34S Values Research Articles

Multiple sulfur and oxygen isotope compositions in Beijing aerosol

Multiple sulfur isotopes (32S, 33S, 34S, 36S) and oxygen isotopes (16O, 18O) in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ 34S values of Beijing aerosol samples range from 1.68‰ to 12.57‰ with an average value of 5.86‰, indicating that the major sulfur source is from direct emission during coal combustion. The δ 18O values vary from -5.29‰ to 9.02‰ with an average value of 5.17‰, revealing that the sulfate in Beijing aerosols is mainly composed of the secondary sulfate. The main heterogeneous oxidation of SO2 in atmosphere is related to H2O2 in July and August, whereas H2O2 oxidation and Fe3+ catalytic oxidation with SO2 exist simultaneously in September and October. Remarkable sulfur isotope mass-independent fractionation effect is found in Beijing aerosols, which is commonly attributed to the photochemical oxidation of SO2 in the stratosphere. In addition, thermochemical reactions of sulfur-bearing compounds might be also a source of sulfur isotope anomalies based on the correlation between Δ33S and CAPE.

Sulfur Isotope and Mineralogical Studies of Ni-Cu Sulfide Mineralization in the Bovine Igneous Complex Intrusion, Baraga Basin, Northern Michigan

The Bovine Igneous Complex (referred to as the BIC intrusion) occurs within the Marquette-Baraga dike swarm in the Upper Peninsula of Michigan. The intrusion is likely related to the ~1.1 Ga Midcontinent Rift system based on chemical similarities with the nearby Eagle mine and other Midcontinent Rift-related picrites, the lack of deformation fabric, and well-developed hornfels that overprints Penokean deformation fabrics. However, there is currently no age date for the BIC intrusion to confirm that it is a rift-related intrusion. The BIC is a relatively small layered intrusion with dimensions of ~1,100 × 400 × 732 m thick. Units include feldspathic wehrlite/olivine melagabbros, feldspathic olivine clinopyroxenite, and gabbro. The Little BIC, a satellite intrusion located ~100 m from the main intrusion, is primarily feldspathic wehrlite. Ni-Cu sulfide mineralization occurs in both intrusions, with a higher relative proportion in the Little BIC intrusion. Sulfide assemblages are comprised predominantly of pyrrhotite, chalcopyrite, and pentlandite; textural types vary from disseminated through globular to semimassive net-textured and locally massive. The δ 34S values of sulfide minerals in the BIC intrusion range from −6.0 to +1.5‰, with ~ 80% of the values between 0 and 1.5‰. The Proterozoic Michigamme Formation country rocks show δ 34S values between 3.0 and 9.8‰. The δ 34S values of the semimassive sulfides in the Little BIC intrusion are similar to those in country rock (3.8−6.7‰), whereas the massive sulfide values are similar to those of the sulfide minerals in the BIC intrusion. Although many values are near those of mantle-derived sulfur, the presence of strongly negative values in both intrusions indicates that crustally derived sulfur was involved in the mineralization process. In addition the distinctly positive values of disseminated sulfides in the Little BIC intrusion indicate that a large fraction of the sulfur involved in the mineralization was of country-rock origin and that at least two pulses of sulfide-saturated liquids were involved in its genesis. The Δ33S values for sulfide minerals in the BIC and the Little BIC intrusions range from −0.33 to +0.35‰, indicating that a component of Archean sulfur was also involved in the mineralization. Olivine Fo and Ni contents are consistent with rock types being related via fractional crystallization, but this process cannot account for the wide range of sulfide zones found throughout both intrusions. Multiple pulses of magma, several sulfide saturated and with distinct sulfur isotope compositions, were involved in the formation of the BIC and the Little BIC intrusions. Both sulfide concentration and isotopic composition suggest that sulfide saturation was promoted via the addition of country rock-derived sulfur.

The Erbutu Ni-Cu Deposit in the Central Asian Orogenic Belt: A Permian Magmatic Sulfide Deposit Related to Boninitic Magmatism in An Arc Setting

The Erbutu Ni-Cu sulfide deposit is hosted in a small ultramafic intrusion located at the southern margin of the Central Asian orogenic belt, Inner Mongolia. This deposit is the first case of a magmatic sulfide deposit related to boninitic magmatism in an arc setting. The host intrusion is composed of orthopyroxenite and olivine orthopyroxenite. More than three quarters of the intrusion contains economic, disseminated sulfide mineralization. SHRIMP U-Pb dating of zircons from the intrusion gives a crystallization age of 294.2 ± 2.7 Ma, similar to the age of the Permian Tarim plume in northwest China. Olivine orthopyroxenite is characterized by olivine crystals with relatively high Fo contents (85–88 mol %) and extremely low Ca contents (<250 ppm). Coexisting orthopyroxene crystals have clinoenstatite composition with enstatite from 86 to 88 mol %. Whole-rock data show characteristic enrichments of light REE relative to heavy REE, pronounced negative Nb-Ta anomalies, and moderately positive Hf anomaly. The δ 34S values of sulfide separates are 4 to 5‰, significantly higher than the typical mantle value (0 ± 2‰). The ɛ Hf values of zircons are from −4 to −9. These data indicate that the parental magma was a boninite. Crustal contamination was involved during magma evolution and ore formation.

Fluid inclusion and sulfur isotope thermometry of the Inkaya (Simav-Kütahya) Cu-Pb-Zn-(Ag) mineralization, NW TURKEY

AbstractThe Inkaya Cu-Pb-Zn-(Ag) mineralization, located about 20 km west of the Simav (Kütahya-Turkey), is situated in the northern part of the Menderes Massif Metamorphics. The mineralization is located along an E-W trending fault in the Cambrian Simav metamorphics consisting of quartz-muscovite schist, quartz-biotite schist, muscovite schist, biotite schist and the Arıkayası formation composed of marbles. Mineralized veins are 30–35 cm in width. The primary mineralization is represented by abundant galena, sphalerite, chalcopyrite, pyrite, fahlore and minor amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, limonite, hematite and goethite with gangue quartz.Fluid inclusion studies on the quartz samples collected from the mineralized veins indicate that the temperature range of the fluids is 235°C to 340°C and the salinities are 0.7 to 4.49 wt. % NaCl equivalent. The wide range of homogenization temperatures indicates that two different fluid generations were trapped in quartz.Sulfur isotope studies of the sulfide minerals showed that all of the δ 34S values are between −2.1 and 2.6 per mil. These values are a typical range for hydrothermal sulfide minerals that have sulfur derived from a magmatic source.Pyrite-galena and pyrite-chalcopyrite sulfur isotope fractionation is consistent with an approach to isotopic equilibrium, and calculated temperatures are 254.6 and 277.4°C for pyrite-galena and 274.7°C for pyrite-chalcopyrite. The microthermometric data and sulfur isotope thermometry indicate the existence of a hydrothermal fluid that circulated along the fault crossing the Simav metamorphics and Arıkayası formation.Fluid inclusion and sulfur isotope thermometry can be used in combination with ore petrographical and geological information to provide site-specific targets for meso-hypothermal metal concentrations.

Reconstruction of Physicochemical Environment of Hydrothermal Mineralization at Malanjkhand Copper Deposit, Central India: Constraints from Sulfur Isotope Ratios in Pyrite, Molybdenite and Chalcopyrite

Abstractδ34S values of pyrite, molybdenite and chalcopyrite were determined from the Malanjkhand copper deposit. These minerals constitute the primary sulfide phases that were deposited after the initial magnetite deposition in the main orebody and host granitoid. Pyrite exhibits a depleted range of values (−2.63 to −0.56‰), chalcopyrite, a very narrow range of values around zero (−0.039 to 0.201‰) and molybdenite furnishes a range of enriched values (0.68 to 1.98‰). On back calculation of the δ34S values of H2S in the fluid from which the minerals were likely to have precipitated, using standard expressions for equilibrium fractionation at the temperature range obtained from fluid inclusion and mineral fluid equilibria, it is observed that H2S in the fluid at pyrite deposition was depleted and gradually became enriched towards molybdenite and chalcopyrite deposition. This trend is best explained as being due to inorganic reduction of SO42− in the fluid and is very much in agreement with the paragenetic sequence indicating increasing activity of H2S in the fluid. The very restricted range in the δ34S values of sulfide minerals in the fluid does indicate a single, possibly magmatic, source of sulfur that also agrees well with the earlier deduced model of genesis of the deposit as an ancient geothermal system associated with granitic magmatism.

Stable isotope geochemistry of the Ulldemolins Pb-Zn-Cu deposit (SW Catalonian Coastal Ranges, Spain)

The Pb-Zn-Cu deposit of Ulldemolins occurs within the Carboniferous sedimentary series of the southernmost Catalonian Coastal Ranges. It consists of sulphide-bearing calc-silicate assemblages, with epidote, Ca-amphiboles and Ca-garnet, which develop selectively along a dolomicrite bed near the contact with a granite porphyry. Two mineralisation styles can be differentiated: a) banded and b) irregular. Fluid inclusions and stable isotope compositions of sulphur in sulphides (sphalerite, galena and chalcopyrite) and carbon and oxygen in carbonates (calcite and dolomite) were studied in order to constrain the genesis and the source of mineralizing fluids. Fluid inclusions in sphalerite and calcite are aqueous, liquid+vapour and have a salinity between 1.2 and 7.2 wt% NaCl eq. and homogenization temperatures in the range of 273o to 368oC. The 34S(V-CDT) values in the banded mineralisation are mostly between –1.5 and +2.1‰, and those from the irregular mineralisation are between –1.1 and +20.5‰. These 34S values of the banded mineralisation are in agreement with a magmatic origin of sulphur. In addition, the 18O(SMOW) values of hydrothermal calcite, from +6.9 to +12.5‰, are consistent with a magmatic origin of the fluids that formed the banded ore deposit. Later, a new input of fluids interacted with the previously formed mineral assemblages and modified part of the deposit, leading locally to an irregular skarn mineralisation.

Petrology, Geochemistry, and Stable Isotope Studies of the Chehelkureh Cu-Zn-Pb Deposit, Zahedan, Iran

The Chehelkureh base metal deposit in southeast Iran is in an abandoned historic copper district that is fault controlled and hosted in a sequence of slightly Eocene interbedded graywackes, siltstones, and shales. Several stocks and dikes of Oligo-Miocene granodiorite to quartz monzodiorite and granite composition, oriented parallel to the dominant northwest-southeast fault system, intruded into the sedimentary sequence. The sedimentary rocks were metamorphosed to the hornfels facies in some outcrops. The intrusions are spatially and temporally related to mineralized faults. The deposit consists of numerous irregular lenses and veins located along faults that cover an area 1,500 m long by 80 to 280 m wide. There are two periods of primary Cu-Zn-Pb mineralization that crosscut each other. The first stage includes quartz, calcite, dolomite, ankerite, siderite, ilmenite, rutile, molybdenite, pyrrhotite, arsenopyrite, pyrite, and chalcopyrite. The second stage consists of quartz, dolomite, ankerite, siderite, chalcopyrite, sphalerite, pyrite, galena, selenian galena, marcasite, nevskite, and paraguanajuatite. The gangue minerals are dominated by quartz and various carbonates, locally associated with chlorite. Hypogene alteration consists of silicification, carbonatization (ankerite, magnesite, siderite, and dolomite), chloritization, kaolinitization, sulfidation, and, less commonly, sericitization. The intrusive rocks at Chehelkureh are calc-alkaline and have chemical features typical of I-type granitoids. Based on Nb-Y and Ta-Yb discrimination diagrams, the geotectonic environment of Chehelkureh granitoids is an intracontinental volcanic arc (Nb/Y ~ 0.4), which is the same setting as that in the multiphase granitoid batholiths of Zahedan, located southeast of Chehelkureh. Granitoids of the Chehelkureh area have moderate REE (rare-earth element) contents (∑REE = 110–174 ppm; average 153 ppm), moderate light REE/heavy REE ((La/Lu)cn = 7–8), and strong negative Eu anomalies (Eu/Eu* ~ 0.2), but no Eu anomaly is evident in monzodiorites. Spider diagram patterns for samples of igneous rocks show Nb and Ta, Sr, and Ti-V negative anomalies, with high amounts of Cu, U, and Th. Fluid inclusion studies of quartz intergrown with sulfides in quartz veins show three main types of fluid inclusions: type 1 inclusions consist of liquid + vapor + daughter crystal (solid); type 2 inclusions are composed of liquid + minor vapor, with vapor/liquid ratios of 0.1 to 0.4; and type 3 inclusions are vapor rich with liquid/vapor ratios up to 0.05 (liquid phase is minor or absent). Homogenization temperatures (Th) for type 2 inclusions vary between 330° and 480°C, whereas their salinities range from 5 to 15 wt % NaCl equiv. The δ 18Owater values of quartz in sulfide-bearing veins are 8.8 to 11‰, with an average of 10‰. Most of the δ 18Owater values of quartz veins are in the range of typical magmatic, metamorphic, and connate waters, so the source of the ore fluids cannot be distinguished based on oxygen isotopes alone. The δ 18Owater and δ Dwater values calculated from chlorite range from 5.6 to 10.6‰ and −31 to −23‰, respectively. These data lie in the metamorphic water box, in the formation water box, or about midway between the magmatic water field and typical seawater. For kaolinite at ~200°C, the calculated δ 18Owater varies from 4.2 to 10.7‰ and the δ Dwater values range from −88 to −49‰. The carbon isotope values (Pee Dee Belemnite) of carbonates vary between −5.7 and −0.9‰, whereas the δ 18O values (Standard Mean Ocean Water) are between 12.4 and 14.9‰. The coupled oxygen and carbon isotope values shift from magmatic values and can be related to metasedimentary decarbonation reactions and metasomatic exchange of oxygen with magmatic fluid. The range of δ 34S values of sulfide minerals is small (2.0–4.2‰, with a mean value of 3‰), consistent with a magmatic origin for sulfur. Isotope thermometry, based on quartz-carbonate pairs, yields an average of 450°C, which is consistent with fluid inclusion temperatures. Isothermal f O2-pH diagrams constructed at 450°C and 1 kbar suggest that the ore formed in the H2S-predominant field with f O2 and pH ranging from 10−29 to 10−24 and 5.0 to 6.2, respectively. The petrogenetic model proposed for the Chehelkureh deposit suggests that during the Oligocene a quartz-monzodiorite stock intruded the Eocene turbidites and provided a magmatic component to the ore-forming system, but also acted as the heat source for hydrothermal convection cells, although metamorphic and connate waters may also have contributed to the ore-forming fluids. In this model, magma is the main source of sulfur, base metals, and carbon, although Eocene turbidites also contributed some metals and carbon.

Source of molten elemental sulfur and hydrogen sulfide from the Inigok well, northern Alaska

Elemental sulfur (S0) and high-pressure hydrogen sulfide (H2S), the first recorded occurrence of both from a well in northern Alaska, were encountered in the Husky 1 Inigok exploratory well in 1978. Located about 100 mi (160 km) southwest of Prudhoe Bay, the well was targeting an anticlinal structure on the northeast flank of a large late Paleozoic basin beneath the coastal plain and foothills region of the eastern National Petroleum Reserve in Alaska. The sulfur and gas first appeared at a depth of 17,570 ft (5355 m) while drilling in dark-gray to black organic carbon–depleted Carboniferous limestones (the Lisburne Group) at a temperature of 347F, well above the melting point of S0. Solidification of the molten sulfur by cooling during the drilling operation caused the drillstem to stick and delayed drilling operations for several months before being released. To determine the nature and source of the sulfur and H2S and to establish any relationship between them, we performed chemical analyses on S0, drilling mud, and cuttings. Numerous holes and vesicles in some sulfur samples indicate the presence of gas, but other samples, without vesicles, contain sharp edges, fractures, and x-ray diffraction patterns characteristic of orthorhombic and not amorphous sulfur, thus arguing against a molten source in these samples. Isotopic values suggest that the sulfide in widely separated mud samples has a common source, and that the 34S values for S0 are slightly more enriched in 32S in all deeper samples. The S0 from the drill pipe at 17,240 ft (5254 m) has a 34S value similar to that of the sulfur in mud samples. The results appear to indicate that H2S is the source for the S0. The source of the original H2S is an enigma. We consider several possibilities, among them, formation by biological sulfate reduction, thermal sulfate reduction during burial, a volcanic source, or generation in the deeply buried sediment from thermal disproportionation of pyrite. Here, we evaluate several possible origins based mostly on the properties of the enclosing limestone or shale host rocks, the downhole temperatures, and the stable isotope ratios measured and conclude that pyrite is the most probable source.

The Early Cretaceous Yangzhaiyu Lode Gold Deposit, North China Craton: A Link Between Craton Reactivation and Gold Veining

The Yangzhaiyu gold deposit is one of numerous lode gold deposits in the Xiaoqinling district, southern margin of the North China Craton. Gold mineralization is hosted in Neoarchean to early Paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein-proximal alteration zone. Ore-related hydrothermal alteration is dominated by sericite + quartz + sulfide assemblages close to gold veins, and biotite + quartz + pyrite ± chlorite ± epidote alteration generally distal from mineralization. Pyrite is the predominant sulfide mineral, locally coexisting with minor amounts of chalcopyrite, sphalerite, and galena. Gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with Au-bearing tellurides, mainly petzite and calaverite coexisting with hessite, tellurobismuthite, and altaite. Fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures (175°–313°C) from aqueous or aqueous-carbonic fluids with moderate salinity (5–14 wt % NaCl equiv). δ 34S values of sulfide minerals range mainly from 2.0 to 4.4‰, whereas auriferous quartz vein samples have δ 18O values of 12.4 to 9.6‰, with calculated δ 18OH2O values of 6.0 to 3.2‰. Gold-related pyrite grains yield elevated 3He/4He ratios (1.51-0.32 Ra) relative to crustal reservoirs and mantle-like 20Ne/22Ne and 21Ne/22Ne ratios (9.90-9.68 and 0.029, respectively). The stable and noble gas isotopes thus suggest deep-seated, most likely magmatic and mantle-derived, sources for the ore fluids, sulfur and, by inference, other components in the ore system. 40Ar/39Ar dating of ore-related sericite and biotite separates indicates two episodes of gold genesis at 134.5 to 132.3 and 124.3 to 123.7 Ma. The mineralization ages overlap zircon U-Pb ages of 141.0 ± 1.6 to 125.8 ± 1.4 Ma (2 σ ) for the Wenyu and Niangniangshan monzogranite Plutons and a number of mafic to intermediate dikes intruding these Plutons, all being proximal to the Yangzhaiyu gold deposit. The synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur. The geochronologic data also suggest that gold veining took place billions of years after the stabilization of the North China Craton and associated metamorphism in the Late Archean to early Paleoproterozoic. This contrasts sharply to lode gold deposits in other Precambrian cratons that formed predominantly in Late Archean to Paleoproterozoic, temporarily and genetically related to regional high-grade metamorphism and compressional or transpressional tectonism. Available data have demonstrated that the North China Craton was reactivated in the late Mesozoic, as marked by voluminous igneous rocks, faulted-basin formation, high crustal heat flow, and widespread metamorphic core complexes in the eastern part of the craton. It is thus suggested that the Yangzhaiyu gold deposit, together with other deposits of similar ages in the Xiaoqinling district, were products of this craton reactivation event. Lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy, fluid, and sulfur required for the formation of the gold deposits.

Multiple Sulfur and Iron Isotope Composition of Magmatic Ni-Cu-(PGE) Sulfide Mineralization from Eastern Botswana

We report here high-precision multiple sulfur and iron isotope compositions for a series of mineralized samples from Ni-Cu-(PGE) sulfide deposits in the Archean Tati greenstone belt and the Phikwe Complex of eastern Botswana. Mineralized samples from the Phoenix and Selkirk Ni-Cu-(PGE) deposits in the Tati greenstone belt display slightly positive δ 34S isotope values, ranging from 0.2 to 0.8‰ V-CDT. Δ33S values of sulfides at Phoenix and Selkirk are −0.01 to −0.08‰ V-CDT, suggesting either a dominantly mantle sulfur source or effective eradication of a crustal Δ33S anomaly through equilibration with large amounts of silicate melt. In the Selebi-Phikwe belt, a granite-gneiss terrane with abundant amphibolite lenses of either volcanic and/or intrusive nature, mineralized lower grade samples from the Phikwe, Phokoje, and Dikoloti Ni-Cu-(PGE) deposits have more variable δ 34S values ranging from −3.1 to +0.3‰ and display significant mass independent anomalies (Δ33S values ranging from −0.89 to −0.27‰), suggesting that barren sulfides associated with distal or low-temperature sea-floor hydrothermal activity contributed sulfur to these deposits. Iron isotopes of sulfides from these deposits show a relatively small range of negative Δ56Fe values (−0.29 to −0.04‰), consistent with high-temperature fractionations in magmatic systems, with the exception of one sample from the Dikoloti Ni-Cu-(PGE) deposit of the Selebi-Phikwe greenstone belt, which shows a more negative δ 56Fe value of −0.61‰, consistent with assimilation of sedimentary or hydrothermal sulfides rather than fractionations in high-temperature magmatic systems. Data from this study highlight the complexity and variability that characterize ore-forming processes in magmatic systems. We suggest that the presence of sulfur-bearing lithologic units in host rocks of mafic and ultramafic intrusions may not be essential toward the assessment of the prospectivity of a province to host orthomagmatic nickel sulfides. Geologic settings without any or little sulfur in the stratigraphy, which have been traditionally neglected in terms of their prospectivity, should thus be revisited and possibly reassessed considering the potential importance of external source of sulfur to generate ore deposits.

Indicating atmospheric sulfur by means of S-isotope in leaves of the plane, osmanthus and camphor trees

Foliar δ 34S values of three soil-growing plant species ( Platanus Orientalis L., Osmanthus fragrans L. and Cinnamomum camphora) have been analyzed to indicate atmospheric sulfur. The foliar δ 34S values of the three plant species averaged −3.11 ± 1.94‰, similar to those of both soil sulfur (−3.73 ± 1.04‰) and rainwater sulfate (−3.07 ± 2.74‰). This may indicate that little isotopic fractionation had taken place in the process of sulfur uptake by root or leaves. The δ 34S values changed little in the transition from mature leaves to old/senescing leaves for both the plane tree and the osmanthus tree, suggestive of little isotope effect during sulfur redistribution in plant tissues. Significantly linear correlation between δ 34S values of leaves and rainwater sulfate for the plane and osmanthus trees allowed the tracing of temporal variations of atmospheric sulfur by means of foliar sulfur isotope, while foliage δ 34S values of the camphor is not an effective indicator of atmospheric sulfur.

Iron and sulphur isotopes from the Carajás mining province (Pará, Brazil): Implications for the oxidation of the ocean and the atmosphere across the Archaean–Proterozoic transition

Mineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations (BIFs) and pyrite-bearing sandstones from the Carajás mineral province, Brazil. The BIFs belong to the 2.7 Ga old Grão Pará Group and show a rather simple mineralogy (hematite and quartz or cryptocrystalline silica). Their REE + Y patterns suggest deposition under marine sub-oxic conditions. Fe isotopes show highly positive values (δ 57Fe IRMM-14 = 2.06 ± 0.34‰ in average) which can be explained by the partial oxidation of Fe 2+ aq in the surface ocean, subsequent to the upwelling of deep anoxic seawater. The resulting iron oxy-hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a Rayleigh distillation model. The pyrite-bearing sandstones belong to the Aguas Claras Formation of (Palaeoproterozoic) younger age and were cored at the base of the giant Azul manganese deposit. Diagenetic pyrite is characterized by positive δ 57Fe IRMM-14 = 1.02 ± 0.2‰ and δ 34S VCTD (11.97 ± 0.12‰) average values, that are different from values of modern marine biogenic pyrite. Results likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time. Near-zero Δ 33S values (0.013 ± 0.003‰) indicate minimal mass-independent sulfur isotope fractionation (MIF-S), consistent with the 2.1 Ga age previously obtained from the Aguas Claras pyrites. This result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough (10 − 5 to 10 − 2 PAL- or Present Atmospheric Level-) to hinder MIF-S by photochemical reactions. Incidentally, this also confirms that the giant Mn deposit of Carajás is in the same age range (2.1 ± 0.2 Ga) as other Mn ores in Gabon and South Africa, pointing to the importance of Mn precipitation in Paleoproterozoic times.

Tracing the sources of cave sulfates: a unique case from Cerna Valley, Romania

In order to reliably distinguish between different genetic processes of cave sulfate formation and to quantify the role of thermo-mineral waters on mineral deposition and cave morphology, it is critical to understand sulfur (S) sources and S transformations during hydrological and speleogenetic processes. Previous work has shown that sulfuric acid speleogenesis (SAS) often produces sulfate deposits with 34S-depleted isotopic signatures compared to those of the original source of S in sulfate rocks. However, 34S-depleted isotopic composition of S-bearing minerals alone does not provide enough information to clearly distinguish SAS from other speleogenetic processes driven by carbonic acid, geothermal heat, or other processes. The isotopic composition (δ 18O and δ 34S) of sulfate minerals (mainly gypsum) from seven caves of the Cerna Valley (Romania) defines three distinct populations, and demonstrates that the δ 34S values of SAS-precipitated cave sulfates depend not only on the source of the S, but also on the H 2S:SO 4 2− ratio during aqueous S species reactions and mineral precipitation. Population 1 includes sulfates that are characterized by relatively low δ 34S values (− 19.4 to − 27.9‰) with δ 18O values between 0.2 and 4.3‰ that are consistent with oxidation of dissolved sulfide produced during methane-limited thermochemical sulfate reduction (TSR) that presently characterizes the chemistry of springs in the upper Cerna Valley. Population 2 of cave sulfates has 34S-enriched δ 34S values (14.3 to 19.4‰) and more 18O-depleted δ 18O values (from − 1.8 to − 10.0‰). These values argue for oxidation of dissolved sulfide produced during sulfate-limited TSR that presently characterizes the chemistry of springs further downstream in the Cerna Valley. The δ 18O values of cave sulfates from Population 1 are consistent with oxidation under more oxic aqueous conditions than those of Population 2. δ 34S values of cave sulfates within Population 3 (δ 34S: 5.8 to 6.5‰) may be consistent with several scenarios ( i.e., pyrite oxidation, oxidation of dissolved sulfide produced during methane-limited TSR coupled with O 2-limited oxidation during SAS). However, comparatively 18O-enriched δ 18O SO4 values (11.9 to 13.9‰) suggest the majority of this sulfate O was derived from atmospheric O 2 in gas-phase oxidation prior to hydration. Thus, the combined use of oxygen- and sulfur-isotope systematics of sulfate minerals precipitated in a variety of cave settings along Cerna Valley may serve as an example of how more complex cave systems can be deconvoluted to allow for more complete recognition of the range of processes and parameters that may be involved in SAS.

Marble-Hosted Submicroscopic Gold Mineralization at Asimotrypes Area, Mount Pangeon, Southern Rhodope Core Complex, Greece

Gold mineralization at Asimotrypes, Mount Pangeon, Greece, occurs within amphibolite facies rocks of the Southern Rhodope Core Complex, one of the largest metamorphic core complexes in the world. Exhumation of the complex resulted from middle Eocene to middle Miocene northeast-southwest–oriented extension in the northern Aegean and was controlled by the Kerdylion detachment zone. Host rocks are mylonitic, impure dolomite marbles of marine provenance ( δ 13C = 1.9 – 2.9‰), which are intercalated with paramica schists, and amphibolites, and intruded by early Miocene syntectonic granitoids. In the Asimotrypes area, metamorphic rocks and granitoids exhibit flat mylonite-type ductile fabrics with consistent top-to-the-southwest sense of shear, as does the entire Complex. Two mineralogically similar and spatially coincident gold mineralization styles, with a supergene overprint, exist: (1) strata-bound replacement bodies that contain up to 17 ppm gold, concentrated at and controlled by the intersections of several hydrothermally altered top-to-the-southwest marble mylonites, with crosscutting northwest-southeast to east-west–trending high-angle brittle normal faults and fractures, and (2) structurally controlled quartz veins, pods, and lenses with 4 to 13 ppm gold, which occur along the northwest-oriented subvertical brittle structures; the latter crosscut the ductile shear foliation of the host rocks, together with the granitoids, and dip steeply to the southwest. Gold-bearing replacement bodies typically occur as discordant wide halo adjacent to the centrally located brittle structures. Ductile top-to-the-southwest shear zones and cross-cutting brittle structures are considered contemporaneous within the regional extensional deformation and exhumation history of the core complex host rocks. The distribution of gold mineralization is related to the geometry of the brittle structures, strongly suggesting that faults acted as major fluid feeder conduits during gold mineralization. Hydrothermal alteration associated with the auriferous bodies and veins, overprinting the metamorphic rocks at Asimotrypes, consists of quartz, muscovite (sericite), chlorite, calcite (dedolomite), and sulfide minerals (locally, as much as 35 vol %). Gangue quartz occurs as (1) peripheral banded quartz with mylonitic texture, (2) dominant gold-bearing jasperoidal quartz, and (3) late, fine drusy quartz. The gold assemblage consists of arsenopyrite (41.7–43 wt % As; electron microprobe analyses) and arsenian pyrite encompassed by jasperoidal quartz; chalcopyrite, galena, tetrahedrite-tennantite, and sphalerite are trace phases. Secondary ion mass spectrometry (SIMS) spot analyses revealed that gold in replacement ore is submicroscopic and occurs in arsenopyrite and arsenian pyrite (As = 0.01–3.8 wt %), ranging from 0.5 to 29 ppm (mean = 11.6 ppm), and 0.14 to 11 ppm (mean = 2.3 ppm), respectively. Supergene overprint includes colloidal goethite + hematite containing native gold grains (size range, 20–40 μ m) and lesser covellite, malachite, cerrussite, and chrysocolla. SIMS analysis also shows a primary, inhomogeneous distribution pattern for gold that appears to mimic finely banded growth twinning lamellae or growth zones. The form of the vein-related gold is unknown. Fluid inclusions trapped during gold mineralization are low to medium salinity (<10 wt % NaCl equiv), aqueous-carbonic H2O-CO2-NaCl inclusions with highly variable carbonic to aqueous contents and naturally decrepitated or reequilibrated inclusions, interpreted to represent decompression by concurrent exhumation of the Southern Rhodope Core Complex. Trail-bound aqueous H2O-NaCl inclusions are interpreted as a late extensional brittle deformation-related hydrothermal event unrelated to gold-bearing sulfide precipitation. Trapping temperatures of the H2O-CO2-NaCl inclusions and oxygen isotope equilibrium temperatures between quartz and muscovite (sericite) indicate formation of gold-bearing arsenopyrite, arsenian pyrite, and quartz bodies at ~270°C, with pressures of 1,800 to 2,000 bars corresponding to depths between 6 and 9 km under lithostatic load. Measured hydrogen and calculated oxygen isotope compositions of the aqueous-carbonic mineralizing fluids ( δ Dwater = −125 to −105‰, δ 18Owater = 11.9 to 13.7 ‰ at 250°C, and 13.9 and 15.7 ‰ at 300°C) indicate an evolved meteoric origin. Water/rock calculations indicate these values could derive from heated meteoric water that had undergone isotope exchange during circulation through marbles at low water/rock ratio. Gold-associated sulfide minerals have δ 34S values between 2.2 and 3.1 per mil, interpreted as leaching of the core complex Paleozoic marine metasedimentary (marble), and interlayered mafic metavolcanic (amphibolites) and Miocene granitic rocks through fluid/rock interaction. Gold was probably precipitated from an H2S-rich fluid when the host sulfide minerals were stabilized by pyritization of marble wall rock. Asimotrypes gold mineralization is interpreted as postmetamorphic and postmagmatic, and linked to late stages of exhumation of the Complex by middle Eocene to middle Miocene extension in the northern Aegean. The location and shape of gold orebodies are controlled by interactive ductile-then-brittle deformation, fluid flow and fluid-marble interaction processes. High paleogeothermal gradients associated with extension may have driven the dominantly meteoric fluid circulation downward within the exhuming Complex. Asimotrypes may represent a potential new gold mineralization style for the Rhodope region.

Application of sulphur isotope ratios to examine weaning patterns and freshwater fish consumption in Roman Oxfordshire, UK

This study investigates the application of sulphur isotope ratios (δ 34S) in combination with carbon (δ 13C) and nitrogen (δ 15N) ratios to understand the influence of environmental sulphur on the isotopic composition of archaeological human and faunal remains from Roman era sites in Oxfordshire, UK. Humans ( n = 83), terrestrial animals ( n = 11), and freshwater fish ( n = 5) were analysed for their isotope values from four locations in the Thames River Valley, and a broad range of δ 34S values were found. The δ 34S values from the terrestrial animals were highly variable (−13.6‰ to +0.5‰), but the δ 34S values of the fish were clustered and 34S-depleted (−20.9‰ to −17.3‰). The results of the faunal remains suggest that riverine sulphur influenced the terrestrial sulphur isotopic signatures. Terrestrial animals were possibly raised on the floodplains of the River Thames, where highly 34S-depleted sulphur influenced the soil. The humans show the largest range of δ 34S values (−18.8‰ to +9.6‰) from any archaeological context to date. No differences in δ 34S values were found between the males (−7.8 ± 6.0‰) and females (−5.3 ± 6.8‰), but the females had a linear correlation ( R 2 = 0.71; p < 0.0001) between their δ 15N and δ 34S compositions. These δ 34S results suggest a greater dietary variability for the inhabitants of Roman Oxfordshire than previously thought, with some individuals eating solely terrestrial protein resources and others showing a diet almost exclusively based on freshwater protein such as fish. Such large dietary variability was not visible by analysing only the carbon and nitrogen isotope ratios, and this research represents the largest and most detailed application of δ 34S analysis to examine dietary practices (including breastfeeding and weaning patterns) during the Romano-British Period.

Preservation of bone collagen sulphur isotopic compositions in an early Holocene river-bank archaeological site

This study investigates the reliability of the sulphur isotopic compositions (δ 34S) of collagen in archaeological bones from an early Holocene river-bank site, Noyen-sur-Seine (France). The chemical composition (C, N, S) of whole bones compared to those of bones from cave sites suggests that contamination with sulphur is higher in the bones sampled from river bank deposits compared to those from caves, especially those that occur well above the water table. Sulphur content in fresh bone collagen suggests specific values for different mammal taxa, while sulphur content in reptile bones may not always be higher than those of mammals. In the early Holocene bones from Noyen-sur-Seine, the collagen has chemical characteristics within the overall range observed in modern bone collagen. However, co-variation between some diagenetic indicators, such as sulphur content and N/S in whole bone, %S in collagen, and S yield, and δ 34S values of collagen from the same species or ecological groups indicate that some diagenetic alteration may have influenced the collagen. Excluding samples possibly affected by this alteration, a difference in δ 34S is measured between freshwater and terrestrial fauna. We recommend further work on the collagen sulphur contents in different species. Moreover, whole bone chemical compositions may help to screen samples for sulphur isotopic analyses of collagen that are to be used for palaeodietary reconstructions.

Silver–base metal epithermal vein and listwaenite types of deposit Crnac, Rogozna Mts., Kosovo. Part I: Ore mineral geochemistry and sulfur isotope study

Pb–Zn–Ag vein and listwaenite types of mineralization in Crnac deposit, Western Vardar zone, were deposited within several stages: (i) the pre-ore stage comprises pyrite, arsenopyrite, pyrrhotite, quartz, kaolinite and is followed by magnetite–pyrite; (ii) the syn-ore stage is composed of galena, sphalerite, tetrahedrite and stefanite; and (iii) the post-ore stage is composed of carbonates, pyrite, arsenopyrite and minor galena. The vein type mineralization is hosted by Jurassic amphibolites and veins terminate within overlying serpentinites. Mineralized listwaenites are developed along the serpentinite–amphibolite interface. The reserves are estimated to 1.7 Mt of ore containing in average 7.6% lead, 2.9% zinc, and 102 g/t silver. Sulfides from the pre- and syn-mineralization assemblage of the vein- and listwaenite-types of mineralization from the Crnac Pb–Zn–Ag deposit have been analyzed using microprobe, crush-leachates and sulfur isotopes. The pre-ore assemblage precipitated under high sulfur fugacities ( f(S 2) = 10 − 8 –10 − 6 bar) from temperatures ranging between 350 °C and 380 °C. Most likely water–rock reactions, boiling and/or increase of pH caused an increase of δ 34S of pyrite toward upper levels within the deposit. The decomposition of pre-ore pyrrhotite to a pyrite-magnetite mixture occurred at a fugacity of sulfur from f(S 2) = 8.7 × 10 − 10 to 9.6 × 10 − 9 bar and fugacity of oxygen from f(O 2) = 2.4 × 10 − 30 to 3.1 × 10 − 28 bars, indicating a contribution of an oxidizing fluid, i.e. meteoric water during pre-ore stages of hydrothermal activity. The crystallization temperatures obtained by the sphalerite-galena isotope geothermometer range from 230 to 310 °C. The δ 34S values of pre- and syn-ore sulfides (pyrite, galena, sphalerite, δ 34S = 0.3–5.9‰) point to magmatic sulfur. Values of δ 34S of galena and sphalerite are decreasing upwards due to precipitation of early formed sulfide minerals. Post-ore assemblage precipitated at temperature below 190 °C. Based on data presented above, we assume two fluid sources: (i) a magmatic source, supported by sulfur isotopic compositions within pre- and syn-ore minerals and a high mol% of fluorine found within pre- and syn-ore leachates, and (ii) a meteoric source, deduced by coincident pyrite–magnetite intergrowth, sulfur isotopic trends within syn-ore minerals and decrease of crystallization temperatures from the pre-ore stage (380–350 °C), towards the syn-ore (310–215 °C) and post-ore stages (< 190 °C). Post-ore fluids are Na–Ca–Mg–K–Li chlorine rich and were modified via water–rock reactions. Simple mineral assemblage and sphalerite composition range from 1.5 to 10.1 mol% of FeS catalog Crnac to a group of intermediate sulfidation epithermal deposit.

Ore genesis of Pb–Zn deposits in the Nappe zone of Northern Tunisia: Constraints from Pb–S–C–O isotopic systems

The Jalta and Jebel Ghozlane ore deposits are located in the extreme North of Tunisia, within the Nappe zone. The mineralization of Jalta, hosted in Triassic dolostones and the overlying Mio-Pliocene conglomerates, consists of abundant galena, barite, and cerussite with accessory sphalerite, pyrite, and jordanite. At Jebel Ghozlane, large Pb–Zn concentrations occur in the Triassic dolostones and Eocene limestones. The mineral association consists of galena, sphalerite, barite, and celestite and their oxidation products (cerussite, smithsonite, and anglesite). Lead isotope ratios in galena from both districts are relatively homogeneous ( 206Pb/ 204Pb = 18.702–18.823, 207Pb/ 204Pb = 15.665–15.677, 208Pb/ 204Pb = 38.725–38.875). The δ 34S values for sulfates from both areas (+ 12.2 to + 16.2‰ at Jalta and + 14.3 to + 19.4‰ at Jebel Ghozlane) are compatible with a derivation of sulfur from marine sulfates, possibly sourced from the Triassic evaporites. The δ 34S values of the sulfides have a range between − 10 and + 12.5‰ at Jalta, and between − 9.1 and + 22.1‰ at Jebel Ghozlane. The large range of values suggests reduction of the sulfate by bacterial and/or thermochemical reduction of sulfate to sulfur. The high δ 34S values of sulfides require closed-system reduction processes. The isotopically light carbon in late calcites (− 6.3 to − 2.5‰) and authigenic dolomite (− 17.6‰) suggests an organic source of at least some of the carbon in these samples, whereas the similarity of the δ 18O values between calcite (+ 24.8‰) and the authigenic dolomite (+ 24.7‰) of Jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates. The secondary calcite isotope compositions of Jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200 °C, but temperatures as low as 50 °C may be indicated by the late calcite of Jebel Ghozlane (δ 18O of + 35.9‰). Given the geological events related to the Alpine orogeny in the Nappe zone (nappe emplacement, bimodal volcanism, and reactivation of major faults, such as Ghardimaou-Cap Serrat) and the Neogene age of the host rocks in several localities, a Late-Miocene age is proposed for the Pb–Zn ore deposits considered in this study. Remobilization of deep-seated primary deposits in the Paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the Nappe zone as a whole.

Ages and Sources of Components of Zn-Pb, Cu, Precious Metal, and Platinum Group Element Deposits in the Goodsprings District, Clark County, Nevada

The Goodsprings district, Clark County, Nevada, includes zinc-dominant carbonate replacement deposits of probable late Paleozoic age, and lead-dominant carbonate replacement deposits, copper ± precious metal-platinum group element (PGE) deposits, and gold ± silver deposits that are spatially associated with Late Triassic porphyritic intrusions. The district encompasses ~500 km2 although the distribution of all deposits has been laterally condensed by late Mesozoic crustal contraction. Zinc, Pb, and Cu production from about 90 deposits was ~160,000 metric tons (t) (Zn > Pb >> Cu), 2.1 million ounces (Moz) Ag, 0.09 Moz Au, and small amounts of PGEs—Co, V, Hg, Sb, Ni, Mo, Mn, Ir, and U—were also recovered. Zinc-dominant carbonate replacement deposits (Zn > Pb; Ag ± Cu) resemble Mississippi Valley Type (MVT) Zn-Pb deposits in that they occur in karst and fault breccias in Mississippian limestone where the southern margin of the regional late Paleozoic foreland basin adjoins Proterozoic crystalline rocks of the craton. They consist of calcite, dolomite, sphalerite, and galena with variably positive S isotope compositions ( δ 34S values range from 2.5–13‰), and highly radiogenic Pb isotope compositions (206Pb/204Pb >19), typical of MVT deposits above crystalline Precambrian basement. These deposits may have formed when southward flow of saline fluids, derived from basinal and older sedimentary rocks, encountered thinner strata and pinch-outs against the craton, forcing fluid mixing and mineral precipitation in karst and fault breccias. Lead-dominant carbonate replacement deposits (Pb > Zn, Ag ± Cu ± Au) occur among other deposit types, often near porphyritic intrusions. They generally contain higher concentrations of precious metals than zinc-dominant deposits and relatively abundant iron oxides after pyrite. They share characteristics with copper ± precious metal-PGE and gold ± silver deposits including fine-grained quartz replacement of carbonate minerals in ore breccias and relatively low S and Pb isotope values ( δ 34S values vary from 0–~4‰; 206Pb/204Pb <18.5). Copper ± precious metal-PGE deposits (Cu, Co, Ag, Au, Pd, and Pt) consist of Cu carbonate minerals (after chalcocite and chalcopyrite) and fine-grained quartz that have replaced breccia clasts and margins of fissures in Paleozoic limestones and dolomites near porphyritic intrusions. Gold ± silver deposits occur along contacts and within small-volume stocks and dikes of feldspar porphyry, one textural variety of porphyritic intrusions. Lead isotope compositions of copper ± precious metal-PGE, gold ± silver, and lead-dominant carbonate replacement deposits are similar to those of Mojave crust plutons, indicating derivation of Pb from 1.7 Ga crystalline basement or from Late Proterozoic siliciclastic sedimentary rocks derived from 1.7 Ga crystalline basement. Four texturally and modally distinctive porphyritic intrusions are exposed largely in the central part of the district: feldspar quartz porphyry, plagioclase quartz porphyry, feldspar biotite quartz porphyry, and feldspar porphyry. Intrusions consist of 64 to 70 percent SiO2 and variable K2O/Na2O (0.14–5.33) that reflect proportions of K-feldspar and albite phenocrysts and megacrysts as well as partial alteration to K-mica; quartz and biotite phenocrysts are present in several subtypes. Albite may have formed during emplacement of magma in brine-saturated basinal strata, whereas hydrothermal alteration of matrix, phenocrystic, and megacrystic feldspar and biotite to K-mica, pyrite, and other hydrothermal minerals occurred during and after intrusion emplacement. Small volumes of garnet-diopside-quartz and retrograde epidote-mica-amphibole skarn have replaced carbonate rocks adjacent to one intrusion subtype (feldspar-quartz porphyry), but alteration of carbonate rocks at intrusion contacts elsewhere is inconspicuous. Uranium-lead ages of igneous zircons vary inconsistently from ~ 180 to 230 Ma and are too imprecise to distinguish age differences among intrusion subtypes; most ages are 210 to 225 Ma, yielding a mean of 217 ± 1 Ma. K-Ar and 40Ar/39Ar ages of magmatic (plagioclase, biotite) and hydrothermal (K-mica) minerals span a similar range (183–227 Ma), demonstrating broadly contemporaneous intrusion emplacement and hydrothermal alteration but allowing for multiple Late Triassic magmatic-hydrothermal events. Imprecision and range of isotopic ages may have resulted from burial beneath Mesozoic and Tertiary strata and multiple intrusion of magmas, causing thermal disturbance to Ar systems and Pb loss from zircons in intrusions. Separate late Paleozoic (zinc-dominant carbonate replacement deposits) and Late Triassic (all other deposits) mineralizing events are supported by form, distribution, and host rocks of metal deposits, by hydrothermal mineral assemblages, isotope compositions, metal abundances, and metal diversity, and by small intrusion volumes. These characteristics collectively distinguish the Goodsprings district from larger intrusion related carbonate replacement districts in the western United States. They can be used to evaluate proximity to unexposed porphyritic intrusions associated with PGE and gold ± silver mineralization.

Deciphering fluid sources of hydrothermal systems: A combined Sr- and S-isotope study on barite (Schwarzwald, SW Germany)

Primary and secondary barites from hydrothermal mineralizations in SW Germany were investigated, for the first time, by a combination of strontium (Sr) isotope systematics ( 87Sr/ 86Sr), Sr contents and δ 34S values to distinguish fluid sources and precipitation mechanisms responsible for their formation. Barite of Permian age derived its Sr solely from crystalline basement rocks, whereas all younger barite also incorporate Sr from formation waters of the overlying sediments. In fact, most of the Sr in younger barite is leached from Lower and Middle Triassic sediments. In contrast, most of the sulfur (S) of Permian, Jurassic and northern Schwarzwald Miocene barite originated from basement rocks. The S source of Upper Rhinegraben (URG)-related Paleogene barite differs depending on geographic position: for veins of the southern URG, it is the Oligocene evaporitic sequence, while central URG mineralizations derived its S from Middle Triassic evaporites. Using Sr isotopes of barite of known age combined with estimates on the Sr contents and Sr isotopic ratios of the fluids' source rocks, we were able to quantify mixing ratios of basement-derived fluids and sedimentary formation waters for the first time. These calculations show that Jurassic barite formed by mixing of 75–95% ascending basement-derived fluids with 5–25% sedimentary formation water, but that only 20–55% of the Sr was brought by the basement-derived fluid to the depositional site. Miocene barite formed by mixing of an ascending basement-derived brine (60–70%) with 30–40% sedimentary formation waters. In this case, only 8–15% of the Sr was derived from the deep brine. This fluid-mixing calculation is an example for deposits in which the fluid source is known. This method applied to a greater number of deposits formed at different times and in various geological settings may shed light on more general causes of fluid movement in the Earth's crust and on the formation of hydrothermal ore deposits.