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Best Method of Saving Gold at the Thames.
Dr. Purchas said that he was aware that on that occasion he had promised to give a viva voce description of the various processes employed in saving gold. He had, however, had no time to get up his subject as he should have wished, but would, as there was so little business on the paper, say a few words on the subject. The speaker then went on to describe the manner in which gold was treated in South America, saying that far poorer ores than those at the Thames, were crushed and made payable. Speaking of the space required for the working of some of the machinery in South America, he said that on many claims, a space as large as six men's ground at the Thames, was required for amalgamating ground. He then briefly explained the process by which the amalgamation took place. The ore, speaking more particularly of silver ore, was laid upon the ground mixed with salt, and horses were kept going round, treading upon it, and so breaking it fine. It was also dressed three or four times with quicksilver, and, in some seasons of the year, small quantities of lime were added. It was a remarkable circumstance that in the winter the temperature was made higher, and in the summer it was made lower, by the process. If the ore was poor in sulphur, then another ore, having sulphur, was mixed with it, and trodden down in it to make it work, and left on the ground, in summer sixteen days, and in winter twenty-five days. The way in which the thorough amalgamation and separation was afterwards carried on, by means of certain machinery, was fully explained by the speaker. Then there was another process, by which ores were roasted, and mixed with salt, and placed in barrels having certain machinery, for separation and amalgamation. So perfect was this system, that a very minute portion of metal was left in the ore. The heat, dews, wet, and the magnetic state of the atmosphere, all played a part towards the extraction of the metal from the ore. They might say this process was very rough, but if it saved the gold, what mattered it? At present, at the Thames, a great part—he might say the greater part—of the gold was lost, even with the best machinery. One reason of which, he believed, was because the process was gone through far too quickly; and another thing that militated against the thorough saving of gold, was the immense quantity of undecomposed sulphurets that pass through the mills. Speaking of the amount of gold that might be
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extracted from these iron pyrites, Dr. Purchas said that in Australia as much as forty ounces to the ton had been obtained.
Captain Hutton said, ninety in some places.
Dr. Purchas said that if that were the case, there must be an enormous quantity of gold lost at the Thames. He was much struck, in reading over a book on the subject of gold separating and amalgamating, to find that in one mine in California, a shaft had been sunk thirteen hundred feet, and yet notwithstanding the immense depth, the shareholders said that it paid better than ever it had done before. Even then it was only yielding an ounce to the ton; and if this could be done in California, surely it could be done here where there was a yield of three or four ounces. Another thing he wished to say about the Thames, and that was, that a great deal of the soil that was thrown away, in fact, in the majority of cases, contained a large per-centage of gold.
Captain Hutton asked whether the earth was meant, or the casing of the veins.
Dr. Purchas said it would be the casing he was referring to. With regard to the processes he had mentioned of getting the gold from the stone, many people would grumble at the time taken, but everything of this sort required to be done by companies. He thought it was a mistake to attempt to mine at the Thames as diggers were doing at the present time; the right way to do it was to mine with companies, and with large areas of ground and proper machinery. He believed an immense amount of labour was wasted: certainly a large amount of gold was.
Mr. Gillies said he would not discuss the question of gold-saving, but there was one thing which he would ask the Society and the people at large not to admit, and that was, that large public companies were always the best. While he admitted the advantages which the companies had for working the ground by means of capital, he did not believe in their finding out anything new in the mode of saving gold. If anything new was to be found it would be done by individual miners.
Dr. Fischer thought the only sure way of saving the whole of the gold, was by the hot-blast process, as it was termed. The speaker then explained, by means of diagrams, the whole process from beginning to end.
Captain Hutton thought the idea of the last speaker, with regard to the zinc plates, was a fallacious one, saying they would stop the very stuff intended to be thrown off the tables. It would be, in his opinion,
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far better to have what was known as a broken table, with movable copper plates, so that as soon as they were fully charged with amalgam, they could be removed and others substituted, which would in many instances effect a large saving of the precious metal. With regard to what had been said, and what was always being said, about new inventions for saving gold, he believed, for his own part, that those machines which had been used in Australia and California were thoroughly good; and it was a mistake to get any on new principles till they had tested the good old ones. Many ingenious inventions had been put forward for saving gold, more inventions than for anything else, but all he could say about most of them was, that they were very much advertised and very little used. With regard to what had been said by Dr. Purchas, the processes he had described were applicable mainly to the saving of silver from ores containing gold, which was very different from the requirements of the Thames. In Victoria, at the starting of the gold-fields, the same high charges ruled for crushing as were now paid at the Thames; and the consequence was that only a few claims really paid, whereas, now that prices were low, two thousand reefs were worked. In his opinion, to have the thing properly worked, every claim must have its own machine, going night and day, and crush everything before it. Another great drawback was the want of security; and until claims were held on the same kind of leases as other property, no man of sense would put much money in them. But, given these two things—security and machinery—for every claim, and he was convinced that the Thames, for its area, would turn out more gold than any other field yet known; and continue to do so, perhaps, for centuries to come. Speaking of the gold contained in the iron pyrites at the Thames, Captain Hutton said that it would yield from three ounces to thirty ounces to the ton (of pyrites, of course); but that would not pay under the present system. He hoped he would see the day when the whole face of the rock would be taken down, and everything treated properly, either by the roasting system or chlorine, so as to make it all pay; though, no doubt, it would be some time before that would come to pass.
Captain Hutton proposed that Dr. Ferdinand Hochstetter should be elected the first Honorary member of the Auckland Institute.
Mr. Gillies seconded the proposition, and, in doing so, said it was doing honour to themselves more than to the doctor. Carried unanimously.
The Chairman then declared the present session of the Institute closed for the season, but stated that Council meetings would take place as usual.