Directions:

Tilkerode was the source of selenium-rich lead ores, which led to the discovery of thallium by Crookes in London. The Tilkerode ore was processed in Oker, Germany {LINK: to Oker}.
This map gives the general area of the East Harz Mountains, the region of interest. The roads of access to the mines (left) are from the east in Hettstedt (right). See following maps.