MINERALOGICAL AND PETROLOGICAL INVESTIGATIONS OF EARLY BRONZE AGE COPPER‐SMELTING REMAINS FROM THE KIECHLBERG (TYROL, AUSTRIA)

Abstract

The prehistoric settlement on the Kiechlberg hilltop is located a few kilometres to the north‐east of Innsbruck, in the Tyrolean Inn Valley. Despite its rather isolated location, a multiphase settlement between the fifth and the second millennium bc was confirmed by archaeological investigations in 2007 and 2008. Metallurgical artefacts, such as copper ore fragments, copper slag and raw copper, as well as finished copper and bronze artefacts, are concentrated mainly in Late Copper Age to Middle Bronze Age layers. The chemical compositions of the slag and raw metals confirm Fe—Zn tetrahedrite–tennantite (fahlore) smelting. The ore was most probably imported from the 30–50 km distant copper ore deposits (mainly fahlore) of Schwaz–Brixlegg, in the Lower Inn Valley. The small amount of slag and the presence of slagged and thermally altered ceramic fragments suggest copper production in small‐scale workshops. Most probably, sulphide‐rich ores were smelted in crucibles in a hearth fire. The process was relatively reducing below the 2Sb + 1.5O2 → Sb2O3 reaction (−8.5 log fO2 at 1100°C), producing Sb‐rich (>10 wt% Sb in metal) raw copper. Inhomogeneous slag remains containing high amounts of sulphide and metal inclusions suggest a poor separation of the metal, matte (copper sulphide) and silicate/oxide melt during the smelting process.