TY - THES

T1 - Geophysical ore prospection at Straßegg (Breitenau,Styria)

AU - Biedermann, Stefan

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - Due to the growing demand for raw materials, it is necessary to continuously explore new mineral deposits. This is time-consuming and expensive, and in some cases also has a major impact on the environment. Alternative ways of meeting the demand for raw materials are therefore becoming increasingly important. For example, known deposits that proved to be no longer profitable in the past can be reassessed for their suitability as deposits with the aid of modern technologies. Such a reassessment was carried out in the Straßegg mining district near Breitenau am Hochlantsch. From the 15th to the 19th century, gold-bearing arsenopyrite, galena and pyrite were mined with the focus of the mining activities being restricted to the Zuckenhutgraben north of Straßegg. Using non-destructive geophysical methods, an area of about 1 km² surrounding the Pramerkogel was investigated for a possible continuation of the gold-bearing arsenopyrite mineralization to the south and possible further mineralizations related to arsenopyrite. Furthermore, these investigations should provide information on possible other mineralization types to be able to use the full potential of this deposit. Based on the areal applied methods of geomagnetics and self potential measurements, two sub-profiles were selected, which were investigated in more detail by the application of geoelectrics. In addition, paleomagnetic measurements were performed on rock samples to determine the magnetic minerals contained therein. For the interpretation of the geophysical anomalies on the one hand already existing geochemical and aeromagnetic data and on the other hand the results of a prospecting program of the company MINREX are used. By comparing the collected geophysical data, several anomaly groups could be determined, which can be distinguished from each other based on their physical properties. The magnetic anomalies can be attributed mainly to the pyrrhotite contained in the rock, subordinately also to hematite and maghemite. By a comparative presentation with the results from geoelectrics and the self potential, increased values of polarizability, specific resistivities up to 400 ¿m and potentials up to -500 mV can be attributed to pyrrhotite. Furthermore, differences in the occurrence of pyrrhotite were found. In addition to vein mineralization, stratiform intercalations are also recognized. The occurrence of self potential anomalies is, besides pyrrhotite, associated with graphite and pyrite. Large potential drops of about 1000 mV were measured in the western part of the area, which are attributed to graphite lenses. These can also be evidenced by the low resistivity values of lower than 10 ¿m and the high values of polarizability with phase angles of up to 70 mrad. Several non-magnetic sulfidic mineralizations can be located in the east of the survey area. These show similar polarizabilities to the graphite lenses but differ in higher resistivities of up to 250 ¿m and generally smaller potential drops. Potential drops of up to 500 mV and resistivity values of 10 ¿m can occur in association with these mineralizations. This is explained by intercalations of graphite. Based on geoelectrics, these mineralizations are interpreted as steeply inclined. By comparison with the main mineralization of the gold-bearing arsenopyrite near the formation boundary described in the literature, a relation with one of the localized sulfidic mineralizations is established.

AB - Due to the growing demand for raw materials, it is necessary to continuously explore new mineral deposits. This is time-consuming and expensive, and in some cases also has a major impact on the environment. Alternative ways of meeting the demand for raw materials are therefore becoming increasingly important. For example, known deposits that proved to be no longer profitable in the past can be reassessed for their suitability as deposits with the aid of modern technologies. Such a reassessment was carried out in the Straßegg mining district near Breitenau am Hochlantsch. From the 15th to the 19th century, gold-bearing arsenopyrite, galena and pyrite were mined with the focus of the mining activities being restricted to the Zuckenhutgraben north of Straßegg. Using non-destructive geophysical methods, an area of about 1 km² surrounding the Pramerkogel was investigated for a possible continuation of the gold-bearing arsenopyrite mineralization to the south and possible further mineralizations related to arsenopyrite. Furthermore, these investigations should provide information on possible other mineralization types to be able to use the full potential of this deposit. Based on the areal applied methods of geomagnetics and self potential measurements, two sub-profiles were selected, which were investigated in more detail by the application of geoelectrics. In addition, paleomagnetic measurements were performed on rock samples to determine the magnetic minerals contained therein. For the interpretation of the geophysical anomalies on the one hand already existing geochemical and aeromagnetic data and on the other hand the results of a prospecting program of the company MINREX are used. By comparing the collected geophysical data, several anomaly groups could be determined, which can be distinguished from each other based on their physical properties. The magnetic anomalies can be attributed mainly to the pyrrhotite contained in the rock, subordinately also to hematite and maghemite. By a comparative presentation with the results from geoelectrics and the self potential, increased values of polarizability, specific resistivities up to 400 ¿m and potentials up to -500 mV can be attributed to pyrrhotite. Furthermore, differences in the occurrence of pyrrhotite were found. In addition to vein mineralization, stratiform intercalations are also recognized. The occurrence of self potential anomalies is, besides pyrrhotite, associated with graphite and pyrite. Large potential drops of about 1000 mV were measured in the western part of the area, which are attributed to graphite lenses. These can also be evidenced by the low resistivity values of lower than 10 ¿m and the high values of polarizability with phase angles of up to 70 mrad. Several non-magnetic sulfidic mineralizations can be located in the east of the survey area. These show similar polarizabilities to the graphite lenses but differ in higher resistivities of up to 250 ¿m and generally smaller potential drops. Potential drops of up to 500 mV and resistivity values of 10 ¿m can occur in association with these mineralizations. This is explained by intercalations of graphite. Based on geoelectrics, these mineralizations are interpreted as steeply inclined. By comparison with the main mineralization of the gold-bearing arsenopyrite near the formation boundary described in the literature, a relation with one of the localized sulfidic mineralizations is established.

KW - Geomagnetik

KW - Geoelektrik

KW - Eigenpotential

KW - Paläomagnetik

KW - Arsenopyrit

KW - Sulfidische Vererzungen

KW - Grafit

KW - Grazer Paläozoikum

KW - Straßegg

KW - geomagnetic

KW - geoelectric

KW - self potential

KW - paleomagnetic

KW - arsenopyrite

KW - sulfidic mineralization

KW - graphite

KW - Paleozoic of Graz

KW - Straßegg

M3 - Master's Thesis

ER -