Background on Tailings Storage Facilities
Tailings are residues created as part of mining processes and Tailings Storage Facilities (TSFs) are structures built for the purposes of storing uneconomical ore from the mining process. The design of a TSF is one of the biggest decisions in the development of a mine. Site conditions such as topography, rainfall, seismic activity, mineral characteristics, and proximity to people are key factors in determining appropriate tailings strategies. The aim is to safely contain the tailings under all circumstances.
Kenmare’s Tailings Storage Facilities
Kenmare’s TSFs are regulated, permitted and have been managed for many years to comply with local laws, licences, and other requirements. Kenmare identifies geotechnical risk as a principal company/corporate risk, and therefore actively manages it through our site and corporate risk registers. Our Tailings Management Standard and Procedure sets out the rules by which we hold ourselves accountable to manage this risk. Visit our Annual Report for more detail on our site and corporate risk management.
Kenmare uses a variety of mining techniques (dredge, dry and hydro mining) across the three mining areas that we operate, with the majority of the mining performed by dredges which float in the mining pond. The dredges mine paths which are 250-350m wide in a continuous process, mining the front of the pond and depositing tailings at the back. There are no upstream raised methods of construction of containment embankments. The TSFs consist of the processed sands being redeposited at the back of the pond, behind berms in a series of smaller tailings paddocks. Because Kenmare does not use any chemicals in our mining or processing, the returned water does not require treatment.
Slimes are finer materials which are separated during the mining process. The slimes are initially suspended in the return water, but then naturally settle within these smaller tailings paddocks, where they gradually consolidate against the sidewalls and upstream cross-berm slopes. This process significantly reduces surface permeabilities, enabling greater water recirculation and increasing the stability of the berms. Once the surface elevation of the tailings within the far rear trailing paddock is judged sufficient, the paddock is progressively covered by sand tailings. This methodology is repeated in each of the far rear paddocks as the pond advances, returning the land topography to that similar to pre-mining.
Our risk management approach
We take a risk-based approach to the management of our TSFs. Our Tailings Management Standard and Procedure currently adheres to the Mozambican National Regulation for Tailings Dams and we are upgrading our standard to align with International Commission of Large Dams (ICOLD) Tailings Dam Safety Standards. In 2022, Kenmare is also reviewing alignment of its current operations with the Global Industry Standard on Tailings Management (GISTM) and will report on the findings of this review and steps to work towards alignment. Any future TSFs associated with new ore bodies will be designed in alignment with the global standards from the outset.
Internal risk management protocols include risk focused surveillance systems and processes, internal geotechnical risk reporting, and tailings and water management meetings. In addition to our internal geotechnical controls, Kenmare implements an annual external audit with NOSA CMB 253 EHS integrated management system which is in line with best practice guidelines ISO 45001:2018 (Occupational Health and Safety Management System) and ISO 14001:2015 (Environmental Management System). Geotechnical auditing of TSFs is undertaken by internationally reputable geotechnical specialists.
Further detail on our geotechnical risk management is as follows:
- We employ permanent staff with geotechnical engineering skills
- We undertake prudent geotechnical design and controls
- We conduct daily inspections and circulate daily reports
- We commission interlocking external audits from two separate and independent geotechnical consultants
- We design and construct safety/diversion berms between the mining path and nearby community structures/properties/mining infrastructure
- We install and monitor decanting pipelines between trailing paddocks and ponds
- We use electronic piezocone penetration tests (CPTu) equipment for geotechnical investigations of subsurface conditions and input parameters for geotechnical design.
The use of TSFs at the Moma Titanium Minerals Mine differs significantly from the conventional permanent construction of tailings dams, such as those that failed in the tragic tailings dam disasters in Brazil. However, these incidents have highlighted the need to ensure that slope stability analyses are carried out on the appropriate shear strength parameters and mode of failure, with reference to undrained shearing and liquefaction. Kenmare conducts regular reviews to ensure these mitigation measures are undertaken at Moma, to protect communities and infrastructure and maintain safe operations.
Global database of Tailings Storage Facilities
The Church of England Pensions Board investments group has called on publicly listed extractives companies to provide information for a tailings database, to increase transparency on TSFs following the tailings dam disasters in Brazil. Please view Kenmare’s Sustainability Fact Book and click on the tab called 'Tailings' to view our disclosure in line with the database’s requirements.