Robert Gelson
Mining at depth poses many challenges for operations, requiring the adoption of unconventional and innovative solutions to achieve the best outcome.
At Xantho Extended, Golden Grove’s highest grade ore source, we encounter three main challenges which are typical in the mining of deep orebodies:
1. Maximising time at the face to achieve greater equipment utilisation and efficiency.
2. Overcoming ventilation issues caused by heat and contaminants to achieve required air quality and quantity.
3. Addressing geotechnical challenges caused by seismicity due to an increasing in-situ and post mining induced stress.
Golden Grove currently consists of two operating mines, Gossan Hill and Scuddles, producing 1.5-1.6Mtpa of ore annually. This is both copper and zinc ore which is inclusive of precious metals.
Gossan Hill is the largest of the two mines and contributes the majority of the annual production tonnes. Gossan Hill is now mining the high grade Xantho Extended orebody at a depth of 1.6 kilometres, with plans to mine to a depth of 1.8 kilometres.
The team at Golden Grove has worked exceptionally hard over the last 12 months to focus on solving these three major challenges arising from mining at depth. Our solutions have included major infrastructure upgrades, analysis of data for engineered solutions and the adoption of innovative technologies.
Maximising time at face
Time at the face, referring to operating hours for development and production activities, becomes increasingly difficult with depth due to increased travel times. Mine clearances for firings can also have a major impact.
To address this challenge, the team at Golden Grove has had tremendous success with the upgrade of the mining automation system for both underground loaders and production drill rigs.
This process included the expansion of the underground fibre network along with the upgrade of communications systems underground to permit the utilisation of the Automine system.
Automine is an autonomous and remotely operated system for mobile mining equipment in which operators can simultaneously control and monitor multiple underground machine operations from a control room. Golden Grove is utilising the Automine system for remote bogging and production drilling of underground stopes. Loaders and productiondrills are operated from surface during the period of blasting and mine re-entry. This can permit effective ‘hot seating’ of equipment with operators on surface at shift change ensuring there is minimal equipment downtime, resulting in increased operating hours for machines and improved utilisation.
This has in turn reduced idle times for the trucking fleet with greater volumes of ore being available for loading at the start of shift ensuring trucks are transporting as much material as possible during operation. These changes now place Golden Grove as one of the industry top performers for tonnes per kilometre per machine hour for our trucking fleet.
Overcoming ventilation issues
Increasing temperatures at depth is often a restriction and significant challenge to overcome in most deep mines. The team at Golden Grove resolved this by supplying chilled air directly to the bottom of the mine through rises and segregating it from the addition of heat and contaminants to permit the purest source of air to the deepest active working areas. This was accomplished by having both a forced intake and forced exhaust primary ventilation system. To do this, significant booster fans were installed in the fresh air circuit as well as having surface primary exhaust fans to overcome the large pressure differentials associated with depth. As a result, the main decline is a return airway unlike most conventional ventilation systems, where the decline is an intake.
Addressing geotechnical challenges
Seismic activity and seismic risk increases with depth requiring the adoption of seismic mitigation methods. At Golden Grove this involved resourcing the geotechnical team to gather highly detailed structural information. This information is used to design excavations and extraction sequences, along with the type of support systems applied, to limit exposure to seismic hazards and prevent disruptions to the production profile. Since this strategy was implemented over two years ago, there has essentially been no unplanned disruptions caused by major seismic activity.
Structural mapping methods are completed by geotechnical cover drilling ahead of development and face mapping. This allows us to avoid known seismically active structures, or ensures the intersection of development drives are at favourable orientations with pre-conditioning methods applied. Pre-conditioning, where drill holes are charged with explosives and fired to pre-fracture insitu rock ahead of the development face, effectively locally de-stress the strata. Stope sequencing is also analysed and modified based on the structural information. The safety of the team is of the utmost importance and applying this industry leading practice permits safe operations at depth.
These solutions applied by the team at Golden Grove have proven to be very successful in overcoming the three main challenges faced when mining at depth.
