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Osisko’s Windfall project yields 9.7 g/t Au head grade

Published by , Assistant Editor
Global Mining Review,

Osisko Mining Inc. (Osisko) has provided preliminary results from Zone 27 bulk sampling.  The Zone 27 bulk sample is the first of three planned 5000 t samples in the ongoing evaluation work at the Windfall project.

The results represent 2078 t mined from Zone 27 wireframe 115. The balance of 2922 t will be processed in the new year, with reconciled results from the full 5000 t sample expected to be available by March 2019. The average head grade obtained from the 2082 t is 9.7 g/t Au and 5.5 g/t Ag. These initial results successfully confirm prior drill hole information and the visible mineralisation along the mined portion of Zone 27. The average head grade from the sample is 39% higher than indicated in the resource block model for this area of Zone 27 (7.0 g/t Au).  

Osisko President and CEO John Burzynski commented: “We are very pleased to deliver an early Christmas gift to our shareholders with these great preliminary results from the Zone 27 bulk sample. Having the grade come in 39% higher than anticipated is a strong result, and it is particularly encouraging given the recent increase in grades shown in the Lynx Zone resource update (see Osisko news release dated 27 November 2018). 

The infill drilling programme, recent resource update and now the initial bulk sampling results have all been demonstrating that the more detailed work we do at Windfall, the better it gets.”

Mill feed tonnages were provided by the custom mill used in the sample processing (Northern Sun Mining, operator of the Redstone mill in Timmins region, Ontario). Daily composite samples collected during the processing of the bulk sample were assayed by ALS Laboratories in Val d’Or.

Processing and resource block model reconciliation

Processing of the bulk sample produced gold/silver gravity and flotation concentrates. The first 2078 t has been processed at an average throughput of approximately 350 tpd. The total amount of gold and silver contained and produced from the full 5000 t bulk sample, incorporating all underground data, will be used to reconcile the representative area in the Zone 27 resource block model once the full sample has been processed.

The resource block model was upgraded in this part of the deposit using recent 12.5 m infill drilling and PEA block modelling parameters, and an average of grade of 7.0 g/t Au was estimated in the area mined. 

The preliminary results returned 9.7 g/t Au head grade from the first 2078 t test milled.  PEA metallurgical testwork indicated recovery of 92.5% for Zone 27 (communition, gravity and whole ore leach) which is most appropriate given the nature of ore. Test mill availability dictated using a mill with a different process flowsheet consisting of comminution, gravity and flotation.  Final recoveries will be determined in the new year based on the concentrate volumes and reconciliation upon the completion of processing of the full 5000 t sample. Osisko’s current mill design work anticipates using communition, gravity and whole ore leach as noted in the PEA and the corporation anticipates ultimate recoveries to be within the parameters outlined (92.5%) from the metallurgically simple ore at Windfall.

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