This map shows where silt was laid down untold ages ago. According to its brief description on Wikimedia Commons, it depicts: Loess sediments distribution and its thickness in western part of the Nałeczów Plateau according to Mroczek and Rodzik (2015)
Loess is a fine silt usually deposited by wind or the meltwater of a glacier. The Nałeczów Plateau is in Poland’s Lublin Uplands, and is home, nowadays, to a spa famed for its healing waters. I haven’t looked this up, but it’s a good bet that those waters are rich with minerals from loess deposits. With this map, maybe you could find the waters with the strongest mojo.