Sepon Mine Closure Strategy
SRK assisted with the development of closure plans for the western and central development areas at Sepon, a large open-pit copper mine in the Vilabouly District of Savannakhet Province in central southern Laos. These areas include more than 40 pits, some backfilled, and 13 waste rock dumps (WRDs). The main objective of the work was to advance preparation of a closure plan for the areas to pre-feasibility level.
To support development of the closure strategy and design, a range of technical studies were completed, including:
- Geotechnical assessment of all pits and dumps to allow ranking in terms of potential geotechnical hazard posed post-closure
- Hydrological assessment with detailed delineation of water catchments within the project area, and the development of a closure water balance model
- Geochemical assessment to understand the distribution of ongoing sources of solute production around the site
- Geochemical modelling of water chemistry at source and downstream following mixing with other water sources.
After the specialist studies were completed, SRK reviewed the main risks to be addressed by the closure plan, then evaluated closure options and developed recommendations for each area. This included addressing key issues including potential for acid mine drainage associated with oxidising pit wall rocks and potentially acid forming waste rock, and physical stability of high pit walls and waste rock dumps.
Future water quality predictions were combined with the site-wide water balance to develop an integrated closure strategy for the site, identifying optimal closure measures to mitigate water quality impacts to downstream receptors (drinking water resources) and ensure public safety.
Conceptual closure designs for the WRDs and pits were developed incorporating both passive and active water management infrastructure. Required closure works were described for each mine precinct, on a catchment by catchment basis.
