A study was undertaken to characterize a natural jarosite sample from an acid sulfate soils site and to experimentally determine the kinetics of dissolution and major ion release from jarosite under a range of different conditions. The jarosite was sourced from a degraded acid sulfate soil site that displays spatiotemporal variability in acidity on the mid north coast of NSW, Australia. Dissolution reaction rates varied as a function of solution composition but were roughly proportional to the degree of undersaturation, and the reaction pathway towards saturation was complex. The short-term reaction rates (b 12 days) decreased with increasing acidity, sulfate or iron. Over the longer term, there was a shift from congruent to incongruent dissolution, with precipitation of Fe-(OOH) solid, and with little further change in saturation index. The dissolution rates of the natural mineral were 1-3 orders of magnitude slower than experimentally determined reaction rates of synthetic jarosite samples run under similar experimental conditions, suggesting that residual solids were inhibiting reaction. The slow reaction rates of this study are probably more typical of jarosite in natural acid sulfate environments than the faster dissolution of clean synthetic jarosite. However, the shift in mechanism over a few days from near-congruent dissolution producing little acidity but much mobile Fe 3+ , to production of acidity as that Fe 3+ precipitates, indicates that acidity can readily spread from jarosite dissolving under moderately acid conditions.

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Acid and metalliferous drainage (AMD) impacts may be a cause of significant long term environmental liabilities, as evidenced on many historic mine sites containing legacy AMD issues worldwide. These historical precedents have led to AMD being recognised as a key closure risk by industry and regulators, which in turn has driven progressive advances in geochemical assessment and management in recent times. Many AMD risks on a typical mine site are based on mineral waste management strategy and practice. By association, mine planning and scheduling may therefore have a significant bearing on the potential for AMD related closure liabilities. Despite this, the assessment of AMD risk is often packaged into the environmental approvals and management process, which is often not directly connected with the mine planning and scheduling process. Consequently, AMD assessments and management plans are frequently progressed by an approvals team that is often somewhat disconnected from the mine planning and scheduling team. Subsequently, AMD management measures may be conceived after the scheduling process has moved into a more advanced and less flexible phase. Sometimes, this may be the result of a lack of early coordination and/or budget leading to a lack of hard geochemical data with which to begin classifying potentially acid forming material. Using an integrated approach to managing closure risk can be achieved via a method of assessment utilising 3D geochemical block modelling that can operate concurrently with (or within) the mine planning and scheduling process from early in the mine planning process. A more integrated approach sees AMD assessment and management being advanced concurrently with resource modelling to optimise results and minimise risk. Three case studies are presented in this paper where an integrated approach was used for conceptual closure planning through the environmental approvals stage. A further case study is presented where an integrated approach was taken to develop a mine plan. The application of this approach has so far proven encouraging.

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