EXPLORING FOR DIAMONDS AND THE NORTH — A tour of the

There are now more than 200 companies active in North American diamond exploration. Much of this exploration is under challenging Arctic conditions. One group with a proven track record in that domain is the Russian diamond enterprise Almazy Rossia-Sakha (ARS). Toronto-based engineering and consulting firm Watts, Griffis and McOuat (WGM) has established a joint venture with ARS. Earlier this year, the joint venture organized a seminar and tour of the diamond mines of the Siberian platform in the Republic of Yakutia (Sakha), Russia. An abridged version of the WGM report, written by tour leader and WGM vice-president David Wahl, follows.

For the 19 participants, who represented a variety of aspects of the North American and Australian mining communities, their arrival in Anchorage, Alaska, was the start of a 10-day around-the-world odyssey. The expedition, to use the Russian vernacular, participated in numerous technical sessions, visited four producing diamond mines, one past-producing mine, two diamondiferous placer operations, one underground diamond-bearing paleoplacer mine, a large mill complex and a diamond sorting operation spread through three mining centres in Siberia.

The tour departed Anchorage on May 23, en route to Mirny via Khabarovsk. Our flight path took us over the Bering Sea, across the International Date Line, Kamchatka Peninsula, the Sea of Okhotsk, the northern portion of Sakhalin Island and into Khabarovsk.

Our flight to Mirny, more than 2,000 km away, would take us westerly over the Buseninskiy Khrebet and into Blagoveshchensk, on the Russia-China border, to take on fuel. From Blagoveshchensk, our heading was northerly along the Amur River, which defines the border with neighboring China, over the Zeya Reservoir, one of the largest in Russia, and the Stranovoy Khrebet into the Chul’man for our second fuel stop. After a short station stop at Chul’man, we resumed our flight northwest across the Lena River and into Mirny. We were met on the tarmac by hosts Vladimir Tchiganov and Victor Smolnikov and escorted towards two shuttle buses waiting to take us to our hotel. The trip took 15 minutes but covered almost 40 years. Leaving the airport, the narrow gravel road passed clustered weather-beaten clapboard shanties built by the early miners and now occupied by residents unable to obtain the more desirable apartments in town. The shanties behind us, the gravel road transformed into a tree-lined boulevard between large apartment buildings constructed on pilings typical of permafrost construction.

The Papagaya Hotel, named for the woman who discovered the first kimberlite pipe in Russia, is at the centre of Mirny. The check-in went smoothly; however, the two elevators, each capable of carrying two people with limited luggage, resulted in some delay getting out of the lobby.

After lunch, the tour met with officials of ARS, who presented an overview of the seminar. Following the introductory briefing, we were divided into two groups and boarded the shuttle buses for the first of many site visits. Our first site visit had to be, and was, the Mir pit.

The Mir kimberlite pit was discovered in 1955 by geologists of the Amakinskaya Expedition. It was the first economic diamond deposit found in Russia. The deposit has been mined by open pit methods since 1958. The town of Mirny, named after the pipe, grew up around it.

In plan, the pipe is oval, elongated in a northwest direction, and slightly constricted in the middle. In vertical dimension, it is a typical funnel in its upper part and cylindrical, slightly narrowing downward body in its lower part. The Mir pipe is in the centre of a well-pronounced domal structure composed of lower Paleozoic sedimentary rocks. Kimberlitic rocks crop out and consist of two main varieties, (1) massive xenocrystic kimberlite and (2) typical kimberlite breccia that contains fragments of kimberlite, pyrope, picroilmenite, less frequent olivine, chromite, chrome-diopside, and fragments of various deep-seated rocks entrained en route to the surface. The Mir pipe contains on average about 4-5 kg of indicator minerals per tonne of kimberlite.

The Mir pit, about 2 km in diameter and about 460 metres deep, is undergoing expansion. The ultimate depth of the pit will be 525 metres, at which point mining will continue from underground. On completion of the expansion, the mining rate is expected to be in the range of 1.5-2 million tonnes per year. After an extended stay at the observation platform overlooking the Mir pit, the tour visited a seasonal placer operation immediately east of the Mir pit. The deposit was discovered in 1955 as part of a regional program which resulted in the discovery of the Mir pipe. The deposit is confined to an area about 2.5×3 km. A portion of the deposit lies beneath the Mirny airport. The deposit was formed in regional depression. The diamondiferous gravel, located at the base of recent alluvium, are on average 1.5 metres thick but can be up to 8 metres thick. The diamonds are reported to average about 30 mg in weight. However, every month about 60 diamonds are recovered in the 8-9 carat range. Diamonds of up to 60 carats in size have also been recovered. The diamonds are thought to be derived from the Mir pipe.

Mining is seasonal and is accomplished using hydraulic monitors. The diamondiferous gravel slurry is pumped to Factory #3 in Mirny for processing. After several questions concerning grade, which were left unanswered, the tour assembled at the Yakutian Geological Research and Prospecting Department. Following a brief presentation on the structure of the department, we sampled more Russian hospitality with beer and wine provided for all. Soon it was time to return to the hotel and get ready for our welcoming dinner. The dinner was hosted by Vladimir Zuev, the director for mineral resources for ARS.

The Wednesday technical session in Mirny started at 9 a.m. and was staged in an amphitheatre at the ARS complex. Part I of the seminar touched on the stratigraphic column of Siberian platform, primary deposits, placers and exploration methods.

The Siberian Platform is underlain by Archean basement rocks which are overlain by up to 6 km of late-Proterozic, Paleozoic, Mesozoic and Cenozoic sediments. Sedimentation has occurred in four cycles, each culminating in a period of intense magmatic activity related to major structural rift zones. Kimberlites are thought to have been injected during the later stages of the magmatic cycle along these crustal breaks and related structures which have divided the platform into six structural domains. The kimberlites of the Siberian Platform exhibit an age/domain relationship. Proterozoic kimberlites have been identified in the southwestern part of the platform; Middle Paleozoic kimberlites occur in the central and northeastern portions of the platform; and Middle-to-Late-Triassic and late Jurassic-Cretaceous kimberlite have been mapped in the northern region of the platform. Currently, the Middle Paleozoic kimberlites host the economic diamond deposits. Except in the extreme north, the Siberian Platform has not been scarred by the effects of glaciation as has the Canadian Shield.

Diamond exploration carried out by ARS relies very heavily on airborne magnetic data and on the results of indicator mineral sampling programs. ARS also utilizes gravity, seismic, magnetotelluric and radio-shading technology to assist in anomaly definition and discrimination.

The prime geochemical techniques used to evaluate kimberlites were developed by N. Sobolev in the late 1960s. He developed the technique of evaluating the diamond-bearing potential of various kimberlites based on the chemistry of pyrope garnets and chromite. ARS has also put considerable effort into understanding the effects of transportation on indicator mineral assemblages. Following lunch, the afternoon session began with a visit to the Botuobinskaya Expedition for an overview of their facilities. We then drove to the airport fora short helicopter flight north of Mirny to the Vostochny underground paleoplacer exploration site. We were transported from the helicopter landing site to the office by track-mounted all-terrain vehicles. Access to the underground workings was by inclined shaft. The 20C surface temperature contrasted sharply with the cold permafrost air as we descended the 15-degree shaft. The shaft was timbered the entire length to the exploration level driven below the placer deposit. The deposit occurs at the unconformity at the top of the Carboniferous carbonates and the overlying Jurassic sediments. Diamonds in the placer are thought to be derived in part from the nearby International pipe and in part from undiscovered pipes. The diamond and indicator mineral morphology suggests contributing sources. Upon our return to the ARS complex, we were taken for a quick look at the core treatment plant where we had an opportunity to see one of ARS’s portable skid-mounted processing plants.

On Thursday in Mirny, a technical session began at 9 a.m. and lasted until noon. The session was a continuation of the previous morning’s theme. Following a brief lunch, the technical seminar was reconvened at 2 p.m. for Part 1 of a series of papers on mining operations on primary diamond deposits and placers, and mining and treatment of diamond-bearing ores. At 4 p.m., the technical seminar concluded for the day and we were directed to our jitney buses for a tour of a dredging site and the 23rd Party Congress pipe open pit. The placer dredge is located east of Mirny, downstream from the Mir placer site. A 30-km section of the river has been reworked several times with a conventional “gold type” dredge. The diamondiferous gravels are concentrated in a bed averaging 2-2.5 metres thick immediately above the bedrock gravel interface. The diamond-bearing gravels vary in thickness from 0.5 metres to 6 metres. Questions concerning grade were again left unanswered. The dredge was not in operation at the time of our visit.

As we approached Mirny on our return, we turned south along an all-weather gravel road past numerous gas wells to the open pit at the 23rd Party Congress pipe. This pipe was discovered in 1966 by geologists of the Botuobinskaya Expedition during an investigation of a geophysical anomaly. The deposit was mined during the period 1979-1982. The pipe is overlain by a 12-20-metre-thick body which takes on a dyke-like form at a depth of 150 metres. At surface, the pipe is oval with long axis oriented in a northwest direction. The pipe is composed of carbonatized eruptive breccia with a microlitic groundmass. Pyrope and chrome-spinel are characteristic minerals, and picroilmenite occurs in far lesser amounts.

This was our first opportunity to actually break some rock and collect some representative samples of kimberlite. After several hours of sample collecting, we climbed aboard our buses for the return trip to Mirny. We made one last stop at the miners’ museum which graciously stayed open past normal hours to accommodate the tour. The history of Mirny is not unlike any northern Canadian mining town.

On Friday, the technical session started at 9 a.m. It was Part 2 of the mining operations seminar. These technical sessions ended around noon. We returned to our hotel to pack for a 2-day trip to Udachny and Aiykhal. Udachny is located on the Arctic Circle, about 450 km due north of Mirny. Upon our arrival, we were greeted with a lunch replete with the usual libations and were then taken to the Udachny pipe open pit and Treatment Plant No. 12.

The Udachny kimberlite pipe was discovered by geologists of the Amakinskaya Expedition in 1955 when diamond indicator minerals were found in a heavy mineral concentrate from Quaternary sediments. The pipe consists of two bodies (western and eastern) which resemble a distorted figure-eight in plan. The two bodies are in direct contact with each other in their upper parts, but separate at depth. Host rocks are massive dolostones, limestones, siltstones, and calcareous conglomerates of Lower Ordivician and Middle Cambrian age.

The western body is the older of the two. It contains three varieties of kimberlite, each related to an independent stage of kimberlite emplacement. Kimberlite breccias of different stages of emplacement, predominantly grey and green-grey in color, differ from each other in picroilmenite and garnet proportions, diamond morphology and chemical characteristics of the rocks. Kimberlite breccias have undergone serpentine-carbonate alteration. They contain serpentine pseudomorphs after olivine, autoliths, xenoliths of sedimentary and metamorphic rocks cemented in a carbonate-serpentine groundmass. In the eastern body, kimberlite breccia is less serpentinized and contains less pyrope and picroilmenite than the western body. The western pipe is richer in grade than the eastern pipe, but grade can vary two to three times within each pipe on a local scale.

The Treatment Plant No. 12 at Udachny is an immense facility. The processing is done by wet grinding in large (9 metres in diameter), rubber-lined auto genous mills. ARS claims to have perfected this technique so as to minimize damage to stones. From the autogenous mill, concentrate is sized, with plus 5 mm fraction going through X-ray separators; minus 5 to plus 2 mm goes to a gravity separation circuit then either to flotation cells or grease tables. Final product goes to a classification plant for sorting and grading. There are about 60 X-ray sorters at the plant, of which about 60% are in use at any one time. They differ from most South African operations in that the Russian machines process a wet concentrate as opposed to a dry concentrate. The Russians are proud of their flotation technology which they claim can be adapted to processing other minerals. It is unique in the diamond processing industry because it recovers very small stones (minus 2 to plus 0.2 mm). Saturday morning we boarded the bus back to Udachny en route to Aiykhal, situated about 75 km southwest of Udachny. On our arrival in Aiykhal, we were given a professional briefing on the area by the Amakinskaya Expedition. We visited their mineral display and had our first opportunity to see some large diamonds which ranged in size from 3 carats to 5 carats. After lunch, we visited the Jubilee (Yubileynaya) pipe open pit and the Aiykhal pipe open pit. Also scheduled was a visit to the Sytykanskaya pipe open pit but lack of time precluded a visit to that pipe.

The Jubilee kimberlite pipe, the largest at 56 hectares, was discovered by geologists of the Amakinskaya Expedition in 1975 in the course of aerial prospecting. In plan, the pipe is pear-shaped with a long axis oriented in a northeast direction. Vertically, the pipe is funnel-shaped in its upper part and columnar in its lower part. Host rocks are Ordovician and Lower Silurian carbonate and terrigenous sediments. The pipe is covered by 70-110 metres of Upper Paleozoic sediments which are intruded by diabase sills (trap rocks). The body has a complex internal structure; the upper part (that is, funnel) is filled with inequigranular tuffs and the vent facies is kimberlite breccia. The characteristic feature of the kimberlite breccia is its relatively uniform composition throughout the stripped section. The Aiykhal kimberlite pipe was discovered in 1960 by geologists of the Amekinskaya Expedition during stream prospecting in Sokosolookh-Markhinsky Creek. The pipe has been mined by open pit since 1961. In plan, the Aiykhal pipe is a steeply dipping dyke-like body, strongly elongated in a northeast direction. With depth, the pipe thins out and gives way to a dyke. The kimberlite intrudes Ordovician and Lower Silurian limestones, dolostones, marls and mudstones.

Following our tour of the Aiykhal pit, we were ready to fly back to Mirny. Heavy rain during the previous 24 hours had made the gravel strip too soft for our plane to land. We were left with no other option but to reboard the buses and drive back to Udachny to pick up our charter to Mirny. It was at the Udachny airport that we hit our first glitch: a security guard was not going to let us through security to our charter with any of our kimberlite samples. Several anxious calls were placed to Mirny and we finally received our clearance through security.

Our Sunday morning session in Mirny was a trip to the ARS sorting facilities. On arrival, we were separated into two smaller groups and taken into the sorting and diamond storage room, which was actually a large vault. The entire back wall was lined with numerous smaller vaults, each of which contained a number of what appeared to be enamel bedpans. One of the technicians opened several of the vaults and brought some of the pans to a sorting table. He spilled out the contents, all $2-3 million worth. The pile of 1-3 carat stones was about 12 cm wide and 6 cm high. After taking pictures, we were directed to the sorting room where numerous technicians were sorting rough diamonds according to size and color. Some of the rough stones were perfect dodecahedrons. As in the storage room, we could take as many pictures as we liked.

Following our tour of the sorting plant, we visited the Yakutniproalmaz Institute for a briefing on the Institute’s role as consultant to the various expeditions. Then it was back on the buses for a tour through Pilot Plant No. 7, and a picnic lunch on the site of our final technical session. The site was an hour-and-a-half drive from Mirny, and appeared to be specially set up for the occasion. As always, the table was well charged with beer, wine and vodka.

By the time the technical session started, the liquid refreshments had started to take hold and our powers of concentration were waning fast. A free vote was held and it was unanimously agreed to hold the technical session as a poster presentation. Those who wished to ask questions about certain papers could enter into a one-on-one discussion with the author. This was a totally new concept for the Russians and resulted in a very free exchange of information. So after three hours of eating and drinking, it was time to return to Mirny for more eating and drinking.

We arrived back at the hotel in just enough time to change and walk down the street to the Vietnamese restaurant which had been leased out for our farewell dinner. The evening was quite emotional. We enjoyed the excellent food, and made many toasts.

Our Monday wrap-up session in Mirny with ARS was a success as many ideas were exchanged. After lunch we packed up our gear, boarded the buses and headed for the airport. After much discussion, I received the necessary receipts for my currency reconciliation, and individual letters granting the participants permission to take their kimberlite samples out of the country. We cleared security at Mirny and boarded our flight to Moscow. Our routing took us west-southwest to Krasnogarsk and then westerly over the Ural Mountains into Moscow.

Tuesday was a day to enjoy the sights and sounds of Moscow. On Wednesday, we ate breakfast, packed and left for the airport all before 7 a.m. With our letter from ARS, clearing customs was a formality.