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Dry Diggings (suite)

The foregoing has been devoted to the consideration of the manner in which the diamantiferous rock-mass actually occurs in the pipes. The question, which naturally follows, namely how the diamond itself was formed in its original mother-rock, the kimberlite, will be treated generally below. We must first, however, notice certain other theories as to the formation of the pipes, which are more or less opposed to that of Cohen, as set forth above. According to the theory first promulgated by the late Professor H. Carvill Lewis, and which has some substantial support, the "blue ground" is not fragmentary material or tuff, but was forced up from below into the pipe as a molten mass which consolidated on cooling. According to this view, therefore, the "blue ground" is an ordinary igneous rock, which solidified in the situation in which it is now found, and it was with this supposed origin in his mind that the name kimberlite was proposed for the diamantiferous rock by Carvill Lewis. This rock, which was originally an olivine-rock, is supposed to have subsequently undergone the same alteration processes as described above.

There appears to be a similar, though very sparing occurrence, of diamonds near the village of Carratraca in the province of Malaga in Spain. According to the statement of A. Wilkens, a mine-owner resident there, a few diamonds were found in 1870s along with pebbles of serpentine in a stream, in the neighbourhood of which serpentine with nickel ores occurs in situ. It is therefore not impossible that these diamonds had been derived from the serpentine. Similar relations between diamonds and serpentine rocks have also been reported from Australia and the western part of North America.

Although the association of diamond with serpentine in South Africa renders it very probable that the former has been derived from an olivine-rock, yet it is a noteworthy fact that the only mineral found actually inter-grown with and firmly attached to the diamond is garnet. Professor Bonney has in 1899 and 1901 described the occurrence of colourless octahedra of diamond as a constituent of rounded boulders of eclogite. These boulders of eclogite, which is an igneous rock composed of garnet and green diopside, came from the "blue ground" of the Newlaud's Diamond Mine in Griqualand West, about forty-two miles North-West of Kimberley. The same observer describes the occurrence, also in this mine, of rocks rich in olivine, such, for example, as saxonite and lherzolite, in which, however, diamonds have not yet been observed.

At all other known diamond localities, especially those of India, Brazil and Lapland, olivine or serpentine as a mineral associated with diamond is conspicuous by its absence. In such localities, therefore, the mother-rock of the diamond cannot be an olivine-rock. On the other hand, diamonds have occasionally been found in meteoric stones, of which olivine is an invariable constituent, and the association of these two minerals in extra-terrestrial matter is a fact of considerable interest and importance.

The mining operations for obtaining the diamonds at the dry diggings were commenced at the end of the year 1870; by 1872 the industry was in a flourishing condition, and since this date it has steadily developed. At first the deposits were worked, regardless of future inconvenience, in an irregular and haphazard fashion, the aim of the miners being to amass the greatest possible amount of treasure with the least possible immediate expenditure of labour and money. Thus much valuable ground was covered with debris, which subsequent workers were forced to remove at a great sacrifice of time, labour and capital. In the deposits more recently discovered, the authorities have profited by former mistakes and mining operations have from the first been carried out in a systematic manner, with due regard to future necessities.

Each diamantiferous area was at first divided into square lots or claims, as was the custom in the goldfields of California and Australia and also at the river diggings of South Africa. These claims in the Kimberley and De Beer's mines were 31 feet, and in the Du Toit's Pan mine 30 feet square; each claim therefore had an area of 100 square yards or a little more. In the Kimberley mine there were 331 such claims, in the De Beer's mine 591, in the Bultfontein mine 886 and in Du Toit's Pan, 1430. In the three last-named mines the claims were laid out in such a way that there was no means of access to those in the centre except over the surrounding lots; this inconvenient arrangement materially increased the difficulty of mining and transporting material. When the Kimberley mine was opened, the Government Inspector of Mines in what was then the Orange Free State, profiting by past experience, arranged that every claim should be directly accessible by the construction of fourteen or fifteen road-ways, each 15 feet wide and all running in a north and south direction across the narrowest part of the mine. By this regulation every possessor of a claim lost 7 1/2 feet of ground, and until the advantage of the arrangement was realised it was bitterly opposed. In Plate VII is shown the Kimberley mine as it appeared in 1872, with these roadways.

Up to 1877, no single individual was permitted to possess more than two claims, the only exception to this rule being that of the discoverer of the mine, who was allowed three. Every intending digger had the choice of any of the claims, which happened to be vacant, and each tenant of a claim paid the owner of the land l0 shillings per month in return for a licence permitting him to work the claim. Until 1873, the penalty enforced for leaving a claim unworked during a period of seven days was forfeiture of the claim, which could then be transferred to another digger.

To keep the whole of a claim constantly worked proved somewhat too heavy a tax on the energy and resources of a single individual, the claims therefore came to be divided up, one man making himself responsible for a half; a quarter or even one-sixteenth of a claim.

More important than the sub-division of the claims was the amalgamation of several under one management; a system that began to be adopted in 1877, after the regulation preventing it had been rescinded. Companies were formed to buy up a number of claims, and these, being under one central control, could be worked more expeditiously and economically before very long, there were very few claims, or portions of claims, worked by single individuals. Thus in the middle of the eighties, almost all the claims into which the Kimberley mine was divided were in the possession of one or two large companies, while ten years before, these same claims were the separate property of about 1600 persons; the same change also took place in the management of the other mines. The number of claims in the possession of each company, of course, varied considerably, some having as few as four and others as many as seventy. Many of these companies were formed with perfectly legitimate objects, others however were nothing more than swindles, and the claims they had acquired were usually very soon abandoned.

Diamond Geology [ 1  India  3  4  5  6  7  8  Brazil  10  11  12  13  14  15  16  17  18  19  20  Borneo  22   South Africa  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  Venezuela, Guyana  42  Australia  44  Argyle  Congo  46  47  48  49  50  51  52  53  54  55  Angola  57  58  59  Guinea  ]

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Rafal Swiecki, geological engineer email contact

This document is in the public domain.

March, 2011