St Ives gold mine - Mine planning and scheduling
Cut-off grades are used to define potentially economic underground mining panels, taking into consideration direct mining and processing costs, Company set commodity prices and other parameters. The economic viability of future mining panels is tested by determining whether the margin, after applying the appropriate cut-off grade, is sufficient to cover the required capital development and mining costs.
Open pit optimisation software, in conjunction with economic parameters and physical constraints is used to generate a series of nested pits for open pit mining. An optimal shell is then selected and a detailed design used to confirm the mineability.
Underground mining methods are largely determined by the geometry of the mineralised zones and evaluation may involve review of more than one method. Fit-for-purpose proprietary software is used for mine design and scheduling.
Mine planning is based on 3D resource block models of in situ mineralisation, with allowances made for minimum mining widths, dilution and ore loss in line with the mining method being considered.
The next major mine project at St Ives will be the development of the Invincible South underground mine. Decline development extending from the Invincible Underground decline is scheduled for late in 2018. Additionally, development of Neptune Stage 5 and 6 pits commenced in 2017, and will continue in 2018.
Infrastructure, waste disposal and ore stockpile management requirements are incorporated into the planning process. Ore stockpile management at St Ives strives to optimise the metallurgical blend requirements of the Lefroy Mill, with regard to material types and grade management. This in turn helps to maximise cash-flow from the operations.