Identifying groundwater resources for mining prospects
The availability of suitable groundwater resources may be a significant factor in the decision to progress a mineral deposit from the prospect stage into an operating mine. CMJA has conducted hydrogeological investigations for Peak Hill Gold Mine, Golden Cross Resources NL (Cargo gold prospect and Kempfields silver/barite prospect) and David Mitchell-Melcann Pty Ltd (Attunga limestone quarry) to identify suitable groundwater resources for mining and ore-processing operations. This usually requires a multi-phase approach, involving review and assessment of existing geological and hydrogeological data sets, structural interpretation of aerial photographs and remotely sensed images, geophysical surveys (preferably using electromagnetic techniques), and good geological instinct.

Assessing the potential impact of mining operations upon groundwater resources
Before consenting to the development and/or expansion of a mining operation, the regulatory authority usually requires an assessment of that operation's impact on groundwater conditions and resources. Frequently, when mining is to proceed below the water table, the assessment must take into account impacts of dewatering and depressurisation. Similarly, the potential impact of an open-cut or underground mine on natural surface water and groundwater flow systems must be assessed. Alternatively, risk-based assessments of the potential for aquifer contamination, or to identify contaminant migration pathways, may be required.

CMJA has conducted many such assessments. Our clients have included Enhance Place Pty Ltd (Enhance Place Colliery near Lithgow, NSW), David Mitchell Pty Ltd (Sulcor limestone mine and Attunga limestone quarry, both near Tamworth), Concrite Quarries Pty Ltd (Exeter Basalt Extraction Area, Southern Tablelands, NSW), ACI Industrial Minerals (silica sand mining at Tanilba Northern Dune, Port Stephens, NSW), Chadcole Pty Ltd (Kempsey Clay operations, north coast, NSW) and Calga Sands/Rocla (Calga, Central Coast, NSW).

Typically, we approach impact assessments in a staged fashion. First, potential aquifers that may be at risk must be identified by review and assessment of existing geological and hydrogeological data sets. Secondly, it is necessary to deduce or estimate the baseline hydrogeological properties of the aquifers and surrounding geological medium. These include hydraulic conductivity, porosity, lateral and vertical hydraulic gradients, and groundwater geochemistry. Finally, having reviewed and interpreted all relevant information sets, we can assess the impact of a particular mining operation. Such assessments can be qualitative and/or quantitative, depending upon the requirements of the client.

Acid generation at McKinnons Gold Mine, Cobar, NSW
In order to meet the requirements of regulatory authorities, Burdekin Resources NL commissioned CMJA to conduct a preliminary study to estimate the final open-pit water chemistry following closure of the mine. Hydrogeochemical speciation modelling using MODPHRQ, a development of the well-established code PHREEQC, was used to model the hydrogeochemical processes controlling the geochemical evolution of groundwater. This allowed predictions of the final open-pit water quality.

Development of a groundwater monitoring plan, Sulcor Limestone Mine, NSW
So that David Mitchell Pty Ltd could comply with licensing requirements, CMJA was commissioned to design a full groundwater monitoring plan. This plan included design and construction specifications for the required groundwater monitoring network in addition to a groundwater sampling and groundwater level measurement plan specifying monitoring schedules and analytical suites, standard operating procedures for collecting measurements, sampling, sample handling and documentation, quality assurance/quality control procedures and reporting schedules.