Matt Freeman, Inside Resources
Over the last few years Winstone Aggregates’ Belmont quarry has been undergoing a transformation to enable it to better serve the greater Wellington region.
This has included the removal of large amounts of weathered greywacke to the large roading project in the area which has opened up the ability to quarry increased volumes of unweathered greywacke (‘blue rock’) from the quarry, that otherwise would have taken longer to expose.
Other initiatives have included stripping, investment in plant, and people and traffic management to cope with the increased demand.
Winstone Wellington quarries manager Shane Hagai says the benefits of the buoyant market in recent times has allowed the upscaling and upgrading of the quarry. “We’ve brought in new staff and trained them up on new and different equipment,” he says. “It’s really given the quarry a lift.”
“Some of the hard fill and weathered greywacke we have been supplying to the market has been material we may have stripped otherwise, and we have also kept stripping on top of that.”
Extraction at Belmont is occurring on the northern face (see picture) at RL145 and on the adjacent ‘Firth block’.
The current mine plan will see the Firth block lowered to RL40 leaving a ridge for amenity value.
Hagai says pre the Covid-19 Level 4 lockdown they started stripping on the northern face and moved about 180,000 m3.
Over time the mine plan takes the quarry northwards to the northern boundary. A new haul road is to be built for a more efficient route down from the Firth block to the processing plant.
Extraction on the southern face has stopped and a levelled area below is being turned into a product bay area to deal with customer traffic flows that were otherwise very congested.
Hagai says previously trucks would circle closer to the processing plant components for pick-up, so this new move allows better separation of customer and quarry vehicles.
In terms of year-round steady-state production, concrete sand demand is a big driver for the quarry, feeding the adjacent Firth concrete plant and others in the vicinity on demand.
A new $900,000 Rocktec sand plant was commissioned last year and has been performing well, says Hagai.
Belmont’s concrete sand product includes a blend of Belmont manufactured sand and about 35 per cent imported sand from Winstone’s Petone sand plant – a barge and excavator operation on the Hutt River – and dune sand from the Kapiti coast.
One of the challenges of manufacturing sand is the output of by-product in the form of chip. “We make the sand and the chip comes with it.”
The new plant has increased efficiencies measurably, doing a lot of the sand blending which was previously handled manually using a loader. “A combination of intelligent weigh-belts and VSD controls allows the right mix to be controlled by the plant operator,” says Hagai.
In the spirit of innovation and the drive for greater efficiencies the Belmont team has trialed different plant modes to increase yields, with a good degree of success. “This has resulted in us being able to produce far less by-product and we are at the point now where we can produce just sand without any by-product using a sand-only mode.”
During the month of October last year, the quarry was able to reduce plant hours from 6am–9pm to 6am-5pm. Hagai says despite the reduction in plant time they were able to produce more product, simply through being smarter. “We didn’t have any unscheduled shutdowns during the month.”
Hagai says the next big plant upgrade would be the secondary plant in the next couple of years or so.
Another of the upgrades at the quarry has been the installation of a new two-lane weighbridge providing a one-way traffic flow system to deal with the high volume of trucks passing through. This was accompanied by a new driveway, wheel wash and improved computer system for operating the weighbridge.
A Powerscreen Warrior mobile crushing plant produces GAP65. The efficiencies of this plant are impressive, producing 1500 tonnes per day for a diesel burn of 25 litres.
Belmont’s average monthly production has been running at around 70,000 tonnes.
Other jobs Belmont has been supplying include concrete aggregate supply for a large shopping centre rebuild and other developments in the region.
Belmont quarry is a pretty tidy operation to observe. Every day at 4am the quarry starts with haul road grading and preparation. The overburden area has just seen 14,000 new trees planted.
The site currently employs 21 people.