A critical assessment for reclamation of the waste dumps at Águas Claras mine under Brazilian regulatory standards

Authors: Freu, P; Costa, T; Silva, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2515_04

Cite As:
Freu, P, Costa, T & Silva, A 2025, 'A critical assessment for reclamation of the waste dumps at Águas Claras mine under Brazilian regulatory standards', 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. 1-15, https://doi.org/10.36487/ACG_repo/2515_04



Abstract:
Águas Claras mine in southeastern Brazil had its activities ceased in late 2002 after 29 years of high-grade iron ore exploitation. Since then, actions have been carried out to close the mine and reduce the risks related to more than 60 Mm³ of mine waste stored in dumps surrounding the mine. Although already revegetated and integrated into the environment, the waste dumps present in some cases Factors of Safety (FoS) lower than the values established by the new standards of the Brazilian regulatory agencies (FoS ≥ 1.5), which would require geometry adjustments (reshaping or buttressing), in addition to surface drainage improvements, to meet the criteria for reclamation and post-mining land use. To support decision-making and define actions for physical stabilisation and closure, a risk-based method was chosen over the conventional ‘minimum FoS’ approach. The ‘residual risk rating’ index (R³) proposed by Hawley et al. (2024) and updated by de Graaf et al. (2025) was applied to define a target stability reliability (TSR), assessing design confidence levels, the ‘waste dump hazard class’ (WHC), and the consequences of a potential failure. According to Hawley et al. (2024), three of the five dumps evaluated obtained a moderate level of R³, demanding a FoS close to the range required by current Brazilian standards (1.3 < FoS ≤ 1.5), while two of them obtained a high and a very high level, which means rigorous analyses and higher FoS are recommended for closure (1.5 < FoS ≤ 1.8 and 1.8 < FoS ≤ 2.0, respectively). However, when following the model updated by de Graaf et al. (2025), four dumps fell into the high-risk category, requiring a FoS ≥ 1.5, and one of the dumps obtained a very high R³ level (FoS ≥ 1.7 suggested). The 2025 framework proved to be more conservative than the 2024 version, grouping dumps of varying WHCs and failure consequences into the same high-risk category. The adoption of an FoS higher than those defined by the Brazilian standard (NBR) 13029/2024, resulting in greater interventions for closure, should be evaluated considering technical, economic and environmental feasibility, also accounting for the advanced state of recovery and integration of the dumps into the environment. Ideally, minimum adjustments should be made to meet the criteria established by current Brazilian standards and actions taken to increase confidence level and ensure the maintenance of these values in a long-term scenario. The results demonstrate the importance of defining a TSR for closure while still in the operational phase, enabling the use of available resources, reducing costs and avoiding issues related to environmental and third part organisations after deactivation of the waste dumps. The approach discussed in this paper offers a practical benchmark for future reclamation efforts and contributes to the development of more adaptive, risk-based closure policies.

Keywords: mine closure, reclamation, waste dumps, Factor of Safety, performance assessment

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