Geossítios
GEO

Mina do Lousal

justificação do valor científico

The Lousal mine operated, to a 500 m depth, from 1900 to 1988, mostly for pyrite (Silva 1968, Matos e Oliveira 2003, Relvas et al. 2005, Matos e Relvas 2006, Oliveira et al. 2006, Matos e Martins 2006, Matos et al. 2008, Matos 2009).
The open pit exposes the gossans (iron hats) and the zones of supergene enrichment of the West, Central, South and Extreme South orebodies. These were exploited until the 1920’s mostly for copper. In 1928 SAPEC starts production of superphosphates in its Barreiro plant (south of Lisbon). The ore, once hand-picked, was crushed, granulated and sorted in a treatment plant, and subsequently transported by railway. The extraction galleries were filled with rubble extracted in quarries located within the current open pit. They were fed to the underground mine through dedicated shafts.
The Lousal mine depicts marked structural complexity, enhanced by late, subvertical, right-lateral strike-slip faults trending N5ºE, with vertical downthrow of the west block, such as the Corona and Poço Miguel faults. The aforementioned sulphide-bearing horizons occur in the flanks of an antiform whose core is occupied by the PQ Group Corona Formation. The orebody is part of the VS Complex. At Lousal VS is composed of 3 main units, from base to top (i) dark gray, pyritic shales with lenses of sulphides (Lousal orebody). These contain subordinate, xistified spilites and felsic metavolcanics, locally with fiamme textures and volcaniclastic facies, gray shales with siliceous nodules and coherent, rhyodacitic volcanics, (ii) siliceous shales with thin layers of cherts and fine, sericitic, strongly xistified acid metavolcanics, and intrusive diabases associated to the upper spilites, iii) spilites, locally as pillow-lavas, with sparse layers of jasper and purple shales.
After closure of the mine in 1988, Foundation Frederic Velge (FFV), which includes the former mine operator, SAPEC, and the Grândola municipality, has started an initiative for revitalization of the mining village of Lousal (Relvas et al. 2005). The initiative includes already a mining museum, a Live Science centre, handicraft production and sales, a restaurant and a comfortable inn. A major, ambitious visiting circuit is being implemented, which will include an underground visit to the mine.
In the bottom of the mine there is an acid water spring (Silva et al. 2005, 2006). The open pit circuit leads already to an underground sector, along the Valdemar gallery, the former explosives storeroom of the mine (Matos and Oliveira 2003).
The Lousal open pit is a geosite of Iberian dimension in the context of the Iberian Pyrite Belt. However, the recent geotourism developments, including the Live Science Centre and the Undergroung Mine Visit project already under construction will render Lousal a prime geosite of international value, with excellent conditions of access and visit.

References:
Matos, J.X., Oliveira, V. (2003) - Mina do Lousal (Faixa Piritosa Ibérica) - Percurso geológico e mineiro pelas cortas e galerias da antiga mina. IGME, Pub. Museo Geominero, nº2, pp. 117-128.
Matos, J.X., Martins, L. (2006) Reabilitação ambiental de áreas mineiras do sector português da Faixa Piritosa Ibérica: estado da arte e perspectivas futuras. IGME, Bol. Geológico y Minero España, v. 117, nº2, pp. 289-304.
Matos, J.X., Relvas, J.M.R.S. (2006) Mina do Lousal (Faixa Piritosa Ibérica). Livro Guia Excursão C.4.1, VII Cong. Nac. Geologia, Estremoz, Un. Évora, Portugal, pp. 23-25.
Oliveira, J.T., Relvas, J.M.R.S., Pereira, Z., Matos, J.X., Rosa, C.J., Rosa, D., Munhá, J.M., Jorge, R.C.G.S., Pinto, A.M.M. (2006) O Complexo Vulcano-Sedimentar da Faixa Piritosa: estratigrafia, vulcanismo, mineralizações associadas e evolução tectonoestratigráfica no contexto da Zona Sul Portugesa. in Dias R, Araújo A., Terrinha P, e Kulberg JC ( eds.), Geologia de Portugal na Ibéria, VII Cong. Nac. Geologia, Univ. Évora, Portugal, pp. 207-244.
Reis, P., Ferreira da Silva, E., Matos, J.X., Patinha, C., Sousa, A.J. E Cardoso Fonseca, E. (2006) - Combining GIS and stochastic simulation to define spatial patterns of variability for lead at the Lousal mine, Portugal. Land Degradation and Development, Wiley Europe.
Relvas, J.M.R.S., Póvoas, L., Costa, T. Matos, J., Varela, T., Lopes, C., Barriga, F.J.A.S., 2005. Project “Underground Visit to the Lousal Mine”: a contribution to Geoconservation and Sustainable Development, IV Int. Symposium ProGEO on the Conservation of Geological Heritage, Braga, Portugal.
Silva, E.F., Fonseca, E.C., Matos, J.X., Patinha, C., Reis, P., Santos Oliveira, J.M. (2005) - The effect of unconfined mine tailings on the geochemistry of soils, sediments and surface waters of the Lousal area (Iberian Pyrite Belt, Southern Portugal). Land Degradation; Development, Wiley InterScience Ed., 16, pp. 213-228.
Silva, E.F., Patinha, C., Reis, P., Fonseca, E.C, Matos, J.X., Barrosinho, J., Oliveira, J.M.S. (2006) Interaction of acid mine drainage with waters and sediments at the Corona stream, Lousal mine (Iberian Pyrite Belt, Southern Portugal). Environ Geology Vol. 50, 7, DOI 10.1007, Springer Verlag, pp. 0943-0105 (Print) 1432-0495 (Online).
Silva, F. (1968) – As Minas do Lousal. Bol. Minas, Dir. Geral de Minas e SGP, 5 (3), pp. 161-181.

Outros valores e sua justificação

The Lousal open pit is the main geosite in this area of mining archaeology. Its trails are complemented by visits to the museum, the Live Science Centre and, in the already near future (early 2012) the underground visit to the as well. The mining environmental impact near the Corona creek and the presence of natural wetlands are an additional aspect to observe on the downstream side of the open pit.