The causes and petrological significance of cathodoluminescence emissions from alkali feldspars

The cathodoluminescence (CL) of a variety of alkali feldspars from South Greenland has been examined in an attempt to understand the causes of the CL and its petrological significance. Analytical methods have included CL spectroscopy, secondary ion mass spectrometry (SIMS) and electron paramagnetic resonance (EPR) to correlate the presence of certain CL emissions to the presence of certain trace element and point defects. Where possible, blue and red luminescent fractions of the same rock samples have been separated and analysed separately. Blue CL appears to relate to the presence of electron holes on bridging oxygens, particularly on the Al-O-Al bridge, as determined from EPR studies. No correlation with other proposed activators for blue CL such as Eu²⁺, Ga³⁺ or Ti⁴⁺ was observed. Some blue luminescent feldspars also have an emission in the infra-red (IR), invisible during normal visible CL petrography. The red and IR CL emissions correspond to features in EPR spectra attributed to Fe³⁺ and support previous suggestions that Fe³⁺ is related to this emission. However, our studies indicate that the visible red CL relates specifically to Fe³⁺ on the T1 site, whereas the equivalent CL from disordered feldspars lies in the IR. The difference between red and IR CL emissions therefore relates to the state of Fe³⁺ order across the tetrahedral sites. These data allow more meaningful interpretations of CL as a petrographic tool in alkali feldspar-bearing rocks. Received: 5 March 1998 / Accepted: 23 November 1998     

Quantitative quality assessment of the greenhouse gas inventory for agriculture in Europe

The greenhouse gas inventory of the European Communities and its estimation of the uncertainty is built from 15 individual and independent greenhouse gas inventories. This presents a particular challenge and is possible only if homogeneous information is available for all member states and if a proper evaluation of correlation between member states is performed. To this end, we present a methodology that estimates a quantitative measure for the aggregated Tier-level as well as the uncertainty for the main categories in the agriculture sector. In contrast to the approach suggested in the IPCC guidelines, which uses uncertainty estimates for activity data and emissions factors for each source category, the method presented uses quantitative information from individual parameters used in the inventory calculations, in combination with a well defined procedure to aggregate the information. Not surprisingly, N₂O emissions from agricultural soils are found to dominate the uncertainty. The results demonstrate the importance of correlation, if uncertainties are combined for the whole of Europe. The biggest challenge seems to be to conceptually harmonize the uncertainty estimates for the activity data (which tend to be underestimated) and emission factors (which tend to be overestimated).     

δB, Sr, Mg and B in a modern Porites coral: the relationship between calcification site pH and skeletal chemistry

Sr/Ca, B/Ca, Mg/Ca and δ¹¹B were determined at high spatial resolution across ∼1 year of a modern Hawaiian Porites lobata coral by secondary ion mass spectrometry (SIMS). We observe significant variations in B/Ca, Mg/Ca, Sr/Ca and δ¹¹B over short skeletal distances (nominally equivalent to periods of <20 days). This heterogeneity probably reflects variations in the composition of the extracellular calcifying fluid (ECF) from which the skeleton precipitates. Calcification site pH (total scale) was estimated from skeletal δ¹¹B and ranged from 8.3 to 8.8 (± ∼0.1) with a mean of ∼8.6. Sr/Ca and B/Ca heterogeneity is not simply correlated with calcification site pH, as might be expected if Ca-ATPase activity increases the pH and decreases the Sr/Ca and B(OH)₄⁻/CO₃²⁻ ratios of the ECF. We produced a simple model of the ECF composition and the skeleton deposited from it, over a range of calcium transport and carbonate scenarios, which can account for these observed geochemical variations. The relationship between the pH and Sr/Ca of the ECF is dependent on the concentration of DIC at the calcification site. At higher DIC concentrations the ECF has a high capacity to buffer the [H⁺] changes induced by Ca-ATPase pumping. Conversely, at low DIC concentrations, this buffering capacity is reduced and ECF pH changes more rapidly in response to Ca-ATPase pumping. The absence of a simple correlation between ECF pH and skeletal Sr/Ca implies that calcification occurred under a range of DIC concentrations, reflecting variations in the respiration and photosynthesis of the coral and symbiotic zooxanthellate in the overlying coral tissues. Our observations have important implications for the use of coral skeletons as indicators of palaeo-ocean pH.     

CHIM-geoelectrochemical method in search of concealed mineralisation in China and Australia

A version of the geoelectrochemical prospecting technique developed in China was demonstrated in China and Australia to test its suitability under both Chinese and Australian conditions. This paper briefly describes the mechanism and effectiveness of the technique applied to search of concealed mineralisation through regolith cover, based on both experimental and field tests. This paer deals with three main aspects of the method： a） how metallic ions are released from orebodies by electrochemical dissolution; b） how these ions migrate to the collector and are deposited as elements by electrochemical extraction in the presence of an electric field; and c） the effectiveness of the method illustrated by some case studies.     

Laser combustion analysis of δS of sulfosalt minerals: determination of the fractionation systematics and some crystal-chemical considerations

Laser sulfur combustion in the presence of O₂ is the most commonly used method of in situ sulfur isotope analysis. Previous workers indicated that a small but reproducible fractionation of ³⁴S/³²S exists between the product SO₂ gas and the mineral. The magnitude of this fractionation varies with bond strength, as reflected in Gibbs free energy of formation at 298.15K. The correction factors are known for common sulfides and anhydrite but not, hitherto, for stibnite and the sulfosalt minerals, which are important constituents of many classes of ore deposits. We present the correction factors for the following chemically and crystallographically well-characterized minerals: stibnite (weighted mean = −1.2‰), bournonite (+0.6‰), tetrahedrite (+1.3‰), and boulangerite (+1.4‰). The Gibbs free energies of formation of these phases have been approximated by the sulfide summation method, and the correlation of ΔG₂₉₈⁰ with the correction factor for the sulfosalts fits well with the trend previously established for simple sulfides. There is an excellent correlation between the fractionation factor and mineral composition, a parameter that does result in bond strength variations (e.g., mol fraction of PbS in sulfosalts), allowing estimation of the correction factors for simple intermediate compositions. Finally, bond strength also varies with variation in interatomic distances, and we have, therefore, investigated the behaviour of stibnite, a strongly anisotropic mineral. Our results indicate that there is a significant variation in fractionation factor, depending on crystal orientation. The fractionation factor along the prismatic b-axis, which displays the strongest chemical bonds (as monitored by the shortest bond lengths), is more negative (−1.7‰) than along the other crystallographic directions (−0.7 to −1.0‰), which is in full agreement with theoretical predictions. We demonstrate the application of the technique in unravelling source- and process-related sulfur isotope systematics in two hydrothermal vein systems in the classic mining area of the NE Rhenish Massif, both studies requiring resolution beyond the scale of conventional sulfur isotope analysis.     

Seasonal and interannual behaviour of groundwater catchment boundaries in a Chalk aquifer

Groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis. We investigated whether this was true for a highly permeable carbonate aquifer in England, the Berkshire and Marlborough Downs Chalk aquifer, using both borehole hydrograph data and a physics‐based distributed regional groundwater model. Borehole hydrograph data time series were used to construct a monthly interpolated water table surface, from which was then derived a monthly groundwater catchment boundary. Results from field data showed that the mean annual variation in groundwater catchment area was about 20% of the mean groundwater catchment area, but interannual variation can be very large, with the largest estimated catchment size being approximately 80% greater than the smallest. The flow in the river was also dependent on the groundwater catchment area. Model results corroborated those based on field data. These findings have significant implications for issues such as definition of source protection zones, recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater systems. Copyright © 2015 John Wiley & Sons, Ltd.     

A pre-Ipswichian cold stage mammalian fauna from the Balderton Sand and Gravel,Lincolnshire, England

The Balderton Sand and Gravel has yielded one of very few mammalian faunas dated to the penultimate Cold Stage in Britain. The assemblage is dominated by mammoth and woolly rhinoceros, with subordinate horse, red deer, bison, straight-tusked elephant, musk ox, reindeer, wolf, lion, brown bear and cf. narrow-nosed rhinoceros. This fauna indicates cold stage conditions, probably including one or more interstadial episodes. The presence of straight-tusked elephant and cf. narrow-nosed rhinoceros supports its pre-Devensian age, and provides corroboration for the occurrence of these taxa in the British Wolstonian. An attempt is made to analyse the fossil collection by preservation type and adhering sediment: the occurrence of individual species appears to be largely uncorrelated with lithology. The Balderton assemblage corresponds well to other British mammal faunas assigned to a cold interval between the Hoxnian and Ipswichian Interglacials.     

On the genesis of lava cracks in Hawaii

The orientation structures of lava flows and lava cracks in Hawaii (Big Island) have been analysed statistically. It is shown that the lava flows do not follow epigenetic random directions, but instead follow channels that have been endogenically predesigned. Similarly, the cracks in these flows have consistent directions at 45° to the edges of the lava flows. Thus, these cracks are not simply ‘cooling joints’ but features that correspond to the edge-crevasses in glacier-flow: they are shearing phenomena that occur in a similar fashion in any plastic-type flow.