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Highlights • Aggregates of uraninite nanocrystals host inclusions of native gold. • Oil droplets triggered precipitation of gold precipitated from hydrothermal fluids. • Hydrocarbon inclusions in native gold contain in-situ grown uraninite nanocrystals. • Water-oil emulsions were responsible for the in-situ growth of gold and uraninite. • Lanarkite formed in local oxidation zones on galena – uraninite interfaces. High-resolution scanning- and transmission-electron microscopy of pyrobitumen-hosted uraninite reveal that uraninite grains are highly porous aggregates of uniformly sized nanocrystals, and that many of their pores are filled by native gold. These texturally late gold grains, in turn, contain small pores occupied by former oil droplets that were converted to pyrobitumen during burial and metamorphism. The pyrobitumen in the pores of the gold grains contains in situ-formed uraninite nanocrystals. Galena also occupies the pores of the uraninite aggregates. In addition, this study reveals the first occurrence of rare lanarkite that engulfs the galena in the pores of the uraninite. On the basis of the nature of the uraninite and the filling of some of its pores with native gold, we propose a mineralization model for the deposition of the uranium and gold in the Carbon Leader Reef that calls upon the interaction of oil and aqueous (hydrothermal) fluids to form micro-emulsions. According to this model, uraninite nanocrystals precipitated from uranium-bearing hydrocarbon liquids and flocculated to form porous, uraninite aggregates. These liquids interacted with auriferous hydrothermal fluids in the Carbon Leader Reef, leading to the formation of a micro-emulsion at the interface between the two fluids. Gold precipitated as native metal around droplets of the oil owing to a reduction in oxygen fugacity, which destabilized the bisulfide species responsible for gold dissolution. Commonly, this process went hand in hand with the flocculation of the uraninite nanocryst

Highlights • Aggregates of uraninite nanocrystals host inclusions of native gold. • Oil droplets triggered precipitation of gold precipitated from hydrothermal fluids. • Hydrocarbon inclusions in native gold contain in-situ grown uraninite nanocrystals. • Water-oil emulsions were responsible for the in-situ growth of gold and uraninite. • Lanarkite formed in local oxidation zones on galena – uraninite interfaces. High-resolution scanning- and transmission-electron microscopy of pyrobitumen-hosted uraninite reveal that uraninite grains are highly porous aggregates of uniformly sized nanocrystals, and that many of their pores are filled by native gold. These texturally late gold grains, in turn, contain small pores occupied by former oil droplets that were converted to pyrobitumen during burial and metamorphism. The pyrobitumen in the pores of the gold grains contains in situ-formed uraninite nanocrystals. Galena also occupies the pores of the uraninite aggregates. In addition, this study reveals the first occurrence of rare lanarkite that engulfs the galena in the pores of the uraninite. On the basis of the nature of the uraninite and the filling of some of its pores with native gold, we propose a mineralization model for the deposition of the uranium and gold in the Carbon Leader Reef that calls upon the interaction of oil and aqueous (hydrothermal) fluids to form micro-emulsions. According to this model, uraninite nanocrystals precipitated from uranium-bearing hydrocarbon liquids and flocculated to form porous, uraninite aggregates. These liquids interacted with auriferous hydrothermal fluids in the Carbon Leader Reef, leading to the formation of a micro-emulsion at the interface between the two fluids. Gold precipitated as native metal around droplets of the oil owing to a reduction in oxygen fugacity, which destabilized the bisulfide species responsible for gold dissolution. Commonly, this process went hand in hand with the flocculation of the uraninite nanocryst

Steel production is currently the largest industrial source of atmospheric CO2. As annual steel production continues to grow, the need for effective methods of reducing its carbon footprint increases correspondingly. The carbonation of the calcium-bearing phases in steel slag generated during basic oxygen furnace (BOF) steel production, in particular its major constituent, larnite {Ca2SiO4}, which is a structural analogue of olivine {(MgFe)2SiO4}, the main mineral subjected to natural carbonation in peridotites, offers the potential to offset some of these emissions. However, the controls on the nature and efficiency of steel slag carbonation are yet to be completely understood. Experiments were conducted exposing steel slag grains to a CO2–H2O mixture in both batch and flow-through reactors to investigate the impact of temperature, fluid flux, and reaction gradient on the dissolution and carbonation of steel slag. The results of these experiments show that dissolution and carbonation of BOF steel slag are more efficient in a flow-through reactor than in the batch reactors used in most previous studies. Moreover, they show that fluid flux needs to be optimized in addition to grain size, pressure, and temperature, in order to maximize the efficiency of carbonation. Based on these results, a two-stage reactor consisting of a high and a low fluid-flux chamber is proposed for CO2 sequestration by steel slag carbonation, allowing dissolution of the slag and precipitation of calcium carbonate to occur within a single flow-through system.

Steel production is currently the largest industrial source of atmospheric CO2. As annual steel production continues to grow, the need for effective methods of reducing its carbon footprint increases correspondingly. The carbonation of the calcium-bearing phases in steel slag generated during basic oxygen furnace (BOF) steel production, in particular its major constituent, larnite {Ca2SiO4}, which is a structural analogue of olivine {(MgFe)2SiO4}, the main mineral subjected to natural carbonation in peridotites, offers the potential to offset some of these emissions. However, the controls on the nature and efficiency of steel slag carbonation are yet to be completely understood. Experiments were conducted exposing steel slag grains to a CO2–H2O mixture in both batch and flow-through reactors to investigate the impact of temperature, fluid flux, and reaction gradient on the dissolution and carbonation of steel slag. The results of these experiments show that dissolution and carbonation of BOF steel slag are more efficient in a flow-through reactor than in the batch reactors used in most previous studies. Moreover, they show that fluid flux needs to be optimized in addition to grain size, pressure, and temperature, in order to maximize the efficiency of carbonation. Based on these results, a two-stage reactor consisting of a high and a low fluid-flux chamber is proposed for CO2 sequestration by steel slag carbonation, allowing dissolution of the slag and precipitation of calcium carbonate to occur within a single flow-through system.

Subduction zone recycling of volatiles (H2O, Cl, S, F) is controlled by the nature of subducted materials and the temperature-pressure profile of the downgoing slab. We investigate the variability in volatile and fluid-mobile trace element enrichment in the Sunda arc using melt inclusion data from Kawah Ijen and Tambora volcanoes, together with published data from Galunggung, Indonesia. Combining our results with data from other arcs, we investigate the mobility of these elements during slab dehydration and melting. We observe correlations between Sr, H2O and Cl contents, indicating coupling of these elements during subduction zone recycling. Sulfur is more variable, and fluorine contents generally remain at background mantle values, suggesting decoupling of these elements from H2O and Cl. Partial melting and dehydration models constrain the source of Sr and the volatiles and suggest that the altered oceanic crust (AOC) is the main source of the hydrous component that fluxes into the mantle wedge, in agreement with thermo-mechanical models. Sediment melt remains an important component for other elements such as Ba, Pb, Th and the LREE. The Indonesian volcanoes have variable concentrations of volatile and fluid-mobile elements, with Kawah Ijen recording higher AOC-derived fluid fluxes (Sr/Nd and H2O/Nd) compared to Galunggung and Tambora. Kawah Ijen has H2O/Ce ratios that are comparable to some of the most volatile-rich magmas from other cold slab subduction zones worldwide, and the highest yet measured in the Sunda arc. © 2012. American Geophysical Union. All Rights Reserved.