Core sample documentation follows a structured sequence that begins the moment drill core is recovered from the ground and ends with verified data stored in a project database. The key stages are: core recovery and preparation, geological logging, photography and visual documentation, sample selection for geochemical analysis, and data management. Each stage builds on the previous one, and skipping or rushing any step compromises the quality of the entire dataset. Below, we walk through each stage and explain what good practice looks like at every point.
How is drill core recovered and prepared for documentation?
Drill core is recovered by removing core barrels from the borehole and placing the core sections into labelled trays in the correct depth order. Preparation involves cleaning the core, marking orientation lines where applicable, measuring recovery rates, and confirming that tray labels match the drill log before any documentation begins.
Recovery preparation is more than just physical handling. Before a geologist picks up a marker, the core needs to be arranged so that depth intervals are continuous and traceable. Each tray should carry clear labels showing the hole ID, the from depth, and the to depth. Any core loss intervals must be recorded and flagged so that missing material is not accidentally interpreted as a geological feature later.
Orientation marking, where the driller has used a core orientation tool, should be transferred to the core surface at this stage. Wet grinding or simply wetting the core surface with water can help reveal rock textures and mineralogy that are otherwise invisible on a dry, dusty surface. This small step significantly improves the accuracy of everything that follows.
What does geological core logging involve?
Geological core logging is the systematic description of drill core by a trained geologist. It captures rock type, mineralogy, alteration, structure, veining, and any features relevant to the exploration target. The geologist records these observations at defined depth intervals directly onto a logging form or into digital logging software.
A complete log typically includes lithological codes, grain size, colour, texture, and structural measurements such as foliation angles or vein orientations. Geotechnical parameters like rock quality designation (RQD) and fracture frequency are also recorded, particularly when the data will be used for mine planning or geotechnical assessments.
Consistency is the backbone of useful logging. When multiple geologists work on the same project, they need to agree on a shared codebook before logging begins. Differences in how two geologists describe the same rock type can introduce systematic errors that skew resource estimates. Regular calibration sessions, where geologists compare their logs on the same core intervals, help keep the dataset coherent across a long project.
How is core photographed and visually documented?
Core photography involves capturing standardised images of trays in both dry and wet conditions using consistent lighting, a colour reference card, and a scale bar. Wet photography is done first because wetting the core reveals textures and alteration that dry surfaces hide. Images are named with the hole ID and depth interval so they can be linked directly to the geological log.
Good core photography requires controlled conditions. Natural light variation, shadows from overhead lighting, and inconsistent camera angles all reduce the usefulness of the images. Dedicated photography stations with fixed lighting rigs and overhead camera mounts produce far more consistent results than handheld photography on a field tray.
Beyond standard tray photography, close-up images of specific intervals are valuable for documenting visible mineralisation, unusual structures, or sampling cut lines. These detail shots should be cross-referenced to the main log so that anyone reviewing the data later can locate the photographed feature quickly. All images should be backed up immediately and stored alongside the core log files in the project database.
When and how are core samples selected for geochemical analysis?
Core samples are selected for geochemical analysis after geological logging and photography are complete. Selection is based on the geologist’s log, with priority given to mineralised intervals, alteration zones, and lithological contacts. The geologist marks cutting lines directly on the core, and the core is then split, with one half sent for analysis and the other half retained as a reference.
Sampling intervals are typically defined by geological boundaries rather than fixed lengths. A one-metre sample that straddles two different rock types will produce a mixed assay result that is difficult to interpret. Sampling to geological contacts, even if that means some samples are shorter or longer than the nominal interval, produces cleaner data.
Core splitting is usually done with a diamond saw or a core splitter. Diamond sawing is preferred for mineralised intervals because it produces a flat, reproducible cut. The retained half should always be stored in the correct depth order in the tray so that future reference or re-sampling is straightforward. Sample numbers are written on both the cut face of the retained core and the sample bag to maintain the chain of custody throughout the sample processing and geological services workflow.
What data management practices are used in core documentation?
Core documentation data is managed through a combination of standardised field forms or digital logging software, a central project database, and a version-controlled file system for photographs and supporting documents. Data entry should be validated at the point of collection, and all records should be backed up to a secure location before the end of each working day.
Digital logging tools have largely replaced paper forms on most modern exploration projects. They allow geologists to enter data directly into a structured database, apply validation rules that catch obvious errors in real time, and export data in formats that feed directly into geological modelling software. This reduces transcription errors and speeds up the time between logging and interpretation.
Regardless of whether logging is digital or paper-based, a clear data management protocol should define who is responsible for entering data, who checks it, and how corrections are recorded. Overwriting original entries without an audit trail is a common source of data integrity problems. Good practice is to flag corrections clearly and retain the original entry so that the history of the dataset is transparent.
What are the most common errors in core documentation and how are they avoided?
The most common errors in mining core sample documentation are depth errors, inconsistent geological coding, poor photography quality, and a broken chain of custody for samples. Most of these errors are preventable through clear protocols, regular quality checks, and adequate workspace setup.
Depth errors occur when core trays are mislabelled, core loss is not recorded, or orientation marks are transferred incorrectly. Checking tray depths against the drillers’ rod count at the end of each run, before the core is moved, catches most of these mistakes early.
Inconsistent geological coding is a subtler problem. It builds up gradually when geologists use personal shorthand, apply codes differently, or do not follow the agreed codebook. Periodic inter-logging checks, where two geologists independently log the same interval and then compare results, are one of the most effective ways to identify and correct this drift before it becomes embedded in the dataset.
Poor photography is often a workspace problem rather than a skill problem. Inconsistent lighting, cluttered tray backgrounds, and missing scale bars all reduce the value of the photographic record. Investing in a properly equipped logging facility with a fixed photography station removes most of these variables and makes high-quality documentation the default rather than the exception.
Chain of custody errors happen when sample numbers on bags, cut core faces, and the sample dispatch form do not match. A simple check at each handover point, comparing the physical sample number against the dispatch record, prevents most of these discrepancies from reaching the laboratory.
At Palsatech, we support every stage of this workflow through our geological services, sample processing services, and purpose-built PalsaCenters. Our logging facilities are designed with ergonomics and workflow efficiency in mind, equipped with high-quality adjustable logging tables, integrated photography stations, and the infrastructure needed to keep documentation accurate and consistent from the first core tray to the final database entry. If you want to know more about how we can support your project, get in touch with us directly.