EXTBACTION OF GOLD FROM PYRITES

Tuapeka Times, Volume V, Issue 224, 16 May 1872, Page 8

EXTBACTION OF GOLD FROM PYRITES

Mr. E. A. Kayser, writing to the " Mine," says : — Our enterprising friend, Mr. Parker, erected a machine, called a buddle, for separating the pyrites from the tailings — a very simple contrivance, but yet a very efficient one. It consists of a large pan, rising from the centre, with pipes running from uprights in the centre to tbe edge of the pan. Into these pipes the tailings are run by a jet of water poured on them in a sort of hopper. The tailings are thus distributed evenly around the pan, and fall on the outer edge. Bound this a sort of scraper stirs up the tailings, their points being directed towards the outer edge, so as to keep the tailings up for some time. Being lighter than the pyrites, they are thus washed down into a cavity in the centre, and carried away. The stream of water in the centre is sufficient to wash away the sand, but not strong enough to move the pyrites further down ;han the circuit of the lowest scraper or knife. When the pyrites have accumulated, ijhe pan is cleaned out, and so the process goes on. There is, another invention for extracting pyrites from failings called Brown and Stanfield's concentrator, which is in use by Mr. Harry Koch in Bendigo, and seems to eclipse the buddlo, being of exceedingly simple construction, and very economical. We are therefore not in want of contrivances for saving the pyrites : and this being the case, the question is, what is the good of saving the pyrites if you do not invent some process of extracting the gold from them ? To scud the pyrites concentrated here to Victoria or England to have the gold extracted would never pay, as the cost of transmission is too expensive. Mr. Harry Koch has erected, besides his concentrator, a machine for extracting gold from pyrites, and he has been rewarded for his enterprise. I know for a fact that he got out of five tons of blanket tailings from Menzie's New Chum, as much as 18oz. 6 dwts. of gold, and the quartz was not nearly as much stained with mundic and pyrites as it is on this field below the water-level. His process is the following: — The pyrites having been separated from the sand, is taken to a heap, and thence put into a sort of hopper, whence it falls upon the floor of the furnace for burning. This fur: nace is in the shape of a half pyramid, built of the best fire-bricks. It rises one foot in height. At the lower part is situated the fire-place, two logs being sufficient to keep it going after the furnace is thoroughly heated. The fire runs through the structure to the top, and being arched .close,. the flame as it passes up is thrown upon the pyrites, which is- spread upon the nar-

row space, and kept continually turned by men with long - handled rakes through small loopholes in the sides, thus presenting it to the action of the flame in such a manner that it is thoroughly roasted, and the arsenic, sulphide, &c, driven off. Tbe moving also causes the pyrites to fall down the incline, and it gradually moves on until it . drops through a small aperture near the fire into a space, whence, | thoroughly burnt, it is taken away to undergo the third and most important process. Having been burned, the pyrites, which before that process was of a blue colour, but is now rusty red, is taken to the house containing the grinding pans (Wheeler's) and there put into the pans. These are more difficult to describe. Around the pan are fixed between the outer edge and the standard pipes knives, or whatever one may call them, which are curved and converge into the centre, where two iron faces meet when the standard is turned round, and between these two iron faces the pyrites passes and is ground, going down underneath, and then by the action rising up through an aperture round tho outer edge, and being brought down to the iron faces again by the action of tho pyrites, for the plates do not move, but guide the pyrites into the centre, whero the grinding machinery is at work, so that they may be said to run into a circle. After the pyrites is ground for some time, and is supposed to be ready, a certaim amount of quicksilver is mixed with it, and tho grinding ,process is repeated until the quicksilver is thoroughly mixed with the pyrites. The pyrites and the quicksilver now pass, when they are supposed to be ready, into an amalgamating pan filled with water, which is continually stirred. The quicksilver containing the gold sinks to the bottom, while the water carries off the dross into af small buddle, designed exactly like the one described. The floor of this buddle is covered with copper, and this catches the smallest particles of silver which may have escaped, allowing the other matter to flow away.

It may be as well to mention a few particulars concerning the furnace which are of great importance. In burning pyrites the great objection is the effect of the arsenical fumes in poisouing the air. Mr. Koch's mode to prevent this is as follows : — The flame, after passing up the passage referred to, on the floor on which is placed the pyrites, has to go back underneath this floor into another flue, which goes back again into the fireplace, and heats the floor on which the pyrites is spread. It then goes up another passage, underneath this again, having thus 120 feet of a passage in the furnace before passing out of it. From the furnace the flame passes to a square chamber next to the chimney stack of the crushing machine. Upon the flame when it enters this chamber a multitude of small jets of water are poured, causing the condensation of all the poisonous matter, and their precipitation to the floor of the chamber in the form of white powder, while the vapour, cleared of all obnoxious particles, passes off up the chimney with the other smoke.