At a recent meeting of the Institution of Civil Engineers, the paper read was "On the Diamond Fields and Mines of South Africa," by Mr. James N. Paxman, Asoc. M. Inst. C.E.
The author commenced by stating that Kimberley was situated in Griqualand West, above 700 miles northeast from Table Bay, and 450 miles inland from Port Elizabeth and Natal on the east coast. Lines of railway were in course of construction from Table Bay and Port Elizabeth to Kimberley, and were about half completed. In Griqualand there were several diamond mines, the principal of which were Kimberley, De Beer's, Du Toit's Pan, and Bultfontein.
In the Orange Free States there were also two mines, viz., Jagersfontein and Koffeyfontein, the first of which produced fine white stones. The mines were all divided into claims, the greatest number of which were to be found in the Du Toit's Pan mine. Bultfontein came next.
The deepest and most regularly worked was the Kimberley mine. The next deepest was De Beer's, which, however, was very unevenly worked. Then followed Du Toit's Pan and Bultfontein. The Du Toit's Pan mine ranked next in importance to Kimberley mine. Diamonds were first discovered in 1867 by Mr. O'Reilley, a trader and hunter, who visited a colonist named van Niekirk, residing in Griqua. The first diamond, on being sent to the authorities, was valued at 500l. Considerable excitement was caused throughout the colony, and the natives commenced to look for diamonds, and many were found, among which was one of eighty-three and a half carats, valued at 15,000l. In 1868 many enterprising colonists made their way up the Vaal River, and were successful in finding a good number of diamonds. The center of the river diggings on the Transvaal side was Klipdrift, and on the opposite side Pniel. In all there were fourteen river diggings. Du Toit's Pan and Bultfontein mines were discovered in 1870 at a distance of twenty-four miles from the river diggings. The diggers took possession of these places. Licenses were granted giving the first diggers a right to work.
In 1871 De Beer's and Kimberley mines were discovered, and in 1872, Mr. Spalding's great diamond of 282½ carats was found at the river diggings.
The mines were of irregular shape, and were surrounded by reef. The top reef was a loose shale, and had given great trouble from the frequent slips. Below this were strata of trachitic breccia and augite; the formation was then seamy to an unknown depth.
Within the reef, the surface soil was red, and of a sandy nature. The next stratum was of a loose, yellow, gravelly lime, and the third blue, of a hard, slaty nature. This last was the real diamantiferous soil. Large stones had been found in the "yellow," but the working of this generally did not pay. Kimberley mine, however, had paid very well all through. The method of working in deep ground was determined by roadways running north and south. The soil was hauled up to these roadways, and taken to the sorting tables. The roadways decaying shortly after exposure to the atmosphere, a system of hand windlass was adopted, which worked very well for a time until horsewhims were adopted in 1873. The depths of the mines increasing, horsewhims had to give way to steam-engines in 1876.
The first diggers treated on an average ten loads per day each party. At the present time the least taken out by any engine, when fully employed, was 250 loads per day. The cost of working, with present appliances, the first one hundred feet in depth, was 3s. 6d. per load; the second one hundred feet (mostly blue) 5s.; the third one hundred feet 8s.; and the fourth one hundred feet 11s. Through scarcity of water a system of dry-sorting had to be resorted to for several years; but it was superseded by the introduction of washing machinery, which was now generally employed.
At the commencement, through inexperience, many serious mistakes were made. When the first diggers reached the bottom of the red sand, they thought no diamonds would be found in the next stratum. When, however, diamonds were found in the second stratum, the diggers had again to remove the debris, and so also when the "blue" was reached. Some of the claims in the Du Toit's Pan and Bultfontein mines were irregular in shape. The other mines, however, had been properly and regularly laid out. One or two shafts had been connected with the mines by underground galleries. These galleries were convenient in the case of falls of reef. Labor, at first, was cheap; but from 20s. per month, wages rose to 30s. per week, and food. The yellow soil offered no difficulty in working, being loose and broken, but the blue soil required blasting.
Several methods were adopted for extracting the soil and carrying it from the mine before steam was introduced. The cost of wood for heating purposes was a serious item, but good coal had now been found at 160 miles from Kimberley, costing 13l. per ton; another serious item of expense was the transport over natural roads only, costing from 18l. to 30l. per ton.
The machinery designed by the author for this industry was described. A sixteen horse-power direct-acting winding engine was introduced for hauling up loads at the rate of about one thousand feet per minute, and a twenty-five horse-power geared engine, for hauling up heavier loads at the rate of from six hundred feet to seven hundred feet per minute.
Water was dear, and water-heaters were fitted to each engine, by which thirty-three per cent. of the water was again used, thus saving one third. The boilers were of the locomotive type, mostly of steel, to save weight, and thus reduce the cost of transit. The fire-boxes were also made of steel of very soft and ductile quality. A semi-portable engine was made for driving the wash mill. The engine was so arranged that it might be removed from the boiler and placed separately. The boiler was made to work at a pressure of 140 pounds per square inch. Automatic cut off gear was fixed to each engine, and the governors were provided with a spiral spring for adjusting the speed. A screen, or cylinder wash mill and elevator, were used for dealing with the diamantiferous soil, and were described. Standing wires were fixed at the back of the machinery, and passed over a frame fixed at the top of the mine, the end of the mine being secured to strong wooden posts. After the blue soil had been blasted and collected into trucks, it was placed in tubs, which ascended the standing wires. It was then emptied into the depositing box. The yellow soil might be put into the wash mill direct, also that portion of the blue which had passed through the screen fixed over the depositing box.
The remainder of the blue, which was spread out to a thickness of four inches or six inches on the depositing ground, some distance from the mine to dry, was delivered into the upper part of the screen. The return water from the elevator, with a portion of fresh water, was also discharged at this point, and operations were thus greatly facilitated, the soil becoming thoroughly saturated, and passing more easily down the shoots. The large pieces which would not drop through the meshes of the screen were discharged into trucks at the lower end and carried away. The smaller pieces with water, in the form of sludge, fell through into a shoot, and thus were conveyed into the wash mill pan, and there kept in constant rotating motion by agitators. The diamonds and other pieces of high specific gravity sank to the deepest part of the pan, and the remainder of the sludge was forced over the inner ledge to the elevator. The sludge was then lifted and thrown upon an inclined screen and down the shoot over the side of the bank. The residue left in the pan at the end of the day's work was passed through a pulsator, in which, by the force of water, the mud and lighter particles were carried away, leaving behind the diamonds, agates, garnets, and other heavy stones.
It was the practice occasionally to put a few inferior stones in the soil, to test the efficiency of the machinery.
In 1881 the author paid a visit to Kimberley, and found the industry a large one. The Post Office return showed the value of diamonds passed through the office in one year to be 3,685,000l. Illicit diamond traffic had hitherto been a source of great trouble at the fields. It was a question whether this industry would ever cease; in any case there was no doubt but that it would last for over a century. It was believed that the main bed of diamonds had not yet been reached, and that the mines in operation were merely shafts leading to it. Now that the water works were finished, with a bountiful supply of water, coupled with the great boon of railways to the Fields, and the advantage of a law recently passed for the prevention of illicit buying, a great and prosperous future was in store for the Diamond Fields.