We determined the boron isotope and chemical compositions of tourmaline from the Hira Buddini gold deposit within the Archean Hutti-Maski greenstone belt in southern India in order to investigate the evolution of the hydrothermal system and to constrain its fluid sources. Tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization. The Hira Buddini tourmaline belongs to the dravite-schorl series with variations in Al, Fe/(Fe+Mg), Ca, Ti and Cr contents that can be related to their host lithology. The total range of δ 11 B values determined is extreme, from-13.3‰ to +9.0‰ but 95% of the values are between-4 and +9‰. The boron isotope compositions of metabasalt-hosted tourmaline shows a bimodal distribution with peak δ 11 B values at about-2‰ and +6‰. The wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources, which entered the hydrothermal system separately and were subsequently mixed. The estimated δ 11 B values of the hydrothermal fluids, based on the peak tourmaline compositions and a mineralization temperature of 550°C, are around +1‰ and +10‰. The isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies, whereas the 11 B-rich fluid is attributed to degassing of I-type granitic magmas that intruded the greenstone sequence, providing heat and fluids to the hydrothermal system.

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Alkaline rocks are worldwide observed as hosts for rare metal (Zr-REE-Nb) minerals. The classification of the ore bearing rock type is challenging due to the fact that textures and mineral assemblage are obscured by post-magmatic alteration. In addition, the alteration causes fine and intricate intergrowth of the ore minerals with associated gangue. Hence, intensive comminution is necessary to liberate the ore minerals, which is one parameter hampering the economical use of this deposit type. This study provides a quantitative mineralogical investigation of the ore bearing rock suite at Khalzan Buregtei as an example of rare metal deposits. R1-R2 multication parameters are shown to be highly appropriate as quantitative mineralogical indicators based on readily available major element datasets to visualize and quantify alteration types of the ore bearing rock suite. The ore minerals were found to be associated with a cluster-forming assemblage of post-magmatic phases. Automated mineralogy was applied to quantify the textural properties of the ore mineral clusters. This finding permits efficient pre-concentration of rare metal ore at coarser particle size fraction, requiring less energy consuming comminution.

Basalts and other mafic rocks are frequently used for road construction. The aggregates have to provide intrinsic mechanical strength and skid resistance. However, smectite contents stemming from alteration processes may deteriorate these mechanical properties considerably because of the resulting contrast in hardness. Quantitative relationships between smectite content, kind of distribution, and aggregate stability are rare except for a recent study by Kaufhold et al. (2012). In this work thirteen basalt and andesite samples from German quarries were analysed by X-ray diffraction (XRD) for their mineral contents (including clay minerals), their cation exchange capacities (CEC) and their resistance against disaggregation in dimethyl sulfoxide. Smectite contents from XRD exceeded those calculated from the CEC regardless of the kind of occurrence of smectite observed in thin sections. The hypothesis that rocks with smectites occurring mostly in patches should differ in terms of CEC and mechanical properties from those rocks where smectites are more disseminated could not be confirmed. However, the amounts of smectite accessible to cation exchange correlated with the DMSO losses. Therefore, the fast CEC determination with Cu-Trien exchange can be substituted for the time-consuming DMSO test.