How to reconstruct old mining activities when proper archives like lake sediments are missing? Try overbank sediments in the forehills of the mining region. Two cores (6 and 2.3 m) reveal the dissipation history of trace elements related to hydrothermal ore deposits which were being processed further upstream in the catchment. Both slags of a wide particle size range and adsorbed cations on clay and silt particles help to reconstruct probable mining and smelting phases.
The cores were taken in a delta of the Uferbach stream which drains a 8 km2 catchment of the western Harz mountains where archaeologists found evidence for several mining and smelting phases (Anding, 1977; Bode, 1928). The sediments (fraction < 63 µm) have been analyzed using WD-XRF- (Philips PW 1850) and AAS-techniques (Perkin Elmer 3030 with HGA 400 and 4100) after total digestion. Though absolute concentrations vary between the two cores, the relative element bahavior is in good agreement and shows two distinct signals within the first 2.3 m (Fig. 1).
Another two signals have been observed in the longer core at 2.7 and 4.1 m. Slags from the cores could be grouped (glassy, platy and foamy slag). Each of these give distinctively different geochemical "fingerprints". The slags cannot be differentiated as related to time intervals but rather to different physico-chemical zones of the smelting process. The Pb-rich glassy slags most probably stem from the roast-reaction-process of Pb-ore melting. The ores are most likely from the upper Harz hydrothermal vein deposits (Clausthal, Lautenthal, Buntenbock).
The different signals are attributed to subsequent periods on the basis of three 14C-dated sediment samples, and sedimentation rates calculated from those dates. According to those calculations, the signals represent medieval (1140-1345 AD), carolingian (825-890 AD), roman (425-500 AD) and early (825-625 BC) mining phases respectively, which would be in good agreement with other recent results from montan-archaeological and chemical investigations (Brockner et al., 1990; Klappauf et al., 1990).
Anding, E., Unter dem Harze, Blätter Osteroder Kreisanz Heimatpfl. Heimatkde 900, 16 (1977).
Bode, A., Jahrb. Geogr. Ges Hannover 141-197 (1928).
Brockner W., Heimbruch, G., Koerfer, S., Materialhefte Ur- Frühgesch Niedersachsen 22, 137-151 (1990).
Klappauf, L., Linke, F.A. & Brockner, W., Z Archäol. 24, 207-242 (1990)
Fig. 1: Cu, Pb and Zn concentrations in the cores BKI (straight line) and BKII (dotted line).