0361-0128/01/3319/125-21 $6.00 125

The Himalayan Yulong Porphyry Copper Belt: Product of Large-Scale Strike-Slip Faulting in Eastern Tibet

HOU ZENGQIAN,†

Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, China 100037

MA HONGWEN,China University of Geosciences, Beijing, China 100082

KHIN ZAW,Centre for Ore Deposit Research, University of Tasmania, Private Bag 79, Hobart, Tasmania, Australia 7001

ZHANG YUQUAN,Guanzhou Institute of Geochemistry, Chinese Academy of Sciences, Guanzhou, China 510640

WANG MINGJIE, WANG ZENG, PAN GUITANG,Chengdu Institute of Geology and Mineral Resources, Chengdu, China

AND TANG RENLI

Xizang Bureau of Geology and Mineral Resources, Lahsa, China

AbstractThe Yulong porphyry copper belt is the most significant porphyry copper belt in Tibet and is located in the

Qiangtang terrane of the Himalayan-Tibetan orogen. The terrane is a collage of continental blocks joined byophiolitic sutures and volcano-plutonic arc complexes. The Yulong belt is approximately 300 km long and 15 to30 km wide, contains one giant, two large, and two medium- to small-sized porphyry copper deposits, and morethan 20 mineralized porphyry bodies. The Yulong belt is located in the Changdu continental block that com-prises Proterozoic to early Paleozoic crystalline folded basement and middle to late Paleozoic platform faciescarbonate and clastic sedimentary rocks similar to the Yangtze continent. The porphyry belt is closely associ-ated with Tertiary potassic volcanic rocks and alkali-rich intrusions in the area and controlled by north-south–north-northwest, large-scale, strike-slip faults, which are perpendicular to the collision zone between theIndian and Asian continents. Isotopic age determinations of the ore-bearing porphyries indicate that the mag-matism occurred over at least three stages, peaking around 52, 41, and 33 Ma, respectively. The timing of mid-dle and late shallow-level emplacement of these magmas is consistent with the ages of associated potassic vol-canism and alkali-rich magmatism in the area. Although the porphyry deposits in the Yulong belt weredeveloped in the intracontinental convergent environment, their mineralization styles and features are compa-rable to porphyry copper deposits in arc environments.

Compared to ore-bearing calc-alkaline porphyries in island arcs or continental margin arcs, the porphyriticintrusions in the Yulong belt are characterized by high K2O contents and enrichment in Rb and Ba, suggestinga shoshonitic magmatic affinity. Strong negative anomalies for Nb, Ta, P, and Ti and positive anomalies for Rb,Ba, Th, and LREE, normalized by chondrite, are characteristic of arc magmas. These intrusions yield a narrow143Nd/144Nd range varying from 0.51243 to 0.51253 and 87Sr/86Sr values from 0.7065 to 0.7077, which are tran-sitional between type II enriched mantle and mid-ocean ridge basalt (MORB) values and closer to the formerin terms of εNd-εSr. This suggests that the porphyritic magmas were derived either from a hydrous-enrichedmantle metasomatized by components such as H2O, K, Rb, Ba, Th, and LREE or by melt derived from thesubducted oceanic slab of the Paleozoic Jinshajiang oceanic plate. The hypothesis is supported by Pb isotopedata for the intrusions.

Large-scale strike-slip faults in eastern Tibet, which accommodated the compressive strains produced by theAsian-Indian continent collision, also localized the porphyry Cu mineralization. North to north-northeast–di-rected convergence and collision produced a dextral strike-slip fault system around 60 to 70 Ma. Northeast-di-rected wedging of the Indian continent and subsequent collision with the Yangtze continent during the Pale-ocene-Eocene produced conjugate strike-slip fault zones. The transition from a dextral strike-slip fault systemto conjugate strike-slip zones resulted in stress relaxation and formation of strike-slip pull-apart basins. Crustal-scale strike-slip faulting may have caused upwelling and partial melting of the hydrous-enriched mantle by de-compression and facilitated the rise of a large volume of volatile-enriched porphyry magma that had pondednear the base of the lithosphere during this period.

Economic GeologyVol. 98, 2003, pp. 125–145

† Corresponding author: e-mail, hzq@cags.cn.net

IntroductionSINCE SILLITOE (1972) and Mitchell (1973) published theirsignificant works, a widely accepted structural model forporphyry copper deposits has been developed, i.e., porphyrycopper deposits occur in island arcs and continent marginarcs along convergent plate boundaries. This model hasbeen verified by studies of a large number of porphyry cop-per deposits discovered in circum-Pacific metallogenic beltsin the last few decades (e.g., Griffiths and Godwin, 1983;Sillitoe and Camus, 1991; Camus et al., 1996; Camus andDilles, 2001). However, not all porphyry copper depositsoccur in subduction orogenic environments. They also occurin continent-collision orogenic belts and in continentaltransform fault zones (Bowen and Gunatilaka, 1977). De-posits in these latter environments are less well recognizedand understood compared to those in the subduction-re-lated orogenic environments.

The Yulong porphyry copper belt is the most economicallysignificant porphyry copper belt in the region. It is up to 300km in length and 15 to 30 km wide and hosts one giant de-posit, two large deposits, and two medium-sized deposits, inaddition to dozens of mineralized porphyry bodies. Althoughmuch research has been conducted on the belt (e.g., Zhou,1980; Li et al., 1981; Ma, 1983, 1984, 1990; Rui et al., 1984;Liu et al., 1993; Wang et al., 1995), there are divergent viewsregarding the geodynamic setting and tectonic environmentof the deposits. Ma (1990) and Rui et al. (1984) argued thatthe Yulong porphyry copper deposit was formed in an island-arc environment analogous to the Andean porphyry copperdeposits. Chen and Liao (1983) and Wang et al. (1995) con-sidered that the Yulong deposit occurred in an intracontinen-tal environment and is related to a strike-slip fault zone. Newevidence in this paper indicates that the Yulong porphyrycopper belt was formed during tectonism associated with theHimalayan-Tibetan collisional orogeny. A compilation of newand previously published age data shows that ore-bearingporphyries were not emplaced in a Permian continental mar-gin arc environment. Rather, they were developed in a Ter-tiary intracontinental convergent environment related to thecollision and uplift of the Tibetan plateau. This paper de-scribes the regional geologic setting of the belt and discussesthe ore-forming environment and possible structural controlson the porphyry copper belt, based on the latest observationsin the Tibetan plateau and adjacent areas.

Regional Geology

Tectonic setting

The Yulong porphyry copper belt is located in the Qiangtangterrane of the Himalayan-Tibetan orogen (Fig. 1; Chang andZheng, 1973; Allegre et al., 1984; Sengor and Natalin, 1996;Yin and Harrison, 2000). The tectonic evolution of the Qiang-tang terrane is important for understanding the genesis of theore-bearing porphyry intrusions and the tectonic constraintson the porphyry copper belt and is described briefly below.

The Qiangtang terrane is bound by the Jinshajiang andBangonghu-Nujiang sutures (Fig. 1) and extends northwardfor several hundreds of kilometers to the Karakunlun Moun-tains. The western segment of the terrane is characterized by

development of high-pressure metamorphic rocks and con-tains late Paleozoic marine strata, whereas the eastern seg-ment contains Triassic-Jurassic shallow-marine carbonate andarc volcano-sedimentary sequences (Liu, 1988). In easternTibet the Qiangtang terrane comprises the Changdu-Simaocontinental block and two volcano-plutonic arcs (JWA =Jiangda-Weixi arc; ZJA = Zugong-Jinghong arc; Fig. 2a). Theterrane is bounded by two Paleozoic sutures (Fig. 2a; Liu etal., 1993; Mo et al., 1993; Hou et al., 1999). The Changdu-Simao continental block consists of a folded crystalline base-ment of Proterozoic and lower Paleozoic age. The Proterozoiccrystalline basement is 2,000 to 5,000 m thick and composedpredominately of lower amphibolite facies (1594–2200 Ma)and upper greenschist facies metamorphic rocks (876–999Ma; Wang et al., 2000). The lower Paleozoic folded basementconsists of Middle to Lower Ordovician rocks, mainly low-grade, flyschoid metamorphic sandy slate and carbonates.Devonian to Permian cover rocks are widespread in the studyarea and contain a 3,000-m-thick suite of platform transitionalfacies carbonate and clastic sedimentary rocks. On the east-ern side of the continental block, the Permian Jiangda-Weixiarc, a volcano-sedimentary sequence related to the Jinsha-jiang suture (Liu et al., 1993; Mo et al., 1993; Li et al., 1999),is unconformably covered by an Upper Triassic flyschoidcomplex and is locally overthrust onto folded crystalline base-ment. On the western side of the continental block, the Per-mian Zuogong-Jinghong arc volcanic sequence, which is aproduct of eastward subduction of the Lancangjiang oceanicslab (Liu et al., 1993; Mo et al., 1993), is covered by a 3,000-m-thick sequence of basal molasses-type clastic rocks, plat-form facies carbonate rocks, and coal-bearing sedimentaryrocks (Wang et al., 2000).

The Lhasa terrane, to the west of Qiangtang, is bounded bythe Bangonghu-Nujiang suture (Fig. 1; Chang and Zheng,1973; Allegere et al., 1984; Dewey, 1988; Pierce and Mei,1988). This terrane has been shortened about 180 km by theIndia-Asia collision since about 70 Ma (Murphy et al., 1997;Yin and Harrison, 2000). The Gangdese volcano-magmaticarc, consisting of late Paleocene and early Eocene calc-alka-line volcanic rocks and Cretaceous and early Tertiary granitebatholiths, was developed along the southern margin of theterrane (Fig. 1). The Songpan-Ganze-Hoh Xil terrane, to thenorth of Qiangtang, is characterized by a Triassic marine sed-imentary sequence that is over 3,000 m in thickness andcrosscut by numerous thrusts (Fig. 1; Rao et al., 1987; Burch-fiel et al., 1995). The Late Triassic Yidun arc, to the east ofQiangtang, a product of westward subduction of the Paleo-zoic Garze-Litang oceanic slab (Hou, 1993; Hou et al., 1995,2001), developed in the southern end of the terrane (Fig. 1).

The Songpan-Ganze-Hoh Xil terrane, to the north ofQiangtang, is characterized by a Triassic marine sedimentarysequence that is over 3,000 m in thickness and crosscut by nu-merous thrusts (Fig. 1; Rao et al., 1987; Burchfiel et al.,1995). In the southern end of the terrane, the Late TriassicYidun arc, a product of westward subduction of the PaleozoicSongpan-Garze-Litang oceanic slab, was developed (Hou,1993; Hou et al., 1995, 2001). Owing to Indian-Asian conti-nent collision since the Paleocene, the terrane was subductedsouthward underneath the Qiangtang terrane (Yin and Harri-son, 2000), along the Jinsha suture, which was formed by

126 HOU ET AL.

0361-0128/98/000/000-00 $6.00 126

southwestward subduction of the Paleozoic Jinshajiangoceanic plate during the Permian period (Liu et al., 1993).

Structural geology

Since 70 Ma, the Indian-Asian continental convergenceand collision (Yin and Harrison, 2000; Zhong, et al., 2000) hasbeen accommodated by the extensive development of a seriesof large-scale left-lateral strike-slip faults to the east of the Ti-betan plateau. Examples of these are the Kunlun, Xianshuihe,Honghe, and Gaoligong faults (Fig. 1; Tapponnier and Mol-nar, 1976; Molnar and Tapponnier, 1978; Peltzer and Tap-ponnier, 1988; England and Molnar, 1990). The Honghe faultwas a Tertiary left-lateral strike-slip fault, though current mo-tion appears to be dextral (Dewey, 1988). The 500-km-longAilaoshan-Diancangshan metamorphic belt formed along theHonghe fault (Tapponnier et al., 1990; Leloup et al., 1995)and contains the alkali-rich intrusions. Extensive strike-slipmovement along this sinistral shear belt at about 23 Ma dis-placed the Indochina block at least 500 km southeastwardagainst South China (Tapponnier et al., 1990). Owing to thenorth-striking right-lateral shearing and northeast-southwestcompression, the upper crustal plates among these three

faults were rotated clockwise at 12°/m.y. and were latitudi-nally shortened by 1,000 m/m.y. (England and Molnar, 1990).

The Paleocene-Eocene Asian-Indian continental collisionresulted in the Jinshajiang strike-slip fault system, whichstrikes roughly orthogonal to the orientation of convergence(Fig. 1). The fault system is composed of a series of strike-slipfaults, including the Chesuo, Wenquan, and Tuoba faultswithin the Changdu-Simao continental block (Figs. 2, 3).Right-lateral movement along the Wenquan fault produced aset of associated northwest-north-northwest–trending en ech-elon folds and compressional sinistral faults that intersect theWenquan fault at acute angles, and these appear to have con-trolled development of the Yulong porphyry copper belt (Fig.3).

Geology of the Porphyry Belt

Spatial distribution of porphyry intrusions

Over 100 Himalayan porphyry intrusions are recognized inthe Changdu-Simao continental block (Tang and Luo, 1995).The block is bordered by several strike-slip pull-apart basins,the Gonjo basin on the eastern side, and the Nangqen and

YULONG PORPHYRY COPPER BELT, E. TIBET 127

0361-0128/98/000/000-00 $6.00 127

FIG. 1. Simplified tectonic map of the Himalayan-Tibetan orogen (modified after Yin and Harrison, 2000).

Lawu basins on the western side (Fig. 2). Within the basinsthere is a more than 4,000-m-thick, Tertiary gypsum-bearingred molasse formation intercalated with alkaline volcanicrocks that have K-Ar ages varying from 42.4 to 37.5 Ma (Fig.2b, Table 1; Zhang and Xie, 1997; Wang et al., 2000).

The Himalayan porphyry intrusions are divided into twobelts. The first one is the 200-km-wide × 1,500-km-long

Yulong mineralized porphyry belt that contains over 20 por-phyry bodies (Fig. 2b). The second is a 250-km-long, alkali-richintrusion belt, which is part of the 1,000-km-long Jinshajiang-Honghe belt farther south (Zhang and Xie, 1997). The Yulongporphyry bodies are typically emplaced into Triassic volcanicand sedimentary sequences and have relatively shallow em-placement depths, generally 1 to 3 km from the paleosurface.

128 HOU ET AL.

0361-0128/98/000/000-00 $6.00 128

FIG. 2. Tectonic framework and spatial distribution of two porphyry belts in the Changdu-Simao continent block, easternTibet. The inset map in the left lower corner (a) shows the tectonic framework of the region that includes a collage of thecontinental blocks joined by ophiolitic sutures and magmatic arcs (Liu et al., 1993). The porphyries located in the Changdu-Simao continental block constitute two belts, the Yulong porphyry belt and the Ritong-Mamupu alkali-rich porphyry belt.

Table 2 summarizes the geologic and mineralization fea-tures of several typical porphyry intrusions. The porphyrybodies commonly form steeply dipping vertical pipes withsmall outcrop areas of less than 1 km2 for individual bodies.Cryptoexplosive pipes and explosive breccias are commonlydeveloped around the mineralized porphyry bodies. The

clastic rocks in these breccia pipes consist predominately ofmagmatic detritus hosted within a tourmaline-rich matrix(20–25%) with subordinate quartz. Sulfide-bearing quartzveins, containing abundant tourmaline, typically occur withinor around the breccia pipes and crosscut the tourmaline-richbreccias. These breccia bodies suggest that the boiling and

YULONG PORPHYRY COPPER BELT, E. TIBET 129

0361-0128/98/000/000-00 $6.00 129

FIG. 3. Structural features and porphyry distribution in the Yulong porphyry copper belt, eastern Tibet (after Liu et al.,1993). The Yulong ore-bearing porphyry belt is mainly controlled by a set of the secondary north-northwest–directed sinis-tral strike-slip faults and folds derived from the Wenquan strike-slip fault. The boxed area in the left lower corner shows theseries of strike-slip faults, such as the Chesuo, Wenquan, and Tuoba faults. These faults resulted in the formation of thestrike-slip pull-apart basins such as the Gonjo, Nangqen, and Lawu basins. CFS and LCJF are the major bounding faults ofthe Changdu-Simao block and adjacent magmatic arcs.

130 HOU ET AL.

0361-0128/98/000/000-00 $6.00 130

TABLE 1. Summary of Age Dating of the Himalayan Porphyries and Volcanic Rocks in Eastern Tibet

Analytical Sampling site Rocks Analyzed objects method Age (Ma) Reference

Ridanguo Monzogranite porphyry Feldspar K-Ar 41.5 This studyRidanguo Monzogranite porphyry K feldspar K-Ar 42.3 This studyXiariduo Monzogranite porphyry K feldspar K-Ar 46.0 Ma (1990)Hengxingcuo Monzogranite porphyry K feldspar K-Ar 40.7 Tang and Luo (1995)Hengxingcuo Monzogranite porphyry K feldspar K-Ar 41.0 Tang and Luo (1995)Hengxingcuo Monzogranite porphyry Whole rock K-Ar 42.7 Liu et al. (1981)Yulong Monzogranite porphyry K feldspar K-Ar 37.9 Liu et al. (1981)Yulong Monzogranite porphyry K feldspar K-Ar 38.0 Zhang and Xie 1987)Yulong Monzogranite porphyry K feldspar K-Ar 38.2 Liu et al. (1981)Yulong Monzogranite porphyry K feldspar K-Ar 39.0 Tang and Luo (1995)Yulong Monzogranite porphyry K feldspar K-Ar 40.0 Liu et al. (1981)Yulong Monzogranite porphyry Biotite K-Ar 40.7 Chen (1983)Yulong Monzogranite porphyry Biotite K-Ar 41.0 Tang and Luo (1995)Yulong Monzogranite porphyry Biotite Rb-Sr 41.0Yulong Monzogranite porphyry Biotite K-Ar 41.5 Liu et al. (1981)Yulong Monzogranite porphyry Biotite K-Ar 48.2 Chen (1983)Yulong Quartz monzonite porphyry Whole rock Rb-Sr 52.0 Ma (1990)Yulong Quartz monzonite porphyry Biotite K-Ar 52.6 Chen (1983)Yulong Quartz monzonite porphyry Biotite Ar/Ar 52.8 Tang and Luo (1995)Yulong Quartz monzonite porphyry Whole rock K-Ar 53.0 Tang and Luo (1995)Yulong Quartz monzonite porphyry K feldspar K-Ar 55.0 Chen (1983)Zhanaga Alkali-feldspar granite porphyry K feldspar K-Ar 33.9 Liu et al. (1981)Zhanaga Alkali-feldspar granite porphyry K feldspar K-Ar 34.0 Zhang and Xie (1987)Zhanaga Alkali-feldspar granite porphyry Biotite K-Ar 40.0 Zhang and Xie (1987)Mangzong Monzogranite porphyry K feldspar K-Ar 41.0 Chen (1983)Mangzong Monzogranite porphyry K feldspar K-Ar 33.9 Liu et al. (1981)Duoxiasongduo Granite porphyry Zircon U-Pb 41.0 Ma (1990)Duoxiasongduo Monzogranite porphyry Whole rock Rb-Sr 52.0 Ma (1990)Malasongduo Granite porphyry Zircon U-Pb 33.7 Ma (1990)Malasongduo Syenogranite porphyry Feldspar K-Ar 35.8 Tang and Luo (1995)Malasongduo Monzogranite porphyry Zircon U-Pb 40.9 Ma (1990)Malasongduo Monzogranite porphyry Whole rock K-Ar 50.9 Tang and Luo (1995)Gegongnong Monzogranite porphyry Whole rock K-Ar 38.2 This studyGegongnong Monzogranite porphyry Whole rock Rb-Sr 40.0 This studyGegongnong Monzogranite porphyry Whole rock K-Ar 49.4 This studyJiaodonqing Syenite porphyry Whole rock K-Ar 41.0 Chen and Liao (1983)Ritong Syenite porphyry Whole rock K-Ar 30.0 Wang et al (1995)Chongbomada Amphibole syenite porphyry Whole rock K-Ar 45.1 Yong (unpub. data, 1995)Larima Quartz syenite porphyry Whole rock K-Ar 36.0 Yong (unpub. data, 1995)Gicuo Syenite-porphyry Whole rock K-Ar 40.7 This studyMamupu Amphibole quartz syenite Whole rock Rb-Sr 37.6 Wang et al. (1995)

porphyryBada Quartz syenite Whole rock K-Ar 38.4 Yong (unpub. data, 1995)Gonjo basin Trachyandesite Whole rock K-Ar 37.5 This studyNangqen basin Trachyte Plagioclase Ar/Ar 38.7 Pan (1990)Lawu basin Trachyte Whole rock K-Ar 42.4 Yong (unpub. data, 1995)

Note: Whole-rock and mineral samples in this study were analyzed for K-Ar and Rb-Sr isochron age methods at Chengdu Institute of Technology, Chengdu(after Wang et al., 2000)

YULONG PORPHYRY COPPER BELT, E. TIBET 131

0361-0128/98/000/000-00 $6.00 131

TAB

LE

2. G

eolo

gy a

nd M

iner

aliz

atio

n of

the

Mai

n C

oppe

r D

epos

its in

the

Yulo

ng P

orph

yry

Cop

per

Bel

t, E

aste

rn T

ibet

Sulfi

de z

onin

gPo

rphy

ry

Out

crop

St

ruct

ural

A

ltera

tion

Gra

de a

nd

Ore

body

O

rebo

dy

Ore

Su

lfide

(o

utw

ard

from

M

etal

lic

intr

usio

nar

ea (

km2 )

Wal

l roc

kpo

sitio

nR

ock

type

zoni

ngto

nnag

efo

rmsi

zest

ruct

ure

asse

mbl

age

the

cent

er)

type

Yulo

ng0.

64U

pper

So

uthe

rn

Mon

zogr

anite

O

utw

ard

6.22

Mt C

u St

ratif

orm

L

entic

ular

Ve

inle

t ch

alco

pyri

te +

M

olyb

deni

te +

C

u +

Mo

Tria

ssic

en

d of

po

rphy

ry;

from

cen

ter:

C

u: 0

.99%

oreb

ody

oreb

ody:

diss

em-

mol

ybde

nite

+

chal

copy

rite

→±

Au

±A

g cr

ysta

lline

G

anlo

ngla

Q

uart

z K

sili

cate

M

o: 0

.028

%in

ska

rn;

1,00

0 m

in

ated

pyri

te ±

copp

er-b

eari

ng

±R

e ±

Pt

limes

tone

an

ticlin

e m

onzo

nite

→

quar

tz-

Au:

0.3

5 pp

mL

entic

ular

lo

ng, 6

00 m

bo

rnite

±m

agne

tite

+ ±

Pd ±

Co

axis

porp

hyry

seri

cite

→or

ebod

y w

ide,

500

m

tetr

ahed

rite

±ch

alco

pyri

te →

±Pb

±Zn

argi

llic

→ho

sted

in

deep

;cu

bani

te ±

copp

er-b

eari

ng

prop

yliti

c po

rphy

ry

Stra

tifor

m:

gold

±si

lver

py

rite

+ c

oppe

r-in

trus

ions

200–

300

m

bear

ing

limon

ite

wid

e, 2

0–→

gale

na +

10

0 m

thic

k sp

hale

rite

Mal

ason

gduo

0.13

L

ower

So

uth-

Mon

zogr

anite

O

utw

ard

1.0

Mt C

u Ir

regu

lar

950

m lo

ng

Vein

let

Cha

lcop

yrite

+

Cha

lcop

yrite

+

Cu

+ M

o Tr

iass

ic

wes

t of

porp

hyry

;fr

om c

ente

r:

Cu:

0.4

4%le

ntic

ular

80

0 m

wid

e,

diss

em-

pyri

te +

m

olyb

deni

te →

±A

u ±

Ag

rhyo

litic

M

alas

ong-

Syen

ogra

nite

K

sili

cate

M

o: 0

.14%

oreb

ody

694

m d

eep

inat

ed;

mol

ybde

nite

+

pyri

te +

±

Re

±Pt

ro

cks

duo

anti-

porp

hyry

→

quar

tz-

Au:

0.0

6 pp

m

host

ed in

lo

caliz

ed

gale

na +

ch

alco

pyri

te →

±Pd

clin

e ax

is

seri

cite

→po

rphy

ry

perv

asiv

e sp

hale

rite

±ga

lena

+ s

phal

erite

pr

opyl

itic

intr

usio

ns

born

ite ±

and

the

tetr

ahed

rite

su

rrou

ndin

g w

all r

ock

Duo

xia-

0.30

U

pper

A

djac

ent t

o A

lkal

i-O

utw

ard

0.5

Mt C

u Ir

regu

lar

600

m lo

ng,

Vein

let

Cha

lcop

yrite

+

Mol

ybde

nite

+

Cu

+ M

o so

ngdu

o Tr

iass

ic

Man

gzon

g fe

ldsp

ar

from

cen

ter:

C

u: 0

.38%

lent

icul

ar

500

m w

ide,

diss

em-

pyri

te ±

chal

copy

rite

→±

Au

±A

g

sand

y

antic

line

gran

ite

K s

ilica

te

Mo:

0.0

4%

oreb

ody

570

m d

eep

inat

ed;

mol

ybde

nite

±ch

alco

pyri

te +

m

udst

one

axis

po

rphy

ry;

→qu

artz

-A

u: 0

.05

ppm

host

ed in

ve

inle

t m

agne

tite

±py

rite

→ga

lena

+

Mon

zogr

anite

se

rici

te →

porp

hyry

st

ockw

ork

gale

na ±

spha

leri

te

porp

hyry

pr

opyl

itic

intr

usio

ns

spha

leri

te ±

and

the

born

ite

rhyo

lite

wal

l roc

k

Man

gzon

g0.

28

Upp

er

Nor

thw

est

Mon

zogr

anite

O

utw

ard

0.25

Mt C

u Ir

regu

lar

1100

m lo

ng,

Vein

let

Cha

lcop

yrite

+

No

clea

r zo

natio

n C

u +

Mo

Tria

ssic

se

gmen

t of

porp

hyry

fr

om c

ente

r:

Cu:

0.3

4%pi

pelik

e 25

0 m

wid

e,di

ssem

-py

rite

±±

Au

sa

ndy

M

angz

ong

K s

ilica

te

Mo:

0.0

3%or

ebod

y 80

0 m

dee

pin

ated

m

olyb

deni

te ±

mud

ston

e an

ticlin

e →

quar

tz-

Au:

0.0

2 pp

mho

sted

in

gale

na ±

axis

se

rici

te →

porp

hyry

sp

hale

rite

±pr

opyl

itic

in

trus

ions

te

nnan

tite

±an

d ho

rnfe

l ch

alco

cite

un

it

Zhan

aga

0.60

U

pper

A

djac

ent t

o M

onzo

gran

ite

Fro

m s

outh

0.

3 M

t Cu

Pipe

like

539

m d

eep

Vein

let

Cha

lcop

yrite

+

No

clea

r zo

natio

n C

u +

Mo

Tria

ssic

M

angz

ong

porp

hyry

;to

nor

th:

Cu:

0.3

6%or

ebod

y 20

0 m

in

diss

em-

mol

ybde

nite

+

±A

u ±

Ag

sand

y

antic

line

Syen

ogra

nite

to

urm

alin

iza-

Mo:

0.0

3%ho

sted

in

diam

eter

in

ated

py

rite

±m

udst

one

axis

po

rphy

rytio

n (q

uart

z-A

u: 0

.03

ppm

po

rphy

ry

mag

netit

e ±

seri

cite

) →

intr

usio

nsch

alco

cite

±ar

gilli

c bi

smut

hini

te

alte

ratio

n →

prop

yliti

c al

tera

tion

Not

e: T

able

is c

ompi

led

afte

r R

ui Z

ongy

ao e

t al.

(198

4), M

a H

ongw

en (

1990

), an

d W

ang

Zeng

et a

l. (1

995)

degassing of the magmatic-hydrothermal systems occurred ata relatively shallow depth.

Ages of porphyry intrusions

Although the porphyry intrusions in the Yulong belt are ofsmall size and volume, they typically comprise complex mul-tiphase intrusions. K-Ar dating of the Yulong porphyry belthas delineated three main periods of emplacement: 55.0 to48.2, 44.0 to 35.8, and 34.0 to 33.7 Ma (Table 1). These cor-respond to three peaks at 52 ± 2.8, 40 ± 2.3, and 33 ± 3.3 Ma,respectively (Fig. 4). Bulk-rock and igneous biotite separatesfor the Yulong porphyry body yielded two Rb-Sr isochronages of 52 and 41 Ma respectively, and 40Ar/39Ar dating of ig-neous biotite yielded an age of 52.84 ± 1.68 Ma (Ma, 1990).Zircons from monzogranite porphyries at Duoxiasongduo alsoyielded two U-Pb ages of 52 and 41 Ma (Tang and Luo, 1995).Monzogranite porphyry at Malasongduo yielded zircon U-Pbages of 40.9 and 33.7 Ma (Ma, 1990). These results indicatethat ore-hosting porphyry intrusions were emplaced duringall three of the main periods of magmatism in the Yulong belt(Fig. 4). The porphyry intrusions at Yulong and Duoxiasong-duo were emplaced in the early (~52 Ma) and middle (~40Ma) stages. Those in Ridanguo, Hengxingcuo, Mangzong,Gegongnong, and Mamupu were emplaced around 40 Ma,whereas those in Zhanaga were emplaced relatively late, dur-ing the middle and late (~33 Ma) stages.

Mineralization of the Porphyry BeltThe Yulong belt is the most important porphyry copper belt

in Tibet. It was discovered and subsequently explored duringthe 1970s and 1980s. Over 80 drill holes, totaling more than

20,000 m had been completed for the Yulong belt by theTeam 1 of the Xizang Bureau of Geology and Mineral Re-sources. The preliminary evaluation shows that the porphyryCu belt contains reserves of over 10 million metric tons (Mt)of contained copper, including one giant (Yulong), two large(Malasongduo and Duoxiasongduo), and two intermediate tosmall copper deposits (Table 2).

Yulong Cu deposit

The 630 Mt Yulong copper deposit is the largest deposit inthe Yulong belt. It has reserves of over 6.22 Mt containedcopper, averaging 0.99 percent Cu and 0.028 percent Mo(Tang and Luo, 1995). High-grade zones within the depositcontain about ~3 Mt of copper with a grade of over 1 percent(including supergene enriched zones with up to 13.7% Cu).

Geology and alteration: The Yulong porphyry intrusion(1,000 × 600 × 850 m) is a complex multiphase intrusionwith individual intrusive phases between 55 and 38 Ma (Table1). The dominant host rock to mineralization is a strongly al-tered monzogranite porphyry. Concentric alteration zonesrange from an inner K silicate zone out through quartz-sericite and argillic alteration zones to an outer propyliticzone (Fig. 5). K silicate alteration is typically developedwithin the porphyry intrusion and is characterized by largeamounts of secondary quartz and potassic feldspar. Quartz-sericite alteration zones occur as fine-grained replacements oforiginal rock constituents with associated quartz veinlets andhave been developed along the margins of the porphyry in-trusion, typically inside the contact zone. Quartz-sericite al-teration is superimposed on the K silicate alteration andgrades into an outer zone of advanced argillic alteration inwhich kaolinite group minerals and quartz predominate. Apropylitic alteration zone is present in the strata surroundingthe intrusions and the quartz-sericite zone and is character-ized by large amounts of chlorite, epidote, and tourmaline(Fig. 5). These hydrothermal alteration zones have locallyoverprinted earlier formed contact metamorphic zones thatshow a crude zonation from inner hornfels, through to skarnalteration, and marble on the margins (Fig. 5).

Mineralization styles and orebody shape: The Yulong de-posit consists of a pipelike orebody hosted in the porphyry in-trusion and an overlying stratiform or tabular ore zone that ishosted in the thermally metamorphosed strata surroundingthe intrusion (Fig. 6a). At least three styles of mineralizationhave been recognized in the deposit. These form concentriczones that surround the inner potassic intrusive core. The firststyle is veinlet-disseminated quartz-pyrite-chalcopyrite in theinterior of the porphyry intrusion. The mineralization forms apipelike, steeply dipping orebody, 1,000 m long, 600 m wide,and about 500 m deep (Fig. 6a). Pockets of high-grade Cu-Momineralization typically occur within the center of this zone,whereas lower Cu-Mo grades (2.0% Cu and 0.06% Mo) occuralong the margins of the body (Fig. 6a). The second mineral-ization style consists predominantly of fine-veinlet pyrite-chal-copyrite or pyrite-chalcopyrite-molybdenite ores that formsteeply dipping orebodies hosted within the hornfels zone be-tween the porphyry intrusion and the surrounding wall rocks(Fig. 6a). The third mineralization style occurs within a ring-shaped halo of stratiform or lenticular replacement orebodieshosted in the Late Triassic strata surrounding the porphyry

132 HOU ET AL.

0361-0128/98/000/000-00 $6.00 132

FIG. 4. Summary of isotopic ages of the porphyry bodies in the Yulongporphyry copper belt.

intrusion (Fig. 6a). The orebodies are gently dipping and areabout 200 to 300 m wide and 20 to 100 m thick, thinning out-ward from the porphyry intrusion to the wall rocks. Theseorebodies have been oxidized, with supergene enrichmentzones containing Cu grades of up to 13 percent (Tang andLuo, 1995).

Three main hydrothermal stages are recognized (Li et al.,1981; Rui et al., 1984): (1) an early K silicate alteration stage(400°–700°C), in which the porphyry intrusions underwentstrong potassic alteration and silicification while the sur-rounding host rocks were metamorphosed and altered toskarn associated with Cu-Mo mineralization; (2) a stage ofquartz-sericite alteration (200°–500°C) with associated Cu-Mo-Fe mineralization; and (3) a final stage (~230°C) ofargillic and propylitic alteration, which developed in the con-tact zone and in the surrounding Late Triassic sedimentarystrata, with associated hydrothermal Au-Ag polymetallic min-eralization (Rui et al., 1984; Tang and Luo, 1995). The min-eral assemblages for these stages are pyrite + chalcopyrite +

molybdenite + magnetite in the veinlet-disseminated oresformed during the K silicate alteration stage; pyrite + chal-copyrite + magnetite + ilmenite with minor molybdenite, bis-muthinite, and covellite for lenticular orebodies in skarnsduring middle-late stages; and pyrite + chalcopyrite + galena+ sphalerite for the sulfide mineralization in Late Triassicsedimentary sequence far from the porphyry intrusions.Minor amounts of bornite, cubanite, gold, silver, and tetra-hedrite ores are also found within the porphyry copper de-posits (Table 2).

Malasongduo Cu deposit

The 230 Mt Malasongduo deposit is the second largest por-phyry copper deposit in the Yulong porphyry copper belt,with contained copper reserves of about 1.0 Mt averaging0.44 percent Cu (Tang and Luo, 1995). The deposit is locatedon the southwest flank of the core of the Malasongduo anti-cline (Fig. 3) and consists of a mineralized multistage por-phyry body that has intruded Early Triassic rhyolite lava and

YULONG PORPHYRY COPPER BELT, E. TIBET 133

0361-0128/98/000/000-00 $6.00 133

FIG. 5. Plan map and cross section of hydrothermal mineralization and alteration in the Yulong porphyry copper deposit(modified from Tang and Luo, 1995).

134 HOU ET AL.

0361-0128/98/000/000-00 $6.00 134

FIG

.6.

Sket

ch g

eolo

gic

map

s an

d cr

oss

sect

ions

of t

he th

ree

larg

est p

orph

yry

copp

er d

epos

its in

the

Yulo

ng p

orph

yry

Cu

belt

(mod

ified

from

Tan

g an

d L

uo, 1

995)

.

pyroclastic rocks. Owing to the limited erosion in the area, theoutcrop expression of the deposit is only about 0.1 km2 (Fig.6b).

Geology and alteration: The Malasongduo porphyry intru-sion is a columnar, stocklike body with an age range from 51to 34 Ma (Table 1). The dominant mineralized phase is amonzogranite porphyry. The alteration assemblages hostedwithin the intrusion are similar to those at the Yulong deposit,including K silicate alteration, silicification, and sericitization.Rhyolitic units surrounding the porphyry intrusion displayproximal K silicate alteration, grading to a transitionalsericite-quartz zone and a distal propylitic alteration halo.The K silicate zone adjacent to the intrusion hosts significantCu-Mo mineralization.

Mineralization styles and orebody shape: The porphyry in-trusions and the surrounding rhyolitic wall rocks host veinlet-disseminated pyrite-chalcopyrite ± molybdenite mineraliza-tion that forms a relatively simple, steeply dipping orebody,which is 950 m long, 800 m wide, and 690 m deep (Fig. 6b).Mineralization is both laterally and vertically zoned. Laterally,an inner Cu zone grades to a Cu-Mo zone and an outer Ag-Pb-Zn zone. Vertically, the orebody ranges from a veinlet-dis-seminated Cu ore zone at depth, to a fine veinlet Cu ore zoneat shallower levels, overlain by a supergene enrichment zone(Tang and Luo, 1995). Veinlet-disseminated Cu and Cu-Momineralization is hosted in the monzogranite porphyry.Minor Pb-Zn mineralization is restricted in the surroundingrhyolites.

Four generations of veinlets are recognized in the mainorebody: (1) quartz sulfide veins, including quartz-pyrite-chalcopyrite veins, quartz-pyrite-bornite veins, and quartz-chalcocite veins; (2) biotite-chalcopyrite veins; (3) calcite-sul-fide veins (calcite, quartz, pyrite, and chaclopyrite); and (4)tourmaline-sulfide veins (tourmaline, quartz, chalcopyrite,pyrite, and molybdenite).

Duoxiasongduo Cu deposit

The 130 Mt Duoxiasongduo deposit is the third largestporphyry Cu deposit in the Yulong belt and contains about0.5 Mt of Cu, grading on average 0.38 percent Cu (Tang andLuo, 1995). The Cu porphyry intrusion is situated within theMalasongduo anticline (Fig. 3) and has intruded the LateTriassic sandstone-mudstone sequence (Fig. 6c). The intru-sion has a small outcrop area of about 0.3 km2 owing to thelimited erosion.

Geology and alteration: The Duoxoasongduo deposit occurswithin a multiphase porphyry intrusion with radiometric agesranging from 41 to 52 Ma (Table 1). An early monzograniteporphyry and a late-stage granite porphyry are the dominanthost rocks to ore. These intrusions crosscut Late Triassic sand-stone and mudstone, which have been metamorphosed tohornfels along the margins of the porphyry intrusion (Fig. 6c).Hydrothermal alteration occurs in both the intrusive body andthe surrounding hornfelsed sandstone-mudstone sequenceand shows porphyry-style alteration zoning similar to the Yu-long and Malasongduo deposit (Ma, 1990; Tang and Luo,1995). The orebody, composed of veinlet-disseminated Cuand Cu-Mo ores, is hosted in K silicate and sericite alteration.

Mineralization style and orebody shape: The mineralizationat Duoxiasongduo forms a 600-m-long, 500-m-wide, and at

least 570-m-deep veinlet-disseminated orebody. It is locatedin the southern part of the porphyry intrusion and within thesurrounding hornfelsed and hydrothermally altered sand-stone and mudstone units (Fig. 6c). The orebody is pipeshaped and displays vertical zonation from Cu-Mo rich atdepth to Cu rich at shallower levels. Erosion is interpreted tohave removed any preexisting supergene enrichment.

Two vein styles are recognized: quartz sulfide veins and sul-fide veins. Quartz sulfide veins are <2 mm wide, consisting ofquartz, pyrite, chalcopyrite, and minor molybdenite, bornite,and chalcocite. Sulfide veins consist of pyrite, chalcopyrite,and minor bornite and chalcocite.

Other deposits

In addition to the three largest copper deposits describedabove, the Yulong belt also contains two medium- to small-sized deposits (e.g., the Zhanage and Mangzong) and dozensof minor prospects and mineralized porphyry intrusions.These deposits and occurrences, though smaller in size, stillexhibit geologic features similar to the larger porphyry copperdeposits (Table 2).

Petrological and Geochemical CharacteristicsAccording to the classification of Streckeisen and Lemaitre

(1979), the major rock types in the Yulong belt are monzo-granite porphyry, quartz monzonite porphyry, syenograniteporphyry, and alkali-feldspar granite porphyry. Quartz mon-zonite and monzogranite porphyries are typically early em-placement phases, whereas the more evolved syenograniteporphyry and alkali-feldspar granite porphyry are typically em-placed late in the intrusive history (Zhang et al., 1998a). Thephenocryst assemblage consists of quartz, calcic hornblende,Mg-rich biotite, andesine-oligoclase, and sanidine potassicfeldspar with accessory magnetite, zircon, apatite, and sphene,similar to that of I-type or magnetite series granites.

Major elements

More than 50 samples of porphyritic intrusions from theYulong belt have been analyzed for major and trace elementsby AAS and ICP-MS techniques (Ma, 1990; Tang and Luo,1995; Zhang et al., 1998a, b). Results for representative sam-ples are reported in Table 3.

A limited variation of major element compositions exists forthe ore-bearing porphyries (Table 3). The K2O content in-creases systematically with increasing SiO2 content from earlyto late porphyry phases, whereas CaO, Al2O3, MgO, andNa2O decrease, suggesting fractional crystallization of phe-nocryst minerals, i.e., hornblende, magnesian biotite, and an-desine-oligoclase. Alkali enrichment (K2O + Na2O > 8 wt %)and high K2O/Na2O ratio (K2O/Na2O > 1.0) characterize theore-bearing porphyries. The K2O contents vary from 4.15 to8.06 wt percent and are much higher than those for typicalcalc-alkaline porphyries (e.g., Escondida deposit, Chile;Richards et al., 2001) but are lower than those of the alkali-rich intrusions for similar SiO2 concentrations from the Ri-tong-Mamupu belt and volcanic rocks in the Nangqen andLawu basins (Wang et al., 2000; Fig. 7). All porphyries fromthe Yulong belt fall in the field of the shoshonitic series, sug-gesting a shoshonitic magmatic affinity (Fig. 7).

YULONG PORPHYRY COPPER BELT, E. TIBET 135

0361-0128/98/000/000-00 $6.00 135

136 HOU ET AL.

0361-0128/98/000/000-00 $6.00 136

TAB

LE

3. M

ajor

Ele

men

ts, T

race

Ele

men

ts, a

nd R

EE

of R

epre

sent

ativ

e O

re-B

eari

ng P

orph

yriti

c In

trus

ions

and

Oth

er V

olca

nic

Roc

ks in

the

Cha

ngdu

-Sim

ao C

ontin

enta

l Blo

ck

Rito

ng-M

amup

u N

angq

enYu

long

por

phyr

y co

pper

bel

tal

kali-

rich

intr

usio

n be

ltba

sin

Gon

jo b

asin

Yulo

ngM

alas

ongd

uoD

uoxi

ason

gduo

Mon

gzon

gZh

anag

aR

iduo

Man

upu

Shan

gji

K fe

ldsp

arSy

enite

and

M

onzo

gran

ite

Mon

zogr

anite

Mon

zogr

anite

gr

anite

M

onzo

rani

teM

onzo

gran

itesy

neni

ticSy

neni

tic

Wt %

Porp

hyry

1, 2

porp

hyry

1, 2

porp

hyry

1, 2

porp

hyry

1, 2

porp

hyry

1, 2

porp

hyry

1po

rphy

ry1,

2po

rphy

ry3

Trac

hyte

3

SiO

264

.80

67.6

468

.90

70.9

563

.11

69.4

267

.04

68.9

468

.21

68.1

669

.33

71.9

473

.53

66.4

167

.29

67.6

968

.31

67.3

773

.90

69.7

370

.24

64.7

062

.99

61.4

560

.87

57.1

359

.36

63.2

460

.74

71.2

5Ti

O2

0.52

0.39

0.35

0.31

0.34

0.28

0.30

0.27

0.27

0.28

0.28

0.23

0.21

0.22

0.42

0.22

0.33

0.33

0.22

0.38

0.28

0.47

0.44

0.56

0.70

0.85

0.70

0.33

0.35

0.39

Al 2O

316

.44

15.2

214

.95

14.1

818

.00

14.1

214

.14

14.2

613

.04

14.3

014

.01

13.1

113

.33

14.8

414

.58

15.5

815

.15

14.9

913

.00

14.9

115

.21

15.3

014

.60

14.8

615

.00

13.4

315

.66

15.8

115

.09

13.8

4F

e 2O

31.

231.

371.

160.

541.

871.

090.

941.

591.

011.

021.

491.

430.

661.

461.

681.

711.

501.

220.

631.

181.

011.

661.

682.

562.

192.

113.

392.

412.

451.

79F

eO1.

761.

671.

441.

501.

031.

511.

101.

232.

710.

430.

741.

361.

381.

001.

681.

130.

821.

331.

061.

211.

241.

661.

751.

322.

143.

851.

420.

520.

370.

67M

nO0.

060.

060.

070.

050.

050.

150.

060.

080.

120.

060.

070.

120.

130.

090.

070.

070.

100.

110.

070.

110.

110.

130.

150.

110.

070.

130.

060.

130.

060.

02M

gO2.

471.

420.

791.

231.

450.

831.

221.

010.

990.

961.

270.

630.

591.

381.

471.

770.

991.

190.

071.

151.

111.

372.

013.

253.

044.

582.

740.

942.

100.

60C

aO2.

942.

342.

831.

272.

761.

861.

481.

301.

672.

290.

760.

650.

620.

702.

820.

650.

991.

810.

972.

002.

143.

124.

464.

303.

777.

785.

123.

224.

771.

72N

a 2O

3.77

3.67

3.32

2.87

4.39

3.67

3.27

3.12

2.01

2.82

2.84

2.44

2.95

3.11

3.72

2.68

3.80

3.31

2.36

4.09

4.54

4.35

4.62

4.39

4.12

3.07

4.54

5.38

3.15

3.58

K2O

4.27

4.33

4.52

6.04

4.89

4.85

5.79

6.25

5.57

4.76

5.52

5.60

5.32

5.23

5.01

6.75

5.45

5.80

6.29

4.28

3.66

5.59

6.18

5.14

6.83

6.39

5.43

5.07

5.20

3.48

P 2O

50.

030.

070.

110.

050.

400.

100.

110.

100.

110.

130.

120.

130.

140.

190.

230.

220.

120.

140.

100.

090.

080.

220.

240.

400.

560.

680.

380.

250.

320.

21H

2O0.

600.

670.

540.

531.

210.

500.

761.

041.

321.

271.

080.

780.

730.

711.

090.

700.

970.

460.

300.

290.

260.

460.

940.

40–

Tota

l98

.89

98.8

598

.98

99.5

299

.50

98.3

896

.21

99.1

997

.03

96.4

897

.51

98.4

299

.59

94.6

399

.68

99.5

698

.26

98.5

799

.13

99.4

399

.91

98.8

399

.58

99.2

899

.69

100.

0098

.80

97.3

094

.60

97.5

5Pp

mL

a82

.17

67.0

463

.04

51.9

397

.35

45.3

082

.11

48.8

532

.50

72.7

677

.34

60.3

386

.25

60.4

762

.01

60.9

957

.45

68.7

279

.75

76.5

139

.98

109.

1075

.17

117.

4372

.00

86.2

814

5.76

170.

3742

.40

Ce

161.

5012

3.10

119.

4096

.42

174.

9887

.09

158.

786

.59

55.5

013

6.90

142.

9011

1.60

149.

1010

7.58

120.

1011

6.83

99.1

412

1.90

152.

0914

6.80

77.8

020

4.90

161.

1825

4.32

131.

1012

4.20

295.

9229

1.30

79.4

8N

d65

.88

45.7

645

.92

34.4

172

.41

33.5

155

.28

29.7

020

.00

47.0

350

.50

38.2

143

.38

43.3

145

.68

47.3

933

.05

43.0

964

.93

57.9

328

.60

70.7

370

.68

130.

8952

.10

72.6

611

6.26

105.

5725

.72

Sm10

.37

7.08

7.36

5.25

10.7

25.

568.

264.

773.

606.

977.

535.

515.

356.

217.

247.

365.

326.

5810

.32

9.73

4.69

10.5

510

.64

19.6

69.

8713

.66

17.3

514

.71

4.46

Eu

1.90

1.49

1.52

1.06

2.28

0.97

0.94

0.88

0.78

1.32

1.46

0.88

0.66

1.36

1.53

1.84

0.95

1.36

2.32

2.06

0.97

2.22

2.48

4.89

2.22

3.10

4.16

3.50

1.01

Gd

7.44

5.19

5.45

3.81

6.36

4.41

6.20

3.76

4.20

4.87

5.15

3.98

3.83

3.74

5.33

5.26

4.21

4.81

6.76

7.26

3.63

7.39

6.12

11.0

76.

5610

.06

10.5

58.

862.

87T

b0.

540.

490.

400.

160.

850.

390.

650.

450.

780.

340.

570.

310.

310.

510.

500.

710.

430.

530.

930.

760.

280.

480.

801.

341.

161.

481.

251.

080.

42D

y3.

902.

822.

992.

113.

852.

983.

892.

541.

902.

742.

832.

272.

302.

422.

933.

532.

502.

734.

413.

982.

293.

822.

423.

564.

656.

745.

244.

791.

70H

o0.

690.

510.

590.

390.

680.

580.

770.

540.

620.

500.

520.

400.

410.

440.

560.

670.

430.

490.

790.

720.

430.

650.

600.

890.

851.

290.

950.

890.

34E

r1.

891.

371.

461.

071.

871.

612.

071.

420.

741.

451.

431.

201.

270.

321.

441.

911.

211.

372.

261.

961.

211.

911.

712.

512.

202.

982.

282.

240.

82T

m0.

290.

220.

220.

140.

240.

260.

350.

260.

240.

240.

190.

180.

190.

180.

250.

260.

200.

250.

300.

280.

190.

300.

220.

290.

530.

450.

350.

370.

14Yb

1.52

1.18

1.31

0.94

1.50

1.62

1.92

1.50

1.10

1.30

1.31

1.16

1.17

1.26

1.24

1.72

1.11

1.20

1.93

1.57

1.19

1.54

1.41

1.88

2.11

2.38

1.89

2.04

0.68

Lu

0.28

0.29

0.30

0.19

0.23

0.30

0.36

0.36

0.54

0.26

0.24

0.28

0.20

0.20

0.21

0.27

0.19

0.32

0.29

0.36

0.25

0.22

0.21

0.28

0.30

0.37

0.28

0.31

0.10

Y16

.79

12.3

913

.71

9.33

19.6

915

.94

19.3

113

.88

12.8

012

.73

12.9

211

.11

10.6

214

.17

13.1

520

.75

10.5

612

.67

23.8

519

.21

11.2

216

.37

18.0

225

.06

22.9

033

.30

24.1

123

.55

10.0

2Sc

8.02

5.12

5.51

4.20

4.84

53.

533.

843.

163.

652.

911.

975.

094.

123.

945.

443.

945.

206.

408.

00R

b23

721

722

524

622

422

926

823

624

025

731

520

328

717

822

729

326

928

712

4.62

296

294

321

139

234

148

196

Sr12

2099

587

863

189

955

949

155

048

049

363

848

629

827

610

6862

830

673

510

0268

569

818

3415

4515

8510

4027

5522

76B

a44

093

963

636

276

057

175

458

074

049

868

237

925

556

283

589

367

858

352

450

453

813

8619

9521

1611

0018

9618

95T

h27

2927

2820

3837

3628

4748

4854

3238

3334

4534

2931

6055

3436

38N

b9

68

672

1317

1516

119

1213

177

156

1017

78

1015

1113

1525

23Ta

0.95

1.37

1.22

1.33

0.81

0.98

2.0

2Zr

159

113

124

115

288

114

148

101

138

109

101

104

119

242

9426

714

611

426

511

111

319

433

723

817

225

048

930

2H

f19

88

97

615

86

44

65

69

76

67

47

159

512

9Pb

1028

3322

2232

1828

3064

5068

3931

3235

8555

2169

7560

4123

Not

e: M

ajor

ele

men

ts w

ere

anal

yzed

by

wet

met

hod,

trac

e el

emen

ts a

nd R

EE

wer

e an

alyz

ed b

y IC

P-M

SD

ata

sour

ces:

1 M

a (1

990)

, 2

Zhan

g et

al.

(199

8b),

3 Yo

ng (

1995

), 4

Wan

g et

al.

(200

0)

Trachyte3

Rhyolite4

Trace elements

Trace element compositions for representative porphyriesfrom the Yulong belt are presented in Figure 8. Strong posi-tive anomalies for Rb and Ba relative to oceanic ridge gran-ites (ORG, Fig. 8a; Pearce et al., 1984), combined with highercontents of K2O (4.15–8.06 wt %) and Rb (203–315 ppm)compared to those of arc calc-alkaline ore-bearing porphyriesin the Escondida district, northern Chile (K2O = 2.13–3.17 wt%; Rb = 52–140 ppm; Richards et al., 2001), support ashoshonitic magmatic affinity. The enrichment in large ionlithophile elements (LILE; K, Rb, Ba) suggests that eitherthe source of the porphyry magma was highly enriched inLILE compared to the oceanic ridge granites or represents amixture of mantle and crustal materials. The concentrationsof high field strength elements (HFSE; Zr, Hf, Nb, Ta, Ti, U,and Th) are close to or lower than those of the oceanic ridgegranites (Fig. 8a). Of these, the Zr and Hf contents vary from90 to 148 and 5 to 19 ppm, respectively, slightly lower thanthose of the oceanic ridge granites, whereas the Nb contentvaries from 6 to 18 ppm, similar to those of the oceanic ridgegranites. This implies that the amount of crustal materialsthat either mixed with a mantle source or contaminated theascending porphyry magma was small, because crustal mate-rials are extremely enriched in Nb and Ta (Miyashiro, 1977;Bonin et al., 1978).

Strong negative anomalies for Nb, Ta, P, and Ti and positiveanomalies for Pb, Th, Rb and Ba (Fig. 8b) suggest an arc mag-matic affinity for the Yulong belt porphyries (e.g., Nakamura,1985). Rare earth element (REE) patterns for the Yulongporphyries are consistent with their shoshonitic character,

with light REE enrichment (Ce/Yb = 54.1–109.1; Fig. 9). Rel-atively depleted patterns for the middle REE and slight tomoderate negative Eu anomalies suggest fractionation ofhornblende and plagioclase during differentiation of thesefelsic magmas.

Overall, these data suggest that the shoshonitic magmaticaffinity of the ore-bearing porphyries is most likely related tosome component of slab subduction, though they were em-placed in an intracontinental convergent setting. Comparedto the porphyries from the Yulong and Litong-Mamupu belts,the potassic volcanic rocks in the Nangqen and Lawu basinsexhibit similar REE patterns with slightly enriched LREE(Fig. 9b, c) and trace element abundance patterns but muchstronger positive anomalies for K, Rb, and Ba (Table 3). Thissuggests either a difference in the degree of partial meltingfrom a common source or a series of magma sources, eachwith various degrees of metasomatic enrichment in traceelements.

Sr-Nd-Pb isotopes

Three Rb-Sr isochrons of Yulong belt porphyries at Yulong,Duoxiasongduo, and Malasongduo, with initial values of 87Sr/86Sr of 0.7066, 0.7065, and 0.7077, respectively, yield a rangeof 87Sr/86Srinitial values from 0.7065 to 0.7077 (Ma, 1990; Wanget al., 1995; Table 4). These 87Sr/86Srinitial values are within therange of the alkali-rich intrusions from the Jinshajiang-Honghe belt (0.7052–0.7072; Zhang and Xie, 1997; Zhang etal., 1998b) but are slightly higher than those of the potassicvolcanic rocks in the Nangqen basin (0.7049–0.70614; Sun etal., 2001). The 143Nd/144Nd values of five porphyries in the

YULONG PORPHYRY COPPER BELT, E. TIBET 137

0361-0128/98/000/000-00 $6.00 137

FIG. 7. Plot of K2O vs. SiO2 for porphyry intrusions from the Yulong porphyry copper belt. The diagram shows that por-phyries from the Yulong belt share a shoshonitic magmatic affinity with the alkali-rich porphyries of the Ritong-Mamupu beltand potassic volcanic rocks in the Nangqen and Lawu basins but are different from the porphyries from the Cordillera beltof Chile, which have a calc-alkaline magmatic affinity (Richards et al., 2001). CA = calc-alkaline series, K-CA = high K calc-alkaline series, SH = shoshonitic series, TH = tholeiitic series.

Yulong belt yield a narrow range of values varying from0.512427 to 0.512532 (Wang et al., 1995; Zhang et al., 1998b),within the range of 143Nd/144Nd values for the Jinshajiang-Honghe alkali-rich intrusions (0.512333–0.512536; Zhangand Xie, 1997). However, these values are lower than those ofthe Nangqen volcanics (0.5124727–0.512606; Sun et al., 2001).These data indicate that the source of the Yulong porphyries

is transitional between the type II enriched mantle and theNangqen volcanic rocks and is near the mixing line betweenMORB and crust, similar to the alkalic intrusions of the Jin-shajiang-Honghe belt (Fig. 10a).

This suggests an enriched mantle source, modified or meta-somatized by MORB-derived melts or fluids (cf. Hawkeworthand Vollmer, 1979; Hart, 1984). Pb isotope compositions for

138 HOU ET AL.

0361-0128/98/000/000-00 $6.00 138

FIG. 8. Incompatible element abundances, normalized to oceanic ridge granite (ORG) (a) and chondrite (b), respectively,for the representative porphyries from the Yulong porphyry copper belt. Normalization values from Pearce et al. (1984) forORG. Data source for Chilean porphyries from Richards et al. (2001).

YULONG PORPHYRY COPPER BELT, E. TIBET 139

0361-0128/98/000/000-00 $6.00 139

FIG. 9. Chrondrite-normalized REE patterns of the monzonitic granite porphyry from the Yulong porphyry copper belt(a), syenite porphyries from the Ritong-Mamupu alkali-rich porphyry belt (b), and trachytes in the Tertiary pull-apart basins(c).

these porphyries are also consistent with this interpretation.These porphyries yield a range of 206Pb/204Pb values from18.75 to 18.89, 207Pb/204Pb values from 15.49 to 15.68, and208Pb/204Pb values from 38.53 to 39.12 (Ma, 1990; Zhang etal., 1998b). The lead isotope ratios are close to those of theNangqen volcanic rocks and Jinshajiang-Honghe alkali-richintrusions, which vary from 18.53 to 18.97 for 206Pb/204Pb,15.51 to 15.72 for 206Pb/204Pb, and 38.38 to 39.24 for208Pb/204Pb (Zhang et al., 1998b). Part of these porphyries fallwithin the type II enriched mantle field, whereas others fall

within the transitional field between the type II enrichedmantle field and MORB. These data support a hypothesisthat the Yulong belt porphyries were derived from a sourcesimilar to type II enriched mantle but metasomatized byMORB-derived fluid (or melt), as suggested by the Sr-Nd iso-tope data.

DiscussionThe spatial and temporal relationships and lithogeochemi-

cal characteristics of the Yulong porphyry belt reveal that (1)

140 HOU ET AL.

0361-0128/98/000/000-00 $6.00 140

TABLE 4. Summary of Nd, Sr, and Pb Isotope Data on the Yulong Porphyry Belt

Intrusions Rocks 206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 143Nd/144Nd 87Sr/86Srinitial

Yulong Monzogranite porphyry 18.733 15.626 38.890

18.890 15.682 39.11918.608 15.488 38.52818.805 15.648 38.86618.740 15.636 38.890

0.512451 0.7066

Malasongdo Monzogranite porphyry 18.861 15.608 38.821

18.826 15.608 38.87218.888 15.643 38.95518.864 15.615 38.869

0.512485 0.7077

Duoxiasongduo Monzogranite porphyry 18.871 15.622 38.920

18.867 15.586 38.79918.788 15.583 38.80118.869 15.627 38.911

0.512495 0.7065

Sources: Pb isotope data from Ma (1990), Nd and Sr isotope data from Wang et al. (1995)

FIG. 10. 87Sr/86Sr vs. 143Nd/144Nd diagram (a) and 207Pb/204Pb vs. 206Pb/204Pb diagram (b) for monzonitic granite porphyriesfrom the Yulong copper belt. DMM, HIMU, EMI and EMII represent four types of mantle end members, respectively(Zindle and Hart, 1986; Norman and Leeman, 1989). DMM = depleted MORB mantle, HIUM = high U/Pb mantle, EMI= type I enriched mantle, EMII = type II enriched mantle. Data for Yulong porphyry belt is from Wang et al. (1995), Ri-tong-Mamupu alkali-rich porphyry belt from Zhang and Xie (1997) and Zhang et al. (1998b), and Nangqen basin volcanicsfrom Sun et al. (2001). Data in (b) is from Ma (1990; Yulong porphyry belt). Nangqen basin volcanics from Zhang et al.(1998b) and Sun et al. (2001).

the mineralized porphyries occur along an intracontinentalconvergent zone, (2) they appear to be related to extensivestrike-slip faulting along this zone, and (3) the porphyry in-trusions have geochemical affinities similar to arc magmas.

Possible sources of ore-bearing porphyries

The trace element characteristics of the Yulong belt por-phyries show an arc magmatic affinity and suggest a mantlesource metasomatized by a hydrous fluid derived from wetsubducted oceanic slab (cf. Gill, 1981; Tatsumi, 1983, 1986).These enriched fluids are interpreted to have metasomatizedthe mantle wedge, resulting in not only the formation of is-land-arc mantle enriched in LILE, LREE, and Th, but also inthe formation of H2O-bearing minerals in the mantle wedge.Phlogopite harzburgite xenoliths have been found in alkali-rich intrusions and lamprophyres from the Litong-Mamupubelt (Huang and Wang, 1996; Huang et al., 1997). This com-bined with the low TiO2 content and high abundance of K andRb for the Yulong porphyries supports the idea of metasoma-tism of the mantle source regions.

A type II enriched mantle source, with high radiogenic Srand low nonradiogenic Nd, indicated for the Yulong belt por-phyry is commonly attributed to mixed metasomatism be-tween mantle wedge material and crustal material introducedby ancient subducted oceanic slab and sediments. The Sr, Nd,and Pb isotope compositions of the porphyries usually are atransitional zone between MORB and type II enriched man-tle compositions but closer to the latter (Fig. 10). This sup-ports the suggestion that the porphyry magmas were derivedfrom the enriched mantle, metasomatized by subducted slabcomponents (H2O, LILE, LREE, Th, etc.).

Two candidates exist for a mantle source that may havebeen melted to produce the felsic magmas: subduction of theSongpan-Ganze-Hoh Xil terrane or the Jinshajiang paleo-oceanic crust. Yin and Harrison (2000) suggest that subduc-tion of the Songpan-Ganze-Hoh Xil terrane (Fig 1) to thesouth probably accounts for the seismic structure of theQiangtang terrane. They interpreted that potassic volcanismwith an age of 20 Ma in central Tibet originated from this sub-ducting plate. If the model is reasonable, a potassic porphyrybelt associated with these potassic volcanic rocks could havedeveloped along the subduction zone. However, no such beltexists along the northern margin of the Qiangtang terrane.

Alternatively, the development of the Permian Jiangda-Weixi volcanic arc and fragments of the Jinshajiang ophiolitewith U-Pb zircon ages varying from 296 to 340 Ma (Zhan etal., 1998; Wang et al., 1999) suggest that subduction of theJinshajiang paleo-oceanic crust occurred beneath theChangdu continental block (Fig. 2b; Liu et al., 1993; Mo etal., 1993; Hou et al., 1996; Wang et al., 1999). The velocitystructure of the Qiangtang terrane indicates westward sub-duction at an angle of about 45° under the Changdu conti-nental block (Liu et al., 2000). This subducted slab presentlylies at depths of 100 to 300 km and extends beyond the west-ern margin of the block toward the Lahsa terrane (Zhong etal., 2000, 2001). This slab might have been shallower than 100km underneath the eastern margin of the Changdu block inthe Paleocene. For example, a 20-km-thick, gently dipping,high-velocity (7.881 km/s) layer occurs 50 to 60 km beneaththe Dali area (Fig. 2; Zhong et al., 2000, 2001) and may

represent the relic subducted slab. The depth of the Yulongbelt magma source is estimated to be 48 to 60 km by mineral-melt equilibrium calculation (Ma, 1990), which is roughly thesame as that for the interrupted relic slab (Zhong et al., 2000,2001). Wang et al (1995) and Zhang and Xie (1997) estimatedthat TCHURNd ages of the ore-bearing porphyries and alkali-rich intrusions vary from 230 to 250 Ma, according to data forthe Yulong and Honghe belts. If these ages represent the ageof the formation of the source, the age is identical to the ageof subducted Jinshajiang oceanic slab and its likely interactionwith the overlying mantle wedge.

Role of strike-slip fault system on magma genesis and emplacement

The distribution of porphyry deposits in eastern Tibetstrongly suggests that a regional-scale strike-slip fault systemcontrolled the development of the porphyry Cu belt, eitherdirectly or indirectly. This situation is broadly similar to thestructural setting of porphyry Cu deposits in the Andean mag-matic arcs (e.g., Camus and Dilles, 2001; Richard et al., 2001)but in a continental orogenic setting. Emplacement of theporphyry intrusions appears to have coincided with stress re-laxation and a transition in the orientation of strike-slip move-ment. The dextral shear along the Jinshajiang strike-slip fault-ing system is consistent with the plate reconstruction thatshows north-directed subduction of the Indian continentaround 60 to 70 Ma. This collision also formed the extensiveGangdese granite belt with a peak age of about 55 Ma. Theseobservations suggest that the stress relaxation in the Yulongregion was probably related to northeastward wedging of theIndian continent during the Paleocene and Eocene. Thiswedging caused intense east-west compression and the con-jugate strike-slip movement with an X-shaped structural knotcentered just south of Yulong (Fig. 11). In this model, theChangdu block was displaced northward along strike-slipfaults that formed a group of strike-slip extensional basins.These basins include the Gonjo basin on the eastern side ofthe Yulong belt and the Nangqen and Lawu basins on thewestern side of the Litong-Mamupu alkali-rich intrusion belt(Figs. 2, 11). The Gonjo basin is a dextral strike-slip pull-apartbasin bounded by the Chesuo right-lateral strike-slip fault tothe east (Wang et al., 2000). The Nangqen and Lawu basinsare sinistral strike-slip pull-apart basins controlled by theTuoba left-lateral strike-slip fault (Wang et al., 2000), with re-versed shear direction. These basins contain more than 2,600-m-thick Tertiary red-bed sedimentary rocks interlayered withlatitic-trachytic volcanic rocks. The ages of the potassic vol-canic rocks range from 42.4 to 37.5 Ma, thus it is estimated tocommence at ca. 42 Ma for the strike-slip extension that con-trolled the eruption of these volcanic rocks and the formationof the extensional pull-apart basins. This suggests that the pe-riod of the stress relaxation and transition, from a single dex-tral strike-slip fault system to a conjugate strike-slip faultzone, coincides generally with the time (ca. 36 Ma; Du et al.,1994) of the formation of porphyry copper mineralization bythe Re-Os age of molybdenites (Du et al., 1994).

Transtensional structures, such as pull-apart basins, mighthave facilitated the ascent and shallow-level emplacement ofthe porphyry-related plutons. Similar transtensional modelsfor plutonism in arcs have been proposed to explain the

YULONG PORPHYRY COPPER BELT, E. TIBET 141

0361-0128/98/000/000-00 $6.00 141

spatial-temporal localization and formation of porphyry hy-drothermal-magmatic systems (e.g., Lindsay et al., 1995;Richards et al., 2001). In the Tibetan orogen, large-scalestrike-slip fault systems and associated transtensional struc-tures not only could have provided the dilatational conduitsfor the emplacement of Cu porphyries and associated potas-sic volcanism but may also have been factors responsible formelting of a metasomatized mantle source.

Seismic profiles across the Qiangtang terrane indicate thatthe strike-slip faults are translithospheric and accommodatedlocal mantle uplift, with the Moho rising about 2 to 3 km rel-ative to the surrounding area (Fei, 1983; Tang and Luo,1995). This suggests that these faults probably caused the de-compression of the lithosphere in the area, which inducedmelting of a mantle source.

Regional tectonic model for the formation of ore-bearing porphyry in the Yulong belt

The convergence and collision between the Indian andAsian continents that occurred at 60 to 70 Ma (Yin and Har-rison, 2000; Zhong et al., 2001) resulted in the Himalayan-Tibetan orogen and the Gangdese collisional granite belt (55–36 Ma). A broad, north-south–trending right-lateral strike-slip fault system, perpendicular to the collision zone, devel-oped in eastern Tibet to adjust to the collisional strain.Translithospheric faulting triggered the rise and partial melt-ing of a hydrous, enriched source, manifested by the occur-rence of Tertiary potassic basalt and trachyte in the Nangqenand Gonjo basins. The northeastward migration of the Indiancontinent, and subsequent collision with the Yangtze continent

142 HOU ET AL.

0361-0128/98/000/000-00 $6.00 142

FIG. 11. Proposed strike-slip system and strike-slip pull-apart basin model for eastern Tibet (modified from Liu et al.,1983). (a). Shows the distribution of the Himalayan strike-slip system and strike-slip pull-apart basin in the Changdu-Simaocontinental block. (b). A mechanical model for the strike-slip structure. (See text for discussion).

in the Eocene and later, was accompanied by the formation ofthe regional conjugate strike-slip fault zones (Fig. 11). Thetransition from a single dextral to conjugate strike-slip shearsresulted in the formation of strike-slip pull-apart basins andalso permitted the ascent of a large volume of volatile-en-riched felsic magma that had pooled near the base of thelithosphere. In the western Yunnan region, left-lateral strike-slip movement along the Honghe fault controlled the forma-tion of the Honghe alkali-rich intrusion belt and the develop-ment of the Ailaoshan metamorphic belt. In eastern Tibet,the Wenquan right-lateral fault and a series of northwest-trending folds and compressional shear faults controlled thedistribution of the Yulong porphyry belt (Fig. 3).

Westward subduction of the Jinshajiang oceanic plate in thePaleozoic is thought to have played a key role in the genera-tion of the Yulong porphyry belt. The dehydration of the sub-ducted slab at 40 to 60 km probably produced an H2O-richfluid that was enriched in LILE, LREE, and Th (Tatsumi,1983, 1986). The fluid moved upward and metasomatized themantle wedge to form the source for the Jiangda-Weixi mag-mas. Magmas generated from the partial melting of the meta-somatized mantle wedge subsequently mixed with melt de-rived from the subducted slab to form a unique source for theYulong granite porphyry magmas.

Comparison to other deposits in the world

The alteration and mineralization geometries and assem-blages of the Yulong belt deposits are similar to those ob-served in the porphyry and related copper-gold deposits inthe western Pacific region (e.g., Sillitoe, 1979, 1989, 2000).Most of these deposits have magnetite-bearing K silicate al-teration associated with copper mineralization and are goldrich (e.g., Panguna, Papua New Guinea: Eastoe, 1978, 1982;Ford, 1978; Far Southeast-Lepanto, Philippines: Hedenquistet al., 1998; Grasberg, Indonesia: McDonald and Arnold,1994; Bajo de la Alumbrera, Argentina: Ulrich and Heinrich,2001; Ulrich et al., 2001). Appreciable amounts (up to 0.35ppm) of gold within the K silicate assemblage also have beenobserved in the Yulong belt (Table 2). Telescoping of alter-ation assemblages and formation of chalcocite blankets arealso features of the Ceno-Mesozoic porphyry-related copperdeposits in the western Asia-Pacific region (e.g., Sillitoe, 1989;Ojeda, 1990; Kyaw Win and Kirwin, 1998; Peng et al., 1998;Khin Zaw et al., 1999; Perello et al., 2001). Many of the en-richment blankets are interpreted to have formed in responseto regional synmineralization tectonic uplift (Maksaev andZentilli, 1999). However, such similar supergene zones andoverprinting of porphyry-style alteration by epithermal assem-blages have not been observed in the Yulong belt. The lack ofoverprinting by epithermal assemblages and telescoping of al-teration assemblages may suggest that there was not signifi-cant tectonic uplift during the lifetime of the Yulong systems.

ConclusionsThe Yulong porphyry copper belt in eastern Tibet is tec-

tonically located in the Qiangtang terrane of the Himalayan-Tibetan orogen. It is controlled by the Jinshajiang strike-slipfault system that was formed by the convergence and collisionbetween the Asia and Indian continents at 60 to 70 Ma andstrikes roughly orthogonal to the convergent zone.

The mineralized porphyries are characterized by high K2Oand enrichment in LILE (K, Rb, Ba), LREE, and Th, sug-gesting a shoshonitic magma affinity. Geochemical analysisand Sr-Nd-Pb isotope data indicate that these felsic magmasevolved to increasingly felsic and volatile-rich compositionsby fractional crystallization and were mainly derived from ahydrous, enriched mantle source that was metasomatized bysubducted oceanic slab components (e.g., H2O, K, Rb, Ba,LREE, and Th). The oceanic slab is probably the Jinshajiangoceanic plate during the Paleozoic.

The timing of Cu-bearing porphyry emplacement (33–54Ma) with respect to regional structural evolution suggests thatplutonism occurred in response to the stress relaxation andtransition from a single dextral strike-slip fault system to a sys-tem of conjugate strike-slip fault zones with the formation ofstrike-slip pull-apart basins that facilitated the rise of a largevolume of volatile-enriched melt. The same faults may alsohave caused the uplift of the mantle and the decompressionthat caused the partial melting of the source.

AcknowledgmentsThe authors thank the local mining geologists for supplying

important materials on the porphyry copper deposits and re-searchers from the Chinese Academy of Geological Sciences(CAGS), Beijing, and Center for Ore Deposit Research, Uni-versity of Tasmania, for their constructive discussions andcomments. We are deeply indebted to Stephen Peters, ByronBerger, and Warren Nokleberg of the U.S. Geological Surveyand an anonymous referee of Economic Geology for theirtime and efforts, incisive reviews, valuable comments, andsuggestions to improve the earlier draft of this manuscript.Special thanks are due to Rohan Wolfe and Thomas Ulrichwho critically read the manuscript. Advice and encourage-ment of Mark Hannington, editor of Economic Geology, topublish this paper is also appreciated. This work is supportedby grants from the Ministry of Science and Technology, China(Basic Research Project G1998040807; Key Program 95-Pre-39) and NSFC (49773177). May 30, 2001; September 4, 2002

REFERENCESAllegre, C.J., et al., 1984, Structure and evolution of the Himalayan-Tibet

orogenic belt: Nature, v. 307, p. 17–22.Bonin, B., Grelou-Orsini, C., and Vialette, Y., 1978, Age, origin and evolution

of the anorogenic complex of Evisa (Corsica): A K-Li-Rb-Sr study: Contri-butions to Mineralogy and Petrology, v. 65, p. 425–435.

Bowen, R., and Gunatilaka, A., 1977, Copper: Its geology and economics:London, Applied Science Publishers Ltd., 150 p.

Burchfiel, B.C., Chen Z.-L., Liu, Y.-P., and Royden, L. H., 1995, Tectonics ofthe Longmen Shan and adjacent regions, central China: International Ge-ology Review, v. 37, p. 661–735.

Camus, F., and Dilles, J. H., 2001, A special issue devoted to porphyrycopper deposits of northern Chile: Preface: ECONOMIC GEOLOGY, v. 96,p. 233–237.

Camus, F., Sillitoe, R.H., and Petersen, R., eds., 1996, Andean copper de-posits: New discoveries, mineralization style and metallogeny: Society ofEconomic Geologists Special Publication 5, 198 p.

Chang, C.-F., and Zheng, S.-L., 1973, Tectonic feature of the Mount JolmoLungma region in southern Tibet, China: Scientia Geologica Sinica, v. 1,p. 1–12.

Chen, F.-Z., and Liao, G.-X., 1983, The geology and major mineral resourcesin the Changdu area: Contribution to the Geology of the Qinghai-TibetPlateau (13), Beijing, Geological Publishing House, 168 p. (in Chinese)

YULONG PORPHYRY COPPER BELT, E. TIBET 143

0361-0128/98/000/000-00 $6.00 143

Chen, W.-M., 1983, Relationship of the Yulong porphyry copper deposit withsandstone copper deposits: Contribution to Geology in the Qinghai-TibetPlateau (13), Beijing, Geological Publishing House, 234 p. (in Chinese)

Dewey, J. F., 1988, Extensional collapse of orogens: Tectonics, v. 7, p. 1123–1139.Du Andao, He Hongliao, and Yin Wanning, 1994, The study on the analyti-

cal methods of Re-Os age for molybdenites: Acta Geologica Sinica, v. 68, p.339–346 (in Chinese with English abs.).

Eastoe, C. J., 1978, A fluid inclusion study of the Panguna porphyry copperdeposit, Bougainville, Papua New Guinea: ECONOMIC GEOLOGY, v. 73, p.721–748.

——1982, Physics and chemistry of the hydrothermal system at the Pangunaporphyry copper deposit, Bougainville, Papua New Guinea: ECONOMICGEOLOGY, v. 77, p. 127–153.

England, P., and Molnar, P., 1990, Right-lateral shear and rotation as the ex-planation for strike-slip faulting in eastern Tibet: Nature, v. 344, p. 140–142.

Fei, D., 1983, Regional structure in the northern part of the South China Seaand transition from continental crust to oceanic crust: Journal of Geo-physics, v. 26, p. 459–467 (in Chinese with English abs.).

Ford, J.H., 1978, A chemical study of alteration at the Panguna porphyrycopper deposit, Bougainville, Papua New Guinea: ECONOMIC GEOLOGY, v.73, p. 703–720.

Gill, J. B., ed., 1981, Orogenic andesite and plate tectonics: Berlin, Springer-Verlag, 390 p.

Griffiths, J.R., and Godwin, C.I., 1983, Metallogeny and tectonics of por-phyry copper-molybdenum deposits in British Columbia: Canadian Journalof Earth Sciences, v. 20, p. 1000–1018.

Hart, S.R., 1984, A large-scale isotope anomaly in the southern Hemispheremantle: Nature, v. 309, p. 753–757.

Hawkeworth, C.J., and Vollmer, R., 1979, Crustal contamination versus en-riched mantle: 143Nd/144Nd and 87Sr/86Sr evidence from the Italian vol-canics: Contributions to Mineralogy and Petrology, v. 69, p. 151–169.

Hedenquist, J.W., Arribas, A., Jr., and Reynolds, T.J., 1998, Evolution of anintrusion-centered hydrothermal system: Far Southeast-Lepanto porphyryand epithermal Cu-Au deposits, Philippines: ECONOMIC GEOLOGY, v. 93, p.373–404.

Hou, Z-Q., 1993, Tectono-magmatic evolution of the Yidun island-arc andgeodynamic setting of kuroko-type sulfide deposits in Sanjiang region,China: Resource Geology, v. 17, p. 336–350.

Hou, Z.-Q., Hou, L.-W., Yie, Q.-T., Liu, F.-L., and Tang, G.-G., 1995,Tectono-magmatic evolution of the Yidun island-arc and volcanogenic mas-sive sulfide deposits in the Sanjiang region, S.W. China: Beijing, Earth-quake Press, 185 p. (in Chinese)

Hou, Z.-Q., Mo, X.-X., Zhu, Q.-W., and Shen, S.-Y., 1996, Mantle plume inthe Paleozoic Tethys: Evidence from the mid-oceanic ridge basalt: ActaGeoscientia Sinica, v. 17, p. 362–375 (in Chinese with English abs.).

Hou, Z.-Q., Deng, J., Sun, H.-T., and Song, S.-H., 1999, Volcanogenic mas-sive sulfide deposits in China: Setting, feature and style: Exploration andMining Geology, v. 8, p. 149–175.

Hou Z.-Q., Khin Zaw, Qu, X.-M., Ye, Q.-T., Yu, J.-J., Xu, M.-J., Fu, D.-M.,and Yin, X.-K., 2001, Origin of the Gacun volcanic-hosted massive sulfidedeposit in Sichuan, China: Fluid inclusion and oxygen isotope evidence:ECONOMIC GEOLOGY, v. 96, p. 1491–1512.

Huang, Z.-L., and Wang, L.-K., 1996, Geochemistry of lamprophyres in theLaowangzhai gold mine, Yunnan: Geochimica, v. 25, p. 255–263 (in Chi-nese with English abs.).

Huang, Z.-L., Wang, L.-K., and Zhu, C.-M., 1997, Petrological study of lam-prophyres in the Laowangzhai gold mine, Yunnan: Geological Sciences, v.32, p. 74–87 (in Chinese with English abs.).

Khin Zaw, Burrett, C.F., Berry, R.F., and Bruce, E., 1999, Geological andmetallogenic relations of mineral deposits in SE Asia: Australian MineralIndustry Research Association (AMIRA) Final Report, February 1999,University of Tasmania, unpublished, 225 p.

Kyaw Win and Kirwin, D., 1998, Exploration, geology and mineralisation ofthe Monywa copper deposits, central Myanmar: Porphyry and Hydrother-mal Copper and Gold Deposits: A Global Perspective, Perth, Australia, No-vember 30-December 1, 1998, Conference Proceedings, p. 61–74.

Leloup, P.H., Lacassin, R., Tapponnier, P., Scharer, U., Zhong, D., Xiaohan,L., Liangshang, Z., Shaocheng, J., and Phan Trong Trinh, 1995, The AilaoShan-Red River shear zone (Yunnan, China), Tertiary transform boundaryof Indochina: Tectonophysics, v. 251, p. 3–84.

Li, X.-Z. Liu, W.-J., Wang, Y.-Z., and Zhu, Q.-W., 1999, The tectonic evolu-tion of the Tethys and mineralization in the Sanjiang, southwestern China:Beijing, Geological Publishing House, 258 p. (in Chinese with English abs.)

Li, Y.-Q., Rui, Z.-Y., and Cheng, L.-X., 1981, Fluid inclusions and mineral-ization of the Yulong porphyry copper (Mo) deposit: Acta Geologica Sinica,v. 55, p. 18–23 (in Chinese with English abs.).

Lindsay, S.D., Zentilli M., and Rojas de Rivera, J., 1995, Evolution of an ac-tive ductile to brittle shear system controlling mineralization at theChuquicamata porphyry copper deposit, northern Chile: International Ge-ology Review, v. 37, p. 945–958.

Liu, R.-M., Zhao, D.-H., and Huang, X-R., 1981, Discussion on isotopic agesof acid intrusions in the eastern Tibet: Geological Review, v. 27, p. 326–332(in Chinese with English abs,).

Liu Z.-Q., 1988, Geologic map of the Qinghai-Xizang plateau and its neigh-boring region (1:500000): Beijing, Geological Publishing House (in Chinese).

Liu, Z.-Q., Li, X.-Z., Ye, Q.-T., Luo, J.-N., and Shen, G.-F., 1993, Division oftectono-magmatic belts and the distribution of deposits in the Sanjiangarea: Beijing, Geological Publishing House, 246 p. (in Chinese with Eng-lish abs.)

Ma, H.-W., 1983, Petrology and mineralization of the porphyry in the Mala-songduo district, eastern Tibet: Earth Science, Journal of Wuhan Collegeof Geology, v. 19, p. 115-128 (in Chinese with English abs.).

——1984, Physical-chemical conditions of the hydrothermal alterations inthe Malasongduo porphyry copper deposit, eastern Tibet and its relation-ship with mineralization: Earth Science, Journal of Wuhan College of Ge-ology, v. 20, p. 147–158 (in Chinese with English abs.).

——1990, Granitoid and mineralization of the Yulong porphyry copper beltin eastern Tibet: Beijing, Press of China University of Geosciences, 157 p.(in Chinese with English abs.)

Maksaev, V., and Zentilli, M., 1999, Fission track thermochronology of theDomeyko cordillera, northern Chile: Implications for Andean tectonics andporphyry copper metallogenesis: Mining Geology and Exploration, v. 8, p.65–89.

McDonald, G.D., and Arnold, I.C., 1994, Geological and geochemical zon-ing of the Grasberg igneous complex, Iran Jaya, Indonesia: Journal of Geo-chemical Exploration, v. 50, p. 143–178.

Mitchell, A.H.G., 1973, Metallogenic belts and angle of dip of Benioff zones:Nature, v. 245, p. 49–52.

Miyashiro, A., 1977, Nature of alkalic volcanic rock series: Contributions toMineralogy and Petrology, v. 66, p. 91–110.

Mo, X.-X., Lu, F.-X., Shen, S.-Y., Zhu, Q.-W., and Hou, Z.-Q., 1993, TheTethyan volcanism and mineralization in the Sanjiang region: Beijing, Ge-ological Publishing House, 250 p. (in Chinese with English abs.)

Molnar, P., and Tapponnier, P., 1978, Active tectonics of Tibet: Journal ofGeophysical Research, v. 83, p. 5361–5375.

Murphy, M.A., Yin, A., Harrison, T.M., Durr, S.B., Chen, Z., Ryerson, F.J., Kidd,W.S.F., Wang, X., and Zhou, X., 1997, Significant crustal shortening in south-central Tibet prior to the Indo-Asian collision: Geology, v. 25, p. 719–722.

Nakamura, E., 1985, The influence of subduction processes on the geo-chemistry of Japanese alkaline basalts: Nature, v. 316, p. 55–58.

Norman, M.D., and Leeman, W.P., 1989, Geochemical evolution of Creta-ceous magmatism and its relation to tectonic setting, southwestern Idaho,USA: Earth and Planetary Science Letters, v. 94, p. 78–96.

Ojeda, J.M., 1990, Geology of the Escondida porphyry copper deposit, II re-gion, Chile: Pacific Rim Congress, Gold Coast, Queensland, Australia, Aus-tralian Institute of Mining and Metallurgy, 1990, Proceedings, v. 2, p.473–483.

Pan, G.-T., 1990, Tectonic evolution of the Qinghai-Tibet plateau: Beijing,Geological Publishing House, 243 p. (in Chinese with English abs.)

Peace, J.A., Harris, N.B.W., and Tindle, A.G., 1984, Trace element discrimi-nation diagrams for the tectonic interpretation of granitic rocks: Journal ofPetrology, v. 25, p. 956–983.

Peltzer, G., and Tapponnier, P., 1988, Formation and evolution of strike-slipfaults, rifts and basins during the India-Asia collision: An experimental ap-proach: Journal of Geophysical Research, v. 93, p. 15085–15117.

Peng, Z., Watanabe, M., Hoshino, K., Sueoka, S., Yano, T., and Nishido, H.,1998, The Machanqing copper-molybdenum deposits, Yunnan, China—anexample of Himalayan porphyry-hosted Cu-Mo mineralization: Mineralogyand Petrology, v. 63, p. 95–117.

Perello, J., Cox, D., Garamjav, D., Sanjdorj, S., Diakov, S., Schissel, D., Munkh-bat, T.-O., and Oyun, D., 2001, Oyu Tolgoi, Mongolia: Siluro-Devonianporphyry Cu-Au-(Mo) and high-sulfidation Cu mineralization with a Cre-taceous chalcocite blanket: ECONOMIC GEOLOGY, v. 96, p. 1407–1428.

Pierce, J.A., and Mei, H., 1988, Volcanic rocks of the 1985 Tibet GeotraverseLhasa to Golmud: Philosophical Transactions of the Royal Society of Lon-don, v. A327, p. 203–213.

144 HOU ET AL.

0361-0128/98/000/000-00 $6.00 144

Rao, R.-B., Xu, J., Chen, Y., and Zou D., 1987, The Triassic system of theQinghai-Tibet plateau: Beijing, Geological Publishing House, 149 p. (inChinese)

Richards, J.P., Boyce, A.J., and Pringle, M.S., 2001, Geologic evolution of theEscondida area, northern Chile: A model for spatial and temporal locationof porphyry Cu mineralization: ECONOMIC GEOLOGY, v. 96, p. 271–305.

Rui, Z.-Y., Huang, C.-K., Qi, G.-M., Xu, J., and Zhang, M.-T., 1984, The por-phyry Cu(-Mo) deposits in China: Beijing, Geological Publishing House,350 p. (in Chinese with English abs.)

Sengor, A.M.C., and Natalin, B.C., 1996, Paleotectonics of Asia: Fragmentsof a synthesis, in Yin, A., and Harrison, T. M., eds., The tectonics of Asia:New York, Cambridge University Press, p. 486–640.

Sillitoe, R.H., 1972, A plate tectonic model for the origin of porphyry copperdeposits: ECONOMIC GEOLOGY, v. 67, p. 184–197.

——1979, Some thoughts on gold-rich porphyry copper deposits: Mineral-ium Deposita, v. 14, p. 161–174.

——1989, Gold deposits in Western Pacific island arcs: The magmatic con-nection: ECONOMIC GEOLOGY MONOGRAPH 6, p. 274–291.

——2000, Gold-rich porphyry deposits: Descriptive and genetic models andtheir role in exploration and discovery: Reviews in Economic Geology, v.13, p. 315–345.

Sillitoe, R.H., and Camus, F., eds., 1991, A special issue devoted to gold de-posits in the Chilean Andes: ECONOMIC GEOLOGY, v. 86, p. 1153–1345.

Streckeisen, A., and Lemaitre, R.W., 1979, A chemical approximation to themodel QAPF classification of igneous rocks: Neues Jahrbuch für Mineralo-gie, Abhandlungen, v. 136, p. 169–206.

Sun, H.-J., Deng, W.-M., and Zhang, Y.-Q., 2001, Petrogenesis of Cenozoicpotassic volcanic rocks in the Nangqen basin: Acta Geologica Sinica, v. 75,p. 27–40 (in Chinese with English abs.).

Tang, R.-L., and Luo, H.-S., 1995, The geology of Yulong porphyry copper(molybdenum) ore belt, Xizang (Tibet): Beijing, Geological PublishingHouse, 320 p. (in Chinese with English abs.)

Tapponnier, P., and Molnar, P., 1976, Slip-line field theory and large-scalecontinental tectonics: Nature, v. 264, p. 319–324.

Tapponnier, P., Lacassin, R., Leloup, P.H., Scharer, U., Zhong, D-L., Haiwei,W., Liu, X-H., Ji, S-C., Zhang, L-S., and Zhong, J-Y., 1990, The AilaoShan/Red River metamorphic belt: Tertiary left-lateral shear between In-dochina and South China: Nature, v. 343, p. 431–437.

Tatsumi, Y., 1983, Generation of arc basalt magma and thermal structure ofthe mantle wedge in subduction zones: Journal of Geophysical Research, v.88, p. B5815–B5825.

——1986, Chemical characteristics of fluid phase released from a subductionlithosphere and origin of arc magma: Evidence from high pressure experi-ments and natural rocks: Journal of Volcanology and Geothermal Research,v. 29, p. 293–309.

Ulrich, T., and Heinrich, C.A., 2001, Geology and alteration geochemistry ofthe porphyry Cu-Au deposit at Bajo de la Alumbrera, Argentina: ECO-NOMIC GEOLOGY, v. 96, p. 1719–1742.

Ulrich, T., Gunthur, D., and Heinrich, C.A., 2001, The evolution of a por-phyry Cu-Au deposit, based on LA-ICP-MS analysis of fluid inclusions:Bajo de la Alumbrera, Argentina: ECONOMIC GEOLOGY, v. 96, p. 1743–1774.

Wang, L.-Q., Pan, G.-T., and Li, D.-M., 1999, Temporal-spatial architectureof the Jinshajiang arc-basin system and geological evolution: Acta Geolog-ica Sinica, v. 73, p. 206–218 (in Chinese with English abs.).

Wang, M.-J., Peng, Y.-M., Wang, G.-M., Shentu, B.-Y., Yao, P., and Chen, M.,2000, Evolution of the Changdu basin and mineralization: Chengdu Insti-tute of Geological and Mineral Resources Open File no. 95-02-001-02, 268p. (in Chinese)

Wang, X.-F., Metcalfe, I., and Jian, P., 1999, Division of tectono-strata andgeological times in the Jinshajiang suture zone: Sciences in China, v. 29, p.290–296 (in Chinese).

Wang, Z., Shentu, B.-Y., Ding, J.-C., Yao, P., and Geng, Q.-R., 1995, Grani-toid and it’s mineralization in the eastern Tibet, China: Chengdu, Publish-ing House of the Southwestern University of Communication, 150 p. (inChinese with English abs.)

Yin, A., and Harrison T.M., 2000, Geologic evolution of the Himalayan-Ti-betan orogen: Annual Review of Earth and Planetary Sciences, v. 28, p.211–280.

Zhan, M.-G., Lu, Y.-F., and Chen S-F., 1998, The Yangla copper deposit inthe Deqen district, western Yunnan: Wuhan, Publishing House of ChinaUniversity of Geosciences, 168 p. (in Chinese with English abs.)

Zhang, Y.-Q., and Xie, Y.-W., 1997, Chronology and Nd-Sr isotopes of theAilaoshan-Jinshajiang alkali-rich intrusions: Sciences in China, v. 27, p.289–293 (in Chinese).

Zhang, Y.-Q., Xie, Y.-W., Qiu H.-N., Li, X.-H., and Zhong S.-L., 1998a, Pet-rogenesis series and the ore-bearing porphyries of the Yulong copper orebelt in eastern Tibet: Geochimica, v. 27, p. 236–243 (in Chinese with Eng-lish abstract).

——1998b, Shoshonitic series: Sr, Nd, and Pb isotopic compositions of ore-bearing porphyry for the Yulong copper ore belt in eastern Tibet: ScientiaGeologica Sinica, v. 33, p. 359–366 (in Chinese with English abs.).

Zhong, D.-L., Ding, L., Zhang, J.-J., and Ji, J.-Q., 2000, Multi-periodic colli-sional process between Indian and Asian continents: A case of eastern Hi-malayan syntaxis and Hengduan mountains [abs.]. Abstract of the 15th

Workshop of the Himalaya, Karakoram and Tibet (HKT): Earth Frontiers,v. 7, p. 47–48.

Zhong, D.-L., Ding, L., Liu, F.-T., Liu, J.-H., Zhang, J.-J., Ji, J-Q., and Chen,H., 2001, The poly-layered architecture of lithosphere in the orogen and itsconstraint on Cenozoic magmatism: Science in China, v. 30, p. 1–8 (in Chi-nese).

Zhou, Y.-J., 1980, Constraint factors and origin of porphyry copper depositsin the Yulong belt: Geological Review, v. 269, p. 40–48 (in Chinese withEnglish abs.).

Zindle, A., and Hart, S. R., 1986, Chemical geodynamics: Annual Review ofEarth and Planetary Sciences, v. 14, p. 493–573.

YULONG PORPHYRY COPPER BELT, E. TIBET 145

0361-0128/98/000/000-00 $6.00 145