Arizona republican., 1903-10-17
MODERN CONCENTRATING.
The Percentage of Extraction in Ore
 Treatment.

The endcavor of every mill ana smelter man is to secure as high per ccntage of extraction from the ore he treats as he can possibly obtain eco- no1nically. In former years the gold saved from, what was considered at that time, free-milling ore, was often rot in excess of 50 per cent to 70 per cent. reminders of which are seen in the tailings dumps throughout the mining regions which have in more le- cent time been retreated by the cyanide process. yielding usually from 80 per cent to over 90 per cent or the values formerly lost, says the San Francisco Mining and Scientific Press. In smelting much the same thing has occurred. Shelter dumps are not usually worked over. but better results are now obtained In smelling opera tions because of superior furnaces and advanced methods in ore treatment.
 Concentra tion, which has been pro- nounced feature in ore treatment i'll Europe for many years, has really only lately been given the widespread at tention in the United States that its importance deserves, and to concen- tration is due much of the increased percentage of saving. There has been no very material change in recent years in methods Of amalgama ton or in the construction of stamp mills. though the arrangement of mills has been improved, their action becoming automatic in the several stages of ore crushing, from rock breaker to con- centrators. The mills are also built more substantially in most cases than formerly, but these factors influence -f har hh percentage of values saved.
 After amalgamation, whether inside the batteries, or on the outside plates, the object is to save that which es- capes amalgamation. The modern mill man is more flexible than formerly. If his values are high after amalgama- tion he does not hesitate to experiment with a view to making better saving by some other nethods In former years he had fixed ideas concerning almost everything about the mill. He used given amount of water in the battery, rega rdless of any change in character of the ore; the stamps were given a4=stated height of drop and maintained at that whether, according to modern ideas. it was the drop best suited to the ore or not. He employed a high or low discharge and nothing could induce him to change it. Screens were hobby and but one kind was good-the kind he used The result of these rule of thumb arrange ments was usually high-g grade tailings. And the higher grade the ore the greater was not only the amount but the percentage of loss
 In these days of modern ideas, and practice, thought and careful experi- ment, the result is very different. Often we find larger tonnage being crushed than formerly. and the percentage of loss much lower, even in the battery. Concentrating machines have been greatly improved and many devices to secure the highest possible results have been introduced-amongt them hydraul- ic sizers. which make the saving of the valuable contents of the ore. us- ually sulphide minerals of high specific gravity, a matter of easy accomplish ment, the machines and auxiliary de- vices working automatically. Each of these mechanical contrivances, wheth- CT a form of Spitzkasten- or a concen- trating machine, are subject to adjust ment, and this feature adapts them to many variations in the ore.
 After arnalgamation and concentra- tiOn. although over 80 per cent of the values have been extracted, there still remains in many cases sufficient value to justify additional Urea tment by cyanidation and this branch of metal lurgy has added largely to the output of the gold mines within recent years. Not only are additional values saved from the ore as it comes from the mills from day to day, but the old tail- iugs dumps, which for many years possessed no available value, have been successfully trea ted.
 In every branch of ore reduction the same constant effort is being made to save a higher and still higher percent age of values: but there is limit beyond which the mill man can not go with satisfactory economic results. Wherever the cost of securing a higher percentage of extraction exceeds the value of the result obtained the limit Of economy has been reached, and this principle is equally applicable whether it be in reducing the cost of smelting, of saving the ultimate atom of free gold in the battery, in an attempt to extract a few additional cents per ton by the cyanide process or by any other method.