferous basal conglomerate at the Axi deposit(Fig. 12) occurs in the overlying, late Early to mid-Carboniferous intertidal sedimentary rocks of the Aq-alhe Formation (Liu et al. 1996). This may representaccumulations of gold eroded from older epithermalquartz veins at Axi, although the intertidal environmentis an unlikely setting for such a conglomerate. Perhaps,however, this is some type of coastal-margin, wave-formed bar or channel-ll accumulation.

The age of mineralization at Axi is unclear. Li et al.(1998) report a series of RbSr and 40Ar/39Ar dates on

Fig. 12. a Local geology map and b cross section of the Axiepithermal gold deposit. The epithermal veins are hosted alongfaults in volcanic breccia within the Early Carboniferous Dahala-junshan Formation. Additional gold resources are contained in anoverlying auriferous conglomerate of the Aqalhe Formation.Figure generalized from Liu et al. (1996)

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quartz veins that range between 344 and 301 Ma. Theoldest date agrees well with the hypothesized geneticassociation between Early Carboniferous volcanism andepithermal gold deposition. The Late Carboniferousdates are younger than the volcanic rock host sequences,but are not inconsistent with other magmatism in thispart of the Yili block that continued until the end of theCarboniferous (Gao et al. 1998; Li et al. 1998).

Gold deposits of the Kunlun Shan

The Kunlun Shan, along the southern margin of theTarim basin, have relatively little recognized gold re-sources. However, small paleo-terrace and bench typeplacer gold deposits are scattered along the northernfoothills of the Kunlun Shan for more than 1,000 km.These occurrences extend from Hetian in the west,across all Xinjiang, and into Qinghai province in theeast. In addition, broad areas with extremely anomalousgold values in stream sediments have been identiedthroughout the western Kunlun Shan (Minco Miningand Metals Corp News Release, 21 May 1997).

The source for much of this gold is the high peaks ofthe Kunlun Shan, reaching 6,2007,600 m in Xinjiang,where dicult access has prevented signicant explora-tion for lode sources. Because much of this remotecountry is covered by extensive ice and snow, nding thesources for the anomalies and placer accumulations willcontinue to be dicult. It is likely, however, that sourcelodes are orogenic gold deposits located in the upliftedysch of the Tianshuihai terrane. These deposits theo-retically could have formed during hydrothermal eventsthat would have occurred during Late Triassic to EarlyJurassic (i.e. Indosinian time), greenschist facies meta-morphism and magmatism within the metasedimentaryrocks as they collided with the Precambrian TarimQaidamKunlun nucleus. The small Wulonggou, Tanj-ianshan, Qinglonggou, Kaihuangbei, Dongdatan, andDachang orogenic gold occurrences in the easternKunlun Shan (Yu et al. 1998; Cui et al. 2000), where therange extends into adjacent Qinghai province, are likelya part of the belt that has contributed to the placers.Orebodies at the Wulonggou deposit cut granitoids asyoung as early Mesozoic (Yu et al. 1999) and, therefore,provide support for a post-Paleozoic origin for lode golddeposits in the Kunlun Shan. Absolute dates of ca. 160200 Ma, using RbSr and KAr methods on ore-relatedminerals, conrm a Jurassic timing (Qian et al. 2000;Wang and Hu 2000).

Synthesis of gold metallogeny of Xinjiang

The mountain ranges of Xinjiang are favorable for theoccurrence of Variscan (late Paleozoic) or Indosinian(early Mesozoic) gold-bearing orogenic, epithermal, re-placement and VMS deposits. The former gold deposittype may be associated with economic placer accumu-

lations, especially in the northernmost Altay Shan andthe northern foothills to the Kunlun Shan. Good de-posit-scale maps of the deposits and main districts arenotably lacking. Almost no well-documented ore depositstudies exist in the western literature that describe indi-vidual deposits over this vast part of China. There is afair amount of geochronology, uid inclusion microth-ermometry, and stable isotope studies within the Chi-nese literature, but the general contradictory nature ofmuch of the data make these dicult to evaluate. Nev-ertheless, combining (1) preliminary eld examination ofsome of these deposits by some of us, (2) the publishedcharacteristics of many of the deposits as described inthe Chinese literature, and (3) our evaluation of thespatial distribution of the gold resources, allows for abetter understanding of the gold resources in Xinjiang.

Late Paleozoic terrane accretion and collisional oro-genesis of early to mid-Paleozoic marine sequencesbetween Precambrian blocks provided a tectonic envi-ronment highly favorable for the formation of orogeniclode gold deposits. Growth of the Altaid complexthroughout the Paleozoic included formation of oro-genic gold deposits that young to the southwest within agrowing continental margin. Latest hydrothermal eventsof the orogen led to the development of gold vein sys-tems in the Early Carboniferous(?), and perhaps earliertimes in northernmost Xinjiang, and in the southern-most part of the Altay Shan and adjacent areas nowsurrounding the Junggar basin in the Late Carbonifer-ous and Early Permian. Overlapping the nal stages ofAltaid orogenesis, and likely elsewhere along the samenorthern Paleo-Tethys Ocean continental margin,Permian translation of terranes accreted in the mid-Paleozoic was also associated with localized orogenicgold-vein formation in the southern Tian Shan. Therestriction of orogenic gold deposits in the Chinese TianShan to the Sawyaerdun deposit and the area south ofUrumqi may reect the predominance of unfavorableshallow crustal rocks in the eastern Tian Shan and thelimited exploration in the rugged alpine country of thewestern part of the mountain range. The occurrence ofthe Kumtor deposit in the latter, very close to theXinjiang border, further identies this as an area that isextremely permissive for the discovery of importantorogenic gold deposits. Continued collisions in the earlyMesozoic, to the south of the Tarim basin, led todevelopment of the youngest gold lodes in Xinjiang,localized in the mainly inaccessible high elevations of theKunlun Shan.

The recognition of epithermal gold deposits as old asPaleozoic and within areas of extensive regional uplift isexceptional and of great scientic and economic interest.These include small epithermal deposits in the southernAltay Shan, the Early Carboniferous Axi deposit in thecentral Tian Shan, the Early(?) Permian Xitan deposit inthe southern Tian Shan, and Early Carboniferous (?)Jinshangou deposit in the East Junggar area. Whereasmany deeper types of gold deposits are cla

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