Magmatic fluids, both vapour and hypersaline liquid, are a primary source of many components in hydrothermal ore deposits formed in volcanic arcs. These components, including metals and their ligands, become concentrated in magmas in various ways from various sources, including subducted oceanic crust. Leaching of rocks also contributes components to the hydrothermal fluid—a process enhanced where acid magmatic vapours are absorbed by deeply circulating meteoric waters. Advances in understanding the hydrothermal systems that formed these ore deposits have come from the study of their active equivalents, represented at the surface by hot springs and volcanic fumaroles.

The role of magmas in the formation of hydrothermal ore deposits

Fluid inclusions in hydrothermal ore deposits

https://digital.library.unt.edu/ark:/67531/metadc736199/m2/1/high_res_d/799444.pdf

Uranium Co-precipitation with Iron Oxide Minerals

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1246&context=usdoepub

Reduction of U(VI) in goethite (α-FeOOH) suspensions by a dissimilatory metal-reducing bacterium

There is a continual influx of heavy metal contaminants and pollutants into the biosphere from both natural and anthropogenic sources. A complex variety of abiotic and biotic processes affects their speciation and distribution, including adsorption onto and desorption from mineral surfaces, incorporation in precipitates or coprecipitates, release through the dissolution of minerals, and interactions with plants and microbes. Some of these processes can effectively isolate heavy metals from the biosphere, whereas others cause their release or transformation to different species that may be more (or less) bioavailable and/or toxic to organisms. Here we focus on abiotic adsorption and precipitation or coprecipitation processes involving the common heavy metal contaminant lead and the metalloids arsenic and selenium in mine tailings and contaminated soils. We have used extremely intense x-rays from synchrotron sources and a structure-sensitive method known as x-ray absorption fine structure (XAFS) spectroscopy to determine the molecular-level speciation of these elements at concentrations of 50 to several thousand ppm in the contaminated environmental samples as well as in synthetic sorption samples. Our XAFS studies of As and Pb in the mine tailings show that up to 50% of these contaminants in the samples studied may be present as adsorbed species on mineral surfaces, which makes them potentially more bioavailable than when present in sparingly soluble solid phases. Our XAFS studies of Se(VI) sorption on Fe2+-containing sulfates show that this element undergoes redox reactions that transform it into less bioavailable and less toxic species. This type of information on molecular-level speciation of heavy metal and metalloid contaminants in various environmental settings is needed to prioritize remediation efforts and to assess their potential hazard to humans and other organisms.

https://www.pnas.org/content/pnas/96/7/3388.full.pdf

Mineral surfaces and bioavailability of heavy metals : a molecular-scale perspective

A combination of X-ray absorption, optical luminescence, and Raman vibrational spectroscopies along with ancillary techniques such as energy dispersive scanning electron microscopy and powder X-ray...

/pdf/speciation-of-uranium-in-fernald-soils-by-molecular-1bnhq8qo8m.pdf

Speciation of Uranium in Fernald Soils by Molecular Spectroscopic Methods: Characterization of Untreated Soils

N2-Ar-He compositions in fluid inclusions: Indicators of fluid source

In uncontaminated natural materials, plutonium and technetium exist exclusively as products (daughters) of nuclear reactions in which uranium is the principal reactant (parent). Under conditions of chemical stability over geologic periods of time, the relative abundances of daughter and parent elements are fixed by the rates of nuclear reactions and the decay of the daughter radionuclide. The state of this nuclear secular equilibrium condition is the primary basis of the geochemical study of these elements in nature. Thus, it is critical that nuclear parent and daughter abundances are measured in the same sample. We have developed a quantitative procedure for measuring subpicogram quantities of plutonium and technetium in gram quantities of geologic matrices such as uranium ores. The procedure takes advantage of the aggressive properties of sodium peroxide/hydroxide fusion to ensure complete dissolution and homogenization of complex materials, the precision provided by isotope dilution techniques, and the...

Analysis of naturally produced technetium and plutonium in geologic materials.

Quantitative bulk analysis of fluid inclusion volatiles measures the composition of trapped geothermal liquids and vapor. Fluid-inclusion gas-analyses may identify fluid boiling and mixing, and the analyses can be used as a fluid tracer. Fluid boiling is indicated by excess gaseous species. Linear arrays of data points on gas ratio diagrams indicate fluid mixing. Nitrogen-argon ratios are used to discriminate atmospheric fiom magmatic volatiles. Crustal components in geothermal fluids are best indicated by concentrations of methane and helium. Methane strongly correlates with other organic compounds, and N2-Ar-CH4 plots are similar to N2-Ar-He diagrams. Alkene to alkane ratios of C2-7 organic species indicate the oxidation state of geothermal fluids. The Geysers inclusion analyses are an example of how inclusion fluids may be used to understand the paleo hydrology of a geothermal system.

/pdf/gaseous-species-in-fluid-inclusions-a-tracer-of-fluids-and-1gd6z8iu90.pdf

John Musgrave

Papers

Speciation of Uranium in Fernald Soils by Molecular Spectroscopic Methods: Characterization of Untreated Soils

N2-Ar-He compositions in fluid inclusions: Indicators of fluid source

Analysis of naturally produced technetium and plutonium in geologic materials.

Gaseous species in fluid inclusions: A tracer of fluids and indicator of fluid processes

Exploration drilling and reservoir model of the Platanares geothermal system, Honduras, Central America