128 ECONOMIC GEOLOGY 



source of the mercury. The ores of mercury occur in regions 

 of crustal movement and are newer than the disturbed rocks. 

 They are not confined to any particular formation, nor to any 

 type of rock. 



Geographical Distribution. Mercury has a wide geographical 

 range but its occurrence is often in so small a quantity that only 

 a few localities have become actual producers. California has 

 been the only large mercury producer in the United States. It 

 occurs in many western states, New Mexico, Nevada, Oregon, 

 Texas and Utah. 



According to H. Ries, the California ores occur chiefly in meta- 

 morphosed Cretaceous or Jurassic rocks, and some even are 

 as late as the Miocene and Quarternary. The deposits are in 

 fissured zones. Eruptive rocks seem in many cases to be in- 

 volved in the ore formation. At the New Almaden mine a 

 rhyolite dike extends parallel with the ore body. The ore oc- 

 curs along the contact between serpentine and shale, filling in 

 part the interstices of a breccia. Branch fissures have ore-bear- 

 ing channels extending into the country rock. The chief gangue 

 minerals are quartz, calcite and dolomite. The ore is cinnabar 

 with a little native mercury. The new Almaden mine has been 

 one of the most important mercury deposits of the world. It 

 has been worked to a depth of nearly 3000 ft. and the deposits 

 are diminishing in their mercurial content. This locality is 

 named from Almaden, Spain, where the metal has been obtained 

 for years in great abundance. 



The New Idria mine, named from Idria in Carniola, has been 

 worked almost continuously since 1853. The ore occurs in the 

 metamorphic shales and limestones of Lower Cretaceous age. 

 The ore is irregularly distributed between a false hanging wall of 

 clay and a foot wall of shale. The ore is cinnabar-bearing pyrite, 

 with a gangue of silicified and brecciated shales and sandstones. 

 It also occurs as impregnation deposits and in reticulated masses. 

 Below the zone of oxidation the ore body contains tabular masses 

 of cinnabar. Other deposits occur at Clear Lake, Sulphur Bank, 

 and the Great Western mine. At the Great Western mine the 

 ore occurs as chimney deposits in opalized quartz. At Steam- 

 boat Springs, Nevada, cinnabar is intimately associated with 

 hot springs and occurs as impregnation deposits in decomposed 

 granite. In Texas cinnabar occurs in Cretaceous limestone 

 often faulted, in fissure veins with a gangue of calcite. 



