Treatment of Auriferous Pyrites.

Cromwell Argus, Volume III, Issue 115, 23 January 1872, Page 6

Treatment of Auriferous Pyrites.

The following excellent article, by Mr J. W. Hunt, appears in a recent number of the Town and Country Journal (a Sydney paper), and we have no doubt it will be read by the miners on this held with interest:— Gold-mining, for want of sufficient capital and experienced men in the treatment of sulphurous ores, containing gold, is far in the rear compared with Victoria. Most Victorian quartz companies have to contend with iron and arsenical pyrites, from which is obtained a great per centage of their gold. So far, quartz-miners in New South Wales have paid little attention to this matter. I have known of instances where pyrites have been encountered, and have entirely baffled the managers ; they lose a great portion of the gold, and a considerable quntity of mercury, which they are unable to account for. In many instances this is caused by using quicksilver in the stamper-boxes ; the pyrites is stamped with it, and by this means it gets divided into minute particles, which are sickened by the arsenic and sulphur contained in the pyrites, and will not unite with the mercury in the ripple boxes, and a great deal of this fine quicksilver, always containing more or less gold, goes off in the tailings. The gold obtained under these circumstances is not unfrequently of a dirty lead colour after being retorted. Some parties have obviated this by burning the quartz, but this becomes a very expensive process, and will not pay with poor stone. Supposing the reef to contain from eight to ten pennyweights to the ton, it will cost from 15s. to 255. per load for burning, so that a very small margin is left for crushing, &c. It is true that the quartz crushes easier, and that gold is more readily extracted, but what is the use of saving one or two pennyweights per ton, and expending 10s. to 15s. per ton more in labour ? The loss of a few shillings per load in the treatment of quartz often has the effect of condemning what would otherwise be a good reef. 1 do not mean to say that using quicksilver in the boxes is altogether objectionable, but in some circumstances it certainly is, and particularly in the cases I have above mentioned. The gratings generally used in this colony are of perforated iron. These are now getting out of date and are being superseded by wire gratings. The advantage of this is obvious. In the pierced gratings such as generally used for crushing purposes, there are about 120 holes to the square inch ; in the wire grating there are over 400 holes of the same size. By using the wire grating a great saving is therefore effected, the crushed quartz having a much better chance of escaping from the stamper-box, once it is reduced sufficiently fine ; with perforated plate the quartz once' reduced to powder, is repeatedly thrown up against the space between the holes, and does not go through near as fast as the stamps are able to reduce it; the consequence is that the discharge being slow, the stamps can only be fed accordingly. The question now arises, which is the best and cheapest mode of heating quartz containing pyrites, See. In my opinion the process now generally adopted in Victoria is undoubtedly the best, viz ; The quartz is crushed through brass wire grating, varying from 200 to 300 holes to the inch ; it then passes over two or three quicksilver ripples, a copper plate, and about 12 to 14 foot of blanket tables ; after which the iron pyrites in the tailings is concentrated by means of the round table or concentrator; the pyrites is afterwards roasted thoroughly and amalgamated in a Chilian mill. As a rule, pyrites containing under 2 ozs. to the ton by essay is not found very remunerative. The average yield of auriferous pyrites may be said to be from 5 ozs. to 12 ozs. per ton, though I have seen some yield over 180 ozs. per ton, after being well concentrated. The gross yield of this ore, that is as it came from the lode, was 2 ozs. per ton, and the loss in the tailings 1 dwt. per ton.