Ouellet, S & Brunet, F 2010, 'Design of the paste backfill recipe for the Pinos Altos Mine, Mexico — influence of tailings clay mineral fraction on strength and rheology', in R Jewell & AB Fourie (eds), Paste 2010: Proceedings of the Thirteenth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 217-227, https://doi.org/10.36487/ACG_rep/1063_19_Ouellet
(https://papers.acg.uwa.edu.au/p/1063_19_Ouellet/)
Abstract: Agnico-Eagle Mexico S.A. de C.V. (AEM) plans to commission a new paste backfill plant at the Pinos Altos 
mine (Mexico) in March 2010. In 2008–2009, the paste recipe was designed to develop required strength for 
free standing of the backfill in stope after 28 days. This recipe development was not as easy as usual because 
the tailings contain a significant proportion of clayey minerals and these cohesive minerals control the 
rheology of tailings. This paper presents the different laboratory investigations performed to achieve the 
required strength considering the flow characteristics of the tailings. 
The paste recipe design was performed in two phases. The first one included testing of different paste recipes 
with varying water and binder (Chihuahua cement) content. The main investigation of the rheology 
(laboratory rheometer tests) of the paste was performed during this phase. The second phase was carried out 
to optimise the paste recipe by changing different ingredients to improve the geomechanical properties 
considering the clay mineral content in tailings. Tests with slag (Lafarge Canada), with deslimed tailings 
and with water reducing admixtures (BASF Glenium 7700™ and 7102™) were performed (Glenium 7102 
and 7700 are trademarks from BASF Construction Chemicals). In this phase, five backfill samples were also 
cured under 300 kPa of vertical pressure, which is similar to the one estimated at the bottom of a typical 
stope.  
Among mixtures tested, paste with 7% Chihuahua cement/71% solids and paste with 7% Chihuahua cement 
and Lafarge Slag in a 20:80 proportion/71% solids gave the best results. These mixtures were selected for 
tests under vertical pressure and results showed significant strength increases at 28 curing days relative to 
the standards. Thus, significant strength increase is expected in stope due to consolidation relative to 
laboratory results. Tests with deslimed tailings and admixtures were not conclusive, and these options to 
increase strength were not retained. The rheological measurements performed on all mixtures tested showed 
a Bingham plastic behaviour. A clear influence of the water and binder content were observed on the yield 
stress of the paste.