Applied Earth Science: Transactions of the Institutions of Mining and Metallurgy

The geological mapping of central Australia – an area some 1500 km by 1000 km – began in 1950, was completed in 1979, and formed part of a program to map the continent at 1∶250 000 scale. The program arose out of the Australian Government's realisation during the Second World War that knowledge of Australia's petroleum and mineral resources was meagre and scattered, and that exploration for these commodities needed systematic geological maps. Aerial photography of the continent also started at this time, and proved indispensable to the mapping, as did four-wheel-drive vehicles. The procedure for making geological maps from a blank sheet of paper in the pre-digital age is set out, including the use of aerial photographs, planning a week's work, the necessity for recording all the evidence at an outcrop, compilation, correction and printing of the map.

The Brahmaputra River of Bangladesh is a potential source of significant amounts of heavy mineral (HM) sand concentrates. This study provides the first ever reported characterisation data for a bulk titanium-rich HM sand sample sourced from the river system. The prepared concentrate contained ∼10–15 wt-% HMs with the remaining 85–90 wt-% of the sample comprising silicate and aluminosilicates. Modal analysis for the Fe- and Ti-rich components indicated that the HM concentrate contained 4·7% primary ilmenite, 4·4% Fe-oxide (magnetite), 0·91% titanomagnetite, 0·94% titanite and 0·08% rutile. Quantitative analysis of the ilmenite component showed the TiO₂ content of the ilmenite was within the range 40–52 wt-%TiO₂ (average ∼48 wt-%TiO₂) with major impurities including MnO (1·83 wt-%) and MgO (0·20 wt-%) and minor impurities being Al₂O₃ (0·02 wt-%), Cr₂O₃ (0·03 wt-%), SiO₂ (0·08 wt-%) and V₂O₅ (0·08 wt-%). Based on the composition of ilmenite and current specifications regarding ilmenite compositional purity, the most likely method for processing would be via the sulphate route.

Gravity recoverable gold characterisation methodologies are the single- or three-stage tests, which generally use a standard feed sample mass. A case study of low-grade coarse gold-dominated mineralisation is presented that demonstrates the high variability of test results using different sample masses. Samples were processed using the single-stage test and subsequently entire development rounds were batched through a plant for comparison. Unsurprisingly the results indicate that the small (≤50 kg) test samples grossly understate plant gravity recoverable gold and display poor precision. Larger samples display improved precision, but still understate plant gravity recoverable gold. The small mass samples are unrepresentative as they do not contain the full gold particle size distribution. Poor representivity is enhanced by gold particle clustering. Small samples generally capture finer more abundant and disseminated gold particles, but rarely contain clustered gold. The use of standard GRG test sample masses is challenged. Test work should be based on spatially distributed representative field samples, that if required are split to representative sub-samples for testing. An early stage gold particle size characterisation programme is required to optimise sample mass and improve representivity.

All available data should be used to build a geostatistical model. In underground mining, data have different support volumes: drillhole data are defined at a quasi-point support, while production data represent tonnes of ore mined during a period of time (stopes). Due to the support difference, production data are frequently ignored to update the block grade model. We propose a block kriging approach to combine these two sources of information (point and volumetric support data). A synthetic underground mining case is presented. Two estimation scenarios are evaluated: the first considers only drillhole data, while the second considers both drillhole and production data. Results show that the use of production data improves grade estimation. The improvement is more pronounced where diamond drillholes are sparsely located.