Chasing a subtle mag low beneath about 1–2 m of colluvium in central Yukon, our 100 m soil grid at -80 mesh with an Olympus Vanta on pathfinders is barely resolving the Au–Cu signal. Has anyone run ultrafine fraction soils alongside handheld/drone VNIR–SWIR (tracking the 2200 nm white mica shift and illite crystallinity) and found spectral vectors to beat geochem for tightening drill collars?
And we cracked a subtle Au–Cu under about 1–2 m of colluvium by switching to ultrafine soils and running SWIR on the same dried pulps — tracking a 2205→2211 nm illite shift and a tighter 2200 nm band gave a cleaner vector than the Vanta and let us infill to 50 m. “Don’t shoot wet fines” was key; oven-dry and a quick mill first. If you want a workflow, CSIRO’s UltraFine+ is a good template: UltraFine+ – UltraFine+ Next Gen Analytics.
Quick example: we tightened a subtle Au–Cu under about 1–2 m of colluvium by switching to ultrafine (<2 µm) soils and running SWIR on the same pulps; tracking a 2207→2211 nm white‑mica shift plus a narrower Al–OH FWHM outlined the core better than the -80 mesh geochem. @ethan_p85’s point holds, but a small tweak helped us: a weak HCl rinse to strip carbonates and low-temp drying (<50 °C) kept moisture/carbonates from wobbling the band centers — like tuning a radio. If you’re drone-mapping, fly midday after a dry spell or you’ll chase a hydration signal.