Company: RTNTF
Filing Date: 2025-02-20
Form Type: 20-F
Source: 0001628280-25-006642
Chunk: 518

Company: RIO TINTO LTD
Filing Date: 2025-02-20
Form: 20-F
Chunk 518
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 sampled in 2m composites and collected in alpha-numerically numbered calico bags. Due to potential fibre mineral intersections, water injection has been used throughout the programs since 2014. ‘A’ and ‘B’ splits are collected and always taken from the same respective chute of the splitter, keeping any possible biases constant. Regular cleaning of the splitter and cyclone is undertaken to avoid smearing and contamination across intervals. Respective splits are laid out in separate rows on the ground adjacent to bulk reject samples, avoiding mixing of bags and ensuring only ‘A’ sample splits and one in every 20 ‘B’ sample splits are collected and sent to the laboratory. The particle size of RC chips is around 6mm and the primary sample collected post splitting is between 5 and 8kg, depending on the density of the material. Each diamond hole is sampled in 1m composites using a ‘crushing sheet’ created by a geologist and collected in alpha- numerically numbered calico bags (the ‘crushing sheet’ allocated bag numbers to each metre drilled and showed where check standards are to be inserted). Field check standards are inserted selectively by the rig/logging geologist at a rate of one in every 30 samples in mineralised zones and one in every 60 samples in waste with a minimum of one per drill hole. All check standards contained a trace of strontium carbonate that is added at the time of preparation. These standards are used to check sample preparation and analytical precision and accuracy at the laboratory. No direct recovery measurements of RC samples are performed. Sample weights are recorded at the laboratory upon receipt and are qualitatively estimated for loss per drilling interval at the rig. Diamond core recovery is maximised via the use of triple-tube sampling and additive drilling muds. Diamond core recovery is recorded using rock quality designation measurements with all cavities and core loss recorded. Sample recovery in some friable mineralisation may be reduced however it is unlikely to have a material impact on the reported assays for these intervals. There were no other factors that materially affected the accuracy or reliability of the results recorded. Geological logging is performed on 2m intervals for all RC drilling and either 1m or 2m intervals for diamond holes, depending on the level of detail required. Magnetic susceptibility readings are recorded for each interval. All diamond drill core is photographed. Since 2001, all drill holes have been logged geo- physically for gamma trace, calliper, gamma density, resistivity and magnetic susceptibility. Open-hole acoustic and