Until mid-2020, the Newmont Éléonore mine cemented paste backfill (CPB) recipes were chosen from charts comparing binder contents and strengths at specific curing ages up to 56 days. However, these charts were based on Mitchells method using Éléonores biggest stope dimensions. They also did not consider any rheology, maximum surface pump pressure capacities or mix density. Using the new system, and its resulting template, backfill personnel can tailor a recipe for each stope to meet the latest sequence and environment conditions. This paper explains how the new paste recipes are selected, as well as the costs savings and productivity increases they enabled.
?Turmalina Mine has been unsuccessful on mining a high-grade thick zone of its orebody using a sublevel stoping bottom-up sequence with rock fill by having high dilution and ore losses. Being one of few mines in Brazil with a paste fill plant, Turmalina Mine that used to paste fill only open stopes in old areas saw as an alternative using paste fill on a primary and secondary stoping sequence to reduce probability of ground falls and successfully extract ore from the high-grade thick zone without leaving rib pillars, increasing recovery Empirical formulas and Map3D boundary element numerical method - were used to define needed plug and mass fill strengths to reduce risk of liquefaction, to use paste filled areas as working platforms and for vertical exposure after secondary mining with low dilution. A binder created for Turmalina tailings considering its rheological characteristics to achieve good flowability and sufficient compressive strength made possible to reach an optimal cycle, combining low binder utilization and sufficient compressive strength for each step of the cycle confirmed by uniaxial compression tests done in specimens with different binder content and ages. Filling consists of a 5% plug fill and then a 3% mass fill after a two days wait for the plug fill to reach 100kPa. Filled stope is ready to serve as a working platform after 3 days, when it reaches 170kPa. Secondary stoping is sequenced after 28 days when mass fill finishes, as it is ready to have a vertical exposure with a strength of over 500kPa. Paste fill specimens collected are tested to confirm the strengths needed before each step. By implementing paste fill in the sublevel stoping sequence, the mine is planning to control operational dilution at a maximum of 15% and increase ore recovery to 95% in the high-grade thick zone.
The long-term strength of cemented backfill mass with ordinary Portland cement binder generally decreases with sulphide content due to the formation of expansive phases such as gypsum. This paper investigates the potential of using commercial reactive MgO-activated ground granulated blast furnace slag (MgO-GGBS) in cemented backfill from high sulphide content lead-zinc mine tailings to prevent long-term strength loss. The study focuses on the effect of MgO-GGBS content and the reactive MgO dosage on the unconfined compressive strength (UCS) and the shrinkage/expansion rate. The test results showed that the 28-day UCS of cemented backfill achieved the target strength (?1.0 MPa) with 14 wt% MgO-GGBS content, and the reactive MgO dosage affected the long-term UCS and the shrinkage/expansion rate of cemented backfill body. The main hydration products when using MgO-GGBS were hydrated calcium/magnesium silicate (C-S-H/M-S-H) and hydrotalcite-like phases (Ht). Cemented backfill has a porous opening microstructure. Micro-expansion produced by appropriate MgO content can increase microstructure density, which increases short- and longterm UCS of cemented backfill body, while sustained expansion produced by excessive MgO could destroy the MgO-GGBS microstructure, decreasing the UCS of cemented backfill. We conclude that the mechanical and extension properties of cemented backfill body are highly dependent on the reactive MgO content of the MgO-GGBS. The optimum value of responsive MgO content of MgO-GGBS was 2.57.5 wt% to achieve the long-term stability of cemented backfill.