6
Tailings and water management
The tailings and water management requirements have been estimated based on the consequence categories assessed in Section 5 for Stage 1 and Stage 2.
6.1 Water storage
The water storage requirements for the TSF have been assessed assuming the following:
— No operational pond volume — PMP stored within the TSF (no spillway). — The PMP storage allowance will provide more than adequate capacity to meet the Queensland Design Storage Allowance (DSA) and Emergency Storm Storage (ESS) requirements.
6.2 Deposition
Tailings deposition into the Upper Mundic Gully TSF was modelled using Muck3D to estimate the maximum available tailings storage and to develop the construction staging of the embankment. The estimated volumes for the two embankment stages are presented in Table 6.1, including sufficient storage to contain the PMP runoff. The PMP rainfall depth calculations are presented in Appendix C.
Table 6.1
Estimated tailings storage capacity
Stage
Elevation (m RL)
Tailings beach (m RL)
Tailings storage (Mm³) 1
Tailings storage (Mt)
Water storage (Mm³)1
1
360
350.3
1.15
1.26
1.32
2
390
386.8
8.09
8.90
1.32
Total
-
9.24
10.16
1.32
(1) Required PMP storage – does not include operational pond volumes.
The resultant tailings beach surfaces stage-storage curves are presented in Figure 6.1 to Figure 6.4. An operational decant pond has not been allowed for in this assessment at this stage and will need to be incorporated in the next stage of design.
6.3 Decant pond
Deposition into the TSF will be conducted from the embankment to keep the decant pond well away from the embankment. A suitable return water pump system will be required and may comprise a floating pontoon pump, or other suitable mobile system.
Considerations of the pumping set up and required pumping capacity will be determined in the next stage of the design.
6.4 Spillway
A spillway with capacity to pass the PMF will be required for the closure of the Upper Mundic Gully TSF, to limit water storage in the longer term. Construction of this spillway for the 2 nd and final stage of the TSF would allow for additional tailings storage within the Upper Mundic Gully TSF.
Project No PS213278 Upper Mundic Gully TSF Concept Design to RL 390 m Mount Morgan Project Heritage Minerals
WSP October 2025 Page 8
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