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Iron oxide copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe oxides, and may contain Au, Ag, Co, rare earth elements (REEs), U, and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the hydrothermal unit and manto orebodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three types of magnetite: magnetite with inclusions (type I) is only found in the manto, is the richest in trace elements, and crystallized between 459° and 707°C; type Dark (D) has no visible inclusions and formed at around 543°C; and type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443°C. Temperatures were estimated using the Mg content in magnetite. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n = 9), an average δ18O ± 2σ value of 2.19 ± 0.45‰ (n = 9), and Δ’17O values that range between –0.075 and –0.047‰. Sulfide separates yielded δ65Cu values that range from –0.32 to –0.09‰. The trace element compositions and textures of magnetite, along with temperature estimations for magnetite crystallization, are consistent with the manto magnetite belonging to an iron oxide-apatite (IOA) style mineralization that was overprinted by a younger, structurally controlled IOCG event that formed the hydrothermal unit orebody. Altogether, the stable isotopic data fingerprint a magmatic-hydrothermal source for the ore fluids carrying the Fe and Cu at Mina Justa and preclude significant input from meteoric water and basinal brines.

This paper provides the first comprehensive sourcing analysis of the tin ingots carried by the well-known Late Bronze Age shipwreck found off the Turkish coast at Uluburun (ca. 1320 BCE). Using lead isotope, trace element, and tin isotope analyses, this study demonstrates that ores from Central Asia (Uzbekistan and Tajikistan) were used to produce one-third of the Uluburun tin ingots. The remaining two-thirds were derived from the Taurus Mountains of Turkey, namely, from stream tin and residual low-grade mineralization remaining after extensive exploitation in the Early Bronze Age. The results of our metallurgical analysis, along with archaeological and textual data, illustrate that a culturally diverse, multiregional, and multivector system underpinned Eurasian tin exchange during the Late Bronze Age. The demonstrable scale of this connectivity reveals a vast and disparate network that relied as much on the participation of small regional communities as on supposedly hegemonic institutions of large, centralized states.

Fractionation factors for the isotopes of O, H, S, or Cu (as appropriate) were determined for the minerals brochantite [Cu4(SO4)(OH)6], libethenite [Cu2(PO4)(OH)] and olivenite [Cu2(AsO4)(OH)] and corresponding aqueous solutions at temperatures between 30 and 70°C. All samples used for this determination were synthetic and the degree of fractionation was expressed as 1000 ln α = (A × 106/T2) + B, where A and B are empirical parameters. A few natural libethenite samples from its type locality Ľubietová-Podlipa were also analysed and compared to the prediction based on the isotopic composition of meteoric water and our fractionation factors. The hydrogen fractionation factors agreed with the prediction well, whereas those for oxygen did not. A possible explanation is the disequilibrium of aqueous phosphate (and also arsenate) species and the solution in our experiments or the interaction of meteoric fluids with the isotopically heavy (in terms of oxygen) country rocks. Because the effects of isotopic disequilibrium in our experiments cannot be ruled out, the oxygen fractionation factors should be used with caution. The determined fractionation factors can be used as an isotope geothermometer, given that it can be proven that the phases of interest precipitated from the same fluid in equilibrium. Libethenite is predicted to have slightly lower δ65Cu values than its parental solution, but brochantite slightly higher δ65Cu values than its parental solution. Simple forward models, simulating neutralisation or reduction of mine drainage, show that precipitation of these minerals and removal of the co-existing fluid, could cause isotopic variations (in δ65Cu) on the order of 1‰ or more.

In order to characterize antimony (Sb) isotope fractionation in hydrothermal systems, we present Sb isotope compositions of primary stibnite ores from a large Sb deposit in south China. A total number of 39 analyses reveals a large δ123Sb range of −0.27 to +0.86‰, representing an up to 1.13‰ variation in this hydrothermal system. A gradual increase of Sb isotope ratios from the proximal to the distal parts was observed in stibnite ores. Rayleigh distillation models the systematic variation trend of the Sb isotope values, demonstrating that ore fluids are preferentially enriched in heavier Sb isotopes during the precipitation of isotopically light stibnite. In this way, we consider that separation of stibnite from a Sb-bearing fluid related to reaction kinetics as a cause for Sb isotope fractionation. The modeled data constrain a Sb isotope fractionation factor (αfluid-stibnite) between hydrothermal fluid and stibnite at approximately 0.9994. The model also constrains an initial Sb isotope value of ~0.45‰, which indicates metal sources in the basement rocks of the study area. Given that distal stibnites possess higher Sb isotopic values, Sb isotopes could be used to fingerprint hydrothermal fluid flow and unravel different processes in natural systems.

Studies of the equilibrium isotope properties of stable isotopes of minerals have been initiated principally because of their application to the solution of geochemical problems. Therefore, we examined malachite, a common secondary mineral in the oxidation zone of ore deposits. Stable isotope characterization can contribute needed information on the formation of malachite by establishing the isotopic composition of the parental waters. The equilibrium oxygen and hydrogen isotope fractionations between malachite and solution were determined by precipitation experiments over the temperature range from 10 to 65 °C and could be distinguished in two sets of fractionation factors depending on the temperature. For 45–65 °C, the fractionation is expressed as 1000 ln α mal - sol oxygen = 2.87 ( 10 6 / T 2 ) + 0.96 and 1000 ln α mal - sol hydrogen = - 1.47 ( 10 6 / T 2 ) - 22.3 with temperature (T) in Kelvin. With the application of the fractionation factors of oxygen and hydrogen of malachite onto source water from the meteoric water line, we were able to calculate the “malachite line” which represents the isotopic compositions of malachite that would precipitate from such water. We also examined the copper isotope fractionation factors between solution and malachite from 10 to 65 °C: 1000 ln α sol - mal copper = 0.033 ( 10 6 / T 2 ) - 0.19 with fractionation shift of Δ 65 Cu malachite - solution = - 0.17 ± 0.05 ‰. This fractionation shift implies that chemical reactions without change of the redox state yield only minor copper isotope fractionation. The calculated fractionation factors of oxygen and hydrogen were used to determine the oxygen and hydrogen isotopic composition of the parental waters of natural malachite samples from a number of localities worldwide. With δ 18 O VSMOW values of +22.1 to +29.5 ‰ and δ D values of - 132 to - 61 ‰ for the natural malachite and δ 18 O VSMOW values of - 14.5 to - 7 ‰ and δ D values of - 107 to - 36 ‰ for the parental water together with the Cu isotopes, it is to assume that all investigated malachite samples are supergene samples which formed from meteoric water. Even in massive malachite samples from Ural Mts. (Russia), no signs of other fluids were detected from the isotopic composition.

The Zhaxikang Sb–Pb–Zn–Ag deposit is the only super-large deposit in the North Himalayan Metallogenic Belt, but its genesis is debated. Genetic models include hot springs, magmatic-hydrothermal flu...

The important role of the Balkans in the origin and development of metallurgy is well established with respect to copper. In addition, Aleksandar Durman, in his 1997 paper ?Tin in South-eastern Europe??, essentially initiated studies into the role of the Balkans in Europe?s Bronze Age tin economy. He identified six geologically favourable sites for tin mineralisation and associated fluvial placer deposits in the former Yugoslavian republics, and suggested that these may have added to the tin supply of the region. The viability of two of these sites has been confirmed (Mt Cer and Bukulja, Serbia) but the exploitation potential for the other locations has remained untested. River gravels from these four sites (Motajica and Prosara in Bosnia and Herzegovina; Bujanovac in Serbia; Ograzden in North Macedonia) were obtained by stream sluicing and panning. The sites of Prosara and Bujanovac were found to be barren with respect to cassiterite (SnO2). Streams flowing from Motajica and Ograzden were both found to contain cassiterite, but in amounts several orders of magnitude less than at Mt Cer and Bukulja. Although it is possible that minor tin recovery occurred at Motajica and Ograzden, it is unlikely that they could have contributed meaningfully to regional tin trade. This is supported by the fact that the isotopic signature (?124Sn) of cassiterite from Motajica is highly enriched in light isotopes of tin compared to that associated with Late Bronze Age artefacts of the region.

The role of rock-water reactions, leakage of sedimentary brine, evaporite dissolution and variations in lithology on the chemical and isotopic evolution of groundwater draining the active arc and Preandean basins in the Antofagasta Region of northern Chile has been investigated using Li, B and Sr isotopes. The studied basin is that of the upper Loa river and its sub-basins, which is adjacent to the basin occupied by the Salar de Atacama where Li-rich brines are commercially exploited. Due to the arid climate, water draining this part of the Andes does so primarily through the subsurface. Water from a thermal source is a common component of water sampled, but its geochemical signature evolves through multiple processes including dilution, cold rock-water reactions, influxes of sedimentary brine and evaporite mineral dissolution. These processes lead to a range of Li and B concentrations in groundwater (0.01–14 mg/L and 0.18–20 mg/L) and isotope compositions (−1 to +12‰ and −6 to +14‰). The effect of rock dissolution on δ7Li and δ11B within aquifers is apparent from their low values, but even in streams these values only undergo small increases relative to other rivers worldwide. This may be due to the weathering of ignimbrites producing water with less Al and limited clay formation, the large reservoir of thermally-sourced Li and B of which only a small component is removed, and because the streams acquire groundwater through their beds. The wider range in δ11B is a result of variable lithology and dissolution of evaporite minerals, which have lesser effects on δ7Li. Our multi-isotope approach highlights the role of lithology and different processes in defining groundwater chemistry. Isotopic signatures derived from marine sediments are recognizable in some springs even though this type of rock has nearly no surface exposure due to extensive volcanic rock cover, and are acquired directly or via incorporation of these sediments into volcanic systems. These high-Cl rocks can weather to produce water with a chemical composition like that of sedimentary brine but is distinguishable through δ11B composition. Combination of 87Sr/86Sr, δ7Li and δ11B also indicate that mixed salts which contribute to groundwater draining the ignimbrite covered areas of the basin did not form following cold temperature weathering, but from water where thermal contributions dominated solute budgets keeping δ7Li low, and Li/Cl and B/Cl high compared to other fluid reservoirs such as seawater. We propose that these saline systems lay within the confines of one of the multiple late-Miocene-Pliocene calderas following the active stage of volcanism and while heat gradients remained high.

Multiple mechanisms have been proposed to induce fractionation of tin in ores and rocks. Experimental evidence to support and characterize the causes for fractionation is lacking. Here, we present laboratory vapor-induced and redox-driven experiments to resolve the directionality and relative magnitude of fractionation caused by these geologically prominent mechanisms. Vapor-induced fractionation without redox reactions at 150 °C resulted in the residual solution becoming isotopically lighter by 0.15‰ (δ124Sn with all values reported in comparison to NIST 3161A). Tin chloride solutions that were electrolytically reduced to form metal produced residual solutions that were 0.40‰ heavier (δ124Sn). The reduced metal from these experiments was lighter than the solutions and starting materials. These experiments confirm that heavier tin isotopes are favored in a stronger bonding environment associated with oxidation, and that the vapor favors heavier tin in SnCl4. Empirical confirmation of the magnitudes and directions of tin isotope fractionation determined through experimentation are evident in the comparison of the isotopic composition of cassiterite ores from contrasting mineralizing environments. Pegmatites and associated greisen ores that formed deep within the Earth, and so experienced redox reactions without vapor partitioning (Etta, South Dakota; Elsmore, New South Wales) display a variation of only 0.8‰ (δ124Sn). In contrast, cassiterite that formed from vapor-rich fluids in volcanic to subvolcanic environments, and so experienced both redox and vapor fractionation mechanisms (Taylor Creek, New Mexico, Durango, Mexico; Potosi and Oruro, Bolivia) display a much larger range of cassiterite values, of up to 2‰ (δ124Sn). It is likely that tin isotope fractionation via these mechanisms contribute to the observed variations in igneous rocks.

Copper and Fe are redox-sensitive metals, and their isotopic compositions may potentially record changes of oxidation conditions in high-temperature magmatic Ni–Cu mineralization systems. High-precision Cu and Fe isotope data for sulfides (chalcopyrite) and whole-rock samples of the Tulaergen magmatic Ni–Cu system (NW China) were analyzed to evaluate redox-induced fractionation during segregation of sulfide melt from silicate melt and internal fractionation within segregated sulfide melt. Sulfide mineralization includes disseminated and massive types, with massive sulfides being further divided into Cu- and Fe-rich ores. Numerical modeling using mass-balance and Rayleigh equations indicate that disseminated sulfide mineralization was generated from a common parental magma, and massive sulfides were formed by monosulfide solid-solution (MSS)–residual sulfide liquid fractionation. During segregation of sulfide melt from silicate melt, crystallization of olivine and pyroxenes with sulfide segregation, in an Fe2+-dominated phase, led to the incorporation of lighter Fe isotopes in these minerals. The residual silicate melt became progressively more oxidized, with δ56Fewhole-rock values increasing as melts evolved. The disseminated chalcopyrite formed in early stages has lighter Cu and heavier Fe isotopic compositions than the disseminated sulfides formed in later stages due to charge-balance effects. Minor accumulated Ni–Cu sulfide melt was fractionated into an Fe-rich MSS cumulate and a Cu-rich sulfide liquid. MSS crystallization caused the oxygen fugacity of the evolved sulfide liquid to increase, which was accompanied by increasing δ65Cu and decreasing δ56Fe values in chalcopyrite. Iron isotopic compositions of the whole system were shifted towards heavier values from MSS cumulate to the evolved sulfide melt. Numerical modeling using the Rayleigh equation indicates that the fractionation factors α65Curesidual sulfide melt–MSS and α56Feresidual sulfide melt–MSS are ∼1.0011 and ∼1.0005, respectively, during internal fractionation within segregated sulfide melt. This study demonstrates that redox reactions play a key role in Cu and Fe isotope fractionation in high-temperature magmatic Ni–Cu mineralization systems. Furthermore, Cu and Fe isotopes can be used to trace concealed orebodies. Elevated δ65Cu and δ56Fewhole-rock values may indicate Cu-rich mineralization potential, while light Cu and Fe isotopic compositions imply favorable hosts for disseminated and Fe-rich orebodies in mafic–ultramafic intrusions.

The Zhaxikang Sb–Pb–Zn–Ag deposit, the only super-large deposit identified within the North Himalayan Metallogenic Belt (NHMB), is still debated to date with perspectives of mineralization age and genesis. The previous genetic models mainly include hot-spring, magmatic hydrothermal fluid, coarse-grained hydrothermal Pb–Zn vein overprinted by Sb-rich magmatic hydrothermal fluid, and SEDEX overprinted by hydrothermal fluid. Here, we present new and credible isotope geochronological evidence to discuss the genesis and mineralization age of Zhaxikang deposit. The isotopic ages of minerals from different mineralization stages in Zhaxikang deposit coincide with the mineralization ages of three main regional mineralization events. In detail, the older 206Pb/238U (218 ± 10 Ma), Sm–Nd (173.7 ± 7.4 Ma) and Rb–Sr (147 ± 3.2 Ma) isochron ages match three regional extensive seafloor volcanic events during synsedimentary period (220–130 Ma); the younger 206Pb/238U (62 ± 8.2 Ma) and older Re–Os (47.7 ± 7.9 Ma; 43.1 ± 2.5 Ma) ages are in accord with the formation age of regional orogenic Au–Sb deposits associated with metamorphic fluid system during syn-collision period (60–42 Ma); and the Ar–Ar (19.3 ± 1.1 Ma) and younger Re–Os (9.0 ± 1.9 Ma) isochron ages are consistent with the regional magmatic-hydrothermal mineralization event during post-collision period (25 Ma to now). We thus proposed that Zhaxikang deposit is a superimposed deposit that experienced three pulses of mineralization corresponding to three regional mineralization events: the first pulse of mineralization (stages 1 and 2) is related to multiple seafloor volcanic events during synsedimentary period with submarine hydrothermal sedimentation (metasomatism) genesis; the second pulse of mineralization (stages 3 and 4) is associated with metamorphic fluid system during syn-collision period that overprint the Pb–Zn mineralization; and the third pulse of mineralization (stages 5 and 6) relates to magmatic-hydrothermal activity during post-collision period and also overprints early mineralization. Furthermore, the complicated superimposed mineralization results in the discordance of different geochronological methods.

The copper and zinc isotope ratios of massive sulfide and stockwork ores of Honghai volcanogenic massive sulfide (VMS) deposits in eastern Tianshan Orogen, NW China, were measured by multiple collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). The overall range of δ65Cu (where δ65Cu = [{(65Cu/63Cu)sample / (65Cu/63Cu)NIST976} − 1] × 1000) values of 16 mineral separates from Honghai deposit varies from −0.28 to 0.70‰, with near-surface massive Zn ores having isotopically heavy values compared to massive Cu ores from deeper levels. This suggests that a kinetic fractionation of copper isotopes could be encouraged during precipitation of chalcopyrite. However, the δ65Cu values of mineral separates from Massive Zn ores in drill hole ZK0302 are considerably higher than those of other mineral separates, which might be associated with the development of secondary mineralization. We also obtained zinc isotope data from 6 sphalerite-bearing samples. The range of δ66Zn (where δ66Zn = [(66Zn/64Zn)sample / (66Zn/64Zn)JMC 3-0749L − 1] × 1000) values varies from 0.05 to 0.17‰, with central parts of mineral separates having isotopically light values (δ66Zn = 0.05‰) compared with that from distal (δ66Zn = 0.12–0.17‰) of VMS system. The results suggest that Cu and Zn isotopes could provide a valuable tool for tracing flow paths toward the center of hydrothermal systems.

Rodingites are metasomatic rocks, frequently found in ophiolitic complexes. They offer important information about the interaction between ultramafic-mafic rocks and metasomatizing fluids, as well as about the post-magmatic evolution of ophiolitic suites (Tsikouras et al., 2009; Hu & Santosh, 2017; Surour, 2019; Laborda-Lopez et al., 2020). Metasomatism, such as rodingitization, is a very intricate process, which depends on the mineralogy of the initial rock, the nature of the metasomatic agent, the fluid/rock ratio, the duration of metasomatism and the chemical disequilibrium at the time of metasomatism between the host rock and the metasomatic medium (Poitrasson et al., 2013). Rodingites from the Veria-Naousa and Edessa ophiolites, in Northern Greece, were geochemically analyzed and characterized by substantial overprint of primary textures. Their field observation, their neoblastic mineral assemblages and metasomatic textures reveal that they derived from ultramafic and mafic protoliths. The mineral phases in the ultramafic derived rodingites (UDR) include mainly diopside, garnet, chlorite, epidote, tremolite and Fe-Ti oxides whereas mafic derived rodingites (MDR) consist of diopside, garnet, vesuvianite, chlorite, quartz, prehnite and actinolite. The studied rodingites present δ65Cu values varying from -0.17‰ to 0.62‰ and for ultramafic and mafic parent-rocks from -0.49‰ to +0.50‰. The UDR and MDR from both ophiolites display δ66Zn range from -0.06‰ to 0.74‰ and their photoliths present a narrower range from +0.04‰ to +0.41‰. Rodingitization affects in different way UDR and MDR samples. On one hand, Cu isotope ratios are systematically heavier in rodingites compared to their respective protoliths, except for one rodingite sample that requires confirmation due to large error bar. On the other hand, Zn isotopes show enrichment in light isotopes (group 1: comprising all UDR and some MDR samples), or in heavy isotopes (group 2, only MDR samples). Intriguingly, the same protolith can lead to both group 1 and 2 rodingites, as defined here. No mineralogical or geochemical trend can be found to understand the dual behavior of Zn stable isotopes during rodingitization so far. Fe isotopes do not show any significant fractionation of δ56Fe, ranging from +0.07‰ to +0.19‰ for the rodingites and from +0.12‰ to +0.23‰ for their protoliths, indicating that Fe isotopes are highly resistant to rodingitization. Our study shows that rodingitization enriches metasomatized samples in heavy Cu isotopes and has no impact on Fe isotopes. It remains unclear why Zn isotopes can be affected both ways.

Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for 90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (

The supergiant Chuquicamata porphyry Cu-Mo deposit in northern Chile is truncated on its west side by a N-S-trending regional fault (the West fault), juxtaposing its ore to a relatively barren granodiorite (Fortuna Igneous Complex). There has been much speculation about the fate of, and extensive exploration for, the “missing half” of the deposit. It has been proposed that the west side of the fault hides the ore at depth, or that it was uplifted and the ore eroded; however, regional geologic mapping suggests that the West fault had a postore left-lateral strike-slip displacement of ca. 35 km. Accordingly, exploration, so far unsuccessful, has been focused in an area 35 km south near the Loa River and the city of Calama. In 1989, the Mina Ministro Hales (MMH) deposit was unexpectedly discovered west of the fault, under thick gravels, only 7 km south of the main mine. A previous study at MMH had suggested that mineralization was as old as 39 Ma, hence its ores were correlated with deposits of that age near Calama. Our recent U-Pb and Re-Os dating indicates that MMH mineralization was formed between 35 and 31 Ma, thus concurrently with Chuqui. The geochemistry of host Triassic and Eocene porphyry intrusions, ore mineralogy, and common Pb isotope ratios of hypogene sulfides at MMH and Chuqui proper are indistinguishable. Fluid inclusion data for paragenetically early porphyry assemblages at MMH closely mimic Th-salinity data from earlier studies at Chuqui, showing little or no evidence of boiling but indicating widely fluctuating confining pressures, compatible with hydraulic fracturing and fault movement during and after mineralization at a minimum initial lithostatic constraint of 5- to 8-km depth. We propose that MMH is a sheared-off portion of Chuqui, wedged in a fault cymoid loop and spared the full 35-km displacement of the West fault.

Tin isotope geochemistry of cassiterite may allow for reconstructing the fluid evolution of tin ore deposits. Here, we present cathodoluminescence (CL) imaging, trace element, and in situ Sn isotope compositions of two cassiterite crystals from an early and a relatively late stage of ore formation of the Xiling vein-style Sn deposit, southeastern China, by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). Our results show that the early-stage cassiterite from a high-temperature feldspar-stable hydrothermal environment has core, mantle, and rim zones with a systematic decrease in δ124/117Sn3161A (relative to the Sn standard NIST 3161 A) from +0.38 ± 0.06‰ in the crystal core to –0.12 ± 0.06‰ (2 SE) in the mantle zone. This isotopic evolution, also paralleled by a decrease in Ta content by two orders of magnitude, suggests a fluid batch evolving toward isotopically lighter Sn. The very rim zone of this crystal has an intermediate tin isotope composition at about +0.05‰ δ124/117Sn3161A, combined with elevated Ta, suggestive of a second fluid batch. The late-stage cassiterite crystal from a muscovite-stable hydrothermal environment has a core with an evolved Sn isotope composition at about –0.15‰ δ124/117Sn3161A combined with low Ta, and a rim with heavier Sn isotope compositions up to +0.30 ± 0.08‰ δ124/117Sn3161A and higher Ta contents. As for the early-stage crystal, two different fluid batches must be involved in the formation of this crystal. Our pilot study highlights the advantage of spatially resolved analysis compared to conventional, solution Sn-isotope analysis of bulk cassiterite crystals. The Sn isotope variations at the microscale reveal the complexity of cassiterite crystal growth by a combination of closed- and open-system fluid evolution and isotope fractionation.

The Troodos ophiolite is widely accepted to be a fragment of Mesozoic oceanic crust, which uplifted during Alpine orogeny, due to the collision of Eurasia and Africa (Gass and Masson-Smith, 1963; Vibetti, 1993; Adamides, 2011; Antivachis, 2015). It belongs to supra-subduction ophiolites, which probably set up during subduction initiation associated with back-arc spreading (Pearce, 1975; Rautenschlein et al., 1985; Pearce and Robinson, 2010; Martin et al., 2019). The Troodos ophiolite is mentioned to be one of the most well studied and well-preserved ophiolitic sequences (Moores and Vine, 1971; Benn and Laurent, 1987; Patten et al., 2017), presenting significant Cyprus-type sulphide deposits (Constantinou and Govett, 1973; Adamides, 2014).Cyprus-type deposits are generally, considered as mafic type volcanogenic massive sulfide deposits (VMS), mainly rich in copper and subsidiary zinc, with average grade of 1.3 ± 1.1% Cu and 0.8 ± 0.4% Zn (Hannington et al., 1998; Barie and Hannington, 1999; Patten et al., 2016). VMS deposits are formed in the sea floor, along mid-ocean ridges, by the circulation of high temperature hydrothermal fluids, which their source is seawater (Gillis and Robinson, 1988; Richards et al., 1989; Patten et al., 2017; Martin et al., 2019). In many different regions along the Troodos ophiolite, the VMS deposits are covered by thick, Fe oxides enriched gossans (Bear, 1960; Herzig et al., 1991). In general, those can be formed, when the VMS deposits are exposed to weathering and oxidizing conditions (Herzig et al., 1991), but still the conditions for their formation are debated. The studied gossans from Troodos ophiolite are variegated due to the presence of white silica, red hematite and yellow jarosite. Gossans are always a very interesting part of the ophiolitic sequence from an economic point of view, as they present not only significant amount of extractible copper and zinc, but also, gold and silver (Bear, 1960; Herzig et al., 1991).We aim to examine the major and trace elements of gossans, which have been collected from different mines (West Apliki, Skouriotissa and Agrokipia mines) of Troodos ophiolite, and define their enrichment or depletion in copper and zinc, by coupling copper and zinc stable non-traditional isotopes. We combined copper with zinc isotopes in a very novel and original approach in order to give information about the conditions prevailing in the system of interest. As many authors mentioned before, supergene enriched environments are the best places to examine the behavior of Cu isotope fractionation under the weathering conditions of ore deposits (Mathur et al., 2008). On the other hand, Zn isotopes are not redox sensitive, but pH-sensitive (Pons, 2016). By coupling them, it can bring light in understanding the way, the nature of fluids that led to gossans formation and their enrichment in copper and zinc in different locations of Troodos ophiolite.