Bisbee daily review., 1904-05-14
The Concentration
 OF ORES IN
 Two Divisions
THE CONCENTRATION OF ORES isl A PROCESS PRELIMINARY TO SOME SUBSEQUENT
 OPERATIONS.
Selection Of the Method Depends Upon the Character of the ore--The Cost of Concentration Per Ton of Ore is influenced to Great extent By Ca pacity of the Plant.

In most instances the concentration of ores is a process preliminary tC | some subsequent operation of treat ment, as, with few exceptions, the na tive metal is not produced by concen I tration. A notable exception in tht | concentration of native copper from its ores at the Lake Superior copper mines. The sluicing of gold from sands and gravel is rude concentra- tion. effected by the use of water and the simplest mechanical devices. Dia- montis are recovered from their crushed matrix by concentration. and some other gems are obtained, like gold. by sluicing. These, with few others, are the most important ex captions. The metal-bearing ores are concentrated for the purpose of en ly treated. by eliminating the less val uable and generally worthless and lighter banbue.
 There are two divisions in the concen. tration of ores-cCarse concentration and fine concentration That sys- tenn is employed which seems the best suited to the character of ore, and with many ores both coarse and fine concentration is practiced at various stages of the process. The selection of the method, as above stated. de bends upon the character of the ore no: altogether upon it's value or the kind of mineral contained. but upon the physical condition inwhich the mineral sought to be concentrated eX- ists in the ore. An ore in which the mineral il is desired to concentrate occurs in coarse crystals or masses is adapted to coarse concentration, while one in which the mineral ap- pears in finely disseminated grains must be crusher fine in orGer to free the valuable mineral praticles from the matrix. Generally speaking, for coarse concentration at least, rolls are superio. to stamps, as the fromer may be adjusted to crush to any desired nntutcS- 4Atf OAeCl hoN0 A-< series, from coarser to finer.
 The process through which an ore must qass is usually as follows: The ore is delivered to a rock breaker, either jawcrusher or one of the gy- ratory type. From the breaker it passes through rolls tone or more sets), being crushed either dry or wet. The rolls are of several different types: Those which are run ia high speed; those which are at a moderate speed; those having fixed bearings. those adjusted by means of springs; belt driven rolls and geared rolls, and other differences in construction They all crush ore and each type has it's friends-a condition noticeable in every kind of mining machinery.
 From the rolls the ore passes to trommels Gnclined cylindrical of cone shaped revolving screens), which are divided into sections, each provided with a screen of different mesh. through which both ore and gangue AAllCl 04S Vaoo- A1t sized" That is, the ore is mechan- ically and automatically divided into a series of sizes, both particles of mir eral and gangue in each lot being Of approximteiy the same diameter. The purpose of this sizing is to render the subsequent separation of mineral and gangue more complete and easy of ac- complishment.
 From the trommel the ere passes to jigs, each size going to a separate jig It is with jigs as with every other class of mill machinery-there are many types, anG all of them capable of good work in competent hands. The jig is an effective concentrator, and continuously separates the heavy min ersl from the gangue, in a rapid and satisfactory manner. The finest ma terial being treated-that passing the finest jig screens, and the over flow-are known as shines, and this class Of material is treated in the same manner as ores that are crush ed fine. The tailings from the jigs are usually returned by belt convey veyors or elevators 10 rolls or stamps for finer crushing. and concentration, either on figs or on other concentrat- ing machines.
 The matrix, or gangue, must be crushed fine enough to free the sul- phide or other mineral particles or concentration cannot be effected. In the earlier stages of the process the coarser particles. constituting often over 60 per cent of the entire miner al contents of the ore, are separated. and the remainder in recovered later by recrushing and recommendation. The degree of concentration is deter mined as in almost every other phase of milling operations by commercial limitations. Concentration of ores may often be successfully carried to a mechanical point beyond that justified