Controlled riverine tailings management system, Grasberg minerals district.The effective and safe management of tailings continues to be one of PT-FI’s most important environmental priorities. PT-FI operates a controlled riverine tailings management system, which was implemented based on methods approved and permitted by the Indonesia government.

PT-FI’s controlled riverine tailings management system uses an unnavigable river to transport the tailings from the concentrator in the Highlands along with natural sediments to a large engineered and managed deposition area in the Lowlands. The Aghawagon/Otomona River was chosen for tailings transportation from the mill to the tailings deposition area because that part of the river is unnavigable and not used for potable water, agriculture, fishing or other domestic or commercial uses.

Situated in the Lowlands, the Modified Ajkwa Deposition Area or ModADA, is the containment and retention system for tailings produced at the concentrator, as well as other sediments transported down the river. The ModADA is the terrestrial portion of the tailings management deposition area covering an area of approximately 219 square kilometers. Below the ModADA to the south is the estuary portion of the tailings management area encompassing approximately 220 square kilometers.

PT-FI has designed and constructed approximately 85 kilometers of levees on both sides of the ModADA to laterally contain the depositional footprint of the tailings and natural sediment within the approved boundary. Quantities of finer tailings and other sediments deposit in the estuary and the sea to the south.PT-FI continues to employ tailings management techniques that are aimed at enhancing the depositions of tailings onshore within the ModADA.


Mangrove forests are revegetated in Central Papua, Indonesia.Tailings are the finely ground natural rock particles that remain after economically valuable minerals have been processed or extracted from the mined ore. PT-FI’s tailings are specifically managed to be geochemically benign, helping to ensure safety for the environment. This is partly possible due to the ore body characteristics and mine plan sequencing as well as PTFI’s extensive monitoring and sampling programs. Before the tailings enter the controlled riverine tailings management system, the tailings are sampled several times daily to determine that the desired geochemical balance has been achieved and avoid generation of acid-forming tailings. PT-FI analyzes the tailings samples to understand their acid production and neutralization potential in addition to the metal content, particle size and spatial distribution. The information from this sampling program informs the mill operators about the expected behavior of the tailings with respect to potential acid generation, and if any adjustments to mill feed should be made such as the addition of limestone. This process is the basis for the mill to be able to confirm and maintain production of geochemically-neutral tailings to be deposited in the ModADA. In addition to monitoring and managing the tailings at the mill, PT-FI also regularly tests the neutralization potential versus acid production potential of the deposited sediments within the ModADA. If the measured ratio is not at the desired level, PT-FI can blend the material with higher neutralizing material until it reaches the desired level.


Best Site-Specific Tailings Management System

PT-FI’s mines and concentrator complex are located in the mountainous area of the Highlands at an elevation of more than 2,700 meters above sea level, which presents limited options for effective tailings management. Various tailings management options were studied in detail during the early phase of PT-FI’s mining operations, in particular, when PT-FI developed plans to increase its ore production and processing capacity in the 1990s. Given the unique and challenging site-specific topographical, hydrological and geotechnical conditions at PT-FI, the controlled riverine tailings management system remains the best approach when considering the volume of tailings produced (more than 1.7 billion tons through 2022), the limited cleared and level land available for a conventional tailings storage facility, the extremely high annual rainfall (up to 12 meters per year) and the active seismic loads associated with being situated in the tectonically active “Ring of Fire” where earthquakes are common. In this unique setting, a large-scale conventional style tailings dam would not be safe, stable or effective. Independent environmental management expert audits have reaffirmed that this system is the best management alternative given the site-specific conditions of the area. The system has been in service for more than 25 years and has performed reliably, safely, and in line with initial design plans. Nearly three decades of engineering analyses, extensive monitoring and data collection, and computer modelling confirm that the current tailings management system poses the lowest risk to people and the environment, and that the impacts of sedimentation, with the exception of elevation changes, are reversible at the end of the mine life. PT-FI continues to assess and evaluate additional ways to manage and further reduce the potential impacts of its controlled riverine tailings management system on the environment and communities, with a view toward continuous improvement.

To learn more, please see our 2022 ANNUAL REPORT ON SUSTAINABILITY