Topaz as an important host for Ge in granites and greisens

Abstract

AbstractThe composition of topaz from different granites and greisen in the Krušné Hory/Erzgebirge area was investigated using electron microprobe analysis (EMPA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). All topaz grains are rich in F (17.9 19.8 wt.%, 1.73 1.90 a.p.f.u.) and the most important minor/trace elements are P, Ge and Ga. Contents of P up to 1 wt.% P2O5 (0.025 a.p.f.u.) were found in topaz from the strongly peraluminous P-rich magmatic systems at Podlesí. Regardless of genetic type, topaz from granites typically contains 50 100 ppm Ge. The greatest amounts (up to 204 ppm Ge) were found in topaz from quartz-topaz-apatite greisen in Krásno. In fractionated granites and greisens, topaz is calculated to contain 23 87% of the bulk Ge content in the rock. In contrast, topaz does not concentrate Ga. The Ga content of topaz (typically 5 35 ppm in S-type granites, <10 ppm Ga in A-type granites) is usually smaller than the bulk Ga content of the rock. In addition, up to 16 ppm Sc, 23 ppm Sn and >400 ppm Fe may be present.