Tailings management is an expensive yet necessary requirement for ongoing operation... Advisian’s Leon Gray demonstrates how we helped Fosterville Mine implement a tailings storage solution that’s not only cost-effective, but also provides significant social benefits.

1. www.advisian.com
Full Cycle Tailings
Management –
Fosterville Gold Mine
Leon Gray, Principal Consultant, Advisian
October 2016

2. Fosterville Gold Mine has paved the way with the
first metalliferous in-pit tailings storage facility (TSF)
in Victoria.
They have developed a deposition methodology to
optimise their tailings storage capacity and provide
a final rehabilitated surface that replicates the pre-
mining topography.

3. As the name suggests, in-pit tailings storage
involves backfilling abandoned open pit surface
mines with tailings.
It has proven not only as a cost-effective solution
for tailings management, but also one that provides
significant economic, social and environmental
benefits.

4. Fosterville Gold Mine
Site Background

5. History
• Mining has occurred since the
late 1890s
• ‘Modern’ open pit mining during
the 1980s
• Current operation running since
the mid-2000s
• Primary ore is sourced from the
underground mine
• Currently owned by Newmarket
Gold
Image after Fosterville Gold Mine, 2012

6. Features
• Processing method:
• Flotation circuit
• Bacterial Oxidisation (BIOX®) circuit
• Carbon In Leach (CIL) circuit
• Throughput 680,000 tpa
• 95% of tailings generated by the flotation circuit
• Tailings slurry is 25% solids (w/w)
• Tailings particle size:
• 100% passing 0.3 mm
• 96-98% passing 0.075 mm
• Deposited dry density 1.2-1.5 t/m³

7. • Increased mine life and costs associated with
above-ground tailings storage were a crucial driver
for change
• A combination of in-pit and above-ground
storage was implemented, with strategic
deposition periods within each facility
• The combined approach enables effective drying
and consolidation of the tailings, and helps
optimise the available storage capacity
• Because of its economic and social benefits, in-pit
deposition is used over above-ground
deposition where possible
Tailings storage rationale

8. RSF1
TSF4
RSF3
RSF2
Current tailings storage facility layout
Process pant
and facilities
Tailings storage facility layout
RSF: Residue Storage Facility
TSF: Tailings Storage Facility
Above-ground tailings
storage is provided at
RSF1 and TSF4
In-pit tailings storage is
provided at RSF2 and
RSF3

9. Above-ground
Tailings Storage

10. Above-ground tailings storage
• RSF1 approx. 45 ha
• TSF4 approx. 25 ha
• Embankments 20-25m above ground level
• Gravity decant system
• Underdrainage/seepage interception
• RSF1 stability driven monitoring
• Monitoring of phreatic surface
• Monitoring for movement

11. To support the upstream raising methodology, the
design of RSF1 has incorporated a network of
underdrainage pipes throughout the base of the
facility and on the tailings beaches adjacent to the
base of each raise.
The intention of this network is to help keep the
phreatic surface within the deposited tailings as
low as possible.

12. Monitoring
Standpipe Piezometers Prism Monitoring
During operation the phreatic surface is
monitored using standpipe piezometers.
Water samples are taken to enable
geochemical characterisation of water in
the facility.
The potential for embankment movement is
monitored using survey prisms which have
been installed throughout the downstream
slope of the embankments.

13. Placeyourscreenshothere
Monitoring
Information gained from the standpipe
piezometers is used to monitor the response
of the phreatic surface to the deposition and
drying cycles.
Charting the data enables easy identification
of trends and associated changes.
This data is used to evaluate the facilities
where tailings deposition should occur
without promoting instability.

14. In-pit
Tailings Storage

15. Factors to consider
Pit Identification
Pit availability
Pit sizes
1
2
3
4
Social and
Economic Factors
Ore sterilisation
Community land use
Cost effective
disposal
Geo Factors
Faults/structures
Pit wall stability
Pit access
Site Logistics
Dewatering
Distance from
plant
The following factors/considerations were evaluated when identifying an
appropriate open-pit facility for use as an in-pit tailings storage facility.

16. Pros and cons
Long narrow
geometry
Deposited tailings
will promote stability
Empty/disused pit
Resource largely
exhausted
Groundwater impact
Faulting present
Large volume of
water within pit
When selecting the best tailings storage option for
RSF2, the social and environmental benefits were key.
The ‘pros’ of an in-pit tailings storage solution clearly
outweighed the ‘cons’ and so this solution was
selected.
Pros
Cons

17. Wall-scale failures
Even before being filled with
tailings, wall-scale failures were
slowly progressing at RSF2.
The deposition of tailings will
stabilise these pits and limit the
risk of failure.
This was a key benefit when
the land use and post-closure
risk to the community was
evaluated.

18. Removal of tailings into RSF2
These photos show the
progressive deposition of
tailings into RSF2.
The ‘current state’ photo
shows where the southern
end (Fosterville Pit) has
been filled and capping of
the pit has commenced.
Pre-deposition During deposition Current state

19. Monitoring
Monitoring bore
Production bore
Water and contaminant movement outside the
RSF2 area needed to be limited, preventing
adverse impacts to the surrounding environment.
Monitoring and production bores were installed
to enable monitoring of groundwater levels and
the geochemistry.
Production bores were also installed to enable the
recovery of water and prevent the migration of
water and contaminants away from the facility.

20. Placeyourscreenshothere
Monitoring
The data obtained from the monitoring helps
with evaluating when to operate the
production bores.
Groundwater level data shows the response
of the groundwater levels to the dewatering
and deposition cycles.
The impact of the production bores can be
seen by the rapid drop in groundwater levels
for several of the monitoring bores.

21. Closure Planning
& Implementation

22. Criteria for RSF2
closure design
• Long-term sustainability
• Consideration of surrounding environment
• Low cost
• Consideration of pre-mining condition
• Social benefits

23. Closure design
Consolidation modelling was conducted to identify
the expected surface profile in the facility once closure
was complete.
Ecological Assessment
of the adjacent land was
used to identify
appropriate species of
flora to be planted within
the capped RSF2.

24. Storage Optimisation - tiering
Causeways were constructed across
the deposited tailings to create
smaller ‘cells’ which were used to
raise the tailings surface to replicate
the adjacent natural ground level.

25. Final surface
Rehabilitation trial
A trial was conducted in a small
tailings filled and capped void
adjacent to RSF2.
The results from this trial will be used
to evaluate the final flora species
appropriate for installation in the
wider RSF2 area.
Slope Varies 1% - 5% Slope Varies 1% - 5%
Working layer placement
Final surface of RSF2 after placement
of the working layer.

26. Rates of consolidation
Survey prisms have been installed
throughout the partially capped RSF2 surface
to monitor the consolidation rates.
These will be compared with the forecast
consolidation rates and used to evaluate the
requirements for further fill placement.
Lysimters have been installed to evaluate the
rate of infiltration of rainfall runoff through
the placed working layer. This will be used to
evaluate the requirement for installing the
low permeability layer.
Prism Monitoring (consolidation) Lysimeter Monitoring

27. Learnings for RSF3
The learnings from the deposition and
closure of RSF2 will be used in the closure
design and process evaluation for RSF3.
The photos below show RSF3 in its current
state. It is currently undergoing consolidation
before further tailings are deposited,
consuming the void provided by the
consolidation process.

28. Results
As with many sites, the tailings management practices
at Fosterville will continue to be an expensive yet
necessary requirement for ongoing operation.
Whilst in-pit tailings storage has provided a low-cost
tailings storage solution, the same concept has
provided significant social benefit by enabling a
number of mined-out pits to be backfilled, and now
approaching a point where they will soon be
revegetated to reflect their pre-mining conditions.
Thankyou to Fosterville Gold Mine and their staff
for their support and assistance in preparing this
paper.

30. DISCLAIMER
This presentation has been prepared by a representative of Advisian.
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herein may not always necessarily reflect the position of Advisian as a whole, its officers or executive.
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