THE MECHANICAL ASSAY OF QUARTZ.

Mount Ida Chronicle, Volume III, Issue 196, 29 November 1872, Page 6

THE MECHANICAL ASSAY OF QUARTZ.

-lAJ- a meeting of the Royal Society of Victoria hold recently, Mr. Foord read a paper on the mechanical assay : >t quanz. He commenced by explaining the immense value of assay from r-he practical point of view ; that it wis the means of preventing the outlay of i-apitai in developing quartz which night not contain a particle of gold; and then stated that assay, as a test of whether stone was auriferous or not, was comparatively ignored in Victoria. He then explained the process of assay by fire, p >inting'out that however valuable the method might be to the anal) tic chemist, it would he useless in the hands of the uuskille !, or of the miner who at a moment's notice was desirous of discoverimr whether a newly-found reef contained any of the precious metal. The method followed by him in the mechanical assny was as follows:—The stone was at first pu'verised in a large cas*\iron mortar. A sieve of bras 4" wire of fine mesh —about the thirty-fifth of an inrh square —was then used, and after the sample had passed through the wire,the powderwas ground still finer in a shallow cast-iron mortar about eleven inches in diameter and five inches deep. A weighted quantity of this very finely-ground sample was submitted to careful washing in a porcelain dish. A residue was obtained almost entirely of the metallic sulphides of the or. These were transferred to a large agate mor- ! tar, 'were again ground washed until a small grey residue showed that no gold remained. The grey residue consisted almost entirely of" particles of cast-iron or wrought-iron abraded during the operations. Such particles may be easily separated. A darning needle or steel-pin is magnetised by drawing it once or twice, a ways in the same"direction, over the surfi.ee of an ordinary horse-shoe magnet, and to the little steel magnet thus obtained the particles of iron will attach themselves, and may be freed from any entangled particles of gold by drawing them backwards and forwards through the water with which the agate mortar is filled. When the cast-iron particles have been removed by the magnet, the gold in the sample, if any, will be revealed, and can be examined, collected, and weighed. A little chemical treatment, such as can be done by the aid of the most portable instruments, will | often prove advantageous at the close jof the purely mechanical treatment The residue can be cupelled, and a spherical button of gold will be obtainecj, and the return per ton can be ascertained by the diameter of the bead, measuring instead of weighing it. The tools necessary tor'the'mechanical treatment just mentioned will cost a few pounds, but the outlay will in many cases repay itself, and would in most cases be warranted as a preliminary expense, rather than :-oing blindly to work with a newly discovered reef", —rather than proceeding to sink and erect machinery without acquaintance with the contents of the stone. By this treatment it cannot be said that no gold will escape, but at least as high a return can be obtained by the samples as the yield on the large scale, nf course even for these trials a certain amount of skill and some delicacy of manipulation would amply repay the miner's trouble in mastering them ; and as there was now a movement towards the establishment of mining schools, it was desirable that the mechanical assay of quartz should be taught, among other matters in such institutions. The old

method of simply burning the quartz was a pernicious one, because when the burnt pyrites was brought to a fusion point, it locked up the gold, which could be separated afterwards only with great difficulty. He thought it would be well if the quartz were properly roasted in a kiln before being crushed, but pointed out that this operation, taking into consideration the general average of the quartz, would not repay the outlay.