Clausthalite (PbSe) and tiemannite (HgSe) from the type locality: New observations and implications for metallogenesis in the Harz Mountains, Germany

Clausthalite and tiemannite from the type locality, Clausthal, in the Harz Mountains, Germany, have virtually gone undocumented since their discovery in the nineteenth century. The minerals and their selenide assemblages are here documented in historical samples from the Königin Charlotte mine in the former Clausthal Pb–Zn–Ag mining district. Clausthalite and tiemannite are the main selenide components; naumannite is generally subordinate, whereas klockmannite and eskebornite are accessory minerals. The absence of inversion lamellae in naumannite constrains the formation temperature to < 130 °C, a temperature that is compatible with salbands of tiemannite and clausthalite that occur in the wall rock of bleached and reddened greywacke along a calcite–quartz veinlet. The veinlet calcite and quartz trapped highly saline, Ca-rich brines (26–33 wt% NaCl equivalent), at temperatures between 96 and 212 °C. Tiemannite and clausthalite also form massive to semi-massive pockets. Tiemannite hosts inclusions of celestine, anhydrite and carrollite. This inclusion assemblage indicates that tiemannite precipitated from sulfate-bearing brines that likely originated from the overlying Zechstein evaporitic sediments. Such an origin is reflected in the less radiogenic 87Sr/86Sr values of 0.70914 and 0.71133 for two samples of tiemannite aggregates containing celestine–anhydrite inclusions. The Clausthal selenide assemblages postdated the main sulfide-bearing, polymetallic vein-style mineralisation of the Harz Mountains.