Tailings Hazard

Overview

Tailings storage facilities are a common and widely used method to store the waste material generated from many forms of mining activity. Often such facilities include dams and other structures that could remain in place well after active mining operations have ceased. These legacy sites may still require maintenance and monitoring to ensure the safety of the structure. 

In August of 2020, the mining industry released the Global Industry Standard on Tailings Management (GISTM) as a response to the catastrophic failure of a tailings storage facility (TSF) in Brazil that occurred in 2019. Included in this document is a provision that facilities considered closed safely have met the standards because they would be considered similar to landforms that are largely inert and pose little risk to humans and the environment [1]. 

The purpose of this project was to develop a method to identify legacy facilities that are eligible for safe closure status. The method proposed was a decision matrix based on facility type and location, structural stability indicators, hazard indicators, water management, and consequence of failure. Newmont Corporation has committed to incorporating the GISTM for its facilities. With numerous legacy facilities to manage in addition to active mines around the world, determining closed safe status for legacy facilities would help Newmont achieve their goal of implementing the GISTM. Furthermore, identifying facilities that are closed safely can help Newmont prioritize efforts and  allocate resources among facilities still requiring management. 

A preliminary decision matrix was created and tested against the Equity Silver Mine legacy site which has a TSF with permanent water cover. The initial testing revealed the need for improvements. Such improvements include determining a probability of failure from the structural stability indicators, refining criteria, expanding criteria and useability to other locations and types of TSF, and providing an automated and user-friendly computer-based program to quickly obtain results. However, the decision matrix allows users to obtain a big-picture assessment of the TSF and indicates those areas where structural improvements could be made to reach a safe closure condition. 

References

[1]Global Tailings Review, “Global Tailings Review.org,” August 2020. [Online]. Available:

https://globaltailingsreview.org/. [Accessed 19 September 2020].

To meet these criteria of safe closure, the decision matrix focuses on four general indicators: structural stability, geologic hazards, consequences, and water management. The matrix was developed in several steps as listed below:

1. Identify potential legacy sites for testing and calibration.
2. Determine the relevant indicators and criteria for safe closure based on Newmont’s definition of safe closure
3. Compile criteria from regulations and guidelines from the United States of America and  countries where legacy TSFs proposed for decision matrix development are located
4. Generate a decision matrix that accounts for location, facility type, stability, and consequence of failure
5. Test the matrix using legacy sites
6. Determine issues with matrix and revise

To develop our decision matrix, the team began by narrowing down the key features that may be looked at when deciding if a TSF is closed safely and the Newmont definition of safe closure [1]. The decision matrix also needed to account for geographic and climate variability and relevant regulations. The general process is shown in Figure 1. Together, the probability of failure, consequence of failure, and water management would determine the classification of safe, not safe, active management, or need additional data. 

Figure 1. General overview of decision matrix process.

References 

[1] K. Morrison, Slide describing Newmont definition of safe closure, 2020.