080121-08MN006-Sabina Hackett River Project Proposal ... - NIRB

Project DescriptionOre and waste from the underground operations will be hauled to surface by underground hauledtrucks via the open pit ramp system and transferred to larger open pit trucks for haulage to thesurface crusher or waste rock storage facility.Due to the relative locations of the East Cleaver and Boot Lake deposits, the prefeasibility studywill consider the potential to access the East Cleaver underground resource from the Boot Lakeunderground mine2.4.5.4 Crown Pillar ExtractionThe current mining method and extraction methodology for the Boot Lake underground minerequires that a crown pillar be left in place between surface and the operating mine during theinitial underground mining phase. The preliminary mine plan includes mining of the crown pillarlater in the operational life of the Boot Lake underground mine, which would necessitate theremoval of overburden overlying the crown pillar area prior to mining. The crown pillar could bemined as a small open pit or by underground methods, whereby the crown pillar would be drilledand blasted as a series of stopes and extracted via the underground mine.The current mining method for the East Cleaver and Main Zone underground mines does notrequire the provision of a crown pillar.The prefeasibility study will review the requirement for a crown pillar for each underground mineand propose an appropriate method of extraction if any pillars are required.2.4.5.5 GroundwaterThe influence of groundwater inflows and pressures on underground stope stability, dewateringrequirements and underground operating conditions are expected to be negligible in that portionof the underground mines under permafrost conditions, namely all of the East Cleaver and MainZone mines and the majority of the Boot Lake mine. Water inflows under these conditions willcome mainly from production and development drilling activities associated with theunderground operations, which will require the use of a re-circulating calcium chloride brinesolution in order to prevent water freezing issues in drillholes.The dewatering system for each underground mine will involve pumping unsettled water tosurface and discharging into the re-circulation process water tank in the mill plant.The prefeasibility study will review the mine dewatering requirements and discharge locationsfor each underground mine, with particular emphasise placed on estimating ground waterinflows, pressure and water quality into the Boot Lake underground mine below the permafrostlayer, and appropriate mine dewatering systems planned.2.4.5.6 ExplosivesThe supply of explosives will be provided by the same third party supplier of emulsionexplosives for the open pits, and would deliver product to underground storage magazines asrequired. Under normal operating conditions, it is envisioned that no more than one month’ssupply of emulsion explosives would require storage on site at any one time. BlastingJanuary 2008 Hackett River Project – Project Proposal Sabina Silver CorporationReport Version B.1 2–16 Rescan Environmental Services Ltd. (Proj. #833-2)