Brazil: Minas Gerais Gems & Minerals
Mining Locations in Minas Gerais, Brazil
Article Copyright © 2012 AllAboutGemstones.com
The state of Minas Gerais (Portuguese: "general mines") is one of 26 Brazilian states, located on the western side of Brazil's Southeastern Subdivision. Belo Horizonte is the state's capital, located near the center of Minas Gerais. Portuguese colonists created the state of Minas dos Matos Gerais, later renamed "Minas Gerais," in 1720, while exploring this region of Brazil in search of gems, gold, and other valuable natural resources.
The town of Ouro Prêto (fromerly Villa Rica) was established as one of the region's first mining settlements, when gold was discovered at the Passagem Gold Mine in 1719. A gold-rush ensued in Minas Gerais, and soon other gold and gem mines began to appear. The Mina do Chico Rei gold mine was founded soon after, and the Rodrigo Silva imperial topaz mines were established as a commercial gem deposit in the mid 1700s. Ouro Prêto (below, left) became the state's capital during the 1800s.
During the last 100 years, the cities of Governador Valadares and Teófilo Otoni to the north-east, have established themselves as major hubs of the gem-trading industry, due to their proximity to some of the richest gem deposits in Brazil.
Although topaz was one of the first gems to be discovered here, a wide variety of valuable minerals have since been discovered. Minas Gerais has vast quantities of aquamarine, chrysoberyl, diamond, emerald, kunzite, morganite, and tourmaline, making it one of the most productive gem-mining regions on earth.
During the 1700s, when Minas Gerais was under Portuguese control, gold and gem mining labor was conducted by slaves taken from the west coast of Africa. This accounts for the large percentage of African descendants who now populate the region.
Garimpo Mining in Minas Gerais
Currently, much of the mining in this region is done by small-scale freelancers known as "garimpo" or artisanal miners, who conduct what is know locally as "informal mining." These garimpeiros work the alluvial gravel-deposits along Minas Gerais' riverbanks and stream-beads, mining and/or sluicing by hand to unearth the region's gems or gold.
Slave Gem Miners in Brazil c. 1780
Mechanized hard-rock and open-pit mining (aka "formal mining"), is done by larger multi-national companies, under the supervision of the Miners Union of Nova Lima, and SISNAMA (Sistema Nacional de Meio Ambiente) or the "National System for the Environment."
Geology of Minas Gerais
The gem-bearing pegmatites of the Minas Gerais region are some of the most significant deposits in Brazil and the world. The topography consists of hilly country defined by mounds called inselbergs, which are pegmatites that eroded more slowly than the surrounding schists and metamorphic rock .
As the pegmatites began to erode after prolonged exposure, tougher material such as beryl, topaz, tourmaline and quartz were transported to secondary eluvial and alluvial deposits located in downstream drainage basins.
The Gems of Minas Gerais - Aquamarine
The finest Brazilian aquamarine comes from the Marambaia valley region of Minas Gerais, 100 kilometers north of Teófilo Otoni. The highest concentration of aquamarine occurs with gem-bearing pegmatites located near the villages of Catugi, Ponto de Marambaia, and Padre Paraíso (see map below).
Just to the north-west of Catugi is the Arazuai-Itinga region with the Pioneer mine, Três Barras, Salinas, Serra do Urubu, and Ouro Fino aquamarine and tourmaline deposits.
Significant aquamarine finds in Minas Gerais included the near-flawless 244 lbs, 552,500 carat Papamel Aquamarine, found in 1910 from the Papamel mine (aka Batadal mine) along the Marambaia River, 12 miles east of the village of Ponto de Marambaia.
Map of Marambaia Valley (left), Diamantina (right)
Runner-ups to the Papamel were the 173,500 carat Marta Rocha Aquamarine, 110,000 carat Quarto Centenario aquamarine, 96,000 carat Estrela de Alva or 'Dawn Star' aquamarine, and the 10,395 carat Dom Pedro Aquamarine found in 1993.
Aquamarine is also located in the Município de Pavão region, to the immediate west of Marambaia valley in the Vale do Mucuri (Mucuri river valley). This valley stretches along route 409/105, between the villages of Crisólita, Pavão, and Topázio, north-west of Teófilo Otoni.
Imperial Topaz from Minas Gerais
Topaz mining in the vicintity of Ouro Prêto dates back to the 1700s. Imperial Topaz was originally mined in the "topaz belt" of Minas Gerais, which was comprised of three distinct regions (Dom Bosco, Rodrigo Silva, Saramenha) near the mining town of Ouro Prêto. In 1768, he Portuguese government designated all gem deposits in the region as property of the crown, under state control. The Mina do Capão, near Ouro Prêto has produced some of the finest imperial topaz (topázio imperial) in the Brazil.
Brazilian Imperial Topaz
Diamonds from Minas Gerais
Brazilian diamond mining in Minas Gerais was short lived. In 1714, Brazil's first diamond discovery was made by miners prospecting for gold along the Rio Jequitinhonha river near the town of Tejuco (now Diamantina), in the Espinhaço Mountains (el 4,100 ft). By 1729, the Portuguese government had declared the placer mines as the property of the crown, labeling the area as a "forbidden district," and proclaiming a "royal monopoly" on all mining.
In the years that followed, there was a diamond-rush to the Rio Jequitinhonha and Rio Abaeté alluvial deposits, and diamond production in the region reached its peek between 1785 and 1807. Thereafter, there was a rapid decline as the area became mined out. Recent diamond exploration and development is being conducted by Brazilian Diamonds Limited, CODEMIG, Tejucana and Mineração Rio Novo Ltda.
Emeralds from Minas Gerais
Brazil is the one of the largest volume producers of emerald in the world, and the states of Minas Gerais, Bahia, and Goias have the largest deposits in the country. Significant emerald deposits in Minas Gerais are found at the Capoeirana mine and Itabira mine in Nova Era, Município Itabira, about 90 kilometers east of Belo Horizonte. Brazil has been known to produce large rough emeralds up to 200 carats in size.
Tourmaline from Minas Gerais
Brazilian tourmaline is found in igneous rock pegmatite dikes and alluvial deposits (cascalho), located in the area around the Município de Virgem da Lapa, north of Teófilo Otoni. The Ouro Fino, Arazuai-Itinga, and Arazuai-Salinas mining areas north of Marambaia are a significant source for green (chrome) tourmaline in the Teófilo Otoni/Marambail region.
Bibliography on the Gems of Minas Gerais
1. Caltech, Ouro Preto District . minerals.gps.caltech.edu
2. Wyoming State Geological Survey, W. Dan Hausel, Gems of the World - Geology, Occurrence & Exploration.
3. Jstor, Slavery in Brazil - Diamantina . links.jstor.org
4. Escola de Minas Diamantes do médio rio Jequitinhonha' Minas Gerais . www.scielo.br
5. Diamantes Qual terá sido o caminho das pedras . PDF
6. Walter Schumann, Gemstones of the World . NAG Press; 2Rev Ed edition