The final crush

Lunn Ave quarry in Mt Wellington closed some time ago, however it has one last resource of basalt to deliver before the site is completely transformed into a new Auckland suburb.   BY ALAN TITCHALL

Winstone Aggregates’ Lunn Ave Quarry in Mt Wellington used to be the largest quarry operation in the country, supplying basalt for the original infrastructure of the Queen City.

The site has long ceased production and the 3190 square metre (110 hectare) site is now under transformation as a huge suburban development called, suitably enough, Stonefields. The master plan provides for 27 kilometres of roading, a school, a sports arena, commercial offices and 2900 dwellings capable of housing up to 6500 people. The first sections are already under construction.

The construction site is a hive of activity with a fleet of articulated dump trucks, excavators and bulldozers moving around what appears to be an endless amount of earth from what was the old quarry floor. A lake has been created under the quarry cliffs to serve as a recreational feature. The original rehabilitation plans for the Winstone quarry involved turning the entire site into a lake, until it dawned on Auckland’s authorities that this was prime land for a new inner-city suburb.

On the southern boundary of the development site, just off busy Lunn Ave, is a miniature quarry operation working its way through a sizeable hill of basalt boulders. These large, car-size rocks were disregarded in the past because they were too hard to crush. During the first stage of the Stonefields development, they were rounded up and bulldozed into a massive pile.

Adams Landscaping, a division of RM Adams, has the contract to quarry the boulders and supply aggregate for the foundations of Stonefields – namely for drainage and road surfaces. Equipment used on this operation is mostly sourced from SCS screening and crushing equipment.

“Adams Landscaping, an old client of ours who uses other Powerscreen products, initially approached Quality Road Services of Wairoa to lease their heavier, SCS-supplied crushing and screening equipment for the site,” says SCS North Island sales manager Simon, explaining the connections.

“We sold a combined cone and Powerscreen system to Quality Road Services so Adams Landscape could use them on this operation. It has been a successful arrangement between the three companies to complete what has proved to be a very tough job.”

That job is to turn a pile of huge boulders into 20/7 aggregate for Stonefields’ developer Landco (Hick Bros Civil Construction is the main contactor) for the drainage, and Minus 7 product to use in the concrete and roading hotmix.

Stage one of the Stonefields development has already taken three years and stage two is two due for completion around 2012. The Quarry operation is located on the southern side of the old quarry and away from the main earthworks.

The original contract called for 10,000 metres of aggregate, made up of 20/7 and Minus 7. The total resource is a 60,000 cubic metre stockpile of old rock that nobody wanted to know about in the past, says Stocker.

“Because of irregularity of the structure of this stone, you just don’t know what you will get during crushing. And there’s some awfully hard stuff in there that has created problems, putting every body’s gear to the test,” he says.

“Normally you have reasonable consistency with blasted quarry, but this stuff has no consistency.”

The rock busting is done by a CAT 350 excavator fitted with a TX500 Terminator from Rocktec. The hard rock has bent a pin or two on the Terminator, says Stocker. “This rock is pretty ugly stuff,” he stresses.

The staccato sound of the breaker resounds around the old quarry walls and the shattered rock is loaded into another crusher and not without a few jam-ups during a day’s work. 

In the early days, they used a Pegson metro track HA with 36/24 jaw crushers. “This worked successfully until we got into the bigger rock, which we weren’t expecting to encounter, and it’s just too big for that machine.

The 140mm stone is then is stockpiled before being feed by a front-end loader into a SCS cone and Powerscreen reticulation crushing system.

Made in Christchurch by SCS, the 1235TC (tracked) cone is powered by a 350HP Cummins engine. Stocker says the demand for these cone crushers since SCS set up in Australia recently, has moved the company to raise production next year to making one machine every week. The majority of cones are heading over the ditch to Australia.

“We just cannot keep up since opening a branch over there, and we are going to double the size of the workshop in Christchurch to cope with the demand.”

The closed-loop operation is feed oversize 140mm product from the top of the screen into the cone which feeds it back to the screen until the product gets to the right size.

“We are producing 350 tonne an hour of 40mm and 65mm aggregate on this recirculation system, and 85 metres an hour of 20-7, plus the Minus 7 that is mixed with gap 65 for concrete and hotmix product.”

The 1235TC is also economical on fuel, says Stocker, burning 35 litres an hour. The Turbo Powerscreen Chieftain with a Deutz engine is burning 9-10 litres an hour.

Stocker says SCS expects in excess of 100,000 metres from the crusher cone before changing the manganese mantle.

The quarry operation at Lunn Ave started at the beginning of the winter and is expected to be completed by the end of the year.

“Originally the job was for 10,000 metres but now the contractor, Adams Landscaping, has the green light to keep going. The operation so far belies the success of the equipment,” says Stocker.

Although the final amount of product that will be quarried from the site is unknown, Stocker says the gear is capable of processing the full resource of 60,000 metres.

“These guys are going to be here for a while because it’s so hard going.”

And could the equipment last the full 60,000 metres?

“Absolutely,” he says emphatically.