Case History: Large Tailings Containing Precious Metal Resources, Australia
Tasmania, Australia, Large Tailings Lake Remediation with Significant Gold and Silver: Provided independent assessment of mine tailing from a large base- and precious metal mine to remediate some 11 million tonnes of waste after zinc and lead to be removed by multi-stage processing. The tailings consist of 70% sulfide minerals of pyrite, arsenopyrite, sphalerite galena, chalcopyrite, and tetrahedrite, all of which would oxidize to form acidic mine drainage if allowed to sit in piles open to the atmosphere and oxidizing rainfall.
To minimize oxidation, the tailings are currently being stored below a large engineered lake. Subsequent analysis by I2M personnel of sampling laboratory results showed that significant concentrations of gold and silver are available within the sulfide minerals’ crystalline structures (of arsenopyrite and pyrite) and free gold contained in the submerged tailings. I2M made recommendations based economic modeling for removal and transportation with offsite recovery of the precious metal. After the tailings have been removed , remediation would likely consist of constructing multiple down-gradient dams to contain the original tailings dam materials. The new lake-water chemistry would need to be adjusted as before. By physically removing the tailings by dredging while covered by the lake water, this eliminates oxidation of the sulfide minerals.
Dredging and treatment of the tailings to create metal concentrates are likely to begin in 2017 or early 2018.