A view of the Milky Way arm mixed with some clouds with planet Saturn shinning against the galaxy core, near Scorpius constellation. In the top right corner of the image, a pink/red emission from North America Nebula (NGC7000) is well visible near Deneb star, forming a triangle with the blue star Vega (top center) and Altair star (left center). This mosaic of the Milky Way was captured above a puddle of acid water reflecting the starlight from Scorpius and Saturn, located in Achada do Gamo, that was – since the beginning of modern mining activities in the São Domingos Mine – the center of metallurgical activities on extracted minerals. Already during the 20th century, between the 30s and 40s, a new direction of industrial exploration took place: the sulfur, however much valued, began to be extracted from the copper pyrites through furnaces (Orkla process) in two plants installed in the Achada do Gamo during the years of 1934 and 1943.

São Domingos Mine is located in Baixo Alentejo, about 240 km from Lisbon, in the municipality of Mértola, which recently joined the Dark Sky® Alqueva Route for the great quality of the night sky. The São Domingos mining area is part of the Iberian Pyrite Range and is a decisive source of basic metals (S, Zn, Pb, Sn, Ag, Au, Fe, Co, Cd, etc.) and other elements such as sulfur (S). It has been a sought after place for the extraction of ores since antiquity, with evidence of gold, silver and copper mining in the pre-Roman and Roman times. The pyritic deposit of São Domingos (St. Dominic) was explored in various historical periods, namely: for several centuries of the first millennium BC (Eastern period), during the period between 14 BC and 395 AD (Roman period), during the Islamic period and during the modern period that was initiated in 1858 for the extraction of copper, gold and silver and was maintained until 1966, the year in which the reserves were considered exhausted. During this period, the work was done in the open air up to 120 meters deep, with work continued through wells and galleries up to 400 meters. Over 108 years of regular exploration, more than 20 million tons of materials were removed from the site, producing about 14.7 million tons of waste accumulated in heaps up to 14 meters high with a dozen different materials such as pyrite , gossan, slag, ash, iron oxides, barren rock, sludge, debris, etc. The areas of heaps, slag and channels of water, give the landscape a “lunar” aspect. The heaps are composed of different materials with high levels of metals, such as slag and ash, whose leaching through the rainwater leads to the production of acid mine drainage, usually with an ocher or reddish color.|