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DIAMOND IN BRAZIL

As may be gathered from the scene pictured in an old ilustration, the whole of the work was done by hand, the "cascalho" being carried in baskets on the heads of the Negroes, and no attempt made to save time and labor by the introduction of machinery or mechanical appliances. Even at the present day the same primitive methods are still in use, the difficulties in the way of the transport of large and heavy pieces of machinery to such inaccessible regions being almost insuperable. It is always more practicable therefore to employ hand labor, especially as, in addition to previous considerations, there is the fact that since any one locality is soon exhausted it would be necessary to move the machinery very often. The occupation of diamond mining is very lucrative only under exceptionably favorable circumstances; as a rule, the working expenses are very high and the losses by embezzlement considerable.

Brazilian diamonds, when they first appeared in the market, were not favorably received by the diamond-buying public, and were asserted to be either not diamonds at all or inferior stones from India. On this account many Brazilian stones were sent first to Goa, a Portuguese possession in India, and from thence entered the market as Indian stones. When this arrangement came to the ears of the Dutch merchants, they at once entered into a contract by which they secured a monopoly of the trade in Brazilian diamonds, which were subsequently sent direct from Rio de Janeiro and Bahia to Amsterdam. In consequence of a treaty entered into at a later date with the English Government, the whole output was sent to London; in recent times the majority of Brazilian stones are purchased by French houses and put on the Paris market.

In the preceding pages the production and occurrence of diamonds in the State of Minas Geraes, and especially in the district of Diamantina, have been described in some detail, the total output from this State alone having exceeded that of the rest of Brazil. Other States in which diamonds occur have been already named with the exception of Bahia they are much less known than is the district of Diamantina; their production is also much below that of either Bahia or Minas Geraes and is now probably everywhere at an end; this being so, only a short notice of them will be given.

In the State of Sao Paulo, to the south of Minas Geraes, diamonds have been found in the rivers flowing into the Rio Parana.

In the State of Parana diamonds have been found, in ore especially in the basin of the Rio Tibagy. This river runs through the Canipos of Guarapuavas and empties itself into the Rio Parapanema, which is a tributary of the Parana. Diamonds are found also in the tributaries of the Rio Tibagy, especially the Yapo and the Pitangru, and are everywhere associated with a somewhat considerable amount of gold. These rivers are remarkable for the presence in their beds of potholes and channel-like depressions, very local in their occurrence, and often containing a large quantity of stones. Just as in the districts previously considered, the diamantiferous deposits may be distinguished as river-, valley-and plateau-deposits. The discovery of diamonds in Parana was accidental; the stones found were invariably small, rarely exceeding a carat in weight; they were usually, however, of good color and luster. Systematic, search was undertaken years ago, but the yield was small and uneconomical, in spit of the considerable amount of gold present; it was, therefore, soon abandoned. The stones here are supposed to have been washed out of the Devonian sandstone through which the rivers mentioned above flow, and the sandstone itself may have been formed from the weathered debris of itacolumite.

In the State of Goyaz, on the western border of Minas Geraes, diamonds have been found in the Rivers Guritas, Quebre-Anzol, S. Marcos, and Paranayba. The upper part of the River Araguaia, bordering on the State of Matto Grosso and its right tributary the Rio Claro (lat. 16º 10' S., long. 50º 30' W.), and others in Goyaz are especially rich. The yield from these rivers has been considerable, the diamonds found up to the year 1850 in the Rio Claro alone amounting to an aggregate weight of 252,000 carats.

In the State of Matto Grosso diamonds have been searched for in some of the rivers as far as the Bolivian frontier, and in places a rich yield has been obtained. The majority of the stones have been found in the neighborhood of Diamantino (not to be confused with Diamantina, formerly Tejuco, in Minas Geraes), in the district of the source of the Paraguay and its tributaries, especially the Rio Cuyaba, a tributary on its right bank (lat. 15º 45' S., long. 56º W.). The stones from here are usually small and often colored, some, however, are of the purest water they are distinguished by the possession of a very brilliant surface, a feature that is usually absent from Brazilian stones. Up to 1850 the State of Matto Grosso had yielded diamonds to the weight of about 1,491,600 carats.

The geology of Goyaz and Matto Grosso is but little known; travelers, however, state that itacolumite is widely distributed; we may therefore assume that the occurrence of diamond in these States agrees in all essential points with that in Minas Geraes.

With respect to productiveness, the State of Bahia stands second to Minas Geraes; while the latter, however, is now for the most part exhausted, in the former new and rich deposits have been discovered. Thus the present yearly production of Bahia exceeds that of Minas Geraes, but the reverse is the case when the total production of the two States is compared. Diamonds had been discovered in Bahia as far back as the year 1755. Further search, however, was at that time prohibited by the Government in the fear that the agricultural prosperity of this fertile State might suffer. In spite of this prohibition more and more finds were made, until at the beginning of the nineteenth century the production was quite considerable. It has continued to grow, until now the yearly output exceeds that of Minas Geraes. The first finds were made on the eastern slopes of the Serra da Chapada and, north of this, in the Serra do Assuaria, which forms the continuation northwards of the Serra do Espinhao, a range of mountains stretching across the greater part of Minas Geraes and passing through the district of Diamantina. The stones are found in sands and gravels in the watercourses, and are accompanied by the minerals, which constitute the most important associations of diamond at Diamantina, namely, the oxides of titanium and of iron, tourmaline, and quartz (rock-crystal). In addition to these are a few others, which do not occur in Minas Geraes. In a sample of diamond-sand from the Serra da Chapada, Damour determined the following minerals: pebbles of rock-crystal, crystals of zircon, tourmaline, hydro-phosphates, yttrium phosphates, diaspore, rutile, brookite, anatase, ilmenite, magnetite, cassiterite, feldspar, cinnabar, and gold. Garnet and staurolite have also been observed here and recently euclase, but the last only as a rarity. Of these minerals, cassiterite, feldspar, and cinnabar have never been found in Minas Geraes in association with diamond. Schrauf argued "…from the occurrence of these minerals, and especially from the association together of tourmaline, garnet, zircon, staurolite, rutile, etc., the rocks, from which have been derived the diamond-sands of the Serra da Chapada, were allied to the gneisses and syenites of southern Norway." It has been stated in descriptions of the geological structure of these mountains that they are built up of these particular rocks, but neither in this nor in other diamond districts in Bahia has any thorough geological investigation been made at that time, and since the minerals associated with diamond are the same in Bahia and in Minas Geraes, it is probable that the occurrence is also the same, namely, in itacolumite.

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