Sukhoy Log – one of the world’s largest gold reserves
With estimated reserves of some 2,000 tonnes of gold (64.3 million Troy ounces) Sukhoi Log in the Irkutsk region of Russia is one of the world's largest untapped deposits of gold.
Sukhoi Log – the name means “dry valley” – was discovered in 1961 and intensively explored in the 1970’s. Many internal reports were written and a few papers published in Russia, but little was known of the deposit abroad because of former official secrecy restrictions. But the exploration for –and discovery of – the Sukhoi Log deposit was in fact the culmination of many years of study and development of the Lena Goldfields by several generations of geologists and miners. The deposit is entirely “blind”, i.e. has no surface outcrop, and was discovered only by geologists using new ways of geochemical prospecting. Intensive exploration started in 1971 and was completed in 1977. The work included 209.6 km of diamond core drilling in 846 drill holes, 11.7 km of underground drives, 61 raises, 1,546 m of which were in ore, 110.3 km of trenches, 13,000 channel samples, three bulk samples of 150 t, 800 t and 980 t – and many tens of thousands of assays for gold.
In addition to the Sukhoi Log deposit, several smaller gold deposits of the same type were discovered in the region, including Verminsky, Vysochaishy and Nevsky.
The two major underground drives of the 1970’s programme were re-opened in 1995, and provided direct access to – and observation of – a large part of the interior of the orebody for the feasibility study that was conducted in 1995-96 by Star Mining Corporation, Sydney, Australia.
Sold in auction Jan 2017
In January 2017, the right to develop Sukhoi Log was sold to a joint venture of miner Polyus and state conglomerate Roster. The joint venture, SL Zoloto, will buy the deposit for 9.4 billion roubles (158 million USD), compared with the starting bid price of 8.6 billion roubles. Polyus is the largest gold producer in Russia and one of the top ten gold miners globally by ounces produced. It also holds the fourth largest mineral resources base in the world.
SL Zoloto intends to conduct additional exploration works and a feasibility study, which is expected to last for approximately three to four years, supported by international mining and engineering consultants. Based on the results of the study, the company will evaluate options to initiate construction activities at Sukhoi Log. CAPEX is estimated at 90-100 billion roubles with development costs of some 4 -5 billion USD.
The development of such a large project is expected to have a significant impact on the social and economic development of the Irkutsk region, where Sukhoi Log is based, with considerable investments in infrastructure, etc.
Location and geology
The area covers 105,000 km2 and lies between 57 and 60 degrees North latitude, approximately 900 kilometres south of the Arctic circle. The region comprises a broad, subcircular topographic dome approximately 350 km in diameter, termed the Patom Highland, rising to more than 1,800 meters. It is partly encircled by the Vitim and Lena Rivers. The deep alluvial and colluvial deposits in most channels and river valleys result from long periods of gentle drainage and glacial erosion. The major high-level landforms developed during several episodes of Pleisticene ice-sheet erosion, a late phase of trunk valley glaciation, lengthy periods of periglacial erosion and several phases of interglacial warm climate chemical erosion.
The regional geological setting of Sukhoi Log and the Lena Goldfleld is that of a complex folded sedimentary sequence at the exposed northeast end of the Akitkar Foldbelt and the included Olokit Zone, parts of which extend into the western side of the goldfield.