The influence of volcanological and sedimentological processes on diamond grade distribution in kimberlites: examples from the EKATI Diamond Mine,NWT, Canada

The distribution of diamonds within individual kimberlite pipes is poorly documented in the public domain due to the proprietary nature of the data. The study of the diamond distribution within two pipes, Fox and Koala, from the EKATI Diamond Mine, NWT, Canada, in conjunction with detailed facies models has shown several distinct relationships of deposit type and grade distribution. In both pipes, the lithological facies represent grade units which can be distinguished from each other in terms of relative size and abundance of diamonds. A positive relationship between olivine grain size and abundance with diamond size and abundance is observed, indicating that sorting of fragmental kimberlites influences diamond distribution. Though surface geological processes do not control the diamond potential of the erupting magma, they can be responsible for concentrating diamonds into economically significant proportions. A good understanding of the eruption, transport and depositional processes responsible for the individual lithological units and the diamond distribution within them is important for successful resource estimation. This may lead to recognition of areas suitable for selective mining, making a marginal deposit economic.     

Kink Wave Propagation in Thin Isothermal Magnetic Flux Tubes

We investigated the propagation of kink waves in thin and isothermal expanding flux tubes in cylindrical geometry. By using the method of radial expansion for fluctuating variables we obtained a new kink wave equation. We show that including the radial component of the tube magnetic field leads to cutoff-free propagation of kink waves along thin flux tubes.     

Photometric activity and rotational velocities of ux ori stars and related objects

The rotational velocities of young stars of the UX Ori type and related objects are analyzed. It is shown that there is a weak but statistically significant correlation between υsin i and the amplitudes of photometric variability of these stars. It reflects the fact that the brightness variability of this type of star is determined mainly by variations in the column density of circumstellar dust along the line of sight. The latter depends, in turn, on the orientation of the circumstellar disk and is greatest when the disk is oriented edgeon to the observer or at a small angle to the line of sight. Translated from Astrofizika, Vol. 43, No. 3, pp. 329-337, July– September, 2000.     

Sedimentary and drainage evolution of the Condamine Valley Transition Zone (eastern Australia)

The basal succession of the Condamine Valley, which overlays the boundary between the Surat and Clarence-Moreton basins (eastern Australia), contains a clay-rich horizon ‘the Transition Zone’ that marks a pronounced unconformity between the Jurassic Walloon Coal Measures and the Quaternary Condamine Alluvium. This paper provides insights into the tectonic and drainage evolution of the Condamine Valley through integrated analysis of U–Pb ages of detrital zircon from three samples (494 concordant analyses), stable oxygen isotope analysis on eight authigenic clay samples, X-ray fluorescence of primary and trace elements, and hyperspectral mineral analysis from two drill cores (Lone Pine 17 and Daandine 164). The Transition Zone is interpreted to consist of both weathered Jurassic sediments and Cenozoic clay deposits. Two sequential cycles of erosion, deposition and pedogenesis, related to geomorphological and climatic conditions are recognised. Distinctive oxygen isotope signatures of the two weathering fronts demonstrated an initial Early Cretaceous phase (δ¹⁸O?=?11.9–15.7‰ VSMOW) associated with laterisation and possible uplift, followed by Paleogene (δ¹⁸O?=?16.4–17.3‰ VSMOW) silcretisation of reworked Jurassic sediments. Detrital zircon geochronology yielded Jurassic maximum constraints for the age of deposition of three samples that are indistinguishable within error, the oldest of which (163?±?8?Ma from the lateritic profile) corresponds to the age of the underlying Walloon Coal Measures. The two overlaying samples from a silcrete profile and granular alluvium yielded overlapping yet younger ages of 150?±?6?Ma and 156?±?9?Ma, respectively. Vitrinite reflectance used as a proxy for the thermal condition of the coal strata enabled an estimated 2–3?km of burial and subsequent (likely Early Cretaceous) uplift. Geochemical insights from the Condamine Valley correspond to broad-scale climatic and tectonic conditions, suggesting that ‘transition zone equivalents’ and corresponding groundwater dynamics may occur in similar sedimentary settings throughout eastern Australia.