THE BEST GOLD-SAVING PROCESSES.

Otago Witness, Issue 1825, 12 November 1886, Page 12

THE BEST GOLD-SAVING PROCESSES.

The following letter appears in the last number of the Wakatipu Mail to hand. As Mr Evans is manager of the most successful quartz mine in Ofcago, and has had a very extensive mining experience, h:3 views on the important question which he deals with should carry cou» faidorable weight : — Sis,— Having made a strong assertion In re* fcrence to wing gold from quartz crushing & ft

communication in your columns on 15th ultimo, I would like to discuss this subject with any of tbe managers iv Otago or Westland, and ascertain, if possible, whether any improvement can be ma<l« in any of the methods now in vogue in the different mines. I have onfe particular reanou for thi?, and it is—" That it is commonly t-tated by various sections of the press tfoit a very large quantity of gold is lost in the proce-s of mining." That a portion is lost uo one can deny, but what proportion? We often read or hebrstatinientsmadeas if gold were wantonly wasted— which I am quite sure is not the case,— and I firmly believe, so far as comes within the range of my knowledge, that tbe managers of the mines of New Zealand are not a whit behind their compeers of other colonies, or even of America, ho far as I could gather from the Auieiican press. Thus the question arises, why do we differ so widely ? I will partly answer that by saying— Firstly, that those who use mercury in the process of crushing have no finality, and differ widely in themselves in ways of applying it; and secondly, that because I believe the trituration of gold in mercury is the direct cause of a very large percentage of the loss that does take place. I will now give you my reasons. In the first instance, it is well known that the pyrites in the. stone of this colony is, as a rule, exceedingly dense, and that it is usually accompanied with galena, antimony, and sometimes other ores. Now, it is a well known chemical fact that mercury will combine with all these, and that these in Quantity will destroy its property as a gold saver. I think any mauager will admit that. Secoudly. In the process of crushing, the violence of the blows of the stampers (illustrated by the blow of a hammer on a piece of quarts held in the hand) sets free a large ainouut of fumes of bulphur, which at once combine with the water, this latter in its turn being robbed of the sulphur by its stronger neighbour, mercury; as the water passes over the ripples it deposits the sulphur in the bhape of " black scum," completely covering the surface and forming a plat* form, over which unanialgamaterl gold can travel. I am quite aw are that the scum contains gold amalgam, and the richer the htone the more you g«t, but, at the same time, the more you lose. Again, if amalgam as it flows from the stamper box is examined under a microscope, it will be seen to resemble snow — it may be hundreds of craggy particles sticking together by their points, and offering a reMbtance to the stream a long way in excess of the sppcific gravity, and consequently it must succumb, and a large portion of floured silver is the result. Again, in the trituration of mercury in water contaiuingsulphur in any form, the mercury becomes disunited, and h^nce floured silver. The more trituration the more floured bilver, and the more floured silver the greater loss of gold. Then what is floured silver? Simply disunited amalgam; and no process has yet been devised that will save the whole of this said amalgam directly. I am quite aware that it can be united, but not directly. It is in some cases presumed to be, but it is not so. It is to be fouud left behind every process, no matter how extensive or elaborate, and when retorted always yields gold. The loss i« more or less, according to the amount of trituration given.

I think I have said enough to show that mercury and sulphurets will not agree. And now I will ask, What is the character of the gold that is lost ? or, in other words, what is the difficulty in saving gold, or what part gives the trouble and causes so many traps to be s< t to snare it ? Well, simply this, " the fine gold." Then, ia there no difficulty to save the rough ? No, not the slightest in a pure state. You cannot wash it away in the ordinary manner, provjrlJDg you have plenty of clear water. Then it must be conceded that the whole general process in the use of mercury is simply to endeavour to secure the fine gold. As to whether it does so, I think I have clearly shown that exactly the reverse is the case. This is my argument : that the whole expense of the grinding process is not only a waste of money, but that it adds to the loss. Managers are in the position of being obliged to do these things for themselves!, there being no practical authority outride of their circle from which to get information. We hear a great deal about mining schools, but not one of them yet has made any attempt to grapple with the subject further than showing, chemically, what may take place. Tt behoves us as a class, however, to so deal with ♦his matter that we can declare the lo's, and in no sense to follow local mannerisms or to be carried away by prejudice. — I am, &c,

Feed. Evaks, Phconix Mine, Skippers, October 30.