Arizona republican., 1898-07-16
PROGRESS IN MINING.

Zona. The following On the treatment of low grade ores is taken from the Colliery Engeneer and Metal Miner, from an article on Mining" by H. Van F. Furman, B. M:
 During the past four years there has been a remarkable development of the gold resources of the state of Colo rado. The production of gold in Colo rado in 1892 was $500 ,000, while the production in 1895 was $15,00O, 900, ac- cording to the report of the director of the United States mint The produc- tion of 1896 is variously estimated at from $15, 900 ,000 to $18,0O0, ,00O.
 The present methods for the extrac- tion of gold from it's ores may be class flied as follows:
 Milling Processes - Milling and amalgamatfon; milling and amalgama- tion, followed by concentration; con- amalgamation. tF
 Chemical Processes.-Cyanide leach ing, chlorination. bromination.
 Smelling ProcesSes.-Lead smelting, copper, matte smelting, pyritic smelt- ing. rsi, . fa
 While numerous patented processes have been proposed, those which have proven successful may be considered simply as notifications of the above.
 The ores of California, until consid- erable depth is gained, consist princi- rally of quartz schists carrying free gold. For these ores the California stamp mill is a very successful ma chine, being an effective crushing ap- paratus, and as the amalgamation of the gold is simple this method results, in many cases, in the saving of from so to 90 per cent of the gold contents of the ores. As considerable depth has been gained in many of the mines the Cres have changes to sulphides, the re- suit being that the amount of free gold, or gold which may be saved by this simple amalgamation, is much less than in the upper workings. This has resulted in the introduction of vanners, bump tables or some suitable concen- trating machinery below the amalaga- mated plates, to endeavor to save the escaping su1phides which carry a con- siderable portion of the fine gold. While this method results in an in- creased saving when handling the sul- phide ores, the saving is in many cases far from satisfactory. owing to the difficulty of successfully handling these extremely fine sulphides by concentra, ticn. At present we have no slime saving apparatus which is really ef- fective, and when the difficulty of sav- ing such fine material is seriously con- sldered, it would not appear as though an effective device would ever be ob- tainable
 The surface ores of Colorado are quite similar to those of California ex- cept that the oxidized portion oe our Colorado veins extend to comparatively slight depths (frequently less than 100 feet) while the oxidized area of the California veins is generally much greater, extending frequently % a depth of 700 feet. These varying con. ditions have led to the different meth. ods of stamp milling in vogue, as in d:cated above. With the sulpS.de ores of Colorado, the successrll extraction of the gold by amalamation requires fine crushing and the introduction of amalgamated plates inside of the nor tar. While the utility of the Colorado battery has been disputed by some, the fact remains, as has been fully demon. strated by actual results, that this method gives better returns on our sulphide ores than the California method. The Colorado practice in- wolves fine crushing and this neces- sarily results in the production of a maximum amount of shines The fine crushing of these ores is essential to effective amalgamatfon, as the gold is usually extremely fine, and is inti- mately combined, or associated with the pyrites and other sulphides. This fine crushing is not only an expense, the amount crushed per stamp being much less than in the California prac- tice (about one ton to three tons per stamp per twenty-four hours) but it also results in the production of a large amount of extremely fine sul- 'phides. which generally contain con- siderable gold escaping amalgamation thus entailing loss, as they can only be partially recovered by concentra, tion
 According to the above classification the third method consists of coarse concentration followed by amalgama- tion. This method of treatment is not Few, but until the past few years it has not proven successful for the treatment of the gold ores of Colorado The reason for the failure of the early attempts at concentration are not ciffi- cult to explain.
 (l) As most of our sulphide ores are extremely friable, fine crushing (as stamp milling) necessarily results in the production of large amount oi shines which frequently carry off me. chanically large amounts of the prec. ious metals. By coarse crushing an6 proper sizing, the amount of slime. may be reduced to minimum. By this method most of the contained mar. ticles of sulphides are left in a coarse condition when they can be readily separated from the worthless gangut by comparatively simple and inexnen sive means.
 CD After the separation of thes, heavy sulphides, the tailings, shoult they carry precious metals, which ii
 generally the case with our ores, ar
 in the best possible condition fo treatment by amalgamation They ar already quite finely pulverized, and a