Pit Lake Water Quality Modelling at Century Mine

Author(s): 
C Linklater, A Watson, A Hendry, J Crosbie and P Defferrard
Date: 
Monday, November 20, 2017
First presented: 
9th Australian Workshop on Acid and Metalliferous Drainage
Type: 
Published paper
Category: 
Geochemistry

The Century open cut zinc mine at Lawn Hill recently changed ownership from MMG Limited (MMG) to New Century Resources (NCR). Closure planning for the site was initiated by Zinifex, developed further by MMG, and is continuing under the new ownership. The waste rock dumps will be covered with a store and release cover system to meet closure objectives. However, the open pit, which is partially backfilled with waste rock, is expected to fill with water post closure to form a pit lake. As part of developing the site closure strategy, the final pit lake level (i.e. risk of discharge), and water quality that may develop within the lake post closure, were identified as potential risks to meeting downgradient water quality objectives. To evaluate this risk, a pit lake model has been developed that integrates outputs from geochemical characterisation programmes, water balance studies and hydrogeological modelling. The model quantifies solute production from pit walls and mineralised wastes located within the pit, and accounts for potential influence from out-of-pit waste dumps. Pit lake water quality is calculated over time, allowing assessment of potential impacts to surface and groundwater, and third party receptors. Using the predictions from the model, it has been possible to compare potential environmental outcomes for different closure strategies and assumptions, thus allowing prioritisation of forward works and informed selection of optimal closure measures.

Feature Author

Claire Linklater

Claire Linklater has 22 years’ experience in interpretation of geochemical data, building conceptual models of processes which control in situ geochemical behaviour and the application of geochemical modelling codes.  Her early career was focused on management of radioactive wastes; understanding and quantifying the geochemical behaviour and mobility of radionuclides in the ‘geosphere’ surrounding a proposed underground repository and assessing the long-term stability of engineered and natural barriers.  More recently, she has focused on sulfidic materials management: acid/alkaline rock drainage (ARD) assessment and prediction; water quality and pollutant mobility from waste rock dumps, tailings storage facilities, underground workings and pit walls; assessing the effectiveness of potential mine closure strategies.

Principal Consultant (Geochemistry)
PhD (Geology), FGS, FAusIMM
SRK Sydney
Alex Watson

Alex Watson has 20 years’ experience in environmental projects gained from working in the UK, South Africa and Australia. While his main area of expertise is geochemistry, he also has experience in water and waste management, mine closure planning, environmental impact and management and due diligence studies. Alex has experience in site investigation, characterisation and assessment (mine site/mineral waste and contaminated land). He has provided consulting expertise to both the private and public sectors on projects concerning mining, industrial and waste management issues in order to achieve legal compliance, improve environmental performance or manage risk.

Senior Consultant (Environmental)
MSc (Analytical Chemistry), BSc Hons (Physics and Chemistry), MAusIMM
SRK Sydney
Alison Hendry

Alison Hendry is a Chartered Geologist with over 10 years’ experience in environmental geochemistry and water quality impact assessments. Alison began her career researching the geochemical soil mineral surface associations of uranium resulting from the use of deplete uranium (DU) munitions in the Balkans, and utilising isotope geochemistry to assess the mobility of uranium from nuclear process plants in the UK. She has worked on a diverse range of geochemical characterisation (acid and metalliferous drainage, AMD) assessments for mine sites, predictive pit lake water quality assessments, water quality compliance reporting, contaminated site investigations, remediation design projects, landfill hydrogeological risk assessments and environmental impact assessments. Alison has extensive field experience of sampling environmental media for assessment, and has gained experience in hydrogeological testing and assessment methods including drilling supervision, well installation design and permeability testing.

Senior Consultant (Geochemistry & Hydrogeology)
PhD (Uranium Geochemistry), BSc (Geology & Environmental Chemistry), CGeol, FGS
SRK Perth
John Chapman

John Chapman has more than 26 years of relevant experience and has developed multi-disciplinary skills relating to mining environmental impacts assessment and environmental controls.  He is a recognised expert in ARD assessment and prediction, mine waste characterisation and management, and mine closure with recent project experience in Australia, South East Asia, Canada, USA and Europe.  John has facilitated enterprise-wide risk assessment workshops, undertaken due diligence and environmental risk assessments for a wide range of mining projects.  Recent projects include detailed geochemical assessment of the tailings properties for the Olympic Dam Project in SA, design and development of the geochemical characterisation program for the Cannington Life Extension project in QLD as well as for the Yeelirrie Project in WA.

Principal Consultant (Geochemistry and Environment)
MSc (Chemical Engineering), P Eng (British Columbia), P.Eng (Yukon Territory)
SRK Brisbane
SRK Worldwide