Mineralogical, bulk and field leachate compositions are used to identify important processes governing the evolution of discharges from a coal spoil heap in County Durham. These processes are incorporated into a numerical one-dimensional advective-kinetic reactive transport model which reproduces field results, including gas compositions, to within an order of magnitude. Variation of input parameters allows the effects of incorrect initial assumptions on elemental profiles and discharge chemistry to be assessed. Analytical expressions for widths and speeds of kinetic reaction fronts are developed and used to predict long-term development of mineralogical distribution within the heap. Results are consistent with observations from the field site. Pyrite oxidation is expected to dominate O2 consumption in spoil heaps on the decadal timescale, although C oxidation may stabilize contaminants in effluents on the centennial scale.

Transmission electron microscope samples were prepared of ALH 78045 and ALH 88045, two clay-and phyllosilicate-bearing Antarctic meteorites, using argon ion milling and focused ion beam (FIB) techniques. ALH 78045 contains clay- and phyllosilicate-filled veins that have formed by terrestrial weathering of olivine, orthopyroxene and metal. Very narrow (∼10 nm) intragranular clay-filled veins could be observed in the TEM samples prepared by argon ion milling, whereas differential thinning and lack of precision in the location of the electron-transparent areas hindered the study of wider (5 — 15 μm) phyllosilicate-filled intergranular veins. Using the FIB instrument, electron-transparent slices were cut from specific parts of the wider veins and lifted out for TEM study. Results show that these veins are occluded by cronstedtite, a mixed-valence Fe-rich phyllosilicate. This discovery shows that silicates can be both dissolved and precipitated during terrestrial weathering within the Antarctic ice. ALH 88045 is one of a small number of known CM1 carbonaceous chondrites. This meteorite is largely composed of flattened ellipsoidal aggregates of serpentine-group phyllosilicates. To determine the mineralogy and texture of phyllosilicates within specific aggregates, TEM samples were prepared by trenching into the cut edge of a sample using the FIB instrument. Results show that Mg-rich aggregates are composed of lath-shaped serpentine crystals with a ∼0.73 nm basal spacing, which is typical of the products of low temperature aqueous alteration within asteroidal parent bodies. Results of this work demonstrate that the FIB has enormous potential in a number of areas of Earth and planetary science.

The discovery in 1966 of Ni sulphide deposits at Kambalda, Western Australia resulted from the interpretation of siliceous limonitic material containing up to 1·0% Ni and 0·3% Cu as the gossanous expression of Ni sulphides. In many cases analysis for Ni, Cu, Zn, Co, Cr, Mn and Pb will distinguish Ni–Cu gossans from other oxidised sulphide assemblages and pseudo-gossans. However, most geochemical classification schemes cannot always distinguish strongly silicified or sulphide-poor Ni gossans from Fe sulphide gossans enriched in Ni and Cu or from some nickeliferous oxidised and lateritic products which have no sulphide source. Ambiguous cases may be resolved by analysis for Pd and Ir but this method is expensive and requires very sophisticated analytical techniques.

The use of reflected light microscopy to examine microtextures preserved in the surface gossans from a supergene pyrite-violarite-marcasite sulphide assemblage has allowed the refinement of geochemical classification schemes. The preservation of supergene zone textures by pseudomorphous Si–Fe replacement often permits the original sulphide proportions and Ni–Cu grade to be reliably assessed. Relict microtextures are usually preserved, even in pale coloured, highly siliceous gossans containing less than 0·01% Ni.