r/mining • u/Jinbidedrilling • 23m ago
Asia Core Logging: Small Oversights That Can Cause Big Problems
One question that comes up in core logging is deceptively simple:
When core is heavily broken, how do you decide what length to record?
It sounds straightforward until you're standing in front of a core tray full of fragments, some of which fit together, some that don't, and others that could have broken during drilling, handling, or transport.
You still need to complete the log. The depth records need to make sense, and the recovery calculation needs to be defensible.
But forcing every fragment into a neat sequence doesn't necessarily make the data more accurate.
The problem with measuring broken core
Imagine a drill run with heavily fractured rock.
If you simply line up all the fragments and measure their combined length, you may overestimate the recovered core length. Gaps between pieces, incorrect ordering, and fragments from different positions can all affect the result.
On the other hand, leaving the core scattered in the tray and estimating its length by eye isn't a reliable solution either.
A sensible starting point is to reconstruct the core wherever possible.
Match natural fracture surfaces, preserve the original sequence, and measure along the core axis. If sections cannot be reliably reconstructed, document the uncertainty and follow the project's established procedure for handling those intervals.
The important point is to distinguish a measured length from an estimated one.
They aren't interchangeable, and the log should make that clear.
Not every broken piece tells the same story
This is where things get more complicated.
A core fragment may have broken along a natural joint or fracture. It may also have broken during drilling, extraction, transport, or handling.
Those possibilities can have very different implications for geological interpretation and rock mass assessment.
Unfortunately, the distinction isn't always obvious from the core alone.
Fresh-looking surfaces may provide clues, but appearance by itself is not definitive. The interpretation should consider the geological context, drilling records, handling history, and the logging procedures used on the project.
If the origin of a break is uncertain, it's better to record that uncertainty than to confidently label every break as natural or drilling-induced.
The same caution applies when interpreting RQD (Rock Quality Designation).
RQD is not simply the total length of recovered core divided by the drilled interval. It uses a defined method for measuring qualifying intact core pieces, commonly those at least 10 cm long, subject to the applicable standard and project procedure.
A run can have high core recovery but low RQD. One measurement cannot substitute for the other.
What about core loss?
Core loss creates another challenge.
If part of a run is missing, the missing interval should not be quietly filled in with an assumed length or treated as though the core had been recovered.
Check the drilling records, confirm the run boundaries, and document the discrepancy according to the project's procedure.
Also, be careful when comparing recovery figures between runs. The calculation method, depth references, and treatment of any residual core need to be consistent.
If the measurements don't reconcile, investigate the discrepancy before changing the numbers.
A clean-looking spreadsheet is not the same thing as reliable geological data.
A practical approach in the core shed
For heavily broken intervals, a few basic habits can prevent a lot of rework:
1.Reconstruct the core where the pieces can be matched reliably.
2.Keep the original sequence and run boundaries clear.
3.Measure along the core axis rather than estimating from a scattered pile.
4.Distinguish measured values from estimates and document uncertainty.
5.Record unexplained core loss instead of forcing the figures to agree.
6.Follow the project's procedure for recovery and RQD calculations.
These steps won't make every broken interval easy to interpret. Sometimes the evidence simply isn't good enough to reconstruct the original core with confidence.
That's a limitation worth recording, not something to hide.
How do you handle heavily broken core?
I'm interested in what actually works in the field.
When core is too fragmented to reconstruct confidently, do you have a standard method for recording recovered length and documenting uncertainty, or does the approach vary between projects and logging teams?
I'm especially interested in hard-rock exploration where natural fracturing and drilling-induced breaks can be difficult to distinguish.
Different teams may have different procedures, but the goal should be the same: produce a record that another geologist can understand, review, and defend later.
