924 burdens, making co-disposal a potentially attractive option when supported by robust geotechnical and hydraulic characterizations. However, these approaches often require more detailed characterization and QA/QC during operations, and thus must be supported by rigorous demonstration testing to meet regulatory expectations. 2.6 Implications for Tailings Technology Selection Across all reviewed documents, a consistent conclusion emerges, regulatory frameworks are increasingly prioritizing safety, water efficiency, stability, and long-term stewardship, and are gradually disfavouring tailings technologies that rely heavily on water retention and large embankments. At the feasibility stage, operators are expected to demonstrate that they have: • evaluated multiple tailings options, • compared them using transparent and robust criteria, and • selected the method that best reduces risk and aligns with GISTM principles. This does not mandate adoption of filtered tailings; rather, it mandates a rational, defendable process. For many sites—particularly those in water-scarce, seismically active, or socially sensitive regions—filtered tailings frequently emerge as the most aligned solution. But the decision is ultimately grounded in site-specific governance expectations, risk appetite, and closure objectives. 3. COMPARATIVE EVALUATION OF THICKENED, PASTE, FILTERED, AND CO-DISPOSAL TAILINGS APPROACHES 3.1 Evaluation Framework and Criteria To provide a balanced comparison of thickened, paste, filtered, and co-disposal tailings approaches, this paper uses a set of criteria consistently applied across each option: Water recovery and water efficiency • Geotechnical stability and risk profile • Environmental footprint and permitting considerations • Capital and operating costs (including closure) • Operational complexity and reliability • Suitability for different climatic and site conditions These criteria reflect both the technical performance and the life-cycle implications of each approach. They are grounded in published comparative studies of tailings technologies, large-scale filtration case studies, and life-cycle economic analyses for Western Australian and Chilean operations, as well as conceptual evaluations of co-disposal systems. 3.2 Thickened Tailings Thickened tailings involve the use of high-density or deep cone thickeners to increase the solids concentration of the tailings stream before deposition. This produces a non-Newtonian slurry with higher yield stress than conventional slurry, which can be deposited at relatively steep beach slopes, often into a surface or in-pit facility with embankments that are smaller than those required for conventional slurry storage. Thickened tailings are commonly considered where: • water recovery is important but not critical, • site geometry still allows for a central or downstream-type embankment, and • operators seek an incremental step away from conventional slurry without a full transition to dry stacking.
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