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01 October 2025
Peter Mellor Heritage Minerals Pty Ltd PO Box 6, Mount Morgan QLD, 4714
Heritage Minerals EA Amendment Application – Updates to Water Balance Model July 2025 (Final)
Dear Mr Mellor,
1.
Introduction
1.1 Background GHD Pty Ltd (GHD) were engaged by Heritage Mineral Pty Ltd (Heritage) to undertake a water balance update study to understand the impact of amended activities in the Open Cut Pit (OCP) and Upper Mundic Gully (UMG) on the Heritage Minerals water balance in relation to findings presented from the assessment were submitted in the Water Balance Modelling Report – Heritage Minerals EA Amendment Application (GHD, 2022a). The phased approach of implementing the Tailings Storage Facility (TSF) is subject to amendments, which pertain to changes to catchment areas and the operational rules, as decided by the board of Heritage Minerals. This letter-report documents the updates to the water balance study following the GHD (2022a) report. The key assumptions, climatic and other data inputs from the 2022 study still apply to this update and as such, this letter should be read in conjunction with the 2022 report. Study Area The Mount Morgan mine, located 32 km south-west of Rockhampton, began operating in 1882 and produced approximately 250 tonnes of gold and 360 000 tonnes of copper over its 108-year life (Queensland Government, 2015). The presence of heavy metals and sulphur bearing compounds (iron, pyrite, zinc, molybdenum and others) within tailings and waste material have caused several legacy issues on the site, predominantly concerned with the issue of acid rock drainage and water quality impacts on the environment. The Queensland Government has held the management responsibility for the Mount Morgan Mine since 1992. The main pit is currently flooded, and legacy waste and tailings storages are scattered around the site. 1.2 The Department of Resources (DOR), previously known as Department of Natural Resources Mines and Energy (DNRME), in 2006 commissioned a water treatment plant (WTP) to the north-east of the Open Cut Pit (OCP). The purpose of this facility was to maintain water levels and reduce the likelihood of the increasing acidic OCP water overtopping and discharging into the receiving environment. The contaminated water is treated for acidic pH and metals via a dosing and flocculent clarification with the residual sludge being discharged back into the OCP. The treated water extracted from this process is then released into the Dee River.
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