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Cuiabá TSF, Brazil
At 10 April 2024
Coordinates: Lat -19.866392°, Long -43.727225°
Guidance Note
Refer to our guidance note.
Description and Lifecycle Design
The Cuiabá TSF is a cross-valley earth fill impoundment that was designed and constructed as a water-retaining structure in 2005. The structure is a homogeneous compacted fill, with a vertical filter for each raising, connected by horizontal drains between them, making a stepwise pattern, and a blanket drain on top of the foundation. The TSF is currently at an elevation of 904mamsl and has a maximum height of 97m. A spillway is positioned in the right-hand shoulder of the TSF. The spillway is at an elevation of 902 mamsl and has been constructed as a rectangular concrete channel.
The Cuiabá TSF is currently undergoing decharacterisation works, which include two construction phases. Phase I encompasses the disposal of compacted filtered tailings downstream of the dam, which are protected by waste-rock, forming a buttress for the dam. Phase II includes the disposal of filtered tailings inside the dam reservoir.
AngloGold Ashanti has an internal corporate tailings management team and is in the process of appointing a Responsible Tailings Facility Engineer (RTFE) for the Cuiabá TSF. An external Engineer of Record (EoR) and an Independent Tailings Review Board (ITRB) has been appointed for this facility to oversee and govern the operations, maintenance, and surveillance (OMS) of the facility.
Cuiabá TSF General Information
| Start of Operation | 2006 |
| Construction Method | Downstream Earth Wall |
| Current Deposition Method | Deposition of Filtered Tailings to meet the closure design. |
| Target Annual Deposition Rate | 1,44Mtpa (Cuiabá Mine Production) |
| Current Tailings Volume | 10.9Mm3 |
| Design/License Capacity – Volume/Tonnage | 10.9Mm3 |
| Filtered Tailings deposited as part of Decharacterisation | 3.9Mm3 |
| Crest Elevation | 904 mamsl |
| Spillway Elevation | 902 mamsl |
| Maximum Height | 97m |
| Outer Wall Profile | 1V:2H (Downstream) |
Consequence Classification
| GISTM Classification | Extreme |
Risk Assessment
AngloGold Ashanti’s comprehensive risk management system uses designs and controls to eliminate risks and where there are remaining risks, these are mitigated such that the residual risk is a As Low As Reasonably Practicable (ALARP).
Risk assessments are conducted by a multi-disciplinary team and in collaboration with the EoR for each facility in line with nationally or internationally accepted best practices. This report provides a summary of the key details of the structure, including site investigation, geotechnical parameters, foundation, embankment, drainage system, spillway, monitoring, and tailings disposal plan. It also details the risk-analyses methodology (using the qualitative bowtie method), potential failure modes along with their susceptibility and consequences, and control and mitigation measures.
From this process, 10 risks were mapped that could, in theory, lead to a reduction in the dam’s structural performance, and all risks were classified as acceptable. Actions were recommended for these risks and general recommendations to be applied in the operation and maintenance of the TSF. All these action plans aim to reduce the probability of possible risks, as well as minimise possible impacts resulting from occurrences in the structure.
Impact Assessment
The impact of a potential flow failure has been assessed considering the impact to human health and life, the environment, social and cultural impacts, as well as the infrastructure and economic impacts. These potential impacts have been used to inform the TSF Classification, the risk assessment consequence definition and the mitigation measures to be implemented.
The impact zone covers a distance of 77.4km downstream of the Cuiabá TSF, the Self-Rescue zone (ZAS) extends to 10,6km and the Secondary-Rescue Zone (ZSS) 66.8km.
The municipalities and areas affected by the impact zone and the main social information of the potential floodplain in the event of the rupture of the Cuiabá TSF is shown in the tables below.
Areas affected by Impact Zone
Cuiaba TSF
| Municipalities in ZAS | Sabará (MG) & Caeté (MG) |
| Municipalities in ZSS | Sabará (MG), Belo Horizonte (MG), Santa Luzia (MG), Lagoa Santa (MG) & Raposos (MG). |
| Main Watercourses Impacted | Córrego Padrão, Córrego Padrão, Córrego Padrão, Ribeirão Sabará, Córrego do Gainha, Córrego da Rocinha, Ribeirão Sabará, Córrego Caeté, Ribeirão do Gaia, Córrego Padrão, Rio das Velhas, also covering Ribeirão Arrudas, Ribeirão da Laje or Bom Destino, Ribeirão Vermelho, Ribeirão das Bicas, Ribeirão Baronesa, Ribeirão do Gaia, Ribeirão da Mata, Córrego Malheiros, Córrego Campo Santo Antônio, Córrego das Lajes, Córrego Quarta-Feira ou Cachoeira, Córrego Frio, Córrego Capitão, Córrego do Inferno & Córrego Bombinha ou Grajaú. |
| Watersheds | Rio das Velhas |
| Areas with Potential for Interference | Private properties – permanent presence of people; Road infrastructure (MG-030, AMG-150, MG-437, MG-262, BR-381, AMG-145 and MG 020), Streets and bridges; Commercial, industrial establishments, religious buildings, as well as inns and historical and heritage sites. |
Summary of the socio-territorial characterization of the impact zone
| Type of Property | Quantity |
|---|---|
| Occupied Houses | 283 |
| Summer Houses | 15 |
| Houses without a resident | 36 |
| Houses under Construction | 19 |
| Demolished Houses | 6 |
| Establishment | 28 |
| Establishment under Construction | 2 |
| Closed Establishment | 7 |
| Public Equipment | 4 |
| Institution | 1 |
| Plot with Improvement | 5 |
| Plot without House | 11 |
| Total Population in ZAS | 762 |
| Population with mobility difficulties | 51 |
| Population with Special Needs | 31 |
| Number of Sensitive buildings in ZAS | 6 |
Performance Reviews
AngloGold Ashanti has a comprehensive Tailings Review System which incorporates reviews from multiple levels and internal and external parties. All AngloGold Ashanti TSFs are subject to the following reviews:
- EoR Inspections – Monthly, with two safety declarations submitted to the Brazilian National Mining Agency (ANM) in March and September of each year.
- ITRB Review – Annually
- AngloGold Ashanti Corporate Review – Annually
- Independent 3rd Third Party Regulatory Review – Annually
- Dam Safety Review – Typically every five years
| Reviews | Most Recent Review | Next Planned Review |
|---|---|---|
| EoR | March 2024 | Monthly – 2024 |
| ITRB | July 2023 | October 2024 |
| DSR | N/A | Dec 2024 |
AngloGold Ashanti has adopted the following ranking system for independent reviews: Priority 1 actions are classified as a material finding.
Priority 1 – A dam safety issue considered immediately dangerous to life, health, or the environment, or presents a significant risk of regulatory enforcement.
Priority 2 – If not corrected, a concern that could result in a dam safety issue leading to injury, health impact or discontinuity of operations.
Priority 3 – Single occurrence of deficiency or non-conformance that alone would not be expected to result in dam safety issues, discontinuity of operations or regulatory intervention.
Priority 4 – A recommendation based on good practice, improvement, or risk reduction.
No material findings (Priority 1) have been identified for the Cuiaba TSF.
Environmental and Social
Environment and Social monitoring programmes form part of AngloGold Ashanti’s Health, Safety, Environment (ISO14001) and Social Communities (HSEC) management systems, which act to fulfill the environmental social management system requirements under the GISTM. These environment and social monitoring programmes are comprehensively reviewed, and mitigation measures implemented as and where required. Further information on of our environment and social monitoring programmes, and performance results can be found in AngloGold Ashanti’s Sustainability Reports.
There is potential for ground water seepage from TSFs and ground water conditions around all our TSFs are regularly monitored. Where groundwater impact plumes exist, their migration is modelled and managed, as necessary to avoid interactions with potential receptors.
No material findings have been made in relation to the environmental and social monitoring programme, in relation to the TSF in 2023.
An easily accessible and effective grievance mechanism has been implemented so that any formal complaints can be submitted by stakeholders and resolved.
Emergency Response and Preparedness
Emergency preparedness and response planning (EPRP) relies on an emergency notification system that consists of remote stations equipped with sirens that are linked to the control room at the Queiroz plant, and to the RTSs, which scans prisms located on the dam face. Manual activation of the sirens is available locally as redundancy. Mobile sirens are also installed on emergency vehicles that are assigned to predefined emergency routes as an additional notification measure.
The latest dam breach study was conducted in May 2022, and an EPRP training exercise, involving community members, was documented as having been undertaken in June 2023. Training exercises have included military civil organisations (police and fire) for various communities.
The escape routes and meeting points are sign posted. These were developed based on the zone of influence, in which a maximum walking distance of 1,000m was considered to allow a quick and safe route to meeting points. The meeting point signage has information such as telephone numbers of emergency agencies and safety recommendations for the population, among other self-preservation information.
A copy of the Cuiabá EPRP and be downloaded on the following link: https://www.anglogoldashanti.com.br/barragens/nossas-barragens/barragem-cuiaba/
Financial Capacity
AngloGold Ashanti confirms it has adequate financial capacity to cover the agreed share of estimated costs of planned closure, early closure, reclamation, and post-closure monitoring and maintenance of the Cuiabá TSF and its appurtenant structures.
Guidance Note
This document provides the information required under Requirement 15.1.B of the GISTM.
This document should be read in conjunction with the information relating to AngloGold Ashanti’s tailings management practices that is available on the AngloGold Ashanti website, as well as the risk factors and other disclosures in AngloGold Ashanti’s annual report on Form 20-F for the year ended 31 December 2023 to be filed with the United States Securities and Exchange Commission (SEC) (the “Form 20-F”).
Certain statements contained in this document, other than statements of historical fact, including, without limitation, those concerning the economic outlook for the gold mining industry, expectations regarding gold prices, production, total cash costs, all-in sustaining costs, all-in costs, cost savings and other operating results, return on equity, productivity improvements, growth prospects and outlook of AngloGold Ashanti’s operations, individually or in the aggregate, including the achievement of project milestones, commencement and completion of commercial operations of certain of AngloGold Ashanti’s exploration and production projects and the completion of acquisitions, dispositions or joint venture transactions, AngloGold Ashanti’s liquidity and capital resources and capital expenditures, the consequences of the COVID-19 pandemic and the outcome and consequences of any potential or pending litigation or regulatory proceedings or environmental, health and safety issues, are forward-looking statements regarding AngloGold Ashanti’s financial reports, operations, economic performance and financial condition.
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