I recently saw a question on a portable X-Ray Fluorescence (pXRF) networking discussion group that asked how to prepare pulps onsite for pXRF analysis from reverse circulation (RC) chips. The exploration geologist was trying to develop a method for instructing where rig geologists can use pXRF on RC chips as they are logging with the rig (an on-site method). Most of her research indicated pulverized samples were better for pXRF in her company’s iron ore exploration because they dealt with significant microbanding. However, she wondered if there was a good method for on-site pulverization that avoided contamination of the sample. One geologist mentioned to her that there was a case study on iron ore mining and grade control from the Pilbara area of Western Australia which addressed the effects of sample preparation. For light elements [Aluminum (Al), Silicon (Si), Magnesium (Mg), Sulfur (S), and Phosophorus (P)], the best method is to have the sample pressed in the field (pelletized) and not use a sample cup (cups use a 4 micron support film which absorbs the majority of light element signal). So if these light elements were important to her, she should pelletize. If these elements were not essential, she could use cups. There are several sample preparation tools that would enable her rig geos to pulverize samples on site and make pellets or cups. Here’s a 6-minute step-by-step tutorial video of sample preparation using both a direct rock sampler as well as a hammer mill kit. You can see how to crush, mill, and pelletize in order to perform elemental analysis of geological materials on-site within minutes rather than days or weeks. In the Pilbara example, thirty five RC samples were analyzed. Each sample was analyzed both in RC piles (chips were variable in grain size – starting at 10 mm in diameter) as well as in a pulp specimen. The study showed a high correlation between the analyzer data and the lab data for Iron (Fe), Manganese (Mn), and Titanium (Ti), as well as penalty elements, Si and Al. P concentrations were below detection limits in the analyzed samples. This investigation also indicated the importance of sample preparation in improving accuracy and precision of the portable XRF assay. For example, correlation with lab data increased from 0.8910 in the piled samples to 0.9957 in the prepared, pulp specimen. Similar improvements were seen in the penalty elements as well. The improved correlation data for the RC pulp data versus the RC sample piles data set suggests that better accuracy and precision can be achieved through better sample preparation. The fewer variables in the samples, the less error there was in the assay data. You can read the entire application summary, including methodology, correlation charts, and results here: Iron Ore Mining and Grade Control Using Portable XRF Analyzers
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