As with most metalliferous ores that have been formed later than the deposition or solidification of their inclosing rocks, the ores of quicksilver are most likely to be found in regions of eruptive activity and complex geologic structure, especially in regions of comparatively late volcanic disturbance. It follows that new deposits are most likely to be discovered within the areas of Tertiary or post-Tertiary volcanic activity, as in the Cordilleran belts of North and South America, the eastern coast of Asia, certain parts of Oceania, and the shores of the Mediterranean. Alaska, Mexico, and the western part of South America seem to offer the greatest possibilities of future productivity, but there is little probability of any important changes in the sources of quicksilver taking place in the near future. The value of a quicksilver deposit can be ascertained as a rule only by mining exploration, and in very few quicksilver mines can any safe estimate be made of “undeveloped” ore. The known facts afford no secure basis for predicting that in the near future some now unimportant district will, within the next ten years, wrest the supremacy in production from Spain, or compete with Austria, Italy, California, or Texas. As regards the principal known sources, it appears that the high-water mark of productivity in California has long been passed, although the mines are still capable of increasing their present production under sufficient stimulus. The Italian output has been increasing of late years, but whether this represents the discovery of new ore bodies or indicates a longer life for the Monte Amiata district is uncertain. A permanent improvement in the political conditions in Mexico, with a continuance of the present, or higher, prices, would probably lead to a notable increase in yield from that country. There is some probability also that Peru may again become an important source of quicksilver.
CHANGES IN PRACTICE
The quicksilver industry is less likely to be modified by changes in mining methods than by improvements in metallurgy. Although very simple in principle, the treatment of quicksilver ores, owing to the mobility and elusiveness of the metal both in the liquid and vaporized condition, is beset with many practical difficulties.
Coarsely broken ore is generally treated in various types of simple shaft furnaces, the fuel being either mixed with the charge or burned in a firebox. Finely broken or pulverulent ore, however, such as forms the larger part of the material from most quicksilver mines, requires different treatment. In Europe the common type of furnace for fine ore is the Spirek and in the United States the Scott-Hütner, or, as more commonly called, the Scott furnace. In both, the ore descends by gravity over tiles of fire-clay so shaped and placed as to permit the flame to pass back and forth through passages under tiles, the passageways or flues being formed partly by the tiles and partly by the ore itself. From the furnace the mercury-laden vapors are conducted through a series of condensing chambers of brick, iron, wood, or other material, in which the metal collects.
When intelligently operated, the Scott furnace is remarkably economical and efficient; but its construction is expensive and requires specially skilled masons. Moreover the furnace is difficult to repair, and once erected can not be moved. These are serious disadvantages to the man of small capital who is developing a new mine, and he usually has to fall back on retorts which are expensive to operate and are unsatisfactory except for relatively small quantities of rich ore.
Of late years attempts have been made in California and Texas to use slightly modified rotary cement-kilns for treating quicksilver ores. This innovation is promising and seems likely to prove successful. Such a furnace, although it may not displace the Scott under some conditions, does not require elaborate masonry structure, and its use may lead to a considerably increased production from the smaller mines.
The condensing systems used with quicksilver furnaces differ greatly and at no two mines in the United States are they identical. The brick condensing chambers formerly so extensively used with the Scott furnace are expensive to build; also the bricks are poor conductors of heat and absorb large quantities of quicksilver. The recent tendency in California has been to replace the brick chambers with large boxes or cylindrical tanks of wood. European practice, followed by one mine in Oregon and one in Texas, favors condensers constructed of vitrified earthenware pipe. The whole question of quicksilver condensation calls for study and skillful experiment. The establishment of a standard of practice would increase production by elimination of much of the loss and discouragement that come from inefficient individual efforts to collect the mercury from the furnace vapors and gases in the most complete and economical way.
POLITICAL CONTROL
The quicksilver industry offers two conspicuous examples of the direct political control of mineral resources. The Almaden mine, whose output is such as in normal times to determine the market for quicksilver, has been owned and worked by the Spanish government since 1645, and the Idria mine up until the close of the war was owned by the Austro-Hungarian government.
The Spanish government, on the basis of competitive proposals, contracts with the successful bidder for the sale of the quicksilver for periods of ten years. For a number of successive periods the contract has been awarded to the Rothschilds of London, the present one dating from June 1, 1912. The contractors bind themselves to sell, in London, the greatest possible quantity of quicksilver, which they take f.o.b. at the reduction plant at Almaden, at prices above 7 pounds per flask, They receive a commission of 1¹⁄₄ per cent. of the amount of the sale; 6 shillings for each flask shipped from Spain to London; and 10 per cent. of the amount by which the sales price exceeds 8 pounds 2 shillings per flask. The Spanish government reserves from the operation of this contract 500 flasks[144] annually for the national requirements of Spain. By this arrangement, although the mine is owned by Spain, the market has been controlled in London. During the war the sale of Almaden mercury was taken over by the Admiralty through Messrs. Rothschild. The quantity received in London from Almaden in 1917 was about 25,000 flasks.