Geological storage of CO₂ in deep saline aquifers is a promising strategy for reducing atmospheric emissions, but mineral-fluid reactions induced by CO₂ injection can mobilise trace metals and pose groundwater-quality risks. In June 2024, Queensland banned CO₂ storage in their part of the Great Artesian Basin due to concerns about long-term change to groundwater quality particularly the risk that dissolution of carbonate cements could release trace metals. This study evaluates trace metal behaviour in the Paaratte Formation at the Otway International Test Centre. Baseline water chemistry from CRC-3 and detailed mineralogical data from CRC-8 cores were used as inputs for reaction-path modelling. Carbonate minerals were commonly present at very low concentrations (< 1.5 wt%) and were identified as hosts of Ba, Cd, Co, Cu, Ni, Pb, and Zn. Simulations were run over a maximum of 10 years to track whether these metals remain in solution after primary carbonates dissolved or whether they adsorb onto mineral surfaces and/or co-precipitate with secondary minerals. Model results indicate that although trace metals are released during early carbonate dissolution, competing immobilisation processes quickly reduce their levels in formation waters. Sorption onto clays via ion exchange and surface complexation is a major sink, complemented by precipitation of secondary phases such as metal sulfides or, where sulfide formation is inhibited, secondary carbonates. These findings suggest that while short-term mobilisation of carbonate-hosted trace metals occurs during early CO₂ -water-rock interaction, re-incorporation mechanisms substantially reduce dissolved concentrations within a short time (~ months to years). This study highlights the importance of accounting for both mobilisation and re-incorporation pathways when evaluating potential water-quality impacts of CO₂ storage in carbonate-bearing saline aquifers.