Monday, 25 November 2013

Gemstones of Minas Gerais, Brazil

Brazil produces the greatest variety of gems and semi-precious stones in the world, including diamonds, emeralds and amethyst.
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.

Some of the most spectacular gems come from the state of Minas Gerais. This area produces emerald, aquamarine, rubellite (pink tourmaline), green tourmaline, imperial topaz, alexandrite and amazonite.
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.
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 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.
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 Brazil.
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.
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 peak between 1785 and 1807. Thereafter, there was a rapid decline as the area became mined out. The largest red diamond known, the "Moussaieff Red" was discovered in the 1990s by a Brazilian farmer in the Abaetezinho river in 1990. The rough stone weighed 13.9 carats (2.78 g).
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.
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.





Tuesday, 19 November 2013

Diamond Mining of Angola

Angola, the world's fourth-largest diamond producing country by value and sixth by volume, could regain record production levels enjoyed before 2002 thanks to its new mining law and higher quality diamonds, says a new study.
Angola’s diamond industry, which began a century ago under Portuguese colonial rule, is successfully emerging from a long period of difficulty as a result of a civil war that ended in 2002.

The country’s production volume has remained relatively stable at 8 million carats per year since 2006.
Over the last five years, while production remained fairly steady at the Catoca mine – the world’s fourth largest diamond mine in which Russia’s Alrosa is a joint venture partner – the impact of the financial crisis slowed production across the country and prompted international mining companies to abandon their operations. That trend is now starting to reverse.

Angola is also known for its significant gold and oil reserves.



http://www.mining.com/angolas-diamond-industry-to-regain-record-production-levels-report-29501/

Sunday, 17 November 2013

The Madre de Dios region of the Peruvian Amazon


A combination of field surveys, airborne mapping, and high-resolution satellite imaging have determined that small clandestine operations now make up more than half of all gold mining activities in the Western Amazonian forests of Peru.
The Carnegie Institution for Science and Peru’s Ministerio del Ambiente in Lima assessed road- and river-based gold mining in the Madre de Dios region of the Peruvian Amazon from 1999 to 2012. During this period, the geographic extent of gold mining increased 400%. In the year 2008, the average annual rate of forest loss as a result of gold mining tripled.

Madre de Dios now supplies more than 70% of Peru’s gold production; however, mining activities remain mostly unpermitted by the government.

The authors discovered hundreds of new small mines in the foothills in the headwater region of the Colorado, Inambari, and Malinowski Rivers.
Their discovery was confirmed by air in July 2011 and again in September 2013.

“Critically, as of 2012, small mining operations constituted 51% of the total mining activity throughout the region,” the authors observed. “Our results reveal far more forest damage than has been reported in the past, both in terms of the current area affected and the rate of clearing over time,”
While the total land loss in Madre de Dios appears small compared to other tropical regions undergoing deforestation, the study emphasized that “Madre de Dios is world-renowned for its unusually high biological diversity."


http://www.mineweb.com/mineweb/content/en//mineweb-sustainable-mining?oid=210498&sn=Detail

Friday, 15 November 2013

The Marange diamond fields, Zimbabwe

The "Marange" is the name of a vast diamond field in eastern Zimbabwe. It is about the size of the German capital Berlin and in its depths huge deposits of diamonds lie waiting to be discovered. Many experts believe it to be the largest diamond field in the world. This year alone, the state-owned Zimbabwe Mining Development Corporation (ZMDC) expects to extract diamonds weighing some 17 million carats.

In terms of carats produced, the Marange field is the largest diamond producing project in the world.
Now Zimbabwe can again sell its precious stones to buyers in Europe. In September the European Union (EU) lifted sanctions imposed on the ZMDC for its alleged involvement in acts contrary to to democracy in the southern African nation.

The embargo on Zimbabwe's national mining corporation was imposed by the EU in the wake of brutal attacks by security forces against members of the opposition after the 2008 presidential election.
Five years later, the EU's foreign ministers have now said the embargo can be lifted – even though election observers from the African Union (AU) and the Southern African Development Community (SADC) expressed severe doubts about the credibility of parliamentary elections held in Zimbabwe in July this year.
The EU has also spoken of democratic deficits in Zimbabwe but the bloc's foreign policy spokesman Michael Mann says there have also been some small improvements.

The EU wants to encourage Zimbabwe to undertake economic reforms so that the population as a whole also benefits from the trade in diamonds. So far, ordinary Zimbabweans have seen little of the revenue. The country's economy is in a poor state and many people do not have enough to eat. The UN World Food Program estimates that 2.2 million Zimbabweans will rely on international food aid in the coming months.


http://www.dw.de/zimbabwean-diamonds-set-to-return-to-the-european-market/a-17198729
_____________________________________________