Genesis of the Halılar Metasediment-Hosted Cu-Pb ( ± Zn) Mineralization, NW Turkey: Evidence from Mineralogy, Alteration, and Sulfur Isotope Geochemistry

: This study contributes to our understanding of the evolution of Halılar Cu-Pb ( ± Zn) mineralization (NW Turkey) based on mineralogical and geochemical results and sulfur isotope data. The study area represents local Cu-Pb with some Zn brecciated-stockwork vein type mineralization along the NE–SW fault gouge zone at the lower boundary of the Sakarkaya and Düztarla granitoid rocks. Two main zones, consisting of sericite–quartz–chlorite ± kaolinite ± pyrite (i.e., zone-1) and calcite–epidote–albite ± chlorite ± sericite (i.e., zone-2), were observed within the central ore mineral zone at the mining site. Different mineralization assemblages were recorded; the main ore mineral contains chalcopyrite, galena, pyrite, and sphalerite within alteration zone-1, and the oxidation/supergene mineralization includes covellite and goethite. The mass balance calculations show that the samples of zone-1 show an increase in SiO 2 , Fe 2 O 3 , K 2 O, and LOI along with Ag, As, Cu, Mo, Pb, S, Sb, and Zn, reﬂecting high pyritization with sericitization and siliciﬁcation. On the other hand, the samples from zone-2 are rich in CaO; Na 2 O; P 2 O 5 ; TiO 2 ; LOI; and carbon-reﬂecting calcite, epidote, and albite alterations. A uniform magmatic sulfur source of Halılar sulﬁdes is suggested by their mean δ 34 S value of − 1.62‰. Furthermore, the primary metal source is metasediments and intrusive Düztarla granitoid magmatism. These observations suggest that the Halılar metasediment-hosted Cu-Pb ( ± Zn) mineralization was formed by epigenetic hydrothermal processes after sedimentation/diagenesis and metamorphism.


Introduction
Studies of hydrothermal alteration are important in the exploration of copper deposits in order to determine the processes of ore formation, as well as to identify potential ore zones [1].Spectroscopic methods, geophysics, or multispectral remote sensing techniques are used in mapping alteration zones, as well as in identifying their mineral assemblages [1][2][3][4][5][6][7][8][9].In addition, the geochemical changes from host rock to alteration zones provide alteration type and its degree, as well as the genesis and evolution of the hydrothermal system [5,[10][11][12][13][14][15][16][17][18][19].Hydrothermal alteration processes are responsible for mineralogical and chemical changes in the rock-forming minerals as a result of interactions between the hydrothermal fluids and host rocks along fracture zones and grain boundaries [1,2,20,21].Schwartz [22] stated that the alteration generally depends on: (1) temperature, pressure, and chemical composition of the fluid; (2) the chemical and physical nature of the wall rocks; and (3) the water-rock ratio.The mechanism and types of mineral deposits are assigned by the nature of the alteration assemblages and the different hydrothermal systems.In addition, the mineral assemblages of the altered rocks are important to help identify the alteration types (e.g., phyllic alteration refers to assemblages of quartz + sericite + pyrite minerals; potassic alteration: orthoclase + biotite + sericite; propylitic alteration: epidote + chlorite + albite) [23].Gifkins et al. [24] defined different types of mineral deposits by their alteration type and mineralogy, such as porphyry Cu deposits having potassic, phyllic, argillic, and propylitic alterations, while the low-sulfidation, epithermal, geothermal, VHMS, and sediment-hosted massive sulphide deposits having sericitic (or phyllic) and propylitic (or saussuritization) alterations.
In Turkey, mineralization in the structural zone of the Anatolian tectonic belt represents part of the Tethyan-Eurasian metallogenic belt (TEMB), which formed during the Mesozoic and Early Cenozoic [25].This mineralization was controlled by extensional events that formed after the Neo-Tethys closure.It is associated with calc-alkaline magmatic activity during the Oligocene-Miocene/Pliocene within the post-collision continent-continent environments and led to the formation of Pb-Zn, Sb, As, and Au-Cu deposits [25].
The study area (Halılar area) is located about 25-30 km northeast of Edremit in Balıkesir Province (Biga Peninsula, Turkey) (Figure 1).Halılar Cu-Pb (±Zn) mineralization occurs in a vein-type deposit that formed in the volcanogenic metasediments of the Sakarkaya Formation.It is associated with the NE-SW fault gouge zone along with the lower boundary of the Ba gca gız Formation and the Düztarla granitoid intrusion.
Although geological and geochemical studies of the Halılar area have been published [26], the genesis of base-metal Cu-Pb (-Zn) mineralization in this area remains ambiguous, as it has not been studied in detail.Therefore, this study focuses on mineralization in the Halılar area by reporting new data obtained from mineralogical, petrographical, and geochemical investigations of the mineralization and altered host rock.Using mass balance calculations, enrichment and/or depletion in the chemical components of the different alteration zones associated with this mineralization were calculated on the basis of their mass/volume changes (gain and loss).Sulfur isotope data from the sulfide minerals, including pyrite, chalcopyrite, and galena, were collected to understand the sulfur source(s), as well as to determine the δ 34 S H2S values of the hydrothermal fluid that caused the Halılar Cu-Pb-(±Zn) mineralization.[27].

Geological Setting
The Halılar area contains two groups: the clastic Halılar Group, which is slightly metamorphosed and overlain by the pre-Late Triassic age or Permian limestone [28], and the Bilecik group.These two groups are in contact with the intrusive rocks to the N and NW of Halılar village (Figure 2).The Halılar Group consists of two formations: the Bağcağız and Sakarkaya Formations; the Bilecik Group is represented by two formations: the Taşçıbayırı Formation and Günören Limestone (Figure 2).The granitoid rocks intruded the Sakarkaya and Bağcağız Formations of the Halılar Group in the study area (Figure 2).

Geological Setting
The Halılar area contains two groups: the clastic Halılar Group, which is slightly metamorphosed and overlain by the pre-Late Triassic age or Permian limestone [28], and the Bilecik group.These two groups are in contact with the intrusive rocks to the N and NW of Halılar village (Figure 2).The Halılar Group consists of two formations: the Ba gca gız and Sakarkaya Formations; the Bilecik Group is represented by two formations: the Taşçıbayırı Formation and Günören Limestone (Figure 2).The granitoid rocks intruded the Sakarkaya and Ba gca gız Formations of the Halılar Group in the study area (Figure 2).The Halılar Group was classified by Krushensky, Akcay, and Karaege [28] into the Bağcağız Formation (sandstone and shale) and the Sakarkaya Formation (sandstone and conglomerate).The Bağcağız Formation (sample IDs: H63 and H64) was intruded by the Düztarla granitoid at its lower boundary (Figure 2).It has dark siltstone at its upper boundary, which is overlain by the sandstone of the Sakarkaya Formation.This formation also has sandstone and siltstone alternations from bottom to top, consisting of dark-grayish-colored siltstones and silty shales with yellowish-colored, medium-bedded sandstones from the Lower Triassic to Middle Jurassic.The Bağcağız Formation is represented by carbonaceous dark metasiltstone and rhyolitic metatuffs (Figure 3a).The rhyolitic The Halılar Group was classified by Krushensky, Akcay, and Karaege [28] into the Ba gca gız Formation (sandstone and shale) and the Sakarkaya Formation (sandstone and conglomerate).The Ba gca gız Formation (sample IDs: H63 and H64) was intruded by the Düztarla granitoid at its lower boundary (Figure 2).It has dark siltstone at its upper boundary, which is overlain by the sandstone of the Sakarkaya Formation.This formation also has sandstone and siltstone alternations from bottom to top, consisting of dark-grayish-colored siltstones and silty shales with yellowish-colored, medium-bedded sandstones from the Lower Triassic to Middle Jurassic.The Ba gca gız Formation is represented by carbonaceous dark metasiltstone and rhyolitic metatuffs (Figure 3a).The rhyolitic metatuffs are fine-grained light gray to yellowish rocks (Figure 3a) microscopically consisting of microp-erthite and quartz crystals embedded in a finer-grained tuffaceous matrix of kaolinitized and carbonatized feldspar, quartz, and Fe-oxide (Figure 3b).
The Sakarkaya Formation (sample IDs: H05, H07, H09, H14, H15, H18, H20, H22a, H55, and H60) outcrops approximately 500 m south of Sakarkaya Hill and 1.5-2 km north and northeast of Halılar village (Figure 2).It is represented by fine-grained, yellowishcolored metasandstone (Figure 3c).It has a sharp contact with the dark metasiltstones of the Bağcağız Formation.The unit rests with a distinct contact on the Bositra-bearing dark silty shale of the Bağcağız Formation [26].The metasandstone ranges from subarkosic to wackes in composition and consists of poorly sorted quartz, sericitized and kaolinitized feldspar, and mica grains cemented by iron oxide (Figure 3d,e).These components are embedded in altered feldspar and silicified fine-grained matrix (Figure 3d,e).The upper portion of the formation is represented by cross-stratified beds.The Sakarkaya Formation (sample IDs: H05, H07, H09, H14, H15, H18, H20, H22a, H55, and H60) outcrops approximately 500 m south of Sakarkaya Hill and 1.5-2 km north and northeast of Halılar village (Figure 2).It is represented by fine-grained, yellowish-colored metasandstone (Figure 3c).It has a sharp contact with the dark metasiltstones of the Ba gca gız Formation.The unit rests with a distinct contact on the Bositra-bearing dark silty shale of the Ba gca gız Formation [26].The metasandstone ranges from subarkosic to wackes in composition and consists of poorly sorted quartz, sericitized and kaolinitized feldspar, and mica grains cemented by iron oxide (Figure 3d,e).These components are embedded in altered feldspar and silicified fine-grained matrix (Figure 3d,e).The upper portion of the formation is represented by cross-stratified beds.
The Bilecik Group is part of the Callovian-Hauterivian (Middle Jurassic-Lower Cretaceous) stratigraphy in NW Anatolia known as the Bilecik Limestone (Figure 3f-h).It has been divided into the two formations; Taşçıbayırı and Günören Limestone formations.The Taşçıbayırı Formation (sample IDs: H56, H57, and H58) underlies the Günören Limestone (sample ID: H59); they contain sandy limestone and dolomitic limestone, respectively.The sandy limestone of the Taşçıbayırı Formation is composed of calcite with feldspar, mica, and volcanic rock fragments (Figure 3g).The volcanic rock fragments are composed of broken and/or eroded volcanic rocks consisting of quartz and feldspar (Figure 3g), while the Günören dolomitic limestone consists of calcite and dolomite with Fe-oxide minerals (Figure 3h).
The Halılar area has a well-described Upper Triassic-Liassic continuous succession (Figures 1 and 2).The tectonic sedimentary rocks formed at the Sakarya divergent margin, which evolved in the Late Triassic-Aptian interval [29,30].As a result of the diachronic closure of the Tethys basin in western Anatolian, the Upper Triassic black shales were deposited in the Lias in the Karakaya euxinic basin throughout the Edremit region.This shale and the Hettangian arkosic sandstones were later intruded by the Düztarla granodioriticgranitic body due to the southward subduction of the Paleo-Tethys [29].

Sampling and Analytical Methods
A total of 45 host rocks, altered rocks, and mineralized samples were collected from the study area.Thin sections and a subset of polished sections were examined optically using transmitted and reflected light microscopes.Whole-rock major, trace, and rare earth element analyses were conducted at the Geochemistry Research Laboratories of Istanbul Technical University (ITU/JAL).The samples were grounded using a tungsten carbide milling device.Major elements were analyzed using a BRUKER S8 TIGER model X-ray fluorescence spectrometer (XRF) (Östliche Rheinbrückenstraße 49, 76187 Karlsruhe, Germany) with a wavelength range from 0.01-12 nm.Trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) using an ELAN DRC-e Perkin Elmer model (PerkinElmer, Waltham, MA, US).Approximately 100 mg of powdered sample was digested in two steps.The first step was completed with 6 mL of 37% HCl, 2 mL of 65% HNO 3 , and 1 mL of 38%-40% HF in a pressure-and temperature-controlled Teflon beaker using a Berghoff Microwave™ at an average temperature of 180 • C. The second step was completed with the addition of 6 mL of 5% boric acid solution.The remaining solution sample was analyzed by ICP-MS.The altered rocks were also analyzed for mineralogy using a BRUKER X-ray diffractometer (XRD) (Östliche Rheinbrückenstraße 49, 76187 Karlsruhe, Germany).Calculation of the normative mineral abundances from the major element analyses and rare earth element diagrams were created using Igpet 2.3 [31].The GEOISO-Windows of Coelho [32] were used to determine the absolute mobility of the elements using equations from Gresens [33] and isocon diagrams from Grant [34,35].
Sulfide minerals for sulfur isotope analysis were separated from slightly crushed (200 mesh) lode samples (>95 % pure pyrite, chalcopyrite, and galena).They were washed and handpicked under a binocular microscope.These analyses were carried out at the Geochron Laboratory (USA) using EA-IRMS (Elemental Analysis-Isotope Ratio Mass Spectrometry) techniques.All stable isotope data are reported in the delta (δ) notation, relative to Vienna-Canyon Diablo Troilite (V-CDT) for sulfur isotopes with 0.5‰ (1 σ) analytical uncertainty.

Halılar Cu-Pb (±Zn) Mineralization
The Halılar base metal mineralization represents Cu-Pb with some Zn brecciatedstockwork-veining-type mineralization.The mineralization is restricted to a fault gouge zone directed NE-SW, as well as along the lower boundary of the Sakarkaya and Düztarla granitoid rocks (Figure 2).It is also closely associated with intense hydrothermal alteration within the breccia and quartz stockwork veining (Figure 4a-d).Based on the field investigation and petrographic and mineralogical (XRD) data, the mineralized quartz veins and brecciated ore bodies are accompanied by two types of hydrothermal alteration zone with gradational boundaries: zone-1 (sericite-quartz-chlorite ± kaolinite ± pyrite) and zone-2 (calcite-epidote-albite ± chlorite ± sericite).The ore zone is represented by mineralized and brecciated quartz stockwork veining (Figure 4a-c).It has high amounts of Cu (9.9 %), Pb (11.3 %), and Zn (0.29 %) mineralization, with high amounts of chalcopyrite and galena with sphalerite and pyrite (Figure 4a-c).It contains quartz with a subordinate amount of wollastonite, kaolinite, andradite, and calcite (Figures 4e-h and 5 and Appendix A).These calc-silicate assemblages refer to the skarn that resulted from the metasomatism of sandy limestone in the Taşçıbayırı Formation in association with andradite (Figures 4e-h and 5 and Appendix A).The XRD data show quartz (low), wollastonite (1A, manganoan), kaolinite (1A), microcline, calcite, chalcopyrite, andradite, anglesite, and cubanite (high) with smaller amounts of pyrite, sphalerite (ferrous), galena, and quartz (high) (Figure 5 and Appendix A).
Alteration zone-1 (sericite-quartz-chlorite ± kaolinite ± pyrite) forms the main alteration zone developed outwards from the ore zone and has high amounts of sericite and quartz, with lesser amounts of chlorite, kaolinite, and pyrite (Figures 4i-l and 6 and Appendix B).It is characterized by the preferential replacement of the original K-feldspar and/or plagioclase-biotite by sericite/muscovite-kaolinite.XRD studies reveal a paragenesis of quartz (low), kaolinite (1A), clinochlore (1MIa), and sericite (2M1) with a subordinate amount of chamosite (1MIIb), pyrite, and chalcopyrite (Figure 6, Appendix B).

Ore Mineralogy
The ore mineral assemblage includes chalcopyrite, galena, pyrite, and sphalerite with covellite and goethite in abundant gangue minerals such as quartz, sericite, chlorite, and calcite forming along the quartz stockwork veins as well as in the brecciated ore zones (Figures 4-7 and Appendices A-C).Chalcopyrite and galena are the most common sulfide minerals in the ore bodies, occurring as yellow and whitish gray in color and with a subhedral granular texture (up to 2 mm), respectively (Figure 8a,b).Pyrite is either associated with or occurs as inclusions in chalcopyrite (Figure 8c,d).Sphalerite is characterized by dark gray coloring associated with chalcopyrite and pyrite, forming exsolution textures produced by chalcopyrite (Figure 8b,c,e).These minerals were developed in the main ore mineralization phase (Figure 9).On the other hand, the oxidation and supergene mineralization events represent the second phase of mineralization, including covellite and goethite formed after chalcopyrite and pyrite, respectively (Figures 8 and 9).

Ore Mineralogy
The ore mineral assemblage includes chalcopyrite, galena, pyrite, and sphalerite with covellite and goethite in abundant gangue minerals such as quartz, sericite, chlorite, and calcite forming along the quartz stockwork veins as well as in the brecciated ore zones (Figures 4-7 and Appendices A-C).Chalcopyrite and galena are the most common sulfide minerals in the ore bodies, occurring as yellow and whitish gray in color and with a subhedral granular texture (up to 2 mm), respectively (Figure 8a,b).Pyrite is either associated with or occurs as inclusions in chalcopyrite (Figure 8c,d).Sphalerite is characterized by dark gray coloring associated with chalcopyrite and pyrite, forming exsolution textures produced by chalcopyrite (Figure 8b,c,e).These minerals were developed in the main ore mineralization phase (Figure 9).On the other hand, the oxidation and supergene mineralization events represent the second phase of mineralization, including covellite and goethite formed after chalcopyrite and pyrite, respectively (Figures 8 and 9).

Geochemistry of the Least-Altered Metasediments
Ten representative samples collected from the least-altered metasediments of the Sakarkaya Formation were analyzed for major, trace, and rare-earth element contents (Table 1).Samples from the metasandstones are classified as mainly wackes and, rarely, Fe-sand and Fe-shale based on the geochemical classification of the terrigenous sandstones and shales by Herron [36] (Figure 10a).The samples have SiO2/Al2O3 ratios ranging from 2.7 to 5.5 with an average of 4.3, which are similar to upper continental crust (UCC) [37] (~4.3 SiO2/Al2O3 ratio), suggesting that they were sourced from the crustal felsic rocks.It also appears in Figure 10b,c that the Sakarkaya metasediments have acidic/intermediate characteristics, which lie mostly in the field of the metavolcanic tuffs, metagreywackes, and arkosic sands [38] according to their low K/Rb ratios (mean = 312.8).In the F1-F2 classification diagram (Figure 10d), the metasediments are mostly comparable with the compositional characteristics of the P4-quartoze sedimentary provenance that form within the passive and active continental margins (Figure 10e) due to recycling from old sedimentary rocks derived from highly weathered felsic terrains.The metasandstones have low total rare earth element contents (∑REE) (up to 145.14 ppm with an average of 88.96 ppm), ∑REE/∑HREE = 6.59-10.43ppm, (La/Yb)N = 5.38-14.29 ppm, and positive Eu anomaly

Geochemistry of the Least-Altered Metasediments
Ten representative samples collected from the least-altered metasediments of the Sakarkaya Formation were analyzed for major, trace, and rare-earth element contents (Table 1).Samples from the metasandstones are classified as mainly wackes and, rarely, Fe-sand and Fe-shale based on the geochemical classification of the terrigenous sandstones and shales by Herron [36] (Figure 10a).The samples have SiO2/Al2O3 ratios ranging from 2.7 to 5.5 with an average of 4.3, which are similar to upper continental crust (UCC) [37] (~4.3 SiO2/Al2O3 ratio), suggesting that they were sourced from the crustal felsic rocks.It also appears in Figure 10b,c that the Sakarkaya metasediments have acidic/intermediate characteristics, which lie mostly in the field of the metavolcanic tuffs, metagreywackes, and arkosic sands [38] according to their low K/Rb ratios (mean = 312.8).In the F1-F2 classification diagram (Figure 10d), the metasediments are mostly comparable with the compositional characteristics of the P4-quartoze sedimentary provenance that form within the passive and active continental margins (Figure 10e) due to recycling from old sedimentary rocks derived from highly weathered felsic terrains.The metasandstones have low total rare earth element contents (∑REE) (up to 145.14 ppm with an average of 88.96 ppm), ∑REE/∑HREE = 6.59-10.43ppm, (La/Yb)N = 5.38-14.29 ppm, and positive Eu anomaly

Geochemical Characteristics 5.1. Geochemistry of the Least-Altered Metasediments
Ten representative samples collected from the least-altered metasediments of the Sakarkaya Formation were analyzed for major, trace, and rare-earth element contents (Table 1).Samples from the metasandstones are classified as mainly wackes and, rarely, Fe-sand and Fe-shale based on the geochemical classification of the terrigenous sandstones and shales by Herron [36] (Figure 10a).The samples have SiO 2 /Al 2 O 3 ratios ranging from 2.7 to 5.5 with an average of 4.3, which are similar to upper continental crust (UCC) [37] (~4.3 SiO 2 /Al 2 O 3 ratio), suggesting that they were sourced from the crustal felsic rocks.It also appears in Figure 10b,c that the Sakarkaya metasediments have acidic/intermediate characteristics, which lie mostly in the field of the metavolcanic tuffs, metagreywackes, and arkosic sands [38] according to their low K/Rb ratios (mean = 312.8).In the F1-F2 classification diagram (Figure 10d), the metasediments are mostly comparable with the compositional characteristics of the P4-quartoze sedimentary provenance that form within the passive and active continental margins (Figure 10e) due to recycling from old sedimentary rocks derived from highly weathered felsic terrains.The metasandstones have low total rare earth element contents (∑REE) (up to 145.14 ppm with an average of 88.96 ppm), ∑REE/∑HREE = 6.59-10.43ppm, (La/Yb) N = 5.38-14.29 ppm, and positive Eu anomaly (Eu/Eu* = 0.68-1.27ppm) that are similar to the upper continental crust (UCC) of Taylor and McLennan [37] (Figure 10f).[38].Fields of unmetamorphosed arkosic sands after van de Kamp et al. [39], low−grade metagreywackes after Condie et al. [40] and Caby et al. [41], and higher-grade metavolcanic tuffs after van de Kamp [42]; (d) plot of samples in discriminant functions F1 vs. F2 (provenance fields are after Roser and Korsch [43]; (e) plot of discriminant scores along Function 1 vs. 2 after Bhatia [44]; (f) upper continental crust (UCC)−normalized REE patterns [37].

Alteration Geochemistry
Two main alteration zones surround the Cu-Pb±Zn-bearing ore mineralization in the Halılar area.These are represented by zone-1 (sericite-quartz-chlorite ± kaolinite ± pyrite) and zone-2 (calcite-epidote-albite ± chlorite ± sericite), and they were analyzed for major, trace, and REEs (Table 2).Based on the alteration index (AI) [45] and advanced argillic alteration index (AAAI) of Williams and Davidson [46], samples from each zone show opposite alteration trends (Figure 11a).The ore zone and alteration zone-1 fall along the trend of silicification/potassic alteration, while alteration zone-2 falls along the carbonation/chloritization alteration trend (Figure 11a).Based on the alteration boxplot relationship between the chlorite-carbonate-pyrite index (CCPI) of Large et al. [47] and the AI of Ishikawa et al. [45], the samples of the ore zone and zone-1 are clustered in the field of strongly altered rock, having chlorite-sericite-pyrite alteration while the ore zone is affected by extensive pyritization (Figure 11b).On the other hand, zone-2, within the carbonate-altered host rock field, shows Mn-carbonate-sericite-chlorite alteration (Figure 11b).[45] vs. AAAI [46]; (b) AI [45] vs. CCPI [47] of the studied alteration samples from the Halılar area.

Mass Balance Calculations
The behavior of different elements, excluding immobile ones, is changeable during hydrothermal alteration processes depending on their volume changes and their mass transfer [48,49].Gresens [33] and Grant [34,35] used mass-balance calculations to quantify hydrothermal alteration effects on the host rock within the mineralized regions and to determine the relative gain and loss of the various major and trace elements during hydrothermal alteration.
Based on the trace element geochemical analyses, the ore zone and alteration zone-1 have high amounts of Cu and Pb, with an average of 9.9% and 11.3%, respectively, for the ore zone, and 0.32% and 0.12%, respectively, for zone-1 (Table 2).They are classified as a Cu-Pb type (Figure 12), which refers to the high concentrations of chalcopyrite and galena.Alteration zone-2 represents the Cu-Pb-Zn type (Figure 12), having low Cu, Pb, and Zn contents, with averages of 28.18ppm, 47.95ppm, and 98.07ppm, respectively.
Al2O3 and TiO2 are immobile in all alteration zones during hydrothermal alteration; therefore, they were selected to assess the chemical changes due to the process of hydrothermal alteration by using the GEOISO-Windows software developed by Coelho [32].The results of these calculations are illustrated through the isocon diagrams of Grant [34] and show the different patterns of major and trace element gains and losses (Figures 13  and 14 and Table 3).The samples from zone-1 are rich in SiO2, Fe2O3, K2O, and LOI, with lesser increases in the amount of CaO, P2O5, and MnO (Figure 14a).Gains in Ag, As, Cu, Mo, Pb, S, Sb, and Zn are also recognized within this alteration zone (Figure 14b).This zone is characterized by higher amounts of sulfur and iron, with variable copper, lead, and zinc contents reflecting high pyritization, with the main base metals providing higher mass (MC = 170.42)and volume change (VC = 182.1)(Table 3).SiO2 and K2O increases reflect high silicification and sericitization, which are comparable with the petrographic and mineralogical (XRD) data.In zone-2, CaO, Na2O, P2O5, TiO2, LOI, and carbon are enriched, reflecting calcite, epidote, and albite alterations (Figure 14c).The loss of Cu, Pb, and Zn is observed in this zone, providing lower MC (−3.18) and VC (−1.80) values (Figure 14d and Table 3).[45] vs. AAAI [46]; (b) AI [45] vs. CCPI [47] of the studied alteration samples from the Halılar area.

Mass Balance Calculations
The behavior of different elements, excluding immobile ones, is changeable during hydrothermal alteration processes depending on their volume changes and their mass transfer [48,49].Gresens [33] and Grant [34,35] used mass-balance calculations to quantify hydrothermal alteration effects on the host rock within the mineralized regions and to determine the relative gain and loss of the various major and trace elements during hydrothermal alteration.
Based on the trace element geochemical analyses, the ore zone and alteration zone-1 have high amounts of Cu and Pb, with an average of 9.9% and 11.3%, respectively, for the ore zone, and 0.32% and 0.12%, respectively, for zone-1 (Table 2).They are classified as a Cu-Pb type (Figure 12), which refers to the high concentrations of chalcopyrite and galena.Alteration zone-2 represents the Cu-Pb-Zn type (Figure 12), having low Cu, Pb, and Zn contents, with averages of 28.18ppm, 47.95ppm, and 98.07ppm, respectively.Al 2 O 3 and TiO 2 are immobile in all alteration zones during hydrothermal alteration; therefore, they were selected to assess the chemical changes due to the process of hydrothermal alteration by using the GEOISO-Windows software developed by Coelho [32].The results of these calculations are illustrated through the isocon diagrams of Grant [34] and show the different patterns of major and trace element gains and losses (Figures 13 and 14 and Table 3).The samples from zone-1 are rich in SiO 2 , Fe 2 O 3 , K 2 O, and LOI, with lesser increases in the amount of CaO, P 2 O 5 , and MnO (Figure 14a).Gains in Ag, As, Cu, Mo, Pb, S, Sb, and Zn are also recognized within this alteration zone (Figure 14b).This zone is characterized by higher amounts of sulfur and iron, with variable copper, lead, and zinc contents reflecting high pyritization, with the main base metals providing higher mass (MC = 170.42)and volume change (VC = 182.1)(Table 3).SiO 2 and K 2 O increases reflect high silicification and sericitization, which are comparable with the petrographic and mineralogical (XRD) data.In zone-2, CaO, Na 2 O, P 2 O 5 , TiO 2 , LOI, and carbon are enriched, reflecting calcite, epidote, and albite alterations (Figure 14c).The loss of Cu, Pb, and Zn is observed in this zone, providing lower MC (−3.18) and VC (−1.80) values (Figure 14d and Table 3).δ 34 S isotopic data from the sulfide-bearing ore deposits were obtained to determine the source of the sulfur and the origin of the sulfur-bearing fluids [51].The δ 34 S isotope values of ten pyrite, chalcopyrite, and galena samples collected from the highly altered and mineralized altered metasediments host rocks are in the range of −1.1 to −0.1‰V CDT (n = 3), −2.7 to −0.5 ‰V CDT (n = 3), and −3.5 to −2.1‰V CDT (n = 4), respectively (Table 4).Pyrites from a quartz vein have an average δ 34 S of 0.4‰VCDT (Table 4 and Figure 15a).By assuming the H 2 S as the sulfur species in solution, and based on the fractionation equations of Czamanske and Rye [52] and Ohmoto and Rye [51], the δ 34 S H2S values of the fluid have a narrow range of −2.54 to −0.08 ‰ V CDT (Table 4 and Figure 15b).  (1Based on the fluid inclusion thermometry (unpublished data), (2) Calculated by using the sulfur isotope fractionation equations in Czamanske and Rye [52] and Ohmoto and Rye [51].δ 34 S isotopic data from the sulfide-bearing ore deposits were obtained to determine the source of the sulfur and the origin of the sulfur-bearing fluids [51].The δ 34 S isotope values of ten pyrite, chalcopyrite, and galena samples collected from the highly altered and mineralized altered metasediments host rocks are in the range of −1.1 to −0.1‰VCDT (n = 3), −2.7 to −0.5 ‰VCDT (n = 3), and −3.5 to −2.1‰VCDT (n = 4), respectively (Table 4).Pyrites from a quartz vein have an average δ 34 S of 0.4‰VCDT (Table 4 and Figure 15a).By assuming the H2S as the sulfur species in solution, and based on the fractionation equations of Czamanske and Rye [52] and Ohmoto and Rye [51], the δ 34 SH2S values of the fluid have a narrow range of −2.54 to −0.08 ‰ VCDT (Table 4 and Figure 15b).

Sources of Sulfur
There are many sulfur sources with distinct δ 34 S values: (1) the mantle source has a 0 ± 3‰ δ 34 S value [53]; (2) the magmatic source, in which the sulfur resulted from desulfidation and/or dissolution or from magmatic sulfides, has 0 to +9‰ δ 34 S [54]; (3) the seawater sources have a mean value of +20 ‰ δ 34 S; and (4) the strongly reduced sulfur source in the sedimentary rocks has very negative δ 34 S values [55].
In the Halılar area, the mean δ 34 S value of the sulfides is close to −1.62‰, suggesting a uniform magmatic sulfur source in which the sulfur originates either from the leaching and remobilization of the old magmatic sulfide or from the mantle source (Figure 16).Furthermore, the δ 34 S values of the studied sulfide minerals decrease from pyrite (−1.1 to 0.4 ‰V CDT ) and chalcopyrite (−2.7 to −0.5 ‰V CDT ) to galena (−3.5 to −2.1‰V CDT ) (Figure 17), which is compatible with the suggested trend of differentiation of Ohmoto and Rye [51].Thus, the ore-bearing fluid appears to have a magmatic (mantle) source [51] with magmatic-hydrothermal signatures [56] (Figure 18).  (1Based on the fluid inclusion thermometry (unpublished data), (2) Calculated by using the sulfur isotope fractionation equations in Czamanske and Rye [52] and Ohmoto and Rye [51].

Sources of Sulfur
There are many sulfur sources with distinct δ 34 S values: (1) the mantle source has a 0 ± 3‰ δ 34 S value [53]; (2) the magmatic source, in which the sulfur resulted from desulfidation and/or dissolution or from magmatic sulfides, has 0 to +9‰ δ 34 S [54]; (3) the seawater sources have a mean value of +20 ‰ δ 34 S; and (4) the strongly reduced sulfur source in the sedimentary rocks has very negative δ 34 S values [55].

Metal Source
The metasediments of the Sakarkaya Formation that host the Halılar Cu-Pb (±Zn) mineralization are slightly enriched in metallic elements (average of Ag = 6.7 ppm, As = 101.9ppm, Au = 0.04 ppm, Cu = 53.8ppm, Mo = 1.8 ppm, Pb = 274.7 ppm, S = 389.0ppm, Sb = 2.0 ppm, and Zn = 371.3ppm) relative to the average UCC (Table 5).Moreover, the contents of the metallic elements in the Düztarla granitoid rocks also show higher values than typical UCC (mean values of Ag = 1.When the sulfur is normalized to the UCC of Rudnick et al. [65], it is highly rich in granitoid rocks, but not in metasediments (Figure 19a,b).Thus, the primary metal suppliers appear to be the metasediments and intrusive Düztarla granitoid magmatism; together, they account for the metals in the Halılar brecciated-stockwork-type mineralization.Based on the geologic features and mode of occurrences, the Halılar metasedimenthosted Cu-Pb (±Zn) mineralization appears to be formed by epigenetic hydrothermal processes after sedimentation/diagenesis and metamorphism.

Metal Source
The metasediments of the Sakarkaya Formation that host the Halılar Cu-Pb (±Zn) mineralization are slightly enriched in metallic elements (average of Ag = 6.7 ppm, As = 101.9ppm, Au = 0.04 ppm, Cu = 53.8ppm, Mo = 1.8 ppm, Pb = 274.7 ppm, S = 389.0ppm, Sb = 2.0 ppm, and Zn = 371.3ppm) relative to the average UCC (Table 5).Moreover, the contents of the metallic elements in the Düztarla granitoid rocks also show higher values than typical UCC (mean values of Ag = 1.14 ppm, As = 84.05ppm, Au = 0.36 ppm, Cu = 368.91ppm, Mo = 324.68ppm, Pb = 49.52 ppm, S = 1396.7 ppm, Sb = 2.34 ppm, and Zn = 414.69ppm).When the sulfur is normalized to the UCC of Rudnick et al. [65], it is highly rich in granitoid rocks, but not in metasediments (Figure 19a,b).Thus, the primary metal suppliers appear to be the metasediments and intrusive Düztarla granitoid magmatism; together, they account for the metals in the Halılar brecciated-stockwork-type mineralization.Based on the geologic features and mode of occurrences, the Halılar metasediment-hosted Cu-Pb (±Zn) mineralization appears to be formed by epigenetic hydrothermal processes after sedimentation/diagenesis and metamorphism.

Conclusions
The Halılar area contains two groups: the clastic Halılar Group that overlies the metamorphics of the pre-Late Triassic age or Permian limestones and the Bilecik Group.The Halılar Group consists of the Bağcağız and Sakarkaya Formations, and the Bilecik Group is represented by two formations, including the Taşçıbayırı Formation and the Günören Limestone.The Sakarkaya and Bağcağız Formations were later intruded by Oligo-Miocene Düztarla granitoid rocks.
The Halılar base metal mineralization consists mainly of Cu-Pb sulfide with some Zn sulfide in the brecciated stockworks and veins.This type of vein mineralization is restricted to a fault gouge zone directed NE-SW and along the lower contact of the Sakarkaya and Düztarla granitic rocks.Two types of hydrothermal alteration zones with gradual boundaries can be observed in the main ore zone.These include zone-1 (sericitequartz-chlorite ± kaolinite ± pyrite) and zone-2 (calcite-epidote-albite ± chlorite ± sericite).The main ore mineral assemblage consists of chalcopyrite, galena, pyrite, and sphalerite in an abundant amount of gangue minerals such as quartz, sericite, chlorite, and calcite forming along the quartz stockwork veins, as well as in the brecciated ore zones.The other oxidation and supergene mineralization includes covellite and goethite formed after chalcopyrite and pyrite, respectively.
The least-altered Sakarkaya metasediments are classified mainly as wackes and, rarely, Fe-sand and Fe-shale, which are relatively similar in chemical composition to the upper continental crust (UCC).They are sourced from the crustal felsic rocks and a

Conclusions
The Halılar area contains two groups: the clastic Halılar Group that overlies the metamorphics of the pre-Late Triassic age or Permian limestones and the Bilecik Group.The Halılar Group consists of the Ba gca gız and Sakarkaya Formations, and the Bilecik Group is represented by two formations, including the Taşçıbayırı Formation and the Günören Limestone.The Sakarkaya and Ba gca gız Formations were later intruded by Oligo-Miocene Düztarla granitoid rocks.
The Halılar base metal mineralization consists mainly of Cu-Pb sulfide with some Zn sulfide in the brecciated stockworks and veins.This type of vein mineralization is restricted to a fault gouge zone directed NE-SW and along the lower contact of the Sakarkaya and Düztarla granitic rocks.Two types of hydrothermal alteration zones with gradual boundaries can be observed in the main ore zone.These include zone-1 (sericite-quartzchlorite ± kaolinite ± pyrite) and zone-2 (calcite-epidote-albite ± chlorite ± sericite).The main ore mineral assemblage consists of chalcopyrite, galena, pyrite, and sphalerite in an abundant amount of gangue minerals such as quartz, sericite, chlorite, and calcite forming along the quartz stockwork veins, as well as in the brecciated ore zones.The other oxidation and supergene mineralization includes covellite and goethite formed after chalcopyrite and pyrite, respectively.
The least-altered Sakarkaya metasediments are classified mainly as wackes and, rarely, Fe-sand and Fe-shale, which are relatively similar in chemical composition to the upper continental crust (UCC).They are sourced from the crustal felsic rocks and a quartzose sedimentary provenance formed within the passive and active continental margins.Massbalance calculations reveal that the samples of zone-1 are enriched in SiO 2 , Fe 2 O 3 , K 2 O, and LOI, with Ag, As, Cu, Mo, Pb, S, Sb, and Zn reflecting a high degree of pyritization with sericitization and silicification.On the other hand, the samples of zone-2 show an increase in CaO; Na 2 O; P 2 O 5 ; TiO 2 ; LOI; and carbon-reflecting calcite, epidote, and albite alterations.
The mean δ 34 S value of the sulfides in the Halılar area is close to −1.62‰, suggesting a uniform magmatic sulfur source in which the sulfur originates either from leaching and remobilization from the old magmatic sulfide or from the mantle source.There is also a sulfur isotope having a differentiation trend from pyrite to galena.The ore-bearing fluid has δ 34 S values of H 2 S, ranging from −2.54 to −0.08 ‰, typical of a magmatichydrothermal signature [47].
Based on the normalization of the metallic elements in the Sakarkaya metasediments and Düztarla granitoid rocks to the UCC [38] and [65], these metasediments and granitoid rocks represent the primary source of metals forming the Halılar brecciatedstockwork-veining-type mineralization.Overall, the geologic features and the mode of occurrences of the Halılar metasediment-hosted Cu-Pb (±Zn) mineralization suggest that they were formed by epigenetic hydrothermal processes after sedimentation/diagenesis and metamorphism.chemistry Research Laboratories at Istanbul Technical University (Turkey).Great appreciation goes to M. Kumral (ITU, Turkey) and A. Abdelnasser (Benha University) for their support during all stages of work on the article.Z. Doner (ITU, Turkey) and A. Unal (ITU, Turkey) are also thanked for their help during fieldwork.The help of F. Yavuz (ITU, Turkey) and G. Ustunisik (South Dakota School of Mines, USA) were highly appreciated during the review of the article.The editor and two anonymous reviewers are thanked for carefully reading the manuscript and for their constructive comments.

Conflicts of Interest:
The author declares no conflict of interest.

Figure 3 .Figure 3 .
Figure 3. (a) Rhyolitic metatuffs of the Bağcağız Formation; (b) XPL photomicrograph of the mineral composition of rhyolitic metatuffs; (c) yellowish-colored metasandstone of the Sakarkaya Formation; (d,e) XPL photomicrograph of the poorly sorted quartz, feldspar, and mica grains bounded by iron oxide in the subarkosic-to-quartz arenitic of the metasandstone; (f) general view of the Bilecik Limestone; (g) XPL photomicrograph of the calcite with feldspar, mica, and volcanic rock fragments in the sandy limestone of the Taşçıbayırı Formation; (h) XPL photomicrograph of the Figure 3. (a) Rhyolitic metatuffs of the Ba gca gız Formation; (b) XPL photomicrograph of the mineral composition of rhyolitic metatuffs; (c) yellowish-colored metasandstone of the Sakarkaya Formation; (d,e) XPL photomicrograph of the poorly sorted quartz, feldspar, and mica grains bounded by iron oxide in the subarkosic-to-quartz arenitic of the metasandstone; (f) general view of the Bilecik Limestone; (g) XPL photomicrograph of the calcite with feldspar, mica, and volcanic rock fragments in the sandy limestone of the Taşçıbayırı Formation; (h) XPL photomicrograph of the calcite and dolomite with Fe-oxide minerals in Günören dolomitic limestone; (i) granodiorite of Düztarla intrusive rocks; (j) XPL photomicrograph of the oligoclase, quartz, and microperthite with subordinate amount of biotite and Fe-oxide minerals in granodiorite; (k) granite from the Düztarla intrusion invaded into the Ba gca gız Formation; (l) XPL photomicrograph of the mineral composition of the Düztarla granite intrusion.Abbreviations: biotite (bt), calcite (cal), dolomite (dol), K-feldspar (kfs), kaolinite (kln), muscovite (ms), opaque (opq), plagioclase (pl), quartz (qz), and sericite (ser).

Figure 9 .
Figure 9. Paragenetic sequence of mineralization phases in the Halılar area.

Figure 9 .
Figure 9. Paragenetic sequence of mineralization phases in the Halılar area.

Figure 9 .
Figure 9. Paragenetic sequence of mineralization phases in the Halılar area.

Figure 14 .
Figure 14.Gain/loss of major oxides (wt.%) (a,c) and trace elements (ppm) (b,d) in the alteration zones during hydrothermal alteration based on the mean data of the representative least−altered samples as a reference for calculations.

Figure 15 .
Figure 15.Histograms of (a) the δ 34 S isotopic compositions for sulfide minerals (pyrite, chalcopyrite, and galena) and (b) the δ 34 SH2S of the fluid that formed the sulfides in the Halılar area.

Figure 15 .
Figure 15.Histograms of (a) the δ 34 S isotopic compositions for sulfide minerals (pyrite, chalcopyrite, and galena) and (b) the δ 34 S H2S of the fluid that formed the sulfides in the Halılar area.

Figure 17 .
Figure 17.Distribution of the δ 34 S values in the studied sulfide minerals from the Halılar area.Figure 17.Distribution of the δ 34 S values in the studied sulfide minerals from the Halılar area.

Figure 17 .
Figure 17.Distribution of the δ 34 S values in the studied sulfide minerals from the Halılar area.Figure 17.Distribution of the δ 34 S values in the studied sulfide minerals from the Halılar area.

Figure 17 .
Figure 17.Distribution of the δ 34 S values in the studied sulfide minerals from the Halılar area.

Table 1 .
The major oxides and trace and rare-earth elements (REE) of metasediments in the Sakarkaya Formation.

Table 2 .
Major oxides and trace and rare-earth elements (REE) of the ore zone and alteration zones 1 and 2 in the Halılar area.

Table 3 .
Element/oxide mass changes in relation to the original whole-rock mass ((Mfi-Moi)/Mo) and in relation to the original element/oxide mass in the original rock ((Mfi-Moi)/Moi).

Table 4 .
Sulfur isotope values of sulfides from the Halılar area.

Table 4 .
Sulfur isotope values of sulfides from the Halılar area.

Table A1 .
XRD analyses of representative samples from the ore zone.