δ34S Values Of Sulfides Research Articles

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

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

Multi-layer metallogeny of the maoping carbonate-hosted Pb–Zn deposit, SW China: Constraints from C–O–S–Pb isotopes

The Maoping carbonate-hosted Pb–Zn deposit, located in the Sichuan-Yunnan-Guizhou metallogenic belt (SYGMB), comprises numerous ore bodies hosted in Devonian and Carboniferous Systems. Multi-layer Pb–Zn mineralization (two or more systems) at deposit scale is still rare in the SYGMB and poorly understood. Although δ18O values (+9.4 to +12.3‰) of calcite in Devonian System is similar to those (+9.2 to +12.0‰) of calcite in Carboniferous System, δ13C values (−1.7 to −0.2‰) of calcite in Devonian System is significantly higher than those (−5.4 to −2.7‰) of calcite in Carboniferous System. Such C–O isotopic characteristics suggest that the source of C was ore-hosting carbonate rocks, whereas the source of O was basement metamorphic rocks. The simulation of C–O isotopes shows that water-rock interaction was the main mechanism for calcite precipitation. The δ34S values (+18.3 to +22.7‰) of sulfides in Devonian System are higher than those (+7.1 to +17.5‰) of sulfides in Devonian System. This implies that reduced sulfur in Devonian System originated from Devonian marine sulfate, while those in Carboniferous System originated from Carboniferous marine sulfate. Such S isotopic compositions also show that thermochemical sulfate reduction (TSR) was the dominant mechanism for the reduction of marine sulfate. The isotopic ratios (206Pb/204Pb = 18.680–18.744, 207Pb/204Pb = 15.753–15.764, 208Pb/204Pb = 39.282–39.399) of galena in Devonian System and those (206Pb/204Pb = 18.554–18.581, 207Pb/204Pb = 15.722–15.752, 208Pb/204Pb = 39.018–39.109) of galena in Carboniferous System are similar to those of basement metamorphic rocks and cover carbonate rocks. This indicates that ore-forming metals had mixed sources. Considering the above results, the multi-layer metallogeny is the mixing of metal and sulfate-bearing fluids with metal-rich but reduced sulfur-poor fluids at the depositional site where methane or other organic matter reduces sulfate and precipitates sulfides. In the future, A multi-layer exploration strategy for Pb–Zn deposits in the SYGMB should be emphasized.

Vapor-phases as Cu transport agents for the shear-zone-hosted mineralization system: A perspective from H-O-S-Cu isotopes

Abstract Elucidating metal transport agents is the key to understanding the genesis of deposits and tracking the locations of concealed orebodies. Here, we integrate H-O-S-Cu isotopic data from the shear-zone-hosted Lingyun Cu deposit, China, as a means to fingerprint metal transport agents. Sulfide mineralization can be divided into early and late stages, which consist of chalcopyrite + bornite + quartz veins and chalcopyrite + bornite + ankerite veinlets, respectively. Both δ18Ofluid and δD values of fluid inclusions hosted by quartz (δ18Ofluid: 0.5‰ to 9.9‰, δD: –103.9‰ to –60.1‰) and δ65Cu values of sulfides (–1.85‰ to +0.39‰) from the early stage progressively decrease from the southeastern to northwestern portions of the Lingyun deposit, whereas sulfide δ34S simultaneously shifts toward heavier values (–14.4‰ to 5.0‰). The δ34S and δ65Cu values of sulfides from the late stage have restricted ranges from –11.2‰ to –9.3‰ and –0.30‰ to 0.05‰, respectively. The possibilities of meteoric water addition, water-rock interaction, inter-mineral Cu partitioning, diffusion, and oxidation could be ruled out as reasons for having caused systematic H-O-S-Cu isotope variations. Vapor-liquid separation resulted in preferential incorporation of light Cu, H, and O isotopes into the vapor phase. The decrease in oxygen fugacity in the fluids resulted in a shift toward heavier δ34S values as fluid flowed outward. Vapor-phases are the dominant transport agents for Cu in the Lingyun deposit, which may be widely applicable to shear-zone-hosted deposits. The direction of progressively increasing δ65Cu, δD, and δ18O values and decreasing δ34S values allows identification of potential locations of concealed orebodies.

Genesis of the Fenghuangshan gold deposit, eastern Hebei, China: Insights from ore geology, fluid inclusion and H–O–S isotopes

The Jidong area is a vital gold province in North China, including plenty of metamorphic rock-hosted gold deposits. Whether ore-forming fluids are magmatic or metamorphic remains controversial. The genesis for gold mineralization in this gold province is ambiguous. The Fenghuangshan gold deposit lies on the eastern fragment of the Jidong gold province. In this paper, we present a detailed study on ore geology, fluid inclusions, and stable isotopes for the deposit to illustrate the characteristics of ore-forming fluids and ore genesis.The deposit occurs as gold-bearing quartz vein and disseminated- and veinlet-type mineralization. The main orebody named 7# is hosted in migmatitic granite, controlled by NE trending secondary fracture system. Four hydrothermal mineralization stages were identified, including: (Ⅰ) white quartz, (II) pyrite-quartz, (III) quartz-polymetallic sulfide, and (IV) calcite-chlorite-quartz. The Stage II and III belong to main gold mineralization stage. Fluid inclusions from different stages show that a lowering trend of fluid inclusion homogenization temperature was observed. They ranged from 222 °C to 407 °C (early-stage), 144 °C to 375 °C (main-stage), and 86 °C to 174 °C (late-stage), respectively. The salinities of the ore-forming fluids were typically low, ranging from 0.83 to 15.47 wt% NaCl equivalent. On the basis of Laser Raman analysis and fluid inclusion microthermometry, the ore-forming fluids belonged to a low- to moderate-temperature, low-salinity H2O-NaCl-CO2 system. Fluid immiscibility gave rise to rapid gold deposition. The early-stage δD and δ18OH2O values from quartzs ranged from –96.4‰ to –92.5‰ and from 1.74‰ to 2.44‰, whereas main-stage fluids had δ18OH2O values of –4.10‰ to –3.50‰ and δD values of –91.5‰ to –89.5‰. The early- and main-stage sulfide δ34S values varied from –2.0‰ to + 2.2‰, with average values of + 0.4‰. H-O-S-isotope data indicated that the primary ore-forming fluids were magmatic water mixing meteoric water during mineralization, and ore-forming materials were derived from a homogeneous magmatic source. Ore geology, fluid inclusions, and stable isotopes illustrate that the Fenghuangshan gold deposit is a low- to moderate-temperature magmatic-hydrothermal gold deposit. Future deep-seated and surrounding gold exploration should center on this area.

Gold–Sulfide Mineralization in the Manitanyrd Region, Polar Urals, Russia

This article describes the characteristics of gold–sulfide–quartz and gold–sulfide (gold–arsenic) ore occurrences in the Manitanyrd region of the Polar Urals. Ore occurrences are confined to NE-trending shear zones and have the common features of a geological structure. The host rocks are metamorphosed volcanic and volcanic–sedimentary rocks. We analyzed the mineral and chemical composition of the ore mineralization in all studied ore occurrences, showing that they belong to the same mineral type—pyrite–arsenopyrite, with a variable ratio of the main minerals. Arsenic pyrite is present in all ore occurrences. Two stages of ore formation were distinguished: early gold–pyrite–arsenopyrite with finely dispersed gold and late gold–galena–chalcopyrite–sphalerite with coarse gold, fahlore, and sulfosalts Pb, Cu, Bi, Sb. Native gold of the first generation, finely dispersed in arsenopyrite and pyrite, had an average to high fineness (800‰–1000‰) with a relatively low dispersion. Native gold of the second generation was larger, and its fineness in ore occurrences varied; in one of them, it varied from 300‰ to 950‰, while in others, it varied from 800‰ to 950‰. The isotope composition of sulfur in sulfides (δ34S) ranged between −0.2‰ and −8.0‰. δ34S values of sulfides in the range of −0.2‰ to −3.5‰ were similar to meteorite, indicating the participation of a single deep magmatic source of sulfur in the ore formation. According to the study of fluid inclusions, the formation of ore quartz veins occurs in the temperature range of 467–109 °C. The similarity of the geological–structural, mineralogical–geochemical, and isotope–geochemical features of the gold–sulfide–quartz and gold–sulfide occurrences in the area suggest their formation in a single hydrothermal system.

Ore-forming material sources of the Pb–Zn–(Ag–Fe–Cu) deposits in the northern Gangdese belt, Lhasa terrane: Constraints from geology, geochronology and S–Pb isotopes

Many new skarn Pb–Zn–(Ag–Fe–Cu) deposits have been identified in the northern Gangdese polymetallic belt (NGPB). The NGPB comprises skarn deposits with different metal associations: Pb–Zn–(Ag), Pb–Zn–Fe–Cu, and Fe–Cu. The sources of ore-forming materials and whether intrusions contribute materials to these deposits, remain debated subjects. This study focused on zircon U–Pb dating and S–Pb isotopes of metal sulfides, ore-forming rocks, and wall rocks from the typical deposits in the three systems. Zircon U–Pb dating indicates that the biotite granite in the Longmala deposit was emplaced at 54.6 ± 0.6 Ma, which is consistent with its metallogenic age. The δ34S values of sulfides from the Pb–Zn–(Ag) deposits (Yaguila: −2.1‰ to + 6.0‰, Mengya’a: −0.8 ‰ to + 4.6 ‰) are similar to those from Pb–Zn–Fe–Cu deposits (Longmala: +1.6‰ to + 3.6‰, Lietinggang–Leqingla: −8.3 ‰ to + 2.0 ‰), suggesting a magmatic source of sulfur. The Pb isotopes of sulfides in Pb–Zn–(Ag) deposits (206Pb/204Pb = 18.4804–18.6935, 207Pb/204Pb = 15.6637–15.7331, and 208Pb/204Pb = 38. 0164–39.2612) are similar to those of the contemporaneous intrusions, as are those of Pb–Zn–Fe–Cu and Fe–Cu deposits, suggesting that the intrusions provided metals for the three systems. In comparison, the sulfides from the Pb–Zn–(Ag) deposits have higher 207Pb/204Pb values (15.6637 to 15.7331, mostly > 15.70) than the Fe–(Cu) deposits (15.6186 to 15.6848) and the Pb–Zn–Fe–Cu deposits (15.6163 to 15.7197), indicating that the metals of Pb–Zn–(Ag) deposits were derived from the upper-crust magma, whereas the metals of Fe–(Cu) and Pb–Zn–Fe–Cu deposits originated from the deep magma that required the involvement of mantle-derived components. Combined with previous research, we propose that the metals of Pb–Zn–(Ag) deposits originated from S-type granites, whereas those of Pb–Zn–Fe–Cu and Fe–(Cu) deposits were derived from I-type granites in the NGPB.

Petrology of the Kureika Graphite Deposit in the Roof of the First-Rapid Trap Intrusion (Siberian Platform)

Abstract —The leading role of lithostratigraphic, structural/tectonic, magmatic, metamorphic, and fluid geologic factors in the formation of a graphite deposit is substantiated. We present the petrographic and chemical compositions of rocks and minerals of igneous rocks, the δ13С values of graphites and calcitites, the δ18O values of carbonates, the δ34S values of sulfides, and the 87Sr/86Sr and 87Rb/86Sr ratios in calcitites and microdolerite injections. The thermal effect of magmatic melt on coal led to its degassing and graphitization. The steaming of microdolerite injections with hydrocarbon fluids was probably accompanied by the removal of iron from them and the crystallization of low-Fe clinopyroxene, and the interaction of fluids with basaltic melt in the upper endocontact zone of the intrusion led to the segregation of the melt and the formation of a globular structure of rocks. The presence of a calcitite lens and a sulfide vein between the roof of the intrusion and the graphite bed is due to the earlier intrusion of sulfate salt melt and its subsequent interaction with hydrocarbon fluids, which resulted in sulfate reduction and the formation of calcitites. The sulfate reduction terminated with iron sulfurization in the basaltic melt and the formation of a sulfide vein. Sulfate salt melt was a source of heavy sulfur isotope (δ34S = 14.9–17.5‰) for sulfides and of calcium for calcitites. The similar isotope compositions of calcitites (δ13СPDB = –22.5 to –23.5‰), coals (–22.6 to –25.5‰, n = 25), and graphites (–23.5 to –25.0) suggest that coal is a source of carbon for calcitites. In the isotopic compositions of strontium (87Sr/86Sr ≈ 0.70834–0.70885) and oxygen δ18O ≈ 15‰) the calcitites are similar to the Devonian evaporites of the Siberian Platform. The isotope data (δ34S, δ18O, δ13С, and 87Rb/86Sr) point to the participation of the coal seam and anhydrite as sources of substance in the formation of calcitite and sulfide mineralization.

Mineralization and genesis of the orogenic gold system in the Kalamaili area, East Junggar, Xinjiang, northwestern China

There are many lode gold deposits and occurrences in the Kalamaili area of the East Junggar, northwestern China. However, little is known about the specifics of ore geology and geochemistry of these gold deposits because of very limited exploration and research work in this region. Field geology, fluid inclusions, stable isotopes, trace elements in quartz, and hydrothermal zircon U-Pb dating are combined in this study to constrain the nature and source of ore fluids, the timing of mineralization, and the mechanism of gold precipitation in Kalamaili. The gold deposits are confined to a narrow zone between two regional NW- to NWW-trending shear zones and are structurally controlled by secondary, high-angle faults of the shears. The orebodies occur in the Middle Devonian and Lower Carboniferous, zeolite to lower greenschist facies clastic sedimentary and pyroclastic rocks. Gold mineralization occurs as auriferous quartz-sulfide ± tourmaline veins/veinlets and disseminated ores in the immediate altered wall rocks. The ore mineralogy is relatively simple and dominated by quartz with minor to trace amounts of sulfides (pyrite and arsenopyrite), sericite, calcite, and native gold. Quartz of various generations contains three types of fluid inclusions, including predominant H2O-CO2-NaCl inclusions and subordinate H2O-NaCl inclusions and CO2 ± CH4 ± N2 inclusions. The mineralizing fluid is uniformly characterized by a medium to high homogenization temperature (mostly 240−330 °C), low salinity (typically <6 wt% NaCl equivalent), reduced, and CO2-rich-H2O-NaCl ± CH4 fluid. The hydrogen and oxygen isotope data (δ18OH2O = +5.6‰ to +14.3‰, δDH2O = −99‰ to −62‰) indicate a metamorphic origin for the mineralizing fluid. The majority of sulfide δ34S values range between 0‰ and +10‰, indicative of a largely sedimentary rock reservoir of sulfur in the ore-forming fluids. Geochemically, the auriferous quartz is characterized by low concentrations of most trace elements including Ti, Al, Li, Ge, and Sb. Laser ablation−inductively coupled plasma−mass spectrometry U-Pb isotope dating of hydrothermal zircons from the auriferous quartz vein yielded a weighted mean 206Pb/238U age of ca. 313 Ma. Phase separation of ore fluids and fluid-rock interaction are suggested as key mechanisms for the gold precipitation. Integrated geological and geochemical evidence indicates that formation of the orogenic gold system in Kalamaili is related to the transition from compressional to transcurrent deformation during the Late Carboniferous. Target gold exploration in this region should focus on the northeast side of the Kalamaili fault zone, where there exist suitable structural and stratigraphic trap sites with high fluid flux and potential gold mineralization.

The Peña do Seo W-Sn deposit, NW Iberia: Petrology, fluid inclusions and O-H-S isotopes

The Peña do Seo W-Sn ore deposit in NW Iberia consists mainly of quartz veins hosted in schists. Vein mineralogy comprises wolframite, cassiterite and minor molybdenite. Peraluminous S-type granites and minor metaluminous granitoid breccias crop out in the same location. Whole rock geochemistry, mineral characterization, fluid inclusions and stable isotope geochemistry have been combined to infer hydrothermal mineralization conditions. A pre-ore stage (0) involving the alteration of host rocks, three stages of mineralization (I, II and III), and a supergene stage (IV) have been identified. Stage I (oxide-halide-sulfide stage) consisted of a cassiterite-pyrite-fluorite mineralization in granitoid breccias. Stage II (main oxide stage) involved wolframite-rich selvages and wolframite-cassiterite-(molybdenite) quartz veins. Stage III (main sulfide stage) consisted of a sulfide mineralization in quartz veins comprising pyrite and minor arsenopyrite and chalcopyrite. Three types of fluid inclusions were found in vein quartz: (1) aqueous two-phase inclusions, with homogenization temperatures (Th) between 445 °C and 280 °C and moderate salinities (9-14 wt.% NaCl eq.), (2) aqueous-carbonic three-phase fluid inclusions, with Th from 340 °C to 260 °C and low salinities (2-7 wt.% NaCl eq.), and (3) aqueous two-phase fluid inclusions, with Th from 270°C to 155 °C and low salinities (0-6 wt.% NaCl eq.). δ18O values in quartz from mineralized veins range from +11.2‰ to +13.4‰, and between +15.0‰ and +15.4% in quartz from mineralized granitoid breccias. δ34S values in sulfides (pyrite, arsenopyrite and chalcopyrite) range between +13.0 ‰ and +37.1 ‰, thus suggesting a marine source of sulfate and possible equilibration with host-rock sulfides. δD values in muscovite and chlorite from quartz veins range between -105.7 ‰ and -71.5 ‰ and between -69.4 ‰ and -67.1 ‰, respectively, indicating a transition from magmatic to magmatic-metamorphic conditions. An aqueous (H2O–NaCl) magmatic-hydrothermal fluid led to the W-Sn mineralization, as deduced from the studied fluid inclusions and isotopic signatures. High W and Sn contents in the peraluminous granites indicate that the W-Sn mineralization in Peña do Seo could partially be related to the granites and granitoid breccias. Whereas the Sn (± W) likely derived from hydrothermal fluids exsolving from the crystallizing magmas, host quartz schists would have supplied other elements required for wolframite deposition such as Fe and Mn. Sulfide mineralization in stage III was probably driven by fluid dilution.

Cd isotope constraints on metal sources of the Zhugongtang Zn–Pb deposit, NW Guizhou, China

The Sichuan–Yunnan–Guizhou metallogenic province (SYGMP) includes > 400 Zn − Pb deposits and prospects, eight of which are large-scale deposits with large reserves of critical metals such as Cd and Ge, including the Huize Zn − Pb − Cd − Ge and Daliangzi Zn–Pb–Ge–Cd deposits. The newly discovered Zhugongtang Zn − Pb deposit is a super-large deposit with Zn–Pb reserves of > 3 Mt. Its geochemical features are similar to those of the Huize deposit, with similar sulfide δ34S values and concentrations of critical elements in sphalerite (e.g., Cd and Ge). However, the two deposits have different host strata, and it remains unclear as to whether they have similar oregenesis. In this study, δ114/110Cd values and major- and trace-element compositions of sphalerites collected from a drill-core and tunnels of the Zhugongtang deposit were determined in an investigation of metal sources. Drill-core samples were impure and exhibited strong correlation (R2 = 0.89) between Zn and Cd contents. For samples from mining tunnels, the Cd and Fe contents of selected sphalerites were positively correlated, especially yellow sphalerites (R2 = 0.76). Cadmium is likely hosted in sphalerite by the substitution mechanism of (Fe2+, Cd2+) ↔ Zn2+. The δ114/110Cd values of all samples ranged from − 0.43 ‰ to 0.06 ‰. Based on Zn/Cd ratios, and excluding geochemical processes that may have caused the variable Cd isotopic compositions, we suggest that the metal sources of the deposit were derived from the mixing of sedimentary and basement rocks. This model is supported by the strong relationship between the δ114/110Cd and 1/Cd values of sphalerites from 11 typical Zn–Pb deposits in the SYGMP (R2 = 0.81). The quantification of metal contributions of source rocks indicates that deposits derived mainly from sedimentary rocks generally have relatively low sphalerite Ge contents and small Ge reserves, whereas those derived mainly from basement rocks have higher Ge contents and larger Ge reserves. This study provides a new model for explaining the enrichment of critical metals in Zn–Pb deposits of the SYGMP, thus extending the applications of Cd isotopes in hydrothermal systems.

Genesis of the Yawan Sb deposit, West Qinling Orogen, Central China: Constraints from S–Pb–C–O isotopes and Sm[sbnd]Nd geochronology

The Yawan Sb deposit is a large deposit located in the Xihe County, Gansu, northwestern China. Ore bodies are hosted in the Triassic limestone and are controlled by the NE- trending faults, occurring as lamellar, lenticular, veined, and lentil. Based on the cutting relationship between veins and mineral assemblages, the ore-forming process can be divided into four stages: I) pyrite + stibnite + milky quartz stage, II) stibnite + pyrite + gray-black cryptocrystalline quartz stage, III) stibnite + calcite + fluorite stage, and IV) clear and colorless calcite stage. The δ34S values (−2.5 ‰ to 5.8 ‰) of sulfides from stage II are similar to those associated with magmatic systems, but significantly different from the values (δ34S = −12.8 ‰ to 18.8 ‰) of pyrites from strata, suggesting that magmatic sulfur was the source for S2− in stage II. The δ34S values (−9.5 ‰ to −7.5 ‰) of stibnites from stage III are depleted in 34S relative to those of stage II, probably due to the increasingly mixing of meteoric water and SO42− from the strata. The Pb isotopes of sulfides from stage II and III (206Pb/204Pb = 17.745–19.176, 207Pb/204Pb = 15.478–15.711, 208Pb/204Pb = 37.7–38.742) show a mixed source of crust and mantle. The δ13C and δ18O values of calcites range from −0.84 ‰ to 3.94 ‰ and from 4.74 ‰ to 13.24 ‰, respectively, indicating that the ore-forming fluids originated from magmatic water, but influenced by water-rock interaction and meteoric water in the late stage. The SmNd isochron age of five calcite simples from stage III is 199.9 ± 1.7 Ma (MSWD = 1.6) with initial εNd values of −8.4, indicating that Yawan Sb deposit formed in the Late Triassic to Early Jurassic. On the basis of the data obtained in this paper, we consider that the Yawan Sb deposit is a distal magmatic-hydrothermal deposit formed during the transitional tectonic regime from the syn-collision to post-collision. Combined with previous studies, future exploration should focus on the distal magmatic-hydrothermal Sb deposits controlled by faults around concealed granites, and skarn-type deposits also need attention in Yawan-Daqiao district.

MINERAL ASSEMBLAGES, FLUID INCLUSIONS, PYRITE TRACE ELEMENTS, AND S-O ISOTOPES OF GOLD ORES FROM THE CENOZOIC DAPING DEPOSIT, SW CHINA: IMPLICATIONS FOR THE GENESIS OF COMPLEX OROGENIC LODE GOLD SYSTEMS

Abstract The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins. There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with –4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.

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.

Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit, NW Kerman, Iran: Evidence from fluid inclusions, Laser Raman spectroscopy, and S[sbnd]O isotope systematics

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ34S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ34S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ34S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO2-rich, indicating a typical post-collisional porphyry system.

Implications of multiple fluids in the deposition of Pb-Zn-Ba deposits in the Alvand Mountain, Golpayegan, Iran: Evidence from fluid inclusions and O, C, S isotopes

Middle Cretaceous sedimentary carbonates of Alvand Mountain host Pb-Zn-Ba veins. This mineralization occurs mainly as veins, breccia fillings, and to a lesser extent disseminated and host rock replacements. Ore mineralogy is simple and consists of sphalerite, galena, and barite, with minor pyrite, rare chalcopyrite, and tetrahedrite. Host rock dolomitization and hydrothermal silicification are typically associated with ore. Two types of primary liquid–vapor fluid inclusions were distinguished in sphalerite, quartz, and barite. Type I (salinity, 17–23 wt% NaCl; Th, 130 ± 30 °C) is dominant in sphalerite, whereas type II (salinity, 4.5–10 wt% NaCl, Th, 190 ± 40 °C) is dominant in quartz and barite; these fluids have characteristics of basinal brines and show a negative mixing trend in an evolving process of sulfide and gangue saturation. The δ18O and δ13C values for host rock and altered minerals range from 22.0 to 12.9 ‰ and 3.8 to −3.2 ‰, respectively, which suggest the influence of increased temperature fluids, presence of organic carbon, and fluid mixing. The δ34S values of sulfides and barite varies from 2 to 17 ‰ and 23 to 24 ‰, respectively, suggesting that reduced sulfur could be derived by thermochemical reduction of Paleogene seawater sulfate in the presence of organic matter; however, the wide ranges of δ34S sulfide values (15 ‰) exhibits that reduction of sulfur probably originated by different sulfur reduction processes. The data present in this study suggest that during increased tectonic activity in the late Cretaceous-Paleogene, mixing of basinal brines and water–rock interaction resulted in Pb-Zn-Ba deposition in carbonate host rocks. Therefore, it may represent low-temperature mineralization, possibly analogous to MVT depositional systems.

Geological, fluid inclusion, and H–O–S–Pb isotopic constraints on the genesis of the Bajiazi mesothermal lode gold deposit in the Jiapigou ore cluster, northeast China

The Bajiazi gold deposit, located in the northeast of the North China Craton, is a typical representative of the Jiapigou ore cluster in northeast China. The deposit is hosted within the Neoarchean–Paleoproterozoic supracrustal rocks (greenstone belts) and metamorphosed plutonic rocks. The orebodies occur along NE-trending ductile–brittle faults as auriferous quartz veins. The mineral assemblages reveal three stages of mineralization: quartz–pyrite (early), quartz–polymetallic sulfide (main), and quartz–carbonate (late). Three types of primary fluid inclusions (FIs), namely A-type (aqueous), C-type (aqueous–carbonic), and PC-type (pure carbonic) FIs, have been distinguished in different stages of quartz. The early- and main-stage quartz grains contain C-, A-, and a few PC-type FIs, while the late-stage quartz grains contain only A-type FIs. The early-, main-, and late-stage FIs homogenized at temperatures of 288–397 °C, 183–281 °C, and 120–190 °C, corresponding to salinities of 8.8–19.5, 3.9–18.8, and 3.2–11.3 wt% NaCl eqv., respectively. The ore fluid system evolved from H2O–NaCl–CO2 to H2O–NaCl during ore formation. The gold precipitation resulted from fluid immiscibility during the main mineralization stage. The HO isotope data reveal that the ore fluids originally came from magmatic water, and mixed with meteoric water during ore formation. The δ34S values (−0.2 ‰ to 8.3 ‰) of ore-related sulfides suggest that the sulfur in the ores was originally magmatic-sourced, and mixed with the sulfur in wall rocks during fluid migration. The Pb isotope ratios (206Pb/204Pb = 15.890–16.794, 207Pb/204Pb = 15.188–15.530, and 208Pb/204Pb = 36.589–37.710) of ore-related sulfides indicate the metals in the ores originated primarily from the lower crust, with a minor mantle contribution, and most likely came from a deep magmatic system. The Late Triassic gold mineralization has a clear genetic link to a quartz syenite porphyry. Based on the geological, FI, and isotopic constraints, the Bajiazi deposit is classified as a mesothermal lode gold deposit, which formed in an extensional setting after the closure of the Paleo-Asian Ocean.

Geochronological, mineralogical and geochemical studies of sulfide mineralization in the Yueyawan mafic intrusion in the East Tianshan orogenic Belt, NW China

The Yueyawan Cu-Ni sulfide deposit, located in the northern part of Dananhu island arc, is a new case of Cu-Ni mineralization related to Early Permian mafic magmatism in the East Tianshan orogenic belt, NW China. Olivine gabbro, hornblende gabbro, and gabbro are the major rock types of this complex. Disseminated sulfide mineralization with a pentlandite + pyrrhotite + chalcopyrite assemblage occurs in olivine gabbro. Zircon crystals from olivine gabbro yielded a U-Pb age of 275 ± 2 Ma, almost contemporaneous with the postcollisional extension-related Cu-Ni deposits in the East Tianshan nickel belt (e.g., Tulaergen, Xiangshan, Huangshan, Tudun, and Baixintan deposits). The Yueyawan olivine gabbro is characterized by light rare earth element enrichment, pronounced negative Nb-Ta anomalies, low initial 87Sr/86Sr ratios from 0.703282 to 0.703420, positive εNd(t) values from 3.4 to 7.2, zircon εHf(t) values from + 15.5 to + 18.5, indicating that the parental magma of the Yueyawan intrusion was derived from a metasomatized mantle source, similar to other contemporaneous mafic–ultramafic intrusions in the region. The δ34S values of sulfide of the Yueyawan deposit are similar and vary from 0.60 to 1.85 ‰, which are within the range of typical mantle values as well as that of the country rocks, providing no direct evidence for addition of external sulfur. However, the negative correlation between Se/S (54.01 to 77.56 × 10−6) ratios and sulfur contents in the disseminated sulfides indicate crustal contamination played a critical role for sulfide segregation of the magma. The olivine Fo and Ni contents from sulphide-bearing mafic rocks show a negative correlation. Olivine chemistry and Sr-Nd-Hf-S isotope data indicate that fractional crystallization and crustal contamination played a role in triggering sulfide saturation in the Yueyawan mafic magma.

Genesis and prospecting significance of the Buziwannan gold-polymetallic ore deposit in the West Kunlun Orogen Belt, China: Constraints from mineral geochemistry and in situ S–Pb isotope analyses of sulfides

The Buziwannan gold-polymetallic deposit is located in Northwest China's West Kunlun Orogen Belt (WKOB). There are two metallogenic stages that have been identified: skarn and hydrothermal. In this research study, in situ mineral geochemistry and sulfur–lead isotopes are used to precisely constrain the genesis and ore-forming process.Pyrite is the most dominant sulfide, and four types have been identified. Py0 is a sedimentary euhedral crystal; Py1 is a subhedral grain occurring in skarn ores, and coexists with Po1, Apy1, Ccp1 and Gn1; Py2, which coexists with Apy2, Po2 and Ccp2, is a subhedral to irregular crystal; and Py3 is a colloform crystal. Gn2 is the most recent sulfide. Magnetite and Ccp1 LA–ICMPS analyses indicate a skarn origin. Py0 and Py1 have the highest Co/Ni ratios and Ni contents, respectively, and Au has positive correlations with Pb, Ag and As, according to the trace element compositions of pyrite (LA–ICPMS). With the exception of four spots, most pyrites have Au (0.01–30.23 ppm) and As (1.47–15,709 ppm) concentrations below the Au saturation line, indicating that the majority of gold is present as lattice bound Au+. Py3 has clearly higher Sb contents indicating that Sb-rich fluids were added.The δ34S values of sulfides show that the sedimentary Py0 and skarn sulfides have the highest and lowest δ34S values of +13.30 to +14.67 ‰ and +4.48 to +7.77 ‰, respectively, and other sulfides possess δ34S values that fall between the two members, indicating a mixed source of magmatic and sedimentary. The lead isotope values also indicate that the sulfides from the hydrothermal stage have a mixed Pb source of magmatic and sedimentary.The skarn ores are spatially and genetically related to the Triassic granodiorite, indicating a Triassic age for ore formation. The Triassic magmatic intrusions hold the potential for future gold deposit exploration in the WKOB.

Heavy Copper Isotopes in Arc‐Related Lavas From Cold Subduction Zones Uncover a Sub‐Arc Mantle Metasomatized by Serpentinite‐Derived Sulfate‐Rich Fluids

AbstractSerpentinite dehydration during subduction releases fluids into the sub‐arc mantle, yet the oxidizing capability of these fluids remains controversial. Here, redox‐sensitive Cu isotopes and in situ S isotopes of magmatic sulfides in fresh lavas from three subduction zones in the western Pacific were analyzed to determine the speciation of multi‐valence elements in the serpentinite‐derived fluids. Notably, the basaltic lavas from the Mariana Arc, eastern Manus Basin, and southern Okinawa Trough have isotopically heavy Cu (δ65Cu = +0.26 to +0.67‰) compared to the mantle‐like δ65Cu values of the middle Okinawa Trough and Mariana Trough basalts (+0.11 to +0.14‰). In addition, positive correlations between δ65Cu and slab fluid indicators (e.g., B/Nb, Ba/Th, and Ba/La) combined with positive δ34S values (∼+4‰) of magmatic sulfides in the Mariana Arc lavas, suggest that fluids with isotopically heavy Cu and S metasomatized their mantle sources. Theoretically, the bearing fluids released by serpentinite dehydration have extremely heavy Cu and S isotope compositions. Consequently, the sulfate‐rich fluids infiltration into the sub‐arc mantle produces heavy Cu and S isotopes in arc‐related magmas. Comparatively, sulfate‐rich fluids are absent at back‐arc depths due to the complete breakdown of serpentine minerals during the early stages of subduction, which results in the mid‐ocean ridge basalts‐like δ65Cu and δ34S values (∼−1‰) observed in the middle Okinawa Trough and Mariana Trough basalts. Therefore, heavy Cu isotopes in arc‐related magmas uncover that the sub‐arc mantle was metasomatized by serpentinite‐derived sulfate‐rich (oxidizing) fluids, which accounts for the oxidized nature of arc magmas in cold subduction zones.

Episodic Au-Mo mineralization events in the Xiaoqinling district, southern margin of the North China Craton

The Xiaoqinling district, located in the southern margin of the North China Craton, is one of China’s most significant gold districts (resources of > 630 t Au). A complex series of overprinting Mesozoic tectonic and related hydrothermal events associated with the metallogenic evolution in this region has led to controversial interpretations and models. Here we present new geological, mineralogical, ore texture, geochronological, and in-situ S isotope data from the Dahu Au-Mo, Qinnan Au-Mo, and Tonggou Au deposits from this region which indicate that the Mo and Au were introduced in two discrete mineralization events. The Mo-bearing mineral assemblage mainly comprises quartz, anhydrite, pyrite, molybdenite, and rutile that yielded an age of 216.1 ± 9.7 Ma at Dahu. In-situ LA-ICP-MS δ34S values for the molybdenite and related pyrite cluster tightly at -10 to -9‰. On the other hand, the Au-bearing mineral assemblage mainly comprises quartz, pyrite, galena, sphalerite, chalcopyrite, native gold, and Te (±Bi) minerals. Hydrothermal rutile and monazite associated with auriferous pyrite yielded ages of 124.7 ± 3.9 Ma (Dahu), 121.5 ± 1.3 Ma (Qinnan), and 122.1 ± 2.0 Ma (Tonggou). The in-situ δ34S values of gold-related sulfides fall within a range of -4 to + 3 ‰. Although Mo and Au ores are both present in the same ore veins, their mineral assemblage, mineralization age, fluid properties and sources are different. Textural relationship shows that the earlier Mo-bearing quartz-anhydrite veins were overprinted by later auriferous fluids. Several lines of evidence support a multiphase mineralization process of Mo and Au, which are genetically linked to the post-collisional extension of the Qinling orogen and the Paleo-Pacific post-subduction tectonics, respectively. The episodic hydrothermal mineralization in Xiaoqinling represents a protracted and complex lode system.