Resin-in-pulp Plant

The resin-in-pulp plant was commissioned in July 2002. The first gold from this production facility was produced on 7 September 2002. The plant uses resin-in-pulp technology, which is commonly used in Russia. The process involves crushing and grinding the ore, resin in pulp absorption and electro-winning to produce doré bullion. The barren tailings are treated by a cyanide destruction process before being pumped to a tailings dam. 

The RIP plant was originally commissioned in 2002 with a design capacity of 0.75 million tonnes/year and has been gradually expanded since then without interruption to production.  In 2006 the next stage of the RIP plant's expansion was successfully accomplished on time and on budget which brought the plant's annual capacity to 1.9 million tonnes of ore.  This was an increase of almost 27% on 2005 and ensured an increase in gold produced despite a 7% decrease in the average grade of ore delivered to the mill.

About 82% of the mill feed in 2006 was delivered from the Pokrovskiy pit.  Approximately 3% was from technological sampling at the Pioneer deposit whilst the remaining feed was part of the blending of ore from the Pokrovskiy Rudnik stockpiles.  Due to the fact that primary ores were included in proccessing for the first time, blending at the intermediate stockpile near the plant was expanded and optimised both from the point of view of technological characteristics and average grades.

This productivity increase was principally accomplished through the expansion of the RIP circuit and the optimisation of the grinding circuits and classifiers.  The main challenge for the plant's operators in 2006 was an adjustment of the technological process and maintenance of the stable recovery rates for the mixed type of material produced by the mine which included some primary ore.  The process was modified in order to maintain stable recovery rates for the mixed ore types.  The significant changes were an increase in resin volume and commencement of ore cyanidation in the SAG mill which increased the total resin surface area and leaching time.  As a result, in 2006 the recovery rate was approximately the same as in 2005 (90.8% compared to 91.5% in 2005) although part of the material treated was primary ore. 

In 2007 expansion of the blending stockpile, to a capacity of c.200,000 tonnes, enabled optimisation of the mixing ratio of the mill feed, both in terms of processing quality and average grade. 

The optimised mill feed and a number of other adjustments to the milling and recovery process helped keep recovery rates at c.90% in 2007, in spite of the inclusion of more difficult primary ore.  These changes included grind size, leach time, and the concentration and the consumption of cyanide.

In 2006 separation of the flows of pregnant solutions and the installation of additional electro-winning cells optimised gold recovery and doubled the recovery of silver, increasing silver production by 350%. 

Heap leach

The first gold from Pokrovskiy Rudnik was produced through heap leach operations in 1999.  Before the commissioning of the resin-in-pulp plant, all of the ore from Pokrovskiy was crushed, screened and then agglomerated before being stacked onto heaps for leaching. The pregnant solution was then drained from the heaps onto a pad connected to a Merrill Crowe circuit and the gold was recovered by precipitation. This gold was then smelted into doré bars and the barren solution recycled. After the 60-day cycle, the leached ore was reclaimed and stockpiled for future grinding and subsequent treatment in the new plant. Following the commissioning of the resin-in-pulp plant, the pregnant solution is now treated within the resin-in-pulp plant and the Merrill Crowe circuit is being refurbished for potential use at Pioneer. 

A major development in the heap leach operation was introduced in 2004 when the Group implemented double stacking technology for the process; this simply entails stacking a proportion of the ore before applying the treatment solution and then stacking the heap higher and again applying the solution – the bottom layer thus receives approximately two times the leaching. Double-stacking has increased recovery by 40% to 60% which has generated a similar increase in the gold recovered from only a 23% increase in stacked ore.  The enhancement in heap leach technology preserved production costs in 2005 at the same level as 2004 and also allowed for the economic treatment of grades lower than originally anticipated. Double stacking has also allowed the Group to carry out the heap leach maintenance schedule.

Test work carried out in 2005 in order to improve heap leach technology proved successful and has allowed the application of new methods in 2006 on a larger scale.  These involve ore being left on heap leach pads through the winter until spring for futher leaching and ore for the following year's treatment being stacked on pads during the autumn of the previous year.  This method allowed the start of leaching one month earlier than in 2005 and produced 2,000 oz of additional gold from these test works during the first 6 months of 2006, improving recovery rates at the pads under test from 30.7% in the first half of 2005 to 68.3% in the same period of 2006.  In 2006 recovery rates from the Heap Leach process increased by 50% up to 73%.  This has allowed the Group to treat a larger amount of low grade ore through the heap leach process and also to increase recovery rates using this process.

In 2007 the increased capacity of the RIP plant and the higher price of gold allowed lower grade ore to be economically processed on the heap leach pads without an increase in the amount of mining works undertaken.  Recovery rates remained in line with the previous year at c.69%.