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QEMSCAN® analysis can be applied to bauxite ores, allowing a rapid quantification of mineralogy (including trace detrital phases) and assessment of the individual textural characteristics of the bauxite lithotypes, showing a detailed image of the distribution of economic and non-economic minerals and their intergrowths. The published data on this subject are currently relatively scarce, and are unhelpful for understanding the basic principles and advantages of applying QEMSCAN® analysis to this kind of ore. In this study the QEMSCAN® development work has been applied to the South Italian karst bauxites, which consist of small deposits that are currently uneconomic, but that can be considered as a model analogue for truly economic karst bauxite ores. The representative samples considered for this study come from two different localities: the Matese Mountains and the Caserta district. The mineralogical composition of bauxite has been quantified by combined QEMSCAN® and XRD Rietveld Quantitative Phase Analysis (QPA), as well as with SEM-EDS techniques. Our results show that the QEMSCAN® data allow a detailed textural characterization and add significant information on the major and trace mineral distribution. This methodology can augment or replace other time-consuming quantitative phase analyses for mineralogical studies of bauxites, provided that the SIP (species identification protocol) database has been carefully validated by preliminary use of XRD and SEM-EDS. However, the XRD (QPA) and QEMSCAN® analytical techniques can be complementary for bauxite ore evaluation, and a very powerful tool for exploitation and mineral processing, as shown in several examples. The results obtained with each technique are compared, and the advantages extensively discussed

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The Kabwe Zn-Pb deposit (central Zambia) consists of a cluster of mixed sulfide and non-sulfide orebodies. The sulfide ores comprise sphalerite, galena, pyrite, chalcopyrite and accessory Ge-sulfides (±Ga and In). The non-sulfide ores comprise: (1) willemite-dominated zones encasing massive sulfide orebodies and (2) oxide-dominated alteration bands, overlying both the sulfide and Zn-silicate orebodies. This study focuses on the Ge, In and Ga distribution in the non-sulfide mineralization, and was carried out on a suite of Kabwe specimens, housed in the Natural History Museum Ore Collection (London). Petrography confirmed that the original sulfides were overprinted by at least two contrasting oxidation stages dominated by the formation of willemite (W1 and W2), and a further event characterized by weathering-related processes. Oxygen isotopic analyses have shown that W1 and W2 are unrelated genetically and furthermore not related to supergene Zn-Pb-carbonates in the oxide-dominated assemblage. The δ18O composition of 13.9–15.7‰ V-SMOW strongly supports a hydrothermal origin for W1. The δ18O composition of W2 (−3.5‰ to 0‰ V-SMOW) indicates that it precipitated from groundwaters of meteoric origin in either a supergene or a low-T hydrothermal environment. Gallium and Ge show a diversity of distribution among the range of Zn-bearing minerals. Gallium has been detected at the ppm level in W1, sphalerite, goethite and hematite. Germanium occurs at ppm levels in W1 and W2, and in scarcely detectable amounts in hemimorphite, goethite and hematite. Indium has low concentrations in goethite and hematite. These different deportments among the various phases are probably due to the different initial Ga, In and Ge abundances in the mineralization, to the different solubilities of the three elements at different temperatures and pH values, and finally to their variable affinities with the various minerals formed.

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