Built by a geologist

Introduction to Core Logging

Core logging is one of the most important skills in exploration and mining geology. It involves the systematic description and documentation of drill core to understand subsurface geology. What is Core Logging? Core logging is the process of: 1. Examining cylindrical rock samples drill core extracted from the ground 2. Describing lithology, structure, alteration, and mineralization 3. Recording observations in a standardized format 4. Interpreting the geological significance Why Core Logging Matters Exploration - Understand subsurface geology - Identify mineralization styles and controls - Vector toward ore zones - Plan follow-up drilling Mining - Define ore body geometry - Estimate grades and tonnages - Plan extraction methods - Ensure ore/waste discrimination Financial - Resource/reserve estimation - Feasibility studies - Investment decisions - Regulatory compliance Core Sizes Diamond drill core comes in standard sizes: | Size | Diameter mm | Common Use | |------|---------------|------------| | AQ | 27.0 | Reconnaissance, deep holes | | BQ | 36.5 | General exploration | | NQ | 47.6 | Standard exploration | | HQ | 63.5 | Detailed work, soft ground | | PQ | 85.0 | Large samples, geotechnical | NQ and HQ are most common for mineral exploration. Core Handling Upon Receipt 1. Verify hole ID and depth markings 2. Check core blocks align with depths 3. Assess recovery and condition 4. Photograph before disturbing Best Practices - Work in a clean, well-lit area - Handle core gently to preserve structures - Keep core in boxes in correct order - Mark sample intervals clearly - Never remove core without documentation The Logging Process Overview 1. Layout : Arrange core boxes, verify depths 2. Geotechnical : RQD, recovery, structural data 3. Lithology : Rock types and contacts 4. Alteration : Mineralogical changes 5. Mineralization : Ore minerals and grades 6. Sampling : Mark intervals for assay 7. Photography : Document the core