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Strontium isotopes of marine archives provide a significant means for tracing physical and chemical processes operating over geologic time. Modern articulated brachiopods and halite samples were collected from all depths of the world's main water bodies. Material from the Arctic, North and South Atlantic, North and South Pacific, Indian and Southern oceans, as well as Caribbean and Mediterranean seas provide baseline parameters for diagenetic screening and reconstruction of seawater curves. The Sr isotopic ratio of modern brachiopods is unobscured by latitude, depth, and biologic factors (Order, valves, and shell segment). However, there is a small but significant impact of external sources reflected by salinity and temperature on the Sr isotope ratio of modern brachiopods. We found a significant difference in [.sup.87]Sr/[.sup.86]Sr of brachiopods from polar and temperate-tropical habitats (p= 0.001), which should be considered when working with deep-time archives. The average [.sup.87]Sr/[.sup.86]Sr value of all our modern shells (0.709160 [+ or -] 0.000019; N= 95) and halite (0.709153) is similar to values measured for modern seawater (0.710167 [+ or -] 0.000009; p = 0.118). The radiogenic Sr content of present-day seawater does not vary significantly, and modern biogenic-calcite [.sup.87]Sr/[.sup.86]Sr ranges from 0.709126 to 0.709233 with a fluctuation of about [+ or -]0.000054. With the most rigorous diagenetic evaluations and stratigraphic assignment of deep-time samples, and applying the Sr isotope fluctuation recorded by modern biogenic calcite to ancient carbonates and a 1 Myr interval, reconstructions resulted in a seawater-[.sup.87]Sr curve with greater details during the Phanerozoic and Neoproterozoic. Les isotopes du strontium d'archives marines sont un important outil pour retracer les processus physiques et chimiques s'etant operes au fil du temps geologique. Des brachiopodes articules et echantillons de halite modernes ont ete preleves de toutes les profondeurs des principaux plans d'eau du monde. Du materiau des oceans Arctique, Atlantique Nord et Sud, Pacifique Nord et Sud, Indien et Austral, ainsi que des mers Mediterranee et des Caraibes, fournissent des parametres de reference pour l'evaluation de la diagenese et la reconstitution de courbes pour l'eau de mer. Le rapport des isotopes du Sr de brachiopodes modernes n'est pas masque par la latitude, la profondeur ou des facteurs biologiques (l'ordre, les valves ou le segment de coquille). Il y a toutefois une incidence faible, bien que significative, de sources externes representees par la salinite et la temperature sur le rapport d'isotopes du Sr de brachiopodes modernes. Nous avons constate une difference significative des [.sup.87]Sr/[.sup.86]Sr de brachiopodes entre les habitats polaires et temperes-tropicaux (p = 0,001), qui devrait etre prise en consideration dans l'etude d'archives tres anciennes. Les valeurs de [.sup.87]Sr/[.sup.86]Sr pour tous nos echantillons de coquilles (0,709160 [+ or -] 0,000019; N = 95) et de halite (0,709153) modernes sont semblables aux valeurs mesurees pour l'eau de mer moderne (0,710167 [+ or -] 0,000009; p = 0,118). La concentration de Sr radiogenique dans l'eau de mer actuelle ne varie pas de maniere significative et le [.sup.87]Sr/[.sup.86]Sr de la calcite biogenique moderne va de 0,709126 a 0,709233, avec une fluctuation d'environ [+ or -]0,000054. Sur la base d'evaluations diagenetiques et d'affections stratigraphiques les plus rigoureuses d'echantillons tres anciens, et en appliquant la fluctuation des isotopes du Sr enregistree dans la calcite biogenique moderne aux carbonates anciens et un intervalle d'un million d'annees, les reconstitutions donnent une courbe de [.sup.87]Sr de l'eau de mer plus detaillee pour le Phanerozoique et le Neoproterozoique. [Traduit par la Redaction], Introduction The interplay between Earth's continental and oceanic activities and climate processes controls the strontium (Sr) isotopic composition of modern seawater, whereas their evolution through time changed the marine Sr [...]

The Omatapati copper and silver prospect within the Kaoko Belt is located in the Opuwo district, Kunene region, Namibia. The prospect is hosted by dolomite and interbedded argillites of the Neoproterozoic Devede Formation, the Ombombo Subgroup. An ore body is exposed in shallow artisanal mining pits and drill‐cores of the prospect have grades of 0.4 to 5.2 wt% Cu, and 23 to 312 g/t Ag. The prospect was formed by both hypogene and supergene mineralization processes. The hypogene mineralization occurred in three stages. Stage 1 is represented by calcite veins containing chalcopyrite, bornite, sphalerite and galena. Stage 2 consists of quartz and calcite veins with chalcopyrite and bornite. Stage 3 consists of quartz‐calcite‐barite veins with chalcopyrite. The veins of stages 1 and 2 are subparallel or discordant to the foliation of argillites, and those of Stage 3 are NE‐striking and steeply dipping in the brecciated dolostone and argillite. The mineralization stages 1, 2, and 3 are overprinted by supergene chalcocite, digenite, annite, covellite, malachite, delafossite, hematite, and goethite. The supergene process forms a semi‐massive chalcocite‐covellite zone, which extends from the surface to ~50 m depth. The veins show average concentrations of 2.1 wt% Cu, 80 ppm Ag, and 532 ppm Pb for the stage 1, 3.1 wt% Cu, 118 ppm Ag, and 66 ppm Pb for the stage 2, and 18.6 wt% Cu, 675 ppm Ag, and 565 ppm Pb for the Stage 3 with supergene overprinting. Silver occurs as impurity in supergene chalcocite (6303 ppm Ag), digenite (4425 ppm Ag), and covellite (3060 ppm Ag). Fluid inclusions in quartz and calcite revealed that the hypogene mineralization occurred under a pressure >7–8 MPa. Temperatures of ore formation of the stages 1, 2, and 3 were >145–155 °C, >290–300 °C, and >190–230 °C, respectively. Large variation of salinities in each fluid inclusion assemblage suggests fluid mixing and dilution processes. Fluid inclusion gas compositions in the Stage 3 have weighted means of 98.98 mol% H2O, 0.75 mol% N2, 0.52 mol% CO2, 0.02 mol% CH4, 0.0021 mol% Ar, 0.0009 mol% H2S, and 0.00006 mol% He and indicate a signature of magmatic fluids mixed with meteoric waters or seawater. δ34SCDT values of sulfides in the stages 1, 2, and 3 in the prospect have three data clusters, (1) near 0 ‰ of chalcopyrite in the stages 1 and 2, (2) near −11 ‰ of bornite in the stage 2, and (3) +5 to +11 ‰ of the supergene chalcocite and covellite. Modes of occurrence of ores, fluid inclusions and sulfur isotope data show that the prospect is likely the same type as sediment‐hosted copper‐silver deposits with veining found in the Central African Copperbelt. [ABSTRACT FROM AUTHOR]

Abstract: The Lower Head Formation in the Parson's Pond area (western Newfoundland, Canada) comprises siltstones with very fine grained to fine-grained sandstones. Petrography confirms that these sandstones are matrix rich, [...]

Stable isotope compositions of ancient halite fluid inclusions have been recognized to be valuable tools for reconstructing past environments. Nevertheless, in order to better understand the genesis of halite deposits, it could be of great interest to combine both δ2H and δ18O measurements of the water trapped as inclusions in the defects of the mineral lattice. We developed a method combining off‐axis integrated cavity output spectroscopy (OA‐ICOS) connected on line with a modified elemental analyzer (EA‐OA‐ICOS) to perform those measurements. The first step was to test the method with synthetic halite crystals precipitated in the laboratory from isotopically calibrated waters. Water isotopic signatures have been measured with conventional techniques, equilibration for δ18O and chromium reduction for δ2H. Then, we modified and optimized a conventional EA to connect it online with an OA‐ICOS instrument for H2O measurements. The technique is first evaluated for calibrated free water samples. The technique is also evaluated for salt matrix effect, accuracy, and linearity for both isotopic signatures. Then, the technique is used to measure simultaneously δ2H and δ18O values of halite water inclusions precipitated from the evaporation experiments. Data generated with this new technique appeared to be comparable with those inferred from prior off‐line technique studies. The advantages offered by the OA‐ICOS technique are the simultaneous acquisition of both isotopic ratios and the substantial reduction of data acquisition time and sample aliquot size. Natural halite samples have been analyzed with this method. Natural halite samples as old as Precambrian have also been analyzed with this method. [ABSTRACT FROM AUTHOR]

Several high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization. [ABSTRACT FROM AUTHOR]

Speleothems frequently host "fossil" fluids that were trapped in small inclusions during growth. Such fluids may provide valuable clues to past microbial, geochemical, and climatic processes during their formation. However, one difficulty is to understand which gases represent background atmosphere and fluids within a given cave system at a particular time, and which may be the product of post-trapping residual microbial activity or abiotic chemical reactions? Do we have any hope of sorting out these differences? The success depends on a quantitative understanding of the gas composition trapped in the inclusions and an understanding of the interactions of cave mineralogy, air and water chemistry, and microbiological processes that may interfere with climatic or geochemical interpretations. Our proof-of-concept project uses time synchronous samples from several sites. We report here on this pilot investigation of speleothem inclusions using a methodology for quantitatively analyzing gases dissolved in inclusion fluids. We use incremental crushing of highly spatially resolved samples by mass spectrometry. Here, we report primarily on CH4, CO2, O2, and N2, but have included other detectable gases. The detection limit for He within aqueous fluid inclusions is ~0.2 ppm and gas ratios have ~5% precision using natural standards. We used chemically inert argon as a tracer gas to normalize results to air or air-saturated water. This enables interpretation of gas data despite variability in hydrological and geological cave histories. Results are variable. For example, in one case oxygen was depleted while nitrogen was increased, which may be attributable to the breakdown of nitrate or nitrogen-containing biomolecules. In other cases, oxygen is enriched which may be attributed to several factors both geochemical and biological. We suggest potential interpretations between the competing hypotheses with larger future data sets. This first attempt tackles the complex and intertwined speleological questions using the inclusion gas method. [ABSTRACT FROM AUTHOR]