Mineralogical and geochemical characteristics of hydrothermal alteration and episyenitization in the Konigshain granites, northern Bohemian Massif, Germany

The late-Hercynian granites of Konigshain underwent multistage hydrothermal processes. Extensive high-temperature late-magmatic alteration is, for exa mple, indicated by low Zr/Hf and an REE pattern displaying the tetrad effec t. Intensive post-magmatic alteration of the granite occurred along brittle structures. At least two main stages of post-magmatic hydrothermal alterat ion are involved. The first high-temperature stage, which is characterized by albitization and/or quartz leaching (episyenitization), resulted from fl uid-rock interaction with late-magmatic fluids that very probably mixed wit h external low-salinity fluids. Quartz dissolution was triggered by vapour condensation and/or the cooling of these fluids (below 450 degrees C) along brittle structures. The high porosity resulting from quartz leaching durin g stage 1 assisted subsequent circulation of low-temperature fluids at stag e 2: the latter is characterized by the chloritization and illitization of episyenites. Almost all major and trace elements were enriched or depleted during one of the main alteration stages. However, Zr, Hf, Th, and Ti were immobile during post-magmatic alteration. The significant depletion of LREE and the enrichment of HREE in albitized samples is controlled by the disso lution of monazite and the new formation of HREE-rich polycrase-(Y) or aesc hynite-(Y) during post-magmatic stage 1. Negative Ce anomalies of episyenit es are associated with illitization and suggest oxidizing conditions during stage 2.