Discoveries and Inventions of the Nineteenth Century

and south is 30 miles. From such data it has been inferred that the reefs contain altogether not less than 450 million pounds worth of gold. The conglomerate of these reefs consists of rounded quartz pebbles (which contain no gold), and pieces of sandstone and of argillaceous material, the whole cemented together into a very hard mass by iron pyrites. This last is the matrix in which the gold exists, in the form, for the most part, of minute scarcely visible crystals. To a depth of from 50 to 150 feet, air and moisture have acted on the pyritic matter, and the material of the reef becoming in consequence easily disintegrated, has yielded by mere mechanical treatment most of its gold, whereas by the same operations on the underlying hard, tough conglomerate, only about half its gold could be obtained. Hence, after breaking up the ore, the pyritic matter is sorted out and transported to the stamp battery, reduced to powder, from which about five-eighths of the contained gold is removed by quicksilver. The residue is concentrated by washing in a special machine called the “Frue vanner,” and the concentrates, after roasting in order to oxidize base metals, are subjected to the action of chlorine gas, by which the gold is converted into a soluble chloride, from the solution of which it is precipitated by ferrous sulphate. The tailings, slimes, and other residues are further acted on by a solution of potassium cyanide, which dissolves the minute remaining particles of gold, and from the solution the metal is obtained by electrolysis. By these supplementary chemical processes the total of the gold recovered from the ore is raised to 90 per cent. or more of all that chemical analysis shows to exist. When it is said that the reefs are arranged in a basin-like form, it must be understood that this applies to their general disposition, for the regularity of geometrical shape does not belong to geological basins. There are considerable variations in the inclinations of the reefs: at some places they are nearly vertical, but generally they dip towards the centre at various angles, a slope between 25° and 45° being quite usual; and the inclination becomes less and less the deeper they go, so that it is presumed that the beds are level towards the centre of the basin. In the Randt the vertical shaft is rather the exception, the entrance to the mine usually following the inclination of the reefs, and the trucks of ore are drawn up sloping rails. From the inclined adits horizontal galleries are excavated right and left at various depths by which the main reef is 696worked, and there are cross cuts by which the reefs to the north and south may be reached. The most active district of the Randt is that which extends eastward of Johannesburg, where a long succession of tall chimneys and winding headgears together with the other appurtenances are visible. But there is nothing of a picturesque character about a gold mine, more than is presented by the aspect of an ordinary colliery. The importance of the Randt gold-fields does not consist in the actual richness of the crude material, which indeed in places here and there cannot be profitably worked,—in mining parlance, it is not “pay ore.” It is rather the great ascertained extent of these gold-bearing beds and the general persistence of their character throughout that give to the Randt its unique character amongst metalliferous workings. This contrasts with the comparative uncertainty attending the exploitation of auriferous quartz veins, which occur in detached unconnected patches, that often end suddenly where least expected. There are in the Randt nearly one hundred companies working mines, and of these there are many that pay very handsome dividends on their original capital. A few pay 100 per cent., while a considerable number distribute 25 per cent. and upwards; so that some of these Gold Companies are amongst the richest and most influential financial houses in the world. The Randt is second only to the United States in the quantity it adds annually to the world’s production.