TREATMENT OF REFRACTORY ORES IN CALIFORNIA.

New Zealand Herald, Volume XXIV, Issue 7920, 12 April 1887, Page 4

TREATMENT OF REFRACTORY ORES IN CALIFORNIA.

The following very interesting information regarding the treatment of refractory ores in California is published in one of the Sin Francisco papers received by the last mail, ':• and at the present moment will be read with considerable interest, as it clearly demonstrates that the most difficult ores are now successfully treated there with satisfactory results. The question is referred to in jj California as a "promising outlook," bat the quartz there is of a very poor assay value in comparison with thai f to be fonnd in the Thames Peninsulj here. The seventy tons of ore treated yielded about £90 value in all, and if such a return is regarded, there as a "promising outlook," what ought to be said of our pro< ' spects with such stone as that recently tested at the La Monte furnace, and that still more recently sold in the London market? The ; following is the paragraph from our S»d "■.!, Francisco contemporary :— The Meadow Lake district has always been a source of much interest to mining men, and any information of the recent successful experiments in working the ore will doubt- I :.'..'■ lees prove interesting. The many different B reports recently published by up-country ?■■■'■■. papers are so hornbly mixed on the subject !; of electricity processes, etc,, as to be totally f unreliable, and oftentimes absolutely unintelligible. No ' process' was used by the company now in possession different from tbemetbods commonly employed, consisting of a combination of all the best. The ore was simply crushed and pulverised to a 40 mesh screen, concentrated, roasted (the concentrates) thoroughly in a reverberatory furnace at a moderate heat. The roasted snlphureta were then ground to an impal. pable (dry) powder, then washing out with 1 plain water the soluble sulphates formed ' during the roasting, and which so frequently hinder the subsequent process of free amalgamation, then amalgamated without grinding in pans at a temperature of about ISOdeg, F., and settled in the usual way in a settler, the tuilings from which in passing out of the mill pass over amalgamated plates and 1 blankets, together with the original tailings from the concentrator which catch some rina gold, amalgam, flowered mercury, and sulphurets, which would otherwise go to waste. Between the battery and the concentrator are some large revolving amalgamated plate!, ; ■which secure a considerable percentage of ' free' gold in the ore; These plates are electrically connected with the dynamo, which causes a far stronger adhesion : of the free gold particles to the surface of the amalgamated plates than without it, and from this simple and ; well-known application of electricity the rumour got abroad that some new • electrical process' was being tried at Meadow Lake, :'/ The principal use of the dynamo in question is for operating two arc lampa for illumin- -\*t ating purposes in the mill. About six dayi /, run was successfully made before it was found necessary to close down on account oi the lateness of the season and the imperfection of the pulverizer. Seventy tons of ore were milled, yielding in. free gold 223d01s 70c, and in concentrates 228d01s OSi, working up to 85 per cent., of assay value. After roaating and washing, the gold amalgamates . " very readily, and the often-made assertion that Meadow Lake ores cannot be worked has been demonstrated to be false, and that they are as easy to work as any other bare ores, and by the processes ordinarily employed without seeking any complicated or unusual methods. The ore is base, but grows free :■,:• ;:• for every foot of depth. On top about one* third of the gold is ' free, , the balance in the v • sulphurate, which are almost wholly clean of pyritio iron, generally very free from til other bases, and only in one part of the . ' mine carrying near the top a percentage of , zinc blende."