Hypogene Zn carbonate ores in the Angouran deposit, NW Iran

Abstract

The world-class Angouran nonsulfide Zn-Pb deposit is one of the major Zn producers in Iran, with resources estimated at about 18 Mt at 28% Zn, mainly in the form of the Zn carbonate smithsonite. This study aims to characterize these carbonate ores by means of their mineralogy and geochemistry, which has also been extended to the smithsonite II. The variable, but still relatively heavy carbon isotope values of supergene smithsonite II, suggests only a very minor contribution by organic soil carbon, as is generally the case in supergene nonsulfide deposits.

Full text

ARTICLE
Hypogene Zn carbonate ores in the Angouran deposit,
NW Iran
Maria Boni &H. Albert Gilg &Giuseppina Balassone &
Jens Schneider &Cameron R. Allen &Farid Moore
Received: 12 March 2007 / Accepted: 22 May 2007
#Springer-Verlag 2007
Abstract The world-class Angouran nonsulfide Zn–Pb
deposit is one of the major Zn producers in Iran, with
resources estimated at about 18 Mt at 28% Zn, mainly in the
form of the Zn carbonate smithsonite. This study aims to
characterize these carbonate ores by means of their miner-
alogy and geochemistry, which has also been extended to the
host rocks of mineralization and other local carbonate rock
types, including the prominent travertines in the Angouran
district, as well as to the local spring waters. Petrographical,
chemical, and stable isotope (O, H, C, Sr) data indicate that
the genesis of the Zn carbonate ores at Angouran is fairly
distinct from that of other “classical”nonsulfide Zn deposits
that formed entirely by supergene processes. Mineralization
occurred during two successive stages, with the zinc being
derived from a preexisting sulfide ore body. A first, main
stage of Zn carbonates (stage I carbonate ore) is associated
with both preexisting and subordinate newly formed
sulfides, whereas a second stage is characterized by super-
gene carbonates (Zn and minor Pb) coexisting with oxides
and hydroxides (stage II carbonate ore). The coprecipitation
of smithsonite with galena, pyrite and arsenopyrite, as well
as the absence of Fe- and Mn-oxides/hydroxides and of any
discernible oxidation or dissolution of the sphalerite-rich
primary sulfide ore, shows that the fluids responsible for the
main, stage I carbonate ores were relatively reduced and
close to neutral to slightly basic pH with high fCO
2
.
Smithsonite δ
18
O
VSMOW
values from stage I carbonate ore
range from 18.3 to 23.6‰, while those of stage II carbonate
ore show a much smaller range between 24.3 and 24.9‰.
The δ
13
C values are fairly constant in smithsonite of stage I
carbonate ore (3.2–6.0‰) but show a considerable spread
towards lower δ
13
C
VPDB
values (4.6 to −11.2‰) in stage II
carbonate ore. This suggests a hypogene formation of stage
I carbonate ore at Angouran from low-temperature hydro-
thermal fluids, probably mobilized during the waning stages
of Tertiary–Quaternary volcanic activity in an environment
characterized by abundant travertine systems throughout the
whole region. Conversely, stage II carbonate ore is
unambiguously related to supergene weathering, as
evidenced by the absence of sulfides, the presence of Fe-
Mn-oxides and arsenates, and by high δ
18
O values found in
Miner Deposita
DOI 10.1007/s00126-007-0144-4
Editorial handling: B. Lehmann
M. Boni (*):G. Balassone
Dipartimento Scienze della Terra,
Università di Napoli “Federico II”,
Via Mezzocannone, 8,
80134 Naples, Italy
e-mail: boni@unina.it
M. Boni
Geologisch-Paläontologisches Institut, Universität Heidelberg,
Heidelberg, Germany
H. A. Gilg
Lehrstuhl für Ingenieurgeologie,
Technische Universität München,
Munich, Germany
J. Schneider
Département de Minéralogie, Université de Genève,
Geneva, Switzerland
C. R. Allen
Teck Cominco American,
Spokane, WA, USA
F. Moore
Geological Department, University Shiraz,
Shiraz, Iran
Present address:
J. Schneider
Geodynamics and Geofluids Research Group and Centre
for Archaeological Sciences (CAS), K.U,
Leuven, Belgium

smithsonite II. The variable, but still relatively heavy carbon
isotope values of supergene smithsonite II, suggests only a
very minor contribution by organic soil carbon, as is
generally the case in supergene nonsulfide deposits.
Keywords Angouran .Iran .Nonsulfide zinc .Smithsonite .
Stable isotopes
Introduction
Nonsulfide Zn deposits have experienced a significant
revival over the recent years, as a consequence of new
developments in hydrometallurgical acid-leaching, solvent-
extraction, and electrowinning techniques (Boni 2003;
Hitzman et al. 2003). Iran is a country particularly endowed
with nonsulfide ores. Typical examples currently under
exploration are, among others, the Iran-Kuh, Kuh-e-Surmeh,
and Mehdi-Abad deposits, all located in the Kerman
province (Ghazban et al. 1994; Borg 2005) and the smaller
nonsulfide bodies of the Kuhbanan-Bahabad area (Amiri
et al. 2005; Amiri and Rasa 2006). All these deposits are of
Mississippi Valley-type affiliation with hypogene sphalerite
+ galena ores at depth, capped by irregular supergene ores
closer to (paleo)surface.
The world-class, high-grade Angouran nonsulfide Zn–Pb
deposit, situated in the western Takab–Zanjan province
about 450 km northwest of Tehran (Fig. 1a), is one of the
major Zn producers in Iran, a country whose total Zn
production will attain 200,000 tonnes in 2007. Nonsulfide
ore resources at Angouran are estimated at about 18 Mt of
ore at 28% Zn, mainly in the form of Zn carbonates, and
4.5% Pb (Annels et al. 2003; Borg and Daliran 2004). The
deposit is currently owned by Iranian Mines & Mining Indus-
tries Development & Renovation Organization (IMIDRO)
and has been exploited by Iran Zinc Mines Development
Company (IZMDC) in an open pit at >3,000-m elevation.
Additional yet unexploited sulfide reserves amount to about
5 Mt at 40% Zn (Gilg et al. 2006). There is also a project to
process a substantial volume of smithsonite-bearing tailings
from earlier mining operations so as to reduce the problem
of environmental pollution (Moradi et al. 2004).
The renewed interest in nonsulfide mineralization
throughout the world has stimulated a new wave of
scientific research on the Angouran deposit, focused both
on the sulfide and nonsulfide ores (Annels et al. 2003;
Daliran and Borg 2003,2005a,b; Gilg et al. 2003a, Gilg
and Boni 2004a,b;2006; Borg and Daliran 2004). The
Angouran nonsulfide ores are distinct from those known
from the “classical”supergene Zn deposits elsewhere
(Large 2001; Hitzman et al. 2003). One of the most striking
macroscopic characteristics is the association of nonsulfides
and primary sulfides, dominated by sphalerite, which are in
textural equilibrium and commonly do not show any
obvious indication of oxidation or dissolution. There is
also a marked difference in the main and trace element
contents between sulfide and nonsulfide ores (Table 1).
Both factors are obviously related to the specific nature and
circulation mechanisms of the mineralizing fluids that
precipitated the nonsulfide assemblages as well as to the
source of the metals. In earlier studies, the smithsonite-
dominated nonsulfides, which represent the economically
most significant part of the Angouran deposit, have been
generally interpreted to be a product of exclusively
supergene processes (Borg and Daliran 2004; Daliran and
Borg 2003; Hitzman et al. 2003). The discovery of a unique
sulfide–carbonate association in the deposit, as well as
preliminary stable isotope data of the zinc carbonates (Gilg
et al. 2003a), has challenged this conventional genetic
interpretation. The latter authors suggested that the main
stage nonsulfide ores at Angouran are of hypogene origin
and precipitated from low-temperature hydrothermal fluids.
This process was followed by a limited supergene miner-
alization phase. On the other hand, Angouran does not
show the typical mineralogical characteristics of other
nonsulfide deposits that have been interpreted to be of
hypogene–hydrothermal origin (Hitzman et al. 2003). The
main nonsulfide mineral is the Zn carbonate smithsonite,
whereas willemite and hydrothermal dolomite are com-
pletely lacking. The geological setting is also totally
different from other Zn silicate-dominated hypogene non-
sulfide deposits like Vazante (Brazil) or Beltana (Australia),
which consist of structurally controlled veins or pipe-like
bodies with variably developed halos of hydrothermal
dolomite.
This study, which follows a previously published paper
on the Angouran sulfides (Gilg et al. 2006), focuses on the
nature and origin of the Zn carbonates at Angouran. We
present new mineralogical, petrographical, and (isotope)
geochemical data on these ores and derive formational
conditions. To trace the source of the metals and the origin
of the mineralizing fluids, we have extended our analyses
not only to the host rocks of the main deposit but also to
several carbonate types and spring waters in the immedi-
ate surroundings of the mine and the adjacent Takab
district.
Geological setting and sulfide ores
The Angouran Zn(–Pb–Ag) deposit is situated in the
western Zanjan Province, NW Iran. This area belongs to
the northwestern part of the Sanandaj-Sirjan Zone, a
metamorphic belt within the Zagros orogen (Fig. 1a). The
Zagros orogen formed by Cretaceous subduction of the
Neotethys ocean, followed by Tertiary continental collision
Miner Deposita

Fig. 1 a Location of the Angouran deposit in the Zagros orogenic belt. bSchematic regional geological map of the Takab–Zanjan area, with the
location of the mine area, and of the sampled travertines and hot/cold spring area (after Gilg et al. 2006)
Miner Deposita

between the Afro-Arabian plate and Gondwana-derived
microplates (Alavi 1994; Glennie 2000).
The Angouran deposit is hosted by a metamorphic core
complex that has been rapidly exhumed during an exten-
sional phase in the Lower Miocene (Gilg et al. 2006). This
metamorphic complex (Gazanfari 1991) consists of
amphibolites, serpentinites, gneisses, micaschists, and var-
ious, mainly calcitic and rarely dolomitic marbles. The
marbles are in part intercalated as thin layers between
schists, gneisses and amphibolites and form the more than
300-m thick, uppermost “Angouran”marble horizon that
hosts the main orebody. The age of the protoliths of the
metamorphic rocks are not well constrained but are
presumably of Neoproterozoic (to Cambrian?) age (Hamdi
1995; Stockli et al. 2004). The metamorphic complex at
Angouran shows complex internal thrusting, isoclinal
folding, and a superimposed prominent open folding.
Shortly after exhumation, a sequence of Miocene subvol-
canic and volcanic rocks (mostly andesitic to rhyolitic
pyroclastics), minor late basaltic dikes, as well as sedimen-
tary rocks of both shallow marine (Qom Formation) and
red-bed type continental origin including evaporites (Upper
Red Formation), were deposited unconformably on the core
complex. In the Pliocene, the metamorphic complex with
its cover was thrust onto the Tertiary volcanic and
sedimentary rock sequence (Stockli et al. 2004; Gilg et al.
2006), and significant uplift started. Probably during this
change from a Miocene extensional to a Pliocene compres-
sional tectonic regime, marine evaporative brines infiltrated
the metamorphic complex depositing the Angouran sulfide
orebody at the contact between footwall micaschists and the
Angouran marbles. The sulfide orebody is tabular, replacive,
associated to abundant breccias, lacks an obvious wallrock
alteration, and is clearly postmetamorphic. The ore compo-
sition is simple with predominantly Fe-poor sphalerite,
minor pyrite and galena, traces of Ni–Co arsenides. The
main gangue comprises sulfates (mainly anhydrite, possibly
barite) and minor quartz, muscovite and dolomite. In a
successive stage, the sulfates have been almost completely
dissolved and the cavities filled with euhedral Zn carbon-
ates. The ore-forming fluids were Ca–Na–Cl brines of
seawater evaporation origin with high and constant salinity
(∼24 wt.% total dissolved solids). The temperatures of ore
formation are estimated from about 80 to less than 200°C at
depths of less than 1–2 km (Gilg et al. 2006).
Subsequent Quaternary sediments in the Angouran area
comprise widespread gravel fans, alluvium, and very exten-
sive travertine deposits that are related to numerous low to
moderately hot springs in the area. Most travertines are
located to the west of the Qeynarjeh-Chartagh fault, on the
gypsiferous Upper Red Formation of the Takab depression
(2,100–2,200 m a.s.l.) and follow 55° (NE-SW), 90° (E-W),
and 120° (NW-SE) striking structures (Damm 1968).
Examples are the large Berenjeh travertine field with a
length of 3 km, a width of 1.7 km, a thickness of at least
200 m (Damm 1968), and the E-W-trending, 4 km long and
1.3 km wide Zendan travertine field with many still active
hot springs (11–39°C) near Ahmadabad as well as the
remarkable 110-m-high Zendan-e Soleiman travertine
mound (Figs. 1band2b). This volcano-like cone contains
a hollow cylindrical feeder channel with 70-m diameter
(Zendan-e Soleiman means Solomon’s prison) and was
probably filled with hot water about 2,500–3,000 years ago,
as suggested by archeological remains on the flanks of the
cone (Naumann 1961). Damm (1968) estimated that the
cone took about 10,000 years to form from an artesian
spring. The nearby Taxt-e Soleiman (Solomon’s throne)
travertine mound with a height of 50 m still contains a
circular spring lake with a diameter of 110 m and 64-m
depth (Geological Survey of Iran 1999). The 18–21°C
warm spring at Taxt-e Soleiman is the most productive in
the area with about 100 l/s (Damm 1968; Naumann 1961).
The mound is host to a Zoroastrian fire temple and to
Sassanian remains. Other smaller travertine deposits and
hot spring areas are located near the Zarshuran (As-Au) and
Agh-Darreh (Sb-Au) mines (Damm 1968). The hot springs
in the Takab geothermal field are of mostly artesian origin,
with temperatures ranging from 11 to 50°C (Houtum-Schindler
1881; Damm 1968). They discharge strongly mineralized
(0.7–2.0 g TDS/l) Ca-HCO
3
waters with elevated sulfate
contents (up to 0.69 g/l), often accompanied by degassing,
and have a pH of 6.4–7.8 (Damm 1968). The spring gases
are CO
2
-rich (96 vol.%) and contain minor H
2
S (0.4 vol.%),
N
2
(2 vol.%), and O
2
+ Ar (0.4 vol.%). The muddy
sediments in the Taxt-e Soleiman warm spring contain about
4 wt.% Fe, 1.62 wt.% As, and traces of Zn (Naumann
1961). Earthquakes are frequent in the region and influence
the discharge and temperature of the hot springs (Houtum-
Schindler 1881). The commonly encountered cold springs in
the Angouran region have temperatures of less than 10°C,
mostly around 8°C (Houtum-Schindler 1881).
The only significant travertine deposits in the mountainous
area to the east of the Qeynarjeh-Chartagh fault is located
Table 1 Selected trace elements in sulfide vs carbonate ore
Element Sulfide ore Carbonate ore
Zn 37.70% 26.60%
Pb 1.00% 5.20%
As 760 ppm 6,100 ppm
Sb 300 ppm 570 ppm
Hg 20 ppm 10 ppm
Ag 213 ppm 35 ppm
Co 403 ppm 490 ppm
Ni 344 ppm 350 ppm
Cu 250 ppm 400 ppm
Miner Deposita

along theE-W trending Zendan-e Soleiman fault only 500 m to
the east of the Angouran mine. Over an area of 3-km length
and up to 0.5-km width, a series of cascade-like travertine
plateaus stretch from the discharge area at a minimum eleva-
tion of 2,500 m in the east, down to less than 2,000 m in the
west. The Angouran travertine plateau with the Angouran
mine camp on top (Fig. 2a) is one of the most prominent and
rests unconformably on Miocene pyroclastic rocks.
Geometry and zoning of the ore types
The ore zone at Angouran has a complex geometry. The
ores are located in the crest of an open anticlinal structure
within the metamorphic basement that plunges eastward at
10 to 20°. The dimensions of the mineralized zone range
from some 600 m in length (N-S) to 200 to 400 m in width
(Fig. 3). The orebodies are delimited by two major NNW-SSE
and NW-SE trending faults and a third NE-SW fault. The
up to 200-m-thick Zn carbonate ores, which occur discor-
dantly in the hanging-wall marbles (Fig. 3), overlie a tabular
sulfide orebody (Gilg et al. 2006). Smaller bodies of mixed
sulfide and carbonate ore occur at the contact between sul-
fide and nonsulfide zones, as well as within the nonsulfide
ores. Both sulfide and carbonate ore types also fill a wide
variety of breccias, especially along the three main fault
zones that are laterally controlling the deposit. In fact, there
is no sulfide ore that does not contain traces of smithsonite
mineralization due to the variable degree of carbonatization
of the primary ore. One of the most peculiar breccia types,
consisting originally of marble clasts cemented by sulfides
(sphalerite ≫galena > pyrite), has been transformed into a
mixed sulfide–carbonate mineralization style. Concretionary,
vuggy smithsonite (Fig. 2c), ranging in color from pinkish to
white (Fig. 2d,e), has completely replaced the former marble
clasts. Small concentrations of soft “calamine”ore (Fig. 2g),
in which both Zn carbonates and silicates replace patchily
the host rock carbonates (Daliran and Borg 2005b), occur
along the border of the main deposit. Karstic cavities filled
with travertine-like carbonates and stalactites in the marble
adjacent to the “oxidized”orebodies have been encountered
locally.
Following a descriptive classification by the IZMDC
geologists, seven distinct ore types have been distinguished
at Angouran (see also Gilg et al. 2003a; Daliran and Borg
2003,2005b):
–Predominant hard carbonate ore (HCO; in close
contact with sulfides),
–Soft carbonate ore (SCO) with a high clay content,
usually overlying the hard carbonate ore,
–Very porous, vuggy breccia ore (BO) with clasts of
hard carbonate ore,
–Creamy white massive calamine ore (rare; CO),
–Very low grade ore (VLGO),
–Sulfide ore (SO),
–Mixed sulfide–carbonate ore (MSO).
Materials and methods
The samples analyzed for this study were taken from
drillcore DB 90 and selected outcrops within the Angouran
open pit (partly provided by M. Sadeghi). We have also
sampled the carbonate host rocks, several travertines, and
the waters from thermal springs in the surroundings of the
mine. A.E. Annels (SRK) collected for us an extra set of
carbonate samples (characterized by letter A- in Table 5).
Brief sample descriptions are given in Table 5. Mineral
samples were characterized by optical microscopy, X-ray
powder diffraction (XRPD, Seifert MZVI automated dif-
fractometer, CuKαradiation), and scanning electron mi-
croscopy (SEM, Jeol JSM-5310). Silicates, oxides, and
pure elements were used as standards; operating conditions
were 15-kV acceleration voltage and 10-μm spot size.
Polished thin section (∼30 μm thick) of most samples were
also examined by cold cathodoluminescence (CL) petrog-
raphy, utilizing a CITL 8200 Mk3 Cold Cathodolumines-
cence instrument at the Geologisch-Paläontologisches
Institut, Universität Heidelberg (Germany), operating at
23–25-kV voltage and 500–550-μA beam current.
Main-element analyses of selected samples were carried
out using energy-dispersive spectroscopy (EDS) mode
(Link Analytical 10000, ZAF corrections). Additional
chemical analyses of smithsonite were performed using
wavelength dispersion spectrometry (full WDS) on a
Cameca SX50 electron microprobe (IGAG at the CNR,
Rome) operating at 15 kV, 15 nA, and 10-μm spot size.
Data were corrected using the PAP program of Pouchou
and Pichoir (1991) on the basis of minerals and pure
element standards. Ca and Zn carbonates were analyzed for
a total of 36 elements using inductively coupled mass
spectrometry (ICP-MS) following digestion with aqua regia
at 95°C by ACME Analytical Laboratory (Vancouver,
Canada).
Fluid inclusion microthermometry was performed at the
Geological Survey of Canada (GSC) on a US Geological
Survey heating/freezing stage at GSC-Quebec with preci-
sion of ±0.2 for ice melting temperatures and ±1°C for
homogenization temperatures.
Thermodynamic calculations have been performed using
The Geochemist’s Workbench® 4.0 (Bethke 2002) and a
modified version of the Thermo2000 database (Cleverley
et al. 2003, with Δ
f
G
01.298
of arsenopyrite [FeAsS] from
Pokrovski et al. 2002).
Miner Deposita

b
a
c
de
f
gh
ijk
1 cm
0.5 cm
0.5 cm
1 cm
1 cm
Fig. 2 a Angouran mine camp travertine (500 m east of the mine); b
Ahmadabad hot spring: in the background, the travertine cone of
Zendan-e Soleiman; cmineralized breccia: former marble clasts (now
replaced by concretionary smithsonite), cemented by massive sulfides
(stage I carbonate ore); dpink colloform smithsonite (Ib) in vug (stage I
carbonate ore); ecolloform smithsonite around a core of hard carbonate
(stage I carbonate ore) (ANG B15-A); fzoned smithsonite concretions
(Ib) growing on sulfide ore (stage I carbonate ore) (ANG B13); gsoft
“calamine”ore; hyellow mimetite crystals on oxidized surface; istage
I carbonate ore which has undergone oxidation. The white carbonate
concretions on the top are replacing former silicates (hemimorphite?)
(ANG B15-B2); joxidized stage I carbonate ore crossed by a zoned
band of stage II carbonate ore (Sm II) (ANG B15-B1); kprimary stage
I carbonate ore, oxidized on a pit face
Miner Deposita

Stable oxygen and carbon isotope ratios of carbonates
were determined using an automated on-line device
operated in continuous flow mode (Finnigan Gasbench II)
and a Finnigan Deltaplus mass spectrometer at the GeoBio-
Center, LMU Munich. The carbonate samples were reacted
with anhydrous phosphoric acid at 72°C. We used phos-
phoric acid fractionation factors for the various minerals
from Gilg et al. (2003b). The isotope analyses are reported
as permil deviations (δvalues) from Vienna Standard Mean
Ocean Water (VSMOW) for oxygen and Vienna Peedee
Belemnite (VPDB) for carbon. The precision of analyses based
on repeated measurements of laboratory (LM) and interna-
tional standards (NBS-18, NBS-19) is about 0.1‰(1σ).
For Rb–Sr isotopic analysis, carbonate samples were
completely dissolved in 14 N HNO
3
and rock samples
dissolved in a 5:1 mixture of 24 N HF and 14 N HNO
3
. The
rock solutions were totally spiked with a mixed
87
Rb–
84
Sr
tracer for Rb and Sr concentration analysis by isotope dilu-
tion and simultaneous determination of the
88
Sr/
86
Sr ratios
during the Sr run. All solutions were then dried at 110°C
and subsequently rewetted with 3 N HNO
3
. Rb and Sr were
separated with 3 N HNO
3
using EICHROM Sr resin on
50-μl Teflon columns, following the methods of Horwitz
et al. (1991a,b). The first 600 μlofHNO
3
wash of the spiked
rock solutions were collected and used for measurement of
Rb. Sr was stripped from the columns with 1 ml of H
2
O.
For mass spectrometry, Sr was loaded with TaCl
5
–HF–
H
3
PO
4
solution (Birck 1986) onto W single filaments. Rb
was loaded with DDW onto the evaporation ribbon of a Ta
double-filament assemblage. All isotopic measurements were
performed on a FINNIGAN MAT 262 solid-source mass
spectrometer running in static multicollection mode. Sr iso-
topic ratios were normalized to
86
Sr/
88
Sr=0.1194. Repeated
static measurements of the NBS 987 standard over the
duration of this study yielded an average
87
Sr/
86
Sr ratio of
0.71025± 2 (2σmean, n= 18). Individual uncertainties (2σ)
are given for Rb–Sr elemental concentrations and isotope
ratios (Table 5). Total procedure blanks amounted to 30 pg Sr
and were found to be negligible with respect to the results.
Rb–Sr ages were calculated after Ludwig (2003) using the
ISOPLOT/Ex version 3.00 program; errors on the ages are
quoted at the 2σlevel.
Petrography and paragenesis of nonsulfide
mineralization at Angouran
In almost all sulfide ore samples, there is a variable content
of Zn carbonates (Gilg et al. 2003a,2006; Daliran and Borg
2005b). The latter replace former sulfate minerals, marble
clasts in the breccias, and sulfides, suggesting that Zn
carbonate ore formation has pervasively overprinted the
sulfide ore. Zn carbonates occur also (along with minor
hemimorphite) as cavity and fracture fill. According to
Gilg et al. (2003a), two main paragenetic stages of Zn
nonsulfide mineralization can be distinguished, They are
2800 m
2700 m
2900 m
Marble
Marble breccia
Calamine ore
Breccia ore
Mixed sulfide and
oxide ore
Sulfide ore
Mineralized schist
Schist
?
?
?
50 m
SECTION 700 N
50 m
800E
I
DB69
DB64
24% Zn
25m
25% Zn
62m
42% Zn
30m
20% Zn
60m
41% Zn
24m
48% Zn
58m
W E
Fig. 3 Geological E–W section
through the Angouran orebody;
the mixed sulfide and oxide ores
display an inverted mushroom
shape. Elevation in meters
above sea level. Average Zn
content is shown for two drill
cores
Miner Deposita

Fig. 4 a Tabular ghost minerals (former sulfates) in sphalerite
(brown-yellow) ore partly filled with smithsonite Ia (Sm) of stage I
carbonates. Transmitted light (ANG B14); bnewly formed galena
(Ga) in cavity (former sulfates) of sulfide ore. Reflected light (ANG
B3); cstage I carbonate ore with arsenopyrite (Asp) in smithsonite
(Sm) and quartz (Qz). Transmitted light (ANG B15B2); darsenopyrite
rhombs (Asp) in smithsonite Ia from stage I carbonate ore. Reflected
light (ANG B14); ecolloform zoned smithsonite Ib (Sm) from stage I
carbonate ore. Transmitted light (ANG B15-B); fenlargement of one
of the dark, fluid inclusion-rich bands from e. Transmitted light (ANG
B15-B); gstage I carbonate ore with zoned crystals of smithsonite Ia.
Transmitted light (ANG B15-B2); hstage II carbonate ore with
smithsonite II crystals (Sm) alternating with bands of Fe (hydr)oxides.
Transmitted light (ANG B15-B1); istage II carbonate ore with
smithsonite II on Fe (hydr)oxides (black) and prismatic euhedral
mimetite (Mi) in the center. Transmitted light (ANG B15-B1); jzoned
band of stage II carbonate ore (smithsonite II) with Fe (hydr)oxides
and arsenates. Transmitted light (ANG B15-B1); kwhite carbonate
crusts of smithsonite II from stage II carbonate ore replacing former
silicates (hemimorphite?). Transmitted light (ANG B15-B2); lpartly
oxidized arsenopyrite crystal (Asp) in smithsonite Ia (Sm); brown
patches correspond to goethite (Goe). Transmitted light (ANG B14);
msame as l. Reflected light
Miner Deposita

defined as: (1) stage I zinc carbonate ore (partly coexisting
with sulfides), (2) stage II zinc carbonate ore (coexisting
with oxides). These ore assemblages comprise the various
types of smithsonite-dominated “oxide”ores.
The deposition of the different phases of stage I zinc
carbonate ore did not directly follow that of the latest Zn
sulfides (Fe-poor, honey sphalerite, Gilg et al. 2006).
During a hiatus after sulfide mineralization, most of the
sulfates (anhydrite and/or barite) were dissolved creating
porosity available for Zn carbonate precipitation (Fig. 5).
The clear distinction between the nature of the ore fluids
depositing the sulfides (Ca–Na–Cl brines of seawater
evaporation origin) and the composition (that will be
reported later) of the waters depositing the Zn carbonates is
evidence for two distinct mineralization processes.
Stage I carbonate ore
Stage I carbonate ore represents the dominant Zn non-
sulfide phase in the hard carbonate ore, breccia ore,
calamine ore, mixed sulfide–carbonate ore and is also a
trace component in almost all examined sulfide ore
samples. The texture of the carbonates in the breccia ore
is particularly intriguing, as the marble clasts of a sulfide-
cemented breccia have been almost completely replaced by
pinkish smithsonite concretions with irregular vugs
(Fig. 2c). The stage I carbonate ore is dominated by
smithsonite I (Fig. 5) that displays a variety of textures
from massive to brecciated, botryoidal, and colloform to
euhedral dogtooth-shaped, and vuggy to dense (Figs. 2d–f,
4a,e,g, and 6a,b). Stage I carbonate mineralization associat-
ed with sulfide ores fills the cavities of former sulfate laths
(Fig. 4a) and replaces marble fragments or even primary
sulfide ores without apparent oxidation or dissolution of the
sulfide minerals (Fig. 2e). The earliest mineral is a peculiar
generation of galena in small cubes (Fig. 4b), growing along
the border of cavities produced by dissolution of former
sulfate minerals (anhydrite, after Gilg et al. 2006, or barite,
after Daliran and Borg 2005b). Based on CL imaging,
several generations of smithsonite I (Sm Ia, Ib, Ic) could be
distinguished. Smithsonite Ia occurs in the former sulfate
cavities as zoned, dogtooth-shaped crystals (Fig. 7a).
Smithsonite Ib commonly displays a cloudy, dark core
with abundant, less than 1-μm-sized fluid inclusions fol-
lowed by a clear, zoned rim (Figs. 4e,f and 7b,c), with
sulfides and quartz on specific growth zones. CL colors of
smithsonite Ia are variable from deep red to purple (Fig. 7a),
while those of Ib are extremely zoned, grading to bluish
varieties (Fig. 7b). Irregular, inclusion-rich bands in smith-
sonite Ib are strongly luminescent in purple tones (Fig. 7c).
A third generation of smithsonite (Ic), strongly purple under
CL, is visible in late fillings and as thin veins cutting
generations Sm Ia and Ib. There is no apparent correspon-
dence between CL zoning and gross chemical composition
of smithsonite, as detected by Götte and Richter (2004).
Smithsonite Ia exhibits abundant euhedral, acicular arseno-
Primary sulfides
HYPOGENE 1
2 sphalerite generations, pyrite,
galena, Ni-Co arsenides,
anhydrite/barite, quartz, muscovite, dolomite
DISSOLUTION OF SULFATES & GENERATION OF POROSITY
microcrystals of idiomorphic galena on the HYPOGENE 2
rim of empty cavities (former sulfates)
Nonsulfides
STAGE I CARBONATE ORE
smithsonite Ia scalenohedra (strong CL),
filling empty crystals of former sulfates
arsenopyrite laths, pyrite, greenockite, euhedral
quartz co-existing with smithsonite Ia
smithsonite Ib, collomorph (CL zoned), with
rows of fluid inclusions, quartz, calcite
& few galena cubes & dendrites
smithsonite Ic, thin veins (purple CL),
cutting smithsonite Ia & Ib
STAGE II CARBONATE ORE SUPERGENE
late smithsonite II veins & crusts (zoned CL), co-existing
with hemimorphite, hydrozincite, mimetite, cerussite,
calcite, hematite, goethite, Mn-oxides, litharge,
jarosite, plumbojarosite, beudantite, pyromorphite,
montmorillonite, illite, kaolinite
Fig. 5 Paragenesis of sulfide and nonsulfide ores at Angouran
Miner Deposita

pyrite inclusions (Fig. 4c,d), and subordinately, euhedral
quartz, galena, pyrite, and greenockite crystals (all <5 μm).
It is noteworthy that arsenopyrite is not found in the early
sulfide ore paragenesis (Gilg et al. 2006). Tiny cubes, as
well as dendrites of galena and euhedral quartz crystals
(Fig. 4c), are found also in some growth zones of the
colloform smithsonite Ib. In some samples, the association
smithsonite I-arsenopyrite seems to replace earlier sulfide
ores, while in many other areas, direct replacement of the
marbles by zebra-textured smithsonite-calcite ore could be
observed. The general absence of Fe or Mn oxides or (hydr)
oxide minerals and the presence of the sulfide mineral
inclusions are the distinguishing features of the stage I
carbonate ore.
abc
def
Sm Ia
Sph
Sm I
Sm IIa
Sm II
Mi Hem
Fig. 6 Scanning electron
microscope (SEM) images.
aSmithsonite I (Sm I) crystals
growing in cavities of sphalerite
(Sph) ore (stage I carbonate ore)
(ANG B3); bsparry smithsonite
I (Sm I) vein cutting sulfides
(stage I carbonate ore) (ANG B3);
cslightly oxidized smithsonite I
crystals (ANG B15B); dsmith-
sonite II (Sm II) with mimetite
crystal in the middle (ANG
B15B); ehemimorphite crystals
(Hem) in a druse of smithsonite
II (ANG B15A); fempty Fe
(hydr)oxide crusts around dis-
solved smithsonite (ANG B16)
S
S
m II
m II
Mi
ab
deg
f
0.1 mm
0.1 mm
0.5 mm
0.5 mm
0.5 mm
0.5 mm
0.5 mm
0.5 mm
0.2 mm
0.2 mm
0.2 mm
0.2 mm
Sm II
Sm II
Sm II
Sm II
Sm II
Sm II
Sm II
Sm II
Sm Ia
Sm Ia
Sm Ib
Sm Ib
Sm II
Sm II
Sm II
Sm II
0.2 mm
0.2 mm
Sm Ib
Sm Ib
c
Fig. 7 a Former sulfate minerals filled with smithsonite Ia (Sm) of
stage I carbonates, zoned under CL (ANG B14-1); bcolloform zoned
smithsonite Ib, showing under CL a blue color and a zoned structure
(ANG B15-B1); cenlargement of image b. (CL); dtwo generations of
smithsonite II (Sm II) (ANG B15-B1); eSame as dunder CL; fBand
of smithsonite II (Sm II) alternating with Fe hydr(oxides) (ANG B15-
B1); gsame as funder CL
Miner Deposita

Stage II carbonate ore
Stage II carbonate ore is characterized by the association of
newly precipitated smithsonite (smithsonite II, Fig. 5) with
hemimorphite, mimetite (and possibly hedyphane), goe-
thite, hematite, various Mn oxides, calcite, and cerussite. It
is commonly found in vein fillings as reddish colloform
bands with alternating layers of smithsonite, goethite, and
mimetite crosscutting stage I carbonate ores (Figs. 2j and 4j),
as euhedral crystals in vugs and open fractures (Figs. 4h,i
and 6c), or as part of the friable soft carbonate ore. Stage II
carbonate ore, however, represents only a very minor percent-
age of the total amount of carbonate ores.
Stage II Zn carbonates could be distinguished also under
CL light due to the much smaller dimension and brighter
colors of the smithsonite crystals occurring in the newly
formed crosscutting bands (Fig. 7d–g). As a result of super-
gene oxidation (Fig. 2i–k), the sulfide minerals occurring in
the stage I carbonate ore, mainly arsenopyrite and galena, are
oxidized (Fig. 4l,m) and transformed into goethite and
cerussite, while the host smithsonite I remains fairly
unchanged during oxidation. The presence of Fe and Mn
oxides (Fig. 6f) and arsenates (Figs. 2h, 4i, and 6d) and the
absence of sulfide minerals clearly document the oxidizing
conditions during stage II carbonate ore formation. We note
that some botryoidal smithsonite crusts (Figs. 2i and 4k) are
devoid of both sulfide and oxide inclusions and thus cannot
be unambiguously attributed to either one of the two
carbonate ore stages. Hemimorphite crystals (Fig. 6e), locally
replaced and/or overgrown by smithsonite crusts (smithson-
ite III?), are mainly associated to the late stages.
We suspect that some stage II smithsonite reflects ground
water dissolution of stage I smithsonite in the porous and
friable ore mass and its subsequent reprecipitation in the
vadose zone.
Calcite
Numerous veins and cements in breccias containing sparry
calcite, as well as dogtooth euhedral crystals and travertine-
like encrustations in karstic cavities, are found in the host
marbles surrounding the Angouran orebody. Calcite was
mostly deposited also during the formation of the two Zn
carbonate ore stages, associated in prevalence with the
stage I carbonate ore.
Fluid inclusions of the stage I carbonate ore
Dogtooth smithsonite crystals from the stage I carbonate ore
generally show cloudy cores with primary, submicrometer-
sized fluid inclusions that appear to be monophase. Rare,
slightly larger (6–12 μm) monophase liquid-only inclusions
are found isolated in the crystals or along growth zones.
Formation temperatures for these monophase inclusions
are estimated to be less than 70°C or even less than 50°C
(Roedder 1984). Overheating to about 350°C caused stretch-
ing of the monophase inclusions and formation of a small
vapor bubble. Thus ice melting in the presence of vapor
could be measured in these inclusions. The few micro-
thermometric results with ice melting temperatures ranging
from −0.8 to −1.8°C (n=3) show a significantly lower
salinity of 1.4–3.0 wt.% NaCl equivalent (and formation
temperature) compared to the fluids related to sulfide ores
(23–25 wt.% total dissolved solids; Gilg et al. 2006).
Geochemistry
Main and trace elements
Primary sulfide ores are characterized by a very high Zn
(>35 wt.%) and generally low Pb content (<3 wt.%, Gilg
et al. 2006; Table 1). Conversely, the Zn content of “oxide”
ores is more variable, typically <40 wt.% in calamine ore,
hard carbonate ore, breccia ore, and <30 wt.% in soft
carbonate ore and very low grade ore (Fig. 3). Pb contents
in “oxide”ores (∼5–7 wt.%) are generally higher than in
the primary sulfide ores. Table 1lists the average trace
element composition of 21 sulfide and “oxide”bulk ore
Table 2 Selected trace element concentration (parts per million) of some Angouran smithsonite samples
Sample Cr Mn Co Ni Cu As Ag Cd Sb Pb Au (ppb)
ANG B3-S Stage I b.d. 632 201 259 3 9 b.d. 5 3 668 2
ANG B13-A Stage I b.d. 110 240 216 9 68 b.d. 259 11 1234 3
ANG B13-R Stage I b.d. 609 857 1425 81 27 b.d. 159 7 1146 7
ANG B14 Stage I 1 198 261 366 2 26 b.d. 142 4 2251 1
ANG B15 Stage I b.d. 235 153 146 6 115 1 517 4 2268 28
ANG B15-A Stage I b.d. 52 101 97 43 124 b.d. 2400 b.d. 4877 6
ANG B15-B2 Stage II b.d. 22 186 260 24 663 1 3500 13 4572 4
AA 34 Stage II 15 610 721 1057 27 568 18 837 11.7 3532 1.8
b.d. below detection limit
Miner Deposita

samples, which are dominated by stage I carbonate ores
(Teck Cominco, average assay data). Whereas the sulfide
ores reveal high Ag, As, Sb, Hg, Co, and Ni contents and
low Cu and Mn, the “oxide”ores are enriched in As
(6,100 ppm), Sb (570 ppm), and Mn (750 ppm), and
depleted in Ag (35 ppm).
The trace element composition of a few bulk smithsonite
samples, comprising both stage I and stage II Zn carbonate
ores, is shown in Table 2. Stage I Zn carbonate ore, both as
smithsonite concretions and veins cutting primary sulfides,
has variable Mn (from 50 to 630 ppm) and Pb (from 660 to
4,800 ppm) contents. As is quite low (from 9 to 124 ppm).
Stage II Zn carbonate ore has a much higher As content
(560–660 ppm). All samples have elevated, although variable
Ni and Co contents (Ni from 97 to 1,400 ppm and Co from
100 to 850 ppm). Ni and Co are locally enriched compared to
the average values measured in sulfide ores (Gilg et al. 2006),
where these elements occur as tiny inclusions of Ni and Co
arsenides in quartz.
Microanalyses of smithsonite samples, belonging to both
the stage I and stage II Zn carbonate ores, have been carried
out also by EDS and WDS analysis (Table 3). The results
for the stage I smithsonite samples show only some slight
differences in Fe and Mn, with pink and orange varieties
having the higher contents. In the stage II samples, the Fe
content can be higher than 2 wt.%, while Mn is absent. In
the yellow SCO, MnO can reach 0.5 wt.%, together with
PbO values around 1.2 wt.%.
Selected trace element data (As, Zn, Pb, Mn, Fe, Sr, Cd,
Ba, Ni, Co) for various unmineralized carbonate rocks
(marbles, limestones, travertines) are given in Table 4.Com-
pared to the chemical composition of the mineralized marble
clasts contained in the sulfide and carbonate ore breccias,
the unmineralized carbonate rocks have generally very
low metal contents (Zn<30 ppm, Pb<4 ppm, Ni< 6 ppm,
Co< 1 ppm, As < 20 ppm, and Cd<1 ppm in the basement
marbles and in the Qom limestone). The Qom limestone is
only slightly enriched in Cu, Ba, and As compared to the
marbles. Conversely, the mineralized marble clasts (both
calcitic and dolomitic) are enriched in Zn, Pb, Ni, Co, As, and
Cd.
All Quaternary travertine samples (Angouran mine
camp, Taxt-e Soleiman, and Zendan-e Soleiman) are
characterized by relatively high As and Ba contents
(Table 4). The samples from the Angouran mine camp
travertine are strongly enriched in Zn (440–1,320 ppm), Cd
(1–8 ppm), and Ni (9–14 ppm), as compared to the
travertines from Takht-e Soleiman and Zendan-e Soleiman.
Similar values have been observed in vein carbonates from
the open pit area and in the carbonates from small solution
cavities occurring in the DB 90 drill core. Both types of
carbonates have Zn values varying between 200 and
2,800 ppm and Pb values ranging from 80 to 970 ppm.
As (maximum values around 150–350 ppm), Mn, Ni, Co,
and Cd are also enriched in these samples.
C, O, and H isotope data
Carbon and oxygen isotope data of smithsonite, cerussite,
and calcite from the Angouran mine and adjacent areas and
oxygen and hydrogen isotope data of spring waters are
presented in Tables 5and 6.
Smithsonite from stage I carbonate ore displays variable
δ
18
O
VSMOW
values ranging from 18.3 to 23.6‰(n=21),
while the carbon isotope composition is fairly constant and
unusually high (+3.2 to +6.0‰) with an average value of
4.9‰±0.8‰(1σ). In contrast, the smithsonite from stage II
carbonate ores shows a much smaller range of δ
18
O
VSMOW
values from 24.3 to 24.9‰but a considerable spread
towards lower δ
13
C
VPDB
values (−0.8 to 4.6‰). Cerussite
shows C–O isotope values similar to stage II carbonate
ores, with relatively constant δ
18
O(12.7–15.1‰)but
highly variable δ
13
C(−11.2 to +1.9‰). Such C–O isotope
patterns (Fig. 8) are quite characteristic for supergene
carbonate minerals in sulfide oxidation zones (Gilg and
Boni 2004a,b; Gilg et al. 2007), meteoric carbonate
cements (e.g., Lohmann 1988), and pedogenic carbonates
(e.g., Salomons and Mook 1986; Talma and Netterberg
1983). The observed
13
C enrichments are characteristic for
travertine-depositing systems (e.g., Turi 1986; Minissale
et al. 2002).
Sparry vein calcite, euhedral crystals in the carbonate ore,
and travertine-like cavity fillings in and around the ore bodies
at Angouran have variable δ
18
O
VSMOW
values ranging from
15.6 to 21.7‰and δ
13
C
VPDB
values from −1.3 to +6.1‰
(Table 5,Fig.9). The carbon and oxygen isotope values are
negatively correlated. We interpret this isotope variation as
indicative of calcite precipitation from a mixture of two
isotopically distinct fluids. The majority of calcite samples
with low δ
18
O
VSMOW
(17± 2‰) and high δ
13
C
VPDB
values
(5± 1‰) are related to precipitation from hydrothermal,
travertine-depositing solutions. Few calcite samples with
heavy oxygen and light carbon isotope values (δ
18
O
VSMOW
=
21± 1‰;δ
13
C
VPBD
=−1±1‰) were formed from the second
end member fluid, corresponding to cold groundwater.
The Angouran marble samples exhibit a large spread in
carbon (0.5–4.6‰) and oxygen isotope values (17.7–
27.1‰), which are negatively correlated (Table 5, Fig. 9).
The isotope composition of the least altered marble samples
(δ
13
C
VPBD
=1.3±0.5‰;δ
18
O
VSMOW
=26±1‰) is consis-
tent with a marine origin and a rather limited isotope
exchange during diagenesis and greenschist-facies meta-
morphism. Marble clasts from mineralized and some barren
but calcite-veined breccias display a distinct alteration trend
towards lower oxygen and higher carbon isotope values.
The isotope composition of the altered marble overlaps
Miner Deposita

Table 3 Chemical analyses (EDS–WDS) of representative Angouran smithsonite samples (mean of five- to ten-point analyses)
Sample ANG
B3-1
Stage I
ANG
B3-2
Stage I
ANG
B13-A
Stage I
ANG
B13-R
Stage I
ANG
B14-1
Stage I
ANG
B14-2
Stage I
ANG
B14-3
Stage I
ANG
B15-1
Stage I
ANG
B15-3
Stage I
ANG
B15A-B
Stage I
ANG
B15A-R
Stage I
ANG
B15A-M
Stage I
ANG
B15B
Stage I
ANG
B15-B1
Stage II
a
ANG
B18
Stage II
a
ANG
B20
Stage II
a
ZnO 62.33 62.37 62.85 62.34 63.34 63.02 64.35 63.02 62.51 62.12 62.83 62.33 60.97 62.11 63.51 54.64
CaO 0.25 0.34 0.57 1.39 0.84 0.39 0.21 1.02 0.84 0.98 0.85 0.25 0.25 1.46
MgO 0.38 0.68 0.34 0.27
FeO 1.87 1.64 1.38 0.56 0.36 0.10 0.68 0.69 1.87 2.80 9.63
MnO 0.36 0.48 0.16 0.68 0.36 0.07 0.53
CdO 0.64 0.13 0.71 0.55
PbO 0.56 0.56 0.58 0.21 1.23 0.49
CO
2b
35.42 35.45 35.43 35.51 35.48 35.50 35.12 35.21 35.40 35.27 35.26 35.42 35.61 35.12 35.07 35.68
Sum 100.23 100.28 100.23 100.52 100.04 99.95 99.68 99.91 99.77 100.27 99.76 100.23 100.68 99.45 100.34 100.44
Structural formulae on the basis of 6 O
Zn 1.91 1.906 1.921 1.902 1.934 1.923 1.985 1.930 1.91 1.91 1.930 1.91 1.86 1.92 1.96 1.66
Ca 0.01 0.015 0.025 0.062 0.037 0.017 0.009 0.05 0.04 0.04 0.04 0.01 0.011 0.065
Mg 0.023 0.042 0.02 0.017
Fe 0.07 0.057 0.048 0.019 0.012 0.02 0.03 0.65 0.097 0.331
Mn 0.01 0.017 0.006 0.02 0.01 0.002 0.017
Cd 0.01 0.014 0.011
Pb 0.006 0.01 0.01 0.002 0.014 0.005
C 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000
See text for sample description.
a
Traces of Fe oxides and cerussite
b
Calculated from stoichiometry
Miner Deposita

with the isotope composition of hydrothermal calcite and
hypogene smithsonite.
Travertine samples from Zendan-e Soleiman, Taxt-e
Soleiman, and the Angouran mine camp travertine have
very similar oxygen isotope compositions (20.1–22.4‰;
Table 5) and display the characteristic
13
C enrichment
(δ
13
C
VPBD
=3.3–11.3‰) of thermogenic travertine (Pentecost
2005). The high C isotope values in thermogenic travertine
are generally explained by high-temperature, contact-
metamorphic decarbonatization of marine carbonates and
deposition of carbonate at the surface at much lower tem-
peratures, usually below 100°C (Turi 1986; Pentecost
2005). Our carbon isotope value for the Zendan-e Soleiman
travertine (11.3‰) is broadly consistent with the isotope
data (8.7–10.8‰) reported in Savelli and Wedepohl (1969).
We note that the Angouran mine camp travertines have
carbon isotope values of 3.3–5.4‰, which are similar to
carbon isotope values of stage I smithsonite and of the calcite
in vugs or fissures and travertine-like carbonate karst infills
around and in the Angouran ore body (Fig. 9).
Hydrogen and oxygen isotope compositions of water
from several cold springs (<10°C) close to the Angouran
Zn–Pb deposit and from hot springs (18–38°C) from the
Taxt-e Soleiman travertine-depositing geothermal field
(Table 6) are homogeneous with δ
18
O
VSMOW
of −9.9±
0.1‰and δD
VSMOW
of −60.5±1.0‰. We suggest that the
hot waters emanating in the Taxt-e Soleiman–Ahmadabad
geothermal area (∼2,140–2,240 m above sea level) are
mainly derived from the easterly mountain ranges (>2,500–
3,580 m a.s.l.) that host the Angouran deposit. The meteoric
waters are characterized by a strong deuterium excess
parameter of +20‰, which is also reported from several
areas in the Zagros belt (e.g., Moser and Stichler 1980;
Farpoor et al. 2004) and from other areas in the Eastern
Mediterranean and Middle East (e.g., Gat and Carmi 1970;
Gat and Dansgaard 1972). Such high deuterium excess
values in meteoric waters are considered to be related to
evaporation of seawater under low-humidity conditions
(Gat and Carmi 1970). Slightly heavier hydrogen and
oxygen isotope compositions are found in cold waters from
Table 4 Minor and trace elements concentration in selected Angouran Ca(-Mg) carbonate samples
Samples Mn Fe V Cr Co Ni Cu Zn As Sr Cd Sb Ba La Pb Au
wt.% ppm ppb
AA 1 travertine (Ang mine camp) 0.01 0.12 3 5 b.d. 14 2 448 133 274 1 b.d. 26 b.d. 6 b.d.
AA 2 travertine (Ang mine camp) 0.01 0.2 562951327 115 188 8 1 29 2 60 b.d.
AA 3 travert. (Taxt-e Soleiman) 0.01 0.03 1 b.d. b.d. 2 b.d. 8 192 461 b.d. b.d. 14 b.d. 1 b.d.
AA 5 travert. (Zendan-e Soleiman 0.09 0.22 4 3 b.d. 5 2 17 258 273 b.d. b.d. 87 b.d. 6 b.d.
AA 6 marble 0.13 0.41 3 8 b.d. 6 1 4 6 243 b.d. b.d. 11 4 4 b.d.
AA 7 marble 0.01 0.04 6 b.d. b.d. 3 b.d. 15 1 193 b.d. b.d. 2 b.d. 2 b.d.
AA 8 Qom limestone 0.07 0.28 4 3 b.d. 4 6 23 20 80 b.d. 4 60 b.d. 3 b.d.
AA 12 sparry calcite 0.12 0.18 6 b.d. b.d. 3 1 440 12 136 479 6 5 38 689 b.d.
ANG B3 C dol. marble clast in sulfides 0.01 1.00 15 1 68 131 1 9980 7 18 3 b.d. 2 b.d. 42 5
ANG B6 marble clast in carbonate ore 0.10 b.d. 10 3 157 91 6 9991 130 47 420 43 b.d. 6 3155 2
ANG B9 marble clast in sulfide ore b.d. b.d. 2 b.d. 7 9 5 975 105 298 213 141 b.d. 3 2004 4
A1-1 calcite in vug DB90 0.06 0.13 7 b.d. 32 5 7 911 39 31 32 3 16 3 905 5
A1-2 calcite in vug DB90 0.01 0.02 5 b.d. 1 3 3 645 14 17 102 b.d. 2 3 977 4
A1-3 calcite in vug DB90 0.02 0.08 3 b.d. 6 4 5 793 26 50 9 b.d. 9 1 390 7
A1-4 calcite in vug DB90 0.01 0.02 4 b.d. 2 1 2 361 7 16 5 b.d. 5 b.d. 112 2
A1-5 calcite in vug DB90 0.05 0.22 12 b.d. 17 4 8 614 55 11 25 4 10 6 793 3
A2 lamin. marble 0.03 0.05 38 2 b.d. 3 15 109 14 94 b.d. 3 1 1 149 1
A3 marble 0.01 0.11 22 1 b.d. 34 7 62 7 149 b.d. b.d. b.d. b.d. 89 8
A5-1 marble clast 0.02 0.09 7 2 3 14 6 603 26 69 47 25 1 6 886 5
A5-2 red vein calcite 0.04 0.1 17 2 12 16 14 1767 61 46 126 61 1 7 2170 2
A6-1 marble clast 0.02 0.07 9 2 b.d. 2 9 67 8 105 b.d. b.d. 2 b.d. 33 12
A6-2 red calcite 0.07 0.37 14 11 b.d. 335 44 319 36 44 b.d. 7 3 b.d. 31 6
A7-1 vein calcite open pit 0.04 0.01 4 b.d. b.d. b.d. b.d. 39 2 293 b.d. 1 1 b.d. 14 1
A7-2 vein calcite open pit 0.03 0.04 4 b.d. b.d. b.d. 5 207 6 177 b.d. 11 1 b.d. 81 1
A7-3 vein calcite open pit 0.02 0.26 4324181014 150 117 16 81 1 b.d. 733 1
A7-4 vein calcite open pit 0.01 0.23 3 7 2 224 14 2817 357 45 9 60 1 b.d. 333 4
A7-5 vein calcite open pit 0.04 0.03 4 b.d. b.d. 3 6 232 15 172 b.d. b.d. 9 b.d. 18 2
b.d. below detection limit
Miner Deposita

Table 5 Carbon, oxygen, and strontium isotope compositions of Ca, Zn, and Pb carbonate samples
Sample No Location Description Mineral δ
13
C
VPDB
δ
18
O
VSMOW 87
Sr/
86
Sr
±2σ
Stage I carbonate ore
ANG B15A-B OP2930,700E–1000N HCO, concr. ,white, core sm 4.95 18.33 0.70865 ± 2
ANG B15A-R OP2930,700E–1000N HCO, concr., pink, rim sm 5.09 21.44 0.70821± 1
ANG B15B-G OP2930,700E–1000N HCO, concr., gray crystals sm 5.51 23.58
ANG B15B1-A OP2930,700E–1000N HCO, vein with oxidized asp sm 4.19 20.76
ANG B15B1-B OP2930,700E–1000N HCO, vein with oxidized asp sm 4.89 21.89
ANG B15B1-C OP2930,700E–1000N HCO, matrix with asp sm 5.70 20.41
ANG B15B1-D OP2930,700E–1000N HCO, matrix with asp sm 5.43 22.26
ANG B15-1 OP2930,700E–1000N HCO, concr., light (gray-pink) sm 5.91 21.00
ANG B15-3 OP2930,700E–1000N HCO, reddish concr. sm 5.86 20.65
ANG B15A-M OP2930,700E–1000N HCO, massive, brown, with asp sm 4.74 20.29
ANG B3-1 DB90-200 m SO, concr., pink, rim sm 4.33 18.87 0.70863± 1
ANG B3-2 DB90-200 m SO, concr., white, core sm 4.60 21.02
ANG B13R OP2930,870E–1070N MSO, concr., pink sm 4.25 20.45
ANG B13A OP2930,870E–1070N MSO, concr., orange sm 4.74 21.73
ANG B14-1 OP2960,570E–980N SO, white concr. sm 6.00 20.59
ANG B14-2 OP2960,570E–980N SO, geodic-type matrix sm 5.84 21.26
AA0 OP2930,870E–1070N MSO, pink concr. sm 4.32 20.99
AA37B OP2930,870E–1070N MSO, pink concr. core sm 4.24 19.42
AA37A OP2930,870E–1070N MSO, pink concr., rim sm 3.21 22.71
AT-1A DB98-18.6 m BO, laminated, brown sm 5.83 22.16
AT-7A OP-Teck Cominco SO, massive vug infill, white sm 3.96 20.51
Stage II carbonate ore
ANG B15B-B OP2930,700E–1000N HCO, concr., white sm on Fe oxides sm II 4.62 24.92 0.70824 ± 3
AT-3A DB98-97.0 m BO, breccia cement, brown sm II 3.08 24.33
AT-4A DB98-113.9 m MSO, brecciated, laminated, brown, sm II ± hm −0.78 24.93 0.70895±1
AA-10 OP2910,750E–990N MSO, crystal in vug ce −1.41 13.46
AA-9 OP2910,750E–990N SCO, black, massive ce −11.15 12.70
AA36B OP2910,750E–990N SCO, white, massive with Fe oxides ce 1.93 14.64
AA36A OP2910,750E–990N SCO, dark, massive with Fe oxides ce −2.61 15.09
ANG B20 OP2940,880E–1040N SCO, red fine-grained matrix + Fe
(hydr)ox+qz
sm + cc 2.12 18.53
ANG B18 OP2940,850E–1090N SCO, green fine-grained matrix cc + sm 1.88 17.23
ANG B18 OP2940,850E–1090N SCO, green fine-grained matrix cc + sm 2.12 16.32
Ca carbonates, marbles, and travertines
AT-2A DB89-50.8 m BO, sparry, vein cc + hm +
sm
5.62 18.33 0.70851 ±1
ANG B10-1 DB90-20 m BO, white sparry, vug filling cc 5.11 16.84
ANG B10-2 DB90-20 m BO, dark sparry, vug filling cc 5.16 18.30
ANG B11-A OP2930 near DB90 sparry cc in breccia cc 2.70 19.53
ANG B19-A OP2940,890E–1060N SCO, white cc with goe cc 2.23 20.11
ANG B7-1 DB90-94 m Travertine-like banded white cc in
marble
cc 5.13 16.94
ANG B7-2 DB90-94 m Travertine-like banded reddish cc in
marble
cc 5.05 15.60
A7-1 OP2970 Fissural vein, white cc cc 5.91 16.13
A7-2 OP2970 Fissural vein, yellow to green cc cc 6.12 16.69
A7-3 OP2970 Fissural vein, orange cc cc 4.11 16.68
A7-4 OP2970 Fissural vein, red cc cc 4.93 17.78
A7-5 OP2970 Fissural vein, brown cc cc 1.04 18.72
A1-1 DB62-31.5 m Dark brown sparry, vug filling cc 3.30 19.09
A1-2 DB62-31.5 m White sparry, vug filling cc 3.63 18.57
A1-3 DB62-31.5 m Orange, vug filling cc −0.30 20.69
A1-4 DB62-31.5 m Colorless vug filling cc 4.73 19.45
A1-5 DB62-31.5 m Light brown, vug filling cc −1.32 21.67
Miner Deposita

the Ayagh Bolaghi spring at the Zarshuran As mine and in
the Amirabad cold spring.
Rb–Sr isotope data
Sr and Rb–Sr isotope data for smithsonite and calcite from
the mineralization, host marbles, and two samples of meta-
morphic host schists of the Angouran deposit have been
obtained. The carbonate minerals and host marbles have
unradiogenic
87
Sr/
86
Sr ratios between 0.7074 and 0.7089
(Table 5). However, vein calcite and stage I smithsonite
samples are mostly slightly more radiogenic than the
(possibly hydrothermally altered) marble fragments occur-
ring in the breccia and hard carbonate ore types. One
sample of stage II smithsonite is even more radiogenic, with
87
Sr/
86
Sr=0.70895. The two analyzed schist samples show
low
87
Rb/
86
Sr ratios of about 1.24 and 7.58 (Table 7), and
their
87
Sr/
86
Sr ratios are 0.70888 and 0.71104, respectively.
Stage II smithsonite samples are even more radiogenic. In
the
87
Sr/
86
Sr vs
87
Rb/
86
Sr space, the slope of a straight line
through the two schist samples corresponds to an early
Miocene two-point Rb–Sr isochron age of 24.0± 0.4 Ma
that, if interpreted as a two-point isochron with geochrono-
logical significance, most likely records a metamorphic
recrystallization age.
Thermodynamic calculations
Figure 10 depicts the results of thermodynamic calculations
performed to explore the geochemical conditions responsible
Table 5 (continued)
Sample No Location Description Mineral δ
13
C
VPDB
δ
18
O
VSMOW 87
Sr/
86
Sr
±2σ
A5-2 DB84-58.1 m Red cc vein in breccia cc 5.06 18.44
A6-2 DB84-107.5 m Red, fine-grained cc in breccia cc 2.01 21.46
AA12 Open pit Sparry cc cc 2.40 18.14
A5-1 DB84-58.1 m Gray clast from marble breccia Marble 4.53 19.30
A6-1 DB84-107.5 m Clast from marble breccia Marble 1.74 23.68
ANG B3 DB90-200 m Dolomite marble clast in sulfide ore Marble 3.51 21.19 0.70836 ± 1
ANG B6A DB90-104.5 m Dark gray marble clast in breccia Marble 3.30 21.02
ANG B9A DB90-34.5 m Marble clast in breccia ore Marble 1.51 27.09 0.70746±1
ANG B9B DB90-34.5 m Marble clast in breccia ore Marble 2.87 24.00 0.70846±1
ANG B8A DB90-40 m Marble clast in hard carbonate ore Marble 3.61 18.81 0.70820 ±1
ANG B8B DB90-40 m Marble clast in hard carbonate ore Marble 4.58 17.69
ANG B6B DB90-104.5 m Marble clast in breccia Marble 2.50 21.14
A3 DB62-135 m Marble Marble 0.83 26.07
A2-1 DB62-116.8 m Laminated marble Marble 2.87 26.46
AA7 Outcrop, far from ores Marble Marble 0.84 24.15
AA-14a OP Marble at contact to calamine ore Marble 0.54 26.82
AA6 Outcrop, far from ores Footwall marble layer in schists Marble −3.94 16.03
AA8 Outcrop, far from ores Qom limestone Limestone −1.85 21.11
AA1 Ang mine camp,
bottom
Travertine 5.37 20.08
AA2 Ang mine camp, top Travertine 3.31 21.34
AA3 Zendan-e Soleiman Travertine 11.31 20.74
AA5 Taxt-e Soleiman Travertine 4.79 22.43
sm Smithsonite, ce cerussite, cc calcite, qz quartz, asp arsenopyrite, chl chlorite, ms muscovite, goe goethite, hm hematite, concr concretion, OP
open pit, DB90 drill core, DB62 drill core, HCO hard carbonate ore, SO sulfide ore, BO breccia ore, MSO mixed sulfide-carbonate ore, SCO soft
carbonate ore.
Table 6 Hydrogen and oxygen isotope data of waters from hot and
cold springs in the Angouran region
Temp
(°C)
Elevation
(m a.s.l.)
δ
18
O
(‰)
δ
2
H
(‰)
Deuterium
Excess (‰)
Soulakhan spring <10 −10.09 −60.5 20.2
Explosive storage
spring
<10 2380 −9.84 −59.7 19
Covered spring (tap
water mine camp)
<10 2680 −10.07 −60.2 20.4
Amirabad spring <10 2389 −9.32 −55.1 19.5
Ahmadabad 1 spring 37.8 2142 −10.15 −61.3 19.9
Ahmadabad 2 spring 28.5 2139 −10.01 −61.5 18.6
Taxt-e Soleiman 18.3 2235 −9.85 −60.2 18.6
Ayagh Bolaghi
spring-Zarshuran
8−9.42 −56.3 19.1
Miner Deposita

for the observed mineral paragenesis of stage I carbonate
ores (smithsonite + quartz + arsenopyrite + galena ±
sphalerite). The diagram in Fig. 10a shows the stability
field of smithsonite + quartz relative to willemite, as a
function of temperature and CO
2
fugacity. The observed
assemblage smithsonite + quartz requires high CO
2
fugacities (log f
CO2
>0) if temperatures were higher than
40°C. Such high CO
2
fugacities would be consistent with
travertine-depositing systems (e.g., Chiodini and Marini 1998;
Minissale et al. 2002). At temperatures above 100–150°C,
smithsonite + quartz is unlikely to be a stable paragenesis, as
the necessary CO
2
fugacities would be unrealistically high
(see also Brugger et al. 2003,p.824).Figure10bshowsthe
stability of various Zn and As species as a function of oxygen
fugacity and pH at a temperature of 50°C and a high log f
CO2
of 2:3aPAs¼103
;aPS¼105
;aFe¼105
;aZn¼106.A
small field of coexisting smithsonite + arsenopyrite (±sphal-
erite) exists at pH values above 7.5 and very reducing
conditions (log f
O2
<−60).
Discussion
Origin of stage I carbonate ore
The Angouran deposit is located in a recently strongly
uplifted, mountainous, relatively arid region, which does not
have particularly favorable conditions for deep weathering of
sulfides. Thus the significant and deep reaching Zn carbonate
mineralization at Angouran can hardly be explained by
supergene processes. The narrow, pipe-like nonsulfide ores,
which contain very few relicts of primary sulfide ores but
show ample evidence of marble replacement, overlie the
tabular sulfide orebody like an inverted mushroom (Fig. 3), as
if Zn was transported and dispersed upwards rather than
δ13C(
‰)
VPDB
δ18O(‰)
VSMOW
10
5
0
-5
-10
-15
10 15 20 25 30
Smithsonite
(stage 2)
Cerussite
(stage 2)
Smithsonite (stage 1)
Supergene
smithsonite
Super-
gene
cerussite
Fig. 8 Stable oxygen and carbon isotope compositions of smithsonite
and cerussite from Angouran. The shaded fields of supergene
smithsonite and cerussite from Gilg et al. (2007) are shown for
comparison. Note that the majority of supergene cerussite samples in
Gilg et al. (2007) have δ
13
C values of less than −15‰. Stage 1
smithsonite samples have an unusual pattern in this δ–δplot with
constant and heavy carbon isotope values and variable oxygen isotope
values that is interpreted as indicating a hydrothermal travertine-
Table 7 Rb–Sr isotope data of metamorphic schists from Angouran
Sample No Location Composition Rb (ppm) ±2σSr (ppm) ±2σ
87
Rb/
86
Sr ±2σ
87
Sr/
86
Sr ±2σ
ANG B1 DB90-205 m Schist with chl + qz + ms −py 12.9±0.2 30.3 ±0.3 1.24 ± 0.02 0.70888± 0.00001
ANG B17 DB90-
2935 m
Schist with chl + qz + ms −py 30.7 ±0.5 11.7±0.2 7.58 ± 0.09 0.71104±0.00002
qz quartz, chl chlorite, ms muscovite, py pyrite
13C (‰)
VPDB
18O (‰)
VSMOW
10
5
0
-5
15 20 25 30
Marble
Foot wall marble
Qom limestone
Travertines
0.7075
0.7085
0.7084
0.7084
87 86
Sr/ Sr
0.7082
Calcite
veins, fissures,
crystals in vugs
Fig. 9 Stable oxygen and carbon isotope composition of Ca
carbonates from veins, fissures, and crystals in karstic vugs in and
around the Angouran ore bodies (red squares), travertine-like
encrustations in similar cavities (orange triangles), travertines in the
area (green triangles), Angouran marble from mineralized breccias
and outside the mineralized zone (blue dots), foot wall marble (brown
dot), and Miocene Qom limestone (violet dot). Strontium isotope
composition of selected marble samples is indicated. The blue arrow
shows a trend of increasing carbon and strontium and decreasing
oxygen isotope ratios as a consequence of increasing hydrothermal
alteration
Miner Deposita

laterally or downwards, as in the classical supergene wall-
rock replacement model of Hitzman et al. (2003).
Furthermore, the coprecipitation of smithsonite with
galena, arsenopyrite, and rare pyrite, as well as the absence
of both Fe-Mn-oxides/hydroxides and typical oxidation-
dissolution textures of the sphalerite-rich sulfide ore,
suggest that the fluids responsible for stage I Zn carbonate
ore deposition were relatively reduced (low Eh) and from
slightly basic to close to neutral. On the basis of micro-
thermometric data, fluid temperatures during precipitation
were relatively low (<50°C) and salinities did not exceed
those of common meteoric waters. However, the stage I Zn
carbonate ore has high contents of certain elements such as
Hg (25 ppm), As (14,000 ppm), Co (350 ppm), Mo (125 ppm),
and Sb (440 ppm). These elements (with the exception of
cobalt) are quite scarce in the primary sulfide ore (Gilg et al.
2006) but have been commonly detected in hot springs
throughout the region and in the nearby Zarshuran As–Au
mine. This clearly rules out the hypothesis of meteoric
weathering being exclusively responsible for the formation of
the nonsulfide ores at Angouran. The same elements are also
contained in significant amounts in several travertine deposits
of the area, such as the mine camp travertine and the Taxt-e
Soleiman deposit, along with several hundreds of parts per
million Zn and Pb.
The δ
18
O values of smithsonite from the stage I carbon-
ate ore are up to 7‰lower and much more variable than
those from carbonate-oxide ore (Fig. 8), thus indicating
higher and more variable formation temperatures (consistent
with the fluid inclusions data) and/or the involvement of two
isotopically distinct fluid types during the stage I phase.
Assuming an oxygen isotope composition of waters identical
to the present-day hot springs in the area (δ
18
O
water
=−10‰)
and the new smithsonite–water fractionation equation of
Gilg et al. (2007), we calculate temperatures of 40–15°C for
the formation of stage I smithsonite. As exothermal sulfide
oxidation can be excluded as a heat source (Gilg et al.
2007), we suggest that stage I Zn carbonate mineralization
at Angouran was deposited by a distinct, low-temperature
hydrothermal system, most probably related to one or more
stages of Tertiary–Quaternary volcanic activity. This hypoth-
esis is well supported by the presence of arsenopyrite in the
carbonate-sulfide ore.
As shown in Fig. 10a, smithsonite (relative to willemite)
is stable and coexistent with quartz in an environment with
maximum temperatures of 100–120°C and very high CO
2
fugacity. High CO
2
fugacity and high pH (8–10), combined
with a low oxidation state, are also required for the
simultaneous deposition of arsenopyrite and smithsonite at
fairly low temperatures, as deduced from the small
coexistence field of both minerals resulting from the
superposition of the two graphs for the As and Zn species
at 50°C (Fig. 10b). These are very peculiar conditions for
arsenopyrite deposition, a mineral that is generally replaced
by other As minerals or by As-bearing pyrite at lower
temperatures (Kretschmar and Scott 1976). We note that the
paragenesis of arsenopyrite with smithsonite at Angouran is
probably one of the lowest temperature occurrence (<40°C)
of arsenopyrite ever recorded, as arsenian pyrite is the most
common Fe-bearing arsenic phase at such low temperatures
5 4 3 2 1 0 12
50 50
75 75
125 125
25 25
100 100
150 150
logfCO
2
(g)
Smithsonite
Willemite
Temperature (ºC)
a=1
Quartz
AsO OH
2
H AsO (aq)
33
H AsO
24
HAsO
23
H AsO4
Zn
++
As
Smithsonite
Orpiment
Realgar
Sphalerite
Arsenopyrite
50°C
pH
246810
-70
-60
-50
-40
log f O (g)
2
ZnHCO
3
+
C
CO
3
HCO
3
CO (g)
2
CH (g)
4
a
b
Fig. 10 a Stability field of smithsonite and willemite in the presence
of quartz as a function of temperature and CO
2
fugacity in the gas
phase. bDiagram to illustrate the stability fields of arsenic (black) and
zinc (blue) species in the Fe–Zn–As–S–C–H–O system as a function
of oxygen fugacity in the gas phase and pH at 50°C using
Geochemist’s Workbench and the modified Thermo2000 database
(Cleverley et al. 2003). Solid phase are shown in bold type and their
stability fields in light colors. The stability fields of predominant
aqueous carbon species are separated by dotted brownish lines. Note
the presence of a small red field of coexistence of smithsonite and
arsenopyrite
Miner Deposita

(D.K. Nordstrom, personal communication, 2003). Howev-
er, our petrographic observations and thermometric calcu-
lations and the thermodynamic models including those by
Vink (1996) and Craw et al. (2003) clearly show the
stability of arsenopyrite at temperatures less than 100°C.
The fact that hypogene smithsonite and calcite have similar
87
Sr/
86
Sr ratios around 0.70821–0.70895, slightly more
radiogenic than those of the marbles, reflects some
influence of a radiogenic source, probably the host
metamorphic schists and marbles of the Angouran deposit.
The Sr isotopic composition of smithsonite and calcite may
reflect a mixture of Sr derived from the host marbles, with
some contribution of slightly more radiogenic Sr mobilized
from metamorphic schists. The Miocene two-point isochron
age of 24.00±0.44 Ma given by the two analyzed schist
samples, if significant, is not very far from a
40
Ar/
39
Ar age of
20 Ma, proposed as a maximum age for the sulfide
mineralization at Angouran by Gilg et al. (2006). The
initial
87
Sr/
86
Sr ratio of the two-point line is 0.70846 ±
0.00002, lower than the
87
Sr/
86
Sr ratios obtained for calcite
and most smithsonite samples. Therefore, the schists could
have delivered slightly radiogenic Sr, to contribute to the
composition of “altered”marbles and smithsonite, at any
time between 24 Ma ago and the present.
Comparison of the O, C, and Sr isotope data (Fig. 9)forthe
host marbles of the deposit with those obtained for the clasts
of the breccia ore reveals a common alteration trend expressed
by a marked increase in radiogenic Sr and δ
13
C and decrease
in δ
18
O values. This trend points towards the C, O, and Sr
isotope signatures measured in calcite crystals occurring in
vugs, veins, and fissures, as well as in the travertine-like forma-
tions in the Angouran marble in and around the orebody. The
latter, being characterized by heavy δ
13
C(+5)andlowδ
18
O
values (+17), show a clear hydrothermal signature indicating a
hydrothermal karstic environment. The fact that some calcite
samples have high δ
18
Oandlowδ
13
Cvaluesimpliesthatthe
main mechanism of calcite precipitation around the Angouran
orebody was not simple cooling and CO
2
degassing but
should have involved mixing of an ascending hot,
13
C-rich
fluid with cold,
12
C-rich ground waters.
We note the high and consistent δ
13
Cvaluesof+5‰of the
hypogene carbonate alteration, of hypogene stage 1 smithson-
ite, and of the Angouran mine camp travertine. This suggests
a common origin of these carbonates. The carbon did not
originate locally from the Angouran marble wall-rock bearing
δ
13
Cvaluesof+2‰, but from a deeper, hotter source.
Zn carbonates deposited by hypogene–hydrothermal fluids
have been recorded from elsewhere in the literature, although
not producing economic ore deposits. Kucha and Czajka
(1984) were the first to describe “primary”-hydrothermal
Zn–Pb carbonates that often precede sulfides in the
carbonated-hosted Zn–Pb ores in Poland. Minčeva-Stefanova
(1989) described a rare hydrothermal mineralization phase
consisting of dolomite, pink cobaltian smithsonite, calcite,
aragonite, and sulfides in veins and cavities of the stratiform
Sedmochislenitsi Pb–Zn(–Cu) deposit, Bulgaria. Relvas et al.
(2006) have recently quoted the presence of hydrothermal
smithsonite (120–145°C based on oxygen isotopes) in the
late alteration stages of the Neves-Corvo deposit in Portugal.
One of us (CRA) has seen mylonitized, stylolitic smithsonite
replacing Jurassic/Cretaceous limestone in the Orecks zinc
prospect, Kayseri district, central Turkey, a district dominated
by supergene smithsonite. This smithsonite-calcite assem-
blage has every textural indication of being a hypogene ore
type along a late thrust fault. However, other Angouran-type
nonsulfide deposits have not been described from elsewhere
so far, not even among the “hypogene”nonsulfide ores
mentioned by Hitzman et al. (2003).
Origin of stage II carbonate ore
Compared to the economic stage I carbonate ores, the stage
II carbonate ores are much less voluminous. The sulfide ores
at depth are shielded by the stage 1 carbonate ores from
oxidation by infiltrating surface waters, and the trace amount
of sulfides within stage 1 carbonate ore is not sufficient to
produce a significant supergene oxidation zone. The miner-
alization stage that is unambiguously related to supergene
weathering at Angouran is evidenced by a paragenesis
mainly containing hemimorphite, smithsonite II, Fe-Mn-
oxides, and Pb-Ca-arsenates occurring near the surface,
where even traces of sulfides are now absent. The C–O
isotope signatures (constant O isotope values and variable
and light C isotope values) of smithsonite II and cerussite are
quite characteristic for supergene carbonate minerals precip-
itated in oxidation zones (Gilg and Boni 2004a,b; Gilg et al.
2007) and distinct from stage I carbonate ores. The low but
variable C isotope values of the supergene smithsonite and
cerussite suggest mixing of heavy carbon derived from the
wall rocks with some minor contribution of organic soil-
derived or microbially derived carbon, a process also reported
for supergene smithsonite deposited in Sardinia, Belgium,
and Namibia (Gilg et al. 2007). We calculate temperatures of
smithsonite II precipitation at about 15–20°C from their
oxygen isotope data using the present-day local meteoric
water isotope values and the smithsonite–water oxygen
isotope fractionation equations of Gilg et al. (2007). These
calculated temperatures are compatible with the average
day temperatures in the area during the summer but clearly
higher than the temperatures of the local cold springs.
Conclusions
The formation of the large, high-grade Angouran non-
sulfide Zn deposit occurred during two successive stages.
Miner Deposita

During the first and more significant stage, the circulation
of CO
2
-rich hydrothermal fluids, possibly driven by the
waning phases of volcanic activity in the Takab district,
caused the deposition of a large amount of Zn carbonate ore
(stage I carbonate ore), coexisting with and partly replacing
a body of associated, primary sulfides. This could be
defined as a massive carbonatization process of a sulfide
orebody caused by carbonic hydrothermal fluids. We
consider the age of hypogene sulfide–carbonate mineral-
ization at Angouran (stage I carbonates) to be very young
(possibly Pleistocene) due to the strict relationship between
this mineralization phase and the Angouran metal-enriched
travertines, which do not show any evidence of tilting or
strong erosion. The very distinct main and trace element
budget of the primary sulfides compared to the sulfide–
carbonate ores suggests an external origin of some elements
(As, Sb, and Cu) during the deposition of stage I non-
sulfides. Among these, arsenic is the most important one,
being abundant in stage I nonsulfides (>6,000 ppm As in
the carbonate ore) in the form of arsenopyrite. Arsenic is
also present in the Takab travertines (115–258 ppm As) and
in several hot springs throughout the region (1.62% As in
the bottom sediments of the Taxt-e Soleiman lake,
Naumann 1961). This proofs a regional-scale circulation
of hydrothermal fluids.
During a minor weathering phase (?Holocene), the
sulfide-bearing stage I carbonate ores were partly oxidized,
resulting in the deposition of small amounts of newly
formed Zn carbonates, silicates, and arsenates derived from
arsenopyrite oxidation (oxide-carbonate ore). The bulk of
primary sulfide ores were at that time not outcropping at the
surface; they were sheltered from supergene oxidation by
the massive cap of hypogene Zn carbonates.
Oxygen, carbon, and strontium isotope data constrain the
temperature and origin of the fluids responsible for the two
Zn carbonate ore stages. The formation temperatures of
stage I smithsonite were higher than the ambient temper-
ature. The very heavy carbon isotope compositions of stage I
smithsonite are similar to those of some of the hot-spring
travertines in the Takab region. We interpret these heavy C
isotope compositions as product of very high temperature
(>500°C) decarbonatization (which might be related to
contact metamorphism) and low-temperature deposition
(<100°C; see Pentecost 2005). The paucity of isotopically
light carbon, even in the stage II smithsonite (weathering), is
indirect evidence for the absence of a significant vegetation
cover at Angouran, because it is the organic matter from the
soils that is usually controlling the highly variable carbon
isotope distribution in supergene nonsulfide deposits (Gilg
et al. 2007). Supergene stage II smithsonite formed from
very light meteoric waters (−10 permil) at T<25°C,
consistent with the high elevation of the deposit in relatively
recent times.
The results of our study open new insights in the genesis
of nonsulfide deposits because they advocate a hypogene
origin for most Zn carbonate ores that are currently mined
at Angouran, a presently unique process, although probably
not an isolated instance. It must be kept in mind, however,
that nonsulfide ores belonging to both mineralization stages
in Angouran have generally lower ore grades than primary
sulfide ores (Table 1), implying an overall dispersion of Zn
during the carbonatization process. Nevertheless, owing to
their still high metal grades (>25% Zn) and tonnages,
Angouran-type nonsulfide ores would represent without
doubt a most desirable exploration target, especially if cheap
extraction techniques could be applied. New deposits of this
type could well be encountered in other Middle East volcanic
areas of recent uplift, where carbonate-hosted primary Zn-
rich sulfide orebodies may have been in contact with a
travertine-style hydrothermal activity.
Acknowledgements Thanks are due to M. Sadeghi (Shiraz
University) for collecting part of the samples and to A.E. Annels
and M. Pittuck (SRK) for providing carbonate samples from the
mining district. We thank also R. Mohammadi Niaei (IZMDC) and
S. Modabberi for help during fieldwork. We are indebted to
F. Daliran (Karlsruhe University, Germany) and G. Borg (Halle
University, Germany) for fruitful discussions. We acknowledge the
help of U. Struck (LMU, Munich, Germany) and W. Stichler (GSF,
Neuherberg, Germany) in measuring isotope compositions of
carbonate and water samples, respectively. J. Cleverley (JCU,
Townsville, Australia) kindly provided a revised version of his
Thermo2000 database. This study was partly financed by funds of
Università di Napoli to GB and MB.
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