Elsevier

Ore Geology Reviews

Volume 125, October 2020, 103667
Ore Geology Reviews

Geological, geochemical and microthermometric characteristics of the Hakkari region Zn-Pb deposits, SE Turkey

https://doi.org/10.1016/j.oregeorev.2020.103667Get rights and content

Highlights

  • Hakkari region Zn-Pb deposits are stratigraphically continuous for a few tens of km as a lateral, and show stratiform and sub-sea floor replacement features.

  • δ34SCDT data of the deposits distribute in a narrow range with an average 1.74‰, and sulfur is sourced from seawater and reduced by the TSR.

  • The fluids have an average 205 °C (up to 289 °C) and 10% wt equiv. NaCl salinity, and reflects the mixing of seawater with basinal brines.

  • Trace element associations of ore is As-Hg-Tl-Sb-Mn elements, and these are typical trace elements of SEDEX-type deposits.

  • Hakkari region Zn-Pb deposits formed in late Triassic as a vent-proximal SEDEX type.

Abstract

The Hakkari region in SE Turkey contains large Zn-Pb deposits, primarily of non-sulfide ore in Upper Triassic passive margin carbonates. In the Karakaya, Meskantepe and Üzümcü Zn-Pb deposit, the 3 main and >15 ore layers alternate with a thick-bedded limestone. The feeder in the region veins are well defined, containing both non-sulfide and sulfide ore. Primary sulfide ore contains between 1 and 37 % Zn, has transformed to “non-sulfide” ore containing Zn > 10%. Both non-sulfide and sulfide ore is associated with As, Se, Hg, Tl, Mn and Sb, which is similar to other SEDEX deposits. The average δ34S of the stratiform and feeder zone sulfides are 2.1‰ and 1.67‰, respectively. Sulfur isotope data of sphalerite, galena and pyrite (from −3.4 to 8.8‰) indicates that sulfur came from a homogeneous large source. Sulfate was reduced by the process of thermochemical sulfate reduction (TSR) rather than bacterial sulfate reduction (BSR). Lead isotope values (206Pb/204Pb ≈ 18.49, 207Pb/204Pb ≈ 15.66 and 208Pb/204Pb ≈ 38.69) reflect an evolved upper crustal source. The homogenisation temperature (Th) and salinity of fluid inclusions is from 165 to 289 °C, and from 1 to 22% equiv. NaCl salinity. Such a wide range of Th and salinity, and Cl/Br ratio (409 from sphalerite and galena; 662 from barite) of fluid inclusions may indicate mixing of basinal brines and seawater.

Successive ore levels, laminated with shale-carbonate rich in organic matter, formed on the seafloor as banded and replacement ore. Trace element associations, fluid inclusion and isotope data indicate that the Zn-Pb deposits were formed as synsedimentary processes associated with feeder systems during the initiation of the Triassic rifting as a vent-proximal SEDEX-type. The metals (Pb, Zn, Fe) were leached from Palaeozoic and older clastic rocks in the Arabian platform by seawater sourced fluids, and ascended through deep fractures. The metalliferous fluids should have formed vein type mineralization in feeder zone, sub-seafloor replacement type ore under the ocean floor, and stratiform ore on the seafloor.

Graphical abstract

Trace element associations (As, Se, Hg, Tl, Mn and Sb), fluid inclusion (Th from 165 to 289 °C; salinity from 1 to 22% equiv. NaCl) and isotope data indicate that the Hakkari Zn-Pb province were formed as synsedimentary processes associated with feeder systems during the initiation of the Triassic rifting in as a vent-proximal SEDEX-type.

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Introduction

The Tethyan Metallogenic Belt (TMB) stretches for over 12,000 km from Europe through Turkey to Pakistan, Tibet, China and Southeast Asia (Reynolds and Large, 2010, Richards, 2015) and hosts a wide diversity of metallic mineral deposits. In western part of TMB, the Turkish section contains three main Pb-Zn region that are temporally and spatially distinct (Yiğit, 2009, Hanilçi et al., 2019). The eastern Pontide Pb-Zn ± Cu province was related to Late Cretaceous arc magmatism, the western Anatolian Pb-Zn ± Cu ± Au ± Ag province was related to Oligocene to Miocene arc magmatism. The third province, in the Tauride-Anatolide Tectonic unit, contains carbonate-hosted Pb-Zn ± Ba ± F deposits (Fig. 1a).

Sediment-hosted Pb-Zn deposits are generally classified as “clastic-dominated (CD), sedimentary exhalative (SEDEX)” and “Mississippi Valley-type (MVT) deposits (Leach et al., 2010). The SEDEX deposits occur in the shale, sandstone, siltstone and/or carbonates of clastic sedimentary sequences, often with a distinct stratiform character. The tectonic settings of the SEDEX deposits are interpreted to be passive margin, back arc, continental rifts and sag basins (Goodfellow, 2004, Goodfellow and Lydon, 2007, Leach et al., 2010). In contrast, the MVT Pb-Zn deposits occur in passive margin platform carbonates (e.g. Leach and Sangster, 1993, Bradley and Leach, 2003).

Sediment-hosted Zn-Pb deposits of the Taurides-Anatolides tectonic unit (Şengör and Yılmaz, 1981) occur within passive margin carbonate rocks. Most of these deposits were identified as Mississippi Valley Type (MVT), e.g. the deposits in Hadım-Bozkır and Aladağ–Zamantı provinces, based on their geological setting, ore-wall rock relationships, formation temperature and the isotope geochemistry data (Alp, 1976, Hanilçi and Öztürk, 2005, Hanilçi and Öztürk, 2011). However, although carbonates occur in the Horzum region the Pb-Zn deposits are defined as carbonate replacement (CRD) type, because of the relatively high formation temperature (avg. 235 °C) and the presence of bornite, arsenopyrite and argentite in paragenesis (Hanilçi et al., 2019).

In the southeast corner of Turkey, between Hakkari and Çukurca, there are important Zn-Pb deposits within the passive margin carbonates of the Arabian Platform. The geological setting of these Zn-Pb deposits was determined by Hanilçi and Öztürk (2008) and the mineralogy of the non-sulfide ores by Santoro et al. (2013). In last decade, the region has seen extensive mining activity and 1.1 million tons of ore has been extracted by underground and open pit mining. This activity has facilitated detailed field observation, especially in the mineralized zones, and detailed geochemical analysis of the primary sulfides and their oxidation products. The aims of this study is to define the ore forming process, deposit type, and to propose a formation model for the Zn-Pb deposits of Hakkari region in relation to the evolution of the Tethyan Ocean in this region. The required information will come from ore textures, ore-host rock relationships, ore and isotope (S, Pb) geochemistry, chemistry and microthermometric measurements of fluid inclusions.

Section snippets

Geological setting

The geology of the Hakkari region consists of Palaeozoic and Mesozoic age carbonates and clastic rocks that were deposited on a passive margin on the southern edge of the Arabian microplate. The ophiolitic mélange of the Cretaceous, Yüksekova Complex (Perinçek, 1990) was obducted over these basement units during the Eocene to the Miocene (Fig. 1b). During this period the basement units were folded and thrusted producing the present day steep mountainous terrain. Sedimentary basement rocks

Zn-Pb deposits and their occurrence

The Hakkari region Zn-Pb deposits are found both as concordant (the Meskantepe, Karakaya, and Üzümcü), and discordant (Kurşuntepe and Akkaya) types. The concordant ore bodies are located in the northern part of the region and have a synsedimentary stratiform character but were subsequently subjected to strong orogenic deformation and are now folded. They occur within late Triassic limestone and limestone shale alternations and locally exhibit a reaction contact with the hanging wall limestone

Methods

The mineralogical composition of both oxide-carbonate and sulfide Zn-Pb ores was investigated by petrographic examination of polished sections and by XRD (X-Ray Diffraction). The XRD studies were performed in the Istanbul University-Cerrahpasa, Department of Geological Engineering, with a Rigaku D/Max-2200 model instrument using a Cu Kα tube with settings of 40 kV, 20 mA and 2 thetas. The minerals were identified using the database from the Jade 6.5 software. The geochemical analysis was

Ore mineralogy and petrography

The Zn-Pb deposits in the Hakkari province are primarily “non-sulfide” zinc deposits whose characteristics can be used to distinguish a number of sub-types (e.g., Heyl and Bozion, 1962, Large, 2001, Hitzman et al., 2003, Boni and Large, 2003). However, primary sulfide ore zones (Figs. 5 c, d, 7b) have been preserved from oxidation within the non-sulfide ore in some of the deposits (Meskantepe, Üzümcü, Kurşuntepe and partly in the Karakaya deposits). These sulfide ore zones are very important in

Ore geochemistry

The minor and trace element concentrations of non-sulfide (NSO) and sulfide ore (SO) samples from the Karakaya and Meskantepe deposits are summarized in Table 1. The low Mg content (<1%) of both ore types reflects that the dolomitization, common in MVT type deposits, did not occur. Wide ranges of Fe (from 4 to 32%), Zn (from 4 to 47%) and Pb (from 0.5 to 28%) in the NSO zones (Table 1) indicate the variability of oxidation conditions laterally and vertically though the ore zones during

Sulfur and lead isotopes

Sulfur isotope analysis was performed on 39 samples (19 sphalerite, 12 galena and 8 pyrite) from seven different Zn-Pb deposits/mineralization in the Hakkari province (Table 2). While most of the galena samples were collected from the oxide carbonate ore zone, the sphalerite and pyrite were collected from the primary sulfide ore lenses (Fig. 5c, d; 7e) that were preserved in the oxide-carbonate ore zones. δ34SCDT values are between −3.43‰ and 5.13‰ (avg. 0.99‰) for galena, −1.46‰ and 3.98‰

Fluid inclusion studies

Fluid inclusion studies were measured in suitable transparent minerals that occur with the primary sulfides. Measurements were undertaken in quartz from the Üzümcü and Meskantepe deposits (Fig. 13a–d), quartz, barite and calcite from the Karakaya deposit (Table 4; Fig. 13e, f) and honey coloured sphalerite (Fig. 14g) and quartz from the vein-type ore zone of the Kurşuntepe deposit.

Microthermometry was performed on primary (P) and pseudeosecondary (PS) fluid inclusions, which could be observed

Tectonic setting and ore formation

Zn-Pb mineralization in the Hakkari region is located in a 6 km thick sedimentary rock package as shown in Fig. 1b. These sediments were deposited on the passive continent margin of the southern edge of Gondwana during the early Palaeozoic to the late Mesozoic. No magmatic rocks are present in these sediments in the Hakkari region. The underlying rock units of the Palaeozoic are the Derik formation, which consist of a thick volcano-sedimentary unit >2 km thick. This formation can be observed

Conclusion

The Zn-Pb deposits in the Hakkari region were developed within the late Triassic shale intercalated carbonated rocks deposited on the passive continental margin of the Arabian plate. Three different types of mineralization are observed in the region, which are (i) synsedimentary, (ii) sub-seafloor replacement and (iii) the vein-type which occurs in the feeder zones. Synsedimentary and sub-seafloor replacement type deposits have 10’s of km of lateral continuity. The mineralization has been

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

Acknowledgements

The authors thank to Fatih Turan (GÖK-FA Company-Turkey), Karakaya Mining Company (Turkey), Ölmez Mining Company (Turkey) for their sharing unpublished company reports and logistic supports during the field study, Çavuş Altunbulak (Geological Eng.) for the discussing the Üzümcü deposit data, and the anonymous reviewers, and the editors Franco Pirajno and İbrahim Uysal for their valuable suggestions that help to improve this paper.

This paper was supported by İÜ-BAP (YADOP-37096; BEK-03506) and

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