DIAMOND MINING IN BRAZIL.
It was in 1729 that the Portuguese government learned of the discovery of the diamond that had been made in the rivers of the environs of Diamantina by some adventurers who had entered this region in search of gold. Since that epoch the exploitation of this gem, pursued under varied regimes, and with diverse success, has never ceased. As soon as it heard of this discovery, the Portuguese government thought it would make as much profit out of it as possible, so it no longer authorized any other exploitation in the Diamantina regions than that of the diamond, and it imposed upon such exploitation a tax that was fixed at 28 francs per laborer in 1729 and 224 in 1734. From 1734 to 1739 all operations were suspended, and a more lucrative organization for the treasury was sought for. In 1739 the era of contracts was inaugurated. The exploitation of the diamond was farmed out for four years to a contratador, who was to work a certain territory with a number of men, fixed at 600 as a maximum, and to pay into the treasury a sum per workman (whether working or not) that varied from 1,288 francs per year in 1734 to 1,344 francs for the last contract, that ended in 1772. At this epoch the government took the exploitation of the diamond in hand, and gave it in charge of a special administration, which was submitted to the direction of the treasury of Lisbon, and which had at its head a comptroller. This new regime lasted till 1845. In order to render the surveillance of the treasury agents efficient, and prevent smuggling (which can be so easily done with an object like the diamond), it was necessary to impose a special regime over the entire region of Diamantina, and, in fact, the latter was, up to the independence of Brazil, submitted to Draconian regulations.
FIG. 1.—DAM ON THE RIBEIRAO INFERNO AT PORTATO DE FERRO.
We only know the quantity of stones that were discovered during the period when operations were directed by the Royale Extraccao, from 1772 to 1845, and this was 269,870 grammes, or more than 1,300,000 carats. It should be understood that what was taken by stealth does not enter into this total, and it must be stated that during the latter years, when the Extraccao existed only in name, smuggling must have been active.
FIG. 2.—ARRANGEMENT OF THE MACHINERY AT THE PORTATO DE FERRO DIAMOND DEPOSITS.
Since that epoch the exploitation has been continued by lessees of the diamondiferous grounds. It is almost impossible to estimate what the territory has produced. The discovery of the Cape deposits has given it a terrible blow. Although the Brazilian diamond is much more beautiful, and for this reason is held at a much higher price, these new exploitations, by annually throwing large quantities of stones upon the market, have led to a great reduction in the price, and the Diamantina exploitations, which have become long, difficult, and costly, have received a serious set-back. So the annual production of this region, which was estimated for the years preceding 1870 at 3,000 oitavas (about 52,000 carats), is now scarcely 500.
The rivers in the environs of Diamantina rim at the bottom of deep and narrow gorges that have been scooped out to depths of 300 or 400 meters through the denuded plateau in whose center stands the city of Diamantina. In the bed of these rivers, in places where they have not yet been worked, there may be found, underneath a stratum of modern sand, another of rocks, and finally a diamondiferous deposit of rounded pebbles, mixed with sand. This gravel, which is characterized in the first place by the fact that all its elements are rounded, and next by the presence of a large number of minerals (among which the most important are all the oxides of titanium, different oxides of iron, tourmaline, and a whole series of hydrated phosphates of complex composition), is called in the language of the country cascalho. It is the matrix of the diamond, and the latter is extracted from it by washing. It is arranged in roundish masses upon the beds of the rivers, and is met with at depths ranging from a few decimeters up to 25 and 30 meters.
The same material, with the same name, is also found deposited at all heights upon small terraces at the sides of the valleys through which the rivers flow. It is coarser and less rolled, and has very likely been deposited by risings of the rivers during the period when the valleys were being formed. These deposits bear the name of gupiarras. Finally, it is found in a still coarser state, mixed with red earth and deposited in horizontal strata upon the upper plateau. It is then called gorgulho.
Of these different deposits, the most important are those of the river beds, the material here having undergone a true mechanical preparation and being richer. These are the deposits that have been the object of the most important exploitations.
The year is divided into two distinct seasons—the dry, from May to September, during which rain is exceptional, and the rainy, from October to April. As water is necessary for all the operations, no work can be done upon the high plateaux except through rain water stored up in large reservoirs. These beds form what are called the "rainy season washings." In the rivers the working of the beds requires a preliminary drying, which is effected by diverting the river's course. Now in all this rocky and denuded region the water that falls runs immediately to the river, and causes terrible freshets therein; so operations capable of keeping the bed dry would be out of proportion to the probable results of the exploitation, whence it follows that the latter is only possible in dry weather, and these deposits are therefore called "dry season washings."
These deposits are still worked in our day as they were in the time of the Portuguese. In order to dry the bed a dam is constructed, and the river is either diverted into a plank flume supported by piles, or into a canal dug along the shore, or by means of tight walls, according to the lay of the place. The second process, which is preferable to the first, is in fact impossible when the river runs, as is often the case, in a narrow, abrupt, walled channel. These works are sometimes very important. In 1881, the Acaba Mundo flume was 140 meters in length and 5.2 m. wide, and, with a velocity of 2.25 m., discharged 4,500 liters per second; still longer ones might be cited that discharged as much as 8,000 liters.
In the dry part of the river the extraction of the sand, stones, and cascalho is done solely by hand. The men carry the sand upon their heads in small wooden bowls called carumbés, which hold about 15 kilogrammes, and throw it somewhere where the deposit will not interfere with the exploitation. Almost all of these men are negroes, who run with their load upon their head over the white sand, singing some song of their country. It, is very picturesque, but it is doubtful whether it is economical.
Since the century and a half that these rivers have been dug and redug, it may be admitted that wherever the cascalho has been easy of access it has been removed; and that wherever it has not been, little attempt has been made to work it. How have these attempts, which have doubtless been made at several periods, come out? This would at present be very difficult to ascertain. The exploitations have been too numerous to allow us now to estimate the value of a bed from the data furnished by geology, and local tradition is too uncertain or exaggerated to allow us to place much confidence in it.
We can, at the very most, say that if some points still remain intact it must be because the exploitation of them was too difficult with the processes that were employed, and this should be a reason, were it desired to attempt new operations, for having recourse to entirely different modes of work.
It would seem rational, as regards this, to try to put to profit the hydraulic power that the flumes and canals render disposable for mechanically extracting the sand. The field to be worked being naturally long and narrow, it would be the proper thing to employ a series of inclined planes distributed along the banks, actuated by water wheels, and corresponding to so many small working points. The river often flows through a genuine canon with nearly vertical walls, where space would be absolutely wanting for installing wheels elsewhere than at the exit of the canal, and if may become necessary to distribute the power of these wheels along the works. In these regions of difficult access and few resources it is necessary to dispense with complicated apparatus, and one might in such a case, it would seem, try electric motors, whose installation would be easy. An exploitation in accordance with these ideas was begun for the first time in 1883 upon the Ribeirao de Inferno at Portao de Ferro. We shall describe it.
Once established in the country, the first thing to do is to form roads so as to secure communications with the neighboring villages and forests, and afterward to cut down trees for building houses. These latter are usually constructed, for these works, of untrimmed wood and mud, with thatched roof. There were thus constructed at Portao de Ferro a few kilometers of roads, then some houses for the engineers and special workmen, barracks for 200 laborers, stores, kitchens, etc., a forge, and a shop with a lathe and a saw run by a wheel at the side. It was afterward necessary to repair the old lateral canal which had been dug out of the rock in the times of the Royal Extraction, but which had been torn open for a considerable length. This necessitated the erection of tight walls of dry stone, grass, and mud, for a length of 200 meters, and with thicknesses of from 6 to 10 meters.
In order to divert the water into this canal, it was necessary to raise its level 5 meters. The dam, then, had to support a strong pressure, and it could not be built upon sand. It therefore became necessary to build a temporary dam and to turn the river into a plank flume, so as to make it possible to dig at the location of the permanent dam in order to reach a solid bottom at a depth of nearly 4 meters. The permanent dam thus had a total height of 10 meters, with a thickness of 15 at the base and 7 at the top. It was constructed of dry stone, grass, and earth, with the addition of strong wood-work. The rocks upon which it had to be built were full of fissures, and when it was desired to close it great leakages of water occurred, which came near ruining it and necessitated the construction of a second wall behind it and a talus of earth in front. The dam as shown in Fig. 1, when finished, had a thickness of 25 meters at the base. It was closed on the second of July, and had a storage capacity of 55,000 cubic meters.
The principal excavation was begun at the point where the bed was deepest, and which consequently the older miners must have had most trouble in reaching. Here were set up two Letestu pumps that were actuated by a four-horse wheel.
These pumps lifted 50 cubic meters per hour. All except the pump chambers and pipes was made of wood on the spot. The water that was lifted was carried away from the works in a flume 160 meters in length, which likewise removed the water from the motive wheels.
For the service of the same excavation two simple acting inclined planes were installed that were moved by a four-horse wheel. Fig. 2 gives a general view of the arrangement.
The tracks of these planes were made of wood. Steel rails, however, had been brought for the cars, along with the cables and the metallic parts of the windlass; but all else was made upon the spot, including all the wooden pulleys for transmitting motion from the wheel to the windlasses.
This excavation reached bottom at a depth of 16 meters. The second touched bottom at about 10 meters, and gave access to a subterranean canal, which was followed for about 20 meters. The extraction of sand was effected here by an inclined plane moved by a Gramme machine. The generatrix had to make 1,500 revolutions, and be set in motion by an overshot wheel. As time was wanting, it became necessary to diminish to as great a degree as possible the number of parts to be employed in the transmission of motion, and since there was an abundance of water, a velocity of 15 revolutions was accepted for the wheel, which, with a total fall of 4.8 meters, had to give a power of eight horses. A three meter pulley was placed upon the shaft of the wheel. This was made of freshly cut wood that had been exposed to the sun. In order to give it sufficient stability and prevent its warping, it was placed against the wheel in such a way as to rest upon the latter's spokes. This rendered it necessary to give up the idea of using a belt, since it was not possible to prevent its getting wet. Cords could not be found in the country, and so it was necessary to make use of a too heavy chain, which was in no wise intended for such a purpose, and which at a velocity of 15 revolutions began to swing and necessarily absorbed much power. The large pulley drove one of 0.4 m. upon an intermediate shaft. Upon this latter a 2.6 m. wooden pulley directly drove, through a belt, the 0.2 m. pulley of the generatrix.
From this may be judged what the country's resources are. The motor, by means of a belt, actuated a windlass provided with suitable checking gearings. The distance of the two machines was 116 meters. Save the transmission by chain, the whole worked in a satisfactory manner. The performance could only be estimated in a lump, by comparing on the one hand the theoretical work of the fall of water, and, on the other, that of the vertical elevation of the car; and, further, one was obliged to estimate the weight of the latter. If we allow 1,000 kilogrammes for the weight of a car that received 360 liters of dry sand or 300 of wet, the performance was 19 per cent., and appeared to be satisfactory, considering the conditions under which the installation was made. This experiment was at all events of such a nature as to indicate the use of these machines in cases where the arrangement of the locality absolutely necessitates a transmission of power.
The first workmen reached Portao de Ferro December 15, 1882, and the material shipped from France did not arrive until April 25, 1883. Operations were suspended about the 25th of September, since, for a fortnight already, there had no longer been any doubt as to the manner in which the river bed had been cleaned by former operators.
As a result of this first experiment, the proof remained that it would be easy in future exploitations to introduce into the country methods of work that are quicker and more economical than those now in use. In fact, all the operations were performed with natives of the country, with the exception of a carpenter and blacksmith from Rio Janeiro.—La Nature.