At the Groß Schönebeck site, Germany, an Enhanced Geothermal System (EGS) has been created in Lower Permian (Rotliegend) volcanic and sedimentary rocks. Short-term production tests have shown success of the applied hydraulic stimulation treatments, with an up to 6-fold increase of the initial productivity. Until 2013, extensive circulation tests were carried out with a cumulative production volume of approx. 20.000 m³. A non-linear trend towards lower productivities is observed. Production logging revealed that inflow from the main production zone is variable, explaining short-term changes in productivity. Additionally over time, an obstruction of the well at successively shallower depths was observed. Downhole sampling showed that the well was clogged with scales, mainly comprised of variable amounts of native copper (up to 50 wt%), laurionite and barite. After a partial clean-out of the well the accessible depth of the well could be increased again, allowing for an inspection of the well liner in the Perforation interval. Average metal losses in the order of 7-12 % have been observed. This is in accordance with a geochemical model for the formation of the copper scaling, enabling to unmask the original mineralization of the formation fluid. The results up to now clearly show the challenges related to utilization of this potentially vast geothermal resource in Central Europe, and the need for further research: The initial increase of productivity gained through stimulation treatments was not sustainable. As possible mechanisms of permeability reduction, the formation of a free gas phase by degassing of formation fluid, clogging of pores by copper scales, and impairment of the hydraulic fractures were identified. The observed scaling revealed a previously unquantified composition of the geothermal brines of Rotliegend reservoirs in the North-East German Basin, asking for modified well completion or water treatment concepts.