Iranian Zinc - Mehdiabad/Mehdi Abad, Emarat, Angouran, Koushke/Kushk, Nakhlak, Kuh e Surmeh, Irankuh


Main commodities: Zn Pb Ag
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A series of significant zinc deposits are known in Iran, including:

Mehdiabad or Mehdi Abad - 394 Mt @ 4.2% Zn, 1.6% Pb, 36 g/t Ag (Union Resources, 2006)
    #Location: 31° 1' 59"N, 55° 16' 50"E.
Angouran - 22 Mt @ 24% Zn, 6% Pb, 110 g/t Ag (USGS Mineral Resources On-Line, viewed 2014)
    #Location: 36° 37' 28"N, 47° 24' 21"E.
Emarat - 26.3 Mt @ 2.1% Zn, 3.1% Pb, 50 g/t Ag (USGS Mineral Resources On-Line, viewed 2104)
    #Location: 33° 51' 0"N, 49° 36' 12"E.
Irankuh or Iran Koh - 17 Mt @ 11% Zn, 2.5% Pb (Res., 1990, RTZ, 1991)
    #Location: 32° 27' 26"N, 51° 34' 8"E.
Koushke or Kushk - 5.4 Mt @ 11% Zn, 2.3% Pb (USGS Mineral Resources On-Line, viewed 2014)
    #Location: 31° 45' 14"N, 55° 45' 39"E.
Kuh e Surmeh - 2.8 Mt @ 10% Zn, 4.8% Pb (USGS Mineral Resources On-Line, viewed 2014)
    #Location: 28° 4' 57"N, 52° 5' 38"E.
Nakhlak - 3 Mt @ 5% Zn, 75 g/t Ag (Res., 1990, RTZ, 1992)
    #Location: 33° 34' 4"N, 53° 50' 49"E.
Anjireh-Vejin - 2 Mt @ 3.7% Zn, 2% Pb (USGS Mineral Resources On-Line, viewed 2014)
    #Location: 32° 43' 50"N, 51° 8' 56"E.
Ãhangarãn - 0.52 Mt @ 10% Zn, 10% Pb (USGS Mineral Resources On-Line, viewed 2104)
    #Location: 34° 5' 22"N, 49° 14' 41"E.
Lakan - 0.3 Mt @ 2% Zn, 5% Pb (USGS Mineral Resources On-Line, viewed 2014)
    #Location: 33° 44' 15"N, 49° 53' 34"E.

Angouran, Koushke and Irankuh, along with a number of other open cut and underground mines, including Lakan and Shankuh, produced around 65 000 t of Zn in concentrate in 1990.

Mehdi Abad

  The Mehdi Abad (or Mehdiabad) deposit is located ~100 km SE of the city Yazd and ~500 km SE of Teheran in central Iran. The main part of the orebody, the Valley Orebody (VOB) is located in a depression surrounded by hills and mountains, whilst the second orebody, the Mountain Orebody (MOB) represents the highest parts of the oxide ore mineralisation.
  The Mehdi Abad zinc-lead deposit is located in the Central Iranian Shield, where Cretaceous limestones and sandstones were deposited over Jurassic rocks. A marine transgression commenced at the beginning of the Cretaceous with orbitulina-bearing carbonates and shales. Major faults became active during the Kimmerian Orogeny, producing horst and sediment filled graben structures in Central Iran (Azari and Sethna, 1994). The Mehdi Abad deposit was deposited within a sedimentary basin which occurs is between the Chapedony fault to the east, and the Nain Deshir fault to the west (Azari and Sethna, 1994). Except on the mountains and ridges, the Mehdi Abad deposit is covered by alluvial overburden.
  The Cretaceous sequence has been subdivided into the Sangestan Formation as the base, the Taft Formation in the middle, and the Abkou Formation on top of the succession. Together these formations are composed of detrital siliciclastic rocks with carbonates that increase upwards..
  The Sangestan Formation, comprises ~200m of partly cross-bedded sandstone, shales and siltstones with intercalated calcarenite layers and fine- to coarse-grained quartzo-feldspathic sandstones, sandy shales and limestones (containing fragments of corals). The base is marked by red to purple sandstones.
  The Taft Formation unconformably overlies the Sangestan Formation, and consists mainly of ~260 m of dolomite and dolomitic to ankeritic limestone, commencing with nodular limestone, overlain by massive, grey to yellowish limestone with dolomitic zones and ore.
  The Abkou Formation is a ~250 m thick succession, unconformably overlying the Taft Formation, commencing with a basal limestone and chert, followed by massive and porous grey reefal limestone that may be mineralised, shales with intercalated limestone, chert bearing shaly limestone, massive grey to dark grey, rarely chert-bearing limestone and an upper band of alternating limy shales and bedded gray limestone which is rarely chert bearing.
  The VOB is located in a valley and is covered by up to 250 m of alluvial overburden, whereas the MOB is exposed on a mountainside in the northwestern part of the deposit. The MOB is completely oxidised, whereas the main portion of the VOB comprises sulphides. The non-sulphide, calamine ore of the MOB is hosted in the Abkouh Formation whereas both the sulphide ore and the non-sulphide ore of the VOB are hosted in the Taft formation. The distribution illustrates the large vertical (stratigraphic) extent of the mineralisation.
  The VOB zinc and lead mineralisation of the Taft Formation is laterally limited by faults. Beyond these terminating structures, the same Formation shows no notable lead and zinc mineralisation. Generally, the sulphide ore of the VOB is associated with dolomite or ankeritic limestone.
  The Abkou Formation occurs in the north, NW and west of the deposit area, overlying the Taft Formation, hosting the mineralisation of the MOB, in brecciated karstic limestones overlying limy shales and marly limestones. The mineralisation only occurs in the brecciated limestones, but is repeated by folding (G.S.I., 1988) due to movements of the two adjoining faults. Beyond the Mehdi Abad orebody, the Abkou and other formations are not folded, and the Abkou sequence is not mineralised in other non-folded and non-brecciated regions.
  The structural geology is controlled by three main fault systems striking north-south, NE-SW and NW-SE., These faults apparently represent one of the main controlling factors of mineralisation.
  The Mountain Orebody (MOB) is limited to the west by the Black Hill Fault, and in the east by the Forouzandeh Fault. The Black Hill Fault is a normal dip slip fault, striking NNW-SSE and dipping ~65 to 70°NE. The Forouzandeh Fault is a dextral strike-slip structure, striking ~60° to NE and dipping ~50 to 80°NW. The enclosed strata between these faults are intensively folded, whilst no folding can be recognised beyond these two major faults. The folding is due to lateral displacement on the two faults and is unique to the area of the Mehdi-Abad zinc-lead deposit.
  The non-sulphide zinc-lead ore at the MOB mainly occurs at three different levels within the Abkouh Formation, which is the result of fold repetition (GSI., 1988), with the mineralisation predominantly hosted within the massive limestone. Mineralisation is exclusively composed of non-sulphide minerals, including hemimorphite, smithsonite and hydrozincite. No sulphide minerals have been observed. The host rocks to the MOB are intensely faulted, brecciated, and locally mylonitised.
  The occurrence of the MOB non-sulphide zinc ore is strata-bound on a regional scale, but in detail is spatially related to faults, fault-breccias, and possibly to localised (karst-) solution collapse breccias. It can be subdivided into a red and a white zinc ore. The red zinc ore contains up to ~30% Zn, ~17% Fe and other metals such as Pb and lesser As. In contrast, the white zinc ore has typically has up to 40% Zn, but low concentrations of Fe (<7%), Pb and As. The most important non-sulphide zinc minerals are hydrozincite and hemimorphite with traces of smithsonite. The red zinc ore occurs over the full stratigraphic range of the MOB, as lenses or irregular shaped bodies with varying dimensions that vary from several metres up to several tens of metres. The distribution of of red zinc ore compared with the white variety increases upwards. Common associated minerals in the red zinc ore are Fe-oxyhydroxides, goethite, hematite, hemimorphite, hydrozincite, smithsonite and cerrusite, occurring as the matrix of a carbonate breccia with limestone clasts of a broad size range (cm up to several tens of metres). Hemimorphite, a zinc-hydro-silicate, is one of the most important zinc minerals of this ore-type, although the ore is carbonate-hosted. The occurrence of the white zinc ore is similar to the red zinc ore. The ore pods are irregularly shaped and vary from several up to several tens of metres, increasing with depth, and is most common at the base level of the MOB. The most common minerals of this white zinc ore type are hydrozincite, smithsonite and hemimorphite. Iron-bearing minerals are rare compared with the red zinc ore. Hemimorphite is less common compared with the red zinc ore. These minerals occur as a fine-grained cement of a carbonate karst-collapse breccia. The size of the breccia clasts is similar to the red zinc ore and ranges from cm to several tens of cm.
  These supergene, non-sulphide ores of the MOB are characterised by very high Zn-, varying Pb-, and very low Ag-content, with high concentrations of As, Sb, Tl, and Sr within the red zinc ore, suggesting complex and exotic metal source(s) not expected for typical carbonate-hosted Zn-Pb deposits. A hydrothermal input from a magmatic source appears to be likely.
  The Valley Orebody (VOB) is hosted by the Taft and Abkou Formation (Azari and Sethna, 1994). The contact zone between the Sangestan and Taft Formation is characterised by an unconformity, which comprises an irregular surface with shallow water sediments between the para-reef limestone at the top of the Sangestan Fomation and the limestone of the Taft Formation. These shallow water sediments consist of red and green mudstone with worm tubes, nodular limestone and cross-bedded limestone (BRGM, 1993), probably reflecting a period of emergence, and has been used as a marker horizon.
  The Taft Formation, which host the main portion of the sulphide ore of the VOB, is characterised by an intensive and extensive brecciation, which is common within most of the VOB at Mehdi Abad (BRGM, 1993), and is probably the result of emergence, palaeocarstification, and finally collapse. Breccia fragments are angular, with fragment-sizes ranging from a cm- to tens of cm. The contact zone between the Taft and overlaying Abkou formations is also characterised by an unconformity, similar to that between the Sangestan- and Taft formations. Here, the cherty limestone of the Taft Formation shows a channelled surface, overlain by a conglomeratic bed, which consists of limestone and chert clasts (BRGM, 1993) and can be interpreted as a renewed period of emergence and probably the stage, during which karstification and collapse of the Taft Formation occurred.
  The most abundant minerals within the VOB sulphide ore are galena, sphalerite, barite, pyrite and traces of chalcopyrite. The sulphide ore occurs as impregnations within the Taft Formation breccia, filling the interstitial space between the breccia fragments, predominantly sphalerite, galena, pyrite and traces of chalcopyrite, and other sulphides, including subordinate traces as marcasite or chalcopyrite. Disseminated sulphides are commonly found as low-grade mineralisation within the barren dolomite of the adjacent strata. The sulphide mineralisation is not associated with a vein-system or with stratiform horizons, but as matrix mineralisation in a complex fracture and breccia system. In some cases, the sulphide ore itself occurs as breccia fragments. Pyrite occurs as angular crystals and masses accompanied by Zn and Pb sulphides or as spherical framboidal pyrite within dolomite and limestone. Sphalerite and galena have been partly replaced by barite in the dolomite breccia.
  Barite is ubiquitous within the mineralised dolomite breccia as well as in fractures, veins, and veinlets within the non-brecciated barren dolomite and limestone of the Taft and Abkouh formations. The barite size distribution varies over a wide range from microcrystalline sub-mm to cm-sized euhedral crystals, and grew in pores and open spaces of the dolomite.
  The sulphide mineralisation occurs as fine-grained crystals that range from euhedral to anhedral crystals. The observed sphalerite/barite ratio changes irregularly but is generally between 1:1 and 2:1 (BRGM, 1993).
This summary is drawn from "Reichert, J., 2007 - A metallogenetic model for carbonate-hosted non-sulphide zinc deposits based on observations of Mehdi Abad and Irankuh, Central and Southwestern Iran; a thesis for the degree of Doctor rerum naturalium at Martin-Luther-Universität Halle-Wittenberg, 157p."


  The Emarat deposit is located ~45 km south of Arak city and 280 km SSW of Tehran, in Markazi Province. Mineralisation is stratabound and restricted to Early Cretaceous limestones and dolostones. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz and dolomite.
  Emarat lies within the NW-SE trending, 1500 km long, and up to 200 km wide Sanandaj-Sirjan tectonic zone, the sandwiched middle member of the three parallel zones that comprise the Zagros Orogenic Belt (Ghasemi and Talbot, 2006). The other two, to the northeast to southwest respectively, are the Tertiary Urumieh-Dokhtar magmatic belt and the Zagros fold belt (Alavi, 1994). These zones were the result of subduction of the Neo-Tethyan ocean floor beneath Iran during the Cretaceous, followed by collision, which sutured Iran to Arabia (e.g., Alavi, 1980, 1994), and the subsequent continued continental convergence that built the Zagros Orogenic Belt (Ghasemi and Talbot, 2006) that separates the stable Central Iran Block from the Afro-Arabian Plate to the SW (Stöcklin, 1968). The Sanandaj-Sirjan tectonic zone is composed mainly of Mesozoic rocks deposited during the opening of the Neo-Tethyan ocean with some Palaeozoic strata (Berberian, 1977). The history of the opening of the Neo-Tethyan ocean between the late Permian and Early Cretaceous was complex, involving the NE migration of a series of microcontinental slivers from the Arabian Plate in the SW, accommodated by subduction of the oceanic crust ahead, and oceanic rifting behind (Muttoni et al., 2009; McQuarrie et al., 2003; Hessami et al., 2001).
  The oldest units outcropping in the Emarat region are Lower and Middle Jurassic metamorphic rocks. The Lower Jurassic is composed of dark grey to black, intensely folded sericite-chlorite schists, with local Intercalations of impure metamorphosed limestones. The metamorphic grade is lowermost greenschist facies. The Middle Jurassic rocks include metamorphosed phyllitic silty and clayey shales with intercalations of metamorphosed iron oxide-bearing greywacke sandstones (Kholghi, 2004; Sahandi et al., 2006).
  Progradation of the sequence in the Cretaceous sedimentary basin of the Emarat region began with the progressive, disconformable deposition of basal terrigenous deposits, composed of lower conglomerate and upper sandstone members. Occasional vesicular andesite and andesite-basalt units occur above the basal conglomerate, locally accompanied by a pyroclastic facies of variable thickness that does not always appear in this exact stratigraphic position (Sahandi et al., 2006). The volcanic unit is overlain by the ~ 100 m thick cream- to buff-coloured kdl1 unit that is composed of calcareous and dolomitic shales, argillaceous dolomite, clayey limestone, dolostone, sandy dolostone, and calcareous and dolomitic sandstones. Where the andesite-basalt lava unit is absent, Kdl1 conformably overlies the Cretaceous basal clastic unit and is conformably overlain by the orbitolina limestone Kol1 unit. Except for Kdl1, these Cretaceous units do not crop out in the Emarat region (Sahandi et al., 2006) to the west.
  The Kol1 unit comprises thick-bedded to massive orbitolina-bearing limestones, dolomitic limestones, and dolostones that grade conformably upward into the upper Kml1 unit, which is composed of marl, calcareous shale, and clayey limestones that weathers to give a low hilly landscape (Sahandi et al., 2006). In the Emarat area, white calcite veins that vary from a few mm to cm and are a few tens of cm to a few tens of metres in length, giving the rock a zebra texture in the dark grey limestones of the Kol1. These veins are parallel to subperpendicular to the bedding plane. Due to the relative abundance of organic matter, the Kml1 shale and limestone layers have a bluish to dark grey colour that becomes pale to yellow or cream-coloured after weathering. Paleontological studies suggest an Aptian to Albian age for Kol1, Albian to Cenomanian age for the Kml1 (Sahandi et al., 2006). The contact between these two units is occasionally accompanied by stratabound Zn-Pb mineralization. This is evident at the Emarat deposit and smaller Muchan and Tekyeh occurrences.
  The Lower Cretaceous sequences have been subjected to a very weak regional metamorphism, resulting from the Upper Cretaceous orogenic phase (Sahandi et al., 2006).
  In the Emarat area, the youngest rocks are Tertiary to Quaternary conglomerate, sandstone, siltstone, silty marl and alluvium (Kholghi, 2004).
  The major structural features in the Emarat area are dominantly NW-SE trending folds and faults that parallel the Zagros Orogen. The Emarat deposit is found on a NW-SE trending syncline, that has its northeastern flank overturned. The axis of the syncline is ~1.5 km long, with a core of the Kml1 shale unit, and flanks of Kol1 limestones.
  Two distinct faults systems are apparent in the Emarat area. The first is a group of relatively long, NW-SE trending faults that dominate in the mine area, and tend to be reverse faults, related to the convergence of the Arabian and Iranian plates. The second, includes a set of shorter, NE-SW trending structures with a little displacement. Whilst the ore body is occasionally crosscut and displaced by minor faults belonging to the second system, the mineralisation is not fault-controlled. Joints and fractures with no displacement are common within the host rock.
  Whilst Palaeozoic to Mesozoic magmatic rocks are widespread in the region (Ghorbani, 2002), none are evident in the Emarat area, and theclosest volcanic rocks ~12 km to the east and 20 km to the NW (Sahandi et al., 2006). There is no proven relationship between intrusives and the mineralization in the Emarat deposit.
  Stratabound Zn-Pb mineralisation occurs at the contact between the Kol1 orbitolina-bearing limestone and Kml1 shale. The sheet-like orebody is ~3 m thick (Vanaei, 1998), with small-scale folding causing local thickening. The contacts between the ore body and host rocks are frequently sharp, although contacts with the footwall limestones are occasionally diffuse.
  The ore is mainly sphalerite and galena with calcite and quartz gangue. The sulphides are commonly fine-grained disseminations and aggregates within the Kol1 limestone, although sphalerite also occurs as massive patches. The ore is not sheared or recrystallised, and all observed textures are interpreted to have formed during deposition. In thin-section, the Kol1 limestones is seen to include micrite, biomicrite, dismicrite and dolosparite rock types, with Orbitolina, algae, echinoid debris and bryozoa among the limestone constituents. Fine, clear quartz grains comprise up to 4 to 5% of the rock matrix. Some of the quartz grains are euhedral with poikilitic carbonate inclusions, whilst stylolitic calcite and quartz veinlets are common. Kml1 shale layers are dark to black coloured due to abundant organic material, with common euhedral to subhedral pyrite crystals, especially close to the mineralisation. The characteristics of the host rocks of the Emarat deposit, suggest deposition within a shallow marine epeiric platform, dominated by low-energy restricted lagoonal environments and dispersed patch reefs.
  The most abundant ore mineral is sphalerite, occurring as anhedral grains, accompanied by variable amounts of galena, pyrite and chalcopyrite. Galena commonly occurs as anhedral grains as well as veinlets in a carbonate matrix. Both sphalerite and galena contain abundant carbonate relicts from the host rocks, indicating the ore replaced host rock and had an epigenetic origin. Pyrite forms anhedral to euhedral grains in the host rocks, whilst chalcopyrite mostly occurs as blebs in sphalerite, probably due to exsolution from the sphalerite structure. The carbonate matrix of the ore is composed of calcite with minor dolomite constitutes. Quartz is commonly found as fine- to medium-grained, anhedral to subhedral crystals within the carbonate matrix, but also contains carbonate inclusions from the host rock. Locally, the carbonate host rocks has been totally replaced by quartz and sulphide minerals.
  Textural studies of the ore show that mineralisation to have taken place during two stages. The first was the main stage of ore formation, where sulphide minerals (mainly sphalerite) and fine-grained quartz replaced the host rock. The second stage involved remobilisation of calcite, quartz, sphalerite and minor galena into cracks and fissures, resulting in the formation of coarse-grained veins of calcite and quartz, which contain relatively large masses of sphalerite and galena. Occasionally, thin veinlets of calcite and quartz are seen cutting the earlier formed minerals, including those of the second stage, although similar veinlets are found in the host rock distal to mineralisation.
  Wall-rock alteration is also simple, comprising silicification, recrystallisation, brecciation, and minor dolomitisation. The most important of these is silicification which has occurred in both footwall and hanging wall rocks, but it is more extensive in the footwall limestones than in the hanging wall shales. There is a close relationship between sulphides and silica, with the sulphides locally occurring as disseminations and veinlets within the silica. Recrystallisation produced sparry calcites from microcrystalline calcite and the appearance of idiomorphic pyrite crystals at the expense of fine-grained syngenetic crystals. Although host rock brecciation is recorded at the Emarat deposit, it is not widespread and is restricted to a few places. The brecciated fragments are cemented by a matrix of calcite, quartz and some sphalerite. According to Karimzadeh (1992), dolomitisation not only produced fine-grained dolomite crystals in the rock matrix, but also formed coarse-grained automorphic dolomite crystals, some of which are zoned. Because of intensive silicification, the effects of the dolomitisation is unclear.
  This summary is drawn from Ehya et al. (1994).


  Irankuy is located ~20 km southwest of the city of Esfahan, in west-centraI lran. It is hosted by Lower Cretaceous dolostone strata in a sequence of folded shallow-marine carbonates underlain by Jurassic shales and conglomerates and overlain by limestones of the Late Cretaceous. Granodioritic stocks are mapped in the Kolahghazi area, 30 km SE of the deposit, intruded into the Jurassic shales, but show no evidence of intrusion into the Cretaceous carbonates, nor is any igneous intrusion is in direct contact with the orebodies.
  The Upper Jurassic Shemshak Formation is the lowermost in the stratigraphic unit in the sequence. It consists of ~900 m of olive-green to dark grey laminated shales with alternating clay-rich and quartz-rich layers. These shales are composed of illite, albite and quartz, with local fracture-fill barite withn the shales.
  The basal unit of the Lower Cretaceous, mainly carbonate sequence is a conformably underlying basal, 20 to 60 cm thick, red siltstone-conglomerate composed of angular fragments within an argillaceous matrix. The clasts consist of poorly sorted quartz and unweathered feldspar grains, largely derived from weathering of basement granodioritic intrusions (Zahedi, 1976). This unit rests unconformably on the Upper Jurassic shales.
  Two major carbonate sequences are recognised in the overlying succession:
Brown-coloured dolostones, which are composed of two facies: i). an argillaceous sandy unit that is ~2 to 5 m thick grading into a cryptalgal-Iaminated unit with preserved fossils (mainly Orbitolina and rudists). The dolostone strata is composed of laminae that range from several cm to 1 m in thickness, which weather to brown at the surface, with randomly distributed fractures. This unit is the exclusive host to ore mineralisation, with a strong correlation between dolomitisation and base metal mineralisation. Light grey-coloured fossiliferous limestones, which often form lens-shaped bodies 'floating' within the dolostones, surrounded by an envelope of dolomitised carbonates, represent the 'un-dolomitised' part of the sequence. The dolostones also interfinger with these limestones, with a relatively sharp mineralogical transition.
Grey bedded limestones overlying the dolostones are rich in bioclasts of Orbitolina and echinoderms (mostly crinoid stems). In many areas the limestones are overlain by shales of Albian age (Seyed-Emami et al., 1971). Extensively karstified massive Orbitolina limestone units with solution cavities form the main ridges in the district. They contain no major ore mineralisation.
  Ore occurs as a steeply dipping, generally stratabound, but transgressive body in detail, which is tabular, and appears to occur along a fault zone at the contact between the Jurassic and Cretaceous.
  The major structural features in the district are dominantly NW-SE trending folds and faults which parallel the main Zagros thrust fault. The first major deformation in the Zagros belt took place during the Late Cretaceous (Kashfi, 1976) as a result of convergence of the Arabian and Iranian plates.
  Faulting in the Irankuh district represents two well defined systems. The major east-west trending, high-angle Irankuh fault strikes parallel to bedding, and where it cuts across the bedding at low angles, is considerably downthrown to the south. The absence of a marker horizons precludes an estimate of the magnitude of displacement. This fault also brings the shales into contact with dolostones. The Goushfil orebody is localised by this major fault structure. The second system is a group of faults which are north-south trending and are mainly responsible for the formation of valleys. The host-rock generally dip att ~45°, steepening to 75 to 85°N at the Goushfil mine site.
  Brecciation occurs in the host rocks adjacent to the ore zone and associated fault, comprising angular, unoriented, poorly sorted fragments of finely crystalline dolostone set in a matrix of sparry dolomite and barite with sharp contacts indicating open-space filling. This implies that the dolostones were lithified prior to brecciation and mineralisation. Much of the ore mineralisation in the Goushfil mine is developed within dilatant fault and structurally controlled fractures.
  Sulphide mineralization in the Goushfil mine is predominantly open-space filling. The deposit is stratabound, but occurs as sheetlike lens which are usually discordant within the enclosing dolostone hosts. The mineralisation mainly comprises sphalerite, galena, pyrite and marcasite. Nonsulfide minerals are barite, dolomite, smithsonite and minor quartz.
  Virtually all the ore consists of massive microcrystalline aggregates of anhedral to subhedral grains. Sphalerite is the most abundant sulphide, occurring as rounded grains or aggregates of ~0.2 x 0.5 mm diamete grains, commonly uniformly dispersed through the galena-pyrite-rich matrix, often forming spherulites, which are relatively common in both the host rock and in the ore. Crystals of sphalerite are both veined and surrounded by galena, whilst galena and sphalerite rarely occur together as intergrowths. There is also evidence of replacement of both sphalerite by dolomite and dolomite by sphalerite. Sphalerite is sometimes replaced by pyrite. Microscopic examination shows the coarse-grained reddish-brown variety of sphalerite to have colour banding and weak zonation. Galena occurs as ~4 mm subhedral crystals, and as strained crystals with bent cleavage pits. Galena is also found as a late phase filling the interbreccia space in sphalerites. These observations suggest at least two generations of galena, precipitated during and after sphalerite. There are also reaction rims surrounding galena indicating that it has been affected by later hydrothermal fluids.
  Pyrite occurs as: i). spherulites and framboids, occurring as inclusions in sphalerite and galena, ii). laminated veins or stringers, and iii). up to 4 mm, isolated late-stage, euhedral cubic crystals, associated with massive dolomite and barite.
  Barite and dolomite are persistent minor components of the mineralisation, intimately associated with sulphide minerals, but are more concentrated in the periphery of the orebody. Large barite and dolomite crystals also dominate late-stage mineralisation, forming a white coarse-grained monomineralic cement in brecciated dolostones. Dolomite that is intergrown with galena and sphalerite often displays a perfect rhombic habit.
  Most of the sulphides in the host rock surrounding the orebody are fine grained and disseminated.
  Black, brittle, obsidian like bitumen and organic material frequently occurs both in vugs within the ore and in the intercrystalline porosity in the host.
  Although the contact between the orebody and the host rock is often sharp, it is occasionally diffuse. Dolostone recrystallisation of the host-rock appears as a crystalline bleached fringe, commonly restricted to a zone <5 cm from the contact with the orebody. In most places this contact is marked by a characteristic 'salt and pepper' texture, composed of rhombohedral crystals of dolomite in a matrix of quartz and organic matter. Other minerals found in the deposits are minor chalcopyrite, pyrrhotite, Pb sulphosalt and dendritic manganite.
  Discordant veins, veinlets and fractures containing coarsely crystalline barite (>5 mm), often accompanied by minor sulphide minerals, are frequently abundant, occurring as white masses in the fractured host rocks. They are sporadically distributed throughout the host rock, but are most abundant in the vicinity of the ore zones. The veins commonly have sharp, well-defined contacts with the host rock. Tabular, up to 2.5 x 0.25 m lenses of massive barite with irregular walls often grade into planar veins along their long axes. They contain angular fragments of dolostones up to 10 cm in diameter that commonly appear to float in the matrix ofcoarse sparry dolomite and barite. In some areas a considerable amount of the dolostones is weakly mineralised, mainly by barite. Deformed sulphide and barite veins are widespread throughout the area, commonly boudinaged, with en echelon vein structure.
  This summary is drawn from Ghazban et al., 1994).


  The Koushke (Koushk or Kushk) deposit is located 35 km NE of Bafq, 165 km east of Yazd, in Yazd Province. It is part of the Bafq metallogenic province of central Iran, which together with the Arabian Shield.
  The deposit has been intermittently mined on a small scale for centuries, with modern exploration, followed by mining from the 1960s.
  The host sequence is late Neoproterozoic Ediacaran (Infracambrian or Vendian) Rizu-Dezu (or Kushk) Series dated at 583 to 550 Ma, is the younger and less metamorphosed predominantly sedimentary section of the Neoproterozoic complex od the Central Iran terrane. It overlies the ~750 to 583 bimodal volcano-plutonic assemblage attributed to multistage rifting that hosts the 'Kiruna-type' Bafq magnetite deposits.
  The pyritic carbonaceous shales (the hosts) and intercalated limestone and dolostone, also contain units of green mafic meta-tuff and potassic rhyolitic volcanics, locally intruded by microdiorite. This sequence is locally overlain by erosional remnants of Jurassic sandstone.
  Kushk is interpreted as a sediment hosted stratiform (SEDEX) deposit that comprises bedding-conformable massive pyrite lenses (some with relic metacolloform texture) in the black (carbonaceous) slate, gradational to a pyritic ore with dolomitic containing disseminated crystals of brown sphalerite.
  The main ore occurs as lenticular, stratabound, semi-massive sphalerite-galena-pyrite, with minor chalcopyrite.
  The pyritic bodies and black slate are frequently intersected by fracture-fill veinlets of apple-green variscite (AlPO4•2H2O). Where exposed and in the shallow subsurface the sulphide ores are converted to jarosite, then goethite.
  A second, less frequent ore variety comprises galena and sphalerite replacements in dolomite, adjacent to permeable structures.
  As an alternative to the resource quoted above, Laznika (2012) states that in 2010, the remaining reserves quoted by mine geologists were 1.5 Mt of high-grade ore (~40% pyrite, 12 to 13% Zn, 2 to 3% Pb) and 10 Mt of low-grade ore.


  The Kuh-e-Surmeh deposit lies within the Permian to Triassic Zagros carbonate platform, hosted by Permian dolomites and limestones of the Lower Dalan Formation. Mineralisation is broadly stratabound within highly fractures carbonate breccia, dolomite and dolomitic limestone. See the separate record on Kuh e Surmeh for details.

The most recent source geological information used to prepare this summary was dated: 2012.     Record last updated: 4/9/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.






  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Ehya, F., Lotfi, M. and Rasa, I.,  2010 - Emarat carbonate-hosted ZnPb deposit, Markazi Province, Iran: A geological, mineralogical and isotopic (S, Pb) study: in    J. of Asian Earth Sciences   v.37, pp. 186-194.
Ghazban, F., McNutt, R.H., Schwarcz, H.P.  1994 - Genesis of sediment-hosted Zn-Pb-Ba deposits in the Irankuh district, Esfahan area, west-central Iran: in    Econ. Geol.   v.89, pp. 1262-1278.
Gilg H A, Boni M, Balassone G, Allen C A, Banks D and Moore F,  2005 - Marble-hosted sulfide ores in the Angouran Zn-(PbAg) deposit, NW Iran: interaction of sedimentary brines with a metamorphic core complex: in    Mineralium Deposita   v41 pp 1432-1866
Rajabi, A., Rastad, E. and Canet, C.,  2012 - Metallogeny of Cretaceous carbonate-hosted ZnPb deposits of Iran: geotectonic setting and data integration for future mineral exploration: in    International Geology Review   v.54, pp. 1649-1672.
Rajabi, A., Rastad, E., Alfonso, P. and Canet, C.,  2012 - Geology, ore facies and sulphur isotopes of the Koushk vent-proximal sedimentary-exhalative deposit, Posht-e-Badam Block, Central Iran: in    J. of African Earth Sciences   v.54, pp. 1635-1648.

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