At Star Diamond Corporation’s Star-Orion South Diamond Project, located in the Fort à la Corne forest of Saskatchewan, Canada, mining is to be carried out using conventional open pit methods. The Orion South kimberlite will be mined first, followed by the Star kimberlite. However, in the Technical Report filed recently with the PEA and prepared by SGS, the company outlines that to remove the considerable amount of unconsolidated overburden required during a four-year Stage 1 pre-stripping period it will use three bucket-wheel excavators (BWEs) to mine over 39 Mt of sand and clay and almost 33 Mt of till. After that at the operations in Stage 2 of the Orion South kimberlite operations (project years 4-8), the BWEs will have to move over 90 Mt of sand and clay and over 155 Mt of till.
“Merchantable timber is harvested prior to stripping. A fleet of excavators and articulated trucks excavates a 20-30-metre-deep starting “key” or “slot” for a BWE. After that BWE has progressed for a period, enough space will be cleared behind it to allow a second, deeper key to be excavated – again using the excavator and articulated truck fleet. Then, the second BWE starts operating. The same procedure is used to establish the third BWE. BWE spoil is removed from the pit on overland conveyors and delivered to a single, large spreader. This crawler-mounted spreader places the spoil on the waste pile.”
Hydraulic shovels load the kimberlite into rigid-frame trucks. It is estimated that 70% of the kimberlite will require drilling and light blasting. The powder factor will be quite low to avoid diamond breakage. The trucks transport the kimberlite to an in-pit mineral sizer, which crushes larger lumps before placing the kimberlite onto an overland conveyor for transport to the mill stockpile. The Orion South kimberlite is mined first, followed by the Star kimberlite. After Orion South is mined-out, waste from Star and mill tailings are placed in the Orion South pit.
In summary, a fleet of articulated trucks and hydraulic excavators will be used for clearing and levelling the surficial sands, and developing the starter slots for the three bucket-wheel excavators. A fleet of three bucket-wheel excavators will feed an overland conveyor system to a large stacker, and a small fleet of 200 t, rigid-frame trucks will work in the kimberlite and mine waste below the overburden, dumping into kimberlite and waste feeder breakers to conveyors out of the pits.
The truck and shovel fleets are sized to meet the production requirements of the bucket-wheel excavator stripping rate and the processing plant feed rate. As the kimberlite is mined, the mill stockpile will be managed to ensure continuous plant feed. The report specifies up to 42 Caterpillar 745 ADTs and up to 8 Caterpillar 390F excavators. The BWE preferred manufacturer has not been specified but will likely be from the main OEMs of thyssenkrupp, TAKRAF, Sandvik or FAM. They will include a belt wagon, hopper car, cable reel car, in-pit conveyor, and head conveyor. The kimberlite fleet will include up to 8 Caterpillar 789Ds plus two large Cat 6040 hydraulic shovels: a face shovel and a backhoe. The fleet will also include 992K and 994K wheel loaders, as well as numerous dozers, graders and other equipment.
For the Star – Orion South Diamond Project PEA, DRA designed a diamond Process Plant that is best suited to treati
ng the kimberlites at FalC. The FalC Kimberlites are generally categorized as “soft” and are amenable to autogenous grinding (AG) milling. The functions encompassed in the Process Plant are comminution, classifying of coarse kimberlite based on density and size, identifying and recovering diamonds and discharging processed kimberlite. The plant includes AG mills in the comminution section, 510 mm dense medium separation (DMS) cyclones in the DMS section, and in the recovery section the diamond sorting equipment includes X-Ray Transmission (XRT) sorting, X-Ray Fluorescence (XRF) based X-ray sorting and grease technology.