In-pit tailings disposal at Langer Heinrich TSFs in a unique hydrogeological setting

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Millicent Blankenship
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in proceedings Prepared by: Cameron Hore

1 In-pit tailings disposal at Langer Heinrich TSFs in a unique hydrogeological setting Tailings and Mine Waste Management for the 21 st Century 2015 Page number 373 in proceedings Prepared by: Cameron Hore chore@srk.com.au Dave Luppnow dluppnow@srk.com.au

2 Introduction / Setting Location Langer Heinrich Uranium Mine Owned by Paladin Energy Current production: 5.1 Mlb pa U Current tailings production: 2.4 Mt pa (320 tph) dry basis Mine is within the Namib-Naukluft National Park

Introduction / Setting Climate Extremely arid

additional moisture Occasional storms on the

3 Introduction / Setting Climate Extremely arid climate Annual average rainfall of 67 mm Evaporation in excess of 2,300 mm per annum Dense fogs off the Atlantic Ocean bring additional moisture Occasional storms on the surrounding granite mountains result in flash floods in the area

4 Introduction / Setting Mine Plan Ore body follows an ancient river bed Long narrow pit shell Maximum depth approximately 60 m General approach is to mine east and west from Pit A near the plant

5 Introduction / Setting Hydrogeological features Two aquifer systems are present Surficial Gawib shallow alluvium aquifer - waste Deeper paleochannel aquifer systems partially forms part of ore body Gawib shallow alluvium aquifer ORE BODY Paleochannel aquifer

6 Introduction / Setting Process The ore is separated at the plant: 60% proceeds to the leaching process 40% is scrubber reject. A coarse (cobble sized) reject and a fine (coarse sand) reject material. During the leach process, the ore is dewatered in a thickener, producing a thickened tailings stream and transported as thickened slurry to the TSF (47-52% solids). Ore Scrubber 40% Reject Coarse Rejects Barren Sand Mining Waste Rock 60% Leach Product Tailings

7 Introduction / Setting Process The ore is separated at the plant: 60% proceeds to the leaching process 40% is scrubber reject. A coarse (cobble sized) reject and a fine (coarse sand) reject material. After the leach process, the spent ore is dewatered in a thickener and transported as thickened slurry to the TSF (47-52% solids). Coarse Rejects 40% Reject Barren Sand Mining Ore Waste Rock Scrubber 60% Leach Product Tailings

Tailings Storage Objectives Cost effectively achieve: Maximum capacity for LOM

the groundwater Reinstate the shallow alluvium and paleochannel aquifers and

non-impacted waters Compliance with relevant standards and guidelines

8 Tailings Storage Objectives Cost effectively achieve: Maximum capacity for LOM (15 years) of operation Maximum water return Minimum risk of contamination of the groundwater Reinstate the shallow alluvium and paleochannel aquifers and pre-mining natural topography at closure Separation of impacted and non-impacted waters Compliance with relevant standards and guidelines Constraints: Limited space, water and dollars. Opportunities: A range of waste materials produced.

9 Tailings Storage LOM Plan The TSF design is an exercise in storing tailings while isolating the tailings from surface and sub-surface water flows, and optimizing mine waste disposal costs. In-pit Drainage layer scrubber rejects Waste rock embankments Waste rock aquifer reinstatement

10 TSF Design Isolation Concept Partial pervious surround Preferential flow paths Low permeability tailings High permeability surrounds

practice guidelines Maximise Water recovery Filter and drainage

11 TSF Design Drainage System Maximise Capacity: Enhance consolidation Two way drainage bodies and international best practice guidelines Maximise Water recovery Filter and drainage layers Thickened tailings Cost effective: Utilise waste products Short haul opportunities

short haul opportunity Proactive planning can reduce the consequences of failure

12 TSF Design Aquifer reinstatement Lower aquifer reinstated with waste by mining operations as soon as mining completed Short haul opportunity Upper aquifer reinstated at closure Also short haul opportunity Proactive planning can reduce the consequences of failure Historically, most dam break studies undertaken for water dams Currently a requirement of many regulatory bodies

Utilise mining operations Proactive planning can reduce the consequences of failure Historically, most dam break

13 TSF Design Embankment design Three materials Bulk fill waste rock Transition material selected waste rock Compacted low permeability liner subgrade layer selected waste Maximise bulk fill component - balanced Short haul Utilise mining operations Proactive planning can reduce the consequences of failure Historically, most dam break studies undertaken for water dams Currently a requirement of many regulatory bodies and international best practice guidelines

from the collection sump to the surface Slotted HDPE pipe

14 TSF Design Decant Design Decant supernatant water from pond Provide casing for submersible pumps Transport of the water from the collection sump to the surface Slotted HDPE pipe wrapped in geotextile Sand drainage layer Coarse rejects sump

15 TSF Design Closure Reinstatement of the paleochannel - done Basal containment system and the pervious surround - done Closure capping/cover of the tailings mass Reinstatement of the upper aquifer Use of waste in closure capping short haul and avoids double handling

16 TSF Design Closure Currently assessing the closure requirements and planning to undertake closure cover testing on the existing TSF 2.

failure Downstream Embankment Drainage Layer Partial Pervious Surround Historically, most dam break studies

17 TSF Design TSF 3 One bulk fill embankment one in-situ wall. Makes use of existing pit shell Provides 3 years storage Proactive planning can reduce the consequences of failure Downstream Embankment Drainage Layer Partial Pervious Surround Historically, most dam break studies undertaken for water dams In situ wall Currently a requirement of many regulatory bodies and international best practice guidelines Sumps/Decants Deposition Point

18 TSF Design TSF 4 Two bulk fill embankments Embankments provide foundation for flood channels across pit Locations fixed by natural drainage paths Relatively small storage capacity relative to fill volume justifiable due to short haul of waste rock and need for flood channels. Proactive planning can reduce the consequences of failure Historically, most dam break studies undertaken for water dams Currently a requirement of many regulatory bodies and international best practice guidelines

19 TSF 3 Construction

20 TSF 3 Construction

21 TSF 3 Construction

22 TSF 3 Construction

23 TSF 3 Construction

24 TSF 3 Construction

25 TSF 3 Construction

26 TSF 3 Operation Construction was overall a success Some lessons learnt carried forward to TSF 4 design Now operating

27 TSF 3 Operation

28 TSF 3 Operation

29 TSF 3 Operation

30 TSF 3 Operation

31 TSF 3 Operation Capacity checked against production, design densities are being achieved Beach slope is being acheived

32 TSF 3 Operation

33 TSF 3 Operation

TSF Design Objectives achieved The TSF design is/was an exercise in storing tailings while isolating the tailings from surface and sub-surface water flows, and optimizing mine waste

34 TSF Design Objectives achieved The TSF design is/was an exercise in storing tailings while isolating the tailings from surface and sub-surface water flows, and optimizing mine waste disposal costs. In-pit partial pervious surround Reinstatement of aquifers TSF deposition to mimic natural gradients Short haul opportunities for waste rock Use of other waste materials

35 Thank you Q&A Questions?

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