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Deep hydrothermal Mo, W and base metal mineralization found in the Detroit City portal of the Sweet Home mine in the Alma district (Colorado Mineral Belt) was deposited in response to magmatic activity and the formation of Climax-type Mo deposits during the Oligocene. This study presents extensive geochemical analyses of fluid inclusions inminerals from early greisen-like vein mineralization to better understand the fluid system responsible for ore formation. Quartz and fluorite, which are associated with molybdenite, huebnerite and/or pyrite mineralization, precipitated from low- to medium-salinity (1.5-11.5 wt.% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415°C and probably under a fluctuating pressure regime at depths of at least 3.5 km. The formation of greisen-like and base metal mineralization at the Detroit City portal of the Sweet Home mine is related to fluids of different origin. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases) and mixed with significant amounts of heated meteoric water. Fluid mixing of magmatic fluids with meteoric water is constrained by δ 2H-δ 18O relationships of fluid inclusion water in different minerals (Fig. 1). Whether molybdenum was derived from magmatic fluids remains unclear. Fluid inclusions in huebnerite suggest that W originated from source rocks that are enriched in organic matter rather than from magmatic fluids. The deep hydrothermal mineralization at the Detroit City portal of the Sweet Home mine shows features similar to deep hydrothermal vein mineralization found in Climax-type Mo deposits and their periphery, suggesting that fluid migration and the deposition of ore and gangue minerals in the Sweet Home mine was triggered by a deep-seated magmatic intrusion. The findings of this study are in good agreement with the results of previous fluid inclusion studies of the mineralization of the Sweet Home mine (Lüders et al., 2009) and from Climaxtype Mo porphyry deposits in the Colorado Mineral Belt (Hall et al., 1974).

Deep hydrothermal Mo, W, and base metal mineralization at the Sweet Home mine (Detroit City portal) formed in response to magmatic activity during the Oligocene. Microthermometric data of fluid inclusions trapped in greisen quartz and fluorite suggest that the early-stage mineralization at the Sweet Home mine precipitated from low- to medium-salinity (1.5–11.5 wt% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415 °C and at depths of at least 3.5 km. Stable isotope and noble gas isotope data indicate that greisen formation and base metal mineralization at the Sweet Home mine was related to fluids of different origins. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases), which subsequently mixed with significant amounts of heated meteoric water. Mixing of magmatic fluids with meteoric water is constrained by δ2Hw–δ18Ow relationships of fluid inclusions. The deep hydrothermal mineralization at the Sweet Home mine shows features similar to deep hydrothermal vein mineralization at Climax-type Mo deposits or on their periphery. This suggests that fluid migration and the deposition of ore and gangue minerals in the Sweet Home mine was triggered by a deep-seated magmatic intrusion. The findings of this study are in good agreement with the results of previous fluid inclusion studies of the mineralization of the Sweet Home mine and from Climax-type Mo porphyry deposits in the Colorado Mineral Belt.

Tectonic forces generated during thrust emplacement along active margins may drive complex fluid-flow patterns in fold-thrust belts and foreland basins. Isotope data (d2Hand d18O) of fluid inclusions hosted in calcite vein cements are used to reconstruct regional fluid migration pathways in the Albanide fold-thrust system. The calcite veins used in this study developed in a sequence of naturally fractured Cretaceous-Eocene carbonate rocks as a result of episodic throughput of fluids fromthe early stages of burial onward. The acquired fluid inclusion isotope data demonstrate that fluids circulating in the carbonates were derived from an underlying reservoir that consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin and ascended as soon as fracturing induced a sufficient increase in permeability. Structural and petrographic observations provide time constraints for the various phases of fracture infilling and reveal an increasing dominance of meteoric water in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out. Similar fluid-flow evolutions have previously been recorded in various fold-thrust belt settings elsewhere in the world.

Rationale Since their introduction more than a decade ago, isotope ratio infrared spectroscopy (IRIS) systems have rapidly become the standard for oxygen (δ18O) and hydrogen (δ2H) isotope analysis of water samples. An important disadvantage of IRIS systems is the well-documented sample-to-sample memory effect, which requires each sample to be analyzed multiple times before the desired accuracy is reached, lengthening analysis times and driving up the costs of analyses. Methods We present an adapted set-up and calculation protocol for fully automated analysis of water samples using a Picarro L2140-i cavity ring-down spectroscopy instrument. The adaptation removes memory effects by use of a continuously moisturized nitrogen carrier gas. Water samples of 0.5 μL are measured on top of the water vapor background, after which isotope ratios are calculated by subtraction of the background from the sample peaks. Results With this new technique, single injections of water samples have internal precisions (1σ) below 0.05‰ for δ18O values and 0.1‰ for δ2H values, regardless of the isotope ratio of the previous sample. Precision is worse, however, when the isotope difference between the sample and background water is too large (i.e., exceeding approximately 9‰ for δ18O values and 70‰ for δ2H values). Isotope ratios show negligible drift across the four weeks within which the experiments were performed. The single-injection 1σ precision for 17O excess (Δ′17O) determined with this method is 60 per meg. Conclusions Our experiments demonstrate that by removing sample-to-sample memory effects with a moisturized carrier gas, the time for measurement of δ18O and δ2H values using an IRIS system can be reduced markedly without compromising the analytical precision and accuracy. Thorough replication is needed to achieve sufficiently low uncertainties for Δ′17O., Rapid Communications in Mass Spectrometry, 35 (8), ISSN:1097-0231, ISSN:0951-4198

High CO2 contents were encountered by some exploration wells in the southern part of the upper Permian Zechstein-2-Carbonate (Ca2) fairway of the Lower Saxony Basin in northwestern Germany. The origin of high CO2 accumulations in this part of the Lower Saxony Basin is controversial. In a combined geochemical and structural study, we aimed to decipher the fluid evolution and trace the origin and migration paths of CO2 in the Ca2 reservoirs of the Lower Saxony Basin. The results of comprehensive analyses of fluid inclusions in fracture-filling minerals hosted by Ca2 and sub-Permian strata prove there were multiple stages of fluid and gas migration in the Lower Saxony Basin. Dry gas generated from upper Carboniferous coals charged the Ca2 reservoirs beginning in the Late Triassic and was partly altered in situ by thermochemical sulfate reduction. However, major amounts of CO2 were supplied by rising overpressured hot hydrothermal fluids in response to tectonic movements during Late Cretaceous inversion of the Lower Saxony Basin. Migration of CO2-rich fluids was recorded by fluid inclusions in minerals from fracture-fill mineralization in Devonian, upper Carboniferous, and Ca2 strata. Compelling fluid inclusion evidence indicates that CO2 released during high-temperature metamorphism of deeply buried Devonian platform carbonates ascended with hot hydrothermal fluids through deep-reaching faults into some Ca2 reservoirs. Locally, reservoirs that were charged with CO2 during Late Cretaceous basin inversion were significantly diluted by sweet gas that migrated laterally from the Pompeckj block southward into the Ca2 fairway beginning in the Paleogene.

© 2020 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd Rationale: Oxygen (δ18O) and carbon (δ13C) isotope analysis of foraminifera and other CaCO3 samples has been a key technique for paleoceanographical and paleoclimatological research for more than 60 years. There is ongoing demand for the analysis of ever smaller CaCO3 samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel. Methods: We present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample CO2 to analyse CaCO3 samples in a weight range between 10 and 3 μg. These are considerably lower sample weights than achievable on most currently available standard instrumentation. The technique is automated, so that sample throughput lies at >60 samples per day. The method involves an on-line vial-flushing routine designed to remove machine drift due to blank CO2 build-up in the sample vials. Results: In a series of experiments the effect of blank CO2 build-up is quantified, and outgassing from the chlorobutyl septa identified as the source. An improved flushing routine together with the use of a cryo-focusing step in the analysis is demonstrated to provide the analytical stability and sensitivity to analyse CaCO3 samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ18O and δ13C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples. Conclusions: This study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO3 samples smaller than 5 μg by use of a continuous-flow isotope technique. Of key importance are (1) the application of a cold trap that drastically reduces sample gas loss, and (2) a modified flushing regime that eliminates increasing background CO2 build-up in sample vials during longer automated sample runs., Rapid Communications in Mass Spectrometry, 34 (19), ISSN:1097-0231, ISSN:0951-4198

Rationale Online oxygen (δ18O) and hydrogen (δ2H) isotope analysis of fluid inclusion water entrapped in minerals is widely applied in paleo‐fluid studies. In the state of the art of fluid inclusion isotope research, however, there is a scarcity of reported inter‐technique comparisons to account for possible analytical offsets. Along with improving analytical precisions and sample size limitations, interlaboratory comparisons can lead to a more robust application of fluid inclusion isotope records. Methods Mineral samples—including speleothem, travertine, and vein material—were analyzed on two newly setup systems for fluid inclusion isotope analysis to provide an inter‐platform comparison. One setup uses a crusher unit connected online to a continuous‐flow pyrolysis furnace and an isotope ratio mass spectrometry (IRMS) instrument. In the other setup, a crusher unit is lined up with a cavity ring‐down spectroscopy (CRDS) system, and water samples are analyzed on a continuous standard water background to achieve precisions on water injections better than 0.1‰ for δ18O values and 0.4‰ for δ2H values for amounts down to 0.2 μL. Results Fluid inclusion isotope analyses on the IRMS setup have an average 1σ reproducibility of 0.4‰ and 2.0‰ for δ18O and δ2H values, respectively. The CRDS setup has a better 1σ reproducibility (0.3‰ for δ18O values and 1.1‰ for δ2H values) and also a more rapid sample throughput (, Rapid Communications in Mass Spectrometry, 34 (16), ISSN:1097-0231, ISSN:0951-4198

Oxygen (δWe present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample COIn a series of experiments the effect of blank COThis study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO

Vein-hosted fluid inclusions may represent remnants of subsurface paleo-fluids and therefore provide a valuable record of fracture-controlled fluid flow. Isotope data (δ2H and δ18O) of fluid inclusions are particularly useful for studying the provenance and type of paleo-fluids circulating in the subsurface. Although isotopic analysis of sub-microliter amounts of fluid inclusion water is not straightforward, major steps forward have been made over the past decade through the development of continuous-flow set-ups. These techniques make use of mechanical crushing at a relatively low-temperature (110˚C) and allow for on-line analysis of both δ2H and δ18O ratios of bulk fluid inclusion water. However, continuous-flow techniques have mostly been used in speleothem research, and have not yet found a widespread application on vein systems for hydrogeological reconstructions.We used isotope data of fluid inclusions hosted in calcite vein cements to reconstruct regional fluid migration pathways in the Albanian foreland fold-and-thrust system. Tectonic forces during thrust emplacement typically instigate distinct phases of fracturing accompanied by complex fluid flow patterns. The studied calcite veins developed in a sequence of naturally fractured Cretaceous to Eocene carbonate rocks as a result of several fracturing events from the early stages of burial onward. Fluid inclusion isotope data of the veins reveal that fluids circulating in the carbonates were derived from an underlying reservoir, which consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin. The fluid inclusion isotope data furthermore show that meteoric water becomes increasingly dominant in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out.The diagenetic stability of fluid inclusions is of key interest in the study of their isotope ratios. Recrystallization, secondary fluid infiltration and isotope exchange processes could potentially drive alterations of fluid inclusion isotope signatures after entrapment. In this case, however, isotope signatures of fluid inclusions seem to have remained largely unaltered, despite the Cretaceous to Tertiary age of the vein system. Oxygen isotope exchange processes between the fluid inclusion water and host mineral could have been inhibited at the relatively low temperatures of vein formation (i.e.

Hydrothermal fluid flow along fault zones in the Harz Mountains led to widespread formation of economic vein-type Pb–Zn ore and Ba–F deposits during the Mesozoic. We reconstruct the fluid flow system responsible for the formation of these deposits using isotope ratios (δ2H and δ18O) and anion and cation contents of fluid inclusions in ore and gangue minerals. Building forward on extensive studies in the 1980s and 1990s, our new geochemical data reveal that seawater evaporation brines, which most likely originated from Zechstein evaporites, descended deeply into Paleozoic rocks to leach metals at depth. In Jurassic times, these metal-rich brines episodically recharged along fault zones and mixed with shallow crustal H2S-bearing brines. Primarily in the Upper Harz Mountains, this mixing system led to the formation of economic Pb–Zn–Cu mineralization, which locally shows banded textures with alternations of sulfide minerals and quartz or carbonate (mostly calcite). In the Middle and Lower Harz Mountains, Zechstein-derived brines interacted with K- and F-bearing basement rocks and/or magmatic rocks to deposit fluorite mineralization upon ascent in the Upper Cretaceous. The proposed model of mineralizing fluids originating as (evaporated) seawater has been shown to hold for numerous basin-hosted base-metal sulfide and fluoride deposits elsewhere in Europe.

Stable isotope analysis of biogenic carbonates has remained one of the most important tools in paleoceanography since Emiliani (1955) first described the fluctuation of oxygen isotopes in planktic foraminifers over the Pleistocene. Many laboratories now possess equipment with the capability to analyse foraminifer specimens singularly, at least for larger planktic forms.Being able to run single specimens of planktic foraminifers is significant, because it yields entirely different information than when one would analyse multiple specimens from the same species. Planktic foraminifers have an average life span of about one month, so analysing single specimens, makes paleoceanographic data at seasonal resolution available (e.g. Ganssen et al., 2011; Metcalfe et al 2019, and references therein).Most modern equipment for stable isotope analysis of CaCO3 samples yields good precision down to 10 microgram sample size. The smallest samples are generally measured with a dual inlet technique, because that quantitatively collects the CO2 gas sample in a cold trap before analysis, leading to a more efficient use of the sample gas. Modern dual inlet equipment has a sample size limit somewhere between 10 and 6 microgram CaCO3 sample weight, and in that range usually operates at increased analytical uncertainty when compared to larger samples (e.g. Ganssen et al., 2011). Smaller samples are problematic, because at small amounts of sample gas, the dual inlet system is not able to maintain viscous flow conditions required for precise isotope analysis. To circumvent that barrier, one can use continuous-flow (CF) mass spectrometry because in CF systems the carrier gas ensures proper flow conditions even if there is (virtually) no sample gas produced. Doing so has previously allowed for the isotope analysis of CaCO3 samples in the 10 – 6 microgram range at an external precision (1SD) of ~0.12‰ for both δ18O and δ13C (e.g. Metcalfe et al 2019).To further improve the performance of CF mass spectrometry for small CaCO3 samples, we ran experiments on a Thermo GASBENCH system, equipped with a cold trap (cf. Fiebig et al 2005) and interfaced with a Delta-V mass spectrometer. The experiments consisted of replicate analysis of CaCO3 standards between 10 and 3 micrograms in weight, which is the weight range of many of the smaller specimens of planktic foraminifers.Several hardware modifications were implemented to improve system stability and remove observed effects of contribution of blank CO2 building up in the sample vials. With these modifications, external reproducibility of the set-up for carbonate standard aliquots between 10 and 4 microgram reached a precision of ~0.10 ‰ for both δ18O and δ13C (1SD). This is similar to precisions typically attained for routine analysis of much larger samples in standard operation on the same equipment, and demonstrates that precise stable isotope analysis of smaller single-specimen planktic foraminifers than we could achieve so far is within reach of CF mass spectrometry.References:Emiliani, C. 1955, DOI: 10.1086/626295Fiebig, J., et al. 2005, DOI: 10.1002/rcm.2060Ganssen, G.M., et al., 2011, DOI:10.5194/cp-7-1337-2011Metcalfe, B., et al., 2019, DOI: 10.1029/2018PA003475

Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Jandaíra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post-rift stage of the Potiguar rift (NE Brazil). The Jandaíra Formation in the present onshore domain experienced 1000 km2. The carbonates have a gentle, 0, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub-vertical veins, and sub-vertical as well as sub-horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Jandaíra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Jandaíra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400-500 m. Deformation was accommodated by a dense network of sub-vertical mode I and hybrid fractures associated with sub-vertical stylolites developed in a stress field characterised by a sub-horizontal σ1 and sub-vertical σ2. The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Açu sandstone underlying the Jandaíra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800-900 m entering a depth interval characterised by a sub-vertical σ1. At this stage, sub-horizontal stylolites developed liberating calcite which sealed the sub-vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre-existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures. Basin Research

The Eastern Mediterranean Sea (EMS) is the last remnant of the Tethys Ocean that has been subducted to the north since the Jurassic. Subduction has led to the formation of multiple island arcs in the EMS region where the Aeolian and Aegean arcs are currently active. The EMS is surrounded by continents and receives a large sediment input, part of which is transported down with the subducting slab into the mantle and potentially contributes a major flux to the arc volcanism. An along-arc gradient in the composition of subducting sediment has been evoked to explain the distinct geochemical signature of the easternmost volcanic centre of the Aegean arc, but direct evidence for this proposal is lacking. We present a detailed study of the mineralogical, major-, trace elements and Sr–Nd–Hf–Pb isotope composition of 45 Neogene EMS sediment samples obtained from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill sites and box cores to characterise their geochemical composition, distinguish provenance components and investigate the temporal and spatial variation in provenance to evaluate the potential changing contribution of subducted EMS sediment to Aegean and Aeolian arc volcanism. Based on trace element characteristics of EMS sediments, we can distinguish four provenance components. Nile sediment and Sahara dust are the main components, but contributions from the Tethyan ophiolite belt and arc volcanic rocks in the north are also recognised. Pliocene and Quaternary EMS sediment records a strong geochemical gradient where Nile River sediment entering the EMS in the east is progressively diluted by Sahara Desert dust towards the west. Pre-Messinian samples, however, have a remarkably homogeneous composition with Nile sediment characteristics. We relate this rapid increase in Sahara dust contribution to a late Miocene climate shift leading to decreased Nile runoff and aridification of the Sahara region. EMS sediment has a restricted range in Pb isotopes compared to Aegean volcanic rocks and therefore cannot account for the total variation in Aegean arc lavas. The bulk addition of 0.5–5% of EMS sediment satisfactorily explains most of the variation in volcanic rocks from the western and central centres, but the low 207Pb/204Pb and 206Pb/204Pb seen in the eastern volcanic centre Nisyros requires a distinct mantle source. In the Aeolian arc, a subducted EMS sediment input can only be detected in Stromboli volcanic rocks.

The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation. As a consequence, the Jandaíra Formation accommodated fluid flow only during specific moments in time. We reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements. The Jandaíra Formation, which belongs to the post-rift sequence of the Potiguar Basin in northeast Brazil, was deposited from the Turonian onward until a marine regression exposed it in the Campanian. Due to the subaerial exposure, meteoric waters flushed out marine connate waters, leading to an event of early diagenesis and full cementation of the Jandaíra Formation. Fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing. Fracturing in the Late Cretaceous induced a drastic increase in permeability, giving rise to extensive fluid circulation. Host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network, causing it to regain an impermeable and sealing character. In the research area, fluid flow occurred during early burial of the Jandaíra Formation at estimated depths of 400–900 m. This study documents the first application of fluid inclusion isotope analysis on vein precipitates, which allowed full isotopic characterization of the paleo-fluids responsible for calcite vein cementation. The fluid inclusion isotope data indicate that upwelling of groundwater from the underlying Açu sandstones provided the fluids to the fracture network. In Miocene times, renewed tectonic compression of a lower intensity created a secondary fracture network in the Jandaíra Formation. The density of this fracture network, however, was too low to induce a new episode of fluid circulation. As a result, this tectonic event is associated with the development of barren extensional fractures.

A simple initialisation of distillation models is presented. It is robust and shows to have a much wider convergence radius for this notorious problem than the traditional approaches. The procedure uses a model that, compared to the traditional models, adds the gas dynamics. The current implementation has also been used to implement a new portable thermodynamic module, which adds significant flexibility and accuracy to the use of thermodynamic information. The new approach is evaluated against the traditional method on an industrial C4 splitter taken from a gas plant.