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Geology in Sobrarbe

Mining heritage

Treasures in the subsoil of the upper reaches of the Cinca river have been coveted from Prehistory to the middle of the 20thC: iron, silver, lead and zinc; and also those in the Chistau Valley: cobalt, among other economically valuable minerals. Currently, we only find the remains of those ore deposits, witness to a rich mining heritage, and essential to understanding the history of these valleys..

Nowadays, all the ore deposit mining works in Sobrarbe that have been exploited since ancient times are inactive. Although they were never very rich ore deposits, they are didactic examples of both the geological formation of minerals and of the development of extraction techniques.

Most of these minerals accumulated in seams, which is the name for a long thin layer of a mineral which has been formed between layers of other rocks. These layers were deposited by the subterranean flow of hot water laden with dissolved metals at the end of the Paleozoic and the beginning of the Mesozoic.

Metallic elements (iron, lead, cobalt etc.) in the rocks are usually found scattered, so their extraction is not economically viable. However geological processes can gather those elements together, transport and accumulate them, forming ore deposits (siderite, galena, cobaltite, etc.). In the high valleys in Sobrarbe, this process was carried out by subterranean water flow through a network of crevices in the Hercynian massif.

Mining Works. Lower station of the Luisa aerial cable at the entrance of the Barrosa River Valley.

At the end of the Hercynian, the fracture in Pangea caused a stretching of the earth's crust, enabling the deposition of magma by the Paleozoic rocks, which were the base of the Hercynian Mountains. The increase of temperature caused a metamorphosis and set water in movement through the network of crevices. Water transported metallic particles of the rocks (metamorphic and magmatic) in solution through the cervices, and they were deposited there when water became colder, forming the metallic ore deposits. Different metals were not formed at the same time; the formation order depends on the changes in the chemical composition of the fluid.

Tileworks by Almazorre.

Besides those metallic minerals, the usage of the Eocene turbidic limestones from ancient times is worth mentioning. They were used as ashlar blocks, as can be observed in village centre buildings, constituting a popular architecture that is beautifully integrated into its natural environment. .

Other natural resources have also been used, such as clays (tileworks in the south of the county) or those related to the subterranean waters: salt springs (saltworks in Trillo), thermal waters (the Puyarruego Spring) or sulphurous waters in the ancient spa in Arro.