Case Study
Paste Fill Hole Reaches 2,152 ft in a One-Shot Pass
At Paulsens Gold Mine, Boart Longyear drilled a 656 m paste fill hole in one pass, reaching the target in 39 shifts and intersecting within 2.1 m of center.
Executive snapshot
- Client
- Northern Star Resources
- Service Used
- Directional Drilling
- Operating Environment
- Active gold mine
- Project Outcome
- 656 m / 39 shifts
Project Requirements
What the project required
Project Conditions
A 310 mm bore was required so the full hole could be lined with 203.2 mm casing.
Technical Requirement
The hole had to intersect a 5 m underground target at 656 m depth with accurate trajectory control.
Operational Requirement
Complete the hole efficiently in one pass while coordinating frequent surveys and adapting drilling parameters.
Operational Challenge
What made the project challenging
A large-diameter paste fill hole had to reach a small underground target without relying on the conventional multi-pass method.
Project Condition
The required diameter and casing were too large for a regular mineral exploration rig.
Technical Constraint
The hole needed to remain on trajectory and intersect a 5 m target deep in the underground development.
Operational Pressure
Surveying, bit changes and drilling parameters had to be coordinated as formations changed.
Boart Longyear Approach
How Boart Longyear approached the work
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Experienced Crews
The crew mobilized and had the rig operational within one week, then completed the one-pass hole through changing formations.
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Method And Equipment Planning
Boart Longyear selected a water-well-style rig with 130,000 lb pullback to accommodate the large-diameter casing and full 656 m depth.
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Equipment And Tooling
A booster compressor and conventional DTH hammers supported cuttings removal; bits and hammers were changed as formations hardened.
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Safety Systems And Field Controls
The program combined frequent surveying and controlled parameter changes; the client described the work as safe and accurate.
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Site Planning
The hole was collared and cased in stages, reducing from 470 mm to 381 mm and then to the final 310 mm diameter.
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Technical Supervision
Surtron Technologies and Boart Longyear completed regular multi-shot surveys and adjusted drilling parameters to keep the hole on trajectory.
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Regional And Field Support
Boart Longyear coordinated with Surtron Technologies for specialist surveying throughout drilling.
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Execution Discipline
Regular rod pulls supported bit inspection, replacement and surveying, with tooling adjusted as ground formations became harder.
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Quality / Project Outcome
The 656 m hole reached the target in 39 12-hour shifts and intersected approximately 2.1 m from target center.
Outcome / Proof
What the work delivered
39 Shifts
Reached target in 39 12-hour shifts versus roughly 40–50 shifts expected with multi-pass methods.
2.1 m From Target Center
The 656 m hole intersected within approximately 2.1 m (6.9 ft) of the target center.
~$5M Future Gold Value per Level
The paste fill hole supports pillar extraction estimated to add about $5 million in gold value per mining level.
Why It Mattered
Impact
A one-pass directional approach reduced drilling time while delivering accurate paste-fill access for continued mining.
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