The remediation of the former Giant Mine in Yellowknife, NWT, co-managed by the governments of Canada and the Northwest Territories, is a massive undertaking. The Giant Mine Remediation Project’s focus is on managing the arsenic trioxide waste and remediating the entire site. The project is complex, covering over 800 hectares, including several open pits, kilometers of underground development, and surface infrastructure such as tailings containment areas and former mining and milling buildings. Golder supports the project with a multi-disciplinary team of experts leading many aspects of this remediation, including mobilizing a diverse suite of remote investigation methods and tools to guide planning.
Developing a plan for remediating the underground requires a detailed investigation process, including gathering detailed information about current mine geometry and excavation conditions such as water inflow, rock mass stability and presence and type of backfill. As with many historic mines that operate for a long period of time with different operators, historic hand drafted mine plans can be unclear or incomplete, particularly when complex 3D geometry is concerned. Knowing where connections exist between underground excavations and the volume and condition of those excavations is critical to remediation planning. As in many abandoned mines, access is often impeded by unsupported ground, inaccessible voids and, in this instance, presence of hazardous arsenic trioxide, a byproduct of the gold extraction process. Because of this, a visual inspection is not always possible. Various tools, from borehole-based laser survey scans (known as cavity monitoring scans, or CMS), to mine plans, and now even Unmanned Aerial Vehicles (UAVs), are being deployed to overcome these access constraints.
Golder has been designing, building and deploying UAVs, commonly known as drones, underground since 2016. These UAVs carry lighting packages and onboard imaging including infrared, thermal and visual light cameras. They allow us to keep workers out of harm’s way while still investigating the required areas. Data from the onboard cameras have been used for conducting thermal scans of open voids looking for water inflow, conducting visual inspections of inaccessible or high-risk areas, and creating 3D photogrammetry models.
Combining this suite of advanced investigative tools enables our team to provide clients with the results they need for effective mine closure planning in a variety of conditions.
Better Together: UAVs and Kinetic Scanners
Employing a UAV underground can yield useful information but combining it with hand-held kinetic laser scanners greatly expands the usefulness of both systems and supports the development of accurate 3D photogrammetry models. These accurate 3D models of the current mine geometry form the basis for guiding closure decisions.
At Giant Mine, the Golder team developed a system whereby we combined the imagery collected from the drone’s onboard visual light camera with output from a hand-held kinetic laser scanner (from GeoSLAM). With the kinetic scanner, we were able to collect highly accurate, detailed data of underground areas which can be safely accessed right up to the point of drone launch that was easily tied into accurate geodetic mine survey points.
Drone use typically started at the entrance of a stope or drift that was not safe for access. We deployed the drone at these locations to collect additional mine geometry data while reducing the need for expensive ground support rehabilitation to make the area safe for inspection. The data from the kinetic scanner and drone were then combined and tied to the geodetic grid using the scan from the kinetic scanner to orient and scale the drone data. Then available CMS data and surveyed mine plans were used for quality checks.
Beyond improved data quality and increased speed of collecting the information, the need for extensive scaling effort and 3D data post processing was greatly reduced – saving the project significant time and money.
Using the UAV with the kinetic scans had the added benefits of mapping the orientation of geologic structures, generating Discrete Fracture Network (DFN) models, and linking observations of seepage to develop a hydrogeological flow model. The addition of UAVs in other aspects of underground investigations at Giant Mine has also proven beneficial. Supplementing CMS scans with UAV imagery and custom-built borehole camera lighting matrices to document the condition of backfill deposition and potential leakage points was used to improve efficiency for a 60,000 m3 stope backfilling program.
Finding the right mix of investigative tools and balancing quality with cost-effectiveness is simplified when you have access to a suite of tools and are adaptable in their implementation. Through collaboration across disciplines and integration of technology, Golder is collecting high quality data more quickly and increasing worker safety while also facilitating the environmentally-sound closure of legacy mine sites like Giant Mine.