wagner et al cg 2005

satisfactorily modelled by mixing of andesitic magmatic water with heated local meteoric water. Rhodochrosite, which formed13

1. Introduction

Although subduction-associated vein-type AuAg

Chemical Geology 219 (200T Corresponding author. Present address. Institut fqr Geowissen-only during a discrete episode at the onset of cockade breccia formation, has unusually low y C (18.3 to 14.8x) and ratherhigh y18O (+22.7 to +26.2x) values. These data are consistent with a short-lived episode of open-system boiling. Based on thedata presented in this paper and other isotopic data sets for arc volcanics and current models of plate-tectonics in the region, we

propose a metallogenic model, which involves mixing of magmatic and meteoric waters, and explains the unusual and

progressive enrichment in Sn and W at Cirotan by increased recycling of slab-derived sedimentary material during Pliocene

subduction.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Cirotan; Epithermal system; AuAgSnW deposit; Stable isotopes; Mixing; Fluid sourceStable isotope-based modeling of the origin and genesis of an

unusual AuAgSnW epithermal system at Cirotan, Indonesia

Thomas Wagnera,T, Anthony E. Williams-Jonesa, Adrian J. Boyceb

aDepartment of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal QC H3A 2A7, CanadabScottish Universities Environmental Research Centre (SUERC), East Kilbride, Glasgow, G75 0QF, Scotland, UK

Received 4 June 2004; received in revised form 16 December 2004; accepted 23 February 2005

Abstract

The Pliocene Cirotan low-sulphidation epithermal gold deposit, western Java, Indonesia, is characterized by complex

polymetallic assemblages and progressive enrichment in SnWand AuAg in the late stages of mineralization. Five distinct ore/

alteration stages are distinguished: (1) wallrock silicification; (2) siliceous breccia; (3) cockade breccia; (4) high-grade veins;

and (5) late drusy quartz. The y34S values of the vein sulphides are very homogeneous and lie mostly between +2.5 and +5.4x,with a mean of +3.8F0.9x. These values closely match values from recent arc lavas and volcanic gases in the SundaBandaisland arc, indicating direct incorporation of magmatic sulphur into the epithermal fluid system. By contrast, y18O values ofquartz/chalcedony decrease systematically from siliceous breccia (+8.5F0.4x) to cockade breccia (+8.1F0.5x), high-gradeveins (+7.4F0.2x), and drusy quartz (+6.9F0.4x). This isotopic shift cannot be explained by cooling or boiling, but is0009-2541/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.chemgeo.2005.02.006

schaften, Univ

Tqbingen, Germany.E-mail address: [email protected] (T. Wagner).5) 237260

www.elsevier.com/locate/chemgeonetically related toand SnW ore deposits are geersit7t Tqbingen, Wilhelmstrasse 56, D-72074magmatic processes along convergent plate bounda-

ries (subduction zones), these two metal associations

combines characterization of the bulk isotopic sig-

natures of ore and gangue minerals with a very

l Georarely occur together. This likely reflects differences

in the oxidation state of the magmas and in the

physicochemical conditions of the fluids responsible

for metal transport. The major SnW provinces of the

World are linked to Andean-type subduction zones,

where magmas are relatively reduced (ilmenite-series)

and contributions from the underlying continental

crust are significant (e.g., Heinrich, 1990; Lehmann,

1990). In contrast, the majority of AuAg deposits,

notably in the western Pacific region, occur in

subduction settings, where magmas tend to be more

oxidized (magnetite-series) and input of continental

crustal material is less important (e.g., Candela, 1989;

Thompson et al., 1999). Moreover, the chemical

transport properties of Sn, W, Au, and Ag differ

substantially. Whereas solubilities of Sn and W are

highest in acid and alkaline aqueous liquids (Jackson

and Helgeson, 1985a,b; Taylor and Wall, 1993; Wood

and Samson, 1998, 2000), Au is most effectively

transported in near-neutral pH solutions and Ag in

near-neutral to mildly acidic solutions (Gammons and

Williams-Jones, 1995, Benning and Seward, 1996;

Seward and Barnes, 1997; Wood and Samson, 1998).

As a result, the two metal associations tend to deposit

in different environments. Gold and silver are readily

transported by dilute, relatively low temperature

solutions, and consequently are able to reach the

shallow levels of the low-sulphidation epithermal

environment (e.g., Cooke and Simmons, 2000). By

contrast, transport of Sn and W requires much higher

temperature, and, in the case of Sn, higher salinity and

relatively low fO2, which favour their deposition

proximal to the magmatic source (e.g., Jackson and

Helgeson, 1985a; Heinrich, 1990).

Despite these general observations, a number of

shallow, low-sulphidation (adulariasericite) Pliocene

(1.52.1 Ma) epithermal gold deposits of western

Java, Indonesia, show unique features indicating co-

transport and co-deposition of Au, Ag, Sn, and W.

The Cirotan deposit, located 80 km SW of Jakarta, is

the most prominent example of this unusual epither-

mal vein deposit type (e.g., Marcoux et al., 1993;

Marcoux and Milesi, 1994; Milesi et al., 1994).

Cirotan, along with other epithermal deposits in the

district, is characterized by extensive formation of

polymetallic hydrothermal breccia, culminating in

T. Wagner et al. / Chemica238complexly banded cockade breccia (Genna et al.,

1996), and progressive enrichment in Sn, W, Au, anddetailed small-scale analysis of the evolution of

isotopic compositions with mineral growth. We then

quantitatively model the importance of fluid cooling,

boiling, and mixing in the evolution of the hydro-

thermal system at Cirotan. Finally, we propose a

metallogenic model for the Cirotan deposit, which

satisfactorily explains the isotope signatures of the

mineralization as resulting from processes operating

in the plate-tectonic environment of the SundaBanda

island arc.

2. Geological framework

Java and Sumatra form part of the western Sunda

Banda island arc (Fig. 1), where ongoing subduction

of the IndianAustralian plate beneath the Eurasian

plate has resulted in abundant calc-alkaline volcanism

and associated formation of magmatic-hydrothermal

gold deposits (Carlile and Mitchell, 1994). The

southwestern edge of the Eurasian plate was con-

structed through collision and suturing of several

discrete microplates in the pre-Tertiary, and the onset

of oblique subduction beneath Sumatra is manifested

by the occurrence of andesitic to basaltic lavas of

JurassicCretaceous age (McCourt et al., 1996;

Soeria-Atmadja et al., 1998). Magmatic activity in

Java and the eastern Sunda arc commenced in theAg in the late stages of mineralization. This feature

has been interpreted as being a signal of increasing

input of magmatic-derived hydrothermal fluids

enriched in Sn and W into the shallow epithermal

system (Milesi et al., 1994). Based on radiogenic

isotope data, the unusual element association at

Cirotan has been attributed to mobilization of

elements from Precambrian crustal slices underlying

the westernmost part of Java (Marcoux and Milesi,

1994). These studies suggest some general reasons for

the complex metal association found at Cirotan, but

they do not provide the data needed to constrain the

sources of fluids and the mineralizing processes

responsible for co-deposition of Au, Ag, Sn and W.

In this paper, we report results of a stable isotope

(S, O and C) study of the Cirotan deposit, which

logy 219 (2005) 237260Early Tertiary and has continued until the present-day

(Soeria-Atmadja et al., 1994, 1998). There is a marked

ah d

l GeoCibaliung Bay

EURASIANPLATE

INDIAN-AUSTRALIAN

PLATE

Java

Sumatra

Borneo Sulawesi Moluccas

Sumbawa

Wetar

Australia

Lerokis

Lebong Tandai

Lebong Donok

Kelian

Pongkor

Cirotan

Mesel

Sunda-Banda arc

T. Wagner et al. / Chemicacontrast in the nature of the crust underlying the

eastern and western parts of the island of Java. The

crust beneath eastern Java and the islands to the east is

essentially oceanic, whereas Sumatra and western-

most Java rest on slices of continental crustal material

(Hamilton, 1979; De Hoog et al., 2001). The arc

magmatism has remained calc-alkaline (mostly ande-

sites to basaltic andesites) in character since the early

Miocene (Nicholls et al., 1990), but the Pb and ReOs

isotope signatures indicate a significant increase in the

contribution of slab-derived sedimentary material for

the Pliocene magmatic series (Marcoux and Milesi,

1994; Alves et al., 1999).

The Cirotan deposit is located in the Bayah dome,

a TertiaryQuaternary volcanic structure covering an

area of about 40 by 80 km, which is separated from

the Bandung basin to the east by a major N 708 E left-lateral strike-slip fault zone (Milesi et al., 1994; Malod

Quaternary volcanicsQuaternary sedimentsPliocene magmatics

Pliocene sMiocene vEocene vo

Cik

20km

Fig. 1. Geological map showing the location of the Cirotan AuSnW de

shows the location of major epithermal gold deposits of Indonesia within

Milesi et al. (1994) and Milesi et al. (1999).Pongkor

JAKARTA

ome

logy 219 (2005) 237260 239et al., 1995). The central part of the Bayah dome

contains Oligocene to Miocene andesiticdacitic

volcanic rocks and Pliocene to PlioceneQuaternary

diorite to andesite intrusions (Fig. 1), whereas the

margins are dominated by Pliocene to Quaternary

volcanic rocks (Milesi et al., 1994). Eocene to

Miocene sedimentary rocks, mostly shallow marine

siliciclastics and limestones, are widespread in the

southwestern part of the Bayah dome. It is important

to note that the sedimentary sequence records two

different depositional environments, which are sepa-

rated by a major erosional surface. Eocene to early

Miocene sediments are predominantly quartz sand-

stones, conglomerates, and shales with intercalations

of limestones, coal layers, and volcaniclastics, which

were deposited in a very shallow marine to littoral

setting. By contrast, the middle to late Miocene

sediments indicate more open marine conditions, with

edimentsolcanicslcanics

Au-Mn (Pongkor type)Au-Sn-W (Cirotan type)

Cirotan

BAYAH

otok

posit, as well as other epithermal Au deposits in the region. Insert

the plate-tectonic setting of the region. Redrawn and modified after

ceous breccia with minor sulphides; (3) polymetallic

cockade breccia in which cockades are characterized

l Geoabundant reef limestones and intercalations of shales

and fine ash tuffs (Sukarna, 1994). Intensive folding

and faulting of the Tertiary volcano-sedimentary rocks

occurred in the late Miocene (Sukarna, 1994).

Most of the important gold deposits of the Bayah

dome occur in a NS striking structural corridor,

which is defined by a system of conjugate NNWSSE

right-lateral and NNESSW left-lateral strike-slip

faults (Milesi et al., 1994). The fault zones are related

to a N 208 E directed compressional regime, and someof the faults are interpreted as megatension cracks

(Genna et al., 1996). Based on the internal vein

structures and the style of mineralization, two distinct

groups of low-sulphidation epithermal gold deposits,

termed Cirotan-and Pongkor-type, are distinguished

(Marcoux and Milesi, 1994). Deposits of the Cirotan-

type occur within mineralized fault zones, up to 30 m

wide, which contain abundant breccia hosting fairly

complex polymetallic ore mineral assemblages. These

deposits are very rich in pyrite and base metal

sulphides, and the gold-rich ores are associated with

anomalous enrichments of Sn, W, and Bi (Marcoux et

al., 1993; Milesi et al., 1994). The gangue mineralogy

is comparatively simple, with quartz, chalcedony, and

sericite being predominant, and hydrothermal carbo-

nates rather rare (Marcoux et al., 1993; Milesi et al.,

1994; Leroy et al., 2000). In contrast, deposits of the

Pongkor-type show symmetrically banded structures,

with brecciation being restricted to the contacts with

the wallrock. These deposits are characterized by very

low sulphide contents, the presence of large amounts

of carbonate gangue (calcite and minor rhodochro-

site), and a generally much simpler ore mineralogy

(Milesi et al., 1999; Greffie et al., 2002; Warmada et

al., 2003). Most of the Pongkor-type deposits show

extensive supergene weathering, resulting in signifi-

cant secondary gold enrichment in the upper zones of

the veins (Milesi et al., 1999; Greffie et al., 2002).

Radiometric KAr and ArAr dates of adularia from a

number of epithermal veins demonstrate that both the

Cirotan- and Pongkor-type epithermal gold deposits

were formed within the same narrow time interval

between 2.4 and 1.5 Ma (Marcoux and Milesi, 1994;

Milesi et al., 1999; Rosana and Matsueda, 2002). The

radiometric age data and Pb isotope patterns indicate a

temporal and genetic link to Pliocene magmatism

T. Wagner et al. / Chemica240(Marcoux and Milesi, 1994). The presence of active

geothermal systems in western Java, most notably theby numerous concentric rims of rhodochrosite, quartz

and base metal sulphides; (4) high-grade precious

metal ore breccia; and (5) late drusy quartz (Marcoux

et al., 1993; Milesi et al., 1994). The deeper levelscurrently producing Awibengkok geothermal field

SW of Bogor, shows that magmatic-hydrothermal

activity is ongoing in the Bayah dome area (Allis,

1999; Moore and Norman, 1999).

3. The Cirotan deposit

The Cirotan epithermal gold deposit is hosted by a

system of mineralized fractures in a right-lateral

strike-slip fault, which subsequently evolved into a

normal fault (Genna et al., 1996). The vein structure,

which strikes N 108 W and dips 50608 to the E,extends for a distance of 800 m and reaches a

maximum thickness of 2530 m. Ore grade mineral-

ization has been mined over a length of 560 m and

vertically from the top of Gunung Dahbow mountain

(843 m) down to a depth of 350 m (Milesi et al.,

1994). Mining operations included an open pit on the

peak of Gunung Dahbow and a series of underground

levels separated by intervals of 100 ft (L100 to

L1000). The mine was closed in 1993, but gold

exploration in the area is still continuing, with recent

diamond drilling being the most notable activity. The

Cirotan vein cuts Miocene rhyodacitic ignimbrites

(KAr: 9.5F0.3 Ma), older dacitic to andesitic lavas(KAr: 14.3F0.7 Ma), and a stock of weaklypropylitized Pliocene quartz microdiorite (KAr:

4.5F0.3 Ma), which has intruded the Miocenevolcanics (Milesi et al., 1994; Marcoux and Milesi,

1994). Hydrothermal adularia from the Cirotan

deposit has been dated at 1.7F0.1 Ma (Marcouxand Milesi, 1994).

Hydrothermal alteration is dominated by intense

silicification, particularly in the footwall, and is

accompanied by weak to intense sericitization; both

types of alteration are superimposed onto regional

propylitic alteration. Based on relative age relation-

ships, five distinct mineralization/alteration stages can

be distinguished: (1) wallrock silicification; (2) sili-

logy 219 (2005) 237260(L800L1000) of the Cirotan deposit are dominated

by complex breccia bodies, 1015 m in thickness, in

bearing layers, which encrust nuclei of altered micro-

diorite or fragments of siliceous breccia. The size of

l Geowhich siliceous breccia grades into breccias with

progressively larger cockades. The Cirotan vein is

composed of several of these breccia bodies, which

are separated by discontinuity zones marked by 520

cm thick quartz veins. Structural analysis suggests that

the polymetallic cockades formed through a sequence

of rolling-accretion and collapse at relatively high

fluid pressure (Genna et al., 1996). Above L800,

breccia bodies comprise fragments of siliceous breccia

cemented by a polymetallic sulphide assemblage

similar to that of the cockade breccia. The precious

metal breccia ore, which hosts the bulk of the gold in

the Cirotan deposit, consists of an anastomosing

network of 110 cm wide veinlets, which crosscut

the siliceous and cockade breccia units. These

bonanza veins have average gold grades of 912 g/t

(locally gold grades can attain 700 g/t), and anom-

alous concentrations of Sn, W, and Bi. Ore textures

demonstrate that electrum is spatially associated with

wolframite, cassiterite, and scheelite. The deposit

shows a pronounced vertical metal zonation, with

the average Ag/Au ratio of the ores decreasing

systematically from 64 in the upper levels to 7 in

L900 (Milesi et al., 1994).

Milesi et al. (1994) reported that fluid inclusions in

the deposit are two phase (LV) and homogenize

exclusively to liquid, suggesting that the system most

likely did not boil. Their homogenization temper-

atures are in the range of 207292 8C with a clearmode around 240260 8C for the main ore-formingstages (siliceous breccia, cockade breccia, brecciated

precious metal ore), and decrease to 159212 8C forthe late drusy quartz. The salinities range between 2.9

and 7.2 wt.% equivalent NaCl. Somewhat different

findings were reported by Leroy et al. (2000) based on

a detailed study of fluid inclusions in cockade

breccias. These authors observed the coexistence of

liquid- and vapour-rich inclusions in samples from the

early stage of cockade breccia evolution, which

provides evidence that there was at least episodic

boiling. Furthermore, the salinities reported by them

are systematically lower and have a much narrower

range (between 1.0 and 2.2 wt.% equivalent NaCl)

than those reported by Milesi et al. (1994). The

homogenization temperatures reported by Leroy et al.

(2000) are 162300 8C for liquid-rich inclusions and

T. Wagner et al. / Chemica360380 8C for vapour-rich inclusions (the higherhomogenization temperatures of the vapour-richthe cockades increases systematically as the hanging-

wall contact of the vein is approached. Early cockadesinclusions are not unexpected and likely reflect

unavoidable entrapment of liquid with the vapour).

4. Mineralogy and textures of the epithermal veins

We have studied a suite of ore and wallrock

samples from the Cirotan deposit, which cover the

principal mineralization stages of the epithermal

system. The samples originate from the underground

exposures of mine levels L700 and L900, as well as

from small workings on L200. Detailed grid sampling

was carried out on L900, to obtain a series of cross

sections through the entire vein. The samples have

been investigated by microscopy and electron-microp-

robe analysis. Based on the results of these studies, a

subset of samples was selected for stable isotope

analysis; these samples are listed in Table 1. In the

following paragraphs, we provide a general descrip-

tion of these samples, and establish a detailed para-

genesis for the polymetallic cockade facies and the

high-grade ore, which formed the basis of a texturally-

constrained oxygen and sulphur isotope investigation.

Exposures of the footwall alteration zone of the

Cirotan vein on L900 show that silicification increases

as the vein is approached, and that the transition into

siliceous breccia is relatively continuous. Altered

portions of the microdiorite are impregnated by finely

layered chalcedonic silica, which forms a network of

very fine veinlets. The contact with the vein is

indicated by zones of intense brecciation of the

wallrock, in which larger wallrock fragments have

been rotated and show internal fragmentation. The

siliceous breccia is composed of angular, highly

silicified wallrock fragments, which are encrusted by

layered, mostly clear chalcedonic silica (Fig. 2a). The

breccia contains abundant pyrite and, in places,

fragments of massive sphaleritegalena ore. With

increasing distance from the footwall contact, the

siliceous breccia evolves continuously into cockade

breccia. The onset of cockade formation is indicated

by the presence of several narrow rhodochrosite-

logy 219 (2005) 237260 241are between 2 and 5 cm in diameter, and comprise

wallrock fragments with narrow, sulphide-free, rims

gSn

extura

sphale

yrite

inlets

inlets

inlets

yrite

inlets

of fi

of co

ckade

ckade

10 c

cm)

cm)

cm)

5 cm

einlet

quart

l GeoTable 1

Descriptions of samples analyzed from the Cirotan epithermal AuA

Sample Location Mineralization style and t

CIR-201 Workings below open pit Cockade breccia, banded

CIR-704 Level 700, crosscut 770 High-grade ore, banded p

CIR-707 Level 700, crosscut 770 High-grade ore, quartz ve



CIR-723 Level 700, crosscut 770 High-grade ore, banded p


CIR-905 Level 900, crosscut 967 Siliceous breccia, network

CIR-906 Level 900, crosscut 967 Siliceous breccia, network

CIR-907 Level 900, crosscut 967 Cockade breccia, small co

CIR-909 Level 900, crosscut 967 Cockade breccia, small co

CIR-911 Level 900, tunnel 966967 Cockade breccia, small (5

CIR-912 Level 900, tunnel 967969 Cockade breccia, large (15



CIR-919 Level 900, crosscut 969 Cockade breccia, small (2

CIR-921 Level 900, crosscut 969 Siliceous breccia, quartz v

CIR-926 Level 900, crosscut 967 Siliceous breccia, banded

T. Wagner et al. / Chemica242of rhodochrositerhodonitequartz. Later cockades

have diameters up to 50 cm and the mineralogy

evolves towards complex polymetallic assemblages

(Fig. 2b,c). Cockade breccias are not found on L700

and L200, but the siliceous breccia on these levels

contains abundant sulphide-rich polymetallic miner-

alization, which encrusts the angular wallrock frag-

ments. Based on the paragenetic sequence and textural

relationships, this assemblage can be considered as an

analogue of the polymetallic facies observed in the

cockade breccia. The siliceous and cockade breccia

bodies are crosscut by the later high-grade bonanza

veins, which are texturally distinct from the previous

mineralization stages. These veins are very rich in

pyrite, are laminated (Fig. 2d), and display clear

evidence of shearing and cataclastic deformation of

the sulphides, as previously noted by Milesi et al.

(1994).

Detailed textural investigation of the cockade

breccia indicates a rather complex succession of

CIR-927 Level 900, tunnel 967969 Cockade breccia, large (30 cm)

CIR-928 Level 900, tunnel 967969 Cockade breccia, large (25 cm)

CIR-933 Level 900, tunnel 966967 Cockade breccia, small cockade

CIR-935 Level 900, crosscut 966 Siliceous breccia, banded quart

CIR-936 Level 900, crosscut 966 Cockade breccia, banded sphale

CIR-940 Level 900, tunnel 964966 Siliceous breccia, quartz veinlet

CIR-941 Level 900, crosscut 964 Siliceous breccia, network of co

CIR-943 Level 900, crosscut 958 Siliceous breccia, quartz veins c

CIR-944 Level 900, crosscut 958 Cockade breccia, fragments of cW deposit

l relationships

ritegalena ore with comb quartz veinlet

galenasphalerite vein with electrum

with wolframite, electrum and cassiterite



sphalerite ore, crosscut by quartzwolframite veinlets


ne quartz veinlets crosscutting silicified wallrock fragments

arse quartz veinlets crosscutting silicified wallrock fragments

s (25 cm) with chalcedony and rhodochrosite, no sulphides present


m) cockades with rhodochrosite and polymetallic sulphide rims

cockade with sulphide rims, enclosing fragments of siliceous breccia

cockade with rhodochrosite and polymetallic sulphide rims

cockade with sulphide rims, enclosing fragments of siliceous breccia

) silica-rich cockades encrusting fragments of siliceous breccia

s with silicified wallrock fragments, overgrown by late drusy quartz

z veins crosscutting silicified wallrock fragments

logy 219 (2005) 237260concentric sulphide and silica rims. The sulphide-rich

polymetallic facies shows a distinct sequence of

layers, which can be correlated among cockades.

Cockade formation began with the deposition of a

Mn-rich, sulphide-poor, zone, which is composed of

acicular rhodonite, rhodochrosite, and fine-grained

quartz. This zone contains three distinct rhodonite

rhodochrosite layers, which are separated by quartz

layers. Leroy et al. (2000) also noted the presence of

platy calcite, which they interpreted as additional

evidence of boiling. The Mn-rich zone is followed by

a zone of alternating coarse- and fine-grained quartz

layers, which contain abundant inclusions of euhedral

pyrite crystals, 200800 Am in diameter, and subhe-dral sphalerite grains. Quartz in the coarse-grained

layers exhibits idiomorphic terminations, indicating

open-space growth. The last of the fine-grained quartz

layers is overgrown by a massive sphalerite layer,

which contains rare inclusions of pyrite and quartz.

This coarse sphalerite is followed by two identical




z veins crosscutting silicified wallrock fragments

ritegalena ore encrusting siliceous breccia

s

arse quartz veinlets crosscutting silicified wallrock fragments

rosscutting silicified wallrock fragments

ockades with polymetallic sulphides, overgrown by late drusy quartz

l GeoT. Wagner et al. / Chemicasequences of pyritesphalerite(galena)quartz. Tex-

turally, the first of these two sequences is coarser-

grained (Fig. 3a) than the second sequence (Fig. 3b).

Both are composed of bladed to blocky pyrite, which

appears to have grown initially as skeletal aggregates.

This pyrite is rimmed by sphalerite and minor

amounts of galena. Pyrite is now present as small

euhedral to subhedral crystals, indicating that the

original pyrite has recrystallized. Subsequent to these

two pyritesphalerite layers, a wide quartz-rich zone

formed, containing numerous alternating layers of

very fine-grained skeletal and arborescent pyrite and

fine-grained quartz (Fig. 3c). This zone is very poor in

sphalerite and galena, and the outermost part contains

scattered fine wolframite needles. The outermost layer

of the polymetallic cockade facies is composed of

coarse sphalerite, which contains abundant inclusions

of coarse skeletal galena crystals and irregularly-

shaped chalcopyrite grains. The sphalerite shows

distinct euhedral terminations (Fig. 3d). Electron

Fig. 2. Photographs of representative handspecimens showing textures of or

bar is 2 cm. (a) Siliceous breccia, with fractures filled by late-stage drusy

sulphide and silica rims overgrowing a silicified wallrock fragment. Sampl

of rhodochrosite, silica, and sulphide rims overgrowing a fragment of silice

sulphide-rich zone and wolframiteelectrumcassiterite veinlets (top of splogy 219 (2005) 237260 243microprobe analyses of the different sphalerite gen-

erations of the cockade breccia indicate a distinct

compositional zonation with highly variable iron

contents, ranging between 0.7 and 18.8 mol% FeS.

The open space between the individual fragments of

the cockade breccia has been infilled by late-stage

drusy quartz, which contains rare pyrite inclusions.

The laminated Au-rich (bonanza) veins, which

crosscut the siliceous and cockade breccia bodies,

exhibit a variety of complex ore assemblages. Two

texturally distinct ore types can be recognised. The first

of these, a laminated ore type, is composed of

alternating layers of very fine-grained pyrite and

sphaleritegalena in which individual grains are

commonly elongated and deformed (Fig. 3e). Galena-

rich layers host local enrichments of canfieldite

(Ag8SnS6). Electronmicroprobe analyses of canfieldite

indicate elevated concentrations of Se (0.43.0 wt.%)

and trace amounts of Te (0.10.3 wt.%). Marcoux et al.

(1993) described a distinctly Te-rich variety of can-

e samples from the Cirotan epithermal AuAgSnW deposit. Scale

quartz. Sample CIR-940. (b) Cockade breccia with a sequence of

e CIR-928. (c) Section through a large cockade showing a sequence

ous breccia. Sample CIR-914. (d) High-grade vein with a laminated

ecimen). Sample CIR-912.

l GeoT. Wagner et al. / Chemica244fieldite, which was not observed during our study.

Electrum is present as 50400 Am diameter grains,which occur mainly within fractures crosscutting the

pyrite layers or along the contacts between pyrite and

sphalerite layers. The second ore type forms a network

of mm- to cm-wide quartz veinlets, which host a

wolframiteelectrumcassiteritescheelite assem-

Fig. 3. Photomicrographs in reflected light showing representative textur

deposit. Scale bar is 200 Am. (a) Coarse-grained bladed pyrite (py), comsphalerite (sp) and quartz (qz). This texture is typical for the earliest laye

Fine-grained bladed pyrite (py), composed of pyrite crystals, which have

(qz). This second layer of pyritesphalerite in the cockade breccia is invaria

fine-grained arborescent pyrite (py), intimately intergrown with quartz (q

layer in the cockade breccia typically contains arborescent pyrite, and is

euhedral sphalerite (sp) with anhedral chalcopyrite (cp) inclusions forming

frequently associated with mm-sized skeletal galena crystals. Late-stage d

Fine-grained high-grade gold ore containing intimately intergrown pyrite

fine galena (ga) veinlets. Sample CIR-704. (f) Very rich high-grade gold o

bladed wolframite (wol) with very fine anhedral electrum (el) grains cem

cassiterite (cas) has overgrown both wolframite and electrum. Sample CIRlogy 219 (2005) 237260blage. Wolframite is present as bladed to prismatic

crystals, 200 Am to 8 mm in diameter, which containrare pyrite inclusions. Parts of the wolframite crystals

show replacement by scheelite. Numerous minute

anhedral electrum grains, 110 Am in diameter, havegrown directly on the crystal faces or within cleavage

planes of wolframite (Fig. 3f). The electrum grains are

es of ore assemblages from the Cirotan epithermal AuAgSnW

posed of numerous pyrite crystals, which have been overgrown by

r of pyritesphalerite in the cockade breccia. Sample CIR-914e. (b)

been overgrown and partially corroded by sphalerite (sp) and quartz

bly more fine-grained than the first layer. Sample CIR-914e. (c) Very

z). Following deposition of two layers of pyrite-sphalerite, the next

almost free of base-metal minerals. Sample CIR-912b. (d) Coarse

the outermost sulphide layer in a cockade breccia. This sphalerite is

rusy quartz (qz) overgrows these sulphides. Sample CIR-912b. (e)

(py) crystals and anhedral sphalerite (sp), which are infilled by very

re, containing a characteristic assemblage of pyrite crystals (py) and

ented on crystal faces and along cleavage planes. Twinned euhedral

-723c.

dochrosite, calcite) and oxide minerals (quartz,

chalcedony, wolframite) were prepared by careful

l Geohand-picking under a binocular microscope, followed

by cleaning in doubly-distilled water. Sulphide min-

erals (pyrite, arsenopyrite, sphalerite, galena) were

analyzed by in situ laser combustion from standard

polished blocks.

Sulphide minerals were combusted in an oxygen

atmosphere using a SPECTRON LASERS 902Q CW

Nd:YAG laser (1 W power); typical spot sizes in this

study were 200300 Am. Laser extraction was followedby cryogenic purification of the SO2 gas and subse-enclosed by roughly coeval twinned euhedral cassiter-

ite and sphalerite. The high-grade quartz veinlets host

atoll-textured pyrite and sphalerite, whose exact

temporal relation with the wolframiteelectrumcassi-

terite assemblage is uncertain. Electron microprobe

analyses show that electrum in these quartz veinlets has

a higher fineness (Au48Ag52 to Au76Ag24) than

electrum in the laminated, sulphide-rich gold ore type

(Au33Ag67 to Au52Ag48), indicating different deposi-

tional conditions.

5. Stable isotope geochemistry

A representative suite of samples from the princi-

pal mineralization stages of the Cirotan deposit

(siliceous breccia, cockade breccia, high-grade ore,

late drusy quartz) was selected for sulphur, oxygen,

and carbon isotope analyses. The samples cover a

wide range of textures of hydrothermal sulphides and

oxides, and permit characterization of the general

isotopic trends along the paragenetic sequence as well

as detailed small-scale study of the cockade breccia

and the high-grade ores. The carbon isotope analyses

refer only to a very restricted interval in the hydro-

thermal history, because rhodochrosite was only

precipitated during the onset of cockade breccia

formation. For comparison, a series of calcite samples

from the Pongkor deposit was analyzed for C and O

isotope composition as well.

5.1. Analytical techniques

Mineral separates of hydrothermal carbonate (rho-

T. Wagner et al. / Chemicaquent on-line mass-spectrometric analysis. Details of

the laser extraction technique, calibration, and correc-tion procedures are provided by Kelley and Fallick

(1990), Kelley et al. (1992) and Wagner et al. (2002).

Reproducibility of the analytical results, and mass

spectrometer calibration, was monitored through rep-

licate measurements of international standards NBS-

123 (y34SV-CDT: +17.1x) and IAEA-S-3 (y34SV-CDT:

31.0x), as well as the internal lab standard CP-1(y34SV-CDT:4.6x). The analytical precision (1j) wasaround F0.2x. All sulphur isotope compositions aregiven in standard delta notation relative to V-CDT.

Oxygen was extracted from quartz, chalcedony,

and wolframite by reacting 15 mg of sample with

purified chlorine trifluoride in a laser fluorination

system, based on techniques of Sharp (1990) and

Mattey and Macpherson (1993). The oxygen was

converted to CO2 by reaction with a heated graphite

rod; the isotopic composition of the cryogenically

purified CO2 gas was measured on-line with a VG

PRISM III mass spectrometer. Analytical precision

was controlled through replicate measurements of the

internal laboratory standard SES-2 (y18OV-SMOW:+10.2x) during the course of the study. The latterwas calibrated against international standards IAEA-

NBS28 (y18OV-SMOW: +9.6x) and IAEA-NBS30(y18OV-SMOW: +5.1x). Precision (1j) was found tobe better than F0.2x for the whole data set. All Oisotope data are reported relative to V-SMOW.

Hydrothermal carbonates were analysed for their C

and O isotope composition using an Analytical

Precision AP2003 continuous-flow mass spectrome-

ter, equipped with an automated carbonate preparation

system. About 1 mg of sample powder was placed in a

6 ml vacutainer, then sealed and loaded onto the

autosampling unit. Each sample was flushed with

helium, then a pre-determined amount of 103%

phosphoric acid was injected into each tube, essen-

tially following the procedure of McCrea (1950). The

acid reaction was conducted at a temperature of

70F0.1 8C; reaction times were 24 h for pure calcitesamples and 120 h for all other carbonates. After

completion of the reaction, the samples were trans-

ferred to the processing system and analyzed with the

AP2003 mass spectrometer. Oxygen isotope data for

rhodochrosite were corrected using a fractionation

factor aCO2-MnCO3 of 1.00819 calculated fromBottcher (1996). Reproducibility of the analytical

logy 219 (2005) 237260 245results was monitored through replicate measurements

of the internal Mab2b standard (y13CV-PDB: +2.48x;

Table 2

Sulphur isotope data for the Cirotan epithermal deposit

Sample Mineral Textural description y34SV-CDT(x)

Siliceous breccia

CIR-912a-1 Arsenopyrite Crystals, replacing

lamellar pyrite

+3.1

CIR-912a-2 Arsenopyrite Crystals, replacing

lamellar pyrite

+4.4

CIR-912a-3 Sphalerite Anhedral grains

intergrown with pyrite

+3.2

CIR-912a-4 Pyrite Fine-grained aggregate +3.5

CIR-914b-1 Sphalerite Anhedral grains

intergrown with pyrite

+4.1

CIR-914b-2 Galena Idiomorphic skeletal

crystal

+2.5

CIR-914b-3 Pyrite Aggregate of small

crystals

+4.0


crystal

+4.0

Cockade breccia

CIR-201-6 Sphalerite Coarse-grained massive

band

+4.2

CIR-201-7 Galena Idiomorphic skeletal

crystal

+3.4

CIR-201-9 Sphalerite Narrow massive band +3.3


crystal

+3.5

CIR-912b-1 Pyrite Large bladed crystals +4.1

CIR-912b-2 Sphalerite Crystals overgrowing

bladed pyrite

+4.1

CIR-912b-3 Pyrite Small bladed crystals +4.2


bladed pyrite

+3.8

CIR-912b-5 Pyrite Fine-grained lamellar

aggregates

+3.8

CIR-912b-6 Pyrite Fine lamellar aggregates

in quartz

+4.7

CIR-912b-7 Pyrite Fine lamellar aggregates

in quartz

+4.1


lamellar pyrite

+3.7

CIR-912b-9 Sphalerite Coarse-grained band,

with wolframite

+3.6


crystal

+2.9

CIR-914e-1 Pyrite Large crystals, early

zone

+3.2


zone

+4.5


zone

+3.1


zone

+4.5

l Geology 219 (2005) 237260y18OV-PDB: 2.40x) before and after each batch ofsamples. Accuracy was controlled by replicate meas-

urements of international standards IAEA-CO1

(y13CV-PDB: +2.48x; y18OV-PDB: 2.44) and IAEA-

NBS19 (y13CV-PDB: +1.95x; y18OV-PDB: 2.20x).

External precision (1j) was found to be better thanF0.2x for both carbon and oxygen isotope compo-sitions. Carbon and oxygen isotope data are reported

relative to V-PDB and V-SMOW, respectively.

5.2. Sulphur isotope data

A total number of 87 spot analyses of the sulphur

isotope composition of pyrite, arsenopyrite, sphalerite,

and galena were carried out and are listed in Table 2.

The y34S values of sulphide minerals from siliceousbreccia, cockade breccia, and precious brecciated ore

are remarkably homogeneous and range between +0.1

and +5.4x (Fig. 4), with a mean composition of +3.8F0.9x. Most data are confined to an even narrowerrange of y34S values between +2.5 and +5.4x, withonly two small pyrite grains from the early zones of

cockade breccia having lower y34S values of +0.1 and+1.1x. The y34S values of sulphides from siliceousbreccia (+3.6F0.6x), cockade breccia (+3.7F0.9x)and precious metal breccia ore (+4.0F0.9x) areidentical within analytical error, indicating that there

was no shift of the sulphur isotope composition of the

epithermal fluid with time. The homogeneity of the

sulphur isotope composition is even more evident from

the results of the texturally-constrained analysis.

Representative samples of the polymetallic cockade

breccia facies were analyzed in great detail, with the

data set covering texturally coexisting pyrite, sphaler-

ite, and galena from all individual sulphide layers of

these cockade samples (Fig. 5). The results show that

there was no detectable change in sulphur isotope

composition during the evolution of the hydrothermal

system. Sulphides from both principal types of pre-

cious metal breccia ore (laminated sulphide-rich ore

and wolframiteelectrumcassiterite veinlets) also dis-

play identical sulphur isotope compositions (Fig. 5).

The y34S values of Milesi et al. (1994) are generallysomewhat lower than those reported here, and lie in the

range between +0.4 and +2.9x.The sulphur isotope data set from the Cirotan

T. Wagner et al. / Chemica246deposit exhibits another important feature. The

measured isotopic fractionation between texturally


Cockade breccia

CIR-914e-5 Pyrite Fine-grained, with

coarse sphalerite

+4.0

CIR-914e-6 Sphalerite Coarse-grained massive

band

+4.3


band

+4.5

CIR-914e-8 Pyrite Large bladed crystals +4.9


CIR-914e-11 Sphalerite Crystals overgrowing

bladed pyrite

+2.9


bladed pyrite

+3.8

CIR-914e-13 Pyrite Small bladed crystals +3.0


bladed pyrite

+3.0

CIR-914e-15 Pyrite Small bladed crystals +3.4


bladed pyrite

+2.9

CIR-914e-17 Pyrite Fine lamellar aggregates

in quartz

+5.1


band

+3.5


band

+3.7

CIR-914e-20 Galena Idiomorphic skeletal

crystal

+3.7


CIR-927-1 Pyrite Small crystals in wall

rock fragment

+1.1

CIR-927-2 Pyrite Small crystals in wall

rock fragment

+0.1


band

+3.4

CIR-927-4 Pyrite Fine-grained aggregate +3.3

CIR-927-5 Pyrite Large bladed crystals +3.1

CIR-927-6 Sphalerite Crystals overgrowing

bladed pyrite

+4.2

CIR-927-7 Pyrite Small bladed crystals +4.6

CIR-927-8 Sphalerite Crystals overgrowing

bladed pyrite

+3.9

CIR-927-9 Pyrite Fine lamellar aggregates

in quartz

+3.3


band

+3.8


crystal

+2.8


crystal

+3.4


band

+4.1


crystal

+4.3

Table 2 (continued) Table 2 (continued)

(continued on next page)


Cockade breccia

CIR-936b-1 Sphalerite Anhedral, rims around

galena

+4.1

CIR-936b-2 Sphalerite Anhedral, rims around

galena

+3.7


crystal

+3.2


crystal

+3.1

High-grade veins

CIR-704-2 Sphalerite Fine-grained, in

microshear-zone

+3.9

CIR-704-3 Galena Fine-grained, in

microshear-zone

+3.5

CIR-704-4 Galena Fine-grained, in

microshear-zone

+3.1

CIR-704-5 Sphalerite Brecciated, inclusion in

pyrite

+3.8

CIR-704-6 Pyrite Coarse-grained band in

veinlet

+2.6

CIR-704-7 Pyrite Coarse-grained band in

veinlet

+4.5

CIR-707a-1 Pyrite Fine-grained, core of

large crystal

+2.3

CIR-707a-2 Pyrite Coarse-grained, rim of

large crystal

+4.1


large crystal

+2.9

CIR-707a-4 Pyrite Coarse-grained, rim of

large crystal

+4.0


large crystal

+2.8

CIR-707c-1 Sphalerite Coarse-grained crystals,

with wolframite

+4.3

CIR-707c-2 Pyrite Spongiform, enclosing

pyrite crystals

+3.1

CIR-707c-3 Pyrite Small crystals, with

wolframite

+4.7


with wolframite

+4.2

CIR-712b-4 Sphalerite Coarse-grained crystals,

with wolframite

+3.0

CIR-712b-5 Pyrite Large coarse-grained

aggregate

+3.8

CIR-723c-1 Pyrite Large idiomorphic

crystal

+4.6


pyrite crystals

+4.3

CIR-723c-3 Pyrite Large idiomorphic

crystal

+5.4

CIR-723c-4 Sphalerite Spongiform, enclosing

pyrite crystals

+5.3

T. Wagner et al. / Chemical Geology 219 (2005) 237260 247

precious metal ore breccia (Fig. 6b,c), indicating a

significant shift in fluid y18O composition (assumingconstant temperature) at or immediately prior to the

onset of gold mineralization. The y18O values of wol-framite in the high-grade veinlets are in the range be-

tween 3.6 and 2.8x. Calculated equilibriumtemperatures for five texturally coexisting quartzwol-

framite pairs, using experimentally determined cali-

brations for wolframiteH2O (Zhang et al., 1994) and

quartzH2O (Matsuhisa et al., 1979) isotopic ex-

change, are in the range of 204238 8C, with amean of 226F14 8C. Considering the analyticaluncertainties, these temperatures are in reasonably

good agreement with fluid inclusion homogenization

temperatures.

5.4. Carbon and oxygen isotope data for hydro-

thermal carbonates

Carbon and oxygen isotope data for rhodochrosite

from Cirotan and calcite from Pongkor are given in

Frequency

l Geology 219 (2005) 237260coexisting mineral pairs, such as sphaleritegalena

and pyritesphalerite, is much smaller than the

equilibrium fractionation factor. At a temperature of

250 8C, which conforms to the mean homogenizationtemperature reported in fluid inclusion studies (Milesi

et al., 1994; Leroy et al., 2000), the calculated

equilibrium values of Dsp-ga and Dpy-sp are +2.6 and+1.1x (Ohmoto and Goldhaber, 1997), whereas theaverage measured values are +0.7F0.4 and+0.3F0.4x, respectively. Based on the measuredand equilibrium fractionation factors, the degree of

equilibrium between minerals and fluid (Ohmoto and

Goldhaber, 1997) was 0.3 or 30% for both sphalerite

galena and pyritesphalerite pairs.


High-grade veins


pyrite crystals

+5.2


with wolframite

+4.6


with wolframite

+4.5


with wolframite

+4.4

CIR-723c-10 Pyrite Coarse-grained bladed

band

+4.9

CIR-723c-11 Sphalerite Crystals overgrowing

bladed pyrite

+4.8

All samples were analysed by in situ laser combustion system.

Table 2 (continued)

T. Wagner et al. / Chemica2485.3. Oxygen isotope data for quartz/chalcedony and

wolframite

The oxygen isotope compositions of quartz/chal-

cedony and wolframite are listed in Table 3. The y18Ovalues of silica minerals from siliceous breccia,

cockade breccia, precious brecciated ore, and late-

stage drusy quartz are in the range between +6.1 and +

9.1x. In contrast to the y34S values, which remainedremarkably constant during mineral deposition, the

y18O values show a distinct evolution with time (Fig.6). The mean y18O value is highest in the siliceousbreccia (+8.5F0.4x), and decreases systematicallytowards cockade breccia (+8.1F0.5x), preciousmetal ore breccia (+7.4F0.2x) and drusy quartz(+6.9F0.4x). This isotopic trend is strongest for thetransition between quartz in cockade breccia and the34SV-CDT (% )

Cockade breccia

b-2 -1 0 1 2 3 4 5 6 7 8

24201612840

28

Siliceous breccia

-2 -1 0 1 2 3 4 5 6 7 8

840

a

High-grade ore

-2 -1 0 1 2 3 4 5 6 7 8

1612840

c

Fig. 4. Histograms displaying the sulphur isotope composition ofimportant ore types from the Cirotan deposit. (a) Siliceous breccia.

(b) Cockade breccia. (c) High-grade veins.

Fig. 5. Digital images showing millimetre-scale textural relationships and sulphur isotope data for representative polished sections from the

Cirotan deposit. The polished sections have a diameter of 3.75 cm.

T. Wagner et al. / Chemical Geology 219 (2005) 237260 249

Table 4. The y13C values of the Cirotan rhodo-chrosite are distinctly negative and range between

18.3 and 14.8x, whereas those for calcitesamples from Pongkor are more positive, with y13Cvalues ranging between 6.2 and 2.0x (Fig. 7).The Cirotan values are also very much lower than

those reported for low-sulphidation epithermal gold

deposits elsewhere (e.g., Robinson, 1975; Matsuhisa

et al., 1985; Shikazono, 1989; Simmons and Chris-

tenson, 1994; Brathwaite and Faure, 2002). Similarly,

the y18O values of the rhodochrosite from Cirotan(+22.7 to +26.2x) are significantly heavier thanthose of calcite from Pongkor (+6.6 to +17.2x),

Table 3

Oxygen isotope data for quartz, chalcedony, and wolframite from

the Cirotan epithermal deposit

Sample Mineral Textural description y18OV-SMOW( x)

Siliceous breccia

CIR-905 Chalcedony White-grey, banded

chalcedony

+7.9

CIR-906 Chalcedony White-grey chalcedony +8.5

CIR-926-1 Quartz Clear quartz, vein close

to cockade breccia, margin

+8.2

CIR-926-2 Quartz Clear quartz, vein close to

cockade breccia, centre

+8.1

CIR-935-1 Quartz Clear quartz, vein close to

siliceous breccia, margin

+8.6

CIR-939 Quartz White quartz, encrusting

wallrock fragments

+9.1

CIR-940-1 Quartz Clear quartz, enclosing

wallrock fragments

+8.3

CIR-941 Quartz White quartz, veinlet

network within wallrock

+9.1

CIR-943 Quartz White chalcedony, highly

silicified material

+8.7

Cockade breccia

CIR-907-2 Chalcedony Clear, banded chalcedony,

overgrown by rhodochrosite

+7.5

CIR-911 Quartz Clear quartz, overgrown by

sulphide rims

+8.4

CIR-912 Chalcedony Clear, banded chalcedony,


+8.4



+7.8

CIR-913-4 Quartz White quartz, overgrown by

sulphide rims

+8.5



+7.9

CIR-914-2 Chalcedony Grey chalcedony,

overgrown by sulphide rims

+7.5



+8.0


overgrowing rhodochrosite

+8.2

CIR-928-3 Quartz Fine-grained, grey quartz,

overgrowing sphalerite

+9.0

High-grade veins

CIR-704-1 Quartz White quartz, enclosing

wolcasel assemblage

+7.4

CIR-704-2 Wolframite Wolframite blades, enclosed

in white quartz

2.8

CIR-707c-1 Quartz White quartz, enclosing

wolcasel assemblage

+7.4

CIR-707c-2 Wolframite Wolframite blades, enclosed

in white quartz

3.2


wolcasel assemblage

+7.4

Late drusy quartz

CIR-907-1 Quartz Clear drusy quartz,

overgrowing small

cockades

+7.1

CIR-913-1 Quartz White drusy quartz,

outermost rim of large

cockade

+6.4



cockade

+6.6

CIR-921 Quartz Drusy quartz, overgrowing

siliceous breccia

+7.6



cockade

+6.8

CIR-935-2 Quartz Clear drusy quartz, vein

close to siliceous breccia

+7.0

CIR-940-2 Quartz White drusy quartz, over

growing siliceous breccia

+7.2

CIR-944 Quartz White drusy quartz,

encrusting fragments of

cockades

+6.7

T. Wagner et al. / Chemi l Geo250 caSample Mineral Textural description y18OV-SMOW( x)

High-grade veins


in white quartz

3.2


wolcasel assemblage

+7.1


in white quartz

3.1

CIR-724c-1 Quartz White quartz, enclosing

wolcasel assemblage

+7.6

CIR-724c-2 Wolframite Wolframite blades, enclosed

in white quartz

3.6

Table 3 (continued)

logy 219 (2005) 237260indicating that the carbonates in the two deposits

formed under very different conditions. The Pongkor

32

l Geoa10

2 3 4 5 6 7 8 9 10 11 12

5432

Cockade brecciaFrequency

Siliceous breccia54

T. Wagner et al. / Chemicadata are similar to those for epithermal deposits

elsewhere and are linearly distributed, which is

consistent with them being the result of progressive

cooling, boiling, or fluid mixing (e.g., Matsuhisa et

al., 1985; Zheng, 1990; Simmons and Christenson,

1994).

6. Discussion and conclusions

The sulphur, oxygen, and carbon isotope signatures

of the Cirotan deposit place important constraints on

the environment of ore deposition and the nature of

10

2 3 4 5 6 7 8 9 10 11 12

b

543210

2 3 4 5 6 7 8 9 10 11 12

c

High-grade veins

543210

2 3 4 5 6 7 8 9 10 11 12

d

Late drusy quartz

18OV-SMOW (% )Fig. 6. Histograms displaying the oxygen isotope composition of

vein quartz and chalcedony of the four major mineralization stages

of the Cirotan deposit. (a) Siliceous breccia; (b) cockade breccia; (c)

high-grade veins; (d) late drusy quartz.the sources of the epithermal gold-bearing fluids. A

meaningful interpretation of the sulphur and carbon

isotope data, in particular, requires estimation of the

mineralization temperatures and the fO2-pH condi-

tions. The y34S and y13C values of sulphide andcarbonate minerals precipitating from hydrothermal

solutions are most effectively modified by variations

in oxidation state and pH during fluid evolution

(Ohmoto, 1972; Ohmoto and Goldhaber, 1997) and

only the initial (unmodified) isotopic compositions are

characteristic of the fluid source.

6.1. Conditions of ore deposition

The fluid inclusion studies by Milesi et al. (1994)

and Leroy et al. (2000), despite important discrep-

ancies with respect to the range of salinity and the

presence of vapour-rich inclusions, agree that homog-

enization temperatures for fluid inclusions represent-

ing the major stages of ore formation at Cirotan are

typically in the range 240260 8C. We have carriedout microthermometric measurements of representa-

tive samples from L700 and L900, which confirm

these temperatures (Table 5). Our homogenization

temperatures for LV inclusions in quartz and

sphalerite are in the range of 211267 8C and 226262 8C, respectively, with a clear mode around 240260 8C. Measured salinities are between 0.2 and 2.6wt.% equivalent NaCl, which is consistent with the

findings of Leroy et al. (2000). Considering the

shallow level of mineralization and the evidence for

episodic boiling (presence of VL inclusions and the

nature of the breccias), it is reasonable to conclude

that pressure fluctuated from slightly greater than

lithostatic to that of saturated water vapour (SWVP).

Using these estimated PT conditions (250 8C,SWVP), we have calculated a series of phase

diagrams, combining aqueous and mineral equilibria

in the CuFeSCOH system with those for

important alteration reactions and those for isolines

of sulphur and carbon isotope fractionation. Thermo-

dynamic data for aqueous species were taken from the

SUPCRT92 database (Johnson et al., 1991; Shock et

al., 1997; Sverjensky et al., 1997), whereas the

thermodynamic data for the solid phases came from

Holland and Powell (1998) and Robie and Hemi-

logy 219 (2005) 237260 251ngway (1995). All calculations of reaction log k

values were performed with the UNITHERM program

n and

sulph

sulph

s in v

s in v

de

de

de

s in v

sulph

s in v

s in v

l GeoTable 4

Carbon and oxygen isotope data for vein carbonates from the Cirota

Sample Mineral Textural description

Cirotan deposit

CIR-907 Rhodochrosite Small cockades, no

CIR-909-1 Rhodochrosite Small cockades, no

CIR-909-2 Rhodochrosite Idiomorphic crystal

CIR-911 Rhodochrosite Idiomorphic crystal

CIR-913-1 Rhodochrosite Rims of large cocka

CIR-913-2 Rhodochrosite Rims of large cocka

CIR-914 Rhodochrosite Rims of large cocka


CIR-933-1 Rhodochrosite Small cockades, no

CIR-933-2 Rhodochrosite Idiomorphic crystal


Pongkor deposit

T. Wagner et al. / Chemica252of the HCH software package (Shvarov and Bastra-

kov, 1999). The set of equations of Zhang and Spry

(1994) and the most recent set of isotopic fractiona-

tion factors given in Ohmoto and Goldhaber (1997)

were used for calculation of sulphur isotope isolines.

The model of Zhang and Spry (1994), which excludes

the aqueous S2 species, is preferred over the originalformalism of Ohmoto (1972), because the second

dissociation constant of H2S is too small for S2 to be

a significant species at geologically realistic values of

pH (e.g., Migdisov et al., 2002).

A comparison of the calculated phase equilibria

(Fig. 8) with the observed ore and gangue assemb-

lages was used to constrain the fO2 and pH conditions

during the major stages of ore formation (siliceous

breccia, cockade breccia, and precious brecciated ore).

PON-1 Calcite Coarse sparry calcite, on

PON-5 Calcite Coarse sparry calcite, cen

PON-7 Calcite Veinlets crosscutting alter

PON-8 Calcite Coarse calcite in vugs, on

PON-9 Calcite Idiomorphic crystals, on

PON-10 Calcite Coarse sparry calcite, cen

PON-13 Calcite Idiomorphic crystals in v

PON-16 Calcite Fine-grained, intergrown

PON-17 Calcite Coarse, intergrown with q

PON-18 Calcite Very coarse transparent c

PON-19 Calcite Very coarse transparent c

PON-34 Calcite Veinlets crosscutting alter

PON-37-1 Calcite Coarse zoned veinlet, wh

PON-37-2 Calcite Coarse zoned veinlet, bro

PON-37-3 Calcite Coarse zoned veinlet, wh

PON-39 Calcite Late calcite in vugs on d

PON-42 Calcite Calcite pockets in banded

PON-43 Calcite Veinlets crosscutting alterPongkor epithermal deposits

y13CV-PDB(x) y18OV-SMOW(x)

ides present 14.8 +20.6ides present 18.3 +23.7ug 15.0 +22.7ug 18.1 +24.9

15.6 +25.515.1 +24.117.8 +24.7

ug 15.8 +25.3ides present 17.3 +23.0ug 15.9 +24.4ug 17.2 +26.2

logy 219 (2005) 237260The alteration mineralogy clearly demonstrates that

the epithermal fluid was in equilibrium with a

muscoviteadulariaquartz assemblage, which indi-

cates a pH of about 57 for a range of geologically

reasonable K+ activities. For subsequent calculations,

we adopted a pH value of 5.9, which was calculated

for a fluid in equilibrium with the full mineral

assemblage (muscoviteadulariachloritequartz

albitepyrite) found in strongly altered rocks from

the footwall zone of the Cirotan vein. The oxidation

state of the Cirotan fluid can be inferred from the

measured Fe substitution in sphalerite applying

pyritesphalerite equilibria (Scott and Barnes, 1971),

the absence of phases other than pyrite in the FeS

OH system, and the predicted trends for sulphur

isotope variations for increasing or decreasing fO2.

drusy quartz 3.5 +17.2tre of veinlet 5.7 +8.7ed wallrock 4.9 +13.5drusy quartz 4.8 +11.2

drusy quartz 2.9 +16.1tre of veinlet 3.7 +7.4ug 3.5 +14.1with quartz 5.5 +8.1uartz 5.7 +8.6alcite 6.2 +7.2alcite 5.6 +6.6ed wallrock 2.0 +16.3ite calcite 1 2.6 +11.2wn calcite 2 6.0 +9.6ite calcite 3 5.9 +7.5rusy quartz 2.9 +11.6chalcedony 5.3 +7.1ed wallrock 5.9 +7.3

brium during sulphide precipitation. These observa-

tions are consistent with skeletal and arborescent

growth textures indicating that sulphide mineral

precipitation was relatively fast under conditions of

strong supersaturation (Marcoux et al., 1993; Milesi et

al., 1994). It is thus likely that sulphur species did not

respond isotopically to the changing physicochemical

conditions, notably fO2 and pH, and consequently that

the sulphur isotope composition of sulphide minerals

reflects conditions in the source region, where, by

contrast, equilibrium probably prevailed (Reed and

Spycher, 1984; Spycher and Reed, 1989; Pang and

Reed, 1998). We therefore conclude that the sulphur

isotope signature of the polymetallic mineralization at

Cirotan can be used with a reasonable degree of

confidence to fingerprint potential fluid sources.

Pongkor

18OV-SMOW (% )

0

-5

-10

-15

-205 10 15 20 25 30

Cirotan

13CV-PDB (% )

Fig. 7. Binary y13C and y18O diagram comparing the composition ofrhodochrosite in cockade breccia from the Cirotan deposit, and

T. Wagner et al. / Chemical Geology 219 (2005) 237260 253All these indicators point to formation of the poly-

metallic assemblage under relatively reducing con-

ditions in the lower part of the pyrite stability field,

with the estimated log fO2 being around 39 to 36(Fig. 8). However, variations in the Fe content of

different generations of sphalerite indicate that there

were significant fluctuations in fO2, particularly

during formation of the cockade breccia.

As discussed earlier, the sulphur isotopic data show

little change with evolution of the hydrothermal

veins from the Pongkor deposit.system, and comparison of predicted equilibrium

and measured fractionation factors point to disequili-

Table 5

Summary of fluid inclusion data from the Cirotan deposit, based on Mile

Mineralization stage Host mineral Inclusion type T

Silicification Quartz Liquid-rich Cockade breccia Quartz Liquid-rich

Sphalerite Liquid-rich Precious metal ore breccia Quartz Liquid-rich

Sphalerite Liquid-rich Late drusy quartz Quartz Liquid-rich Cockade breccia Quartz Liquid-rich

Quartz Vapour-rich

Late drusy quartz Quartz Liquid-rich

Quartz Vapour-rich

Siliceous breccia Quartz Liquid-rich Cockade breccia Quartz Liquid-rich Precious metal ore breccia Quartz Liquid-rich

Sphalerite Liquid-rich 6.2. Effects of cooling, mixing, and boiling

The mean y18O values of silica minerals from theprincipal mineralization stages at Cirotan show a

significant decrease with evolution of the related

hydrothermal system, which must reflect a systematic

change in the oxygen isotope composition of the fluid.

In order to constrain the nature of this isotopic

evolution, we have quantitatively modelled the

isotopic effects of cooling, boiling, and mixing

processes (Fig. 9). For these calculations, we have

assumed that the initial y18O value of the fluid was+0.5x, which corresponds to that for water in

si et al. (1994), Leroy et al. (2000), and this study

m ice (8C) Salinity(wt.%)

Th (8C) Reference

2.3 to 2.1 3.53.9 232275 Milesi et al. (1994)2.2 to 1.7 2.93.7 2392683.3 to 2.0 3.45.4 2072803.5 to 1.7 2.95.7 2012924.5 to 3.0 5.37.2 2202613.6 to 2.4 4.05.9 1592121.3 to 0.6 1.02.2 162316 Leroy et al. (2000)

360380

1.9 180287

257377

1.3 to 0.1 0.22.2 221267 This study0.8 to 0.1 0.21.4 211265

1.5 to 0.1 0.22.6 2292570.8 to 0.1 0.21.4 226262

L-2

-3

-3

-4

-42

2-pH

e usin

spar

stab

l Geoequilibrium with early quartz of the siliceous breccia

(y18O=+8.5x). The equilibrium temperature was

HSO4- SO42-

H2S HS-

-20.7

Log fO2

pH

-28

-32

-36

-40

-440 2 4 6 8 10 1

a-20.6

-20.0-10.0

0.0+3.7

+3.

8

+3.

9

+4.0

hematite

pyrite

pyrrhotite mag

netit

e

Fig. 8. Phase diagrams constructed at 250 8C and SWVP. (a) Log COlog aAS=2 and superimposed S isotope isolines calculated for pyritOhmoto and Goldhaber (1997). Also shown is the muscoviteK-feld

101. (b) Log CO2-log aAS diagram constructed at pH=5.9, showingisotope isolines.

T. Wagner et al. / Chemica254assumed to be 270 8C, which is the highesthomogenization temperature that we measured in

fluid inclusions from the siliceous breccia. For all

models, we have used the experimentally determined

quartzH2O fractionation factor of Matsuhisa et al.

(1979). Boiling effects were calculated for a closed-

system, applying both single stage vapour separation

and continuous vapour separation models (Truesdell

and Nathenson, 1977; Matsuhisa et al., 1985; Matsu-

hisa, 1986) with temperature increments set to 5 8C.For the closed-system models, the calculated effect is

largest for single stage vapour separation. Vapour

fractions at each temperature increment were calcu-

lated using enthalpy data from steam tables. The

liquidvapour fractionation was calculated from the

equation of Horita and Wesolowski (1994). Given the

very low salinities of the epithermal system at Cirotan,

no correction was made for the effect of salt on the

liquidvapour partitioning of oxygen isotopes (Horita

et al., 1995). Mixing models were constructed

assuming progressive mixing of the deep epithermal

fluid with a surface-derived meteoric water. We chose

a y18O value of 5.8x for the meteoric end-member,which corresponds to the measured oxygen isotopecomposition of Pongkor river water (Rosana and

Matsueda, 2002). This value is slightly more negative18

pyrrhotite

pyrite

og fO2

Log aS

8

2

6

0

4-5 -4 -3 -2 -1

b

+3.8

-20.7

-20.6-20.0-10.00.0+3.7

SO42-

H2S

cpbn+py

hematite

magnetite

diagram showing stability relationships in the system FeSOH at

g equations of Zhang and Spry (1994) and fractionation factors from

phase boundary (shaded area) for activities of K+ between 103 andility relationships in the system CuFeSOH and superimposed S

logy 219 (2005) 237260than the y O value of 4x reported for averagerecent precipitation in Java, reflecting the higher

altitude of the Cirotan and Pongkor mine sites

(Alderton et al., 1994). Mixing lines were calculated

for temperatures of the meteoric component of 100,

150, 175, 200, 225, and 250 8C, respectively.The results of our model calculations clearly

demonstrate that neither cooling nor boiling scenarios

can explain the observed relationship between fluid

inclusion temperatures and the y18O values of quartz/chalcedony. Only progressive mixing between a deep-

sourced epithermal fluid and heated meteoric water

appears to explain the data. Although there is

evidence for boiling from fluid inclusion measure-

ments (Leroy et al., 2000), isoenthalpic or isothermal

boiling cannot have been of major importance for the

evolution of the epithermal system at Cirotan. The

results of our calculations are consistent with the

conclusions drawn from fluid inclusion and structural

studies, which demonstrate that boiling occurred only

during discrete episodes correlated with major open-

ing of the Cirotan vein (Genna et al., 1996; Leroy et

al., 2000). This has important implications for under-

standing the principal processes responsible for Au

l GeoBoiling

18OV-SMOW (% )

14

12

10

8

6

4

2

0

16

T ( C)140 160 180 200 220 240 260 280

Cooling

Mixing 250225

200

175150

100

High-grade veinsLate drusy quartz

270

Fig. 9. Diagram showing the effect of cooling, boiling, and mixing

processes on the oxygen isotope composition of vein quartz

precipitated from hydrothermal fluids at different temperatures.

T. Wagner et al. / ChemicaAgSnW mineralization. Precipitation of the pre-

cious-metal assemblage at Cirotan is thus best

explained by fluid mixing, rather than boiling, the

mechanism most commonly invoked for the Au-rich

stage of epithermal deposits (e.g., Spycher and Reed,

1989; Cooke et al., 1996; Cooke and Simmons, 2000;

Cooke and McPhail, 2001).

Based on textural and fluid inclusion evidence

(Leroy et al., 2000), however, boiling appears to be a

reasonable mechanism to explain the formation of

the Mn-rich zone of the cockade breccia. We

therefore applied cooling and boiling models to the

carbon and oxygen isotope data for rhodochrosite to

test this idea. This involved calculating equilibria

among aqueous carbon species using thermodynamic

data from the SUPCRT92 database (Johnson et al.,

1991) and liquidvapour partitioning of CO2 using

the equation of Giggenbach (1980). In the absence of

experimental or theoretical fractionation factors for

Black squares indicate quartz y18O values calculated for the non-meteoric (deep hydrothermal fluid) and the meteoric end-member.

The lines depict the y18O values of quartz that would precipitate viaprogressive cooling, boiling, and mixing at the specified temper-

ature. The solid and dashed lines show cooling and boiling paths,

respectively, whereas the dotted lines show mixing between the

non-meteoric fluid and meteoric water. Mixing lines were calculated

for temperatures of the meteoric water of 100, 150, 175, 200, 225,

and 250 8C. Shaded fields show the ranges of quartz y18O valuesand the corresponding fluid inclusion homogenization temperatures

from Milesi et al. (1994) and this study. See text for model

constraints, isotopic fractionation factors, and equations used for the

calculations.the carbon isotope exchange between CO2 and

rhodochrosite, we used the experimentally-deter-

mined fractionation factor for siderite-CO2 (Car-

others et al., 1988), which should reasonably well

predict the general trend of carbon isotope distribu-

tion. In order to calculate the oxygen isotope

fractionation between CO2 and rhodochrosite, we

applied the theoretical factor derived by Zheng

(1999), because the experimental data of Bottcher

(1996) are only valid up to temperatures of about 90

8C. The results of our calculations show that neithercooling nor closed-system boiling models can sat-

isfactorily explain the shift in oxygen isotope compo-

sition towards the strongly positive y18O values of therhodochrosite samples (+22.7 to +26.2x). However,if an open-system (Rayleigh-type fractionation) boil-

ing model is used instead (Stewart, 1981; Faure et al.,

2002), the resulting progressive loss of low-y18Owater vapour results in the strong 18O enrichment of

the residual liquid H2O needed to explain the oxygen

isotopic composition of the rhodochrosite. The iso-

topic effect for carbon is much smaller, because the

fractionation factor between aqueous and gaseous

CO2 is very close to unity above temperatures of

about 100 8C (Ohmoto and Goldhaber, 1997). Theshift in y13C of the rhodochrosite (and other hydro-thermal carbonate minerals) will largely reflect (1) the

cooling effect on the fractionation factor for rhodo-

chrosite-fluid, and (2) the change in the relative

abundance of aqueous carbon species (HCO3 versus

aqueous CO2) as a consequence of pH increase during

boiling (e.g., Drummond and Ohmoto, 1985; Matsu-

hisa, 1986; Simmons and Christenson, 1994). Our

calculations show that progressive closed-system

boiling results in a systematic increase in the y13Cvalues of precipitated rhodochrosite with decreasing

temperature. For the temperature interval 270140 8C,boiling would cause a relatively small positive

isotopic shift of 2.1x, which is smaller than theobserved range in y13C values of rhodochrosite(3.5x). Consequently, as is the case for the oxygenisotope data, only open-system boiling can satisfac-

tory explain the carbon isotope variation of the

rhodochrosite. If the initial fluid y13C values weresimilar to those of other epithermal deposits (e.g.,

Pongkor), boiling would not be able to shift them to

logy 219 (2005) 237260 255the unusually negative values displayed by the

Cirotan rhodochrosite. These values must, therefore,

l Georeflect a primary feature characteristic of the fluid

sources that contributed to the epithermal system at

Cirotan.

6.3. Sources of the hydrothermal fluids

Comparison of the stable isotope data of the

Cirotan deposit with corresponding data sets available

for potential fluid sources in the SundaBanda island

arc allows a comprehensive discussion of the con-

tributions of magmatic, recycled sedimentary and

meteoric components to the epithermal system. The

y34S values of the vein sulphides, which are tightlydistributed around a mean value of +3.8F0.9x,closely match the sulphur isotope composition of

recent arc lavas from Indonesia. Whole-rock y34Svalues of basaltic and basalticandesitic lavas from

seven major volcanoes, representing the different

parts of the SundaBanda arc, range between +1.7

and +7.8x, and average +4.7F1.4x (De Hoog et al.,2001). The reported y34S values from volcanoes in thewestern Sunda arc (Krakatau and Guntur) lie between

+3.2 and +4.5x, which is in even closer accord withthe Cirotan data. The isotopic pattern observed in the

SundaBanda arc is consistent with data sets from

active volcanoes for other circum-Pacific island arcs

such as Japan and the Marianas (Ueda and Sakai,

1984; Alt et al., 1993). De Hoog et al. (2001) have

related the 34S-enriched sulphur isotope composition

of the recent arc lavas in the SundaBanda arc to a

significant contribution of a slab-derived sedimentary

component. Considering the S isotope systematics of

the arc volcanics, we interpret the isotopic homoge-

neity of our sulphur isotope data set and the close

match with magmatic sulphur values as a clear

indication of direct incorporation of magmatic sulphur

into the epithermal fluid system at Cirotan. This

interpretation is supported by isotopic data from

volcanic gases in the eastern Sunda and Banda arc

sections, which display a similarly enriched compo-

sition, with bulk y34S values of +4.9 to +5.5x(Poorter et al., 1991).

The carbon and oxygen data for the Cirotan deposit

indicate that there were also contributions to the

epithermal system from formational and/or meteoric

waters. The y18O values of water in equilibrium with

T. Wagner et al. / Chemica256quartz from the early stage of siliceous breccia

formation, calculated for temperatures of 2503008C, range between 0.4 and +1.6x. This compositioncould be reasonably explained by mixing of andesitic

magmatic water having a y18O value of +7 to +10x(Giggenbach, 1992a,b) with local meteoric water,

which has a y18O value of about5.8x. Alternatively,it could reflect oxygen exchange between local

meteoric water and basaltic to basaltic andesitic vol-

canics; the latter have y18O values between +5.6 and+6.5x (Vroon et al., 2001). Both models have beenproposed for epithermal systems in similar settings,

e.g., Hishikari in Japan (e.g., Matsuhisa and Aoki,

1994; Faure et al., 2002; Shikazono et al., 2002). Thus,

in the absence of yD data from fluid inclusions, whichcould not be obtained due to the abundance of

secondary inclusions of likely meteoric origin in our

samples, we cannot discriminate between these mod-

els. However, irrespective of which model is correct,

the results of our modelling clearly indicate that there

was a significant meteoric contribution to the oxygen

budget of the epithermal system at Cirotan.

The y13C values of the rhodochrosite are signifi-cantly more negative than reported for most other

epithermal systems, and most likely reflect a contri-

bution of sedimentary carbon. Considering that sur-

face-derived CO2-rich water mixes with deep-sourced

sodium chloride waters in many epithermal systems

(e.g., Simmons and Christenson, 1994; Brathwaite

and Faure, 2002), it is reasonable to propose that the

isotopically light carbon of the Cirotan fluids was

derived from organic-rich Eocene to early Miocene

shallow-marine sediments, which are widespread in

the southern part of the Bayah dome.

The available radiogenic isotope data from the

Cirotan deposit and from different suites of volcanic

rocks in the Bayah dome shed light on the most likely

sources of the ore metals. Lead isotope data show a

close match between galena from Cirotan and the

Pliocene volcanics, with both having a distinctly

radiogenic Pb isotope signature compared to the older

Miocene volcanic rocks (Marcoux and Milesi, 1994;

Milesi et al., 1994). The radiogenic Pb isotope data of

the Pliocene volcanics and the Cirotan mineralization

were interpreted as an indication of recycling of old

crustal material underlying westernmost Java (Milesi et

al., 1994). Based on a thorough discussion of the

potential contributions from mantle sources, recycled

logy 219 (2005) 237260sediments, and crustal contamination, Alves et al.

(1999) have shown that a significant shift in the Os

Scottish Universities. AJB is funded by NERC

1500 bar. Geochim. Cosmochim. Acta 60, 18491871.

Bottcher, M.E., 1996. 18O/16O and 13C/12C fractionation during the

l Geoisotope composition of the Pliocene rocks compared

to Miocene volcanics coincides with a dramatic

increase in sediment supply to the Java trench. This

increased sedimentation can be correlated with a

major period of intense erosion of old crustal

material in the Australian Craton (Whitford and

Jezek, 1982; Alves et al., 1999). Alves et al. (1999)

have also shown that their model can explain the Pb

isotope data of both the Miocene and the Pliocene

volcanics as well, whereas the model presented by

Milesi et al. (1994) fails to satisfactorily explain the

ReOs isotope data.

6.4. Controls of AuAgSnW mineralization

The above discussion and the results of our stable

isotope modeling place important constraints on the

key factors and processes responsible for transport

and deposition of Au, Ag, Sn, and W in the

epithermal system at Cirotan. The stable and radio-

genic isotope signatures indicate substantial mag-

matic contributions to the sulphur and metal budget,

coupled with a significant crustal contamination of

the magmatic-hydrothermal system, which was most

likely related to recycling of slab-derived sedimen-

tary material in the subduction zone. Ore formation

in the epithermal environment at Cirotan was not

controlled by fluid boiling, but rather by fluid

mixing, which lead to the effective co-deposition of

the AuAgSnW assemblage through changes of

the oxidation state and dilution of the deep-sourced

hydrothermal fluid. In conclusion, it appears that the

unusual metallogenic features of the Cirotan deposit

are a consequence of three main favourable factors.

These are (1) a dramatic change in subduction mode

in the Pliocene, which resulted in increased sediment

supply and the generation of fluids strongly enriched

in crustal components such as Sn and W, (2) the

formation of comparatively reduced fluids capable of

transporting Sn and W into shallow epithermal

levels, and (3) a structural and palaeohydrological

setting, which enabled efficient mixing of deep-

sourced epithermal fluids with meteoric waters.

Subduction-related volatilization and transport of

Sn and W into magmatic-hydrothermal systems like

Cirotan appear to be on-going processes in the

T. Wagner et al. / Chemicawestern Sunda arc, as evidenced by significant

enrichment of these metals in the fumarolic gasesreaction of carbonates with phosphoric acid: effects of cationic

substitution and reaction temperature. Isot. Environ. Health

Stud. 32, 299305.support of the Isotope Community Support Facility

at SUERC. David Dolejs is thanked for inspiring

discussions on geochemical aspects of boiling

phenomena. Careful reviews by Kevin Faure and

Anne-Sylvie Andre-Mayer helped us to improve the

manuscript. [PD]

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Acknowledgements

This project was made possible by funding from

the German Research Council (DFG) to TW and an

NSERC discovery grant to AEW-J. PT Aneka

Tambang Ltd. is thanked for granting access to the

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