Abstract
Two major challenges facing mining operations are seepage water quality from mine rock stockpiles (MRSs) and liability associated with the geotechnical stability of tailings storage. We highlight methods and critical design considerations for co-disposal, or co-mingling, of tailings and mine rock that achieves long-term geotechnical stability and improved water quality.
Oxygen availability in an MRS is a primary control of sulphide mineral oxidation and resultant metal leaching and acid rock drainage from the MRS. Achieving low oxygen concentrations by limiting re-supply of atmospheric oxygen into the MRS during and immediately following rock placement may limit the generation of oxidation products within an MRS. Additionally, low oxygen concentrations may promote passive water treatment by geochemical reduction of oxidation products to inert or less mobile forms.
A common challenge with limiting oxygen availability in an MRS is the predominance of coarser-textured mine rock through which oxygen flow readily occurs. We demonstrate how layers with finer-textured tailings may be included in an MRS to lower the air permeability and reduce oxygen flux rates. The result is limited re-supply of oxygen from the atmosphere to the MRS and creation of large-scale suboxic zones. Critical to the approach is that the water permeability and geometry of the finer-textured layers allow appropriate (timely) pore-water pressure dissipation in response to changes in seepage rates or loading, and geotechnical stability is not adversely impacted.
Guideline specifications are presented for tailings and mine rock co-disposal that achieve the dual benefit of reducing risk and liability of tailings storage while also improving water quality through source term control and passive water treatment.