Metal source and the origin of the Darıderesi Pb-Zn (Ag) veins in the Balya Mining District, NW Türkiye: constraints from ore mineral chemistry, fluid inclusions and S-Pb isotopic signatures

ABSTRACT The Darıderesi mineralisation was recently discovered in the Balya district, which hosts Pb-Zn (Ag) deposits including Arı Mağara-Balya Main and Hastanetepe-Balya North. Darıderesi is a structurally controlled hydrothermal and associated replacement mineralisation hosted in the shale-mudstone and carbonaceous horizons within the Karakaya Complex. The mineralisation was formed in three main stages as pre-ore calc-silicate alteration, main ore, and supergene alteration. The substages of the sulphide-sulphosalt mineralisation can be summarised as: pyrite-arsenopyrite galena, sphalerite, ferrokesterite, chalcopyrite, fahlore group and geocronite-jordanite solid solution series members, xanthoconite, pyrargyrite and goldfieldite. Fluid inclusion studies indicate that both boiling and fluid mixing were the most effective processes causing the precipitation of sulphides and sulphosalts. Along its pathway, fluid–rock interaction coupled with decreasing temperature evolved the fluid to a lower sulphur and oxygen fugacity and nearly neutral to weakly alkali state which promoted the precipitation of base metal and the following silver-bearing sulphides and sulphosalts. The lead isotope composition of sulphides implies that lead was essentially derived from Oligo-Miocene magmatic rocks in the region with some interaction with basement rocks. The similarity of the lead and sulphur isotopic compositions between Darıderesi and Balya deposits suggests that they may relate to the same magmatic source.


Introduction
Hydrothermal vein-type deposits have made a major contribution to the global supply of Pb, Zn, Cu, Ag, and Au.The ore-bearing hydrothermal fluids are temporally, spatially, and genetically associated with the adjacent magmatic systems which also formed economically important porphyry-type deposits.The porphyry-epithermal gold provinces of Türkiye occur in three main tectonic domains including the Western Anatolian Extensional Province (WAEP), Pontides, and the Central Anatolian Volcanic Complex (CAVC).Epithermal deposits of Türkiye are hosted essentially by fairly eroded volcanic terrains which are genetically linked with relatively young and/or active subduction zones.
The Biga Peninsula, as part of the WAEP, is a metallogenic province that covers part of the Sakarya Block and a slice of Rhodope Massif (Figure 1).Pre-Jurassic basement rocks, including the Kazdağ Metamorphic Core Complex and numerous exhumed igneous bodies with coeval volcanic rocks (e.g.Bonev & Beccaletto, 2007;Cavazza et al., 2009;A. I. Okay et al., 1991), are found throughout the Sakarya Block (Figure 1(b)).
The Biga Peninsula is a globally recognised metallogenic province due to its diversity in metallogeny and high frequency of mineral occurrences of more than 50 hydrothermal Pb-Zn-Cu ± Ag ± Au and Au-Ag deposits (e.g.Koru, Tesbihdere, Balya, Arapuçandere, Kalkım-Handeresi and Küçükdere) and prospects (e.g.Şahinli, Kartaldağ, Kestanelik, Çataltepe, Kirazlı, Ağı Dağı and TV Tower) (Figure 1(b)).Porphyry Cu-Au orebodies are in association with magmatic rocks that are subalkaline and calc-alkaline with metaluminous to slightly peraluminous characteristics, and they range from basaltic-andesite and trachy-andesite to trachyte in composition and their intrusive counterparts.Oligocene and Miocene porphyry systems are common in the adjoining countries in the Balkans and Iran but are only known in the western Anatolia region of Türkiye.The Middle Oligocene to Early Miocene plutonic rocks are mostly high-K calc-alkaline, whereas the volcanic rocks of the same group exhibit two distinct groups; tholeiitic and high-K calc-alkaline to shoshonitic rocks.Several porphyry-type orebodies (e.g.Halilağa and Ağı Dağı) are related to the Late Oligocene (28-25 Ma) volcano-plutonic magmatism associated with near surface intermediate composition that are juxtaposed with high-sulphidation volcanichosted epithermal deposits of economic importance (Kuşcu et al., 2019).
The Pb-Zn-Cu (±Ag ± Au) deposits in the Biga Peninsula can be classified as volcanic-hosted intermediate-sulphidation (IS) epithermal and polymetallic skarn-type mineralisation in the distal parts of the plutons (Akıska, 2020;Akıska et al., 2013;Bozkaya, 2009;Bozkaya & Banks, 2015;Bozkaya & Gökçe, 2001;Bozkaya et al., 2008Bozkaya et al., , 2014Bozkaya et al., , 2020;;Çiçek & Oyman, 2016;Çiçek et al., 2021;Demirela & Akıska, 2022;Kuşcu et al., 2019;Oyman, 2019;Ünal-İ ̇mer et al., 2013;Yigit, 2012;Yılmaz et al., 2010).Most of the base metal-rich intermediate sulphidation epithermal deposits are mainly  Okay & Tüysüz, 1999), and (b) Regional geological map of the Biga Peninsula and distribution of significant epithermal mineralisation in the region (modified from Akbaş et al., 2017;Emre et al., 2013).located in the northwest and east of the Biga Peninsula.In the northwest, Koru and Tesbihdere mining districts cover a large mineralised area and consist of 12 Au-Ag enriched base metal IS epithermal veins which are mainly hosted by Late Oligocene rhyolitic volcanic rocks (Çiçek & Oyman, 2016).The field, fluid inclusion and mineralogical data suggest that the veins in the Koru and Tesbihdere mining districts share common features with each other and their O, H, S and Pb isotopes support a magmatic component to ore genesis (Bozkaya & Gökçe, 2009;Bozkaya et al., 2014Bozkaya et al., , 2020;;Çiçek & Oyman, 2016;Yılmaz et al., 2010).In the east, Çiçek et al. (2021) examined the Arapuçandere deposit and other mineralisations (including Alandere Pb-Zn distal skarn) in the Yenice region and focused on Cu, Fe, Pb and S isotope compositions of sulphide minerals from the proximal to distal portions of the magmatic-hydrothermal environment.The results show that the metals and sulphur within all the various styles of mineralisation in the Yenice region were derived from Oligo-Miocene granitoids, with no significant contamination from the local basement rocks.
Base and precious metals have been mined in the Balya district since the Phoenician civilisation (Ağdemir et al., 1994).Early mining took place from 1880 to 1939 in the Balya property by a French company called 'Société de Mines de Balya Karaaydın'.The Balya district was divided into two sub-properties, Arı Mağara-Balya Main and Hastanetepe-Balya North (Figure 2(a)).The Darıderesi mineralisation is located 3 km south of the Arı Mağara-Balya Main deposit.A NE-SW trending structure defined a horse-tail-like trend Darideresi Pb-Zn (Au-Ag) of veins that vary significantly in thickness over 4 km strike length at the surface.Arı Mağara-Balya Main, Hastanetepe-Balya North, and Darıderesi are spatially associated with Hallaçlar volcanics and the basement rocks, with the metal association marked by Pb-Zn-Ag-Au-As under a strong structural control (Table 1).The Eczacıbaşı Industrial Minerals Ltd Company ('Esan') has been producing Pb-Zn ore since 2009 at the Arı Mağara-Balya Main.Nine million tons run-of-mine silver bearing lead-zinc ore with variable grades were extracted from the Arı Mağara-Balya Main deposit during the 11 years of operation.Production of lead and zinc ores in Balya is about 1.5 million tons per year.The indicated resource of Balya deposit 16.6 million metric tons (Mt) @ 5.64% Pb +Zn with 45.37 g/t Ag (Aydar, 2018).The Dedeman mining company sold the mining and related permits of the Hastanetepe-Balya North deposit to Esan in 2020.Exploration licences and related permits for Darıderesi mineralisation were acquired in 2010 by Esan.The early drilling program by Esan for sub-surface evaluation led to the discovery of multiple intersections, revealing a series of assays with Pb+Zn concentrations of up to 9.6%.The resource expansion drilling program has been designed to further delineate and extend the mineralisation.Several holes intersected in significant mineralised intervals at 60, 150, 240 and 480 m below surface to deeper levels, while some also intersected intermittent subeconomic ore zones (Figure 2).
Previous studies have focused on the geological characteristics, host rocks, and mineral paragenesis of the Balya deposit (Aygen, 1956;Kaaden, 1957;Kovenko, 1940;Krushensky, 1975).Since mining started in 2009, the Balya district is further studied for isotope geochemistry, geochronology, geochemical and fluid inclusions (Aydar, 2018;Bozan, 2016;Yavuz & Çiftçi, 2012).The small variations in sulphur isotope ratios imply a homogeneous magmatic source for the sulphur (Bozan, 2016;Yavuz & Çiftçi, 2012).In the Balya district, the only radiometric ages were reported on dacite porphyry and crosscutting andesite dikes of Arı Mağara-Balya Main ore shoot, which act as both host and feeder magmatic rocks of Pb-Zn mineralisation.The main Pb-Zn mineralisation at the Arı Mağara-Balya Main relates to calc-silicate skarn-type alterations at the contact of dacite and limestone clearly cross-cut by andesitic dikes ca.26 Ma in age associated with calc-silicate (skarn)-hosted Cu-Mo-Au-Bi mineralisation (Aydar, 2018).The age of 24.67 ± 0.19 Ma for the andesite and 25.17 ± 0.14 Ma for the dacite indicate that Pb-Zn mineralisation at Arı Mağara-Balya Main deposit mainly formed before the emplacement of andesitic dikes (Aydar, 2018).Lead isotope data by Yavuz and Çiftçi (2012) on galena from the Arı Mağara-Balya Main indicate that lead would be derived from combined lower crustal and mantle sources and emplaced by plutonism with a minimal contribution from the upper crust.Although a close genetic relationship between buried andesitic porphyries and base metal vein-type mineralisation has been recently suggested for the Arı Mağara-Balya Main (Aydar, 2018;Bozan, 2016), the source of ore-forming fluids and the origin of the deposits around the Darıderesi and Hastanetepe-Balya North are still debated.
Previously published data from Arı Mağara-Balya Main and Hastanetepe-Balya North, are briefly summarised and compared with the new data.We present Pb isotopic compositions of different sulphides from the three deposits; Arı Mağara-Balya Main, Hastanetepe-Balya North, and Darıderesi, and spatially associated sedimentary, metamorphic, and volcanic rocks.In addition to Pb isotopes, sulphur isotopic compositions from the three deposits of the various sulphides from mineralised areas are also presented.Microthermometric studies were conducted on the main minerals of the Darıderesi vein system including quartz, calcite, and sphalerite.In addition, electron microprobe (EPMA) and energy-dispersive spectroscopy (EDS) analyses were conducted on sulphide and sulphosalt minerals to establish the composition and chemical zonation in these minerals.The approach and results of this study are useful to decipher the source of metals, and to better understand the characteristics of the mineralising fluids and corresponding evolutionary trend, and to unravel the genetic relationship with the spatially associated magmatic-hydrothermal system for future work in the western Anatolia.
The İzmir-Ankara-Erzincan suture zone (IAESZ; Brinkmann, 1966;Ketin, 1966) represents the closure of the northern branch of the Neo-Tethys along the northern-dipping subduction, and the following continental collision between the Pontides of Laurasia and the Tauride-Anatolide block of Gondwana during the Late Cretaceous-Eocene (Harris et al., 1994;Karacık & Yılmaz, 1998; A. I. Okay & Tüysüz, 1999;Şengör & Yılmaz, 1981).The IAESZ, extending nearly 1500 km between Rhodope-Stranca in the west and Caucasus in the east, separates the Sakarya Zone of Pontides (Laurasia) from the Kırşehir Block and Anatolide-Tauride Platform (Gondwana) (A.I. Okay et al., 1996;Şengör & Yılmaz, 1981).Following the collision and amalgamation of the fragments of crustal blocks in Late Carboniferous, subduction and collisional events regarding the opening and closure of some oceanic basins in Mesozoic and extensional tectonic as a main mechanism for the exhumation of core complexes and post-collisional magmatism in Cenozoic (e.g.Şengör & Yılmaz, 1981;Şengör et al., 1984;Stampfli & Borel, 2004).Due to its complex geology, the Pontide Belt hosts numerous kuroko, porphyry, skarn, and epithermal prospects and deposits in association with Late Cretaceous-Mid-Eocene magmatism.The northern part of Türkiye where the Biga peninsula is located comprises three main tectonic zones, namely Istranca, Istanbul, and Sakarya, which are collectively known as Pontides (Figure 1(a); Şengör and Yılmaz, 1981).In the Sakarya Zone, Permo-Triassic subduction-accretion units are represented by Karakaya Complex.
The first stage of the closure of the northern branch of the Neotethys led to Andean-type subduction, which produced syn-to post-collisional magmatic complexes since the Late Cretaceous throughout Türkiye in roughly E-W trending belts extending from the Balkans to the Pontides.The main magmatism at the WAEP and the Biga peninsula is interpreted to be derived from the jump in the subduction from the northern branch to the southern branch starting from the Middle Eocene (Dilek & Altunkaynak, 2009).The migration of the subducted slab and associated magmatism is continuous with the increased velocity of southward slab retreat since the Early Eocene.Middle Eocene magmatic complexes are mainly exposed along and north of the IAESZ.These complexes are the major hosts for the porphyry and associated epithermal deposits in the Biga Peninsula (Ş.Altunkaynak & Genç, 2008;Kuşcu et al., 2019;Yigit, 2012).Continental accretion and formation of less fertile calc-alkaline magmatic complexes are the points to be emphasised in the Palaeocene-Eocene period.
In the Biga peninsula and the WAEP, the mineral deposits are of intrusion-related type and are primarily Middle Eocene to Late Miocene in age (Kuşcu et al., 2019) (Figure 1).Mineralisation in association with the magmatic-hydrothermal system is spatially and temporally associated with fault dynamics closely related to the extensional tectonic regime (Sánchez et al., 2016).The subduction and magmatism in the WAEP and the Biga peninsula were accompanied by back-arc extension related to slab rollback or differential upper plate advance on the Hellenic trench (Agostini et al., 2010).Syn-extensional magmatism that started in the Late Oligocene, was initially calc-alkaline but shifted to more potassic (shoshonitic) compositions in the Early-Middle Miocene.Calc-alkaline magmatism relates to porphyry Cu -Mo-Au and epithermal Au mineralisation in the Biga Peninsula (e.g. the Kirazlı, TV Tower, Halilağa and Tepeoba).The recent slab tearing event between 15 and 9 Ma (Jolivet et al., 2015) temporally coincides with the formation of alkalic porphyry and epithermal Au deposits (e.g.Kışladağ, Afyon-Sandıklı, Efemçukuru, and Red Rabbit) in the WAEP.

Host rocks and alteration
Near Arı Mağara-Balya Main, the basement is unconformably overlain by the Upper Karakaya Complex, which consists essentially of strongly deformed and partly metamorphosed Permo-Triassic clastic and volcanic rocks (A.İ. Okay & Göncüoğlu, 2004) (Figure 3(a)).Rocks of the Upper Karakaya Complex were derived from accretion processes related to the subduction of Palaeo-Tethys.Rocks of the subduction-accretion complex are unconformably overlain by Palaeogene-Neogene volcanic, volcaniclastic, and sedimentary sequences and pierced by coeval plutons throughout the western Anatolian province (Figure 2).
South of Balya, close to Darıderesi village, the Hodul unit of the Karakaya Complex, exhibits olistoliths of Carboniferous and Permian limestone range in size from a few centimetres to several kilometres in strongly folded carbonaceous and clay-bearing siltstone.
In the Darıderesi, basement rocks are unconformably overlain by Late Oligocene-Early Miocene Hallaçlar volcanics and Early Miocene Şapçı volcanics (Figure 3(a)).Hallaçlar volcanics are essentially calcalkaline andesite, basaltic andesite, dacitic lavas, and pyroclastic.They are overlain and crosscut by the early phase ignimbritic tuffs of rhyodacitic to dacitic rocks of the Şapçı volcanics which evolve to later andesitic and pyroclastics phases.
The host rocks of the Darıderesi mineralisation are pelites of the Hodul unit of the Karakaya complex that consists of alternating metasandstone, siltstone, claystone, and silty limestone and limestone olistholiths (Figures 2, and 3).Proximal calc-silicate hornfelsing occurs in calcareous shale mudstone near intrusions, felsic dikes and vein networks.Distally from plutons carbonate and/or impure carbonate rocks are recrystallised and carbonatised or metasomatised to calcsilicate minerals.Drilling indicates that calc-silicate alteration is more widespread between 60 and 240 metres below the ground level.The calc-silicate hornfels and limited skarn alteration are defined by garnet, clinopyroxene, and epidote in carbonate rocks and along the boundaries between silty limestone and sandstone, and in the fractures of the carbonate rocks (Figure 4(a, b)).Fine-grained (<50 µm), euhedral to subhedral, anisotropic crystals of garnet represent the earliest prograde calc-silicate alteration phase.Replacement of garnet by clinopyroxene at the later stage is quite common in the overall prograde stage (Figure 4(a)).Epidote formed after garnet and clinopyroxene is common during the retrograde alteration stage and is accompanied by calcite and quartz.The main body of mineralisation is hosted by the base metal quartz-carbonate veins at the Darıderesi mineralisation.The sulphides of the distal Pb -Zn-Ag mineralisation post-date the formation of the alteration assemblages occurring through dissolution, ion exchange, replacement, precipitation, and (or) recrystallisation processes.
The carbonatisation resulted in the quartz-carbonate veins as the early stage of ore-bearing silica alteration.The fracture, fissure, and cavities of the quartz-carbonate veins are filled by fine-grained comb quartz during the relatively later phase of carbonatisation.The comb quartz crystals are filled by interstitial calcite of the late hydrothermal stage (Figure 4(b, c)).Clasts of early-stage ore-bearing silica alteration are surrounded by comb quartz perpendicular to the fragment (Figure 4(c)).The carbonate wall rock, which is represented by fossiliferous (i.e.Benthic Foraminifera) sand-bearing package, was partly replaced by silica along the pathway of the hydrothermal solutions (Figure 4(d)).
These veins form essentially two distinct ore bodies; (i) those hosted by the pelitic rocks and (ii) those along the tectonic contact between the limestone and the pelitic rocks.However, appreciable amounts of ore have been also intersected at the tectonic contact between the recrystallised limestone and the calc-silicate hornfels.Geochemical sampling of trenches in altered volcanic rocks of Hallaçlar with disseminated sulphides has returned ore-grade assays up to 0.3 ppm Au.In some places, the gold and silver enrichment seems to be in association with the sulphide-rich quartz-carbonate alteration.

Structural geology
Well-exposed thrust faults are the oldest structural features in the study area.Olistostromes and olistholitic blocks of various sizes are thrusted over the Hodul unit of the Karakaya Complex.
One of the most important structures directly associated with the ore bodies in the region is the N40°-50° E striking Büyük Fault.The role of the Büyük Fault in the development of the Arı Mağara-Balya Main deposits has been discussed by several studies (Aydar, 2018;Booth, 2015;Bozan, 2016;Özışık, 2009).The Büyük Fault marks the contact between olistostromesolistholitic blocks of the Hodul unit and dacitic tuffs and pyroclastic rocks of the Hallaçlar volcanics (Figure 2).The main faults closely associated with the mineralisation are the NE-SW to N-S striking Darıderesi and Balya Faults.These strike-slip faults, dip between 70° and 85° to NW, and are connected to each other by the Büyük Fault (Figure 2).The Darıderesi and Balya Faults were crosscut and dissected by younger NE-SW to E-W striking normal faults.Normal faults and related

Analytical methods
Microthermometric studies were carried out at the Geological Engineering Department -Fluid Inclusion Laboratory (Dokuz Eylül University, İzmir, Türkiye) using a Linkam THMS600 freezing-heating stage mounted on a Leica DM LP microscope.The precision of the freezing-heating stage was ± 0.1°C for cooling and ± 0.2°C for heating, and the measurement temperature range varies from − 196°C to 600°C.The stage was calibrated with hexane (−94.3°C),distiled water (0.0°C) and caesium nitrate (414.0°C).Fluid inclusions were carried out on three ~100 µm-thick, double polished sections including quartz, calcite, and sphalerite of Substage IIB associated with the main hydrothermal ore formation in Darıderesi.Prior to microthermometric measurements, four doubly polished sections were carefully examined under a microscope equipped with a high near-infrared (NIR) sensitive Hamamatsu type C11440-22CU camera to determine the distribution, shape, size, and phase changes of the fluid inclusion assemblages in quartz, calcite, and sphalerite.Freezing-heating conditions, morphology, and petrographic characteristics of the fluid inclusion assemblages were selected based on the criteria and recommendations of Roedder (1984) and Goldstein (2003).Salinities (wt.%NaCl equivalents) were calculated from the last ice melting temperatures using the equation of Bodnar (1993).
In the Darıderesi Pb-Zn±Au±Ag mineralisation, the dominant ore and gangue mineralogy was determined by transmitted-and reflected-light microscopy, and electron microprobe.Elemental line scan analysis on sphalerite, pyrite, galena, arsenopyrite, ferrokesterite, and geocronite, across the minerals from the rim through the core to the rim, was carried out by electron-probe microanalyzer (EPMA).Chemical analyses of ore minerals were performed using the Cameca S×100 electron-probe microanalyzer equipped with a wavelength dispersive spectrometer (WDS) at the Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich (Germany).Mineral analyses were carried out using an acceleration voltage of 15 kV and a beam current of 20 nA at a beam diameter of 1 μm.The counting time for each peak was set to 10 to 100 s for different elements in sulphides.The electron beam was focused to ~1 µm in diameter.Pure elements, materials (i.e.Au, Cd, Ag, Te, GaAs and Bi 2 Se 3 ) and minerals, including pyrite, chalcopyrite, sphalerite, galena, cassiterite, and covellite, were used as standards.The detection limits were as follows: 0.02 wt.% for Mn, Sb, Fe, As, Se, S; 0.03 wt.% for Ag, Cu, Zn, Sn; 0.04 wt.% for Te; 0.05 wt.% for Cd; 0.06 wt.% for Au; and 0.07 wt.% for Pb.
Radiogenic isotope ratios of Pb ( 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, 208 Pb/ 204 Pb) were measured at the Department of Earth Sciences (University of Geneva, Switzerland).The method is described in detail in Chiaradia et al. (2020).A few mg of galena, sphalerite, and pyrite were dissolved in 2 ml 14 M HNO 3 and 1 ml 7 M HCl in sealed Teflon vials at 180°C.A tiny amount of galena was dissolved in 14 M HNO 3 .For the rocks, the procedure of Chiaradia and Fontboté (2003) was adopted.Briefly, this method consists of leaching the powdered rock overnight with 2 ml 14 M HNO 3 and 1 ml 7 M HCl in sealed Teflon vials at 120°C and then separating the leached fraction from the residue.The residue is subsequently dissolved in Savillex® Teflon vials using 4 ml of concentrated HF and 1 ml of HNO 3 14 M, at a temperature of 140°C.Leachate and residue fractions are then dried and re-dissolved in 3 ml of HNO 3 14 M and dried again.Pb of the rocks and ore minerals was separated using an AG-MP1 resin.The purified Pb fraction was dissolved in 2% HNO 3 solutions, and isotope ratios were measured using a Thermo Neptune PLUS Multi-Collector ICP-MS in static mode.To monitor the internal fractionation a thallium standard was added to the solution ( 203 Tl/ 205 Tl = 0.418922).The long-term external reproducibility of the SRM981 Pb standard is 0.0083% for 206 Pb/ 204 Pb, 0.0071% for 207 Pb/ 204 Pb and 0.0095% for 208 Pb/ 204 Pb (1σ).Pb isotope ratios were further corrected for external fractionation (due to a systematic difference between measured and accepted standard ratios using the SRM981 values of Baker et al., 2004) by a value of +0.36‰ amu.Total procedural blanks were <500 pg Pb which are insignificant compared to the amounts of Pb purified from the ore minerals and whole rock samples investigated.Detailed descriptions of the samples that were analysed in this study are given in Table 2.

Ore petrography
Representative ore-bearing samples were collected from different depths from the drill holes in order to decipher the paragenetic sequence and textural features in the Darıderesi mineralisation (Figures 5, and 6).
Metal zonation in deposit scale together with textural and mineralogical-petrographical data from surface and drill core samples show that the ore-forming process can be divided into three stages represented by the calc-silicate stage, sulphide-sulphosalts stage and supergene alteration stage.
The calc-silicate alteration (Stage I) is structurally controlled and is observed especially in the selvage of the veins where the ascending hydrothermal fluids interacted with the carbonate rocks.In these carbonate-hosted distal vein systems, the amount of calcsilicate minerals including garnet, clinopyroxene, and epidote decreased with increasing distance from the magmatic source.Typically, sulphides of Substage IIA accompany calc-silicates, quartz, and calcite of Stage I.In some places, sulphides of Substage IIB post-dates and/or replace precedent minerals including pyrite, arsenopyrite, quartz and calcite.
The calc-silicate stage is followed by Stage II, which can be divided into three substages: Substage IIA (Fe-As sulphides, quartz and calcite), Substage IIB (base metal sulphides, calcite and quartz) and Substage IIC (Ag-sulphide-sulphosalts, realgar and orpiment).The mineral assemblage of Stage III (Mn-Fe-As oxides) is represented by secondary oxide minerals grown onto sulphide minerals of the Substage IIA and IIB after surface oxidation.
Pyrite is the dominant sulphide phase of Substage IIA and defines euhedral to subhedral individual grains or clusters that can reach grain sizes ranging between <l μm and >500 μm (Figure 5  to >100 μm (Figure 5(d)).The grain sizes of pyrite in association with arsenopyrite reach up to 50 μm, with the minimum of <1 μm.In places, arsenopyrite is surrounded and partly replaced by sphalerite of the Substage IIB (Figure 5(d)).
The grain size of galena is variable and ranges between a minimum of <10 μm and a maximum of millimetre scale.It is often replaced by sphalerite, fahlore group minerals, and silver-bearing sulphide and sulphosalts of Substage IIC.
Although the copper content of the rock chip and channel samples that are collected from the Darıderesi vein does not exceed 2% Cu, chalcopyrite, fahlore group, and ferrokesterite are the main copper sulphide and sulphosalts in descending order of abundance.Chalcopyrite is observed as fine to medium grains and with grain sizes up to 500 μm.Chalcopyrite is anhedral, granular, and intergrown with sphalerite in deeper parts of the system.Chalcopyrite is intergrown with sphalerite in deeper parts (approximately between −50 m and −200 m below sea level) and is replaced by fahlore group minerals at intermediate depths (approximately between 25 m and 100 m above sea level) (Figure 5(e)).
Sphalerite is the main ore mineral associated with galena in the Darıderesi hydrothermal system.Sphalerite is subdivided into three types: sphalerite with chalcopyrite disease texture (Figure 5(f)), sphalerite with ferrokesterite exsolution (Figure 5(g)) with or without chalcopyrite bleb, and sphalerite without any inclusion.Overall, the sphalerite with chalcopyrite disease increases with the chalcopyrite content of the sample in deeper parts of the system.In these samples, regular and irregular distributions of chalcopyrite blebs are both observed in sphalerite.The sizes of the blebs range from a few tens of microns down to submicroscopic particles.Where intergrowth between sphalerite and chalcopyrite increases intensively, the development of chalcopyrite blebs in sphalerite is more widespread.
Ferrokesterite is the most common accessory phase in association with sphalerite.Ferrokesterite is observed in sphalerite with limited chalcopyrite disease, i.e. which is characterised by lesser amounts of chalcopyrite exsolutions.In these samples, both replacement and rimming of sphalerite by ferrokesterite are quite common (Figure 5(h)).In some samples, ferrokesterite is observed in the growth zones of sphalerite without chalcopyrite disease, suggesting the crystallographically controlled distribution of ferrokesterite in sphalerite (Figure 5(g)).The size of the ferrokesterite crystals in association with pyrite varies from only a few µm up to 50 µm (Figure 5(i)).
The subordinate sulphide and sulphosalts assemblage of Substage IIC consists of geocronite-jordanite solid solution series members, xanthoconite, pyrargyrite, and goldfieldite.At Darıderesi, phases of the geocronite-jordanite solid solution series are observed at intermediate depth of the deposit in low quantities as anhedral grains in association mostly with galena (Figure 5(j)).The galena is surrounded and replaced by later minerals of the geocronite-jordanite solid solution series.Pyrargyrite is dominantly present as anhedral masses interstitial to pyrite (Figure 5(k)).Pyrargyrite grains range in size from a few µm to a few hundred µm.Xanthoconite was also observed as small grains of up to 5 µm included in pyrargyrite (Figure 5(l)).Goldfieldite is present as tiny irregular inclusions in pyrargyrite grains.Realgar, orpiment, Mn-oxides, Fe-oxides, and Pb-oxides dominate in outcrops.

Fluid inclusion study
Fluid inclusions from type samples of Substage IIB were examined in order to characterise the evolution of the hydrothermal fluids of the main base metal deposition.Examination of the fluid inclusion assemblages in calcite, quartz, and sphalerite from the Darıderesi vein system is useful to decipher the nature and origin of the ore-forming fluids in order to better understand the ore-forming processes.
Sampling for microthermometric analyses was carried out on core samples (DRD-12 and DRD-19) of the deeper levels of the Pb-Zn±Au±Ag mineralisation in Darıderesi.The two drill platforms (DRD-12 and DRD-19) are situated at 400 m and 335 m elevation above sea level, respectively.Drill hole DRD-19 was drilled towards the NW (320°) with a dip of 55°.The first sample was collected at 273.5 m in hole DRD-19 which corresponds to 110.96 m above sea level (asl).The second sample was collected at 318 m in hole DRD-19 which corresponds to 74.5 m (asl).Drill hole DRD-12 is 961-m-deep hole that was drilled towards the north with a dip of 75°.The sample was picked up from 848.9 m in hole DRD-12 which corresponds to −419.97 m below sea level (bsl).
In this study, we focused on the primary fluid inclusions hosted in quartz, calcite, and sphalerite of the base metal-rich veins to constrain the main ore-forming conditions in Darıderesi (Figure 7).Quartz and calcite are two main gangue minerals in association with ore minerals (sphalerite, galena, pyrite and chalcopyrite) of the main economic mineralisation stage (Substage IIB).Fluid inclusion studies focused on quartz and calcite, which were formed coprecipitated and earlier than sphalerite and galena (Figure 3(b-d)).
The primary inclusions were well developed along the crystal growth zones parallel to crystal faces of euhedral quartz and calcite, whereas sphalerite-hosted inclusions were sparse and occurred as isolated single and random inclusions within crystals.Most of the primary fluid inclusions in the minerals consist of liquid-rich two-phase inclusions, accompanied by lesser vapour-rich inclusions at room temperature (25°C) (Figure 7(c)).The fluid inclusions in quartz from both upper and deeper levels of the vein are mostly irregular, with ellipsoidal and elongated shapes ranging from 5 to 30 μm in size (Figure 7(a,b)).Calcite-hosted fluid inclusions can have angular and subangular shapes and vary in size from 5 to 20 μm (Figure 7(c)).The inclusions in sphalerite are commonly dark-coloured and semi-rectangular in shape, with sizes ranging from 3 to 10 μm (Figure 7(d)), smaller than those of inclusions in quartz and calcite.
A total of 73 microthermometric measurements were performed on the primary inclusions, which have a narrow variation in size from 3 to 30 μm and a liquid/vapour (L/V) ratio ranging from 7% to 60%.The fluid inclusion microthermometric results are reported in Table 3.

Microthermometric data
The quartz-hosted inclusions have different first (eutectic) -last ice-melting (salinity) and homogenisation temperatures at elevations of 110.96 m asl and 419.97 m bsl (Figure 8).Fluid inclusions in quartz from shallow level (sample DRD 19) have lower first icemelting temperatures, ranging from −48 to −35 ºC (Figure 8(a)), which is compatible with the presence of fluid with a mix of salts such as H 2 O-KCl-CaCl 2 and H 2 O-NaCl-MgCl 2 in the hydrothermal fluid system (Crawford, 1981;Goldstein & Reynolds, 1994;Shepherd et al., 1985).These inclusions yield final icemelting temperatures ranging from −0.3 to −7.8 ºC, which correspond to a salinity range from 0.5 to 11.5 wt.% NaCl equivalent (Figure 8(b)).Fluid inclusions from quartz at deeper levels of the vein system (sample DRD-12) yielded first ice-melting temperatures ranging from −55 to −46 ºC, indicating that H 2 O-KCI-CaCl 2 are the dominant components of the hydrothermal fluids (Crawford, 1981;Goldstein & Reynolds, 1994;Shepherd et al., 1985).Inclusions have final ice-melting temperatures of −1.2 to −6.5 ºC, with corresponding salinities of 2.1 to 9.9 wt.% NaCl equivalent (Table 3, Figure 8(b)).More specifically, fluid inclusions in quartz representing different crustal levels of the vein show different average salinities of 4.2 wt.% NaCl equivalent for the upper level and 7.0 wt.% NaCl equivalent for the deeper level.The highest homogenisation temperatures occur in quartz of shallower crustal levels of the vein system (275.0 to 343.8 ºC with an average of 312.9 ºC), whereas these homogenisation temperatures are dropping to the interval between 219.0 and 314.8 with an average of 278.4°C at deeper levels (Figure 8(c)).
Inclusions in calcite and sphalerite at the elevation of 74.5 m asl display similar variations in measured temperatures (Table 3, Figure 8).Most of the inclusions have an initial ice-melting temperature of −55 to −50 ºC that is indicative of common CaCl 2 components within the H 2 O-KCl-NaCl-MgCl 2 -CaCl 2 salts system (Crawford, 1981;Goldstein & Reynolds, 1994;Shepherd et al., 1985), compared to quartz from the shallow and deeper levels of the vein system (Figure 8(a)).The range of salinity for calcite  and sphalerite indicates moderately saline fluids between 3.9 and 13.0 wt.% NaCl equivalent (Table 3, Figure 8

Mineral chemistry
In the Darıderesi Pb-Zn±Au±Ag mineralisation, two drill-core samples representing the dominant styles of mineralisation were selected for mineral chemistry by EPMA from drill holes DRD-07 and DRD-19 at an elevation of 252 m and 318 m, respectively.The results of EPMA analyses on sulphides (Substage IIB) and sulphosalts (Substage IIC) are summarised in Table 4.

Pyrite
Two zoned pyrite from DRD-07 and two zoned pyrites from DRD-19 were analysed.Each one exhibits a similar element composition and their Fe and S contents range from 44.    4).

Sphalerite
The
of ferrokesterite and sphalerite, because these grains were not in contact with sphalerite.Assuming equilibrium conditions between coexisting ferrokesterite and sphalerite in line-4, the calculated temperatures range from 335.6 to 358.2 ºC and are consistent with the measured homogenisation temperatures of the fluid inclusions in quartz, calcite, and sphalerite from drill hole DRD-19.

Arsenopyrite
Arsenopyrite  Kretschmar and Scott (1976) and Sharp et al. (1985).The atomic As concentrations of Apy-1 and Apy-2 display a wide range of variation from 28.4% to 31.0% with an average of 29.4% and 28.3% to 31.4% with an average of 29.6%, respectively.The precipitation of arsenopyrite is coeval with the early-stage pyrite formation in Darıderesi.Based on the arsenopyrite composition for the pyrite-arsenopyrite assemblage at Darıderesi mineralisation, the calculated temperatures show that the crystallisation of Apy-1 and Apy-2 occurred at temperatures between 268-395°C and 263-415°C, respectively (Figure 9(f)).The average temperatures of 318°C (Apy-1) and 322°C (Apy-2) obtained from arsenopyrite grains substantially overlap with each other.

Sulphur and lead isotope systematics
Sulphur isotope analyses were performed on galena, sphalerite, and pyrite extracted from sulphide ores in Darıderesi, Arı Mağara-Balya Main and Hastanetepe-Balya North deposits.The δ 34 S ‰ values for these deposits are compiled in Table 5 and Figure 10.The sulphur isotope values of galena and sphalerite range from −0.4 to 0.9 ‰ and from 1.4 to 2.7 ‰.The sulphur isotope values of pyrites show a range of 1.9 to 3.1 ‰.These sulphur isotope data fall in the typical ranges of magmatic sources (Hoefs, 1987;Ohmoto & Rye, 1979;Seal, 2006).The differences between sulphur isotope values of galena, sphalerite, and pyrite (δ 34 S Py > δ 34 S Sp > δ 34 S Gn ) is consistent with an equilibrium sequence indicating that sulphide precipitation occurred under equilibrium conditions in the hydrothermal system.Lead isotopic compositions of the three sulphide minerals (galena, sphalerite and pyrite) analysed within each one of the three deposits are virtually identical to each other within analytical uncertainties.In contrast, minor but measurable lead isotopic differences (beyond analytical uncertainty) exist amongst the deposits.In fact, considering the averages of the three minerals (galena, sphalerite and pyrite) measured at each deposit with associated uncertainties (2SD) values, Arı Mağara and Hastanetepe-Balya North have identical 207 Pb/ 204 Pb values (15.708 ± 0.003) that are slightly more radiogenic than that of Darıderesi (15.703 ± 0.001).Arı Mağara has slightly less radiogenic 206 Pb/ 204 Pb values (18.809 ± 0.005) than Hastanetepe-Balya North (18.826 ± 0.002) and both have 206 Pb/ 204 Pb values less radiogenic than Darıderesi (18.833 ± 0.009).
The bulk rock analysed were two dacites and six sedimentary rocks from the host sequence.Age-corrected 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios of the two dacitic rocks from Hallaçlar Volcanics are 18.806-18.815, 15.703-15.714 and 38.967-38.999,respectively.The residual and leachate fractions (Chiaradia & Fontboté, 2003)  With respect to the plumbotectonics model evolution curves of Zartman and Doe (1981), all samples plot along the upper crust evolution curve in the 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb plot (Figure 11(a, c)) and are slightly displaced towards more thorogenic values in the 208 Pb/ 204 Pb versus 206 Pb/ 204 Pb plot (Figure 11(b, d)).

Source of metals
Possible sources of metals for hydrothermal fluids are as follows: (a) magmas which can concentrate metals in the fluids and exsolve them as a result of magmatic crystallisation, and (b) crustal rocks with which hydrothermal fluids interact along their flow path outside of the magma body.In order to constrain the source of the metals and to determine the genetic relationship to the host lithologies, we have compared our new lead isotope compositions of the sulphides with those of various surrounding rocks including sandstone, mudstone, greywacke, limestone, and dacite.
The debate on the origin of metals and the role of different mechanisms as a trigger of ore precipitation in Pb-Zn mineralisation of the Biga Peninsula is still ongoing.One possibility favours the basement rocks of the Karakaya complex as the main source of metals which were mobilised either by metamorphism or by the fluid plumbing system associated with the Oligo-Miocene magmatic activity in the Biga Peninsula (Anıl, 1979(Anıl, , 1984;;Anıl & Yaman, 1985;Bozkaya, 2011;Çağatay, 1980;Çetinkaya et al., 1983;Demirela & Akıska, 2022;İ ̇lbars et al., 2010).Another possibility asserts that the Cenozoic magmatic activities were split between intrusion-dominated hydrothermal activity and subvolcanic-volcanic dominated hydrothermal activity (Arvas & Önder, 1976;Bozkaya & Banks, 2015;Çiçek et al., 2021;Orgün et al., 2005;Ovalıoğlu, 1973;Özocak, 1977;Yücelay, 1971Yücelay, , 1976)).On the basis of their lead isotope data, Yavuz and Çiftçi (2012) proposed that the lower crust and mantle could be the sources of the lead of the sulphide minerals in the Hastanetepe-Balya North mineralisation.They also noted that the mineralisation was associated with magmatic-hydrothermal fluids with a minimal contribution from the upper crustal host rocks.In the same study, the 34 S values of the main-stage sulphide minerals vary within a fairly narrow range (−0.28 to +3.89‰) implying a magmatic and homogeneous source for the sulphur.
The Pb isotopic compositions of the ore minerals of the Arı Mağara-Balya Main and Hastanetepe-Balya North and Darıderesi mineralisation fall in the middle of the compositional field defined by other deposits of the Biga Peninsula (Figure 11), which is comprised between 206 Pb/ 204 Pb values of 18. 75-18.84,  20Pb/ 204 Pb values of 15.65-15.71and 208 Pb/ 204 Pb values of 38.77-39.00.Although the sample dataset for each one of the three deposits investigated consists of only three minerals, at each deposit the isotopic compositions of these minerals are indistinguishable within uncertainty, suggesting a very homogeneous Pb isotope composition.In contrast, the three deposits display subtle but measurable differences from each other.These differences suggest that despite the Pb source or sources were broadly the same for the three deposits they might identify three distinct hydrothermal systems.
In terms of possible sources, it is significant that all sulphide deposits from the Biga Peninsula, including those of the present study, fall within the field of Oligo-Miocene magmatic rocks (Figure 11).Also, the two dacite samples analysed in this study, which belong to the Hallaçlar Volcanics spatially associated with the mineralisation, fall in the same field as previously analysed Oligo-Miocene magmatic rocks.This would support the origin of the Pb, and by inference of the other metals, from the Oligo-Miocene magmas and their exsolved fluids.
(2003) leachate fractions of rocks approximate the Pb isotope composition that a hot acidic fluid would acquire by percolating through the rock, whereas the residual fractions would represent the refractory Pb that would remain locked in the leached rock.
As expected from Pb isotope systematics of residueleachate fractions of siliciclastic sedimentary and metasedimentary rocks discussed by Chiaradia and Fontboté (2003), leachate fractions of the four investigated sedimentary rocks are less radiogenic than corresponding residues because the latter contain radiogenic lead from abundant leach-resistant zircons.Since the host sedimentary rocks were collected outside the mineralised area and are devoid of alteration, their leachate fractions approximate the Pb isotope composition that an acidic fluid would acquire by leaching them (Chiaradia & Fontboté, 2003).Interestingly, the Pb isotope compositions of the leachates of the greywacke and especially that of the sandstone fall very close to the field of the ores in the two Pb isotope plots of Figure 11, although all together they are more scattered than the isotopic composition of the Hallaçlar dacites.This cannot exclude the possibility that some leads in the mineralisation were derived from the sedimentary rocks.Nonetheless, the close coincidence between Pb isotope composition of the ores and that of the Hallaçlar dacites make the latter the most likely and dominant Pb source for the mineralisation at the Arı Mağara-Balya Main, Hastanetepe-Balya North, and Darıderesi.The subtle differences among these three deposits could be related to subtle differences of the associated magmatic systems or to the incorporation of slightly different amounts of Pb from host rocks.With the current limited dataset, we cannot solve this problem.
With respect to the plumbotectonics model evolution curves (Zartman & Doe, 1981), all ore samples and the dacites plot along the upper crust evolution curve in the 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb plot, and are slightly displaced towards more thorogenic values in the 208 Pb/ 204 Pb versus 206 Pb/ 204 Pb plot (Figure 11).This suggests therefore that the Pb of these deposits and that of the Hallaçlar dacitic magma is essentially crustal.
The sulphide assemblage of the Balya district is dominated by pyrite, sphalerite, galena, and chalcopyrite, with no occurrence of sulphate minerals.The δ 34 S values of sulphide minerals including galena, sphalerite, and pyrite from the Arı Mağara-Balya Main, Hastanetepe-Balya North, and Darıderesi are similar.The δ 34 S values in these minerals are clustered near 0‰ which is the typical value of magmatic sulphur (Rye, 1993).Therefore, sulphur isotopic ratios in the Balya district suggest that the mineralisation can be related to a magmatic fluid contribution or at least was in equilibrium with the magmatic rocks, in agreement with the dominantly magmatic derivation of Pb as well.
Characteristic intervals of sulphur isotope compositions of some geological environments are given in Figure 10.The δ 34 S values of sulphide minerals from various epithermal deposits in Türkiye are scattered in the interval of δ 34 S values of granitic rocks.Attention should be drawn to the use of sulphur isotopes to distinguish between ore deposits originating in sedimentary (seawater if present) and igneous environments due to the extensive overlap of δ 34 S values (Figure 10).Both intermediate and high sulphidation epithermal mineralisation (ISEM and HSEM) tend to have more variation in the sulphur isotope composition of ore minerals because of the crystallisation of significant quantities of both sulphide and sulphate from the hydrothermal fluids at the time of mineralisation.
All of the analysed sphalerite grains are classified as Fe-rich sphalerite due to their high Fe content.The overall FeS content in sphalerite is between 13.61 and 21.48 mol% (Figure 9(a)), which is consistent with the FeS contents of intermediate sulphidation epithermal deposits ranging from 1 to 20 mol% (Einaudi et al., 2003) (Figure 12).In most base metal-rich ISEM type deposits, galena is a common sulphide mineral with sphalerite.They co-precipitate under equilibrium conditions during at least one of the ore deposition stages of an individual deposit.This makes galena-sphalerite the most reliable pair for S isotope-based geothermometry.In epithermal systems, pyrite is the most common sulphide which tends to crystallise at different stages and at different temperatures of ore deposition.Similar to pyrite more than one generation of sphalerite and/or galena precipitation could be responsible for widely scattered δ 34 S values in epithermal deposits.Additionally, in most ISEM systems, the broad distribution of sulphide δ 34 S values suggests either a mixture of several sulphur sources or disequilibrium mineralisation in an open system.

Evolution of ore forming fluids and related ore-forming processes
After the emplacement of an igneous intrusion, which is the deeper equivalent of Hallaçlar volcanics as the heat and metal source, the hydrothermal fluid exsolved from the magma should be ascending via moderately dipping fractures through dilation related to extensional tectonics.Ascending hydrothermal fluid formed the Darıderesi vein system and interacted with the carbonaceous basement rock prompting to form weak calc-silicate alteration.Exsolution and upward migration of the magmatic fluid through pelitic and carbonate rocks were followed by infiltrational metasomatism between fluid and carbonaceous rocks along pathways.Early calcsilicate alteration formed at comparatively high  enriched in As and arsenopyrite.The atomic weight (At.%) of As for the individual, euhedral crystals of arsenopyrite from Substage IIA ranges from 28.3% to 31.4% which indicates that temperatures ranged from 263°C to 415°C (average 322°C and 318°C).
The paragenesis of Substage IIB includes the bulk of the economic mineralisation and consists mainly of sphalerite, galena, chalcopyrite, fahlore group minerals, ferrokesterite, and pyrite.Galena is the main sulphide mineral which is known to be one of the main Ag carriers in the hydrothermal system (Dorfmann, 1974).The precipitation of the economic mineralisation started when the temperature decreased between 311.8°C and 253.0°C with an average of 285.0°C, based on homogeneous temperatures of fluid inclusions hosted in ferrokesterite-free sphalerite with chalcopyrite disease.In addition, the temperature calculated from mineral chemistry data from the sphalerite-ferrokesterite mineral pair is 335-358°C (Nakamura & Shima, 1982) indicating that sphalerite in association with ferrokesterite has a higher crystallising temperature than that of sphalerite without ferrokesterite intergrowth.It has been shown that the higher iron content in sphalerite is related to Fe-Zn substitution as a function of increasing temperature and decreasing fS 2 (Keith et al., 2014) (Figure 12).As a result of fluid-rock interaction, the mudstone-shale dominated parts of the host-rock promoted buffering of the fluid to lower fO 2 and triggered the precipitation of iron-rich dark-coloured sphalerite in the veins and stringers.
At the main ore stage (Substage IIB), both vapourrich and liquid-rich fluid inclusions were observed in sphalerite and calcite.In the veins hosted in mudstone and shale calcite, which precipitated during the sulphide stage yielding higher homogenisation temperatures (226.0° to 338.1°C with an average of 302.0°C) is believed to be associated with a metal-rich brine that ascended from a deep-seated source.The salinity of the fluid inclusions in calcite is also similar to the salinities (between 4 and 13 wt.%NaCl equivalent) of fluid inclusions hosted by sphalerite.
Fluid inclusions hosted by quartz, which coprecipitated with base metal sulphide assemblage in Substage IIB from the upper crustal levels, have homogenisation temperatures between 275.0ºC and 343.8ºC (average 312.9ºC) with salinities of 0.5 to 11.5 wt.% NaCl equivalent.Relatively constant fluid inclusion liquid to vapour ratios with increasing salinity and increasing temperature suggests dilution of the higher temperature hydrothermal fluid by mixing with meteoric water.It has been demonstrated that the mixing of hydrothermal fluids with meteoric waters is one of the key factors to decrease the solubility of metals and successively promoted the formation of Ag -Pb-Zn deposits (Baumgartner et al., 2008;Ke et al., 2017;Zhang et al., 2019).However, relatively higher salinities and lower homogenisation temperature were obtained from quartz from deeper parts  where the boiling began.The higher salinities of ore fluids in Darıderesi compatible with a general rule of salinities of ore fluids show a systematic increase with decreasing precious metal to base metal ratio.Under these conditions, the base metals and Ag were preferentially transported as the chloride complexes in relatively high temperatures and fO 2 aqueous fluids.On the base of physicochemical calculations, Zhai (2022) inferred that the silver bisulphide species (AgHS 0 ) was the dominant species responsible for Ag transport in an intermediate-low temperature (170° to 220°C), strongly reducing, and nearly neutral to weakly alkaline aqueous fluid.
At lower temperatures, Ag-Sb sulphide and sulphosalts including pyrargyrite, xanthoconite, and geochronite-jordanite series (±Ag-bearing tetrahedrite) precipitated from Ag-rich and Sb-rich hydrothermal fluids.During the later stages, by decreasing temperatures, it seems like that the fluids had been evolved to a lower fS 2 state leading to the precipitation of Ag-Sb sulphide and sulphosalts in association with Fe-rich sphalerite and silver-rich galena (Li et al., 2019;Zhai et al., 2019) (Figure 12).Textural relationships suggest that silver-rich galena is coprecipitated with these Ag-Sb sulphides and sulphosalts and also post-dated by them.

Comparison with other deposits in Balya district
Epithermal vein type polymetallic base metal deposits were developed under significant structural control at some considerable distance from the granitoid intrusion (Baumgartner et al., 2008;Bendezú et al., 2008;Rottier et al., 2018;Sillitoe, 2010;Zhai et al., 2017Zhai et al., , 2018Zhai et al., , 2019Zhai et al., , 2020;;Zhang et al., 2019).The mineralisation in Balya district is similar in many aspects to Cordilleran ore districts, in which porphyry deposits are associated with distal Ag-Pb-Zn deposits (Baumgartner et al., 2009;Bendezú & Fontboté, 2009).Some of the vein-type base metal-rich epithermal deposits in association with deep fault systems in western Anatolia are mainly hosted either within Cenozoic volcanic rocks (Şahinli, Tesbihdere, Koru and Arapdağ) or the older basement rocks (Arapuçandere, Kalkım, Efemçukuru, Buca and Gümüldür).Apart from the deposits mentioned above, only the Karakoca and Sudöşeği deposits are hosted in deep fault systems within eroded granitoids.
Mineralisation at Darıderesi shares many characteristics with other base metal-rich epithermal deposits in western Anatolia, including (1) source of metals, (2) association of silver and base metals with multiple episodes of carbonate and silica gangue, (3) veining within normal faults in association with extensional tectonic and (4) existence of both boiling and mixing trends as a function of homogenisation temperatures and salinity.However, comparison of the characteristics of Darıderesi to other base-metal rich epithermal deposits reveals also some differences, including (1) a complex multistage paragenesis involving silver, antimony, tin and base metal bearing sulphides and sulphosalts reflecting changing conditions of different stages, and (2) well-developed metal zonation from deeper crustal levels to the present-day surface of exposures.
The geology, fluid inclusion, mineral chemistry, and isotope geochemistry data suggest that Darıderesi is spatially and genetically linked to the hydrothermal mineralisation (Balya North and Main) in the Balya district.In the Balya district, regional tectonism played a critical role in the mode of emplacement of subvolcanic porphyritic intrusions and the related circulation of ore-forming hydrothermal fluids (Figure 13).In contrast to Darıderesi and the Arı Mağara-Balya Main, which are hosted mainly in basement rocks, the Hastanetepe-Balya North mineralisation is mainly hosted within tuffs and pyroclastic rocks of dacitic composition.Calc-silicate alteration is prominent in mineralisation at Arı Mağara-Balya Main and Hastanetepe-Balya North but is only weakly developed within carbonate-poor shales (mudstone) at Darıderesi, and both are attributed to an initial expulsion of fluid related to a deep-seated intrusion.
During the migration of mineralising hydrothermal fluids from the parent magma chamber to the site of ore deposition, infiltrational and diffusional processes play an important role in the generation of metasomatism and associated hydrothermal alteration.The infiltration of hydrothermal fluids in carbonate rocks (including limestone lenses and olistholiths, calcareous shale and silty limestone) distal to the intrusion contact new minerals such as clinopyroxene, epidote, and garnet were formed.However, the interaction between the hydrothermal fluid and organic-rich shale-mudstone resulted in poorly developed hydrothermal alteration composed mainly of quartz, calcite, ankerite, and clay minerals.The organic material in the shale and/or mudstone might have acted as a reductant, destabilising fluids and resulting in sulphide precipitation.The vein is thicker (up to 2 m in width) when it is hosted by brittle rocks such as limestone.In the Arı Mağara-Balya Main deposit, the basement rocks have been cut and overlain by Oligo-Miocene aged dacitic lava, tuff and pyroclastic rocks of Hallaçlar volcanics, and Lower Miocene aged andesitic dike, lava, and agglomerates of Şapçı volcanics.In the Balya district, the development of alteration and characteristics of the mineralisation are variable.The vein-type Pb-Zn mineralisation with an intermediate sulphidation epithermal character associated with early calc-silicate alterations formed by the dacite porphyry located at shallower depths, and Cu-Mo-Au-Bi mineralisation associated with the deeper and late calc-silicate alterations formed by andesitic dikes.At the Balya deposit, the calcic skarn zone at the contact between the dacite porphyry and exotic limestone hosts the main Pb-Zn mineralisation operating at shallower depths.The Cu-Au-Bi mineralisation in association with deeper calcsilicate alterations formed by andesitic dikes.
In contrast, the surface and underground drill holes at the Balya deposit revealed that the main mineralisation is hosted by the Hallaçlar volcanics and the faultcontrolled calc-silicate dominated contact zone between Hallaçlar volcanics and the limestone blocks.Lesser amount of ore is also found in Permian limestone blocks as disseminated, veinlets and cavity fillings.Oligo-Miocene andesitic and dacitic lavas of Hallaçlar volcanics form a large proportion of the outcrops in the Balya district and overlie both Permian and Triassic formations.The dacitic porphyritic lavas and the mineralisation are both crosscut by later andesite dikes.The U-Pb zircon age data suggest that dacitic porphyritic lavas of Hallaçlar volcanics in the Balya deposit took place at 25.06 Ma and the crosscutting andesitic dikes intruded at 25.4 Ma (Aydar, 2018).
The Balya Pb-Zn mineralisation and associated calcsilicate alteration were formed due to the interaction between limestone olistholiths and the subvolcanic rocks at shallower depths.At Arı Mağara-Balya Main, an early fluid responsible for the formation of the oscillatory zoned garnets of prograde and metasomatic processes is a high-temperature fluid (258 to 585 ºC) with a salinity ranging from 1.1 to 17.8 wt.% NaCl.Declining temperatures due to the cooling of the igneous rocks and circulating meteoric water involve the development of the retrograde-phase mineral assemblages including actinolite (±tremolite), epidote, sulphides, quartz and calcite.Retrograde stage alteration and mineralisation represented by quartz at a temperature ranging from 206 to 392ºC with salinity ranging from 6 to 8 wt.% NaCl, calcite type 3 temperature ranging from 321 to 422ºC with salinity ranging from 2 to 18 wt.% NaCl, calcite type 4 temperature ranging from 295 to 301ºC with salinity ranging from 33 to 35 wt.% NaCl, and sphalerite temperature ranging from 329 to 354ºC with salinity ranging from 1.1 to 6.2 (wt.% NaCl) (Aydar, 2018).Moreover, fluid inclusion data (Yavuz & Çiftçi, 2012) obtained from sphalerite of the Hastanetepe-Balya North mineralisation emphasise precipitation from moderate saline fluids between 1 and 10 wt.% NaCl equivalent, with a temperature range between 340 and 450 ºC.We interpret the base metal mineralisation Darıderesi, Hastanetepe-Balya North and Arı Mağara Balya Main as part of a magmatic-hydrothermal mineralised system, showing similar characteristics in terms of homogenisation temperature, salinity, and composition of fluids.

Conclusions
We consider that there is a genetic relationship among the porphyry, skarn, breccia-hosted, vein, and replacement mineralisation in the Balya district and that the source of the metals was derived from the Oligo-Miocene granitoid intrusions (Figure 13).
The distal Darıderesi Pb-Zn (Ag) mineralisation has a distinct structural control marked by at least two fracture sets that are NE-SW and N-S trending.The geometry of the fault-zone(s) and structurally controlled permeability networks are crucial to the deposition of ore in Darıderesi (Figure 13).These fracture sets affect all stratigraphic units and play an important role in the hydrothermal fluid migration and the morphology of the mineralisation.Fluid inclusion studies and mineral chemistry based geothermometry on sphalerite indicate that base metal precipitation of sphalerite took place at temperatures between 253°C and 358°C with a salinity range between 5 and 13 wt.%NaCl equivalent.Fluid inclusions in calcite associated with base metal precipitation yielded temperatures ranging from 226.0°C to 338.1°C with salinities of 3.9 to 13.0 wt.% NaCl equivalent.The homogenisation temperatures of fluid inclusions in quartz from different levels range from 219.0 to 343.8 ºC with salinities of 0.5 to 11.5 wt.% NaCl equivalent, respectively.Isotope and fluid inclusion data support both boiling and mixing processes between meteoric water and the magma-derived fluid, which is characterised by higher temperature and salinity.The paragenesis, characteristics of the ore-forming fluids, as well as the sulphidation state as indicated by FeS compositions of sphalerite suggest that Darıderesi is an intermediate-sulphidation epithermal mineralisation representing the distal vein system hosted by carbonaceous rocks.The mineralisation is divided into three main stages as Stage I, II, and III and among them the main sulphide and sulphosalt minerals were formed in Stage II.The sulphide mineral assemblage consists of pyrite, sphalerite, galena, chalcopyrite, and arsenopyrite.Minor amounts of tin-bearing, antimony -bearing and silver -bearing sulphide and sulphosalts (ferrokesterite, geocronite -jordanite series, fahlore group, pyrargyrite, goldfieldite and xanthoconite) have been identified.
Lead and sulphur isotopic data combined with isotopic data from some recent studies (Figures 10, and 11;Aydar, 2018;Bozan, 2016;Yavuz & Çiftçi, 2012) show that there is a genetic relationship among the Main Balya, Hastanetepe-Balya North, and Darıderesi mineralisation and that the ore-bearing fluids were mostly derived from the parental magma of volcanic rocks and subvolcanic porphyritic intrusions.The fluids responsible for the formation of the Darıderesi vein and associated replacement mineralisation are hot and saline, reduced, and chloride-complex dominated intrusion-centred hydrothermal fluids which extract, transport, and precipitate metals.With an increasing distance from the intrusive source, hydrothermal fluids with a magmatic component were mixed and diluted by the sedimentary and meteoric waters (Figure 13).
The genetic model (Figure 13) of the Darıderesi mineralisation shows that magmatism-derived fluid can show impressive evolution along its pathway due to fluid rock interaction with reasonable meteoric water income.Changing physicochemical conditions enhanced the fertility of ascending hydrothermal fluids along favourable structures to form zoned hydrothermal Pb-Zn-Ag veins.This genetic model is applicable to other magmatism derived polymetallic vein-type deposits with a similar geological background.

Figure 1 .
Figure 1.(a) Tectonic framework of Türkiye showing the major sutures and continental blocks (modified after A. I. Okay & Tüysüz,1999), and (b) Regional geological map of the Biga Peninsula and distribution of significant epithermal mineralisation in the region (modified fromAkbaş et al., 2017;Emre et al., 2013).

Figure 2 .
Figure 2. (a) Geological map of the Balya district including location of mine adits and drill holes in the study area.(b) Schematiccross-section showing vein type Pb-Zn (Ag) mineralisation at Darıderesi.

Figure 4 .
Figure 4. (a) Euhedral garnet and pyroxene with later epidote in early calc-silicate alteration.(b) Calcite filling the void of the earlier quartz-geode.(c) Opaque minerals surrounded with fine-grained quartz in a later calcite matrix.(d) Fractured and deformed fossiliferous sand bearing package as a host-rock.
(a)).Scanning electron microscopy-backscattered electron observations revealed that pyrite at Substage IIA has either irregular complex-zoned and oscillatory-zoned patterns.The majority of pyrite grains are of the irregular complex-zoned, accompanied by lesser oscillatory-zoned pyrite (Figure5(b)).All other sulphide and sulphosalt phases fill cracks, cavities and partly replace some of the pyrite aggregates.Pyrite is associated closely with arsenopyrite and coexists with it (Figure5(c)).Arsenopyrite is either euhedral to subhedral and most commonly intergrown with pyrite (Figure5(c)).The arsenopyrite crystals are fine-grained and their size vary from <5 μm

Figure 6 .
Figure 6.Paragenetic sequence for the assemblages of the ore and alteration minerals in the Darıderesi mineralisation.The thickness of the bars indicates the relative abundance of the minerals.
(b)).The ice-melting temperatures in calcite vary from −2.3 to −9.1 ºC, which corresponds to a salinity range from 3.9 to 13.0 wt.% NaCl equivalent with an average of 7.5 wt.% NaCl equivalent.The ice-melting temperatures in sphalerite vary from −3.0 to −9.1 ºC, which corresponds to a salinity range from 5.0 to 13.0 wt.% NaCl equivalent with an average of 7.5 wt.% NaCl equivalent.The inclusions show a range of homogenisation temperatures from 253.0°C to 311.8°C with an average of 285.0°C in sphalerite and 226.0°C to 338.1°C with an average of 302.0°C in calcite (Figure8(c)).In general, microthermometric data show trends of decreasing homogenisation temperatures and increasing salinity through the deeper level (Figure8(d)) and might point out the existence of mixing of at least two different types of hydrothermal solutions during the ore-forming process in Darıderesi.
temperature in an environment of high fluid flux proximal to the veins and was dominated by calcsilicates of Stage I.The calc-silicate stage (Stage I) is followed by the precipitation of the As-bearing sulphides within the veins.Substage IIA is represented by the pyrite

Figure 12 .
Figure 12.(a) R S -1000/T diagram showing the sulphidation state, according to FeS content in sphalerite from Darıderesi mineralisation.Contours of mole percent FeS in sphalerite coexisting pyrrhotite or pyrite are from Scott and Barnes (1971) and Czamanske (1974).(b) LogfS 2 -1000/T diagram showing the sulphidation stages of hydrothermal fluids in the Darıderesi mineralisation.Both diagrams were modified from Einaudi et al. (2003).

Figure 13 .
Figure 13.Schematic cross section through Balya ore district (non-scaled), showing the structural and geological controls on vein type base metal-rich epithermal mineralisation.

Table 1 .
Main characteristics of Pb-Zn deposits in Balya district.

Table 3 .
Statistics of the homogenisation temperatures, salinity, and eutectic temperatures of fluid inclusions from Pb-Zn±Au±Ag mineralisation in Darıderesi (N, the number of measurements).

Table 4 .
The representative compositions of sulphides and sulphosalts from drill holes DRD-07 and DRD-19 at Darıderesi mineralisation (N, the number of measurements).
Sb > As) due to the fact that the majority of the data fall into the area between ideal geocronite and Sb-rich jordanite.Based on the EPMA data, the general formula of geocronite from Darıderesi mineralisation is Pb 13.42-14.88Sb 2.62- 5.27 As 0.26-3.65Ag 0.00-0.13S 22.39-23.22 .

Table 5 .
Sulphur isotope values and lead isotope ratios of minerals and rocks from Pb-Zn±Au±Ag mineralisation in Balya district.