Art. LII.—On the Occurrence of Platinum in Quartz Lodes at the Thames Goldfields
[Read before the Auckland Institute, 23th October, 1882.]
Some months ago, while the shaft in the Queen of Beauty Gold-mining Company was being deepened from the 540 to the 600 feet level, a quartz vein was cut which descended nearly vertical, and finding this to be impregnated with massive pyrites, I decided to assay portions to prove as to its gold-bearing character. The first assay of 200 grains yielded bullion .021, which, on parting in nitric acid, still retained its silvery lustre and appearance, showing that some other metal than gold was present, and this led me to continue the further examination of this vein. Making assays of the different portions of the stone, I obtained various values, the highest being .776 grs. of bullion from 400 grs. of ore, which, after parting, was reduced to .126 grs., or equal to 10 ozs. to the ton.
Placing the various beads together, I proceeded to isolate the metal, obtaining silver, gold, platinum, and iridium. My examination has only been a qualitative one as yet, as the breaking of a flask containing the whole
of my solution resulted in the loss of an unknown amount; and hence the absence of exact data. The assays made from this leader varied considerably, the lowest being at the rate of 1 oz. 5 dwts. 18 grs. to 10 oz. 6 dwts., showing that it was very irregularly present in the stone. When the peculiar characteristics of its presence are found it will be possible to isolate sufficient of the group to show the quantity of the other members of the platinum group which accompany it.
In the continuation of this investigation I have found this metal present in the large reef, both at the 540 feet and 600 feet levels, by assay, but in very much smaller proportions, and have washed several packets of tailings from the battery, the result of the crushing of this reef, and obtained the metal in the shape of minute grains accompanying the escaped gold. These grains viewed under the microscope are generally rounded, but a great many take the octahedral shape, some being beautifully perfect crystals. As it is intended to commence sinking immediately to the 670 feet level, I shall have ample opportunity of continuing my examination of this subject with a view to finding whether it is possible to note its presence in the stone by any visible peculiarity.
The rarity of this metal being found in situ may be gathered from Ure, who remarks of a sample of ore containing platinum from Guadalcanal in Spain, “This would be the only example of platinum existing in a rock and in a vein.” Since then, however, Edison in America and Roscoe and Schorlemmer have shown that it exists more largely than is generally presumed, and I think it is highly probable that if it was looked for systematically at the Thames, it would result in its being found much more widely distributed in the network of reefs and leaders than is generally supposed.