Wednesday 3 June 2026
Because RC drilling produces chips there is no intact sample to return to if the geological log is wrong. Errors in RC chip logging compound silently through the database, surfacing at resource estimation as diluted or inflated blocks that cannot be reconciled against the original material. By the time the resource geologist identifies the problem, the chips have been bagged, submitted, and assayed. The geological record is whatever was written down at the rig and a few tablespoons of chips in a tray.
The cost of a bad RC log is invisible until it is expensive, and unlike diamond core, there is no opportunity for a second opinion. These five habits keep the log honest and the grade estimate defensible.
1. Set your chip tray intervals before the rig starts
Mismatched intervals between what the driller records and what the geologist logs create sample misallocation from the very first metre. If the driller is collecting on 1m intervals and the geologist is logging on 2m composites, geological boundaries will not align with assay data. The misalignment propagates through the database and becomes a systematic error in every cross-section and resource block that relies on those intervals.
The fix is straightforward: agree on intervals before the first rod goes in the hole, write up the trays with the intervals, and verify alignment at every rod change. This is a two-minute conversation that prevents weeks of data reconciliation.
2. Wet-sieve a representative portion of every interval before logging
Wet sieve a representative portion of every interval before logging but check the dust and fines first. Clues to the lithology and sulphide content lie in both the fines and the chips. A quick wet sieve takes less than a minute per interval and reveals grain size, colour, and mineralogy that are invisible in a dusty, dry chip tray.
3. Log colour, grainsize, and mineralogy as separate fields
Combined descriptions like "grey fine-grained moderately silicified" are readable by a human reviewing a single interval but cannot be queried across a database of hundreds or thousands of intervals. When the resource geologist needs to filter for all intervals with a specific alteration assemblage or grain size range, combined-description fields require manual re-interpretation of every entry.
Separate fields for colour, grain size, and mineralogy let the database do what databases do: filter, sort, cross-reference, and flag anomalies. The logging template should enforce this separation before the program begins. Retro-fitting structured data from free-text descriptions is time-consuming and error-prone.
4. Photograph every chip tray with a reference card visible
RC chips cannot be re-examined once bagged for assay. Unlike diamond core, which sits in a core shed and can be re-logged years later, RC chips leave the site and may never be found again. The photograph is your permanent geological record and the only visual evidence that survives beyond the field season.
A colour reference card in every frame ensures consistency across lighting conditions, between different geologists on the same program, and across seasons. Without a reference card, chip tray photographs are difficult to compare reliably. With one, they become a standardised archive that supports re-interpretation, audit, and competent person review.
5. Cross-check your geological boundaries against the driller's water injection and sample recovery records
A geological boundary that coincides with a water loss or recovery drop may be a drilling artefact rather than a real geological contact. Logging it as geology contaminates the model with false contacts that propagate into resource block boundaries, affecting grade distribution and tonnage estimates.
The driller's records, including water injection rates, return water quality, and sample recovery percentages, are an independent check on whether what appears in the chips reflects what is actually in the ground. When a logged boundary coincides with a drilling parameter change, flag it in the log and investigate before committing it to the model as a geological contact.
The bottom line
The core tells you what happened. The chip tray tells you what you think happened. Log accordingly.
RC programs are often the backbone of infill and grade control drilling, meaning the chip logs feed directly into the resource model that underpins mine planning and financial decisions. The discipline applied at the chip tray determines whether those decisions rest on structured, verifiable data or on field notes that cannot withstand scrutiny.
At Norwest Exploration and Mining Services, we deploy geologists and field technicians who treat RC logging discipline as a core professional standard. Whether you are running a maiden RC program or infilling for a resource upgrade, the quality of the geological log is where the grade estimate begins.