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GEMLAB REPORT:
November 1997 - Issue #5
by: Ted Themelis
themelis AT mail.otenet.gr
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In This Edition:
- Diamonds from Venezuela
http://www.ganoksin.com/borisat/nenam/gemlab5.htm
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Diamonds from Venezuela
Venezuela currently produces about one percent of the world's
total diamond output and represents one of the most important
sources of diamonds in the Americas. Of special interest are
the white and fancy colored diamonds found there, about which
very little has been written.
History of Production
Diamonds were first discovered in Venezuela in 1902. There
followed sporadic and limited production from that point until
1913. In 1915, diamondiferous fields were discovered in Rio
Paragua and Rio Caroni. The first diamond company was formed,
known as "Compania Anonima El Pao", which lasted until 1943.
Around 1927, settlers arrived in Gran Sabana, and by 1930,
diamond exploitation had initiated with Brazilian
collaboration. While considerable mining activity ensued at
the Paratepui and Rio Surukun areas, production was limited.
Gradually, additional diamond sites were exploited at the
upper Caroni River (Santa Teresa, Agua Negra, Salva La Patria,
El Vale, and El Polaco). However, production was limited and
inconsistent untill 1942.
In 1942, the recovery of a 154 carat diamond crystal, the
largest found in Venezuela and known as El Liberdador, created
intense interest and a diamond rush followed. That same year,
additional diamondiferous areas were discovered at Rio
Icabaru, Rio Uaiparu, Guari, and others. In the subsequent
years, other areas were exploited: in Gran Sabana, Uriman,
Capaura, and Avequi in 1943; Cinco Ranchos in 1950; and in the
fields at upper Paragua: El Casabe, Manare, Oris, Asa, and
Chiguao in 1954.
The introduction of mass mechanized mining operations then
dramatically increased the production of Venezuelan diamonds.
Diamondiferous areas at the lower Caroni -- Caruachi, Playa
Blanca, Rio Claro, and Merey - were exploited in 1961. In
1963, the practical gold and diamond method of mechanized
barges, known locally as chupadoras, was introduced, which
also resulted in a considerable increase in production. In
1968, the rich deposits of San Salvador de Paul and the nearby
areas of Rio Parupa were exploited, followed by the most
important diamondiferous deposits at Guianiamo in 1970.
Guianiamo alone produced 85% of the total gem-quality diamonds
mined in Venezuela for the period 1970-1978. During the last
decade 1978-1988, diamond production there has risen steadily.
No reliable diamond production figures are available in the
last decade.
Geology
All of the Venezuelan gold and diamond mining districts (which
generally occur together) are situated within the
physiological structure of the Guyana Sector (Escudo de
Guyana) that occupies nearly 423,000 square kilometers, or
roughly 45% of the total Venezuelan area. It is considered by
many geologists to be an extension of the Guyana/Roraima group
formation, one of the planet's oldest.
The Guyana Sector consists of the State of Bolivar and the
Venezuelan Amazon Territories. The sector stretches from the
northern banks of Rio Orinoco to the Brazilian border at the
extreme south. The eastern part of the sector is located along
the side of the politically disputed Venezuelan/Guyanese
territories: the western part ends at the Colombian border.
Venezuelan diamonds are found in either eluvial or alluvial
deposits. Eluvial deposits are formed by weathering and
concentration in place by erosion agents of wind or rain wash.
La Hoyada, El Polaco, and Leoncio are representative
localities.
Alluvial deposits are gravelly and are derived from
conglomerate formation. They are transported from other
localities and placed on land by various erosion agents, such
as streams, wind, and soon. In most cases, gravel and
conglomerate containing diamonds are covered with river sand.
Representative localities include Chiguao, Rio Icabaru, and
Rio Oris. Kimberlite pipe has not yet been found in Venezuela.
Well-informed geologists, however, have found indications that
it may exist.
Diamondiferous Localities
Based on morpho-phyiological criteria, the diamondiferous
areas may be classified into several zones, namely Guyaniamo,
Rio Caura, Rio Aro, and Caroni. ( Numbers enclosed in
parentheses following mining sites refer to the corresponding
diamondiferous localities shown on the map in Figure 2.)
Rio Guyaniamo Zone. The remote, largely inaccessible
mining sites of Caicara (8), Guyaniamo (15). And Guebrada
La Grande (19), are dispersed along the banks of the Rio
Guianiamo, ending at the Venezuelan Amazon territories.
By far, the most productive diamondiferous area in
Venezuela since its discovery in 1970 is the Guyaniamo
(15) diamond fields. This zone is determined as inferior
Precambrian.
Rio Caura Zone. The riverbeds and banks of the nearby
creeks at the upper Caura (28) River.
Rio Aro Zone. The riverbeds and nearby banks at the lower
Aro River (7); also at Veri (13) and Dori (17), in the
upper Rio Aro.
Rio Caroni Zone. This zone occupies the riverbed and the
nearby banks of the Caroni River, which may be divided
into three sections, namely: lower, central , and upper
Caroni. The Caroni zone is determined as superior
Precambrian.
The lower Caroni section consists of the following
diamondiferous mining areas: Rio Caroni with Caruachi (1),
Playa Blanca (2), Ancho Caroni (3), Rio Claro (4), El Merey
(5), Caroni (6), Piar (9), Paviche (10), El Pao (11), San
Pedro de las Rocas (14 and 16); also El Casabe, Manare, and El
Perro. Currently, the most important areas are the Rio Claro
and Caruachi. Both are located about 30-35 kilometers east of
Cuidad Bolivar and extend West along the south banks of the
Rio Orinoco up to the tiny town of Passo Caruachi.
The central Caroni section consists of Caroni (18), Rio Oris
(21), Rio Asa (22), San Salvador de Paul (23), Chisguao (24),
Asa (25), Caparo (26), Parupa (27), Guacharaca (29),
Guachaquita (30), and Capaura (31); also Sute, Islas Monagas,
Carrao, Los Frijoles, and others.
The upper Caroni section has a morphological formation with
three distinct diamondiferous areas, known as: oriental,
central, and occidental, with their corresponding mining
districts.
The oriental area of the upper Caroni consists of the eastern
part of the upper Caroni with the following localities noted:
Gran Sabana (32 and 35), C.O.D.S.A. (36), Santa Elena (37);
also Rio Kukenan, Guara, Rio Aponguao.
In the central area of the upper Caroni there are La Hollada
(38), El Polaco (39); also Rio Surukun, Santa Teresa, Agua
Negra, Salva La Partia, El Valle, and Paraitepui.
The occidental area occupies the western part of the upper
Caroni and includes Caroni (34), Rio Icabaru (40), and Los
Caribes (41). The upper Paragua may also be included in the
same section with La Paragua (33) and Paramichi (42). Other
localities include Surukun, Los Caribes, etc.
Mining Operations
Extensive mining operations devoted exclusively to diamonds do
not exist in Venezuela. The focus, emphasis, and prime target
sought by the miners is gold. The diamonds are considered the
by-product of the gold operations. At least one once of gold
must be recovered daily to justify all operating costs and
make the mining efforts worthwhile.
Depending on the type of diamond deposits, the mining
operations are generally carried out by one of two methods:
river or open pit mining.
In river mining, mechanized barges equipped with suction hoses
up to 10 inches in diameter extract the diamondiferous gravel
from the riverbed; the suction hose is directed by a diver.
The gold and diamond-bearing gravel is brought up for
subsequent mass mechanized screening and washing.
In open pit mining, the prospected diamondiferous area is
divided into 10x10 meter parcels. The miners typically work in
groups of three or four persons using a type of mechanical
sieve known as a jig or something as a pulsator jig. This is
used to separate diamonds and other heavy minerals from
lighter concentrate. The diamondiferous gravel is fed through
a revolving screen known as a trommel. A series of separation
screens bearing holes of different sizes, ranging from one to
1/8 inches in diameter, are used for screening. Running water
is necessary to carry out the subsequent sorting and washing
operations. Open pit operations may range up to 15 meters in
depth.
In many areas, the recovery of gold and diamond is performed
with sluice methods.
Color and Sizes
The diamondiferous Venezuelan districts, together with certain
mining districts of Guyana (formerly British Guiana), Sierra
Leone, and Borneo, represent one of the most significant
sources of fancy colored diamonds in the world market;
reddish, brown-reddish, pinks, blues, blue-green, greens,
yellow-green, and so on, and their counteless intermediate
hues. Recently, black diamonds were found in Venezuela and
were offered at astronomically high prices.
Colorless diamonds of various qualities and sizes are readily
available, right on the mining site. Very often the crystals
are coated with "skins" of green, yellowish, and other colors.
Diamonds recovered from the Paragua River and its banks are
characteristically coated with an iron oxide skin. However,
fine quality gems have been cut from these crystals.
In spite of the general belief that all natural blue diamonds
are of type IIb, it is reported that some Venezuelan as well
as the Guyanese natural blue diamonds are of type I, since
they contain no boron, neither are they electrically
conducted. Furthermore, they do not exhibit significant
absorption/emission infrared spectra.
Most of the gem-quality diamonds found are up to 1-1.5 carats
in size in well-formed octahedra, macles, dodecahedra, and
cubic crystals. El Liberdador, the largest Venezuelan diamond
found, was recovered in 1942 by Jaime Hudson "Barabbas" while
working in an old dump at the Surukun area near Icaburu. The
154 carat stone, also known as Bolivar, was sold for $63,000
and cut ceremoniously by Harry Winston. It yielded one
beautiful 40 carat, flawless stone and two smaller stones, one
18 carat and one 12 carat diamonds. The 40 carat stone was
sold for $185,000.
Production & Marketing
It is very difficult to obtain verifiable production figures
of the total diamond production in Venezuela. Figures on Table
1 and 2 may be used as an indication only. It is based on the
diamond production reported to the Ministry of Mines; however,
the actual figures may very considerably. Nonetheless, diamond
production in the last few years has increased significantly,
especially at the diamondiferous zones of Guaniamo and San
Salvador de Paul.
The rough diamonds are marketed right at the various mining
centers through a network of licensed buyers/dealers under the
supervision of the Ministry of Mines. These centers are mainly
at Icaburu, San Salvador de Paul, Guaniamo, and Cuidad
Bolivar. Nearly all the rough diamonds are exported to Belgium
and Holland. The upper grade and larger diamonds are cut in
Antwerp; all other grades are cut in Israel, India, and
elsewhere. Very limited diamond cutting facilities are
available in Venezuela. The workmanship performed there is
rated below the international standards.
Prospects for the Venezuelan fancy color diamond market may be
termed good. A stable political situation, positive government
intervention to diamond operations, increased fancy color
diamond demand, well-controlled diamond prices, updated mining
technology and equipment, and improved transportation, among
other factors, contribute to a reasonably reliable and
effective output of fancy color diamonds.
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All rights reserved. Copyright Ted Themelis Users are
permitted to download the information for their own private,
non-commercial use. Any other use or reproduction of this
document (text or graphics) without the express written
consent of Ted Themelis themelis AT otenet.gr is strictly
prohibited.
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