1
Project Background
1.1
Introduction
Heritage Minerals Pty Ltd (Heritage Minerals) has engaged WSP Australia Pty Ltd (WSP) to undertake a Dam Break Assessment (DBA) and a Consequence Category Assessment (CCA) for the proposed new Upper Mundic Gully Tailings Storage Facility (TSF) at their Mt Morgan Gold Mine. The objective of this study is to estimate the potential flooding impact that might occur in the event of a catastrophic failure of the proposed TSF, with the CCA being completed in accordance with the methods outlined by the Australian National Committee on Large Dams (ANCOLD) [1] [2] and the Queensland Department of Environment, Tourism, Science and Innovation (DETSI) [3]. This report documents the data review, methods, assumptions, development of input parameters and outcomes of the DBA modelling based on the proposed layout of the new facility. The results supported the basis to develop the CCA, focusing on conservative failure scenarios likely to be critical in terms of downstream impact, considering the embankment layouts proposed for the Stage 1 (initial stage) and Stage 2 (final configuration). The final configuration of this TSF is designed for a tailings deposition of 10.16 Mt.
1.2
Site description
The Mt Morgan mine site is located near the town of Mt Morgan, approximately 38 km south-west of Rockhampton in Central Queensland. The site’s dominant feature is an open cut pit (OCP), excavated to a depth of approximately 320 m below the original summit of Mount Morgan and was substantially filled with tailings and water. The OCP extends over the historic Sandstone Gully TSF footprint to the southwest, forming an interconnected water pond. A spillway on the eastern side of the OCP manages excess runoff from storm events. Several TSFs and mine waste dumps are located around the site. The location of the proposed Upper Mundic Gully TSF is a natural area adjacent to the mine site, located immediately northwest of a mine spoil dump near the OCP. The progression of the mine spoil dump across the Gully caused stormwater to pond at the gully’s base. A stormwater tunnel was excavated to the northeast of the dump to divert ponded water to Dam 8. As Heritage Minerals proposes to re-mine and re-process the tailings on site, Upper Mundic Gully was identified as a potential area for additional tailings storage, triggering the design of a new TSF to support this operation. The proposed Upper Mundic Gully TSF will initially (Stage 1) provide storage for 1.15 Mm 3 of tailings, with a potential expand to a total capacity 9.24 Mm 3 in total in its final stage (Stage 2).
An overview of the site layout is presented in Figure 1.1.
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 1
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