What’s CBE Worth, page-926

With pXRF the most crucial thing is sample presentation/preparation. With diamond drill core you are limited to "scoring" or filletting the drill core drilled and preferably grinding into a powder or just taking readings more frequently within the 1m intervals (say at 50cm intervals or 25cm intervals or even more frequently) and then attempting to average over the metre interval. Its actually quite difficult to get a reliable pXRF reading over a metre of drill core.

For RC drilling - the sample is usually collected in 1m composite sample bags and the sample is already much more homogenized (smashed up by hammer and blown into a cyclone by high pressure air) so for RC/percussion/air-core drilling the more homogenous sample is actually better for the pXRF and its often quite accurate in RC chips/dust. I have seen 1m RC composite samples have pXRF readings of say 1.0% Cu and the same 1m interval often comes back with either 1.1% Cu or 0.9% Cu, so its in the ballpark but obviously lab assays are superior because of their more representative sample size and better sample preparation and robust QA/QC geochemistry. Depending on the calibration mode used and how wet/dry the samples are I have found that for most base metals the pXRF is most accurate in the 0.3% to 5% range of metal content which conveniently is often decent grades for Cu Pb and Zn drill discoveries, higher grade ores often require special "calibration" of the pXRF instrument, by that stage you can see it, and you want to get a lab assay on it anyway.

The pXRF is limited in that its X-Ray emission and reading/detection window is small in size (often 1cm x 2cm) and the depth of penetration for electron excitation may only be 4-5cm in solid rock. as opposed to seeing more deeper into homogenized chips/dust (higher surface area to volume ratio).