Geological, geochemical, and fluid inclusion evidences for the origin of the Ravanj Pb–Ba–Ag deposit, north of Delijan city, Markazi Province, Iran

The Lower Cretaceous sequences of the Ravanj anticline in Iran host the Ravanj Pb–Ba–Ag mineralization. Economic orebodies are restricted to the thrust zone within the brecciated massive limestone and immediately above the Jurassic shale and/or shale–limestone intercalations of the Lower Cretaceous.

http://journals.tubitak.gov.tr/earth/ (2016) 25: 179-200

© TÜBİTAKdoi:10.3906/yer-1501-26

Geological, geochemical, and fluid inclusion evidences for the origin of the Ravanj

Pb–Ba–Ag deposit, north of Delijan city, Markazi Province, IranMostafa NEJADHADAD 1 , Batoul TAGHIPOUR 1, *, Alireza ZARASVANDI 2 ,

Alireza KARIMZADEH SOMARIN 3

1 Department of Earth Sciences, Faculty of Sciences, Shiraz University, Shiraz, Iran

2 Department of Geology, Faculty of Earth Sciences, Shahid Chamran University (SCU), Ahvaz, Iran

3 Department of Geology, Faculty of Sciences, Brandon University, Manitoba, Canada

1 Introduction

Sandstone and carbonate hosted Pb-rich deposits, with Zn/

(Zn+Pb) < 1, are an unusual end member of MVT deposits

(Sverjensky, 1984a; Leach et al., 2005) Correlation of metal

ratio with lithology is reported by Gustafson and Williams

(1981) Sverjensky (1984a) has proposed that different

rates of water–rock interaction in sandstone and carbonate

aquifers could form galena- and sphalerite-rich deposits

from single basinal brine In this model, low Zn/Pb ratio

deposits are associated with sandstone aquifer, while

high Zn/Pb ratio deposits occur in carbonate aquifers

The basinal brine model (Sverjensky, 1984a) specifically

explains mineral paragenesis and the Zn/Pb ratio of MVT

deposits Some investigations on the Viburnum Trend

deposits, USA, show that Pb-rich ores were deposited as

a result of fluid mixing Mixing of a metal-rich and H2

S-poor (or sulfate-rich) brine with another less saline, H2rich fluid (or organic and methane bearing) better explains

S-Pb mineralization in this area (Rowan and Leach, 1989; Anderson, 1991; Plumlee et al., 1994) An anomalous Pb-rich fluid reported by Appold and Wenz, (2011) in sphalerite hosted fluid inclusions showed that one of the aforementioned fluids was enriched in Pb

The well-known episode of Pb–Zn mineralization

in Iran took place in the Cretaceous carbonate rocks, including well-known world-class MVT deposits such as Emarat, Mehdi Abad, and Irankuh (Rajabi et al., 2012) Dixon and Pereira (1974) suggested that these deposits range from sedimentary exhalative (SEDEX) to MVT, but most of these deposits are characterized by carbonate host rock and are classified as MVT (Lisenbee and Uzunlar, 1988; Ghazban et al., 1994; Ehya et al., 2010) The Ravanj

Abstract: The Lower Cretaceous sequences of the Ravanj anticline in Iran host the Ravanj Pb–Ba–Ag mineralization Economic

orebodies are restricted to the thrust zone within the brecciated massive limestone and immediately above the Jurassic shale and/or shale–limestone intercalations of the Lower Cretaceous Paragenetic sequence and distinct zoning of mineral assemblages indicate that ore-forming fluid migrated through thrust zones along the NE-trending faults The REE pattern of mineralized host rock is characterized

by HREE-enrichment ((La/Lu)PAAS = 0.24) The Ce/Ce* ratio of mineralized host samples shows negative Ce anomalies, which is most likely inherited from seawater The positive Eu/Eu* anomaly suggests high ƒO 2 during ore deposition Negative δ 34 S values of the Ravanj sulfide minerals (–27‰ to –11‰) suggest bacteriogenic sulfate reduction, whereas positive δ 34 S values of barite (+20‰) fall

in the range of Tertiary marine sulfates Multiple isotopic sulfur sources of sulfides and sulfate minerals support mixing of a reduced negative isotopic sulfur-bearing fluid and a positive isotopic sulfate-bearing fluid The average of homogenization temperatures of fluid inclusions from the early and late-stage mineralization calcites are 165 and 160 °C, respectively The salinity of fluid inclusions varies between 0.66 and 18 wt% NaCl equivalent with an outlier at 22.2 Wide variation in the salinity of fluid inclusions can be explained

by fluid mixing between a higher salinity group with 14–18 wt% NaCl equivalent and a lower salinity group with 0.66–8 wt% NaCl equivalent In the Ravanj, fine grained sulfide minerals are consistent with a sulfur supersaturated fluid High concentrations of Pb can

be present in oxidized, chlorine-bearing fluids if the concentration of total H 2 S is very low Therefore, mixing of two geochemically different fluids could precipitate both galena and barite These data show that the Ravanj Pb–Ba–Ag deposit is comparable with Pb-rich Mississippi Valley-type deposits such as the Viburnum Trend district in the USA.

Key words: Ravanj Pb–Ba–Ag deposit, rare earth elements, multiple isotopic sulfur sources, microthermometry, fluid mixing

Received: 27.01.2015 Accepted/Published Online: 28.09.2015 Final Version: 08.02.2015

Research Article

Pb–Ba–Ag deposit is located 20 km north of Delijan

(Figure 1a) in the Urumieh–Dokhtar magmatic belt

(Figure 1b) Ore mineralization is found in 7 separated

and/or partially attached pockets and lens-like orebodies

(Figure 1c) The Ravanj deposit has been in operation for

40 years and total extracted ore is estimated to be about 4

million metric tons (Mt) at 2.5% Pb cutoff grade (Samani

et al., 2010) There are two hypotheses regarding the origin

of the Ravanj deposit:

• Based on geology, semiconcordant to concordant

morphology of orebodies, mineralogy, and ore textures,

Modabberi (1995) suggested an early diagenetic origin

for the Ravanj deposit In his model, the economic

metals were probably derived from continental

weathering or distal volcanism and then deposited

due to reaction with bacterial reduced sulfur in the

progressive carbonate facies of tidal flats

• In another study, based on host rock type, ore textures,

and ore mineralogy, Aliabadi (2000) suggested that

deposition of low-grade metal-bearing sediment

was followed by subsequent remobilization and

concentration of the metals by circulation of connate

and meteoric waters (MVT model)

Although general geology and ore mineralogy of the

Ravanj Pb–Ba–Ag deposit have been studied and generally

are known, the source of metals and fluids and mechanism

of the mineralization are controversial This study covers

rare earth elements geochemistry of country shale, host

rock, and ore samples to gain a better understanding of

the source of metals In addition, sulfur isotope data

and microthermometric investigations are carried out

in order to understand the source of sulfur and possible

mechanisms of ore precipitation

2 Geological setting

The Ravanj Pb–Ba–Ag deposit is located in the Zagros

orogenic belt in western Iran From northeast to southwest

of Iran, this belt is subdivided into three parallel belts

including the Urumieh–Dokhtar magmatic arc (UDMA),

the Sanandaj–Sirjan metamorphosed zone (SSZ), and the

Zagros folded-thrust belt (Alavi, 1994; Golonka, 2004)

The southern boundary of SSZ with the Zagros

folded-thrust belt is clearly visible but the northern boundary

with the UDMA is not obvious in Central Iran due to the

extensive coverage of Tertiary rocks, lateral facies changes,

and complex deformation The main differences between

the SSZ and UDMA are age and intensity of the magmatic

events; the SSZ and UDMA are characterized by intense

magmatic events of Mesozoic and Cenozoic, respectively

(Berberian and King, 1981)

The Ravanj Pb–Ba–Ag deposit is hosted by the Lower

Cretaceous strata that are exposed in the core of the Ravanj

anticline in the UDMA (Emami, 1996) The Cretaceous

units start with disconformable terrigenous sediments consisting of a basal conglomerate, upper quartzose sandstone, and bedded cream sandy dolomite These strata (Cd strata in Figure 1c) show maximum thickness of about

50 m The Lower Cretaceous strata overlays the Jurassic strata of the Shemshak formation (J.Sh) The latter consists

of dark gray laminated shales with interbeds of rich sandstone Shale layers are composed of clay, sericite, and quartz These types of progradation from Jurassic

quartz-to Lower Cretaceous rocks are also reported in other deposits in the region such as Emarat (Ehya et al., 2010) and Anjireh-Vejin (Lisenbee and Uzunlar, 1988) Bedded Orbitolina limestone with minor shale and mudstone overlays conformably the progressive Cd strata The shale content of bedded Orbitolina limestone increases upwards and grades into shale The thickness of the shale-bearing limestone sequence (Ksb) is about 250 m Minor Pb–Ba mineralization locally occurs in the Ksb strata The economic ore zone (5 – 30 m thick) is hosted by a massive to thick-bedded Rudist-bearing limestone (Km2),

up to 130 m thick The orebodies occur above the thrust contact of the Jurassic shale/shale-limestone and massive limestone There is a sharp contact between mineralized and unmineralized zones in the NW part of the deposit whereas mineralization splays towards the SE region It appears that mineralization was controlled by NE–SW trend faults These normal faults dip ~60° to the SE and crosscut the host rock and thrust faults The host rock carbonates alternate with two shale-bearing strata The Km2 is conformably overlain by Albian shale (U.Sh) The Lower Cretaceous units are unconformably superimposed

by a succession of Eocene conglomerate, shale, marl, tuff (E.5), volcaniclastic rocks (E.6), Oligocene conglomerate, shale, sandstone and gypsum (Lower Red Formation, L.R), and the Oligo-Miocene marl and limestone of the Qom formation (Qm) Post-lower Miocene granodiorite (Gd) stocks and dykes (Dy) intrude along NW–SE normal faults and also cut all strata from the Jurassic shale to the Qom formation These post-mineralization younger dykes (Figure 1c) also cut orebodies Pyrite is the only opaque mineral in these dykes Post-Cretaceous rocks do not show any evidence of Pb mineralization; however, an Fe deposit (e.g., Sarvian magnetite deposit in northeast part

of Ravanj Anticline) occurs in the Eocene volcanic rocks Cross cutting relationships indicate that these post-lower Miocene granodiorite (Gd) stocks and dykes were injected after Pb–Ba mineralization and seemingly played no distinct role in the Ravanj Pb–Ba mineralization

3 Methodology

Representative samples were collected from the open pit parts of A, Bw, Cn, and Cs, and from A and Bs tunnels (Figure 1c) Detailed mineralogical studies were performed

Gd

Dy

Alluvium Dyke (mainly acidic) Granodiorite, Diorite (Post L Miocene)

Limestone and Marl (Qom F)

Conglomerate, Sandstone, Gypsum (L.Red F)

Volcanic rocks Conglomerate, Shale, Tuff, Sandstone Shale with Limestone intercalations Massive Limestone, bedded in upper part Bedded Limestone, Shale with thin bedded limestone Conglomerate, Sandstone,Dolomite

Cs

0 125 250

City Mine

Cd

Hamadanan Tehran

Figure 1 a) Simplified map showing location of the Ravanj deposit in Iran b) Other Pb–Zn deposits in region

(modified after Alavi, 1997) c) Geological map of the Ravanj anticline (modified after Modabberi, 1995) UDMA:

Urumieh-Dokhtar magmatic arc, SSZ: Sanandaj-Sirjan zone, ZFB: Zagros Folded belt

on 67 polished thin sections Thirty samples were selected

from the A and Bs orebodies for geochemical studies of

major and minor elements of host rocks These samples

were analyzed by inductively coupled plasma-mass

spectrometer (ICP-MS) method under high temperature,

hydrofluoric acid digestion of a 0.25 g split giving total to

near total values for all elements at LabWest in Australia

Detection limits of major and trace elements are 0.01

wt.% and 0.02–1 ppm, respectively (Table 1) Six samples

of Jurassic shale and unmineralized and mineralized limestone were analyzed for REE content Samples were dried at 110 °C, crushed to less than 2 mm, and pulverized

to –75 µm and analyzed using ICP-MS following acid digestion of a 0.25 g split giving total to near total values for rare earth elements at LabWest (Table 2) The REE detection limit varies between 0.1 and 0.01 ppm Five sulfide samples of main stage (2 samples) and late-stage galena (1 sample), colloform (1 sample), and main stage pyrite (1 sample), and three barite samples from Cs orebody were handpicked under a binocular microscope and analyzed for their isotope sulfur composition Analyses were carried out at Washington State University

multi-in the US, usmulti-ing a contmulti-inuous flow isotope ratio mass spectrometer (IRMS) Sulfur isotopic ratio is reported

in ‰ relative to Vienna Canon Diablo Troilite (VCDT)

by assigning a value of –0.3‰ to IAEA S1 silver sulfide (Table 3) Homogenizations, first and last ice melting temperatures, and clathrate temperature of 101 fluid inclusions were measured using a Linkam THMS600 Heating and Freezing Stage with a temperature range

of –196 to +600 °C, at the University of Lorestan, Iran Final ice melting temperatures and homogenization temperatures, respectively, were measured with a precision

of ±0.2 °C and ±0.1 °C (Table 4)

4 Results 4.1 Ore and gangue zoning

At Ravanj, galena and barite show zoning from lower

to upper parts of all orebodies Sphalerite and pyrite are also found in the Cs (southern part of C) orebody The southwestern part of the Cs orebody is highly pyritized and is characterized by a Zn/(Zn+Pb) ratio greater than 0.3 Toward the outside of the orebody, galena and barite increase Gradually towards the southeast part, barite increases, Zn decreases, and the Zn/(Zn+Pb) ratio reaches lower than 0.1 (Figure 2) Similar metal zoning

in carbonate hosted MVT deposits has been described

in other districts such as Pine Point, Southeast Missouri, and Irish Midland deposits (Leach et al., 2005) From bottom to top of the orebodies, ore grade decreases (Figure 3), whereas barite and calcite content increase Minor dolomite mineralization occurs outward from the orebodies where ore grade is low

This type of mineralization could be consistent with the direction of the fluid flow path Metal zoning in the Ravanj Pb–Ba–Ag deposit provides the opportunity to correlate the mineral paragenesis with metal zoning

4.2 Mineralization

Stratabound and lens-shape orebodies occur semiconcordant to concordant at the stratigraphic base of the massive limestone (Km2) at the tectonic contact with

Table 2 REE concentrations (in ppm) of the Jurassic shale (S1,

S2), mineralized (S3–S5), and unmineralized rock (S6).

S1 Barite 474722, 3781530 20.67 Main stage barite

S2 Galena 474773, 3781540 –23.38 Late-stage galena

S3 Barite 475043, 3781491 20.92 Main stage barite

S4 Galena 474911, 3781463 –27.32 Main stage galena

S5 Barite 474978, 3781619 20.35 Main stage barite

S6 Galena 475041, 3781398 –25.56 Main stage galena

S7 Pyrite 474830, 3781507 –11.88 Main stage pyrite

S8 Pyrite 474980, 3781800 –14.21 Colloform pyrite

shale The breccias and replacement ore are localized by

thrust and normal faulting (Figure 4a) Minor ore is also

deposited in the lower shale and in thin carbonate layers

Sulfide textures are mostly consistent with open-space

filling (Figure 4b) of breccias (Figure 4c) and fractures

as massive aggregates of anhedral grains as well as replacement and disseminated grains Both hydrothermal (Figure 4d) and fault breccias (Figure 4e) exist, but the carbonate host solution is more important Ore-matrix breccia include fragments of the host carbonate rocks

Host mineral Inclusion type T m , carb T m , clath (°C) T e (°C) T m , ice (°C) T h (°C) Salinity (wt% NaCl equiv.) N

T m , carb: first CO 2 melting; T m , clath: last clathrate melting; T h , CO 2 : melting temperature of CO 2 phase; T e : first ice melting; T m , ice: last ice melting;

T h , total: total homogenization; T h : homogenization to liquid; T s , NaCl: halite dissolution; N: number of measurements.

475450

Mineralized drilling(from old to recent) Unmineralized drilling(from old to recent) Thrust

Other faults than thrust Mineralized limestone Pond

Post Miocene intermediate dyke Lower Cretaceous upper shale Lower Cretaceous massive limestone Lower Cretaceous thin bedded limestone and shale

Csw-03

Csw-09

Figure 2 Geological map of the Cs and Bw orebodies.

supported by a matrix of host rock fragments, calcite,

barite, and fine sulfide grained minerals (Figure 4f) In

veins and open spaces galena and barite are deposited

contemporaneously (Figure 4g) Calcite (Figure 4h) and

pyrite (Figure 4i) veins are abundant

There is no evidence of syngenetic ore deposition The

ore has simple mineralogy The following primary ore

minerals were identified: galena and pyrite as major ore

minerals, and sphalerite, tetrahedrite, and chalcopyrite

as accessory ore minerals Calcite, barite, dolomite, and

quartz are gangue minerals Supergene minerals include

cerussite, Fe-oxides, smithsonite, covellite, malachite, and

azurite

Galena: Galena is the main ore mineral It occurs as

anhedral disseminated grains (0.1–0.6 mm) and open

space filling (1–5 mm) It seems that galena was deposited

in the early, main, and late stages of mineralization

Early stage galena is paragenetically associated with

tetrahedrite and shows intergrowth texture Galena at the

main stage contains inclusions of sphalerite (Figure 5a),

tetrahedrite (Figure 5b), and pyrite These two stages of

galena mineralization were separated from each other by

pyrite type III and stage 1 sphalerite mineralization that occurred after the early stage of galena and shows a hiatus between galena mineralization stages A similar hiatus between galena mineralization stages during which bladed marcasite was precipitated is reported in the Viburnum Trend in SE Missouri (Mavrogenes et al., 1992) Finally, during the late stage, rare inclusion-free galena, up to 5

mm in size, was deposited with calcite and dolomite in open spaces (Figure 5c)

Pyrite: Four types of pyrite are distinguished Type I:

Spherules and framboidal fine-grained pyrite This type occurs as inclusions and partially engulfed aggregates in galena, unmineralized limestone, and in the lower organic-rich shale layers Framboidal pyrites associated with the ore are considered to be indicators of biogenic activity (Love, 1962; Mavrogenes et al., 1992; Kucha et al., 2010) Type II: Colloform pyrite, 0.2 to 2 mm in size (Figure 5d), formed after framboidal pyrite It is found with minor barite in host rocks Carbonate and barite relicts are found within colloform pyrite Colloform texture of pyrite is a function of the saturation rate of iron and sulfur in fluid,

45 –47 –49 –51 –45

–33 –35 –37 –39 –41 –43

–19 –21 –23 –25 –27 –29 –31

–3 –5 –7 –9 –11 –13 –15 –17

2 High grade ore Low grade ore

m

Shale

Massive limestonem

DDH–Csw09

–1

45 –47 –49 –51.7 –45

–33 –35 –37 –39 –41 –43

–19 –21 –23 –25 –27 –29 –31

–3 –5 –7 –9 –11 –13 –15 –17

2 Medium grade ore Low grade ore

Shale

Massive limestone

%Pb

%Pb Figure 3 Strip logs of two drill holes (Csw03 and Csw09) Locations of drillholes are shown in

Figure 2.

and indicates rapid crystallization from a supersaturated

ore fluid (Anderson, 2008; Anderson and Thom,

2008) Colloform pyrite was deposited after host rock

sparitization and minor barite deposition, but framboidal

pyrite was deposited as early diagenetic mineral Type III:

Most of pyrite at Ravanj is type III It occurs as euhedral

or aggregates, veins, and veinlets (Figure 5e) These

veins are composed of pyrite with or without galena and

barite Pyrite veins crosscut type I and II pyrite, stage 1

galena, barite, and main-stage calcite Type IV: Anhedral

to subhedral disseminated pyrite associated with open

space filling calcite This uncommon pyrite accompanies

late-stage galena and represents the final stage of sulfide

mineralization Absence of marcasite suggests that the

ore-forming solution had a pH of higher than 5 (Stanton and

Goldhaber, 1991)

Sphalerite: Paragenetically, sphalerite formed earlier

than main-stage galena Dark green to black sphalerite occurs as fine disseminated anhedral grains and rarely intergrowth with galena (Figure 5f)

Fahlore group: Fahlore minerals are distributed

randomly and usually occur as inclusions in galena They rarely show intergrowth textures with galena or engulfed sphalerite

Chalcopyrite: Rare chalcopyrite occurs as anhedral

blebs in galena It is deposited before and during galena deposition

Calcite: Calcite precipitation has taken place in 3

stages First, calcitization occurred as micrite replacement

by sparite, which predated sulfide mineralization Large calcite crystals (up to 1 cm, Figure 5g) and veinlets formed during the second stage This calcite occurred before

H

C3

C2

Gn Py

h

Py Ca

Figure 4 a) Cretaceous massive limestone (Km2) thrusted over the Jurassic shale (J.sh) b) Mineralized brecciated massive

limestone c) Galena (Gn) and barite (Ba) deposited as open space filling of the breccia zone d) Open space filling ore and gangue minerals Rhythmic mineral deposition includes galena, pyrite, and calcite e) Rhythmic fracture-filling galena (Gn) and calcite (Ca) f) Late-stage disseminated galena in the brecciated host rock cemented by dolomite (Do) and late-stage calcite (C3) g) Barite and galena intergrowth in the Cn orebody h) Late-stage calcite (C3) crosscutting pre-main stage calcite (C2) in a low grade ore sample i) Vein type pyrite (Py) in black massive limestone

the main stage galena because they show evidence of

dissolution and replacement by main-stage galena (Figure

5h) Finally, fractures and dissolution cavities were filled

with post-mineralization stage calcite

Barite: Dispersed platy and prismatic crystals,

bundles, and stellate aggregates of barite, as a few mm to

cm in length, are ubiquitous in open spaces and vugs of

host rocks Where barite is a main gangue mineral, ore

minerals are generally disseminated among barite grains

Most barite mineralization occurred during and after

main-stage galena mineralization (Figure 5i)

Dolomite: Dolomite occurs as a minor gangue mineral

formed during pre-main and late-stage mineralization

Quartz: Trace amount of anhedral to euhedral

fine-grained quartz (smaller than 50 microns) are found in dolomite as well as open spaces It is generally surrounded

by galena

Secondary minerals: At Ravanj, oxidation processes

caused formation of Fe-oxyhydroxides, cerussite, smithsonite, covellite, malachite, and azurite Oxidation of sulfide minerals in near-surface condition in most Iranian Pb–Zn deposits could be due to the arid climate and a low water table (Reichert and Borg, 2008) A summary of mineralization paragenesis in the Ravanj deposit is shown

Figure 5 a) Rhythmic deposition of sphalerite and galena Stage 2 sphalerite (Sph2) coated stage 1 galena (Gn1) containing

sphalerite inclusion Main stage galena engulfed the whole set b) Sphalerite engulfed by tetrahedrite hosted by galena c) stage galena without sulfide mineral inclusion d) Colloform pyrite associated with calcite and barite Note the replacement of calcite and barite by colloform pyrite e) Pyrite engulfed by galena and both are in bitumen matrix between calcite grains f) Sphalerite intergrowth with galena engulfed pyrite g) Stained thin section with alizarin red-S from mineralized host rock of the

Late-Cs orebody, h) Galena filling space between calcite grains in mineralized rock Note the dissolution and replacement of calcite i) Fan-like texture of barite H: Host rock, Ca: Calcite, Ba: Barite, B: Bitumen, Do: Dolomite, Py: Pyrite, Gn: Galena, Sp: Sphalerite, T: Tetrahedrite b–h under the PPL and the rest under CPL.

(average 0.6%), suggesting that extensive dolomitization

did not take place The Ag content of whole rock samples

ranges from <2 ppm to 576 ppm, with an average of 80

ppm Ag shows a moderate positive correlation with Pb

(r = 0.52) and a strong positive correlation with Sb (r =

0.95) in all samples (Table 5a; Figure 7a) Ag in low grade

samples (Ag <53 ppm) shows a higher correlation with Pb

(r = 0.66) and a lower correlation with Sb (r = 0.36) (Table

5b; Figure 7c) It is notable that in high grade samples (Ag

>53 ppm), Ag–Pb correlation decreases to 0.22 and Sb–Ag

correlation increases to 0.97 (Table 5c; Figure 7d)

Total rare earth elements concentration (∑REE) of

the Jurassic shale ranges from 197.3 to 200.6 ppm It is

comparable with the ∑REE content of the PAAS (Post

Archean Australian Shale, 184.69 ppm; McLennan, 1989)

∑REE values of unmineralized carbonate host rock are

very low and fall within the narrow range of 2.49 to 2.95

ppm ∑REE in mineralized samples (13.03–29.68 ppm)

is higher than that in the unmineralized host rocks (2.39

ppm) The PAAS-normalized REE pattern of the studied

samples is shown in Figure 8 REE patterns of the Jurassic

shale samples show a fractionation of the MREEs [negative

(Lu/Ho)PAAS = 0.69–0.74] Moreover, the Jurassic shale

exhibits a positive (La/Lu)PAAS anomaly [(La/Lu)PAAS =

1.5–2.3] Mineralized samples have a negative (La/Lu)

PAAS anomaly [(La/Lu)PAAS = 0.22–0.25] (Figure 8a) A

positive Eu anomaly (Eu/Eu* = 2.01–2.40) is seen in

both mineralized and unmineralized carbonate samples

(Figure 8b) Mineralized samples display a low negative

Ce anomaly (Ce/Ce* = 0.73–0.9), while unmineralized

samples (Ce/Ce* = 0.98) do not show such a negative

anomaly (Figure 8c) Another notable characteristic of the

REE patterns includes (La/Sm)PAAS values <1, except for

unmineralized host rock samples

δ34S values of galena, pyrite, and barite samples from the Cs orebody in the Ravanj deposit show a wide range (Figure 9) This value in sulfide minerals ranges from –27.32‰ to –11.88‰ and in barite samples from 20.35‰

to 20.92‰ The δ34S values in galena vary between –27.32‰ and –23.38‰; these values in pyrite range from –14.21‰ to –11.88‰

4.4 Microthermometry

Fluid inclusion samples were collected from calcite and barite of the Cs orebodies Sphalerite was not suitable for microthermometric studies due to its small grain size and dark color Suitable fluid inclusions are found

in three types of gangue minerals: 1) stage 2 calcite (C2, Figure 10a) that was deposited before main-stage galena Microthermometric measurements were done on two (Figure 10b) and three phase inclusions (Figure 10c)

of this type of calcite 2) late-stage calcite (C3) that was deposited after main-stage galena (Figure 10d) 3) barite that was deposited during and after main-stage galena (Figures 10e and 10f)

Double polished sections were prepared using the procedure of Shepherd et al (1985) with a maximum thickness of about 100 um The studied fluid inclusions consist of a liquid and vapor phase (2–25 µm in size); these are the most common group of inclusions The liquid/vapor ratio (0.75–90) is almost constant in these inclusions Less common monophase liquid (L) and three phase (H2OL

+ CO2L+ CO2V) types were also found It appears that monophase inclusions are secondary in origin The criteria

of Roedder (1984) are used to determine the primary origin of the fluid inclusions

The first melting temperature of two phase inclusions (Te) varies from –59.8 to –37.2 °C, indicating the