REE contents, REE minerals and Sm/Nd isotopes of granite- and unconformity-related fluorite mineralization at the western edge of the Bohemian Massif: With special reference to the Nabburg-Wolsendorf District, SE Germany

摘要

Fluorite vein-type deposits occur along the western edge of the Bohemian Massif in SE Germany, from Bayerischer Wald to Frankenwald. They are emplaced in various host rock lithologies, as old as Late Variscan granites and low-grade metasediments of late Paleozoic age. The Nabburg-Wolsendorf mining district in NE Bavaria, Germany, used to be the largest in Germany and one of the most important in the world. A minor proportion of fluorite is also concentrated in the Permo-Mesozoic siliciclastic sediments resting unconformably upon the basement rocks near Pingarten. Fluorite is investigated in the present study for its REE variation, the REE minerals associated with it and its Sm/Nd isotope ratios. The primary blue-black fluorites precipitated from aqueous hydrothermal solutions during early stages without noticeable interaction with wall rocks and were poor in REE and Y. The secondary green, white and yellow fluorites formed from remobilization of older fluorite and through the interaction of more viscous fluids with the wall rocks and they are abundant in REE plus Y. Monazite-(Ce) is the major source for the REE re-deposited into fluorite. In a double cross plot, designed during this study and using the Ce-, Eu anomalies and the skewness (fractionation) of the REE pattern, the geological and hydrological evolution of fluorite vein mineralizations are related to the granite and the unconformity, which is the hydraulic reference plane for the fluorite mineralizatioa