A two-phase backfill approach to dilution control at the Doyon Mine
The Doyon Mine’s Zone 1 (Altered Zone), found along the southern boundary of the mine, encompasses approximately 20% of the mining reserves. The mineralisation is found in a series of steeply dipping narrow veins, which are contained in an extremely weak host rock: a sericitic schist with RQD values ranging from 0 to 20. Longhole mining methods are used, with either longitudinal or transverse approaches, depending on the width of the ore zone.
Dilution is of critical importance in the mining of this zone, particularly in longitudinal stopes, where dilution levels have averaged 60% since 2000. Major factors influencing dilution in this zone include the stope geometry and stand-up time. A two-phase approach has been developed to mine and backfill longitudinal stopes: the top of the stope is pastefilled after approximately half of the broken ore has been extracted; the remainder of the ore is extracted once the plug has cured; and the remaining void is filled. This method has been used in five stopes to date, resulting in an average dilution of 20%. This paper details the application of this technique and its effect on dilution.