Gold in the historic copper deposits at Flatschach, Styria

Thomas Leitner

Research output: ThesisMaster's Thesis

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Abstract

The project area is located north of Knittelfeld (Bezirk Murtal, Styria), at Schönberg and Tremmelberg. In this historic mining district copper was mined from vein type Cu deposits. The veins are hosted by medium-grade metamorphic rocks (various gneisses, metabasites etc.) of the Austroalpine basement and are NNE-SSW to NE-SW oriented with steep NW dip. These deposits are currently re-investigated by Noricum Gold Ltd for their gold contents. During extensive fieldwork in summer 2011 a new geological map (1:10,000 scale) was prepared and the lithologies, the geological structures and former mining activities were documented/analysed. In a next step a microscopic study of the main lithologies (polarisation microscopy on thin sections) was made and ore samples (polished sections) were investigated using reflected light microscopy and an EMPA analyser. Most sections are from archive material from Universalmuseum Joanneum and Prof. W. Paar’s private collection; a few new samples collected from dumps were included in this study. Three paragenetic stages can be distinguished. All three stages are gold bearing. Stage 1 includes the primary hydrothermal ore mineralisation of the veins. Gold of this stage is typically associated with the Fe-rich sulfides chalcopyrite, pyrite and arsenopyrite. Stage 2 includes Cu-rich Fe-poor sulfides like digenite, anilite, covellite etc. and the rare Cu arsenides domeykite and koutekite. Gold of Stages 1 and 2 has similar chemical composition ranging from pure gold (95% Au) to electrum (~70% Au, ~30% Ag). Stage 3 is characterized by a strongly oxidised alteration assemblage with hematite, cuprite, and various (not determined in detail) Cu- and Fe-hydroxide and carbonate minerals. Gold of Stage 3 is Ag-rich electrum and has higher Hg contents. The Cu-(Au) deposits in the Flatschach area show some similarities to orogenic lode gold deposits, however they show an unusual subsequent alteration overprint (e.g. Cu arsenides of Stage 2; oxides of Stage 3). Low temperature hydrothermal as well as supergene processes are possible causes of this later alteration, which both mobilised gold.
Translated title of the contributionGold in den historischen Kupferlagerstätten bei Flatschach, Steiermark
Original languageEnglish
QualificationDipl.-Ing.
Supervisors/Advisors
  • Raith, Johann, Supervisor (internal)
Award date22 Mar 2013
Publication statusPublished - 2013

Bibliographical note

embargoed until 06-11-2017

Keywords

  • gold
  • Flatschach
  • ore
  • copper
  • orogenic lode gold deposit

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