Investigation of the Element Content of Black Shale Samples by INAA and EDXRF

Why It Matters

Accurate elemental certification of black shales underpins reliable geochemical standards for mining, environmental monitoring, and academic research, and validates INAA and EDXRF as complementary techniques.

Key Takeaways

• Over 50 elements quantified in two black shale reference materials.
• INAA and EDXRF achieved <10% relative error for most elements.
• 100 mg aliquots insufficient for accurate gold determination.
• Results support further certification of these shale standards.
• Inter‑lab consistency validates both analytical techniques.

Pulse Analysis

Black shales are widely used as reference materials in geochemical laboratories because they contain a complex suite of trace and major elements. Reliable certification of these matrices enables analysts to benchmark instrument performance, verify method accuracy, and ensure data comparability across research institutions and commercial labs. The recent inter‑laboratory study of samples SChS‑1A and SLg‑1A adds a critical data set, confirming that these shales meet the stringent criteria required for international standardization. By providing a transparent statistical framework—mean values, standard deviations, and 95 % confidence intervals—the work strengthens the credibility of black shale standards in mining exploration, environmental assessment, and academic investigations.

Instrumental neutron activation analysis (INAA) and energy‑dispersive X‑ray fluorescence (EDXRF) represent two complementary analytical approaches. INAA offers high sensitivity for a broad range of elements without chemical preparation, while EDXRF delivers rapid, non‑destructive screening with minimal sample handling. The study’s nine parallel 100 mg aliquots demonstrated that both techniques achieved relative errors below 10 % for the majority of the 50‑plus elements examined, and the measured concentrations aligned closely with the previously certified values. This level of inter‑lab agreement underscores the robustness of the methods and supports their continued use in quality‑control programs and regulatory compliance testing.

The investigation also revealed a practical limitation: 100 mg aliquots do not reliably capture gold concentrations in the examined shales, likely due to gold’s heterogeneous distribution at the microscale. For industries that depend on precise trace‑gold measurements—such as mineral exploration and precious‑metal recycling—this finding prompts a reassessment of sampling protocols, possibly requiring larger or multiple subsamples to achieve statistical confidence. Moreover, the validated data set paves the way for additional certification cycles, expanding the utility of SChS‑1A and SLg‑1A as benchmark materials. Ultimately, the research enhances analytical confidence, reduces uncertainty in downstream decision‑making, and contributes to more accurate resource assessments.