No description available.

No description available.

No description available.

The study was based upon five Pb-Zn districts located in S.E. Bulgaria, these were Madan, Madjarovo, Laki, Zvezdel and Spaheivo districts with most of the work concentrating on Madan and Madjarovo. The Madan district consists of approximately twenty vein and replacement deposits hosted within amphibolite grade metamorphic rocks. The Madjarovo district comprises approximately forty five veins which are predominantly hosted within an eroded strato-volcano but with some of the veins passing down into the underlying metamorphic basement. The deposits of the Laki district are also hosted within the metamorphic basement and can be considered as an analogue to Madan, while Zvezdel and Spaheivo are volcanic-hosted and similar to Madjarovo. Fluid inclusion micro-thermometry shows that the mineralization in Madan, Madjarovo and Laki was deposited by fluids with a salinity of 3-5 eq. wt. %. NaCl and at temperatures of between 240°C and 300°C. In Madan and Laki the associated alteration is dominated by sericite while in Madjarovo both sericite and adularia are present, such an assemblage suggests neutral to slightly alkaline conditions. In addition a zone of sericitic - advanced argillic alteration is present at Madjarovo, this contains a range of minerals including kaolinite and alunite and is believed to have formed in a strongly acidic environment. The trace element geochemistry of the differing alteration types at Madjarovo also suggests that the alteration was produced by two separate fluids. A range of stable isotope analyses were undertaken to attempt to identify the source of the fluids and other constituents. The δ³⁴S sulphide values from the mineralization and alteration ranges between -1‰ and +7‰ for all districts except Spaheivo which has values of -5‰ to -7‰. Whole rock sulphur data from the metamorphic basement varies from - 7‰ to +5‰ and so is a viable source alongside igneous sulphur. The δ¹³C calcite in the metamorphic-hosted districts ranges from -4‰ to +2‰. This indicates that the carbon was predominantly derived from marble horizons within the basement which have a similar range of values. This contrasts with the delta δ¹³C calcite in the volcanic-hosted districts which is typically more depleted and suggests a different or additional source of carbon.

<p> A geologic map was drafted of the northern Highland Range (1:24,000 scale), rock units defined, and samples of the volcanic units were obtained and analyzed to produce a representative suite of chemical analyses to characterize the range of geochemical variability. The style, relative timing, and orientation of faults and dikes, and the magnitude and variability of stratal tilting was examined to evaluate the structural and magmatic evolution of the northern Highland Range in the context of models for the Colorado River Extensional Corridor and Black Mountains accommodation zone. Methods involved field mapping of the range scale structure and geometry of faulting, structural interpretation, and geochemical analysis of ten representative samples by X-ray spectrometry. Structural data was interpreted with stereonets; geochemical whole rock, and major elemental data was analyzed by comparing elemental oxides; trace elemental data was analyzed by normalizing to chondrite concentrations. The northern Highland Range is a ca. 3,000 m-thick sequence of volcanic and volcaniclastic flows and breccias overlain by regionally extensive tuffs (Mt. Davis and Bridge Spring). Unique mineralogy, geochemistry and lithologic character of some units and volcanic vent facies, as well as the presence of domes and dikes feeding the extrusives argue for local derivation from a dome/stratocone volcanic complex that was mostly restricted to the northern Highland Range. </p>

<p> The fate of metal(loid)s in the environment depends on a variety of physical and geochemical factors. Assessing metal(loid) transport in soil solution and surface water requires detailed knowledge of the speciation, which can often control mobility, toxicity and bioavailability of a given element. The present study details the geochemical analyses of two end member types of systems: a &lsquo;pristine&rsquo; Arctic watershed and a military shooting range with an overall focus on understanding lead (Pb) and antimony (Sb) mobility in shooting range soils. The project uses bulk speciation analyses coupled with micro-scale methods to quantify variations in metal(loid) concentration as a function of environmental conditions and characterize metal(loid) speciation and distribution in relation to parent source material in order to understand the impact that metal(loid) retention versus mobilization has on a given system. </p><p> In the Arctic, stream water concentrations of Al, Ba, Fe, and Mn in Imnavait Creek were highest in the late fall (September and October). This pattern appears to correlate with the depth of the active layer throughout the watershed. Increased water infiltration at the permafrost-active layer boundary could significantly impact stream water trace metal(loid) signatures due to mineral weathering of unfrozen soil. In the central Alaskan shooting range, there were significant contributions of Pb and Sb to both the soil and soil solution as a result of the weathering of fragmented bullets. Aqueous concentrations of Sb were higher than Pb in all soil types, indicating Sb is more mobile, despite the fact that bullets introduce approximately two orders of magnitude more Pb than Sb. We observed an association of both Pb and Sb with Fe in soils, which impacts remediation scenarios for ranges as Fe treatments have potential to be effective for system-wide immobilization of major contaminants. Overall, the results from this study highlight the complexity of metal(loid) speciation, transport and mobility as a function of seasonality, soil type and environmental conditions.</p>

<p> In this study, we conduct high-pressure (HP) high-temperature (HT) diffusion experiments in anhydrous rhyolite near 1000 &deg;C and 1100 &deg;C at 100 MPa using the cold seal pressure apparatus to diffuse argon into natural obsidian charges. We use electron microprobe measurements of the argon concentration gradients to calculate the argon diffusivity <i>(D_Ar)</i> as a function of temperature and pressure. The range and mean of <i> D_Ar</i> calculated from these measurements are in good agreement with previous studies (Carroll 1991, Behrens and Zhang 2001). Even so, we observe significant variability in our <i>D_Ar</i> results, beyond what is likely due to analytical or experimental uncertainty; nearly as much variability as Carroll (1991) and Behrens and Zhang (2001) reported. In particular, we notice a small systematic geometric bias in the distribution of argon in our samples, which appears to correlate with sample deformation. We attribute this effect to distortion of concentration gradients by viscous advection.</p>

This work examines the petrogenesis of layered ultramafic- gabbro bodies from the Scourian and the metamorphic evolution of the Assynt district of Sutherland. The layered bodies comprise ultramafic rocks (amphibole-spinel- lherzolites) and garnetiferous gabbros derived from the same tholeiitic magma which had about 15-20 MgO. The ultramafic rocks are partial cumulates formed by olivine and orthopyroxene after settling; with the gabbros being derivative liquids. The flat to LREE enriched patterns and trace element levels suggest the magma formed by 30-40% partial melting of undepleted mantle. The bodies are fragments of Archaean oceanic crust invaded by tonalitic magma generated at a convergent plate boundary followed by ductile deformation and metamorphism to granulite facies. The gabbros show evidence of two periods of granulite facies mineral growth, the first producing a clinopyroxene-garnet plagioclase assemblage at about 12-15 kb and 1000C. Uplift caused partial breakdown of the garnet to orthopyroxene-plagioclase spinel amphibole symplectites at about 800-900 C and 9-14 kb. Garnet stability depends on both P-T conditions and whole rock Fe/Mg ratio. The Lewisian complex in Assynt suffered widespread retrogression during the Inverian caused by the influx of large volumes of mantle- derived hydrous fluids associated with the development of NW-trending monoclinal folds. During retrogression the development of a uniform hornblende-plagioclase quartz assemblage in mafic and intermediate gneisses caused a redistribution of elements. Hornblende and biotite compositions depend on whole-rock composition and paragenesis. The assemblages developed suggest retrogression occurred with falling temperatures in the range 700-500C remaining above 500 C for the duration of the Inverian and Laxfordian events. The style of deformation became more brittle with time as the complex was uplifted. Amphibolite dykes from Clashnessie Bay are tholeiitic andesites formed from a tholeiitic magma by hornblende fractionation. They were deformed and metamorphosed before the intrusion of the main Scourie dyke swarm. The Canisp shear zone was the site of deformation over a protracted period and there may have been 5-10 km of right-lateral displacement.

No description available.

No description available.