The reclamation of potentially acid forming waste rock is site specific, being a function, among other factors, of the rock types, the dumping and storage method employed and, importantly, the climatic setting. The "store/release" cover developed to manage acid rock drainage from mineralised waste rock dumps at Kidston Gold Mines' open pit operations in the semi-arid, seasonal, sub-tropical climate of North Queensland, Australia, has been monitored for up to 9 years. The paper describes the philosophy behind the store/release cover design and its adaptation over time to suit Kidston's conditions. The results of monitoring of the store/release cover system over 9 years are presented, and estimates are made of the water balance of the store/release cover for a range of annual rainfall totals and of the overall water balance of the waste rock dumps. The Kidston story is a valuable case study of a successful approach to remediating an identified source of acid rock drainage in a semi-arid climate, which has actively engaged all Stakeholders.

The rehabilitation of potentially acid forming waste rock is site specific, being a function, among other factors, of the rock types, the dumping and storage method employed, and the climatic setting. At Kidston Gold Mine in north Queensland, Australia, a vegetated “store/release” cover was developed (Williams et al., 1997) for the flat top surfaces of the encapsulated mineralised waste rock dumps to manage acid rock drainage in this semi-arid, seasonal, sub-tropical climate. The covers were instrumented with moisture and suction sensors and lysimeters and have been monitored for up to nine years. In the first part of the paper, the philosophy behind the “store/release” cover design and its adaptation over time to suit Kidston’s conditions are described. The results of monitoring of the cover are presented, along with the data collected on seepage rates and water quality, and projected seepage rates.

Along with material characteristics and geometry, the climate in which a mine is located can have a dramatic effect on the appropriate options for rehabilitation. The paper outlines the setting, mining, milling and waste disposal at Kidston Gold Mine's open pit operations in the semi-arid climate of North Queensland, Australia, before focusing on the engineering aspects of the rehabilitation of Kidston. The mine took a holistic and proactive approach to rehabilitation, and was prepared to demonstrate a number of innovative approaches, which are described in the paper. Engineering issues that had to be addressed included the geotechnical stability and deformation of waste rock dumps, including a 240 m high in-pit dump: the construction and performance monitoring of a “store and release” cover over potentially acid forming mineralised waste rock; erosion from the side slopes of the waste rock dumps; the in-pit co-disposal of waste rock and thickened tailings; the geotechnical stability of the tailings dam wall; the potential for erosion of bare tailings; the water balance of the tailings dam; direct revegetation of the tailings; and the pit hydrology. The rehabilitation of the mine represents an important benchmark in mine site rehabilitation best practice, from which lessons applicable worldwide can be shared.