Martha mine tailings storage facilities: how do they stack up?

Waste rock at the Martha open-cast Au-Ag mine in New Zealand is excavated from the mine, transported by conveyor to the waste disposal area, and used to form engineered earth/rockfill embankments which abut rising ground to form large impoundments containing the tailings ponds. Construction of the first tailings storage facility, Storage 2, commenced in 1987, and a database covering almost fifteen years shows that it is performing very well. Storage 2 has now reached its final crest height. Construction for the second tailings storage facility, Storage 1A, began in 1998. The predominant rock type at the pit is andesite, with volcanic breccia, clays, tuffs and ignimbrite also present. All oxidised rock, ignimbrite, clays and tuffs are non-acid forming, while the mixed and unoxidised andesite and volcanic breccia contain variable amounts of sulphide sulphur, mainly pyrite, much of which is potentially acid forming. The embankments are designed as earth/rockfill water-retaining structures. Following the cessation of tailings deposition and completion of tailings consolidation the risk of the release of tailings is almost impossible due to its inherent strength. The tailings slurry contains around 38% solids which are predominantly silt size, with some clay- and sand-sized particles. The tailings are deposited from spigots located around the crest of the embankment. Cyanide decay and transformation processes are very effective in reducing cyanide concentrations both within the decant pond water and within the tailings itself. In the long term, generation of acid leachate is prevented by isolating potentially acid-forming rock from atmospheric oxygen by the construction of a special layer on the outside of the embankment which acts as an oxygen diffusion barrier and controls infiltration of water into the embankments. Diversion drains above both tailings ponds intercept clean surface runoff from the adjacent hill and direct it to nearby streams to reduce the amount of wa
Waste rock at the Martha open-cast Au-Ag mine in New Zealand is excavated from the mine, transported by conveyor to the waste disposal area, and used to form engineered earth/rockfill embankments which abut rising ground to form large impoundments containing the tailings ponds. Construction of the first tailings storage facility, Storage 2, commenced in 1987, and a database covering almost fifteen years shows that it is performing very well. Storage 2 has now reached its final crest height. Construction for the second tailings storage facility, Storage 1A, began in 1998. The predominant rock type at the pit is andesite, with volcanic breccia, clays, tuffs and ignimbrite also present. All oxidised rock, ignimbrite, clays and tuffs are non-acid forming, while the mixed and unoxidised andesite and volcanic breccia contain variable amounts of sulphide sulphur, mainly pyrite, much of which is potentially acid forming. The embankments are designed as earth/rockfill water-retaining structures. Following the cessation of tailings deposition and completion of tailings consolidation the risk of the release of tailings is almost impossible due to its inherent strength. The tailings slurry contains around 38% solids which are predominantly silt size, with some clay- and sand-sized particles. The tailings are deposited from spigots located around the crest of the embankment. Cyanide decay and transformation processes are very effective in reducing cyanide concentrations both within the decant pond water and within the tailings itself. In the long term, generation of acid leachate is prevented by isolating potentially acid-forming rock from atmospheric oxygen by the construction of a special layer on the outside of the embankment which acts as an oxygen diffusion barrier and controls infiltration of water into the embankments. Diversion drains above both tailings ponds intercept clean surface runoff from the adjacent hill and direct it to nearby streams to reduce the amount of wa