Framework for mining feasibility

For the past five-and-a-half years, the mining industry has been quietly working with the Department of Conservation and other government authorities on a framework to work out the environmental impact on any project – particularly aquatic. By ALASTAIR MCKENZIE.

According to Straterra, the association representing the natural resource industries, mining uses 40 square kilometres of land area, or less than 0.1 percent. Dairying uses 20,000 square kilometres of land and produces $3,500 exports per hectare. Mining generates $175,000 exports per hectare.

But despite its relatively small environmental footprint and relatively large contribution to the country’s economy, acute public sensitivity over mining’s environmental impact makes it the country’s favourite environmental whipping boy.

The issue of mining within the nation’s conservation estate was raised recently and this produced howls of outrage.

Whatever the rights and wrongs involved, it’s clear that the mining industry will go nowhere fast in the near future without jumping through a virtual tunnel of consenting hoops, and complying with planning regulations is typically an expensive and lengthy exercise. For the past five-and-a-half years, the mining industry has been quietly working with the Department of Conservation (DOC), regional councils (West Coast Regional Council and Environment Southland) and scientists from CRL Energy (the lead agency in the project), Canterbury University, Landcare Research, and Otago University to develop a framework to streamline the process.

Specifically, the framework is intended to streamline the process of investigating the feasibility of mining on the West Coast and in Southland. The development team hopes the document will provide consistency and transparency to the decision-making processes involved – specifically around projects involving the potential impact of the proposed mining on the water quality of streams.

The framework is a flowchart outlining a series of steps to determine the likelihood and extent of impacts from the proposed mining on aquatic systems, particularly regarding chemical impacts such as pH and metals. If a company follows the framework, the regional council involved and/or DoC should have all the information related to these impacts it requires to make a decision, saving frustrating delays and costs.

Prediction of mine drainage chemistry and downstream water quality at proposed mine sites requires information on the target commodity, region, and geological formation as well as a good understanding of downstream biota and ecosystems. Developing the framework has involved a lot of cross-discipline collaboration, including research on rock geochemistry, aquatic chemistry, freshwater ecology, aquatic toxicology, and management, and remediation techniques.

The framework includes details on predicting downstream quality for four mine types: coal – potentially acid forming (PAF), coal – non-acid-forming (NAF), gold – alluvial and gold hard rock. The acid-forming potential and trace element content of the rocks to be disturbed by any proposed mining are key environmental considerations for both coal and gold mines. An assessment of this requires sample collection and acid base accounting analysis. Once mine drainage chemistry is predicted, site specific hydro-geological information and background water quality information is used to predict likely impacts on downstream water quality.

The most severe conditions are usually associated with acid-forming geology. These geological conditions have the potential to produce acidic waters, high in toxic metals (e.g. Iron (Fe), Aluminium (Al)). They may also create metal hydroxide precipitates in streams and create highly turbid waters.

Gold mining is more likely to create sediment and turbidity issues and possibly release metals such as arsenic (As), antimony (Sb), and mercury (Hg) – metals which can be toxic to many animals.

Of these, arsenic is the main environmental issue associated with hard-rock gold mines, and acidity is almost invariably controlled by surrounding rocks to pH 7-8. Typical gold mine ore contains about 2000 times as much arsenic (as arsenopyrite) as gold. The gold and arsenic are closely interlinked in the ore rocks, so that all gold-extraction techniques affect the arsenopyrite as well. The arsenopyrite will dissolve in water during all mining and processing activity and removal of arsenic from mine water before discharge is often necessary.

While the framework is intended for new mining operations, the information is also relevant to existing mining operations or when selecting remediation options for historic mining operations.

Information on likely downstream water quality is combined with information on the likely ecological effects to determine whether any potential impact is acceptable or not. This information can be used internally by mining companies when planning their operations, or in a regulatory context such as during the consenting process.

Framework development project leader Dr Jo Cavanagh says the framework makes no value judgment on what is environmentally acceptable and what is not, instead it simply provides information. The framework doesn’t establish explicit ‘acceptable’ water quality criteria because these are likely to be different at different sites and because there are social, economic and cultural factors that may also influence decision making. Instead, the framework provides a robust scientific basis to discuss water quality issues during the consultation processes.

Jo says if it’s clear the potential impact of a proposal is not acceptable, the framework offers different options for remediation or management to prevent poor quality mine drainage. Guidance on what sort of monitoring should be undertaken to ensure any systems put in place are working, and to ensure that no unanticipated environmental impacts occur when mining commences. Mitigation or prevention of poor quality mine drainage can be achieved through appropriate management of waste rock and tailings (operational management) and/or treatment of mine drainage through active or passive remediation systems.

‘The framework could even indicate at a very early stage that a project is not worth continuing because of potential financial or environmental costs.”

A draft of the framework will be available for public comment at the end of the year.