When MEC Mining was asked to complete a feasibility study for a steeply dipping resource in a complex metallurgical coal project, Vulcan Pit Optimiser provided the solution.
The deposit contained 5 seam groups, 3 major overthrust faults and shears, and normal faults in a single pit. Information supplied included a block model, economic assumptions and a geotechnical assessment. Margin rankings provided some clarity on basal seam and economics.
The primary goals were to define the location of the final highwall, low wall and basal seam. In this instance of multiple occurrences of single overlapping seams, Pit Optimiser provided a ‘shortcut’ to the basal seam. Running advanced reserves in Vulcan validated the volumes and the final block model.
Variables for cost and revenue were assigned in the block model, including volume of coal recovered after mining losses, and mining coal to ROM, product tonnes, processing and rail costs.
A variable was created for each price point before haul roads were digitised, to derive a waste cost per block, a critical requirement when mining waste at depth.
Six price thresholds were set and profit was assigned to each block. Vulcan Pit Optimiser was run on a 30 x 30 x 5 metre block size.
By flagging the variable ‘Pit’, grade shells could be run to generate a shell for each price increment to guide staging for early mining and final shell extents.
Mining stages were designed based on the Vulcan Pit Optimiser shell sequence which delivers optimum NPV.
Pit Optimiser delivers superior results to margin ranking by adding the third dimension. With outputs provided as images, the tool promotes instant acceptance and confidence in the results.
In this project Pit Optimiser showed the low wall changing dynamically between seams as mining moved along strike. Duplicates which might not otherwise have been recovered using margin ranking were included in the optimisation.
Following the staged mining shells, MEC incorporated haulage and in-pit dumping considerations into the sequence to ensure the most profitable coal recovery.
Trimming the block model to remove blocks outside the pit shell cut run time from 1.5 hours to 10 minutes.
Pit Optimiser setup panels allow users to enter and calculate economic value. Alternatively the economic value can be assigned through block model variables, as was the case in this project.
Vulcan Pit Optimiser provided the sequence of resource development, final highwall location, basal seam and coal recovery strategy around major faults. This allowed MEC Mining to deliver accurate mining plans quickly and within budget.
Thanks to Ted Boulton, MEC Mining
Extract from paper presented at Maptek Users Conference, Brisbane, 2013