Learning Library

Belmont

The largest open pit mine in Brazil.



Although there are a few states in Brazil where artisanal Emerald mining is still in full swing, there is one mine operating in the Cinturao Esmeraldífe-ro (‘Emerald belt’) of Minas Gerais that is at the cutting edge of mining technology.
This story is set in Itabira and begins in the late 1930s when a young entrepreneur farmer, Mauro Ribeiro, started to transport diesel from Belo Horizonte (the capital city of Minais Gerias)to the local iron mines. He pushed his business hard and within just a few years had many diesel trucks travelling the route every day. He then opened his own iron mine and eventually was so successful that the authorities forcefully took over the concern and Mauro went back to farming. On his land a new railway track was built to transport the extracted minerals from the mines and many years later in 1977, whilst switching the points on the track, a young train driver spotted a green gemstone lying on the ground.

The worker took the gem to Mauro and suggested that he allowed him to take it to a nearby town where he knew gemstones were often traded. Mauro agreed and when the railroad worker returned, they shared the profits.

As Mauro already had a wealth of mining experience, it wasn’t long before he was granted a licence by the government to start mining for Emeralds. Over the years the mine has had periods of strong production followed by long periods of minimal production. I met with the mine’s owner Marcelo Ribeiro (Mauro’s grandson) and he kindly gave us an in-depth tour of his facility.

The open pit mine is incredibly vast and is the second largest I have seen (the only one bigger is Gemfields Emerald Mine in Zambia). The top soils are a vibrant red colour formed from the Baltic rocks below. The pit is now some 300 to 400 feet deep. JCBs work at the rock face and when they hit a layer where their geologists believe there is potential of Emeralds being discovered, they scoop up all of the soil and rocks into the back of a gigantic dumper truck and the extracted minerals are taken to the sorting facility, where hopefully a green treasure or two will be found.
Marcelo explained that currently for every full dumper truck, which holds over 20 tonnes, they extract approximately 5 grams of rough Emerald of which approximately 20% is of gem quality. That’s a lot of work for very few grams, especially when you consider how many thousands of tonnes of earth have already been excavated just to reach the pay dirt (pay dirt is a phrase used by miners to describe the reaching of a gem rich pocket or layer).

When you get to a certain depth in an open pit mine, if the gem rich vein continues to dip lower into the earth, there comes a point when it’s no longer possible to dig any deeper. You will notice in photographs how these types of mines have big steps rising to the surface. The reason for this is that the rock faces would be unstable and liable to collapsing if they were cut vertically Therefore if at the bottom of the mine you want to dig 10 metres deeper, you need to push back and excavate soil and rocks at every level from the top of the mine to the bottom. If you want to go deeper at the bottom of the mine, it can take as long as a year to push back each level allowing the bottom area to eventually be mined.

With so much cost involved in labour and fuel, in 2005 Marcelo decided to extend the Belmont Mine underground. Today they still operate the open pit mine, but a lot of attention and effort has gone into building a vast network of tunnels and shafts as they chase Emeralds further and further into the Earth’s crust.

Before we put on our helmets and went underground to see the operation, Marcelo paused to tell me a story: In the late 1980s, his grandfather hit a pocket of Emerald that produced many grams of weight. Everyday more and more Emeralds were coming out of the ground. For a while he had more gemstones than he had customers. So he instructed the mine’s manager to take all of the scree (waste from the mine) and rough rocks that they had excavated which were rich in Emeralds and to secretly cover them in earth. He was concerned that if he continued to mine so much and stored the gems that they would get stolen (theft and security is a real concern for gemstone mines all over the world). After the rich ore was covered, he instructed the miners to work on another area in the mine. Only later in a period of low yields did they return to the area where they had had a great success.
For many years the hidden rich scree and ore remained a secret of the grandfather and the mine manager. A few years ago after a period of lack-lustre performance Marcelo confided in the mine manager that he was concerned whether the mine was still viable and that if he didn’t hit a good vein soon they may have to close. The mine manager, now in his late sixties, took Marcelo to one side and told him the story about his grandfather’s great find and led Marcelo to where the mound of highly gem rich rock was buried.  

Today Marcelo does not rely on luck in mining but uses the very latest technology in prospecting for gems. Whilst his open pit mine is the second largest I have seen, his underground mine is the most impressive I have ever had the pleasure of entering. At four metres high and five metres wide, big articulated trucks can travel through its three kilometres of tunnels.  

During my visit fifteen miners and security guards were currently working the underground mine. The tunnel descends 40 metres from the height at the mine entrance and at various points the tunnel splits and weaves in several directions as miners chase an area known as the “reaction zone”. The reaction zone is located alongside volcanic pegmatites that have been pushed up through cracks and crevices in the earth. The pegmatites are rich in beryllium, the building block for members of the Beryl family such as Emeralds, Aquamarine and Morganite. As the pegmatite cooled along its edge it picked up trace elements from the surrounding rocks and structures, in this area the rocks often had traces of chromium, which is the second building block needed for the formation of Emeralds. But that’s just the foundations, for an Emerald crystal to grow it has to be exposed to the correct temperature for the right period of time; it then has to cool at a particular rate, all of this happening at the correct pressure. Of course if it wasn’t this difficult, if it did not need the coming together of many elements all at the right time, then there would be gemstones aplenty. But then they wouldn’t be rare and they would possess no inherent value: in fact there would then be very little separating them from manmade crystals.

Not only does Marcelo employ the latest technology  in both prospecting for Emeralds and then extracting them, he uses an incredibly advanced process to sort and identify the gems. When miners are working at the rock face often they will see with their own eyes larger pieces of rough gemstones. However, identifying smaller pieces amongst tonnes of excavated rough is sometimes like looking for a needle in a haystack. In fact it’s worse! At least if you are looking for a needle you have lost in a haystack, you have the encouragement of knowing it is there somewhere. When you are sifting through tonnes of rocks, pebbles and dirt in the vain hope that you might find a precious gemstone, the task becomes very difficult. Marcelo a few years ago decided to look for a solution that was less labour intensive and one that retrieved a higher percentage of the Emeralds sporadically hidden in the rough. Traditionally miners would put the excavated material in a wire mesh pan and then swirl it around in a river to wash it and hopefully they would find a gem or two. This technique is similar to the way you may have seen images in Wild West movies where they were panning for gold. Next came big industrial washing machines that then spit out the clean rough rocks on to a conveyor belt, at which either side stood a team of eagle eyed gem sorters. But Marcelo wanted to revolutionise his operation and had heard about a technology that was used in the coffee bean industry for automatically sorting good beans from bad.

This technology is breathtaking. First the rough rocks are washed and tumbled and any obvious pieces of Emerald are removed. Next the clean rocks are spread out on a high speed conveyor belt at the end of which is a three foot drop. As the stones free-fall over the end, a set of digital cameras film them and instantly analyse their colour. If the computer spots any pieces are green it fires a series of air jets at the stone altering the direction of its fall, and blows the potential gem into a separate container. It is incredible to watch and what is even more impressive is that it has an accuracy higher than that of human gem sorters.

When it comes to the environment, Belmont take their corporate responsibilities very seriously. Rather than just pump their waste water back into the river, which is what unfortunately happens in some areas, they have designed a series of man-made filtration lakes. As each one steps down the hillside you can physically see the muddy water getting cleaner and cleaner and by the time it is pumped into the river it’s good enough to drink!

I really enjoyed my time at the Belmont Mine in Itabira and would like to thank Marcelo for giving so much time to explain how his mine operated. Whilst I am a huge supporter of small artisanal miners, it is also important to appreciate the impact larger companies such as Belmont have in terms of growing the market for the wonderful coloured treasures that we all love to collect.



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