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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



one of the world’s biggest mercury deposits, in the northern foothills of the Sierra Morena, in the Ciudad Real Province of New Castile in Spain. Until the tenth century the deposit was mined in order to obtain cinnabar paint; later Almadén became one of the world’s major mercury suppliers. At present the extraction of the metal reaches 1,500 -2,000 tons a year, about 40 percent of the world total. The total mercury extraction for all the time the deposit has been exploited is estimated at 250,000 tons. The mercury content in the ore dropped from 10 percent in the early period of the exploitation of the deposit to 5–6 percent in the mid-20th century.

The deposit is composed of Lower Paleozoic shales, sandstones, and quartz, compressed into steep folds and broken folds. Some folds are filled with diabasic and quartz porphyries of the Cenozoic age; these porphyries are thought to be at the origin of the deposit. Ore is found in a band 20 km in length; these are linked with quartz seams forming three parallel ore deposits. Some of the ore beds are 300 -500 m long, with a thickness of 3–12 m, and the mines run as deep as 500 m. The ore consists of fine-grained quartz and cinnabar, with admixtures of pyrite, sericite, calcite, dolomite, barytes, zeolites, and bitumens. Almadén is a hydrothermal deposit; the ore is formed through sedimentation from hot mineral water solutions filtered through seams of cracked quartzite.


Park, C. F., and R. A. MacDiarmid. Rudnye mestorozhdeniia. Moscow, 1966. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.