Getting Gold: A Gold-Mining Handbook for Practical Men

by J. C. F. Johnson

It is not contended that the effect of the internal fires had no influence on the formation of metalliferous veins, indeed, it is certain that they had, but the action was what is termed hydro-thermal (hot water); and such action we may see in progress to-day in New Zealand, where hot springs stream or spout above the surface, when the silica and lime impregnated water, reduced in heat and released from pressure, begins forthwith to deposit the minerals previously held in solution. Hence the formation of the wondrous White and Pink Terraces, destroyed by volcanic action some sixteen years since, which grew almost while you watched. So rapidly was the silica deposited that a dead beetle or ti-tree twig left in the translucent blue water for a few days became completely coated and petrified.

Gold differs in its mode of occurrence from other metals in many respects; but there is no doubt that it was once held in aqueous solution and deposited in its metallic form by electro-chemical action. It is true we do not find oxides, carbonates, or bromides of gold in Nature, nor can we feel quite sure that gold now exists naturally as a sulphide, chloride, or silicate, though the presumption is strongly that it does. If so, the deposition of the gold may be ceaselessly progressing.

Generally reef gold is finer as to size of the particles, and, as a rule, inferior in quality to alluvial. Thus, in addition to the extra labour entailed in breaking into one of the hardest of rocks, quartz, the madre de oro (“mother of gold”) of the Spaniards, there is the additional labour required to pulverise the rock so as to set free the tiniest particles of the noble metal it so jealously guards. There is also the additional difficult operation of saving and gathering together these small specks, and so producing the massive cakes and bars of gold in their marketable state.

Having found payable gold in quartz on the surface, the would-be miner has next to ascertain two things. First, the strike or course of the lode; and secondly, its underlie, or dip. The strike, or course, is the direction of the lode lengthwise.

In Australia the term “underlie” is used to designate the angle from the perpendicular at which the lode lies in its enclosing rocks, and by “dip” the angle at which it dips or inclines lengthwise on its course. Thus, at one point the cap of a lode may appear on the surface, and some distance further the cap may be hundreds of feet below. Usually a shaft is sunk in the “reef” to prove the underlie, and a level, or levels, driven on the course to ascertain its direction underground, also if the gold extends, and if so, how far. This being proved, next a vertical shaft is sunk on the hanging or upper wall side, and the reef is either tapped thereby, or a cross-cut driven to intersect it.

We will now assume that our miners have found their lode payable, and have some hundreds of tons of good gold-bearing stone in sight or at the surface. They must next provide a reducing plant.

Of means for crushing or triturating quartz there is no lack, and every year gives us fresh inventions for the purpose, each one better than that which preceded it, according to its inventor. Most practical men, however, prefer to continue the use of the stamper battery, which is virtually a pestle and mortar on a large scale. Why we adhere to this form of pulverising machine is that, though somewhat wasteful of power, it is easily understood, its wearing parts are cheaply and expeditiously replaced, and it is so strong that even the most perversely stupid workman cannot easily break it or put it out of order.

The stone, being pounded into sand of such degree of fineness as the gold requires, passes through a perforated iron plate called a “grating,” or “screen,” on to an inclined surface of copper plates faced with mercury, having small troughs, or “riffles,” containing mercury, placed at certain distances apart.

The crushed quartz is carried over these copper “tables,” as they are termed, thence over the blanket tables—that is, inclined planes covered with coarse serge, blankets, or other flocculent material—so that the heavy particles may be caught in the hairs, or is passed over vanners or concentrating machines. The resulting “concentrates,” consisting for the most part of sulphides of iron, copper, and lead, are washed off from time to time and reserved for secondary treatment.

First, they are roasted to get rid of the sulphur, arsenic, &c., which would interfere with the amalgamation or lixiviation, and then either ground to impalpable fineness in one of the many triturating pans with mercury, or treated by chlorine or cyanogen.