7: Extensional tectonics and the timing and formation of basin-hosted deposits in Europe

In this paper we review a number of the major basin-hosted ore deposits in Europe and argue that most of them are formed in extensional settings. The mineralizing fluids originated as seawater or as evaporated seawater and migrated downwards through the sedimentary basin and into the basement. In regions characterized by pronounced extension and elevated heat production, the fluids were subsequently expelled along extensional faults. During the Palaeozoic, this circulation pattern caused the formation of the sediment-hosted exhalative Zn-Pb deposits of Meggen and Rammelsberg, similar deposits in Sardinia and the mineralization in the Irish basin. The latter could have been formed during a more prolonged period of hydrothermal activity. In the Verviers (Belgium), Upper Silesian (Poland) and other areas, such fluids could have remained in the deeper subsurface for tens of millions of years. During periods of extensional tectonic activity, the fluids were tapped from the basement to form Zn-Pb deposits, hosted by overlying carbonate rocks, and the copper deposits of the Kupferschiefer in SW Poland.