The Belmont Mine and an Emerald’s Journey from Mine to Market
May 22, 2015
Introduction: BrazilBrazil gained its independence in 1822 from Portugal, which had ruled the country since the early 1500s. Today, Brazil is South America’s largest and most populous country, and also its strongest in economic terms. With a total area of 8,514,877 square kilometers, Brazil is the fifth largest country in the world, with abundant natural resources. A leading contributor to its economic strength is the mining of precious metals, iron ore, manganese, nickel, phosphates, tin, rare earth elements, uranium, and petroleum.
Another of Brazil’s main economic resources is its agricultural output, which includes crops such as coffee, soybeans, wheat, rice, corn, sugarcane, cocoa, citrus, and beef. Its largest industries include textiles, shoes, chemicals, cement, lumber, tin, steel, aircraft, motor vehicles, and machinery. Brazil is sixth in the world in the size of its labor force, which employs over 107,300,000 citizens. Its $244.8 billion in annual exports places it 23rd in the world. China is its main trading partner, followed by the U.S.
Brazil is also rich in terms of its gemstone and jewelry industry. For decades, Brazil has been a leading supplier of colored gemstones, including emerald, amethyst, citrine, agate, tourmaline, topaz, alexandrite, cat’s-eye chrysoberyl, opal, iolite, garnet, and many others.
Minas GeraisWhen you translate the Portuguese name Minas Gerais into English, it literally means “general mines.” Mining is one of the most important industries in this large Brazilian state. The northwest part of the state is known for its huge pegmatite deposits that produce tourmaline and other colored gemstones. The business center for the mines is Governador Valadares. This city hosts gemstone cutting, trading, and industry shows. Diamonds have also been produced in the area around the town of Diamantina.
The southern part of the state has massive iron-ore mines and a railway to transport the ore to the coast. Near the UNESCO World Heritage Site of Ouro Preto are the world’s only commercial sources of imperial topaz and a famous source of pink topaz. The name Ouro Preto translates into “black gold,” alluding to the historic importance of gold mining to the area.
The capital of Minas Gerais is Belo Horizonte, a city of over four million people. It is a center for Brazil’s gem and jewelry industry. A number of important gemstone cutters, jewelry designers, and jewelry manufacturers are located there.
ItabiraItabira lies in the southeastern part of Minas Gerais and has over 100,000 inhabitants. The town’s most important industry is iron-ore mining and its most important company by far is Vale, the iron-ore mining giant. Vale is the third largest mining company in the world, the largest producer of iron ore, and the second largest producer of nickel. The largest iron-ore mines near Itabira are Cauê and Conceição. The ore is transported to the Port of Tubarão in Vitória, in the state of Espírito Santo, by the Vitória Minas railroad that goes across the entire state of Minas Gerais. While iron-ore mining supports the town’s economy, emerald mining is important to the global colored gemstone industry.
General Location Map South America
As the most productive emerald region in the country, Itabira is also the only place where large emerald mining companies are located. Among them, Belmont is the largest. It’s also one of the world’s most sophisticated and important emerald mines. Established in 1978, this family business is now entering its third generation.
Belmont Mine HistoryOur team interviewed Belmont mine manager and family member Marcelo Ribeiro at the original pit mine, where emeralds were first discovered. He related the entire amazing story of how this area came to be one of the most sophisticated colored gemstone mining operations in the world.
Belmont Mine Location
The source was discovered in 1978 by Mauro Ribeiro, the owner of the farm where the property lies. Mr. Ribeiro was born on the farm and lived there until he moved to Itabira to participate in the construction business. After starting an iron-ore mining company in Itabira with several hundred employees, he began to suffer from the stress of overwork and his doctor told him he needed a vacation.
Being more of a country man than a traveler, he returned to the family farm to relax for a month. Mr. Ribeiro had inherited the farm from his parents. Then, after buying out all the shares from his other family members, he kept the farm as a hobby and raised cattle on it.
When Mr. Ribeiro arrived at the farm he used a front loader to make a small dam near a stream in the south of the property to create a watering spot for the cattle. As he was excavating the site, and the small lake started to fill with water, some green stones washed up the sides. Unbeknownst to Mr. Ribeiro, he had reached an area where emeralds formed.
Mr. Ribeiro was very happy with the small lake he built himself and went back to running his company, feeling more relaxed. He did not know what the green stones he saw were and didn’t pay that much attention to them.
A rail line near the Belmont property links Itabira to the harbor and is used to transport the coal from the massive coal mine nearby. A railroad track crossing point, operated manually by a lever, was located near Mr. Ribeiro’s new manmade lake. The lever operator at the track crossing was from Teofilo Otoni, a city in Minas Gerais that had become a gemstone cutting and trading center for many of the emeralds from the state of Bahia. Having observed emerald cutting and trading in Teofilo Otoni, the railroad worker had some knowledge about emeralds and emerald rough.
One day the railroad worker decided to jump the fence and get some water out of the newly made lake. As he explored the lake area, he saw the green stones, which he recognized as emerald. He found Mr. Ribeiro and made a proposal: He would collect as many stones as he could, take them to Teofilo Otoni, sell them, and split the money fifty-fifty with Mr. Ribeiro. The deal was agreeable to Mr. Ribeiro as he had no idea about emeralds at that time. When the railroad worker brought Mr. Ribeiro’s share to him, he was amazed. After just a week of picking up stones by hand, the worker was able to bring Mr. Ribeiro more money for his share than he made in the iron-ore business in a month.
Mr. Ribeiro called Pedro, a friend and mining engineer in the iron-ore industry who lived in Belo Horizonte. When Mr. Ribeiro told him that he had emeralds on his property, Pedro told him it was impossible, as there were no emeralds in the area around Itabira. He instructed Mr. Ribeiro to heat the stones in a flame for a while and see if the color changed, thinking they might be aquamarines. Mr. Ribeiro did so and called Pedro to report that there was no color change. When Pedro came to take a look, he confirmed the stones were emeralds.
Mr. Ribeiro was very experienced in iron-ore mining and knew about the laws regarding minerals and mining rights in Brazil. As in other parts of the world, ownership of the land does not mean you own the mineral rights. There are various criteria involved in qualifying for the mineral rights on property you own. Mr. Ribeiro went to the Brazilian government’s mining department to apply for the mining concession on his property.
A concession is usually granted to the first person or company to properly apply for it. Shortly after Mr. Ribeiro submitted his application, many others applied for the mining concession on his property, as the news was spreading fast. In the years 1978 through 1979, over 500 independent miners, called garimpeiros, invaded the emerald-bearing area on the property, built tents, and started mining.
While the mining concession application was slowly working its way through the Brazilian bureaucracy, Mr. Ribeiro made a deal with the garimpeiros. He organized them and laid down rules: There would be no guns, no alcohol, and no women on the property. He also made an arrangement where everything that was mined would be grouped together as parcels and sold. The revenues would be split among everyone. He also constructed a fence around the mining area and informed the miners that outside the fence were his farm, his cattle, and his family, and they must be respected.
At the time, there was a lot of corruption in the Brazilian government and Mr. Ribeiro thought that his mining concession application was taking too long to get approved. If it was rejected on some technicality, he feared that the next application would be accepted, possibly as the result of a bribe. Mr. Ribeiro went to a politician he had known for years and had supported in elections, and expressed his concerns about the application and the number of garimpeiros invading the property.
The politician demanded payment to help with the mining concession application, which offended Mr. Ribeiro. He resented being asked for a bribe to do what the government should be doing anyway, especially by someone he considered a friend and someone he had supported in the past without asking for favors in return. The politician said this was how things worked and Mr. Ribeiro replied he would think about it.
Mr. Ribeiro told his wife he was going to Brasilia, the capital, and promised to return when the mine was his. Standing in front of the Mining Bureau building, he began wondering how he could get the application approved or even find out where it was sitting. As he watched people coming and going, he saw an honest looking man going in and asked him if he worked there and what he did. The man replied that he was one of the people who cleaned all the offices. Mr. Ribeiro explained the situation to the man and asked if he could help him find out where his application was and who he should speak with.
The janitor agreed to help, and later informed Mr. Ribeiro that his paperwork was on the desk of the Minister of Mines with a lot of other paperwork, and it was all very disorganized and neglected. Mr. Ribeiro asked the janitor if there was any way he could bring it to the attention of the Minister. After all, his application had been sitting there for a very long time.
The janitor took it upon himself to speak with the Minister, and said, “Mr. Minister, I noticed that these papers that need signing had been misplaced, and I organized them for you with the one waiting the longest on the top.” The Minister was grateful to the janitor for cleaning up the disorganized piles of papers and signed Mr. Ribeiro’s application by the next day. Mr. Ribeiro was so happy that he gave the janitor enough money for a new car. He returned home with the signed mining concession and it was officially published in the papers.
Mr. Ribeiro stopped working in the iron-ore industry and formed a company to mine the area in an organized way. He brought the entire family into the business as there was a lot of work involved in getting a professional mining operation underway as well as security problems such as theft and invasion to deal with.
In late 1979 to 1980, heavy rains flooded the mining area. With operations halted, they brought in pumps to remove the water and looked at ways to improve their mining technology and methods. At the same time, the garimpeiros became interested in emerald mining at Santa Terezinha in the state of Goias, and many of them moved to that area. This alleviated some of Belmont’s theft and invasion problems for a while, but limited the mine’s manpower.
These circumstances allowed time for establishing a proper mining plan for the deposit. Mining engineers were brought in, the open pit was developed, the processing plant was built in 1980 using a conveyor belt hand-picking system, and production resumed at even stronger levels.
Another obstacle arose when the garimpeiros who had previously worked the property hired a lawyer to help them return to the area. The emerald yield at Santa Terezinha proved to be not as high as they hoped. Their lawyer went to the government to claim that Mr. Ribeiro was not paying the required tax. The government then audited his bank account.
Mr. Ribeiro’s problem was that when he was selling emeralds for the others, all the proceeds were coming through his account. He gave the miners their share in cash, but he was paying the tax only on his 20 percent share. This made it appear as if he was not paying enough tax. There was no way to successfully fight the government over the tax bill so he had to sell a lifetime’s worth of possessions to raise enough money to pay the tax and keep possession of the mine. Luckily, a mining concession is not considered an asset so he was able to protect it during those tough times.
By 1982, the family’s legal problems were behind them. They still owned the mining concession, so they resumed mining and implemented larger-scale mechanized methods. At the time, they utilized a dragline pit-mining method. They dragged the earth up in buckets, taking mud, overburden, and ore to be sent all together to the processing plant. The mass of materials made processing difficult.
By 1985, they had purchased their first hydraulic shovel, an expensive piece of equipment that was rarely used for colored stone mining in Brazil at the time. Despite warnings by the salesperson, who suggested something smaller for emerald mining, the equipment paid for itself within a month. After that, mining was less expensive, as the stones were brought closer to the surface, making them easier to extract.
The operation remained strictly open-pit until the mid-1990s, but it became more difficult as the pit grew deeper and larger, with more and more waste removal required. At that time, exploration and core sampling became more critical, along with more sophisticated mining methods. One of Belmont’s geologists suggested making vertical shafts to get a better understanding of the geology, as well as to determine future production rates and the potential for underground mining. They thought underground mining could be useful and economically viable in areas where the quantity of overburden that needed to be removed to reach the emeralds was prohibitive. Studying the mine with an underground perspective would also help to plan future mining areas. Their first shaft was 35 meters deep, in the area of the original pit and, as expected, it provided helpful information for mine planning.
Core sampling began in the late 1970s and intensified in the 1990s. At first, they hired a contractor for core drilling rather than using their own geologist. But the contractor tried to use Belmont’s own data to make surveys for nearby properties, so by the late 1990s, Belmont put together their own core-drilling team. In 2001, just when planning for future mining activities at Belmont was heavily underway, Mr. Ribeiro’s grandson, Marcelo Ribeiro, graduated college with a degree in mining engineering.
The major decision that needed to be made at that time was whether mining the open pit was possible for a longer period of time and whether it would be economically viable. Marcelo was involved in that decision-making process and the family decided to invest more heavily in the open-pit operation. They installed more pumps for water removal, which lowered the water level to allow deeper mining.
These events led to the development of what is now one of the highest-technology colored gemstone mines in the world. A constant quest for knowledge about the deposit, aided by new technology, has led the way to continued development. Belmont management is tirelessly devoted to fully mapping out the deposit, learning where the emeralds are, and determining the best mining methodology and most effective technology. This devotion is what brought the mine to its present state.
Belmont GeologyPrevious regional field mapping shows four main geologic units underlying Itabira, Santa Maria de Itabira, and Nova Era: (1) an Archean cratonic basement composed of gneisses and granitic rocks; (2) an Archean greenstone belt (mafic oceanic crust accreted to the continental margin during subduction); (3) Lower Proterozoic metasediments that belong to the Minas Supergroup; and (4) Medium Proterozoic metasediments that are essentially quartzite. Two main tectonic events influenced this area: the Paleoproterozoic (~2.1 Ga—billion years ago) transamazonic orogeny and the Neoproterozoic Brasilian orogeny (~600 Ma—million years ago). The latter belongs to the global Pan-African frame.
In Itabira, the Early Proterozoic Minas Supergroup includes, from bottom to top, paragneisses that formed through the metamorphism of sedimentary rocks; greenschists; the Caraca group, made of micaceous quartzites and some phyllites; the Itabira group, containing the most economically important itabirite and hematite-iron ore; and the Piracicaba group, composed primarily of quarzites, sericites, and phyllites. The entire sequence was subjected to regional metamorphism.
The formation of emerald at Belmont is a result of the metasomatic reaction between beryllium-rich pegmatites and chromium-rich ultramafic rocks. At Belmont, the deeply weathered Archean greenstone belt is in contact with Borrachudu metagranitoids and fluorite-bearing foliated metagranitoids. The mafic formations were metamorphosed to biotite, talc-chlorite schists. The schists dominate the mining area at Belmont and are 750 to 1000 meters wide, striking NE to SW.
A number of pegmatites intruded into the schists. Intense weathering resulted in a lot of the pegmatites converting to kaolin, and quartz pockets are distributed between the metagranitoids and the schists. Emeralds are found only in the metasomatic reaction zones within the chlorite schist and black phlogopite schist or in the highly altered pegmatite bodies.
The origin of the pegmatites is still being debated. Some researchers propose that they are related to the Brasilian orogeny (about 500 Ma) and others think that they formed during the earlier Transamazonic orogeny (about 1.9-2.1 Ga), with some of the lower-temperature minerals such as biotite rejuvenated by the later Brasilian tectono-thermal event.
Cross-section of Mining Area
Business ModelIt’s difficult to predict the actual life of a mine because the mining rate depends on many economic factors. When demand is high, mining activity is high, and when demand decreases, such as during a recession, mining activity is reduced. Marcelo has no fear of running out of emeralds, but he is concerned about economic factors that can make mining expensive, such as recessions that lower emerald’s per-carat price, fluctuations in currency rates, and even fuel costs.
This has led Belmont to pursue operations that take it higher in the value chain. While they have continually improved their sorting, parcel creation, and customer base, several years ago they moved into manufacturing and selling cut stones rather than just rough, hoping to not only increase the return on the emeralds they mine but also to make it more economically viable to continue mining, and to prolong the life of the mine.
Belmont now cuts the majority of the facet-grade rough they produce—about 70 percent by value, about 60 percent by volume. When deciding what rough they will retain for cutting and what rough they will sell, Belmont looks primarily at market demand and cost effectiveness factors. Currently, they cut all their facet-grade rough in Brazil. However, labor costs are not as low as in other areas of the world, so they must determine if a faceted stone fashioned in Brazil can be priced at a globally competitive level. Most of their carving, bead, and cabochon-grade material goes to Jaipur, India.
A Special Stone’s ProgressWhile GIA field gemologists often visit mines and study the complete mine-to-market value chain, it is not often that we can follow a particular stone from the mine to the final consumer. We had that chance with a 29.8-gram piece of rough from the Belmont mine. This rough came out of the underground mine at a level 654 meters above sea level and 100 meters underground. As is usually the case with both underground and pit mines, the stone was not discovered during the mining process itself. It was still in the schist after the blasting and extraction processes were complete.
Belmont’s sophisticated optical sorter was the first to “see” the stone. The first human saw it right after optical sorting, in the “safe room” where the emerald-containing ore is stored. No one noted its quality, however, until it came to the sorting and grading facility in Itabira and wound up on mine manager Marcelo’s desk. It was actually Marcelo’s mother who noticed it. She called Marcelo over to see something “extra special.”
The Ribeiro family always checks every production first. When we asked Marcelo how often he finds such large and high-quality crystals, he replied, “It’s a matter of luck. But I believe what brings me luck is hard work. God helps those who work with passion. Belmont mine is amazing: Every production may bring a surprise. I would say we can have one to three stones with that size and quality per year.”
Marcelo showed the stone to his cutter and they discussed their cutting strategy. Marcelo did not allow him to start cutting, as he wanted to let the GIA team set up and document the cutting process. He told his chief cutter, Donizete, that “tomorrow, my GIA friends will make a video,” so he could show them what he has learned in 38 years of cutting emeralds.
As Donizete turned the stone to examine it from all angles, his eyes sparkled and he said, “Listen, you know this is my life, I love what I do and I am very happy your friends are coming to see us. I will do my best and God willing we will have one beautiful stone out of the stones cut from this rough that weighs over 15 carats.” Marcelo jokingly asked, “Do you want to sleep with the stone tonight?” Donizete replied, laughing, “I would, but my wife is very jealous.”
Before they put the stone into the safe for the night, Marcelo and his cutter had a bit more discussion about their strategy for finishing the stone and about where to make the first saw-cut. Marcelo tried to push Donizete for more details about his plans for cutting the emerald but Donizete just replied, “Don’t worry, the stone will tell us what to do.”
Open-pit MiningFor four to five years after the mining concession was established, they continued open-pit mining at the original location—pit #1. But as the pit became deeper, water problems started hampering the operation. The pit was at a low area of the property, very near water level, and rains made flooding a constant problem. To compensate, they moved some mining operations northward.
They also decided to continue mining pit #1 and invested in more pumps to remove the water, adding years to the pit’s life. At the time of our visit, pit #1, called the old pit by Belmont personnel, was still being mined, although it was becoming too expensive and approaching the end of its productive life. Marcelo estimates they will be mining the old pit for another two years.
Currently, the original pit has one mechanized shovel going deeper and another continuing the pushback on the high wall. In the past five years, Belmont has gone about 35 meters deep into the original pit, which is approximately 150 meters by 100 meters in size. Activity was constant while we were there, with the hydraulic shovel removing waste and exposing the reaction-zone ore. They removed the highly weathered white granite overburden to reveal the dark phlogopite reaction-zone ore beneath it. In the earlier mining stages, the weathered phlogopite had been golden in color and easy to remove. At the current depth, the phlogopite reaction zone was dark, hard rock similar to what is encountered in an underground mine.
We observed another type of schist, rich in silica. Marcelo said they call it fool’s schist, after fool’s gold, because it does not contain emeralds. Also, when mining began, the original pit had a concentration of emeralds that had washed down from the hillside into the pit area, making this eluvial emerald deposit easy and profitable to mine. Alluvial river gravel beds of emerald are extremely rare, but these had been weathered free and not traveled far so they were still intact.
While Belmont cannot be as accurate with value estimations as iron-ore mines or gold mines, they feel, on average, they can come up with fairly good predictions. Marcelo estimates there are at least 10 to 15 more years of open-pit mining at Belmont. Pit #1 will also prove very useful over the coming years because it can accommodate all the tailings from the processing plant and all the waste rock from other mining operations. By not having to transport tailings and waste material very far, mine operators can save considerable costs. This cost-saving will be one factor that helps extend the life of the mine.
Current and Future Mining Activities
There are two other open pits being developed at Belmont, with progress moving from south to north. They are identified as pit #2 and pit #3. The third pit is 500 meters from the original pit, with pit #2 between them. Pit #2 is about 200 meters by 80 meters in size, and expected to reach 300 meters by 100 meters. Pit #3 is expected to be 100 meters by 100 meters.
Core Drilling and AnalysisOpen-pit mining at Belmont still has a long potential life span as it continues into the northern areas of the concession. The investment in core drilling over the last 15 years is paying off in helping to plan for open-pit operations over many more years.
Belmont has core-drilled over 15,000 meters, at an average cost of about $200 USD per meter. The Belmont geologists have become experts at reading the lithology of the phlogopite schist core drillings. They send the cores for chemical analysis, then feed the information into a mathematical model Belmont is developing to predict emerald concentrations as well as the quality of emerald in the ore. Core sampling follows the standard mining-block model, where they divide the ore into cubic blocks by three-dimensional computer modeling. Each block is then assigned an estimate of the revenue that can be recovered by mining that block.
The data is compiled from core samplings and mining activity. Projected revenue is determined by mathematically estimating the quantity of emerald in the block, and to some degree its quality and value. This combination of information makes analysis more difficult than it would be for other commercial minerals.
Their quality estimate is actually an estimate of the color quality of the emeralds in the block. Through their mathematical chemistry model, they can measure the amount of chromium present, which helps them understand the potential quality of the green color. By measuring the iron and vanadium content, they can analyze the potential strength of the color modification by blue or yellow hues.
They cannot yet accurately estimate the crystallization or clarity. However, they are working on understanding the relationship between the beryllium, chromium, iron, and possible other elements to potential crystallization. This will not tell them if mechanical cracks are present but they hope to be able to predict if the crystals will be milky or clear.
3D Modeling from Core Sampling
Underground MiningIn 1994, the current ramp-style underground mine started out as three small vertical shafts from which horizontal tunnels called galleries were excavated with the goal of better understanding the formation of the emerald in the hard rock phlogopite schist. At that time, Belmont had only been mining the weathered phlogopite schist in the pit mine. Observing the emeralds underground in the schist provided a better idea of the ratio of emeralds to rock, along with the direction of emerald formation and reaction zones. The vertical shafts were for research, and to study the possibility of progressing to underground mining.
Overall Mining Area
After several years, Belmont felt confident enough to make the considerable investment required to develop a ramp-style underground mine. The ramp needed to be large enough to allow front-loaders and trucks to enter the mine, work in the mine, and haul ore out of the mine. The original vertical shaft was integrated into a ventilation shaft for the ramp mine. Exhaust pipes are used to help remove the dust through the vertical shaft. The shaft also serves as an emergency exit. One of the keys to underground mining is ventilation. Besides the vertical shaft, there is a piping system that provides air throughout the mine.
During full production, 30 to 40 truckloads of material can be removed from the underground mine, totaling about 400 to 500 tons of ore a day. During our visit they were removing about 15 truckloads a day, for a total of about 200 tons of ore. The current state of the underground mine is very impressive, with between two and three kilometers of underground tunnels. The main ramp is about 500 meters long, from the surface to the deepest point in the mine. This ramp is the main road into the mine and it is 4X5 meters in size. This allows enough space for front-loaders to load trucks, and for the trucks to move freely in and out of the mine.
With gemstone mining, it can be advantageous to mine at multiple locations. Belmont’s current production comes half from the underground mine and half from the open pit. It is difficult to predict the quality of material obtained at any production point at any location. By mining both the underground mine and the pit mine, Belmont gets a good range of material for parcels. However, in 20 years the underground mine may need to produce a far higher percentage of ore. Because of this, Belmont has designed the underground mine with the goal of doubling the current rate of production.
While it is easier to mine the open pit, the underground mine requires less removal of waste, as mining is taking place directly in the phlogopite schist. To mine the current underground mine as an open pit, Belmont miners would have to first remove 70 meters of overburden to reach the schist. They determined it was economically more prudent to mine this area as an underground mine.
The underground mining process begins with blasting to remove the phlogopite schist. Scrapers pull the schist that has been blasted free down to the main ramp. There, it can be loaded into the trucks and hauled to the processing plant. The blasting opens up what Belmont calls mining panels in the rock. The panel we saw was a reaction zone about 1.5 meters thick. Belmont had been following this reaction zone, blasting it free and pulling it down with the scrapers. A scraper consists of a winch that hauls buckets of material down from the mining panel through the tunnel, to a point where it can be picked up by a front-loader and then taken to the truck. The truck then takes it out of the mine through the main ramp.
3D Map of Underground Mine
The stones in weathered phlogopite mined from the open pit tend to be smaller than those in the hard-rock phlogopite of the underground mine. However, extraction of the weathered phlogopite in the open pit does not require blasting so there is less damage to emerald crystals. In the end, the stones from both source types often wind up about the same size and quality. Also, the original pit is now so deep that it has reached the level of hard-rock phlogopite schist.
State-of-the-art ProcessingAt the moment, most of the ore from the pit-mining operation looks the same as that from the underground operation. This is due to the fact that most of the pit-mining production is from pit #1, which means it comes mostly from phlogopite schist that is similar to the hard rock in the underground mine. The golden, weathered phlogopite schist has mostly been mined out of pit #1 and they are into the hard-rock schist at this point. For this reason, the processing plant is geared primarily to processing hard-rock schist, where before it was geared mostly to processing weathered schist. Pit #2 has also reached hard-rock phlogopite schist so it requires hard-rock processing methods.
The process starts when the trucks bring the schist to the processing plant and unload it into the first grating. Any schist smaller than 500 millimeters falls through the grating and into the first jaw crusher. A hydraulic hammer breaks up the large pieces of schist so they can fit through the first grating. A series of crushers and screens reduces all the schist down to 40 millimeters in size. Schist that’s less than 40 millimeters in size goes to the hydro-clean, which subjects the schist to high water pressures to thoroughly clean it and make the emeralds more visible to the optical sorter.
Previously, water cannons were used to crush and wash the weathered phlogopite schist. These were ineffective against the hard-rock phlogopite Belmont is currently mining, so crushers and the hydro-clean system have taken their place. Hydro-clean technology is from Germany and is much better than water cannons because it uses much less water and energy, and has much higher capacity.
Directly after hydro-clean processing, screens separate the schist by size. There are three size classifications: small, at less than 10 millimeters; medium, between 10 and 20 millimeters; and large, from 20 to 40 millimeters. Belmont uses two optical sorters—one for the under-10 millimeter schist and the other for the medium and large material.
ProductionCurrently, Belmont needs to move an average of 8 to 10 times more waste rock than reaction-zone ore from its open pits. This means that to recover one ton of phlogopite schist reaction zone, Belmont has to move 8 to 10 tons of waste. Out of the one ton of reaction-zone ore, Belmont recovers an average two grams of emerald rough, which yields on average about two carats of cut stones. Overall, Belmont mines 11 tons of rock for every two carats of cut emeralds from its open pits.
Underground mining requires less rock handling and waste. In the underground mine, Belmont mines one ton of waste to one ton of reaction-zone ore, so they average two tons of rock mined to two carats of cut emerald. Fifty percent of Belmont’s production comes from open-pit mining and 50 percent from underground mining. At this moment, most of the open-pit production is from pit #1. That will change after a couple of years and pits #2 and #3 will dominate open-pit production.
Protecting the EnvironmentBelmont places a high priority on environmental protection and restoration. The reasons for this include:
- They feel it is the right thing to do.
- The mine is their home, where their ranch still exists and the family has a connection to the land.
- The environmental regulations in Brazil have become very strict, especially as the mining operation becomes larger.
- They feel there is a growing marketing advantage to offering ethically mined gemstones as well as promoting environmentally sound, “green,” practices for a green stone like emerald
One of the main concerns in any mining operation is water contamination. Water is necessary for gemstone mining, especially during the processing of the ore and recovery of the gemstones. The main environmental problem with gemstone mining is that the water becomes contaminated with particles from the overburden dirt and gravel, and in this case, also schist, as it washes away these materials to reveal the gemstones.
Belmont uses a seven-pond filtration system to remove particles and to further purify the water used during mining and ore processing. The ponds are at slightly different elevations so gravity causes the water to pass from one pond to the other, becoming purer as it progresses. The pulp (water plus solids smaller than 0.06 mm) passes slowly through the ponds as the water filters through the system, and the solid particles settle into the ponds. Belmont routinely cleans the ponds, removing the particle sediments and bringing them back to the mining area to be used as backfill.
By the time the water is returned to the river, the pond filtration process has removed 99.5 percent of all particles and also introduced oxygen to the water. At the end of the process the water exceeds all parameters to qualify for human consumption and is cleaner than the water in the river it is being returned to. The process cleans 200 cubic meters of water an hour. Belmont is working to refine the process for 100 percent removal of particles from the water.
Besides water reclamation, another goal of green mining is to refill pits and other mined areas and reforest those areas. The mining process removes materials that do not contain emeralds to reach the mineralized zones. Belmont drills and blasts the non-emerald containing rocks, and hydraulic shovels load the material into trucks for transport to the waste pile for dumping. The waste pile is then leveled and reforested. During our visit, we witnessed the leveling of the waste pile for pit #1.
Belmont is currently moving 900,000 tons of waste per year and so far has reforested 50 hectares (about 123 acres). Pit #1 is still being mined, but once its emerald-bearing material is fully depleted, it will be backfilled with the waste from the other pits. Once pit #1 is completely backfilled it will be reforested. That is expected to be completed in about 10 years.
Belmont has its own reforestation team. Its manager has a degree in environmental engineering. They have a nursery where they raise trees for reforestation. Belmont considers it imperative to have enough of a variety of native trees to rebuild the forest to exactly the same state it was in before mining. The Belmont crew takes on all responsibility for rebuilding the natural habitat, including checking to see that the same number of animals return to live in the reforested area that was there originally.
Their methods combine environmental restoration with sound mining economics. They reduce the distance waste has to be transported by placing the pits near each other and mining the same vein. By backfilling pit #1 with the waste from the other pits, transportation costs are reduced. This also allows them to remove waste and place it in an already-mined area so they do not have to degrade virgin land. When Belmont plans mining activities, they also plan environmental protection, such as reforestation, right from the beginning. The two efforts are intimately connected. One of the biggest cost factors in mining today is environmental protection, so planning from the start to minimize environmental degradation is not only the right thing to do but also economically sound.
SortingSorting begins at the processing plant, where optical sorters separate emerald-bearing from non- bearing schist. Belmont has used optical sorting since 2004. Before that, workers handpicked the emerald-bearing schist from conveyor belts. Even in the 1980s, Belmont was looking for a more automated sorting method, but they did not find the proper technology until 2004.
The optical sorters have proven to be more consistent than human sorters in finding emeralds. The original optical sorter has been completely updated with new closed circuit cameras, computers, and software. Also, they added an additional optical sorter. The original optical sorter has been optimized to sort schist that is between 2 and 10 millimeters in size and the second optical sorter from 10 to 40 millimeters in size. Both optical sorters have about a 95 percent accuracy rate for identifying emerald-bearing schist from mine ore, and are consistent from day to day and hour to hour. Belmont feels that with some further refinements to the process they will achieve 97 to 98 percent accuracy.
Basically, the closed circuit cameras scan schist coming through the optical sorter on a conveyor belt for emerald. When emerald-bearing schist is identified, air jets blow it off onto another conveyor belt. The newer optical sorter has stronger air jets that can blow the larger pieces of emerald-bearing schist onto the second conveyor belt.
The capacity of the optical sorter that handles larger schist sizes is 5 to 15 tons per hour, depending on the size of the material coming through. The capacity of the optical sorter that handles smaller schist sizes is only 2 tons per hour. Belmont is preparing to add another optical sorter in the future to increase processing of the smaller schist. The material must be in a single layer in order for the cameras to recognize the presence of emerald. Since smaller schist weighs less, it operates at a lower ton-per-hour rate.
After sorting, the emerald-bearing schist is transported to Belmont’s final sorting and cutting facility in Itabira. The first step is to break away the phlogopite and often quartz to leave just the emerald crystal. Workers use pliers to break the host rock away from the emerald, then to break away any highly included areas in a process called cobbing. The rough is then ready for sorting and grading into parcels.
Belmont sorts emerald rough into categories of size, shape, color, and crystallization or clarity. There are five size classifications, and there are 10 further classifications within each size range. Shape comes into play when the rough stones are flat and will be used for marquises, baguettes, etc. These are placed in a separate group for further grading.
The Cutting CenterBelmont has a small cutting facility that utilizes Israeli cutting machines that are modern improvements over traditional jampeg devices, where the rough gem is attached to a dop that is then inserted into a guide that allows fast adjustment of the cutting angles from facet to facet. Traditional jampegs have long been used throughout Asia. Modern improvements in the Israeli machines allow fast placement of the dop along with improved precision.
Belmont’s girdling and calibration machines are all hand operated, but the equipment also allows for precise calibration measurements. During our visit, they were cutting numerous emeralds into various calibrated sizes for specific jewelry mountings. Cutting is not as inexpensive in Brazil as in other parts of the world, so the cutting must be precise and of high quality. During the faceting process, the Belmont cutters constantly check the stones for symmetry and polish quality.
Cutting the Mine-to-market RoughThis, of course, was not the process used for the large stone being cut from the nearly 150-carat piece of rough we were planning to track from mine to market. This was a large, fine-quality emerald that would be cut to maximize beauty and weight recovery. Any specific measurements were meaningless compared to those two criteria, as the mounting would be custom-made to fit the stone.
The first step in the cutting process was to saw the stone. Marcelo equated sawing an important stone with gambling. It is very exciting, “a moment of high adrenalin.” Marcelo said, “We can get addicted to it.” He also said, regarding the sawing process, “You can go from heaven to hell or the opposite just after one sawing.”
Marcelo and Donizete had high expectations since they found the rough so “amazingly beautiful.” As Marcelo said, “We had a big fear to make a wrong decision and damage what nature made so carefully.”
After the first sawing, Marcelo told us, “We did the right thing,” and their first feeling was a kind of relief from the initial pressure. They immediately regained their excitement for the next sawing steps.
The largest was a 40.68-carat piece of rough, which was sawn several times to get it to the desired point of clarity and quality. Its shape allowed very good weight retention, and the quality was good, so the hope was for a cut stone that was close to 50 percent of the weight of the sawn rough, a good percentage for colored stones, especially bright ones.
There was another included area that could have been sawn off before preforming, but the master cutter decided he would rather remove the area gradually with the grinder. Some emerald rough has internal characteristics that make it brittle and difficult to preform. This rough had good quality and was very stable during the critical preforming stage. Also, the rough itself was partially preformed by nature, with areas of the crystal already shaped like a pavilion and an area shaped for the table. The sawing process removed this advantage for some of the sawn stones but still left the some of the natural useful shape for the largest stone, our mine-to-market stone.
The sawing and preforming stages helped guide the removal of significant value-lowering inclusions as well as table orientation and cutting directions. The faceting step had a strong influence on the brightness of the stone, as the exact proportions of the pavilion angle, crown angle, table percentage, and other facet placements were decided. Again, there is always a compromise with expensive rough between bringing out the best color and brightness, further reducing any visible inclusions, and creating pleasing symmetry and retaining as much of the valuable weight as possible. Through years of experience, Belmont cutters know what their customers are looking for in terms of appearance and cost per carat.
Improving the Stone’s AppearanceThe vast majority of emeralds in the market, including very high-end emeralds, undergo clarity enhancement. This involves filling surface-reaching fissures with a colorless to near-colorless material to make them less visible. Gemstone fissures are filled with air, which makes them very visible in the stone. When a foreign material with similar optical properties to the gem material is used to fill the fissures, they become much less visible. Generally, the closer the refractive index of the colorless to near-colorless filler material is to the refractive index of the emerald, the better it conceals the fissure. A variety of oils, resins, epoxies, and polymers are used to fill fissures in emerald.
For this special mine-to-market emerald, Marcelo told us the customers he has in mind prefer the use of cedarwood oil to fill the fissures. While at the Belmont sorting and cutting facility in Itabira, we witnessed the entire enhancement process.
After cleaning the fissures out with a solvent, the stone was soaked, along with a few of the other stones cut from the same rough, in a beaker full of cedarwood oil, adding heat to allow for better penetration of the oil into the emerald. This is usual practice for enhancement processes like this, where a slight amount of heat and pressure makes the oil flow more thoroughly into the fissures.
The next day, the emeralds were removed from the beaker and the oil was wiped off the surface and then washed with water and baby shampoo before another examination. The visibility of the fissures had lessened, but not as much as they had hoped for, so the emeralds went back into a beaker of cedarwood oil and were again soaked overnight for further enhancement. This process sometimes goes on for several days to achieve the best results.
Re-cutting the StoneAfter enhancement, Marcelo was still not happy with the visibility of one fissure on the pavilion. He decided to re-polish the stone slightly and remove some of the fissure, making it less visible. Re-cutting or re-polishing expensive material is always a decision that requires experience and planning. With inexpensive material, it is sometimes a matter of considering labor costs. For expensive material, it is a question of whether the gain in beauty will raise the per-carat price enough to compensate for the effects of the weight loss. There is also always an element of risk anytime a stone is re-cut.
Emerald in particular is subject to breaking or chipping during re-cutting, more so than some other stones. In this case, a chip occurred during re-polishing of the pavilion, resulting in a reduction of weight from 19.70 carats to 18.17 carats. The stone then went through the enhancement process again and was ready to travel into the global marketplace.
When Marcelo was asked if the final largest cut stone from the rough met his initial expectations, he said “Yes, that was an amazing stone, big and beautiful. I was happy we did a good job. Fine-quality stones like that are so rare that I got jealous and possessive about it, like having a newborn baby.”
Entering the Global MarketMarcelo and the 18.17-carat emerald arrived in New York City on Friday, April 25, at about 8:00 in the morning. After checking into his hotel, he took the stone to the GIA Laboratory in New York for a report. Marcelo felt that a gemological report would add a great deal of value when selling a large, high-quality emerald. Marcelo also showed the stone to a couple of high-end New York jewelers.
His jewelry designs feature colored stones prominently and include ruby, sapphire, emerald, fancy-colored diamonds, Padparadscha sapphire, alexandrite, and other more rare materials like Melo pearls. Fancy diamond colors include shades of yellow, blue, and pink, and may be used as center stones or accent stones. Colorless diamonds are usually used as accent stones. The precious metals used in the jewelers’ pieces include 18K yellow and white gold, 22K yellow gold, 18K rose gold, and platinum.
The jeweler set our mine-to-market emerald in a 22K gold ring with wire prongs. Micro-pavé settings held six orange diamonds, five yellow diamonds, 94 pink diamonds, and 19 colorless diamonds. The deep, velvety, grass-green color of the emerald inspired the floral design. The fancy-colored diamonds add contrast and reflect the range of colors seen in flowers. The yellow, orange, and colorless diamonds represent flower petals, while the pink diamonds on gold wire represent the stems and branches. The emerald was set at an angle to create a more lively appearance.
The person who bought the ring is a regular client who likes to collect fine-quality colored stones in uniquely designed jewelry. Her design taste centers on natural and free-flowing shapes and floral designs. She also was intrigued by the Brazilian source of the emerald and the Belmont mine’s environmental practices.
This emerald, mined from an original pit of the Belmont mine near Itabira, Brazil, received a gemological lab report in New York City while it was being displayed around the NY market, and then traveled to Hong Kong, where it was purchased at a trade show by a jeweler from Thailand. The stone was then mounted in a custom-designed ring, put into the jeweler’s retail store, and sold to someone who highly appreciates unique fine jewelry, thus completing its global mine-to-market journey and eventually becoming a treasure for a consumer to enjoy.
Andrew Lucas is Manager of Field Gemology at GIA in Carlsbad, California; Duncan Pay is Editor-in-Chief of Gems & Gemology and Director of Content Strategy at GIA Carlsbad; Shane McClure is Director, West Coast Identification; Marcelo Ribeiro is General Manager of the Belmont mine; Tao Hsu is Technical Editor of Gems & Gemology; Pedro Padua is the Video Producer at GIA Carlsbad.
GIA staff often visit mines, manufacturers, retailers and others in the gem and jewelry industry for research purposes and to gain insight into the marketplace. GIA appreciates the access and information provided during these visits. These visits and any resulting articles or publications should not be taken or used as an endorsement.
The authors gratefully acknowledge the assistance provided by the Belmont mine and its personnel.