Geochemistry of amphibole asbestos from northeastern Portugal and its use in monitoring the environmental impact of asbestos from quarrying

At Donai, Pena Maquieira, and Mourisqueiro, in northeastern Portugal, amphibole asbestos minerals are associated with serpentinites, amphibole schists and steatitic rocks. In order to assess the environmental impact of these deposits, the Donai quarry and the talc mines of Pena Maquieira and Mourisqueiro were studied in detail, because long-term exposure to amphibole asbestos is known to cause pulmonary diseases. At Donai, tremolite asbestos occurs in shear zones and faults cutting serpentinites, whereas massive (non-fibrous) tremolite occurs as intercalations associated with amphibole schists, and chloritites. Serpentinites from the Donai quarry are mainly tremolite-free. At Pena Maquieira, tremolite asbestos fills faults cutting serpentinites. At Mourisqueiro, actinolite asbestos occurs within amphibole schists and steatitic rocks in a highly deformed zone. Geological mapping, examinations by petrographic microscope and electron-microprobe, and determinations of SiO2, CaO, and MgO for serpentinites, and CaO and MgO for steatitic rocks will help to assess the presence of admixed asbestos within these rocks. The identification of asbestos is essential in order to exploit these serpentinites and steatitic rocks with minimal disturbance of asbestiform minerals.