Acid Mine Drainage Risk Assessment To Inform Mine And Closure Planning

Using drillhole assay data to assess the risk of acid and metalliferous drainage (AMD) early in the planning of a mining operation can have a number of benefits.  These include:

• Early identification of operational and closure AMD risks;
• Optimisation of geochemical characterisation programmes
• Early identification of mitigation and management measures (including engineering design);
• Early technical input to environmental approval applications;
• Preventing project delays due to late identification of environmental risks related to AMD and late commencement of lengthy geochemical testing programmes; and,
• Development and costing of closure strategies early in the planning process.

AMD assessments have been undertaken using drill-hole data (incorporating chemical assays and geological logging information) combined with interpretive geological models and mine planning information for a number of Australian iron ore operations.  The approach has been implemented successfully for mine projects at various stages of development (for example, pre-environmental approvals to post-mining). 

The example discussed herein illustrates the use of geological modelling tools (Vulcan, Leapfrog) to generate 3D visualisations of the distribution of sulfur (a key parameter indicative of AMD risk) within the pit shells.  The final sulfur models were aligned with existing block models to allow examination of past, current and future mine plans in the light of AMD potential.  Volumetric quantities of sulfur-bearing material reporting to waste rock dumps and ore stockpiles respectively were estimated.  Small volumes representing sulfur-bearing ‘hot-spots’ were identified and maps were generated to determine the location of these hot spots on exposed pit walls, and assess closure scenarios with respect to AMD risk and anticipated post-mining water table levels.

This paper describes the overall assessment approach, the benefits of undertaking these assessments as early as possible in mine planning, and how the findings were used to inform the development of closure strategies at the sites.