Implications of dredge mine design on mine optimizations and discussing possible approaches

Abstract

The development of dredging as a major player for surface mine applications has led Royal IHC, a large equipment supplier and consultant for dredging and mining operations, and the TU Delft to work on more advanced optimizations techniques for the design of dredge mines. Three implications of the design of a dredge mine were found to be crucial for optimizations, namely: 1) depth control, 2) mining direction and 3) creation of multiple ponds. The conventional approach for open pit mines, in which a series of nested pits are created to determine an optimal mining sequence, was tested using the core module of Whittle and showed not to be readily applicable on dredge mines, because 1) multiple ponds may be created, 2) the depth to be mined for a certain area changes in time and 3) the nested pits expand randomly towards high graded zones. A new method for optimizing dredge mines was introduced as a second approach, which determines an ultimate depth per stacked block model, based on the cumulative values and finds an optimal route for a pond through these stacked blocks by using an adapted version of the Nearest Neighbour algorithm. Four limitations for this approach are recognized: 1) the depth difference between stacked blocks could become impractical, 2) full utilization of the field is not possible because it may reach a premature dead-end or it may enclose a group of non-mined blocks, 3) the blocks have to meet the same length and width requirements of a pond; therefore not incorporating the accuracy of the data and 4) it lacks the function ability to mine the area in layers. Project Alpha indicated that the new approach finds an optimal mine design; however, the long lifetime of the mine (>60 years) results in a low recovery of 65%. Decreasing the lifetime of the mine would result in a higher recovery. The conventional approach showed to be impractical for the design of a dredge mine, while it created multiple thin deposits. The NPV of the worst case scenario of Whittle turns out slightly lower than the NPV of the optimal route determined by the second approach.