Lomonosov, one of Russia’s newest diamond projects, is located near the historic port of Arkhangelsk on the nation’s European side. GIA senior industry analyst Russell Shor and research scientist Dr. Karen Smit provide the first report from this potentially important source of fancy colored diamonds.
Draw a ring around the world near the far north 64th parallel and it will bisect some of the world’s largest diamond mines, from the Canadian operations north of Yellowknife, through the massive Siberian deposits, to one of the newest operations that sits on Russia’s European side, near the historic port of Arkhangelsk.
The Lomonosov diamond deposit, named for the famed 18th century Russian scientist, came into production four years ago, more than 30 years after its initial discovery. What makes Lomonosov special is that it yields fancy colors – purplish pink, violet, green, yellow and brown − in addition to a high percentage of gem-quality colorless (D-to-Z) diamonds.
Ilya Zezin, deputy chief geologist of Severalmaz, the division of Russia’s largest diamond mining and marketing firm ALROSA, reports that one in every 350 carats of Lomonosov’s 2 million carat yearly diamond production is fancy colors. Compare that against the oft-cited statistic that only one diamond in 10,000 mined around the world can be called fancy colored.
Another unusual feature of the Lomonosov deposit that intrigues geologists is that it contradicts the so-called “Clifford’s Rule,” which states that most diamond exploration programs focus on Archaean cratons. Cratons are extremely old areas of the Earth’s crust that have remained stable for around 3 billion years. In the Arkhangelsk area, the crust lies in a Proterozoic orogenic belt, which is significantly younger, around 2 billion years. Diamonds would not normally be expected to be stable in such a terrane. Argyle, one of the world’s largest diamond deposits (mined in northwestern Australia by Rio Tinto) also occurs in apparent violation of Clifford’s Rule and is famous for its continuous production of fancy pink and red diamonds.
Zezin escorted us to the secure sorting facility in Arkhangelsk city where the diamonds are processed before being sent to the sales office in Moscow. Nearly 70,000 carats of diamond representing around two weeks of production were on display. An array of the best fancy colors were separated out on a round vanity mirror. These fancy color diamonds were selected from two months of production; among the approximately 100 carats of yellow diamonds of various intensities were three 1-carat-plus sized purple-pink stones. A similar-colored, approximately 0.4 carat, polished estimated purple-pink diamond from this deposit sold for more than $1.6 million per carat at a Hong Kong tender in 2015.
There will be a lot more diamonds coming, both fancy colors and colorless, Zezin says, because Severalmaz will reach the most productive areas of the two pipes under operation late next year. Additionally, there are four other economic pipes at Lomonosov held in reserve.
The deposit is located about 60 miles (100 km) north by northeast over densely forested terrain from Arkhangelsk. The city, located near where the Dvina River empties into the White Sea, was Russia’s only deep-water seaport in the North for centuries, and is a key trading center, despite being iced in for nearly five months each year. Travelers reported finding occasional diamonds there as early as the 1740s, but it wasn’t until the late 1970s that Russian geologists began to take a serious look for the possibility of diamonds.
By then, timber had become the lifeblood of the area. Because the White Sea helps moderate the climate, the region is thick with silver birch, larch, pine and spruce − in contrast to the trackless Canadian and Siberian tundra around the other diamond mines at that latitude.
The region’s economy began to deteriorate just as diamond exploration was ramping up. In 1980 a team of geologists checking airborne surveys of the area found a kimberlite pipe in the middle of a river about 60 miles from Arkhangelsk. While ultimately not economic, the discovery spurred wider airborne prospecting and, in the early 1980s came the discovery of the cluster that forms the Lomonosov deposit: Pomorskaya (1980), Karpinskogo I and Karpinskogo II pipes (1981), Lomonosovskaya pipe (1982) and the Arkhangelskaya and Pionerskaya pipes (1983). A second cluster about 14 miles to the northeast, called Verkhotina, was discovered in February 1996 by a De Beers-related exploration company. The V. Grib pipe in this kimberlite cluster is being mined and is operated by Arkhangelskgeoldobycha Company, a subsidiary of LUKOIL, the Russian oil conglomerate.
The discovery of kimberlite pipes is but the first step in a long, costly development process of any diamond deposit. Each deposit must be extensively sampled by sending hollow tubes a hundred or more meters into the kimberlite, then analyzing the results: the size and quality of the diamonds, as well as the potential grade – carats per hundred tons of ore. Nature rarely does things evenly, so core samples must be taken throughout each pipe because the diamond distribution often varies greatly inside them. If the core samples look promising, then bulk samples – a ton or more of kimberlite in each sample − are hauled out and tested to determine whether the grade is economic to mine.
These tests usually take several years to complete. Fortunately for Severalmaz, Arkhangelsk city was fairly close and helicopters could transport supplies until a small winter road was built during the exploration period. Severalmaz opened the current forest road in 1986, which made it possible to transport supplies easily without the need for tenuous ice roads as in Canada or the costly logistics of managing the Siberian permafrost.
In 1987, the results came in: most of the larger pipes were economic, with Karpinskogo I yielding 0.6 carats per ton in the upper levels (crater facies), improving to 1.4 carats per ton in the lower section (diatreme facies) of the pipe. Arkhangelskaya showed similar results, 0.5 carats per ton in the crater facies and 1.06 carats per ton in the diatreme facies. The central government, then under Soviet rule, gave its clearance to develop the deposit.
Geology and logistics were favorable for mining the diamonds, but turbulent times intervened. After several years of political upheavals, the Soviet Union dissolved in 1991, sending the government and finances into disarray. As the new Russian regime emerged from the chaos, the government, along with the newly autonomous Republic of Sakha, where most of the country’s diamond mines are located, created Almazy-Rossii-Sakha (later ALROSA), an organization to manage its diamond resources. In turn, it created a subsidiary named Severalmaz to manage the Lomonosov deposit.
But finances remained tenuous, so while the Russian government did help revitalize production in its money-spinning Siberian mines, development of the Lomonosov deposit would have to wait – another 12 years to be exact, until 2005.
“They chose the Arkhangelskaya pipe to begin, because it had the largest reserves of diamonds and the least amount of overburden (ground cover) – about 30 meters (98 feet), compared to the much larger Lomonosovskaya pipe, which was 54 meters (177 feet) underground,” says Zezin, who notes that, at government insistence, the company tested some unorthodox mining methods for a while, such as shooting water into the ground under very high pressure to raise the kimberlite. They ultimately found them “neither efficient, nor effective,” Zezin notes.
Severalmaz is mining the Arkhangelskaya and Karpinskogo I pipes, leaving the largest two, Pionerskaya and Lomonosovskaya, in reserve while Karpinskogo II and Pomorskaya remain under study. The company reverted to more traditional diamond mining methods, but it does do one thing differently: no blasting.
“The upper part of the ore body is very soft so the excavators can do the work without explosives,” Zezin explains. “As we get deeper, we may have to do blasting in a limited section of the pipe where the ore is the hardest.”
Another difference from other mining operations is that Severalmaz doesn’t send the material to the processing plant right away. Instead, the material weathers in a stockpile for several months before it is milled.
“The weathering further softens the kimberlite, making recovery easier,” Zezin explains.
In the plant, the ore is mixed in water, tumbled in a giant mill to break it up into pieces measuring about 120 mm × 25 mm, which are large enough to avoid damaging the largest crystals. After milling, material is dispatched to hydraulic separators. The largest pieces go directly to X-ray units and the medium-sized pieces to density separators, then to the X-ray units that identify and separate diamonds down to one millimeter. The smallest materials never make it to the X-ray units and are sent to the tailings.
The method appears to work well, says Zezin, who points with pride to a monitor that displays the results of continual tests of the tailings for diamonds that might have been missed. The recovery rate averages about 97%, he says. At this moment the monitor was showing recovery rates over 99%.
The production profile is different for each pipe, and although they are sometimes processed separately, they are mostly processed together. Lomonosov produces few very large diamonds. The largest diamond from Lomonosov weighed 106 carats, a gray industrial found in 2011. Between the two pipes, 82% of the diamonds are gem- or near-gem quality. During the GIA visit to the sorting operations in Arkhangelsk city, about 20 diamonds of various qualities larger than 10.8 carats were among the two weeks of production on view.
Lomonosov’s production will likely double over the next several years as the processing plant is enlarged and they begin to hit the richer ore, explains Igor Nikolaevich, chief engineer of Severalmaz. He says that developing the other pipes is still years away.
“While the plans have not been made final, it is certain we will be mining past 2040 or 2050,” he says.
Editor’s Note: ALROSA is the world’s largest diamond producer by volume – 38.3 million carats (30% of the world total) – and is a joint public-private company. It sold a 14% stake in the company in a 2013 SPO and 10.9% in a 2016 SPO, with the central government, Sakha province and various municipalities holding the difference.