Peralkaline igneous rocks are important parental materials for secondary, regolith-hosted ion-adsorption critical metal deposits. Little work has been completed to assess the potential for this style of mineralisation in Queensland. Here, we present the results of a simple reconnaissance study aimed at evaluating the relative enrichment of rare earth elements (REE) and other high field strength elements (HFSE) in soils proximal to an alkali-rich igneous unit. The Crows Nest region of southeast Queensland was chosen for this study due to accessibility and the observation of deep weathering and soil development associated with the Cooby Trachyte Member; a near-peralkaline felsic unit that exhibits minor enrichment in REE and HFSE. Soil from different depths and parental fresh rock samples were collected from six sites and analysed for major and trace element geochemistry. Other samples of fresh basalt and trachyte were collected from across the area as background samples. One site was interpreted to comprise soil associated with mafic rocks of the Main Range Volcanics while the remainder were developed on the Cooby Trachyte Member. While the degree of weathering/leaching between these sites was variable, the majority showed minor enrichment of REE and HFSE in soils relative to fresh rock. Some sites showed strong correlation between REE and Al2O3 consistent with clay-hosted enrichment, while others exhibited geochemical characteristics more likely associated with detrital accumulation of resistate accessory mineral phases. Consistent geochemical variations with depth at individual sites was not observed.

The broader aim of this work was to assess the potential for ion-adsorption REE deposits in Queensland and to our knowledge, this is the first such investigation undertaken in the state. Future work on samples from our study should include a thorough assessment of soil mineralogy, geochemistry focused on the clay-sized fraction and an investigation of accessory phase mineralogy in fresh rocks. More broadly, the results from this simple pilot study warrant completion of a similar project, with better depth control and in an area associated with more highly peralkaline (and more REE-enriched) parental rock units.