Balancing Production & Environmental Issues at the Mesa A Mine (Rio Tinto)
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Mining IQ Editorial
Posted: 02/02/2012 12:00:00 AM EST | 0
Mining IQ: What are the major environmental issues at the mine site(s) you currently work on?
Posted: 02/02/2012 12:00:00 AM EST | 0
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John Giovannetti is the Senior Production Engineer/ Registered Quarry Manager - Mesa A, Operations Planning at Rio Tinto, speaks to Mining IQ about how his team manage environmental issues, vibrations and balance this with the urgent need for improved production.
John Giovannetti is presenting at the Environmental Management in Mining 2012 Perth event. For more event information, please visit www.environmentalmining.com.au, call 02 9229 1000 or email enquire@iqpc.com.au
Mining IQ: What are the major environmental issues at the mine site(s) you currently work on?
John Giovannetti: There are always a multitude of environmental issues that any mine site faces. These may be behind the scenes/ongoing issues that are part of our day to day operations, or the more high level issues which are allocated EIPs (Environmental Improvement Projects). Currently the drill and blast department at the Robe Valley are involved in an EIP to minimise the impacts on the MEZ (Mining Exclusion Zone) from blasting practices at Mesa A, and to implement a program of vibration monitoring at our established Mesa K deposit.
The project regarding the vibration impacts on the MEZ has been ongoing since the commencement of mining operations in March 2003. This MEZ was identified and defined during the approvals stage of the operation, and is a result of the discovery of troglofauna species that are believed to be unique to each outcropping Mesa A. This project is unique (to the best of my knowledge) within the Pilbara region. It is complicated that in general, when there is an avoidance zone in a mining operation a buffer zone is established to prevent inadvertent access; in the case of Mesa A, the avoidance zone and the pit shell are one in the same, meaning that mining has to be ‘centimetre perfect.’ This is certainly a challenge when using powerful explosives and large mining equipment.
Mining IQ: What sort of strategies does Rio Tinto (or your mine site) have to minimize the damage to the habitat whilst keeping production on track?
JG: There have been several strategies that have been implemented to preserve this habitat. These include:
• A comprehensive permit procedure for any clearing work to be conducted adjacent to the MEZ. Rio Tinto Iron Ore (RTIO) has established land clearance flowcharts to track the progress of any land disturbance, ensuring no land without approval is cleared. However, due to the sensitive nature of this area and the zero tolerance for error, the production and environment teams on site have improved the robustness of this system.
• In order to ensure this area is not adversely impacted by blast damage, standard production holes are not used within a predetermined distance from the MEZ. In order to effectively fragment the material (to enable productive mining) and preserve troglofauna habitat, the hole diameter is reduced significantly. This allows for more even charge distribution, and most critically less explosive initiating at a given point in time, which is one of the most important considerations for ground vibration.
• Every person who works on site undergoes a ‘MEZ induction’ to ensure they are familiar with the location and importance of this area. This is a qualification that employees must keep current.
• If there is an incident involving the MEZ (regardless of how minor it is perceived to be) an incident report is raised, and this is communicated to all the production/drill and blast crews, again to highlight the significance of this area.
• In order to ensure this area is not adversely impacted by blast damage, standard production holes are not used within a predetermined distance from the MEZ. In order to effectively fragment the material (to enable productive mining) and preserve troglofauna habitat, the hole diameter is reduced significantly. This allows for more even charge distribution, and most critically less explosive initiating at a given point in time, which is one of the most important considerations for ground vibration.
• Every person who works on site undergoes a ‘MEZ induction’ to ensure they are familiar with the location and importance of this area. This is a qualification that employees must keep current.
• If there is an incident involving the MEZ (regardless of how minor it is perceived to be) an incident report is raised, and this is communicated to all the production/drill and blast crews, again to highlight the significance of this area.
Mining IQ: What has been the most effective strategy here? Why do you think this is and how can other mine sites learn from your experience?
JG: The permit system for any clearing around the MEZ has definitely been a success for production. It is fairly manually intensive, however this is necessary for quality results. I do however think the entire trim blasting project has been a huge success. Whilst it is an expensive way to mine (as a general rule of thumb, the more holes you have to drill, the higher the cost per tonne for breakage), it is the only way to preserve the MEZ. Several consultants have been involved in the process to ensure maximum recovery with minimal disturbance to the MEZ. Initial trials were carried out away from final MEZ wall with varying levels of success. The first stage of trim blasting adjacent to the MEZ boundary is 75% complete (as at 6/10/2011) and should be complete by the end of November. The design has been modified with every shot to ensure improved results every time, whilst avoiding damage to the final walls.
I believe we have fairly robust systems with regards to the high sensitivity blasting, both in terms of monitoring and in terms of the results we are achieving. I believe other mine sites with similar sensitivity issues could achieve good results by implementing similar processes (including vibration analysis).
Mining IQ: How has your mine site managed vibrations during the mining process? What were the challenges here?
JG: The main strategy in managing vibrations is based around using smaller diameter drill holes. Ground vibration (in it’s simplest form) is a function of distance and Maximum Instantaneous Charge (MIC), which refers to the amount of explosives initiating at any particular time. This has not been easy as in order to reduce the MIC the hole diameter must be reduced, which means more holes, which in turn means increased drilling meterage, blasting accessories, and labour costs. This is compounded by the fact that site does not have a drill capable of such small diameters, and hence a contractor rig was required.
There have been changes in pattern design (hole diameters, burden and spacings), charging configurations, the timing of initiations, firing to free faces, firing with production shots, and firing MEZ adjacent shots into broken ground. As well as this deeper areas of the pit have been blasted using ‘shatter rows,’ which basically aims to create a discontinuous zone between the MEZ and a production shot, which in turn restricts the ability for vibration to pass into the MEZ.
Wherever possible (approximately 80-90% of the time) the vibrations from blasts are measured using near field vibration monitoring equipment. This data is stored and used to refine vibration prediction calculations for future blasts.
Mining IQ: When it comes to dust and noise control, what do you think are the best practices? Where do most companies fall short on in this regards?
JG: Dust and noise control are perhaps a less critical issue in the Pilbara than they are in highly populated areas such as the Hunter Valley. Nevertheless, the need to minimise dust emissions is important at Mesa A due to the close proximity to a major road (the North West Coastal Highway). A significant amount of effort is put into preserving the aesthetics of the natural environment by maintaining the façade of the Mesa; any significant dust generated from mining operations may have an adverse effect on the general public’s perception of mining and hence must be controlled.
Historical vibration measurement (up until June 2011) included an air overpressure reading, which enabled the calculated of noise generated from blasting. A series of measurements indicated that the noise was well below acceptable levels, and hence with the adoption of more accurate vibration measuring equipment (without this capability), these measurements were discontinued.
There are a series of dust monitors throughout the mine and the campsite to measure respirable dust levels and ensure compliance. Blasts are also recorded, which enables observation of dust generation if required.
I believe some companies operating in remote areas may dismiss noise and dust generation as not being important due to the distance from established populations and the general public; however controls must be put in place to minimise the adverse effects of noise and dust on employees, as well as the surrounding natural environment.
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