Ore horizons, ore facies, mineralogy and geochemistry of volconogenic massive sulfide (VMS) deposits of the Varandan Ba-Pb-Cu deposit, southwest of Qamsar - Iran

Introduction The Varandan Ba-Pb-Cu deposits are located15 km southwest of the town of Qamsar and approximately 7 km south west of the Qazaan village, in the Urumieh- Dokhtar magmatic arc. The Kashan region that is situated in west-central Iran hosts several barite-base metal deposits and occurrences, the biggest ones are the Varandan Ba-Pb-Cu (case considered in this study) and the Tapeh-Sorkh (Khalajmaasomi et al., 2010) and Dorreh Ba (Nazari, 1994) deposits. Previous researchers (Izadi, 1996; Farokhpey et al., 2010) have proposed an epithermal model for formation of the Varandan deposit. However, based on some feature of the deposit, it seems that this genetic model may not be correct. Therefore, it is necessary to do more precise research studies on the deposit. The main purpose of this paper is to discuss the genesis of the Varandan deposit based on geological, ore facies, mineralogy, wall rock alterations, and geochemical studies. Materials and methods A field study and sampling was performed during the summer of 2013. To assess the geochemical characteristics of the deposit, about 17 systematic samples from different ore facies of the first, second and third sub-horizon were collected for petrography and mineralogy, and for inductively coupled plasma-atomic emission spectroscopy(ICP-AES), X-ray diffraction (XRD) and X-ray fluorescence (XRF) geochemical analysis methods. The microscopic studies were done in the optics laboratory of the Shahrood University, and the geochemical analyzes were conducted in laboratories of the Center of Research and Mineral Processing Ore Minerals of Iran, Karaj, Iran. Results The host sequence in the Varandan deposit involves three units, from bottom to top: Unit1: grey, green siliceous tuff, brecciated tuff, crystal tuff and andesite; Unit2: white grey nummulitic limestone, limy tuff and marl: and Unit3: tuff breccia and crystal lithic tuff. Mineralization in the Varandan deposit has occurred as four ore sub-horizons in Unit1, as lenticular to tabular ore bodies concordant to layering of the host rocks. Based on textural, structural and mineralogical studies, the Varandan deposit consists of five ore facieses including: 1) veins-veinlets (stringer zone) that involves cross-cuting barite, quartz and sulfide veins-veinlets, 2) brecciated barite and massive pyrite (vent complex zone) involving replacement texture, 3) massive barite and sulfide (massive zone), 4) alternations of barite- and galena- rich bands (Bedded-banded zone) and; 5) iron-manganese-bearing hydrothermal-exhalative sediments. Primary ore minerals are barite, galena, chalcopyrite, pyrite, sphalerite, tetrahedrite, magnetite, oligiste, braunite, pyrolusite and bornite, accompanied with secondary minerals such as native copper, cuprite, digenite, covellite, chalcosite, goethite, hematite and malachite. Gangue minerals consist of chlorite, sericite, quartz and calcite. Major wall rock alterations in the deposit are chloritic and quartz- sericitic. For determining the type of ore of the Varandan deposit, the Cu/Zn ratio for the barite and sulfide ore of the first, second and third sub-horizon are 1.08, 0.12 and 11.08, respectively. This lies in the yellow ore for the first and third sub-horizon, and it falls in the black ore for the second sub-. Discussion According to the basic characteristics of mineralization such as geometry of ore bodies, textures and structures, ore facies, wall rock alterations, mineralogy, fluid inclusions data, metal zonation and geochemical features, the Varandan deposit could be classified as a bimodal-felsic or Kuroko-type voclanogenic massive sulfide (VMS) deposit, similar to those of the Hokuroko basin in Japan (Ohmoto and Skinner, 1983; Hoy, 1995, Huston et al., 2011). The Varandan deposit has been formed in an intra-arc setting due to subduction of the Neo-Tethyan oceanic crust beneath the Iranian plate during the Middle Eocene. Acknowledgements The authors are grateful to the Grant Commission for research funding of Iranian Mines and Mining Industries Development and Renovation Organization (IMIDRO) and the University of Shahrood. References Farokhpey, H., Shamsi-Poor, R. and Nasre-Esfahani, A. 2010. Economic petrology of granitoid Ghazaan: study of metal deposit. The Conference on Applied Petrology, Khorasgan Azad university, Tehran, Iran. Hoy, T., 1995. Noranda/kuroko Massive Sulphide Cu-Zn deposits. In: D.V. Lefebure and G.E. Ray (Editors), Selected British Colombia Mineral deposit Profiles, volum 1- Metallics and Coal. British Columbia Ministry of Energy of Employment and Investment open file, Canada, pp. 53-54. Huston, D., Relvas, J., Gemmell, J.B. and Drieberg, S., 2011. The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic-hydrothermal contributions.Journal of Mineralium Deposita, 46(5-6): 473-507. Izadi, H., 1996. Geology, petrografy and genises of Ba-Pb Kashan Ghamsar Ghazaan. M.Sc. thesis, Khorasgan Azad university, Tehran, Iran. 160 pp. Khalajmaasomi, M., Lotfi, M. and Nazari, M., 2010. Tapeh-Sorkh Mine mineralization model designation Bijegan-Delijan Central Province. Journal of Land and Resources, 1(2): 33-43. (in Persian) Nazari, M., 1994. Study of mineralogy and ore genesis Dorreh deposit in the Kashan. M.Sc. Thesis, Tarbiat-moallem University, Tehran, Iran, 147 pp. (in Persian with English abstract) Ohmoto, H. and Skinner, B.L., 1983. The Kuroko and related volcanogenic massive sulphide deposits: Introduction and summary of new findings. In: H. Ohmoto and B.J. Skinner (Editors), Kuroko and Related Volcanogenic Massive Sulphide Deposits. Economic Geology, Canada, pp. 1-8

Magmatic differentiation in the calc-alkaline Khalkhab–Neshveh pluton, Central Iran

Geochemical and isotopic data (Sr, Nd) are presented for the Khalkhab–Neshveh pluton, an E-W elongated body of quartz monzogabbro, quartz monzodiorite, granodiorite and granite in the Urumieh–Dokhtar magmatic arc of Central Iran. The plutonic rocks are medium- to high-K, metaluminous, and I-type, with 52–71 wt.% SiO2. The geochemistry shows smooth differentiation trends in which most major elements (except Al2O3, K2O and Na2O) are negatively correlated with SiO2; K2O, Ba, Rb, Ce, Nb, and Zr are positively correlated. Na2O, Sr, Eu and Y follow curves that are not considered to represent simple mixing between mafic and felsic magmas, but reflect crystal fractionation of clinopyroxene, plagioclase and hornblende. Initial 87Sr/86Sr ratios (∼0.7047) and εNdt values (∼+3.0) are essentially constant, and the large volume of quartz monzogabbros compared to granites, as well as the lack of mafic enclaves in more evolved rocks, are also indicative of crystal fractionation rather than mixing of magmas from different sources. Clinopyroxene fractionation was the main control in the evolution of the magmas up to 55% SiO2; hornblende took over from 55 wt.%, resulting in decreasing Dy/Yb with increasing silica content in the most siliceous rocks. Sr concentration increases up to 55% SiO2, and then decreases together with CaO, Al2O3, Na2O. Fractionation of opaque minerals and apatite throughout the sequence, and the continuous increase in K2O and Ba vs. SiO2 reflect the absence of significant fractionation of biotite and K-feldspar. Based on geochemical and isotope data, geophysics information and field studies, it seems that suturing of the Arabia and Iran plates caused the Khalkhab and Koush nousrat faults with left-lateral strike-slip in the Urumieh–Dokhtar region, and generated a purely tensional T space at 32° to the faults which was exploited by the emplacement of Khalkhab–Neshveh pluton

Petrology, petrogenesis, and geochronology review of the Cenozoic adakitic rocks of northeast Iran: Implications for evolution of the northern branch of Neo‐Tethys

Cenozoic adakitic rocks of the northern part of the Central Iran Structural Zone (CISZ) are among the notable geological features of the terrains in northeast Iran, so a comprehensive comparison of several of these adakitic sequences is presented. This lithogeochemical analysis is constrained to examining adakitic magmatism of the three magmatic belts within the CISZ, which from southeast to northeast and from oldest to youngest are as follows: (a) south of Shahrood-Damghan, (b) north-northwest of Sabzevar-Neyshabour, and (c) south of Qouchan and west of Esfarayen. Radiogenic isotope analysis using Rb–Sr and Sm–Nd methods show that the adakitic rocks associated with Qouchan-Esfarayen magmatism have 0.512581 to 0.51288 initial 143Nd/144Nd and 0.703903 to 0.705627 initial 87Sr/86Sr, with εNd −0.86 to 4.98. Adakitic rocks in south to southeast Shahrood have 0.512775 to 0.512893 initial 143Nd/144Nd and 0.703746 to 0.705314 initial 87Sr/88Sr, with εNd 3.69 to 6.0, and adakites emplaced into the Sabzevar ophiolite have 0.512846 to 0.512911 initial 143Nd/144Nd and 0.70379 to 0.705019 initial 87Sr/86Sr contents with εNd of 5.26 to 6.54. Isotopic initial ratios of Nd and Sr support an origin involving partial melting of the subducting oceanic lithosphere of the northern branch of Neo-Tethys and the associated suprasubduction mantle wedge in producing these adakitic rocks

Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks, Nain, Central Iran

tKajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a LateMiocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediateand felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies aremedium-K calc-alkaline, with SiO2(wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chem-ical data also show that MgO, CaO, TiO2, P2O5, MnO, Al2O3and Fe2O3define linear trends with negativeslopes against SiO2, whilst Na2O and K2O are positively correlated with silica. Contents of incompatibletrace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO2, whereas Sr shows an oppo-site behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSEand troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed inan active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, con-firmed by REE fractionation (LaN/YbN= 4.5–6.4) with moderate HREE fractionation (SmN/YbN= 1.08–1.57).The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb valuesreflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rockSr and Nd isotope analyses show that the87Sr/86Sr initial ratios vary from 0.704432 to 0.705989, and the143Nd/144Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd iso-topes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr andlow radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. TheKajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotopediagram, a compositional region corresponding to mantle-derived igneous rocks

Petrological constraints on the origin of the plutonic massif of the Ghaleh Yaghmesh area, Urumieh–Dokhtar magmatic arc, Iran

The Oligocene Ghaleh Yaghmesh plutonic massif (GYPM) consists of diorite, quartz-diorite, tonalite and granodiorite and evolving from metaluminous nature. All the samples are predominantly medium-K calc-alkaline series, having typical characteristics of I-type granitoids. A significant geochemical criteria of the GYPM is the impoverishment of high-field-strength elements (HFSE) (e.i. Zr, Nb, Ti and Hf) and the overabundance of large-ion-lithophile elements (LILE) (e.i. K, Sr, U, Ba and Cs), with respect to the light rare elements (LREE) as compared to chondritic concentration. These geochemical criteria suggest the involvement of sedimentary components in the generation of rocks studied. Furthermore, variable Pb/Ce amounts, linear trend of all rocks studied on Ti/Zr vs. Y1)/Hf diagram, as well as some characteristics petrographic features (e.i. acicular apatite, corroded margin of the plagioclases, the amphiboles and some of the pyroxenes, oscillatory zoning of plagioclases) and the presence of mafic microgranular enclave (MME) indicate that the Ghaleh Yaghmesh parental magma was likely generated by the partial melting of a mixed source dominantly composed of amphibolite and possibly meta-sedimentary source. The overall geochemical and petrographic features are consistent with the interpretation of the Urumieh Dokhtar Magmatic Arc as an active continental margin during subduction of the Neo-Tethyan oceanic crust underneath the Central Iranian microcontinent

Oligocene subduction-related plutonism in the Nodoushan area, Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO2 = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO2 = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045–0.707959, εNd(t) = −3.23 to +3.80, and the Nd model ages (TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.705513 to 0.707275 and εNd(t) from −1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite. Keywords: Urumieh–Dokhtar magmatic belt, Granitoid rocks, Subduction, Zircon U–Pb ages, Radiogenic isotopes, Central Ira