Search

The paper by Cardenes et al. [1] reviews the roofing slate standards of different countries, analysing and comparing the current methods of testing. This is always an important and interesting [...]

Recent developments in instrumentation mean that chemical analysis of large drill cores taken for geological purposes can be performed rapidly at sub-millimetre scales using core scanners equipped with energy-dispersive X-ray fluorescence spectrometers. The present study describes the development of a calibration for the Itrax Core Scanner (Cox Analytical, Sweden), intended for whole cores of coal-seam sections, without the need for sample preparation. The calibration was developed for key major elements (Al, Si, P, S, K, Ca, Ti, and Fe) based on pressed pellets of reference coals, allowing semi-quantitative and, at times, quantitative analyses. The influence of core curvature and surface roughness compared with an ideal flat-surface was also examined using model samples, and their influence on the apparent sample composition evaluated.

Quantitative mineralogical analysis using a Rietveld-based X-ray diffraction method has been carried out on a succession of Permian coal seams and associated strata in a small but structurally complex area of the Gloucester Basin, New South Wales, to identify criteria that will assist stratigraphic correlation. The coals are relatively rich in mineral matter, which is dominated by quartz, illite and interstratified illite/smectite of detrital and pyroclastic origin. However, the mineral matter in the coals typically contains higher proportions of kaolinite and lesser proportions of illite than the associated noncoal strata, suggesting at least some leaching and reprecipitation of aluminosilicates in the original peat swamp. When considered on a quantitative basis, several of the seams contain distinctive assemblages in their mineral matter that can assist recognition of the seams in subsurface studies. These include an increased abundance of pyrite and feldspar in the marine-influenced upper Glenview seam, an increased abundance of well-ordered kaolinite in the upper Bowens Road seam, and a higher proportion of quartz in the lower Avon seam. The Roseville seam also contains measurable proportions of phosphate minerals, which are not detected in the other coal beds. Used in conjunction with other factors, quantitative mineralogical studies using XRD thus appear to be sufficiently sensitive to allow discrimination between individual seams in a sequence, even though the coals contain an abundant overprint of detrital and pyroclastic mineral components.

A method for calculating a normative mineral distribution, based on the major oxide percentages, has been developed specifically for clastic sedimentary rocks and coal ash. Unlike previous methods, SEDNORM allows some variation in the method of normative calculation depending on the sample type and the range of chemical data available. Options available include changing the clay chemistry, including or excluding certain minerals and, in the absence of certain component analyses, allowing sufficient CO2and H2O to be added to the system to form selected phases such as calcite until the associated components are exhausted. The method has proved successful for a range of sediment types including sandstones, shales, and carbonate rocks.

A study of the Narrabeen Group in the southern part of the Sydney Basin has provided a more complete understanding of the conditions of deposition in the area during the Lower Triassic. The sedimentology of the sequence indicates that several different types of fluvial deposits are represented, with an upward succession from piedmont conditions with braided streams to a swampy deltaic plain. This sequence is interpreted as the onshore portion of a slow marine transgression, probably brought about by declining erosive activity in the hinterland.The palaeocurrent pattern shows that drainage was principally to the south-southwest, parallel to the basin axis, and the lateral transition from quartzose to lithic sediments across the basin can be interpreted as a blending of sediment from western and northern source areas. In addition several influxes of material from a source east of the present coastline are indicated, with reworked volcanic debris being introduced into the south coast district. This southeasterly source area did not greatly impede the drainage of the basin during lower Narrabeen deposition, but was responsible for a major diversion of stream patterns as the topmost beds were laid down. This diversion was completed by a northeasterly drainage pattern during deposition of the overlying Hawkesbury Sandstone.