Core Logging

Core logging is one of the most important tasks in mineral exploration. It involves examining drill core in detail to document rock types, structures, alteration, and mineralization. Accurate core logging builds the geological database that supports resource estimation, mine design, and exploration targeting.

What Is Core Logging?

Core logging is the systematic recording of geological information from drill core, including:

• Lithology (rock type)
• Mineral content
• Alteration patterns
• Veins and structures
• Rock quality and recovery
• Visible mineralization

The goal is to create a complete geological record of the subsurface.

Why Core Logging Matters in Mining

1. Understanding Ore Geometry

Core reveals the thickness, orientation, and continuity of mineralized zones.

2. Supporting Resource Estimates

Logged intervals define grade domains and geological boundaries.

3. Improving Exploration Models

Core data refines geological interpretations and guides future drilling.

4. Identifying Structural Controls

Faults, fractures, and foliation influence ore distribution and ground stability.

5. Optimizing Processing

Mineralogy and alteration affect grinding, flotation, and leaching.

Key Components of Core Logging

1. Lithology Logging

Describing rock types based on:

• Color
• Grain size
• Mineral composition
• Texture
• Weathering

Lithology forms the foundation of the geological model.

2. Structure Logging

Recording deformation features such as:

• Faults
• Folds
• Joints
• Veins
• Bedding and foliation

Measurements include orientation, dip, and true thickness.

3. Alteration Logging

Hydrothermal alteration often indicates proximity to ore.

Common alteration types:

• Silicification
• Sericitization
• Chloritization
• Carbonatization
• Potassic alteration

Alteration intensity is typically logged on a scale (weak, moderate, strong).

4. Mineralization Logging

Documenting visible ore minerals and their characteristics.

Geologists record:

• Mineral species
• Grain size
• Distribution
• Vein density
• Sulfide percentages

Visible gold, chalcopyrite, sphalerite, and galena are key indicators.

5. Rock Quality Designation (RQD)

RQD measures the degree of fracturing in core.

$$\text{RQD}=\frac{\text{Length of core pieces > 10 cm}}{\text{Total length}}\times 100$$

High RQD indicates strong, competent rock.

6. Core Orientation

Oriented core allows geologists to determine the true orientation of structures.

Tools include:

• Orientation marks
• Alpha and beta angle measurements

Oriented core is essential for structural modeling.

7. Sampling and Marking

Core is marked for:

• Sample intervals
• Assay boundaries
• Geological contacts

Core is then cut, sampled, and sent to the lab.

Tools Used in Core Logging

• Hand lens
• Magnet
• Acid bottle
• Measuring tape
• Core orientation tools
• Portable XRF analyzer
• Digital logging software
• Core photography station

Modern logging often integrates digital databases and 3D modeling.

Best Practices for Core Logging

• Log consistently and systematically
• Use standardized terminology
• Photograph core before cutting
• Verify depth markers and recovery
• Record all structures accurately
• Integrate logging with geochemistry and geophysics
• Maintain clean, organized core boxes

High‑quality logging improves every stage of the mining process.

Conclusion

Core logging is essential for understanding the geology of an ore deposit. By documenting lithology, structure, alteration, and mineralization, geologists build accurate models that guide exploration, resource estimation, and mine planning. Strong core logging practices ensure reliable data and better mining decisions.