Geology, geochemistry, fluid inclusions and O-H stable isotope constraints on genesis of the Lake Siah Fe-oxide ± apatite deposit,NE Bafq, Central Iran

Ebrahim TaleFazel· Mahin Rostami

Abstract The Lake Siah iron ± apatite deposit is situated in the Bafq Mining District (BMD), Central Iran. The iron ± apatite orebodies are hosted by a succession of rhyolite, rhyolitic tuff, trachyandesite, and andesite of Lower Cambrian age. The host rock has undergone widespread alteration and mineralization stages including Na(albite–quartz), followed by Na–Ca (albite–calcite–amphibole–magnetite ± quartz ± epidote), magnetite–apatite,K(biotite ± K-feldspar),hydrolytic(sericite–quartz),and argillic (kaolinite–montmorillonite ± dickite), respectively. Electron microprobe analyses (EPMA) from magnetite and hematite show significant variations of trace elements. Based on Ni/Cr + Mn and Ca + Al + Mn versus Ti + V diagrams, the majority of magnetite samples belong to Kiruna-type deposits. At least, three generations of fluid inclusions, including solid-bearing (L + V + S)(Type I), liquid-rich (L + V) (Type II-A), vapor-rich(L + V) (Type II-B), and liquid or vapor mono-phase(Type III), are recognized in quartz and apatite. The solidbearing fluid inclusions in quartz completely homogenized at temperatures of 150 to ＞530 °C with salinities of 30–58 wt% NaCl equiv. Liquid-rich fluid inclusions in apatite homogenized to a liquid phase at 175–210 °C,whereas the vapor-rich fluid inclusions homogenized to a vapor at 335–350 °C.Oxygen isotope analysis was carried out on quartz and magnetite. The hydrogen and oxygen isotopic compositions of quartz (δ18Ofluid values of 7.57–11.04‰) show that with progress in time the oreforming solutions gradually evolved from a magmatic to meteoric-dominated source.

Keywords Iron oxide-apatite · Lower Cambrian · Kirunatype · Bafq Mining District · Lake Siah

1 Introduction

The iron oxide–copper–gold, which is denoted by IOCG,consists of a wide range of hydrothermal deposits that include economic Fe–P-REE deposits, commonly referred to as Kiruna-type deposits(Corriveau et al.2010;Williams 2010; Groves et al. 2010). The IOCG deposits have been most recently referred to as ‘‘IOA’’ (Iron oxide-apatite;Williams 2010). Fluid inclusions, stable isotopes, and halogen studies in many cases show evidence of mixing between two or more ore-forming fluids in IOCG deposits(e.g.,Haynes et al.1995;Kendrick et al.2008;Baker et al.2008;Bertelli and Baker 2010).Some studies revealed that the hydrothermal fluids in IOCG deposits were predominantly magmatic in origin (Hitzman et al. 1992; Pollard 2000, 2006; Sillitoe 2003; Richards and Mumin 2013),although some researchers proposed that non-magmatic fluids, particularly originate from an evaporitic strata(Barton and Johnson 1996, 2000; Xavier et al. 2008; Chen et al.2007;Barton 2014).Furthermore,some key features,including highly saline ore-forming fluids,pervasive sodic-(calcic) alteration zones, significant volumes of breccia,high content of P2O5and rare earth element (REE) and structurally controlled orebodies, must be considered regardless of the preferred model about IOCG deposits.

The Bafq Mining District (BMD) is a recently defined pre-Cambrian IOCG belt that includes Fe–P-(U-REE)deposits in Central Iran and the Middle East. This district has more than thirty-four major Fe–P orebodies with a total reserve of 1.8 Gt at 45–65% FeO (Daliran 2002; Stosch et al. 2011). Among this, Choghart deposit with reserve of 216 Mt, Chadormalu deposit with reserve of 400 Mt, Se-Chahun deposit with reserve of 140 Mt, Lake Siah deposit with reserve of 50 Mt and Esfordi deposit with reserve of 17 Mt as the main iron deposits at BMD (Torab and Lehmann 2007; NISCO 1979) (Fig. 1). These deposits were mostly emplaced at a data 7500 km2area,along with the N-S striking belt of Kashmar–Kerman Zone (Fig. 1).Also, a few Pb–Zn sulfide deposits such as Kushk deposit(20 Mt at 1.5% Pb and 7.0% Zn; Rajabi et al. 2012), Mn and U deposits(Jami 2005)are distinguished at BMD.The magnetite–apatite deposits at BMD occur predominantly within the un-metamorphosed Early Cambrian rhyolite to rhyodacite tuffs and volcano-sedimentary rocks (Stosch et al. 2011). In this approach, we describe the mineralization style, alteration zones, REE geochemistry and then explain the relationships between various alterations and metal distribution in the Lake Siah deposit. We also attempt to discuss the fluid inclusions and stable (O and H) isotopes data for identifying the source and evolution of the ore-forming fluids and achieving to build the genetic model of the Lake Siah deposit.

2 Geological setting

Fig. 1 Structural map of eastern-Central Iran with main blocks (Lut, Tabas and Yazd)and major iron deposits within Kashmar–Kerman Zone (KKZ)

The BMD in Central Iran is part of a Gondwana fragment located between the Alborz fold belts and Alpine Zagros.This area predominantly is composed of Upper Proterozoic basement and Neoproterozoic to Triassic cover strata(Borumandi 1973; Haghipour 1977; Sto¨cklin 1974). The Upper Proterozoic and Cambrian rocks are exposed in the arcuate Kashmar–Kerman Zone (KKZ), between the Chapedony and Kuhbanan faults (Fig. 1, Fo¨rster and Jafarzadeh 1994). The Lake Siah deposit is situated in the central part of KKZ between Esfordi P2O5-Fe deposit in north and Kushk Pb–Zn deposit in south(Fig. 2).The KKZ mostly is composed of medium- to high-grade metamorphic Late Neoproterozoic rocks (e.g., Boneh-Shurow and Posht-e-Badam complexes) (Ramezani and Tucker 2003;Verdel et al. 2007). The Posht-e-Badam is mainly composed of variable lithology including greenstones, schist,meta-greywacke, gneisses, amphibolite, marble, pyroxenite, serpentinite, meta-basalts, and conglomerates (Haghipour and Pelissier 1977). The Upper Proterozoic cover rocks include slates,quartzite,phyllites,and mafic volcanic rocks of the Tashk Formation (Fig. 2), which have been subjected to greenschist grade metamorphism (Aghanabati 2004). The Upper Proterozoic rocks are covered by a bimodal volcanic sequence with Early Cambrian age (Ca.530 Ma) (Ramezani 1997). Samani (1988) distinguished the Saghand Formation and Rizu to Dezu series(equivalent to Cambrian Volcano Sedimentary Sequence (CVSS) by Ramezani 1997) within this sequence. On the other hand,granitic plutons intruded the Tashk Formation Precambrian sequence in Early Cambrian, and subsequently felsic to intermediate volcanic and volcano-sedimentary rocks of the CVSS were deposited. The Tashk Formation Precambrian sequence is the main host of iron oxide apatite(IOA)(Daliran et al. 2009), SEDEX Zn–Pb and Fe–Mn deposits of Iran (Rajabi et al. 2012).

Fig. 2 Geologic map of the Bafq Mining District and location of major deposits Modified from Soheili and Mahdavi (1991)

The CVSS unconformably overlies the Tashk Formation tuffaceous rocks with 2000–2500 m thick (Fig. 2). The CVSS or ECVSS (Early Cambrian Volcano-Sedimentary Sequence), mainly composed of micro-conglomerates,sandstones, felsic to mafic volcanic rocks, black siltstones and shale, volcanoclastic beds, and tuffaceous shales(Haghipour 1974; Rajabi 2012; Ramezani and Tucker 2003). The Saghand Formation contains a basal conglomerate overlain by a lower basaltic and rhyolitic lavas unit(200–300 m thick), followed by shales and sandstones(150–200 m thick)(Samani 1993).The upper volcanic unit contains more than 400 m of pyroclastic rocks, lavas, and intercalated carbonates. This volcanic unit is host to the main bodies of magnetite–apatite mineralization in the BMD. In the Lake Siah area, Saghand Formation consists of dolomite, shale, sandstone, limestone thin bedded and limestone with chert bands, pyroxene andesite and andesitic basalt, rhyolite to rhyodacite volcanoclastic rocks(Soheili and Mahdavi 1991). Carbonates of the CVSS unconformably underlie the Lower Cambrian red sandstones conglomerates Lalun or Dahu Formation (Fo¨rster and Jafarzadeh 1994).Predominately volcanic rocks of this sequence belong to the alkali–calcic magmatic series(Jami 2005). The major intrusive rocks of the district including Narigan and Zarigan granitoids and Sefid granite that using U–Pb geochronology,with a reported age of 529 ± 16 and 526 ± 2 Ma,respectively(Ramezani and Tucker 2003).In the BMD Upper Pre-Cambrian and Cambrian rocks disconformably overlain by Mesozoic limestone, marl, shale and sandstone, gabbro, diorite to quartz diorite rocks (Soheili and Mahdavi 1991).

The Early Cambrian tectonic regime has been interpreted as a rift by Berberian and King (1981), while Ramezani and Tucker (2003) have proposed that it was an active continental margin along the proto-Tethys ocean,based on trace element characteristics of granitic intrusions and felsic volcanic rocks. But recently Rajabi et al. (2015)suggested that a continental margin for Early Cambrian mineralization of central Iran.

3 Methodology

Over 50 samples were taken from the Lake Siah deposit.The major characteristics of some samples were presented in Table 1.

3.1 Whole-rock analysis

Ten least altered igneous rocks were analyzed for their major oxide concentrations by X-ray fluorescence(XRF)at the Iranian Mineral Processing Research Center (IMPRC)(Tehran, Iran) with a detection limit of 0.01 wt%. Trace and rare earth elements (REE) were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS)at ACME laboratory in Toronto,Canada.Samples prepared by lithium meta-borate fusions and 100 mL of 1% HNO3total digestion. The detection limit for elements varies between 0.01 and 0.1 g/t (ppm) and analytical error is less than 2 wt% for all elements. Ten magnetite and apatite samples were handpicked after examination under a binocular microscope and analyzed for REEs by ICP-MS method at ACME.

3.2 XRD and EPMA

Powder X-ray Diffraction (XRD) from ten altered rock samples were obtained using an X’Pert-PHILIPS diffractometer. Mineral chemistry was examined by electron microprobe analysis(EPMA)at IMPRC.We used a current beam of 20 nA, an acceleration voltage of 30 kV, and a counting time of 15–20 s in microprobe analysis.Elements and X-ray lines used for the EPMA are Au(Mα),Ag(Lα),Bi (Lα), Cu (Kα), Cd (Lα), Fe (Kα), Mn (Kα), S (Kα), Sb(Lα), Se (Lα), and Te (Lα). The chemical composition of minerals was calculated by ZAF corrections with JEOL software.

3.3 Fluid inclusions

Petrography and microthermometric studies of fluid inclusions were carried out at the Department of Earth Sciences, Kharazmi University (Tehran, Iran). Fluid inclusion studies conducted on Linkam THMS600 heatingfreezing stage. Temperatures were measured by the Al–Cr thermocouple stage varies from - 190 to + 600 °C and were calibrated with synthetic inclusions at -56.6 °C(triple point of CO2), 0.0 °C (melting point of ice), and+ 374.1 °C (critical point of H2O). The cooling and heating rate varies from 0.2 and 5 °C/min within ± 0.1 °C in precision. The initial heating and cooling rate was ～10–20 °C/min, which decreased to 0.2–2 °C/min near the phase transition point. Microthermometric data were reduced using the FLINCOR software (Brown 1989).

3.4 Oxygen and hydrogen isotope

Ten quartz and magnetite have been analyzed for their O and H composition. The isotopic composition of O and H was determined at the Department of Geological Sciences at the USGS(Denver,USA),and Stable Isotope Laboratory at Cornell University (Ithaca, USA), respectively. After crushing and washing samples, minerals were separated using a binocular microscope with more than 98% purity.Oxygen and Hydrogen isotope was liberated by reaction with BrF5 by the method of Clayton and Mayeda (1963)and Kyser and Kerrich (1991), respectively. Thermo-Finnigan Delta V Advantage (LABISE) and a Finnigan MAT 252 mass spectrometer(QFIR)were used for stable isotope measurements and the results are expressed in the conventional delta per mil notation (δ, ‰). The oxygen and hydrogen isotopic compositions are reported based on Vienna Standard Mean Ocean Water (VSMOW). The analytical precisions were ± 0.1 per mil for δ18O and ±2 per mil for δD.

4 Deposit geology

The Lake Siah Fe ± P deposit is exposed in KKZ between Esfordi and Kushk mines in north and south, respectively.On the basis of the Aliabad geologic map(Hushmandzadeh et al. 2015), at least two units rocks are recognized in the Lake Siah, including: (1) Early Cambrian Volcano-Sedimentary Sequence (ECVSS or CVSS), and (2) lower part of Late Cambrian Volcano-Plutonic unit (Lake Siah caldera complex). CVSS is the main lithology of KKZ and Posht-e-Badam block. It is composed of largely unmetamorphosed sequence with micro-conglomerate, mafic to felsic volcanic rocks,sandstone,siltstone and carbonaceous black shale, volcanoclastic beds, dolomite, and gypsum(Haghipour 1974; Ramezani and Tucker 2003). CVSS is composed of Kharangan, Kuhbanan I and II complexes.The oldest unit is known Kharangan complex which unexposed in the Lake Siah and consists of green shale,greywacke, sandstone, and laminated algal limestone.Unlike the Kharangan complex, the Kuhbanan I and II complexes are observed in the Lake Siah and Kuhbanan I as the basement rocks of Lake Siah district is composed of three sub-members: Narigan, Nadigan, and Esfordi(Fig. 3). Narigan sub-members exposed in the SE Lake Siah and composed of red to violet colored arkosic sandstones with intermediate shale. These sandstones are comparable with upper part of Lalun sandstone that characterized by the existence of dark-colored cherty grains.The Nadigan sub-member with volcano-sedimentary composition consists of Archaeocyathid bearing limestone with stromatolitic structure (Fig. 4b–d), trachyandesite lava, red-colored sandstone, pale to violet micaseous shales, and dolostone. After the formation of Nadigan and Narigan sub-members as main basement rocks, this assemblage is affected by extremely felsic volcanic activities,Esfordi sub-member,including ignimbrite pyroclastic flows, andesitic lava, and andesitic tuff (Fig. 3). Esfordi sub-member is observed in the 3 Km southeastern of the Lake Siah deposit.

Based on Hushmandzadeh et al. (2015), the contacts of Esfordi with Nadigan, in many places, are faulted and disrupted causing inverse and imbricating of layers.Nadigan and Esfordi complexes and upper red sandstone can be interpreted as equivalent to Narigan complex,which overlie angular unconformably the Kharngan complex.The Nadigan and Esfordi complexes are formed in the deeper marine environments (black shales) compared to the shallow marine of the Narigan complex (sandstone and dolomite) and have intense felsic and basic volcanism activities.The youngest part of CVSS at Lake Siah belongs to Kuh-banan II, which has anextensive outcrop in the south Lake Siah and consists predominately of quartzbearing sandstone, altered dark to grey colored dolomite and thin-bedded fossiliferous (Trilobite and Hylithes)limestone.

The Late Lower Cambrian volcano-sedimentary sequence or Lake Siah caldera complex constitutes the major lithology in the Lake Siah area (Hushmandzadeh et al. 2015) (Fig. 3). The Lake Siah caldera complex with ellipsoid shape geometry is composed of three units:pyroclastic surge, subsidence caldera, lava and rhyolitic domes (Fig. 4a). The pyroclastic surge facies which occur during initial stages formation of the caldera, pyroclastic rocks assemblage, and rhyolitic lava are exposed, which resulted from magma interaction with water saturation rocks. The later of early explosive of magma, subsidence caldera occurred and subsequently, felsic magma intrudes as the rhyolitic domes. In the stage, after the explosive eruption and depletion of the magma reservoir, take place collapse or subsidence the top of a magma chamber and residual magma ascending by fractures and caused the formation of rhyolitic domes (Fig. 4e). The dome interior has spherulitic textures with local flow and banding. The sandstone, green shale and dolomites, belongs to the Nadigan sub-member and occurred in the pyroclastic surge facies of caldera, which indicated the occurrence of this member before the formation of the Lake Siah caldera.The Lake Siah IOA is formed in the different sections of the Lake Siah caldera complex and host pyroclastic surge accompany rhyolite rocks (Fig. 3). Finally, after the formation and evolution of the Lake Siah caldera complex,this assemblage intrudes deep and medium level bodies such as diabasic dykes (Fig. 4f) and syenitic to syenogranite plugs which are exposed in the south of the Lake Siah (Fig. 3).

4.1 Hydrothermal alteration

Based on field observation,petrographic studies,and X-ray diffraction analyses,at least five alteration assemblages are distinguished in the Lake Siah deposit, including sodic(albitization), potassic, sodic-calcic-iron, hydrolithic, and argillic. Mineral assemblages and various hydrothermal alterations of the Lake Siah deposit are presented in Figs. 5, 6, 7 and Table 2.

Fig. 3 Simplified geologic map of the Lake Siah deposit with stratigraphic column Modified after Hushmandzadeh et al. (2015)

Sodic alteration is widespread in iron orebody and occurs as the result of the albitization of plagioclase coarsegrain phenocrysts and matrix of the porphyritic rhyolite and andesitic rocks (Fig. 5a). It also influenced the patchy and/or vein-like replacement zones and distinguished by white and light grey color in the field. In addition to Na,depletion of Ca and K, accompanied with an intensive change in Fe,Mg,and Mn,results in sodic alteration which is shown in precipitation of fine- to medium-grained albite and quartz (Figs. 6a, 7a).

Potassic alteration represented by biotite, K-feldspar,epidote,magnetite,calcite,chlorite,and minor titanite.The chloritization of biotite is released significant quantities of Fe to the environment and formed magnetite along biotite cleavages (Fig. 6b, c). This alteration is observed in the andesite host rocks from the southern part of No. 1 orebody.

Sodic–calcic-iron alteration assemblage at the Lake Siah is distinguished by pervasive albite–amphibole replacements. In this alteration, amphibole (mostly actinolite) ± magnetite veins occur with Na-plagioclase veins.Quartz, actinolite, epidote, and accessory minerals of magnetite, apatite and calcite are distinguished in this alteration(Figs. 6d,e,g,7b).Underlying the sodic–calcic–iron alteration is sodic assemblage which is overprinted by potassic ± iron alteration.

Hydrolytic alteration consists of sericite, quartz, hematite, and calcite assemblages well developed proximal to the magnetite ± apatite ore (Fig. 7c). This assemblage distinguished by a white to a gray color and is mainly observed in the southern part of No. 1 orebody (Fig. 3).The felsic and mafic rocks are affected by H+rich hydrothermal fluids and leading to the replacement of plagioclase by sericite. Sericitization occurs due to interaction between hydrothermal fluids and walls of the pores in the plagioclase, resulting in the growth of sericite and conversion of the remaining plagioclase in the cores to a more sodic composition (Fig. 6h). The replacement of plagioclase by sericite is associated with the alteration of biotite to chlorite, and both alterations are associated with the development of epidote. Samples contain chloritized biotite in particular, have been subjected to pervasive saussuritization of plagioclase (Fig. 6f), probably due to necessary K and Fe2+provided by chloritized biotite.

Fig. 4 a Rhyolitic lava (looking to the SW), b laminated limestone with stromatolites structure, c alternating layers of dark and light grey dolomite,d dolomitization along the fracture systems in the Archacocyathid bearing limestone(looking to the SW),e rhyolitic domes with low grade iron oxide mineralization in the northeast of deposit,f diabasic dikes with N-S trend,intruded into micaseous shale(looking to the south)

Argillic alteration assemblage occurs contact of massive iron ore (Fig. 5b) in the Lake Siah and was distinguished by occurring of the clay minerals (kaolinite–montmorillonite ± dickite). The clay minerals, which replaced the plagioclases and some mafic minerals, are identified with montmorillonite and kaolinite with quartz ± hematite(Figs. 6i, 7d).

4.2 Mineralization

The Lake Siah iron oxide–apatite deposit contains 50 Mt at FeO = 30–60% (Rostami 2016). Three Fe ± P orebodies are distinguished at Lake Siah deposit that two main orebodies have been outcrops in the local geologic map(Fig. 3). No. 1 orebody as the main ore is 500 m long and 15–30-m thick, contain about 60% of the total reserve of the Lake Siah. No. 1 orebody is in the 25°–40° direction with an angle of 25°–50° dipping to the NE. Two schematic lithological profiles from the northern and southern part of No. 1 Fe ± P orebody are shown in Figs. 8 and 9,respectively. No. 3 orebody, as the other largest one, is 350 m long, 8–10 m thick, and strikes in direction of 20°–35°, dips to NNE with an angle of 10°–35°.

Fig. 5 Field photographs from the a sodic and hematite-argillic alteration and b argillic alteration near to the Fe-oxide ore

The ores are massive, disseminated, brecciated, and to some extent, banded in texture (Figs. 8, 9, 10). Three orebodies have similar ore mineral assemblages including magnetite, hematite, and minor pyrite and chalcopyrite.Quartz, apatite, plagioclase, hornblende, biotite, epidote,sericite, garnet, calcite, and minor titanite, monazite and allanite occurs as non-metal gangue minerals.Subhedral to anhedral magnetite grain generally with 0.1–1.0 mm in diameter occurs in massive ores commonly associated with hematite (Fig. 10). Hematite mineralization occurs as elongate crystals associated with magnetite. Pyrite occurs as micro-inclusions in magnetite and hematite.Interbedded magnetite with calcite is distinguished in banded magnetite texture (Fig. 10). Disseminated magnetite ore occurs with anhedral magnetite, pyrite and chalcopyrite mineral assemblage (Fig. 10). Brecciated magnetite ore occurs as brecciated magnetite, hematite, and disseminated pyrite.

5 Results

5.1 Petrography and igneous geochemistry

Felsic to intermediate volcanic rocks is the main volcanic lithology at Lake Siah. The volcanic rocks contain propylitically-altered trachyandesiticrocks in bottom and rhyolite and rhyolitic tuff pyroclastic rocks occur in the upper part.The sequence mentioned was affected by intense alteration processes. Rhyolite lava domes are in the upper of the volcanic sequence (Fig. 3). Trachyandesite rocks with porphyritic texture are located in the vicinity of the orebody and have a mineral assemblage biotite, plagioclase phenocrysts, K-feldspar, and hornblende with minor apatite, opaque minerals, and fine-grain rutile and zircon. The rhyolite rocks comprise quartz, biotite phenocrysts,K-feldspar, plagioclase, and opaque minerals. Based on field evidence, andesitic and rhyolitic lavas and volcanoclastic rocks are intruded by diabasic dykes.

The whole-rock analyses (including major oxide, trace,and rare earth element) of representative rock samples are presented in Table 3. Based on, they contain 56.0–72.3 wt% SiO2, 2.0–7.4 wt% Na2O, 9.1–18.6 wt% Al2O3,2.8–6.6 wt% FeO, 0.4–1.7 wt% MgO, 1.9–7.4 wt% CaO,2.3–10.2 wt% K2O and 0.1–0.9 wt% TiO2. They also include 121–812 ppm Ba, 73–184 ppm Rb, 97–678 ppm Sr, 5.3–34 ppm Th, 198–375 ppm Zr, 12–25 ppm Y and 2–8.5 ppm Yb.

The classification and interpretation of volcanic rocks were carried out by using fewer mobile elements during alteration processes such as Ti, Zr, Nb, and Y (MacLean 1990; Barrett and MacLean 1991). The high LOI(1.5–9.5 wt%), and the enrichment and/or depletion in the content of SiO2, MgO, Na2O, and K2O show the effect of alteration to variable degrees. Zr, Ti, and Nb in green schist-grade metamorphism show immobile behavior and Y is mostly immobile and sometimes mobile in chloritization zones (Kranidiotis and MacLean 1987; Shriver and MacLean 1993).Based on the volcanic rock samples of the Lake Siah plotted in trachyandesite and rhyolite fields, the Nb/Y versus Zr/TiO2diagram (Winchester and Floyd 1977)was used for the classification of igneous rocks.The volcanic rock samples of the Lake Siah plotted in trachyandesite and rhyolite fields (Fig. 11a). In the Th/Yb versus Ta/Yb (after Pearce 1983) and Th versus Co discrimination diagrams(after Hastie et al.2007)the volcanic rock samples completely fell in shoshonite and high-K calc-alkaline fields, respectively (Figs. 11b, c). In the A/NK versus A/CNK molar diagram (Maniar and Piccoli 1989), the volcanic rock samples plotted in the metaluminous to peraluminous field (Fig. 11d).

Fig. 6 Photomicrographs of various type of alterations in the Lake Siah deposit. a sodic alteration consist of albite phenocryst in quartz-albite fine-grain matrix,b chloritization of biotite in potassic alteration,c the magnetite crystals developed along the cleavage of biotite phenocrysts in potassic alteration,d,e epidotization of plagioclase in sodic–calcic alteration,f pervasive epidotization of plagioclase and calcite,g sodic–calcic alteration with specular hematite and tremolite-actinolite, h plagioclase grain with sericitized core and fresh unaltered rim, i quartz and clay minerals in argillic alteration.Abbreviations of minerals after from Whitney and Evans(2010)(Mag magnetite,Hem hematite,Kln kaolinite,Mnt montmorillonite, Cal calcite, Ab albite, Bt biotite, Ep epidote, Pl plagioclase, Opq opaque mineral, Ser sericite, Ap apatite, Chl chlorite, Zr zircon, Act actinolite, Tre tremolite). All figures are taken in cross-polarized light (XPL)

The trace element patterns of all the Lake Siah igneous rocks were normalized to N-MORB(Sun and McDonough 1989) and show a negative Nb anomaly relative to Th and negative Ti anomaly relative to Zr and Y, with Zr and Y values close to 10 and 1, respectively (Fig. 12). These patterns suggest a calc-alkaline magmatic affinity,probably derived from a sub-arc mantle situation, with scarce or no garnet in the source (Pons et al. 2007). Rollinson (1993),believe that enrichment and depletion in the specific element are controlled by stable and trace minerals. For example, Ti and Nb abundance is controlled by ilmenite,rutile or sphene. Negative Nb anomaly is also an indicator active continental margin and may indicate a contribution of crust in the magmatic processes.

5.2 Mineral chemistry

5.2.1 Trace elements of magnetite

Magnetite and hematite originate dominantly form sedimentary, magmatic, and metamorphic rocks (Scheka et al.1980).Ni/(Cr + Mn)versus Ti + V and(Ca + Al + Mn)versus Ti + V binary diagrams are useful tools to distinguish various iron oxide deposit types such as IOCG,Kiruna-type, BIF, and orthomagmatic or Ti-rich Fe ore deposits (Dupuis and Beaudoin 2011; Beaudoin et al.2007).Results of electron probe micro analysis(EPMA)of magnetite are presented in Table 4. In the Lake Siah deposit magnetite crystals contains variable amounts of Si(0.5–0.9 wt%), Mg (0.0–0. wt%), Ca (0.0–0.02 wt%), Al(0.0–0.07 wt%), Mn (0.0–0.03 wt%), V (0.14–0.38 wt%),Ti (0.4–0.37 wt%), Cr (0.1–0.2 wt%) and Ni(0.0–0.05 wt%).

Fig. 7 X-ray diffraction photographs of various alteration assemblages at the Lake Siah.a quartz and albite in sodic alteration(sample LS-24),b sodic–calcic alteration (sample LS-15), c sericite, quartz and hematite mineral assemblage in hydrolytic alteration (sample LS-12), d argillic alteration (sample LS-08). Abbreviation of minerals from Whitney and Evans (2010) (Mag magnetite, Cal calcite, Ab albite, Ac actinolite, Qz quartz, Hem hematite, Mnt montmorillonite, Chl chlorite, Ser sericite, Dck dickite, Kln kaolinite)

Table 2 Representative mineral parageneses of the main alteration types in the Lake Siah

Based on these diagrams, all of the magnetite samples fall in ‘‘Kiruna type’’ field (Fig. 13a, b). The average composition of mineral deposit types illustrating in spider diagram and shown in Fig. 13c.Magnetite chemistry in the Lake Siah deposit is similar to Kiruna type iron deposits displays the higher Ti (0.04 to ＞0.37 wt%), and V(0.14–0.38 wt%) contents and low Mn and Al values(Table 4) in contrast with IOCG and skarn deposits.

5.2.2 Rare earth elements (REEs) of magnetite and apatites

The REE content of the individual magnetite and apatites are represented in Table 5.The apatite samples(LS-04 and LS-05, Fig. 8) were picked from separated large apatite crystals. Apatite at Lake Siah deposit have high ∑REE contents (7214.9–17,171.4 ppm) LREE/HREE(31.24–43.42), (La/Yb)n (18.91–39.52) and Eu/Eu*(0.294–0.319).Based on Mokhtari et al.(2013) the LREE/HREE high ratio is a common feature of magmatic apatite related to alkaline rocks.The REE contents from magnetite of the Lake Siah deposit shows flat patterns with a weak LREE/HREE fractionation (1.59–14.14) and ∑REE contents (85.92–2786 ppm), (La/Yb)n (1.12–12.32) and Eu/Eu* (0.17–0.45) (Table 5).

The distribution of REE in apatite, magnetite and felsic host rocks, presented in Tables 3 and 5 and are shown in Fig. 14.A similar REE pattern with negative Eu anomalies is shown in apatite, magnetite and felsic host rocks. The negative Eu anomaly indicates that parent magma has undergone K-feldspar crystal fractionation (Budzinski and Tischendorf 1989).The apatite samples show higher LREE content relative to magnetite and felsic host rock(Fig. 14a)because apatite contains high contents of REE substituting for Ca2+(Rønsbo 1989). REE patterns of apatite, magnetite and felsic host rocks of the Lake Siah deposit are similar to Kiruna-type magnetite apatite systems(Fig. 14b).These similarities may suggest a similar sourcefor REE and mineralization (Frietsch and Perdahl 1995;Nabatian et al. 2012; Mokhtari et al. 2013).

Fig. 8 Schematic E-W profile from the northern part of No. 1 Fe-orebody (see Fig. 3),including photographs of the main alteration and mineralization styles in the profile. Sample LS-04: green granular apatite filled open space of the massive Fe-oxide.Sample LS-05: Intergrowth of euhedral apatite and magnetite.Sample LS-05: intergrowth of apatite ± quartz as open space filling in the breccia magnetite.Sample LS-07: poorly mineralization of Fe-oxide in the argillite zone; quartz veins cutting the Fe-oxide mineralization. Sample LS-09:The contact between the Feoxide ore and quartz vein is sharp and liner. Sample LS-14:calc-silicate skarn alteration with epidote and tremoliteactinolite assemblages, showing a green color outcrop. Sample LS-12: argillic alteration characterized by quartz grains and clay minerals ± hematite

5.3 Fluid inclusions

5.3.1 Petrography

Fluid inclusions studies were carried out in apatite (samples LS-04,LS-05,and LS-06,Fig. 8)and quartz(samples LS-06 and LS-07, Fig. 8). Fluid inclusions hosted in the apatite as primary, hexagonal shape and 7–20 μm in size.Three types of fluid inclusions are distinguished based on classification of Shepherd et al. (1985) including threephase solid-bearing (L + V + S) (Type I), two-phase liquid-rich (L + V) (Type II-A) and vapor-rich (L + V)(Type II-B),and mono-phase(L or V)(Type III)(Fig. 15).The size of fluid inclusions vary from 6 to 15 μm and distinguished by a less-shaped, negative crystal and rounded forms. Primary fluid inclusions were studied in this research and commonly occurs in the growth zone of quartz and apatite crystals. Fluid inclusions within apatite are relatively simple and have a liquid-rich phase.Trappedcrystals such as black magnetite and/or red hematite occur in quartz and apatite crystals. The transparent cubicdaughter minerals identified in the solid-bearing fluid inclusions are halite (Fig. 15a, d) and a hexagonal shape,reddish-brown, slightly translucent opaque that is assumed to be hematite (Fig. 15a–c, f). Type I, II and III fluid inclusions occur in quartz crystals.

5.3.2 Microthermometric measurements

Fig. 10 Photographs of caldera setting characteristics and mineralization of Lake Siah.a brecciated ore body,b brecciated tuffs,c photograph of breccia hematite, d quartz veinlet cut the orthoclase crystal, e matrix quartz cross cut by calcite and dolomite veinlet, f BSE image of apatite grain intergrown with magnetite, g remnant core of magnetite in intensive martitized Fe-oxide zone, h inclusions of pyrite and chalcopyrite.Abbreviations of minerals after from Whitney and Evans (2010) (Hem hematite, Or orthoclase, Qz quartz, Mag magnetite, Dol dolomite, Cal calcite, Ap apatite, Pl plagioclase, Ep epidote, Py pyrite, Ccp chalcopyrite)

The fluid inclusions microthermometric data in quartz and apatite are shown in Figs. 16 and 17. Solid-bearing fluid inclusions (type I) in apatite homogenized to liquid at 280–420 °C (avg. 350 °C) by halite dissolution between 255 and ＞450 °C (avg. 350 °C) and salinities vary between 35 and 53 wt% NaCl equiv (avg. 44 wt%). and densities range from 1.1 to 1.26 g cm3(avg. 1.03 g cm3)(Table 6). Three-phase inclusions have salinities between 30 and 59 wt% NaCl equiv. Liquid-rich fluid inclusions(type II-A) homogenized to a liquid at 175–210 °C (avg.190 °C),whereas the vapor-rich fluid inclusions(type II-B)homogenized to a vapor at 335–350 °C(avg.340 °C).The first ice-melting temperatures (TFM) of these liquid-rich fluid inclusions range from - 37 to - 48 °C (avg.- 39 °C). The type II-B fluid inclusions have little liquid phase and no measurement of TFM. The final ice-melting temperature (Tmice) for the two-phase fluid inclusions range between - 6 and - 13 °C (avg. - 10 °C) and indicating a fluid salinity between 10 and 17 wt% NaCl equiv.(avg.14 wt%).Three-phase fluid inclusions(Type I)are abundant within the quartz, and homogenized to a liquid at temperatures 150 to ＞530 °C (avg. 340 °C), by halite dissolution between 165 and 490 °C (avg. 327 °C).These fluid inclusions have 30–58 wt% NaCl equiv. (avg.44 wt%),with densities vary from 1.08 to 1.25 g/cm3(avg.1.14 g/cm3). The homogenization temperature and salinityof fluid inclusions in the quartz tend to be higher than those at apatite.

Table 3 Major and trace element geochemical compositions of the Lake Siah igneous rocks

Table 3 continued

Fig. 11 Chemical characterization of least altered igneous rocks of the Lake Siah.a total alkalis versus silica classification(Le Bas et al.1986),b determination of the alkaline affinity of igneous rocks by Ta/Yb versus Th/Yb plot(Pearce 1983),c Th versus Co binary diagram(Hastie et al.2007), d alumina saturation of magmatic rocks in the A/CNK versus A/NK (Maniar and Piccoli 1989)

5.4 H and O isotopes

The measurements of hydrogen and oxygen isotopic compositions carried out in four magnetite and six quartz samples from main ore stage of the Lake Siah. Values of δ18Ofluidin quartz and magnetite samples were calculated using the formula of Sharp et al. (2016) and Cole et al.(2004), respectively (Table 7). The data showed that δ18-Ofluid(‰)and δDfluid(‰)values in quartz samples have a range from 1.7 to 10.7‰ (avg. 6.2‰, n = 6) and a narrow variation ranging from - 101 to - 73‰ (avg. - 87‰,n = 6), respectively (Table 7 and Fig. 18). Also, δ18Ofluid(‰) values in magnetite samples have a range from 9.9 to 11.3‰ (avg. 10.6‰, n = 4).

Fig. 12 Trace element abundance normalized to N-MORB (Sun and McDonough 1989) for the Lake Siah igneous rocks

6 Discussion

6.1 Geodynamic setting

The subduction of Proto-Tethys oceanic crust under Central Iranian plate caused the formation of Zarigan-Chahmir lithotectonic domains (including Bafq Mining District and Kashmar–Kerman Zone). With the formation of the Precambrian basement consisting of the Chapedony and Boneh shurow complexes,the granitic plutons intruded the Precambrian sequence during the early Cambrian. After this event, felsic to intermediate volcanic and volcanosedimentary rocks of the ECVSS occurred.

According to Rajabi (2012) at least two different lithologies can be identified in the Zarigan–Chahmir lithotectonic domains which includes: (I) Lower volcanosedimentary unit(with thickness of 1800 m)was deposited in rifting regime, unconformably overlies the Tashk formation,and characterized by coarse-grained conglomerate,pyroclastic rocks and mafic and felsic volcanism, and (II)Upper sedimentary unit (with thickness of 2500 m) was deposited in post rifting or sag-phase condition, including carbonate shales, siltstones, carbonates, and minor tuffaceous rocks.The sag-phase sequence is classified by Rajabi(2012) as four main members: a basal sedimentary member, Nadigan, Esfordi, and Zarigan members. Based on geologic studies, many Iron Oxide Apatite (IOA) deposits in Central Iran occurred within the western part of the Zarigan–Chahmir basin with host rocks of welded rhyolitic and ash-flow tuffs (Daliran et al. 2009; Jami et al. 2007;Stosch et al. 2011).

Table 4 The maximum,minimum and average of the elements in the magnetite ore in different types of iron deposits and chemical comparison of magnetite in the Lake Siah with other iron deposits represented by Beaudoin et al. (2007)

Fig. 13 a,b discrimination diagrams origin of iron deposits(after Beaudoin et al.2007).According to these diagrams,sample rocks of the Lake Siah iron plot within the Kiruna type.c The comparison spider diagram of the different types of iron deposits with Lake Siah deposit on the basis of major and minor element concentrations in the magnetite minerals, Lake Siah magnetite show similar pattern with Kiruna type deposits

For the achievement of the tectonic setting of the Lower Cambrian sequence of the Lake Siah deposit, several samples of rhyolite and andesite host rocks are plotted in TiO2/Al2O3versus Zr/Al2O3and Zr/TiO2versus Ce/P2O5binary diagrams (Mu¨ller and Groves 2016) (Fig. 19).The samples mainly are plotted in an arc-related fieldon theTiO2/Al2O3versus Zr/Al2O3diagram (Fig. 19a). Ce/P2O5versus Zr/TiO2are useful discriminatorplotsthat can differentiate the continental arc of post-collision arc setting and indicate a continental arc environment for all samples(Fig. 19b). In the Rb–Hf–Ta ternary diagram (Harris et al.1986),rock samples fall in the volcanic arc field(Fig. 19c).The Rb versus Yb + Ta binary diagram (Pearce et al.1984), indicate that the intrusions were formed in a volcanic arc system (Fig. 19d). Moreover, enrichment of Rb,Ba, K, and Cs elements (LILE), and depletion of Nb, Ti,Ta, Zr, and Y elements (HFSE) were confirmed this evidence.

6.2 Relationship between hydrothermal alteration and mineralization

Voluminous intermediate-felsic (bimodal) intrusions of syn-rift sequence of ECVSS emplaced into sedimentary sequences containing abundant calcareous shales, limestone, and calcareous, were interpreted to have resulted in the circulation of saline brines and production of sodic plagioclase. Hildebrand (1986) and Cline and Bodnar(1991) suggested that highly saline fluids are developed during the evolution of bimodal magma (intermediate tofelsic) and move along down-temperature flow paths.Pollard(2001)proposed that fluids released during magma crystallization were largely responsible for the albitization.On the other hand evolved fluids are contributions from fluid involved of the metamorphic crystalline basement such as the Boneh–Shurow complex, crystallization bimodal melts and interaction with interbedded evaporatebearing portions of the Saghand Formation. These processes lead to generation Na–Ca rich fluids and the development of sodic–calcic. Moreover, depletion in Na observed with comparison to halite dissolution trend with seawater. This depletion in Na is related to Na–Ca exchange reactions(albitization and scapolitization)(Smith et al. 2013). A fluid/rock interaction between saline fluid and calc-silicate rocks results in a quartz-rich alteration at the highest fluid/rock ratios, which precedes an albite-rich assemblage with dominant quartz and fewer amounts of calcite, magnetite and zircon, followed at low fluid/rock ratios by potassic alteration assemblages (biotite, magnetite, quartz, and plagioclase).

Table 5 ICP-MS analyses of REE content of magnetite and apatite samples of the Lake Siah deposit

Fig. 14 a Spider diagram(normalized to Boynton 1984)related to REE distribution in the apatite,magnetite and host rock in Lake Siah,b REE pattern in the Kiirunavaara magnetite–apatite deposit (after Harlov et al. 2002)

Fig. 15 Photomicrographs of fluid inclusions hosted in quartz crystals (a–c) and fluid inclusions hosted in apatite (e, f). a multisolid-bearing fluid inclusions, b homogenization to a liquid by vapor bubble disappearance at temperature of 160 °C, c homogenization to a liquid by halite dissolution at temperature of 538 °C, d three-phase fluid inclusions in quartz, e two-phase, liquid rich fluid inclusions in apatite, f three-phase fluid inclusions in apatite. Abbreviations Qz quartz, Ap apatite, Ha halite, Hem hematite, L liquid, V vapor

Fig. 16 Histograms of homogenization temperatures (a) and salinities of fluid inclusions (b) from the quartz and apatite

The best albitization model results are produced with a fluid having an initially elevated Na/K ratio. With decreasing P and T during infiltration, albitization is still predicted, and there is a large amount of iron liberated during the albitization of calc-silicate rocks (Oliver et al.2004). Final fluids with low fluid/rock ratio progressively enriched of Fe and K that caused ore-related potassic alteration.

Fig. 17 Histograms showing first ice-melting temperature (a) and final ice-melting temperature (b) in apatite and quartz

6.3 Origin and fluid evolution

In many pieces of literature(e.g.,Criss and Farquhar 2008;Huang et al. 2011) it is proof well established that the examination of the hydrogen and oxygen isotopes can effectively point to the source of the ore-forming fluids and track their evolution. The hydrogen and oxygen isotopic values of the Lake Siah deposit are present in Fig. 18.The stable isotope data δ18Ofluidvalues for magnetite and quartz are vary from 1.7 to 11.3‰ and located near to or slightly lower than the values for magmatic water,which vary from 5.5 to 10‰ (Barnes 1979). These values show that the initial ore-forming fluids in the Lake Siah deposit have formed due to a major part of magmatic fluids.

The stable isotope studies in quartz and magnetite of the Lake Siah deposit indicate that the source of hydrothermal fluids was formed due to the mixing of magmatic(Narigan Granite or rhyolites of the Saghand Formation) and meteoric waters.Moreover,fluid inclusion studies show that ore solutions of the Lake Siah are concordant with a fluidmixing pattern. The trends in Th(°C) versus salinity (wt%NaCl eq.) diagram showed a progressive evolution fromhigh salinity and temperature to solutions contain relatively low homogenization temperature and salinity(Fig. 20).As above mentioned, the stable isotopic evidence proposed that at least two or more hydrothermal fluids play roles in the formation of the Lake Siah (Fig. 21). Based on previous studies on origin of large hydrothermal ore systems(e.g., Cooke and McPhail 2001; Fan et al. 2011; Gu et al.2011;Zhu et al.2001),at least two different fluid evolution mechanism including fluid mixing and fluid boiling are recognized for ore-forming controlling in most mineral deposits. It clear that fluid mixing is the main mechanism,more than fluid boiling,for the formation of the Lake Siah deposit.

Table 6 Microthermometric data of primary fluid inclusions from the Lake Siah deposit

Table 7 Oxygen and hydrogen isotope compositions of the Lake Siah deposit

Fig. 18 δ18Ofluid and δDfluid diagram of the Lake Siah deposit and comparison of δ18O magnetite in Lake Siah with other Kiruna-type iron deposits.The primary magmatic and metamorphic water boxes are from Barnes (1979) and Sheppard (1986), and the meteoric water line is from Craig (1961)

6.4 Proposed genetic model

Fig. 19 Peterogenetic characteristic of Lake Siah igneous rocks. a arc related nature of sample rocks at Zr/Al2O3 versus TiO2/Al2O3 diagram(Mu¨ller and Groves 2016),b Zr/TiO2 versus Ce/P2O5 diagram and sample rocks in the continental arc(Mu¨ller and Groves 2016),c volcanic arc situation of sample rocks at ternary Rb/30–Hf–Ta × 3 diagram (Harris et al. 1986), d Rb versus Yb + Ta diagram (Pearce et al. 1984)

Fig. 20 Homogenization temperature(Th)versus salinity for primary fluid inclusions contained in quartz and apatite. The arrows represent fluid evolution trends modified after Wilkinson (2001)

Fig. 21 Schematic model for the Lake Siah deposit. See text for further reading

Based on Mokhtari et al. (2013), the formation of IOA deposits in Central Iran occurs due to three mechanisms including (1) intrusion of magmatic rocks with alkaline to sub-alkaline composition, (2) large and active fault systems, and (3) existence of a metamorphic beneath rocks.On the base, magmatism occurrence at Lake Siah deposit probably is produced by fractionation of mantle-derived magmas in an extensional environment.The extension was accompanied by intense intra cratonic plutonism, molassetype sedimentation and ensialic volcanism (andesitic and dacite flows,caldera formation,and high silica ignimbrites)which accurse associated with active caldera system (e.g.,Fo¨rster and Jafarzadeh 1994; Daliran et al. 2010). The lithological units of around Lake Siah deposit belong predominantly to late Lower Cambrian volcano- intrusive or Lake Siah caldera complex (Hushmandzadeh et al. 2015).The Lake Siah caldera complex, with ellipsoid geometry,consists of a pyroclastic surge,subsidence caldera and lava and rhyolitic dome (Fig. 21). In the pyroclastic surge which occurs during the first stage of caldera formation,pyroclastic rocks assemblage with rhyolitic lava is formed.This assemblage(ignimbrite and tuff)occurs the effect first explosive caused by interaction magma and fluids resulted from crystallizing intermediate to felsic (andesite and rhyolite).In the second stage,subsidence caldera from that felsic magma appears as a rhyolitic dome that demonstrably occurs after the early explosive. In the stage, after the explosion and extrusion of large volume lava from the central vent, the roof of magma chamber is collapsed and residual magma ascends through fractures in the rhyolitic dome. Alkaline magma as the main source of Fe and incompatible elements such as P, REE, Th, U, F and Cl occurs as the result of magmatic differentiation and hydrothermal fluid were released.These fluids were derived by partial melting of upper mantle and havea relatively high temperature, salinity and concentration. FeCl2is the major complex for Fe migration mechanism especially in vapor phase, therefore the correlation between Fe2+and Cl-ions was expected (Simon et al. 2004). On the other hand, there is a close association between the formation of Fe–Cl ligands and the salinity content. Based on Kodera et al. (2005), infiltration zones formed aftercaldera subsidence, and hydrothermal fluid-flow observed along marginal caldera faults.Based on evidence,the source of metal and saline (Na+, K+and Cl-) constituents for the hydrothermal mineralizing fluids was likely provided by differentiated magma chamber.Furthermore,hydrothermal fluids seem to have risen from depth to shallow and allow for efficient fluid mixing with meteoric water (Fig. 21).Thus, after the proto-Fe oxide mineralization which generated as fine-grained magnetite and apatite ores, in the following stage, volatiles solutions with Fe, P, and REE occurs IOA mineralization adjacent to sodic, sodic–calcic,argillic, and hydrolithic alterations. So, mineralization is typically hosted by volcanic rocks and located near inferred subsidence caldera margins with central rhyolitic domes and ring ignimbrites and tuffs.

7 Conclusions

1. Lake Siah iron oxide- apatite deposit occurs within a sequence of Lower Cambrian felsic-intermediate volcanic and intrusive rocks, in the Kashmar–Kerman Zone (KKZ).

2. In the Lake Siah deposit sodic alteration, sodic–calcic and potassic alteration occur in deep to intermediate depth,and hydrolithic and argillic alterations occur at a shallow level. (a) Na alteration represented by albite and quartz, and spatially occurs associated with Feapatite mineralization; (b) Na–Ca alteration characteristic by plagioclase (–Na), amphibole (actinolite),epidote, and accessory minerals including opaque minerals, apatite and calcite (c) potassium alteration accompanied by the formation of K-feldspar, biotite and accessory minerals plagioclase, epidote,magnetite; (d) pervasive and widespread hydrolithic and argillic alterations.

3. Fluid inclusions evidence indicate that the Lake Siah ore-forming fluids involved high- to medium-temperature, high- to medium salinity and high density in NaCl–H2O system.

4. H and O isotopic measurements indicate that the Lake Siah mineralization spatially was associated with volcanic–subvolcanic magmatic activity with early Cambrian age.

5. Fluid inclusions, geochemistry, ore geology, and O–H isotope evidence indicated that the mixing of fluids(magmatic and meteoric) with different metal constituents have a significant event in the deposition of iron ore in the Lake Siah deposit.