δ34S Values Of Barite Research Articles

Microscale δ34S and δ18O variations of barite as an archive for fluid mixing and microbial sulphur metabolisms in igneous rock aquifers

ABSTRACT The stable isotope compositions of sulphur (δ34S) and oxygen (δ18O) in barite are frequently used as proxies for microbial sulphate reduction (MSR) in diverse environments, such as in relation to anaerobic oxidation of methane in marine cold seeps. There, isotopically heavy barite is used as a marker for MSR from a sulphate pool that has undergone semi-closed system conditions. Closed-system MSR is also a commonly observed feature in igneous rock hosted fracture aquifers, as shown by extremely 34S-enriched pyrite. What is less well-constrained is whether δ34S in barite can be used as a proxy for MSR in such systems. Here we explore the microscale heterogeneity of δ34S and δ18O via secondary ion mass spectrometry and the trace element Sr via LA-ICP-MS maps in barite precipitated in granite-hosted boreholes during a 17-year experiment, at Äspö, Sweden. We compare it with δ18Osulfate, δ34Ssulfate, and δ34Ssulfide of the fracture fluids and with paragenetic pyrite with δ34S values reflecting closed system MSR. The δ18O values in barite (+9.4 to +16.9 ‰) represent two generations of barite, one with low values and one with high values. The latter are likely impacted by sulphur disproportionating or -oxidizing bacteria. The barite reflects a much smaller span in δ34S (+14.5 to +28.6 ‰) than the pyrite (−47.2 to +53.3 ‰). This lack of extremely high δ34Sbarite values is proposed to be due to that barite saturation only occurred in the early parts of the Rayleigh cycle. Additionally, fluid migration has affected the δ34S values to lower values, accompanied by higher Sr concentrations. Taken together, barite δ34S values cannot be regarded as a reliable independent proxy for MSR in deep sulphate-poor igneous rock hosted aquifers. However, the relation between the δ34S values of coeval barite and pyrite is regarded as a useful proxy for MSR-related fractionation during early stages of MSR.

Sulfur isotopic systematics of hydrothermal precipitates in the Okinawa Trough: Implication for the effect of sediments and magmatic volatiles

The Okinawa Trough is a sediment-covered intra-continental back-arc basin with active hydrothermal activities. The sulfur isotopic systematics of the hydrothermal systems in the Okinawa Trough remain unclear owing to the complex sulfur reservoirs. To address these uncertainties, we conducted in situ S isotopic combined with whole-rock geochemical, Pb isotopic, and barite Sr isotopic analyses of typical hydrothermal precipitates from three hydrothermal fields with varying sediments thickness (Iheya North Knoll (INK) < Yonaguni Knoll IV (YK) < Noho) in the Okinawa Trough. The δ34S values of barite from INK (+16.4‰ to +19.6‰, median + 18.5‰) and YK (+16.2‰ to +22.2‰, median + 19.5‰) mostly indicate lower values than those obtained for seawater (~ +21‰), combined with the observation of high S and O fugacity (fO2–fS2) mineral assemblages (e.g., low-Fe sphalerite ± enargite ± tennantite ± chalcopyrite), and high Cu and Au contents of hydrothermal precipitates, consistent with the addition of magmatic volatile to these two fields. In contrast, the in situ δ34S values of sulfide minerals from INK (+5.6‰ to +10.4‰, median + 9.0‰) and YK (+3.5‰ to +5.5‰, median + 4.7‰) fields were all positive, inconsistent with the S isotopic characteristics of H2S formed from SO2 disproportionation. We conclude that a large proportion of thermochemical SO42− reduction-derived heavy sulfur likely obscure the characteristics of H2S sourced from disproportionation. This was likely resulting from (1) sediment controlled long-scale lateral hydrothermal circulation, (2) the existence of early precipitated anhydrite, and (3) high concentrations of H2 in the high-temperature reaction zone. The Noho field have low δ34S values (−0.2‰ to +5.3‰, median + 0.9‰) of sulfide minerals, combined with high sediment contributions reflected by high Pb isotopic ratios and low-fS2–fO2 mineral assemblages (e.g., high-Fe sphalerite ± pyrrhotite ± isocubanite), which indicates that the low δ34S value sulfur was derived from leaching of biogenic pyrite in thick sedimentary strata by hydrothermal fluid. Near surface, the high-temperature discharging hydrothermal fluids interacted with different thicknesses of sedimentary strata and leached different proportions of biogenetic pyrite, resulting in a negative correlation of sedimentary strata thickness and sulfide δ34S values of the Okinawa Trough hydrothermal fields.

The Eocene Poshteh Ba–Pb–Zn–Cu deposit, Iran: geological, mineral–chemical, fluid inclusion, and S–O isotopic analysis of a Kuroko-type VMS deposit with paleo-hydrothermal vent chimneys

The Poshteh deposit is the first documented paleo-hydrothermal chimney-bearing volcanogenic massive sulfide (VMS) deposit in Iran. It occurs in the form of well-developed lensoid orebodies within the Eocene volcano-sedimentary sequence, and comprises of laminated, brecciated, banded, massive, and disseminated textures. The stratiform part of this deposit is approximately 500 m long and up to 20 m thick, and consists of massive to semi-massive sulfides and barites, some of which are banded, which are overlain by barite and siliceous exhalites. The stringer zone stratigraphically underlies the stratiform mineralization. Veins within the stringer zone are composed of quartz, barite, pyrite, galena, sphalerite, and chalcopyrite. Three thin layers of exhalative Mn–Fe-bearing chert overlies the sulfide–sulfate orebodies. Four types of fluid inclusions were recognized in barite and quartz encompassing monophase vapor, monophase liquid, two-phase liquid-rich inclusions, and two-phase vapor-rich fluid inclusions. The homogenization temperatures of fluid inclusions mainly vary between 86.2 and 241.9 °C, whereas their salinities focus on 0.99–21.23 wt.% NaCl equiv. The ore-forming fluids of the barite and quartz minerals are characterized by low-to-medium temperature and low-to-medium salinity. The δ34S values of barite associated with the stratiform and stringer barite orebody range from 8.37 to 21.83 ‰, indicating that the sulfur was derived from the seawater. The sulfur isotope values of sulfide (− 5.18 to 9.33 ‰) are similar to those of VMS deposits from other parts of the world. The δ18O data suggest that the ore-forming fluids of the Poshteh deposit were mainly derived from deep subseafloor circulation of seawater. The well-preserved chimneys typically contain distinct concentric outer and inner sulfide- and axial sulfate-rich zones. The outer zones of the chimneys contain mainly pyrite and chalcopyrite. The sulfides within the inner zone consist predominantly of sphalerite, argentite, and galena. The axial conduits are commonly dominated by barite and calcite. The sulfide-rich chimney zones are also characterized by significantly higher metal contents. The presence of paleo-hydrothermal vent chimneys in the Poshteh Kuroko-type deposit and their trace-element contents also provides significant data for understanding the physicochemical conditions of VMS mineralization.

The ore genesis of the Jebel Mecella and Sidi Taya F[sbnd]Ba (Zn[sbnd]Pb) Mississippi Valley-type deposits, Fluorite Zaghouan Province, NE Tunisia, in relation to Alpine orogeny: Constraints from geological, sulfur, and lead isotope studies

Jebel Mecella and Sidi Taya F–(BaPbZn) deposits are located within the Fluorite Zaghouan Province (NE Tunisia). The mineralization occurs along the unconformity surface between the Jurassic limestones and Upper Cretaceous rocks. The mineralization consists mainly of fluorite, barite, sphalerite, and galena. The δ34S values of barite at Jebel Mecella (14.8–15.4‰) and at Sidi Taya (21.6–22.2‰) closely match those of the Triassic evaporites and Messinian seawater, respectively. The range of δ34S values of galena and sphalerite in both deposits (−6.9 to +2.4‰) suggests the involvement of thermochemical sulfate reduction and possibly organically-bound sulfur in the generation of sulfur. Lead isotope data with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.893–18.903, 15.684–15.699, and 38.850–38.880, respectively suggests a single homogeneous source reservoir of Paleozoic age and/or the homogenization of the Paleozoic–Cretaceous multireservoir-derived fluids along their long migration paths to the loci of deposition during the Alpine orogeny.

The genesis of the Dahebian Zn-Pb deposit and associated barite mineralization: Implications for hydrothermal fluid venting events along the Nanhua Basin, South China

The Dahebian stratiform barite deposit, which is situated in the Nanhua Basin, is one of the world’s largest and most important barite deposits. This deposit was formed through sedimentary exhalative processes in the early Cambrian stage. Recently, beneath stratiform barite ore, stratabound Zn-Pb-(Fe-bearing) sulfide mineralization, which is hosted by the Doushantuo Formation, was discovered. Ores that represent Zn-Pb sulfide mineralization are mainly discordant but stratabound. The Doushantuo Formation consists of laminated interbedded layers of micritic dolomite and carbonaceous mudstone, associated with phosphorite and chert. The sulfide ores consist primarily of sphalerite, pyrite and galena. The associated gangue minerals are barite, quartz, minor calcite, as well as trace amounts of apatite and hyalophane. Hyalophane found in the stratiform barite ore is richer in barium but poorer in potassium than that associated with the sulfide ores. This outcome corresponds to ascending hydrothermal fluids that are richer in barium along with sulfide mineralization. Investigation of the ore fluid reveals relatively high temperature (142–368 °C) with scattered salinity (0.53–25.62 wt% NaCl eq.). This finding suggests that fluid cooling and/or mixing with seawater could be the primary mechanisms that prompted the ore formation. Sulfides selected from the zinc-lead sulfide ores and stratiform barite ore have similar sulfur isotopic compositions, with δ34S values ranging from 13.5‰ to 30.0‰; δ34S values of barite from these ores are analogous, with δ34S values ranging from 29.5‰ to 55.1‰. The sulfur isotopic fractionation between minerals (barite and sulfide) and the early Cambrian seawater is ΔBarite-Seawater = 7.8‰ and ΔSulfide-Seawater = −12.1‰, respectively, demonstrating that the sulfur in the Dahebian zinc-lead deposit and the stratiform barite deposit were derived from the early Cambrian stratified seawater column. Lead isotopic compositions of sulfide ores indicate that these ore metals are mainly sourced from rocks of the Doushantuo Formation and the underlying fold basement.Therefore, the Dahebian zinc-lead deposit and stratiform barite deposit probably arose from Selwyn-Type sedimentary exhalative hydrothermal fluids. Zn-Pb sulfides were mineralized in the feeder zone of these hydrothermal fluids, and the stratiform barite ore deposits represent the upper sedimentary-exhalative mineralization. This finding points to intensive Zn-Pb-Fe-Ba hydrothermal fluid venting into the Nanhua Basin and to relatively oxic deep ocean waters during the early Cambrian.

A combined fluid inclusion and S–H–O–He–Ar isotope study of the Devonian Ashele VMS-type copper–zinc deposit in the Altay orogenic belt, northwest China

The Altay orogenic belt of Kazakhstan and China incorporates one of the world-class volcanogenic massive sulfide (VMS) polymetallic metallogenic belt. More than 12 large and superlarge VMS deposits have been found in this belt. The Ashele Basin is located at the western end of the Chinese Altay bordering Kazakhstan and hosts the large Ashele copper–zinc deposit, which is a typical VMS deposit and the largest one in this basin. The principal orebodies are stratabound and located between basalt and tuff units in the Ashele Formation. The mineralization has a two-layered structure that consists of an upper stratiform, concordant, massive Cu–Zn (or barite) orebody, and a lower veinlet–disseminated and stockwork Cu (or Cu–Pb–Zn–Ag) orebody associated with silicic alteration. Several exhalative rocks, such as barite, hematitic jasper, pyrite and silicified units also occur.Here we investigate the ore-forming fluids of the exhalative–sedimentary units including jaspilte, stratiform barite and Cu–Zn orebodies which carry fluid inclusions that show homogenization temperatures of 100–410 °C, with two peaks around 230 and 150 °C, and low salinity (clustering between 2 and 8 wt% NaCl equiv), corresponding to NaCl–H2O fluids. The ore-forming fluids of the vein orebody and silicified zones are characterized by low to medium temperature (peak homogenization temperatures between 120 and 280 °C), low to medium salinity (0.7–12.3 wt% NaCl equiv), and H2O–CO2 (±CH4/N2)–NaCl fluids. The δ34S values of barite associated with the stratiform barite orebody range from 20.4‰ to 21.4‰, indicating that the sulfur was derived from the seawater. The sulfur isotope values of sulfide (−3.7‰ to 7.7‰ with a mean of 3.1‰) are similar to those of VMS deposits from other parts of the world. The host volcanic rocks are inferred to be the major source from which the mineralizing fluid leached the ore-forming elements. The 3He/4He ratios of fluid inclusions in pyrite are in the range of 0.136–0.260 (R/Ra), broadly similar to the helium ratios of the crust. The 40Ar/36Ar ratios range from 394 to 9515, and are higher than those of atmospheric argon. The 40Ar/4He ratios of the ore fluids range from 0.002 to 0.064 with a mean of 0.034. The helium and argon isotope compositions of fluid inclusions suggest that the ore fluids of the Ashele deposit were mainly derived from the crust and were mixed with a minor amount of mantle component. The δ18OSMOW values of quartz from the silicified zones and vein orebody range from 8.3‰ to 11.1‰, with corresponding δ18Ofluid values of −4.45‰ to 2.24‰, whereas the δD values of fluid inclusions are between −140‰ and −90‰. The δ18OSMOW values of barite from the stratiform barite orebody range from 7.7‰ to 9.1‰, with corresponding δ18Ofluid values of –3.03‰ to 1.79‰, with δD values of fluid inclusions showing a range of –162‰ and –135‰. The combined isotopic data (H–O and He–Ar) suggest that the ore-forming fluids of the Ashele deposit were mainly derived from deep circulation of seawater and mixed with magmatic fluids. The decrease in temperature and pressure, water–rock exchange, and changes in the composition of ore fluids played important roles in the ore-forming processes of the Ashele Cu–Zn deposit.

A salt diapir-related Mississippi Valley-type deposit: the Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: fluid inclusion and isotope study

The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian–Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ∼110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained simply by the evaporation of seawater to halite saturation and requires a dilution of more than two times by meteoric water. The higher K/Na values in fluid inclusions from barite suggest that the brines interacted with K-rich rocks in the basement or siliciclastic sediments in the basin. Carbonate gangue minerals (ankerite and calcite) have δ13C and δ18O values that are close to the carbonate host rock and indicate fluid equilibrium between carbonate host rocks and hydrothermal brines. The δ34S values for sphalerite and galena fall within a narrow range (1 to 10 ‰) with a bulk value of 7.5 ‰, indicating a homogeneous source of sulfur. The δ34S values of barite are also relatively homogeneous (22 ‰), with 6 ‰ higher than the δ34S of local and regional Triassic evaporites (15 ‰). The latter are believed to be the source of sulfate. Temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of Triassic sulfate via hydrocarbons produced probably from Late Cretaceous source rocks. The 87Sr/86Sr ratio in the Bou Jaber barite (0.709821 to 0.711408) together with the lead isotope values of Bou Jaber galena (206Pb/204Pb = 18.699 to 18.737; 207Pb/204Pb = 15.635 to 15.708 and 208Pb/204Pb = 38.321 to 38.947) show that metals were extracted from homogeneous crustal source(s). The tectonic setting of the Bou Jaber ore deposit, the carbonate nature of the host rocks, the epigenetic style of the mineralization and the mineral associations, together with sulfur and oxygen isotope data and fluid inclusion data show that the Bou Jaber lead-zinc mineralization has the major characteristics of a salt diapir-related Mississippi Valley-type (MVT) deposit with superimposed events of fluorite and of barite deposition. Field relations are consistent with mineral deposition during the Eocene–Miocene Alpine orogeny from multiple hydrothermal events: (1) Zn-Pb sulfides formed by mixing of two fluids: one fluid metal-rich but reduced sulfur-poor and a second fluid reduced sulfur-rich; (2) barite precipitation involved the influx of a meteoric water component that mixed with a barium-rich fluid; and (3) fluorite precipitated from a highly saline fluid with higher temperatures.

Geological, geochemical, and fluid inclusion evidences for the origin of the Ravanj Pb–Ba–Ag deposit, north of Delijan city, Markazi Province, Iran

The Lower Cretaceous sequences of the Ravanj anticline in Iran host the Ravanj Pb-Ba-Ag mineralization. Economic orebodies are restricted to the thrust zone within the brecciated massive limestone and immediately above the Jurassic shale and/or shale-limestone intercalations of the Lower Cretaceous. Paragenetic sequence and distinct zoning of mineral assemblages indicate that ore-forming fluid migrated through thrust zones along the NE-trending faults. The REE pattern of mineralized host rock is characterized by HREE-enrichment ((La/Lu)PAAS = 0.24). The Ce/Ce* ratio of mineralized host samples shows negative Ce anomalies, which is most likely inherited from seawater. The positive Eu/Eu* anomaly suggests high ?O2 during ore deposition. Negative Δ34S values of the Ravanj sulfide minerals (-27? to -11?) suggest bacteriogenic sulfate reduction, whereas positive Δ34S values of barite (+20?) fall in the range of Tertiary marine sulfates. Multiple isotopic sulfur sources of sulfides and sulfate minerals support mixing of a reduced negative isotopic sulfur-bearing fluid and a positive isotopic sulfate-bearing fluid. The average of homogenization temperatures of fluid inclusions from the early and late-stage mineralization calcites are 165 and 160 °C, respectively. The salinity of fluid inclusions varies between 0.66 and 18 wt% NaCl equivalent with an outlier at 22.2. Wide variation in the salinity of fluid inclusions can be explained by fluid mixing between a higher salinity group with 14-18 wt% NaCl equivalent and a lower salinity group with 0.66-8 wt% NaCl equivalent. In the Ravanj, fine grained sulfide minerals are consistent with a sulfur supersaturated fluid. High concentrations of Pb can be present in oxidized, chlorine-bearing fluids if the concentration of total H2S is very low. Therefore, mixing of two geochemically different fluids could precipitate both galena and barite. These data show that the Ravanj Pb-Ba-Ag deposit is comparable with Pb-rich Mississippi Valley-type deposits such as the Viburnum Trend district in the USA.

مطالعات کانی سازی، ژئوشیمی، سیالات درگیر و ایزوتوپ پایدار گوگرد کانسار Cu-Zn-As باقرق با سنگ میزبان کربناته (شمال شرق انارک)

کانسار Cu-Zn-As باقرق در شمال شرق شهر انارک و در استان اصفهان قرار دارد. کانی‌سازی به‌صورت دیرزاد، ماهیت چینه‌کران و بافت و ساخت پرکننده فضای خالی در سنگ میزبان کربناتی رخداده است. کانی‌شناسی بخش درون‌زاد شامل کالکوسیت، کالکوپیریت، پیریت، اسفالریت، گالن، انارژیت، باریت و کلسیت و کانیهای بخش برون‌زاد شامل مالاکیت، آزوریت، کوولیت، کریزوکولا، کالکوسیت، سروزیت، اسمیت‌زونیت، مس طبیعی، هماتیت، گوتیت و لیمونیت می‌باشد. سنگ میزبان کربناتی در اطراف زون‌های کانه‌دار متحمل دگرسانیهای دولومیتی‌شدن و کلسیتی‌شدن شده است. مس به‌عنوان عنصر اصلی ذخیره (با میانگین 28/20 درصد وزنی) و پس از آن عناصر روی (با میانگین تقریبی 1 درصد وزنی) و آرسنیک (با میانگین تقریبی 1 درصد وزنی) می‌باشند. مطالعات سیالات‌درگیر روی کانی باریت نشان می‌دهد سیال کانه‌دار سولفیدی دارای محدوده دمای همگن شدن بین 259 تا 354 درجه سانتی‌گراد و میزان شوری بین 8 تا 13 درصد وزنی معادل NaCl می‌باشد. سیال کانه‌دار در مراحل پایانی کانی‌سازی با آبهای جوی دچار اختلاط شده و فاز تأخیری غیر سولفیدی کلسیتی با محدوده دمای نسبتا پایین ‌(78 تا 112 درجه سانتی‌گراد) و درجه شوری پایین (بین 3 تا 6 درصد وزنی معادل NaCl) را تشکیل داده است. محدوده مقادیر 34Sδ کانی‌ باریت کانسار باقرق بین 13+ تا 14+ در هزار بوده در حالی‌که محاسبه مقدار 34Sδ مربوط به سیال کانه‌دار پس از تصحیح دمایی بین 7- تا 8- در هزار به‌دست آمد. منشأ گوگرد باقرق با توجه به شباهت ایزوتوپ باریت با سولفات‌های دریایی کرتاسه، احتمالا از لایه‌های تبخیری این دوره زمانی تأمین شده است. این سولفا‌ت‌ها توسط فرآیند‌های ترموشیمیایی به‌صورت بخشی به گوگرد احیایی با مقدار ایزوتوپی سبک‌تر (حدود 21 در هزار) تبدیل و جهت ته‌نشست سولفیدها مورد استفاده قرار گرفته است. کانسار باقرق با توجه به خصوصیاتی همچون سنگ میزبان کربناته، غیاب فعالیت آذرین، بافت پرکننده فضای خالی، دگرسانی دولومیتی،کانی‌شناسی، ژئوشیمی ماده‌معدنی (وجود As و Sb بالا و عدم حضور Bi)، داده‌های دماسنجی و مقادیر ایزوتوپ گوگرد، شباهت زیادی با کانسارهای مس با سنگ میزبان کربناته در افریقا و به‌ویژه نوع سومب (Tsumeb) در نامیبیا نشان می‌دهد. کانسار باقرق احتمالا مرتبط با سیالات دگرگونی آزاد شده در حین فازهای کوه‌زایی مرتبط با بسته‌شدن اقیانوس نئوتتیس می‌باشد.

Geology, geochemistry, sulfur isotope composition, and fluid inclusion data of Farsesh barite deposit, Lorestan Province, Iran

Farsesh barite in the central part of Iranian Sanandaj-Sirjan zone is a sample of epigenetic hydrothermal mineralization in dolomitized limestone, which provides appropriate chemicophysical conditions making the passage of mineral-bearing fluids possible. Barite veins may range from a few centimeters to 2 m in thickness that increases downward. The microthermometry measurements obtained from more than 30 fluid inclusions show relative homogenization temperatures ranging from 125 to 200 °C with an average of 110 °C for Farsesh barite deposits. The mean salinity measured proves 16 times as much as weight percentage of NaCl for barite. Coexistence of liquid- and vapor-rich fluid inclusions in barite minerals may provide an evidence of boiling in ore veins. Moreover, occurrence of bladed calcite, high-grade ore zones, and presence of hydrothermal breccia are all consistent with boiling. Thermometric studies indicate that homogenization temperatures (Th) for primary and pseudosecondary fluid inclusions in barite range from 125 to 200 °C with an average of 1,100 °C. The δ34S values of barite also lie between 8.88 and 16.6 %. The relatively narrow spread in δ34S values may suggest uniform environmental conditions throughout the mineralization field. Thus, δ34S values are lower than those of contemporaneous seawater, which indicates a contribution of magmatic sulfur to the ore-forming solution. Barite is marked by total amounts of rare Earth elements (REEs) (6.25–17.39 ppm). Moreover, chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (i.e., LREEs) from La to Sm, similar to those for barite from different origins. The LaCN/LuCN ratios and chondrite-normalized REE patterns reveal that barite in Farsesh deposit is enriched in LREEs compared with heavy rare Earth elements (HREEs). Similarity between Ce/La ratios in barite samples and those found in deep-sea barite supports its marine origin. Lanthanum and Gd exhibit positive anomalies, which are common features of chemical marine sediments. Cerium shows a negative anomaly in most samples inherited from the negative Ce anomaly of hydrothermal fluid that is mixed with seawater at barite precipitation. The available data including tectonic setting, host rock characteristics, REE geochemistry, and sulfur isotopic compositions may support a hydrothermal submarine origin for Farsesh barite deposit.

Isotopic Compositions of Sulfur in the Jinshachang Lead–Zinc Deposit, Yunnan, China, and its Implication on the Formation of Sulfur‐Bearing Minerals

Abstract:The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn–Ag multi‐metal mineralization area in China. Sulfides minerals including sphalerite, galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite, quartz, and barite, making this deposit distinct from most lead‐zinc deposits in the SYG. This deposit is controlled by tectonic structures, and most mineralization is located along or near faults zones. Emeishan basalts near the ore district might have contributed to the formation of orebodies. The δ34S values of sphalerite, galena, pyrite and barite were estimated to be 3.6‰–13.4‰, 3.7‰–9.0‰, −6.4‰ to 29.2‰ and 32.1‰–34.7‰, respectively. In view of the similar δ34S values of barite and sulfates being from the Cambrian strata, the sulfur of barite was likely derived from the Cambrian strata. The homogenization temperatures (T≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria, therefore, the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district. Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur, it was not the main mechanism. Considering other aspects, it can be suggested that sulfur of sulfides should have been derived from magmatic activities. The δ34S values of sphalerite were found to be higher than those of coexisting galena. The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions, suggesting that the sulfur isotopic composition in ore‐forming fluids had reached a partial equilibrium.

Regional sulfate–hematite–sulfide zoning in the auriferous Mariana anticline, Quadrilátero Ferrífero of Minas Gerais, Brazil

The distribution of mineral deposits, characterised as barite deposits, hematite-rich auriferous deposits and auriferous tourmaline–sulfide deposits, displays a regional sulfate–hematite–sulfide zoning along the thrust-delineated limbs of the Mariana anticline, in the south-eastern part of the Quadrilatero Ferrifero of Minas Gerais, Brazil. Cross-cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late-tectonic context, which is here attributed to the collapse of the ∼0.6-Ga Brasiliano thrust front. Reconnaissance S-isotopic data from barite and pyrite (Antonio Pereira barite deposit and its adjacent gold deposit, respectively), and arsenopyrite (Passagem de Mariana gold deposit), suggest a new interpretation for the hydrothermal fluid overprint in the Mariana anticline. The Antonio Pereira barite has Δ33S values that are near zero, constraining the sulfate source to rocks younger than 2.45 Ga. The barite-δ34S values are between +19.6 and +20.8 ‰. The Passagem arsenopyrite and tourmaline have Co/Ni ratios that define a positive linear trend with the Antonio Pereira pyrite. The latter has homogenous δ34S values, between +8.8 and +8.9 ‰, which are compatible with thermochemical reduction of aqueous sulfate with the S-isotopic composition of the Antonio Pereira barite.

Paleozoic bedded barite deposits from Sonora (NW Mexico): Evidence for a hydrocarbon seep environment of formation

The Mazatán barite deposits, Sonora, NW Mexico, represent an outstanding example of Paleozoic bedded barite, a poorly understood type of mineral deposit of major economic interest. The deposits of this type commonly occur hosted by shales and are characterized by the lack of base-metal sulfide mineralization, in contrast to classic sedimentary-exhalative (or SEDEX) deposits. A throughout study of the Mazatán barite deposits, based on petrography, fluid inclusions analyses and isotope geochemistry, confirmed the link between bedded barite and fossil hydrocarbon seeps, thereby leaving hydrothermal vent-related processes ruled out. Hence, modern cold seeps in continental margins would account for the geological setting and genetic aspects of this type of deposit.The largest barite bodies of Mazatán are hosted within an Upper Carboniferous flysch succession, which formed part of an accretionary wedge related to the subduction of the Rheic Ocean beneath Gondwana. As well, a few barite occurrences are hosted in Upper Devonian, pre-orogenic turbidites. A variety of mineralized structures is displayed by barite, including: septaria nodules, enterolitic structures, rosettes and debris-flow conglomerates. Barite is accompanied by chalcedony, pyrite (framboids) and berthierine. Gas-rich fluid inclusions in barite were analyzed by micro-Raman spectroscopy and methane was identified, suggesting the occurrence of light hydrocarbons in the environment within which barite precipitated. 13C-depleted carbonates (δ13C: −24.3 to −18.7‰) were found in the barite deposits; they likely formed through anaerobic oxidation of methane coupled to sulfate reduction. Besides, these carbonates yield negative δ18O values (−11.9 to −5.2‰) reflecting the isotopic composition of Devonian–Carboniferous seawater; alternatively, this 18O-depletion could reflect late diagenetic processes. Methane-derived carbonates occur at modern hydrocarbon seeps and have been reported from Mesozoic, Cenozoic and even Paleozoic seep sediments, but they have never before been described in Paleozoic bedded barite deposits. δ34S values of barite vary from +17.6 to +64.1‰, with the lowest values overlapping the range for coeval seawater sulfate; this distribution indicates a process of sulfate reduction. Barite precipitation can be explained by mixing methane- and barium-rich fluids with pore-water (seawater) containing sulfate residual from microbial reduction. Two analyses from barite gave an 87Sr/86Sr within and slightly above the range for seawater at the time of deposition, with 0.708130 and 0.708588, which would preclude the involvement of hydrothermal fluids in the mineralization process.

REE and isotope (Sr, S, and Pb) geochemistry to constrain the genesis and timing of the F–(Ba–Pb–Zn) ores of the Zaghouan District (NE Tunisia)

The F–(Ba–Pb–Zn) ore deposits of the Zaghouan District, located in NE Tunisia, occur as open space fillings or stratabound orebodies, hosted in Jurassic, Cretaceous and Tertiary layers. The chondrite-normalized rare earth element (REE) patterns may be split into three groups: (i) “Normal marine” patterns characterizing the wallrock carbonates; (ii) light REE (LREE) enriched (slide-shaped) patterns with respect to heavy REE (HREE), with small negative Ce and Eu anomalies, characteristic of the early ore stages; (iii) Bell-shaped REE patterns displaying LREE depletion, as well as weak negative Ce and Eu anomalies, characterizing residual fluids of subsequent stages. The 87Sr/86Sr ratios (0.707654–0.708127±8), show that the Sr of the epigenetic carbonates (dolomite, calcite) and ore minerals (fluorite, celestite) are more radiogenic than those of the country (Triassic, Jurassic, Cretaceous, lower Miocene) sedimentary rocks. The uniformity of this ratio, throughout the District, provides evidence for the isotopic homogeneity and, consequently, the identity of the source of the mineralizing fluids. This signature strongly suggests that the radiogenic Sr is carried by Upper Paleozoic basinal fluids.The δ34S values of barite, associated to mineralizations, are close to those of the Triassic sea water (17‰). The δ34S values of sulfide minerals range from −13.6‰ to +11.4‰, suggesting two sulfur-reduced end members (BSR/TSR) with a dominant BSR process.Taking account of the homogeneity in the Pb-isotope composition of galenas (18.833–18.954±0.001, 15.679–15.700±0.001 and 38.690–38.880±0.004, for the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios respectively), a single upper crustal source for base-metals is accepted. The Late Paleozoic basement seems to be the more plausible source for F–Pb–Zn concentrated in the deposits. The genesis of the Zaghouan District ore deposits is considered as the result of the Zaghouan Fault reactivation during the Late Miocene period.

Sulfur and lead isotopes of Guern Halfaya and Bou Grine deposits (Domes zone, northern Tunisia): Implications for sources of metals and timing of mineralization

The Pb–Zn ore deposits in the Guern Halfaya and Bou Grine areas (northern Tunisia) are hosted mainly by dolostones in the contact zone between Triassic and Upper Cretaceous strata and by Upper Cretaceous limestones. The deposits occur as lenticular, stratiform, vein, disseminations and stockwork ore bodies consisting of sphalerite, galena, pyrite, chalcopyrite and sulfosalt (gray copper). Barite and celestite dominate the gangue, with lesser calcite. The δ34S values of barite and celestite (12.7–15.0‰) at the Oum Edeboua mine are consistent with the reduction of sulfates in Triassic evaporites within the study area (12.8<δ34S<14.0‰). The δ34S values in base-metal sulfides from both study areas (2.6–9.5‰) and the presence of bacterial relics suggest involvement of bacterially-mediated sulfate reduction in the mineralization. The present Pb isotope data are homogeneous with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.723–18.783, 15.667–15.685 and 38.806–38.889, respectively, which suggest a single source reservoir of Pb at depth in the upper crust. The syn-diagenetic mineralization in the Bahloul Formation and the calculated age from the Pb isotopic data suggest an Upper Cretaceous age for the Pb–Zn deposits in the Guern Halfaya and Bou Grine areas. During this period, NE–SW to ENE–WSW trending regional extensional tectonic structures likely favored migration of mineralizing fluids and eventual deposition at Guern Halfaya and Bou Grine.

The role of the Kupferschiefer in the formation of hydrothermal base metal mineralization in the Spessart ore district, Germany: insight from detailed sulfur isotope studies

The Spessart district (SW Germany), located at the southwestern margin of the Permian Kupferschiefer basin in Central Europe, hosts abundant stratabound and structurally controlled base metal mineralization. The mineralization styles identified are (1) stratabound Cu-Pb-Zn-(Ag) ores in Zechstein sedimentary rocks, (2) structurally controlled Cu-As-(Ag) ores in Zechstein sedimentary rocks, (3) crosscutting Co-Ni-(Bi)-As and Cu-Fe-As veins, (4) stratabound metasomatic Fe-Mn carbonate ores in Zechstein dolomite, (5) barren barite veins, and (6) Fe-Mn-As veins in Permian rhyolites. Building on previous work that involved mineralogical, textural, and chemical characterization of the major mineralization types, we have performed a comprehensive sulfur isotope study that applied both conventional and novel laser-ablation multi-collector inductively coupled plasma mass spectrometry techniques. The δ34S values of sulfide minerals from the different ore types are consistently negative and highly variable, in the range between −44.5‰ and −3.9‰, whereas the δ34S values of barite are all positive in the range between 4.7‰ and 18.9‰. Remarkably, stratabound and structurally controlled mineralization in Zechstein sedimentary rocks has the least negative δ34S values, whereas vein-type deposits have consistently more negative δ34S values. The observed pattern of sulfide δ34S values can be best interpreted in terms of fluid mixing at the basement-cover interface. Hydrothermal fluids originating from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters that were flowing in the post-Variscan sedimentary cover. These groundwaters had interacted with the Zechstein sedimentary rocks, resulting in fluids characterized by elevated concentrations of reduced sulfur (with negative δ34S values) and alkaline pH. Repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative δ34S values.

Isotopic evidence for microbial activity during supergene oxidation of a high-sulfidation epithermal Au-Ag deposit

The light stable isotope chemistry of barite and acanthite in the Pierina Au-Ag deposit, Peru, provides strong support for microbial involvement at the economically critical supergene oxidation stage. Early hypogene barite yields δ34S values of 23.6‰ to 28.5‰ and δ18O values of 5.8‰ to 10.9‰, and was precipitated with the original precious metal-enriched sulfide assemblage. In contrast, late barite, deposited during formation of supergene goethite and hematite, the main ore-hosts, yields δ34S and δ18O values of 1.4‰ to 14.2‰ and −2.8‰ to 4.7‰, correlated mutually and with the δ34S values of coprecipitated acanthite (δ34S = 0.4‰ to 3.9‰). Low δ34S values of barite and acanthite record sulfide mineral oxidation by meteoric waters. Increasing δ34S and δ18O values of barite and δ34S values of acanthite indicate enrichment of the sulfate reservoir in 34S and 18O, reflecting the preferential utilization of light isotopes by microbes during aqueous sulfate reduction. Continued sulfate reduction locally reduced supergene fluids, remobilizing iron and locally destroying the goethite-hematite assemblage. Precious metals were released but reacted with sulfide in the reduced waters to form Au-rich acanthite.

Barite–pyrite mineralization of the Wiesbaden thermal spring system, Germany: a 500‐kyr record of geochemical evolution

AbstractBarite–(pyrite) mineralizations from the thermal springs of Wiesbaden, Rhenish Massif, Germany, have been studied to place constraints on the geochemical evolution of the hydrothermal system in space and time. The thermal springs, characterized by high total dissolved solids (TDS) contents and predominance of NaCl, ascend from aquifers at 3–4 km depth and discharge at a temperature of 65–70°C. The barite–(pyrite) mineralization is found in upflow and discharge zones of the present‐day thermal springs as well as at elevations up to 50 m above the current water table. Hence, this mineralization style constitutes a continuous record of the hydrothermal activity, linking the past evolution with the present state of this geothermal system. The sulphur isotope signatures of the mineralization indicate a continuous decrease of the δ34S of sulphate from +16.9‰ in the oldest barite to +10.1‰ in the present‐day thermal water. The δ34S values of barite closely resemble various recently active thermal springs along the southern margin of the Rhenish Massif and contrast strongly with different regional ground and mineral waters. The mineralogical and isotopic signatures, combined with calculations based on uplift rates and the regional geological history, indicate a minimum activity of the thermal spring system at Wiesbaden of about 500 000 years. This timeframe is considerably larger than conservative models, which estimate the duration of thermal spring systems in continental intraplate settings to last for several 10 000 years. The calculated equilibrium sulphur isotope temperatures of coexisting barite and pyrite range between 65 and 80°C, close to the discharge temperature of the springs, which would indicate apparent equilibrium precipitation. Kinetic modelling of the re‐equilibration of the sulphate–sulphide pair during water ascent shows that this process would require 220 Myr. Therefore, we conclude that pyrite is formed from precursor Fe monosulphide phases, which rapidly precipitate in the near‐surface environment, preserving the isotope fractionation between dissolved sulphate and sulphide established in the deep aquifer. Equilibrium modelling of water–mineral reactions shows slight supersaturation of barite at the discharge temperature. Pyrite is already strongly supersaturated at the temperatures estimated for the aquifer (110°C) and processes in the near‐surface environment are most probably related to contact of the thermal water with atmospheric oxygen, resulting in formation of oxidized intermediate sulphur species and precipitation of Fe monosulphide phases, which subsequently recrystallize to pyrite.

Sulphur and sulphate-oxygen isotopes and the origin of the silvermines deposits, Ireland

New sulphur and sulphate-oxygen isotope measurements for the main discordant and stratiform lead-zinc-barite orebodies at Silvermines Co. Tipperary, allow reappraisal of previously offered differing interpretations (Graham, 1970; Greig et al., 1971) of the bearing of sulphur isotopes on the genesis of this important Irish deposit. The following aspects of the data are confirmed: barite δ34 S-values range from 17–21‰, similar to lower Carboniferous seawater sulphate: stratiform sulphide lens pyrites have δ34 S-values ranging from −13 to −36‰; vein sulphide δ34 S-values range from −8 to 4‰; sulphide δ34 S-values increase upwards and outwards respectively in the related discordant and stratiform “G” orebodies; galena-sphalerite isotope palaeotemperatures are not too consistent, ranging from 40 to 430°C (using the calibration of Czamanske and Rye (1974). New facts are as follows: barite δ18O-values range from −13 to −17‰, stratiform barites ranging from 13 to 14.5‰; sulphides separated from a single stratiform ore lens hand specimen usually have δ34 Ssl > δ34 Sga > δ34 Spy; the outward decrease in δ34 S-values in the stratiform “G” orebody is confined to the first few hundred feet only; pyrite δ34 S-values progressively increase downwards through one stratiform sulphide orebody; yet variations of 13‰ occur within a single colloform pyrite structure from another stratiform orebody. It is concluded that there were at least two sources of sulphur, seawater sulphate and deep-seated sulphur. The former was the dominant source of all sulphate and, via biogenic reduction, of the sulphur in the bulk of the stratiform sulphide. The latter was the source of the sulphur in the vein sulphides. There was minimal isotopic interaction between the cool seawater sulphate and the warm unwelling ore fluid sulphur species, even though the latter precipitated under near isotopic equilibrium conditions when the temperature dropped and/or the pH and Eh increased. The lack of isotopic equilibrium between pyrite and ore sulphides in the stratiform ore lenses may result from the latter having precipitated slightly later than the former because of solubility relationships. Overall the present isotopic evidence supports considerable geological evidence favoring a syngenetic origin for the stratiform Silvermines orebodies.

Sulfur isotope study of the Kuroko-ores of the Shakanai No. 1 deposits, Akita Prefecture, Japan

Sulfur isotope data of the Kuroko-ores from the No. 1 deposits of the Shakanai mine reveal that the δ34S value of sulfide minerals decreases gradually towards the top of the sequence of the stratigraphic and mineralogical zonation of the ores. For example, δ34S values of pyrite show a gradual decrease towards the top of the sequence: +8.2 to +7.2‰ in disseminated ores and veins in the footwall rocks; +6.2 to +5.4‰ in pyrite-ores; +5.5 to +4.6‰ in yellow-ores; +5.6 to +3.0‰ in black-ores; +4.6 to -6.0‰ in hematite-quartz layers. δ34S values of barite in the black-ores are fairly uniform, giving +22∼s+23‰. Sulfur isotope temperatures obtained from coexisting sulfides from different types of ores are fairly consistent, giving temperatures around 250°C (from temperature scales by KAJIWARA and KROUSE, 1970), which is in good agreement with the_ maximum value of a temperature range indicated by fluid inclusion and mineral equilibria studies (ISHIZAKA, 1968; KAJIWARA, 1968). Applications of equilibrium concepts to the observed mineralogy and sulfur isotope data of the ores give the following information: 1) The major source of the ore-forming sulfur was Miocene sea-water sulfate with a δ34S value of around +20‰. 2) Total sulfur content of solutions responsible for the ore-deposition was probably around 0.01 mole/Kg -H2O, which is very close to the value of the present-day sea-water. 3) The observed trend of decreasing δ34S values of sulfide minerals towards the top of the sequence can best be explained by the increase in fo2, pH, and total sulfur content of solutions due to the increasing contribution of sea-water during the ore-deposition. It is thus suggested that the stratigraphic and mineralogical zonation of the ores was also caused by the same mechanism.