Isotope Compositions Of Sulfides Research Articles

Origin of Ag-Pb-Zn mineralization at Huanaote, Inner Mongolia, NE China: Evidence from fluid inclusion, H-O-S-Pb and noble gas isotope studies

The newly-discovered Huanaote Ag-Pb-Zn deposit, containing 1173 tons Ag with a grade of 154 g/t, is situated in the western part of the Great Xing’an Range metallogenic belt. The source of metals and the fluid evolution for this large metallogenic system are still ambiguous. Mineralized Ag-Pb-Zn veins are primarily hosted in Late Carboniferous monzogranite and Devonian slate. Three paragenetic stages of mineralization were recognized at Huanaote, including (stage I) early pyrite + arsenopyrite + quartz ± K-feldspar; (stage II) the main ore stage sulfide (sphalerite, galena, chalcopyrite and pyrite) + sulfosalt (freibergite, bournonite, wittichenite and tetrahedrite) + quartz + sericite + chlorite ± epidote ± fluorite; and (stage III) late pyrite + quartz + calcite. The homogenization temperatures of fluid inclusion assemblage for stages I and II range from 254 to 337 ℃ and 143 to 270 ℃, respectively, while the fluid salinity varied from 2.3 to 14.2 and 0.9 to 11.8 wt% NaCl equiv. for stages I and II, respectively. The fluid δ18OH2O and δDH2O values range from −0.4 to +6.2‰ and −116.8 to −104.8‰, respectively, indicating that the source of the fluids was primarily derived from a magma with less contribution from meteoric waters. Sulfur isotope analyses of sulfides exhibit δ34S values from −4.3 to +8.0‰, consistent with those observed in other Ag-Pb-Zn deposits in this region, suggesting the sulfur was mainly magmatic origin with minor sedimentary sulfur addition. Similarly, the Pb isotope compositions of sulfides resemble those of local Mesozoic magmatism, implying a Mesozoic magmatic source for the metals. Additionally, the noble gas isotope compositions, specifically the 3He/4He ratios (ranging from 4.41 to 7.18 Ra, mean of 5.56 Ra) for fluid inclusions,strongly support a deep magmatic fluid responsible for the formation of Huanaote deposit. Fluid cooling, mixing with meteoric waters and dilution are suggested to be important processes for Ag-Pb-Zn deposition at Huanaote.

S, Pb, and Fe isotope compositions of sulfides in middle and southern Okinawa Trough: Implying the complicated hydrothermal systems in back-arc spreading centers

Sulfur, lead, and iron isotopic systematics of sulfides from the Iheya North hydrothermal field in middle Okinawa Trough and the Yonaguni Knoll IV hydrothermal field in southern Okinawa Trough were investigated to understand the origin of ore-forming material and isotope fractionation during sulfide precipitation in back-arc spreading centers. The δ34S values (from 8.60‰ to 9.68‰) of sulfide minerals in Iheya North field suggest sulfur was derived from the leaching of basement rocks and the reduction of seawater sulfate. But an additional light sulfur source from the dissolution of biogenic sulfides in sediments is indispensable for the observed low δ34S values (between 4.78‰ and 4.97‰) of Yonaguni Knoll IV sulfides. Lead isotope compositions of all sulfides vary in a relatively wide range (206Pb/204Pb = 18.432 to 18.563, 207Pb/204Pb = 15.579 to 15.671, and 208Pb/204Pb = 38.539 to 38.979, respectively) which involves the mixing of mantle-derived and sediment-derived lead in varying proportions. Unusually high radiogenic lead isotope ratios of Yonaguni Knoll IV sulfides (207Pb/204Pb = 15.628 to 15.671, and 208Pb/204Pb = 38.854 to 38.979) imply the presence of old crustal fragments beneath southern OT. The hydrothermal fluids in OT are characterized by extremely low calculated δ56Fe values (−1.00‰ to −1.32‰) which is attributed to reducing sediments. The paired Fe-isotope compositions of pyrite and chalcopyrite revealed significantly different iron isotope compositions of hydrothermal fluids in study areas and extremely complicated ore-forming processes. Rapid precipitation of pyrite from FeS precursors accompanying iron isotopic disequilibrium moves from FeS-fluid equilibrium to pyrite-fluid equilibrium during pyrite recrystallization. The combination of sulfur, lead, and iron isotopic data suggests that hydrothermal systems in back-arc spreading centers related to plate subduction are generally affected by mantle, overlying sediments as well as potential old continental crust fragments, which results in various hydrothermal fluids and complicated mineralization processes.

Isotope Geochemistry of the Heihaibei Gold Deposit within the Kunlun River Area in the Eastern Kunlun Orogen in Northwest China and Its Metallogenic Implications

The Heihaibei gold deposit is located in the Eastern Kunlun Orogen in Northwest China. The gold mineralization here occurs predominantly in quartz veins within faulted granite zones. The sulfide mineral assemblage is dominated by pyrite and arsenopyrite, with minor chalcopyrite, galena, sphalerite, tetrahedrite, and micro-native gold. Weak alterations in Heihaibei granites include silicification and sericitization, with minor chloritization and carbonatization. The measured δDH2O and δ18Oquartz values of quartz in auriferous quartz veins range from −104.2‰ to −81.1‰ and +9.2‰ to +13.9‰, respectively. The δ34S values of sulfides in auriferous quartz veins range from +7.60‰ to +8.65‰, and the lead isotope compositions of sulfides in ores range from 18.7219 to 19.0007 for 206Pb/204Pb, 15.6959 to 15.7062 for 207Pb/204Pb, and 37.7359 to 38.8055 for 208Pb/204Pb. The Pb isotope compositions of potassic feldspars from Heihaibei granites vary from 18.3532 to 19.4864 for 206Pb/204Pb, 15.6475 to 15.6812 for 207Pb/204Pb, and 37.1750 to 38.4598 for 208Pb/204Pb. Collectively, the isotope (H, O, S, and Pb) geochemistry suggests that the ore-forming fluid was a special metamorphic water evolved from the deep slab-derived fluids, and the sulfur and lead were predominantly sourced from such metamorphic fluids, and from the deep parts of the Heihaibei granites. Therefore, the Heihaibei gold deposit can be classified as an orogenic gold deposit, which is closely associated with the subduction of the Paleo-Tethys oceanic plate, and even the final closure of this ocean by the Later Triassic.

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.

Ore forming and reworking processes in the Xitieshan Pb–Zn deposit, Qinghai Province, China: Constraints from in situ trace-element and S isotope compositions of sulfides

Although volcanogenic massive sulfide (VMS) deposits always form in extensional settings, many have been reworked by metamorphism, deformation, and the circulation of hydrothermal fluids during subsequent accretionary events. The genesis of VMS deposits has been well documented, however, the mechanisms that rework the mineralization have been relatively poorly constrained. An understanding of these mechanisms, though, is critical to the development of robust mineral deposit models as they are capable of remobilizing ore-forming metals. The Xitieshan Pb–Zn deposit, located in Qinghai Province, western China, is the third largest Pb–Zn deposit in China, with a total Pb–Zn metal reserve of 6.4 million tons. The occurrence of laminated and non-laminated orebodies in the Xitieshan deposit make it an ideal candidate to i) constrain the effects of metamorphic and hydrothermal processes on remobilization of metals in these base-metal systems, and ii) assess the genetic nature of this deposit. This is accomplished here by integrating new S isotope data and trace-element chemistry of sulfides from laminated ores with previous information on regional and deposit geology, and deformation characteristics preserved by the mineralized system. The S isotope composition of pyrite and sphalerite grains from laminated ores are consistently positive and range from 2.08 ‰ to 5.81 ‰, indicative of mixing of reduced sulfur from three distinct sources — volcanic rocks, seawater and thermochemical reduced sulfate, which is typical of VMS deposits globally. Greigite (Fe3S4) grains in laminated ores exhibit oscillatory zonation with respect to Cu, Co, Mn, Sb, and Tl concentrations; such compositional variations indicate that at least some of the primary VMS mineralization characteristics have been preserved despite subsequent reworking by metamorphism, deformation, and hydrothermal circulation. Combined with the results of previous studies, a two-stage genetic model is proposed for the formation and modification of the Xitieshan Pb–Zn deposit — i) initial formation of the primary Pb–Zn mineralization with minor of Cu, and ii) subsequent metamorphism and hydrothermal reworking of the deposit, which did not completely destroy the textural and chemical characteristics of the primary mineralization.

Mixed crustal-mantle source of porphyry Cu-Mo deposits of the Urals: Pyrite trace element geochemistry and Pb – S isotope data

Developing genetic models of porphyry Cu-, Mo-, and Cu-Mo deposits requires knowledge on the source of metals for these deposits. Even though porphyry Cu deposits worldwide were relatively well-studied and the corresponding sources of metals were considered, porphyry Cu-Mo deposits of the Urals were not previously investigated. The paper presents new data on two porphyry Cu-Mo deposits of Paleozoic age: namely Late Devonian to Early Carboniferous Verkhneuralskoe in the South Urals and Late Carboniferous to Early Permian Talitsa in the Middle Urals. Pyrite trace element data indicate minor input of Ni, Tl, and Ag from host rocks of the Talitsa deposit. Talitsa and Vekhneuralskoe deposits are heterogeneous in Pb isotope composition and, on the contrary, homogeneous in S isotope composition which is typical for porphyry deposits worldwide. The both deposits show similar age-corrected Pb isotope compositions of sulfides (18.228 to 18.521 for 206Pb/204Pb, 15.598 to 15.705 for 206Pb/204Pb, and 38.087 to 38.474 for 208Pb/204Pb) and of magmatic and hydrothermal K-feldspars (from 18.291 to 18.449 for 206Pb/204Pb, from 15.598 to 15.608 for 207Pb/204Pb, and from 38.023 to 38.127 for 208Pb/204Pb); δ34S varies from −0.4 to +3.4 ‰. The isotope data suggest that granitoid melts were the dominant source of both sulfides and ore-bearing magmatic rocks. Mantle-crustal mixing model calculated for the Urals shows 95 % of mantle Pb in porphyry Cu-Mo deposits.

In-situ trace element and S isotope compositions of sulfides from the Tonggou Cu deposit, Eastern Tianshan Orogen: Implication for ore-forming process

The Tonggou deposit is located in the western Bogda Orogen, the northern margin of Eastern Tianshan. Porphyry Cu and vein-type Cu-Zn mineralization are both developed in the Tonggou orefield. This well-preserved porphyry-vein system, therefore offers an excellent opportunity to evaluate the genetic relationship and ore-forming process between porphyry Cu and vein-type Cu-Zn mineralization. Porphyry mineralization consists of magnetite-quartz (P1) and chalcopyrite-quartz (P2) stages, whilst vein-type mineralization includes pyrite-quartz (V1), polymetallic sulfide-quartz (V2), and pyrite-calcite (V3) stages. Four pyrite generations are identified, including porphyry Cu ore-related (Py1) and vein-type Cu-Zn ore-related (Py2, Py3, and Py4) ones. In most cases, Py1 (stage P2) occurs as anhedral grains, Py2 (stage V1) as fine anhedral grains, Py3 (stage V2) as euhedral-subhedral grains, and Py4 (stage V3) as anhedral aggregates. The Sb content first decreases from Py1 to Py2, then increases from Py2 to Py3, and finally decreases from Py3 to Py4. Cobalt and Ni contents show opposite trend to that of Sb. The relatively high Sb but low Co-Ni contents in Py1 and Py3 indicate that the main ore stage (P2 and V2) environment was high oxygen fugacity and low sulfur fugacity. Moreover, the contents of Cu (Py1: avg. 4108 ppm, Py2: avg. 735 ppm, Py3: avg. 284 ppm, Py4: avg. 149 ppm) and Ag (Py1: avg. 204 ppm, Py2: avg. 11.1 ppm, Py3: avg. 6.29 ppm, Py4: avg. 2.98 ppm) gradually decrease from Py1 to Py4, indicating that the initial ore fluid was Cu-Ag rich. The δ34S values obtained are 4.6–6.8 ‰ (avg. 5.9 ‰; Py2), 5.7–7.4 ‰ (avg. 6.6 ‰; Py3), and 7.3–8.8 ‰ (avg. 8.1 ‰; Py4), which indicate that the sulfur of vein-type mineralization was initially derived from felsic magma, and subsequently mixed with strata sulfur. Furthermore, the similar δ34S range of Ccp1 (4.7–5.3 ‰) from porphyry ore and Ccp2 (3.3–4.8 ‰) from vein-type ore indicates that they have a similar felsic-magma-derived sulfur source. Combining with principal component analysis (PCA) of pyrite trace elements and REE patterns, the different pyrite generations can be divided into porphyry pyrite and vein-type pyrite, albeit with similar fluid source.Consequently, we suggest that the Tonggou porphyry and vein-type ores have similar ore-fluid source, and may belong to the same porphyry mineralization system with different ore-forming processes. Redox change may have played an important role in the metal enrichment and precipitation at Tonggou.

Genesis of the giant Zijinshan epithermal Cu-Au deposit, Fujian Province, southeastern China: Cu-He-Ar isotope perspective

The giant Zijinshan high-sulfidation epithermal Cu-Au deposit is located in the Zijinshan ore field of southeastern China. A sharp boundary separates the upper Au orebodies from lower Cu orebodies at roughly 650 m below the original pit surface, below which digenite is the predominant Cu-bearing mineral. The current discussion revolves over whether the shallow Au and deep Cu mineralization are cogenetic or reflect independent ore-forming episodes, as well as whether the digenite formation is hydrothermal or supergene. In this contribution, we investigate the He-Ar isotope compositions of ore-related sulfides to decipher the source and history of ore-bearing fluids, and use the systematic variation of Cu isotope in Cu-bearing minerals to reveal the hydrothermal (hypogene and supergene) process.A gradual decrease in fluid 3He/4He and 40Ar/36Ar ratios, as well as a sharp drop in 3He/36Ar ratio, reflects the progressive dilution of a magmatic-sourced hydrothermal fluid by meteoric water. Some pyrites have 3He/4He ratios nearly identical to those of mantle fluid, indicating that the ore-forming fluids were mantle-derived with insignificant crust assimilation. The 3He/heat ratios that are higher than those of mid-oceanic ridges, indicating that the heat was transported by convection of low-temperature fluids with hydrothermal fluids rather than direct magma volatile injection. The copper isotope composition of the sulfides (δ65Cu = -3.59 to 1.33 ‰) increases with depth, which was likely caused by the release and downward transport of heavier copper isotopes near the surface. More than half (14 of 24) of these sulfides have a hypogene origin (δ65Cu = -0.05 ± 0.18 ‰), with 9 of 24 samples are likely of supergene origin. Combining with previous study, we confirm that enriched 65Cu reservoir is absent at Zijinshan.Based on the mass-balance of Cu isotopes and the spatial orebody relationship, we conclude that the leaching by meteoric water contributed to the conversion of low-grade initial hypogene Au mineralization into supergene, friable high-grade ore, resulting in the vertical zoning of Au and Cu at Zijinshan. Furthermore, the 65Cu-rich fluids produced by leaching may have lost to the groundwater, resulting in little exploration potential for 65Cu enrichment zone, while the uniform pattern of Cu isotope in the deep indicates a high exploration potential for hypogene Cu mineralization zone at depth.

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.

Isotope Geochemistry of the Shenshuitan Gold Deposit within the Wulonggou Gold Field in the Eastern Kunlun Orogen, Northwest China: Implications for Metallogeny

The Shenshuitan gold deposit is located within the Eastern Kunlun Orogen in northwest China. The gold mineralization here occurs primarily within the ductile fault XI. The sulfide mineral assemblage is dominated by pyrite and arsenopyrite, with minor pyrrhotite, chalcopyrite, galena, and sphalerite. Host rocks predominantly consist of Ordovician silicic slate and late Silurian granites, and their alterations include silicification and sericitization. The measured δD and δ18O values of quartz and sericite range from −113.9‰ to −93.1‰ and from 4.6‰ to 12.0‰, respectively. Bulk and in situ δ34S values of sulfides range from −7.3‰ to +9.6‰ and from −3.92‰ to 11.04‰, respectively. Lead isotope compositions of sulfides show 206Pb/204Pb ratios from 18.071 to 19.341, 207Pb/204Pb ratios from 15.530 to 15.67, and 208Pb/204Pb ratios from 37.908 to 38.702. Collectively, the isotope (H, O, S, and Pb) geochemistry suggests that the ore-forming fluids were of a metamorphic origin mixed with meteoric water and that the sulfur and lead were sourced from a mixture of host rocks and original ore-forming metamorphic fluids. Lastly, this deposit can be classified as an orogenic gold deposit associated with the final collision between the Bayan Har–Songpanganzi Terrane and the Eastern Kunlun Orogen during the Later Triassic.

Geological, fluid inclusion, and O–C–S–Pb–He–Ar isotopic constraints on the genesis of the Honghuagou lode gold deposit, northern North China Craton

The Honghuagou Au deposit is located in the Chifeng-Chaoyang region within the northern margin of the North China Craton. The auriferous quartz veins are mainly hosted in the mafic gneiss and migmatite of the Neoarchean Xiaotazigou Formation along NNW- and NE-striking faults, with pyrite as the predominant ore mineral. The gold mineralization process can be divided into two stages, involving stage I quartz-pyrite and stage II quartz-calcite-polymetallic sulfide. Three types of fluid inclusions (FIs) have been identified in the Honghuagou deposit, namely, carbonic inclusions, aqueous‑carbonic inclusions, and aqueous inclusions. Quartz of stage I contains all types of FIs, whereas only aqueous inclusions are evident in stage II veins. The FIs of stages I and II yield homogenization temperatures of 275–340 °C and 240–290 °C with salinities of 3.4–10.7 wt% and 1.4–9.7 wt% NaCl eqv., respectively. The ore-forming fluids are characterized by medium temperature and low salinity, belonging to the H2O–NaCl–CO2 system. The δ18OH2O values of the ore fluids are between 2.1‰ and 5.9‰, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ13CPDB = −4.4‰ to −4‰) are also similar to mantle carbon. He-Ar isotope data (3He/4He = 0.38–0.44 Ra; 40Ar/36Ar = 330–477) of fluid inclusions in pyrite indicate a mixed crustal and mantle source for the ore-forming fluids. Whereas, S-Pb isotope compositions of sulfides reveal that ore metals are principally derived from crustal rocks. On the basis of available geological and geochemical evidence, we suggest that the Honghuagou deposit is an orogenic gold deposit.

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.

Timing and origin of the Shesuo skarn Cu-polymetallic deposit in the northern Lhasa subterrane, central Tibet: Implications for Early Cretaceous Cu(Mo) metallogenesis in the Bangong-Nujiang metallogenic belt

The Bangong-Nujiang metallogenic belt is a newly discovered copper-polymetallic belt in the Tethyan domain. To date, the Shesuo skarn Cu-polymetallic deposit is the only productive Early Cretaceous Cu deposit in the middle segment of this belt. We conducted zircon U-Pb and molybdenite Re-Os dating of this deposit, and the results show that the Shesuo skarn Cu-polymetallic deposit formed at 117–112 Ma. Within the mining area, granodiorites and monzogranites are the main metallogenic granitic bodies. The petrogeochemical features imply that the granodiorites and monzogranites were derived from the partial melting of juvenile lower crust resulting from mantle-derived magmatic underplating, with the additional involvement of ancient crust in the magma chamber, whereas the monzogranites experienced significant fractional crystallization. The δ34S values of sulfide ores suggest that they were mainly sourced from the magma and slightly contaminated by surrounding strata. The Pb isotope compositions of sulfides and Re contents of molybdenite indicate that the metals were derived from the juvenile lower crust, with a small fraction from ancient crustal materials. Our study suggests that the generation of the Shesuo deposit was most likely triggered by slab breakoff during the southward subduction of the Bangong-Nujiang Ocean lithosphere. The Shesuo and Xiongmei deposits have low zircon Ce4+/Ce3+ and EuN/Eu* ratios and low whole-rock average V/Sc, Sr/Y and (EuN/Eu*)/YbN ratios. We propose that these values are due to the input of reduced components, leading to the generation of metallogenic magmas with relatively low magmatic oxidation states and water contents and rendering the magmas infertile for later porphyry-skarn Cu formation in the Xiongmei area.

Trace Elements and Sulfur Isotopes of Sulfides in the Zhangquanzhuang Gold Deposit, Hebei Province, China: Implications for Physicochemical Conditions and Mineral Deposition Mechanisms

The Zhangquanzhuang gold deposit is a special deposit in the Zhangjiakou district, on the northern margin of the North China Craton. It is characterized by the enrichment of sulfides, the scarcity of tellurides and zero to positive sulfur isotope compositions compared with the famous Dongping and Xiaoyingpan Te-Au-Ag deposit types of the same district. In this paper, we use the in-situ LA-(MC)-ICP-MS and bulk trace element concentrations of pyrite, and in-situ sulfur isotope compositions of sulfides, to study physicochemical conditions and mechanisms of mineral deposition in the Zhangquanzhuang deposit. Pyrite from stage I (PyI) contains high Te contents, pyrite from stage II (PyII) has the highest Co and Ni contents, and pyrite from stage III (PyIII) contains high Cr, Zn, Pb, Ag, Cu, Sb, Bi and Au contents. The calculated in-situ δ34SH2S values range from 0.9‰ to 6.1‰, and the values for stages I and II are higher than those for stage III. The mineral assemblages and trace element contents in pyrite show that large amounts of metals precipitated during stage III, in which the pH and logfO2 were constrained within the range of 4.1 to 5.2 and −36.9 to −32.1, respectively. Sulfidation and boiling derived from decreasing pressure may be the main mechanisms leading to mineral deposition in stage III. The Zhangquanzhuang gold deposit was formed in a mineral system that was different from the one that formed the Dongping and Xiaoyingpan Te-Au-Ag deposits, and should thus be called the “Zhangquanzhuang−type” deposit and considered a third gold deposit type in the Zhangjiakou ore field.

Hydrothermal evolution and ore genesis of the Laozuoshan Au skarn deposit, northeast China: Constrains from mineralogy, fluid inclusion, and O–C–S–Pb isotope geochemistry

The Laozuoshan mine, located in the central Jiamusi block, is the largest gold skarn deposit in Northeast China. It comprises three ore zones (East, Middle, West) with complex stratigraphic and structural controls. The skarn-type orebodies mainly occur in the East and Middle ore zones along the contact zones between Hercynian granite and Precambrian metasedimentary rocks. The earliest stage of alteration is characterized by potassium hornfels. Subsequently, prograde skarn formation occurred, characterized by garnet in the grossular-andradite series and pyroxene in the hedenbergite-diopside series. This was followed by a retrograde skarn overprint of hydrous silicates and ore minerals. Three types of garnet with distinct textures and elemental compositions are recognized, which indicate fluctuating physicochemical conditions in the hydrothermal fluids.The fluids associated to the prograde skarn are characterized by high temperature and high salinity, which underwent fluid boiling that led to precipitation of minor pyrite and arsenopyrite. The main gold and sulfide mineralization is related to the retrograde skarn overprint, where cooling and strong fluid-rock interactions occurred. Gold precipitation is estimated to have occurred at temperatures of 380–470 °C, based on the arsenopyrite geothermometer and fluid inclusion microthermometry. The fluid inclusion and C-O isotope data indicate that the ore-forming fluids were dominated by magmatic water during the prograde skarn stage and the main ore-forming stages. Mixing between meteoric and magmatic fluids occurred during the latest stages of the retrograde skarn formation. Both sulfur and lead isotope compositions of sulfides support a magmatic origin for the ore-forming materials.On the basis of the available geological and geochemical evidence, we propose that the Laozuoshan deposit is a reduced gold skarn deposit, genetically related to the granitic pluton.

Fluid source and metal precipitation mechanism of sediment-hosted Chang'an orogenic gold deposit, SW China: Constraints from sulfide texture, trace element, S, Pb, and He-Ar isotopes and calcite C-O isotopes

AbstractThe source of fluids and their mechanism of metal precipitation in sediment-hosted, disseminated orogenic gold deposits are ambiguous. Pyrite texture, trace element, S, Pb, and He-Ar isotope compositions of sulfides and C-O isotope data of calcite from Chang'an orogenic gold deposit in the Ailaoshan orogenic belt, southwest (SW) China, were studied to provide a new genetic model for the sediment-hosted orogenic gold deposit, furthering knowledge of the source of fluids and their mechanism of metal precipitation. Orebodies at Chang'an are mainly hosted by Ordovician turbidite with a few in Oligocene syenite. Two stages of mineralization have been identified in the deposit: stage I disseminated quartz-arsenopyrite-pyrite and stage II veined quartz-calcite-polymetallic sulfides. Five generations of pyrite have been identified in turbidite: pre-ore syn-sedimentary pyrite, pyI-1, and pyI-2 in stage I, and pyII-1 and pyII-2 in stage II, and an unzoned pyrite population developed in syenite. PyI-1 commonly overgrows syn-sedimentary pyrite with irregular boundaries and contains arsenopyrite, galena, chalcopyrite, and electrum inclusions along the boundaries. PyI-1 is overgrown by thin and inclusion-free pyI-2, and crosscut by pyII-1, which is rimmed by pyII-2.The syn-sedimentary pyrite is distributed parallel to the sedimentary bedding and contains As (620.8 ppm), Pb (61.6 ppm), Ni (59.8 ppm), Mo (54.4 ppm), Co (23.4 ppm), and Cu (13.0 ppm) with low-Au content of 0.06 ppm. This pyrite has δ34S values of −18.1 to +30.4‰ and high-radiogenic Pb isotope ratios (average 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of 19.05, 15.86, and 39.87, respectively). PyI-1 and coexisting arsenopyrite are enriched in invisible Au (up to 227.1 and 353.3 ppm, respectively), As, Ni, Cu, and Pb, while pyI-2 contain much lower trace element abundances relative to pyI-1 and arsenopyrite. Partial replacement of syn-sedimentary pyrite by pyI-1 plus arsenopyrite, galena, chalcopyrite, and electrum, and similar Pb isotope ratios between syn-sedimentary pyrite and pyI-1 indicate that reaction of external deep Au-rich fluids with syn-sedimentary pyrite is responsible for gold precipitation in stage I. PyI-1, arsenopyrite, and pyI-2 show a narrower δ34S range of −3.2 to 7.1‰ relative to syn-sedimentary pyrite, demonstrating that the fluid-pyrite interaction has homogenized the sulfur. The unzoned pyrite in syenite has similar mineral inclusions (arsenopyrite, galena, etc.), δ34S values (+0.6 to 6.3‰) and Pb isotope ratios to pyI-1, but much lower trace element abundances relative to pyI-1. It may be attributed to different reactions of similar fluids with different wall-rocks. PyII-1 and pyII-2 in stage II contain elevated As, Pb, Cu, Sb, Zn, and Ag with low mean Au content (3.3 ppm) and have δ34S ranges of −2.8 to +1.2‰ and −6.2 and −0.8‰, respectively. Galena in stage II has lower radiogenic Pb isotope ratios than stage I pyrites, indicative of a different Pb source or fluid evolution. The gases released from a mixture of pyII-1-pyII-2 have R/Ra of 0.38 to 0.98 and 40Ar*/4He of 0.50 to 1.34, falling between the fields of mantle-derived and crustal fluids. Late ore calcites have δ13CPDB of −8.7 to 2.7‰ and δ18OSMOW of 8.05 to 25.58‰, also plotting between sedimentary carbonate and mantle fields. These signatures indicate that ore fluids in stage II are base metal-rich fluids with a small amount of contribution from the mantle. Different ore assemblages, trace element composition and isotope data between stages I and II at Chang'an suggest that the deposit experienced an evolution from early Au-rich fluids to late base metal-rich ones. This study highlights that ore metals in sediment-hosted disseminated orogenic gold deposits may be sourced from both deep fluids and local wall-rock, and that fluid-rock interaction behaved as a key control on ore precipitation.

Sulfur isotope behavior during metamorphism and anatexis of Archean sedimentary rocks: A case study from the Ghost Lake batholith, Ontario, Canada

Recycling of surface-derived sulfur into the deep earth can impart distinct sulfur isotope signatures to magmas. The details of sulfur transfer from sedimentary rocks to magmas (and ultimately igneous rocks) through metamorphism and devolatilization and/or partial melting, however, is difficult to trace. To understand this process in detail we studied multiple-sulfur isotope compositions of sulfides in the Archean (c. 2685 Ma) Ghost Lake batholith (GLB) and its surrounding host metasedimentary rocks of the Superior Craton (Ontario, Canada) by high spatial resolution secondary ion mass spectrometry, complemented by high-precision gas source isotope ratio mass spectrometry measurements. The GLB comprises strongly peraluminous biotite+cordierite, biotite+muscovite, and muscovite+garnet+tourmaline granites to leucogranites, which are thought to represent the partial melts of surrounding metagreywackes and metapelites. The metasedimentary rocks display a range of metamorphic grades increasing from biotite-chlorite (280-380°C) at ∼5 km away from the GLB to sillimanite-K-feldspar grade (∼660°C) immediately adjacent to the batholith, thus providing a natural experiment to understand sulfur isotope variations from low- to high-grade Archean sedimentary rocks, as well as granites representative of their partial melts.We find that metasedimentary sulfide δ34S values increase with progressive metamorphism at most 2-3‰ (from −1‰ up to +1 to +2‰). An increase in δ34S values in pyrrhotite during prograde metamorphism can be explained through Rayleigh fractionation during pyrite desulfidation reactions. Pyrite from all but one of the granite samples preserve δ34S values similar to that of the high-grade metasedimentary rocks, indicating that partial melting did not result in significant fractionation of δ34S. The exception to this is one granite sample from a part of the batholith characterized by abundant metasedimentary inclusions. This sample contains pyrite with heterogeneous and low δ34S values (down to −16‰) which likely resulted from incomplete homogenization of sulfur between the granitic melt and metasedimentary inclusions. Small (several tenths of a permil), mostly positive Δ33S are observed in both the metasedimentary rocks and granites.Our results suggest that Archean strongly peraluminous granites could be a high-fidelity archive to quantify the bulk sulfur isotope composition of the Archean siliciclastic sediments. Further, our findings indicate that subduction of reduced sulfur-bearing sediments in the Archean with δ34S at or near 0‰ should result in release of sulfur-bearing fluids in the mantle wedge with similar values (within a few permil). S-MIF (if initially present in Archean surface material) may be preserved during this process. However, the absence of S-MIF in igneous rocks does not preclude assimilation of Archean sedimentary material as either S-MIF may not be originally present in the Archean sedimentary sulfur and/or homogenization or dilution could obscure any S-MIF originally present in assimilated Archean sediments.

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 Zhangquanzhuang gold deposit in the northern margin of North China Craton: Constraints from deposit geology and ore isotope geochemistry

The genesis of orogenic gold deposits in the northern margin of the North China Craton (NCC) is still ambiguous, and this is addressed in this case study on the Zhangquanzhuang gold deposit. This deposit shows features typical of orogenic gold deposits, including quartz vein-type mineralization controlled by shear zones, sericite-quartz-pyrite-carbonate alteration along shear zones, absence of connection to any magmatic intrusion, and occurrence of native gold and electrum. The Zhangquanzhuang gold deposit, which is hosted in Archean high-grade metamorphic rocks, was formed in Mesozoic and largely later than the regional metamorphism. In this deposit, the Pb isotope compositions of sulfides in ores have low 206Pb/204Pb ratios of 16.874–17.007, 207Pb/204Pb ratios of 15.368–15.410, and 208Pb/204Pb ratios of 37.023–37.215, and these are much less radiogenic than those of regional metamorphic and magmatic rocks. This finding precludes the possible derivation of ore fluid from regional magmatism and metamorphism. In pyrite-hosted fluid inclusions in the ores, the 3He/4He and 40Ar/36Ar ratios are 1.26–1.75 Ra and 1622–2816, respectively, showing prominent signature of mantle sources. These geochemical features, together with the large temporal discrepancy between regional metamorphism and mineralization, suggest that ore fluid and metal had a subcrustal source similar to the gold deposits in the Jiaodong gold province in the southeastern margin of the NCC. The calculated δ34SH2S values for the ore fluid are 2.31–4.48‰, which are heavier than the δ34S of depleted mantle. The δ18O of ore-related quartz mostly cluster around 11‰, implying high δ18O of subcrust-derived ore fluid. The stable O and S isotope data indicate that the subcrustal source has been metasomatized by subducted crustal sediments.