Brazilian diamonds were discovered around 1725 by
gold miners along the banks of the Rio Jequitinhonha, in the state of
Minas Gerais. For more than a hundred years, the country was the world’s
most important diamond source, as the famous Golconda deposit in India
was nearly exhausted and South African mines were yet to be discovered.
Diamond mining in Brazil continues today, though largely overshadowed by
the output of other countries. But despite sporadic production,
important stones continue to emerge from Brazil. The country has long
fascinated me. Following many visits to colored gemstone deposits there,
I took an August 2012 trip to Minas Gerais—Portuguese for “general
mines.” What I saw led me to believe that the future of Brazilian
diamond mining looks promising.
Brazil has several alluvial diamond sources, where stones are mined from
the sands and gravels of river banks. There are also some potentially
important diamond pipes that may warrant larger-scale open-pit or
underground mining. Diamonds are mined in several Brazilian states,
including Mato Grosso do Sul, Bahia, and Rondônia. I visited an alluvial
diamond mine in Minas Gerais, which is famous for its gold and colored
gemstones, as well as other commercial minerals. Owned by GAR Minerals,
the mine is located near the diamond-bearing Abaeté River and the town
of Três Marias. GAR Minerals has six properties along the Abaeté River
and six others near the town of Coromandel on the Santo Ignacio River,
also in Minas Gerais. Each property is around 2 hectares—nearly five
acres—and licensed for diamond exploration.
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Coromandel is known for large stones with high clarity that are brown or
colorless to near-colorless. The brown stones can be turned colorless
by a high-pressure, high-temperature (HPHT) enhancement process. The GAR
mines along the Abaeté River mostly contain smaller diamonds, but they
have produced some large top-quality pinks.
Important stones GAR has mined in Coromandel include a 263 ct rough
diamond that yielded two 70 ct pear shapes, both H color. Coromandel
also produced a 140 ct rough that yielded a 10 ct E-color and a 56 ct
H-color diamond, both with high clarity. Although the Abaeté River is
the better-known source for pink diamonds, Coromandel has also produced
some specimens, including a 21 ct Fancy Intense pink rough crystal.
At the Abaeté River, GAR has recovered a 26 ct crystal that yielded a
12.60 ct Fancy Intense purplish pink cushion shape. The company also
found a 7 ct rough diamond that produced a 4.24 ct Vivid pink. Colorless
stones from these mines weigh 10 ct or less. It is believed that the
Abaeté River has supplied some of the most important pink to red
diamonds to come on the market in the last 50 years.
The entire length of the river, where GAR Minerals’ properties stretch
approximately 40 km along the bank, has considerable diamond potential.
GAR is a fourth-generation family-owned business. Company officials
anticipate their Abaeté River properties will remain productive for at
least another two generations.
I visited a GAR mine near the Abaeté on a working farm owned by the
family. Getting there from the town of Três Marias required driving on a
dirt road and then crossing a swaying suspension bridge on foot. Like
other GAR properties, it is an alluvial deposit with diamond-bearing
gravel. This entails small open-pit operations in which excavators
remove the gravel all the way down to bedrock and load it into trucks
for careful examination. Because diamonds are denser than most other
materials in the gravel, depressions indicate where valuable
concentrations might be found. Once an area is mined down to the
bedrock, operations continue by following the alluvial gravel along the
riverbed.
Trucks then haul the diamond-bearing gravel to a processing (or washing)
plant, where diamonds are separated from the gravels and other
minerals, often referred to as
overburden. The processing plant
uses a feeder to bring the gravel into an automated system. There it is
washed with a water cannon before separation. A vibrating screen then
removes coarse material, and sluices transport the remaining gravel to a
worker who washes it by hand while a sorter sifts through the material
looking for the occasional diamond.
In an effort to restore areas damaged by open-pit mining, GAR has
implemented a formal plan to refill the pits, while following guidelines
set forth by an environmental impact study.
