Sulfide Assemblages Research Articles

Genesis of the Haopinggou breccia-hosted Au deposit, western Henan Province, China

Breccia-hosted Au deposits within the North China Craton (NCC) exhibit a complex genesis, with some breccias being genetically linked to Au mineralization and others unrelated. Understanding the origin of these breccias is crucial for elucidating the genesis of associated ore deposits and guiding exploration strategies. The Haopinggou deposit in the Xiong’ershan district, on the southern margin of the NCC, comprises quartz-carbonate vein-hosted Ag–Pb–Zn–Au deposits and related breccia pipe in metamorphic rocks of the late Archean to early Paleoproterozoic Taihua Group. The origin of the Haopinggou breccia is crucial to understand the Xiayu Ag-Pb-Zn-Au mineralization (5640 t Ag). In this study, we evaluate the genetic links between breccia and Ag-Pb-Zn-Au mineralization, with new insights obtained from the Haopinggou deposit characteristics, breccia characteristics, breccia-hosted Au mineralization, and isotopic data, which refine our understanding of Haopinggou Ag-Pb-Zn-Au hydrothermal systems and exploration models in discordant breccia pipes. Recent underground tunnel surveys and drill-core logging reveal a close spatial link between the breccia and hidden granite porphyry. Juvenile magmatic clasts (granite porphyry) and cement (K-feldspar and quartz crystallized from granite porphyry) are present in the breccia pipe above a granite porphyry apophysis, indicating that the breccia was formed by phreatomagmatic brecciation caused by emplacement of the granite porphyry. Fluidization at the cm- to 100-m-scale reveals that the movement direction of clasts inside the breccia pipe was from northwest to southeast after crypto-explosion, creating a northwest-trending breccia zone. Anhedral monazite (131.2 ± 7.6 Ma) encapsulated in pyrite from the breccia constrains the upper limit of brecciation. The δ34S values of pyrite in rock powder and hydrothermal cements range from 3.8 ‰ to 5.3 ‰ (mean: 4.8 ‰) and 2.7 ‰ to 7.5 ‰ (mean: 5.2 ‰), respectively, with δ34S-sphalerite in hydrothermal cement ranging from 5.7 ‰ to 6.1 ‰ (mean: 5.9 ‰) and δ34S-chalcopyrite ranging from − 0.9 ‰ to 5.6 ‰ (mean: 2.9 ‰). The S isotope characteristics of vein-hosted and breccia-hosted mineralization zones are consistent, with complete alignment of the sulfide assemblages and alteration features. These pieces of evidence collectively indicate that both vein- and breccia-hosted mineralization zones are products of magmatic activity. The metallogenic model for the Haopinggou breccia pipe underscores its unique formation mechanism, driven by pre-existing northwest-striking structural weaknesses and fluidization, indicative of a predominant northwest–southeast clast movement, and suggesting the potential for deep-seated porphyry-type Au mineralization.

SIMS U-Pb dating of baddeleyite-zircon pairs in mafic rocks to determine the ages of magmatic mineralization and hydrothermal remobilization in a Ni-Cu-(PGE) deposit

Ni-Cu-(PGE) sulfide deposits associated with mafic–ultramafic rocks are the most important sources of Ni and platinum-group elements (PGE) in the world. These deposits also contain significant amounts of Cu. Such deposits are generally considered to have formed by multiple stages of primary magmatic concentration and secondary hydrothermal remobilization. However, constraining the ages of Ni-Cu-(PGE) sulfide deposits has proven challenging, particularly those that have experienced post-magmatic hydrothermal overprinting and remobilization. The lack of robust geochronology data has hindered understanding of the geological controls on this important type of mineralization. The Chibaisong Ni-Cu-(PGE) sulfide deposit in the North China Craton is characterized by disseminated and net-textured ores formed by magmatic processes and overprinted by hydrothermal Cu-rich vein stockwork. The Cu-rich vein stockwork is fracture-controlled, and contains a mineral assemblage of Ni-Cu sulfides (chalcopyrite, pyrrhotite, pentlandite), amphibole and quartz. Chalcopyrite in the hydrothermal stockwork is relatively depleted in Ni but enriched in Ag and Cd compared with disseminated magmatic chalcopyrite, typical of hydrothermal superimposed ores as documented elsewhere. We identified baddeleyite-zircon pairs associated with Ni-Cu sulfides in hydrothermal superimposed ores of the Chibaisong deposit, in which the baddeleyite is unequivocally of primary igneous origin whereas the zircon represents the replacement product of baddeleyite during hydrothermal alteration. In situ SIMS U-Pb dating of baddeleyite and zircon yielded weighted mean 207Pb/206Pb ages of 2181 ± 21 Ma and 1892 ± 33 Ma, respectively, interpreted as the timing of magmatic mineralization and subsequent hydrothermal remobilization of the Ni-Cu-(PGE) deposit. Our results explain the large discrepancies in sulfide Re-Os ages previously obtained from this deposit. This study demonstrates that on the basis of detailed BSE imaging, in situ SIMS U-Pb dating of baddeleyite-zircon pairs can provide robust age constraints for both magmatic mineralization and hydrothermal remobilization of Ni-Cu-(PGE) sulfide deposits hosted in mafic–ultramafic intrusions, although further studies are needed to test whether the formation of such deposits commonly entails multiple stages of hydrothermal remobilization. Since baddeleyite or baddeleyite-zircon pairs are common accessory minerals in Ni-Cu-(PGE)-bearing mafic–ultramafic rocks, the dating approach employed in this study may be applicable to similar deposits elsewhere.

LA-ICP-MS Analyses of Sulfides from Gold-Bearing Zones at the Perron Deposit, Abitibi Belt, Canada: Implications for Gold Remobilization through Metamorphism from Volcanogenic Mineralizations to Orogenic Quartz–Carbonate Veins

The Perron deposit, located in the northern part of the Archean Abitibi belt, bears some of the highest gold-grade mineralization for orogenic-vein-type deposits worldwide (High-Grade Zone: HGZ). More than 13 gold-bearing zones with different sulfide assemblages, hydrothermal alterations, and gold grades have been recently outlined, and they range from volcanogenic to orogenic in origin. In addition, seven zones are hosted in a restricted volume of ~1 km3, which is called the Eastern Gold Zone. Pyrite, sphalerite, pyrrhotite, and chalcopyrite—each from a different gold-bearing zone—were analyzed with LA-ICP-MS to decipher their genetic links, mineralizing processes, and temperature of formation. The temperatures calculated with the sphalerite GGIMFis thermometer range from 348 to 398 °C. All gold-bearing zones recorded volcanogenic hydrothermal inputs at different intensities, manifested by pyrrhotite. Pyrite was late-metamorphic and related to the orogenic gold system induced by the contact metamorphism of amphibolite facies. The pyrrhotite grains had very homogeneous trace element signatures in all zones, which is a characteristic of metamorphic recrystallization, exhibiting a loss of mobile elements (Au, Te, Bi, Tl, Sn, W, In) but high concentrations of Ni, Co, and As. Conversely, the pyrite was systematically enriched with all elements depleted from pyrrhotite, bearing five specific signatures of element enrichments: W, Tl, Sn, In-Cd-Zn, and Bi-Te-Au. For gold-rich zones (e.g., the HGZ), gold was linked to the Bi-Te-Au signature of pyrite, with Bi enrichment occurring at up to 72,000 times the background level in Archean shale pyrite. It was concluded that gold was transported, at least in part, as Bi-Te melts in the previously documented non-aqueous orogenic fluids, hence accounting for the very-high-grade gold content of the HGZ. Genetically, the metamorphism of primary gold-bearing volcanogenic mineralizations was the main source of gold during the overprinting of amphibolite (600 °C) in a metamorphically induced orogenic mineralizing event. A strong volcanogenic pre-enrichment is considered the main factor accounting for the gold endowment of the Eastern Gold Zone.

Co-Ni distribution and Re-Os isotopic age of the Wuxing complex in the Central Asian orogenic Belt: Implications for sulfide mineralization in Alaskan-type complexes

Alaskan-type mafic–ultramafic complexes have been recognized as potential hosts of magmatic Ni-Cu sulfide deposits. However, the distribution and controlling factors of ore-forming metal elements like Co and Ni within these complexes remain poorly understood. This study offers comprehensive petrological observations and quantifies the Co and Ni contents of silicate minerals and sulfides in the Wuxing complex, the oldest Alaskan-type complex hosting a distinctive PGE-rich Ni-Cu sulfide deposit in the Central Asian Orogenic Belt. The Co-rich minerals, including cobaltite and pentlandite, occur as inclusions or interstitial grains in other mineral phases. Among the sulfide assemblages (pyrrhotite, pentlandite and chalcopyrite), pentlandite exhibits the highest 3.59 ∼ 5.98 wt.% of Co and 28.7 ∼ 32.7 wt.% of Ni contents, with the Co contents being 2 to 10 times higher than those in magmatic Ni-Cu sulfide deposits. Clinopyroxene and hornblende in the Wuxing complex display lower Co and Ni contents compared to those in sulfide-free rocks of typical Alaskan-type complexes. This could be ascribed to the reduction in Co and Ni contents in evolved magmas following sulfide segregation. Additionally, lack of olivine and chromite crystallization would elevate Co and Ni contents in silicate magma and promote the sulfide mineralization in the Wuxing complex. The Re-Os isotopic dating in ore samples at 596 Ma, combined with previously zircon U-Pb ages of 510 ∼ 517 Ma, reveals that long-term magmatism would facilitate mineralization in the Wuxing complex. Our investigations provide a new insight of mineral crystallization for understanding of magmatic Ni-Cu-PGE sulfide mineralization in Alaskan-type complexes.

Cobalt remobilization during tectonic–hydrothermal overprinting: A case from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt, China

Stratiform Cu-Co deposits hosted in (meta-) sedimentary and volcaniclastic rocks contribute two-thirds of the global Co supply. However, the mechanisms driving Co remobilization during tectonic-hydrothermal overprinting events remain poorly understood. As a dominant Co repository, pyrite can provide valuable insights into mineralization history due to its refractory nature. Here, we present the first micro-analytical investigation of pyrite from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt. Ore textures indicate that Co mineralization is attributed to two distinct stages: primary enrichment and subsequent overprinting processes. The former is characterized by pyrite (PyI with up to 3.92 wt% Co) remnants exhibiting oscillatory zones, while the latter is marked by deformation of pyrite (PyII) ores. Three overprinting episodes, namely Da, Db, and Dc, are further distinguished according to varying extents of deformation and mineral assemblages. The Da is characterized by synkinematic PyIIa (up to 4.18 wt% Co) augens, which were most likely formed via pressure–solution mechanism. The Db is represented by polygonal PyIIb (up to 4.75 wt% Co) and siegenite with 120° triple–point junctions. The random orientation and rare intragrain misorientation of cobaltiferous sulfides at Db suggest their formation by recrystallization without plastic strains. The Dc resulted in the formation of Co ± As–rich PyIIc (up to 5.36 wt% Co) along with minor occurrence of cobaltite–gersdorffite, pyrrhotite (up to 1.25 wt% Co), and marcasite (up to 1.28 wt% Co). The PyIIc replacing PyI underscores the role of fluid-coupled dissolution and precipitation during fluid–rock interactions in the formation of these cobaltiferous sulfide assemblages at Dc. The presence of PyIIc infilling within the PyI fissures, in conjunction with the transition from siegenite to cobaltite–gersdorffite, suggests a shift towards low fO2 and low temperature conditions under relatively brittle setting. There is a discernible disparity in sulfur isotope compositions between the two mineralization stages. The PyI exhibits a narrow range of δ34SV–CDT values from –2.14 to 1.35 ‰, indicating a magmatic sulfur origin. In contrast, PyII displays a wide δ34SV–CDT range of –5.22 to 6.16 ‰, suggesting an involvement of strata sulfur during the overprinting stage. Monazite U-Pb dating has effectively constrained two mineralization events. The ca. 453 Ma age implies a potential correlation of the primary Co mineralization with the Late Ordovician to Early Silurian exhalative-syngenetic processes in a Proto–Tethyan-related post–collisional extension setting. Conversely, the ca. 190 Ma age indicates that Co remobilization was instigated by the early Mesozoic ductile–brittle deformation associated with the Paleo-Tethyan orogenesis. Finally, geochemical modeling was performed by simulating the interaction of a Co-rich acidic, reducing fluid with typical quartz-albitite rocks. The simulations demonstrate the appearance of independent Co minerals such as Co-pentlandite during the reaction progression, greatly supporting ore upgrading via tectonic-hydrothermal overprinting.

Copper and zinc isotopic variations in Ni-Cu-PGE ores of the Noril’sk Province (Russia)

Research subject. Mineral assemblages of sulfides from massive and disseminated sulfide nickel-copper-platinum-group element (Ni-Cu-PGE) and low-sulfide PGE ores of the Noril’sk Province, which hosts the richest complex deposits of platinum-group metals, nickel, and copper. Aim. In order to identify sources of ore material and explore new forecasting approaches for Ni-Cu-PGE deposits, we study the Cu- and Zn isotopic compositions of sulfides from economic Kharaelakh and Noril’sk-1 intrusions containing unique and large sulphide Ni-Cu-PGE deposits (Oktyabr’sk and Noril’sk-1, respectively), subeconmic Zub-Marksheider and Vologochan intrusions containing small- to medium-size Ni-Cu-PGE deposits, and non-economic Nizhny Talnakh and Nizhny Noril’sk intrusions containing low grade disseminated Ni-Cu mineralization. Results. The analyzed samples are characterized by sulfide mineral assemblages, which contain mainly chalcopyrite, pyrrhotite, pentlandite, troilite, cubanite, and galena. Sulfide Ni-Cu-PGE ores of the Oktyabr’sk and Noril’sk-1 deposits, associated with economic intrusions (i.e., Kharaelakh and Noril’sk-1), demonstrate distinct δ65Cu values from –2.42 to –1.40‰ and from –0.33 to 0.60‰, respectively, which differ from the δ65Cu values for sulfides from other Ni-Cu-PGE deposits and ore occurrences of the Noril’sk Province (data comprise 36 analyses). We note that the Cu-isotopic composition for sulfide minerals of massive and disseminated ores from the Kharaelakh intrusion has similar “isotope-light” characteristics. The most pronounced shift towards “isotope-heavy” copper was found in the horizon of low-sulfide PGE ores of the Noril’sk-1 intrusion (δ65Cu = 0.51–0.60‰). The isotopic composition of Zn (δ66Zn) for the studied sulfide samples from economic, subeconomic, and non-economic intrusions, with the exception of one sample (0.73 ± 0.14‰), is characterized by similar “isotope-light” values (from –0.65 to –0.03‰). Conclusions. The revealed variations in the Cu- and Zn-isotopic composition in the studied sulfide assemblages from all types of ores reflect their primary characteristics; however, for the unique Oktyabr’sk Ni-Cu-PGE deposit, characterized by the most “isotopically light” composition of copper (δ65Cu = –1.9 ± 0.34‰), the possibility of assimilation of an external source of Cu during the formation of sulfide Ni-Cu-PGE ores cannot be excluded. The combined use of Cu and Zn isotopic parameters proved to be a weakly informative predictive indicator for the detection of high-grade sulfide ores, primarily due to the similarity of the Zn isotopic composition of the ore material in all investigated intrusions of the Noril’sk Province.

Partitioning of highly siderophile elements between monosulfide solid solution and sulfide melt at high pressures

Base metal sulfides (Fe–Ni–Cu–S) are ubiquitous phases in mantle and subduction-related lithologies. Sulfides in the mantle often melt incongruently, which leads to the production of a Cu–Ni-rich sulfide melt and a solid residue called monosulfide solid solution (mss). Even though peridotite-hosted sulfides, which tend to be more Ni-rich, are likely completely molten at mantle potential temperatures, the same is not true for eclogite-hosted Ni-poor, Fe-rich sulfides. Because of this, solid crystalline mss may persist at higher pressures and equilibrate with co-existing sulfide melt along colder geotherms, like those associated with subduction zones. Because highly siderophile elements (HSE—Pt, Pd, Rh, Ru, Os, Ir, and Re) are known to fractionate as a result of mss/sulfide-melt equilibrium, the persistence of an mss/sulfide-melt assemblage to higher pressures may lead to the fractionation of these elements during the subduction process. In this contribution, we carried out an experimental investigation of the partitioning behavior of the HSE, as well as Cu and Ni, between mss and sulfide melt over a pressure and temperature range relevant to equilibration between Earth’s surface and transition zone depths (0.1 MPa to 14 GPa; 930–1530 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C), and variable Ni contents in sulfide. Results show that at higher pressures, the HSE are considerably less fractionated as a result of mss and sulfide melt equilibrium compared to lower pressure conditions. This is exemplified by a lowering of the Dimss/melt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{i}^\\mathrm{mss/melt}$$\\end{document} for the more compatible HSE (Ru, Os, Ir, Rh and Re) from around 10 at 0.1 MPa to just above or below unity at 14 GPa. Moreover, the higher the Ni content of the bulk sulfide assemblage, the larger the degree of change in the magnitude of HSE fractionation seen over the pressure range studied. The exchange coefficient (KDRu-Pt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_D^{\ extrm{Ru}-\ extrm{Pt}}$$\\end{document}) between highly compatible HSE (Ru) and less compatible Pt illustrates a notable contrast. In the Ni-poor composition (E1), KDRu-Pt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_D^{\ extrm{Ru}-\ extrm{Pt}}$$\\end{document} changes from 27 at 0.1 MPa to 6 at 14 GPa. In contrast, the Ni-rich composition exhibits a broader range, with KDRu-Pt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_D^{\ extrm{Ru}-\ extrm{Pt}}$$\\end{document} ranging from 150 to 17 across the same pressure interval. Our results highlight key differences between experimental data obtained at lower and higher pressure, and how composition, namely the Ni content of sulfide, affects HSE partitioning behavior.

The base metal sulfide and Ni–Co arsenide-bearing veins of Valsassina, Lombardy, Italy: a preliminary study

Abstract Valsassina (Lombardy, Northern Italy) is located in the Lombard Southern Alps and is characterised by the presence of a metamorphic basement, by a major late Variscan intrusive complex and by Carboniferous–Permian volcano-sedimentary cover units. These rocks host a pervasive system of inadequately studied mineralised veins. These veins are characterised by base metal (Pb, Zn, Cu and Fe) and complex polymetallic assemblages. In this study, we have investigated the ore textures, mineral compositions of sulfides and sulfosalts (by EMPA–WDS and LA–ICP–MS analyses), and stable isotopes (C and O) in carbonate gangue minerals of various mineralised veins to determine the conditions of deposition of these ore deposits. Two different vein families can be recognised in Valsassina: NNW–SSE veins characterised by a complex polymetallic sulfide–sulfosalt assemblage, also with Ni–Co–Fe arsenides and other Ag–Bi-bearing minerals; and NE–SW veins with a simpler, base metal sulfide assemblage. The Ni–Co-bearing NNW–SSE veins have some distinctive features of the ‘five-element vein’ type deposits, with the Ni–Co–Fe arsenide ore stage pre-dating a sulfide-tetrahedrite-dominated ore stage. LA–ICP–MS data for pyrite and sphalerite, and stable isotopic compositions (C and O) of the carbonate gangue minerals, show no clear differences between the two families of veins, which are probably linked genetically. The isotopic compositions of the Valsassina vein carbonates are closely comparable with the signature of several major five-element ore districts. Preliminary temperature estimates for the Valsassina vein systems were based on the sphalerite composition, applying the GGIMFis geothermometer. The estimated temperatures for the sulfide-dominated ore stage post-dating the Ni–Co minerals precipitation range between 100 and 250°C. The crosscutting relationships, observed for all the veins with the host rocks, suggest a possible late to post Variscan (late Permian) age, making these vein systems comparable with other late–post Variscan polyphase hydrothermal events affecting large sectors of the Southern Alpine domain.

Textural and chemical variations of sphalerite in the Giant Shuangjianzishan Ag-Pb-Zn deposit, South Great Xing’an Range, China: Implications for ore-forming processes

The Shuangjianzishan vein-type Ag-Pb-Zn deposit (145 Mt of ore grading 128.5 g/t Ag, 1.8 wt% Pb and 0.5 wt% Zn) in the South Great Xing’an Range (NE China) is hosted in NW- and NE-trending veins crosscutting the Lower Permian Dashizhai Formation, which is intruded by a granite porphyry. Although Ag-Pb-Zn sulfide mineralization has been extensively studied, the detailed ore-forming processes remain unclear. We have identified four stages of sulfide assemblages containing three generations of sphalerite: (1) Quartz arsenopyrite sphalerite (Sp1) stage; (2) Galena Ag-minerals sphalerite (Sp2) stage; (3) Ag-minerals pyrrhotite sphalerite (Sp3) stage; and (4) Pyrite calcite stage. Stages 2 and 3 are economically important. The textures of Sp1, Sp2, and Sp3 directly record the ore-forming processes, and the mineralization of silver shows an evolution trend from simple sulfides to complex sulfosalts. LA-ICP-MS trace element analyses showed that the Sp1 contains low content of silver and other trace elements (Fe, Mn, Sn, Cu, and Pb), indicating an anoxic to an euxinic environment. Stage 2 contributed largely to the silver endowment, with relatively high silver content in sphalerite or Ag-bearing mineral inclusions in Sp2a, Sp2b, and galena. Most of the silver minerals were deposited during stage 3, with sulfide and sulfosalt assemblages (e.g., pyrargyrite + canfieldite + tetrahedrite with minor pyrrhotite) replacing Sp2b. Selenium is significantly enriched in Sp3 and selenium-rich canfieldite from Stage 3. Sulfur isotopes determined by in situ LA-multicollector (MC)-ICP-MS analyses of sphalerite vary significantly from −9.6 to 2.2 ‰ (δ34SSp1 = -4.1 ∼ 1.1 ‰; δ34SSp2 = -4.2 ∼ 2.2 ‰; δ34SSp3 = -9.6 ∼ -2 ‰). Sulfur was possibly derived from the magmas forming the granite porphyry (δ34S = 1.4 ‰) and the magmatic sulfur reservoir was oxidized by mixing with the Dashizhai stratum sulfur (δ34S: −4.9 to −6.5 ‰). This resulted in lowering of the fluid δ34S value during the deposition of Sp3. The textural, chemical and isotopic data indicate distinct ore-forming episodes at Shuangjianzishan. We suggest that the deposition of abundant Ag-bearing minerals was induced by a new volume of Ag-rich ore-forming fluids and triggered by extensive decompression and cooling during Stage 3. The sulfur isotope and chemical geothermometers suggest the involvement of relatively high-temperature (>330 °C) hydrothermal fluid during Stage 2. Unlike a single cooling mineralization process, the superposition of relatively high-temperature mineralizing fluids may be an important factor in the large-scale Ag-Pb-Zn mineralization at Shuangjianzishan.

Low temperature alteration of massive sulphides below the weathering front

Alteration of magmatic sulphides within the regolith, or soil profile, is well documented, but alteration at depth, where meteoric fluids may infiltrate fresh rock adjacent to faults, is less studied and poorly understood. Yet such alteration may affect the mineralogy of the magmatic sulphides, and the characteristics of this alteration provide insights into the distribution and timescales of fluid flow and redox processes within the upper crust.Pentlandite [(Fe,Ni)9S8] is a Ni-rich sulphide mineral, found in magmatic sulphide assemblages with chalcopyrite (CuFeS2) and pyrrhotite (Fe1−xS). Pentlandite associated with massive sulphides from apparently fresh rock at the Mawson Deposit, Western Australia, shows in-situ partial replacement by violarite (nominally FeNi2S4), whereas pentlandite associated with adjacent disseminated sulphides is unaltered. Petrographic, geochemical, and in-situ sulphur isotope analysis reveals that violarite has variable Fe:Ni ratios. Constant volume and constant sulphur mass balance calculations indicate an overall loss of Ni and other metal cations during violarite formation. In addition, newly formed violarite has a 34S-depleted isotopic composition compared to precursor pentlandite. Altered pentlandite (δ34S = 1.02 ‰) is isotopically fractionated relative to co-existing pyrrhotite (3.44 ‰) and chalcopyrite (3.15 ‰), in contrast to the unfractionated sulphur isotope ratios expected for co-crystallising magmatic sulphides. These features are interpreted as a consequence of electrochemical alteration within electrically connected massive sulphides and addition of isotopically light sulphur derived by bacterial sulphate reduction. Based on previous evidence of deep-seated fluid flow along long-lived regional faults, the alteration is plausibly associated with Cenozoic neotectonic deformation and short-lived pulses of fluid flow with durations of hundreds to thousands of years. Similar petrographic evidence of deep alteration in apparently fresh sulphides from samples across the regional study area indicate this could be an under-reported feature in magmatic sulphides globally.

Micro- to nanoscale textures of gold in arsenopyrite and scorodite from the As-Au-Bi assemblage of Drenjak locality (Serbia)

Arsenopyrite and pyrite are important carriers of Au that is present in the form of microscopic and “invisible” gold. Such gold can be expected to be released upon the process of oxidation of these sulfides. In studied gold mineralization at Drenjak, related to the granitoids of the Oligocene-Miocene Kopaonik Ore District, the main arsenopyrite-pyrite-(bismuthinite) sulfide assemblage was formed in the quartz bodies and partly replaced by scorodite (FeAsO4·2H2O) and Bi-arsenate. With only up to 5 ppm of gold recorded by LA-ICP-MS, aforementioned sulfide minerals are here practically free from lattice-bound gold. Native gold is present in the mineralization, generally ranging in grain size from 20 µm down to the nanoparticles, as revealed by TEM. It is mainly hosted by arsenopyrite and scorodite. In arsenopyrite, gold is polycrystalline and consists of nanocrystallites 20–30 nm in size. It was deposited after arsenopyrite, healing its cavities and microcracks, often associated with native bismuth and bismuthinite. The abundance of gold and Bi minerals correlates with the presence of scorodite. Two types of gold are present in scorodite and Bi arsenate: i) prevailing relict Au grains retained after arsenopyrite oxidation, ii) colloidal-like gold co-precipitated with the arsenates. Based on our observations, we additionally present and discuss indications of low-temperature hydrothermal origin of scorodite, formerly known only as a weathering product

Geology and sulphide geochemistry of the Ni-Cu-Co mineralisation of the Espedalen Complex, Norway: Constraints for the distribution of magmatic sulphides within a variably deformed anorthosite suite

The Espedalen Complex is located in the eastern portion of the Jotun–Valdres Nappe Complex, south-central Norway and comprises three main suites (jotunite-charnockite-augengneiss; main anorthosite–ultramafite–norite; and gabbronorite suites) formed between 1520 and 1500 Ma. The anorthosite-ultramafite-norite suite hosts Ni-Cu-Co mineralisations grouped as: i) ‘primary sulphides’ referring to undeformed occurrences with magmatic textures; ii) ‘deformed sulphides’ which include dismembered ore bodies; and iii) ‘remobilised sulphides’ which comprise thin sulphide veinlets indicating remobilisation. The ‘primary sulphides’ characterise the deposits of Dalen, Megrund, Trona, Veslegruva and Melgard, whereas the ‘deformed sulphides’ characterise the deposits of Stormyra, Storgruva, Andreasberg, Niccoline, Gråhøa, Jørstad and Grimstjønna. The largest mineralisations are the Dalen and Stormyra deposits, which host 5.3 Mt @ 0.29% Ni, 0.12% Cu and 0.02% Co, and 1.01 Mt @ 1.09% Ni, 0.48% Cu and 0.04% Co, respectively. This study provides the first systematic characterisation of the different Ni-Cu-Co mineralisations from the Espedalen Complex.Primary sulphides are typically hosted by medium-grained poikilitic olivine-orthopyroxenite, whereas deformed sulphides are hosted within shear zones, commonly within anorthosites. Primary and deformed occurrences comprise disseminated, net-textured and massive sulphides. The disseminated and semi-massive to massive sulphide ores from different localities comprise pyrrhotite and pentlandite with minor chalcopyrite. Post-magmatic sulphide alteration and recrystallisation (notably at Stormyra Deposit) are marked by variable (5 to 30%) development of pyrite, which replaces pyrrhotite-dominated masses. The remobilised sulphide assemblages are associated with retrograde silicates (e.g., chlorite and talc). Overall, primary and deformed sulphides can be divided into three main compositional groups based on metal tenors and the concentration of platinum-group elements (PGE): (i) Stormyra, Andreasberg (both deformed) and Megrund (primary) have the highest Ni and Cu tenors (7 to 8.5% and 3 to 3.5%, respectively) and no IPGE (Ir-group PGE) depletion relative to PPGE (Pt-group PGE); (ii) Dalen, Trona, Melgard (primary), Jørstad, Gråhøa and Grimstjønna (deformed) are similar regarding PGE distribution but have lower Ni and Cu tenors (4 to 5.5% and 1.6 to 3%, respectively); and (iii) Niccoline, Storgruva (deformed) and Veslegruva (primary) have comparable Ni and Cu tenors to group (ii), but are IPGE-depleted relative to PPGE (i.e. fractionated PGE distribution). The tenors vary from 0.3 to 2% Ni and 0.25 to 1.5% Cu in remobilised sulphides. Variations in metal tenors are interpreted to reflect a combination of different, but invariably PGE-depleted, parental magmas and variable R-factor regimes (R-factor varying from 350 to 700) during ore formation. The parental magmas can be modelled as the product of 15% mantle melting followed by approximately 2% crystallisation with sulphide removal, which lead to a PGE-depleted nature. Redistribution of sulphides during deformation of the Espedalen Complex seems to have taken place at large and small scales. Large-scale tectonic displacement has no major geochemical impact, whereas local remobilisation yielded sulphide veinlets with low metal tenors. We support that assessing if other geological domains, previously assigned to the Jotun-Valdres Nappe, are correlated or not with the Espedalen Complex is essential for further expanding this prospective area as these terrains could represent potential targets for Ni-Cu-Co deposits.

Tectonomagmatic setting and magmatic Cu-PGE metallogeny during the late Neoproterozoic in the Eastern Kunlun Orogen, NW China: Insights from the Hatu Cu-Pt-Pd-bearing mafic-ultramafic intrusion

The Hatu Intrusion is the first late Neoproterozoic Cu-PGE-bearing mafic–ultramafic intrusion in the Eastern Kunlun Orogen. The No. I intrusion with the largest scale and best mineralization delineated six Cu-Pt-Pd ore/mineralized bodies with Cu and Pt + Pd grades of 0.44–1.10% and 0.30–1.00 g/t, respectively. Chalcopyrite-bornite-(pyrrholite) is a common sulfide assemblage that disseminates in ultramafic rocks (e.g., olivine websterite, liherzolite) enriched in chrysolyte (Fo = 76–81) and orthopyroxene (En = 68–69). Zircons from the gabbro show magmatic zircons with blurred oscillatory zoning and Th/U ratios of 0.31–0.71 and yield a weighted mean age of 556 ± 4 Ma, indicating mafic–ultramafic magmatism with Cu-PGE mineralization in the late Neoproterozoic. The Hatu Intrusion exhibits the properties of continental basalt (e.g., 87Sr/86Sr = 0.71317–0.72541, 143Nd/144Nd = 0.51202–0.51246, and Ta/Hf = 0.19–1.16), indicating the geodynamic setting of terminal continental rift-related extension in response to continuous magmatism under the Rodinia supercontinent break-up in the late Neoproterozoic. The primary magma originated from low-degree (∼15–20%) partial melting of slightly metasomatized depleted mantle without accumulating sufficiently radiogenic isotopes, resulting in zircon positive εHf(t) values (5.2–15.0) and some geochemical properties of arc magma. The mafic–ultramafic rocks have Sr-Nd-Pb isotope compositions between depleted mantle and II-type enriched mantle with negative εNd(t) values (-12.4 – −1.7), and their S/Se ratios are 1628–7189, among which most samples (S/Se = 4534–7189) are higher than that of mantle (S/Se = 2850–4350); the δ34S values of sulfide are 0.7–2.6 ‰ and slightly greater than that of depleted mantle (δ34S = -1.8‰). The above geochemical and isotopic signals reveal the contribution of crustal sulfur to the Hatu Intrusion, which is enough to trigger sulfide saturation of Cu-Pt-Pd.

Geology, sulphide geochemistry and geochronology of the Romsås Ni-Cu-Co mineralisation, Norway: Implications for ore formation and regional prospectivity

The Romsås intrusion, located in the southern portion of the Idefjorden lithotectonic unit, is part of a cluster of small to medium-sized mafic intrusive bodies which host NiCu sulphide mineralisation, referred to as the Indre Østfold metallogenic area. The Romsås is an almost 1 km-long intrusion with rounded shape, comprising undifferentiated quartz-norite with local orbicular texture. The assemblage, comprising cumulus orthopyroxene and plagioclase, is partly recrystallised and altered, thus orthopyroxene is partly replaced by amphibole, whereas plagioclase is locally replaced by epidote. Locally, garnet, amphibole, plagioclase and magnetite define a granoblastic texture as product of amphibolite-facies metamorphism. Several sulphide-rich lenses, normally up to 5 m wide, occur within the Romsås intrusion and display a sharp contact with the host noritic rocks. The textures vary from disseminated, net-textured and massive sulphides. The sulphide assemblage is homogeneous within the deposit and consists mainly of pyrrhotite, followed by pentlandite, and minor chalcopyrite, with variable alteration of pentlandite.This contribution provides the first systematic characterisation of the Romsås Ni-Cu-Co mineralisation and constraints for its formation and geodynamic setting. We have measured the concentrations of S, PGE, TABS+ (Te, As, Bi, Sb and Se) and other chalcophile elements in both whole rock and sulphide minerals from different ore textures, and UPb and Hf isotope systematics in zircon. The Ni and Cu concentrations in 100% sulphides are around 2% and 1%, respectively. The PGE concentrations in all sulphide-bearing samples are low, generally below 0.3 ppm, with Pt and Pd displaying a broad positive correlation and Pt/Pd ratios varying from 1 to 2. Different ore types are modelled to have formed from a mantle-derived parental magma with higher Cu/Pd ratios and lower Pd contents than mantle values, interpreted as the result of 5% prior crystallisation under sulphide-saturated conditions. Negative mantle-normalised Nb anomalies relative to Th, As and Sb suggest around 10% of assimilation of a component similar to lower crust by the parental magmas. Moreover, S/Se ratios greater than mantle values likely reflect the combined effect of Se depletion during early sulphide removal and external S addition upon crustal assimilation. The Romsås Ni-Cu-Co mineralisation likely formed as a result of sulphide segregation in response to external S addition during several magma pulses. The composition of the sulphide ores can be modelled by an R-factor of around 500. A significant budget of the chalcophile elements is not hosted by sulphide minerals and must be thus accounted for other discrete phases, such as platinum-group minerals. Nevertheless, trace elements distribution in sulphides supports only local remobilisation of chalcophile elements and records compositions comparable to sulphides from pristine NiCu deposits worldwide. Sulphide alteration may have led to exsolution of a parcel of chalcophile elements from sulphide lattice. A UPb zircon crystallisation age of 1551 ± 10 Ma, εHft values between ca. 3.5 and 6, and regional geological considerations suggest that the intrusion formed as part of an arc or back-arc rift setting in the Idefjorden lithotectonic unit. The Romsås sulphide mineralisation represents another example of magmatic sulphide deposit formed at an arc-related geodynamic setting, normally unconventional for the formation of this type of deposit. Therefore, our findings support that arc-related settings in Idefjorden lithotectonic unit, southern Norway, should also be regarded as potential for the formation of Ni-Cu-PGE deposits.

Geochemistry of indium in magmatic-hydrothermal tin and sulfide deposits of the Herberton Mineral Field, Australia

The Herberton Mineral Field in Northeast Australia hosts world class magmatic-hydrothermal Sn–W polymetallic deposits that are enriched in In. The Baal Gammon and Isabel deposits from the Herberton Mineral Field contains early tin, as cassiterite, overprinted by sulfide mineralization as chalcopyrite, sphalerite, galena, pyrrhotite, and stannite. We investigated the distribution of In in the sulfide ores from these two deposits, calculated the temperature of formation via sphalerite-stannite geothermometer, and deduced the physicochemical conditions favorable for enriching In in this mineralizing environment. The Baal Gammon deposit is dominated by chalcopyrite, with In contained in chalcopyrite, sphalerite, and stannite. The average In concentrations measured by EPMA in chalcopyrite, sphalerite, and stannite are 0.10, 0.68, and 0.92 wt%, respectively. Chalcopyrite, pyrrhotite, and sphalerite textures indicate that In incorporation occurred during exsolution from an intermediate solid solution of cubanite composition. The Isabel deposit is dominated by sphalerite associated with galena and contains only minor amounts of chalcopyrite. The average concentration of In in sphalerite from the Isabel deposit is 0.11 wt%. The stannite-sphalerite geothermometer indicates mineralization temperatures of ~ 290 °C at the Baal Gammon deposit, and ~ 307 °C at the Isabel deposit. At these temperatures, the physicochemical modeling suggests that stable In chlorine complexes occur in acidic conditions (pH < 3). These results when combined with the Eh–pH phase model of the sulfide assemblage further constrain the redox conditions during mineralization.

The carbonate-hosted Gortdrum Cu-Ag(±Sb-Hg) deposit, SW Ireland: C-O-Sr-Nd isotopes and whole-rock geochemical signatures

The Gortdrum Cu-Ag(±Sb-Hg) deposit, consisted of a fault-controlled orebody (3.8 Mt @ 1.19 % Cu and 25.1 g/t Ag) formed at the base of the Irish Midlands basin, in Lower Carboniferous rocks laterally time equivalent to Navan Group rocks hosting the giant Navan Zn-Pb deposit, and form the base of the Irish Midlands basin. The ore body is hosted on the hanging-wall of the Gortdrum Fault either along strata or within a wedge of brecciated carbonate rocks. Vertical zonation based on predominant host rock, ore textures, sulfide assemblages, and whole-rock geochemistry allowed the detailing of three ore types: a) the lower ore, representing Cu sulfides hosted within basal carbonated siliciclastic rocks; b) the upper ore, representing Cu, Cu-Sb, and Hg sulfides hosted within upper calcareous rocks and; c) the vein-associated ore, dominantly hosted in the more competent upper carbonate rocks. The origin of the deposit is unambiguously related to the development of the Gortdrum Fault and its associated permeability, which allowed basement/basin-derived fluids to react with carbonates and induce copper-silver mineralization. The mineralogy, ore shoot geometry, and geochemical association of Gortdrum are shared with classic Zn-Pb Irish-type deposits such as Navan, Lisheen, Silvermines, and Tynagh (sub-seafloor replacement). In these Irish-type deposits, copper-silver mineralization is associated with the late stage of Zn-Pb mineralization and shares a common geochemical footprint with Gortdrum of anomalous Ag, As, Sb and Hg. Additionally, the C-O and Sr-Nd isotope range of Gortdrum and Navan samples overlap, indicating that mineralization processes in both deposits were ineffective in modifying the original host-rock signature. These similarities suggest that Gortdrum could represent a variation of Irish-type mineralization where late-stage Cu-Ag-Sb-bearing fluids succeeded in forming a deposit. Hypothetical early-stage Zn-Pb fluids a) never existed; b) deposited disseminated sulfides in country-rocks, c) formed an undiscovered resource or, d) deposited ore concentrations that were eroded off.

Origin of high-Cr podiform chromitites from Kabaena Island, Southeast Sulawesi, Indonesia: constraints from mineralogy and geochemistry

ABSTRACT The East Sulawesi Ophiolite, one of the three largest ophiolites in the world, contains important podiform chromitites. However, the origin of these chromite deposits is not well constrained. Here, we present the detailed mineralogy and in situ chemistry of chromite and solid inclusions within chromite for podiform chromitites from the Kabaena Island, Southeast Sulawesi. Chromite grains have low TiO2 (0.17–0.27 wt%) and Al2O3 (13.4–15.1 wt%) contents and high Cr# [Cr/(Cr+Al), molar] of 0.70–0.74 and Mg# [Mg/(Mg+Fe2+), molar] of 0.69–0.75, which resemble those of other high-Cr podiform chromitites worldwide. The MORB-normalized patterns for some selected major-trace elements of chromite show slightly positive slopes from Al2O3 to Mn. Chromite-hosted silicate inclusions include olivine, clinopyroxene, orthopyroxene and amphibole and are characterized by higher Mg/Fe ratios than those of host peridotites. The geothermobarometry of chromite-hosted clinopyroxene-orthopyroxene pairs indicates that the estimated T-P conditions of the parental magma of the Kabaena chromitites are 950–1010°C and 7.0–8.4 Kbar. The extreme-Mg-rich olivine inclusions (Fo >96) with extremely high Ni (5300–8200 ppm) and Cr (1500–6700 ppm) contents are interpreted to have crystallized from high-Mg and Cr boninitic melts, and the Fo contents were then elevated by subsolidus re-equilibration (Fe–Mg and Fe–Ni exchange) with chromite. Sulfide inclusions contain base metal minerals containing millerite with rare pentlandite and chalcopyrite, and platinum-group minerals that include the laurite-erlichmanite series, Ir–Ni monosulfide, irarsite and cuproiridsite. This sulfide assemblage reveals that their parental magmas experienced the evolution of high T and low f(S2) to low T and high f(S2) from the early to late stage. Finally, combined with the palaeogeographic reconstruction in Sulawesi, we propose that the high-Cr chromitites in this region were formed by the reaction of depleted mantle and boninitic magma beneath a juvenile island arc, implying the initiation of a new subduction in the Miocene.

The distribution of trace elements in sulfides and magnetite from the Jaguar hydrothermal nickel deposit: Exploring the link with IOA and IOCG deposits within the Carajás Mineral Province, Brazil

The Jaguar nickel deposit represents an important and unconventional discovery of hydrothermal Ni resources (58.9 Mt @ 0.95% Ni) associated with magnetite and apatite within the Carajás Mineral Province, Northern Brazil. The Jaguar deposit shares several similarities with iron oxide copper–gold (IOCG) deposits of the Carajás Mineral Province, especially regarding the structural control, and the hydrothermal alteration. Although IOCG and Kiruna-type iron oxide-apatite (IOA) deposits are closely associated in several geological provinces, this association has not yet been fully constrained in the Carajás Mineral Province. The Jaguar deposit occurs near mafic–ultramafic intrusions, along a regional fault zone, and is hosted either by granitic (northern portion) or felsic subvolcanic (southern portion) rocks. It is characterized by sub-vertical zones hosting a biotite-chlorite (Bt-Chl) hydrothermal alteration with ductile structures and disseminated sulfides (pyrite and millerite) and magnetite. These zones are overprinted by sulfide-magnetite-apatite-bearing breccias, which represent the main mineralization bodies. The sulfide assemblage in the mineralized zones is dominated by pyrite, pentlandite and millerite, with minor sphalerite and chalcopyrite.We have investigated the concentration of trace elements in the magnetite and sulfides from the host rocks, different alteration facies and the mineralization at the Jaguar deposit by LA-ICP-MS. Magnetite composition ranges from higher Al, Mn, Ti and V contents, for at least part of those in host rocks (granitic and felsic subvolcanic) and Bt-Chl alteration, into lower contents in the magnetite-apatite alteration, associated with the main Ni mineralization. Magnetite with higher Ti and V contents in host rocks is associated with discrete hydrothermal alteration pockets, have high Ni/Cr ratios and plot in high temperature hydrothermal fields in multi-element diagrams. Therefore, we support that these features are compatible with a hydrothermal origin. Anomalously high-Ni contents in magnetite point that the Neoarchean mafic–ultramafic layered intrusions of the Carajás Province represent potential Ni sources for hydrothermal remobilization. Anomalously high V contents in magnetite suggest lower fO2 conditions upon the formation of the deposit. The concentration of trace elements in magnetite associated with the Jaguar deposit is similar to those from other IOCG deposits from the Carajás Province (but with higher V and Ni contents), especially the Sossego mine in the Southern Copper Belt, indicating that it could represent a Ni-rich member of the regional-scale IOCG mineral system at Carajás. Pyrite and chalcopyrite have a composition similar to those from magmatic deposits, when using previously proposed discriminant diagrams, but this is also the case for other IOA and IOCG deposits. However, low PGE contents (Ru, Rh, Ir and Os) in pyrite from the Jaguar deposit support a hydrothermal origin. Our results highlight that the classifications provided by available discriminant diagrams are not unequivocal. We suggest that multi-element diagrams represent a complementary approach to binary plots and provide a more comprehensive classification for the use of indicator minerals.

Incipient metal and sulfur extraction during melting of metasomatised mantle

A long-standing debate on the genesis of magmatic-hydrothermal Cu-Au deposits is whether the elevated oxygen fugacity (fO2) and metal endowment of their parental magmas are inherited from the mantle source or acquired during fractionation within the crust. This debate is built mainly on the composition of magmas emplaced into the upper crust that underwent varying degrees of differentiation and assimilation, which inevitably obscure their relationship to mantle processes. Here, we approach this debate from a new perspective by studying melt generation directly in mantle samples. This opportunity is provided by xenoliths from Lake Bullen Merri (Australia), which record partial melting of a pre-existing metasomatic assemblage. Melting occurred when the xenoliths were incorporated in hot basalts and carried towards the surface, where quenching upon eruption froze-in the melt-restite relationships. These samples preserve patches and interconnected networks of silicate glass along grain boundaries, caught in the act of undergoing melting and melt extraction. Melting consumed mainly metasomatic hornblende, phlogopite, and clinopyroxene, generating shoshonitic compositions that can be sulfide-rich, or have negligible sulfide content. We use four independent approaches to estimate the fO2 of glass, including sulfide content, oxybarometry based on spinel-olivine pairs, Fe3+/Fetot of glass determined by synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, and Cu/Fe ratio of the sulfide assemblage. Sulfide-rich melt had higher fO2 compared to the sulfide-poor melt, and these characteristics were inherited from the metasomatic assemblage; the oxidation state of the melts controlled their sulfide content. Subduction-modified mantle can thus store elevated oxidation state, sulfur, and metal content for hundreds of millions of years before low-degree partial melting generates oxidised, sulfur- and metal-enriched high-K/shoshonitic melts in post-collisional settings.

Geology, geochemistry and genesis of Tabei: A newly identified intermediate‐sulphidation epithermal Pb–Zn deposit adjacent to low‐sulphidation Au deposit in the Tulasu Basin, Chinese Western Tianshan

The Tabei Pb–Zn deposit is located adjacent to the well‐known Axi low‐sulphidation epithermal Au deposit in the Tulasu Basin, Chinese Western Tianshan. The homogenization temperatures and salinities of H2O‐rich biphase inclusions in ore‐stage sphalerite and calcite from Tabei range from 100 to 170°C and 0.4 to 6.2 wt% NaCleq, respectively. The δ13CV‐PDB and δ18OV‐SMOW values of calcite range from 0.9‰ to 1.5‰ and 5.6‰ to 6.7‰, respectively. The δ18OH2O and δDH2O values of hydrothermal fluids vary from −7.0‰ to −5.9‰ and −120.8‰ to −111.1‰, respectively. The in‐situ δ34SV‐CDT values of sulphides range from 7.5‰ to 8.0‰ (average 7.7‰). The in‐situ Pb isotopic compositions of galena and (87Sr/86Sr)0 ratios of sphalerite resemble those of Au‐bearing pyrite and quartz of Axi deposit, respectively, as well as the ore‐hosting volcanic rocks. These isotopic compositions indicate that the ore metals were derived from the ore‐hosting volcanic rocks, with the ore‐forming fluids consisting predominantly of circulating meteoric water. The absence of coexisting two‐phase vapour and liquid fluid inclusions and the presence of abundant banded coarse‐grained quartz crystals with dog tooth and comb textures at Tabei, suggest that the sulphides precipitated slowly due to conductive cooling. The high sulphide abundance, sulphide assemblage (pyrite + Fe‐poor sphalerite + galena + chalcopyrite), ore textures and isotopic compositions suggest that Tabei represents an intermediate‐sulphidation epithermal deposit. The Axi‐Tabei Au–Pb–Zn epithermal system constitutes a hybrid consisting of Au veins at shallow level and Pb–Zn veins at depth, suggesting that the base metals remain highly prospective beneath the identified Au orebodies at Axi.