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Development of a Grade Engineering (GE) circuit design and operating strategy requires preliminary information about ore characteristics, mine resource volume and both proportion and spatial location of GE amenable ore in the resource. A concept study on this preliminary information is conducted to provide a starting point in sizing the required equipment for GE circuit design. Any GE circuit must be evaluated as part of the mine operation value chain to examine the influence of the product on up/down stream production units performance. A trade-off study is then conducted in an iterative process between the design and economic evaluation to optimise the GE plant design that includes:

  • Modelling and simulation of several preliminary GE plant circuits deemed capable of upgrading marginal ROM ore.
  • For each proposed plant design
    • Provide a summary of selected equipment and operating strategies.
    • Provide incremental operating cost and major equipment cost comparisons.
    • Extraction of key economic indices such as CAPEX, OPEX, Cash Flow, IRR.
  • Narrow down the list of possible designs in conjunction with the mine plan that generates maximum value over the life of mine.
  • Optimisation of process plant design incorporating learnings from evaluations.

A trade-off study aims to first, develop conventional GE circuit designs for pre-concentrating low grade ROM ore within agreed design criteria and established process parameters, and secondly minimise GE plant direct capital expenditure and operating expenditure. Battery limits for ROM ore storage and crushing stages include supply of ROM ore in mine trucks that unload into gyratory crusher and GE plant ROM bin and delivery of crushed ROM ore from primary gyratory crushing stage, via overland conveyor. This should integrate with other processing equipment capacities downstream that receive GE circuit product as feed material.

Multiple crushing and screening plant configurations are assessed and compared in a trade-off study. Options examine various equipment capacities and number of required devices used in each crushing and/or associated screening stages. This is done in conjunction with the rest of the value chain as adding a stage of material treatment to the value chain influences both existing equipment operation conditions and water/energy requirements along the value chain. At this level of comparison, options considered can present with significantly different economic indices and value generated.

When initial information for a plant design is not available engineering-based assumptions are made that incorporate any available information. These need to be confirmed in practice once a design is completed. In that case, a small GE plant configuration using mobile equipment can be installed and utilised at the operation to assess assumptions made during the economic evaluations and design study to minimise risk in the designing process. Mobile/semi mobile prefabricated equipment can include:

  • Combined ROM ore feed hopper and apron feeder
  • Combined feed hopper and apron feeder with sizer
  • (Semi) mobile conveyor(s)
  • Track mounted transfer conveyor which moves material from mobile conveyor to gyratory crusher product conveyors


Eventually, proposed GE circuit configurations are expected to provide a robust plant with suitable catch-up and surge capability to be able to cater for limited mining plan changes and adverse weather conditions. A best option is chosen based on value added and risk analysis for equipment selection and budgetary costing of the GE plant. Software modelling is used to choose and size equipment for the GE plant and define the optimum operating strategy. As well as predicting combined GE plant and gyratory crushing circuit’s stream specifications; including, stream mass and water flow rates, particle size distributions (PSDs) at the optimum LOM treatment capacity.


Page last modified on Tuesday May 11, 2021 14:43:18 AEST