Development of a NAF/PAF Grade Control Programme for Placement of a WRD Cover

Mount Isa Mines (MIM) has commenced rehabilitation of the Handlebar Hill Open Cut (HHOC) Waste Rock Dump (WRD). This includes reshaping of the WRD and placement of an interim cover over any exposed potentially acid forming (PAF) and neutral mine drainage (NMD) waste rock exposed following the reshape. The interim cover comprises inert oxide non-acid forming (NAF) material recovered from the adjacent Magazine WRD.  A key requirement of the interim cover was that only NAF non-NMD material was used for the cover placement to limit solute release from the WRD, until a final closure cover is designed and agreed with the Department of Environment and Heritage Protection (EHP) (informed by a comprehensive WRD rehabilitation trial).  Since the Magazine WRD contained some PAF and NMD materials, it was necessary to characterise materials during mining (from the Magazine WRD) and selectively utilise only NAF non-NMD material for cover construction.  

The basis for the development of a sampling and control program to identify suitable material from the Magazine WRD for cover placement is described.  This includes the basis for the recommended sampling frequency and specific testing requirements based on first assessing the maximum tolerance for misclassification (i.e. maximum allowable exposure of NMD and/or PAF materials in the NAF cover), and, relating these to the mining method.