wagner et al cg 2005
DESCRIPTION
geologiTRANSCRIPT
-
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-712 Level 700, crosscut 770 High-grade ore, quartz ve
CIR-719 Level 700, crosscut 770 High-grade ore, quartz ve
CIR-723 Level 700, crosscut 770 High-grade ore, banded p
CIR-724 Level 700, crosscut 770 High-grade ore, quartz ve
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-913 Level 900, tunnel 967969 Cockade breccia, large (40
CIR-914 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
with wolframite, electrum and cassiterite
with wolframite, electrum and cassiterite
sphalerite ore, crosscut by quartzwolframite veinlets
with wolframite, electrum and cassiterite
ne quartz veinlets crosscutting silicified wallrock fragments
arse quartz veinlets crosscutting silicified wallrock fragments
s (25 cm) with chalcedony and rhodochrosite, no sulphides present
s (310 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
cockade with rhodochrosite and polymetallic sulphide rims
cockade with rhodochrosite and polymetallic sulphide rims
s (16 cm) with chalcedony and rhodochrosite, no sulphides present
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
CIR-914b-4 Galena Idiomorphic skeletal
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
CIR-201-10 Galena Idiomorphic skeletal
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
CIR-912b-4 Sphalerite Crystals overgrowing
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
CIR-912b-8 Sphalerite Crystals overgrowing
lamellar pyrite
+3.7
CIR-912b-9 Sphalerite Coarse-grained band,
with wolframite
+3.6
CIR-912b-10 Galena Idiomorphic skeletal
crystal
+2.9
CIR-914e-1 Pyrite Large crystals, early
zone
+3.2
CIR-914e-2 Pyrite Large crystals, early
zone
+4.5
CIR-914e-3 Pyrite Large crystals, early
zone
+3.1
CIR-914e-4 Pyrite Large crystals, early
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
-
Sample Mineral Textural description y34SV-CDT(x)
Cockade breccia
CIR-914e-5 Pyrite Fine-grained, with
coarse sphalerite
+4.0
CIR-914e-6 Sphalerite Coarse-grained massive
band
+4.3
CIR-914e-7 Sphalerite Coarse-grained massive
band
+4.5
CIR-914e-8 Pyrite Large bladed crystals +4.9
CIR-914e-9 Pyrite Large bladed crystals +5.3
CIR-914e-11 Sphalerite Crystals overgrowing
bladed pyrite
+2.9
CIR-914e-12 Sphalerite Crystals overgrowing
bladed pyrite
+3.8
CIR-914e-13 Pyrite Small bladed crystals +3.0
CIR-914e-14 Sphalerite Crystals overgrowing
bladed pyrite
+3.0
CIR-914e-15 Pyrite Small bladed crystals +3.4
CIR-914e-16 Sphalerite Crystals overgrowing
bladed pyrite
+2.9
CIR-914e-17 Pyrite Fine lamellar aggregates
in quartz
+5.1
CIR-914e-18 Sphalerite Coarse-grained massive
band
+3.5
CIR-914e-19 Sphalerite Coarse-grained massive
band
+3.7
CIR-914e-20 Galena Idiomorphic skeletal
crystal
+3.7
CIR-914e-21 Pyrite Large bladed crystals +4.3
CIR-927-1 Pyrite Small crystals in wall
rock fragment
+1.1
CIR-927-2 Pyrite Small crystals in wall
rock fragment
+0.1
CIR-927-3 Sphalerite Coarse-grained massive
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
CIR-927-10 Sphalerite Coarse-grained massive
band
+3.8
CIR-927-11 Galena Idiomorphic skeletal
crystal
+2.8
CIR-927-12 Galena Idiomorphic skeletal
crystal
+3.4
CIR-927-13 Sphalerite Coarse-grained massive
band
+4.1
CIR-927-14 Galena Idiomorphic skeletal
crystal
+4.3
Table 2 (continued) Table 2 (continued)
(continued on next page)
Sample Mineral Textural description y34SV-CDT(x)
Cockade breccia
CIR-936b-1 Sphalerite Anhedral, rims around
galena
+4.1
CIR-936b-2 Sphalerite Anhedral, rims around
galena
+3.7
CIR-936b-3 Galena Idiomorphic skeletal
crystal
+3.2
CIR-936b-4 Galena Idiomorphic skeletal
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
CIR-707a-3 Pyrite Fine-grained, core of
large crystal
+2.9
CIR-707a-4 Pyrite Coarse-grained, rim of
large crystal
+4.0
CIR-707a-5 Pyrite Fine-grained, core of
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
CIR-707c-4 Sphalerite Coarse-grained crystals,
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
CIR-723c-2 Pyrite Spongiform, enclosing
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.
Sample Mineral Textural description y34SV-CDT(x)
High-grade veins
CIR-723c-5 Pyrite Spongiform, enclosing
pyrite crystals
+5.2
CIR-723c-6 Sphalerite Coarse-grained crystals,
with wolframite
+4.6
CIR-723c-7 Sphalerite Coarse-grained crystals,
with wolframite
+4.5
CIR-723c-9 Sphalerite Coarse-grained crystals,
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,
overgrown by rhodochrosite
+8.4
CIR-913-2 Chalcedony Clear, banded chalcedony,
overgrown by rhodochrosite
+7.8
CIR-913-4 Quartz White quartz, overgrown by
sulphide rims
+8.5
CIR-914-1 Chalcedony Clear, banded chalcedony,
overgrown by rhodochrosite
+7.9
CIR-914-2 Chalcedony Grey chalcedony,
overgrown by sulphide rims
+7.5
CIR-928-1 Chalcedony Clear, banded chalcedony,
overgrown by rhodochrosite
+8.0
CIR-928-2 Chalcedony Clear, banded chalcedony,
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
CIR-712-1 Quartz White quartz, enclosing
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
CIR-914-3 Quartz White drusy quartz,
outermost rim of large
cockade
+6.6
CIR-921 Quartz Drusy quartz, overgrowing
siliceous breccia
+7.6
CIR-928-4 Quartz White drusy quartz,
outermost rim of large
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
CIR-712-2 Wolframite Wolframite blades, enclosed
in white quartz
3.2
CIR-719-1 Quartz White quartz, enclosing
wolcasel assemblage
+7.1
CIR-719-2 Wolframite Wolframite blades, enclosed
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-919 Rhodochrosite Idiomorphic crystal
CIR-933-1 Rhodochrosite Small cockades, no
CIR-933-2 Rhodochrosite Idiomorphic crystal
CIR-941 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]
References
Alderton, D., Harmon, R., Sloane, H., Sudharto, T., 1994. Fluid
inclusion and stable isotope studies at Gunung Limbung Cu/Pb/
Zn deposit, West Java. J. Asian Earth Sci. 10, 2538.
Allis, R.G., 1999. Present day hydrothermal conditions in the
vicinity of AWI 1-2, Awibengkok geothermal field, Indonesia.
Trans.-Geotherm. Resour. Counc. 23, 1720.
Alt, J.C., Shanks, W.C., Jackson, M.C., 1993. Cycling of sulfur in
subduction zones: the geochemistry of sulfur in the Mariana
Island Arc and back-arc trough. Earth Planet. Sci. Lett. 119,
477494.
Alves, S., Schiano, P., Alle`gre, C.J., 1999. Rheniumosmium
isotopic investigation of Java subduction zone lavas. Earth
Planet. Sci. Lett. 168, 6577.
Benning, L.G., Seward, T.M., 1996. Hydrosulphide complexing of
Au (I) in hydrothermal solutions from 1508400 8C and 500of the active Merapi volcano in central Java
(Symonds et al., 1987).
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
Cirotan and Pongkor mines and for their support
during the field campaign. Special thanks are due to
Thomas Mulja and to our two field assistants,
Muharis and Riza, who were invaluable in helping
resolve many of the logistic problems associated
with the project. The assistance of Terry Donnelly,
Julie Dougans, Andrew Tait, and Chris Taylor during
stable isotope analyses was much appreciated.
SUERC is funded by NERC and the consortium of
logy 219 (2005) 237260 257Brathwaite, R.L., Faure, K., 2002. The Waihi epithermal gold
silver-base metal sulfidequartz vein system, New Zealand:
-
T. Wagner et al. / Chemical Geology 219 (2005) 237260258temperature and salinity controls on electrum and sulfide
deposition. Econ. Geol. 97, 269290.
Candela, P.A., 1989. Felsic magmas, volatiles, and metallogenesis.
Rev. Econ. Geol. 4, 223233.
Carlile, J.C., Mitchell, A.H.G., 1994. Magmatic arcs and associated
gold and copper mineralization in Indonesia. J. Geochem.
Explor. 50, 91142.
Carothers, W.W., Adami, L.H., Rosenbauer, R.J., 1988. Experi-
mental oxygen isotope fractionation between sideritewater and
phosphoric acid liberated CO2siderite. Geochim. Cosmochim.
Acta 52, 24452450.
Cooke, D.R., McPhail, D.C., 2001. Epithermal AuAgTe
mineralization, Acupan, Baguio district, Philippines: numerical
simulations of mineral deposition. Econ. Geol. 96, 109131.
Cooke, D.R., Simmons, S.F., 2000. Characteristics and genesis of
epithermal gold deposits. Rev. Econ. Geol. 13, 221244.
Cooke, D.R., McPhail, D.C., Bloom, M.S., 1996. Epithermal gold
mineralization, Acupan, Baguio district, Philippines: geology,
mineralization, alteration, and the thermochemical environment
of ore deposition. Econ. Geol. 91, 243272.
De Hoog, J.C.M., Taylor, B.E., van Bergen, M.J., 2001. Sulfur
isotope systematics of basaltic lavas from Indonesia: implica-
tions for the sulfur cycle in subduction zones. Earth Planet. Sci.
Lett. 189, 237252.
Drummond, S.E., Ohmoto, H., 1985. Chemical evolution and
mineral deposition in a boiling hydrothermal system. Econ.
Geol. 80, 126147.
Faure, K., Matsuhisa, Y., Metsugi, H., Mizota, C., Hayashi, S.,
2002. The Hishikari AuAg epithermal deposit, Japan: oxygen
and hydrogen isotope evidence in determining the source of
paleohydrothermal fluids. Econ. Geol. 97, 481498.
Gammons, C.H., Williams-Jones, A.E., 1995. The solubility of Au
Ag alloy+AgCl in HCl/NaCl solutions at 300 8C: new data onthe stability of Au(I) chloride complexes in hydrothermal fluids.
Geochim. Cosmochim. Acta 59, 34533468.
Genna, A., Jebrak, M., Marcoux, E., Milesi, J.P., 1996. Genesis of
cockade