Multivariate compositional analysis of groundwater geochemistry in the Georgina Basin: New insights for sediment-hosted mineral systems

The Georgina Basin in northern Australia holds significant potential for strategic minerals, particularly zinc and phosphate, which are crucial for Australia's economy and transition to net-zero. This study applied multivariate statistical tools to groundwater geochemistry from the basin's regional Cambrian Limestone Aquifer to investigate the prospectivity of sediment-hosted phosphate and Zn–Pb mineral systems in the northern half of the Georgina Basin. Robust principal component analysis (rPCA) identified Mo and I⁻ (as well as Rb and Al) as key elements associated with the variation of P in groundwater. K-means cluster analysis then mapped a subset of spatial clusters where these P relationships were evident. This investigation culminated in the creation of a new geochemical index (Phos#) for identifying hydrogeochemical anomalies likely sourced from phosphate mineralisation. Five areas were deemed most prospective using Phos#: three near Elliott, and one in each of the Central Georgina and Undilla Sub-basins.

The hydrogeochemistry was also valuable in detecting regional sediment-hosted Zn–Pb mineralisation. Radiogenic Pb-isotope outliers (²⁰⁶Pb/²⁰⁴Pb of 22.00 to 24.00) in the Alexandria-Wonarah Basement High and Undilla Sub-basin (which were supported by elevated Pb or Zn in groundwater), were spatially correlated with observed sulfides at the surface or in drillholes and consistent with the radiogenic Pb-isotope signature of Georgina Basin's Joplin-type, Mississippi Valley Type Zn–Pb mineralisation.

This regional in-depth assessment of the groundwater chemistry provides an efficient scale-reduction tool with clear targets for follow-up, and is supported by a discussion on how this multivariate, index-based approach can be translated to other sedimentary basins and/or mineralisation assemblages.