The Giant Sukhoi Log Gold Deposit in Siberia

Bryce Wood has worked as an exploration and research geologist in Australia and many other countries since graduating from the University of New Zealand in 1949. From 1992 to 1996 he was the Star Mining Company geologist in the group conducting a bankable feasibility study on the giant Sukhoi Log gold deposit in Siberia.

The deposit is located in Upper Proterozoic carbonacous shale within the extensive alluvial Lena Goldfield, 850km northeast of the city of Irkutsk. It was completely blind and was discovered in 1961 by Russian geologists using new concepts of mineralisation, state-of-the-art methods of geochemical prospecting , and diamond drilling. The disseminated pyritic orebody is defined solely by assay grades, is tabular in form, and is located in the 2.2km long axial zone of a large near-isoclinal, reclining anticline. Highest ore grades occur in pyritic black shale beds, especially where they cross the anticlinal axis and form two higher-grade (4 - 9 g/t) cylindrical zones along the gently plunging anticlinal crest.
The mineralisation assemblage is consistently quartz-pyrite-gold ± carbonate with minor base and platinum group metals, and low levels of arsenic.
The deposit was intensively explored in the 1970' s and the geological reserve was calculated at a cutoff grade of 1 g/t as 384 million tonnes with average grades of 2.5 to 2.7 g/t Au. Additional resources include 165 million tonnes at 2.0 to 2.3 g/t in a low grade possible pit extension, and 205 million tonnes at 0.8 g/t in the mineralisation envelope.
Four stages of origin and mineralisation can be distinguished on textural, geochemical, isotope and structural features.