Abstract

Mineralogical and chemical compositions of residual and sedimentary clays (bulk and <2 μm fraction) from the Nelas region (schist, aplite-pegmatites, granites and Tertiary sediments from both Mondego River margins), Portugal, were studied, aiming to establish indicators for raw materials in ancient ceramic provenance studies. The mineralogy of bulk material does not provide a clear distinction between samples. Among clay minerals, kaolinite dominates, except in the aplite-pegmatites where illite prevails. Smectite was only found in sediments of the left river bank.

A more successful result was the geochemical differentiation of clay types. The weathered schist presents greater enrichment in Cr, whereas the clay fraction of aplite-pegmatites shows enrichment in all the chemical elements studied. The sediments and weathered granites are not easy to differentiate; the best geochemical indicators are U (lower contents in clay-size fraction of sediments) and REE patterns in both bulk and clay-size fraction.

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