©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at JAHRBUCH DER GEOLOGISCHEN BUNDESANSTALT Jb. Geol. B.-A. ISSN 0016–7800 Band 140 Heft 2 S. 193–250 Wien, Oktober 1997 Ground Geophysical and Geological Mapping in the Central Part of the Moldanubian Pluton IVAN GNOJEK & ANTONÍN PÿICHYSTAL*) 57 Text-Figures, 5 Tables and 1 Plate (in pocket) This paper is devoted to the memory of Dr. HERBERT HEINZ Österreich Tschechische Republik Moldanubikum Moldanubischer Pluton Bodengeophysik Bodenmagnetik Gammastrahlenspektrometrie Österreichische Karte 1 : 50.000 Strukturen Blätter 1, 4–6, 16–18, 33–35 Anomalien Contents Zusammenfassung ...................................................................................................... 194 Abstract ................................................................................................................. 194 1. Introduction ............................................................................................................. 195 2. Area Delimination, Survey Objectives ..................................................................................... 196 3. Review of the Previous Geological Investigations .......................................................................... 197 3.1. Mapped Parts of the Area A (Liebenau – Karlstift, SW Surroundings of Weitra) .......................................... 197 3.2. Northern Part of the Area B (Litschau – Kautzen – Heidenreichstein) .................................................... 198 4. Ground Geophysical Methods Applied .................................................................................... 198 4.1. Magnetic Susceptibility Survey ...................................................................................... 198 4.2. Ground Magnetometry .............................................................................................. 199 4.3. Ground Gamma-Ray Spectrometry .................................................................................. 199 4.4. Brief Data Processing Remarks ...................................................................................... 199 4.5. Staff ............................................................................................................... 200 5. Results of the Ground Geophysics ........................................................................................ 202 5.1. Area A: Freistadt – Gmünd ........................................................................................... 202 5.1.1. Magnetic Susceptibility ....................................................................................... 202 5.1.2. Geomagnetic Field Anomalies ................................................................................ 203 5.1.3. Distribution of Natural Radioactive Elements ................................................................... 204 5.1.3.1. Potassium Distribution ............................................................................... 207 5.1.3.2. Uranium Distribution ................................................................................. 208 5.1.3.3. Thorium Distribution ................................................................................. 210 5.1.3.4. Derived Ratio Parameters ............................................................................ 212 5.2. Area B: Schrems – Litschau – Kautzen ................................................................................ 214 5.2.1. Magnetic Susceptibility ....................................................................................... 214 5.2.2. Geomagnetic Field Anomalies ................................................................................ 216 5.2.3. Distribution of Natural Radioactive Elements ................................................................... 221 5.2.3.1. Potassium Distribution ............................................................................... 225 5.2.3.2. Uranium Distribution ................................................................................. 225 5.2.3.3. Thorium Distribution ................................................................................. 227 5.2.3.4. Derived Ratio-Parameters ............................................................................ 227 *) Authors’ addresses: IVAN GNOJEK: Marie Hübnerové 42, 62100 Brno, Czech Republic; ANTONÍN PÿICHYSTAL: Masaryk University, Faculty of Science, Kotláˇrská 2, 61137 Brno, Czech Republic. 193 ©Geol. Bundesanstalt, Wien; download unter www.geologie.ac.at 6. Results of Geological Mapping ........................................................................................... 229 6.1. Mapped Parts of the Area A (Liebenau – Karlstift, SW Surroundings of Weitra) .......................................... 229 6.1. 1. Quartz Dykes ............................................................................................... 231 6.1. 2. Mylonites, Ultramylonites and Mylonitized Granites ........................................................... 231 6.1. 3. The Weinsberg Granite ...................................................................................... 231 6.1. 4. The Mauthausen Granite ..................................................................................... 233 6.1. 5. The Karlstift Granite ......................................................................................... 236 6.1. 6. Gabbro ..................................................................................................... 236 6.1. 7. Aphyric Variety of the Eisgarn Granite (Fine- to Medium-Grained Two Mica Granites) ............................ 237 6.1. 8. Leucocratic Fine-Grained Muscovite (±Biotite) Granites and Aplitic Granites ................................... 237 6.1. 9. The Nebelstein Granitic Complex ............................................................................ 238 6.1.10. Lamprophyres, Diorite and Granodiorite Porphyries ........................................................... 238 6.2. Mapped Part of the Area B (between Litschau – Kautzen and Heidenreichstein) ......................................... 239 6.2.1. The Eisgarn Granite .......................................................................................... 239 6.2.1.1. The Landstejn ˇ Variety of the Eisgarn Granite ........................................................... 239 6.2.1.2. The »ímeˇ ˇ r Variety of the Eisgarn Granite .............................................................. 239 6.2.1.3. The Aphyric Fine- to Medium-Grained Variety of the Eisgarn Granite .................................... 240 6.2.2. Biotite Gneiss ................................................................................................ 240 6.2.3. The Weinsberg Granite ....................................................................................... 240 6.2.4. Dykes of Pegmatites and Aplites .............................................................................. 240 6.2.5. Greisens and Hydrotermally Altered Granites .................................................................. 240 6.2.6. Minette and Granodiorite-Diorite Porphyries ................................................................... 240 6.2.7. Granite-Granodiorite Porphyries with Anomalously High Magnetic Susceptibility ................................ 241 6.2.8. Felsitic Granite Porphyry, Felsitic Microgranite, Vitreous Microgranite .......................................... 241 6.2.9. The Rubitzko Granite ......................................................................................... 241 7. Study of Opaque Minerals (with Z. LOSOS and M. SLOBODNÍK) ............................................................... 241 7.1. Mafic Dyke Rocks ................................................................................................... 243 7.2. Ore Mineralization Connected with Greisens, Greisenized Rocks and Quartz Dykes .................................... 243 7.3. The Rubitzko Granite ................................................................................................ 244 8. Basic Geochemical Data of the Rocks ..................................................................................... 245 9. Discussion and Conclusions ............................................................................................. 246 Appendix ................................................................................................................ 246 References .............................................................................................................. 249 Bodengeophysikalische und geologische Kartierung im Zentralbereich des Moldanubischen Plutons Zusammenfassung Ein ca. 1110 km2 großes Gebiet des Moldanubischen Plutons zwischen Freistadt (OÖ) und Kautzen (NÖ) wurde zwischen 1991 und 1994 mit bodengeophysikalischen Methoden systematisch untersucht. Boden-Magnetik, In-situ-Erfassung der magnetischen Suszeptibilität und Gamma- strahlen-Spektrometrie wurden bei einem Beobachtungsraster von 8–10 Punkten/km2 simultan durchgeführt. Gleichzeitig wurde auf insgesamt 260 km2 großen Teilgebieten zur Erklärung einiger geophysikalischer Phänomene eine detaillierte geologische Kartierung erstellt. Die Boden-Magnetik erbrachte folgende Ergebnisse: 1) Die große Reingers-Anomalie NE von Kautzen, die auf beiden Seiten der österreichisch-tschechischen Grenze entwickelt ist. 2) Die nordwestliche Fortsetzung der Liebenau-Anomalie, die schon aus der Aerogeophysik bekannt war. 3) Präzisierung der kleinen