Dugald River trial stoping, overall hanging wall behaviour

Abstract

Concerns regarding the uncertainty of stope dilution at MMG Limited's Dugald River Underground Mine led to a trial stoping program to acquire full-scale comprehensive geotechnical information and to test the validity of the proposed geotechnical and mining parameters. As part of the trial, a geotechnical instrumentation program was designed to improve the understanding of the rock mass response to the mining of the trial stopes. This included an array of instruments installed from dedicated hanging wall drives, hanging walls that included 66 multipoint borehole extensometers (MPBX), 23 time domain reflectometers, 24 geophones, six accelerometers and 15 observation holes. Trial mining consisted of 19 sublevel open stopes with cemented rockfill (CRF) that extracted 335 kt of ore, with a panel height of 130 m and strike of 100 m. All stopes were monitored with a minimum of two MPBXs at the open span with a MPBX average density in the panel hanging wall of 180 m 2. The MPBXs were 19 m in length and consisted of six nodes. Instrument displacement information was recorded every 30 minutes by dataloggers to a resolution of 0.12 mm. This provided a high quality, detailed and extensive rock mass response to stope extraction. The displacements were interpreted as hanging wall relaxation and shear on structure from specific stope firing and expansion of the mining front. Rock mass creep was also recorded in the hanging wall. The mechanism of displacement consisted mainly of strike-slip movement on high angle bedding and faults that are orientated sub-parallel to the dip of the orebody. Overall hanging wall behaviour was assessed by investigating the near (stope hanging wall boundary to 6 m) and far (>6 m from stope boundary) displacements as the sequence progressed. The primary rock mass response stage was the extraction of the crown pillar. The secondary responses were associated with the cable bolt arrays mitigating some of the deformation of the hanging walls with more movement mid-span compared to the cable bolt horizon. Finally, the displacement results post-filling showed the backfill mass was being slightly compacted by ground movement.

Assessing stope performance using georeferenced octrees and multivariate analysis

“…The data used in this paper are from the underground Dugald River mine in Queensland, Australia (Figure 9). Longitudinal and transversal stopes are used to extract the Zn-Pb Ag ore. Stope dimensions can vary depending on the area of the mine but are approximately 25 m high and 15–30 m long (Hassell et al 2015). Stope width varies between 2 and 35 m depending on the thickness of the orebody.…”

“…Of these 173 stopes, 41 are a part of the north area of the mine and 132 are a part of the south part of the mine. Nineteen stopes were also part of the 2014 trial stoping stage that was conducted to test the validity of the geotechnical and mining parameters (Hassell et al 2015). For the analysis, the 2014 trial stoping, as well as stopes with data quality concerns, has been removed resulting in a total of 130 stopes.…”

Dugald River case study — the importance of understanding your orebody and designing your mine for maximum value

“…More detailed descriptions of the trial stoping program and outcomes can be found in de Vries et al (2015), Hassell et al (2015a;2015b) and Carswell et al (2015). Key mine design and scheduling parameters were established, including:…”

Reduction of ore dilution when mining low-thickness ore bodies by means of artificial maintenance of the mined-out area

“…The authors in the studies [34], [35] argue that, when adhered to the fastening technology, cable bolts are an effective method to manage ore dilution when mining low-thickness ore deposits by mining systems with an open stope space. D.R.…”