Representative, high-spatial resolution geochemistry from diamond drill fines (powders): An example from Brukunga, Adelaide, South Australia

• Drill fines produced diamond drilling are proposed as a new sample medium.
• These drill fines are representative of the lithology intersected by the drill hole.
• The drill fines are transported fast enough to avoid any lag and the depth is accurate.
• The drill fines can be analysed by portable XRF-XRD sensors in near-real time.
• The data can be used to constrain lithologies, alteration and ore types in near-real time.

The analysis of drill powders (drill fines) extracted from fluid that is returned during drilling can provide a sampling media that records cm-scale changes in the geochemistry of the rock being drilled through. In addition to being an ideal sample media (~ 78% of particles are < 38 μm; cf. conventionally pulverised samples where ~ 42% of particles are < 38 μm) that is ready for analysis once dried, diamond drill fines may produce a larger sample per meter drilled than recovered by the core itself, and thus be a better representation of the rock that has been drilled through. For an HQ hole size (for rocks with specific gravity = 3100 kg/m3), the mass of drill fines produced in 1 m of drilling is 12.5 kg, whereas, the mass of the 1 m in length of core for the same interval is 9.7 kg. In this contribution we compare high-spatial resolution geochemistry collected by portable X-ray fluorescence (pXRF) and mineralogy collected by portable X-ray diffraction (pXRD) from 12 m of diamond drill core to the corresponding interval of drill fines to highlight the depth fidelity (at the cm-scale) that this sample source may record. We also demonstrate that the drill fines that were previously discarded show high potential to act as a representative sample media of the lithology intersected by the drill hole and can be successfully used for analysis in real time. The integrated pXRF-pXRD data can be used to constrain lithologies and contacts between various units, hydrothermal alteration and ore types.