A few weeks back I was talking with a mining team about something that comes up more than people admit. Two geologists can look at the exact same piece of core and log it differently.

Neither of them is wrong. They're just seeing it through their own eyes. That's been true for about as long as geology's existed as a discipline.

This piece looks at why that gap exists, and what's finally starting to close it.

Geology's always been part art, part science

The art side is where things get messy. Most of the time, the person building the geological model works from another geologist's log rather than the hole itself.

They're working from someone else's notes, someone else's judgement call, without the context that person had standing on site.

Then there's the roster. Most exploration sites run cross-shift FIFO, which means the same hole can get logged by two different geologists on two different swings. Each one brings their own read on what they're looking at.

Over the length of a program, those small inconsistencies add up. By the time someone's trying to reconcile the model, it's not always obvious where the read changed or why.

None of this is a flaw in the people doing the work. It's just what happens when the main instrument you're measuring with is a trained eye, and every eye's a little different.

The industry's leaning on numbers to close the gap

What's changed, gradually, is the amount of quantitative data sitting alongside that judgement call. Geochemistry gives you the chemical composition of the rock, while geophysics adds another layer.

Handheld devices like XRF readers can bring that kind of reading into the field, in a way that used to require a lab. It gives two geologists looking at the same numbers a much better shot at landing on the same answer, without taking anything away from the geologist's own eye.

The concept underneath all of this is what you'd call a population. Say you're looking across five holes over a couple of kilometres, and metres three to four keep coming back with a hardness rating of five, every single time.

At that point, the data's telling you the same thing every time. That consistency is worth more than any one person's read.

“At that point, the data's telling you the same thing every time, and that consistency is worth more than any one person's read.”
- Victor Cha - CorePlan

It gives that subjectivity a floor to stand on instead of leaving it to float. The subjectivity's still there and probably always will be, and honestly, most geologists wouldn't want it any other way.

The information that's been sitting in the driller's hands the whole time

There's a saying in the industry, especially around iron ore, that a good driller is half geologist. I believed it the day I met one who'd worked out how many metres he'd drilled across his career.

It came out to something like eight round trips to the moon and back. A driller with that many metres behind him doesn't need a screen to tell him when the ground's changed under the bit.

He feels it in the rig. It slows down or speeds up, and he knows before anyone's logged a thing.

That feel's always been real information. Until now, it's mostly lived in that driller's head, passed on the same way trade knowledge usually gets passed on, by working alongside someone long enough to pick it up.

What's starting to change is the ability to put a number next to that feeling. Torque and pressure, the kind of continuous rig data that used to only ever register as a gut sense, they're now something you can actually capture and hand back to a geologist as a second source of information.

One number, less room to drift

What I find genuinely interesting is what happens when you connect the driller's feel to the geologist's model, bringing two separate systems into the same conversation.

You're giving both of them something firmer to check their read against, while keeping each person's judgement in the process. That flows straight through to how confident you can be in your reporting and where you plan your next hole.

That confidence matters more than it sounds like it should. A geological model built on a shakier read costs you later regardless, in a hole placed slightly off target or a report that needs revisiting once someone finally reconciles the inconsistency.

We've been spending a fair bit of time looking at this space at CorePlan. I think it's one of the more interesting directions geology's heading in over the next few years.

I'll leave the specifics for another day, but it's worth watching regardless of who ends up building it.

Quantitative data closing the gap between what a geologist sees and what a driller feels is exactly the kind of shift that changes how confident an entire program can be in its own numbers.

Whether it's numbers or a driller's gut, the read gets better the moment it stops living in one person's head.

If you've had two geos log the same hole two different ways, you already know the problem I'm describing. If any of this sounds familiar and you'd like to talk it through, feel free to reach out.

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Why two geologists can look at the same rock and see two different answers

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