Popular Science Monthly/Volume 69/September 1906/Diamonds and Carbons in Brazil
|DIAMONDS AND CARBONS IN BRAZIL|
By H. W. FURNISS,
FORMERLY AMERICAN CONSUL AT BAHIA
THE best diamonds of the world, those of finest color and fire, come from Brazil, though most of the stones mined are small in size as compared with those from other sections. They occur in various places, more particularly Goyaz, Matto Grosso, Minas Geraes and Bahia. It is only in the latter two states in which they have been found in sufficient quantities to warrant mining.
The exact date of the discovery of diamonds in Brazil is unknown. At the end of the seventeenth century miners were taking out gold in Minas Geraes at Serro Frio and failed to recognize the diamonds which were occurring therewith. It is said that some stones were collected more because of their regularity and beauty of crystallization than from knowledge of their value. These in 1729 found their way to Portugal, where they were recognized as diamonds of unusual purity. The discovery caused quite a sensation at the court of King John V. There was a rush to the newly-discovered region, but the king so restricted mining that little was done until subsequent to 1832, when the present laws became effective.
Diamonds were first discovered in Bahia in 1840 at Santo Ignacio at the extreme northwest of the present region, but not until 1844, when discovery was made by a slave on the banks of the Mocojé river, the present location of São João do Paraguassú, was any great impetus given to mining. The mining area has gradually extended, but no new section was discovered until 1881 when by accident a find was made at Salobro, the diamonds of which usually take the name of Cannavieiras, the port to which they pay tribute.
The quality of Brazilian diamonds varies greatly with the locality in which found, while there is always a considerable difference between those of the same mine. In general, those from Minas Geraes are fairly assorted in quality, about Salobro (Cannavieiras) the beautiful whites and priceless blue whites predominate, while the other Bahia stones are inclined to be more off-colored and frequently contain black specks, thereby lowering their value.
The greater part of the Bahia diamonds differ from those found elsewhere in the world in that they frequently have a thin coat of surface color which gives the whole stone a bad appearance. This color will not yield to acids. To one particularly skilled, the Lying true color can be determined, but to make the stones marketable abroad where this is unknown, recourse is had to heating them red hot and pouring on a chemical when the crust is consumed and the real color appear-. 1 have seen apparently dirty red, green, brown, blackish and yellow stones after burning turn out to be pure whites and blue whites. Stones so treated lose in weight about one per cent., and those with cracks or defects frequently break to pieces.
The largest authentic Brazilian diamond ever found is the famous 'Estrella do Sul' (Star of the South). It weighed 254.5 carats in the rough, and cut and polished weighs 124% carats, with a value of $450,000. The greater number of diamonds found are less than one carat; the average weight is about two carats, while a stone of 10 carats is a great exception.
Carbons which occur along with diamonds are very ordinary looking stones and would be refused as a present by any one not well acquainted with them. Their history is very obscure. Other than a few small ones found in Minas Geraes, and those are of poor quality, Bahia is the only known place where they occur. They seem to have been known in 1848, when a Frenchman traveling through Bahia bought them for twenty-seven cents a carat under the name of 'ferragens' (iron stones). In March, 1856, Mr. Domingos Gomez, of Boncador, took to London 6,475 carats, which he had bought for sixty cents a carat, and was more than pleased to sell them at $1.25 a carat. At that time their sole use was to be pounded to dust for use in diamond polishing.
The later history of the carbon is the history of the so-called diamond drill which now constitutes their principal use. For this purpose stones weighing from 11⁄2 to 4 carats are desired and larger stones have to be broken to these sizes. The drill consists of 6 or 8 carbons set in a crown or cylinder of steel forming the bit. They are set in such a way that they alternately slightly project beyond the inner and outer edge, thereby cutting as they are rotated a core, which is brought to the surface from time to time as desired. Being the hardest known material they will cut the most refractory ores or stones.
As the drill goes around the carbons wear off and have to be from time to time reset, until finally they become so small as to be useless. For this reason, unlike the diamond whose chief use is for adornment, the number of carbons is constantly growing less while the demand is exceeding production. With the perfection of the drill and its great use in cutting tunnels, mines, canals, etc., the price of carbon has steadily gone up from $17 a carat in 1892 to $60 to-day in New York for the best quality of proper size, and the price obtained at the mines has been a fair equivalent.
The average weight of carbons encountered is much larger than that of the largest diamonds. The frequency of occurrence where the two occur together is in the proportion of three of the carbon to one of the diamond, by weight, while good quality carbon is worth more per carat than gem rough diamonds. The miners know this, and it is their constant desire to encounter carbons. Many of them go to the sacred tree near Lenções, where the spirit of Santa Barbara, the patron saint of the miner, is said to have appeared, and place on a limb thereof a stone of the size of the carbon they wish to find. They then pray and it is said that the saint has blessed many of the faithful.
The largest carbon ever encountered was found near Lenções in 1895, on the ledge of a mountain which had been worked some time before. It weighed, when found, 3,165 carats, was purchased from the miner for $16,000 and was finally exported to London, where it sold for $31,145, having lost about 50 carats meantime in drying out. In London it was broken into pieces suitable for drills and these pieces sold for about $40,000, while at the present price of carbon they would be worth about $158,000.
The next largest carbon was found this year, and is still in the bands of the miner. It weighed when found 869 carats, but has lost
several carats in drying. It is of finest quality and almost rectangular shape. The equivalent of $26,400 was offered for it six months ago, but the owner has set a price which to-day is the equivalent of $45,625, an impossible figure, as in breaking there is always considerable loss. When carbon advances beyond a certain figure the sale of necessity decreases, as then there are other products which are used even though lacking in durability and other desirable qualities.
The genesis of the diamond and carbon has not been worked out for this section. Whatever it proves to be, it is certain that at one time they were all confined in a conglomerate which shows evidence of being of more recent geological date. The conglomerate differs in character in the different sections. In the neighborhood of Lavras Diamantinas it consists of many colored water-washed pebbles and boulders, chiefly sandstone of the same nature as the strata found immediately below it; in the Salobro region it consists chiefly of granite pebbles. In both instances the matrix is sand of different degrees of hardness, fineness and color.
With the ages a great part of the conglomerate has disintegrated and the rains and rivers have washed the diamonds and carbons to the places where they are now being found. There are large masses of conglomerate in many places which have resisted this action, and unless mechanical means are brought to bear will continue to yield diamonds and carbons for the ages during their disintegration.
The region about Salobro is comparatively flat, in fact the greatest deposit occurs in an area practically level, doubtless the old river bed. In the other sections of Bahia the country is rocky and mountainous. There is so much of rock and so little of soil that only small plants grow, and then only during the rain time. In some cases the rivers pass through gorges cut into the solid rock and most precipitous and awe-inspiring. On all sides there is much of interest. The rock formation is a very hard reddish sandstone which completely underlies the conglomerate and like it shows the disintegrating effects of water and climate. In places it has deep cracks which have become natural canals, accumulating with the ages a concentrated diamond-and carbon-bearing gravel. In other places immense pieces of sandstone and conglomerate are piled up heterogeneously as if they had been dumped there. The canal Simplicio Braga is a combination of these two varieties and was one of the richest finds of the region.The diamond section of Bahia is much more accessible than that of Minas Geraes. One can arrive at Andarahy, the heart of the region, in four days from Bahia City, five hours of one clay being spent in journey by boat, twelve hours of the next by train and two days by mule. The trip is without hardships to one accustomed to travel. It is along attractive scenery, across rivers and mountains, passing through a section with beautiful calcareous caves, but with an entire
lack of water, except that of the river miles away and that caught during the few rainfalls.
Most of the mining is done by individuals called 'garimpeiros,' who either work for themselves or on shares with the owner of the claim. In Bahia, the number of owners hiring laborers to work their claims is not more than half a dozen.
The miners are almost entirely blacks or of mixed race. The greater part of them live in near-by towns, but many have quarters built beneath an overhanging ledge, from which they have removed the diamond-bearing material.
Their food consists chiefly of native beans with jerked beef and an abundance of mandioca meal, which takes the place of bread, with now and then fresh meat, a much prized boiled dinner or a piece of salt fish. Drinking water is in abundance everywhere. Native rum can be had very cheap, yet the number addicted to intemperance is very small, wonderfully so for a mining region.
Many times provisions are advanced by the grocer until a find is made, when all is paid up, and if there is a balance such high-priced articles as beer, American canned oysters, lobsters, etc., are indulged in as long as the money lasts.
The health of the region leaves much to be desired. Because of the great quantities of semi-stagnant water on every hand, every facility is given to create anopheles mosquitoes, with the result that malaria in it? worst types is always in abundance.
By far the greater part of the successful mining is still done by antiquated methods which have the advantage that they require little capital for an outfit. A miner's tools consist of a short-handled hoe with which to stir up diamond-bearing gravel in a sluice; a crowbar to pry up stone to lay bare deeper layers or to break down banks of clay or gravel; an iron hook on a pole with which to take diamond bearing gravel from beneath large stones or from cracks otherwise inaccessible; a small wooden basin, called 'carimbé,' for carrying the gravel on the head; a large wooden basin, called 'bateia,' for final washing and concentrating the gravel; some kind of a sieve, from a tin can with nail holes to a more pretentious wire sieve, for sorting gravel and sand during the washing or concentrating process; a hammer and drill for making holes in rock for blasting, but quite often instead fire is built upon a rock desired to be removed, and after the
rock has become very hot cold water is poured thereon, effectively cracking it and permitting its removal.
In the home of the carbon there are no carbon or other mechanical drills. At present one man can make from two to three holes a day, which with proper methods could be made in a few minutes.
The method of mining differs in various sections. In the richest areas the work is of two kinds: removing the subsoil surface disintegration and gravel and that in the gullies, cracks and beneath the more accessible stones, or mining by tunnels or following cracks into the pockets of the mountains, taking out the diamond-and carbon-bearing material consisting of soil, sand, gravel, boulders, broken and disintegrated stone, etc., called 'cascalho.'
The other method is in diving to the bottom of rivers and taking out the cascalho from there. This method is confined to a small section of the district where the river runs through a natural canal
cut into the rock. The diving can only be done when the river is low and is chiefly done naked, though there are a few diving suits in use. The naked divers descend a pole planted in the river and fill a sack with the cascalho, which is taken on shore for washing. The ability of some of these men to go to great depths and stay under for long intervals is extraordinary. In some places attempt is made to work the old river bed, but this is done with great difficulty, as water will seep in almost as fast it can be bailed out, leaving little time for the collection of cascalho.
Whatever the method of taking the cascalho out, the great desideratum is an abundant supply of water for washing. Where it is possible water from mountain streams is conducted down by ditches and flumes, and into these the cascalho is thrown. It is worked with a hoe. by which method the lighter particles are washed away, thus leaving a greater concentration which includes the diamonds and carbons. The concentration is taken out of the ditches and accumulated until the week's end, when it is laboriously further concentrated in bateias.
This final concentration and wash-up requires considerable dexterity as well as strength. It consists in revolving and shaking the bowl that the portions of heavier specific gravity accumulate in the point in the bottom, while the lighter particles and the large stones are thrown on the edge of the bowl and are from time to time scraped away with the hand, being examined meantime. While the vision of
those engaged in this process is very sharp and they will frequently take out from sand and pebbles diamonds smaller than a pin's head, yet from investigation I know that by this method many large diamonds and carbons escape them. This in part accounts for the reason why large diamonds and carbons are frequently found in gravel already washed and picked over. I have heard of places which have been washed for the fourth time and paid, though doubtless in some of these instances the later finds were due to disintegration of conglomerate which yielded up stones heretofore inaccessible.
The limit of a good man is to concentrate and pick over a cubic yard of cascalho per clay, but this presupposes that the cascalho is easy of access and that the water is near at hand. If the cascalho has to be taken from the cracks, crevices, caves, etc., and with the present methods of mining those are the only places with virgin material which are accessible, it is accumulated very slowly. When it is remembered that at the South Africa mines there is worked over 192,000 cubic feet per day, it can readily be seen why the output of Brazil with its few thousand of hand-workers sinks into insignificance, if indeed the diamonds are in Brazil to extract.
The mines of Minas Geraes have been worked regularly since their discovery, chiefly by hand methods until during the last ten years when some machinery has been installed to aid in the separation of the diamond-producing gravel from the clay and sand and later on in partly sorting the gravel prior to the final clean-up which is always by hand process. In Bahia a little machinery consisting of a few pumps, a gravel sorter and a so-called automatic separator, which does not separate, has been installed at Salobro, but it is being allowed to rust out, work at present being done by hand entirely ignoring the machinery. The only other machinery in the great Bahia district consists of a few pumps mounted by an English company on the São José river. This company has machinery in transit for mounting a small electro-hydraulic plant, but will still leave the clean-up to hand process instead of adopting the automatic table in use at South Africa.
The diamondiferous lands of Bahia are owned by the state and leased either as small claims or large parcels to parties or companies desiring to work them. About all of the known areas capable of work with groups without machinery have been preempted. The nature of the work already done has been such that many productive areas have been covered with tailings. The river beds and other productive sections which will necessitate machinery are still awaiting exploitation.