Co-disposal of tailings and mine waste: integrated geochemical and geotechnical risk assessment

Authors: Pearce, S; Brookshaw, D; Grohs, K; Elmer, R Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2515_49

Cite As:
Pearce, S, Brookshaw, D, Grohs, K & Elmer, R 2025, 'Co-disposal of tailings and mine waste: integrated geochemical and geotechnical risk assessment', in S Knutsson, AB Fourie & M Tibbett (eds), Mine Closure 2025: Proceedings of the 18th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-10, https://doi.org/10.36487/ACG_repo/2515_49



Abstract:
The co-disposal of waste rock and filtered ‘dry stack’ tailings is increasingly being considered by industry as a potential alternative to traditional tailings facilities. As part of technical review of this method, geotechnical risk is often cited as the primary risk factor related to implementation, however, geochemical risk implications and development of holistic approaches to assess the relative benefits of this method are currently not well understood or documented. This paper provides an integrated overview of both key geochemical and geotechnical risks related to codisposal, and outline how these interact with unsaturated hydrogeological characteristics. In addition, this paper indicates how risks can be assessed to inform the engineering design concept, and how relative benefits can be assessed when comparing the method to traditional methods of tailings and waste rock disposal. We also present results from an instrumented field trial carried out at a site undertaking detailed design studies of a large co-disposal facility. The field trial carried out was fully instrumented with oxygen, volumetric water content, matric potential and temperature sensors. Results indicate that co-disposal results in the creation of an effective barrier to oxygen ingress which is positive for geochemical risk management. Unsaturated zone hydrology characteristics determined from instrumentation data indicates that the permeability of the material is lowest at surface (due to surface compaction) meaning that as well as reducing oxygen ingress, draindown of the material at sub-surface depth can occur at a faster rate than the additional flux of infiltration from surface, which is advantageous from a geotechnical perspective. The results from the field trial, along with findings from theoretical risk assessment, suggests that based on assessment of integrated geochemical and geotechnical risk, co-disposal has the potential to be favourable when compared to mine waste storage in traditional separate waste rock and slurry tailings storage facilities.

Keywords: geochemical risk, geotechnical risk, filtered tailings, co-disposal

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