Geowissenschaftliche und aufbereitungstechnische Untersuchungen an ausgewählten Pegmatiten und deren Nb-Ta-Vererzungen in den Ostalpen, Steiermark, Österreich

Translated title of the contribution: Geoscientific and mineral processing studies on pegmatites and their Nb-Ta mineralization in the Eastern Alps, Styria, Austria

Stefan Ahrer

Research output: ThesisMaster's Thesis

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This master thesis is part of a FFG-project “Optimizing the prospection methods for the search of primary Coltan deposits in Austria”. Spodumene bearing pegmatites from four localities of the Eastern Alps were investigated. They are situated in the Rappold Complex of the Upper Austroalpine Koralpe-Wölz nappe system. The Permian pegmatites lie (sub)concordant in gneisses, micaschists, amphibolites and marbles. Their thickness varies from a few decimetres up to ten metres and their lateral extension is from a few up to more than hundreds of metres. Field work confirmed zoning of the pegmatites, which is defined by different mineral assemblages, modal mineralogy and / or grain size. The pegmatites were geologically mapped and samples were taken from the individual pegmatite zones. The samples were then petrographically and mineralogically characterized. For separating the heavy minerals different beneficiation methods were tested and heavy mineral concentrates were prepared. The comparison of different methods shows that the fast and cheap beneficiation using a jaw crusher and gold washing pan leads to reasonable results with respect to concentrating Nb-Ta-minerals for follow-up mineralogical investigations. The heavy minerals, especially the Nb-Ta-minerals, were analysed using Mineral Liberation Analysis (MLA) and the electron microprobe (EMPA). In addition to columbite-tantalite, minerals of the pyrochlore-supergroup but also other rare Nb-Ta minerals were found. Most of the Nb-Ta-minerals are zoned. There are different types of zonation; oscillatory or patchy zoned grains are often replaced by younger (commonly Ta-rich) zones. The pegmatites show geochemical fractionation. For estimation of the degree of fractionation muscovite was separated from pegmatite samples and the major elements were then analyzed with EMPA and the minor elementes with LA-ICP-MS. Differences in the fractionation of the individual localities/ single outrcrops and zones at one locality are best seen in the elements potassium, rubidium and thallium. Samples from the higher fractionated zones/samples are more likely to be mineralized (i.e., containing Nb-Ta-minerals) than those from lower fractionated ones. At outcrops with and without Nb-Ta-mineralized samples the mineralized sample always is from the higher fractionated zone. At a value of K/Rb below about 40 all but one of the samples studied contain Nb-Ta minerals. Very low K/Rb-ratios of muscovite are therfore a good indicator for Nb-Ta mineralization. In contrast, the absolute Nb-Ta contents of muscovite from pegmatites are poorly correlated with fractionation parameters and are no unequivocal positive indicator for Nb-Ta-mineralization in pegmatites.
Translated title of the contributionGeoscientific and mineral processing studies on pegmatites and their Nb-Ta mineralization in the Eastern Alps, Styria, Austria
Original languageGerman
  • Raith, Johann, Supervisor (internal)
Award date24 Oct 2014
Publication statusPublished - 2014

Bibliographical note

embargoed until null


  • pegmatite
  • coltan
  • Nb-Ta-minerals
  • muscovite
  • trace element analysis

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