The effect of automated mining on the occupational environment
From the proceedings of the MVSSA 2013 conference: The Art of Precision
Underground mining has changed dramatically over the last century reaching depths in excess of four kilometres. Mining operations are continuously looking for new ways in terms of technology to remove people from risk while going even deeper. But, with new technology comes new risks. This paper gives an outline of a project by AngloGold Ashanti (AGA) to mine gold without people through technology and innovation, highlighting the challenges and solutions on the effect of automated mining on the occupational environment.
AngloGold Ashanti South African operations are facing significant challenges and a breakthrough in the operating paradigm is required.
The challenges are:
- Undesirable safety performance
- Declining gold production
- Rising unit costs
- Leaving up to 40% gold behind in pillars
- Diluting the ore by more than 200%
- Mining only 75% of available shifts.
Longer term sustainability will require new technology that will reduce human risk, migrate to a technology intensive business and open up a competitive advantage.
Creating a new mining paradigm
The first steps towards a new mining paradigm will focus on:
- Stop blasting
- Remove people from high risk tasks
- Build a continuous operation
- Maximise the resource.
Technology will be used to drive this change in order to safely mine all the gold, just the gold, all the time. The ocus will be on three dominant projects namely, speed of development, stop blasting and remove people from the face and efficient logistics.
Optimising the foundations will lead to safe operations, real time communication (everyone knows everything all the time), one source of information, reduce energy intensity and automation. All this will enable the operations to mine everything, 365 days a year, 24 hours a day and only the reef (no dilution).
It was realised that most sustainable advances in business performance have usually been delivered through technology change. A consortium could be defined as “an association of two or more individuals, companies, organizations or governments (or any combination of these entities) with the objective of participating in a common activity or pooling their resources for achieving a common goal”.
By following the consortium approach the following benefits will be clear:
- It brings speed and diversity of team members and a proven track record;
- Reduce risk through sharing, and practical experience of team;
- Leverage entrepreneurial incentive of team; and
- Cover the complete range of attributes required to make a breakthrough.
“Open innovation is a paradigm that assumes that firms can and should use external ideas as well as internal ideas, and internal and external paths to market, as the firms look to advance their technology”.
The characteristics of this type of open innovation approach in a consortium could be listed as:
- Define the problems with a wide group of suppliers and potential suppliers.
- Create teams to develop projects and technologies.
The open innovation approach certainly has its strengths and weaknesses.
- Greater potential for unimagined technologies.
- No immediate funding.
- Not based on our understanding of the world.
- Messy process.
- Difficult to ensure that the right companies are participating on the right teams.
- Ambiguity frustrates expectations.
The AngloGold Ashanti Technology and Innovation Consortium, called ATIC, was formed during 2011. It involved more than thirty companies and eighty participants including universities, manufacturers, suppliers, engineering design companies, research and development institutes, technology platform providers and many others.
Initially fifteen teams were set up covering the different aspects of mining:
The roadmap follows three stages:
- Stage 1- No people in stope:
- No drill & blast
- Remote stoping
- Continuous processes
- On-reef exploration and development
- Mechanical mining
- Tunnel boring machine development
- Reef-height stoping
- Consistent rock size at face
- Ore hoisted, backfill sent down
- Immediate high strength backfill
- Containers for material & people
- Reduced water use
- Energy savings
- Accurate information and data management.
- Stage 2 – Intelligent mining:
- People only for control & maintenance
- Closed loop real time process optimization
- Low force fracturing
- Exploration & development in same step
- Underground concentration
- Backfill stays underground
- Hydro hoisting ore
- Hot mine (ventilation on demand)
- UG water recirculation
- No fresh water going down
- Mine knowledge management, weather map.
- Stage 3 – Gold on tap:
- No people underground
- No people underground
- ISL: in-situ leaching
- Ore fractured but not moved
- Autonomous drilling: exploration & production transport in single step
- Real time accurate ore grade measurement at face
- Continuous backfill or support
- Solution pumped or container transported
- Beneficiated water for economic use on surface
- Geothermal surplus power produced
- Coordination by mine knowledge system.
Thirteen groups were formed and allocated into two project groups, namely critical success projects and second order projects as set out below:
Critical success projects
- Mine Design and Analysis
- Prototype block
- RC Drilling incl. Coring vs. Chipping
- Machines for Development
- TBM (Declines)
- HBM (Haulages and Drives)
- Machines for Stoping
- Conventional Raise Borer (Robbins)
- Clara Rig Box hole Borer (Herrenkn.)
- Reef Borer (Wassara/Cubex/Sandvik)
- Slot Borer (Atlas Copco)
- Material Handling ¡V Continuous Processing
- Backfill Design & Sys. Architecture
Second order projects
- Site Preparation
- Site Development
- Information Technology
- IT Backbone
- Hydro Hoisting Study
- Vortex Commination
- Clean and Dirty Water Study incl. Closed Loop Water Filtration
- Ventilation on Demand incl. Filters and Air Locks
- Seismometer Implementation
- ISL Rock Mechanics Software
- ISL Rock Fracturing Study
A matrix was developed incorporating the phases into stages with specific emphasis on each group.
The example below depicts the identified projects within the Environmental group.
Gold on tap
No people in slope
Safe & Reliable
Optimized & Advanced
Figure 4: Roadmap matrix – ventilation
Critical success projects
An initial “Blueprint” was developed based on a mined out section of Mponeng mine. The mine design for the “new” block of ground underwent eighteen iterations for full optimisation.
The new mine design will cater for Tunnel Boring machines (TBM) to develop the main inclines and Haulage Boring Machines (HBM) for developing the reef drives. Smaller Reef Boring Machines (RBM) will be utilized to extract the ore.
The blueprint values for the new mine designs were listed as:
- Simple footwall development 70m under reef
- Most development will be on reef
- Declines will be 4.2m diameter
- Exploration drives will be 4.2m diameter
- Reef drives will be 2.8m diameter
- Drive spacing will be similar to conventional
- Reef boring will be 1.0m diameter.
The optimisation exercise was to determine the full potential of extracting gold with minimum dilution and leaving the least amount of gold behind.
|Maximum gradient (degrees)||8|
|HBM maximum turning radius (m)||150|
|Reef drive spacing (m) (measured on dip skinto-skin)||30|
|Reef drive gradient (percent) (measured above strike)||2|
|Average working days per month||23|
|Geological loss (%)||75|
|Reef boring extraction (%)||78.6|
|Mine Call Factor (%)||70|
Figure 7: Salient design parameters
Exploration and ore body analysis
Knowledge of the geological settings and associated ore-body characteristics ahead of the face, particularly ore-body geometry, represent crucial input parameters for optimal tunnels placement and confident ore-body extraction. The objective of the project was aimed at proving the concept of utilizing enhanced reverse circulation [RC] drilling technology (Megamatic 6 200N) to achieve a dense orebody intersection pattern (intersections being 30m apart) at significantly higher drill advance rates, when compared to conventional, underground diamond drilling. The second part was to test an inhole camera.
A Megamatic 6 200N machine was imported from the USA and testing commenced at Tau Tona mine.
The in-hole camera was tested in a down-hole at Mponeng and despite grease being present along the sidewalls of the hole, hampering camera performance, the images depicted volcanic rock characteristics in great detail and at high resolution.
Machines for development
The approach the group took in identifying machines for development was to look at the available technology on the market, within and outside the mining industry (with some focus given to the civil engineering industry), that could possibly meet the underground development requirements.
The focus was on technology that was currently employed, i.e. proven technologies and therefore not in a development stage, even if in other industries. Among all the cutting technologies evaluated, full face tunnel boring was the only existing and proven technology on the market.
A set of agreed requirements was developed after much interaction with other groups and prospective suppliers / manufacturers (particularly Herrenknecht) for both the HBM (Haulage Boring Machine) and TBM (Tunnel Boring Machine).
These requirements are to be surveyed in the market to determine whether there are machines readily available that can fulfil the requirements with minimum or no design development and testing required.
Such machines from different suppliers / manufacturers will then be evaluated by performing a Technology Readiness Assessment to ascertain the readiness and maturity of each for near term deployment.
The above approach will ensure that requirements are controlled and possible supply risks are identified and mitigated in time with the rest of the mining system design.
A context diagram was drawn up and used to determine all the requirements, their interdependencies and interfaces with other systems such as required by vertical integration and mine design.
A comprehensive set of approximately 244 requirements was compiled for the TBM and HBM which will be used to compile the final Design Criteria for the TBM and HBM.
Machines for stoping
As with the TBM and HBM, the group undertook to identify existing technology for the extraction of reef. The concept is similar to the TBM but on a much smaller scale. The optimum hole diameter was identified to be between 800mm and 1000mm.
The trial would include the boring of six holes extracting the reef. The trials at TauTona were completed for four out of the six trial reef bore holes. The approximate total volume bored is 70m 3. Gold recovered from the four holes was 14 966 grams.
One of the biggest challenges was the control of Silica dust during boring operations. A vacuum sucking unit was identified and trials on the efficiency of dust control will be commenced.
The group’s objectives were to investigate the transport of ore and material. Criteria were laid down and comparisons made between the current available technologies. The ore transport system had to comply with the following design criteria:
- Volume flows up to 500 m 3/h
- Inclinations up to 35°
- Flexible in routing
- Different loading and discharge points
- Mobile System
The final decision was to investigate the railveyor system further due to small size and flexibility.
A similar exercise was performed to identify material handling options. The following criteria were identified:
- 18 – 50 tons payloads
- Inclinations up to 25%
- 8 m turning radius
- Ability to crab
- Drivable from both ends
- Can operate in tunnels from Ø3m and larger
The scope included the development of a cost effective, ultra-fill backfill “recipe”, which on curing will attain a 200MPa strength, in order to prove the idea that stress changes in the in-situ rock mass at depth of over 5 000 m can be minimised.
This will require the manufacture, in-the-hole placement and curing of the backfill to replace the ore removed by drilling, in the quickest possible time.
A curing time of seven days was set as a target and thus far this seems to be achievable with the latest backfill recipes in laboratory tests.
Second order projects
The scope of the group was to achieve the design criteria with integration of the new mining concept into the current infrastructure. The water reticulation system was designed and the objective achieved. A need was identified for an interface shell-and-tube heat exchanger between the mine chilled water (Primary Circuit) and the HBM & RBMs water cooling (Secondary Circuit). The required duty would be 1 193 kW.
The boring machines require a high quality of water for the cooling systems and a filter system has to be designed to obtain the specifications.
As with the water group, the objective was to confirm whether the new mining method can be ventilated within the current infrastructure of the mine.
The conclusion was that it is possible based on the Mponeng blueprint but a huge amount of air would be required due to the large excavations and heat load from the tunnel boring machines. The VUMA software was utilised for simulating all different iterations of the mine design.
In order to achieve the design parameters with one TBM, two HBMs and four RBMs a minimum of 150m 3/s of air would be required.
The 5m diameter haulages would require as a minimum a 75kW fan with a 1200mm ventilation column. For size optimisation it was decided to settle on the twin-duct plastic ventilation column.
A cassette system was designed and built locally that would be fitted on the TBM containing 100m of ventilation ducting extending the column as the TBM moves forward. The cassette was designed for a single duct at the time.
Trade off studies were done between different refrigeration systems including absorption and adsorption chillers. The absorption and adsorption chillers were found to be inadequate for underground use and the decision was taken to utilise the current conventional refrigeration systems.
During the planning of the emergency preparedness it was decided that mobile refuge bays will be part of the TBM.
The Consortium approach proved to be effective by bringing speed and diversity by team members. The thirteen identified groups performed well in identifying and testing new and current technology that can be applied in this new paradigm of mining. From an environmental point of view many challenges faced the team including but not limited to risks such as heat, Silica dust, flammable gas, fires, etc. The team proved that this new mine design can be ventilated in accordance with the company’s design criteria and within the current infrastructure.
- AngloGold Ashanti
- Bluhm Burton Engineering
- ABC Ventilation
M.G. Beukes & J.A. Labuschagne AngloGold Ashanti