Acknowledgements

The research has been supported by the POCTI Program (Fundação para a Ciência e Tecnologia, Portugal). The authors are indebted to Jocelyn McPhie, CODES, University of Tasmania, Jorge Relvas, Faculty of Sciences, Lisbon, Vitor Oliveira and Carlos Inverno, INETI, Geociências, Alfragide, Portugal and Nelson Pacheco, SOMINCOR, for their support and fruitful discussions in the field and in the laboratory. The work of DRNR has been supported by a grant of Fundação para a Ciência e Tecnologia (Portugal). Figure treatments were made by Filipe Barreira, INETI.