The hyper-enrichment of silver through the aggregation of silver sulfide nanoparticles.

Silver deposits have long been considered to form due to the direct precipitation of silver minerals from aqueous fluids, in which the metal is transported as chloride and/or bisulfide complexes. Ultra-high-grade silver ores have silver contents up to tens of weight-percent in the form of silver sulfides and native silver. Ore-forming fluids of most silver deposits, however, typically contain low silver contents of parts per million silver.

The role of an oxidized lithospheric mantle in gold mobilization.

Phanerozoic orogenic gold mineralization at craton margins is related to the metasomatism of the lithospheric mantle by crustal material. Slab subduction transfers Au from the crust to the metasomatized mantle and oxidizes the latter to facilitate the mobilization of Au into mantle melts. The role of volatiles in the mobilization of Au in the mantle is unclear because of the absence of direct geochemical evidence relating the mantle source of Au to Au mineralization in the overlying crust.

The role of CO in the genesis of Dabie-type porphyry molybdenum deposits.

Porphyry-type molybdenum deposits, many of which are in China, supply most of the World's molybdenum. Of particular importance are the molybdenum deposits located in the Qinling-Dabie region that are responsible for more than half of China's molybdenum production. A feature that distinguishes this suite of deposits from the better-known Climax and Endako sub-types of porphyry molybdenum deposits is their formation from CO-rich magmatic-hydrothermal fluids.

Extreme shifts in pyrite sulfur isotope compositions reveal the path to bonanza gold.

Pyrite is the most common sulfide mineral in hydrothermal ore-forming systems. The ubiquity and abundance of pyrite, combined with its ability to record and preserve a history of fluid evolution in crustal environments, make it an ideal mineral for studying the genesis of hydrothermal ore deposits, including those that host critical metals. However, with the exception of boiling, few studies have been able to directly link changes in pyrite chemistry to the processes responsible for bonanza-style gold mineralization.

Colloidal transport and flocculation are the cause of the hyperenrichment of gold in nature.

Aqueous complexation has long been considered the only viable means of transporting gold to depositional sites in hydrothermal ore-forming systems. A major weakness of this hypothesis is that it cannot readily explain the formation of ultrahigh-grade gold veins. This is a consequence of the relatively low gold concentrations typical of ore fluids (tens of parts per billion [ppb]) and the fact that these "bonanza" veins can contain weight-percent levels of gold in some epithermal and orogenic deposits.

Challenging the thorium-immobility paradigm.

Thorium is the most abundant actinide in the Earth's crust and has universally been considered one of the most immobile elements in natural aqueous systems. This view, however, is based almost exclusively on solubility data obtained at low temperature and their theoretical extrapolation to elevated temperature. The occurrence of hydrothermal deposits with high concentrations of Th challenges the Th immobility paradigm and strongly suggests that Th may be mobilized by some aqueous fluids.

The origin of rare alkali metals in geothermal fluids of southern Tibet, China: A silicon isotope perspective.

Geothermal waters from the Semi, Dagejia and Kawu hot springs in the Shiquanhe-Yarlung Zangbo geothermal field of southern Tibet (China) are highly enriched in rare alkali metals (RAM). However, the enrichment mechanism is still hotly debated. Here, we report the first silicon isotope data of these geothermal waters to unravel the origin of the extreme RAM enrichments.

Uranium-rich diagenetic fluids provide the key to unconformity-related uranium mineralization in the Athabasca Basin.

The Proterozoic Athabasca Basin is well known for its unusually large-tonnage and high-grade 'unconformity-related' uranium (U) deposits, however, explanations for the basin-wide U endowment have not been clearly identified. Previous studies indicate that U-rich brines with up to ~600 ppm U and variable Na/Ca ratios (from Na-dominated to Ca-dominated) were present at the sites of U mineralization, but it is unknown whether such fluids were developed solely in the vicinity of the U deposits or at a basinal scale. Our microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz overgrowths from the barren part of the basin indicate that U-rich brines (0.

Uranium transport in acidic brines under reducing conditions.

The behavior of uranium in environments, ranging from those of natural systems responsible for the formation of uranium deposits to those of nuclear reactors providing 11% of the world's electricity, is governed by processes involving high-temperature aqueous solutions. It has been well documented that uranium is mobile in aqueous solutions in its oxidized, U state, whereas in its reduced, U state, uranium has been assumed to be immobile. Here, we present experimental evidence from high temperature (>100 °C) acidic brines that invalidates this assumption.

An approach to determining nickel, vanadium and other metal concentrations in crude oil.

The ability to accurately determine the metal content of crude oils is necessary for reasons ranging from the need to identify the source of the oils (Ni and V) to removing components that might inhibit catalysis during refining or impact negatively on the environment during hydrocarbon combustion. Here we show that ashing followed by chemical oxidation and acid digestion, coupled with ICP-MS analysis, provides an accurate method for determining the concentration of metals in crude oil. Nickel and vanadium concentrations were measured in certified Ni and V oil standards and in various light, intermediate and heavy crude oils after application of a single vessel ashing-chemical oxidation-acid digestion sample preparation and storing technique.

Steel slag carbonation in a flow-through reactor system: the role of fluid-flux.

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.

Physicochemical conditions and timing of rodingite formation: evidence from rodingite-hosted fluid inclusions in the JM Asbestos mine, Asbestos, Québec.

Fluid inclusions and geological relationships indicate that rodingite formation in the Asbestos ophiolite, Québec, occurred in two, or possibly three, separate episodes during thrusting of the ophiolite onto the Laurentian margin, and that it involved three fluids. The first episode of rodingitization, which affected diorite, occurred at temperatures of between 290 and 360 degrees C and pressures of 2.5 to 4.

Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension.

Fiber dimension and concentration may vary substantially between two necropsy populations of former chrysotile miners and millers of Thetford-Mines and Asbestos regions. This possibility could explain, at least in part, the higher incidence of respiratory diseases among workers from Thetford-Mines than among workers from the Asbestos region. The authors used a transmission electron microscope, equipped with an x-ray energy-dispersive spectrometer, to analyze lung mineral fibers of 86 subjects from the two mining regions and to classify fiber sizes into three categories.