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DIAMOND in SOUTH AFRICA

Dry Diggings (suite)

The appearance of water in the mine still further added to the embarrassment of the workers, and constituted a difficulty, which was quite insuperable so long as the owners of the claims worked independently. The necessity for co-operation was met in 1874 by the institution of the Kimberley Mining Board; a body, which undertook all work of public benefit, such as the removal of water, of fallen reef, and of reef about to fall, the expense incurred being shared equally by the owners of the claims. It was about this time that the formation of companies began to take place, although at first this form of co-operation was strongly condemned by individual miners, yet as time went on it became more and more apparent that the increasing difficulties and expense of working could only be overcome in this way. The larger capital at the disposal of the companies enabled them to employ the best machinery and to adopt all the improved modern methods of working, and thus to decrease the working expenses, and at the same time to increase the production.

Although the amalgamation of individuals and capital rendered it possible to prolong for a time the system of open workings, yet, as time vent on, it became very evident that this system could not be continued indefinitely, and that the open workings would have to be replaced by systematic underground workings, if the treasure hidden away in the depths of the mine was ever to be reached. A very successful beginning was made at the Kimberley mine in 1885, and in 1891 at this same mine, a shaft was driven into the reef to a depth of 1,261 feet, from which horizontal galleries or tunnels were excavated to meet the diamond-bearing rock. In the section of the underground workings of the Kimberley mine may be seen these tunnels or galleries, situated partly in the diamantiferous pipe itself and partly in the surrounding reef. The lowest depth at which material could be excavated in the open workings was about 400 feet, so that the construction of the underground workings made accessible large quantities of fresh material. Moreover, the new system did away with the liability of the workers to injury from falling reef, and many of the earlier regulations dealing with this danger, became then unnecessary. The same system was also introduced in the De Beer's mine, a section through which is given, although here the falls of reef had been less troublesome.

The earlier methods of extracting diamonds from the rock when excavated were as primitive as were those first adopted for mining the rock. It has been mentioned above that the dry diggings are situated on an arid plateau, and at the time of their first discovery the water required for every purpose had to be fetched from the Vaal River, many miles away. This necessity forbad the washing of the diamantiferous material as was practised at the river diggings. The mass had therefore to be coarsely broken up with wooden pestles and the coarse and fine material separated by sieves the material of medium grain was then, as in the river diggings, spread out in a thin layer on a sorting-table, and any diamonds it contained picked out by hand.

By this method all the stones, which passed through the fine sieve, the mesh of which was about 1/8 to 3/16 inch, were of course lost, these smaller stones being not then considered worth the time and trouble involved in their collection. The larger rock-fragments separated by the use of the coarse sieve with a mesh of 3/8 to 5/8 inch were thrown aside, though many would of course contain diamonds. It is estimated that during time period in which these methods were practised, at least as many diamonds were overlooked as were found, and in 1873 the debris was reworked and yielded a rich harvest. The material taken from the richest part of the mine has been worked over even a third time, and thanks to the use of improved methods, the result amply repaid the workers for their trouble. Hundreds of poorer miners, who were not fortunate enough to possess a claim obtained a living by working over the material of old mine heaps, as is still was done at some places in India.

The lack of water was not felt for long, very soon a main 18 miles long, bringing water from the Vaal, was constructed, and this supply was further supplemented by the numerous springs in the district, and by the water pumped out from the mines themselves. Thus it soon became possible to treat the diamantiferous material in the same way as at the river diggings, and so the term dry diggings came to be a misnomer. At first, the "blue ground" was reduced to fragments and then washed by the aid of the same simple appliances as had been in use at the river diggings. Improved methods, however, were gradually introduced; thus in 1874, a washing machine worked by hand was employed for the first time, and this in 1876 and 1877 was itself replaced by a machine driven by steam. The construction of this was so much improved that it was capable of dealing with almost two thousand times as much material as could formerly be treated by washing, and of collecting stones which, on account of their small size, had formerly been lost. The diamonds are picked out by hand from the heavy residue, and are finally freed from any foreign matter, which may adhere to them, by treatment with a mixture of sulphuric and nitric acids, after which they are ready for the market.

The "blue ground" excavated from the deeper parts of the mine is too hard and compact to be washed without previous treatment. It is therefore spread out in thin layers on the hardened ground of large fenced-in spaces, known as depositing floors. Here, exposed to frost, rain and sunshine, it gradually weathers, becoming friable and crumbling, when it is fit to undergo the process of washing. The weathering of the material, which is accompanied by a change from the normal colour of "blue ground" to that of "yellow ground", takes from one to nine months, according to the character of the weather to which it has been exposed, and to the mine from which the material was taken. The "blue ground", from the Kimberley mine weathers in about half the time required for the same process by the material from De Beer's mine; the latter sometimes requires several years for the con completion of the process, while a few months is usually all that is necessary for material from the Kimberley mine.

The longer the period required for the weathering process, the more will the profit derived from the yield he diminished. For during this period there are many expenses and losses incurred, such for example as ground rent, which is very high, wages of labourers and watchmen, losses due to thieving, etc. Any means whereby the slow natural process could be hastened was therefore welcomed.

A factor that has largely contributed to the hardships of the South African diamond fields was the high price of the ordinary necessities of everyday life. This scantily peopled region, in which only the barest necessaries could at one time be obtained, became inhabited with comparative suddenness by a population of at least 30,000 white people. The many and various articles necessary to their existence on these barren arid wastes had all to be conveyed from Capetown, Port Elizabeth, or some other seaport town. The transport was effected in wagons, drawn by horses, mules or oxen, and the long and difficult journey to Kimberley occupied several weeks. The rates for transport from Port Elizabeth to Kimberley, a distance of 500 miles and requiring about four weeks, were from 10s. to 30s. per 100 lbs of goods, and from Capetown to Kimberley, a journey of 650 miles, occupying about six weeks, they were still higher. Other prices were of course correspondingly high thus, Cohen relates that in the year 1872 a bottle of beer cost 3s. 6d., and good Rhenish wine 18s. a bottle; a cabbage could never be obtained for less than 3s., potatoes were as high as 1s. per lb., and eggs were 6s. a dozen. At some seasons of the year a day's supply of fodder for a horse cost 15s., English coal fetched £16 10s. per ton, and a wagon load of wood of about 4 1/2 tons was worth £30 ($4,170). The same authority stats that £8,000 ($112,524) was paid for a steam engine of 100 horsepower delivered in Kimberley. It is not surprising then, that with these prices for coal and machinery, steam power was so long in coming into general use, especially as it was not at first known that the diamantiferous deposits were so extensive. The cheapest food available was antelope flesh, a whole animal the size of a deer costing only from 3s. to 8s.; meat, therefore, was the staple article of food, and every drop of water had to be bought.

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  ]


Related links: Diamonds: Large and Famous   Properties   Geology and Mining Diamond Cutting Gem Cutting Diamond Trade  Values of diamonds
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Rafal Swiecki, geological engineer email contact

This document is in the public domain.

March, 2011