doi: 10.1111/j.1751-3928.2011.00177.x Resource Geology Vol. 62, No.

1: 4–18

Thematic Article rge_177 4..18

Highly Oxidized Magma and Fluid Evolution of

Miocene Qulong Giant Porphyry Cu-Mo Deposit,
Southern Tibet, China

Bo Xiao,1,2 Kezhang Qin,1 Guangming Li,1 Jinxiang Li,1 Daixiang Xia,3 Lei Chen1,2 and
Junxing Zhao1,2
1
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, 2Graduate University
of Chinese Academy of Sciences, Beijing and 3Tibet Julong Copper Co., Ltd, Lhasa, China

Abstract
The Miocene Qulong porphyry Cu-Mo deposit, which is located at the Gangdese orogenic belt of Southern
Tibet, is the largest porphyry-type deposit in China, with confirmed Cu ~10 Mt and Mo ~0.5 Mt. It is spatially
and temporally associated with multiphase granitic intrusions, which is accompanied by large-scale hydro-
thermal alteration and mineralization zones, including abundant hydrothermal anhydrite. In addition to
hydrothermal anhydrite, magmatic anhydrite is present as inclusions in plagioclase, interstitial minerals
between plagioclase and quartz, and phenocrysts in unaltered granodiorite porphyry, usually in association
with clusters of sulfur-rich apatite in the Qulong deposit. These observations indicate that the Qulong magma-
hydrothermal system was highly oxidized and sulfur-rich. Three main types of fluid inclusions are observed
in the quartz phenocrysts and veins in the porphyry: (i) liquid-rich; (ii) polyphase high-salinity; and (iii)
vapor-rich inclusions. Homogenization temperatures and salinities of all type inclusions decrease from the
quartz phenocrysts in the porphyry to hydrothermal veins (A, B, D veins). Microthermometric study suggests
copper-bearing sulfides precipitated at about 320–400°C in A and B veins. Fluid boiling is assumed for the early
stage of mineralization, and these fluids may have been trapped at about 35–60 Mpa at 460–510°C and 28–42
Mpa at 400–450°C, corresponding to trapping depths of 1.4–2.4 km and 1.1–1.7 km, respectively.
Keywords: fluid inclusion, Gangdese, highly oxidized, magmatic anhydrite, Qulong porphyry Cu–Mo deposit,
Sulfur-rich magma.

1. Introduction Primary magmatic anhydrite (CaSO4) which precipi-

tates directly from silicate melts is rare in volcanic rocks
Magmas associated with porphyry Cu mineraliza- and has been reported in only a few locations, such as
tion are oxidized and contain sulfur as sulfates, such as El Chichón in Mexico (Luhr et al., 1984) and Mount
SO42- (Ishihara, 1977; Burnham & Ohmoto, 1980; Blevin Pinatubo in the Philippines (Bernard et al., 1991).
& Chappell, 1992; Keith & Swan, 1995). Calc-alkaline The Qulong porphyry Cu–Mo deposit is located at
volcanic rocks, particularly those rich in hornblende or the center part of the newly discovered Gangdese met-
biotite, appear to have crystallized at oxygen fugacity allogenic belt in southern Tibet. The deposit was first
(fO2) high enough to stabilize anhydrite (Imai, 2002). explored in its northern part, and the Tibet Julong

Received 6 June 2010. Accepted for publication 25 October 2011.

Corresponding author: K. QIN, Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of
Sciences, Beijing 100029, China. Email: kzq@mail.iggcas.ac.cn

© 2011 The Authors

4 Resource Geology © 2011 The Society of Resource Geology
 Highly oxidized magma and fluid evolution of Miocene Qulong

Copper Co., Ltd. (2008) reported resources of 7.19 Mt contains more than 10 Cenozoic porphyry deposits.
Cu and 0.35 Mt Mo. During 2008 and 2009, the Qin et al. (2005) emphasized those Miocene porphyry
company prospected in the southern part and gained Cu deposits formed in a transitional tectonic setting
additional resources of about 2.87 Mt Cu and 0.15 Mt from compression to extension. The Qulong porphyry
Mo. The Qulong deposit is now the largest porphyry Cu–Mo deposit is the largest among them, which
Cu deposit in China, with at least ~10.6 Mt Cu, average is located in the southern part of Gangdese orogenic
0.5% and ~0.5 Mt Mo, average 0.03%. Compared with belt (latitude 29°36′–29°40′ N, longitude 91°33′–91°37′
other Cenozoic porphyry deposits in the Gangdese E), about 50 km east of Lhasa city, the capital of Tibet
metallogenic belt, the Qulong deposit is characterized Autonomous Region and 45 km north of the Yarlung-
by larger-scale hydrothermal alteration and mineral- Tsangpo River (the Yarlung-Tsangpo suture zone)
ization zones, and abundance in hydrothermal veins (Fig. 1).
and anhydrite. Hydrothermal anhydrite is one of the The Qulong deposit is intimately associated with the
most abundant hydrothermal minerals in the deposit, Miocene multiphase granitic intrusions, with large-
and magmatic anhydrite occurs in some unaltered scale (4 ¥ 8 km2) hydrothermal alteration and mineral-
intrusive rocks. The occurrence of magmatic and ization zones (with a vertical extent more than 1350 m),
hydrothermal anhydrite indicates that the magmatic- including abundant hydrothermal veins and anhy-
hydrothermal system at Qulong is highly oxidized and drite. The multiphase granitic intrusions range from
sulfur-rich. 18 Ma to 14 Ma (Rui et al., 2003; Wang et al., 2006; Yang
In order to reveal the nature of the highly oxidized, et al., 2009) and molybdenite Re-Os age in the deposit is
S-rich ore-forming magma-hydrothermal system, this 16.0 ⫾ 0.3 Ma (Rui et al., 2003). These ages correspond
paper describes geological and mineralogical features to the timing of the post-collisonal orogenic setting. A
of the Qulong deposit, as well as the result of fluid sequence of Miocene intrusions observed is: grano-
inclusion microthermometry. diorite, biotite monzogranite, monzogranitic porphyry,
granodiorite porphyry and diorite porphyrite. These
2. Geology of the deposit rocks intruded into the volcanic rocks of the Jurassic
Yeba Formation (Dong et al., 2006; Geng et al., 2006)
In southern Tibet, the Lhasa terrane is mainly com- (Fig. 1).
posed of the Gangdese orogenic belt, which resulted Among the intrusive rocks, the granodiorite (Figs 1,
from the northward subduction of the Neo-Tethyan 2b) strikes approximately east–west in the Yeba Forma-
oceanic lithosphere beneath Asia and subsequent tion. It is the earliest intrusion and with an outcrop
India–Asia collision (Yin & Harrison, 2000; Aitchison area of >5 km2. It consists of medium- to coarse-grained
et al., 2007). The Gangdese orogenic belt consists plagioclase (40–45 volume %), K-feldspar (15–20 vol.
mainly of Late Paleocene–Early Eocene (60–40 Ma) %), quartz (10–15 vol. %) and minor hornblende (10–15
Linzizong Formation volcanic rocks and Cretaceous- vol. %) and biotite (10 vol. %). Accessory minerals are
Tertiary (120–24 Ma) granite batholiths (Allègre et al., zircon, apatite, magnetite and sphene.
1984; Coulon et al., 1986; Mo et al., 2007, 2008). Accord- The biotite monzogranite (Figs 1, 2c) is outcropped
ing to Harrison et al. (1992), rapid uplift of southern in an area of 4 km2 in the center part of the ore district.
Tibet took place at about 20 Ma, and then the N-S- This monzogranite is composed of medium- to coarse-
trending rift system developed across the Gangdese grained plagioclase (35–40 vol. %), K-feldspar (20–
belt (Coleman & Hodges, 1995; Harrison et al., 1995; 25vol. %), anhedral quartz (20–25 vol. %) and minor
Williams et al., 2001) due to a regional E-W extension biotite (10–15 vol. %) and lacks in hornblende. Acces-
(Williams et al., 2001). In the Indo-Asian collision, mul- sory minerals are zircon, apatite, magnetite and rutile.
tiple metallogenic events occurred in the different The monzogranite contains more biotites and quartz
tectonic settings: main-collisional convergent setting than the granodiorite.
(~65–41 Ma), late-collisional transform setting (~40– The light gray monozogranite porphyry (Figs 1, 2d)
26 Ma) and post-collisional crustal extension setting is a small dike, intruded into biotite monzogranite,
(~25–0 Ma) (Hou et al., 2006a, b, c, 2009). with an outcrop area of ~0.5 km2 in the eastern part of
The Cenozoic post-collisional Gangdese metallo- the monzogranitic porphyry (Fig. 1). The monozogran-
genic belt is newly identified (Qu et al., 2004; Hou ite porphyry is of granitic composition and typical
et al., 2006a, b, c, 2009; Li et al., 2006a, 2007a; Qin porphyritic texture, with a mineral assemblage of
et al., 2008) along the Gangdese orogenic belt, which plagioclase (15–20 vol. %), K-feldspar (10 vol. %),

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B. Xiao et al.

Fig. 1 Geology sketch map of the Qulong porphyry Cu–Mo deposit after Tibet Julong Copper Co., Ltd. (2008) and Xiao et al.
(2009). 1: Tuff of the Jurassic Yeba Fomation; 2: rhyolite of the Yeba Formation; 3: Miocene granodiorite; 4: Miocene biotite
monozogranite; 5: Miocene monozogranite porphyry; 6: Miocence granodiorite porphyry; 7: Miocene diorite porphyrite;
8: Quaternary; 9: breccia; 10: orebody boundary; 11: unidentified fault.

quartz (10–15 vol. %) phenocrysts in an aphanitic occurs as thin dikes ranging from 0.5 to 80 m in many
groundmass of quartz, plagioclase and K-feldspar. drill cores. The mineral assemblage of this rock is pla-
Biotite phenocrysts are present (3–5 vol. %). Apatite gioclase (20–25 vol. %), K-feldspar (5–10 vol. %), quartz
and zircon are accessory minerals. Anhydrite as (5–10 vol. %) and biotite (5–10 vol. %) phenocrysts
mineral inclusions is occasionally observed in feldspar in an aphanitic groundmass of quartz, plagioclase,
phenocrysts. K-feldspar and biotite. Anhydrite, apatite, zircon and
The gray granodiorite porphyry (Figs 1, 2e) is small magnetite are accessory minerals. Anhydrite occurs as
dike bodies intruding in the northwest part of biotite microphenocryts and phenocryts, usually coexisting
monozogranite with an outcrop area of 0.4 km2. It with apatite or intergrows with plagioclase.

© 2011 The Authors

6 Resource Geology © 2011 The Society of Resource Geology
 Highly oxidized magma and fluid evolution of Miocene Qulong

Fig. 2 Photographs of the rocks from the Qulong porphyry Cu–Mo deposit. a: Tuff of the Yeba Formation, b: Miocene
granodiorite, c: Miocene biotite monozogranite, d: Miocene monozogranite porphyry, e: Miocene granodiorite porphyry,
f: Miocene diorite porphyrite.

The diorite porphyrite (Figs 1, 2f) occurs as a stock alteration. The granodiorite porphyry underwent weak
intruded into biotite monzogranite in the central part argillic alteration with rare disseminated pyrite + chal-
of the ore district. The minerals of this rock is rounded copyrite or pyrite + chalcopyrite thin veins. The porphy-
K-feldspar (10 vol. %), plagioclase (5 vol. %), horn- rite is unaltered and barren. Hydrothermal breccia is
blende (10–15 vol. %) and quartz (3 vol. %) phenocrysts distributed around the granodiorite porphyries.
in a finer-grained groundmass of hornblende and pla- The hydrothermal alteration of the deposit is cen-
gioclase. Apatite, zircon and sphene are accessory min- tered on the monozogranite porphyry and changes
erals. The rounded quartz and K-feldspar phenocrysts from potassic alteration to phyllic, argillic and propyl-
mainly range from 2 to ⱖ20 mm and with a distinct itic alteration upwards. Hydrothermal anhydrite,
corroded boundary which indicates those phenocry- which crystallized together with quartz, biotite, K-
stys are xenocrysts. feldspar, sericite and sulfides, is ubiquitous in the
Except the diorite porphyrite, the Miocene intru- potassic and phyllic zones. The single orebody with
sions are characterized by adakite-like geochemical networks of veinlets, veins and disseminated copper
affinities, with >60 wt% SiO2, >14 wt% Al2O3, usually <2 mineralization, is hosted in biotite monzogranite,
wt% MgO (400–1300 ppm) Sr (5–9 ppm) Y, and Sr/Y monzogranitic porphyry and granodiorite porphyry,
(60–160) (Defant & Drummond, 1990; Yang et al., 2009). but rare in the granodiorite and Jurassic rocks. The
The granodiorite underwent alteration manifested by orebody is rare in supergene enrichment, which occurs
minor secondary biotite and kaolinite replacing biotite, locally on the surface. Sulfides include abundant pyrite,
hornblende and plagioclase, minor chlorite replacing chalcopyrite, molybdenite, a few bornite, chalcocite,
biotite, and along with very small grains of epidote. and trace sphalerite and galena. Main gangue minerals
Chlorite completely or partially replaced hornblende are quartz, anhydrite, biotite, sericite, K-feldspar, pla-
and biotite along mineral rims and cleavage planes. gioclase and clay minerals. Molybdenite is mainly
The biotite monzogranite is characterized by extensive hosted in quartz + molybdenite veins, which usually
weak argillic and potassic alteration, and locally crosscut the early chalcopyrite–pyrite bearing veins;
intermediate argillic alteration in shallow depth and disseminated molybednite is rare.
K-feldspar alteration in deep levels, respectively; sec- The hydrothermal veins at Qulong are classified into
ondary biotite + anhydrite alteration is the most perva- five types based on the mineral assemblages and cross-
sive alteration. The biotite monzogranite is associated cutting relations (Table 1). These are named as A, EB, B,
with abundant disseminated and stockwork chalcopy- C and D veins on the basis of the classification by
rite, molybdenite and pyrite mineralization. The mono- Gustafson and Hunt (1975) and Dilles & Einaudi (1992)
zogranite porphyry underwent argillic alteration and (Fig. 3) The characters of the vein system are summa-
potassic alteration, including local intensive K-feldspar rized in Table 1.

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3. Sample description

Halos of Bi, trace Chl

Chl, weakly calcite

Halos of Ser, argillic,
Halos of weakly Ser,
Halos of weakly Bi,

An, anhydrite; Bi, biotite; Bn, bornite; Chl, chlorite; Cpy, chalcopyrite; Ep, epidote; Gal, galena; Gp, gypsum; Kf, K-feldspar; Mo, molybdenite; Mt, magnetite; Py, pyrite; Qz, quartz;
Halos of Kf, Bi and

argillic alteration
locally advanced
Ser and argillic;
3.1 Anhydrite
Alteration halo

and rare Gp
trace An All the analyzed samples in this study are collected

Chl, Gp
from drill cores. The sample numbers present the drill
hole and downhole depth respectively, for example
sample QZK401-430 is from drill hole ZK401 at the
downhole depth of 430 m. Samples QZK401-430 and

Only rarely in biotite monozogranite

QZK301-142 are hydrothermal anhydrite-bearing
Abundant in biotite monozogranite
porphyry, biotite monozogranite;

porphyry, biotite monozogranite;

monozogranite porphyry, biotite

rarely in granodiorite porphyry
mineralized veins (>2 cm in width), with assemblages
of anhydrite + quartz + chalcopyrite + pyrite ⫾
Abundant in monozogranite

Abundant in monozogranite

molybdenite. Samples QZK812-472 and QZK812-473

Abundant in Jurassic tuff,
granodiorite; rarely in
are unaltered granodiorite porphyry.
rarely in granodiorite

There are two distinctive types of anhydrite. The first

monozogranite type is hydrothermal anhydrite, which is commonly
associated with pyrite, chalcopyrite, molybdenite,
Occurrence

magnetite, quartz, forming hydrothermal breccia

matrixes (Fig. 4a) and mineralized veins (Fig. 4b). The
color is mainly purple in breccia and early A, B veins,
and appear colorless or sky-blue in D veins. In some A
and B veins, anhydrite may account for 25 to >90 vol. %
Abundant Cpy, Py,
locally Mt; trace

Trace Mt, Cpy, Py,

of the gangue minerals and closely adjacent the sul-

trace Cpy, Mo,

fides. In late D veins, anhydrite distinctly decreased in

Mo; rare Bn

Abundant Py;
Trace Py, Cpy
Ore minerals
Cpy, Py, Bn,

volume (<5–10 vol. %). Altered rocks commonly

Gal, Sph
Mo, Bn

include 1–5 vol. % hydrothermal anhydrite.

Mo

The second type is magmatic in origin, and occurs as

inclusions in plagioclase in granodiorite and monzog-
Table 1 Characters of vein system of the Qulong porphyry Cu–Mo deposit

ranitic porphyry, or as phenocrysts with plagioclase

Irregular, continuous,
Commonly irregular,

Regular, continuous;

Regular, continuous,

Regular, continuous,

and quartz in granodiorite and biotite monzogranite

rarely irregular

(Fig. 4c, d). The anhydrite phenocrysts usually co-

discontinuous,

exist with apatite in unaltered granodiorite porphyry

0.1–10 mm

1- >30 mm
Morphology

0.5–5 mm

1–15 mm

(Fig. 4e). The anhydrite microphenocrysts with distinct

2–5 mm

corroded boundaries are observed (Fig. 4e, f).

3.2 Fluid inclusions

Qz-Bi, Qz ⫾ An ⫾ Chl-Mt-Cpy-Py,

Fluid inclusions at Qulong deposit are classified

Bi-Qz-Py-Cpy-Mo ⫾ Bn ⫾ Mt,

Qz-Py-Ser ⫾ Cpy ⫾ Ser, Qz-Ser,

Qz-Bi ⫾ An ⫾ Chl ⫾ Py ⫾ Cpy,

Ep-Cpy-Py, Qz ⫾ An-Sph-Gal
Qz-An, Mt-Qz-Py-Cpy ⫾ An
Qz, Bi ⫾ Qz ⫾ Kf, Kf-Bi ⫾ An,

into three main types which are divided into nine

Qz-An ⫾ Cpy ⫾ Py ⫾ Mo,
Qz-Mo ⫾ An ⫾ Py ⫾ Cpy,
Qz-Kf ⫾ Cpy ⫾ Py ⫾ Bn,

subtypes. These types include: type 1, liquid-rich

inclusions; type 2, vapor-rich inclusions; and type 3,
Cpy-Py ⫾ Qz ⫾ An

polyphase high-salinity inclusions, containing a halite

Chl-Py-Cpy ⫾ Mt

daughter phase and other opaque and/or translucent

Ser, sericite; Sph, sphalerite.

minerals. The characters of all fluid inclusions are sum-

Typical veins

marized in Table 2.
Type 1 inclusions are divided into two subtypes
based on the presence of opaque phase or reddish
rounded (hematite) or transparent unknown silicate
minerals: 1a, containing only two phases (L+V); 1b,
EB vein
A vein

D vein
C vein

usually containing a third phase (L+V+Op/Hem ⫾ M),

B vein

present in A and B veins and quartz phenocrysts. They

are commonly rounded or negative-crystal in shape,

© 2011 The Authors

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 Highly oxidized magma and fluid evolution of Miocene Qulong

Fig. 3 Vein types in the Qulong porphyry Cu–Mo deposit. a: “A” vein with K-feldspar halo; b: “B” vein cuts irregular
discontinuous “A” veins; c: “A” vein with Qz + Mt + Cpy ⫾ Py; d: “EB” vein with biotite halo; e: “B” vein with sericite
and argillic alteration halo; f: “B” vein with weakly feldspar-destructive halo; g: “B” vein with feldspar-destructive halo;
h: “C” vein with sericite halo; i: regular “D” vein; j: “D” vein cuts “B” vein; k: “D” vein with feldspar-destructive halo. Qz:
quartz, Kf: K-feldspar, An: anhydrite, Bi: biotite, Ep: epidote, Chl: chlorite, Py: pyrite, Cpy: chalcopyrite, Mo: molybdenite,
Mt: magnetite, Gal: galena, Sph: sphalerite.

Fig. 4 Photographs, microphotographs and back-scattered electronic (BSE) images of anhydrite in the Qulong deposit. a:
Photograph of hydrothermal breccia, with anhydrite matrix. b: Cross-polarized light photomicrograph of biotite monzog-
ranite, with anhydrite + pyrite vein. c: Cross-polarized light photomicrograph of granodiorite, with interstitial anhydrite.
d: Cross-polarized light photomicrograph of biotite monzogranite, with interstitial anhydrite. e: Cross-polarized light
photomicrograph of granodiorite porphyry, with magmatic anhydrite phenocryst and clusters of apatite. f: BSE image of
magmatic anhydrite microphenocryst and clusters of apatite, magnetite, pyrite. Ab: albite, An: anhydrite, Ap: apatite, Bi:
biotite, Kf: K-feldspar, Mt: magnetite, Plag: plagioclase, Py: pyrite, Qz: quartz.

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B. Xiao et al.

Table 2 Fluid inclusions in the Qulong porphyry Cu–Mo deposit

Type Sub-type Phases present at room temperature Occurrence Homogenization
behavior
Shape Phase Phase Daughter Size(mm)
composition number mineral
1a Negative-crystal, regular, L+V 2 — 3–30 All samples Vapor disappears
rounded forms
1 1b Negative-crystal, regular, L+V+Op/Hem 3–4 Op, Hem, M 3–30 Abundant in A, B veins and Vapor disappears
rounded forms ⫾M quartz phenocrysts, rare
in D veins
2a Negative-crystal, regular, L+V 2 — 4–24 Abundant in A and quartz Water disappear
rounded forms phenocrysts
2
2b Negative-crystal, regular, L+V+M/Op 3–4 M 2–20 Rare in A veins and quartz Water disappears
rounded forms phenocysts
3a Negative-crystal, L+V+H 3 H 4–26 All samples, except Halite/vapor disappear
rounded forms anhydrites or both disappear at
the same temperature
3b Negative-crystal, L+V+H+Op 4 H, Op 5–25 A, B veins and quartz Halite/vapor disappear,
rounded forms phenocysts halite disappearance
dominates
3
3c Negative-crystal, L+V+H+S ⫾ 4–6 H, S, Op, Hem 6–15 A, B veins and quartz Halite disappears
rounded forms Op ⫾ Hem matrixes of breccia
3d Negative-crystal, L+V+H+Hem 4–5 H, Hem, Op 4–14 A, B veins and quartz Halite disappears
rounded forms ⫾ Op matrixes of breccia
3e Negative-crystal, L+V+H+M 4 H, M 4–12 Rare in A, B veins Halite disappears
rounded forms

H, halite; Hem, hematite; M, transparent silicate mineral; Op, opaque mineral; S, sylvite.

© 2011 The Authors

Resource Geology © 2011 The Society of Resource Geology
 Highly oxidized magma and fluid evolution of Miocene Qulong

Fig. 5 Photomicrographs of fluid inclusions in the Qulong porphyry Cu–Mo deposit. a: Type 1, liquid-rich fluid inclusions,
low salinity; b: type 1, liquid-rich fluid inclusions with Op; c: type 2, vapor-rich fluid inclusions with Op; d: type 3,
polyphase fluid inclusions; e: type 3, polyphase fluid inclusions coexist with liquid-rich fluid inclusion; and f: type 1,
liquid-rich fluid inclusions in anhydrite. Op: opaque mineral.

and range 3–30 mm (Fig. 5a, b). The vapor phase occu- Type 3 inclusions vary 4–26 mm in size and have
pies between 5% and 35% volume. Final melting tem- negative-crystal shapes, or rounded forms (Fig. 5d, e).
peratures of ice (Tm.ice) were determined for calculating Vapor-phase contents vary 5–30 vol. %. Halite is iden-
the salinities and all the inclusions were homogenized tified based on its cubic crystal shape and absence of
into liquid phase. birefringence. Besides transparent daughter minerals,
Type 2 inclusions range 4–24 mm in size and vary there are reddish rounded hematite (?) and variously
from negative-crystal shapes to irregular (Fig. 5c). The rounded and/or triangular shape chalcopyrite (?)
vapor phase occupies between >60% and 90% volume. within the inclusions. Based on different phase compo-
They are divided into two subtypes based on the sitions, these inclusions are divided into five subtypes:
presence of opaque phase or transparent unknown 3a contains three phases (L+V+H), homogenized by
silicate minerals: 2a, containing only two phases (L+V), disappearance of vapor (Tf) or halite (TmNacl) or vapor
present in A veins, matrix of breccia and quartz phe- and halite disappearance approximately at the same
nocrysts; 2b, usually containing a third phase (L+V+M/ temperature; 3b contains four phases (L+V+H+Op),
Op) rarely present in A veins and quartz phenocrysts. homogenized by disappearance of vapor (Tf) or halite
It is difficult to observe the process of freezing in these (TmNacl), but halite disappearance dominates, presenting
inclusions because of their dark cavity walls; only a few in A veins, B veins and quartz phenocrysts; 3c contains
final melting temperatures of ice (Tm.ice) are measured. four to six phases (L+V+H+S ⫾ Op ⫾ Hem) with
The limited fluid content makes exact determination of rounded shaped sylvite and/or opaque phase and/or
phase change difficult. A few vapor-rich inclusions, on reddish rounded (hematite?), homogenized by dis-
heating, remained unchanged, until the temperature appearance of halite (TmNacl) in A veins, B veins and
approached to approximately 20°C of the homogeniza- quartz phenocrysts; 3d contains four to five phases
tion temperature, when the vapor phase then rapidly (L+V+H+Hem ⫾ Op) with reddish rounded (hema-
expanded to fill the inclusions; this indicates that these tite?) and/or opaque phases, homogenized by disap-
inclusions contain fluids with near-critical densities pearance of halite (TmNacl) in A veins, B veins and quartz
(Roedder, 1984). phenocrysts; 3e contains four phases (L+V+H+M), with

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Resource Geology © 2011 The Society of Resource Geology 11
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Table 3 Electron probe microanalysis of anhydrite and apatite of the Qulong porphyry Cu–Mo deposit
Magmatic anhydrite
QZK812-472 QZK812-473
CaO 41.12 40.64 40.40 40.68 41.03 40.28 40.16 40.21 40.33 41.15 39.91 40.45 39.83 39.92 39.98
SO3 59.60 58.71 59.62 59.80 58.91 59.67 58.91 59.56 59.13 58.14 58.43 59.04 58.62 58.09 58.44
P 2 O5 0.05 0.07 0.07 0.10 0.01 0.13 0.02 0.07 0.07 0.07 0.22 0.07 0.09 0.28 0.33
SiO2 0.07 0.00 0.03 0.00 0.01 0.05 0.02 0.02 0.08 0.01 0.01 0.03 0.01 0.04 0.00
Ce2O3 0.04 0.04 0.00 0.11 0.00 0.10 0.00 0.05 0.00 0.05 0.15 0.15 0.13 0.10 0.21
MnO 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00
BaO 0.00 0.00 0.02 0.02 0.01 0.00 0.00 0.00 0.06 0.00 0.08 0.00 0.00 0.00 0.00
SrO 0.08 0.02 0.02 0.01 0.04 0.03 0.06 0.00 0.11 0.00 0.00 0.07 0.02 0.00 0.00
Total 100.96 99.48 100.16 100.73 100.01 100.27 99.17 99.91 99.78 99.42 98.80 99.81 98.71 98.44 98.96
Hydrothermal anhydrite
QZK401-430 QZK301-142
CaO 40.31 40.19 39.98 40.30 40.15 39.96 39.51 39.72 39.95 40.17 40.51 40.19 40.07 40.45 40.34
SO3 59.76 60.17 58.87 58.91 59.56 58.62 59.07 59.75 60.22 59.18 59.46 59.87 59.63 59.72 59.14
P 2 O5 0.03 0.05 0.06 0.07 0.16 0.11 0.05 0.08 0.04 0.02 0.04 0.05 0.00 0.02 0.03
SiO2 0.04 0.04 0.03 0.03 0.00 0.01 0.02 0.00 0.00 0.01 0.02 0.00 0.02 0.02 0.00
Ce2O3 0.00 0.07 0.00 0.06 0.16 0.00 0.05 0.00 0.00 0.07 0.01 0.06 0.00 0.05 0.00
MnO 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.02 0.00 0.02 0.02 0.02 0.00 0.01 0.00
BaO 0.00 0.00 0.10 0.00 0.03 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00
SrO 0.10 0.21 0.18 0.15 0.19 0.27 0.34 0.41 0.34 0.34 0.20 0.33 0.22 0.15 0.11
Total 100.24 100.73 99.2 99.52 100.25 99.02 99.04 99.98 100.55 99.81 100.26 100.52 99.94 100.46 99.62
Apatite within and adjacent to magmatic anhydrite
QZK812-472 QZK812-473
CaO 54.36 54.16 53.86 53.43 53.48 53.96 53.58 53.50 53.64 53.29 53.56 52.90 53.27 53.26 53.01
SO3 0.13 0.38 0.11 0.17 0.16 0.26 0.14 0.44 0.19 0.27 0.11 0.16 0.13 0.21 0.13
P 2 O5 42.07 42.07 42.63 43.70 43.17 42.25 43.01 43.57 43.91 43.74 44.14 43.75 42.96 43.95 43.44
SiO2 0.15 0.18 0.15 0.09 0.11 0.19 0.11 0.14 0.18 0.13 0.04 0.15 0.23 0.08 0.13
Ce2O3 0.10 0.19 0.09 0.14 0.14 0.18 0.17 0.25 0.18 0.21 0.18 0.20 0.22 0.14 0.20
Y 2 O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
MnO 0.20 0.17 0.19 0.14 0.17 0.10 0.23 0.18 0.19 0.14 0.17 0.21 0.16 0.14 0.20
BaO 0.00 0.00 0.04 0.04 0.00 0.03 0.00 0.00 0.00 0.00 0.11 0.05 0.00 0.00 0.00
SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
F 3.22 3.12 3.06 3.23 3.14 3.29 3.30 3.25 3.54 3.68 3.39 3.47 3.30 3.22 3.34
Cl 0.30 0.30 0.31 0.17 0.25 0.18 0.35 0.29 0.22 0.09 0.27 0.20 0.31 0.25 0.37
Total 99.11 99.20 99.07 99.72 99.23 99.02 99.41 100.19 100.50 99.99 100.48 99.57 99.12 99.84 99.33

Oxides determined by electron probe microanalysis are reported in weight percent.

a transparent unknown silicate mineral phase, homog- The results (Table 3) show that except strontium,
enized by disappearance of halite (TmNacl) in B veins. other major (CaO, SO3) and trace components (P2O5,
SiO2, Ce2O3 et al.) in hydrothermal and magmatic anhy-
drites are similar. Strontium concentration (SrO) in
4. Results hydrothermal anhydrite (0.10–0.41 wt%) is higher than
that in magmatic anhydrite (0.00–0.11 wt%). Euhedral
4.1 Anhydrite apatite coexisting within and adjacent to magmatic
The anhydrites and apatites were analyzed by electron anhydrite in the unaltered granodiorite has the range
probe microanalysis (EPMA) (JEOL JXA-8100 electron of F and Cl concentrations of 3.06–3.68 wt. %, and 0.09–
microprobe at the Institute of Geology and Geophysics, 0.37 wt. %, respectively. This composition (F: >1 wt%,
Chinese Academy of Science [CAS]) with 10 kV beam F/Cl >1) is typical igneous fluorapatite in granite (Chu
conditions and 10 nA beam current. et al., 2009). The apatites have relative high content of

© 2011 The Authors

12 Resource Geology © 2011 The Society of Resource Geology
 Highly oxidized magma and fluid evolution of Miocene Qulong

Ce2O3 (0.09–0.25 wt%); sulfur (expressed as SO3 wt% inclusions mostly homogenize by disappearance of
ranges 0.11–0.44 wt%); and relative low content of vapor or halite and vapor disappearance over a small
MnO (0.1–0.23 wt%). The Sr and Y contents are below temperature interval. D vein contains a few fluid
detection limit. inclusions, commonly with liquid-rich inclusions and
polyphase high-salinity inclusions which homogenize
by disappearance of vapor. Both the homogenization
4.2 Microthermometry of fluid inclusions temperature and salinity are lower than A and B veins
Fluid inclusions in quartz and anhydrite were used (Fig. 6).
for microthermometry study, analyzed on a Linkam Compared to quartz, anhydrite in A veins and
THMSG600 gas-flow heating-freezing stage at the breccia, only contain two-phase inclusions (Fig. 5f)
Institute of Geology and Geophysics, CAS. The uncer- (mostly type 1, rarely type 2). It is difficult to observe
tainties of measurements are ⫾ 0.1°C for freezing and the process of freezing of fluid in anhydrite, because of
⫾ 1°C for heating. Salinities of fluid inclusions were their cubic negative-crystal shapes and dark cavity
calculated from the final melting point of ice for two- walls. Therefore, this study lacks any salinity data of
phase fluid inclusions and halite melting temperature fluid inclusions in anhydrite. In A veins, fluid inclu-
for polyphase fluid inclusions using the equations of sions in anhydrites homogenize at temperatures
Hall et al. (1988) and Sterner et al. (1988). All the results of 260–393°C, average 339°C. This range is distinctly
are shown in Figure 6. Homogenization of all the inclu- lower than those of the coexisting quartz, which range
sions takes place at temperatures ranging 196–536°C, from 346°C to 405°C (average 370°C) (Fig. 7a). This
rarely >550°C. Most polyphase inclusions have disso- result is consistent with the observation that anhydrite
lution of halite as the last phase change (TmNacl > Tf), usually occurs interstitially between quartz crystals.
which is denoted as halite homogenization (Wilson Polyphase fluid inclusions homogenized by halite
et al., 1980). The dissolution temperature of halite was dissolution are ubiquitous in the Qulong porphyry
used for salinity calculation in this study. The salinities deposit, which is commonly observed in porphyry
are between 2.41 and 60.44 wt% NaCl equivalent. This copper and similar magmatic-hydrothermal ore
study did not find any typical CO2 fluid inclusion. deposits (Becker et al., 2008). Polyphase fluid inclusions
Quartz phenocrysts in monozogranite porphyry homogenized in three different ways (TmNaCl < Tf, TmNaCl
contain all types of fluid inclusions, especially rich = Tf, TmNaCl > Tf), suggesting that pressure varied during
in liquid-rich inclusions and polyphase high-salinity mineralization (Li & Sasaki, 2007; Becker et al., 2008). In
inclusions which mostly homogenize by disappear- this paper, we assume fluid boiling and calculate trap-
ance of halite. Homogenization takes place at tempera- ping pressure of the fluid in the Qulong deposit (Fig. 8)
tures of 384–510°C. Liquid-rich inclusions homogenize as 35–60 Mpa at 460–510°C in quartz phenocrysts and
at 384–536°C, average 443°C; polyphase high-salinity 28–42 Mpa at 400–450°C in A veins.
inclusions homogenize at 414–510°C, average 459°C.
The salinity of liquid-rich inclusions and polyphase
high-salinity inclusions are between 6.45 and 19.45 5. Discussion and conclusions
wt% NaCl equivalent, average 13.00 wt% NaCl equiva-
lent, and between 49.00 and 59.22 wt% NaCl equiva- Formation of giant porphyry copper deposits requires
lent, average 54.54 wt% NaCl equivalent, respectively. either highly efficient collection of Cu from large
Vapor-rich inclusions homogenize at temperatures volumes of magma (Cline & Bodnar, 1991; Cloos,
of 426–505°C, average 473°C; the salinity of these are 2001), unusually Cu-rich parental magmas (Core et al.,
between 4.10 and 9.80 wt% NaCl equivalent, average 2006), and/or an anomalously S-rich source (Halter
5.97 wt% NaCl equivalent (Fig. 6a, b). et al., 2005). In giant porphyry deposits, the amount of
Table 4 shows the results of the homogenization tem- sulfur is too large to be supplied from a small volume
peratures and salinity of fluid inclusions in quartz in of immediate host rocks; sulfur was likely supplied
the phenocrysts and each vein type. A vein contains all from magmatic anhydrite (Hattori & Keith, 2001;
types of fluid inclusions, especially rich in vapor-rich Chambefort et al., 2008). At the Qulong porphyry
inclusions and polyphase high-salinity inclusions Cu–Mo deposit, we confirmed the presence of mag-
which mostly homogenize by disappearance of halite. matic anhydrite and hydrothermal anhydrite, which is
B vein contains all types of fluid inclusions except evidence of a highly oxidized magmatic-hydrothermal
vapor-rich fluid inclusions; the polyphase high-salinity condition.

© 2011 The Authors

Resource Geology © 2011 The Society of Resource Geology 13
B. Xiao et al.

Fig. 6 Salinity versus final homogenization temperature (to liquid or by halite melting) for all inclusions of the Qulong
porphyry Cu–Mo deposit.

© 2011 The Authors

14 Resource Geology © 2011 The Society of Resource Geology
 Highly oxidized magma and fluid evolution of Miocene Qulong

Table 4 Final homogenization temperature and salinity for all inclusions in different veins of the Qulong porphyry Cu–Mo
deposit
Types Tm (°C) Salinity (% NaCl equivalent)
1a,b 384–536, av. 443 6.45–19.45, av. 13.00
Quartz phenocrysts 2a 426–505, av. 473 4.10–9.80, av. 5.97
3a,b 414–510, av. 459 49.00–59.22, av. 54.54
1a,b 369–439, av. 394 10.73–15.86, av.13.47
A veins 2a,b 375–425, av. 402 1.90–2.80, av. 2.43
3a,b,c,e 350–505, av. 405 42.40–60.44, av. 48.13
1a,b 302–344, av. 322 5.71–14.97, av. 10.00
B veins
3a,b,c,d,e 298–346, av. 318 38.01–42.03, av. 39.66
1a 196–273, av. 254 2.41–5.86, av. 3.71
D veins
3a 238–270, av. 249 33.95–35.99, av. 34.65

The sulfur speciation and solution mechanisms expressed as SO3 wt. %) at Qulong is related to the
in silicate melts is controlled by the pressure, oxidized condition of the host magma. Usually, the
temperature, melt composition and oxidation state; sulfur (SO3) contents of apatite in porphyry ore-related
under oxidizing conditions sulfur is dissolved mainly igneous rocks (>0.10 wt%) are higher than that in
as S6+ (>90% of total sulfur) and sulfur solubility in barren igneous rocks (<0.10 wt%) (Imai, 2002, 2004)
oxidized magmas is quite higher than in reduced con- and are also considered to reflect the redox state of the
ditions (Carroll & Rutherford, 1985, 1987, 1988; Luhr, magma source region or fluids encountered during
1990; Nilsson & Peach, 1993; Wallace & Carmichael, magma generation (Imai, 2004). The sulfur concentra-
1994; Fleet et al., 2005; Jugo et al., 2005; Wilke et al., tion in apatite (0.11–0.44 wt% SO3) at Qulong is higher
2008; Jugo, 2009). The anhydrite-bearing rock erup- than that (0.00–0.30 wt% SO3) in the Dexing porphyry
tions of El Chichón volcano in 1982 (Luhr et al., 1984) Cu deposit, Jiangxi Province, southeast China (Yao
and Mount Pinatubo in 1990 (Bernard et al., 1991) dem- et al., 2007).
onstrated that sulfate species (SO42-) are significant in In conclusion, as described above, from quartz phe-
some magmatic systems. Magmas which contain mag- nocrysts in porphyry to A, B and D veins, the final
matic anhydrite are also known to be water-rich (Luhr, homogenization temperatures of all type inclusions
2008). The oxidized and high water content inter- decreased from about 450°C to 250°C (Fig. 6 and
mediate to felsic igneous rocks are common in island Table 4) and the salinities decreased from about 54 wt%
arc environments, and have potential to form mineral NaCl equivalent to 34 wt% NaCl equivalent. Based on
deposits (Ishihara, 1981; Becker & Rutherford, 1996), the crosscutting relations and the mineralization fea-
especially for porphyry Cu-(Au) type deposits (Imai tures between different veins, the changes of tempera-
et al., 1993; De Hoog et al., 2004; Li et al., 2006b, 2007b; ture and salinity may account for mineralization at the
Luhr, 2008; Sillitoe, 2010). Qulong deposit: sulfide precipitation resulted from
In this study, we confirm a highly oxidized, sulfur- the cooling magmatic-hydrothermal fluid system and
rich magma-hydrothermal system in the Gangdese oro- abundant copper-bearing sulfides were deposited
genic setting, which is assumed to be a non-subduction during the formation of A and B veins at about 320–
setting. The oxidized magma can effectively scavenge 400°C. Fluid boiling assumed from the fluid inclusions
sulfur from sulfides in the source region (De Hoog et al., in quartz phenocysts and A veins may suggest the
2004); thus, it could deliver sulfur into the shallow crust depths of fluid trapping at approximately 1.4–2.4 km
during the magma ascent and consequently form a and 1.1–1.7 km, respectively (Fig. 8).
productive porphyry system at the orogenic setting just
as at the subduction setting. Acknowledgments
At Qulong, apatite is included in or clustered with
anhydrite, as at El Chichon (Luhr et al., 1984). In This research was supported by the NSFC (Grant no.
apatite, sulfur dissolved as the sulfate molecule in its 40772066), the National Eleventh-Five years project
crystalline structure principally by the substitution (Grant no. 2006BA01A04) and Chinese Geological
S6++Si4+ = 2P5+ or S6++Na+ = P5++Ca2+ (Streck & Dilles, Survey research project (Grant no. 20089932). The
1998). The high S abundances in apatite (0.11–0.44 wt%, authors would like to extend their gratitude to Dr. Qian

© 2011 The Authors

Resource Geology © 2011 The Society of Resource Geology 15
B. Xiao et al.

Fig. 8 Pressure estimates for boiling fluid inclusions

assemblage from the Qulong porphyry Cu–Mo
deposit (Original plot after Bouzari & Clark, 2006).

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