The Unesco note this on their site on historical mining heritage in Spain here
Minerals from the Tinto River, Tharsis and Zarza mines are mainly poly-metallic sulphurous masses composed of ferrous-copper pyrite with a high concentration of sulphur and trace amounts of gold and other metals.
These mining basins are formed by different archaeological, architectural, industrial and natural sites, all bearing witness to the different cultures and societies which have populated this land as from pre-historic times exploiting its mineral resources. The main interest here is the print these civilisations have left on the landscape, especially dating back to Roman times and to the British presence in the 19th century.
Shaft mining, gallery mining and strip mining are the techniques represented here. At Tinto River (hereafter referred to as Rio Tinto) we would draw attention to Corta Atalaya and annexed installations at Zarandas, Cerro Colorado and Cerro Salomon and at Tharsis-La ? Zarza, the breeding farms of Filon Norte, Sierra Bullones, "Canaleos" and la Corta de Los Silos. A number of mining and industrial installations are conserved such as pumping buildings, inclined plains, winch workshops, foundries and port-side docks. As a result of this intense mining activity, rich mining and railway heritage has been conserved comprised of sections of track, bridges, viaducts, tunnels, stations and a large number of steam locomotives, train cars for the transport of passengers and minerals and crane and workshop cars.
The best examples of residential building heritage are found at the Rio Tinto site in the areas of Bellavista (featuring unique buildings such as the Anglican Chapel, the Casa Consejo and the Protestant cemetery) and El Valle. Here we would draw attention to British style buildings such as the old English hospital (today the Mining Museum), the Casa Direccion (Administrative building) and the labour agency of the RTCL (Rio Tinto Company Ltd.) (today the Historical Archive of the Rio Tinto Foundation). At the Tharsis site the most important buildings are the General Manager's home, the Visitor's home and the neighbourhood of semi-detached homes and the administrative building at La Zarza.