Interactions between sulphide minerals and xanthates,I. The formation of monothiocarbonate at galena and pyrite surfaces

The rate of decomposition of potassium ethyl monothiocarbonate has been determined at pH values between 5 and 10, and its molar absorptivity at 221 nm determined to be 1.24 · 10⁴mol/cm.A novel apparatus for use in the study of reactions between sulphide minerals, oxygen and thiol reagents has been developed, and applied to the reactions of potassium ethyl xanthate with galena and pyrite. It has been shown that both minerals react with ethyl xanthate in the presence of oxygen or oxidation products to form soluble as well as adsorbed xanthate derivatives. The soluble derivative has been identified to be ethyl monothiocarbonate. The adsorbed xanthate at a galena surface, unlike that at a pyrite surface, is gradually converted to a soluble monothiocarbonate under the action of dissolved oxygen. The effect of variables such as pH, the initial xanthate and oxygen concentrations, and the initial state of oxidation of the mineral on the formation of monothiocarbonate has been studied. It is tentatively proposed that an intermediate adsorbed mixed xanthate-hydroxide species is involved in the formation of monothiocarbonate at both galena and pyrite surfaces.The significance of the formation of monothiocarbonate to flotation practice is discussed briefly. The formation of monothiocarbonate represents a wastage of reagent, and could lead to a decrease in flotability of xanthated galena with time of exposure to aerated solutions.     

The significance of Cenozoic magmatism from the western margin of the eastern syntaxis, southeast Tibet

The major and trace-element geochemistry, Sr–Nd bulk-rock isotopes, U–Pb zircon chronology and Lu–Hf isotopic compositions are described for three granitic bodies which intrude the Nyingchi gneisses (Lhasa terrane) along the western margin of the eastern Himalayan syntaxis. The Bayi two-mica granite and Lunan granite–granodiorite were intruded at 22 ± 1 and 25.4 ± 0.3 Ma, respectively, whereas the Confluence biotite granite was emplaced at 49.1 ± 0.4 Ma. All share strong depletions in Y and HREE requiring a garnet-bearing source both during and following the Eocene collision of the Indian plate with the Lhasa terrane. The isotope geochemistry of these intrusives (ε _Nd(t) = −3 to −5, ⁸⁷Sr/⁸⁶Sr_(t) = 0.706–0.707) indicates a crustal source within the Lhasa terrane. Sr–Nd systematics of the garnet-bearing Nyingchi gneisses together with the U–Pb and Lu–Hf isotopic ratios of detrital zircons recovered from this unit identifies it as a potential melt source. The combined element and isotope geochemistry of the plutons indicate a mixed source; the gneisses provide the older component whereas the Gangdese batholith provides a younger, siliceous component. The involvement of garnet-bearing crustal material in melt sources from the Cretaceous (80 Ma) to the Miocene (20 Ma) is consistent with the presence of a thicker continental crust in the eastern Lhasa terrane, as is the presence of magmatic epidote in several plutons which indicates a regional deepening level of exposure eastwards. Post-collision crustal melting is synchronous with proposed slab break-off during the early Miocene, suggesting advective heating by rising asthenospheric melts.     

Syngenetic inclusions in diamond from the Birim field (Ghana) – a deep peridotitic profile with a history of depletion and re-enrichment

Diamonds and their syngenetic mineral inclusions from placer deposits (Akwatia mine) along the Birim River, Ghana were studied, thus providing the first detailed data collection for the West African Craton. Inclusion contents indicate an almost exclusively peridotitic diamond suite, with the vast majority being part of the harzburgitic paragenesis. Chemically the Akwatian diamond inclusions differ from those in our 1100 sample world-wide data base mainly by shifts towards lower Mg/Fe ratios for harzburgitic olivines and orthopyroxenes, extremely high Ni contents in both harzburgitic and lherzolitic olivines, and a higher mean Cr content in chromites. The inconsistency between the low Mg/Fe ratios and the highly refractory compatible trace element signature seems best to be explained by re-fertilisation of a previously depleted source, similar to the metasomatic re-enrichment of deformed, Fe-Ti-rich and hot peridotites discussed by Harte (1983). Geothermometry shows Akwatian inclusions to be 140–190 °C hotter than the peridotitic average (1050 °C) given by Harris (1992). Since garnet-opx equilibria (1100 °C/50 kbar to 1370 °C/67 kbar) indicate a typical shield geotherm (40–42 mW/m²), these elevated temperatures imply an origin of the Akwatian diamonds unusually deep for a peridotitic suite. This is consistent with the presence of extraordinary amounts of silicate spinel component in chromite inclusions, indicative of crystallisation under higher pressures than recorded for most peridotitic suites. In addition, one garnet showed the highest knorringite component (66.4 mol%) so far observed in an inclusion in diamond. The same garnet also contained a minor enstatite solid-solution component, which indicates crystallisation at pressures just below 80 kbar. Akwatian diamond inclusions, therefore, represent the most complete cross-section through peridotitic subcontinental lithospheric upper mantle so far observed, down to a maximum depth between 200–240 km. Received: 1 November 1995 / Accepted 5 January 1997     

New insights into the occurrence of C-depleted carbon in the mantle from two closely associated kimberlites: Letlhakane and Orapa, Botswana

Carbon isotope measurements on diamonds from the Letlhakane kimberlite, and the analyses of their inclusions, permit the examination of km-scale mantle-composition variations by comparing the results with those for the nearby Orapa kimberlite. Diamonds from Letlhakane have a wide range in carbon isotopic composition (−3‰ to −21‰); however, the relative abundance of diamonds depleted in ¹³C is significantly lower than in the Orapa kimberlite. Most of the ¹³C-depleted diamonds belong to the eclogictic or websteritic paragenesis. The relative abundance of inclusions in diamonds and their composition indicate that there are significant differences in petrology in the mantle below the two locations. At Letlhakane, peridotitic compositions are more prevalent than at Orapa and the protolith of P-Type inclusions in diamonds may have experienced a higher degree of partial melting at Letlhakane compared to Orapa. P/T estimates for both W- and E-Type diamonds indicate that a region of ¹³C-depletion may exist beneath the two kimberlites. The relationships between carbon isotopic composition of the host diamond and the Al₂O₃/Cr₂O₃ ratios of their websteritic and eclogitic garnet inclusions indicate that the low δ¹³C regions may represent a primary mantle feature, unrelated to a crustal component.     

The relationship between fire behaviour measures and community loss: an exploratory analysis for developing a bushfire severity scale

Current fire danger scales do not adequately reflect the potential destructive force of a bushfire in Australia and, therefore, do not provide fire prone communities with an adequate warning for the potential loss of human life and property. To determine options for developing a bushfire severity scale based on community impact and whether a link exists between the energy release rate (power) of a fire and community loss, this paper reviewed observations of 79 wildfires (from 1939 to 2009) across Victoria and other southern states of Australia. A methodology for estimating fire power based on fuel loading, fire size and progression rate is presented. McArthur??s existing fire danger indices (FDIs) as well as fuel- and slope-adjusted FDIs were calculated using fire weather data. Analysis of possible relationships between fire power, FDIs, rate of spread and Byram??s fireline intensity and community loss was performed using exposure as a covariate. Preliminary results showed that a stronger relationship exists between community loss and the power of the fire than between loss and FDI, although fuel-adjusted FDI was also a good predictor of loss. The database developed for this study and the relationships established are essential for undertaking future studies that require observations of past fire behaviour and losses and also to form the basis of developing a new severity scale.     

Carbon flux in the northwest Mediterranean estimated from microbial production

Spring profiles of microbial production derived from the dark incorporation of tritiated leucine and tritiated thymidine in the northwest Mediterranean show an exponential decline with depth. Assuming this to represent a steady-state balance between microbial respiration and the downward flux of carbon, the downward flux is estimated as (1−/)p/b, where p is the microbial production, their gross growth efficiency and b the coefficient of exponential decline with depth. Summer profiles, ranging over about 3° of latitude and 4° of longitude, were well fitted by a two-component exponential decline, suggesting two distinct microbial substrates. Values of b for the more rapidly declining component varied between 0.01 and 0.06 m⁻¹ according to location. In the case of the slower component, b was estimated as 0.002 m⁻¹, and did not vary significantly over the region. Estimated fluxes of carbon at the surface are 123–335 mg m⁻² d⁻¹ for the fast and 95 mg m⁻² d⁻¹ for the slow component. Below about 200 m, carbon flux is dominated by the slow component. Flux estimates are compatible with flux estimates from sediment traps in the same region. The observed changes between the spring and summer profiles, combined with the horizontal homogeneity of the summer profiles below 200 m, are consistent with a downward transport of about 5–10 m d^–1, implying a significant dispersive component to the observed fluxes.     

Black material on mineral inclusions and in internal fracture planes in diamond

The black material observed on the surface of crystalline inclusions in diamond and also in adjacent internal fracture planes has been classified as a result of a preliminary examination of several hundred diamonds from Sierra Leone, Ghana, and South Africa (particularly the Premier Mine), as well as diamond slices of unknown origin, followed by a detailed examination of some 100 diamonds. X-ray, electron diffraction, and qualitative electron microprobe techniques were used in identifying this material as graphite, pyrrhotite and pentlandite. The possible origins of these minerals are discussed.     

Marine resources,biophysical processes,and environmental management of a tropical shelf seaway: Torres Strait,Australia–Introduction to the special issue

This special issue of Continental Shelf Research contains 20 papers giving research results produced as part of Australia's Torres Strait Co-operative Research Centre (CRC) Program, which was funded over a three-year period during 2003–2006. Marine biophysical, fisheries, socioeconomic-cultural and extension research in the Torres Strait region of northeastern Australia was carried out to meet three aims: 1) support the sustainable development of marine resources and minimize impacts of resource use in Torres Strait; 2) enhance the conservation of the marine environment and the social, cultural and economic well being of all stakeholders, particularly the Torres Strait peoples; and 3) contribute to effective policy formulation and management decision making. Subjects covered, including commercial and traditional fisheries management, impacts of anthropogenic sediment inputs on seagrass meadows and communication of science results to local communities, have broad applications to other similar environments.