25

C.—s

mineral. The specimens are exactly the same as those from Karangahake in which I first detected the occurrence in New Zealand of telluric silver, in October, 1883 (L/ 3599). The former specimens were given to me by Mr. Pond, who had determined the percentage of silver and gold in them, but had not detected the presence of tellurium. Mr. Skey's analysis showed only traces of gold in the telluric silver, which led him to think that the mineral was hessite, and not sylvanite, as I at first took it to be. There is still some doubt on the subject, which can only be cleared up when more ample specimens are submitted for analysis. " The three specimens were separately examined. No. 1 was treated for gold and silver in various ways, with the view of ascertaining the proportion in which each of the precious metals existed in the various forms of combination indicated by the minerals present. The specimen was finely ground, well mixed, and divided into small portions, which were treated as follows, and gave the results stated, as calculated upon the ton :—

"No. 1.

"No. 2.—B, continued.

" These results show —first, that about one-third of the gold is left in the stone when it is merely amalgamated in its natural state, and 95 per cent, of the silver ; second, that by roasting well and then amalgamating in presence of cyanide of potassium, about 9 to 10 per cent, of gold and 40 per cent, of silver is lost; third, that by the aqua regia process almost all the gold and silver may be extracted. " The other specimens assayed as follows : — Oz. dwt. gr. " No. 2 ... ... ... 211 10 10 alloy of gold and silver per ton. " No. 3 ... ... ... 135 11 4 alloy of gold and silver per ton. "As it is very desirable that the precise nature of the ores present be determined, a richer specimen should be forwarded to the laboratory for this purpose. When this is known with certainty, the best method of extraction can be selected without any difficulty, as it is simply a chemical question. So far as may at present be gathered from these results, it appears that the Mexican or Colorado methods would suit this ore—that is, amalgamation, after its treatment with certain iron and copper salts, in presence of sodium chloride. " Ores of this character are not usually, and can hardly be profitably, reduced by the miners and the simple appliance employed by them for crushing low-grade ores. I visited the works of a large company at Black Hawk, in Colorado, in 1876, the business of which was to purchase high-grade ores, tailings, and ores of base metals, such as zinc, lead, antimony, &c, which are obtained as accessories in ordinary gold- and silver-mines in the district. All these are manufactured into a concentrated matte of uniform composition. Up to 1872 the products in this form were transported to the Eastern States, and shipped to Swansea for reduction and separation; but in 1876 a newprocess of reduction was discovered and introduced that enabled the gold and silver to be separated without the use of acids. I was allowed to inspect the whole of the process except one stage, which was kept a strict secret. " I have always been of opinion that the Thames Goldfield, and also that at Collingwood, will never prosper until works for tke reduction of the ores are established similar to those at Black Hawk, so that the miners can have a satisfactory market on the spot for the crude ores. In this way the miners can attend to their own business of Joining, and leave the difficult and risky chemical 4—C. 5.

Gold. Silver. I Total Alloy. . Amalgamated in natural state '. Amalgamated after roasting Oz. dwt. gr. ... 44 0 20 ... 46 1 16 I Oz. dwt. gr. 11 4 4 52 4 11 I Oz. dwt. gr. 55 5 0 98 6 8 " The residue, after amalgamation of portion B, treated by several additional processes, gave •esults as follows, as per ton :—

Goia. Silver. Total Per Ton. a.) By reamalgamation with cyanide of potassium p.) By treatment with aqua regia of residue from (a) \c.) Obtained by assay of residue from (b) ■ ... Oz. dwt. gr. 13 0 16 6 18 6 Oz. dwt. gr. 52 12 14 79 1 4 Oz. dwt. gr. 65 13 6 85 19 10 0 4 4 2 16 2 5 10 Brought down from Table No. 1, first amalgamation 20 46 3 1 2 16 133 52 15 4 0 11 153 98 18 6 2 3 Total from stone, as per ton 66 4 18 185 19 11 252 4 5