Sulfide ore facies, fluid inclusion and sulfur isotope characteristics of the Tappehsorkh Zn-Pb (± Ag-Ba) deposit, South Esfahan, Iran

Journal Pre-proof Sulfide Ore Facies, Fluid inclusion and Sulfur Isotope Characteristics of the Tappehsorkh Zn-Pb (± Ag-Ba) Deposit, South Esfahan, Iran Mina Boveiri Konari, Ebrahim Rastad, Jan M. Peter, Flavien Choulet, Leyla Kalender, Ali Nakini

PII:

S0009-2819(18)30156-9

DOI:

https://doi.org/10.1016/j.chemer.2020.125600

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CHEMER 125600

To appear in:

Geochemistry

Received Date:

14 September 2018

Revised Date:

6 January 2020

Accepted Date:

10 January 2020

Please cite this article as: Konari MB, Rastad E, Peter JM, Choulet F, Kalender L, Nakini A, Sulfide Ore Facies, Fluid inclusion and Sulfur Isotope Characteristics of the Tappehsorkh Zn-Pb (± Ag-Ba) Deposit, South Esfahan, Iran, Geochemistry (2020), doi: https://doi.org/10.1016/j.chemer.2020.125600

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Sulfide Ore Facies, Fluid inclusion and Sulfur Isotope Characteristics of the Tappehsorkh Zn-Pb (± Ag-Ba) Deposit, South Esfahan, Iran

Mina Boveiri Konaria, Ebrahim Rastada*, Jan M. Peterb, Flavien Chouletc, Leyla Kalenderd,

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Ali Nakinia

Department of Geology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran,

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Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada Chrono-Environnement, Université de Bourgogne-Franche Comté-CNRS, Besançon,

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Iran

France

Department of Geological Engineering, Firat University, Elazig, Turkey

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*Corresponding author. Email: [email protected]

Abstract

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The stratiform, stratabound Tappehsorkh Zn-Pb (±Ag-Ba) deposit, located in the southeastern part of the Malayer-Esfahan Metallogenic Belt of Iran, formed during Lower Cretaceous back-arc extension. Sulfide mineralization occurs within dolostone, black siltstone, and crystal lithic tuff and andesite associated with the Gushfil-Baghabrisham synsedimentary normal fault. Three sulfide ore facies (massive, bedded, and stockwork) occur in the deposit. Sulfide minerals are sphalerite, galena, tetrahedrite and pyrite with minor

chalcopyrite and bornite, and gangue minerals are barite, dolomite and quartz. Sulfide mineralization textures are massive, replacement, vein-veinlet, laminated, disseminated, and breccia. Three mineralization stages are distinguished: early, main and post-ore. An early finegrained sulfide ore (early ore, stage I) occurs in the bedded facies which has synsedimentary textures such as laminated, disseminated and framboidal pyrite, galena and sphalerite. Coarse-grained sulfides in the brecciated, massive replacement, and vein-veinlet

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textures comprise main ore stage of mineralization (main ore, stage II) and formed by during diagenesis via sub-seafloor replacement of protore by mixing of hydrothermal brines

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with cold seawater. Late, coarse-grained sulfides (post-ore, stage III) were formed during deformation and orogenic events and occur as strain fringes, foliation-like, and spindle

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textures. Pervasive hydrothermal alteration styles are predominantly dolomitization and silicification and minor sericitization occurs in all host rocks in the hanging-wall of the

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GBF.

Fluid inclusions within massive sphalerite of the main ore stage have trapping temperatures

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ranging from 118 to 199 ºC, and salinities ranging from 6.2 to >23.32 wt. % NaCl equivalent. The δ34S values of the sulfide minerals from main ore stage range from -2.4 to 34.1‰, whereas barite ranges from +10.3 to +16.9 ‰. The negative values of the δ34S as

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well as the narrow range of δ34S in galena and sphalerite suggest that sulfur was derived by bacterial reduction of seawater sulfate. The back-arc extensional tectonic setting, presence of a normal fault controlling sulfide mineralization and hydrothermal alteration, the siliciclastic-carbonate-volcanic lithology of

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the host rocks, magmatism in the region (pyroclastic and volcanic rocks, that also host the sulfide mineralization), the distribution of the three ore facies, and the negative sulfur isotope values all support a sub-seafloor diagenetic replacement SEDEX-type classification for the Tappehsorkh deposit, which was then affected by Laramide (?) orogenic events which imparted the post-ore stage mineral textures. Keywords: Sulfide ore facies; back-arc; hydrothermal alteration; ore stages; SEDEX-type; Tappehsorkh.

1. Introduction The NW-SE trending Malayer-Esfahan Metallogenic Belt (MEMB) is one of the major metallogenic belts of Iran that hosts numerous sediment-hosted Zn-PbAg±Cu±Ba±Fe deposits and prospects (Fig. 1). Deposits in the belt are thought to include typical Sedimentary Exhalative (SEDEX) (Gushfil: Boveiri et al., 2017; Hosseinabad: Mahmoodi et al., 2018), Irish-type (Kouhkolangeh: Peernajmodin et al., 2018), Missippi Valley-type (MVT) (Irankuh: Hosseini-Dinani and Aftabi, 2016; and Liu et al., 2019),

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transitional SEDEX-Volcanogenic Massive Sulfide (VMS) (Tiran: Yarmohammadi et al., 2017), and transitional Irish-type-SEDEX-VMS (Darrehnoghreh and Salehpeyghambar:

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Fadaei, 2018) deposits.

The Tappehsorkh deposit, located in the southeastern part of the MEMB (Fig. 2), is

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one of the most important Zn-Pb-Ag deposits in Iran and is hosted by Lower Cretaceous clastic-carbonate-pyroclastic (LCCCP) rocks. This deposit, along with the nearby

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Kolahdarvazeh, Gowdezendan, Gushfil and Rowmarmar deposits and the Khanehgorgi, Baghabrisham and Tofangchiha occurrences, comprise the Irankuh Mining District (IMD),

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which extends over 25 km in length and is 3 km wide (Fig. 2). The genesis of the IMD deposits, like MEMB deposits, remains controversial, and previous studies have suggested SEDEX (Momenzadeh, 1976; Boveiri et al., 2017),

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synsedimentary-early diagenetic (Rastad, 1981), MVT (Ghazban et al., 1994; HosseiniDinani and Aftabi, 2016) genetic models. Recently, an early syn-orogenic modified MVT model was proposed for IMD mineralization by Liu et al. (2019). Based on Re-Os dating of pyrite, these authors suggest that ore-formation took place at 66.5 Ma, contemporaneously with the compressional onset of the Zagros Orogeny that resulted in the development of the

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vein ores in structures associated with the Gushfil-Baghabrisham fault (GBF). Despite numerous published geological and geochemical studies, the sulfide

mineralization stages, the nature of ore-bearing fluids, the mode of fluid migration, the source(s) of sulfur, as well as the temperatures of sulfide deposition and the genetic model of the deposits in the IMD remain controversial. Herein, we present new information on the Tappehsorkh deposit, which is a key place to understand mineralization processes in other deposits of the IMD. We aim to develop a genetic model based on the geological,

structural, lithological, mineralogical, mineral textural, stable isotope and fluid inclusion data for the ore and host rocks. 2. Geological context and main features of IMD deposits 2.1 Tectonic setting of the IMD deposits The geological setting of the IMD and its deposits is related to the formation of the

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Sanandaj-Sirjan Zone (SSZ) and associated back-arc basin during the Jurassic-Lower Cretaceous (Mohajjel and Fergusson, 2014; Azizi et al., 2018). The evolution of the SSZ

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commenced with the generation of the Neo-Tethys Ocean in the Permian to Triassic and its subsequent subduction, convergence and continental collision between the Arabian plate

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(southwest) and Iranian plate (northeast) (Mohajjel et al., 2003; Ghasemi and Talbot, 2005). Subduction of the Neo-Tethys oceanic crust beneath the Central Iranian Plate

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(including the Urumieh-Dokhtar magmatic arc (UD), and the SSZ) occurred in the Late Cretaceous (Berberian and King, 1981; Ghasemi and Talbot, 2006; Agard et al., 2011; Mohajjel and Fergusson, 2014; Azizi et al., 2018). This led to development of Late Triassic

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to Cretaceous continental arc magmatism and obduction of Neo-Tethys ophiolite (Shafaii Moghadam and Stern, 2011; Mohajjel and Fergusson, 2014; Azizi et al., 2018).

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The convergence also caused the opening of MEMB and Nain-Baft basins between the SSZ and Central Iranian Plates (Rajabi et al., 2012). Some back-arc basins formed from Mid-Late Jurassic (Ahmadi-Khalaji et al., 2007; Mohajjel and Fergusson, 2014; Azizi et al., 2018) to Lower Cretaceous (Agard et al., 2011) time. At this latter time, extensive Lower Cretaceous volcano-sedimentary sequences were formed (Bagheri and Stampfli, 2008;

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Shafaii Moghadam et al., 2009), and these are contemporaneous with sediment-hosted ZnPb mineralization in the MEMB (Boveiri, 2016; Rajabi et al., 2019). During the Late Cretaceous, the SSZ and Nain-Baft oceanic crust were subducted

beneath the Iranian plate (Ghasemi and Talbot, 2005), and subsequent closure of back-arc basin resulted in the generation of Late Cretaceous to Palaeocene ophiolite melanges (Bagheri and Stampfli, 2008).

2.2 Local Geological aspects of IMD deposits The IMD and its mineral deposits and occurrences, located in the central part of the SSZ (Fig. 1), formed during back-arc extension in the Late Jurassic-Lower Cretaceous. The IMD is bounded by WNW-ESE-trending structures that are nearly parallel to the main trend of the SSZ (Fig. 1). The sedimentary rocks of the IMD are folded into synclines and anticlines (Fig. 2), including in the study area (Nakini, 2013). Three groups of faults affect the IMD and its mineral deposits (Figs. 2 and 3). The

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first is the GBF that marks the northern boundary of the IMD. The GBF shows a WNWESE trend, with a dip direction to ENE at high angles averaging 70º. The dip along the

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GBF is variable; it is gentler (55º) at the surface level of the Gushfil mine (Fig. 3a),

deeper levels of the Gushfil mine (Fig. 3c, 3d).

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whereas it is sub-vertical to vertical (89 to 90º) in the Tappehsorkh I open pit (Fig. 3b) and

Based on detailed investigation of the GBF, Nakini (2013) proposed that the sense

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of movement along the GBF was normal during the Lower Cretaceous, contemporaneous with the formation of a back-arc basin and deposition of sediments. This fault then

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reactivated as a reverse fault during Late Cretaceous compression tectonism. It is notable that the Lower Cretaceous strata in the vicinity of the GBF, are near-vertical to vertical (Fig. 3b-d), perhaps resulting from reverse reactivation of the GBF. This is best observed at

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the Tappehsorkh I and Gushfil mine. At the Gushfil mine the mineralized layer (called bedded further below) has been affected by the GBF where strata shift orientation from horizontal to vertical (Fig. 3c-3d).

A second group of faults includes domino-type normal faults with a NE-SW trend (Fig. 2) which are sub-parallel and perpendicular to the trend of the fold axes (Fig. 2). The

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third group corresponds to sinistral strike-slip faults (NE-SW trend), which mostly control the location of present-day valleys and cut the NW-SE trend of the IMD (Fig. 2). There is no mineralization localized along the latter two fault groups. 3. Sampling and analytical methods Two hundred fifty samples were collected from surface outcrops and underground drill cores in order to understand the mineral paragenesis of the Tappehsorkh deposit. Of

these, one hundred seventy sample are from Tappehsorkh I and eighty samples from Tappehsorkh II orebodies. Among these, forty-eight core samples were selected for microscopic studies from Tappehsorkh I (twenty massive, seventeen breccia, four stockwork, and seven disseminated ore) and thirty-six core samples form Tappehsorkh II (thirteen stockwork, seventeen massive and six bedded ore). Textural and petrographical relationships between sulfide and non-sulfide minerals were studied by means of transmitted and reflected light microscopy, and relations between

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types of dolomites by microscopic studies, staining (Dickson, 1966; Hitzman, 1999) and cathodoluminescence analysis (Boveiri and Rastad, 2018).

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Sulfur isotope compositions were obtained on fourteen core samples of sulfide minerals (nine samples from Tappehsorkh I and five samples from Tappehsorkh II) and six

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core samples of barite (five samples from Tappehsorkh I and one sample from Tappehsorkh II) (Table 1). The samples were separated by hand picking, using a high magnification

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binocular microscope. Sulfur isotope compositions were measured in automated fashion using a Carlo Erba (CE 1100) elemental analyser linked to a Thermo Fisher Delta V mass spectrometer, at University of Lausanne, Switzerland and a Thermo Quest Finnigan Delta

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Plus mass spectrometer, at University of Arizona, Tucson, USA. The results given as δ34S ‰ values relative to the V-CDT (Vienna Canyon Diablo Troilite) standard with a typical

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laboratory precision of ±0.25‰ (1σ).

Seventeen double-polished thin sections were selected for fluid inclusion studies in sulfide, dolomite and quartz minerals at the IMD (Boveiri, 2016; Boveiri et al., 2017; Boveiri and Rastad, 2018). In present study, three doubly-polished thin sections were prepared from massive sphalerite from Tappehsorkh I. The micro-thermometric analysis

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was performed using a LINKAM MDS 600 TS 1500 system attached to a Leica DM 2500P microscope, at the General Directorate of Mineral Research and Exploration, Ankara, Turkey.

4. Geological features of the Tappehsorkh deposit In the Tappehsorkh deposit, a thick LCCCP is exposed which unconformably covers Jurassic shale, siltstone and sandstone (Js; Fig. 4a-d). The LCCCP in the

Tappehsorkh deposit is divided into six major units (Fig. 4): K1 is continental red conglomerate and sandstone (K1c, 1-7 m) and black siltstone (K1s, 1-10 m). Other units are carbonate-dominated and include the following succession: K2l shallow marine Orbitolina limestone (15-20 m), K3l medium-bedded rudist limestone (300 m), K3d red-brown dolostone, K4l grey coloured thin-bedded argillaceous limestone to dolo-mudstone (100 m), Kl massive orbitolina limestone (120 m), and K5Sh shale and marl intercalated with limestone.

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In the Baghabrisham occurrence (western extension of the Tappehsorkh I orebody), crystal lithic tuff and andesite rocks (Kv) and a dacite (Kda) are intersected in drill core, but

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they are not exposed at the surface (Fig. 4c-d). Core logging shows that the Kv unit is overlain by K3d dolostone (Boveiri, 2016). The main hosts of the Zn-Pb (-Ag-Ba) sulfide

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mineralization at the Tappehsorkh deposit are (in order of most abundant to least abundant): dolostone (K3d), black siltstone (K1s), crystal lithic tuff (Kv), and minor

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sandstone.

Orebodiesin the Tappehsorkh deposit is mined from two loctions: Tappehsorkh I

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and Tappehsorkh II (Fig. 5). Based on the NE-SW cross-section, the two orebodies were originally situated along one stratigraphic level which has subsequently been affected by

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folding (Fig. 5b-5c). Tappehsorkh I

The Tappehsorkh I orebody is located along the GBF and is hosted by crystal lithic tuff (Kv), black siltstone (K1s) and dolostone (K3d). Sulfide mineralization occurs as a stratiform lens which has a strike length of about 420 m length and 15-20 m width (Fig. 5).

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Tappehsorkh I has been mined as an open pit since 2000, and present-day reserves are about 4 Mt at 6 wt. % Zn, 4 wt. % Pb, and 500 g/t Ag. In the Tappehsorkh I orebody, the K3l and K3d units dip 89-90º near the GBF (Fig.

6a). Jurassic shale (Js) dips to the NE and is thrusted on the Lower Cretaceous units. Rose diagrams of Tappehsorkh I fault and fracture orientations demonstrate that nearly all features trend N60W and dip 40-50º to the NE (inset, Fig. 2). As shown in Figure 6a, bedding of the strata and Tappehsorkh I orebody are vertical near the GBF, and dip more

gently further from the fault. In this location the orebody has been cut and displaced by later movement of this fault (Fig. 2). This fault, consider to be a reverse fault, experienced normal movement in the time of basin formation, and then reversed during the Laramide Orogeny. Evidence for reverse movement of the GBF during tectonic inversion, originally investigated by Nakini (2013), is further investigated by Boveiri (2016) using detailed deformed textural studies.

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Tappehsorkh II

The Tappehsorkh II orebody is stratiform and stratabound, and hosted solely by

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Lower Cretaceous dolostone (K3d). Sulfide mineralization occurs almost solely within the regional K3d dolostone (Fig. 6b). Mining at Tappehsorkh II commenced in 1986 from an

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open pit. The orebody is 225m long, 8-10 m wide, and has total reserves of 6 Mt with an average grade of 12 wt. % Pb+Zn (8 wt. % Zn and 4 wt. % Pb). In some drillholes through

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the Tappehsorkh II orebody, weak mineralization occurs in the black siltstone and sandstone (K1s).

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In addition to the primary sulfide orebodies in the deeper levels, mining activities in the upper level focus on the secondary non-sulfide ores comprised of smithsonite, hydrozincite, hemimorphite and cerussite. Supergene minerals occur in the karst, breccia,

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or as vein filling within late domino-normal fault system and fractures (Fig. 5a). The Tappehsorkh II orebody is located about 100m south of the Tappehsorkh I orebody (Fig. 5a). K3d dolostone is the only host rock to this orebody, and the unit is about 50 m wide and dips to SW. In one drill hole, weak pyrite mineralization was intersected. Parallel, domino-type NW-SE normal faults bound the southern limits of the

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Tappehsorkh II orebody. These faults imbricated the dolostone layers. The trend of these domino-type faults is perpendicular to fold axes in the IMD. A rose diagram of faults in the western and eastern parts of the Tappehsorkh II pit is

shown in the inset in Figure 2. In the western part, faults trend NW-SE, whereas those in the eastern part have NW-SE (domino-type normal), N-S and lesser NE-SW orientations. Folds in the Tappehsorkh deposit range from open in the dolostone (Fig. 7a), to tight and/or overturned in the limestone (Fig. 7b).

5. Hydrothermal Alteration Hydrothermal alteration styles in the Tappehsorkh deposit are dolomitization, silicification and sericitization (Fig. 8a-f). Based on morphological, mineralogical and geochemical features (colour, size, and their interrelations as well as Mn and Fe content of all dolomites), three styles of dolomitization were distinguished in the Tappehsorkh deposit (Boveiri, 2016; Boveiri and Rastad, 2018): regional diagenetic (D1), hydrothermal (D2 and D3), and deformation-

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related (D4) (Fig. 8a-e).

Regional dolomitization is pervasive in the Tappehsorkh deposit area, and this is

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recognized by the presence of fine-grained euhedral to subhedral dolomite rhombs (D1). D1 dolomite formation, which commonly replaces K3l micritic limestone (Fig. 8a), led to

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major modifications of rock porosity, and this increased porosity likely served as enhanced sulfide precipitation sites (Boveiri and Rastad, 2018).

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Hydrothermal dolomitization mainly occurred in the hanging-wall of the GBF. Based on the size, colour and geochemical studies, hydrothermal dolomites include D2- and

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D3-types (Boveiri and Rastad, 2018).

D2 dolomite is marked by grey-coloured fine to medium-grained euhedral crystals, which crosscut D1 dolomite (Fig. 8b). In places, D2 dolomite wholly replaced all host rock.

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D2 dolomite, along with quartz and sphalerite, have even replaced orbitolina (Fig. 8c). Locally, D2 dolomite is brecciated and cemented by white coarse-grained euhedral to subhedral D3 dolomite (Fig. 8d and 8e). Hydrothermal dolomitization is common in the all host rocks close the GBF and its decreases in intensity away from it. Hydrothermal dolomitization occurs as massive, vein-veinlets, and replacement along laminations within

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the host rocks.

The D4 dolomite only occurs along the GBF and domino-normal fault. This

dolomite is recognized by the presence of very coarse-grained (200 μm diameter) to saddleshaped dolomite crystals. This type of dolomite is discussed in detail later. Silicification is common in the black siltstone, crystal lithic tuff, and dolostone. The silicificationvaries in intensity of from low to high. In places, host dolostone has been wholly altered and transformed to highly siliceous rock in which only ghosts of orbitolina

fossils remain (Fig. 8c). Silicification is also manifest as massive, vein-veinlets, open space fillings and disseminations (Fig. 8e) in the host rocks. Sericitization is the least developed hydrothermal alteration, and has affected the Kv crystal lithic tuff and minor K1 siltstone. Under the microscope, fine mica replaces feldspars in both host rocks (Fig. 8f). 6. Ore style and sulfide mineralization

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Based on field observations, hand specimens and microscopic studies, three types of

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ore facies are distinguished: (1) bedded, (2) stockwork, and (3) massive (Figs. 5c and 9). 6.1. Ore styles in the Tappehsorkh I and II

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Sulfide mineralization in the Tappehsorkh I and II orebodies occurs as replacement of the LCCCP (K1, Kv, K3d) adjacent to, and distally from the GBF (Figs. 5 and 6). In these

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locations, brecciation is common, and host rocks have been almost entirely replaced by

Bedded ore facies

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sulfide minerals.

The bedded facies ore (Figs. 9a, 9e-h) is low-grade and composed of micro- to

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variously-scaled laminae of sulfide minerals alternating with host rock laminae (Fig. 9a). Laminated sulfides are comprised of abundant fine- to medium-grained pyrite and sphalerite, with minor disseminated galena (Fig. 9e-h). Pyrite commonly occurs as framboids (Fig. 9f-h) that are cemented by sphalerite and galena (Fig. 9h). In some cases, framboidal pyrite is replaced by later coarse-grained

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sphalerite and galena (Fig. 9g). In some samples, there are crinoid stem fragments which have been preferentially replaced by pyrite and galena. Alternating layers of colloform sphalerite and pyrite (Boveiri, 2016) are the most common textures. One of the most significant aspects of the bedded ore is the occurrence of organic

matter and its close relationship with the sulfide minerals (Fig. 9e). There are micro-folds and micro-faults that have affected the host rock laminations in which sulfide laminae have been folded with siltstone laminae (Fig. 9e). Quartz and dolomite are the main

hydrothermal alteration minerals. An intra-formational breccia has deformed the underlying laminations, indicating deformational timing was syn-sedimentary. Stockwork ore facies Stockwork ore mainly consists of an irregular vein system which randomly crosscuts the footwall host siltstone and dolostone rocks (Fig. 9b). The veins represent about 8% of the rock volume and range from < 1 mm up to 10 cm wide (Fig. 9b). The veins

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are composed of hydrothermal dolomite, quartz and sulfide minerals (Fig. 9b and 9i). Coarse-grained hydrothermal dolomite and quartz are replaced by sulfide minerals (Fig. 9i).

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Vein-type mineralization occurs in close proximity to the GBF and is developed particularly towards the base of the massive sulfide ore. Sulfide minerals are mainly coarse-

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grained sphalerite, galena and pyrite and minor chalcopyrite. Chalcopyrite disease is

The massive sulfide ore facies

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present within sphalerite. Galena replaces pyrite and is itself replaced by sphalerite.

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The massive ore which occurs in the stratiform-stratabound orebody (Figs. 6 and 9c-d), is now mostly mined out. It is located above the stockwork ore (Fig. 5c). There is partial to nearly complete replacement of host rocks by sulfide and non-sulfide minerals.

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The massive sulfides are coarse-grained sphalerite, galena, tetrahedrite, pyrite and chalcopyrite, with subordinate bornite (Figs. 6j-i). Barite, quartz and dolomite have been pervasively replaced by sulfide minerals. The texture of the massive sulfides are distinct from that of bedded sulfides, as sulfide minerals are coarser grained and they have also replaced the sulfide minerals in the bedded ore.

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Breccia textures are also present, and these are characterized by angular to subrounded, mm- to cm-scale clasts of D2 hydrothermal dolomite, hydrothermal quartz and sphalerite in a matrix of sphalerite and quartz. Four sub-facies are recognized in the massive ore: (1) a galena-sphalerite-

tetrahedrite-(chalcopyrite)-rich (GST(C)) sub-facies (Fig. 9j) developed adjacent to the GBF, (2) a sphalerite-galena-pyrite-rich (SGP) sub-facies (Fig. 9k) more distal from the

GBF, (3) a sphalerite-pyrite-barite-rich (SGB) sub-facies (Fig. 9l-m), and (4) a barite-pyrite (BP) sub-facies (Fig. 9n-o). The GST(C) sub-facies contains high-grade ores (15-20 wt% Pb+Zn). The abundance of tetrahedrite, chalcopyrite and bornite in this sub-facies is also high (Fig. 9j). Rare barite in the GST(C) sub-facies is replaced by sphalerite and galena. The SGP sub-facies is marked by abundant sphalerite, galena and pyrite (Figs. 10bc and 10i) and is of moderate- to high-grade ore (15-25 wt% Zn and 5-10 wt% Pb+Zn).

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The SGB sub-facies is characterized by high abundances of sphalerite, galena and barite in which barite has been replaced by sphalerite and galena. The SGB sub-facies

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displays high Zn contents (12-17 wt.%).

The BP sub-facies is mainly composed of medium- to coarse-grained barite and

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pyrite. The amount of barite in this sub-facies is very high (10-15 vol.%). Sphalerite is also a rare constituent. Mineralization mainly occurs as a replacement of barite crystals (Fig.

considered as a massive barite rock.

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6.2. Ore styles related to deformation

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10d and 10j). In places, the amount of barite in the host rocks is so high that it can be

Among and within the GBF in the Tappehsorkh I orebody, some sulfide and non-

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sulfide minerals exhibit deformation textures (Fig. 10a-m). These features are best observed where tectonic inversion has resulted in the rotation of bedding orientation from horizontal to vertical (Fig. 10a).

There is an increase in the grain size of dolomite, quartz, barite and sulfide minerals in the host siltstone with decreasing proximity to the GBF (Figs. 10a-c and 10j-k). D4

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dolomites have been compressed together and, in places, agglomerations of large crystals produce extraordinarily large crystals (Fig. 10j-k) that show the effect of deformational and compressional events at their outer margins. This type of dolomite is universally larger than the other hydrothermal dolomite (Fig. 10j-k). There are coarse to very coarse-grained sulfide minerals such as pyrite and sphalerite that have been mantled by later sphalerite and galena (Fig. 10d-g) that resemble strain fringes of Passchier and Trouw (2005).

There are coarse-grained galena and sphalerite which disrupt the sulfide and silt laminae within the host siltstone (Figs. 10a and 10h-i) which may indicate the later growth of these minerals during post-depositional deformation. There is an accumulation of large anhedral sphalerite crystals along with coarse-grained D4 dolomite and barite in the high strain deformation area (Fig. 10k). In addition, foliation-like textures of sphalerite and galena in the host siltstone as well as boudinaged galena (Fig. 10l) are further evidence of subsequent deformation after

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sulfide deposition. These textures could suggested during deformation processes, galena was more ductile than sphalerite; and both experienced deformation, and reacted

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differently.

The deformed cleavage pits in galena, together with the presence of complex galena

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and pyrite mixtures near the GBF confirm deformation occurred along this fault (Fig. 10m).

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7. Paragenetic sequence and stages of mineralization

Based on field observations and microscopic studies, there are three (early-, main-,

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and post-ore) sulfide stages for mineralization in the Tappehsorkh deposit. The first two stages (probably overlapping) are considered to be primary mineralization, whereas the third stage is a post-ore deformational event. A paragenetic sequence for the mineralization

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at the Tappehsorkh deposit is shown in Figure 11. Framboidal, disseminated, spheroidal, colloform and laminated pyrite, galena and sphalerite in the bedded ore constitute the early ore stage (S1; Figs. 9e-h). The sulfide minerals formed in this stage are indicated as “I”, whereas “II” and “III” denote the second (S2) and third (S3) stages, respectively (Fig. 11).

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Coarse-grained sphalerite (Sph II), galena (Gn II), tetrahedrite (Tet), pyrite (Py II), chalcopyrite (Cpy) and bornite (Bo) are formed during the second ore stage. As most of the sulfides were precipitated during this stage, it is considered to be the main stage of the mineralization (Figs. 9b-d and 9i-o). The early, fine-grained minerals of S1 have been replaced by newly formed coarsegrained sulfide minerals of S2 (Fig. 9g). S2 sulfide mineralization mainly displays

brecciated, massive, replacement and vein-veinlet textures and predominantly occurs in the massive and stockwork ore in all host rocks. Coarse-grained pyrite (Py III), sphalerite (Sph III), Galena (Gn III), dolomite (D4), and quartz formed during S3 due to deformational processes (Fig. 10a-m). 8. Sulfur isotope studies The δ34S analytical data for pyrite, sphalerite, galena, and barite from the main ore

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stage are presented in Figure 12 and Table 1. Because of the fine grain size and the low sulfide content, sulfide minerals of S1 could not be analysed. All minerals were selected

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from the main ore stage (S2). Only two samples were select from pyrite III formed during S3 (recrystallized and grown framboidal pyrite).

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The δ34S compositions of S2 minerals have a narrow range from -3.4 to -34.1‰ for sulfide minerals and +10.3 to +16.9‰ for barite. As shown in Table 1, pyrite from S3

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presents the lowest values (-34.1 and -23.7‰). The δ34S values for galena range between 5.8 and -9.8‰, with a mode of -8‰, whereas those of sphalerite range from -3.4 to -9.4‰

9. Fluid inclusion studies

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with a mode of -4.9‰.

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Fluid inclusion microthermometry in the Tappehsorkh was carried out on transparent sphalerite from the massive ore of Tappehsorkh II (Table 2). The nature and characteristics of the fluids trapped in the stockwork and massive sphalerite from Gushfil deposit were previously studied by Boveiri (2016) and Rastad et al. (2017). Fluid inclusion microthemometric measurements on hydrothermal dolomite and quartz were also published

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by Boveiri and Rastad (2018).

Generally, there are two types of fluid inclusions at room temperature in the

massive sphalerite of the Tappehsorkh II orebody: (A): primary two-phase (liquid-vapour; L+V), and (B) secondary one-phase (V) fluid inclusions (Fig. 13). There is evidence of necking down and leakage in the inclusions, making their homogenization temperatures unreliable for thermometry (Fig. 13a). The secondary fluid inclusions have intergranular

trails and are too small (<2 μm) to be used for microthermometry studies. Hence, only primary two-phase inclusions were selected for microthermometric analysis. The primary inclusions are between 5 to 26 μm in size, with most ranging from 12 to 20 μm. These inclusions have relatively constant phase ratios. Vapour occupies 15 to 25 percent of inclusion volume, with about 75 to 85 volume percent liquid. The inclusions in sphalerite are darker in appearance are vapour-rich or two-phase (V+L; with large vapour bubbles!). The darkness of the inclusions makes it difficult or even impossible to record

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temperatures (especially during operation below ambient), so in some cases, only homogeneous temperatures could be obtained.

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Homogenization temperatures for the massive sphalerite are given in Table 2. The twenty measurements of fluid inclusions within the sphalerite show homogenization

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temperatures between 118 to 199 ºC (Fig. 14). The ice melting temperatures range from 3.8 to -26.3 ºC. The calculated salinities (based on Bodnar, 1995) range from 6.2 to >23.32

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wt. % NaCl eq. (Table 2, Fig. 14). Summaries of microthermometric measurements of the

10. Discussion

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IMD fluid inclusions are depicted in Figure 17.

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10.1. Structural controls on fluid flow

A suitable tectonic setting with elevated heat flow is required to heat fluid and cause hydrothermal fluid flow (Bradley and Kidd, 1991). Such environments may include crustal thinning of extensional continental margins, extensional back-arc basins and large-scale rift settings (Bradley and Kidd, 1991). Volcanism may also be considered as a further indicator

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of high heat flow, and it has been implicated in the formation of sediment-hosted Zn-Pb deposits (Davies and Smith, 2006). An extensional back-arc setting for the SSZ during the time period from the Mid-

Upper Jurassic to the Lower Cretaceous (Shafaii Moghadam and Stern, 2011; Mohajjel and Fergusson, 2014; Azizi et al., 2018) resulted in crustal thinning and subsequent high temperature gradient.

The occurrence of sulfide mineralization in the vicinity of the GBF, which was a normal fault in the Lower Cretaceous (Nakini, 2013), suggests that mineralization probably was emplaced simultaneously with extension along the fault at this time. The presence of crystal lithic tuffs and flows also indicate the existence of a high temperature gradient at the time of the host rock formation and deposition of sulfide mineralization in the Tappehsorkh deposit. This high gradient situation may have resulted in the generation of hydrothermal fluids that transported the metals and other elements.

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The distribution of hydrothermal alteration and associated sulfide mineralization adjacent to the GBF confirmed the key control of this fault in the Tappehsorkh deposit (Fig.

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5). The emplacement of the orebodies in relation to the suitable permeability of brecciated host rocks also suggests that the GBF largely controlled the morphology and distribution of

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the orebodies.

The original configuration of the Tappehsorkh I and Tappehsorkh II orebodies

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along one ore-bearing horizon which was then affected by later folding also implicates the key role of the GBF in the controlling of lateral hydrothermal fluid flow in permeable

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rocks.

This genetic link is better explained by (1) localization of mineralization in the extensional Lower Cretaceous back-arc basin, (2) presence of products of magmatism as a

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host of sulfide mineralization, (3) existence of the GBF as a normal fault in Lower Cretaceous time, and (4) occurrence of sulfide orebodies in the Lower Cretaceous host rocks associated with the GBF.

10.2. Sulfide depositional processes

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Based on the various types of sulfide ore facies (massive, stockwork, and bedded) each with specific textural characteristics, fluid flow was not homogenous throughout the Tappehsorkh deposit. Some particular sulfide textures such as framboidal and laminated pyrite in the

bedded ore facies may have formed during early stage of mineralization from ore-bearing hydrothermal fluids. This, together with concomitant micro-folding of organic-rich sulfide laminae with silty laminae of the Lower Cretaceous siltstone (Fig. 9e) suggest S1 sulfide

mineralization in the Tappehsorkh deposit formed during, or shortly after, deposition of the Lower Cretaceous host rocks. Based on microthermometric studies, two hydrothermal fluids were responsible for sulfide precipitation in the Tappehsorkh deposit. Higher temperatures hydrothermal fluids (170-260 0C; Figs. 14 and 15; Boveiri, 2016; Boveiri and Rastad, 2018) are involved in the formation of stockwork ore, whereas the massive ore is formed from lower temperature fluids (118-199 ºC; Table 2).

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Hydrothermal alteration and associated sulfide mineralization, together with metal zonation from the GBF outward reflect changes in physico-chemical conditions at the sites

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of ore formation (different ore facies), such as changes in pressure, temperature and chemistry of the ore fluids. Higher temperature, metal-rich fluids precipitated the

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chalcopyrite, bornite, galena and sphalerite in the stockwork and massive ore facies of the Tappehsorkh I orebody adjacent to the GBF, whereas sphalerite, pyrite, and barite were

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deposited further outward and upward along and from the GBF in the Tappehsorkh II orebody.

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Textural observations confirm that continuous fluid outflow caused abundant replacement of early fine-grained sulfide with coarse-grained sulfide generating the main ore stage. The lack of deformational textures in the coarse-grained stockwork and massive

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ore indicate that this stage likely formed soon after the bedded ore facies due to fluid expulsion via fractures and rock-fluid interaction in the sulfide mineralization site. Some sulfide textures such as strain shadows, large crystals (especially pyrite and D4 dolomite), cataclastically sheared (comminuted) and foliated sulfides, which have flattenedf several coarse-grained crystals along their contacts, and the deformed galena

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cleavage pits, collectively indicate later deformational processes acted upon primary mineralization. These deformational textures may have formed during inversion of the GBF.

Regional dolomitization enhanced the porosity of the host rocks, and this allowed

mineralizing fluids to flow through them and precipitate massive sulfide. Collectively, the evidence indicates that primary sulfide deposition (early and main ore stage, S1) in the Tappehsorkh deposit was synchronous with sedimentation to early

diagenesis; this primary mineralization was then were affected by subsequent deformation, perhaps concomitant with fault reversal during inversion tectonism resulting from orogenic events in the IMD. 10.3. Source of sulfur Reduced sulfur, necessary for the formation of sulfide minerals in sediment-hosted massive sulfide environments is produced by bacterial or thermochemical sulfate reduction

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(BSR and TSR) in low-temperature or high-temperature diagenetic environments, respectively (Machel, 2001). BSR is generally active in diagenetic settings from 0 up to 80

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ºC (Machel, 2001), and rarely up to 113 ºC (Jørgensen et al., 1992). TSR, however, is common at higher temperatures at about 100-180 ºC (Machel, 2001).

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Based on the curves produced by Paytan et al. (2004), and Bottrell and Newton (2006), the sulfur isotope composition of seawater sulfates during the Cretaceous was about

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+14 to +20‰. δ34S values of barite in the Tappehsorkh deposit (Table 1) are strongly similar to the Cretaceous seawater values.

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Considering the homogenization temperatures of sphalerite in the massive ore (Th= 118-199 ºC; Table 2) and the published homogenization temperatures for dolomite and quartz of the stockwork mineralization (Th= 170-260 ºC; Fig. 15), TSR is the most likely

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process that contributed sulfur, in the presence of organic matter that facilitated the reducing nature of the main stage ore fluids. Furthermore, the observed association of D3 dolomite with the main ore stage (Boveiri and Rastad, 2018), points to a formation at temperatures > 100 °C, supporting TSR (Machel, 1995). Galena and sphalerite display a relatively narrow range of δ34S between -9.8‰ and -

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3.4 ‰. Compared to barite, formed from seawater sulfate (+10.3 to +16.9‰), the maximum shift of δ34S is in between 20.1 and 26.7 ‰, in good agreement with the fractionation of reduced sulfur from seawater sulfate by TSR. The most negative δ34S values of the two measured pyrite grains does not fit into the reported range typical of TSR, and indicates that framboidal pyrite formed during BSR at an earlier stage. Thus, in the Tappehsorkh deposit BSR was the main process that generated sulfur necessary for the precipitation of early ore stage sulfide minerals under low temperature

conditions. The main ore stages sulfide minerals were deposited where TSR was the main source that provided reduced sulfur for the sulfide mineralization. 10.4. Comparison with other Zn-Pb-Ag sediment-hosted deposits The age of sulfide mineralization in the sediment-hosted Zn-Pb-(Ag-Ba) deposit of the MEMB has long been a subject to controversy and Lower (Momenzadeh, 1976; Rastad, 1981; Rajabi et al., 2012; Boveiri et al., 2017) or Upper (or post-Upper) Cretaceous

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(Ghazban et al., 1994; Ehya et al., 2010) ages for mineralization have both been proposed. Based on Re-Os dating of pyrite, Liu et al. (2018) concluded that the major ore

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formation at IMD took place at 66.5 Ma during the early compressional stage of the Zagros orogeny due to thrusting along the Gushfil fault. Hence, Liu et al. (2018), proposed an

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orogenic, modified MVT model for sulfide mineralization at the nearby Gushfil deposit. Based on the variable dip angle (55-89°) and later deformation of early formed sulfide

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minerals, the GBF is suggested to be a reverse fault at the mine scale and not a thrust fault. It is necessary to note that Liu et al. (2018) do not present detailed geological,

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structural, mineralogical, textural and geochemical (temperature of ore fluids) information about the IMD. As aforementioned above, pyrite I and II, which are fine- and mediumgrained, were formed during early and main ore stage, whereas coarse- to very-coarse

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grained pyrite III formed in the post ore stage (S3) of sulfide mineralization. Thus, the various pyrite types of could have different ages, and it is, therefore necessary to know which type of pyrite was selected for Re-Os dating. Recently, Hnatyshin et al. (2019) studied the Re-Os geochronology of pyrite of different textural styles and timings in some carbonate-hosted Zn-Pb Irish deposits. They

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suggested that Re-Os geochronology coupled with in-situ sulfur isotope and LA-ICPMS analyses were invaluable. Such a study should be done at Irankuh because the pyrite is of multiple generations/stages (pre-ore, main-ore, and post-ore) and each of these may display various textures (massive, vein-veinlet, laminated). Leach et al. (2010) suggest that MVT deposits formed in front of the carbonate platform in the foreland basin with no igneous activities (Table 4), whereas IMD ore deposits are associated with back-arc basin extension (Azizi et al., 2018; Rajabi et al.,

2019). In addition, the presence of Lower Cretaceous magmatism (Kv crystal lithic tuff and andesite) and its close spatial and temporal association with sulfide mineralization, confirm that Tappehsorkh and some other deposits of the MEMB such as Tiran (Yarmohammadi et al., 2016), Darehnoghreh (Fadaei et al., 2018) and Ab-Bagh (Movahednia et al., 2018) are associated with Lower Cretaceous magmatism and could not formed as MVT-type deposits. Considering the texture of sulfide minerals, common occurrence barite, negative sulfur isotope signatures and the large range from low to high temperature of hydrothermal

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ore-bearing fluids in the Tappehsorkh deposit (85-260° C; Table 4), the MVT model is not applicable to the sulfide deposits of the IMD.

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The close spatial association of normal faulting with sulfide mineralization in the Tappehsorkh deposit is very similar to typical features previous reported in numerous

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SEDEX and Irish-type deposits throughout the world. In these deposits, normal faults controlled the transport of ore-bearing fluids to the site of the sulfide deposition (Table 4).

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In the Irish deposits, orebodies were mainly emplaced in the carbonate rocks and to a lesser extent in siltstone (Wilkinson, 2014). Massive replacement, together with minor

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veins and open space fillings are reported (Hitzman et al., 2002; Wilkinson et al., 2005; Wilkinson, 2014). In the case of SEDEX deposits, massive, bedded and stockwork sulfide mineralization also occur in both detrital sedimentary (Goodfellow and Lydon, 2007; Leach

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et al., 2010) and carbonate host rock (e.g., Red Dog District in Alaska, Kelley et al., 2004a; Lady Loretta, Large et al., 2005).

The cross-cutting nature of the sulfide-bearing veins (Figs. 9b and 10a), the location of stockwork beneath the massive ore adjacent to the GBF observed in the Tappehsorkh deposit are similar to the stockwork zone of vent-proximal SEDEX-type deposits (e.g.,

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Sangster, 2002; Goodfellow and Lydon, 2007; Rajabi et al., 2015). The temperatures of the hydrothermal fluids in the Irish and SEDEX deposits is

about 70-280 ºC and 70-300 ºC, respectively (Table 4; Wilkinson, 2014). As observed in Figure 17, inclusions studied in massive sphalerite, stockwork quartz and dolomite of the Tappehsorkh as well as massive and stockwork sphalerite of Gushfil deposit fall within the intermediate to dense brines field of Sangster (2002), and is consistent with SEDEX mineralizing fluids.

The sulfur isotope compositions of sulfide minerals from the Irish deposits are predominantly negative (Wilkinson, 2014), whereas those of the SEDEX deposits are positive (like the Red Dog deposit; Kelley et al., 2004b), negative (like in the Anarraaq deposit; Kelley et al., 2004a), and both negative and positive (at Howard’s Pass; Gadd et al., 2017). Timing of sulfide mineralization in the SEDEX deposit is thought to be syngenetic and/or early diagenetic, whereas in Irish deposits it is early diagenetic (Kerr, 2013; Wilkinson, 2014).

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Numerous worldwide sediment-hosted Zn-Pb deposits are associated with hydrothermal alteration such as dolomitization and silicification (Kelley et al., 2004a;

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Wilkinson et al., 2005; Wang et al., 2014). Such alteration is also well developed adjacent to the GBF in the Tappehsorkh deposit which is spatially associated with sulfide

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mineralization.

Based on geological, geochemical, textural and structural features, the Tappehsorkh

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deposit shares many similarities with Irish- and SEDEX- type deposits. Since the Irish-type deposits can be classified as a diagenetic carbonate-replacement sub-type of SEDEX

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deposits (Goodfellow and Lydon, 2007; Wilkinson, 2014), we consider that the Tappehsorkh deposit is a replacement SEDEX-type Zn-Pb deposit formed during Lower

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Cretaceous. 11. Conclusions

The Tappehsorkh Zn-Pb (-Ag-Ba) deposit is hosted in the LCCCP rocks. Bedded ore facies including framboidal, laminated and disseminated sulfide and some textures such as concomitant folding of sulfide laminae with silty laminae suggested that early stage of

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mineralization in the Tappehsorkh deposit was synsedimentary to early diagenetic. Massive and stockwork sulfide textures associated with the lithology of host rocks

provide unequivocal evidence of replacement as the most important process in the formation of the Tappehsorkh orebodies. Distribution of the sulfide minerals and pervasive dolomitization, silicification, and sericitization in the vicinity of the GBF suggest this fault was a conduit for sulfur-poor, metal-bearing hydrothermal fluids.

The reduced sulfur originated by TSR at the site of sulfide mineralization. Petrographic, textural and structural, geochemical and isotopic data support a model encompassing an early stage of fine-grained sulfide minerals (framboidal and laminated) formed within the host rocks (Fig. 16a). This stage was followed by sub-seafloor replacement and hydrothermal coarsening of sulfide minerals as a consequence of the mineralizing fluid flow within crystal lithic tuff, black siltstone, and dolostone host rocks (Fig. 16a).

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The hydrothermal activity ceased soon thereafter, and is not recorded in the upper stratigraphical rock units (K4l, Kl and K5sh, Fig. 16a). During the Upper Cretaceous

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orogenesis, domino-normal (which crosscut the dolostone host rocks) and reverse reactivation of the GBF caused deformation and minor sulfide remobilization, and the

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formation of post-ore stage sphalerite (Sph III), galena (Gn III) and pyrite (Py III) as strain fringes, cataclastically sheared minerals, foliation-like and other deformational textures

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(Fig. 16b).

Collectively, this evidence shows that the Tappehsorkh deposit should be

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considered as a diagenetic replacement SEDEX-type deposit which affected by later deformation (compressional?) processes. This classification has strong implication for

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further exploration in the MEMB, in the IMD in general. Acknowledgements

Financial support for this study was provided by Tarbiat Modares University of Tehran. We thank the late Donald. F. Sangster for his contribution to the discussion of the ore genesis process, for strongly supporting this study, and for discussion on sulfide

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mineralization in the Irankuh district.

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Movahednia, M., Rastad, E., Rajabi, A., González, F., 2018. Evidence for synsedimentary faulting and reduced formation environment of the Ab-Bagh

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SEDEX-type Zn-Pb deposit, South of Shahreza, Sanandaj-Sirjan zone. Scientific Quarterly J. Geosci 27: 233-244. Nakini, A., 2013. The Structural analysis of Irankuh and Tiran areas (S and W Isfahan). M.Sc. thesis, Tarbiat Modares University, Tehran, 182p. Passchier, C.W., Trouw, R.A.J., 2005. Microtectonics. Springer Heidelberg, 366p. Peernajmodin, H., Rastad, E., Rajabi, A., 2018. Ore structure and texture, mineralogical and fluid inclusions studies of the KuhKolangeh Zn-Pb-Ba deposit, MalayerIsfahan metallogenic belt, Southern Arak, Iran. Scientific Quarterly J. Geosci 27, 287-303.

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Paytan, A., Kastner, M., Campbell, D., Thiemens, M.H., 2004. Seawater sulfur isotope fluctuations in the Cretaceous. Science 304, 1663-1665.

Rajabi, A., Rastad, E., Canet, C., 2012. Metallogeny of Cretaceous carbonate-hosted Zn-Pb deposits of Iran: geotectonic setting and data integration for future

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mineral exploration. Int. Geol. Rev. 54(14), 1649-1672.

Rajabi, A., Mahmoodi, P., Rastad, E, Niroomand, Sh., Canet, C., Alfonso, P., Tabbakh

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Shabani, AA. Yarmohammadi, A., 2019. Comments on “Dehydration of hot oceanic slab at depth 30-50 km: Key to formation of Irankuh-Emarat Pb-Zn

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MVT belt, Central Iran” by Mohammad Hassan Karimpour and Martiya Sadeghi. J. Geochem. Explor. 205, 106346. Rastad, E., 1981. Geological, mineralogical, and facies investigations on the Lower

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Cretaceous stratabound Zn-Pb-(Ba-Cu) deposits of the Irankouh Mountain Range, Esfahan, west Central Iran. Ph.D. thesis, University of Heidelberg, 334p.

Rastad, E., Boveiri Konari, M., Kalender, L., 2017. Implication of Geochemical Investigations on the Genetic Model of Sediment-Hosted Base Metal DepositsAn Example of Zn-Pb-(Ag-Ba) Deposits of the Irankuh Mining District.

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Scientific Quarterly J. Geosci 23, 42-64.

Sangster, D.F., 2002. The role of dense brines in the formation of vent-distal sedimentary exhalative (SEDEX) lead-zinc deposits: field and laboratory evidence. Miner. Deposita 37, 149-157.

Shafaii Moghadam, H., Stern, R.J., 2011. Geodynamic evolution of Upper Cretaceous Zagros ophiolites: Formation of oceanic lithosphere above a nascent subduction zone. Geol. Mag. 148, 762-801.

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Turner, J.S., Campbell, L.B., 1978. The flow of hot saline solutions from vents in the seafloor- some implications for exhalative massive sulphide and other ore deposits. Econ. Geol. 37, 1082-1100. Wang, C., Dengm J., Carranza, E.J.M., Lai, X., 2014. Nature, diversity and temporalspatial distributions of sediment-hosted Pb-Zn deposits in China. Ore Geol. Rev. 56, 327-351. Wilkinson, J.J., 2014. Sediment-hosted zinc-lead mineralization: processes and perspectives. Treatise on Geochemistry 2nd edition, 219-249. Wilkinson, J.J., Eyre, S.L. and Boyce, A.J., 2005. Ore-Forming Processes in Irish-Type

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Carbonate-hosted Zn-Pb Deposits: Evidence from Mineralogy, Chemistry, and Isotopic Composition of Sulfides at the Lisheen Mine. Econ. Geol. 100, 63-86. Yarmohammadi, A., Rastad, E., Rajabi, A., 2016. Geochemistry, fluid inclusion study and genesis of the sediment-hosted Zn-Pb (±Ag± Cu) deposits of the Tiran

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basin, NW of Esfahan, Iran. Neues Jb. Miner. Abh 193, 183-203.

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Figure captions Fig. 1. Tectonic map of Iran showing distribution of sediment-hosted Zn-Pb deposits; note the location of the IMD in the SSZ and MEMB (IMD: Irankuh Mining District; MEMB: MalayerEsfahan metallogenic belt; Al: Alborz zone; CIGS: Central Iranian zone; E: East Iran ranges; K: Kopeh-Dagh; KR: Kermanshah Radiolarites subzone; KT: Khazar-Talesh-Ziveh structural zone; L: Lut block; M: Makran zone; Oph: ophiolite belts; PB: Posht-e-Badam block; SSZ: SanandajSirjan zone; T: Tabas block; TM: tertiary magmatic rocks; UD: Urumieh-Dokhtar magmatic arc;

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Y: Yazd block; Z: Zabol area; Za: Zagros ranges (tectonic and structure map of Iran modified

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after Alavi, 1994 and Aghanabati, 2004).

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Fig. 2. Geological map of the IMD showing the locations of the ore deposits in the Lower

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Cretaceous clastic-carbonate-pyroclastic sequence (modified after Boveiri, 2016).

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Fig. 3. Photographs of main features along the GBF in the IMD. (a) View of the fault plain with gentle dip that separates Jurassic shale (Js) and Lower Cretaceous (K3d) rocks at the Gushfil mine. (b) Photographs showing vertical to semi-vertical dip along the GBF at Tappehsorkh I. (c) Underground pictures of the GBF, exposing the vertical fault plane between Jurassic shale (Js) Lower Cretaceous units (K3d) in deep levels. (d) Images from BOF in which bedding and lamination trends changes from horizontal to vertical (GBF: Gushfil-Baghabrisham fault; BOF:

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Bedded ore facies).

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Fig. 4. (a) Synthetic stratigraphic column of the Tappehsorkh deposit. (b) General stratigraphic units and regional dolomite (K3d) observed in the Tappehsorkh (view to SSW). (c-d)

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photomicrographs of Kv unit.

Fig. 5. (a) Location of the Tappehsorkh I and II deposit at the satellite image and distribution of

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sulfide and non-sulfide mineralization and faults observed in the Tappehsorkh. (b) SW-NE crosssection of Tappehsorkh deposit containing two ore-bearing sulfide horizon. (c) Larger view from the location of two orebodies (rectangle shown in Fig. 5b) which show these two orebodies were originall one ore facies that was subsequently folded (NF: domino-type normal fault). Note that adjacent to the GBF, sphalerite-galena-tetrahedrite is common, and barite and pyrite re common distal from it.

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Fig. 6. Photographs of the sulfide ore facies in the Tappehsorkh deposit. (a) The massive sulfide ore-facies at Tappehsorkh I replacing the host dolostone (K3d). Note ore-bearing strata (yellow lines) has been crosscut and displaced by later fault (view to ENE). (b) Stratiform-stratabound massive sulfide ore-facies (below the drawn yellow line) occurring as a replacement of the host

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dolostone (K3d) in the Tappehsorkh II which is limited to overlying K3l unit (view to SW).

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Fig. 7. Photographs of folding in the Tappehsorkh deposit. (a) Open folding in the dolostone (view to W). (b) Tight and/or overturned folding in the limestone (view to W). π diagram and

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axes plains for all type of folding is also shown at right hand.

Fig. 8. Photomicrographs of the various hydrothermal alteration styles observed at the Tappehsorkh deposit. (a) Regional D1 dolomite which replaced the host micritic limestone. (b) Photomicrographs of hydrothermal D1 dolomite which has been brecciated and then replaced by 36

D2 dolomite. (c) Wholesale replacement of D1 dolomite with D2 dolomite. Note the complete replacement of orbitolina fossils with hydrothermal D2 dolomite, quartz, and sphalerite. (d) D2 dolomite brecciated and cemented by coarse-grained euhedral to subhedral D3 dolomite. (e) Hydrothermal dolomite (D2 and D3) replaced by hydrothermal quartz which itself has been replaced by galena in the K3d host rock. (f) Hydrothermal sericite in the Kv host rock (Sp: sphalerite; Gn: galena; Py: pyrite; Or: orthoclase; Ser: sericite; Qz: quartz; L: lithic; Mic: micrite;

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O: orbitolina; M: Miliolida; B: benthic foraminifera).

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Fig. 9. Hand specimen photographs (a-d) and photomicrographs (e-p) of sulfide ore facies at the Tappehsorkh deposit. (a) Hand specimen of bedded ore showing alternating siltstone and sulfide laminae. (b) Hand specimen of sulfide-rich (sphalerite-pyrite-galena-chalcopyrite) vein-veinlets that randomly crosscut the host siltstone. (c) Hand specimen of the host dolostone which has been almost wholly replaced by massive sulfide minerals. (d) Hand specimen from the brecciated siltstone which is replaced by massive sphalerite and galena. (e) Diagenetic micro-folding of

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sphalerite and organic matter in the laminated siltstone (transmitted light). (f) Photomicrograph (reflected light) of fine-grained, laminated and disseminated sulfides in the host laminated

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siltstone. Photomicrographs (reflected light) of framboidal pyrite in black siltstone (g) and dolostone (h) host rocks. Note the later phase of coarse-grained sphalerite and galena. (i)

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Hydrothermal D3 dolomite-quartz-sulfide vein-veinlets cross-cutting the laminated siltstone. The white arrowhead indicates the lamination of the host siltstone. Pyrite vein-veinlet replaced along the lamination of the siltstone. (j) Photomicrograph (reflected light) of the massive ore (GST(C)

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sub-facies) in the host siltstone. Pyrite is replaced by chalcopyrite and tetrahedrite. Galena is replaced by tetrahedrite, itself replaced by sphalerite. (k) Presence of sphalerite, galena and

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pyrite in the (SGP) sub-facies of massive sulfide ore in Tappehsorkh I. (l-m) Photomicrograph (reflected light) of sphalerite-galena-barite-rich sub-facies (SGB) of massive sulfide ore. (n-o) photomicrographs from barite and pyrite in the BP sub-facies. (p) Replacement of orbitolina with

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sphalerite and galena. Reflected light photomicrographs of abundant framboidal pyrite (l-m) in host dolostone (Sp: sphalerite; Gn: galena; Py: pyrite, Cpy: chalcopyrite; Tet: tetrahedrite; Ba:

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barite; Qz: quartz; D: dolomite; SS: siltstone; om: organic matter; O: orbitolina).

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Fig. 10. Outcrop (a), hand specimen (b-c), transmitted (d, f, h, j, k) and reflected (e, g, I, l, m) photomicrograph from post ore stage related to deformation adjacent and along the GBF. (a) Changing the orientation of bedded ore facies from horizontal to vertical trend. Insets are the location where samples were selected for microscopic studies. (b-c) Increasing the size of dolomite, galena and sphalerite in the host siltstone along the reverse fault. Transparent (d) and reflected (e) microscopic pictures of sphalerite and galena forming in pressure shadow domains around coarse-grained pyrite. Transparent (f) and reflected (g) microscopic pictures which show

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pressure shadows of galena around enlarged sphalerite. Transparent (h) and reflected (i) Photomicrograph from coarse-grained galena and sphalerite which bended the laminae of host siltstone. (j-k) D4 dolomites and quartz have compressed together and formed extraordinary

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crystals than the host siltstone showing later crystal growth. (l) foliation-like textures of sphalerite and galena in the host laminated siltstone showing later coarsening of crystals. Note

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the boudinage-like texture of coarse-grain galena. (m) Various trend of galena cleavage and

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pyrite, Ba: barite; SS: siltstone; Qz: quartz).

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mixtures of galena and pyrite which is observed near the GBF (Sp: sphalerite; Gn: galena; Py:

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Fig. 11. Paragenetic sequence including mineralization stages and textures in the Tappehsorkh

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deposit.

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Fig. 12. Histogram of sulfur isotope ratios measured in sulfide and sulfate (barite) minerals from

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the Tappehsorkh deposit.

Fig. 13. Photomicrographs of primary two-phase (L+V, white arrow) and secondary one-phase (V, blue arrow) fluid inclusions in the massive sphalerite from Tappehsorkh II. Evidence of

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necking down and leakage are shown by yellow arrow.

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Fig. 14. Plot of homogenization temperatures (ºC) vs. salinity (wt. % NaCl eq.) from the fluid inclusions studied in massive sphalerite and stockwork quartz and dolomite in the Tappehsorkh.

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Fig. 15. Homogenization temperatures (ºC) vs. salinity (wt. % NaCl eq.) diagram from the Tappehsorkh deposit (massive sphalerite, stockwork quartz and dolomite) and (massive and stockwork sphalerite) Gushfil deposit (Boveiri et al., 2017) in the IMD. All micro-thermometric

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measurements fall in the buoyant, intermediate and dense brines field of Sangster (2002). The boxes show ranges of homogenization temperature and salinities for different deposit types include SEDEX deposits (from Ansdell et al., 1989; Large et al., 2004) Irish (from Wilkinson, 2014), and MVT (from Leach et al., 2005) deposits. Point A is the position of seawater at 2 ºC. Line AB and AC are isodensity line from Hass (1976) and Turner and Campbell (1987), respectively.

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Fig. 16. Schematic genetic model for the sulfide mineralization in the IMD. (a) Lower Cretaceous syn-sedimentary normal faulting led to the formation of a graben basin filled by clastic-carbonate-pyroclastic rocks (LCCCP). Early ore stage (fine-grained disseminated and

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laminated) and main ore stage (massive sulfide replacement) is syn-sedimentary to early diagenetic in timing. (b). Compressional event (during Upper Cretaceous) led to reverse faulting of the GBF, folding of the LCCCP and precipitation of the post-ore stages mineralization.

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List of tables Table 1. Sulfur isotope ratios (‰ δ34SCDT) of sulfide and sulfate minerals from the Tappehsorkh deposit.

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Th (°C) 118 137 139 140 143 147 150 154 160 161 126 130 137 144 144 195 198 199 180 150

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wt. % NaCl 14.2 12.9 12.9 9.2 nv 8.7 20.91 6.2 8.7 14.2 23.32 23.32 12.9 nv nv nv 12.9 nv nv nv

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Tmice (°C) -10.2 -9 -9 -6 nv -5.6 -18 -3.8 -5.6 -10.2 -24.3 -26.3 -9 nv nv nv 12.9 nv nv nv

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Size 8 16 14 20 20 6 20 16 16 12 16 12 5 8 8 12 26 12 8 16

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Row 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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Table 2. Summary of fluid inclusion microthermometric data from massive sphalerite (main ore

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Th (°C) 118 137 139 140 143 147 150 154 160 161 126 130 137 144 144 195 198 199 180 150

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wt. % NaCl 14.2 12.9 12.9 9.2 nv 8.7 20.91 6.2 8.7 14.2 23.32 23.32 12.9 nv nv nv 12.9 nv nv nv

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Tmice (°C) -10.2 -9 -9 -6 nv -5.6 -18 -3.8 -5.6 -10.2 -24.3 -26.3 -9 nv nv nv 12.9 nv nv nv

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Size 8 16 14 20 20 6 20 16 16 12 16 12 5 8 8 12 26 12 8 16

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Row 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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Table 3. Summary of identical features of SEDEX-, MVT-, and Irish-type deposits compared to IMD and included Tappehsorkh deposit (Based on Wilkinson, 2014). SEDEX (Wilkinson, 2014)

Irish (Wilkinson, 2014)

MVT (Wilkinson, 2014)

Irankuh Mining District (Boveiri et al., 2017, 2018, and this study)

Tectonic setting

Intracontinental or failed rift basins, rifted continental margin

Carbonate ramp and extensional basins on extending continental margin

Platform carbonate sequence at foreland thrust belts

Lower Cretaceous back-arc basin

Host rokcs

Shales, carbonates, calcareous/organic-rich siltstone, less commonly sandstone and conglomerate

Non-argillaceous carbonates within mixed carbonate-siliciclastic succession

Mainly dolostone and limestone, rarely sandstone in carbonatedominant sequences

Mainly dolostone, black siltstone, crystal lithic tuff, minor sandstone

Structural controls

Synsedimentary faults controlling sub-basins

Ore-body geometry

Single or multiple wedge- or lens-shaped, or sheeted/stratiform geometry

Texture

Bedding-parallel, fine-grained, framboidal, layered, banded, with or without coarsergrained brecciated, veined, fragmental or chaotic textures

Stringer zone

Maybe underlain by feeder zone

Ore mineral

Sphalerite, galena, pyrite, pyrhotite, marcasite, minor sulfosalts, chalcopyrite

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Features

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Synsedimentary faults controlling sub-basins Single or multiple lenses with generally stratiform but strictly stratabound

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Dominated by massive sulfide but highly variable and complex textures. Mostly replacement, common veins and locally open space filling Maybe underlain by feeder zone Sphalerite (low Fe), galena, pyrite, marcasite, minor sulfosalts, chalcopyrite Dolomite, calcite, quartz

calcite, siderite, dolomite, ankerite, quartz

Predominantly positive

Predominantly negative

Ore depositional processes

Reduced seawater sulfate (BSR or TSR) in host rock or second fluid

Reduced seawater sulfate (BSR) in host rock or second fluid

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Gangue minerals Barite occurrences sulfur isotope signature

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Barite is common to absent

Normal, transtensional, and wrench faults

Syn-sedimentary faults

Commonly stratabound, pipes or tabular zones

Stratiform and stratabound lensshaped

Coarsely crystalline to fine-grained, massive to disseminated, replacement and open space filling Not observed Sphalerite, galena, pyrite, marcasite, minor sulfosalts Dolomite, calcite

Barite is common, locally economic Barite is minor to absent Predominantly positive Reduced seawater sulfate (TSR) in host rock or second fluid Mostly Low temperature (90-150°)

Low to high temperature (70-300°)

Low to moderate temperature (70280°)

Timing of mineralization

Syngenetic and/or during early diagenesis

mostly during diagenesis, minor syngenetic

Epigenetic

Associate igneous activity

Tuffs related to synchronous distal volcanism maybe present

Close spacial and temporal association with volcanic activity

Not associated with igneous activity

Ore fluid

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Fine-grained, bedded, framboidal, laminated, coarse-grained brecciated, massive sulfide replacement Present below the main ore-body Sphalerite, galena, pyrite, tetrahedrite, marcasite, chalcopyrite, minor bornite Dolomite, calcite, quartz Barite is common Negative Reduced seawater sulfate (BSR) in host rock or second fluid Low to high temperature (85-260°) Syngenetic to early diagenesis in early ore stage, and epigenetic in post-ore stage Close spacial and temporal association with volcanic activity