DIAMOND IN BRAZIL
HISTORICAL REVIEW of DIAMOND GEOLOGY and MINING
Diamonds were first discovered in Brazil about the year l725, in the neighborhood of Tejuco, which is situated in the State of Minas Geraes. According to the usual accounts they were first found during the gold washing of the auriferous sands of the Rio dos Marinhos, a tributary on the right bank of the Rio Pinheiro. The glittering of the stones attracted the attention of the gold-washers, although they were ignorant of their real nature. The stones were collected and taken occasionally (1728) to Lisbon, where they came under the notice of the Dutch consul, who recognized them to be diamonds of the best quality.
Then began an eager search all over the distinct, but specially in the water-courses, and it was found that all the streams and rivers there were more or less rich in diamonds. The Portuguese government claimed the stones as crown property, and marked out a definitely bounded diamantiferous district, called the Serro do Frio district, which was to be under its own control, and subject to special laws and regulations preventing the ingress of unlicensed diamond-seekers, while a strict military supervision forbad any dishonesty among the workers.
More extended search showed that diamonds were not confined to the district of Serro do Frio; numerous important discoveries were made in various parts of Minas Geraes and in other States, namely, in Sao Paulo and Parana towards the south, in Goyaz and Matto Grosso in the west, and towards the north in Bahia and perhaps also Pernambuco. Discoveries of new and rich deposits have from time to time been made up to a quite recent date, so that it may be safely assumed that further discoveries are in store in the future, such discoveries being the more probable on account of the fact that many of the diamond-fields hitherto worked are situated in districts almost wholly unexplored.
Up to the present time the state of Minas Geraes has maintained its reputation as an important diamond-yielding region in spite of the fact that, owing to long years of mining operations, its present yield is now much reduced, especially when compared with the yield of the years immediately following the first discovery of diamonds. The place of Minas Geraes, as the State from which the richest yields are derived, is now taken by the State of Bahia, which came into special prominence in the later decades of the nineteenth century. The yield of other States, compared with that of the two above mentioned, is unimportant, but all are as yet too little explored to permit of a final opinion as to their capabilities.
Minas Geraes and Bahia are, however, the only States of commercial importance in respect to the amount and continuity of their production of diamonds, it being doubtful whether stones are found in anything but insignificant numbers in other States.
The important diamond-bearing districts of Minas Geraes and Bahia are shown in the accompanying map. It is proposed now to deal with Brazilian occurrences, taking the different States in the order of their relative importance, and treating them with more or less fullness according to the greater or less detailed character of published accounts. We will begin with the long famous localities of Minas Geraes, of which the majority has been very fully examined and which, to a certain extent, serve as a type of those that follow.
It is usual to distinguish four diamond-fields in the State of Minas Geraes, namely, those of Serro do Frio or Diamantina, Rio Abaete, Bagagem, and Grao Mogol; of these, the first that of Serro do Frio or Diamantina is the most important.
A sketch-map of the district of Serro do Frio or Diamantina. The area is roughly elliptical in outline, the longer axis, stretching from Serro in the south to the Rio Caethe Mirim in the north, being about fifty miles in length; while the shorter axis, from the Rio Jequetinhonha in the east to a line drawn parallel to the Rio das Velhas through the villages of Dattas and Parauna, is about twenty-five miles. It is a wild mountain district traversed by the northern end of the Serra do Espinhaco; this mountain range runs parallel to the meridian, and forms the watershed separating the Rio de Sao Francisco and its tributary the Rio das Veihas from the Rio Jequetinhonha and the Rio Doce. The district forms, roughly speaking, a plateau, the rugged margins of which are cut by deep, steep-sided valleys. The principal town, Tejuco, which since the discovery of diamonds has been known as Diamantina, is situated at a height of 4000 feet above sea level and in latitude 18º 10' S and longitude 43 º 30' W; the district of which it is the capital is now usually known by the same name.
The diamonds occur both on the plateau itself and in the valleys, which cut into it; the richest and best known of these river valleys is that of the Rio Jequetinhonha, with its two branches Jequetinhonha do Campo and Jequetinhonha do Matto (Rio das Pedras) rising in the Serro do Itambe. The general direction of this river is southwest to northeast, its mouth is in the Atlantic seaboard, near to Belmonte, the latitude of which is about 16º S, and in the lower part of its course it is known as the Rio Belmonte. It yields diamonds from its source down to Mendanha, the stones being found not only in the main river but also in its tributaries. While the tributaries on the right bank, such for instance as the Rio Capivary and Rio Manso, which do not rise on the plateau of Diamantina, are poor in diamonds, the tributaries of the left bank which have their sources on this plateau are rich in diamonds, the Ribeirao do Inferno, Rio Pinheiro, Rio Caethe Mirim, and to a less degree the Rio Arassuahy, being worthy of special notice. Other important diamond-bearing streams are a few small water-courses flowing westward from the plateau directly or indirectly into the Rio das Velbas, a tributary of the Rio de Sao Francisco; of these may be mentioned the Rio das Dattas, Rio do Ouro Fino, Rio do Parauna with its tributary the Ribeirao do Coxocira, and especially the Rio Pardo Pequena, which has yielded a large number of extremely beautiful stones, and is probably, after the Jequetinhonha, the most important of all.
Next in importance come the deposits of the Rio Jequetahy and the Serra de Cabrol to the northwest of Diamantina; these are separated from the deposits previously mentioned by a zone from which diamonds are absent. With these deposits may be mentioned a small working in the Jequetinhonha valley, about sixty miles below Diamantina. Aw occurrence which is remarkable in being completely isolated from the other diamond-yielding localities is that at Cocaes, where a few small diamonds have been found; this is situated considerably to the south of Diamantina, and only thirty miles north of Ouro Preto, the capital of the State of Minas Geraes.
Another locality, which must be specially noticed, is the basin of the Rio Doce, on the east side of the Serra do Espinhaco. The river basin is separated from the rich diamond district of the Rio Jequetinhonha by only a narrow mountain ridge, but in spite of this close proximity, only an insignificant number of stones have been found here, the explanation of which will be given later.
Rafal Swiecki, geological engineer email contact
This document is in the public domain.