Key Highlights

  • Maiden programme of 55 auger holes covered an area of roughly 2.0 by 1.4 kilometres at Florence.
  • Eight holes returned readings above 1,000 ppm XREO, and 32 holes returned readings above 500 ppm.
  • Laboratory assays and desorption testing are still to come before results can be confirmed.
  • Alvo is earning up to an 85 per cent interest in the project through its Brazilian subsidiary.

Alvo Minerals (ASX:ALV) reported on 6 November the first screening results from auger drilling at its Florence prospect, part of the Bluebush ionic adsorption clay heavy rare earth project in Tocantins state, Brazil. The company said the clays host rare earth elements from surface, with the most encouraging readings grouped in the western part of the area drilled.

The maiden programme comprised 55 auger holes across an area of roughly 2.0 kilometres by 1.4 kilometres, within a prospect covering about 656 hectares. Eight holes returned at least one reading above 1,000 parts per million XREO, and 32 holes had readings above 500 ppm XREO.

Understanding the numbers

These figures come from a handheld portable X-ray fluorescence instrument, not from laboratory assays. XREO is an estimate derived from the elements such a device can detect, and it is not equivalent to total rare earth oxide, or TREO, as measured by a laboratory. Portable readings are used to prioritise samples and guide follow-up drilling, but they can differ materially from assay results, particularly for elements present in low concentrations.

With that caveat, the better holes included BLH0289, which returned 5.7 metres from 1 metre at 1,393 ppm XREO, including 4.7 metres at 1,496 ppm from 2 metres. The final sample in that hole read 3,396 ppm, and the hole ended at auger refusal, meaning the base of the enriched profile was not reached. BLH0290 returned 5.5 metres from surface at 1,218 ppm, BLH0293 recorded 8 metres from surface at 1,025 ppm, and BLH0265 produced 5 metres from 2 metres at 1,004 ppm.

Not all of the ground screened as well. An eastern area, tested with 12 truck-mounted auger holes for 156.1 metres, generally returned readings below 500 ppm XREO, and the company has downgraded it as a priority.

Auger drilling is a low-cost method suited to soft, weathered material and is often used as a first step on clay-hosted rare earth projects. Its shallow reach is a limitation. Holes typically stop when they meet harder material, so the thickness of the mineralised clay beneath refusal points remains unknown. Deeper drilling, using methods able to penetrate the full weathering profile, is normally required before thickness and continuity can be estimated with confidence.

Why clay-hosted rare earths draw interest

Ionic adsorption clay deposits hold rare earths loosely bound to clay particles in weathered profiles, which can allow extraction by relatively mild leaching rather than the hard-rock crushing and cracking required for many other deposit types. Such deposits are a significant source of heavy rare earths globally. Their value depends heavily on how readily the rare earths can be desorbed, which is why grade alone is not a sufficient guide.

Managing director Rob Smakman said: "The clays host rare earths from surface, and the most encouraging readings sit in a cluster in the west." Alvo is earning up to an 85 per cent interest in the project through its Brazilian subsidiary, Lanta Resources Ltda, so its ultimate ownership depends on meeting the terms of that earn-in.

Laboratory work comes next

Samples are being sent to SGS Geosol for analysis of the full rare earth suite and for desorption testing, which will indicate what proportion of the contained rare earths can be recovered using ionic clay leaching methods. Leach testwork is also planned with ANSTO. The company said it is working towards a maiden mineral resource estimate, and laboratory results are expected over the coming months.

At this stage Florence is an early exploration target with no mineral resource, no laboratory assays and no metallurgical data. The coming assay and desorption results will determine whether the pXRF anomalies translate into rare earth grades and recoveries that support further drilling and resource definition.