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June 2025
Coordinates: 1.7140484°W 6.2066884°N
Guidance Note
Refer to our guidance note.
Description and Lifecycle Design
The Biox Tailings Storage Facility (TSF) is located at the AngloGold Ashanti Obuasi Mine in Ghana, situated 600m northeast of the existing South TSF. It is an engineered, downstream-raised tailings facility designed to safely store tailings generated from the mine’s BIOX processing circuit and designed to be constructed in phases.
The footprint area of BIOX TSF is approximately 28.6 ha and is formed by four embankments (designated North, South, East and West embankments). The BIOX TSF is fully lined with a composite liner system comprising of a 1.5mm HDPE liner overlying 300 mm of compacted soil to contain the cyanide-bearing BIOX tailings. Phase 1 of the BIOX TSF was designed to contain approximately 0.78 Mm3 of tailings. The Biox TSF Phase 2 comprises a raise over the existing Phase 1 compartment, as well as an extension to the east of the Phase 1 footprint, all to an embankment crest elevation of 190.5m RL. Phase 2 of the BIOX TSF is designed to contain approximately 0.97Mm3 of tailings. BIOX tailings slurry is deposited sub-aqueously into the BIOX TSF through multiple spigots whilst supernatant water is returned to the plant through a decant system comprising of a submersible pump and a standby skid-mounted pump with turret type inlets to Holding Pond 2 via a pipeline corridor.
TSF General Information
| Period of Operation | May 2021 – present |
| Construction Method | Downstream raised |
| Deposition Method | Sub-aqueous spigot deposition |
| Target Annual Production Rate | 0.27 Mtpa |
| Current Tailings Volume / Tonnage | 0.62 Mt |
| Crest elevation of Phase 2 (mamsl) | 190.5 |
| Spillway Elevation | 190.02 m RL |
| Maximum height (m) | 20.9 |
| Outer Wall Profile | 1V : 3H (maximum) |
Consequence Classification
| GISTM Classification | Very High |
Risk Assessment
AngloGold Ashanti’s comprehensive risk management plan aims to implement designs and controls in a way that risks are eliminated risks and where any risks remain, these are mitigated so that the residual risk is a As Low As Reasonably Practicable (ALARP).
Risks are considered in the design stages with mitigation measures incorporated into the design features and operational procedures. Risks are also identified and mitigated through numerous layers of reviews and inspections with follow up actions and recommendations developed to mitigate identified risks. A Potential Failure Modes Assessment was undertaken with a multi-disciplinary team and in collaboration with the EoR. Current and residual risks associated with potential failure modes are reviewed annually to identify additional mitigation measures or controls that can be adopted to further reduce the risks to ALARP.
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.
Modelling of a potential failure indicates that the areas to the south and east of the South TSF could be affected and could impact human settlements, farming, and water resources.
Performance Reviews
AngloGold Ashanti has a comprehensive Tailings Review System which incorporates reviews from multiple levels and internal and external parties. The TSF is subject to the following reviews:
- RTFE Performance Reviews – typically quarterly
- EoR Inspections – typically quarterly and Annual Performance Reviews
- ITRB Review – Annually
- AGA Corporate Review – Annually
- Independent 3rd Party Regulatory Review – Quarterly
- Dam Safety Review – Typically every five years
| Reviews | Most Recent Review | Next Planned Review |
| EoR | Mar 2025 | Q2 2025 |
| ITRB | July 2024 | Q3 2025 |
| DSR | NA | Q3 2025 |
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 at 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 STSF in the most recent reviews.
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 interaction(s) with potential receptors.
AngloGold Ashanti is working with Ghana’s Environmental Protection Authority (EPA) to assess the impact of AGA’s Obuasi BIOX Tailings Storage Facility on the nearby Binsere community.
Community concerns raised with the EPA’s Obuasi office after mine redevelopment work started included dust, noise, odor and water pollution. AGA responded by restricting construction to daytime hours, increasing dust monitoring and suppression, and trialing odor-reduction technology. However, these measures did not fully address community concerns.
Following a mid-2025 EPA meeting, a moratorium was declared preventing further development within 100m of the BIOX TSF based on community safety and proximity concerns, and the EPA committed to undertake additional studies. In the second half of 2025, AGA began Rapid Asset Surveys of properties within the 100m buffer zone ahead of resettlement consultations with traditional leaders, government bodies and community members.
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
The mine has a dedicated Emergency Response Team and Emergency Management and Response Plan (EMRP). The EMRP identifies potential events and incidents, defines those personnel responsible for implementation of the response, and describes procedures for notification, communication and escalation of the emergency response.
The BIOX TSF emergency preparedness and response planning is a dedicated plan that is appended to the site wide EMRP and the facility operation, maintenance and surveillance manual. In the event of a tailings dam related emergency, the Emergency Response Team would be the first responders.
Financial Capacity
AngloGold Ashanti confirms it has adequate financial capacity to cover the estimated costs of planned closure, early closure, reclamation, and post-closure monitoring and maintenance of the 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.