The equation of trend line in these graphs is used to convert portable XRF readings (in unknown samples) from intensity to percent.
As I outlined in my last article about ore grade, mining geologists perform ore grade control to figure out where the most profitable ore bodies are in terms of location and mineral concentration variability. And field-portable x-ray fluorescence (FPXRF) is an effective analytical tool for high grade ore concentrates and grade control, especially when employing Empirical Mode. A case study was carried out on molybdenite (MoS2) concentrate samples, using the UserMethod Empirical Mode on a handheld XRF analyzer. In this method, samples are analyzed and the quantities are reported as intensity (counts per second per microamp rather than as percent or ppm). Then calibration curves are plotted based on known concentrations (from laboratory values) and intensity (from portable XRF). The equation of trend line in these graphs is used to convert portable XRF readings (in unknown samples) from intensity to percent (see Figure 1). Ore grade in such concentrates may vary from 25% to 65% molybdenum (Mo). Concentrations of Mo, iron (Fe) and copper (Cu) in these concentrates along with correlation with lab assay data are shown in Figure 2.
The coefficient of determination, the R2 value, is a measure of how closely the data sets correlate with each other, where a perfect correlation would have an R2 of 1. The correlation for Mo, Cu and Fe are 97%, 99% and 97%, respectively (see Figure 2). The m value beside x in the trendline equation indicates the accuracy of the results, with all three elements showing excellent agreement. For additional information, including the conclusions reached, please view the Using Portable XRF Instruments for Analyzing Ore Concentrates and Grade Control application note.