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. 

Design History

PE801-00139_3 (2010)

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.

PE801-00139_5 (2011)

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.

PE801-00139_10 (2015)

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 This design change was withdrawn from the Modification 3 application along with the application to use CIL at the Dargues Gold Mine.

PE16-01023 (2016)

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.

Design Objectives

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.

Design Criteria Units Quantity
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
Upper permeability
Lower permeability  Description       
m/s 2.3 x 106
1.5 x 107
“Relatively Permeable”
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)
Percentage Solids % 58
SG solids   2.71
SG liquor   1.001
Tailings permeability m/s 4 x 10-7 
     
Tailing Properties    
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
Supernatant Release
Under Drainage Release
  22 – 35  
5 – 8  
Tailings Storage Facility water return
Year 1
Year 2
%  

0 – 34
0 – 43
Water return method   Gravity flow to decant tower
Tailings deposition method   Sub-Aerial Deposition