The Pike River Coal (PRC) mine will open officially later this year and is set to haul its first production coal to the surface at the end of August.
When in full production the mine will be New Zealand’s largest output underground coal mine, producing up to one million tonnes per annum over its 18-year life and earning the country $1.7 billion in export income.
Bringing the $240 million coal mine to production has been an exciting and challenging journey, says Pike River Coal general manager, mines, Peter Whittall.
“But it was worth it. The coalfield holds New Zealand’s largest deposit of high-fluidity, high-quality, hard coking coal and its low ash qualities give it a tremendous competitive advantage in the export market,” he says. The coal will be used to produce coke and steel.
The challenges with this venture started with obtaining resource consent and building the infrastructure, and will continue over the life of the mine.
“So far we’ve done well. And once the mine is working, it will be a day-to-day business to manage the mine’s safety and environmental systems, and ensure the effective application of the proposed hydraulic mining technique to achieve consistently high output,” Whittall comments.
The Pike River coalfield is located 45 kilometres northeast of the West Coast town of Greymouth in the South Island, near the top of the Paparoa Range and between Mount Hawera and Mount Anderson. It shares a boundary with the Paparoa National Park and some of the mine’s coal reserves lie within the National Park boundaries. Except for the Coal Preparation Plant (CPP) site, the mine and its infrastructure sit on and under Crown land administered by the Department of Conservation.
The coalfield comprises the Ecocene-aged Brunner coal measures and the deeper Cretaceous-aged Paparoa measures. The Brunner seam deposit, estimated at an in-ground resource of just over 58.5 million tonnes, has been thrown up about 800 metres above sea level. The seam dips from the outcrop to the Hawera fault at inclinations varying from 11-degrees to 20-degrees to the east.
In 1996 New Zealand Oil and Gas (NZOG) decided to mine the Brunner seam. It took eight years to obtain resource consent, only won due to, Whittall says, “planning that successfully addressed a host of special geological and environmental considerations.”
Pike River Coal was floated on the NZX and ASX in July 2007. NZOG (at 31 percent) and two major Indian investors-customers own 49 percent of the company, with the remaining 51 percent publicly owned and traded.
Detailed mine design, undertaken in conjunction with the consent process, was completed in June 2005. Three months later the PRC board gave its formal approval to proceed with the project. The brand-new mine comprises mammoth construction and engineering activities. Mine construction started with road access works in January 2006.
Milestones: almost there!
The 12 kilometre mine access road runs through previous logged and virgin rainforest.
In August 2006, subcontractor Ferguson Brothers finished around 8.5 kilometres of basic road incorporating seven bridges and six large box culvert crossings through the Pike Stream valley to the tunnel entrance.
This road connected with a further 3.5 kilometres of sealed road constructed by the White Knight JV from the nearest public road, Logburn Road, to the coal preparation plant site at the entrance to the valley.
The next big project was building the 4.5-metre high, 5.5-metre wide, 2.3-kilometre long, five degree-gradient tunnel through metamorphic rock to intersect the coal measures on the western side of the Hawera fault. McConnell Dowell Constructors (NZ) started work in late September 2006, using the conventional drill and blast method to excavate the first two kilometres of tunnel to the pit bottom area east of the Hawera fault. The team reached the pit bottom area adjacent to the fault in April 2008.
To either side of the tunnel in this location, McConnell Dowell also excavated a total of 471 metres of large roadway cavities, up to eight metres wide and 11 metres high, to allow the installation of water and coal slurry tanks and pumping systems.
Tunnelling recommenced through the Hawera fault on July 10 and the team is now just 200 metres away from the 18mt Brunner hard coking coal prize. McConnell Dowell uses a twin-boom Atlas Copco jumbo drilling machine to drill out the face of the tunnel. The crews will use a combination of blasting, drilling, and tunnel support to get through the expected 50 metre-wide crushed rock zone.
Once through the fault and into the coal seam, a flameproof road header will drive a series of 3.3-metre-high, five-metre-wide roadways in the coal and stone west of the Hawera fault before the introduction of two continuous miners to the coal seam later in the year. The three base machines are German Wirth bodies, customised and fitted out with AS/NZ compliant electrics by Waratah Engineering in New South Wales.
Three high-pressure hydraulic monitors, purchased from a Japanese supplier to perform coal extraction, are due for delivery in early 2009. Hydraulic monitoring will commence in June next year. Due to water requirements and sequencing, only one hydro-monitor operates at any one time.
Whittall says underground mining has a minimal environmental impact, but planning had to ensure there will be no adverse effects on the land surface through subsidence, or significant disruption to surface water drainage patterns and associated micro-environments.
“Our duty of care includes maintaining overall stability of the overburden strata against en masse down-slope movement or any steep-slope failure. The relationship between the width of mining panels and the depth of cover offered a means of controlling surface subsidence impacts and the alignment of pillars will reduce the potential for overall down-slope movement of the pillars; which ensures stability in the long term, too,” he explains. The wet-feed CPP, about 8.5 kilometres from the mine portal on a 20-hectare gravel terrace above Big River, is progressing well. The CPP site also accommodates the bathhouse and a substation. Here, the mine’s two one percent ash products (1.2 percent sulphur and 1.9 percent sulphur) will be readied for the market and wastewater will be treated to a very high standard before either returning for use in the mine or being discharged into Big River.
Nelson-based Brightwater-PEAT, a joint venture comprising Brightwater Engineering and an Australian-based designer, designed the CPP. Pike River Coal personnel will manage and operate it.
Work recently began on a 108 metre-deep 4.15 metre-diameter ventilation shaft on the north side of Pike Stream, about 2.3 kilometres from the tunnel entrance. The shaft will be sunk by raise boring. The upper 30 metres of the shaft site has been concrete grout injected to stabilise the ground ahead of shaft excavation.
The initial pre-sink of eight metres and the installation of the ventilation fan and associated plant are all helicopter supported. Whittall says he expects it to be finished by October, which will allow the deployment of all the mining equipment necessary to ramp up production to projected levels.
The 220 metre-deep pit bottom facilities, including underground coal transport systems; a coal preparation plant; a major slurry pump station; high and low pressure underground water supply systems to support hydraulic monitors; and underground ventilation systems are also keeping the teams’ noses to the grindstone.
We came, we saw, we are conquering
Whittall explains the mine will use its elevation and sloping coal seam to advantage to flume both development and production coal hydraulically from the working faces to the pit bottom. This eliminates the use of shuttle cars and conveyors.
At the coalfaces the coal will be initially crushed to <200mm, to aid in its water-borne transport in the flumes. In the roadway development panels this will be by small crushers mounted in the discharge of the roadheader and continuous miners. In the hydro panels, the coal will be directed through a crusher, which will then feed the coal into the flumes. Waratah Engineering will also design the monitor panel crusher.
The coal will travel several kilometres to the pit bottom area where it will be further crushed to <35mm. The crushing station at the pit bottom will incorporate two McLanahan crushers between the raw coal holding pen and the slurry holding pen. While the concrete infrastructure for the pens and machine rooms have been completed, installation of the coal handling facilities are due to commence in the coming months.
From the pit bottom the coal-water slurry will be pumped into a 275mm seamless Sumitomo steel pipe for its 10.5 kilometre journey to the CPP. Running in parallel with a 300mm return water pipeline, the slurry pipeline follows the edge of the mine access road down the valley. Both pipelines are suspended just above the road surface on concrete plinths and held down with brackets drilled into the ground.
Whittall says the slurry pipeline is designed to deliver the coal slurry at a high speed (4.5m/s) to keep the coal in suspension and prevent settling. As the return water line does not have the same imperative, it has been designed as a standard pipe size to deliver the water back up to the mine site at a lower pressure.
“The two pipelines, combined with the engineer-designed stabilising thrust blocks and the periodic dump ponds and valves, have proven to be a very satisfactory engineering solution to the problem of coal transport through the environmentally sensitive DOC estate,” he says. Ferguson Brothers, using Ching as subcontracting installer, installed the pipeline.
Whittall says although the mine has a low to moderate gas content, mine ventilation and monitoring of the mine’s atmosphere are critical to the safety of the mine and its workforce. Ventilation fans installed underground and an emergency backup fan at the top of the mine’s ventilation shaft will control the mine’s environment, ensure fresh air to the working faces, and prevent build up of potentially noxious or explosive gases in the mine.
Australian company Flakt-Woods built the fans, with much of the steelwork fabricated locally by Gray Brothers Engineering. A real-time web-interfaced monitoring system, in the process of being built, will report ventilation conditions to the mine control room.
Getting the coal to market
In June Pike River Coal announced the finalisation of a long-term agreement with Nelson-based TNL Group Limited to truck the coal from the CPP to the new $12 million rail loading facility being constructed at Ikamatua in the Grey Valley, 22 kilometres from the Pike River site and alongside the main rail line.
From there, the coal will be railed to the Port of Lyttelton for export. This port can berth panamax vessels carrying 60,000 tonnes of coal. Brightwater Engineering designed and is building this facility too.
The new rail loading facility sits on unproductive land made up of old dredge tailings and screened by regenerating scrub and other plantings. It includes a rail loop and coal conveyor where trains can stop and be loaded with coal delivered by TNL’s trucks. Whittall says at full production from mid-2009 there will be one to two rail loadings per day.
PRC intends to operate the mine in two 12-hour shifts per day, seven days per week. Peak employment will be 150 operations and support personnel. The schedule calls for the first 100,000 tonnes of coal to be mined by the end of March 2009 and another 100,000 tonnes by the end of June 2009.