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.
Turkish Journal of Earth Sciences http://journals.tubitak.gov.tr/earth/ Research Article Turkish J Earth Sci (2016) 25: 179-200 © TÜBİTAK doi: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, Iran Mostafa NEJADHADAD1, Batoul TAGHIPOUR1,*, Alireza ZARASVANDI2, Alireza KARIMZADEH SOMARIN3 1Department of Earth Sciences, Faculty of Sciences, Shiraz University, Shiraz, Iran 2Department of Geology, Faculty of Earth Sciences, Shahid Chamran University (SCU), Ahvaz, Iran 3Department of Geology, Faculty of Sciences, Brandon University, Manitoba, Canada Received: 27.01.2015 Accepted/Published Online: 28.09.2015 Final Version: 08.02.2015 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 ƒO2 during ore deposition Negative δ34S values of the Ravanj sulfide minerals (–27‰ to –11‰) suggest bacteriogenic sulfate reduction, whereas positive δ34S 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 H2S 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 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 H2S* Correspondence: taghipour@shirazu.ac.ir poor (or sulfate-rich) brine with another less saline, H2Srich fluid (or organic and methane bearing) better explains 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 179 NEJADHADAD et al / Turkish J Earth Sci 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 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 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 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 foldedthrust 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 180 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 quartzrich sandstone Shale layers are composed of clay, sericite, and quartz These types of progradation from Jurassic 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 shalebearing 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 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 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 NEJADHADAD et al / Turkish J Earth Sci 49 00 Tehran Hamadanan Tehran oghre Isfahan -Vejin 50 00 Gd 476000 E.6 3782500 Km2 E.5 Sh Km2 s A Cd Ksb Ksb Km2 Km2 Ksb U.s 3781500 h L.R Qm Sh Cs 475000 L Cretaceous Eocene Oligocene Jurassic Qm L.R E.6 E.5 U.sh Km2 Ksb Cd Sh E.6 E.5 Ksb Bn Bw D Bs Ksb Al Km2 476000 Al Dy Limestone and Marl (Qom F) Conglomerate, Sandstone, Gypsum (L.Red F) Gd Volcanic rocks Alluvium Dyke (mainly acidic) Granodiorite, Diorite (Post L Miocene) Normal Fault Conglomerate, Shale, Tuff, Sandstone Thrust Shale with Limestone intercalations Anticline axe Massive Limestone, bedded in upper part Bedded Limestone, Shale with thin bedded limestone Conglomerate, Sandstone,Dolomite Dark gray Shale with sandsone intercalation h Km2 Cd Cn Km2 L.Miocene U 3782500 f ul 31 00 G A M UD Z B n City Irankuh SS ZF Mine ia rs Km2 Delijan Anjire 1c 475000 t Dare N DA Pe N Ravanj UM Z B ZF SS Arak Emara Iran Dare Noghre Central Iran 3781500 Ravanj 53 00 35 00 1a 1b Caspian Cs Orebody sampling location 125 250 N Figure 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 181 182 3686 0.04 0.43 71.3 146.9 9.38 0.52 41.32 16 199 5.47 20 10.1 72.5 9368 Mg % Ag As Ba % Bi Cd Co Cu Fe % Ni Pb % Sb Zn Zn/(Zn + Pb) 0.08 48.1 8.85 0.22 120 30.13 0.3 15.24 7.7 44.7 0.32 24.5 23.3 Ca % BST-46 BST-204 Element 0.06 679 19.5 1.02 0.76 68 6.6 0.35 3.41 24.1 1.79 0.27 33.9 BST-121 0.18 13205 61.5 6.1 0.87 157 68.25 0.35 13.5 35.8 59.8 0.51 34.6 BST-72 0.01 340 41.8 3.74 0.83 351 0.55 0.42 1.8 21.9 31.41 1.38 36.4 AT -28 0.06 6374 178.7 10.6 0.95 222 40.63 0.32 2.33 35.1 229.5 0.65 29.8 BST-110 0.02 1591 150.9 9.72 0.88 165 31.08 0.29 10.58 40.4 175.5 0.2 30.2 BST-73 0.04 4204 63.5 10.09 0.36 252 12 9.06 0.45 10.04 104.7 113.9 0.15 27.8 BST-22 0.04 4416 46 9.93 0.47 117 30.14 0.21 3.64 9.9 51.6 0.19 32.9 BST-17 0.04 3738 358 9.8 0.55 139 38.98 0.27 14 51.2 408.6 0.27 26.7 BST-85 0.05 1906 23.6 3.47 1.06 161 8.59 0.35 12.73 36.6 13.4 0.3 35.7 BST-124 0.01 1484 121 12.24 10 1.98 710 10 14.93 0.37 6.12 131.6 63.7 0.15 29.8 BST-201 0.06 1242 56.5 1.81 1.81 544 12 11.47 0.35 1.83 161.9 9.1 0.37 36.4 BST-58 0.03 1712 36.6 6.07 21 4.2 424 15 11.36 0.59 5.28 167.1 21.9 0.15 30.7 BST-63 0.24 32025 390.2 10.01 0.57 174 192.69 0.3 5.64 44.7 576.1 0.23 30 BST-78 Table Chemical composition of mineralized whole rock of the Ravanj deposit Ca, Mg, Ba, Fe, and Pb are in % and other elements are in ppm Samples with numbers starting with BST and AT are from BS and A tunnel, respectively n = 30 NEJADHADAD et al / Turkish J Earth Sci AT-17 33.1 0.87 17.31 19.3 2.11 0.41 0.38 896 0.24 2.39 71.84 295 0.01 Element Ca % Mg % Ag As Ba % Bi Cd Co Cu Fe % Ni Pb % Sb Zn Zn/(Zn + Pb) Table (Continued) 153 118.98 3.08 0.61 784 0.33 0.44 6.27 36.2 33.56 1.81 33 AT-19 0.02 1509 25.8 6.49 18 2.84 205 13 6.03 0.41 9.22 100.2 19.5 0.24 35 BST-60 0.03 2367 52 7.82 1.29 283 13.25 0.35 4.86 46.3 46.1 0.18 33.1 BST-21 0.02 1147 25.6 6.67 1.18 88 6.56 0.29 1.25 77.2 27.4 0.49 34.4 BST-3 116 20.46 5.456 0.58 168 0.35 0.43 14.54 27.7 14.91 0.39 38.9 AT-12 0.01 100 85.76 1.73 1.01 1250 0.33 0.43 4.17 32.4 24.85 1.85 30.1 AT-38 0.07 2213 69.3 2.98 23 1.84 665 10 3.02 0.46 0.87 49.8 52.43 2.83 18.8 AT-9 0.01 216 64.82 1.59 16 1.83 1740 0.42 0.43 1.15 55.7 12.59 1.21 25.4 AT-22 0.01 506 52.35 6.25 13 1.66 341 13 0.53 0.44 1.53 53.6 42.49 0.21 37.4 AT-8 0.01 521 73.27 6.43 11 0.76 1304 10 0.82 0.42 4.37 42.2 80.2 0.25 34.6 AT-7 0.01 174 1.23 1.76 0.93 187 1.09 0.37 7.03 35.2 7.4 0.57 34.8 BST-153 0.01 543 51.26 7.36 10 0.95 686 10 1.17 0.46 1.48 29.7 37.14 0.3 36.3 AT-27 0.01 260 43.1 4.76 16 2.98 645 17 3.2 0.3 1.67 270 41.3 0.14 31.2 BST-37 0.03 3480 118.7 10.34 1.63 389 10.25 0.42 2.94 47.3 90.3 1.33 23.9 BST-06 0.04 3319 91.84 6.29 7.9 1.38 660.77 9.2 19.45 0.38 14 64.75 80.83 0.61 31.5 Avg NEJADHADAD et al / Turkish J Earth Sci 183 NEJADHADAD et al / Turkish J Earth Sci Table REE concentrations (in ppm) of the Jurassic shale (S1, S2), mineralized (S3–S5), and unmineralized rock (S6) Element S-1 S-2 S-3 S-4 S-5 S-6 La 1.11 1.04 0.05 0.08 0.04 0.01 Ce 1.07 1.10 0.05 0.05 0.04 0.01 Pr 1.11 1.09 0.06 0.06 0.04 0.01 Nd 1.09 1.11 0.07 0.07 0.04 0.01 Sm 1.25 1.30 0.14 0.11 0.06 0.01 Eu 1.25 1.27 1.80 3.17 1.02 0.06 Gd 1.30 1.27 1.45 2.53 0.88 0.04 Tb 0.97 1.11 0.21 0.18 0.08 - Dy 0.77 0.96 0.20 0.17 0.08 0.02 Ho 0.70 0.93 0.21 0.19 0.08 - Er 0.60 0.84 0.18 0.16 0.08 0.02 Tm 0.59 0.91 0.20 0.20 - - Yb 0.57 0.83 0.49 0.79 0.14 0.02 Lu 0.48 0.69 0.23 0.30 - - ∑REE 197.3 200.6 21.45 29.68 13.23 2.39 Eu/Eu* 1.04 1.06 2.37 2.44 2.21 2.11 La/Sm 0.89 0.80 0.37 0.68 0.73 1.04 Gd/Lu 2.69 1.84 6.26 8.43 - - Ce/Ce* 0.96 1.03 0.87 0.73 0.90 0.88 La/Lu* 2.29 1.50 0.22 0.25 - - Lu/Ho 0.69 0.74 1.11 1.61 - - 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 Table Sulfur isotope data from galena, pyrite, and barite of the Cs orebody Sample Mineral UTM (X,Y) δ34S ‰ (CDT) Description 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 184 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 mm, and pulverized to –75 µm and analyzed using ICP-MS following multiacid 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 latestage 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 in the US, using a continuous 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) 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 NEJADHADAD et al / Turkish J Earth Sci Table Summary of the microthermometric data of the Ravanj deposit (n = 101) Host mineral Inclusion type Tm, carb Tm, clath (°C) Te (°C) Tm, ice (°C) Th (°C) Salinity (wt% NaCl equiv.) N Stage calcite L+V - – –3.3/–13.8 123.7–204.8 5.2–17.9 - 55 Stage calcite L+V - - –37.2/–52.8 –0.4/–19.8 120.7–220.4 0.66–22.2 21 Barite L+V - - – –1.8/11.9 141–200.8 2.95–15.95 17 Stage calcite L1+L2+V –56.7/–58.1 4.2 /7.3 – – 173–194.6 5.2–10.2 Stage calcite L1+L2+V –56.7/–57.8 1.9/6.3 – – 177.1–202 6.87–13.2 Tm, carb: first CO2 melting; Tm, clath: last clathrate melting; Th, CO2: melting temperature of CO2 phase; Te: first ice melting; Tm, ice: last ice melting; Th, total: total homogenization; Th: homogenization to liquid; Ts, NaCl: halite dissolution; N: number of measurements 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 474650 3781830 0.0 475450 3781830 200m Csw-09 Pb (Z n+ Zn / Csw-03 )< 0.1 Zn /(Z n+ Pb )> 0.3 pond Post Miocene intermediate dyke Lower Cretaceous upper shale Lower Cretaceous massive limestone Lower Cretaceous thin bedded limestone and shale Pond Mineralized limestone Other faults than thrust Thrust Mineralized drilling(from old to recent) Unmineralized drilling(from old to recent) 3781230 474650 3781230 475450 Figure Geological map of the Cs and Bw orebodies 185 NEJADHADAD et al / Turkish J Earth Sci m DDH–Csw09 –1 –3 –5 –7 –9 –11 –13 –15 –17 –19 –21 –23 –25 –27 –29 –31 –33 –35 –37 –39 –41 –43 45 –45 –47 –49 –51.7 m Massive limestone Low grade ore Medium grade ore Shale 5%Pb DDH–Csw03 –1 –3 –5 –7 –9 –11 –13 –15 –17 –19 –21 –23 –25 –27 –29 –31 –33 –35 –37 –39 –41 –43 –45 45 –47 –49 –51 –53 –55 –57 Massive limestone Low grade ore High grade ore Shale 5%Pb Figure Strip logs of two drill holes (Csw03 and Csw09) Locations of drillholes are shown in Figure 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 186 pyrite type III and stage 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 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 organicrich 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 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, NEJADHADAD et al / Turkish J Earth Sci c b a Ba Km2 Gn J.sh d e C3 H Gn f Gn Py H Ca C2 Do H g Gn C3 I h H Ca C2 C3 Py Figure 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 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 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 oreforming solution had a pH of higher than (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 stages First, calcitization occurred as micrite replacement by sparite, which predated sulfide mineralization Large calcite crystals (up to cm, Figure 5g) and veinlets formed during the second stage This calcite occurred before 187 NEJADHADAD et al / Turkish J Earth Sci Sph2 a Py Sph Ca d Tt Gn Gn Gn1 Cv Gn2 200um c b Sph1 300um 100um e Py f Gn Py Gn Ca 300um Ca Ba Do Ca Sph Ca B 1mm h g Py I Ca Ca Do Gn Ba 150um 200um 200um Figure a) Rhythmic deposition of sphalerite and galena Stage sphalerite (Sph2) coated stage galena (Gn1) containing sphalerite inclusion Main stage galena engulfed the whole set b) Sphalerite engulfed by tetrahedrite hosted by galena c) Latestage 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 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 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- 188 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 in Figure 4.3 Geochemistry The Zn/(Zn+Pb) ratios in the Ravanj deposit is low (0.01– 0.24 with mean of 0.08) The Mg value is also very low NEJADHADAD et al / Turkish J Earth Sci Pre mineralization S Calcite Surpegene Mineralization Stage C2 C3 Dolomite Pyrite Chalcopyrite Sphalerite Tetrahedrite Galena M Barite Quartz Bitumen Covellite Malachite, Azurite Cerrucite, Goetite Figure Summary of mineralization paragenesis in the Ravanj deposit, C2: pre-main stage calcite, C3: late-stage calcite, M, main-stage galena (average 0.6%), suggesting that extensive dolomitization did not take place The Ag content of whole rock samples ranges from 1000 ppm, up to 5000 ppm; Qian, 1987) Low Ag values (generally