Through in-depth research and discussions with senior product managers at both Herrenknecht & Kramer Direct, we confirmed that the use of microtunnelling technology for our application was not only feasible, but the ideal technology to overcome all of the common challenges in our industry. The maturity of this technology and the vast international catalogue of projects, combined with the diverse geological conditions where TBMs have been successfully deployed, made it clear that this technology was a natural fit for our industry. The ability to achieve large diameter boreholes, coupled with precision, steerability, high rate of advance and small operational footprint make them the perfect tool for targeting and extracting high-grade material from alluvial gold deposits deep underground. Coupled with the guidance provided by an advanced exploration program, this method truly is the key to unlocking sustainability and efficiency in placer mining.
Alluvial gold mining operations across both British Columbia and the Yukon share several challenges and often face significant obstacles. Our method combines the technology and capabilities needed to tackle each of these, opening the door for not only a cleaner and more targeted approach, but increased operating agility.
Solution: to extract only high-grade material and leave the rest undisturbed.
Solution: as the extraction process is fully isolated by design, underground aquifers and groundwater can be easily controlled and contained.
Solution: slurry with high solids content operating from 100% recirculated water in a closed-loop circuit.
Solution: by leaving ground unexposed and being able to excavate through some of the hardest ground conditions, we can bypass this challenge altogether.
Solution: operating underground combined with using a closed loop circuit enables complete operational control.
Solution: targeted approach which requires less earth to be moved and therefore less equipment.
In comparison to open pit mining, with a TBM (Tunnel Boring Machine) operation the overall footprint is significantly reduced and 90% of the work happens underground – remotely controlled by the operator from the command module. The TBM is deployed from a launch shaft (or pit) that houses the pipe jacking system which advances the boring machine along a pre-determined path. Slurry conveyance lines are preinstalled in the pipe tunnel and transport material from the cutter face to the separation plant on the surface. Cuttings are then removed from the bentonite slurry by the separation plant and the slurry is recirculated back to the TBM. This system a closed loop and is constantly monitored and optimized, adapting to changing ground conditions, slurry density, etc. All operations are overseen from the control module and a generator supplies power to each component of the system. In terms of earth moving equipment, all that is required for a typical TBM project is an excavator for pit/shaft excavation and shoring installation, a skid steer for general duties and tailings management, and in the event that the shaft is deeper than 20 feet, a crane to lower the pipe segments.
Herrenknecht – Direct Pipe Installation
Herrenknecht – AVN 2000 Pipe Jacking
Microtunneling has the ability to reduce project risk, increase site safety, constrain the mining footprint within a very small area, minimize surface ground disruption/settlement, and is applicable to a wide range of geological conditions with extreme accuracy and manoeuvrability.
Laser GNS enabled MTBMs can be steered to +/- 5mm deviation off of the planned bore path.
Managed by an operator who monitors and controls pipe jacking operations from a console inside a container on the surface
Slurry is formed by mixing the cuttings with a chemical free bentonite suspension at the tunnel face, passing through slurry lines to the separation plant and back to the TBM – constantly cleaned, optimized, and recirculated in a totally closed loop circuit.
The entire system is isolated by the retractable steel pipe installed along the whole length of the borehole, allowing for complete control of all operational facets with a high degree of accuracy and predictability.
The exploration program is the first and most critical component of all mining projects. The data gathered at this stage guides decision making in virtually all areas and downstream processes. Close collaboration from all key teams is critical and involvement from each is ongoing and iterative.
Compared to sluice systems that utilize riffles, expanded metal and matting and require large volumes of process water per ton of solid material, the IPJ (Inline Pressure Jig) / ISP (Inline Spinner) circuit boasts the ability to handle mass balances with a high solids content (up to 70%) making it the ideal solution for processing the slurry from the tunnel face in an (M)TBM mining operation. In addition to water conservation, the IPJ/ISP circuit can capture particle sizes which are simply out of reach in sluice recovery. At the 75um level (200mesh) standard sluice systems are only able to recover between 15 and 20% of gravity recoverable gold; the IPJ/ISP circuit in comparison, consistently reports recovery rates of 87% for this size and above 90% in all particles larger than 75um.