How Gold Came into the Quartz Reefs

Feilding Star, Volume VII, Issue 75, 3 December 1885, Page 3

How Gold Came into the Quartz Reefs

Professor Black, who has been lecturing to the Thames miners in his last lecture took for his subject, " How Oold came into the quartz Beefs." He approached his topic with some diffidence in consequence of the many opinions as to how it came there, but as we usually find gold with the quartz wo may suppose the same agency which placed the quartz in the reefs must have had considerable influence in placing the gold there. It becomes us therefore to inquire what the agency is. Gold is always associated with sulphides, hence it is probable that the same agencies brought both into the reefs. Chlorine is one of the chief agencies in bringing gold into xeefs, from. the fact that it always combines freely with gold whenever it comes into contact with it. It dissolves in water with the utmost ease, hence water containing chlorine will carry the gold in solution wherever it travels. But where was the gold before it came into reefs ? Sea- water always contains gold to the extent of about 1 grain of gold to 1 ton of seawater. Since this is so, you would suppose that all rocks formed at the bottom of the sea, e.g., mica-schists, slate, &c, must contain gold, although in very small quantities. What reason have we to suppose that this chlorine exists in underground water ? .^ThiSj analysed now, is not found to contain chlorine may not previously iaye existed in the subterranean waters ; for, if you can prove that the ■ compounds exist in the crust of the earth from which chlorine can be iormed, then it" is easy to account for its presence. then, yOuhave a little gold scattered througout miles of m^-ft-flfihie^GOuntry, and suppose jthe fissures exist and also water containing chloride of gold, flowing through the mica-schist country comes across crevices where quartz is being formed, there, by various agencies, the gold may be precipitated from its aqueous solution, and; thence deposed in the growing quartz reef. [Here chlorine was made on the lecture table by the action of muriatic acid on black oxide of manganese, and shown to be a heavy gas of a pale greenish yellow tinge, with a very disagreeable odour]. Now black oxide of manganese occurs plentifully ,-in nature, but

I muriatic acid only rarely — chiefly from I volcanic emanations. But muriatic I can be made from sulphuric acid and • common salt, which is distributed over the globe to an enormous extent. It has been dissolved out of the rocks by the action of water and carried to sea, which owes its saltness to this source. Assuming, then, the existence of salt, where does the sulphuric acid come from ? It is derived by the action, on | iron pyrites, of the oxygen contained in running water % Hence conditions exist under which* muriatic acid can be formed, and this acting on the black oxide of manganese already existing, chloride is formed, which dissolves the gold. The gold remains in solution and is carried away by running water, until it meets something which will release it from the chlorine and leave it in the metallic state. Sulphate of iron, of all other compounds, effects this., and does exist in the rocks. (A piece of pure sulphate of iron, got from a reef on the Thames, was shown to verify this.) Organic matter, sulphurous acid, &c, will also throw down gold in solution. This is one possible way of accounting for the formation of gold in the reefs. Another way in which gold may be dissolved is as follows :— Add sulphuretted hydrogen to gold, and the gold is precipitated as a black sulphide. Alkaline water will dissolve the Bulphide, precipitating the gold in the metallic state. An example of these alkaline waters I have been told exists at Puriri and Te Aroha. The Thames thus affords splendid examples of what does take place in the formation of gold-bearing reefs. The Professor then concluded his lecture by summarising the principal conditions under which gold can be dissolved, viz. : — (1) Presence of iron pyrites, together with table salt and black oxide of manganese, with exposure to the atmosphere and water; (2) quartz at a high temperature, together with muriatic acid and black oxide of manganese; (3) saltpetre, together with iron pyrites oxidising, and common salt; (4) sulphuretted hydrogen, together with alkaline water. Continuation of reading matter on tehpage