Montangeologische Bearbeitung der polymetallischen Eisenerze am Steirischen Erzberg
Research output: Thesis › Master's Thesis › Research
The distribution of polymetallic mineralisation at the Styrian Erzberg was investigated in terms of structural geology, mineralogy and geochemistry. A field study was performed mapping 14 benches with a focus on the southeast part of the pit mining area as well as the north-eastern part by following the Zwischenschiefer outcrop. Geological structures were measured and samples taken between benches Sybold and Vorauer for geochemical and microscopic analyses. Special care was given to prominent fault systems, which are usually middle-steep to steep dipping and show similar macroscopic appearance. The presence of a plastic, chlorite bearing fault gouge is typical. Georeferenced data of structure records and sampling were integrated into a database for further processing. Evaluation of the determined faults using stereo-net and Geovia Surpac allowed the identification of 7 different fault sets. A favourable orientation of the polymetallic mineralisation striking E-W to SE-NW is connected to an extensive fault system of Alpidic age, which can be followed down to the hanging wall of the porphyroid. The resulting three dimensional representation of the acquired dataset allows visualisation of the affected areas. Thin sections were prepared and revised for optical analysis using transmitted and reflected light microscopy, SEM and microprobe application. In siderite and ankerite ore, as well as in vugs and veins, intergrowth of pyrite, hematite, chalcopyrite, siegenite and cinnabarite were found. A relative chronology of the metals could be established taking siderite and ankerite generations into account. Shear bands comprised of sericite, chlorite, quartz as well as accessory appearance of rutile, apatite and zircon was common. 83 samples were analysed by the in-house laboratory of the VA Erzberg for major elements and Actlabs, Canada for trace elements. Due to contamination in the process of sample preparation, the results for chromium, cobalt, molybdenum and nickel were found unreliable and excluded from further evaluations. In siderite and ankerite ore, enrichments of germanium, indium, selenium and mercury can be observed. After classifying the geochemical samples based on their lithology, a statistical analysis using correlations after Pearson and Spearman was performed to indicate dependencies and relationships between occurring elements. The results show trends within the distribution of polymetallic mineralisation, which will help to assist in the planning and development of the open-pit.