1 Introduction The Heritage Minerals Mount Morgan Tailings Reprocessing and Rehabilitation Project (the Project) proposes the reprocessing of historical tailings across the Mount Morgan mine site, with the reprocessed tailings to be managed within a new Tailings Storage Facilities (TSFs). The Project is being developed by Heritage Minerals Pty Ltd and integrates resource recovery with progressive rehabilitation of areas within its mining lease, while legacy impacts outside the operational footprint remain under Queensland Government responsibility. To support the proposed tailings reprocessing activities, the Project requires the development of a new TSF capable of safely and sustainably storing reprocessed tailings in accordance with contemporary design and environmental standards. Following an options assessment undertaken by WSP, Upper Mundic Gully (UMG), formerly referred to as Wattle Gully, was identified as the preferred location for additional tailings storage, situated behind an existing mine spoil dump (Western dump) and north of the historic Sandstone Gully tailings facilities. WSP subsequently prepared a concept TSF design for the UMG TSF [1], including assessment of staging, capacity, and crest elevation options, with a final conceptual design adopted to a crest elevation of RL 390 m. UMG TSF design is documented in WSP’s 2025 report, Heritage Minerals Mount Morgan Project – Upper Mundic Gully Tailings Storage Facility Concept Design to RL 390 m (Report No. PS213278‑WSP‑BNE‑MNG‑REP‑019, Rev C). This Seepage Management Plan (SMP) has been developed based on the current conceptual understanding of the hydrogeological and geological conditions at the site, including the interpreted groundwater flow regime, stratigraphic framework, and potential seepage pathways associated with the proposed UMG TSF. This SMP presents an initial characterisation of potential seepage behaviour during operations and in the period following completion, recognising the current level of site understanding. In this context, the SMP identifies key stages of Project development during which the understanding of potential seepage is progressively advanced through future numerical assessments, including the development and refinement of seepage modelling and, where required, the evaluation and incorporation of mitigation measures into the TSF design. At this stage of the Project, the SMP serves as a guiding framework to inform targeted investigations and assessments required to address current knowledge gaps and to test and refine the current understanding of seepage processes. The SMP defines the information requirements, monitoring activities, and further studies necessary to improve confidence in seepage risk characterisation and to support the progressive refinement of seepage assessments as additional data are collected and the Project advances. Subsequent chapters describe the purpose and scope of the SMP, outline the assumptions and limitations associated with the current assessment, and define the information requirements, monitoring framework, and further studies required to address identified data and knowledge gaps.
1.1
Project background
The Mount Morgan mine is a historic copper and gold operation located approximately 38 km southwest of Rockhampton and approximately 90 km west-northwest of Gladstone. Mining at Mount Morgan commenced in 1881 and ceased 1980, while tailings processing continued for the following ten years until 1991, when the site management transitioned to the Queensland Government. Over the life of the operation, tailings and waste rocks were deposited in multiple facilities across the site, resulting in complex legacy of landforms comprising steep gullies, historic mine spoil deposits and multiple open pits. The proposed TSF is intended to contain tailings generated from the reprocessing of historical tailings at the Project. As such, the development of a new TSF represents a necessary enabling component of the Project, providing a facility for tailings storage that is consistent with contemporary safety standards, environmental protection principles, and regulatory requirements, while also supporting the Project’s rehabilitation objectives.
Project No PS213278 Mount Morgan Mine - Upper Mundic Gully TSF Seepage Management Plan Heritage Minerals
WSP May 2026 Page 1
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