Die Geologie des Kraubather Ultramafitkomplexes zwischen Wintergraben und Lobminggraben (Steiermark, Österreich)

Translated title of the contribution: The geology of the ultramafic massif of Kraubath between Wintergraben and Lobminggraben (Styria, Austria)

Roland Prevorcic

Research output: ThesisMaster's Thesis

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The investigated area is situated 15 km southwest of Leoben in the Mur valley. Geologicaly it is located in the ultramafic massif of Kraubath that is part of the Speik Complex which belongs to the Gleinalm Crystalline Complex (Eastern Alps). The Speik Complex is a tectonically dismembered part of an ophiolite sequence and is composed of dunite, serpentinite, harzburgite and orthopyroxenite with layers of chromite and also interlayered with metapyroxenite and amphibolite. The field work was focused on the area between Wintergraben and Lobminggraben in the south of the village Kraubath/Mur. The orientation of the ultramafic complex strikes in SW-NE direction which correlates with the cleavage. The ultramafic rocks exhibit a distinct variation in lithologic composition changing from north to south. In the northern part dunites and harzburgites are predominant interstratified with coarse-grained orthopyroxenites that occur as centimetre- to metre-wide veinlets and pods. This northern layer contains unserpentinized to weakly serpentinized dunitic rocks with the grade of serpentinization increasing southwards. Also metapyroxenite and amphibole bearing rocks can be found in the southern part near the contact to the Gleinalm Crystalline unit. The metapyroxenite consist of clinopyroxene and tremolite bearing rocks in which tremolite arose from clinopyroxene by metamorphic processes. Tectonic structures are related to the orientations of morphological valleys and also magnesite mineralizations are bound to the main fault directions striking in W-E and NW-SE direction respectively. Mineralogical-petrographical investigations were carried out supplemented by geochemical analysis. It could be shown that the highest MgO-contents of up to 47.7% are related to weakly serpentinized olivine bearing dunites in the northern part of Sommer- and Tanzmeistergraben respectively. In this study, the dissolution of different rock types (dunite, serpentinite, orthopyroxenite and laterite) and grain fractions in solutions of 18% HCl at 90°C was investigated. The experiments showed that the fresh dunite was most efficient at extracting magnesium (up to 100%) from the mineral assemblage (especially olivine). The finest grain fraction exhibited the highest solution potential. Furthermore microprobe analysis showed that calcium bearing minerals, such as amphibole and clinopyroxene, are broadly unaffected by the influence of acid and remain in the residue. Recommendations for further exploration include detailed mapping in the area around the northern Sommer- and Tanzmeistergraben respectively, making additional geochemical explorations, as well as investigation of drill cores obtained from these areas.
Translated title of the contributionThe geology of the ultramafic massif of Kraubath between Wintergraben and Lobminggraben (Styria, Austria)
Original languageGerman
  • Mali, Heinrich, Co-Supervisor (internal)
  • Melcher, Frank, Supervisor (internal)
Award date19 Dec 2014
Publication statusPublished - 2014

Bibliographical note

embargoed until 04-12-2019


  • ultramafic
  • Kraubath
  • Speik Complex
  • serpentinite
  • dunite
  • leaching
  • magnesium oxide

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