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The Morelos district, located in the center of the Guerrero gold belt, Guerrero State, southern Mexico, has been the site of several recent gold ± copper skarn discoveries (total of ~8.5 Moz Au) associated with Upper Cretaceous-Paleocene granodiorite intrusions. The Limon, Guajes, and Media Luna skarn deposits developed along the contact of the El Limon granodiorite and the sedimentary host rocks. Native gold is associated with retrograde alteration of garnet-pyroxene skarn and is accompanied by native bismuth as well as telluride and sulfide minerals. The Media Luna deposit is characterized by a distinct magnesium-rich skarn mineralogy and contains an average of ~1 wt % Cu, in addition to gold and silver. This distinguishes it from the other gold-only skarn deposits in the Guerrero gold belt. This observation suggests that skarns in the Guerrero gold belt, which replaced magnesium-rich sedimentary protoliths, may host significant copper resources in addition to gold. Uranium-lead laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon ages of the El Limon granodiorite range from 66.86 ± 0.40 to 65.88 ± 0.79 Ma. Preskarn molybdenite-quartz veins cut through the El Limon granodiorite and yield Re-Os molybdenite ages between 66.63 ± 0.22 and 65.55 ± 0.25 Ma. A series of pre-, syn-, and postskarn porphyritic dikes intruded the El Limon granodiorite, having zircon ages ranging from 65.9 ± 1.1 to 64.68 ± 0.38 Ma. The timing of skarn formation at Limon and Media Luna was constrained to 64.6 ± 1.2 to 63.2 ± 1.0 Ma, applying U-Pb LA-ICP-MS to garnet. The ubiquitous presence of garnet in skarn deposits and the time- and cost-efficiency of in situ geochronology are striking advantages of this method to constrain the timing of mineralization.

The Montecristo district, northern Chile, is one of the few places worldwide where there is a direct relationship between magnetite-(apatite) (MtAp) mineralization and iron oxide-copper–gold (IOCG) mineralization. The MtAp mineralization includes Ti-poor magnetite, fluorapatite, and actinolite and is crosscut and partially replaced by a younger IOCG mineralization that includes a second generation of actinolite and magnetite with quartz, chalcopyrite, pyrite, and molybdenite. The MtAp stage at Montecristo is interpreted as the crystallized iron-rich melts that used the pre-existing structures of the Atacama Fault System as conduits. These rocks later acted as a trap for hydrothermal IOCG mineralization. Geochronology data at Montecristo indicate that the host diorite (U–Pb zircon 153.3 ± 1.8 Ma, 2-sigma), MtAp mineralization (40Ar-39Ar in actinolite, 154 ± 2 Ma and 153 ± 4 Ma, 2-sigma), and the IOCG event (Re-Os on molybdenite, 151.8 ± 0.6 Ma, 2-sigma) are coeval within error and took place in a time span of less than 3.4 Ma. The εHfi and εNdi values of the host diorite are + 8.0 to + 9.8 and + 4.3 to + 5.4, respectively. The whole-rock 87Sr/86Sri values of the IOCG mineralization (0.70425 to 0.70442) are in the lower end of those of the MtAp mineralization (0.70426–0.70629). In contrast, εNdi values for the IOCG mineralization (+ 5.4 and + 5.7) fall between those of the MtAp rocks (+ 6.6 to + 7.2) and the host diorite, which suggests that the IOCG event was related to fluids having a more crustal Nd (εNdi < + 5.7) composition than the MtAp mineralization. This likely reflects the mixing of Nd from the MtAp protolith and a deep magmatic-hydrothermal source, very likely an unexposed intrusion equivalent to the host diorite. Sulfur isotope compositions (δ34S, + 0.3 to + 3.4‰) are consistent with a magmatic source., NSERC discovery grant to J.M. Hanchar (RGPIN/004649-2015), RTI2018-099157-A-I00 (MCI/AEI/FEDER, UE) research grant to F. Tornos.

The ages of sedimentation and copper-silver mineralization in the late Meso- to Neoproterozoic Kalahari Copperbelt in Botswana, an economically significant copper province, have previously been poorly constrained within an ~600 m.y. period that spans the Neoproterozoic from the assembly and breakup of Rodinia to the assembly of Gondwana. Rhenium-osmium geochronology of molybdenite and copper sulfide minerals and U-Th-Pb laser ablation split-stream inductively coupled plasma-mass spectrometry (LASS ICP-MS) analysis of xenotime grains are utilized to provide absolute and relative age data on the host rocks and mineralizing events within the Ghanzi Ridge region of the Kalahari Copperbelt. The data reveal a prolonged history of events, which is partially comparable with depositional and mineralizing events in the neighboring Central African Copperbelt. Abundant disseminated molybdenite is located within a shale layer near the base of the Proterozoic D’Kar Formation at the Northeast Mango Two deposit. Unusual molybdenite textures suggest organic matter may have been a precursor. Two molybdenite separates from a small calcite-molybdenite stringer in a wall-rock fragment that is enclosed within an epigenetic quartz-calcite-chalcopyrite vein with ill-defined and mismatched margins yielded Re-Os ages of 981 ± 3 and 981 ± 7 Ma. These ages indicate an early hydrothermal mineralizing event in the basin. A xenotime inclusion intergrown with molybdenite and chalcopyrite within the epigenetic vein yielded a younger U-Th-Pb age of 538 ± 8 Ma, suggesting two mineralizing events are preserved in a complex 6-cm-wide vein. Based on vein texture and alteration, the ages represent an ~981 Ma calcite-molybdenite mineralization event overprinted by an ~538 Ma quartz-chalcopyrite-molybdenite mineralization event, perhaps during reopening of the vein. Re-Os and U-Th-Pb geochronology were utilized at the Zone 6 deposit on minerals associated with a hydrothermal quartz-calcite-chalcocite-idaite-bornite vein. Several authigenic xenotime grains that occur along the margin of the vein yielded three concordant U-Th-Pb ages that indicate xenotime growth at ~950 to 925 Ma while other xenotime grains in a similar position yielded mostly discordant data, suggesting disturbance of the isotopic system in the xenotime grains. A coprecipitated chalcocite-idaite mixture within the hydrothermal vein produced an Re-Os age of 549.0 ± 11.2 Ma. Re-Os analysis obtained from a coprecipitated molybdenite-bornite mixture at the Northeast Fold deposit yielded an age of 515.9 ± 2 Ma. Together, the earliest Neoproterozoic Re-Os molybdenite and U-Th-Pb xenotime ages provide both a minimum depositional age constraint for the lowermost D’Kar Formation and clear evidence that diagenetic hydrothermal mineralizing events took place within the Ghanzi basin. The timing of this mineralizing event corresponds with a poorly documented regional thermal event that affected the northern margin of the Kalahari craton during the final stages of the assembly of Rodinia at ~980 Ma. The lower to middle Ghanzi Group of the Kalahari Copperbelt is at least 100 m.y. older than the host rocks within the neighboring Central African Copperbelt, which are associated with the breakup of Rodinia. The latest Neoproterozoic to Cambrian Re-Os and U-Th-Pb ages indicate that hydrothermal copper-silver mineralizing events occurred during the Pan-African (~600–480 Ma) fold-thrust evolution of the Ghanzi-Chobe zone and were broadly synchronous with widespread epigenetic hydrothermal copper-cobalt mineralizing events in the adjacent Central African Copperbelt.

The Ok Tedi copper-gold mine in Western Province, Papua New Guinea, is situated in the western part of the Ok Tedi Complex where monzodiorite to quartz monzonite intrusions are associated with porphyry- and skarn-style copper-gold mineralization. The Pleistocene age of the intrusive rocks and mineralization provides an opportunity to study the longevity of the magmatic and hydrothermal evolution at Ok Tedi through U-Pb dating of zircon and high-precision Re-Os dating of molybdenite. Six main phases of intrusive rocks can be recognized within the mine area, with the sequence of intrusion indicated by contact relationships. Each has been dated by the SHRIMP U-Pb technique with correction for Th-U disequilibrium based on the U and Th content of each sample. In order of intrusion from oldest to youngest these include: Sydney Monzodiorite (1.368 ± 0.045 Ma), Warsaw Monzodiorite (1.269 ± 0.039 Ma), Kalgoorlie Monzodiorite (1.261 ± 0.050 Ma), Ningi Quartz Monzonite Porphyry (QMP)(1.229 ± 0.051 Ma), Bonn Quartz Monzonite (1.219 ± 0.040 Ma), and Fubilan QMP (1.213 ± 0.049 Ma). The intrusions are alkaline, high K to shoshonitic rocks with high Sr/Y ratios typical of Cu-fertile arc magmas. Chondrite-normalized REE patterns have minor or no negative Eu anomalies and downward sloping to listric-shaped HREE patterns typical of arc magmas in which high water contents supress plagioclase fractionation in favor of an evolution by hornblende ± garnet ± titanite fractionation. Cu-Au mineralization at Ok Tedi can be divided into four main stages based on crosscutting relationships: (1) skarn-endoskarn and associated vein-style mineralization in the Darai Limestone, Ieru siltstone, and Sydney Monzodiorite; (2) porphyry-style veins and breccias within the Ningi QMP and older intrusions, and at Siltstone Ridge: (3) porphyry-style veins and breccias in the Fubilan QMP and older intrusions: and (4) skarn-style mineralization in the lower part of the Darai Limestone along the Taranaki thrust. High-precision Re-Os dating of molybdenite has enabled a chronology to be established for the first three stages. Molybdenite from a quartz-mushketovite-epidote-carbonate-pyrite-chalcopyrite-molybdenite vein in clinopyroxene- and garnet-altered Sydney Monzodiorite has an age of 1.3206 ± 0.0020 Ma, and this dates the formation of the Gold Coast and Berlin skarns. Molybdenite from a quartz-pyrite-chalcopyrite-molybdenite vein in the sericite-altered Sydney Monzodiorite yields an age of 1.3166 ± 0.0043 Ma, and a quartz-pyrite-chalcopyrite-molybdenite vein with K-feldspar alteration selvages hosted in Ieru siltstone beneath the Gold Coast skarn has an age of 1.3031 ± 0.0015 Ma. Samples of molybdenite from quartz-sulfide veins from Siltstone Ridge have ages of 1.2116 ± 0.0029 and 1.2078 ± 0.0031 Ma. Molybdenite from a quartz-K-feldspar-pyrite-molybdenite vein, which overprints propylitic alteration in the Sydney Monzodiorite, has an age of 1.2120 ± 0.0024 Ma. These samples date porphyry-style mineralization in and around the Ningi QMP and at Siltstone Ridge. A sample of molybdenite from the matrix of hydrothermal intrusive breccia in the Fubilan QMP has an age of 1.2146 ± 0.0020 Ma, similar to the age of the adjacent Siltstone Ridge mineralization, and is interpreted to have been mechanically incorporated into the breccia during its formation. Several samples have been dated from the Fubilan porphyry system, including molybdenite from the matrix of a hydrothermal intrusive breccia (1.1648 ± 0.0020 Ma) and three samples from veins which postdate the breccias: a vuggy quartz-sulfide vein (1.1532 ± 0.0027 Ma), chalcopyrite-pyrite-molybdenite vein (1.1446 ± 0.0028 Ma), and duplicate analyses of a molybdenite-only vein (1.1326 ± 0.0034 and 1.1297 ± 0.0026 Ma) in agreement at 2σ. Molybdenite from a quartz-K-feldspar-biotite-magnetite-pyrite-chalcopyrite-molybdenite vein in endoskarn-altered Sydney Monzodiorite (beneath the Gold Coast skarn) has an age of 1.1459 ± 0.0012 Ma, and a similar vein without magnetite hosted in Warsaw Monzodiorite has an age of 1.1438 ± 0.0042 Ma, both within error of the chalcopyrite-pyrite-molybdenite vein in Fubilan QMP. Intrusive rocks in the Ok Tedi mine were emplaced over a period of approximately 200,000 years, with Cu-Au mineralization formed in discrete episodes of much shorter duration. The Gold Coast skarn and associated porphyry-style veins in Sydney Monzodiorite and Ieru siltstone formed in 14,000 to 21,000 years (n = 3), the Siltstone Ridge porphyry system in 2,000 to 12,000 years (n = 4), and the Fubilan porphyry system in 31,000 to 40,000 years (n = 6). The Taranaki skarn has not been dated in the mine area due to a lack of molybdenite, but geologic relationships indicate it is younger than the Fubilan QMP.

The Re-Os geochronometer constrains the timing of petroleum formation and provides an oil-source isotopic correlation tool for improved geologic knowledge and exploration success. However, the effects of secondary processes that may sometimes complicate interpretations are not well understood. This paper discusses Re-Os systematics in a petroleum system that experienced extensive asphaltene precipitation upon mixing of different oil phases. The Solveig oil field (formerly Luno II), Utsira high, Norwegian North Sea, comprises three structural compartments that capture different stages of the mixing process. In the central compartment, an Re-Os age of circa 40 Ma for whole-rock extracts sampling the residual (asphaltene-rich and biodegraded) oil below the oil–water contact is consistent with burial models for Paleocene–Miocene generation. A 10-m-thick, asphaltene-rich (65 wt. %) tar mat zone precipitated upon mixing of at least two components does not yield meaningful ages. The Re-Os isochrons for the free-flowing crude oil and whole-rock extracts from the oil leg above the tar mat zone indicate circa 10 to 0 Ma ages for the younger oil phase, supporting independent estimates for recent oil influx. Decreasing 187Os/188Os from maltenes to asphaltenes in oil from the southeastern compartment are highly unusual and provide geochemical evidence for recent mixing, consistent with the strong asphaltene-in-oil gradient. Very low and remarkably uniform Re/Os ratios for all petroleum phases, combined with relatively low and uniform 187Os/188Os ratios, strongly support isotopic overprint of the Re-Os system, likely during water–oil interaction. Despite this overprint, Re-Os ages retain information on primary events, whereas initial 187Os/188Os ratios are strongly affected.

The Kivilompolo molybdenite occurrence is located in the northern part of the Peräpoh jabelt, within the lithodemic Ylitornio nappe complex. It is hosted within a deformed porphyritic granite belonging to the pre-orogenic 1.99 Ga Kierovaara suite. The minerali-zation occurs mostly as coarse-grained molybdenite flakes in boudinaged quartz veins, with minor chalcopyrite, pyrite, magnetite, and ilmenite. In this study, we report new geochemical data from the host-rock granite and Re-Os dating results of molybdenite from the mineralization. For the whole-rock geochemistry, the mineralized granite is similar to the Kierovaara suite granites analyzed in previous studies. Also, the ca. 2.0 Ga Re-Os age for molybdenite is equal, within error, to the U-Pb zircon age of the Kierovaara suite granite. In addition, similar molybdenite and uraninite ages have been reported from the Rompas-Rajapalot Au-Co occurrence located 30 km NE of Kivilompolo. We propose that the magmatism at around 2.0 Ga ago initiated the hydrothermal circulation that was responsible for the formation of the molybdenite mineralization at Kivilompolo and the primary uranium mineralization associated with the Rompas-Rajapalot Au-Co occurrence or at least, the magmas provided heating, and in addition potentially saline magmatic fluids and metals from a large, cooling magmatic-hydrothermal system.

The temporal coincidence between the Late Permian mass extinction (LPME) and the emplacement of Siberian Trap basalts suggests a causal link between the two events. Here, we discuss stratigraphic changes of organic and inorganic (including isotopic) geochemical properties of marine sediments across the Permian–Triassic boundary (PTB) in the Hovea-3 core, Western Australia, a key PTB section in the southern Neo-Tethys ocean. These data are compared with published data from the Meishan section, southern China, and from the Opal Creek section in western Canada, providing a view of Tethys and Panthalassa changes at the PTB. Trace metal and N-isotopic data, together with organic matter properties suggest that anoxic conditions were established prior to the LPME, intensified close to the LPME, and continued with photic-zone euxinia into the Early Triassic. For the Hovea-3 section, Re-Os ages confirm Changhsingian (253.5 ± 1.4 Ma) deposition of the dated interval sampled immediately below the stratigraphic level characterized by major lithological and isotopic changes. Evaluation of Re-Os, N, and Hg elemental and isotopic data for Hovea-3 suggests that anoxic conditions in the latest Permian were generally unrelated to direct magmatic contributions. A major increase in the initial Os isotopic ratio of Lower Triassic shales suggest an ~8× increase in the Early Triassic continental runoff, based on moderately conservative assumptions for end-members contributing Os to the Permian–Triassic ocean. Comparison to other PTB sections confirms a global signal of increasing Re/Os ratios in the Late Permian, and major and long-lived changes in the isotopic composition of the post-extinction ocean. A distinct peak in Hg concentrations carrying a volcanic isotopic signature, also identified in other PTB sections, likely represents a major pulse of Siberian Trap volcanism. This Hg peak in the Hovea-3 section, however, is detected above the stratigraphic level containing multiple other widely recognized and more permanent geochemical changes. Therefore, direct volcanic inputs to the Permian–Triassic Ocean likely post-date the LPME in this Western Australian section.

Petroleum systems are inherently complex, comprising multiple components and processes, which variably interact in space and time to form petroleum accumulations. Improved understanding of these complex systems requires a holistic approach of integrating diverse geological, geophysical and organic and inorganic geochemical data. Here, we present an applied and comprehensive Re-Os geochronological and geochemical study on the Brynhild petroleum system from the Norwegian North Sea. Essential components of this system include shale source rocks of the Mandal and Farsund Formations, reservoir sandstones of the Ula Formation and their bitumen extracts, and produced Brynhild crude oil. Rock-Eval, trace metal and Re-Os data reveal the excellent oil-generation potential of the shaley source rocks (high contents of organic matter containing large amounts of type I kerogens) and constrain their depositional conditions (anoxic bottom waters in a high-productivity regime driven by enhanced supply of land-derived nutrients). Seven Re-Os shale ages between ~146 and ~134 Ma are consistent with existing Volgian–Ryazanian age estimates and constrain the initial 187Os/188Os of the shales to ~0.52 in the lowermost Farsund Formation and ~0.75 in the uppermost Mandal Formation. Solvent-extracted reservoir rocks of the Ula Formation contain insoluble organic matter with type III–type IV kerogens likely supplied by erosion of older (a precise 179 Ma Re-Os age with unrealistically low initial 187Os/188Os) coal-bearing sediments or organic-rich shales. The Brynhild crude oil has relatively low 187Os/188Os and a generation age of ~44 Ma based on an asphaltene-only Re-Os isochron. Maltenes from the Brynhild crude oil are isotopically affected by interaction with organic-rich source rocks that represent the seal for the Brynhild oil field. Compared with the crude oil, bitumen from Ula Formation sandstones have contrasting Re-Os properties: high 187Os/188Os ratios and young generation ages between 8 and 0 Ma based on asphaltene-bitumen-maltene Re-Os triplets, asphaltene-only Re-Os regressions, and Re Os model ages for components with extremely high 187Re/188Os. The 44 Ma and 8–0 Ma Re-Os ages agree well with regional burial models that indicate oil generation from ~44 Ma to present day. A genetic link between crude oil and bitumen is indicated by their similar alkane patterns, V and Ni contents, and V/Ni and pristane/phytane ratios. Modeling of 187Os/188Os for individual organic components through time shows that shales of the Mandal Formation developed 187Os/188Os ratios that match those of the crude oil and bitumen at ~44 Ma and ~8 Ma, respectively, and therefore confirm the source for both hydrocarbon phases. We suggest that bitumen formed during in-reservoir mixing of a ~44 Ma old early mature, asphaltene-poor oil (Brynhild crude oil) with an ~8 Ma old asphaltene-rich oil.

Strandings of various types of bitumen along the coast of southern Australia are long known. Among these, brittle, angular lumps termed ‘asphaltites’ are possibly sourced from Cretaceous source rocks linked to an oceanic anoxic event (OAE), but the exact source remains unclear. The unusual chemical composition of these asphaltites and their survival during transport and shoreline stranding suggest that they formed by nearby submarine seepage of asphaltene-rich crude oils. Here, we provide a detailed organic and inorganic geochemical characterization of asphaltites to constrain their origin and age. High-pressure hydropyrolysis (HyPy) of asphaltene fractions from ten asphaltites released similar assemblages of macromolecularly bound compounds, suggesting a common source for all asphaltites. Comprehensive gas chromatography–time-of-flight mass spectrometry (GC×GC-TOFMS) was used to compare these asphaltene-derived compounds with the maltene fractions, while compound specific isotope analysis (CSIA) was used to compare δ13C and δ2H of n-alkanes and isoprenoids. A large offset between the δ2H of the n-alkanes and isoprenoids suggests oil generation and expulsion at low thermal maturity. The mean concentrations of isorenieratane and chlorobactane, carotenoid derivatives indicative of photic zone euxinia (PZE), in the asphaltites were 8.8 ± 0.8 SEM µg g−1 and 1.4 ± 0.1 SEM µg g−1, respectively. A mean Aryl Isoprenoid Ratio of 0.75 (SD = 0.17) is accompanied by Pr/Ph of ∼1.2. These features strongly support persistent PZE conditions at the level expected for an OAE. Trace metal contents of the asphaltites, including low selenium and high vanadium concentrations, also support anoxic conditions. Rhenium-osmium (Re-Os) analyses constrain the age of asphaltite generation to 103 ± 22 Ma, with a relatively low initial 187Os/188Os ratio of 0.44 ± 0.18. Integrating local geologic knowledge with organic and inorganic geochemistry and Re-Os isotopic results, we identify a Cretaceous unit associated with OAE1a (∼125 Ma) as the most likely source of the asphaltites. Alternative scenarios involving source rocks deposited during OAE1b (∼112 Ma) are possible, but require rapid burial of organic-rich sediments to reach required maturation levels in a shorter time.

The calc-alkalic Mitchell Au-Cu-Ag-Mo porphyry deposit, hosted in intrusive rocks of the Stikine volcanic arc terrane of northwestern British Columbia, is the largest undeveloped gold resource in Canada, with 40.72 Moz of contained gold. It lies within the KSM trend, a 12-km-long linear porphyry array in the Sulphurets district. It is genetically related to Early Jurassic Sulphurets stocks: phase 1 diorite to monzodiorite hosts Cu-Au mineralization in potassic assemblages (stage 1), a phase 2 granodiorite plug cores a molybdenum halo (190.3 ± 0.8 Ma, 191.3 ± 0.7 Ma; Re-Os, molybdenite) that is accompanied by phyllic alteration (stage 2), and a poorly mineralized phase 3 diorite plug temporally overlaps with quartz-pyrophyllite alteration at shallow levels (stage 3). Two deformation events (D1 and D2), attributed to orogen-scale mid-Cretaceous transpression, structurally modified Mitchell. D1 deformation, expressed as steep E-striking pressure solution cleavage (S1) and related W-plunging folded veins (F1), is heterogeneously developed as a function of alteration type. D2 is divided into two progressive events: D2a, defined by N-plunging, folded veins (F2a), and D2b, defined by E-vergent thrust faults, including the Mitchell thrust fault, which offsets the updip continuation of Mitchell (the Snowfield deposit, 192.0 ± 1.0 Ma, 191.1 ± 0.8 Ma; Re-Os, molybdenite) ~1,600 m to the east-southeast. Host structures for the KSM trend may have been long-lived, N-striking basement lineaments that provided transcrustal magma and fluid pathways. East-trending intrusions, hydrothermal veins, alteration and metal distribution at Mitchell are attributed to subsidiary E-striking cross faults. These original anisotropies in turn influenced the geometry of Cretaceous faults and flattening domains within the deposit.

Every so often, an analytical advancement or challenging geological occurrence necessitates re-evaluation of well-established geochronological methods. Rhenium-osmium (Re-Os) dating of sulfide minerals, especially molybdenite, by isotope dilution-negative thermal ionization mass spectrometry (ID-NTIMS) yields demonstrably accurate, robust ages. Difficulty in determining an age is caused by either 1) geological complexity including intra-crystalline heterogeneity or 2) inadequate analytical capabilities. Established, systematic methods overcome most of these difficulties, with exceptions. With respect to molybdenite, geological complexity is encountered as macro-scale polyphase overgrowths. Micro-scale complexity is observed as primary Re oscillatory zoning and secondary intra-granular 187Re parent-187Os daughter decoupling. Macro- and micro-scale geologic heterogeneities are overcome by systematic, targeted sampling protocols built upon careful hand sample and microscopic observations linking molybdenite crystallization to the host rock's geologic history.Advances in instrumentation permit more accurate and precise determination of elemental and isotopic compositions at the micro-scale, which ultimately reveals geological complexity and heterogeneity. Yet, newly produced high-resolution data must be carefully scrutinized and interpreted correctly. Two new micro-scale analytical techniques have been proposed: (1) to use NanoSIMS imaging to reveal heterogeneities that could preclude micro-scale geochronology (spot dating) methods, and (2) enable micro-scale geochronology using LA-ICP-MS/MS to distinguish the interfering masses of parent Re and daughter Os isotopes. We turn first to NIST Reference Material 8599, Henderson molybdenite, to compare its Re-Os characteristics and ID-NTIMS results with the newly published Re-Os molybdenite data. We identify the "best possible results" by quantifying the homogeneity of the NIST molybdenite, including model age variability, precision of ID-NTIMS analyses, and statistical treatment. Subsequently, we examine the limitations of the two newly proposed methods. We demonstrate that parent-daughter decoupling cannot be precluded by visual inspection of NanoSIMS isotopic maps. In addition, we prove mathematically that the quantifying the contribution of 187Os to the total measured mass 187 by LA-ICP-MS/MS is far too imprecise to achieve high-precision geochronology. Statistical data treatment and reporting can also result in misguided conclusions and applications.

SHRIMP (Sensitive high resolution ion microprobe) zircon U-Pb dating of the two main igneous rocks types in the Karkonosze Pluton, porphyritic and equigranular monzogranite, yield 206Pb/238U ages between 312.0 &plusmn, 2.9 and 306.9 &plusmn, 3.0 Ma. These coincide, within uncertainty, with the majority of previous dates from the pluton, which indicate development of the main magmatic processes between ca. 315 and 303 Ma. They also coincide with molybdenite and sulfide Re-Os ages from ore deposits developed during magmatic and pneumatolitic-hydrothermal (e.g., Szklarska Poręba Huta and Michałowice) or/and metasomatic and hydrothermal (e.g., Kowary, Czarn&oacute, w and Miedzianka) processes forming Mo-W-Sn-Fe-Cu-As-REE-Y-Nb-Th-U mineralization. The 206Pb/238U zircon age of 300.7 &plusmn, 2.4 Ma from a rhyolite porphyry dyke (with disseminated base metal sulfide mineralization) in the Miedzianka Cu-(U) deposit coincides with the development of regional tectonic processes along the Intra-Sudetic Fault. Moreover, at the end-Carboniferous, transition from a collisional to within-plate tectonic setting in the central part of the European Variscides introduced volcanism in the Intra-Sudetic Basin. Together, these processes produced brecciation of older ore mineralization, as well as metal remobilization and deposition of younger medium- and low-temperature hydrothermal mineralization (mainly Cu-Fe-Zn-Pb-Ag-Au-Bi-Se, and Th-U), which became superimposed on earlier high-temperature Mo-W-Sn- Fe-As-Cu-REE mineralization. A few 206Pb/238U ages &gt, 320 Ma remain to be reconciled, but might be due to the high U and Th contents of the zircon and the strong influence of overprinting pneumatolitic-hydrothermal processes.

The Re-Os geochronometer can be applied to date petroleum, which is the end product of complex natural processes. Improved interpretation of natural Re-Os datasets requires identification of key controlling factors for Re-Os systematics and their isotopic imprint in oils. Here, we focus on the role of water in (re)setting the Re-Os geochronometer in oils, as formation waters and oils often coexist in basinal systems. To quantify Re-Os systematics during water-oil interaction, we performed a series of equilibration experiments between different oils and dilute aqueous solutions doped with Re and Os. The investigated parameters include the oil composition, water to oil ratio, interaction time and the initial Re-Os content in the aqueous solution. In experiments performed across a high concentration gradient, the oils fully homogenized with respect to their Os isotopic composition but had variable 187Re/188Os ratios. This indicates that the Re-Os geochronometer has been reset during water-oil interaction. However, in experiments investigating partial isotopic overprint, the crude oil and its maltene and asphaltene fractions preserved their isochron-derived age. Thus, the Re-Os radiometric clock of a single crude oil sample remains intact, even during partial equilibration of the 187Os/188Os ratio. These experimental findings provide a new foundation for interpretation of Re-Os systematics in natural water-hydrocarbon systems.

The Lar porphyry Cu-Mo deposit is located 20 km northeast of Zahedan in the Sistan Suture Zone (SSZ), in the southeastern part of Iran. Lar is a sub-economic porphyry Cu-Mo deposit with average grades of 0.16% Cu, 0.01% Mo, and 0.66 ppb Au. The Cu-Mo mineralization developed in post-collisional shoshonitic syenitic to monzonitic intrusions in an Oligocene igneous complex known as the Lar Igneous Complex (LIC). The host and country rocks have undergone variable degrees of supergene and hypogene alteration including silicic, potassic, propylitic, phyllic, and argillic alteration. The Cu-Mo mineralization is mainly controlled by NNW striking faults and fractures, and occurs as quartz veins and veinlets, disseminated sulfides, and stockworks. The mineralization can be divided into two types: hypogene and supergene. Hypogene mineralization is characterized by chalcopyrite, pyrite, bornite, molybdenite and magnetite, whereas supergene mineralization is characterized by enargite, covellite, chalcocite, digenite, malachite, azurite, and iron hydroxides. Sulfur isotope values for hypogene sulfides range from 0.28 to −1.76‰ and suggest an igneous source/or mantle-derived origin for sulfur. The δ18O values for quartz in mineralized quartz veins range from 9.6 to 11.5‰. These values would be in equilibrium with waters having calculated δ18OH2O values of 9.3–11.2‰, suggesting magmatic water. Re-Os dating of two molybdenite samples from two different drill holes yields dates of 29.72 ± 0.11 and 31.95 ± 0.11, suggesting that the system was active for at least 2.0 m.y.

Re and Os (rhenium and osmium) are chalcophile-siderophile elements (transition metals) with a unique position in isotope geochemistry. Unlike other commonly used decay schemes for radiometric dating, these metals take residency in resource-related media, for example, sulfide minerals, the organic component in black shales, coals, and bitumens and oils. In short, the reducing environment is their haven whereas under oxidizing conditions, Re and Os become unmoored and the radiometric clock becomes compromised. The clock is not temperature sensitive, and its applicability spans Early Archean to Pleistocene.This Bunsen Medal lecture will explore and review the challenges in bringing Re-Os from the meteorite-mantle community into the crustal environment. At the center of it all is our ability to turn geologic observation into a thoughtful sampling strategy. The possibility to date ore deposits was an obvious application, and molybdenite [Mo(Re)S2], rarely with significant common Os and lacking overgrowths, became an overnight superstar, yielding highly precise, accurate, and reproducible ages. Yet, molybdenite presented our first sampling challenge with recognition of a puzzling parent-daughter (187Re-187Os) decoupling in certain occurrences. A strategic sampling procedure was employed. From there, the diversity of applications spread, as molybdenite is also an accessory mineral in many granitoids, and can be a common trace sulfide in metamorphic rocks conformable with and/or cross-cutting foliation linking timing and deformation. Pyrite and arsenopyrite can also be readily dated.Applications jumped from sulfides to organic matter. Extracting and dating the organic (hydrogeneous) component in black shales gives us Re-Os ages for sedimentary units in the Geologic Time Scale. This led to construction of an Os isotope seawater curve – an ongoing process. Unlike the well-known Sr seawater curve, the short residence time of Os in the oceans creates a high-definition time record with unambiguous high-amplitude swings in 187Os/188Os. Re-Os puts time pins into the biostratigraphic record, and we have even directly dated fossils. Re-Os opened the door for a new generation of paleoclimate studies to evaluate seawater conditions at the time of organic blooms and organic sequestration in bottom mud. Uplift and continental erosion can be balanced with hydrothermal input into oceans based on changes in the Os isotope composition of seawater. The timing and connectivity of opening seaways can be determined, and the timing of glaciation and deglaciation events can be globally correlated. The timing and instigators of mass extinctions are carried in the Re-Os record. A meteorite impact places an enormous scar in the Os isotope record as seawater drops toward mantle values and recovers in a few thousand years. Most recently, Re-Os has transformed our understanding of the events and fluids involved in the construction of whole petroleum systems.Looking to the future, what kinds of data sets will be explored and what are the interdisciplinary skill sets needed to interpret those data? Re-Os will continue to provide us with new ways to dismantle geologic media for new scientific understanding of processes that have shaped our lithosphere, biosphere and hydrosphere and their intersection and exchange.

In the Qarachilar Cu-Mo-Au deposit of the Ahar-Arasbaran metallogenic zone (AAMZ), northwest Iran, mineralization occurs as three quartz-sulfide veins that cut granodiorite-quartz monzodiorite rocks of the Qaradagh batholith (QDB). Ore formation can be divided into three stages, with chalcopyrite, molybdenite, and gold bearing pyrite appearing mainly in the first two stages. The main wall-rock alteration is silicification, and intermediate argillic, carbonate, and propylitic alteration. Fluid inclusion microthermometry indicates trapping of medium- to high-salinity (9.2-55 wt% NaCl equiv.) fluids at Qarachilar. Fluid inclusion trapping conditions are estimated to be 190 degrees C-530 degrees C and 0.1-3 kbar. The variable phase ratios as well as spatial coexisting of liquid and vapor-rich two-phase and halite-bearing multiphase fluid inclusions homogenizing over the same temperatures are consistent with fluid boiling during ore formation. Obtained delta O-18(H2O) values of quartz from ore stage veins are +5.7 parts per thousand to +9.7 parts per thousand, signifying that the ore-fluid system was predominantly magmatic water. The average calculated delta S-34(H2S) values are 1 +/- 1 parts per thousand for pyrite, chalcopyrite and molybdenite, consistent with a magmatic source for sulfur. Combined, the fluid inclusion and stable isotope data indicate that the ore-forming fluids at Qarachilar were magmatic in origin and were subsequently cooled and diluted by meteoric water. Fluid boiling and mixing facilitated hydrothermal alteration and mineralization. Molybdenite Re-Os dating shows that mineralization occurred at 42.35 +/- 0.16 Ma, coincident with formation of porphyry Cu-Mo mineralization at Agarak deposit, and Hanqasar, Aygedzor and Dastakert prospects in the Lesser Caucasus. However, Qarachilar is older than all porphyry Cu-Mo mineralization in the AAMZ and Urumieh-Dokhtar magmatic arc (UDMA), which suggests that collision between Arabia and Eurasia were oblique and thus diachronous. Our data suggest that mineralization at Qarachilar is related to collisional Eocene magmatic-hydrothermal activity related to Neo-Tethys subduction, and shares a number of similarities with the vein-type Cu-Mo-Au mineralization related to Cu-Mo porphyries.

The Central Lapland Greenstone Belt (CLGB) is well endowed with orogenic gold deposits along major shear zones and structural lineaments. In the northern part of the belt, the Kiistala Shear Zone (KiSZ) hosts the Suurikuusikko gold deposit (Kittila Mine), currently the largest gold producer in Europe. The Iso-Kuotko deposit is located 10 km to the north of Suurikuusikko along the same shear zone. Gold mineralization at Iso-Kuotko formed in two major stages: an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at Suurikuusikko and a late, main stage mineralization with free gold in carbonate-quartz veins with abundant pyrrhotite, native bismuth and other sulphide minerals. This latter ore is absent at Suurikuusikko. Based on U-Pb dating, as well as Re-Os and Pb-isotope systematics of rock-forming and hydrothermal minerals, we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late Palaeoproterozoic in the northern part of the CLGB. Results from in situ U-Pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by LA-ICPMS, and model age calculations using Re-Os isotopic data for arsenopyrite and in situ Pb-isotope data for galena from the Iso-Kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the KiSZ. Data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault-dominated N-S shearing associated with early, micro-continent accretion ushering in the Svecofennian orogeny. This includes the formation of refractory gold ores at Suurikuusikko (1916 ± 19 Ma) and Iso-Kuotko (>1868 ± 15 Ma). Subordinate barren veining took place at ∼1830 Ma during transient extension between the accretion and final collision stage. Xenotime in late stage veins with visible gold at Iso-Kuotko yield U-Pb ages between 1761 ± 9 and 1770 ± 7 Ma. This time-interval is concurrent with widespread granitoid emplacement at the close of the Svecofennian orogeny. Disturbance of the Re-Os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes. Pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post-orogenic hydrothermal system. In situ U-Pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations, highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in Paleoproterozoic orogenic systems. Results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the Central Lapland Greenstone Belt.

Limited chronological information for Upper Jurassic rocks hampers precise age assignment of the Jurassic-Cretaceous (J/K) boundary. This study presents Re-Os geochronology, Rock-Eval pyrolysis and geochemical data for Upper Jurassic rocks in the Nordland VII area, offshore northern Norway. Four intervals of organic-rich shale were investigated, two from the Krill and one from the Alge Member of the Hekkingen Formation and one from the underlying Masnykan Formation (drilled cores 6814/04/U-01 and 6814/04/U-02). Rock-Eval pyrolysis data indicate immature organic matter with mixed (Type II/III) oil-gas potential in these units. Among the four intervals, Re-Os isochroneity prevails only for the Hekkingen Formation samples; data from the shale interval in the otherwise sand-rich Masnykan Formation, deposited in a shoreface-to-foreshore marine environment, are not isochronous. Non-isochroneity of the samples from relatively proximal setting is attributable to non-conservative elemental (desorption of Os from sediments to dissolved phase) and isotopic exchange of Os at this depositional site. The Re-Os isochron age for the Alge Member (153.2 ± 7.3 Ma (Model 3); MSWD = 29; n = 9) is consistent with its biostratigraphic Kimmeridgian age (152.1–157.3 Ma). A Re-Os isochron for the lower part of the Krill Member yields an age of 144.5 ± 1.4 Ma (Model 3; MSWD = 3.7; n = 10) with an initial 187Os/188Os ratio of 0.552 ± 0.007. Given the interval's lower Tithonian biostratigraphic age, the Re-Os age suggests that the J/K boundary must be a few Myr younger than its currently assigned age of ~145.0 Ma (2017/02 time scale; www.stratigraphy.org ). A Re-Os model age for shales from the upper part of the Krill Member places an upper age limit for the J/K boundary at 142 (±2) Ma. Hence, the J/K boundary is between 142 Ma and 144.5 Ma. Fe and S concentrations for the Hekkingen Formation show strong correlation and the S/Fe slope (~1.19) mimics the stoichiometric S/Fe ratio for pyrite (~1.15). A Fe-S-TOC ternary diagram for these samples points to an iron-limiting, sulphidic depositional environment. Anoxic to sulphidic depositional conditions for the Hekkingen shales are also evident from relatively higher authigenic enrichment of Mo compared to U. Unlike the Hekkingen Formation, shales from the more sandy Masnykan Formation have lower S/Fe ratios and lower enrichment factors for redox-sensitive elements, indicating relatively oxygenated marine conditions during deposition.

Precise and accurate measurements of the isotopic composition of rhenium (Re) in geologic samples are of paramount importance for the successful application of the Re-Os geochronometer. Two methods for chemical isolation of Re are used in the geochronology community – column chemistry using anion exchange resin and solvent-solvent extraction using a sodium hydroxide-acetone mixture. Despite their ubiquitous application, a systematic comparison of these two methods is missing. Here we compare Re-isotopic data on a variety of samples (sulfides, hydrocarbons, shales, and in-house standard solutions) that were processed by both chemical methods. Measured 185Re/187Re ratios for both methods have similar precision and overlap within the propagated long-term analytical reproducibility of ~1‰ for samples that yield moderate to strong intensities (>50 mV on the weaker Re mass). In contrast, measured 185Re/187Re ratios for most samples that yield less intense Re signals (

Coal horizons in terrestrial sedimentary sections are key to understanding the structural and thermal evolution of sedimentary basins. Precise and accurate age information for coal horizons can define correlations and the temporal evolution of sedimentary successions. While the biostratigraphy for coal horizons yields relative ages, tied to radiometric ages through the continuously refined geological time scale, direct radiometric ages of coal horizons have been derived only from tonsteins, lithified ash beds. The Re-Os geochronometer has been proven to record accurate and precise depositional ages for sedimentary rocks rich in organic matter. However, the reliability of the Re-Os geochronometer has not yet been assessed for coals deposited in strictly terrestrial environments. Here, in order to test the Re-Os geochronometer, we measure the Re, Os concentrations and isotopic composition of terrestrial coals from two distinct environments: the Finnmark Platform, southern Barents Sea and the Central Appalachian Basin (CAB). Samples from the Finnmark platform (Soldogg Formation) also include an adjacent organic-rich shale horizon. The shale and two coal horizons were also analysed for total organic carbon (TOC) and Rock-Eval data. Results show that the Soldogg coals and shale reached the oil generation widow (Tmax = 448 ± 2 °C), with Type III or mixed Type II/III organic matter, supporting the model for deposition in overbank deposits in a fluvial setting. In contrast, the Fire Clay coals in the CAB were deposited in a broad expanse of mires. Average Re (0.5 ± 0.4 ng/g) and Os (23 ± 26 pg/g) concentrations of terrestrial Soldogg and Fire Clay coals are similar to those of terrestrial Maghara coal and a few orders of magnitude lower than the marine-influenced Matewan coal. Elevated Re/Os* ratio (Os* = Common Os; Os corrected for ingrowth of 187Os since deposition of the sample) for the Fire Clay coals suggests highly reducing and/or euxinic conditions prevailing in the water column of the extensive Carboniferous peat-forming mire in which these coals were deposited. In contrast, lower Re/Os* for Soldogg coals highlight less reducing conditions, likely in a short-lived mire in a dynamic braided stream system. Re and Os* concentrations of terrestrial coals are on the order of Re and Os of plant materials and river sediments, suggesting that debris from plant materials and weathered continental crust are significant contributors of Re and Os to terrestrial coals, with some contribution from water column of the coal mire. This study is the first attempt to apply the Re-Os geochronometer on terrestrial coals. In case of the Soldogg coals and shale, the 187Re/188Os vs. 187Os/188Os relationship displays scatter with no discernible linear trend. The scatter is ascribed to heterogeneity in the initial 187Os/188Os ratios (Osi) and lack of post-depositional isotopic equilibration during subsequent diagenesis. For the Fire Clay coals, 187Os/188Os and 187Re/188Os are well correlated; linear regression of the data, however, does not yield a geologically reasonable age. Rather, the linear relationship results from binary mixing between two end-members: The Fire Clay coal and tonstein, suggesting that Re-Os systematics of terrestrial coals depositing very close to tonstein beds can be significantly disturbed. We conclude that the post-depositional equilibration with a large Re-Os reservoir, as with a marine incursion, is necessary to record a meaningful Re-Os radiometric age for the coals.

Among several gold-sulfide deposits and prospects scattered in the Afif terrane of the Arabian Shield, the Bulghah and Al-Maham prospects are investigated to assess the spatial and temporal relationships between gold mineralization and the host lithologies and regional structures. Both prospects are hosted by the sulfide-bearing Hulayfah Group metavolcano-sedimentary successions, and are confined to cross-cutting granitoid intrusions. Tonalite-granodiorite and monzogranite from the two areas have geochemical characteristics of metaluminous to weakly peraluminous calc-alkaline I-type granitoids. Younger alkali feldspar granite in the Bulghah area exhibits geochemical features of A-type granite, likely formed in a post-collisional or transitional setting. ID-TIMS dating of zircons from two granodiorite samples from the Al-Maham prospect yielded 206Pb/238U ages of ∼662 and 651 Ma. A tonalite sample from the Bulghah mine area gave a concordia age of 674.8 ± 0.8 Ma (2σ; MSWD = 0.42), whereas the alkali feldspar granite sample has an age of ∼631 ± 1 Ma. The newly defined ages can be considered as the upper age limit of the auriferous quartz veins, evidently attendant to the Nabitah orogeny (∼680–640 Ma). Gold-bearing quartz veins in the two prospects are identical in terms of ore mineralogy, textures and paragenesis. Gold-bearing quartz veins are associated with intersecting veinlets and stockwork of arsenopyrite, pyrite, and less common pyrrhotite, chalcopyrite, and sphalerite. Recrystallized pyrite and arsenopyrite are ubiquitous in quartz veins, whereas pyrrhotite-chalcopyrite intergrowths in-fills or replacements prevail in the deformed host metavolcanic rocks. Free gold typically occurs as fine inclusions in quartz veins, commonly in deformed pyrite and arsenopyrite crystals. The sulfides of Al-Maham prospect have significantly higher Re-Os concentrations (ppb level), compared with those in the Bulghah prospect, and define an isochron with a Model-1 age of 360 ± 2 Ma and an initial 187Os/188Os ratio of 1.962 ± 0.032. The obtained Re-Os age and the crustal initial Os isotope ratio do not necessarily define the primary age of gold mineralization since ore textures indicate that pyrrhotite was a paragenetically late sulfide phase in both prospects. Alternatively, this age may be interpreted as the time of remobilization and recrystallization of older sulfides in response to Hercynian uplift and deformation (370 - 290 Ma), manifested as intermittently rejuvenated reverse faults elsewhere in the Arabian Shield.

Over five hundred W-Mo skarns have been reported in the Neoproterozoic Serido belt in the northeastern Brazil. The origin of these mineralizations has been attributed to metasomatic reactions occuring after the infiltration of hydrothermal fluids that are mostly derived from the plutonic magmatic activity that ranged between approximately 600 and 525 Ma. Here we date molybdenite using N-TIMS on Re-Os analysis of three major scheelite deposits (Brejui, Bonfim and Bodo) hosted in the skarn horizons of the metasedimentary sequence. Molybdenite is an integral part of the mineralizations that include scheelite in skarns and, in the Bonfim deposit, gold concentrate in late brittle faults. The Re-Os ages are 554 ± 2 Ma (Brejui), 524 ± 2 Ma (Bonfim) and 510 ± 2 Ma (Bodo). The age of the Brejui molybdenite, however, appears to be anomalous based on the local geology of the deposit, which is located next to the contact of a batholith dated ca. 575 Ma. In turn, the Bonfim molybdenite yields similar ages in replicated samples with variable high Re contents. New U-Pb SHRIMP ages of four biotite (leuco)granite plutons vary from 577 ± 5 Ma to 526 ± 8 Ma, which overlap with molybdenite crystallization. These results indicate a close connection between the W-Mo mineralizations and the plutonic activity that intruded the belt after the peak HT/LP metamorphism. The latest pulses of felsic magmatism, which were contemporaneous with the emplacement of Be-Ta-Nb-Li pegmatites, therefore constitute a potential guide in the Serido belt for prospective W-Mo deposits.

The final publication is available at Elsevier via https://doi.org/10.1016/j.gca.2017.06.046 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

The Chah-Firouzeh deposit with about 100 Mt ore reserves @ 0.5% Cu is a porphyry copper deposit located 14 km west of the Meiduk deposit in the northern section of the Kerman Cenozoic Magmatic Assemblage (KCMA), southeastern Iran. The mineralization is associated with a porphyry quartz-monzodiorite to quartz-diorite stock, which intruded into Eocene volcanic rocks consisting of andesite, basalt, and andesitic to dacitic tuff. Hydrothermal alteration types in the area include potassic, phyllic, and propylitic varieties. Silicic alteration locally occurred at the surface, while supergene argillic alteration overprinted the other alterations at shallow levels. Mineralization occurs as quartz-sulfide veinlets and stockworks, as well as disseminations in the porphyry body and volcanic host rocks, in association with potassic and phyllic alteration. Hypogene minerals in the deposit include pyrite, chalcopyrite, magnetite, molybdenite, and bornite. Supergene enrichment is irregularly developed in the Chah-Firouzeh deposit. Zircon U–Pb dating of two representative samples from the Chah-Firouzeh porphyry stock yielded emplacement ages of 16.9 ± 0.4 Ma and 16.5 ± 0.2 Ma, respectively. The Early-Middle Miocene epoch marks the most important period of porphyry Cu mineralization in the KCMA. During this period, many adakitic magmas intruded the Eocene volcano-sedimentary sequences and formed some of the largest porphyry copper deposits in Iran, such as Sarcheshmeh and Meiduk. Molybdenite Re–Os dating on two samples separated from “B and D type” veinlets show that mineralization occurred at 16.60 ± 0.06 Ma and 15.99 ± 0.06 Ma, implying a time span of about 0.6 Ma for mineralization. The δ^(34)S values for molybdenite, chalcopyrite, and pyrite from “A, B, and D type” veinlets vary from −1.4 to +2.5‰ suggesting a magmatic source for sulfur. The calculated temperatures for sulfide pairs are compatible with those obtained from fluid inclusion microthermometry and show isotope equilibrium due to fluid evolution.

In the paper we present the results of Re-Os isotopic studies as well as the mineralogical and geochemical characteristic of bornite veinlets with chalcopyrite ± chalcocite margins and chalcopyrite veinlets that are parallel to sub-parallel to bedding in Kupferschiefer from the underground workings of the Lubin and Polkowice mines in SW Poland. Kupferschiefer samples are of grade from 2.5 to 14.2% Cu and with silver admixtures from 40 to 900 ppm and organic matter contents ca. 6%. The ratios of Co/Ni = 0.1–0.7, V/Cr = 4–17 and Fe2O3/C org = 0.6–1.9 are in the range of values typical for the Kupferschiefer. Besides, copper sulphides, which commonly contain silver admixtures (e.g. chalcocite – 0.44–5.03 wt.%., bornite – 0.33–0.77 wt.%., chalcopyrite 0.09–0.20 wt.%) are associated with minor galena, sphalerite, Ag-minerals and common pyrite framboids. In the isotopically analysed bornite and chalcopyrite samples Re concentrations ranging from 5.7 to 12 ppb, and total Os concentrations ranging from 27 to 52 ppt. Significant common Os is present in all of the analysed sulphides. The isotopic ratios of 187Re/188Os are very high (range: 2269–2942), and of 187Os/188Os from 9.8 to ca. 12.4. Re-Os model ages calculated for these isotopic ratios are in the range from 256 to 268 Ma and for one of the chalcopyrite veinlet was 217 ±2 Ma. Taking into the account the values of the isotopic ratios of 187Re/188Os, it was possible to construct the Re-Os isochrone age for A Model 1 regression based on four different samples. They yields age of 212 ±7 Ma, with an initial 187Os/188Os ratio of 2.13 ±0.31 (MSWD = 1.3). Re-Os isochrone age indicates for bornite and chalcopyrite crystallization event of the Ag-bearing Cu sulphide mineralization within the Kupferschiefer in the Late Triassic (Norian), ca. 212 ±7 Ma.

The final publication is available at Elsevier via https://doi.org/10.1016/j.chemgeo.2017.03.015 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license

Multiple sulfur isotopes provide a powerful tool to study photochemical and biological processes controlling the Archean sulfur cycle and infer related atmospheric and marine environments. However, our understanding of early Earth’s environment remains limited by the availability of well-preserved geological samples, as most Archean sedimentary rocks have experienced some degree of metamorphic alteration. To evaluate sulfur isotopic behavior during post-depositional processes and elucidate the sulfur cycle at 2.7 Ga, we use high-resolution in situ analytical techniques (EPMA and SIMS) to determine elemental compositions and multiple sulfur isotopic compositions of large diagenetic pyrite nodules and fine-grained secondary pyrite disseminated in quartz veins (formed during a lower greenschist metamorphic event) in shales from the 2.7 Ga Joy Lake sequence in the southwest Superior Province. Results show that trace metals and sulfur in the secondary pyrite were derived from both metamorphic fluid and pre-existing diagenetic pyrite. Diagenetic pyrite nodules could have been partially dissolved by metamorphic fluid. But the surviving nodules show elemental and isotopic features different from those of the deduced metamorphic fluid endmember, suggesting the nodules were not geochemically altered by metamorphism, and thus preserve primary isotopic signatures acquired during diagenesis. The sulfur isotopic ratios of pyrite nodules show strong variations, with decreasing δ 34 S values and increasing Δ 33 S values from cores to rims. This negative Δ 33 S–δ 34 S relationship is different from the commonly observed ‘Archean reference line’ defined by most Archean pyrite data, but similar to the ‘felsic volcanic array’. Our observation provides a first possible case from 2.7 Ga, the age of peak crustal growth in the Archean, to support the hypothesis that photochemical pathways could be different under conditions of intense volcanic emission. This study also shows that high-resolution SIMS and EPMA analyses are a robust method for distinguishing primary geochemical signatures from post-depositional alteration, and thus may be used to evaluate the sulfur cycle in Archean sedimentary rocks with low-grade metamorphic overprints.

Re–Os isochron ages for black shales of the Hekkingen Formation in the Barents Sea constrain the onset ( 157.7 ± 1.3 Ma ) and termination ( 138.8 ± 1.0 Ma ), and thereby indicate a long duration (∼19 Myr) of widespread Jurassic–Cretaceous anoxia in the Arctic. Integration of these new Re–Os ages with published radiometric ages, ammonite biostratigraphy and geomagnetic polarity chrons shows shorter late Oxfordian–late Kimmeridgian and longer Berriasian stages relative to estimates in the 2012 and 2016 Geological Time Scales. Late Jurassic anoxia was likely the result of warming climate due to high atmospheric CO2 levels from increased oceanic crust production. Rising temperatures enhanced weathering and nutrient supply, increased productivity, and slowed ocean circulation before a sea-level rise brought anoxic waters onto continental shelves. Assessment of new and published Os- and Sr-isotopic data suggests that prolonged oceanic anoxia required a sustained CO2 source from fast spreading rates and/or longer subduction zones and spreading ridges to balance large burial of carbon in voluminous Upper Jurassic and Lower Cretaceous black shales.

Re-Os geochronology of black shales provides absolute time pins in sedimentary successions and Os isotopic constraints on paleo-environmental conditions. Recognition and reconstruction of pre-faulting chronology within a visually monotonous shale section are critical to interpretation of the paleo-environmental record, and have relevance for fluid migration routes and basin modelling. Re-Os isochrons for five core intervals spanning 14 m of black shale from the Hekkingen Formation on the northern margin of the Hammerfest Basin document within-unit reverse faulting, which is corroborated by detailed petrography, geochemical profiles, and the Os isotope record. The reverse fault is coincident with a beef-like carbonate vein. The five core intervals provide six isochrons with increasingly younger depositional ages of 153.3 + 4.1/− 1.7 Ma to 148.6 + 3.0/− 4.1 Ma, with increasingly higher initial 187 Os/ 188 Os ratios (0.475 + 0.025/− 0.060 to 0.593 + 0.134/− 0.098), consistent with original stratigraphic position. Our age data and inferred sedimentation rates suggest a vertical displacement of several meters across the fault. We suggest such compressional features are the distal (i.e., down-dip) components of gravity gliding structures. The rocks of the Hekkingen Formation at the studied locality record a period of water column euxinia. With the geochemical data in the correct stratigraphic order, we identify two periods of increased sulfide deposition with distinct trace-metal characteristics that reflect differences in the sharpness of the chemocline. These sulfide-producing events create complexity in cross-plots traditionally used to infer oceanographic conditions. Stratigraphically-corrected Os-isotope profiles allow us to correlate this stratigraphic interval of the Hekkingen Formation from the northern margin of the Hammerfest Basin with other sections in the Barents Sea and offshore Norway.

The National Institute of Science and Technology (NIST) research material (RM) 8505 is a Venezuelan crude oil certified for its vanadium concentration. It has recently been proposed as a matrix-matched standard for interlaboratory comparison of Re-Os isotopic analyses while serving as a benchmark for petroleum-based Re-Os method development. Here, the NIST RM 8505 oil is characterized using a multi-solvent asphaltene precipitation, permitting interlaboratory Re-Os data comparison and evaluation of techniques used to derive Re-Os isochron ages. We present a detailed discussion of analytical blank sources, critical evaluation of analytical uncertainties, method improvements and data corrections. Additionally, we provide a comprehensive discussion on the effect of data population size and analytical uncertainty on isochron statistics and the robustness of isochron ages. In addition to NIST RM 8505 (2.43 ± 0.15 ng/g Re, 30.0 ± 0.7 pg/g Os), we provide the first Re-Os data for NIST SRM 1634c (1.73 ± 0.01 ng/g Re, 32.5 ± 0.8 pg/g Os) and EnviroMAT SCP Science (39 ± 1 pg/g Re, 1.01 ± 0.02 pg/g Os), two other commercially available hydrocarbon trace metal standards. The application of several asphaltene (ASPH) precipitations using different n-alkane solvents (pentane, heptane and decane) for the NIST RM 8505 significantly improved the spread of data in the 187Re/188Os-187Os/188Os space. Multi-solvent asphaltene precipitations yield an asphaltene-only Model 1 isochron (75 ± 24 Ma) and the maltene-crude oil-asphaltene triplets yield a more precise Model 1 isochron age of 78.5 ± 2.3 Ma with a 187Os/188Osinitial of 0.877 ± 0.021. Our age is considerably older compared to a previously reported Model 1 age of 62.7 ± 5.7 Ma based on C7 ASPH-crude oil-MALT triplets ( Liu and Selby, 2017 ) and considerably younger than the Model 1 age of 98.4 ± 9.5 Ma based on ASPH separates ( Liu et al., 2019 ). The analytical reasons leading to these age differences are discussed in this paper. The geological context for the NIST 8505 oil is unknown, therefore we use trace metal data (Ni, V, Fe, Mo, etc.) to derive plausible constraints for the origin of this oil. The NIST 8505 oil shows trace metal data similar to published data for oils from the Urdaneta district, the La Paz, Mara and Lagunillas oil fields and source rocks of the La Luna Formation in the Maracaibo Basin, Venezuela. In this geological context, our ~79 Ma age for the NIST 8505 oil implies a Late Cretaceous early hydrocarbon generation event from older Upper Cretaceous source rocks and overlaps with the youngest age of potential source rocks in the Maracaibo Basin. However, the age of large-scale oil generation in the Maracaibo Basin is significantly younger, lasting from the Oligocene to the Pliocene.

Coal deposits are integral to understanding the structural evolution and thermal history of sedimentary basins and correlating contemporeous estuarine and fluvial delatic strata with marine sections. While marine shales may readily lend themselves to Re–Os dating due to the dominance of hydrogenous Re and Os, the lack of a chronometer for near-shore sedimentary environments hampers basinwide correlations in absolute time. Here, we employ the Re–Os geochronometer, along with total organic carbon (TOC) and Rock–Eval data, to determine the timing and conditions of a marine incursion at the top of the Matewan coal bed, Kanawha Formation, Pottsville Group, West Virginia, USA. The observed range for hydrogen index (HI: 267–290 mg hydrocarbon/gram total organic carbon) for these coal samples suggests dominance of aliphatic hydrocarbons with low carbon ( 107.6 ± 16.4 ng / g ) and Os ( 0.52 ± 0.09 ng / g ) concentrations of the marine-influenced Matewan coal are higher by few orders of magnitude than published data for terrestrial coal. A Re–Os isochron for the Matewan coal provides an age of 325 ± 14 Ma (Model 3; MSWD = 12; n = 19 ; 2σ). This is the first Re–Os age derived from coal samples; the age overlaps a new composite Re–Os age of 317 ± 2 Ma for the immediately overlying Betsie Shale Member. External precision for replicate Os analyses carried out for several Matewan coal samples shows a positive correlation with their HI. The HI, which is low in terrestrial organic matter, reflects the degree of marine influence. Thus, samples with the most profound marine influence also have the best analytical reproducibility. Equilibration of Os isotopes with seawater under marine conditions overwhelms variability inherited from terrestrial plant debris, decreasing scatter on the isochron. The 187Re/188Os ratios of the Matewan coal (∼3300–5135) are higher than most of those previously published for Phanerozoic black shale (mostly

The Palaeoproterozoic Yerrida, Bryah and Padbury Group sedimentary rocks are located on the northern margin of the Archaean Yilgarn Craton and are host to epigenetic gold (Peak Hill, Fortnum and Horseshoe), volcanic-hosted massive sulphide (VHMS; Horseshoe Lights, Red Bore and DeGrussa) and epithermal copper deposits (Thaduna). The DeGrussa Cu–Au–Ag VHMS deposit (12.4 Mt @ 4.7% Cu and 1.8 g/t Au) comprises four lenses and is hosted in turbiditic sedimentary rocks and basalts of the DeGrussa host sediments/Karalundi Formation, the lowest mafic volcano-sedimentary unit of the Bryah Group and crosscut by intrusive dolerite of Narracoota Formation age. Immediate wall rocks to the ore lenses are commonly altered to chlorite and talc-carbonate. A number of geochronological techniques were employed to date mineralisation in the DeGrussa deposit. These include rhenium–osmium (Re–Os) of molybdenite, Pb isotopes of galena and pyrite, and U–Pb on zircon. Re–Os geochronology of molybdenite resulted in ages of 2027 ± 7 Ma and 2011 ± 7 Ma and 2013 ± 7 Ma for mineralisation, similar to Pb–Pb model ages for galena of 2060 ± 50 Ma and 2075 ± 50 Ma. U–Pb for magmatic zircons from intrusive dolerite within the mine sequence provided ages of 1991 ± 7 Ma, 1999 ± 7 Ma and 2003 ± 7 Ma with granodiorite rocks providing ages of 2014 ± 7 Ma and 2018 ± 9 Ma. Remobilisation of DeGrussa sulphides occurred at approximately 1980 Ma given Re–Os ages of pyrrhotite (1982 ± 7 Ma and 1984 ± 8 Ma) and Pb–Pb pyrite ages of 1980 ± 30 Ma. Re-examination of the Pb isotopic evolution models for this area and the Capricorn Orogen suggests that the model of Stacey and Kramers (1975) is more appropriate than Cumming and Richards (1975) ; using the former model leads to revised model ages as follows: Horseshoe Lights VHMS 2000 ± 35 Ma; Nathans 1820 ± 30 Ma, Peak Hill (Main pit: 1610 Ma, 1620 Ma, 1705 Ma, and 2070 ± 30 Ma; Fiveways: 1955 Ma; Mt. Pleasant: 1770 Ma), Horseshoe/Cassidy 1940 ± 30 Ma, Mikhaburra 1915 ± 30 Ma, and Labouchere 1800 ± 30 Ma. These new ages coincide with major regional orogenic events – the Glenburgh from 2005 to 1960 Ma, the Capricorn from 1830 to 1780 Ma, the Mangaroon from 1690 to 1620 Ma, and the Edmundian from 920 to 850 Ma. Although orogenic events are compressional, the Yerrida/Bryah Group sedimentary rocks, along with mineralisation at the DeGrussa and Horseshoe Lights deposits, were formed in an extensional basin setting during the Glenburgh Orogeny. These new ages assist in constraining stratigraphic and mineralising events of the Palaeoproterozoic Yerrida, Bryah and Padbury Group with regional orogenic events and may provide guidance for exploration for significant gold and base metal mineralisation, not only in the Bryah, but also throughout the larger Capricorn Orogen.

Determining and correcting for background contributions of Re and Os from chemical reagents is critical for accurate and precise Re-Os dating of materials with parts per billion to parts per trillion Re and Os concentrations. Here we investigate reducing Os content in nitric acid, as it is the main contributor to the Os blank. Pretreating high-purity nitric acid with hydrogen peroxide (H2O2) significantly reduces nitric acid's Os contribution to femtogram levels, greatly reducing Os blank corrections. The improvement in background Os allows analysis of samples with extremely low Os concentrations (into the low ppt level). We present experimental data identifying key factors in reducing Os blank, including nitric acid to hydrogen peroxide volume ratios, wet versus dry glassware, and dark versus lighted reaction environments. These variables affect the reaction time between the two reagents, which in turn correlates inversely with the final Os content. The volume ratio of H2O2/HNO3 is shown to be the fundamental control on reaction time and final Os content, yielding a well-defined exponential relationship; minor variations in reaction time result from wet/dry glassware and light/dark reaction environment. At a H2O2/HNO3 volume ratio of ∼0.24, the total procedural Os blank is reduced from 6.5 pg (no H2O2) to 0.043 pg. The (187)Os/(188)Os of the Os blank ranges from 0.18 to 0.36, consistent with the Os blank compositions obtained by the AIRIE Program and other Re-Os laboratories worldwide, and is uncorrelated with any experimental variables. In contrast to Os, pretreatment with hydrogen peroxide did not improve the Re blank of nitric acid; Re background reduction requires conventional methods such as sub-boiling distillation.

In an effort to contribute to the discussion concerning the age of rocks of the Moldanubian Variegated Group, we have undertaken Re-Os dating of molybdenite of banded carbonatite-like marbles (CLM) from the graphite mine Václav at Bližná (Southern Bohemia), which belong to the metamorphic sequence of this group. The Re-Os model ages for the molybdenites range between 493 and 497 Ma and apparently correspond to the early stages of metamorphism connected with pre-Variscan rift-related tectono-metamorphic events, which affected and recrystallized sedimentary CLM material rich in Mo-Th-Nb-REE. The molybdenite bearing carbonatite like marbles situated in the footwall of Bližná graphite mine have been interpreted as carbonates with a large share of volcano-detritic material derived from contemporaneous primitive alkaline (carbonatite-like) volcanism deposited in a shallow marine lagoonal environment. There is no geological evidence for the participation of fluids mobilized from host rocks in the formation of the CLM. Because the Re-Os chronometer in molybdenite is demonstrably stable through later Variscan facies metamorphism, the molybdenite chronometer has not been affected by subsequent thermal overprints associated with the Variscan orogeny.

Re-Os dating of three samples of hydrothermal molybdenite collected from the Pueblo Viejo Au-Ag-Cu district (5.5 Moz gold, past production, 16.2 Moz proven plus probable gold ore reserves) yields ages of 112.1 ± 0.4, 112.0 ± 0.4, and 111.5 ± 0.4 Ma. These Re-Os dates confirm an Early Cretaceous age for mineralization, coeval with tholeiitic, intraoceanic island arc volcanism and, in particular, with an episode of felsic magmatism and extension across the Early Cretaceous arc (110–118 Ma). Re-Os dating of a sample of hydrothermal molybdenite collected from the Douvray porphyry Cu-Mo deposit (with inferred resources of 1,257 Mlb Cu, 0.276 Moz Au, 6.84 Moz Ag, and 4,367 tons Mo) yields an age of 93.3 ± 0.3 Ma, coeval with calc-alkaline magmatism along the Greater Antilles island arc.

The geochemical record for the Permian–Triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on Earth. We present inorganic and organic geochemical data, and Re–Os isotope systematics in a critical stratigraphic interval of pre- and post-extinction Upper Permian–Lower Triassic sediments from Opal Creek, western Canada (paleolatitude of ∼30°N). We document significant and long-lived changes in Panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to Late Permian seawater, evidenced by notable decreases of Os isotopic ratios upsection. Geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the Late Permian. Euxinic signals are most prominent in the Upper Permian sediments with low organic carbon and high sulfur contents, and gradually wane in the Lower Triassic. The observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and/or water column, providing hydrogen sulfide to form pyrite. This scenario requires nearly complete anaerobic decomposition of predominantly labile marine organic matter (OM) without the necessity for a complete collapse of primary marine productivity. Similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the Late Permian. Both scenarios could have provided similar kill mechanisms for the latest Permian mass extinction. Despite the moderate thermal maturity of the section, OM in all studied samples is dominantly terrestrial and/or continentally derived, recycled and refractory ancient OM. We argue that, as such, the quantity of the OM in the section mainly reflects changes in terrestrial vegetation and/or weathering, and not in marine productivity. At Opal Creek, a pyrite layer and

The Betsie Shale Member is a relatively thick and continuous unit that serves as a marker bed across the central Appalachian basin, in part because it includes an organic-rich shale unit at its base that is observable in drill logs. Deposited during a marine transgression, the Betsie Shale Member has been correlated to units in both Wales and Germany and has been proposed to mark the boundary between the Lower and Middle Pennsylvanian Series within North America. This investigation assigns a new Re–Os date to the base of the Betsie and examines the palynoflora and maceral composition of the underlying Matewan coal bed in the context of that date. The Matewan coal bed contains abundant lycopsid tree spores along its base with assemblage diversity and inertinite content increasing upsection, as sulfur content and ash yield decrease. Taken together, these palynologic and organic petrographic results suggest a submerged paleomire that transitioned to an exposed peat surface. Notably, separating the lower and upper benches of the Matewan is a parting with very high sulfur content (28 wt.%), perhaps representing an early marine pulse prior to the full on transgression responsible for depositing the Betsie. Results from Re–Os geochronology date the base of the Betsie at 323 ± 7.8 Ma, consistent with previously determined age constraints as well as the palynoflora assemblage presented herein. The Betsie Shale Member is also highly enriched in Re (ranging from 319.7 to 1213 ng/g), with high 187 Re/ 188 Os values ranging from 3644 to 5737 likely resultant from varying redox conditions between the pore water and overlying water column during deposition and early condensing of the section.