Tailings storage facilities (TSF) employ several common measurements to assess risk and relevant considerations. Cerro Vanguardia S.A. (CVSA), an AngloGold Ashanti-owned gold-silver mine in Santa Cruz, Argentina is no stranger to this reality. In fact, over its ~20-year trajectory, CVSA TSF has been lauded for its tight controls. Yet, during the development and design of a seventh wall raise, the possibility to increase the potentially usable storage capacity within the basing was identified. This discovery raised some timely questions, many of which went beyond what the common measurements could answer.

Upon further investigation, I Ezama and S Pastine from SRK Argentina along with J Pinheiro from SRK South Africa concluded that a probabilistic assessment of the potential efficiency in the use of available capacity to facilitate a risk-based decision matrix (and the subsequent performance monitoring) was the route to take with CVSA TSF. The team commenced with a statistical analysis of the beach angle, tailings density, and water storage.

To develop more efficient use of the available space, better assessments of uncertainties in water storage requirements were needed. The team performed a probabilistic reassessment of the depth of rainfall events and obtained an intensity-frequency curve. The incorporation of a probabilistic approach based on the expansion of the rainfall dataset over the operating period improved the understanding of uncertainties in water storage capacity needs as well as the associated risks.

Regarding the beach angle, in previous designs constant beach slopes between 0.5 and 1.0% were considered to estimate storage capacity. A statistical analysis of the beach slope angle along the tailings deposit provided a better characterization and its potential variance. The team estimated a trendline and developed theoretical beach profiles for use in the storage capacity assessment. Once in place, a statistical analysis of the available geotechnical investigation data was undertaken. Tailings density ranges were characterized based on the available geotechnical samples and a short-term density range was considered the most realistic for the analysis.

Lastly, the team considered four beach development profiles for the study - a base case, a favorable case, a worst case, and the original design approach case. Periodic monitoring of the operation was implemented to assess the behavior of the ongoing operating results. With the exception of the October 2020 survey, all beach profiles resided between the average and best cases in line with the adopted case for the operational design.

Good quality data, periodical statistical analysis of incoming data, and methodologies like bootstrapping to test and understand uncertainties all enhance operations with the potential for considerable reductions in costs and risks. The SRK team expanded CVSA TSF’s life-of-mine (LOM), allowing for tighter construction planning and deferral of construction by several years.