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Serra Grande TSF, Brazil
At 10 April 2024
Coordinates: Lat -14.561475°, Long -49.960260°
Guidance Note
Refer to our guidance note.
Description and Lifecycle Design
The TSF at MSG comprises of a conventional cross-valley impoundment facility with a starter dam that was commissioned in 1990. The TSF was raised with a sequence of upstream dam rises using mainly cyclone underflow tailings. Rockfill was placed in 2010, following the downstream method, to an elevation of 455m to improve stability of the dam. The crest elevation of the dam is currently at 470m, with a maximum height of about 92 m and an approximate crest length of 1,210m.
In 1994, the MSG Dam had a major failure when the slip did not sever the dam crest so there was no release of tailings. The mining operation was suspended until the safety and integrity of the dam was re-established. The failure was attributed to a rise of the phreatic surface caused by badly constructed and ineffective filter drains under the starter dam, exacerbated by heavy rainfall during late 1993 and early 1994.
The dam section also includes a thin vertical drain combined with thin sloping drains at the base and within of the rockfill.
As required by the Brazilian legislation, deposition of conventional tailings at the MSG TSF stopped on 15th September 2021. Deposition of filtered tailings then commenced on the 19th of September 2021 and was being deposited in the basin of the TSF to meet the decharacterisation design.
MSG TSF General Information
| Facility Name | MSG TSF |
| Period of Operation | 1989 |
| Operational Construction Method | Upstream – Cyclone Deposition |
| Current Deposition Method | Deposition of Filtered Tailings to meet Closure Design by September 2025 (Operation currently suspended) |
| Target Annual Deposition Rate | No deposition to MSG TSF: De-characterization to commence in 2024. |
| Current Tailings Volume | 17.1Mm3 |
| Designed / Licensed Volume / Tonnage | 17.1Mm3 |
| Crest Elevation | 470 mamsl |
| Spillway Elevation | 464 mamsl |
| Maximum Height | 92m |
| Outer Wall Profile | 1V:3H (Cyclone Deposition) 1V:2H (Rock Cladding) |
Consequence Classification
| GISTM Classification | Extreme |
Risk Assessment
AngloGold Ashanti has a comprehensive risk management system with the aim to implement designs and controls such that risks are eliminated and any remaining risks are mitigated such that the residual risk is a As Low As Reasonably Practicable (ALARP).
Risk assessments are conducted with a multi-disciplinary team and in collaboration with the Engineer of Record (EoR) for each facility in line with accepted best practices. The assessment aims to provide 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, potential failure modes along with their susceptibility and consequences, and the control and mitigation measures.
From this process, 13 risks were mapped that could in theory lead to a reduction in the dam’s structural performance, with two of these risks being classified as intolerable and the remaining 11 in the ALARP (manageable) tolerability range.
The liquefaction failure mode was classified as unacceptable under the Brazilian Legislation, Art 52 of ANM Resolution No. 95/2022. This requires that the operator (AGA), must immediately stop releasing tailings onto the TSF and maintain monitoring, maintenance and conservation of the TSF until it is reclassified to the ALARP (manageable) or acceptable level. In this case, AngloGold Ashanti had already stopped the release of pulp and filtered waste and will propose actions to increase the level of confidence in the structure so that the decharacterisation works can continue with reasonable risk. Due to weak foundation materials at the toe of the TSF, updated design aims to remove tailings material from the crest of the TSF and place this at the back end of the TSF, thereby reducing the load on the TSF wall to improve the safety factor. Additional monitoring equipment will be installed on the TSF to guide the construction process.
For the 11 risks in the ALARP (manageable) range, action plans have been developed to, where possible, further reduce these risks to the acceptable range.
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 and also the risk assessment consequence definition and the mitigation measures to be implemented.
The impact zone covers a distance of 72.8km downstream of the MSG TSF. The first population affected are those living in the southern portion of the urban area of Crixás Town and the operational area of the MSG Mine, where the inundation wave arrives in the first minute after the TSF failure.
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 MSG TSF is shown in the tables below.
Areas affected by Impact Zone
MSG TSF
| Municipalities in ZAS | Municipal Council of Crixás (Goias) |
| Municipalities in ZSS | Municipal Council of Crixás (Goiás ), Uirapuru (Goiás ), Santa Terezinha de Goiás (Goiás) |
| Main Watercourses Impacted | Rio Vermelho, Rio Crixás Açu, Gabiroba Stream |
| Watersheds | Rio Vermelho |
| Areas with Potential for Interference | Private properties, local roads, highways and bridges; Urban facilities, such as City Hall Municipal Council of Crixás, Public Prosecutor’s Office of the State of Goiás, Municipal Chamber of Crixás, hospitals and basic health units, water treatment plant, prison, religious temples, school, commercial establishments; and equipment with potential for contamination such as gas stations; archaeological and speleological sites. |
Summary of the socio-territorial characterization of the impact zone
| Type of Property | Quantity |
|---|---|
| Occupied Houses | 1,106 |
| Establishment | 353 |
| Public Equipment | 16 |
| Closed Establishment | 2 |
| Total Population in ZAS | 3,533 |
| Population with mobility difficulties | 740 |
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 – typically quarterly and Annual Performance Reviews
- Independent Tailings Review Board (ITRB) Review – Annually
- AngloGold Ashanti Corporate Review – Annually
- Independent 3rd Party Regulatory Review – Annually
- Dam Safety Review (DSR) – Typically every five years
| Reviews | Most Recent Review | Next Planned Review |
|---|---|---|
| EoR | March 2024 | Monthly – 2024 |
| ITRB | April 2023 | May 2024 |
| DSR | November 2023 | 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.
Summary of Material Findings and Mitigation Measures:
| Reference | Material Finding | Mitigation Measures to Meet ALARP |
|---|---|---|
| 2023 DSR | Low safety factors at the Main Wall | No deposition of tailings on the TSF. Extensive geotechnical investigation campaign. |
| 2022 & 2023 Risk Assessments | Design of TSF decharacterisation to meet stability requirements. |
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 that acts to fulfill as 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 interaction(s) with potential receptors.
No material findings were made 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 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 fitted on emergency vehicles 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 members of the community, was undertaken in June 2023. Training exercises have included military civil organizations (police, 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, recommendations for the population, among other self-preservation information.
A copy of the MSG EPRP can be downloaded on the following link: BARRAGEM SERRA GRANDE – AngloGold Ashanti Brasil
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 MSG 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.
These forward-looking statements or forecasts are not limited to historical facts, but rather reflect our current beliefs and expectations concerning future events and generally may be identified by the use of forward-looking words, phrases and expressions such as “believe”, “expect”, “aim”, “anticipate”, “intend”, “foresee”, “forecast”, “predict”, “project”, “estimate”, “likely”, “may”, “might”, “could”, “should”, “would”, “seek”, “plan”, “scheduled”, “possible”, “continue”, “potential”, “outlook”, “target” or other similar words, phrases, and expressions; provided that the absence thereof does not mean that a statement is not forward-looking. Similarly, statements that describe our objectives, plans or goals are or may be forward-looking statements.
These forward-looking statements or forecasts involve known and unknown risks, uncertainties and other factors that may cause AngloGold Ashanti’s actual results, performance, actions or achievements to differ materially from the anticipated results, performance, actions or achievements expressed or implied in these forward-looking statements. Although AngloGold Ashanti believes that the expectations reflected in such forward-looking statements and forecasts are reasonable, no assurance can be given that such expectations will prove to have been correct. Accordingly, results, performance, actions or achievements could differ materially from those set out in the forward-looking statements as a result of, among other factors, changes in economic, social, political and market conditions, including related to inflation or international conflicts, the success of business and operating initiatives, changes in the regulatory environment and other government actions, including environmental approvals, fluctuations in gold prices and exchange rates, the outcome of pending or future litigation proceedings, any supply chain disruptions, any public health crises, pandemics or epidemics (including the COVID-19 pandemic), the failure to maintain effective internal control over financial reporting or effective disclosure controls and procedures, the inability to remediate one or more material weaknesses, or the discovery of additional material weaknesses, in the AngloGold Ashanti’s internal control over financial reporting, and other business and operational risks and challenges and other factors, including mining accidents. For a discussion of such risk factors, refer to “Item 3D: Risk Factors” and elsewhere in the Form 20-F. These factors are not necessarily all of the important factors that could cause AngloGold Ashanti’s actual results, performance, actions or achievements to differ materially from those expressed in any forward-looking statements. Other unknown or unpredictable factors could also have material adverse effects on AngloGold Ashanti’s future results, performance, actions or achievements. Consequently, readers are cautioned not to place undue reliance on forward-looking statements.
AngloGold Ashanti undertakes no obligation to update publicly or release any revisions to these forward-looking statements to reflect events or circumstances after the date of this document or to reflect the occurrence of unanticipated events, except to the extent required by applicable law. All subsequent written or oral forward-looking statements attributable to AngloGold Ashanti or any person acting on its behalf are qualified by the cautionary statements herein.