From Drill Core to Data: What Critical Minerals Ask of the Trace Element Laboratory

For decades, a typical exploration assay suite centred on a handful of commodity elements: gold by fire assay, plus copper, lead, zinc and iron by a routine digest. Those methods are well understood, and the laboratories that run them are highly practised.

The shift towards critical minerals has changed the request. Australia’s Critical Minerals List includes lithium, the rare earth elements, gallium, germanium, cobalt, vanadium, tantalum and others. Many of these occur at low concentrations, sit inside minerals that resist dissolution, or are measured alongside elements that interfere with them. Explorers also want more elements per sample, because pathfinder and indicator elements help vector towards mineralisation and characterise deposits earlier.

The result is more pressure on the laboratory to report a wide range of elements, accurately, at low levels, from difficult rock.

Getting the sample into solution

Most trace element methods start with a liquid, so the first decision is how to dissolve the sample. That choice determines which elements are actually measured, and it matters as much as the instrument.

Aqua regia. A partial digest using nitric and hydrochloric acids. It dissolves sulfides, many oxides and carbonates, but leaves silicates largely intact. Useful for base metals and pathfinders in soils and sediments, but not a total analysis.

Four-acid digest. Adds hydrofluoric and perchloric acids to break down most silicates, giving a near-total result for many elements. Some volatile elements can be lost during evaporation, and resistant minerals such as zircon, cassiterite, chromite and some rare earth phosphates may not fully dissolve.

Fusion. The sample is fused with a flux, such as lithium borate or sodium peroxide, then dissolved. Fusion attacks refractory minerals and is generally preferred for rare earths, zirconium, hafnium, niobium, tantalum and tin. Sodium peroxide fusion is also widely used for lithium in pegmatites. The resulting solutions carry a high salt load and are diluted before measurement, and the sensitivity of ICP-MS means low-level elements remain measurable after dilution.

A result that looks low may reflect incomplete digestion rather than low grade. Matching the digest to the mineralogy and the target elements is the starting point for reliable data.

Why ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) measures most of the periodic table in a single run, with detection limits in solution down to nanogram per litre levels for many elements and a linear range spanning several orders of magnitude.

That combination suits critical minerals work. Heavy dilutions after fusion still leave enough signal for low-level elements. A single measurement can cover the full rare earth series, lithium, pathfinders such as arsenic, antimony, bismuth and tellurium, and the major commodity elements.

ICP-MS also complements the other techniques in a mining laboratory. Fire assay remains the reference for gold grade and XRF is valuable for rapid screening of major elements, while ICP-MS delivers the low-level, multi-element data that critical minerals work increasingly depends on.

What modern ICP-MS brings to geological samples

Geological samples combine high dissolved solids, complex matrices and concentrations that swing from barren host rock to high-grade intercepts. Current ICP-MS instruments are designed to handle exactly these conditions.

High-matrix tolerance. Modern sample introduction systems and robust plasma conditions allow ICP-MS to handle fusion digests, four-acid solutions and brines with less manual dilution and better stability than earlier generations of instruments.

Interference removal. Multi-gas collision cells reduce polyatomic interferences, such as argon chloride on arsenic. Together with gas selection and isotope choice, this supports accurate measurement of difficult elements in chloride-rich and rare earth-rich matrices.

Wide dynamic range. Modern detectors cover trace to high concentrations in a single run, so barren host rock and high-grade intercepts can sit in the same batch with fewer over-range re-runs.

Multi-element throughput. The full rare earth series, lithium, pathfinders and commodity elements are reported from one measurement, giving explorers a broad geochemical picture from every sample without separate methods.

Isotope information. Because ICP-MS measures individual isotopes, it supports lead isotope screening for ore source fingerprinting and isotope dilution for high-accuracy work.

Stable long runs. Internal standards and automated drift correction support consistent results across large batches of exploration samples.

QA/QC is part of the result

In mining, assay data feed directly into resource estimates and investment decisions, so quality control is not optional. Typical programmes insert certified reference materials matched to the deposit type, blanks to check for contamination and carryover, and field, coarse and pulp duplicates to measure precision at each stage.

Well-characterised methods, appropriate reference materials and stable long-term performance give explorers confidence in their data, and make it easier to stand behind the numbers they report.

Beyond the orebody

Trace element testing also runs through the rest of the mine life. Groundwater and surface water monitoring, acid and metalliferous drainage assessment, tailings characterisation and rehabilitation all depend on measuring metals and metalloids accurately.

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality set default guideline values for many toxicants, including cadmium, copper and zinc, at low or sub-microgram per litre levels in freshwater. Meeting those limits in samples that may also carry high sulfate and dissolved salts is a direct application of the same ICP-MS strengths described above.

Where this could be heading

Demand for critical minerals data is unlikely to ease. Exploration programmes are asking for broader element suites, lower detection limits and faster turnaround, often from sites a long way from a major laboratory. Modern ICP-MS, with high-matrix tolerance, multi-gas interference removal and a wide dynamic range, is well placed to meet that demand.

ICP-MS sits at the centre of that work. For Australian laboratories supporting the critical minerals sector, its value lies not only in sensitivity, but in how well the full method, from digestion to reporting, is matched to the rock in front of it.