Here’s your 3-minute quick read of Fresh Thinking by Snowden Optiro’s podcast Episode 123.
We’ve pulled out the key insights and takeaways – perfect for when you want the value, minus the headphones.

Why Sampling is Critical for Geologists

In Episode 123 of Fresh Thinking by Snowden Optiro, Executive Consultant Ian Glacken spoke with Mark Murphy, Manager of Geological Services at IGO Ltd, to kick off a three-part series on sampling.

Mark, who has worked across operations, consulting, and resource geology, shared why sampling is such a vital — but often underappreciated — aspect of geological practice.

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Sampling: The Missing Link in Geological Training

Mark highlighted one of the major gaps in geological education – where we learn a lot about geology at university, but next to nothing on sampling and resource estimation.

Yet, sampling underpins everything from exploration decisions to billion-dollar project valuations. Poor sampling leads to false positives, wasted exploration budgets, and, critically, biased resource estimates.

Even small errors can be costly. As Mark explained:

“A 5% bias on a multi-billion dollar project is often half or a third of the ultimate NPV value.”

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Lessons from Gold Mining

Mark’s passion for sampling was sparked during his time working in gold mining — where coarse gold presented unique challenges. At Mount Morgans in the Goldfields, blast hole samples produced confusing grade control maps.

His solution? Increase sample size.

“We were bringing in half-kilo samples… I thought, what would happen if we did 20 kilo samples? Suddenly the grade control map started making geological sense.”

This hands-on experimentation confirmed that sample quality directly impacts the reliability of financial decisions.

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Sampling Principles Apply to All Commodities

While gold often highlights sampling issues, Mark stressed that these principles apply across all commodities:

“Most of the things we desire in our products — gold, nickel, iron, lithium — are dense materials. Once you create a particulate lot, these things move under gravity, and losses create bias.”

For example, dust losses in RC drilling may look minor at 10%, but if critical minerals are concentrated in that fraction, the retained sample could be upgraded by 3–5%. That bias flows directly into the resource estimate.

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Exploration vs Mine Geologists – Different Objectives

Sampling objectives differ depending on context:

• Exploration geologists often need to bias samples to detect weak signals. Mark pointed to stream sediment sampling and newer ultrafine clay methods as examples of techniques designed to highlight anomalies.
• Mine and resource geologists, on the other hand, must focus on representativity, accuracy, and precision to make sound economic decisions.

As Mark put it, the “golden rule” of sampling is simple:

“Every fragment or particle in that lot of material has an equal chance of ending up in the sample. If it doesn’t, you’ve got bias.”

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Advice for Young Geologists

For graduates entering the industry, Mark recommended taking every opportunity to build sampling knowledge:

• Attend industry courses.
• Read books, papers, and online resources — including his own LinkedIn group on the Theory of Sampling.
• Most importantly: do experiments.

“If you’ve got an RC rig blowing a lot of dust, collect some of that dust and see what’s actually in there. For a few hundred dollars, you can learn a lot about what your sampling is really telling you.”

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Key Takeaway

Sampling is often overlooked in training, but it is the foundation of exploration, resource estimation, and mine planning. From coarse gold to base metals, the principles remain the same: minimise bias, ensure representativity, and understand what your samples are really telling you.

This episode is the first in a three-part series. Future discussions will explore sampling in exploration, mining, and processing.

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Snowden Optiro is a resources consulting and advisory group that provides independent advice, consulting and training to mining and exploration companies, their advisors and investors.

We help mine developers to advance their projects, mining companies to improve their operations and their professionals, and investors to de-risk their investments by the provision of quality advice, training and software in the field of Mineral Resources and Mineral/Ore Reserves.

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