Stornoway Optimizes Renard Plant Design

Stornoway Diamond Corporation (TSX:SWY) has optimized its Renard plant design to allow for a Large Diamond Recovery circuit to be fully integrated into the plant’s primary flow-sheet within the existing capital budget and with no change of scope in the existing ore processing capacity of 2.2mtonnes per annum.

As quoted in the press release:

Detailed plant engineering is ongoing, with the first pouring of concrete for the plant’s foundation scheduled for April 2015. However, the work completed to date has already indicated that sufficient design efficiencies and cost savings can be implemented to allow for a Large Diamond Recovery circuit (“LDR”) to be fully integrated into the plant’s primary flow-sheet within the existing capital budget and with no change of scope in the existing ore processing capacity of 2.2mtonnes per annum. Stornoway’s January 2013 Optimized Feasibility Study for the Renard Diamond Project contemplated a diamond plant flow-sheet geared to the recovery of diamonds up to 30mm in diameter (equivalent to a 200 carat round octahedral stone), with room for a LDR circuit to be retrofitted later as required. The direct capital cost for this feasibility plant design, without LDR, was estimated at that time to be C$162.7m, excluding capitalized operating costs. The modified plant design that will be built contemplates the recovery of diamonds up to 45mm in diameter (equivalent to a 600 carat round octahedral stone), with a corresponding direct capital cost estimate of C$147.1m.

The optimized Renard diamond plant flow sheet, developed by DRA, will maintain the three stage crushing regime established in the January 2013 Optimization Study. Run-of-mine ore will be broken down with a primary jaw crusher utilizing a 230mm top size cut-off and fed to a 4 meter diameter rotary scrubber for disaggregation. Direct feed to Dense Media Separation (“DMS”) circuits will be +1mm to -19mm (compared to +1mm to -30mm previously) so as to improve efficiency and reduce diamond breakage risk. Diamond recovery from concentrate will be through magnetic separation and X-ray technology supplied by DebTech, with no grease table. Recent bench tests on Renard diamonds at DebTech suggests a 98% recovery efficiency with the X-ray sorters that will be employed. Direct feed from the scrubber product screen to the LDR circuit will be +19mm to -45mm, with the top size cut-off adjustable to 60mm. Oversize material between +45mm and -230mm will fed to a cone-crusher under choke feed, before returning to the DMS and LDR circuits via a sizing screen. The non-diamond bearing material from the LDR circuit and the DMS tails between +6mm and -19mm will be conveyed to a High Pressure Grinding Rolls (“HPGR”), with the resulting cake returning to the scrubber for disagglomeration. Fine tails at -1mm will be recovered via thickener and degrit cyclone before dewatering by centrifuge and combination with the +1mm -6mm DMS tails for disposal by dry-stacking as previously.

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