Inflow water quality - Hope Bay, Nunavut

Mine water management in the Canadian Arctic involves a unique combination of technical challenges as a function of the geographical and geologic setting. Characterisation and planning for underground mine groundwater inflow management requires a thorough understanding of northern hydrogeology, as well as thermal effects, water quality and logistical challenges.

The Newmont Hope Bay Project, located in Nunavut, is planned to include multiple underground developments, all of which have technical challenges from the perspective of both groundwater characterisation and planning:
• Average annual air temperatures below zero degrees Celsius
• Permafrost (i.e., permanently frozen ground) to depths reaching 400m below surface and taliks (areas of unfrozen ground) below lakes
• Connate groundwater with salinities and metal concentrations often higher than sea water

The potential for saline groundwater inflow at many of the proposed underground developments at Hope Bay is a concern. Developments occurring within lake taliks, often within 100 to 200m vertically of the lake bottom, or below permafrost will not have the benefit of frozen ground to limit inflow. Regionally, some mines have experienced relatively high inflows of saline groundwater.

In 2010, an on-going groundwater quality sampling program was initiated within taliks and below permafrost. To develop a valid baseline, permanent installations were required capable of year-round operation through frozen ground. To provide this capability, SRK designed Westbay multi-level monitoring system installations, providing the ability to physically separate the unfrozen sample zone targets from the access pipe, which can pass through 400m of frozen ground. Using sampling tools passing through anti-freeze-protected access pipe, water samples and pressure data are collected from the target zones, allowing for development of vertical profiles of both water quality and pressure, after correction for density.

Results from repeat sampling have indicated that, at a minimum, inflow salinity will be typical of sea water concentrations. As part of QA/QC procedures, stable isotopes (oxygen & hydrogen) are collected to provide an additional comparison with drilling waters, to ensure that sufficient purging has occurred. Isotope data indicate water quality types different than drilling water, validating the sampling results.

The data collected has allowed SRK to better constrain predictions of potential inflow water quality, and provide valuable input to the development of site water management plans.

Dan Mackie:

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