Assessment and Control of Ore Dilution in Long Hole Mining: Case Studies

Abstract

Unplanned ore dilution has a direct and large influence on the cost of a stope, and ultimately on the profitability of a mining operation. This paper presents the results of an examination of factors influencing ore dilution in a blasthole stoping environment. For the study, a comprehensive database was established, incorporating information related to the design, construction, excavation and cavity surveys of 172 sequentially mined long hole stope case histories from two orezones. Through a review of the case studies, it was demonstrated that, in addition to stope dimension, the amount of unplanned dilution differed according to stope type. Five stope types were identified, based on their position within a tabular blasthole mining sequence. Measured overbreak varies with stope type, with secondary stopes generating a greater volume of hanging-wall dilution than do primary stopes. Furthermore, a case study is presented to demonstrate the role cablebolts installed in the stope hanging-wall play to control ore dilution. The study illustrates relationships between measured hangingwall overbreak, cablebolt orientation and stope type.

Strategies for surface crown pillar design using numerical modelling – A case study

“…Similar trends were previously reported in the field by Henning & Mitri (2008); the measured 172 stope overbreak histories at the Bousquet #2 mine showed a positive correlation between stope volume and stope exposure time.…”

“…The overbreak that occurs in lower-level stopes extends the relaxation/unstressed zone, showing well-known stress shadow effect, which could enlarge the HW overbreak volume in the current level. Henning & Mitri (2008) analyzed HW dilution data measured by the Cavity Monitoring System (CMS) at the Bousquet #2 mine. It was found primary stopes above different heights of backfilled zones exhibit the different overbreak volume due to differing stress settings.…”

Unplanned dilution and ore loss prediction in longhole stoping mines via multiple regression and artificial neural network analyses

“…The importance of unplanned dilution and ore loss control has been emphasized by many researchers. Tatman (2001) reported that reducing unplanned dilution is the most effective way to increase mine profits, and Henning and Mitri (2008) stressed the significant influence of unplanned dilution on the profitability of mining operations. More specifically, in 2008, Stewart and Trueman (2008) reported that unplanned dilution costs A$25 per ton, compared with A$7 per ton for mucking and haulage, and A$18 per ton for milling in typical narrow-vein longhole stoping operations.…”

“…The contour of the relaxation zone (σ 3 = 0) remained nearly constant, while the potential overbreak associated with the rock mass tensile strength increased with depth for a given stope geometry or hangingwall dip. Subsequently, the influence of the mining sequencing on blast-hole stoping dilution was studied (Henning and Mitri, 2008) in 172 sequentially mined longhole stopes. The authors concluded that the overbreak significantly increased in stopes that had one or more backfilled walls.…”

Factors Influencing Stope Hanging Wall Stability and Ore Dilution in Narrow-Vein Deposits: Part 1

“…Consequently, it increases direct and indirect costs and reduces overall mine profitability (Henning and Mitri 2008;Henning 2007). The direct costs of dilution include mucking, hauling, crushing, hoisting, and milling costs, which have been estimated at $20-40/tonne (Wang 2004;Yao et al 1999;Dunne et al 1996;Anderson and Grebenc 1995).…”