Geology, mineralogy and stable isotope geochemistry of the Kabwe carbonate-hosted Pb–Zn deposit, Central Zambia

The carbonate-hosted Kabwe Pb–Zn deposit, Central Zambia, has produced at least 2.6 Mt of Zn and Pb metal as well as minor amounts of V, Cd, Ag and Cu. The deposit consists of four main epigenetic, pipe-like orebodies, structurally controlled along NE–SW faults. Sphalerite, galena, pyrite, minor chalcopyrite, and accessory Ge-sulphides of briartite and renierite constitute the primary ore mineral assemblage. Cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore (willemite) and mineralized jasperoid that consists largely of quartz, willemite, cerussite, smithsonite, goethite and hematite, as well as numerous other secondary minerals, including vanadates, phosphates and carbonates of Zn, Pb, V and Cu.Galena, sphalerite and pyrite from the Pb–Zn rich massive orebodies have homogeneous, negative sulphur isotope ratios with mean δ³⁴S_CDT permil (‰) values of − 17.75 ± 0.28 (1σ), − 16.54 ± 0.0.27 and − 15.82 ± 0.25, respectively. The Zn-rich and Pb-poor No. 2 orebody shows slightly heavier ratios of − 11.70 ± 0.5‰ δ³⁴S for sphalerite and of − 11.91 ± 0.71‰ δ³⁴S for pyrite. The negative sulphur isotope ratios are considered to be typical of sedimentary sulphides produced through bacterial reduction of seawater sulphate and suggest a sedimentary source for the sulphur.Carbon and oxygen isotope ratios of the host dolomite have mean δ¹³C_PDB and δ¹⁸O_SMOW values of 2.89‰ and 27.68‰, respectively, which are typical of marine carbonates. The oxygen isotope ratios of dolomite correlate negatively to the SiO₂ content introduced during silicification of the host dolomite. The depletion in ¹⁸O in dolomite indicates high temperature fluid/rock interaction, involving a silica- and ¹⁸O-rich hydrothermal solution.Two types of secondary fluid inclusions in dolomite, both of which are thought to be related to ore deposition, indicate temperatures of ore deposition in the range of 257 to 385 and 98 to 178 °C, respectively. The high temperature fluid inclusions contain liquid + vapour + solid phases and have salinities of 15 to 31 eq. wt.% NaCl, whereas the low temperature inclusions consist of liquid + vapour with a salinity of 11.5 eq. wt.% NaCl.Fluid transport may have been caused by tectonic movements associated with the early stages of the Pan-African Lufilian orogeny, whereas ore deposition within favourable structures occurred due to changes in pressure, temperature and pH in the ore solution during metasomatic replacement of the host dolomite. The termination of the Kabwe orebodies at the Mine Club fault zone and observed deformation textures of the ore sulphides as well as analysis of joint structures in the host dolomite, indicate that ore emplacement occurred prior to the latest deformation phase of the Neoproterozoic Lufilian orogeny.     

Fluid inclusion and stable isotope study of the Cobre–Babilonia polymetallic epithermal vein system, Taxco district, Guerrero, Mexico

The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ¹³C and δ¹⁸O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ³⁴S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.     

Fluid geochemistry in the Ivigtut cryolite deposit, South Greenland

The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na₃AlF₆] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO₂, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO₂ and H₂O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ¹³C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ¹⁸O of CO₂ (+ 21 to + 42‰ VSMOW) and δ¹⁸O of H₂O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H₂O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.     

Sn-polymetallic greisen-type deposits associated with late-stage rapakivi granites, Brazil: fluid inclusion and stable isotope characteristics

Tin-polymetallic greisen-type deposits in the Itu Rapakivi Province and Rondônia Tin Province, Brazil are associated with late-stage rapakivi fluorine-rich peraluminous alkali-feldspar granites. These granites contain topaz and/or muscovite or zinnwaldite and have geochemical characteristics comparable to the low-P sub-type topaz-bearing granites. Stockworks and veins are common in Oriente Novo (Rondônia Tin Province) and Correas (Itu Rapakivi Province) deposits, but in the Santa Bárbara deposit (Rondônia Tin Province) a preserved cupola with associated bed-like greisen is predominant. The contrasting mineralization styles reflect different depths of formation, spatial relationship to tin granites, and different wall rock/fluid proportions. The deposits contain a similar rare-metal suite that includes Sn (±W, ±Ta, ±Nb), and base-metal suite (Zn–Cu–Pb) is present only in Correas deposit. The early fluid inclusions of the Correas and Oriente Novo deposits are (1) low to moderate-salinity (0–19 wt.% NaCl eq.) CO₂-bearing aqueous fluids homogenizing at 245–450 °C, and (2) aqueous solutions with low CO₂, low to moderate salinity (0–14 wt.% NaCl eq.), which homogenize between 100 and 340 °C. In the Santa Bárbara deposit, the early inclusions are represented by (1) low-salinity (5–12 wt.% NaCl eq.) aqueous fluids with variable CO₂ contents, homogenizing at 340 to 390 °C, and (2) low-salinity (0–3 wt.% NaCl eq.) aqueous fluid inclusions, which homogenize at 320–380 °C. Cassiterite, wolframite, columbite–tantalite, scheelite, and sulfide assemblages accompany these fluids. The late fluid in the Oriente Novo and Correas deposit was a low-salinity (0–6 wt.% NaCl eq.) CO₂-free aqueous solution, which homogenizes at (100–260 °C) and characterizes the sulfide–fluorite–sericite association in the Correas deposit. The late fluid in the Santa Bárbara deposit has lower salinity (0–3 wt.% NaCl eq.) and characterizes the late-barren-quartz, muscovite and kaolinite veins. Oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240–450 °C, and 1.0–2.6 kbar fluid pressure at Correas and Oriente Novo. The hydrogen isotope composition of breccia-greisen, stockwork, and vein fluids (δ¹⁸O_quartz from 9.9‰ to 10.9‰, δD_H2O from 4.13‰ to 6.95‰) is consistent with a fluid that was in equilibrium with granite at temperatures from 450 to 240 °C. In the Santa Bárbara deposit, the inferred temperatures for quartz-pods and bed-like greisens are much higher (570 and 500 °C, respectively), and that for the cassiterite-quartz-veins is 415 °C. The oxygen and hydrogen isotope composition of greisen and quartz-pods fluids (δ¹⁸O_qtz-H2O=5.5–6.1‰) indicate that the fluid equilibrated with the albite granite, consistent with a magmatic origin. The values for mica (δ¹⁸O_mica-H2O=3.3–9.8‰) suggest mixing with meteoric water. Late muscovite veins (δ¹⁸O_qtz-H2O=−6.4‰) and late quartz (δ¹⁸O_mica-H2O=−3.8‰) indicate involvement of a meteoric fluid. Overall, the stable isotope and fluid inclusion data imply three fluid types: (1) an early orthomagmatic fluid, which equilibrated with granite; (2) a mixed orthomagmatic-meteoric fluid; and (3) a late hydrothermal meteoric fluid. The first two were responsible for cassiterite, wolframite, and minor columbite–tantalite precipitation. Change in the redox conditions related to mixing of magmatic and meteoric fluids favored important sulfide mineralization in the Correas deposit.     

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China

The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi (²⁰⁶Pb/²⁰⁴Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores (²⁰⁶Pb/²⁰⁴Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 17.12 to 17.41, ²⁰⁷Pb/²⁰⁴Pb = 15.47 to 15.54, ²⁰⁸Pb/²⁰⁴Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios (²⁰⁶Pb/²⁰⁴Pb = 18.20 to 24.28 and 18.32 to 20.06, ²⁰⁷Pb/²⁰⁴Pb = 15.69 to 16.44 and 15.66 to 15.98, ²⁰⁸Pb/²⁰⁴Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively).Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi.Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating.     

Characteristics and genesis of Gangdese porphyry copper deposits in the southern Tibetan Plateau: Preliminary geochemical and geochronological results

Porphyry-type Cu (Mo, Au) deposits have been discovered along the Gangdese magmatic arc in the southern Tibetan Plateau. Extensive field investigations and systematic studies of geochemistry, S–Pb isotopic tracing, together with Re–Os and ⁴⁰Ar/³⁹Ar isotopic dating indicate that the mineralisation of the copper belt is genetically related to emplacement of late orogenic granitic porphyries during the post-collisional crustal relaxation period of the Late Himalayan epoch. These porphyries are petrochemically K-enriched and belong to shoshonitic to high-K calc-alkaline series. They display enrichment of large ion lithophile elements (LILE) Rb, K, U, Th, Sr, Pb and depletion of high field strength elements (HFSE) Nb, Ta, Ti and the heavy rare earth elements (HREE) and Y without Eu anomalies. These characteristics demonstrate that subduction played a dominant role in their petrogenesis and residual garnet was left in the magma sources. Pb isotope data show a linear correlation in the plumbotectonic framework diagram ranging from orogenic Pb in the eastern segment of the copper belt to mantle Pb in the western segment. These constitute a mixing line of the Indian Oceanic MORB with Indian Oceanic sediments and suggest that the porphyry magmas were dominantly derived from partial melting of subducted oceanic crusts mixed with a minor quantity of sediments and mantle wedge components.The Gangdese porphyry copper polymetallic belt has alteration characteristics and zonation typical of porphyry-type copper deposits which include potassic alteration (K-feldspathisation and biotitisation), silicification, sericitisation, and propylitisation. Mineralisation mainly occurs in strongly altered granitic cataclasite at the exo-contact with veinlet-disseminated textures. The porphyries themselves are weakly mineralised with disseminated pyrite and chalcopyrite. The copper deposits contain simple ore mineral associations consisting of chalcopyrite, pyrite, bornite, molybdenite, sphalerite and oxidised minerals of malachite, covellite and molybdite. During supergene oxidation, primary ores underwent secondary enrichment to form economic orebodies with Cu grade ranging from 1% to 5%.Ore sulphides of the copper belt display S and Pb isotopic compositions identical to the ore-bearing porphyries. Their δ³⁴S values vary between − 3.8‰ and + 2.4‰ and are typical of mantle sulphur. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios vary in the ranges: 18.106 to 18.752, 15.501 to 15.638, and 37.394 to 39.058, respectively, and yielded radiogenetic lead-enriched signatures. Twelve molybdenite samples from the copper belt yielded isochron ages of 14.76 ± 0.22 Ma and 13.99 ± 0.16 Ma for the Nanmu and Chongjiang deposits and model ages of 13.5 to 13.6 Ma for the Lakang'e deposit. Meanwhile, ⁴⁰Ar/³⁹Ar isotopic dating of two biotite phenocrysts from the Chongjiang and Lakang'e deposits give plateau ages of 13.5 ± 1.0 Ma and 13.42 ±0.10 Ma, respectively. During the geodynamic evolution of the Gangdese collision-orogenic belt, intrusion of the ore-bearing porphyries took place just before the rapid uplift and E–W extension of the southern Plateau. And the ore-forming process may have occurred simultaneously with the uplift and extension (14 ± 0.1 Ma).     

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe₇S₈, and its absolute magnetic susceptibility is 2.10^− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (²⁰⁶Pb/²⁰⁴Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (²⁰⁶Pb/²⁰⁴Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO₂ conditions and neither a high temperature nor a low aH₂S (below 10^− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.     

Iron isotopes in acid mine waters and iron-rich solids from the Tinto–Odiel Basin (Iberian Pyrite Belt, Southwest Spain)

The isotopic composition of Fe was determined in water, Fe-oxides and sulfides from the Tinto and Odiel Basins (South West Spain). As a consequence of sulfide oxidation in mine tailings both rivers are acidic (1.45 < pH < 3.85) and display high concentrations of dissolved Fe (up to 420 mmol l^− 1) and sulphates (up to 1190 mmol l^− 1).The δ⁵⁶Fe of pyrite-rich samples from the Rio Tinto and from the Tharsis mine ranged from − 0.56 ± 0.08‰ to + 0.25 ± 0.1‰. δ⁵⁶Fe values for Fe-oxides precipitates that currently form in the riverbed varied from − 1.98 ± 0.10‰ to 1.57 ± 0.08‰. Comparatively narrower ranges of values (− 0.18 ± 0.08‰ and + 0.21 ± 0.14‰) were observed in their fossil analogues from the Pliocene–Pleistocene and in samples from the Gossan (the oxidized layer that formed through exposure to oxygen of the massive sulfide deposits) (− 0.36 ± 0.12‰ to 0.82 ± 0.07‰). In water, δ⁵⁶Fe values ranged from − 1.76 ± 0.10‰ to + 0.43 ± 0.05‰.At the source of the Tinto River, fractionation between aqueous Fe(III) and pyrite from the tailings was less than would be expected from a simple pyrite oxidation process. Similarly, the isotopic composition of Gossan oxides and that of pyrite was different from what would be expected from pyrite oxidation. In rivers, the precipitation of Fe-oxides (mainly jarosite and schwertmannite and lesser amounts of goethite) from water containing mainly (more than 99%) Fe(III) with concentrations up to 372 mmol l^− 1 causes variable fractionation between the solid and the aqueous phase (− 0.98‰ < Δ⁵⁶Fe_{solid–water} < 2.25‰). The significant magnitude of the positive fractionation factor observed in several Fe(III) dominated water may be related to the precipitation of Fe(III) sulphates containing phases.     

Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO₃ type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ¹⁸O of − 8.3‰, δD of − 48.2‰,δ¹¹B of 1.5‰, and ⁸⁷Sr/⁸⁶Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO₄ type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ¹⁸O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ¹¹B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and ⁸⁷Sr/⁸⁶Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO₄ type water with the highest TDS (249.1 g/l, brine) and has δ¹⁸O of − 2.8‰, δD of − 45.8‰,δ¹¹B of 21.2‰, and ⁸⁷Sr/⁸⁶Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ¹¹B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.     

Geochemistry and evolution of ore-forming fluids of the Yueshan Cu–Au skarn- and vein-type deposits, Anhui Province, South China

The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences.Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl⁻(S)–Na⁺–K⁺ chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components.Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits.The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids.Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10^− 1 to 9.8 × 10^− 7 m/s and 3.6 × 10^− 7 to 4.6 × 10^− 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl₂⁻, CuCl₃²⁻ and CuClOH, whereas Au was transported as Au₂(HS)₂S²⁻, Au(HS)₂⁻, AuHS and AuH₃SiO₄ complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO₂, which resulted from fluid boiling and mixing.Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my^− 1, which permitted sufficient heat supply by magma to the ore-forming system.     

Age and sources of gold mineralization in the Marmato mining district, NW Colombia: A Miocene–Pliocene epizonal gold deposit

Epigenetic gold mineralization occurs in the Marmato mining district, within the Calima Terrain of the Setentrional Andes, Colombia. Regional rocks associated with this mineralization include: graphite- and chlorite-schists of the Arquia Complex; metamorphosed during the Cretaceous, Miocene sandstones, shales and conglomerates of the Amagá Formation; as well as pyroclastic rocks (clasts of basalt, andesites and mafic lavas) and subvolcanic andesitic/dacitic bodies of the Combia Formation (9 to 6 Ma). The subvolcanic Marmato stock hosts mesothermal and epithermal low-sulfidation Au–Ag ores in the form of distensional veins, stockwork, and quartz veinlets within brecciated zones. Ore minerals are pyrite, sphalerite and galena with subordinate chalcopyrite, arsenopyrite, pyrrhotite, argentite and native gold/electrum.Sericitized plagioclase from a porphyry dacite yielded a K–Ar age of 5.6 ± 0.6 Ma, interpreted as the age of ore deposition. This is in close agreement with the age of reactivation of the Cauca–Romeral Fault System (5.6 ± 0.4 Ma), which bounds the Calima Terrain. A porphyry andesite–dacite (6.7 ± 0.1 Ma), hosting the Au–Ag veins, shows a measured ⁸⁷Sr/⁸⁶Sr between 0.70440 and 0.70460, ε_Nd between + 2.2 and + 3.2 and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.964 to 19.028; 15.561 to 15.570; and 38.640 to 38.745, respectively. The ⁸⁷Sr/⁸⁶Sr and ε_Nd values of rocks from the Arquia Group range from 0.70431 to 0.73511 and − 12.91 to + 10.0, respectively, whereas the corresponding Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) range from 18.948 to 19.652; 15.564 to 15.702; and 38.640 to 38.885, respectively. ⁸⁷Sr/⁸⁶Sr and ε_Nd values obtained on sulfides from the gold quartz veins, which occur at shallow and intermediate levels, range from 0.70500 to 0.71210 and from − 1.11 to + 2.40. In the deepest veins, ε_Nd values lie between + 1.25 and + 3.28 and the ⁸⁷Sr/⁸⁶Sr of calcite and pyrite fall between 0.70444 and 0.70930. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of all mineralization are in the ranges 18.970 to 19.258; 15.605 to 15.726 and 38.813 to 39.208, respectively. Carbonates have an average ⁸⁷Sr/⁸⁶Sr ratio of 0.70445, which is within the range of values measured in the host dacite. The Sr isotopic data indicate that carbonic fluids have a restricted hydrothermal circulation within the host igneous body, while the Sr, Pb and Nd isotopic compositions of the sulfides suggest that the fluids not only circulated within the Marmato stock, but also throughout the Arquia Complex, inferring that these rocks offer a potential target for mineral exploration. Based on geological and geochronological evidence, the epizonal Marmato gold ores formed during the Miocene to Pliocene, as a result of cooling of the Marmato stock and reactivation along a crustal-scale fault zone related to thermal processes in an accretionary oceanic–continental plate orogen.     

Zircon U–Pb ages, Hf and O isotopes constrain the crustal architecture of the ultrahigh-pressure Dabie orogen in China

The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative ε_Hf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive ε_Hf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ¹⁸O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ¹⁸O rocks. North Dabie shares the same age of Neoproterozoic low δ¹⁸O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower.     

A stable isotope and fluid inclusion study of the Qaleh-ZariCu–Au–Ag deposit, Khorasan Province, Iran

The Qaleh-Zari copper deposit, located in South Khorasan in the Central Lut region of Iran, is a polymetallic vein deposit with major amounts of Cu, Au, Ag and minor amounts of Pb, Zn and Bi. Mineralization occurs in a series of NW–SE trending fault planes and breccia zones in Paleogene andesitic to basaltic volcanic rocks. Argillization, sericitization and propylitization characterize alteration halos bordering mineral veins. The main ore minerals are chalcopyrite, pyrite, galena and sphalerite, with quartz, calcite and minor chlorite as the main gangue phases. Microthermometric measurements of fluid inclusions in cogenetic quartz indicate homogenization temperatures between 160 and 300 °C and salinities from 1 to 4 wt% NaCl equiv. Boiling occurred in the mineralising fluids at 160–1000 m below the paleo-water table at pressures of approximately 15−80 bar at various stages in the formation of the ore body. The wide range of pressures and temperatures reflects the multi-stage nature of the mineralization at Qaleh-Zari. The δ¹⁸O values in quartz (relative to SMOW) and δ³⁴S values in chalcopyrite and galena (relative to CDT) range from 6.5 to 7.5‰ and 0.0–1.5‰ (mean: 7.0‰), respectively. At 300 °C, calculated fluid δ¹⁸O values are close to 0‰. These data suggest a magmatic origin for sulfur and a surficial origin for the mineralizing fluid. Mineralization at Qaleh-Zari is interpreted as epithermal and low-sulfidation in style and was probably related to a deep-seated magmatic system. Ore deposition was the result of boiling, cooling and pressure reduction.     

The sources and evolution of mineralising fluids in iron oxide–copper–gold systems, Norrbotten, Sweden: Constraints from Br/Cl ratios and stable Cl isotopes of fluid inclusion leachates

We have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated Fe-oxide ± Cu ± Au mineralising systems in Norrbotten, Sweden. Fluid inclusions in late-stage veins in Fe-oxide–apatite deposits contain saline brines and have a wide range of Br/Cl molar ratios, from 0.2 to 1.1 × 10⁻³ and δ³⁷Cl values from −3.1‰ to −1.0‰. Leachates from saline fluid inclusions from the Greenstone and Porphyry hosted Cu–Au prospects have Br/Cl ratios that range from 0.2 to 0.5 × 10⁻³ and δ³⁷Cl values from −5.6‰ to −1.3‰. Finally, the Cu–Au deposits hosted by the Nautanen Deformation Zone (NDZ) have Br/Cl molar ratios from 0.4 to 1.1 × 10⁻³ and δ³⁷Cl values that range from −2.4‰ to +0.5‰, although the bulk of the data fall within 0‰ ± 0.5‰.The Br/Cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite. Most of the isotopic data from the Fe-oxide–apatite and Greenstone deposits are consistent with a mantle derived source of the chlorine, with the exception of the four samples with the most negative values. The origin of the low δ³⁷Cl values in these samples is unknown but we suggest that there may have been some modification of the Cl-isotope signature due to fractionation between the mineralising fluids and Cl-rich silicate assemblages found in the alteration haloes around the deposits. If such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low δ³⁷Cl values would be significantly larger.The source of Cl in the NDZ deposits has a crustal signature, which suggests the Cl in this system may be derived from (meta-) evaporites or from input from crustal melts such as granitic pegmatites of the Lina Suite.     

Origin of coarse-crystalline calcite cement in Early Ordovician carbonate rocks, Ordos basin, northern China: Insights from oxygen and carbon isotopes and fluid inclusion microthermometry

The calcite cement in the Lower Ordovician Majiagou Formation in the Ordos basin in northern China can be subdivided into three groups based on preliminary results of oxygen and carbon isotopes and fluid inclusion microthermometry. Group 1 has low oxygen isotopes (− 14‰ to − 18‰), low T_h values (92–103 °C), and low salinities (1.7–4.9 wt.% NaCl equivalent) and is interpreted to have precipitated during early burial from porewater influenced by meteoric water. Group 2 has much higher oxygen isotope values (− 5‰ to − 8‰), which, coupled with the higher T_h values (136–151 °C), suggest that the calcite was precipitated from fluids that were significantly enriched in ¹⁸O, possibly resulting from fluid–rock reaction during burial. Group 3 occurring along fractures is characterized by high salinities (21–28 wt.% NaCl equivalent) and is interpreted to have been precipitated from locally preserved residual evaporitic brines. The occurrence of primary hydrocarbon inclusions and its low carbon isotopes (− 11‰ to − 15‰) suggest that precipitation of group 3 calcite took place in the presence of hydrocarbons.     

Diagenetic mineralization in Pennsylvanian coals from Indiana, USA: C/C and O/O implications for cleat origin and coalbed methane generation

Cleats and fractures in southwestern Indiana coal seams are often filled with authigenic kaolinite and/or calcite. Carbon- and oxygen-stable isotope ratios of kaolinite, calcite, and coalbed CO₂ were evaluated in combination with measured values and published estimates of δ¹⁸O of coalbed paleowaters that had been present at the time of mineralization. δ¹⁸O_mineral and δ¹⁸O_water values jointly constrain the paleotemperature of mineralization. The isotopic evidence and the thermal and tectonic history of this part of the Illinois Basin led to the conclusion that maximum burial and heat-sterilization of coal seams approximately 272 Ma ago was followed by advective heat redistribution and concurrent precipitation of kaolinite in cleats at a burial depth of < 1600 m at  78 ± 5 °C. Post-Paleozoic uplift, the development of a second generation of cleats, and subsequent precipitation of calcite occurred at shallower burial depth between  500 to  1300 m at a lower temperature of 43 ± 6 °C. The available paleowater in coalbeds was likely ocean water and/or tropical meteoric water with a δ¹⁸O_water  − 1.25‰ versus VSMOW. Inoculation of coalbeds with methanogenic CO₂-reducing microbes occurred at an even later time, because modern microbially influenced ¹³C-enriched coalbed CO₂ (i.e., the isotopically fractionated residue of microbial CO₂ reduction) is out of isotopic equilibrium with ¹³C-depleted calcite in cleats.     

Hydrology of a spring complex, studied by geochemical time-series data, Acquarossa, Switzerland

A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types: (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO₄, 700 mg/l HCO₃, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO₂, and with an isotopic composition of δD = − 73.0‰ and δ¹⁸ O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ¹⁸ O = −10.5‰ and tritium as in recent (post-bomb) precipitation.     

Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile

The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S₁ to S₆) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D₁, autumn); August 2001 (D₂, winter); October 2001 (D₃, spring) and January 2002 (D₄, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g^− 1) were found in the northern part of the river (S₁, average D₁–D₄), near the mountains and a copper mine, and then decreased downstream to 209 μg g^− 1 (S₆). Total Zn showed an irregular variation, with higher values at S₁ (1290 μg g^− 1) and high values in some winter sampling (1384 μg g^− 1 S₄, S₅–D₂). Pb showed different trends, increasing from S₁ to S₆ (17 to 61 μg g^− 1), with the highest values in the summer samples (83 μg g^− 1, S₄–S₆, D₄), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g^− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D₁–D₄). The highest values of total organic matter, carbonate and conductivity were found in S₆, which has the smallest size particles, while at S₁ the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g^− 1, S₁) to 16% (32 μg g^− 1, S₆); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S₁) to 34% (S₆), but copper content was lower (214 to 68 μg g^− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g^− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g^− 1, S₁ to S₆). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S₁ were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g^− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S₆ the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g^− 1, respectively).     

Sulfur isotopic compositions of the Huize super-large Pb–Zn deposit, Yunnan Province, China: Implications for the source of sulfur in the ore-forming fluids

The Huize Pb–Zn deposit of Yunnan Province, China, is located in the center of the Sichuan–Yunnan–Guizhou Pb–Zn–Ag district. Four primary orebodies (orebody No. 1, No. 6, No. 8 and No. 10), with Pb + Zn reserves from 0.5 Mt to 1 Mt, have been found at depth in this deposit. This paper provides new data on the sulfur isotopic compositions of the four orebodies. The data show that the principal sulfide minerals (galena, sphalerite and pyrite) in the four orebodies are enriched in heavy sulfur, the δ³⁴S values between 10.9‰ and 17.7‰ and where δ³⁴S_pyrite > δ³⁴S_sphalerite > δ³⁴S_galena. The δ³⁴S values of sulfide are close to that of the sulfates from the carbonate strata within the region. The similarity in sulfur isotope composition between sulfides and sulfates indicates the sulfur in the ore-forming fluids was likely derived by thermochemical sulfate reduction of sulfates contained within carbonate units.     

Two magma series and associated ore deposit types in the Permian Emeishan large igneous province, SW China

The Late Middle Permian ( 260 Ma) Emeishan large igneous province in SW China contains two magmatic series, one comprising high-Ti basalts and Fe-rich gabbroic and syenitic intrusions, the other low-Ti basalts and mafic–ultramafic intrusions. The Fe-rich gabbros are spatially and temporally associated with syenites. Each series is associated with a distinctive type of mineralization, the first with giant Fe–Ti–V oxide ore deposits such as Panzhihua and Baima, the second with Ni–Cu–(PGE) sulfide deposits such as Jinbaoshan, Limahe and Zhubu. New SHRIMP zircon U–Pb isotopic data yielded 263 ± 3 Ma for the Limahe intrusion, 261 ± 2 Ma for the Zhubu intrusion and 262 ± 2 Ma for a syenitic intrusion. These new age dates, together with previously reported SHRIMP zircon U–Pb ages, suggest that all these intrusions are contemporaneous with the Emeishan flood basalts and formed during a major igneous event at ca. 260 Ma.The oxide-bearing intrusions have higher Al₂O₃, FeO (as total iron) and total alkalis (Na₂O + K₂O) but lower MgO than the sulfide-bearing intrusions. All intrusions are variably enriched in LREE relative to HREE. The oxide-bearing intrusions display positive Nb- and Ti-anomalies and in certain cases negative Zr–Hf anomalies, whereas the sulfide-bearing intrusions have obvious negative Nb- and Ti-anomalies, a feature of crustal contamination. Individual intrusions have relatively small ranges of Nd(t) values. All the intrusions, however, have Nd(t) values ranging from − 3.9 to + 4.6, and initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7039 to 0.7105. The syenites have very low MgO (< 2 wt.%) but highly variable Fe₂O₃ (2.5 to 13 wt.%) with initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7039 to 0.7089. Magmas from both series could have derived by melting of a heterogeneous mantle plume: the high-Ti series from a Fe-rich, more fertile source and the low-Ti series from a Fe-poor, more refractory source. In addition, the low-Ti series underwent significant crustal contamination. The two magma series evolved along different paths that led to distinct mineralization styles.