HQ, HQ3, and
NQ Coring
What is HQ, HQ3, and NQ Coring?
HQ, HQ3, and NQ coring refer to different core drilling sizes and equipment standards used primarily in mineral exploration and geotechnical investigations. These designations come from the Diamond Core Drilling system developed by the Canadian Drilling Association and widely adopted internationally.
What Do HQ, HQ3, and NQ Mean?
These terms define the diameter of the drill core, the drill rods used, and the core barrel system:
| Coring System | Hole Diameter (mm) | Core Diameter (mm) | Rod Diameter (mm) | Common Use |
| NQ | ~75.7 mm | ~47.6 mm | 55.6 mm | Standard for most exploration drilling |
| HQ | ~96.0 mm | ~63.5 mm | 70.0 mm | Larger core for better sample recovery |
| HQ3 | ~96.0 mm | ~61.1 mm | 70.0 mm | Triple-tube variant for soft/fragile formations |
Key Differences
- Core Diameter
- HQ and HQ3 recover a wider core than NQ, which is helpful for detailed geotechnical logging and mineral analysis.
- HQ3 uses a triple-tube system (inner tube remains stationary while the outer tube rotates) to minimize core loss or disturbance—ideal in fractured or unconsolidated formations.
- Equipment Size
- HQ and HQ3 systems use thicker rods and barrels than NQ, requiring more powerful rigs but delivering higher quality cores.
- NQ is lighter and more economical for deeper drilling where core size is less critical.
When to Use Which?
- Use NQ coring when drilling deep and cost-efficiency matters.
- Use HQ coring when you need more sample volume for assays or structural analysis.
- Use HQ3 coring in broken, soft, or high-value formations where core preservation is critical.