Arizona weekly citizen., 1882-02-19
What Ores Can Be Concentrated.


 A correspondent in Colorado requests
 us to explain in a plain way what con-
 stitutes an ore of gold or silver suitable for concentration Like most simple ! questions. this is not to be completely | answered in few words. The art of con- [ centrating ores can not be taught m an
 editorial paragraph; and only those who understand the theory and practice of
 that art can judge whether given ore | may be successfully concentrated. Even
 such persons, before actually deciding
 this question, need to study the locality
 and conditions, and probably also to make some actual experiments on the
 ore itself If therefore, we undertake to ! state in plain words and briefly, for the ! benefit Of our correspondent, the charac- ] teristics of ores suitable for cUncentra- | tiou, it must not be supposed that We ! have exhausted the subject, or furnished an iufallible guide of judgment.
 1 At the very beginning, 1t should be re- membered. successful concentration IS | to some extent a relative term h. ! stances occur in which the valuable aLd ! the worthless constituents Of an ore be- ! have 50 much alike under mechanical ! treatment that they cannot be separated at all On the other hand, 1t seldom ! or never happens that a complete sepa- ration can be affected by one operation. | The general rule Is, that the attempt to ! get the headings or concentrates free l from worthless material, that IS, to make them rich, throws more or less valuable material into "tailings or middlings'; while the attempt Co obtain tailings free from valuable material leaves a large amount of worthless material in the other grades of product Between these extremes there are many degrees, in- volviug in well conditioned operations, mnch rewOrking of intermediate grades; and the final choice of that combination Of operations which will give the largest net profit, is a matter of no little diff ficulty.
 The basis of all mechanical separa- tiOns except magnetic separation, as applied to some iron Ores) Is the specific gravity of the minerals contained in the crude material treated. Particles of equal size and similar shape but of diff ferent specific gravity, can be separated into classes according tO their gravity; and this Can be done the more perfectly the greater Is the difference in gravity. X heavy mineral like Galena, for iu- stance, can be readily separated from a EhAHAr lLht H4ullt les. ItNul4N lTO4u heavy-spar or Zlnc-blepde. All minerals and particularly those l which yield good deal of fine stuff in crushing, must be classified as to size before they can be successfully classified | as to gravity; for the simple reason that | a large piece of lighter mineral may behave like a smaller piece of a heavier mineral Without going into the math- l ematical explanation of this fact, 1t is sufficient Co cite the well known experi- ence of gulch miners, who find gold and the largest pebbles or bOulders of quartz lying together at the bottom of the chan | mel on the bedrock.
 in the concentration of gold and sil- ! yer ores (thOugh not m that alone l another principle IS involved. Not only l the gravity and the size, but also the l shape of mineral particles determine l theIr behavior. Fine scales for instance, | even of a mineral of high specific gravity l will float or settle but slowly in a cur | rent ui water. notwithstanding their | gravity, and hence may be lost iu the l mass of worthless material, from which ! they might be expected, on the grounds ]. of weight and size alone. Co separate ]. themselves.
 This difficulty is peculiarly felt in the | treatment of silver ores. Gold associated | with pyrItes can often be saved without | excessive loss; at least, enough can be | saved to pay. But the so-called true | silver ores that IS to say, the minerals | which contain silver as an essential con- | stituent, together with many of the ar- | gentiferOus ores of other metals, break | under the stamp into particles which | cannot easily be separated by gravity. SIlyer-glance, ruby silver, argentiferOus gray copper, etc, belong tO this class, and can be concentrated only at so great | a loss that 1t k usually better to hand sort the ores containing them and not attempt to enrich the product otherwise.
 Argentiferous galena is the most easily separated of the silver-bearlng ores. let lt often happens that an ore bearing ga- lena, and showing by assay a considera- ble value in silver also, proves unsuitable for concentration. In such cases, the difficulty usually Is, that the silver of the ore Is not in the galena, but in some ely-disseminated silver-mineral of the brittle class. The simplest way for the common miner to test the question is to take a careful average of his ore, crush 1t to coarse sand, have a sample of it as- saved for lead and silver, then "pan" down weighed quantity as far as he can without losing too much galena, weigh the remainder, and have a sample of that similarly assayed. A comparison of the two assays will show him his loss in lead, hIs loss m silver, and the proportion of silver to lead in the original ore and in the concentrates. IT, for instance, five pounds of ore containing 10 per cent. of lead and 70 ounces of silver Der ton be 1 banned down to one pound, which IS found to contain +O per cent. lead and p ounces silver per ton, the loss has been 20 per cent lead and D per cent. silver; and 1t IS highly probable that. although the use of machinery and skill in ore dressing on a large scale would greatly reduce the loss in lead, the loss in silver would still remain too large for profta- hle working.
 We say, then, tO our correspondent, if yOu want tO know whether an ore con taininc gold or silver, with some heavy mineral such as galena, Zinc-blende, pr pyrItes, Is suitable for concentration, make a rude concentration of it for your self, and thus detcruine whether the gold or silver is contained in the heavy mineral so that mere crushing will not separate #, or whether it IS some finely disseminated associated mineral which cannot easily be saved. IT this crude experiment gives favorable results, you may feel sure that the use of proper machinery and skill would make them still more favorable. UnfavOrable re- suits, of the kind We have indicated above would not be, under all circumstances, absolutely decisive against any attempt at concentration, even though they iudi- cate that you would lose in that way the larger part of the value of the ore. Sometimes a man is willing to throw away two dollars that he may realize one dollar This may happen when the ore is very rich, or when the man Is very poor: and when both these conditions occur together, the temptation to sacri- flee science for cash Is usually OverpOw- ering. High rates Transportation are the most frequent elements in such coercion; and the choice 1f the miner, if fate leaves him any choice, must be de- termined by a calculation in which the art of ore dressing IS not decisive.
 California News.
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