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Project Background
1.1 Introduction Heritage Minerals Pty Ltd (Heritage Minerals) has engaged WSP Australia Pty Ltd (WSP) to review and update the Dam Break Assessment (DBA) and Consequence Category Assessment (CCA) for the proposed new Sandstone Gully Tailings Storage Facility (STSF) at their Mt Morgan Gold Mine. The previous DBA and CCA were completed by WSP (formerly Golder) in 2021 as a part of the Detailed Design report for Sandstone Gully TSF [4]. The update was triggered by a revision of the proposed TSF layout requested by Heritage Minerals, currently being developed by WSP as a Definitive Feasibility Study (DFS) [5]. The objective of this study is to estimate the potential flooding impact that might occur in the event of a catastrophic failure of the STSF, 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, Science and Innovation (DESI) [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 STSF. 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 Stage 1 (initial stage), Stage 3 raise and Stage 5 (final stage). 1.2 Site description The Mount Morgan mine site is located near the town of Mt Morgan, approximately 38 km south-west of Rockhampton in Central Queensland. The 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. Sandstone Gully adjoins the OCP to the southwest, with 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. Heritage Minerals proposes to re-mine and re-process the tailings on site. A new tailings storage facility is planned to be constructed within Sandstone Gully to support this operation (STSF). The Stage 1 STSF embankment will provide capacity for 3.9 Mt of tailings, the intermediate Stage 3 embankment has a capacity of 10.0 Mt and the final Stage 3 embankment has a capacity of 20.9 Mt, as presented in the Definitive Feasibility Study (DFS) report [5]. An overview of the site layout is presented in Figure 1.1.
Project No PS213278 Sandstone Gully TSF Dam Break and Consequence Category Assessments Mount Morgan Gold Mine Heritage Minerals
WSP January 2025 Page 1
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