The reliable prediction or management of beach slope and stack geometry is integral to realisation of the potential benefits of thickened tailings technology. Stack geometry not only controls the storage capacity for a given footprint, but also strongly influences post-deposition geotechnical and geoenvironmental performance. Unfortunately, accurate prediction in design has proved difficult. However, there has been significant improvement in understanding the behaviour of tailings after they exit the pipe, and a number of methods for beach slope prediction have been proposed and developed. This paper reviews a selection of these methods, and examines their applicability to different deposition scenarios. Some recommendations are made to assist engineers and operators to achieve a given stack geometry.

Prediction of the beach profile of tailings using stream power has been in application for conventional tailings since 1995. Extension of this methodology to high density thickened tailings has been evaluated through the scaling up of flume testing as well as in the prediction of beach profiles from raw rheological data. This paper describes the stream power methodology and the results of the evaluations.

CODELCO is considering the implementation of high density tailings management at their Chuquicamata mine in northern Chile for its long term disposal plan. To achieve this, CODELCO commissioned the design, construction and operation of a 70 tonne/day pilot plant, fed by existing tailings. The testing programme was completed in May 2011 and consisted of laboratory rheological and characterisation assessments, pipe loop testing, beaching trials and analyses of deposition behaviour for solid contents ranging from 57-68% (w/w). This paper describes the characteristics of the pilot plant, the testing programme, the beach trial analyses and the resulting beach profile predictions based on the Stream Power theory. CODELCO also used other predictive beach slope methods, such as the Equilibrium Slope concept, which are not discussed in this paper. The final beach profile for design will be selected after an expert analysis of all methods has been completed. The fundamental objectives of the pilot plant were to determine the deposition behaviour of the tailings at concentrations of 57% (as currently produced), 63, 65 and 68% solids (w/w) and to assess thickener performance to achieve these concentrations. The key components of the pilot plant are summarised as follows and identified in Figure 1:  Pilot paste thickener (2.5 m diameter, 11 m high): Designed and operated by Outotec, with a maximum capacity of 70 tonne/day.  Pipe loops: Designed and operated by P&C. Two pipe loops of 3 and 4 inch diameter (7.6 cm and 10.2 cm) were assembled to allow operation of three configurations (78 m of 7.6 cm, 80 m of https://papers.acg.uwa.edu.au/p/1263_17_Engels/ Evaluation of the behaviour of high density tailings deposition-CODELCO pilot plant J. Engels et al.

Chinova Resources Pty Ltd's Osborne Mine is located in Northern Queensland, approximately 800 km inland from the eastern coast. It commenced operations in 1995 with the development of an open pit mine. In 1996, the operation transitioned to underground mining. In 2015, Osborne will have been in operation for 20 years and will have mined 29 Mt of ore. The site has produced 672, 420 t of copper and 673,295 oz of gold. Osborne Mine produces approximately 112,000 t of tailings per month. In 2003, following progressive evaluation and development of a high-density discharge tailings management system, Osborne implemented the first of two trial depositions forming advancing cones of deposited tailings within their TSF2 site. These trials proved successful and, following successful permit applications to the regulators, TSF2 was converted to high-density thickened tailings discharge. The principal benefit of this change was in the reduction of construction costs for confining embankments. However, an additional major benefit lay in a reduction of make-up water volumes. The majority of water loss in the process water circuit occurs in the tailings system as a result of evaporation. High-density thickened discharge provides a means for significantly reducing water losses, since, by recovering and re-using more water at the thickener and in the plant, less water is discharged onto the tailings facility so there is less water available for evaporation. High-density thickened discharge also enabled a significant improvement in operating costs. High-density thickened discharge operations at Osborne have had to be continuously modified and adjusted as ores from satellite mines have been processed to supplement the diminishing Osborne Mine ore. Mineralogical influences of the supplementary ore significantly affect the thickening and beaching characteristics of the tailings slurry, particularly in the most recent operating period. However, through appropriate modifications and adjustments, the benefits of high-density thickened discharge have been retained. The resulting tailings storage facility (TSF) landform is that of a shallow-sloped shedding mound so that there is no need to retain water on the TSF. Chinova has been proactive with ongoing site monitoring and rehabilitation with a view to shedding runoff to the environment. Their site plans include ensuring that the discharge water from the site will meet the stock-water guidelines, and that the erosion gullies forming in TSF cover materials or on the side slopes of confining embankments will not result in exposure of the tailings over 500 years.

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