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In the servicos do rio, or workings of a river-deposit, the first step is the diversion of the water in order to lay bare the "cascalho" or diamantiferous material. Only a small portion of the river-bed is laid bare at a time, the operation being effected either by cutting a new channel for the river, or by building a dam in the middle of the stream and parallel to its course, so as to confine the water to a bed one-half its previous width, or by conducting the water away in wooden channels. After removing the barren detritus from the surface of the riverbed so laid bare, the diamond bearing "cascalho" is dug out. This latter is loose and easily worked, but the "canga," or masses of conglomerate, are often so compact that blasting must be resorted to, and thus the working becomes more lengthy and expensive. The work of excavating the "cascalho" can only be pursued during the dry season, from May to the end of September, when the volume of water in the rivers is at its smallest. During these months as much as possible of the diamond-bearing "cascalho" is excavated and conveyed to a higher level, being deposited, however, as near the stream or river as safety will permit. In the wet season the level of the river rises rapidly and to a marked extent, thus making the excavation of the "cascalho" a matter of impossibility. At this season the material previously excavated is washed and the diamonds it contains collected the place at which the operation of washing is conducted is known in Brazil as a lavra.

Before the "cascalho" is washed, the larger fragments are separated from the finer material either by hand or by means of 3 sieves (surrucas). This fine material is then placed in a shallow, wooden dish of a special kind, known as a batea, and agitated in running water; the lighter and finer portion is thus carried away, and from the heavier remaining part the diamonds are picked out by hand, the process of washing being all the while proceeding. The washers exhibit a wonderful skill in distinguishing the smallest diamonds, such as might easily be overlooked, from other mineral fragments.

This is a picture of the old working of an old Brazilian diamond washing. The Negroes on the left are standing in the stream and washing the "cascalho" in their bateas. Another party of workers on the right is engaged in filling up the bateas with fresh material from the "cascalho" heaped up on the banks of the stream, and carrying them down when filled to the workers standing in the water. The Negroes are all the time under the strict supervision of overseers armed with whips, whose duty it is to urge on the workers and to guard against thieving. In order to minimize opportunities for stealing, clothing of the Negroes is of the scantiest description. Each time a stone is found the worker, by raising his hand, signs to the overseer, who takes possession of the treasure. This image, in which the overseers are armed with whips, dates back to the days of slavery; since the emancipation of the slaves such coercive measures have, of course, been discontinued, but otherwise the system is unaltered. Modern garimpeiros, to increase the volume of gravel treated, must use water and gravel pumps with portable jig (resumidora) powered by small diesel engines.

The servicos do campo on the sides of the valleys above the present high-water level can be worked at all seasons of the year. The water from a neighboring stream is caused to flow over the deposit to be worked; by this means the surface earth and clay are carried away and the diamond bearing "cascalho" is laid bare. Since sufficient water for this purpose is only to be obtained in the rainy season this part of the work is usually reserved for that period. The "cascalho" when excavated is washed and the diamonds are picked out of the concentrate, in the same way as in the "servicos do rio".

In the servicos da serra the removal of the masses of barren sand and earth covering the "gurgulho" of the plateau-deposits is effected by the agency of running water. As, however, on the plateau there are no natural watercourses having a sufficient head of water, it is necessary to construct artificial reservoirs in which the rainwater may he stored. The water is conducted from the reservoir to the places at which it is required in wooden channels and the diamond-bearing bed thus laid bare as far as possible. As in other cases, the "gurgulho" is first washed and the diamonds then picked out by hand.

In the period immediately following the discovery of diamonds in Brazil, it was the practice of the Portuguese Government to demand in return for the concession of mining rights a certain sum for every slave it was proposed to employ, the total number of slaves so employed to be fixed by agreement. This tax was continually being raised, and so irksome became the conditions imposed on prospective miners that no one could be found to undertake the work. Then from the year 184O concessions were granted on the payment of a fixed sum, but as the mineral wealth of the country still remained undeveloped, the mining was taken over altogether by the Government from the year 1740 until the separation of Brazil from Portugal. The choicest of the stones found in this period therefore found their way to Lisbon, and were preserved with the Portuguese crown jewels, a collection which comprises many unique and matchless gems. The larger proportion of the Brazilian output was bought by merchants and sent to Europe through Rio de Janeiro and Bahia.

In spite of the laws of almost draconic severity leveled against illicit diamond-mining and trading, there was, besides the Government production, a great deal of surreptitious mining by unlicensed persons ("garimpeiros") of which of course no records were made. It has been estimated3 however, that the contraband production was at least equal in amount to that of the Government. However, a large proportion of the most perfect and beautiful stones fell into the hands of illicit traders, since a Government employee would scarcely risk detection for the sake of a stone of average or poor size and quality. According to other accounts the illicit trade was not of such extent and importance; in any case, however, those engaged in it, when relieved from the necessity of meeting the heavy taxes and high cost of production of the legitimate product, must have found their transactions very remunerative.

In 1834, the year in which the independence of Brazil was established, the Government monopoly of diamond mining ceased. Since this date the concession of full mining rights has been granted to any petitioner on the payment of a small tax, varying in amount with the area he proposes to work. The landowner is also entitled to demand 25 per cent of the rough production, and a duty of 1/2 per cent was imposed on exported stones.

The Negro slaves, by whom the whole of the actual labor connected with the mines was formerly done, were subjected to the strictest supervision. To minimize the temptation to conceal valuable stones, the finders of large diamonds received special rewards; thus, at one time, the fortunate finder of a diamond of l7 1/2 carats received his freedom, but later, when the price of slaves rose, this custom was dropped. Those slaves, on the other hand, who were detected in the act of concealing diamonds, were treated with barbaric severity.

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