Petra’s expansion plan at Finsch will take production from ca. 1.4 Mctpa to 1.8 Mctpa by FY 2016 and then increasing to ca. 2 Mctpa by FY 2019. With gross resources of 50.9 million carats, Petra’s initial mine plan has a life of 17 years, but resources in residual Block 6 and the Precursor kimberlite are expected to prolong the actual life of mine for considerably longer.
Production is currently entirely from Block 4, which is a mature block that has mostly been mined out, meaning that the ore is by this point heavily diluted with waste rock. In order to provide earlier access to undiluted ore before the main Block 5 Cave is put in place, Petra will use the sub level cave (“SLC”) mining method over four levels from the 710 metre level (“mL”) to 780 mL at a rate of 3.2 Mtpa. Once the transition is then made from mining the SLC to the main Block 5 Cave, which is currently planned at the 900 mL, tonnages will increase to 3.5 Mtpa from FY 2021.
On 12 August 2013, Petra announced enhancements to the expansion plan at Finsch, which focus on revisions to the ore-handling system (including the implementation of a conveyor system which can transfer 710 – 780 mL SLC material to the existing loading and hoisting infrastructure on 650 mL), a further enlarged footprint of the Block 5 SLC and the doubling up of crusher capacity to complement the enhanced ore-handling and engineering infrastructure planned at the SLC and the Block 5 Cave (originally planned on the Block 5 Cave elevation only).
These measures will serve to improve production flexibility, give the ability to more efficiently manage grades and enable the earlier decommissioning of the Block 4 automated ore-handling infrastructure, resulting in long term savings in operating costs, as well as the added benefit of production efficiencies.
ROM throughput is guided at 2.83 Mt for FY 2014 at a grade of ca. 32 – 33 cpht. As the mine’s production profile gradually changes from diluted to undiluted ore, the ROM grade is expected to increase to ca. 36 cpht by FY 2015, to ca. 43 cpht by FY 2016 and to ca. 56 cpht by FY 2017 (up from previous guidance of 47 cpht, assisted by the aforementioned plant changes), when full production is sourced from undiluted ore.
The development of the declines and access tunnels, which are key deliverables at this stage of the project, are progressing in line with expectations and the development and drilling contractor services have been put in place. The successful progression of the programme is evident by the significant increase in development metres achieved for the Year (2,311 in FY 2013 versus 169 metres in FY 2012). Raiseboring activities also commenced during Q4 FY 2013 and yielded 165 metres.
Treatment of the ‘Pre 79 Tailings’ is planned at 2.65 Mt for FY 2014 and expected to be mined for a further two to three years (including FY 2014) at a grade of ca. 21 – 22 cpht (increased from prior guidance as a result of the abovementioned plant changes). Once the ‘Pre 79 Tailings’ have been depleted, treatment of the ‘Post 79 Tailings’ will continue until FY 2020, at a lower estimated grade of approximately 10 cpht.