Bisbee daily review., 1904-05-14
Jn Particular witb Otber J,s. pcrtant Jnfcrmation from Per. $cnaI Observation e. @e zee
the economic result.
zee ee zee

| tne economic result
 The cost of concentration per ton
 of ore is influenced to a great extent
 by the capacity of the plant, character
 of ore, cost of water and rate of wages
 It will usually vary between s1 and s3
 per ton of ore as il is delivered at
 the mill In very large plants.
 where there are To unusual difficult | ties to overcome, the cost per ton
 may be reduced to less than s1, as at the Lake Superior copper mills. where the ore is crushed under steam
 stamps-over 500 tons per stamp daily and concentration is effected by jigs with intermediate hydraulic ciassifiers to grade the ore to the va rious sizes. before jigging.
 The ores best adapted to coarse con- centration are those inwhich the sul- phi6es of leac, copper, iron and zine occur in coarse masses, like some of sulphide ores of Leadville, and most of those of the Missouri lead-zinc reg
 ion and similar ores elsewhere.
 Where the valuable mineral occurs in finely disseminated crystals of grains, constituting a relatively small percentage of the entire ore, coarse crushing is impracticable, as the rock must be crushed fine to free the min eral from the matrix For fine crush ing, either rolls or stamps are employ nd h.. ho rock passes through ceveral sets of rolls. the last set being known as the furnishing rolls.
 In fine concentration, after the ore has been crushed sufficiently fine generally not finer than through a 30 mesh screen it is passed over one or more of the various types of belt concentrators. or tables, puddles, or other flat, cone-shaped devices for ef- fecting a separation of the lighter from the heavier mineral To facili- | tate this. various forms of hydraulic classiiers are employed. There is usually little difficulty in saving the larger particles of this finely crushed ore, but the shines must be handled with care Experience has long since demonstrated that beth coarse and fine sulphides cannot be satisfactorily | separated from the gangue by a single concentrating operation-that is, by concentrating on a single machine. or other-cevice. without first classifying the material to be treated. The classifers all employ water in their operation. and all are based on the same principal that larger and small Ter particles of mineral do not settle with equal facility in a current of water. This enables the coarser par ticles to be taken out or collected at the bottom of classifier. while the finer shines flow cut at the top. These classifiers are made in great variety of form and size, but, as previously i stated, all operate on the same princi- pie. An extensive classifying plant 1 in successful operation was described in the Mining and Scientific Press in the issue of March 2e, 1904, by F. W. Sherman. In this plant seven sepa- rate classifications are made and this l number could be increased if desir i able. This process admits of send ing perfectly classified product to each machine, when further classifca l ton is necessary. In considering the | above mentioned process it should be | remembered that there is a material difference between sizing by means of graded screens and classifying by i water currents. In the former sepa- l ration Of particles of approximating like size is effected, and in the latter, the particles having been sized by l screen, have a tendency to settle in water controlled to a great extent by the relative specific gravity of par ticles of similar size, the heavier be- {. ing able to sink down through gent i iy rising current, while the lighter ma terial held in suspension floate over the next box or flows away to the i waste laundes.-Mining and Scienti- | fc Press.