The best diamond deposit in the world - the International Diamond Pipe (Internatsionalnaya in Russian) containing more than 7 carats of diamonds per tonne, was discovered by Soviet geologists in 1969. It was put into operation in record time and developed by the open-pit method in 1981. 75% of diamonds in this deposit are of gem quality, exceeding 2 mm in size and priced very high. The country needed high-quality diamonds, and this small diamond pipe was exhausted fairly quickly.
Subsequently, the management of the Yakutalmaz Trust decided to build an underground mine, one of the first in the world. To design it, Academician Gomelauri, the then director of the Yakutniproalmaz Institute, attracted the Dongiproshakht Institute, which had designed the Donbass coal mines. This was the starting point for early problems accumulating over the diamond mine to be run by ALROSA in some future time. The controversial conceptual solutions of Gomelauri, including a reduced diameter of the main and auxiliary shafts (to speed up sinking), technologically unsafe central dual opening-up scheme with an inefficient ventilation system (the legacy of coal mines), development system with expensive stowage, load haulage by railway trolleys as in the early 20th century, resulted in stretching the construction of the underground mine, similar to the Moscow metro, for decades. None of the Yakutalmaz managers believed that the construction would someday end.
In the mid-1990s, the new management of ALROSA inhaled a new life into the mine starting operations to deepen the open pit to its maximum depth and providing for safe mining of the glass-shaped ore body without harming the underground complex. At the same time, the company accelerated works to complete the construction of the mine. As a result, the mine was launched in 1999 and in 2002 it was brought to its maximum capacity of 500,000 tons of ore (limited due to the reduced cross section of the skip shaft designed in the 1980s).
Mining operations were to be completed in 2017. The International Mine, also called Inter (for short), continued to bring the most expensive diamonds to ALROSA’s piggy bank and please with trouble-free work. However, by 2017, the mine’s production fell to 100,000-150,000 tons of ore, so the mine had to be mothballed, while its resource base was to be replenished.
The management of ALROSA made another decision, that is to further sink the mine after additional exploration of deeper horizons. However, the original mine designing strategy of the 1980s did not envisage any deepening, as the safety of people was a big question. Nevertheless, the company began sinking blind shafts and building an ultra-deep diamond mine. Why were such decisions made?
It's very simple – the mine’s underground reserves amount to more than 50 million carats of excellent rough, which ALROSA otherwise has nowhere to take from, with a total value of more than USD 25 billion. According to the company’s 2018 business plan, its investment in the project will be only about RUB 5 billion until 2024. At first glance, the project looks highly efficient, if not for one “BUT” ...
The construction of mine workings at stages 4 and 5 of the 5PK project on horizon -85 and sinking vertical shafts below the -820 m (790) levels by 2021 leads to the same problems as at the distressed Mir mine, which involve the unsafe passage through the Metegero-Ichersky aquifer... But the problem of Inter is not in the application of proven backfill techniques to waterproof mine workings from higher than ususal water inflows of aggressive brines. The problem of Inter is methane, natural gas, the concentration of which in an unventilated mine area is fatal for miners. Inter is bordering the Irelyakh oil and gas condensate field, which has been producing oil and gas using the gas lift technique for more than 30 years. Methane from Irelyakh’s gas caps seeps into the mine through fractured reservoirs under enormous pressure, as gas and oil layers have already been tapped by the mine’s shafts. Even the most reliable shaft lining will not protect from methane. In addition, recall the design concept, namely the sinking scheme, which is central by its type with a single space of the shaft bottom for miners to descend and ascend. One accident, one emergency in the shaft bottom and this will be a very serious problem for the workers below. Currently, miners coming to or leaving from their shift at Inter spend 3 or 4 hours to descend to the shaft bottom and to ascend to the surface. In the middle of 2018, Rostekhnadzor (Russia’s Federal Environmental, Industrial and Nuclear Supervision Service) closed Inter for several months and it was not announced what remedial measures were proposed to mend the situation.
I hope that such decisions were made. The International mine is the last major industrial facility of Mirny. Its safety is more important than any short-term performance indicators.
Sergey Goryainov, Rough&Polished
