In the world of geochemistry, finishes often take a backseat to more headline-grabbing topics like sample digestion. But finishes are crucial to the accuracy and utility of geochemical data, and it is time they took center stage. Analytical finishes are the final analytical step that determines the concentrations of elements in your sample, and your choice can have significant implications for cost, detection limits, and overall data quality.

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The Rise of ICP-MS

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is increasingly the go-to method for geochemists, and for good reason. Its ultra-low detection limits make it ideal for trace element studies. For example, when you’re hunting for subtle geochemical anomalies or characterizing rare earth elements, ICP-MS can deliver unparalleled precision. However, this power comes at a price. ICP-MS is often the most expensive finish available, so its application needs to be justified by the scope and goals of the project.

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ICP-MS vs. ICP-OES and ICP-AES: Know the Difference

While ICP-MS offers exceptional sensitivity, it’s not always necessary. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Atomic Emission Spectrometry (ICP-AES) provide robust alternatives for many applications. These techniques are better suited for higher concentration ranges and are typically less expensive. While the terms ICP-OES and ICP-AES are often used interchangeably, ICP-OES emphasizes the optical aspect of detection, focusing on the wavelengths of emitted light, while ICP-AES generally refers to the broader spectroscopic technique that includes both optical and atomic emission methods. Both are well-suited for major and minor element analysis but lack the ultra-trace detection capabilities of ICP-MS.

Key distinctions include:

• ICP-OES: Higher versatility in handling complex matrices and interference corrections.
• ICP-AES: Typically emphasizes simpler applications where cost-effectiveness is key.

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XRF: The Workhorse of Bulk Analysis

X-ray fluorescence (XRF) remains a staple in geochemical laboratories, particularly for major and trace element analysis. Its non-destructive nature and ability to handle large sample volumes make it ideal for bulk geochemical studies. However, it is worth noting that XRF methods, particularly for whole rock analysis, can be quite expensive. Unless the analysis is for rare earth element (REE) exploration or your program requires SiO2 or loss on ignition (LOI; volatile content), its application is typically limited in mineral exploration.

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AAS: Still Relevant?

Atomic Absorption Spectroscopy (AAS) might feel like an older technology, but it still has its niche. It is particularly useful for single-element analysis, especially when dealing with specific metals like Au, Ag, or base metals. It is often a cost-effective option for targeted studies where a single element of interest is present in relatively high concentrations.

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Fire Assay: The Gold Standard for Precious Metals

When it comes to Au and other precious metals, fire assay remains the gold standard. This technique involves fusing a sample with a flux to create a lead (Pb) button containing the precious metals. The Pb button is then cupelled to remove Pb, leaving a bead of precious metals. This bead either is weighed or further analyzed using methods like ICP-MS or AAS for ultra-low detection limits and high precision.

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Gold by Photon Assay: A New Era

A recent advancement in Au analysis is the Photon Assay method, which is gaining traction as a non-destructive alternative to traditional fire assay. This technique uses high-energy X-rays to excite Au atoms in a sample, allowing for precise and rapid quantification of Au without the need for extensive sample preparation. Photon assay is particularly appealing for its ability to handle large sample volumes and its environmental benefits due to the elimination of Pb-based fluxes.

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LECO Analysis for Sulfur and Carbon

Laboratory Equipment Corporation (LECO) instruments are a key tool for analyzing sulfur, sulfide, sulfate, and inorganic and organic carbon in geochemical samples. Using LECO analysis for the different species of sulfur and carbon have implications ore genesis and environmental considerations. This method provides high precision and is relatively cost-effective for the elements it targets.

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Choosing the Right Finish

Selecting the right finish comes down to understanding your project’s objectives and the limitations of each technique. Key factors to consider include:

• Elements of interest: what are you trying to measure, and at what concentrations?
• Detection limits: are trace or ultra-trace detections required? OR are you going to exceed the detection limit of the instrument?
• Budget constraints: is the added cost of a high-sensitivity finish justified?
• Sample throughput: how many samples are you processing, and what is your timeline?

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Bringing Finishes to the Forefront

By bringing finishes into the spotlight, geoscientists can make more informed decisions that maximize the quality of their data while balancing cost and practicality. Whether you are chasing trace elements with ICP-MS, working in REE exploration with XRF, employing fire assay for precious metals, or leveraging LECO for S and C analysis, understanding your options ensures your geochemical results are fit for purpose.

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Building on the success of the Digest 2025 Soapbox, here’s our call to action for Finishes in 2025:

It costs hundreds of thousands of dollars to drill. Do not skimp on your geochemical analysis. For exploration, your drill core and its accompanying analysis are your greatest assets. Make sure your finishes are up to the task because great data drives great discoveries.