2022 | 75/Special Issue | 303–315 | 9 Figs. | 5 Tabs. | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society 1. INTRODUCTION The Čukaru Peki hydrothermal system is part of the Bor metal- logenic zone, which is hosted by the Timok magmatic complex (JANKOVIĆ, 1990; KOLB et al., 2013). This complex is consid- ered to be the eastern segment of the large magmatic and metal- logenic arc known as the Apuseni-Balkan-Timok-Srednogorje belt (ABTS belt, which is located in Romania, Serbia and Bulgaria (NEUBAUER, 2002). The ABTS belt is characterized by the pres- ence of numerous porphyry and polymetallic ore deposits (Mol- dova Noua, Bor, Elatsite, Chelopech), which were formed during the subduction processes associated with the closure of the Neo- thetys Ocean, between 92 and 75 Ma (NEUBAUER, 2002; FÜ- GENSCHUH & SCHMID, 2005; GALLHOFER et al., 2015). The magmatic activity in the Timok magmatic complex was manifested in two or three volcanic phases (DROVENIK, 1961; JANKOVIĆ, 1990), which altogether lasted around 10 Ma (VON QUADT et al., 2002). It is generally accepted that most of the sig- nificant ore deposits in this complex were formed during the first volcanic phase (JANKOVIĆ, 1990; KOLB et al.,2013; JELENKOVIĆ et al., 2016), which lasted from 89 to 84 Ма (VON Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase hydrothermal system Miloš Velojić1, Viktor Bertrandsson Erlandsson2, Frank Melcher2, Peter Onuk2,3, Rade Jelenković1 and Vladica Cvetković1 1 Faculty of Mining and Geology, Djušina 5, Belgrade, Serbia; (milos.velojic@rgf.bg.ac.rs) 2 Montanuniversität Leoben, Department Applied Geosciences and Geophysics, Peter-Tunner-Straße 5, Leoben, Austria 3 Karl-Franzens University Graz, Institute of Earth Sciences, Austria doi: 10.4154/gc.2022.25 Abstract Čukaru Peki is a recently discovered porphyry- high-sulfidation Cu-Au deposit located 5km south of the mining town of Bor in east Serbia. Three styles of mineralization are distinguished in the Čukaru Peki system: a high-sulfidation type with massive sulfides (named the Upper zone), a porphyry type (named the Lower zone) and a transition type (between porphyries and massive sulfides). This study investigates the concentration and distribution of trace elements in pyrite from these three mineralization zones of Čukaru Peki. The high-sulfidation pyrite contains ele- vated concentrations of V, Mn, Ni, Cu, As, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi, com- pared to pyrite from the porphyry zone. The porphyry zone pyrite contains elevated concentra- tions of Co and Se. The sample from the transition zone contains concentrations between the two other zones, with the exception of the relative enrichment of Co and Ag. This research also aims to separate different stages of ore deposition. The porphyry stage contains several types of veins: quartz A veins, quartz B veins, pyrite D veins, magnetite veins, purple anhydrite veins, sulfide veins and orange anhydrite veins. The high sulfidation stage also formed in several stag- es: pyrite1, pyrite-enargite veins, pyrite-covellite veins, pyrite2 veins and calcite-anhydrite veins. There are distinct differences between various vein generations found within each zone, notable examples are the enrichment of Se in quartz B veins pyrite and Cu in sulfide veins, compared to other veins from porphyry zone veins and the enrichment of several trace elements (Cu, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi) in pyrite from the Py-cov veins in comparison to the other high-sulfidation veins. The trace element data also indicates a change in fluid compositions; the earlier fluids responsible for the porphyry zone mineralization showing a slightly more magmat- ic fluid signature (higher Co/Sb and Se/As values) and the later high-sulfidation fluids bearing a more typical epithermal trace element signature, which indicates cooling and diluting of fluids. Some of the porphyry zone pyrite crystals (from B-type veins and Purple anhydrite-veins) con- tain elevated concentrations of elements attributed to the high-sulfidation zone (e.g. Cu, Ag, Cd, In, Sn, Pb and Bi), which suggests that these veins were affected by later high-sulfidation fluids. QUADT et al., 2002). The simplified map of the Timok magmatic complex is shown in Fig.1. The Bor metallogenic zone hosts several large porphyry de- posits, which have been mined since the beginning of the 20th century (Bor, Majdanpek, Veliki Krivelj) as well as other genetic types of ore deposits, such as high-sulfidation epithermal (Tilva Mika, Kamenjar), low-sulfidation epithermal (Zlaće), hydrother- mal-volcanogenic (Lipa, Kraku Bugaresku), skarns (Valja Saka) and recently discovered Carlin-type deposits (Korkan,Kraku Pešter and Bigar Hill) (JANKOVIĆ et al., 2002; JELENKOVIĆ et al., 2016). Estimated mineral resources of the entire zone are over 20 Mt of Cu and in excess of 1000 tonnes of Au (JELENKOVIĆ et al., 2016). The Čukaru Peki hydrothermal system was located in 2011 and is one of the largest recently discovered Cu-Au deposits in south-eastern Europe. Preliminary estimations suggest that the total mineral resources of copper ore in this deposit could amount to between 500 and 1000 million tonnes grading more than 0,7 % Cu (JELENKOVIĆ et al.2016). It is located just 5km south of the mining town of Bor. BANJEŠEVIĆ & LARGE (2014) have Article history: Manuscript received October 25, 2021 Revised manuscript accepted May 19, 2022 Available online October 17, 2022 Keywords: Porphyry copper, High-sulfidation Cu-As-Au, Pyrite, Trace elements, LA-ICP-MS, Timok magmatic complex, Bor metallogenic zone G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue304 genetically classified the Čukaru Peki system as a porphyry Cu- Au deposit with high-sulfidation epithermal (Cu-As-Au) massive sulfides. Several authors have measured the concentrations and distri- bution of trace elements in the porphyry deposits in the Bor met- allogenic zones and the results of these measurements were pub- lished in several reports and doctoral dissertations (PAVIĆEVIĆ et al. (1981, 1985), MIŠKOVIĆ (1989) and VAKANJAC (2000)). JANKOVIĆ et al. (2002) provide a synthesis of the obtained re- sults of these studies and drew the following conclusions: • Concentrations of Au are increased (up to 49 ppm) in sev- eral studied ore minerals, e.g. in chalcopyrite, pyrite and bornite. • Above detection limit concentrations of Ag are present in almost all of the analyzed minerals. • Enargite contains increased concentrations of Ge (up to 0,46%). • Palladium concentrations are increased (up to 0,5%) in dif- ferent ore minerals: pyrite, chalcopyrite, bornite, digenite, covel- lite, luzonite and tetrahedrite, probably in the form of mineral inclusions. • Selenium concentrations are increased (up to 0,5%) in bor- nite and covellite. • In most sulfide minerals, there is a notable enrichment (from 0,2 to 0,6%) of trace elements, such as Sn, Te, W, Se etc. In this study we report and discuss new results from LA-ICP- MS analyses of trace elements (S, V, Cr, Mn, Fe, Co, Ni, Cu, As, Se, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi) in pyrite grains from different zones and veins of the Čukaru Peki deposit, with a special emphasis on the distribution of trace elements in pyrite from different mineralization zones and ore veins. This research will contribute to a better identification of the veins and minerals in Čukaru Peki that concentrate rare and precious elements, such as gold and silver. The identification will be particularly signifi- cant for the extraction of gold from the high-sulfidation zone. 2. GEOLOGICAL SETTING The hydrothermal system of Čukaru Peki is hosted by interme- diate volcanic and plutonic rocks formed during the first volcanic phase of the Timok magmatic complex (JELENKOVIĆ et al., 2016 and references therein). The volcanic rocks are represented by two distinct types of andesites: altered plagioclase-hornblende phyric, holocrystalline andesites (also called Lower andesites) and unaltered hornblende-plagioclase phyric, hypocrystalline an- desites (known as Upper andesites) (JAKUBEC et al., 2018). The volcanics are overlain by Upper Cretaceous sediments, which consist of three sedimentological units: 1) the Oštrelj formation with grey siltstone and marl (uppermost) 2) the Metovnica forma- tion with red marl and epiclastics and 3) the lowermost coarse- grained Bor clastites (BANJEŠEVIĆ et al., 2019) (Fig. 2). Post-Cretaceous deformation created a series of eastward- dipping faults and caused the formation of basins which were filled with Miocene sediments. The most prominent structure in this region is the Bor Fault that splits into 2 structures, called the Bor 1 and Bor 2 faults, which are considered to be the eastern boundaries of the mineralized zone at Čukaru Peki. These struc- tures also cut through the Miocene sedimentary fill (JAKUBEC et al., 2018). The process of basin formation was important for the preservation of Cretaceous ore deposits in the Timok Mag- matic Complex from subsequent erosion (KNAAK et al., 2016). The Miocene sediments in this area have a thickness of 200-400 m and have a discordant boundary with the Cretaceous sediments (Fig. 3) (JAKUBEC et al., 2018). Figure 1. A simplified geological map of the Timok magmatic complex, adapt- ed from PAČEVSKI et al. (2016) and JELENKOVIĆ et al. (2016). Figure 2. A simplified geological map of the area around the Čukaru Peki ore deposit, with the location of major faults, sections and sampled drillholes. G eologia C roatica Velojić et al.: Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase ... 305 JELENKOVIĆ et al. (2016) have distinguished three zones of mineralization in the Čukaru Peki hydrothermal system: 1) A high-sulfidation zone consists of massive sulfides, py- rite-covellite veins and hydrothermal breccias. This type of min- eralization forms a localized zone, with a horizontal area of 300x300m and a vertical extent of 500 - 600 m and it is located at depths between 400 and 1000m from the surface., which contains the highest grades of Cu (5-19%) and Au (3-12g/t) (JAKUBEC et al., 2018). With increasing depth, the mineralization contains less pyrite and becomes more characterized by veins and stockworks. The dominant type of alteration is advanced argillic alteration, with abundant residual vuggy silica, alunite and subordinate dick- ite (JAKUBEC et al., 2018). The boundary of this zone is repre- sented by a clay-rich argillic alteration (kaolinite+pyrite) halo around massive sulfides. The main Cu-bearing minerals in the high- sulfidation zone (Upper zone) are covellite and enargite, whereas the dominant Cu-bearing mineral in the porphyry zone (Lower zone) is chalcopyrite, with subordinate bornite. Prelimi- nary ore microscopic examinations imply that Au is present in two forms in the high-sulfidation zone of Čukaru Peki: 1) as tel- lurides such as calaverite (AuTe2), sylvanite (Au,Ag)2Te4 and kos- tovite (AuCuTe4); and 2) Sub-microscopic native Au, hosted in pyrite or sometimes bornite (JAKUBEC et al., 2018). 2) The transition epithermal zone is located between the high-sulfidation zone and the porphyry zone. It is characterized by the replacement of early sulfides (chalcopyrite) with high- sulfidation minerals (covellite and enargite). 2) Anhydrite, calcite and gypsum are the three main types of vein in this zone. The main type of alteration is argillic alteration (smectite- + montmo- rillonite) (JAKUBEC et al., 2018), which sporadically overprints the porphyry-type alterations. 3) The porphyry zone is mostly hosted by diorites and over- lying andesites. The dimensions and shape of the porphyry zone have not yet been determined, due to its great depth; it is located at between 750m to more than 2200m from the surface. The dom- inant types of alteration are potassic alteration and chloritization. Quartz veins (with chalcopyrite, pyrite and bornite), magnetite veins (with magnetite, hematite and chalcopyrite) and anhydrite veins (with pyrite and subordinate chalcopyrite and bornite) are the main types of veins (VELOJIĆ et al., 2020). 3. SAMPLES AND METHODS Reflected light microscopy and SEM measurements were per- formed on samples from the Upper, Transition and Lower zones of Čukaru Peki. Analyses were performed at Montanuniversität Leoben, Austria and University of Belgrade- Faculty of Mining and Geology, Serbia. 3.1. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) Trace element analyses were conducted on 5 samples from the Upper zone (cp012, cp018, cp028, cp038A, and cp073), one from Figure 3. Simplified cross-sections through the Čukaru Peki ore deposit, modeled using Leapfrog software, showing zones with different types of mineralization. Legend: 1- Lower andesites; 2- Diorite porphyries; 3- Brecciated zone; 4-Upper andesites; 5- Upper Cretaceous marl; 6- Cretaceous epiclastics; 7- Upper Cretaceous clastics (Bor conglomerates); 8- Cenozoic sediments; 9- Massive sulfides with more than 0,5% Cu; 10- Massive sulfides with more than 1% Cu; 11- Massive sulfides with more than 2% Cu. G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue306 the transition zone (cp126) and 5 samples from the Lower zone of Čukaru Peki (cp084, cp115, cp117, cp119 and cp122). A descrip- tion and location of all samples is shown in table 1 and the loca- tions of drillholes are shown on Figs 2 and 3. Pyrite analyses were carried out using a Nd:YAG laser abla- tion system coupled to an Agilent 8800 ICP-MS at the Depart- ment of Applied Geosciences and Geophysics, Montanuniversität Leoben in Austria. Pyrite crystals were ablated with a spot size of 50 μm and an on-mineral laser fluency of 2-3 J/cm2, at a 10 Hz repetition rate. Helium was used as the carrier gas with a flow rate of 0.75 L/min, which was mixed with Ar during transport to the ICP-MS. Isotopes measured were: 34S, 51V, 52Cr, 55Mn, 57Fe, 59Co, 60Ni, 63Cu, 75As, 82Se, 95Mo, 107Ag, 111Cd, 115In, 118Sn, 121Sb, 197Au, 201Hg, 205Tl, 208Pb and 209Bi. The spot analysis procedure includes a 30 sec pre-ablation background collection, followed by 60 sec of laser ablation and data acquisition. Individual abla- tion cycles were followed by a 30 sec washout delay. Quantifica- tion of the element concentrations of pyrite were calculated using 34S as the internal standard. Data reduction was performed with the Iolite 4 software (PATON et al., 2011). The in-house sphaler- ite matrix-matched sinter pressed powder pellet reference mate- rial MUL-ZnS1 (ONUK et al., 2017) was used as the primary external standard. The MASS-1 USGS powder pressed polysul- fide certified reference material (WILSON et al., 2002) was used as the external standard for the quantification of Au, Tl and Hg, as the reference material MUL-ZnS-1 is not suitable for quanti- fication of these elements. The MASS-1 was also used for quality control of the analyses. Both reference materials were analyzed every 20 spots for the correction of instrumental drift. Detection limits were calculated by the ‘Howell et al. 2010’ method option within the Iolite 4 software (Table 2). Laser ablation spots were set out carefully to avoid inclu- sions, cracks or other visible impurities that could interfere with the measured data. Due to pyrite crystals most commonly being zoned, it was challenging to acquire time-count signals for a sin- gle zone. Thus, it is also difficult to discriminate exotic inclusions from chemical zoning in pyrite as several elements in a Cu-Au system could be attributed to pyrite zoning or separate phases. This may result in a wider range of trace element concentrations in a mineral population, as data was included rather than deleted when uncertain of zoning vs. inclusion. Due to the generally low concentrations of many trace elements in Čukaru Peki (many be- ing below detection limits), values that are below the detection limits are replaced with half the respective detection limit in the production of plots and diagrams in this study. This is a com- monly used approach for handling such data. 4. RESULTS 4.1. Petrography Macroscopic observations of veins and their crosscutting rela- tionhips, as well as reflected light microscopy of polished sections imply that the chronological order of deposition of mineralizing stages in the high-sulfidation (Upper) zone of Čukaru Peki is as follows: 1) Fine-grained pyrite (Py1) 2) Pyrite-enargite (Py-en) veins 3) Pyrite-covellite (Py-cov) veins 4) Py2 veins and 5) Mar- casite veins. A paragenetic sequence of the main ore stages is shown in table 3 and the main characteristics of individual stages are discussed below: 1) Fine-grained pyrite (Py1): Replacement of rocks by very fine-grained pyrite is omnipresent in the Upper zone of Čukaru Peki. It was probably preceded by advanced argillic alteration of rocks (with quartz and alunite) (Figs.4a and 4c). This pyrite also contains subordinate rutile, but no other sulfide minerals (Fig. 5a). This pyrite phase is also present within the transition zone. 2) Pyrite-enargite (Py-en) veins: This type of vein is com- mon in the deeper parts of the Upper zone (Figs.4a and 4b). They contain intergrown grains of enargite and pyrite, with subordi- nate luzonite (Fig.5b). The main gangue mineral in these veins is cryptocrystalline quartz (similar to chalcedony). It is commonly observed that these veins are crosscut by subsequent thin veins with pyrite and covellite (Fig.4b). 3) Pyrite-covellite (Py-cov) veins: This is the most common type of vein in the shallow parts of the Upper zone (Fig.4b and 4c). The veins mostly contain covellite, pyrite and enargite, but sometimes also occur as monomineralic covellite veins (Fig.5b and 5c). Pyrite in these veins often exhibits colloform textures. Zonation can occasionally be recognized in these veins, with col- loform pyrite and enargite filling the outer parts of veins and cov- ellite with gypsum filling the middle part. 4) Pyrite2 (Py2) veins: This is a rare type of thin grey vein- lets that crosscut py-cov veins. They are quartz veins which con- tain very small euhedral pyrite grains. (Fig.5d). 5) Marcasite veins: These veins contain large grains of col- loform marcasite, with subordinate arsenopyrite and small grains of colloform sphalerite (Fig.5e). The transitional epithermal zone contains the same types of veins like the paragenetically later parts of the porphyry zone (purple anhydrite veins, sulfide veins and orange anhydrite veins), as well as Py1 pyrite, which is also found in the high-sul- Table 1. Location and description of samples used for the measurements of trace elements by LA-ICP-MS. Abbreviations: py-pyrite; cov-covellite; en-enargite; su- sulfide. Sample ID Drillhole Ore zone Vein description CP012 TC150096 High-sulfidation Pyrite-covellite (py-cov) vein with clasts of Py1 pyrite. CP018 TC150096 High-sulfidation Pyrite-enargite (py-en) vein. CP028 TC150061 High-sulfidation Pyrite-covellite (py-cov) vein. CP038A TC160117 High-sulfidation Pyrite-covellite (py-cov) vein. CP073 TC150043 High-sulfidation Pyrite-enargite (py-en) vein. CP084 FMTC1327 Porphyry Quartz B vein. CP115 FMTC1328 Porphyry Sulfide vein (Su type). CP117 FMTC1328 Porphyry Sulfide vein (Su type). CP119 FMTC1328 Porphyry Purple anhydrite vein. CP122 FMTC1328 Porphyry Pyrite vein (type D). CP126 TC160125 Transition Py1 pyrite. Table 2. Calculated median detection limits of each element measured by LA-ICP-MS. Detection limits (μg/g). V 0.034 Cd 0.98 Cr 0.34 In 0.018 Mn 0.18 Sn 0.15 Co 0.056 Sb 0.054 Ni 0.20 Au 8E-07 Cu 1.2 Hg 0.28 As 2.6 Tl 0.0037 Se 4.1 Pb 0.024 Mo 0.047 Bi 0.0053 Ag 0.0081 G eologia C roatica Velojić et al.: Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase ... 307 fidation zone. The main ore minerals in this zone are covellite, chalcopyrite, digenite and enargite with occasional native sulfur. The dominant type of alteration is argillic alteration (with quartz, clay minerals and sericite). In the porphyry (Lower) zone of Čukaru Peki, several types of veins can be distinguished. Most of these veins fit into the gen- eral model of veins in porphyry systems (e.g. Sillitoe, 2010), so the names from the general model are used for the description of these veins. The sequence of main ore veins is shown in Table 4 and the main characteristics of veins are shown below (VELOJIĆ et al 2020): 1) Quartz veins (type А): Wiggly high temperature quartz veins that do not contain ore minerals. 2) Quartz veins (type B): Mostly occur as stockwork veins which contain chalcopyrite, with subordinate pyrite and bornite (Fig.4d, Fig. 5f). They are usually accompanied by phyllic alter- ation (with potassic feldspar and secondary biotite, with subordi- nate magnetite and anhydrite). Small grains of native gold and electrum were also detected in these veins by SEM examination (Fig. 6b and 6d). Таble 3. Paragenetic sequence of mineralization in the high-sulfidation (Upper) zone of Čukaru Peki. Py1 pyrite Py-en veins Py-cov veins Py2 veins Marcasite veins Pyrite Quartz Enargite Covellite Gypsum Luzonite Colusite Rutile Marcasite Arsenopyrite Sphalerite Abbreviations: Py- pyrite; Cov- covellite; En- enargite Figure 4. Crosscutting relationhips of different veins in the Čukaru Peki system. A) Py-en vein in andesite altered by advanced argillic alteration (with grains of alunite) and Py1 pyrite, TC150096 564m; B) Py-cov vein crosscutting py-en vein, TC150062 592m; C) Py-cov vein crosscutting Py1 pyrite, TC150096 564m; D) Sul- fide vein crosscutting a quartz B vein, FTMC1328 1348,5m; E) D vein, crosscut by a thin orange anhydrite vein FMTC1328 1581.5m; F) Thin sulfide vein cross- cutting a purple anhydrite vein FMTC1327 1589.2m Figure 5. Reflected light photomicrographs of samples of different types of ore veins in Čukaru Peki. A) Py1 pyrite with small grains of rutile, TC150096 476.8 m; B) Thin covellite vein crosscutting a wide py-en vein with enargite and pyrite, TC150043 591.4 m; C) Py-cov vein with covellite and colloform pyrite, TC160117 535 m; D) Py2 vein with small pyrite grains crosscutting a covellite vein, TC150096 448m; E) Colloform marcasite vein with small grains of round collo- form sphalerite, TC150061 505.5 m; F) Quartz B vein with chalcopyrite, bornite and pyrite, FMTC1327 1246.5 m; G) Pyrite vein type; D, FMTC1328 1581.5 m; H) Magnetite vein with magnetite, partially replaced by hematite and small chal- copyrite grains, TC160125, 1644m; I) Anhydrite vein with a large pyrite grain with inclusions of covellite, FMTC1328 1442 m; J) Sulfide vein with covellite and py- rite, FMTC1328 1312.8 m. G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue308 3) Pyrite veins (type D): These veins contain relatively large and connected pyrite grains, which contain small inclusions of chalcopyrite, bornite and rutile (Fig. 5g). These veins are usually accompanied by chlorite alteration (with chlorite, haematite and sericite) (Fig.4e). 4) Magnetite veins (type М): Common veins in the deeper parts of the porphyry zone. They contain magnetite and hematite, with subordinate pyrite and chalcopyrite (Fig.5h). Magnetite is commonly replaced by hematite in a martitization process. 5) Purple anhydrite veins: These veins have a distinct purple- pink colour and are usually several centimetres wide. The most abundant mineral is pyrite, with smaller grains of chalcopyrite, covellite, chalcocite and bornite (Fig. 5i, Fig. 6c). They are com- mon in both the porphyry and transition epithermal zones. 6) Sulfide (Su) veins : These veins are characterized by the presence of pyrite and covellite, with accompanying anhydrite (Fig. 5j). Like the previous type, these veins are also common in the transition epithermal zone. It is commonly observed that these veins crosscut earlier quartz and anhydrite veins (Fig.4d and 4f). 7) Orange anhydrite veins: They can be distinguished from purple anhydrite veins by colour, the shape of the anhydrite crys- tals and the absence of any ore minerals. These veins are clearly late, since they crosscut all the aforementioned veins (Fig.4e). 4.2. Pyrite trace element variations between the ore zones and intra-zonal variations Median values of measurements on pyrite from the three ore zones (high-sulfidation, transition zone and porphyry zone) indi- cate a general trend of trace elements being enriched in the high- sulfidation zone, compared to the porphyry zone. High-sulfida- tion zone pyrite is enriched in V, Mn, Ni, Cu, As, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi, relative to porphyry zone pyrite (as seen in table 5.) One sample of pyrite from the transition zone was analyzed and it contains concentrations that fall in-between the two other zones, most commonly showing values similar to the porphyry zone. Cobalt, As and Ag are the only outliers of this trend. Cobalt is significantly enriched in the sample from the tran- sition zone (median 64 μg/g) compared to pyrite from both other zones (porphyry with 16 & high-sulfidation with 1.7 median μg/g). Arsenic is depleted in transition zone pyrite (median 2.3 μg/g), whereas porphyry zone pyrite has slightly higher concen- trations with a median value of 16 μg/g. Silver shows similar con- centrations in both the Ag-rich sample from the transition zone and high-sulfidation zone (median 10 μg/g). Nickel is also rather anomalous as it shows values more similar to the high-sulfidation zone pyrite, although the median concentrations are just between 2.3 and 6.7 μg/g. Porphyry zone pyrite is significantly enriched in Co (median 16 μg/g) and Se (median 39 μg/g). Except for three spot measure- ments, porphyry zone pyrite shows concentrations of both In and Sn as being below the detection limit. Although there are characteristic trace element trends be- tween the zones, it is important to note that these trends are not always true for each vein type within each ore zone (Fig.7). For example, Se that is generally enriched in the porphyry zone, shows significantly lower concentrations in pyrite from the an- hydrite veins of the porphyry zone. All measurements of porphyry zone pyrite show values be- low the detection limits for In and Sn, except for three spots from the B-type veins. These three spots also show elevated concen- trations of other elements characteristic of the high-sulfidation zone, i.e. Mn, Cu, Ag, Cd, Pb and Bi. This is also the case for Cd in anhydrite-veins, where only two spot measurements show el- evated Cd contents. Due to these elevated contents of elements typically found in high-sulfidation veins, B-type pyrite crystals show a wide spread in concentrations for the analyzed elements. D-type pyrite shows significantly lower median concentrations for several metals (Cu, Ag, Au and Bi), compared to the other porphyry pyrite crystals. All these elements are typically low in pyrite from the porphyry zone. Anhydrite-vein pyrite shows trace element concentrations typical for the general porphyry Table 4. Paragenetic sequence of veins in the porphyry (Lower) zone of Čukaru Peki (Modified after VELOJIĆ et al., 2020). Quartz B veins Pyrite D veins Magnetite veins Purple anhydrite veins Sulfide veins Pyrite Chalcopyrite Bornite Magnetite Hematite Pyrrhotite Rutile Covellite Enargite Figure 6. BSE image s taken during SEM analysis of samples from Čukaru Peki. A) Clausthalite (lead selenide) grain in a Quartz vein type B, FMTC1327 1246.5 m; B) Grain of electrum in a Quartz vein type B, FMTC1327 1246.5 m; C) Grain of pyrite from a purple anhydrite vein containing inclusions of chalcopyrite, chal- cocite (spot 1) and bornite (spot 2), FMTC1328, 1442m; D) Chalcopyrite grain containing a small inclusion of native Au FMTC1327 1246.5 m. Chalcopyrite grain containing a small inclusion of native Au FMTC1327 1246.5 m. G eologia C roatica Velojić et al.: Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase ... 309 Table 5. Statistical summary for LA-ICP-MS pyrite data from the three different Čukaru Peki ore zones. All values are in μg/g. N: total number of measurements; n: number of measurements below detection limit out of N. N may vary within a pyrite population between elements due to obvious inclusions, which have been re- moved from the dataset. When there are more measurements below the detection limits than above (n > N), median values are indicated by “ n, n is replaced with ½ the median detection limit value of the element, for median calculations. DL: median detection limit value of all measurements for each element. Porphyry zone Quartz veins (type B) Pyrite veins (type D) N n Median Min Max N n Median Min Max V 6 4 <0.034 <0.034 0.24 15 15 <0.034 <0.034 <0.034 Cr 6 6 <0.34 <0.34 <0.34 15 15 <0.34 <0.34 <0.34 Mn 5 0 11 11 19 15 0 11 10 11 Co 6 0 13 0.10 961 15 0 35 0.33 232 Ni 6 2 2.3 <0.2 198 15 1 3.1 0.43 11 Cu 6 1 813 <1.2 6098 15 0 8.2 1.1 81 As 6 4 <2.6 <2.6 27 15 15 <2.6 <2.6 <2.6 Se 6 0 717 437 1041 15 0 64 28 113 Mo 6 6 <0.047 <0.047 <0.047 15 15 <0.047 <0.047 <0.047 Ag 6 1 0.81 <0.0081 1.1 15 10 <0.0081 <0.0081 0.023 Cd 6 3 0.70 <0.98 3.2 15 15 <0.98 <0.98 <0.98 In 6 3 0.35 <0.018 2.3 15 15 <0.018 <0.018 <0.018 Sn 5 2 1.00 <0.15 24 15 15 <0.15 <0.15 <0.15 Sb 6 6 <0.054 <0.054 <0.054 15 15 <0.054 <0.054 <0.054 Au 6 1 0.016 <8E-07 0.46 15 12 <8E-07 <8E-07 0.0011 Hg 6 6 <0.28 <0.28 <0.28 15 14 <0.28 <0.28 0.34 Tl 6 3 0.0046 <0.0037 0.022 15 13 <0.0037 <0.0037 0.021 Pb 6 1 96 <0.024 278 15 15 <0.024 <0.024 <0.024 Bi 5 1 0.26 <0.0053 8.8 15 15 <0.0053 <0.0053 <0.0053 Porphyry zone Purple anhydrite vein Sulfide (Su) vein N n Median Min Max N n Median Min Max V 15 15 <0.034 <0.034 <0.034 25 20 <0.034 <0.034 0.087 Cr 15 14 <0.34 <0.34 0.98 29 23 <0.34 <0.34 3.6 Mn 12 0 11 10 18 29 0 12 11 16 Co 15 1 104 <0.056 158 23 0 3.6 0.072 65 Ni 15 3 2.0 <0.2 7.3 24 3 0.45 <0.2 6.6 Cu 10 0 43 2.9 132 21 0 1561 17 4163 As 15 15 <2.6 <2.6 <2.6 28 28 <2.6 <2.6 <2.6 Se 13 0 40 27 108 25 16 <4.1 <4.1 79 Mo 15 15 <0.047 <0.047 <0.047 26 26 <0.047 <0.047 <0.047 Ag 15 7 0.0041 <0.0081 0.14 29 6 0.12 <0.0081 2.9 Cd 15 13 <0.98 <0.98 1.6 29 29 <0.98 <0.98 <0.98 In 15 15 <0.018 <0.018 <0.018 27 27 <0.018 <0.018 <0.018 Sn 15 15 <0.15 <0.15 <0.15 27 27 <0.15 <0.15 <0.15 Sb 15 15 <0.054 <0.054 <0.054 28 24 <0.054 <0.054 0.16 Au 15 0 0.0031 E2.3-05 0.029 29 8 0.082 <8E-07 1.0 Hg 15 15 <0.28 <0.28 <0.28 29 8 0.33 <0.28 0.93 Tl 15 11 <0.0037 <0.0037 0.029 29 15 <0.0037 <0.0037 0.11 Pb 12 7 <0.024 <0.024 1.4 26 7 0.25 <0.024 14 Bi 12 7 <0.0053 <0.0053 0.39 29 5 0.048 <0.0053 2.3 G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue310 Together with D-type pyrite, the anhydrite-vein pyrite has the lowest median Cu concentrations among the porphyry zone pyrite crystals (8.2 and 43 μg/g respectively). Median Co concen- zone trends. Two out of the fifteen analyzed spots show elevated Cd values, as mentioned previously, which is a major deviation from the porphyry zone trend. Transition High-Sulfidation Fine-grained pyrite (Py1) Fine-grained pyrite (Py1) N n Median Min Max N n Median Min Max V 6 1 0.13 <0.034 0.33 5 0 4.9 1.1 5.7 Cr 8 2 0.57 <0.34 1.3 8 1 1.5 0.17 3.3 Mn 8 0 9.6 8.9 11 7 0 59 16 81 Co 8 0 64 24 88 9 0 66 11 91 Ni 8 0 5.0 2.8 11 9 0 15 7.9 17 Cu 8 0 6442 4324 7787 9 0 9654 7881 16211 As 7 0 2.3 1.9 3.0 9 0 88 26 218 Se 8 0 20 8.7 123 9 1 14 <4.1 17 Mo 8 8 <0.047 <0.047 <0.047 8 0 0.42 0.15 1.1 Ag 8 0 10 7.4 21 9 0 5.7 2.5 11 Cd 8 8 <0.98 <0.98 <0.98 9 9 <0.98 <0.98 <0.98 In 8 8 <0.018 <0.018 <0.018 9 1 0.11 <0.018 0.37 Sn 8 1 0.35 <0.15 0.71 9 0 2.8 1.4 8.6 Sb 8 0 0.21 0.11 0.38 9 0 1.7 0.75 3.3 Au 8 0 0.85 0.64 2.4 9 0 4.0 2.0 20 Hg 8 0 0.52 0.26 0.89 9 3 0.57 <0.28 1.3 Tl 8 0 0.81 0.45 2.9 9 0 24 0.60 140 Pb 8 0 25 10 81 9 0 92 44 797 Bi 8 0 0.97 0.54 1.5 9 0 9.5 1.7 45 High-Sulfidation Pyrite-enargite (Py-en) veins Pyrite-covellite (Py-cov) veins N n Median Min Max N n Median Min Max V 14 0 0.17 0.030 3.3 18 0 6.3 0.68 43 Cr 20 14 <0.34 <0.34 1.7 28 4 1.5 <0.34 22 Mn 18 0 11 8.8 125 26 0 23 9.6 606 Co 20 2 5.3 <0.056 101 29 2 0.19 <0.056 12 Ni 20 1 2.3 <0.2 25 28 0 6.4 0.77 30 Cu 18 0 11066 151 32781 27 0 16545 10453 35235 As 17 10 <2.6 <2.6 23 27 0 66 24 222 Se 20 1 12 <4.1 47 26 2 7.7 <4.1 69 Mo 19 12 <0.047 <0.047 1.1 24 0 1.3 0.13 33 Ag 20 0 1.2 0.061 14 29 0 34 7.1 186 Cd 20 20 <0.98 <0.98 <0.98 29 9 5.9 <0.98 31 In 20 16 <0.018 <0.018 0.14 27 0 2.0 0.18 12 Sn 20 12 <0.15 <0.15 6.6 29 0 11 0.68 33 Sb 20 4 0.20 <0.054 1.6 29 0 5.9 1.0 18 Au 20 0 0.60 0.021 14 29 0 20 2.7 55 Hg 20 13 <0.28 <0.28 1.5 29 2 6.3 <0.28 28 Tl 20 2 0.018 <0.0037 16 29 0 56 6.9 657 Pb 16 0 1.5 0.30 254 28 0 1224 317 4967 Bi 19 0 0.65 0.052 5.1 29 0 27 6.8 103 Table 5. Continued G eologia C roatica Velojić et al.: Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase ... 311 trations are the highest in the anhydrite-vein pyrite crystals with 104 μg/g. Sulfide-vein pyrite crystals have the lowest median Co and Ni concentrations (3.6 and 0.45 μg/g respectively) of all the porphyry zone pyrite crystals. The Co concentrations are in fact more similar to that of pyrite-enargite vein pyrite (median 5.3 μg/g) in the high-sulfidation zone, although this pyrite has a higher median Ni concentrations (2.3 μg/g). Selenium is gener- ally enriched in the porphyry zone pyrite, but sulfide-vein pyrite contains the lowest median Se concentrations (<4.1 μg/g) out of all the pyrite populations measured, with 16 out of 25 measure- ments showing values for Se that are below detection limits. Pyrite1 is the only pyrite type specifically found in two zones, the transition and high-sulfidation zones. This is evident in the trace element concentrations, as they have relatively similar me- dian values in several of the measured elements (Co, Cu, Se, Cd and Hg). Accordingly, pyrite1 from the high-sulfidation zone is significantly enriched in a range of elements: V, Cr, Mn, Ni, As, Sn, Sb, Au, Tl, Pb and Bi. Thus, the high-sulfidation Pyrite1 and pyrite from the pyrite-enargite vein shows the typical high-sul- fidation trace element enrichment trend (eg. SYKORA et al.,2018), compared to the trend of the transition zone. Silver, Au, Pb and Bi in pyrite1 crystals show the lowest concentrations of all the high-sulfidation zone pyrite (median 1.2, 0.60, 1.5 and 0.65 μg/g respectively). These concentrations are still slightly, to signifi- cantly, higher than the porphyry zone pyrite median values. The high-sulfidation pyrite-covellite veins are the most trace element-rich veins (e.g. Cu, Ag, Au and Pb) of the Čukaru Peki ore system and are considered to be paragenetically the last veins formed, of those veins analyzed in this study (as demonstrated in Figs.4B and 4C). Pyrite-covellite veins are significantly enriched in Cu, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi, even in com- parison to the other high-sulfidation zone pyrite that are also com- monly enriched in these elements. Pyrite-covellite veins are the only vein type with substantial Cd concentrations (median 5.9 μg/g), only 9 out of 29 measurements showing values below de- tection limits. The only other Cd measurements above detection limit are 5 (out of 65) spot measurements from the porphyry zone. 5. DISCUSSION 5.1. Stages of mineralization There are distinct mineralogical differences between the three zones of mineralization in the Čukaru Peki hydrothermal system. The Upper zone consists of massive sulfides with pyrite-enargite and pyrite-covellite veins. The transitional epithermal zone con- sists of a system of anhydrite and gypsum veins, whereas the main ore minerals in this zone are covellite, chalcopyrite, digen- ite and enargite with occasional native sulfur. Mineralization in the Lower zone is mostly hosted by quartz and anhydrite veins with chalcopyrite, pyrite, bornite, magnetite, and pyrrhotite as the main ore minerals. Ore microscopic examinations of samples from the Upper zone mineralization (high-sulfidation zone) of Čukaru Peki im- ply that this zone was formed in several successive stages: 1) Massive pyrite (Py1); 2) Py-en veins with pyrite and enargite; 3) Py-cov veins with pyrite, covellite and enargite; 4) Py2 veins with fine-grained pyrite and 5) Marcasite veins with arsenopyrite and sphalerite. The research conducted by VELOJIĆ et al. (2020) implies that the Lower zone mineralization at Čukaru Peki formed in two successive stages. The porphyry stage formed at temperatures between 600 and 400°C and consists of four types of veins: 1) quartz veins type A without mineralization; 2) quartz veins type B with chalcopyrite, pyrite and bornite; 3) pyrite veins type D with subordinate chalcopyrite and bornite and 4) magnetite veins with hematite, pyrrhotite and chalcopyrite. The younger epither- mal stage formed at temperatures between 300 and 200°C and includes three types of veins: 1) purple anhydrite veins with py- rite, with subordinate chalcopyrite, covellite and enargite; 2) sul- fide veins with pyrite and covellite and 3) orange anhydrite veins without mineralization. 5.2. Zonal differences and trends in pyrite trace element composition Several distinctions can be made between pyrite from the differ- ent mineralization zones of Čukaru Peki (Fig.8). Selenium and Co concentrations are relatively high in the porphyry zone (max- imum median value of Co at 104 μg/g and Se at 717 μg/g) and gradually decrease (minimum median value of Co at 0.19 μg/g and Se at 7.7 μg/g; Fig.8a), whereas the opposite is observed for Au, Ag, As and Cu, which are significantly enriched in pyrite from the high-sulfidation zone (Fig.8c, 8d). Notable trends are observed with Ni and Co concentrations (Fig.8b), which are in- creased in purple anhydrite-veins and in transition zone pyrite, but are depleted in porphyry and high-sulfidation veins. Figure 7. Boxplot comparing concentrations of selected elements analyzed in this study. Variation between vein-types from each ore zone is clearly visible. Note: Below detection limits have been replaced by half of the measurement’s individual detection limit, to enable representation of low values. See Table 2. for detec- tion limits. G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue312 Čukaru Peki pyrite demonstrates trace element distribution trends similar to pyrite from other porphyry-epithermal copper deposits (SYKORA et al., 2018). Higher-temperature porphyry- stage pyrite is generally poorer in trace elements compared to the later, lower-temperature epithermal-stage pyrite. SYKORA et al.(2018) show that pyrite crystals from the Lihir (Ladolam) Au porphyry-epithermal deposit in Papua New Guinea, which formed during the earlier, higher-temperature porphyry-stage are enriched in Co, Ni and Se, whereas the later, lower-temperature epithermal-stage is characterized by an enrichment in As, Mo, Ag, Sb, Au and Tl in pyrite. Decreased Cu concentrations in the pyrite from the porphyry zone of Čukaru Peki can be explained by the fact that Cu is usu- ally bound in Cu-bearing sulfides, including chalcopyrite and bornite (KESLER et al., 2002; REICH et al, 2013). Several stud- ies demonstrate that Cu concentrations in pyrite are very low in the first stages of the porphyry deposits and then gradually in- crease in the subsequent stages (MAYDAGÁN,et al., 2013; TAN et al., 2021) and are especially elevated in high-sulfidation pyrite (FRANCHINI et al.,2015; SYKORA et al.,2018). Selenium concentrations in high-sulfidation pyrite that are lower than in the porphyry pyrite at Čukaru Peki are unusual, as Se is typically higher in high-sulfidation pyrite (KEITH et al.,2018; and references therein), although their data does show certain overlaps in pyrite Se concentrations from porphyry to high-sulfidation deposits. Anomalously low Se concentrations in pyrite can be explained by the presence of mineral phases with preferred partitioning of Se, such as selenides, galena or even chalcopyrite (KEITH et al., 2018; PASS, 2010). Selenium concen- trations in chalcopyrite have not previously been investigated. Lead-selenides (clausthalite) have solely been identified within the B-type vein of the porphyry ore zone at Čukaru Peki (Fig. 6a). However, time-resolved count signals of pyrite from the sig- nificantly Se-enriched B-type veins are smooth and suggest that Se is hosted in the pyrite crystal lattice (or as nanoinclusions) rather than microinclusions of clausthalite. Thus, it seems that the fluids responsible for the formation of B-type veins were signifi- cantly Se-enriched, bearing both Se-rich pyrite and clausthalite. Other examples of pyrite from porphyry deposits with elevated Se concentrations have been described, such as a porphyry Cu deposit in the Romanian Metaliferi Mountains (CIOACĂ et al., 2014). Gold preferably precipitates from the hydrothermal fluids under lower temperature conditions within the epithermal zone, rather than under porphyry higher temperature conditions (e.g. DEDITIUS et al., 2014; SIMMONS, 2005; SYKORA et al., 2018). This is the same trend as observed in Čukaru Peki pyrite. Pyrite from the Čukaru Peki porphyry zone has a median Au concen- tration of 0.013 μg/g, with a third of the measurements falling below detection limits, compared to the median of 7.2 μg/g Au in the high-sulfidation zone. Decreased concentrations of Au and Ag in pyrite from the porphyry zone of Čukaru Peki can also be explained by the tendency of gold and silver to mainly concen- trate in chalcopyrite and bornite in porphyry systems (KESLER et al., 2002; COOK et al., 2011; ZWAHLEN et al., 2014). Also, native Au and electrum are relatively common accessory miner- als in these systems (JOHN et al.,2010; SILLITOE, 2010). These accessory minerals are also observed in Čukaru Peki, as demon- strated in Fig.6b, which implies that Au and Ag preferably formed native minerals in this system, instead of being incorporated in pyrite. Recent studies have demonstrated that As-rich pyrite in porphyry systems can concentrate up to 800 ppm Au (REICH et al., 2013; CIOACĂ et al.,2014), but this type of pyrite was not ob- served in the porphyry zone of Čukaru Peki. Cobalt-nickel values correspond to pyrite of volcanic origin, according to CAMPBELL & ETHIER (1984). Čukaru Peki py- rite has cobalt concentrations between <1 and <200 μg/g, along with Ni values of maximum 20 μg/g. These low Co-Ni concen- trations are in agreement with other studies on pyrite trace ele- ment geochemistry (e.g. DEDITIUS et al., 2014; FRANCHINI et Figure 8. Median values of trace element concentration trends in pyrite from different mineralization zones in Čukaru Peki. The elements that are enriched in py- rite from the porphyry zone are coloured red, those that concentrate around the transition zone are coloured blue, whereas elements enriched in the high-sulfida- tion zone are coloured green. A) Se concentrations in pyrite have a decreasing trend from the porphyry to epithermal stages; B) Co tends to concentrate in pyrite from anhydrite-veins and in pyrite from the transition zone; C) Ni is enriched in Py1 pyrite, both from the transition zone and high-sulfidation zone ; D) Au concen- trations increase rapidly in pyrite from high-sulfidation stage; E) Ag is also significantly enriched in pyrite from the high-sulfidation stage; F) Cu concentrations ex- hibit a steady increase in pyrite from – the porphyry to the epithermal stages. G eologia C roatica Velojić et al.: Trace elements in pyrite from the Čukaru Peki porphyry Cu-high-sulfidation deposit, Serbia: implications for ore evolution in a polyphase ... 313 al., 2015; PASS, 2010; REICH et al., 2013), where Co and Ni con- centrations range from tens to a few hundreds of μg/g. This sug- gests that porphyry pyrite predominately has hydrothermal trace element signatures, but may display inherited magmatic trends originating from the magmatic source of the mineralizing hydro- thermal fluids. 5.3. Indications of a poly-stage mineralizing fluid evolution by trace element geochemistry Porphyry–high-sulfidation systems form by multiple pulses of hydrothermal fluids circulating through the overlying host rock, driven by underlying intrusions (SILLITOE, 2010; INGEBRIT- SEN & APPOLD, 2012). Pyrite in these systems commonly ex- hibits zoning associated with polyphase fluid evolution (SYKORA et al., 2018) and may thus have zones with trace element compo- sitions related to the different phases of hydrothermal fluids (FRANCHINI et al., 2015). The epithermal stage in the evolution of porphyry systems is characterized by high-, intermediate- or low-sulfidation veins (and alteration) that form under lower temperatures and salinities than earlier porphyry veins (JOHN et al., 2010; SILLITOE, 2010). In these later stages, hydrothermal events that overprint the por- phyry-style ore commonly remobilize Cu and Au, since the orig- inal chalcopyrite-bornite minerals are dissolved. In this way, Au and Cu are introduced into epithermal systems (KESLER et al., 2002; REICH et al., 2013; GREGORY et al., 2013). This process is particularly interesting in high-sulfidation deposits, since they are genetically and spatially associated with underlying porphyry systems (KESLER et al., 2002; SILLITOE, 2010). In many high- sulfidation systems, pyrite commonly contains invisible gold in the crystal lattice (CHOUINARD et al., 2005; BOGDANOV & KUNCHEVA, 2017), but in some cases it also contains sig- nificant amounts of crystal lattice-bound Cu (PAČEVSKI et al.,2008). POKROVSKI et al. (2019) argue that chemisorption is the most common process in which invisible gold is incorporated into pyrite as Au(I) ions. In Čukaru Peki, the polyphase genesis is evident from mul- tiple generations of veins (Tables 3 and 4; Fig.5). The process of primary sulfide dissolution can be observed in the transition zone of Čukaru Peki, where covellite and enargite replace the primary mineralization of chalcopyrite and bornite. Significantly elevated concentrations of elements are attributed to the high-sulfidation zone (e.g. Cu, Ag, Cd, In, Sn, Pb and Bi). Five spot measurements of the porphyry zone pyrite crystals (B-type veins and Purple anhydrite-veins) suggest that these veins were affected by later high-sulfidation fluids. The later fluids could have resulted in py- rite growth zones that would be enriched in these high-sulfidation associated elements. Elevated Cd is particularly interesting, as Cd is only seen above detection limits in the pyrite-covellite veins, which represent the latest veins investigated in this study. This could indicate that the later hydrothermal fluids, responsible for the pyrite-covellite veins, originated from the deeper parts of the hydrothermal system. An additional argument for this state- ment is the apparent compositional similarity between sulfide- veins (Fig.5.h), which are found in the porphyry and transitional zones and pyrite-covellite veins (Fig.5c) which are found in the high-sulfidation zone. Both of these veins contain abundant cov- ellite, which is a common mineral for the high-sulfidation zone, but uncommon for porphyry conditions (JOHN et al., 2010; SIL- LITOE, 2010). This suggests that sulfide-veins formed by the same or similar fluids that led to the remobilization of primary sulfides and redeposition in the high-sulfidation zone. Pyrite from sulfide-veins differs from pyrite from py-cov veins, both in its textural characteristics (lack of colloform texture) and in its trace element composition (depleted concentrations of Au, Ag and Cu). However, this can possibly be explained by the different temper- atures at which these two vein types were formed, which prob- ably affected the depositional textures and element distributions. DURAN et al. (2019) investigated pyrite trace element com- positions from a range of deposit types (VMS, orogenic Au, por- phyry Cu and magmatic). Based on this, DURAN et al. (2019) were able to distinguish pyrite from hydrothermal and magmatic origins based on their Co/Sb and Se/As variations (Fig. 9). Čukaru Peki pyrite from the porphyry zone (and transition zone) plot pre- dominantly within the magmatic zone (marked with an orange colour), with overlaps into the hydrothermal zone , which is the case for the porphyry Cu field in the DURAN et al. (2019) dia- gram. High-sulfidation zone (marked with a green colour) pyrite plots well within the hydrothermal domain proposed by DURAN et al. (2019). This is reasonable as the fluids responsible for the porphyry zone, especially, would have a significant magmatic signature. This is further demonstrated with fluid inclusion anal- yses by VELOJIĆ et al. (2020). Earlier and deeper porphyry zone veins, such as the B-type veins, show a more magmatic signature Figure 9. Discrimination plot for pyrite formed from hydrothermal or magmatic origins (indicated by the dashed line), based off Se/As vs Co/Sb values. Two do- mains are drawn out, based on where the porphyry and magmatic pyrite data clusters. Plot and domains are made after DURAN et al. (2019). Note: Below detec- tion limits have been replaced by half of the measurement’s individual detection limit, to enable representation of low values. See Table 2. for the detection limits. G eo lo gi a C ro at ic a Geologia Croatica 75/Special Issue314 with homogenization temperatures between 331 and 495oC and salinities between 36.5 and 43 wt% NaCl eq, whereas anhydrite veins were formed by fluids with significantly lower salinities. It is important to note that porphyry zone pyrite would not be ex- pected to plot perfectly within the magmatic domain, as they are still the product of hydrothermal fluids. Rather, the hydrothermal fluids responsible for the mineralization display a slight magmatic signature, inherited from the magmatic source. These pyrites were not formed in the magma itself and thus do not show a true magmatic signature. 6. CONCLUSIONS The results obtained demonstrate that the different veins in Čukaru Peki can be distinguished by both their mineralogy and trace element compositions. The porphyry zone pyrite crystals generally contain lower concentrations of most trace elements and are only significantly enriched in Co and Se. Transition py- rite mostly shows trace element concentrations between the two other zones, having lower concentrations more similar to pyrite from the porphyry zone. High-sulfidation pyrite crystals are char- acterized by enrichment of V, Mn, Ni, Cu, As, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi. Increased concentrations of ele- ments attributed to the high-sulfidation zone in five spot measure- ments of the porphyry zone pyrites crystals from Quartz veins type B and purple anhydrite veins imply that these veins were affected by later high-sulfidation fluids. However, there are many differences in trace element concentrations between the different pyrite crystals of each zone. The ore-microscopic and SEM studies imply that the most important stage for the deposition of Cu and Au in the porphyry system was quartz veins type B. These veins contain the highest amounts of Cu-bearing sulfides (chalcopyrite and bornite). Ad- ditionally, SEM studies have demonstrated the presence of native Au and electrum grains in these veins (Fig.6b and 6d). Concen- trations of Au and Ag in pyrite are low, which indicates that these two elements formed native minerals (native Au and electrum) or were partitioned into chalcopyrite or bornite. Another impor- tant type of vein for Cu deposition are the sulfide veins, which contain abundant covellite and probably represent the transition to the epithermal stage of mineralization. According to the ore-microscopic research and LA-ICP-MS measurements, we conclude that the most important stage for the deposition of Cu and Au in the high-sulfidation zone are the pyrite- covellite (py-cov) veins. They contain the highest amounts of Cu- sulfides (covellite and enargite) as well as the highest concentra- tions of Au and Ag in the analyzed pyrite grains. Pyrite-enargite veins also contain abundant enargite, but much less covellite than the pyrite-covellite veins, thus they have lower Cu contents. How- ever, it should be noted that preliminary measurements indicate that enargite from pyrite-enargite veins contains elevated concen- trations of germanium (VELOJIĆ & ERLANDSSON, 2019). Our pyrite trace element data illustrates the change in min- eralizing hydrothermal fluids; from a magmatic-sourced system (the porphyry zone) to a more typical hydrothermal system that was responsible for the high-sulfidation zone mineralization. There is also evidence for the late high-sulfidation fluids affect- ing the earliest and deeper pyrite in the porphyry zone, by growth of pyrite enriched in elements characteristic of the high-sulfida- tion mineralization. It is established that the main gold-concentrating mineral in this zone is pyrite, which is commonly not considered an ore min- eral during mineral processing and thus it is usually not included in the main sulfide concentrate. The results presented might also be significant for the better targeting of specific gold- and silver- rich veins and mineralization stages during mineral exploration. ACKNOWLEDGEMENT This contribution is supported by the project “rESEErve - Min- eral potential of the ESEE region” funded by the European Insti- tute of Innovation and Technology (EIT), a body of European Union, under the Horizon 2020, the EU Framework Programme for Research and Innovation. The authors would like to thank the geologists from the Rak- ita Exploration Company for their assistance in sampling and geological interpretation (now called Balkan Expploration and Mining). This research was partly funded with an Ernst Mach Grant by OEAD agency and with Ceepus mobility grant. 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