Efficiency of the comminution operations is traditionally assessed based on operating cost and energy consumption. Traditionally, the lowest operating cost was achieved by multi-stage fully autogenous grinding due to elimination of steel grinding media costs which may represent up to 50% of the grinding cost. Significant reduction of the cost associated with grinding was achieved over the years by increasing the size and improving the design of the crushers and mills, however there was no major break-through in improving the energy efficiency of the comminution process. The principles of particle breakage in crushing and grinding equipment remained mainly unchanged over the years with energy efficiency reducing as the product size decreases. Only in the last 20 years the more energy efficient technologies were successfully implemented at industrial scale including high pressure grinding rolls (HPGR) for fine crushing and stirred milling for fine grinding. The capital and the operating cost play crucial roles in the design of a new processing plant as they govern the project economics. A theoretical design study for high capacity processing of a hard, fine grained silica rich magnetite ore, with several circuit options was carried out to assess the energy efficiency, operating cost and the project economics expressed
through NPV. The CO2 emission was estimated and the carbon tax added in the operating cost. The results of the study confirm that application of more energy efficient autogenous grinding technologies offers significant benefits over the conventional grinding circuit options.