volumes of rock into which the gold-bearing solutions have penetrated along multitudes of crevices. The problem of getting the best results in such veins is essentially one of concentrating the values. The peculiar character of the ore renders concentration difficult, if not impossible, by any method other than hand sorting. Ordinarily the concentration of ores may be effected cheaply by mechanical means, depending on the difference in specific gravity between the valuable and the worthless minerals. In the case of Cripple Creek ores this difference can not be depended upon. When the rock is blasted, a large part of the valuable material in the seams is reduced to an extremely fine powder, practically the lightest part of the mass; another part of the values will adhere to the rocks, while another small part is probably heavier than the average.'

Further details of gold and silver milling methods are given in the description of stamp-milling practice under the head of Plate Amalgamation.

The concentration previously described was that applied especially to the sulphurets resulting from stamp-milling gold and silver ores. Under the present heading the treatment of lead-silver ores is dealt with in particular.

Probably the best illustration of the practice in concentrating lead-silver ores is that of the Coeur d'Alêne region, Idaho. Extracts from J. R. Finlay's paper on the Mining Industry of the Coeur d'Alêne, Idaho, are given below:1

"The process employed is substantially the same at all the mines and consists of coarse crushing and separation by jigs. Most of the ores contain the galena in segregated streaks of practically clean material, which separates under crushing, and is easily caught. The difficulty increases greatly when the galena is intimately mixed with iron carbonate, zinc-blende and quartz. Such ores require much finer crushing, and the use of a much greater number of vanners, buddles, shaking tables, etc., to separate the slimes. The following description of the process at the Standard mill will serve as a concrete example of the best current practice:

“The crude ore from the mine is dumped from railroad cars into a bin of about 600 tons' capacity, whence it is fed by gravity to a No. 5 Gates crusher, which reduces it to something over one inch diameter. From the crusher a 15-inch belt conveyor carries it to another bin, whence it passes by gravity to the roughing-rolls, which reduce it to pieces of to inch in diameter. From the T. A. I. M. E., Vol. 33, pp. 256-270, 1903.

roughing-rolls it is elevated to a double set of trommel-screens, which size it into an 'oversize' of more than 15 millimeters diameter, and into sizes which pass through 15, 10, 7 and 3 millimeter screens. The fines which pass the 3 millimeter screens are not jigged, but go at once to V-boxes or hydraulic classifiers. The slimes passing over the V-boxes go to settling-tanks, where the heavier material is caught and sent to Wilfley tables and Frue vanners. All the tailings from Wilfleys and vanners, together with the overflow from the settling-tanks, go to a canvas' plant of 52 tables of 6 square yards each. Material caught on the canvas-tables is reconcentrated on two Wilfley tables.

"Returning to the coarse material classified by the trommels, the oversize, or what passes over the 15 millimeter screens, goes to the coarse or 'bull' jigs, and what passes through the 15, 10 and 7 millimeter screens goes to finer jigs.

"Part of the tailings from the coarse jigs is retained as middlings,' to be further treated, and part is allowed to go directly to the creek as worthless. The middlings thus saved are passed through fine rolls, and then to Huntington mills, which reduce the pulp until it passes a 40-mesh screen.

"The finer jigs, i.e., the 15, 10, 7 and 5 millimeter jigs, also select a percentage of 'middlings,' which are likewise passed through fine rolls, in three sets, according to the coarseness of the material. Thence this material passes to the middling' jigs, which take out some clean ore. All of the tailings from these 'middling' jigs are reground in another set of Huntingtons to 40-mesh. All the material ground by the Huntington mills goes to the Wilfley tables and Frue vanners with the slimes from the settling tanks and V-boxes above described.

"This mill concentrates about 500 tons of crude ore per day. Its machinery consists of the following: A No. 5 Gates crusher; two 15-inch belt-conveyors; six sets of 15-inch by 26-inch beltrolls; four 5-foot Huntington mills; twenty-eight Hartz jigs, arranged in 14 pairs; 2 lines of trommels; an 'oversize' trommel, for middlings; 4 elevators; 18 Wilfley tables; three 4-foot Frue vanners, and 52 canvas tables.

"Power for the main mill is derived from two Pelton wheels, one of 4-foot diameter under a 32-foot head, and one of 6-foot diameter under 235-foot head. A third (24-inch) Pelton, under 235-foot head, runs dynamo for electric lighting, and a fourth runs the Gates crusher."

METALLURGY.

Pyritic Smelting - Process and Practice.

Ores can be decreased in bulk by water and fire concentration. The former method is often rendered impossible or impracticable, as where a partial concentration has been effected by natural means. Rich sulphide ores may be both decreased in bulk and increased in value by fire concentration as results in matte smelting. Ores suitable for smelting may be grouped into two general classes, namely, smelting ores, i.e., ores contain base metals in considerable quantities, and dry ores, or those containing little or no base metals the precious metals predominating.

When lead, copper or zinc were present in the ores in any considerable quantity they became so rebellious that amalgamation was out of the question, and smelting, with its necessary adjunct of concentration, became necessary. As the dressed ores were rich, and contained a large product condensed into a small one, and as this product was usually sold, sampling works sprung up, in which the value of a large quantity of ore was carefully ascertained by processes more or less mechanical, in which, as rapidity of execution as well as correctness of results were necessary, a number of tools for reducing the ore to powder now generally used were invented.

"The first attempts at smelting, as they were usually conducted by persons of no great experience, were not very successful. In fact, the early history of the now very successful American methods is a record of failures. When the smelting of silver ores became a necessity, English methods were first introduced by the Cornish miners, only a few of the German and Swedish furnaces being used. But as the English type of furnaces requires a considerable amount of good fuel, of a kind not generally found in the West, and the use of wood in them requires great skill, shaft furnaces gradually took their place, for the most part for treating ores containing gold, copper, silver, and lead by smelting. Some of the processes adopted from the old works in Europe found themselves in circumstances where the conditions of transportation, labor, or fuel were such that they could not compete with other districts, so that they gradually disappeared, and were succeeded by the same processes in a new dress or in a new phase to such an extent that the plant and the process, as it is now used in the West, would hardly be recognized by their inventors. Little by little it was ascertained that when the ore contained any volatile material, although it might be in small quantities, it would carry off with it very considerable portions of the