With the increased understanding of the occurrence of heavy minerals offshore, the need for efficient marine mining systems is emerging. This marine environment demands a dredge mining solution as dry truck & shovel operations are no longer possible.
For the marine mining of heavy minerals, multiple scenarios can be developed. They can differ both in the mining systems used and in the sequence and location of process steps required. The selection of the dredge mining equipment is generally a function of the required depth of excavation, the soil conditions and the target production. In a marine environment, the climate and sea conditions also need to be accounted for. Examples of dredge mining equipment include wheel suction dredgers, applicable in shallow depths for medium to loose sandy deposits and high productions. Wheel dredgers however have limited tolerance for wave conditions, so will likely find applications in sheltered bay or harbour locations. Trailing suction hopper dredgers are applicable in deeper waters for loose sand deposits and high productions. They have a higher tolerance for wave conditions and can therefore be successfully applied offshore.
Given the relatively low grades of heavy minerals found in the deposits, it is preferable to perform a first concentration step as quickly as possible after the mining to create a concentrate. In conventional, inland dredge mining operations this is done at the floating primary concentrating plant. Spiral concentrators are the equipment generally used for this process. In a marine environment, application of spirals on a floating platform will be strongly dependent on the sea state conditions. Wave induced motions of the floating platform will disrupt the concentration process of the spirals. This limits the application of the spirals to steady platform.
Combining the optimal dredge mining equipment with the optimal processing solution is a complex process. Both aspects cannot be regarded individually and have to be seen as an integrated process where capacities and process characteristics have to matched to find the optimal integrated marine mining solution. As example a case will be presented for the mining of heavy minerals approx. 30 km off the coast of Western Australia. Multiple scenarios for this case were produced. These include the use of a stationary suction dredger that fills barges that were tugged to a port facility where a process facility was located. An alternative scenario would use a trailing suction hopper dredger to mine the ore, sail to port and dump the material in water near the quay, where a small second dredger would re-handle to ore and directly feed a process installation onshore. Selection of the optimal scenario requires careful and detailed evaluation of all applicable variables.