Abstract U–Pb ages of detrital (n = 2391) and magmatic (n = 170) zircon grains from the Harz Mountains were obtained by LA-ICP-MS for provenance studies and absolute age dating. Results point to a complete closure of the Rheic Ocean at c. 419 Ma. A narrow Rhenish Seaway then re-opened in Emsian to mid-Devonian time (c. 390–400 Ma). Devonian sedimentary rocks of the Harz Mountains were deposited on the northwestern (Rheno-Hercynian) and on the southeastern (Saxo-Thuringian) margins of the Rhenish Seaway. A new U–Pb zircon age from a plagiogranite (329 ± 2 Ma) within a harzburgite makes the existence of oceanic lithosphere in the Rhenish Seaway probable. The Rhenish Seaway was completely closed by Serpukhovian time (c. 328 Ma). Existence of a terrane in the seaway is not supported by the new data. Provenance studies and spatial arrangement allow reconstruction of the thin- to thick-skinned obduction style of the Harz Mountains onto the southeastern margin of East Avalonia (Rheno-Hercynian Zone) during the Variscan orogeny. Detrital zircon populations define Rheno-Hercynian and Saxo-Thuringian nappes. Intrusion of the granitoid plutons of the Harz Mountains occurred in a time window of c. 300 to 295 Myr and constrained the termination of Variscan deformation.

Abstract Some sediment-hosted base metal deposits, specifically, the clastic-dominated Zn-Pb deposits, carbonatehosted Mississippi Valley-type (MVT) deposits, sedimentary rock-hosted stratiform copper deposits, and carbonate-hosted polymetallic (“Kipushi-type”) deposits, are or have been important sources of critical elements including Co, Ga, Ge, PGEs, and Re. Cobalt is noted in only a few clastic-dominated and MVT deposits, whereas sedimentary rock-hosted stratiform copper deposits are major producers. Gallium occurs in sphalerite from clastic-dominated and MVT deposits. Little is reported of germanium in clastic-dominated deposits; it is more commonly noted in MVT deposits (up to 4,900 ppm within sphalerite) and has been produced from carbonate-hosted polymetallic deposits (Kipushi, Tsumeb). Indium is known to be elevated in sphalerite and zinc concentrates from some MVT and clastic-dominated deposits, produced from Rammelsberg and reported from Sullivan, Red Dog, Tri-State, Viburnum Trend, Lisheen, San Vincente, and Shalipayco. Platinum and palladium have been produced from sedimentary rock-hosted stratiform copper deposits in the Polish Kupferschiefer. Sedimentary rock-hosted stratiform copper deposits in the Chu-Sarysu basin are known to have produced rhenium. Although trace element concentrations in these types of sediment-hosted ores are poorly characterized in general, available data suggest that there may be economically important concentrations of critical elements yet to be recognized.

Abstract In the Asse salt mine, a system with relatively small pillars and stopes was excavated between 1909 and 1964. From 1965 until 1978, low- and intermediate-level radioactive wastes were disposed there permanently. Most of the chamber volume (∼3.5 million m 3 ) was exposed to free convergence until 1995, when a backfilling campaign was started using pneumatic transportation of granular salt material. The barrier to the overburden rocks is formed by rock salt that has a minimal thickness of only 15 m in the upper part. The flank dips ∼70°SW. The Asse site has been monitored for decades by displacement observations, stress and strain measurements in the pillars, and recording of the backfill pressure built up in the chambers. Softening and damaging in the pillars and stopes of the mining horizon have led to stress redistributions into the overburden rocks, where rupture processes have occurred. Hence, because of the small dimension of the bearing elements on the southern flank and the close distance to the overburden, far-reaching geomechanical interactions exist.