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MEI Online: Plant Operation News: North America: October 23rd 2014


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:: Stornoway Adds Large Diamond Recovery Capacity to Renard Diamond Plant Design


Stornoway Diamond Corporation is pleased to announce the results of an optimization in plant design at the Renard Diamond Project which is expected to allow the immediate addition of a large diamond recovery capacity to the Renard diamond plant for no additional net capital cost.

The Renard diamond plant is being designed and constructed under an EPCM agreement between Stornoway and SNC-Lavalin Inc., with sub-contracted services being provided by AMEC Americas Ltd. and DRA Americas Inc. (DRA) for the specialized engineering and field support services relating to the plant’s crushing, material handling, and diamond recovery circuits. 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.

Matt Manson, President and CEO, commented: ”These plant design optimizations that we will implement at Renard will allow us to recover the potential value upside from large diamonds that is a characteristic feature of the project. The most recent valuation of Renard’s diamond samples, conducted in March 2014 by WWW International Diamond Consultants Ltd., indicated a weighted average of value of US$190/carat for the three kimberlites in the project’s Mineral Reserve, and US$197/carat for Renard 2, which represents 82% of production in the first 11 years. These valuations, being un-escalated base case diamond price models developed in the conventional manner, assume only nominal value from diamonds larger than 10.8 carats in size. However, the size distribution of samples collected at Renard 2 suggest the potential to recover approximately 3 to 6 stones between 50ct and 100ct in size, and 1 to 2 stones greater than 100ct in size, every 100,000 carats (representing 2 to 3 weeks of output at full production). While the presence and quality of such stones can never be assured at any diamond project, their occurrence is predicted by the sample data collected to date and their impact on project revenue could be significant. Ensuring we have the optimal plant design to recover them from day-one, within our existing plant capital budget, is a noteworthy achievement by the project team."

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.

Nameplate ore processing capacity will remain at 6,000 tonnes per day (2.2 mTonnes per annum) at an overall plant utilization (OPU) of 78%, expandable to 7,000 tonnes per day (2.6 mTonnes per annum) assuming an OPU of 83% and further operational optimization. The Renard mine plan contemplates 6,000 tonnes per day of ore feed from the Renard 2 and Renard 3 open pit and underground mine, supplemented by 1,000 tonnes per day from the Renard 65 open pit.




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