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Carbon capture and storage (CCS) is the only currently available technology that can directly reduce anthropogenic CO 2 emissions arising from fossil fuel combustion. Monitoring and verification of CO 2 stored in geological reservoirs will be a regulatory requirement and so the development of reliable monitoring techniques is essential. The isotopic and trace gas composition − the inherent fingerprint − of captured CO 2 streams is a potentially powerful, low cost geochemical technique for tracking the fate of injected gas in CCS projects; carbon and oxygen isotopes, in particular, have been used as geochemical tracers in a number of pilot CO 2 storage sites, and noble gases are known to be powerful tracers of natural CO 2 migration. However, the inherent tracer fingerprint in captured CO 2 streams has yet to be robustly investigated and documented and key questions remain, including how consistent is the fingerprint, what controls it, and will it be retained en route to and within the storage reservoir? Here we present the first systematic measurements of the carbon and oxygen isotopes and the trace noble gas composition of anthropogenic CO 2 captured from combustion power stations and fertiliser plants. The analysed CO 2 is derived from coal, biomass and natural gas feedstocks, using amine capture, oxyfuel and gasification processes, from six different CO 2 capture plants spanning four different countries. We find that δ 13 C values are primarily controlled by the δ 13 C of the feedstock while δ 18 O values are predominantly similar to atmospheric O 2 . Noble gases are of low concentration and exhibit relative element abundances different to expected reservoir baselines and air, with isotopic compositions that are similar to air or fractionated air. The use of inherent tracers for monitoring and verification was provisionally assessed by analysing CO 2 samples produced from two field storage sites after CO 2 injection. These experiments at Otway, Australia, and Aquistore, Canada, highlight the need for reliable baseline data. Noble gas data indicates noble gas stripping of the formation water and entrainment of Kr and Xe from an earlier injection experiment at Otway, and inheritance of a distinctive crustal radiogenic noble gas fingerprint at Aquistore. This fingerprint can be used to identify unplanned migration of the CO 2 to the shallow subsurface or surface. [ABSTRACT FROM AUTHOR]

Abstract: Mineral carbonation is a process whereby CO2 reacts with ultramafic rocks to form carbonate minerals such as calcite (CaCO3) and magnesite (MgCO3). This process can be induced artificially at high pressures and temperatures and therefore has potential to be adapted as a carbon capture and storage (CCS) technology. Large-scale surface and subsurface carbonate deposits of probable Quaternary age are associated with major faulting across the Oman-UAE ophiolite. Here, fractured rock forms a natural fluid pathway and increases the surface area available for carbonation. Modern springs along these faults typically discharge hyperalkaline (pH ∼11), Ca(OH)2-rich waters that precipitate carbonates on reaction with atmospheric CO2. Carbonates formed by absorption of atmospheric CO2 into Ca(OH)2 waters tend to display low δ13C (<<−20% PDB) as result of kinetic fractionation. However, ancient travertines show a large range in δ13C of −10.5 to −21.8% PDB, produced by the mixing of the low δ13C end member with other carbon sources such as limestones or organic-derived soil bicarbonate. Strontium isotope ratios of samples indicate fluids that formed calcite and magnesite veins may have interacted with limestones around and beneath the ophiolite. These are a carbon source which can easily be reworked and incorporated into carbonate deposits elsewhere. Carbonate deposits may not be created solely from atmospheric CO2, but instead represent a mixture of carbon sources. Failure to account for multiple carbon sources or recycled carbon may result in poor estimates of the rates and volumes of carbon that natural systems sequester. Further investigation is therefore necessary to determine how much of the carbon held within carbonate deposits has been incorporated from reworked sources. [Copyright &y& Elsevier]

Abstract: The genesis of hydrothermal ore deposits is of crucial economic importance. This study investigates the extent, causes and consequences of zinc and iron isotope fractionation in a large hydrothermal system at the world-class Navan Zn–Pb orebody, Ireland. Large variations in Zn, Fe and S isotope compositions have been measured in microdrilled sphalerite (ZnS) at the millimetre scale. δ66Zn and δ56Fe display a well-defined positive correlation and both also correlate with δ34S. These relationships represent the combined effects of kinetic Zn and Fe isotope fractionation during sphalerite precipitation, and S isotope variation through mixing of hot, metal-rich hydrothermal fluids and cool, bacteriogenic sulfide-bearing brines. Combined with S isotope data, δ56Fe and δ66Zn data on mine concentrates confirm that hydrothermal sulfide is a minor component of the overall deposit signature. Our data suggest that incoming pulses of metal-rich hydrothermal fluid triggered sulfide mineralisation, and that rapid precipitation of sphalerite from hydrothermal fluids will lead to strong kinetic fractionation of Zn and Fe isotopes at very short time and length scales, thereby limiting the use of Fe and Zn isotopes as exploration tools within deposits, but revealing the possibility of detecting new deposits from isotopically heavy Zn–Fe geochemical halos. [Copyright &y& Elsevier]

Abstract: Miocene igneous rocks (diorites, andesites, dacites, rhyolites and microgranites) of Chetaibi and Cap de Fer massif, NE Algeria, are high-K calc-alkaline to shoshonitic rocks. Fresh diorites have δ34S and δ18O values ranging between −2.5‰ and +5.9‰, +6.5‰ and +6.7‰ respectively, indicating a mantle origin. The relatively low δ34S values (−5.4‰ to −12.2‰) and high δ18O (+8.3‰ to +9.0‰) of altered diorites indicate the input of a crustal component to the initial magma. The microgranites’ I-type signature is indicated by the geochemical data and the δ34S and δ18O values of −1.2‰ and −3.6‰, and +7.8‰ to +10.4‰ respectively. The andesites show a large variation of δ34S, between −33.2‰ and +25.7‰. Massive andesites with δ34S between +6.8‰ and +7.6‰ preserve a 34S-enriched mantle signature. The δ34S of the lava flows between +25.7‰ and +25.8‰ are attributed to open system magma degassing, whereas the low δ34S of two andesitic dyke samples (−13.7‰ and −33.2‰) strongly suggest a crustal sulphur input. High δ18O (+9.2‰ to +15.7‰) of andesites indicate post-magmatic alteration (mainly silicification); the flyschs with δ18O between of +13.3‰ and +21.7‰ are most likely the contaminant. Quartz veins within the andesites gave a δ18O value of +23.0‰ while silica-filling vesicles yielded a value of +13.8‰. Initial Sr-isotope data are rather high for all the rocks (diorites: 0.707–0.708, andesites: 0.707–0.710, and microgranites and rhyolites: 0.717–0.719), and because geochemical and stable isotope data do not indicate a substantial amount of crustal assimilation, an extensive enrichment of the mantle source by subducted sediments is called for. A metasomatized-mantle source, characterized by high radiogenic Sr and relatively high δ18O, has also been indicated for the genesis of similar Tertiary igneous rocks in the Western Mediterranean basin, e.g. the Volcanic Province of southeasten Spain [Benito, R., Lopez-Ruiz, J., Cebria, J.M., Hertogen, J., Doblas M., Oyarzun, R., Demaiffe, D., 1999. Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain. Lithos 46, 773–802] and some plutons of northeastern Algeria [Ouabadi, A., 1994. Pétrologie, géochimie et origine des granitoïdes peralumineux à cordiérite (Cap Bougaroun, Béni-Touffout et Filfila), Algérie nord-orientale. Thèse de Doctorat, Université de Rennes I, France, 257p; Fourcade, S., Capdevila, R., Ouabadi, A., Martineau, F., 2001. The origin and geodynamic significance of the Alpine cordierite-bearing granitoids of northern Algeria. A combined petrological, mineralogical, geochemical and isotopic (O, H, Sr, Nd) study. Lithos 57, 187–216]. [Copyright &y& Elsevier]

The petrogenesis of igneous, metamorphic and mineralized rocks in the Edough massif, NE Algeria, indicates an interplay between crustal and magmatic sources, and magmatic and surface fluids, as determined by sulphur and oxygen isotopic analyses. The Tertiary igneous rocks (microgranites and rhyolites) show a tendency towards I-type granitoids with δ34S values of +5.4±2.2‰ (1σ) and δ18O between +5.6‰ and +6.9‰, with the most hydrothermally altered rocks having the lowest δ18O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34S of sulphide-sulphur in both the microgranites and associated skarn mineralization. However, in the Beleleita W–Sn–(Au) deposit, magmatic fluids dominated the mineralization, reflected by δ34S values of +1.7‰ and +1.8‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with δ18O ranging from +4.9‰ to +8.6‰. Locally altered amphibolite has the lowest δ18O values suggestive of meteoric water interaction, whereas the highest δ18O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their δ34S of −18‰ to +2.1‰, with the most contaminated rocks having the lowest δ34S. Host Palaeozoic mica schists with δ18O of +12.7‰ and δ34S of −13.2‰ and associated marbles (δ34S −9.9‰ to −17.4‰) are thought to be the most likely contaminants. At the Ain Barbar Fe–Cu–Pb–Zn deposit, δ34S values range between −9.6‰ and −10.8‰, indicating that the sulphide-sulphur and base-metals were likely leached from the host Cretaceous flysch and/or the underlying mica schists, with local Tertiary magmatic rocks providing the heat for local convection cells. At Boumaiza Fe-deposit, δ34S values of the sulphide-sulphur extend from −1.2‰ to −8.1‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists. [Copyright &y& Elsevier]

The present study shows the existence of textural, mineralogical, microthermometric and isotopic data that evidences processes such as thermochemical sulfate reduction (TSR) that are not typical features of volcanic-hosted epithermal deposits formed at shallow submarine and/or subaerial environments. Geological evidence and mineralogical, fluid inclusion temperature and geochemistry data suggest that the Mazarrón Zn–Pb–Cu–Ag–Fe deposit is a volcanic-hosted epithermal deposit. It is hosted by dacites with different alteration halos: K–Ar dating of illite from the argillic alteration gives an age of 9.7 ± 1.2 Ma, which suggests that mineralization took place very close to the volcanism. The fluid inclusion study in the ore veins shows epithermal temperatures (between 190 and 260 °C), but moderate salinities, between 12 and 18 wt.% NaCl eq., compatible with mixing between surface waters and polygenic deep hydrothermal fluids. Evolution of the hydrothermal activity shows the existence of three stage of mineralization: in the first and last stages, with Fe-sulfides as main phases, mineralization was mainly formed by interaction between basinal fluids that leached Triassic sulfates (+ surface waters), and C-bearing reduced deep waters. During interaction of both fluids, the sulfur was subjected to extreme and geologically unusual fractionation under TSR conditions, with ranging from − 2.9 to + 28.4‰ δ 34 S, reaching exceptional values up to + 53‰ δ 34 S. The intermediate stage is mainly formed by sphalerite–galena–chalcopyrite–fahlore bearing sulfides; this event is compatible with the influx of a magmatic fluid discharge. Finally, this study suggests that Mazarrón could be classified as an intermediate sulfidation deposit. [ABSTRACT FROM AUTHOR]

Abstract: The Konkola deposit is a high grade stratiform Cu–Co ore deposit in the Central African Copperbelt in Zambia. Economic mineralisation is confined to the Ore Shale formation, part of the Neoproterozoic metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper–cobalt ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, often associated with dolomitic bands or clustered in cemented lenses and in layer-parallel and irregular veins. The hypogene sulphide mineralogy consists predominantly of chalcopyrite, bornite and chalcocite. Based upon relationships with metamorphic biotite, vein sulphides and most of the sulphides in cemented lenses were precipitated during or after biotite zone greenschist facies metamorphism. New δ34S values of sulphides from the Konkola deposit are presented. The sulphur isotope values range from −8.7‰ to +1.4‰ V-CDT for chalcopyrite from all mineralising phases and from −4.4‰ to +2.0‰ V-CDT for secondary chalcocite. Similarities in δ34S for sulphides from different vein generations, earlier sulphides and secondary chalcocite can be explained by (re)mobilisation of S from earlier formed sulphide phases, an interpretation strongly supported by the petrographic evidence. Deep supergene enrichment and leaching occurs up to a km in depth, predominantly in the form of secondary chalcocite, goethite and malachite and is often associated with zones of high permeability. Detailed distribution maps of total copper and total cobalt contents of the Ore Shale formation show a close relationship between structural features and higher copper and lower cobalt contents, relative to other areas of the mine. Structural features include the Kirilabombwe anticline and fault zones along the axial plane and two fault zones in the southern limb of the anticline. Cobalt and copper behave differently in relation to these structural features. These structures are interpreted to have played a significant role in (re)mobilisation and concentration of the metals, in agreement with observations made elsewhere in the Zambian Copperbelt. [Copyright &y& Elsevier]

Magmatic sulfide deposits typically occur in ultramafic-mafic systems, however, mineralisation can occur in more intermediate and alkaline magmas. Sron Garbh is an appinite-diorite intrusion emplaced into Dalradian metasediments in the Tyndrum area of Scotland that hosts magmatic Cu-Ni-PGE-Au sulfide mineralisation in the appinitic portion. It is thus an example of magmatic sulfide mineralisation hosted by alkaline rocks, and is the most significantly mineralised appinitic intrusion known in the British Isles. The intrusion is irregularly shaped, with an appinite rim, comprising amphibole cumulates classed as vogesites. The central portion of the intrusion is comprised of unmineralised, but pyrite-bearing, diorites. Both appinites and diorites have similar trace element geochemistry that suggests the diorite is a more fractionated differentiate of the appinite from a common source that can be classed with the high Ba-Sr intrusions of the Scottish Caledonides. Mineralisation is present as a disseminated, primary chalcopyrite-pyrite-PGM assemblage and a blebby, pyrite-chalcopyrite assemblage with significant Co-As-rich pyrite. Both assemblages contain minor millerite and Ni-Co-As-sulfides. The mineralisation is Cu-, PPGE-, and Au-rich and IPGE-poor and the platinum group mineral assemblage is overwhelmingly dominated by Pd minerals; however, the bulk rock Pt/Pd ratio is around 0.8. Laser ablation analysis of the sulfides reveals that pyrite and the Ni-Co-sulfides are the primary host for Pt, which is present in solid solution in concentrations of up to 22 ppm in pyrite. Good correlations between all base and precious metals indicate very little hydrothermal remobilisation of metals despite some evidence of secondary pyrite and PGM. Sulfur isotope data indicate some crustal S in the magmatic sulfide assemblages. The source of this is unlikely to have been the local quartzites, but S-rich Dalradian sediments present at depth. The generation of magmatic Cu-Ni-PGE-Au mineralisation at Sron Garbh can be attributed to post-collisional slab drop off that allowed hydrous, low-degree partial melting to take place that produced a Cu-PPGE-Au-enriched melt, which ascended through the crust, assimilating crustal S from the Dalradian sediments. The presence of a number of PGE-enriched sulfide occurrences in appinitic intrusions across the Scottish Caledonides indicates that the region contains certain features that make it more prospective than other alkaline provinces worldwide, which may be linked the post-Caledonian slab drop off event. We propose that the incongruent melting of pre-existing magmatic sulfides or ‘refertilised’ mantle in low-degree partial melts can produce characteristically fractionated, Cu-PPGE-Au-semi metal bearing, hydrous, alkali melts, which, if they undergo sulfide saturation, have the potential to produce alkaline-hosted magmatic sulfide deposits. [ABSTRACT FROM AUTHOR]

Abstract: Some recent studies have suggested that the hydrogen isotopic composition (δD) of hydrothermal fluids, released in vacuo by thermal decrepitation of quartz, are not always accurately revealed. We report the results of a step-heating δD value study of vein quartz, hosted by Lower Palaeozoic rocks in SW England, which was analyzed by micro-FT-IR for hydrogen speciation, before and after fluid extraction at temperatures between 750 and 1500°C. The δD values of individual aliquots of released water vary between −3‰ and −208‰, with the lowest values generally corresponding to the highest temperature fractions and samples of relatively low yield. The data show significant departures from geologically reasonable δD. Micro-FT-IR analyses show that a variety of OH species are present within the vein quartz, with significant intra and inter sample variation. Typically a broad absorption due to molecular water, in the region 3400cm−1 is observed, along with bands attributed to Li–OH and Al–OH. On heating, the broad absorption due to molecular water is reduced, accompanied by a measurable loss of Li–OH species. The latter becomes more pronounced in the higher temperature fractions (>750°C). These data support earlier studies which indicated that contributions from the contrasting OH reservoirs in quartz can significantly influence the reported δD values. These new data also suggest that the incorporation of OH released from Li–OH sites in the quartz may be the most important factor in the generation of the anomalous values for these samples. [Copyright &y& Elsevier]