The Dargues Gold Mine Tailings Storage Facility (TSF) is being constructed in accordance with the requirements of the following.
- New South Wales Dam Safety Committee.
- Environmental Guidelines – Management of Tailings Storage Facilities published by the Victorian Department of Primary Industries in 2004.
- ANCOLD Guidelines on the Consequence Categories for Dams.
Knight Piésold Pty Limited (Knight Piésold) was commissioned to provide an update to the Tailings Storage Facility Final Design 2011 (Knight Piésold (2011)) report prepared for the original Project Approval. The updated report took into account changes in the regulatory environment, project approvals and community expectations since Knight Piésold (2011) was completed. The updated design report titled Tailings Storage Facility Final Design Update 2016 Rev01 (Knight Piésold (2016)) was independently reviewed prior to submission to the Dam Safety Committee.
The original design for the Tailings Storage Facility (TSF) was prepared in 2010 and is fully described in the Environmental Assessment for the Dargues Reef Gold Project which was submitted in support of the original project application (PA10_0054). A copy of the Environmental Assessment for the Dargues Gold Mine can be downloaded from here.
A detailed design for the TSF was prepared in 2011 and submitted to the Dam Safety Committee (DSC). This design took into account all the requirements of the Project’s approval conditions as determined by the Land and Environment Court. The DSC indicated that the design met the requirements of the DSC. This design is included as an Appendix to PE16-01023.
A design was prepared in support of the application for Modification 3 to the Project’s approval. This design proposed the storage of a different type of tailings material (tailings from a Cyanide in Leach (CIL) circuit). This design change was withdrawn from the Modification 3 application along with the application to use CIL at the Dargues Gold Mine.
This is the current design for the TSF at the Dargues Gold Mine and takes into account conditions of approval from the original approval by the Land and Environment Court, and Modifications 1 – 3. Note, no changes to the TSF were proposed by Modification 4. The DSC has indicated that the design met the requirements of the DSC.
A copy of the current design can be downloaded from here.
The Tailings Storage Facility (TSF) has been designed to minimise its impact on the environment by:
- Providing permanent and secure confinement of all solid waste materials. The facility was designed in accordance with the requirements of the NSW Dam Safety Committee guidelines on the safe design and operating standards for tailings storages as a minimum;
- Locating the tailing facility on a historically cleared area avoids unnecessary impacts to flora and fauna within the area;
- Minimising the visual impact as the final profile of the TSF (at closure) will resemble a small hill with a cover of light vegetation. The facility will be progressively rehabilitated, and completely rehabilitated soon after de-commissioning. The main focus of the rehabilitation programme will be re-spreading of harvested topsoil, re-vegetation, erosion control (with rock armour protection on the embankment face if required) and stormwater management;
- Controlling impact on the local groundwater by:
- Using a basin liner;
- Seepage minimisation systems; and
- Early detection (a series of groundwater quality monitoring stations will be installed);
- Management practices have been put in place to minimise seepage that incorporates aspects of design, construction, operations and decommissioning. These seek to control seepage at the source by:
- Construction of a cut-off trench, excavated into the foundation soils, that is then backfilled with low permeability fill, to reduce seepage loss under the embankment foundations;
- Constructing a suitable basin lining system for the facility, comprising a combination of in situ soil liner (in the non-critical areas of the basin) and a composite soil liner / HDPE geomembrane in the valley creek lines and the area beneath the supernatant pond;
- Limiting the extent of the supernatant pond on the tailings beach, and thus maximising evaporation potential from the tailings beach surface;
- Capping the TSF, at closure, to reduce the quantity of surface rainfall runoff that infiltrates the facility.
- Water runoff from the vicinity of the capped TSF will be managed to ensure that the quality of surface water runoff from the facility is maintained within environmentally acceptable limits.
The design criteria is summarised in the below table.
|Tailings Dam Construction|
|Dam type||Cross-valley storage|
|Pond liner requirements||Lined|
|Permeability||Equivalent to 600mm clay of permeability <1 x 10-8m/s|
|TSF hydraulic design basis||As required for storm surge|
|Final tailings footprint||ha||8.1|
|Catchment Area (inside diversion channels)||ha||8.6|
|Maximum embankment height (final)||m||30|
|Minimum embankment clearance height (freeboard)||m||0.5|
|Estimated total embankment volume||m3||242,000|
|Tailings dam natural soil permeability|
Lower permeability Description
|m/s||2.3 x 106 |
1.5 x 107
|Underliner requirements||Underdrainage & monitoring|
|Basin underdrainage type||Collector drains|
|Basin underdrainage spacing (at the decant)||m||10|
|Tailings physical properties|
|Plant tailings description (UNC system)||Silty sand with traces of clay (SM)|
|Tailings permeability||m/s||4 x 10-7|
|Time to achieve final density||hrs||<24|
|Final settling density||t/m3||1.35-1.40|
|Pond runoff water classification type||Sub Lethal|
|Tailings Dam Operation|
|TSF Capacity;||T (dry)||910,000|
|Estimated initial dam life (Stage 1)||months||12|
|Distance to plant (mill area to embankment’s centre)||m||480|
|Water release from tailings after settling||%||N/A|
Under Drainage Release
|22 – 35 |
5 – 8
|Tailings Storage Facility water return |
0 – 34
0 – 43
|Water return method||Gravity flow to decant tower|
|Tailings deposition method||Sub-Aerial Deposition|