Getting Gold: A Practical Treatise for Prospectors, Miners and Students

by J. C. F. Johnson

THE GENESIOLOGY OF GOLD—AURIFEROUS DRIFTS

Having considered the origin of auriferous lodes, and the mode by which in all probability the gold was conveyed to them and deposited as a metal, it is necessary also to inquire into the derivation of the gold of our auriferous drifts, and the reasons for its occurrence therein.

When quite a lad on the Victorian alluvial fields, I frequently heard old diggers assert that gold grew in the drifts where found. At the time we understood this to mean that it grew like potatoes; and, although not prepared with a scientific argument to prove that such was not so, the idea was generally laughed at. I have lived to learn that these old hard-heads were nearer the truth than possibly they clearly realised, and that gold does actually grow or agglomerate; and, indeed, is probably even now thus growing, though it is likely that the chemical and electric action in the mineral waters flowing through the drifts is not in this age nearly so active as formerly.

Most boys have tried the experiment of dipping a clean-bladed knife into sulphate of copper, and so depositing on the steel a film of copper, which adheres closely until worn away. This is a simple demonstration of a hydro-metallurgical process, though probably young hopeful is not aware of the fact; and it is really by an enlargement of this process that our beautiful and artistic gold-and silver-plated ware is produced.

In the great laboratory of Nature similar chemical depositions have taken place in the past, and may still be in progress; indeed, there is sound scientific reason to suppose that in certain localities this is even now the case, and that in this way much of our so-called alluvial gold has been formed, that is, by the deposition on metallic bases of the gold held in solution.

We will, however, take, to begin with, the generally accepted theory as to the occurrence of alluvial gold. First, let it be said, that certain alluvial gold is unquestionably derived from the denudation of quartz lodes. Such is the gold dust found in many Asiatic and African rivers, in the great placer mines of California, as also the gold dust gained from the beach sand on the west coast of New Zealand, or in the enormous alluvial drifts of the Shoalhaven Valley, New South Wales. Of the first, many fabulous tales are told to account for its being found in particular spots each summer after the winter floods, and miraculous agency was asserted, while the early beachcombers of the Hokitika district found an equally ridiculous derivation for their gold, which was always more plentiful after heavy weather. They imagined that the breakers were disintegrating some abnormally rich auriferous reefs out at sea, and that the resultant gold was washed up on the beach.

The facts are simply, with regard to the rivers, that the winter floods break down the drifts in the banks and agitate the auriferous detritus, thus acting as natural sluices, and cause the metal to accumulate in favourable spots; whilst on the New Zealand coast the heavy seas breaking on the shingly beach, carry off the lighter particles, leaving behind the gold, which is so much heavier. These beaches are composed, as also are the "terraces" behind, of enormous glacial and fluvial deposits, all containing more or less gold, and extend inland to the foot of the mountains.

It is almost certain that the usually fine gold got by hydraulicing in Californian canyons, in the gullies of the New Zealand Alps, and the great New South Wales drifts, is largely the result of the attrition of the boulders and gravel of moraines, which has thus freed, to a certain extent, the auriferous particles. But when we find large nuggety masses of high carat gold in the beds of dead rivers, another origin has to be sought.

As previously stated, there is fair reason to assume that at least three salts of gold have existed, and, possibly, may still be found in Nature—silicate, sulphide, and chloride. All of these are soluble and in the presence of certain reagents, also existing naturally, can be deposited in metallic form. Therefore, if, as is contended, reef gold was formed with the reefs from solutions in mineral waters, by inferential reasoning it can be shown that much of our alluvial gold was similarly derived.

The commonly accepted theory, however, is that the alluvial matter of our drifts has been ground out of the solid siliceous lodes by glacial and fluvial action, and that the auriferous leads have been formed by the natural sluicing operations of former streams. To this, however, there are several insuperable objections.