Samples were obtained from two mine sites in Queensland, Australia, from which seventeen mesotextural groups were identified (A¨CQ). The ARDI identified mesotextural groups J (quartz¨Cpyrite) and H (quartz¨Carsenopyrite¨Cpyrite) as extremely acid forming. Routinely used geochemical classifications also identified these as the most acid forming groups. Four mesotextural groups (K¨CO) were classified as having acid neutralising capacity after full GMT classification. The remainder of mesotextural groups were classified as not acid forming. Mesotextural groups G (quartz¨Cgalena¨Csphalerite), H and J only require kinetic testing to resolve the lag-time to, and longevity of acid formation, and to measure the concentration of potentially deleterious elements released. The ARDI was not able to confidently discern between samples with the capacity to neutralise acid, and those which are not acid forming. Therefore, further refinement of the ARDI is required. However, in its current form the ARDI is suitable for mineral deposits with low-carbonate contents. This paper demonstrates its use as part of stage-one of the GMT approach at both operational and abandoned mine sites to screen and classify acid forming potential.