ALMADÉN (EN: Almadén; RU: Альмаден) is the mercury deposit in Spain, the largest in the world, and unique according to the quality of the ores. It is developed since the 1st millennium BC.

It is situated on the southern limb of the large (60x40 kilometres) Shilon syncline, which is formed by the Lower Paleozoic schists with three packs of the quartzites, which are often mineralized. The main deposit is confined to one of these packs, to the place of its bending, which is complicated by the oblique fault. The ore-bearing pack (40-60 metres) contains three layers of the ore quartzites (4-12 metres each), which are converging at the depth. The dip of the layers is almost vertical. There is operated (for approximately 50 years) the steeply dipping ore stock. Its length is 650 metres at the surface, its length is 450 metres at the depth of the modern mining (508 m).

The ores are massive, dense; they contain, besides vermilion, the noticeable quantity (up to 1/20) of the native mercury. The content of the mercury naturally decreases with the depth (%): 30-20, 18-12, 7-5, 4-3, 2-1 on the active level. There have been extracted approximately 500 thousand tonnes of the metal. The greatest annual production is up to 2.5 thousand tonnes; the extraction ranges in the 80s within the limits of 1.2-2.0 thousand tonnes. The remaining reserves are evaluated at 250 thousand tonnes. The extraction is performed within the deep underground mines. The system of the development is the overhand stoping with steps, with the selective extraction of the richest parts of the ore depositions (near the hanging block). The roof and walls of the operational workings (the cross section is up to 10x3 metres) are supported by the bolted supports, and are covered with the protective netting, while cementing them at the same time. The native mercury, which is flowing down to the soil of the clearing stopes, is collected separately.