Geochemical study of clay materials in Fornos de Algodres region (Central Portugal) in an archaeometric view

摘要

Within an ongoing archaeometric project clay materials from Fornos de Algodres region (Central Portugal) have been studied. In this paper the results obtained will be presented with a geochemical characterisation. The main purpose of this research is to identify potential raw materials for pottery production in an archaeological context (3rd millennium BC). The geological context for this research is mainly granites, with quartz, doleritic and aplite-pegmatite veins, and also a schist-greywacke complex. Chemical data of the whole sample and the < 2 μm fraction was obtained by instrumental neutron activation analysis. Dolerites clearly are differentiated from the other lithologies by higher contents of Fe, Sc and Cr, also found in the finer ceramics. The Eu anomaly is higher in granites and aplite-pegmatite veins in the clay fraction and especially in the whole sample. Rb and K are related to the presence of feldspars, which have higher levels in granites and ceramics with coarser pastes. The aplite-pegmatite veins have lower iron content and appear not to be related with the pottery production. Chemical differences between clays allowed the definition of geochemical fingerprints for each material. A comparative study with ceramics point generally to a ceramic production with local raw materials, using two main sources - weathered dolerite veins as the plastic component and weathered granites as the non-plastic addition.