Sulfur Isotope Compositions Of Sulfides Research Articles

Metal remobilization at the Nibao gold deposit in Youjiang basin, SW China: Implications from mineral texture, trace element and sulfur isotope compositions of sulfides and TiO2 polymorphs

Multistage mineralization overprinting is important for the formation of giant hydrothermal gold deposits. The Youjiang basin in SW China has undergone at least three major deformation phases in the Mesozoic, but their relationship with the large-scale gold accumulation in the region remains enigmatic. Here, we study the large Nibao gold deposit (reserve > 70 t Au) in the northern part of the basin, which has both fault-controlled and stratabound orebodies. We identified a pre-ore stage and syn-ore stage including four tectono-hydrothermal (T-H) substages (i.e., T-H stage 1, 2, 3 and 4) for the local mineralization at Nibao. The pre-ore stage is dominated by coarse-grained pyrite coexisting with TiO2 polymorphs in the Middle-Late Permian basaltic rocks. The T-H substage 1 is characterized in that the sedimentary pyrites are brecciated in bedding-parallel faults. Fluorination and silicification occur in the T-H substage 2, which is re-brecciated at the T-H substage 3 forming the highest gold grade ore in high-angle thrust fault. The T-H substage 4 presents as fault reactivation within minor calcite and pyrite deposition. Mineralogy and in-situ trace element analyses reveal that mineral dissolution and reprecipitation (incl. dolomite, auriferous pyrite and TiO2 polymorphs) is ubiquitous during the multistage tectono-hydrothermal process, and the continuous alteration overprinting may have promoted gold accumulation. This replacement process of different generations of auriferous pyrite is also recorded by their inherited sulfur isotopes, giving a narrow δ34S (−3.1 to + 2.1 ‰) range. Anatase is the main accessory phase of TiO2 polymorphs, as identified with LA-ICP-MS trace element and laser Raman spectroscopic analyses. Moreover, the anatase can been divided into two types (type-I and II) based on their texture, alteration and chemistry. The type-I anatase commonly occurring in the stratabound ore is characterized by higher Zr (mean 1,730 ppm), V (mean 1,412 ppm), and Cr (mean 110 ppm) contents than type-II that coexists with zoned pyrite in the fault-controlled ore (mean 26 ppm, 187 ppm, and 38 ppm, respectively). Additionally, W (mean 636 ppm) and Mg (10,021 ppm) in type-II are much higher than type-I ones (mean 135 ppm W and 476 Mg). These features show that the sedimentary-stage Zr-V-Cr-rich type-I anatase was dissolved via fluid metasomatism, and reprecipitated as the hydrothermal-stage W-Mg-rich and Zr-poor anatase, with gold gradually enriched. Besides, the anatase phase of TiO2 polymorphs also indicates that the Nibao gold deposit was formed under low pressure–temperature condition. Overall, we propose that the Nibao is a Carlin-type gold deposit, dominated by multistage tectono-hydrothermal events.

Sulfur Isotopic Composition of Sulfides and Sulfates from Rocks of Carbonatite Complexes of the Devonian Kola Alkaline Province

Sulfur Isotopic Composition of Sulfides and Sulfates from Rocks of Carbonatite Complexes of the Devonian Kola Alkaline Province

A modified laser ablation-isotope ratio mass spectrometry method for in situ analysis of sulfur isotope composition of sulfides.

A novel laser ablation-isotope ratio mass spectrometry (LA-IRMS) method for in situ analysis of sulfur isotopes in sulfides has been developed. Instead of the in situ reaction applied by the traditional laser microprobe, the analyte gas preparation in this method is separated temporally and spatially from the LA, resulting in improved precision and accuracy. Our LA-IRMS system combines an ultraviolet LA system, an elemental analyzer (EA), a custom-built cryogenic concentration system, a continuous-flow interface, and an IRMS. The sulfide aerosol particles generated from LA were transferred by a helium carrier gas from the ablation cell into the reaction tube and were then converted into SO2 . Subsequently, SO2 was enriched in two cold traps and was finally introduced into the ion source of the IRMS through the continuous-flow interface. We measured three synthetic and four natural sulfide reference materials to test the performance of this method. Precisions of ±0.25‰-±0.48‰ and ±0.32‰-±0.64‰ (1SD, n = 5) for δ34 S values of synthetic and natural sulfide standards can be obtained for spot sizes ranging from 64 to 80 μm. Measured values and their recommended values showed a good linear relationship (R2 within 0.998 and 0.9995) with the slope of approaching unity (within 1.0509 and 1.1313). Data from the measurement of reference materials showed that the precision and accuracy of our method were satisfactory. This method is a powerful tool for in situ sulfur isotope measurement of sulfides and can be further applied to in situ carbon and oxygen isotope analyses.

Trace elements and sulfur isotopic compositions of sulfides in the giant Dahongshan Fe-Cu-(Au-Co) deposit, SW China: Implications for fluid evolution and Co enrichment in IOCG systems

Iron-oxide-copper–gold (IOCG) deposits are characterized by Cu-Au polymetallic mineralization and may contain large amounts of critical metals (e.g. Co, REE, and U) as by-products. Sources of ore-forming fluids and metals of the IOCG deposits remain controversial, either a magmatic or basinal source has been advocated. The ∼1660 Ma Dahongshan Fe-Cu-(Au-Co) deposit in the Kangdian region in southwestern China has spatially separated Fe and Fe-Cu orebodies, in which Co-rich pyrite has been identified in different types of ores and host rocks. Here, we integrate in-situ sulfur isotopic compositions and trace element geochemistry of sulfides to characterize the nature of ore fluids and the Co enrichment processes.Paragenetic sequences of sulfides in the Dahongshan deposit include: Pyrite (Py I) associated with magnetite mineralization in Fe ores, which has rims (Py II-1) intergrown with hematite-chalcopyrite assemblage; Pyrite and chalcopyrite (Sulfide II) in the Fe-Cu ores with protolith of arenaceous dolostone (Sulfide II-2) and interbedded argillaceous siltstone and dolostone (Sulfide II-3); and Sulfide III in post-ore reworking veins formed during regional metamorphism. Py I shows a magmatic sulfur isotopic signature (−2.2 to 1.2‰) and relatively high Au-Cu-Zn contents, indicating a predominance of magmatic-hydrothermal component during magnetite formation. By contrast, the combined sulfur isotopes and trace element compositions of Sulfides II in Fe-Cu ores indicate the mixing of two distinct fluid endmembers: Sulfides precipitated from one endmember show magmatic affinity with low δ34S values (as low as −2.1‰), high Se/S ratios (∼11.8 × 10-4), high Co contents (∼10600 ppm) and Co/Ni ratios (∼110), likely from a magmatic-hydrothermal source of mafic magmas affinity; whereas sulfides from the other endmember have overall higher δ34S values (up to 15.8‰), relatively lower Se/S ratios (∼0.09 × 10-4), lower Co contents (∼900 ppm) and Co/Ni ratios (∼13). Together with the published B-O isotopic data, the high-δ34S fluid is attributed to externally-derived basinal brine at Dahongshan. The clear negative correlations between δ34S values and Se/S ratios, Co contents, as well as Co/Ni ratios of Py II highlight that the incursion of exchanged basinal brines may be vital for triggering economic sulfide mineralization in Dahongshan. Furthermore, when assuming a similar predominance of magmatic fluids, Py I associated with magnetite ores is less enriched in Co (with lower Co/Ni ratios) than Py II from Fe-Cu ores, which can be tentatively ascribed to the decreasing Co solubility limits and formation of cattierite (CoS2) solid solution in pyrite as the fluid evolved. Finally, sulfide III in reworking veins show comparable δ34S values and Se/S ratios, but higher Co contents (up to 3.1%) than sulfide II, implying that Co can be further enriched during later remobilization events. This study exemplifies the utility of sulfide as a robust monitor of ore-forming process in IOCG system.

Sources and Evolution of Sulfur Isotopic Composition of Sulfides of the Kharaelakh and Pyasino–Vologochan Intrusions, Norilsk Ore Region

Sources and Evolution of Sulfur Isotopic Composition of Sulfides of the Kharaelakh and Pyasino–Vologochan Intrusions, Norilsk Ore Region

Geological Constraints on the Genesis of Jagpura Au-Cu Deposit NW India: Implications from Magnetite-Apatite Mineral Chemistry, Fluid Inclusion and Sulfur Isotope Study

The Jagpura Au-Cu deposit is situated within the Aravalli craton in the northwestern part of India. In the present work, petrography, mineral chemistry, fluid inclusion and sulfur isotopic compositions were used to study the Jagpura Au-Cu deposit. The ore mineral association of the deposit is arsenopyrite, loellingite, chalcopyrite, pyrrhotite and pyrite, along with native gold, magnetite and apatite. The gold fineness ranges from 914–937‰ (avg. 927‰). The presence of Au-Bi-Te phases, pyrite (>1 Co/Ni ratio), magnetite (≥1 Ni/Cr ratio, <1 Co/Ni ratio) and apatite (>1 F/Cl ratio) suggest the hydrothermal origin Au-Cu mineralization. A fluid inclusion study indicates the different episodes of fluid immiscibility with the homogenization temperatures varying between 120–258 °C and salinities range within the 8.86–28.15 wt% NaCl eq. The sulfur isotopic composition of sulfides varies from 8.98 to 14.58‰ (avg. 11.16‰). It is inferred that the variation in the sulfur isotopic compositions of sulfides is due to the cooling and dilution of the metalliferous fluid of mixed origin, derived from the basement meta-sedimentary rocks and the high saline basinal fluid. The iron oxide-copper-gold-apatite associations, structural control of mineralization, pervasive hydrothermal alteration, fluid salinity and sulfur isotope compositions indicate that the Jagpura Au-Cu deposit is similar to the iron oxide-copper-gold (IOCG)-iron oxide-apatite (IOA)types of deposits. Based on the ore geochemistry and the trace elements systematic of magnetite, the deposit is further classified as an IOCG-IOA type: IOCG-Co (reduced) subtype.

Constraints on the genesis of the Laochang Pb–Zn ore, Gejiu district, Yunnan: Evidence from sulfide trace element and isotope geochemistry

The Laochang deposit is an important part of the Gejiu Sn–Cu polymetallic district, containing abundant reserves of tin, copper, lead, zinc and tungsten. The recently discovered sulfide Pb–Zn ore is located 1000 m underground in the Laochang deposit, and its genesis is not clear. In this study, the trace element concentrations and sulfur and lead isotope compositions of sulfides from the newly discovered Laochang Pb–Zn ore were analyzed to constrain mineralization conditions and genesis. Our results show that sphalerite from Laochang Pb-Zn ore contains high Fe, Cu, Ga, Ag, In and Sn, low Co, Ni, Ge and As and moderate Mn and Cd. Pyrite is enriched in Ag, Sb, Pb and As and poor in Co, Ni, Se, Ti and Mn. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ablation profiles of sphalerite show that Fe, Cd, Mn, Ga, and In occur as solid solutions and/or lattice-bound ions, whereas Ag, Cu, Pb, Sb, and Sn are present in both mineral inclusions and solid solutions. Moreover, the profiles of pyrite indicate that Co, Ni and As enter the pyrite lattice by ion replacement and that Sn, Ag, Pb and Sb occur in both solid solutions and mineral inclusions.The Fe/Zn calculation temperature of sphalerites ranges from 299 °C to 344 °C (mean of 320 °C), while the sphalerite geothermometer (GGIMFis) temperatures range from 268 °C to 312 °C, with an average of 290 °C. These results indicate that the Laochang Pb–Zn ore formed under moderate- to high-temperature conditions. The sphalerites in the Laochang Pb–Zn ore is enriched in Ga and In, is poor in Ge, and has moderate contents of Cd which implies that it may be related to magmatic-hydrothermal fluid. Pyrites in this study have relatively low Co and Ni concentrations and low Co/Ni ratios, which also indicate magmatic-hydrothermal origin.The overall sulfur isotope compositions of sulfides from the Laochang Pb–Zn ore, ranging from −1.2 ‰ to +3.7 ‰, indicate that the S may be derived from the Laoka granite with some contribution from the wallrock. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of galena in the five samples range from 18.400 to 18.447, 15.656 to 15.697, and 38.478 to 38.968, respectively. These results imply that the ore-forming metals in the Pb–Zn ore were derived from the upper crust. Therefore, we believe that the Pb–Zn ore may be of magmatic-hydrothermal origin and represents the distal mineralization of the Laoka metallogenic system.

Origin of the Early Cambrian Huayuan carbonate-hosted Zn-Pb orefield, South China: Constraints from sulfide trace elements and sulfur isotopes

The Huayuan Zn-Pb orefield in the southeastern Yangtze Craton contains over 20 Mt Zn + Pb metal resource @ 4%, including several large, Lower Cambrian carbonate-hosted deposits classified as Mississippi Valley-Type (MVT). The source of zinc and lead and the ore-forming processes involved are still unclear. Trace elements and sulfur isotope compositions of sulfides from the large-scale Limei and Danaopo Zn-Pb deposits in the orefield favor a fluid-mixing metallogenic hypothesis. Alteration/mineralization occurred in three stages (S1-S3), forming pale-yellow sphalerite (S1: Sp1), yellow–brown sphalerite and pyrite (S2: Sp2-Py2), and galena-pyrite (S3: Gn-Py3).Syn-sedimentary fine-grained pyrite (Py1) in the Lower Cambrian Qingxudong Formation (Fm.) algal limestone has high Co, Ni, and As concentrations, whereas hydrothermal Py2 and Py3 in sulfide-calcite veins are rich in Zn and Pb, respectively. All the pyrites have low Co/Ni ratios (<2), indicating that the Fe, Co, and Ni are from a sedimentary source. Sphalerites from Limei and Danaopo are rich in Cd, Cl, and Ge but poor in Fe, Mn, and Co. They were formed under low-medium temperature (134–236 °C; determined by the concentrations of Mn, Fe, Ga, Ge, In, and Sb) and in an acidic and low-fO2 hydrothermal system, which are consistent with typical MVT ores. Lower Cambrian algal limestone (δ34SΣS = 34.3–34.4‰) contributed most sulfur to the ore sulfides (δ34S = 29.3–37.2‰). Meanwhile, the Lower Cambrian Niutitang Fm. Pb-Zn-rich black shale is likely the main ore metal source, but its limited sulfate content may not be able to provide sufficient sulfur. We propose a mixing between metal-rich brines leached from the basal Niutitang Fm. black shale with H2S-rich fluid resulting from thermochemical sulfate reduction (TSR) of the Qingxudong algal limestone formation, thus destabilizing the base metal chloride complexes and precipitating the Zn-Pb ores.

Genesis of the Xinfang magmatic-hydrothermal gold deposit, Liaodong Peninsula, China: Constraints from pyrite Re-Os isotopes, C, O, S, Pb, Si, He and Ar isotopes

The Xinfang gold deposit (>20 t@ 2.85 g/t) is situated in the southwest of the Liaodong Peninsula. Ore bodies are hosted by the Archean gneiss in the footwall and Neoproterozoic metasandstone in the hangingwall of the Xinfang Metamorphic Core Complex. Here, we conduct pyrite Re-Os dating, C, O, Si, He-Ar, S, and Pb isotopes in order to constrain the ore-forming age and genesis of the deposit. Field observations show that three ore-forming processes are recognized: (1) quartz- coarse-grained pyrite stage (stage Ⅰ), (2) quartz-polymetallic sulfide-gold stage (stage Ⅱ), and (3) quartz – calcite ± pyrite stage (stage III). Pyrite from the quartz-polymetallic sulfide-gold vein yielded Re-Os isochron age of 121.1 ± 1.2 Ma (Initial 187Os/188Os = 1.49 ± 0.01, MSWD = 1.2), which is interpreted to be the ore-formation age.Theδ13CV-PDB and 18Ov-SMO W values of calcite from stage III range from −5.1‰ to −4.9‰ and from 9.7‰ to 10.1‰, and the δ30Si values of quartz from stage Ⅰto stage III range from −0.5‰ to −0.4‰, −0.1‰ to −0.3‰, and −0.2‰ to −0.1‰, respectively, indicating that ore-forming fluids were derived from a magmatic-hydrothermal source. Sulfur isotopic compositions of sulfides between −1.9 ‰ and 4.4 ‰ (mean = 2.4 ‰), are consistent with that of magmatic sulfur. The galena yielded a wide range of lead isotopic composition (206Pb/204Pb = 16.995–17.252, 207Pb/204Pb = 15.335–16.343, 208Pb/204Pb = 37.461–37.580) suggesting an external lead source. The He and Ar isotope compositions of pyrite and galena (3He/4He = 0.14Ra-0.62Ra), indicate a crustal source with minor mantle contributions. Combining all available data results, we propose that a magmatic -hydrothermal source for the Xinfang gold deposit and the ore formation was related to the subduction of the Paleo-Pacific Plate beneath Eurasia.

The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid

We studied the mineralization and sulfur isotopic composition of sulfides of gold–palladium ores in olivine clinopyroxenites from the Dzelyatyshor massif made up of a continuous layered series of rocks: olivine-free clinopyroxenite–olivine clinopyroxenite–wehrlite. The primary igneous layering of rocks, manifested as different quantitative ratios of clinopyroxene and olivine in them, controls the local trends of variability in the chemistry of mineral-forming medium and the concentrations of ore components, including noble metals, and sulfur in each separate layer during its cooling. The replacement of primary rock-forming minerals by secondary minerals, when the temperature decreases, is a characteristic trend for pyroxenites: (a) olivine → serpentine, secondary magnetite, and (b) clinopyroxene → amphibole, secondary magnetite → chlorite. The deposition of native gold in parageneses with PGM and sulfides at the Ozernoe occurrence took place during the replacement of earlier rock-forming minerals by chlorite. This process completed mineral formation at the deposit and took place at temperatures 150–250 °C and at the high activity of S, Te, Sb, and As of fluid. The variability of mineral formation conditions during chloritization is reflected in the change of native-sulfide forms of Pd by arsenide-antimonide forms and the sulfur isotopic composition of sulfides. The Pd content in native gold increases in the series—Au-Ag solid solution (&lt;1.5 wt.% Pd)—Au-Cu intermetallides (to 6 wt.% Pd)—Cu-Au-Pd solid solutions (16.2–16.9 wt.% Pd). The sulfur isotopic composition of pyrite, chalcopyrite, and bornite varies from −2.1 to −2.9‰. It is assumed that a deep-seated magmatic basic melt was the source of fluid, ore components, and sulfur.

Hydrothermal evolution and mineralization of the Pulang porphyry Cu-Au deposit in the Sanjiang Tethys, Southwest China: Constraints from fluid inclusions and D-O-S isotopes

Pulang is the largest porphyry Cu-Au deposit that formed in the Late Triassic and is located in the eastern Tethys. Its ore-forming fluids and mineral assemblages show some reducing characteristics. Magma and fluid are two key parameters in porphyry mineralization. Studies have shown that syn-mineralization quartz monzonite porphyries have higher oxygen fugacities, which are conducive to mineralization. However, this does not answer the question of why the deposit has reducing characteristics, which should be positively related to fluid activity. Based on detailed geologic observation, hydrothermal evolution and ore-forming process have been divided into three successive periods, namely, pre-mineralization, syn-mineralization (subdivided into three stages, including early-, inter-, and late-mineralization, corresponding to stage 1, 2, and 3 veins), and post-mineralization, in the Pulang deposit. The corresponding fluid inclusions and sulfur isotopic compositions of sulfides are studied on this basis. The results show that the salinity ranges of the stage 1 and stage 2 veins are larger, which indicates that fluid immiscibility may exist. Pyrrhotite is developed in some of the stage 2 veins, and their fluid inclusions contain CH4. However, CH4 was not found in fluid inclusions in veins that do not contain pyrrhotite. The homogenization temperatures and salinities of the fluid inclusions decrease gradually, and the hydrogen and oxygen isotopes gradually approach the meteoric water line overall, from premineralization to postmineralization. Furthermore, sulfur isotopes of pyrrhotite are the highest, indicating a possible additional source of sedimentary sulfur. That is, the ore-forming fluids were dominated by magmatic water, and meteoric water was added in the late stage as the fluid evolved. The trend of the Heishuitang fault is consistent with the extension of the main ore body in the mining area. Because the strata is affected by faults, the strata acts as a good channel for meteoric water. Meteoric water was added to the magmatic fluid after extraction and carried organic matter from the Tumugou Formation and along the cracks. The fluid was mixed, and the ore-forming elements were effectively precipitated in a reducing environment. Therefore, pyrrhotite and CH4 occur in some veins. That may be why the Pulang deposit is giant.

Boiling effects on trace element and sulfur isotope compositions of sulfides in shallow-marine hydrothermal systems: Evidence from Milos Island, Greece

Boiling is a crucial process triggering ore formation in magmatic-hydrothermal systems and controlling the enrichment of precious and rare metal(loid)s in epithermal-porphyry mineralizations. Steep physicochemical gradients during boiling of hydrothermal fluids at shallow water depths caused metal(loid) precipitation along a 3 km long Pb-Zn-Ag vein system on Milos Island in the South Aegean Volcanic Arc. We present new trace element and Pb, Sr, and S isotope data from sulfides providing insights into the diversity of mineralization processes in shallow-marine hydrothermal systems. Lead and Sr isotope compositions of sulfides and sulfates reflect the mixing of fluids that reacted with metamorphic basement and the volcanic host rocks, whereas some of the S were derived from seawater. Investigation of mineralized samples along the Kondaros-Vani fault zone revealed distinct chemical variations that represent a vertical profile through the boiling zone of a hydrothermal system. Boiling during fluid ascent at decreasing temperatures (230–150 °C) and sulfur fugacities triggered the precipitation of sulfides rich in Zn, Pb, Fe, Cu, Ag, Sb, and As, resulting in increasing Pb, Ag, and Sb contents with decreasing depth. A pyrite group with high Tl/Cu and low As/Sb ratios, as well as δ34SVCDT values reaching as low as −6‰, is interpreted as precipitating from high-Cl liquids that underwent vigorous boiling at deeper crustal levels subsequent to tectonic faulting. Condensation of vapor (high Hg, Bi, and As contents) and mixing with seawater (high Mo contents) in the shallow-marine subseafloor sequences at Vani caused Hg-Bi-Mo-As-rich mineralization similar to the active hydrothermal system at Milos.

Metallogenic ages and sulfur sources of the giant Dahutang W–Cu–Mo ore field, South China: Constraints from muscovite 40Ar/39Ar dating and in situ sulfur isotope analyses

• In-situ sulfur isotope compositions of sulfides imply a magmatic origin for sulfur. • The hydrothermal breccia in the Shimensi deposit formed at 142.0 ± 0.6 Ma and was triggered by the BGP . • The coarse quartz vein-type mineralization in the Shiweidong deposit formed at 136.1 ± 0.5 Ma and was caused by the early episode of CPTG. • The W–Cu–Mo mineralization and ore-related granites in the Dahutang ore field formed in a compression–extension transitional setting. The giant Dahutang W–Cu–Mo ore field is one of the largest tungsten ore fields worldwide. Three main types of mineralization are developed at Dahutang, comprising veinlet-disseminated, hydrothermal breccia, and coarse quartz vein-type mineralization. In this study, precise muscovite 40 Ar/ 39 Ar ages and systematic in situ sulfur isotope compositions of sulfides from the Shimensi and Shiweidong deposits were presented to determine the ore-forming ages and mineralizing intrusions of the hydrothermal breccia type and coarse quartz vein-type mineralization, sources of sulfur in the mineralization, and tectonic setting of the Dahutang ore field. The precise muscovite 40 Ar/ 39 Ar dating suggested that the hydrothermal breccia in the Shimensi deposit formed at 142.0 ± 0.6 Ma and was triggered by the biotite granite porphyry (BGP), while the coarse quartz vein-type mineralization in the Shiweidong deposit formed at 136.1 ± 0.5 Ma and was caused by an early episode of coarse-grained porphyritic two-mica granite (CPTG; 144.2–137.5 Ma) and destroyed by the late episode of CPTG (130–128 Ma). The in situ sulfur isotope compositions of sulfides showed that the hydrothermal breccia type and the coarse quartz vein-type mineralization had a narrow range of sulfur isotope compositions (−3.38–+0.39‰), implying a magmatic origin for sulfur. The increased sulfur isotopes in the sulfides from early to late stages were probably caused by a reduction in the oxygen fugacity of ore-forming fluids in the hydrothermal breccia mineral system. The main W–Cu–Mo mineralization event at Dahutang occurred in the 146–136 Ma interval and was only associated with the early episode of magmatism (149–138 Ma), which coincided well with the Cu–Au–Mo–Fe mineral system in the neighboring Middle–Lower Yangtze River Metallogenic Belt (148–135 Ma). The late episode of magmatism (138–128 Ma), however, was commonly emplaced after the tungsten polymetallic mineralization and even destroyed early formed orebodies as ore-barren intrusions. Combined with the regional tectonic evolution, we proposed that the W–Cu–Mo mineralization and ore-related granites in the Dahutang ore field formed in a transitional setting from a compressional regime to an extensional regime.

Sulfur isotopic compositions of sulfides along the Southwest Indian Ridge: implications for mineralization in ultramafic rocks

The recently explored Tianzuo hydrothermal field in serpentinized ultramafic rocks of the amagmatic segment of the ultraslow-spreading Southwest Indian Ridge displays high-temperature sulfide mineralization (isocubanite, sphalerite, and minor pyrrhotite) and low-temperature (pyrite and covellite) phases. Pyrite can be subdivided into pyrite-I and -II, with the former generally having a pseudomorphic texture after pyrrhotite and the latter typically growing around isocubanite, sphalerite, and pyrite-I or occurring as individual grains in quartz veinlets. The sulfide minerals have the greatest range of δ34S values (− 23.8 to 14.1‰), found so far among modern sediment-starved ridges, with distinct δ34S values for low- and high-temperature mineral phases. The high δ34S values of isocubanite (9.6 to 12.2‰) and sphalerite (9.1 to 14.1‰) suggest that sulfate, which precipitated from seawater during an early low-temperature phase of hydrothermal circulation, was the main sulfur source for these sulfides. Pyrite-II has the lowest and most variable δ34S values (− 23.8 to − 3.6‰), suggesting microbial sulfate reduction. Pyrite-I has variable and generally positive δ34S values (− 0.1 to 12.0‰), with sulfur being inherited from pyrrhotite from the original thermochemical reduction of sulfate, mixed with volcanogenic sulfur. Intermittent magmatism represented by gabbroic intrusions, and high permeability caused by well-developed fractures associated with detachment faults, contributed to the formation of sulfides in the Tianzuo hydrothermal field. These factors possibly control sulfide mineralization in amagmatic segments of ultraslow-spreading ridges.

Mercury and sulfur isotopic composition of sulfides from sediment-hosted lead-zinc deposits in Lanping basin, Southwestern China

The Lanping basin is an important Pb-Zn-Cu-Ag polymetallic province in southwestern (SW) China. Mineralization types in the basin include mainly MVT Pb-Zn deposits, vein-type Cu deposits, and minor quartz vein-type Pb-Zn deposits. In this study, we analyzed the total Hg (THg) content and Hg-S isotopic compositions of sulfides from two types of Pb-Zn deposits in the basin, and investigate the Hg isotope fractionation mechanism and its major controlling factors in the Pb-Zn ore-forming process. At the Shangnuluo quartz vein-type Pb-Zn-Sb deposit, sulfides (especially sphalerite) show a wide δ202Hg range (−0.40 to 2.71‰), suggesting that Hg0 evaporation from hydrothermal fluids occurred during the ore formation. Negative THg vs. δ202Hg correlation in the sphalerites suggests a mixing of Hg from the vapor phase (low δ202Hg, high THg) and the residual aqueous phase (high δ202Hg, low THg). The negative ∆199Hg (−0.42 to −0.08‰) suggests that the Hg was sourced from the metamorphic basement, whereas the negative δ34S values (−13.0 to −2.7‰) suggests that the sulfur was mainly sourced from sedimentary sequences, possibly related to the organic matter decomposition and thermochemical sulfate reduction (TSR). For the Liziping and Fulongchang MVT Pb-Zn deposits, sulfides have relatively narrow δ202Hg range (−1.46 to 0.25‰), suggesting limited Hg0 evaporation during the mineralization. Lower δ202Hg values were observed in the early-stage sulfides from these two deposits, probably due to the preferential precipitation of lighter Hg isotopes in these early-stage sulfides. Sulfides from both deposits have negative ∆199Hg values (−0.24 to 0.01‰), suggesting that the Hg was also derived from the metamorphic basement. Sulfide δ34S values from the two deposits are positive, which also suggests that the sulfur was sourced from sedimentary sequences, but mainly related to TSR under relatively low-temperatures. Sulfides from different Pb-Zn deposit types in the Sanjiang Tethyans Metallogenic Belt fall into distinct fields in the δ34S vs. δ202Hg (or ∆199Hg) diagrams, indicating that the integration of S and Hg isotopes is useful to discriminate different types of Pb-Zn deposits.

Sulfur Isotope Fractionation During Sulfide Generation in the Hydrothermal Submarine Systems: The Case of Logatchev, Krasnov, and Rainbow Hydrothermal Fields, Mid-Atlantic Ridge

The sulfur isotope composition of single sulfide grains has been studied taking into account their paragenetic sequence in the samples collected from three hydrothermal fields (Logatchev, Krasnov, and Rainbow), located in the northern part of the Mid-Atlantic Ridge. The δ34S values of sulfides are +3.9 to +6, +7.1 to +9.8, and +2.1 to +8.4 ‰ in the Logatchev, Krasnov, and Rainbow fields, respectively. Late-generation sulfides within the studied domains (1–10 mm) of the samples are enriched in 34S isotope relative to early generations, and the sulfur isotope composition shows no relationship with the composition of sulfide minerals. In single grains of hydrothermal barite, the δ34S values exceed the generally accepted range for modern seawater sulfates. A model of the sulfur isotope fractionation in the hydrothermal system is proposed, based on the assumption of thermogenic sulfate reduction during fluid–rock interaction in the system, which is closed with respect to fluid. The model also takes into account simultaneous sulfur leaching from host rocks, the proportion of released sulfur from which depends on the progress of thermogenic sulfate reduction. Application of this model explains some well-known contradictions found in studying the sulfur isotope composition of sulfides from other hydrothermal fields in the World Ocean.

Ore-forming processes and mechanisms of the Hongshan skarn Cu–Mo deposit, Southwest China: Insights from mineral chemistry, fluid inclusions, and stable isotopes

• Ore-forming fluids are of predominating magmatic–hydrothermal origin at Hongshan. • Positive and uniform sulfur isotopes suggest the magmatic sulfur with predominant H 2 S. • Metals mainly precipitated due to the increased pH caused by water-rock interaction, decreasing temperature and decompression boiling. The Hongshan skarn Cu–Mo deposit is located in the southern Yidun terrane, SE Tibet Plateau, with more than 78.7 Mt resources (Cu: 0.64 Mt @ 1.23%, Mo: 5769 t @ 0.03%). The ore deposit was spatially and temporally associated with post-subduction Late Cretaceous monzogranite porphyries. Detailed geological mapping and deep drill-hole loggings reveal the vertical skarn zonation patterns of pyroxene skarn – garnet skarn – magnetite skarn – pyrrhotite-chalcopyrite skarn – garnet skarn – pyroxene skarn away from the marble, which is similar with typical skarn Cu deposit worldwide. Three hydrothermal stages have been recognized at Hongshan. They are characterized by assemblages of prograde skarn (stage 1), retrograde skarn and Cu–Fe–Mo sulfides (stage 2), and Pb–Zn sulfides associated with calcite and quartz (stage 3). Prograde skarns contain mainly andraditic garnet (two series: And 37–82 Gro 17–61 Spe+Alm+Pyr 0–4 and andradite) and pyroxene (Di 64–88 Hd 12–35 ) resulted from the interaction between magmatic-hydrothermal fluids and carbonate wall-rocks. Retrograde skarn mineralogy is controlled by hydrous Mg–Fe-rich silicate minerals, such as tremolites, actinolites, and epidotes. Petrographical and microthermomertic studies on fluid inclusions (FIs) in garnet, epidote, quartz and calcite from the three stages reveal four types of fluid inclusions: vapor CO 2 –Liquid CO 2 –H 2 O (C-type), vapor-rich two-phase inclusions (V-type), liquid-rich inclusions (L-type) and halite (sylvite)-bearing hypersaline inclusions (H-type). The C-type, l -type and V-type FIs within the garnet of stage 1 have homogenization temperatures between 400 and 550 °C, and salinities of 3.9–11.5 wt% NaCl eqv. A boiling fluid inclusion assemblage with coexisting l -type and V-type FIs was defined within the epidote and quartz of stage 2. The fluids of stage 3 are characterized by lower homogenization temperatures of 100–300 °C, developing a fluid inclusion assemblage defined solely by l -type FIs. The wide range of calculated δ 18 O H2O values in garnet (2.0 to 13.1 ‰), magnetite (10.9 to 26.3 ‰), tremolite (15.9 to 16.4 ‰) and sericite (10.5 ‰) further indicate the mixing of δ 18 O-enriched components with magmatic fluids. Sulfur isotope compositions of sulfides have a narrow range of δ 34 S values, ranging from 3.5 to 5.4 ‰, consistent with a magmatic origin and reducing conditions throughout the process of sulfide precipitation. The increased pH caused by water-rock interaction and CO 2 degassing, decreasing temperatures and decompression boiling could be crucial for the extensive ore deposition.

Genesis of the graphite orbicules in the Huangyangshan graphite deposit, Xinjiang, China: Evidence from geochemical, isotopic and fluid inclusion data

The Huangyangshan graphite deposit in the East Junggar Orogen (China) contains intriguing graphite orbicules. This contribution is designed to present reasonably comprehensive assessment of their origin. In this deposit, the intrusive orebodies are mechanically juxtaposed against contacts with granitic wall rocks. The orbicules are typically concentrically zoned in texture with a notable binary configuration involving a central core and an outer shell. The orbicule cores possess mineralogical and compositional variations that are more or less similar to those of the granitic wall rocks. The orbicule shells are composed of various ferromagnesian minerals (clinopyroxene + hornblende) in stark contrast to the matrix, where hornblende, sanidine and albite have higher Mg#, Ab and An values, respectively. The replacement of silicates by graphite and sulfides (pyrrhotite + chalcopyrite + pyrite) is common. The graphite throughout the matrix and orbicules features a patchy distribution of major elements (C) and dispersed elements (Cr, Ni, Co, S, Cu, Zn, As, Pb, etc.). The carbon isotopic compositions of the orbicular ore are −20.9 to −20.5‰, analogous to those of the surrounding strata, i.e., −25.6 to −19.3‰. The sulfur isotopic compositions of sulfides in the orbicular ore are −4.8 to −2.6‰, which differ from those of the surrounding strata, i.e., 16.0–23.0‰. Fluid inclusions principally comprise the volatile component CH4 and solid daughter minerals (graphite + chalcopyrite) with Tm > 450 °C. Vapor-liquid two-phase fluid inclusions formed under conditions of Th = 143.6–367.5 °C, P = 3–194 bar, and fO2 = −52.76 to −31.15. The hydrogen and oxygen isotopic values of the orbicular ore are δD = −110.3 to −107.0‰ and δ18Owater = 10.1–11.7‰. Zircons from the orbicular ore have 206Pb/238U ages of 304–359 Ma, with a weighted average of 319.0 ± 6.4 Ma, overlapping the geochronological age of the granitic host rocks (305.1–321.4 Ma). The orbicular ore has SiO2 concentrations ranging from 53.30 to 72.61 wt%, falling within the compositional fields of granite, quartz monzonite, granodiorite, diorite, and monzodiorite in the TAS classification diagram. The Sr-Nd and Hf isotopic data from the orbicular ore indicate mixing between materials derived from the depleted mantle and materials derived from the crust, with a dominant mantle contribution. The petrographic, geochemical, isotopic and fluid inclusion characteristics indicate that the processes of incorporation of H2O and wall rock fragments, liquid immiscibility and exsolution of a late magmatic fluid were responsible for orbicule formation in the Huangyangshan deposit. The following genetic model is proposed: (1) In the late Carboniferous, a new orbicular magma containing organic matter-derived CH4 and deep-mantle SO2 emplaced within the Huangyangshan pluton. Contemporaneously, crystal fragments and H2O were incorporated into the orbicular magma from the granitic host rocks. (2) H2O saturation was reached in the orbicular magma and fostered segregation of a hydrous ferromagnesian melt (orbicules) with a silicic residual melt (matrix). (3) At approximately 630 °C, 2000 bar and −18 lgfO2, graphite and sulfides formed en masse through deuteric alteration: 3CH4 + 2SO2 + 2(Fe2+)7[Si4O11]2(OH)2 (hornblende) = 3C (graphite) + 2FeS (pyrrhotite) + 8SiO2 (quartz) + 2(Fe3Si4O10(OH)2 + Fe3(OH)6) (chlorite), following the expulsion of a late magmatic fluid from the ferromagnesian melt.

Mineralogy and sulfur isotope characteristics of metalliferous sediments from the Tangyin hydrothermal field in the southern Okinawa Trough

We present and compare mineralogy and sulfur isotopic composition data of two surface metalliferous sediment samples, TVG11-2 and ROV11-R2, from the newly discovered Tangyin hydrothermal field in the southern Okinawa Trough (S-OT), and one surface metalliferous sediment sample 2-T4 from the Iheya North Knoll hydrothermal field in the middle Okinawa Trough (M–OT). The purpose of this study is to better understand the hydrothermal ore-forming environment and material source in the S-OT. Samples TVG11-2 and ROV11-R2 were derived from different types of chimneys. Sample TVG11-2 was derived from a black chimney which experienced formation process from high temperature to low temperature, with large gradients and fluctuations. ROV11-R2 was directly derived from a low-temperature white chimney or low-temperature diffuse flow. The sulfur isotopic compositions of sulfides and native sulfur in the S-OT are significantly lower than the sulfur isotopic compositions of pyrite and native sulfur in the M–OT, indicating there is another source with a lower sulfur isotopic composition. The low forming temperature and similar basement rocks of rhyolite in Iheya North Knoll, and dacite in Tangyin exclude phase separation and basement rock differences as the main reasons for low sulfur isotopic compositions in TVG11-2 and ROV11-R2. The occurrence of different bacterial communities between S-OT and M–OT may affect the sulfur isotopic compositions, but the influencing mechanism is still unclear. The addition of magmatic H2S may be the most possible reason for lower sulfur isotopic compositions in the Tangyin hydrothermal field.

Major and trace element and multiple sulfur isotope composition of sulfides from the Paleoproterozoic Surda copper deposit, Singhbhum shear Zone, India: Implications for the mineralization processes

The present study combines major and trace element composition, and sulfur (S) isotope data of pyrite and chalcopyrite from the Surda copper sulfide deposit in the Singhbhum Shear Zone, the most important copper and uranium producing belt (Singhbhum Cu-U Belt) in India. Three textural and compositional types of both pyrite and chalcopyrite were distinguished; unzoned to partially zoned Pyrite IA with high Co (up to 54900 ppm) and low Ni content is earliest, followed by oscillatory zoned Pyrite IB with high As (up to 25600 ppm) and Co (up to 46800 ppm), both occurring in pyrite I + chalcopyrite I + pyrrhotite + magnetite + apatite vein; Cobaltite-type substitution (Fe1−xCox)(S1−xAsx)2 is suggested for Pyrite IB. Gold occurs in Pyrite I as minor “invisible” gold and as electrum inclusions. It also occurs along with Cu, Mn, Ni, Hg, Ag, Pb, Sb, Zn, Ce, Y, U, and Th in micro-fractures that transgress the primary zoning pattern defined by As, Co, and Ni in Pyrite IB. The early inclusion-rich chalcopyrite generation (Chalcopyrite I) contains high concentration of Zn and Se, and minor to trace amounts of Co, Ni, Hg, Pb, Sb, Te, and Bi, appeared in between Pyrite I and II. Low Co, high Ni (up to 37700 ppm) content Pyrite II, and inclusion-free Chalcopyrite II enriched in Co, Ni, Hg, Bi, Mn, Ag, Sb, V, and Pb are cogenetic, and occurring in pyrite II + pyrrhotite + pentlandite + chalcopyrite II ± violarite vein. Low Co and Ni containing Pyrite III + Chalcopyrite III occur mainly as disseminated grains. The relative timing of formation of Pyrite II + Chalcopyrite II with Pyrite III + Chalcopyrite III remains uncertain.Pyrite + chalcopyrite textures indicate that all pyrite + chalcopyrite formed at some time prior to the end of deformation and metamorphism.Both in situ and mineral separates of all pyrite types and associated chalcopyrite yield a narrow range of positive δ34S values (between +3.8 and +6.9‰) suggesting sulfur being derived from a similar source. Consistent positive δ34S values and other circumstantial evidence indicate that most sulfur was derived from seawater sulfate or modified seawater (brine/evaporite). Δ33S values revealed mass dependent fractionation (MDF) signature. It is proposed that incorporation of MDF sulfur of the mineralization event in Paleoproterozoic Singhbhum Cu-U Belt took place after the great oxidation event. The high Se concentrations (260–400 ppm) and ∑Se/∑S ratios for both Pyrite I and II from Surda deposit (4.4–5.7 × 10−4) suggest a low temperature of the Cu–rich ores (250°–350 °C), and precipitation from a metalliferous fluid with a high ∑Se/∑S ratio (10−4 to 10−3) consistent with igneous input of these elements.