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.
[Illustration: 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.
[Illustration: 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._
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