Tailings Management Facilities may pose a significant risk to downgradient surface water and groundwater environments. Evaluating the risks these facilities present to water resources is pivotal during mine closure. This paper discusses the use of probabilistic simulation within quantitative analytical models to evaluate these risks, especially in scenarios where limited environmental data may undermine confidence in the predictive outcomes.

The application of probabilistic modelling will be demonstrated through case studies that utilise probabilistic risk assessment to evaluate various closure and remediation strategies for a tailings management facility, as well as to quantify uncertainty levels in risk assessments. The paper will consider the impact of different liner and cover systems and the importance of considering tailings management facility holistically recognising that factors such as closure landform and cover design are as integral to mitigating risk as basal liner design.

Brumadinho and Samarco Mariana tailings storage facilities (TSF) failures in Brazil caused deaths and environmental damage, prompting the Global Industry Standard on Tailings Management (GISTM) in 2020. The International Council on Mining and Metal (ICMM) required members to disclose information on extreme and very high consequence TSFs by 2023 and all TSFs by 2025. This study analyses the integrated knowledge base developed for 56 TSFs across various geographies and commodities, assessing data sufficiency across 25 water topics. Despite generally high compliance, systematic gaps exist globally. The findings are relevant to mining companies, environmental professionals and the ICMM for GISTM compliance.

The Salave Gold Prospect is the largest unexploited and well-known gold deposit on the Iberian Peninsula (measured resources are more than 1 Moz Au at 4.6 g Au/t). It is located in NW Spain, 2 km E of the village of Tapia de Casariego, about 500 m far from the coastline, in the Bay of Biscay. It is an intrusion-related gold deposit, hosted by a Hercynian-age granodiorite (330-287 My), in which gold occurs almost exclusively as refractory and invisible, mainly within the arsenopyrite crystal structure. Although there are appreciable quantities of other metallic sulfides, the main species are pyrite, arsenopyrite, stibnite and molybdenite. This project -currently immerse in the administrative processing phase- is envisioned to be exclusively developed by underground mining. The final product, in order to avoid in situ cyanide employment, is a sulfide concentrate obtained by gravity and flotation.
The flotation tailings obtained in the bench scale and pilot testing (carried out on well mineralized core intervals), are mainly composed by plagioclase, mica, K-feldspar group species and some quartz. They also contain 0.1% of sulfides, mostly arsenopyrite, pyrite and stibnite. Although they will be used in the backfill of the underground workings, it is expected that approximately 2 Mt of these tailings will have to be allocated in an excavated and isolated dam. In order to optimize the long-term behaviour of the tailings deposit, some laboratory studies have been carried out: different mixtures of lime, blast furnace slag, Portland cement and limestone filler were tested to immobilize, from a geochemical point of view, some metal(loid)s and sulfates. The leachability tests were carried out in accordance with European Standards EN-12457:4 (dynamic leaching) and EN-15863 (static leaching).
The mixture formed by 5% of Portland cement, 5% of lime and 1% of limestone filler achieved a reduction in permeability (when compared to the untreated tailings) of more than 90%. The reductions accomplished (after 28 days of setting) in the leachability of As and Sb are 98.37% and 87.23% respectively. For sulfate leachability, the reduction is complete. Although the present work is focused on the behaviour of As, Sb and sulfate, satisfactory results have also been achieved for some of the other metals analysed; Pb is the only one that has shown an erratic behaviour.
Flotation tailings derived from mineral deposits that fit into the intrusion-related gold systems can be expected to behave in a similar way.