USEFUL METALS 129 



Tho most important deposits of im -n -iiri.-il on s in the world 

 ,u ( -iiiiMinl in southern Spain at Almaden. The terranes con- 

 sist of highly tilted and metamorphosed quartzites and shales of 

 Devonian and Silurian age. The ore bodies occur in the quartz- 

 ite as impregnation deposits, or as stringers running through 

 the quartzite beds. The impregnations die out suddenly where 

 the quartzites are in contact with the shales. The ore is cinnabar 

 with some native mercury, pyrite and chalcopyrite. 



Another important mine is situated at Idria in Carniola, 

 Austria. It occurs in limestones, sandstones, shales, marls, 

 dolomites, and conglomerates. The ore body is an impregna- 

 tion deposit in the limestones and dolomitic breccias. The 

 ore is cinnabar with a little native mercury. The gangue min- 

 erals are quartz, calcite, dolomite and fluorite. The richest 

 deposits occupy fissures. 



Geological Horizon. The ores of mercury are not confined 

 to the rocks of any particular age. The Almaden mine in Spain 

 is in Silurian and Devonian terranes. The New Almaden in 

 California is in the Cretaceous. The Peru terranes bearing 

 mercurial ores are Jurassic. 



Methods of Extraction. (1) Distillation. The globules of 

 elemental mercury as obtained from its associated gangue min- 

 erals or in pockets in the vein are contaminated with certain 

 impurities that may be left in the retort upon distillation. 

 The metal distills at a temperature of 350 as free from other 

 metals. In this process the metal must be kept free from oil 

 or oily surfaces for these "deaden" the mercury. This proc- 

 ess is utilized in the recovery of mercury from the amalgams 

 of gold and silver obtained in the reduction of the precious 

 metals. 



(2) Roasting. The ores of mercury are crushed and roasted 

 in large furnaces of from 40 to 50 tons capacity per day until 

 the last traces of the metal are driven off. The temperature 

 used is a bright red heat. This high temperature is needed in 

 order to warm the furnace air and the new feeds of ore. In 

 this process the sulphur is oxidized to sulphur dioxide, which 

 when conducted into water forms sulphurous acid used so 

 largely in the manufacture of paper by the sulphite process. 



(3) Sublimation. As calomel volatilizes without suffering de- 

 composition it is only necessary to crush the rock bearing this 

 secondary mineral and drive off the chloride of mercury as a 



