Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Accessory minerals: a tool for classification of altered granites
Abstract
Comprehensive study of chemical composition of accessory minerals apatite, monazite and zircon, was conducted in order to classify the strongly altered Variscan granites below Tertiary filling of the Sokolov basin. This was necessary for construction of a new geological map of the basin footwall. We compared mineral grains from altered granites from borehole cores and from kaolinised granites from china-clay pits with those from fresh granites cropping out in the surrounding Krušné hory Mts. and Slavkovský les Mts. Zircon is the most stable mineral in the intensively kaolinised granites. Statistically, contents of Al, P, U, Ca are higher in zircons from the younger intrusive complex (YIC) in comparison with zircons from the older intrusive complex (OIC), but zircon composition in each granite sample is very variable. Thus, the use of zircon for classification of individual granite samples is problematical. Chemical composition of apatite and monazite from both granite units is different. Apatite from the YIC is relatively enriched in Mn and Fe, monazite from the YIC is enriched in Th. Based on the mineral data, all studied samples from boreholes were classified as the older granites (OiC).
