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The Practicalities And Implementation Of A NAF Grade Control Programme For Placement Of A WRD Cover

A Hendry, B Luinstra, J Jones, K Mandaran, and J Chapman
Monday, November 20, 2017
First presented: 
9th Australian Workshop on Acid and Metalliferous Drainage
Published paper

Mount Isa Mines (MIM) has commenced rehabilitation of the Handlebar Hill Open Cut (HHOC) Waste Rock Dump (WRD). This includes reshaping of the WRD and placement of an interim inert cover over potentially acid forming (PAF) and neutral mine drainage (NMD) waste rock exposed following the reshape. The interim cover material was recovered from the adjacent Magazine WRD.  To ensure that only non-acid forming (NAF) non-NMD material was used, a grade control programme was implemented which ran simultaneously with the active mining of the Magazine WRD (November 2016 – April 2017).  

To ensure that only NAF non-NMD material was used for construction, a sampling and grade control programme was implemented to delineate NAF non-NMD materials contained in the Magazine WRD.  Material was sampled from test-pits, excavated to a depth equal to the mining flitch, on a variable grid in advance of mining.  Samples were then analysed to support material classification.  Several logistical, scheduling and safety challenges were faced, including:

•    Classification sufficiently in advance of active mining.  
•    Safe working procedures without causing delays or interference to mining.  
•    Strategies to reduce mining time and costs associated with unsuitable materials.

Waste rock classification was found to agree well with the NAF/PAF boundary identified from a preliminary site geochemical field investigation.  Whilst “NAF” and “PAF” materials could mostly be identified based on geological characteristics, in the southern end of the Magazine WRD “NAF” lithologies contained higher sulphur and had been impacted by seepage from overlying PAF materials.

Post-placement verification indicated that the resolution of the sampling and testing was sufficient to meet the requirements of the cover specification.

Feature Author

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
Brian Luinstra

Brian Luinstra has 19 years of experience in the field of geology and hydrogeology working primarily in Canada.  He has executed and managed a wide scope of hydrogeological assessments.  These include regional scale water budgets; water supply assessments; well head protection studies; aquifer hydraulic testing; groundwater monitoring network establishment and program implementation; aquifer conceptualisation and impact assessment; karst investigations and hydrological and hydrogeological modelling.  He is experienced working in remote locations, and has varying levels of proficiency with specialised geological and groundwater modelling packages.  Brian provides technical direction and review on hydrogeological projects, and has been project manager for several key clients.

Principal Consultant (Hydrogeology)
PhD (Earth Science), BSc (Geology)
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 Turkey