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June 2025
Coordinates: Lat –19.8658°, Long -43.7478°
Guidance Note
Refer to our guidance note.
Description and Lifecycle Design
The Filtered Tailings Stack referred to as the Cuiabá Open Pit Stack was developed with the objective of closing the previously depleted open pit. Tailings disposal in the Cuiabá Open Pit began in January 2014 with the deposition of dried out tailings from the drying bays. The filter stack design was developed in 2016 when the filter plant became operational and the stack consisted of downstream walls constructed from waste borrow material, and the placement of filtered tailings on the inside. The initial design geometry included slopes with an inclination of 1.5H:1V, 10.0-meter-high lifts, 8.0-meter-wide berms, and a final design height of 110.0 meters, from ,elevation 990.0 mamsl up to approximately 1,100.0 mamsl. In 2018, a new drainage system was implemented.
Cuiabá Open Pit – General Information
| Facility Name | PDER Open Pit Cuiaba |
| Start of Operation | Co-disposal of filtered tailings and waste rock |
| Current Tailings Volume | 658.637,95 m³ |
| Crest Elevation | 1056 mamsl |
| Maximum Height | ~100m |
| Outer Wall Profile | 1V:2.0H (Outer Slope) |
| Slope Geometry – Temporary Berm between Elevations 1010 m and 1023 m | 1V:1.5H |
Consequence Classification
| GISTM Classification | High |
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.
The risk analysis for the Cuiabá Open Pit Stack is still to be concluded but any potential failure of the structure is expected to be confined to the immediate surrounding area, as indicated by the stack breach analysis.
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 the risk assessment consequence definition and the mitigation measures to be implemented.
Tailings flow if it occurred would be via natural topographic lows downstream of the facility, with limited flow volume being deposited. The tailings are geochemically consistent with the nearby orebodies from which they are derived and are non-acid forming. Environmental remediation would involve recovery of the sandy silt materials using earthmoving equipment.
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 Inspections and Annual Review
- Independent Tailings Review Board (ITRB) Review – Annually
- AngloGold Ashanti Corporate Review – Annually
- RTFE Assessment – Monthly
| Reviews | Most Recent Review | Next Planned Review |
| EoR | June 2025 | Monthly – 2025 |
| ITRB | October 2024 | October 2025 |
AngloGold Ashanti has adopted the following ranking system for independent reviews:
Priority 1 – A stack safety issue considered immediately dangerous to life, health or the environment, or presents a significant risk of regulatory enforcement. Requires immediate action and to be completed as soon as practically possible but certainly within 2 months
Priority 2 – If not corrected, a concern that could result in a stack safety issue leading to injury, health impact or discontinuity of operations. Requires immediate planning and completion by a date and specified by operations but as a minimum within 5-6 months
Priority 3 – Single occurrence of deficiency or non-conformance that alone would not be expected to result in stack safety issues, discontinuity of operations or regulatory intervention. Requires that measures be taken no later than a date that would prevent escalation, but no later than one year
Priority 4 – A recommendation based on good practice, improvement, or risk reduction. Recommendation towards best practices and mitigating risk associated.
No Priority 1 recommendations have been issued by the ITRB for the Cuiabá Open Pit Stack.
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 Filter Stacks and ground water conditions around all our Filter Stacks are regularly monitored. Where groundwater impact plumes exist, their migration is modelled and managed, as necessary to avoid interactions with potential receptors.
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) to address the potential for failure of the Cuiabá Open Pit Stack is not required by Brazilian regulations since the facility is a stack. While an EPRP has not been prepared, AngloGold Ashanti has conducted pre-emptive emergency response activities in response to stability concerns related to the stack.
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 PDR CDS I TSF and its appurtenant structures.
Guidance Note
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, 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 based on 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 Company’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 AngloGold Ashanti’s annual report on Form 20-F for the financial year ended 31 December 2024 filed with the United States Securities and Exchange Commission (SEC). 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 hereof 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.