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PFS announced for Mali gold mine

10th July 2015

  

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ASX-listed gold miner Resolute Mining announced last month the results from an independent revision of the underground prefeasibility study (PFS) at its Syama gold mine, in Mali.

Completion of the updated study confirms an early move to underground mining in 2016 will produce robust economics with operations at strong cash margins. The updated study also delivers a significant increase in underground ore reserves, incorporating recent high-grade results from diamond drilling conducted over 2014, including the previous Stage 2 openpit resource.

Resolute CEO Peter Sullivan says: “Comple-tion of the updated PFS validates our confidence in the underground development at Syama and delivers a capital efficient outcome with strong long-term cash flows until at least 2028.

“Our activities over the past 12 months have significantly boosted the Syama underground reserves and established it as a robust and long-life gold mine. Excitingly, the study has also identified further project upside, as the orebody remains open at depth, which, with additional drilling, should lead to further resource and reserve increases.”

In March 2014, the company released results from a PFS for a proposed underground operation at Syama. The study, which was completed by independent experts Snowden Mining Industry Consultants, identified an opportunity to migrate to a long term, underground mining operation by exploiting the extensive mineral resource beneath the openpit.

During 2014, Resolute completed a 13 600 m drilling programme to infill and extend the underground resource. The results of this drilling were reported throughout the year and were highlighted by many broad high-grade intercepts, emphasising the robust and consistent nature of the Syama gold deposit at depth.

In March this year, the company announced that ore contained within the Stage 2 openpit mine plan was best extracted from underground, providing greater return on capital and a smoother cash flow profile. It was subsequently concluded that a revised underground PFS would incorporate the Stage 2 openpit resource, as well as the remodelled, deeper resources from the highly successful drilling programme, to determine the operational and financial improvements compared with the earlier study.

The longitudinal projection provides a schematic of the results of this revised PFS work, outlining planned underground development, the overall caving outline, the location of interpreted mineralisation and the high-grade intercepts at the base of this envelope reported in 2014, which support mineralisation remaining open at depth and along strike to the south. It is apparent that further drilling is warranted to extend the mineral inventory and diamond drilling has been planned for next year.

Through geotechnical analysis and investigation of various underground mining methods, Snowden determined that the orebody footprint was sufficiently large for a caving operation to be developed and selected traditional sublevel caving (SLC) as the preferred mining method, as the orebody geometry and geotechnical conditions are suited to SLC, which is a highly mechanised mining method that is well-understood and used in many locations around the world that can deliver the required production rate to replace openpit production – about 2-million tons a year – at an acceptable cost. Also, the subsidence zone will not impact on or affect critical infrastructure.

SLC mining methods were selected because the geotechnical conditions are unfavourable for more traditional open stoping methods, making them low production rate and higher cost options. Finally, Resolute’s decision to employ SLC at Syama was supported by the company successfully using a similar method at its Mount Wright operations in Ravenswood, Queensland.

The mine design parameters have been based on Australian experiences, including Mount Wright and other typical Australian SLC operations. Specific mine design parameters may change as more data and information becomes available through the definitive feasibility study (DFS) process. However, the accuracy of assumptions is sufficient to meet the 25% accuracy of a PFS and small changes in parameters are unlikely to materially impact on the production schedule or cost model.

On the hanging wall side, the cave draw angle is expected to be about 65°, while on the footwall side, failure of the footwall would not extend beyond the footwall contact. The footwall domain to the east of the Syama Shear provides competent rock mass conditions determined suitable for the mine infrastructure, such as decline, vent raises, substations, sumps and pumpstations.

In estimating the reserve, Snowden elected to model global dilution and recovery factors on an individual ring basis to improve accuracy in the overall dilution and recovery estimate. For the SLC, mining a total of 79% of the designed tons and 80% of the designed metal has been estimated.

Decline development is expected to commence in early 2016 from within the Stage 1 openpit from a portal located 200 m below the surface. This will allow early access to underground ore, for development of initial production stopes, while continuing to extend the decline to the surface for long-term access to the underground.

Resolute has already commenced the project work required for a DFS to facilitate an early decision to commence underground mining. The DFS is scheduled for completion in the March 2016 quarter.

Edited by Leandi Kolver
Creamer Media Deputy Editor

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