XRF for Mineral Exploration
Olympus portable X-ray fluorescence (pXRF) analyzers provide real-time geochemical data for rapid multi-element characterization of soils, rocks, ores, concentrates, and tailings. Recent advances in portable XRF technology have improved the limits of detection, increased the number of elements measured, and reduced analysis test times. When used for mineral exploration and grade assessment, the Olympus Vanta™ and DELTA® portable XRF analyzers can provide real-time analysis of nickel found in rocks, soil, sediment, drill cuttings, and drill core samples. Pre-screening enables rapid exploration targeting, priority sample selection for laboratory analysis, and improved drill hole decision-making.
Measurements of key elements including nickel (Ni), iron (Fe), magnesium (Mg), sulfur (S), copper (Cu), chromium (Cr), titanium (Ti), and Cobalt (Co), as well as the calculation of their respective ratios, enable rapid assessment of barren or mineralized ultramafic units. These measurements can also enable assessment of the potential for anomalous Ni enrichment or favorable physical volcanic emplacement processes and the stratigraphic relationship to nickel sulfide (NiS) ore formation.
Figure 1. A Vanta handheld XRF analyzer.
Figure 2: Geochemical map of nickel in soils from Pioneer Nickel's Fraser Range Project in Western Australia. Portable XRF results are displayed on the left and laboratory results (Aqua Regia) on the right (image courtesy of Geochemical Services Pty Ltd).
XRF for Grade Control
Portable XRF analyzers are used around the world for monitoring ore grade in active open pit and underground mines. Specifically, XRF analyzers are used for direct analysis of blast hole cuttings in mines, as a preliminary guide on direct rock faces underground, open pit faces, and within Ni mine labs after sample preparation. In mines where rapid grade assessment is beneficial, portable XRF can be used to optimize run-of-mine (ROM) stockpiles and help ensure consistent blending and feeding to the mill. The data and results in Figure 3 illustrate the performance of the DELTA Premium portable XRF analyzer on OREAS 70 Series certified reference materials. Samples tested were in powdered form, contained in XRF sample cups. Each sample was measured for 60 seconds. The DELTA analyzer results indicate excellent correlation with certified values.
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Figure 3. The performance of the DELTA Premium portable XRF analyzer on OREAS 70 Series certified reference materials.
Measurement of Penalty and Deleterious Elements
Portable XRF analyzers can also accurately measure the concentrations of undesirable elements within NiS deposits. The presence of elements like arsenic (As), lead (Pb), bismuth (Bi), and Zinc (Zn) within NiS deposits are penalized at the smelter gate unless blended to dilute their concentration. High Fe:MgO ratios are favored over elevated Mg-rich minerals, such as talc and fibrous serpentine, which can be problematic for conventional process circuits and significantly impact the quality of recovery.
As a final benefit, the XRF analyzer can reduce the use of hydrofluoric acid in the laboratory to analyze some of these elements, such as As. The result is a safer working environment at the mine site laboratory.
Figure 4. Arsenic-rich Gersdorffite veins bordering massive nickel sulfide. High arsenic is penalized in concentrate grades and must be removed or blended down prior to delivery to the smelter (photo taken at Silver Swan Nickel Mine, Kalgoorlie, Western Australia).
Conclusion
Vanta and DELTA portable XRF analyzers provide convenient, rapid measurements of many types of samples associated with NiS exploration, within NiS mines, mine labs, and Ni processing facilities.
