Gridley, NC & Salcedo, L 2013, 'Cemented paste production provides opportunity for underground ore recovery while solving tailings disposal needs', in R Jewell,  AB Fourie, J Caldwell & J Pimenta (eds), Paste 2013: Proceedings of the 16th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 431-441, https://doi.org/10.36487/ACG_rep/1363_33_Gridley
(https://papers.acg.uwa.edu.au/p/1363_33_Gridley/)
Abstract: The first application of cemented paste tailings for underground placement and subsequent ore recovery in Chile has been undertaken at the El Toqui Mine in southern Chile. The authors were closely involved in the review of tailings disposal options, the selection of the preferred option, the design and construction of the paste tailings production, the pumping and delivery system, and the system startup.
The El Toqui Mine is a long-established polymetallic mining operation located in the Aysen Region of Chile, approximately 2,000 km south of Santiago. Ore is mined underground at 1,500 to 2,000 tons per day and processed in a flotation plant; processing is followed by concentrate thickening, filtration, and shipment to offshore markets. Lead, zinc, and gold concentrates are produced. The underground mining is via two methods, with some areas being mined with the room-and-pillar method, and others in longitudinal drifts. In 2005, the company initiated investigations and studies with the intention of reviewing alternatives, and selecting a tailings disposal solution to be implemented by 2012, the time at which the existing conventional tailings disposal deposit site was expected to be reaching capacity.
As a result of option review, site investigations, and economic analyses, the company selected the paste tailings/filtered tailings option as the preferred method of management. A significant consideration was the potential for additional ore recovery in previously mined sectors. Without paste placement, the mined sectors would be abandoned with 15 to 20 per cent of the orebody remaining. With paste placement, the intention was to reduce this to between 0 and 5 per cent. The paste plant was designed, installed and put into operation over an 18 month period. The paste placement process includes pumping of tailings as slurry from the concentrator plant to the paste plant, thickening, adding cement, mixing, and pumping to deposition zones underground with positive displacement pumps. An alternative process involves filtration and placement in a dry stack after thickening. Startup challenges included stability of the thickening operation and cleaning of the delivery piping (greater than 3 km) after short shutdowns. Experience gained has enabled the company to continue to deliver cemented paste and recover pillars as planned.