Defining ancient local mining and metallurgical activities through a combination of metal palaeopollution and archaeological evidence: a case study at central Galicia (NW Spain)

Archaeometallurgy in Europe 2024

Falun. Suecia
Congreso. 2024

Northwest Iberia has been an area of intense mining and metallurgical activity since prehistoric al times. However, the apogee of Roman mining activities in the area has, to some extent, outshined the importance of metal extraction and production processes outside this period.

This study approaches the diachronic development of past mining and metallurgical activities at central Galicia through the combination of palaeoenvironmental, archaeological and historical approaches.

A peat core from a minerogenic peatland (‘Cruz do Bocelo’, NW Iberia), spanning the last 3000 years, was studied by integrating geochemical (XRF, Pb isotopes) and palynological evidence. The most remarkable peaks in the lead anthropogenic signal occurred during Roman, Medieval and Contemporaneous times. Although Roman and Contemporaneous signals could be related to regional processes, the high intensity of the medieval pollution peak, something relatively unusual for the Northwestern Iberian context, together with its lead isotope signature, were interpreted as evidence of local mining and metallurgical operations.

Catalogued mining and metallurgical evidence in the area (considering a radius of 30 km around the peatland) consists of 35 undated open pits, in areas with contrasted mineralogies, likely indicative of a variety of ores (probably gold, tin and iron), 8 references to lost remains related to iron metalworking (blacksmiths and hydraulic mills) and ‘A Roxida’ iron slag heap. We will present the available information on all of them to evaluate their possible connection to the metal pollution detected in the peatland, although we will mainly focus on two particular cases which have been indirectly dated by their mention in medieval civil and ecclesiastical texts: i) a group of three open pits called ‘As Grobas’ and ii) a production site known as ‘A Granxa de Constantin’; and on ‘A Roxida’ iron slag heap, in which a preliminary analysis to characterise and date the slags is being performed.

This study highlights the value of small minerotrophic peatlands, which usually have a small source area, as ideal contexts for the detection of local patterns of environmental change that may be not reflected in environmental archives with a higher source area and emphasises the importance of approaching past metal extraction and production from a multidisciplinary perspective.