Anglo Platinum accounts for about 40% of the world’s newly mined platinum. Its Mogalakwena mine opened in 1991 and can potentially mine ore from five to seven open pits for at least the next 35 years and possibly longer. The Platreef, richer in base metals by comparison with the other PGM reefs in South Africa, outcrops along the entire length of the lease. There are two separate processing plants with combined milling capacity of about 11.4 Mt/y. Steve Burks, Managing Director of Whittle Consulting (Africa) announced the completion of the extensive Enterprise Optimisation study of Mogalakwena in the Limpopo province of South Africa, with a positive outcome.

Output from Mogalakwena of equivalent refined platinum in 2010 was 260,300 oz, an increase of 10% from the previous year according to the 2010 Annual Report. Ore tonnage milled increased by 7% to 10.4 Mt while head grade declined as planned by 4% to about 2.6g/t (3PGM+Au).

Whittle Consulting was appointed to implement the Enterprise Optimisation study in August 2010. The major objectives identified were:

• To facilitate deferral or minimisation of capital expenditure for the next three to five years
• To evaluate the merits of several alternative operating strategies. These included variable versus capped mining rate, strategic stockpiling of low grade ore, deferral of waste stripping where possible but with smaller short term pit phases to access higher grade ore earlier, consideration of several concentrator upgrade or expansion strategies
• To determine the optimal mining rate matching the current concentrator capacity
• To establish the optimum dynamic mining and concentrator processing rates matching current smelter and refinery capacity constraints
• To establish the optimal production rate for Mogalakwena taking into account the latest ore resource data and applying current cost estimates for possible mine, concentrator and downstream process plant expansions.

This work was carried out in three sequential phases between September 2010 and February 2011 with interim reports and presentations being produced at the end of each phase enabling further work to be redirected if appropriate.

Typically Whittle Consulting defines 10 value levers driving Enterprise Optimisation: Pit shells, pit phases, mining schedule, dynamic cut-off grade, strategic stockpiling, plant calibration, dynamic product specifications, logistics, capital expenditure and simultaneous optimisation of all these mechanisms over the entire life of mine. In the case of Mogalakwena, it was possible to apply almost all of these mechanisms.

The objective of any Enterprise Optimisation exercise is to increase and optimise NPV (the sum of the discounted annual cashflows over the whole period) of the overall operation. This measurement of performance reflects the time value of money and maximises the opportunity to generate free cash for re-investment in the early years of operation, providing more flexibility to management and reducing risk. Frequently improvements in NPV in the range 5 to 35% have been demonstrated to be possible at other operations studied.

In this case, the exercise commenced with a half day training seminar and kick-off meeting on site, after which data collection commenced immediately. The existing resource block model was utilised, supplemented by operational data from every section of the operation including geological, mining, processing, operating cost, capital cost and general commercial information. This was collated in a single Business Model for the whole enterprise which was used with the block model data and the mine’s current pit shell and phase designs to prepare a base case Optimisation Run using Whittle Consulting’s proprietary Prober software. This base case was compared closely with the operation’s current Business Plan to ensure that all costs, revenues and operating parameters (particularly capacity limits at each stage of the value chain) had been captured correctly. Potential NPV improvements were then measured against the base case.

In order to determine the potential benefits of each of the three mining mechanisms (scheduling, dynamic cut-off grade and strategic stockpiling) they were tested sequentially. The extensive experience of Whittle Consulting’s specialists was applied using Gemcom Whittle Four X software to prepare revised pit shells and phases with low initial stripping ratios, finer early phases and quicker access to high grade ore pockets. The three mining mechanisms were then applied again based on the revised pit designs. After this, simultaneous optimisation was applied with all of the mining mechanisms switched on.