Core Recovery

Drilling samples and core recovery are essential parts of mineral exploration. Core provides a continuous, three‑dimensional record of the subsurface, allowing geologists to evaluate rock types, structures, alteration, and mineralization. High‑quality core recovery ensures accurate geological interpretation and reliable resource estimates.

What Is Core Recovery?

Core recovery refers to the percentage of drilled rock that is successfully retrieved during diamond drilling. It includes:

  • Solid core pieces
  • Broken fragments
  • Weathered or altered material

Good recovery is critical for evaluating ore bodies and geological conditions.

Why Core Recovery Matters in Mining

1. Accurate Geological Interpretation

Core reveals:

  • Rock types
  • Mineralization
  • Veins and structures
  • Alteration zones

Poor recovery can hide key geological features.

2. Reliable Grade Estimates

Assay results depend on representative samples. Missing or disturbed core reduces confidence in grade continuity.

3. Structural Analysis

Core shows:

  • Faults
  • Folds
  • Fractures
  • Bedding and foliation

These features guide mine design and ground control.

4. Resource Modeling

High‑quality core supports accurate 3D models of ore geometry.

Types of Drilling Used for Core Recovery

1. Diamond Drilling

The primary method for obtaining core.

Advantages:

  • Continuous core samples
  • High recovery rates
  • Deep drilling capability

Core sizes: NQ, HQ, PQ (larger diameters improve recovery)

2. Reverse Circulation (RC) Drilling

Produces rock chips instead of core.

Used for:

  • Rapid exploration
  • Large‑scale sampling
  • Areas where core is not essential

RC is faster but lacks structural detail.

Core Recovery Challenges

1. Fractured or Weak Rock

Broken ground reduces recovery and produces rubble.

2. Fault Zones

Soft or crushed material may wash away during drilling.

3. Highly Altered Rock

Clay‑rich zones can collapse or smear inside the core barrel.

4. Water Inflow

Excess water can erode or displace core.

5. Drilling Technique

Poor drilling practices reduce recovery and damage samples.

Improving Core Recovery

1. Use Appropriate Core Size

Larger diameters (HQ, PQ) improve recovery in weak ground.

2. Adjust Drilling Parameters

  • Reduce rotation speed
  • Lower weight on bit
  • Increase fluid viscosity

3. Use Triple‑Tube Core Barrels

Protects fragile core and improves recovery in broken zones.

4. Stabilize the Hole

  • Casing
  • Drilling muds
  • Polymer additives

5. Skilled Drilling Crews

Experienced drillers maintain consistent recovery and sample quality.

Core Handling and Storage

1. Core Boxes

Core is placed in labeled boxes with depth markers.

2. Orientation Marks

Used to determine the true orientation of structures.

3. Logging and Photography

Core is logged, photographed, and sampled before cutting.

4. Sample Splitting

Core is cut lengthwise:

  • Half for assays
  • Half retained for reference

5. Secure Storage

Core is stored in racks for future review and audits.

Core Recovery Calculations

Core recovery (%) =

Length of core recoveredLength drilled×100

High recovery (90–100%) is ideal for resource estimation.

Conclusion

Core recovery is a critical part of mineral exploration. High‑quality core allows geologists to interpret geology accurately, evaluate mineralization, and build reliable resource models. Proper drilling techniques, careful handling, and consistent documentation ensure that core provides the best possible information for mining decisions.