Analysis of the pit lake closure option for open pit quarries

The suitability of pit lake closure option was assessed for ten open-pit quarry mines in Lugoba and Msata, Tanzania. The study integrated hydrological, geochemical and geotechnical assessment. Hydrological assessment addressed current and future water quality for pit lakes. Geochemical characterisation established hazardous elements and potential for acid generation. Geotechnical analysis established prior and current stability of pit walls. Hydrological assessment revealed good water quality, with pit lakes attaining equilibrium in 14 to 126 years, at depths of 18 to 40 metres. Geochemical assessment showed albite, quartz, and calcite as the dominant minerals. Aluminium and iron mobilisation was considered negligible due to absence of acidic conditions. Geotechnical assessment revealed high stability of pit walls before and after formation of pit lakes. The study proved that pit lake closure is a viable and sustainable option for quarry mine sites. This transforms former quarries into water resources for irrigation, livestock and other secondary uses, while mitigating post-mining environmental risks in nearby communities.