In California the principal deposits occur in the Coast Ranges within a belt that is about 400 miles long and has a maximum width of about 75 miles. The known deposits within this area are numerous. About twenty-five of these are at present productive, while probably three times that number which were once productive are now idle. With a few exceptions, the deposits of this main quicksilver belt are in rocks of probable Jurassic age, or in serpentine which is the alteration product of peridotites. The most notable exceptions are the deposits of the Oceanic mine, San Luis Obispo County, and of the Sulphur Bank mine, in Lake County. Many of the most productive mines of the past have yielded no quicksilver from underground work for years.
The most productive mine in California at present is the New Idria, in San Benito County, which in 1917 yielded 11,000 flasks out of a total for the state of 23,733 flasks and for the United States of 35,954 flasks. The New Idria ore comes from two mines, the New Idria proper and the San Carlos. The New Idria has been extensively opened to a depth of about 1,000 feet. In the San Carlos practically all of the known ore lies within 200 feet of the surface. The two mines contributed nearly equally to the total production in 1917, and the average winnable tenor of the ore in that year was 0.32 per cent. It has been estimated that in the two mines there is available 2,400,000 tons of ore averaging 0.253 per cent. of quicksilver.
The New Almaden mine is in Santa Clara County. At present, all the levels below the 800-foot are under water and of late years very little ore has been taken from the old mine. Most of the recent production of the New Almaden Co., Inc., which for 1917 amounted to 2,683 flasks, has come from the El Senador mine, northeast of the old mine, and from quicksilver recovered from ground under old furnaces and condensers. In the New Almaden, the El Senador, and in the neighboring New Guadalupe, which produced 3,100 flasks in 1917, the ore occurs as irregular bodies in serpentine. Close to the mine now being worked by the New Guadalupe Mining Co., and owned by the same company, is the original Guadalupe mine, once highly productive but now long idle.
The Oceanic mine, in San Luis Obispo County, ranked fourth in productiveness in California in 1917, with an output of 1,246 flasks. The ore occurs as an impregnation of sandstone. The average winnable tenor of the ore in 1917 was 0.185 per cent. Other mines in California which yielded from 500 to 1,000 flasks in 1917 are the Great Eastern, the Cloverdale, and the Culver-Baer, all in Sonoma County. Those whose output was between 400 and 500 flasks are the St. Johns, and the Helen, in Lake County.
Nevada contains many widely scattered deposits of quicksilver ore, no one of which has yet been worked on an extensive scale, although a few have been fairly productive for short periods. The ores occur in rhyolite of Tertiary age and in limestone or associated sedimentary beds of various ages from Paleozoic to Mesozoic. The total yield from Nevada in 1917 was 997 flasks, nearly half of which came from the Farnham and Drew mine, east of Mina, which closed for lack of ore near the end of the year. The next mine in point of yield, the Goldbanks, in Humboldt county, is also at present non-productive.
In Texas the principal quicksilver deposits are in the Terlingua district, in Brewster County. The ore occurs along fissure zones in Cretaceous limestones and shales, generally in proximity to intrusive rock. The principal mines are the Chisos, Mariposa, Big Bend, and Dallas.
In Mexico quicksilver deposits in the states of San Luis Potosi, Guerrero, and Durango are said to be yielding considerable quicksilver, even in the present disturbed condition of the country. A quicksilver dealer, testifying at the Tariff Commission hearing in San Francisco, on June 26, 1918, said that 400 flasks a month was being exported into the United States, but a considerable part of this was probably reclaimed quicksilver that has been used in the amalgamation of silver ores.
South America.
—Quicksilver deposits are known in Colombia, Ecuador, Bolivia, Chile, Brazil, Argentina, and Peru, but only those in Peru seem to be of present economic importance, and the production of that country in 1916 was only 62 flasks (2.1 metric tons). The most famous deposits in Peru are those at Huancavelica, particularly those of the Santa Barbara mine, on the east flank of the western chain of the Andes. These have been worked since 1566 and are said to have yielded 46,500 metric tons (1,366,480 flasks of 75 pounds) before 1790. The production in the 19th century has been estimated at 3,500 metric tons (102,865 flasks). The ore bodies are numerous, irregular, and occur in stratified rocks that are cut by igneous rocks. In 1916 the greater part of the quicksilver-bearing ground in the Huancavelica district was purchased by E. E. Fernandini, of Lima, and there appears to be some prospect of a resumption of active mining.