RPS has been retained by Argyle Diamond Mine to provide regular hydrogeological review of the performance of open pit and underground mine dewatering and depressurisation and to provide input to the design and implementation of, and management of ongoing dewatering and depressurisation schemes by site operations and the ADM geotechnical team.
For the first year, quarterly site visits/ reviews were conducted and the focus was on identifying key areas within the pit walls where depressurisation would be required, designing drainhole drilling programmes and developing drainhole installation and management procedures, identifying key locations for piezometers, monitoring requirements and data management and presentation protocols. These early visits also included review of inflows to the underground mine project exploration decline and assessment of likely future inflows and optimum water management procedures.
Following the implementation of the above, the frequency of site visits and reviews was relaxed to six-monthly and the focus for open pit operations was on maintaining adequate depressurisation of pit walls and confirmation of drain hole patterns, and on dewatering of the final pit cutback prior to underground mining. A scheme was trialled where the main aquifer unit (fault zone) will be dewatered by drain holes drilled from the expanding underground mine development workings. This is both cost effective (the alternative was three short-lived in-pit dewatering bores) and also provides for some continued pit water control prior to the development of the planned block cave underground mine.
With the approaching completion of open pit mining, the nearing of the completion of underground access and development workings and the commencement of underground block cave extraction, recent visits/reviews have focused on maximising advanced dewatering/depressurisation around block cave and on identifying and developing mitigation strategies for water risks to the overall life of the underground mining operation.