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While not quite the most southerly quarry in the country, Greenhill is within a rock throw of the Southern Ocean and enjoys a great view of Stewart Island. By ALAN TITCHALL.
The name is appropriate as the quarry sits in lush green, hilly Southland farmland, bordered by Omaui Road to its north and, to it south, the rugged and rocky coastline sweeping around the south east corner of the South Island. “On a good you can sit here in your truck and look through the Mutton Bird Islands all the way to Half Moon Bay on Stewart Island,” says quarry manager Kerry Sands. Greenhill started its life as a quarry over 50 years ago when the local KcKinnel family opened up the limestone resource. One of the descendants, Ross McKinnel, is the overall supervisor of the quarry, having worked at the site now for some 30 years. The day-to-day operation is managed by Sands who has worked at Greenhill for the past 15 years and spent his career in local quarries, including a stint with Ross McKinnel’s father.
“The rock has about every trace element in it other than gold,” says Sands. “The main reason it has been quarried since the 1950s is because of its large dolomite magnesite content – ideal for the adding into fertilizer manufacturing.” The quarry is owned by Southern Aggregates, a joint venture shareholding between the HW Richardson Group (which also owns Southern Transport) and Fulton Hogan, who also own Blackhead quarry in Dunedin. Southern Aggregates also operates Stoney Creek at Balclutha and a sand and aggregate plant at Oreti Beach near Invercargill. Greenhill is famous for its dolomite dust. “Of the total production, around 20,000 tonne is 2mm minus dust for the Balance fertilizer works very year,” says Sands. “The quantity just depends on what the farmers are doing at the time. If they are getting good rebates they spend the money, but if things slow down for them, then we feel the repercussions.” Over the past year the dolomite has been a slow mover, he concedes, but the roading aggregate product has been moving well. The plant and crew
The drilling and blasting at Greenhill is carried out by crews from Blackhead quarry further north. “We don’t have a lot of cover on the rock – just two metres thick at the most,” says Sands. All the strippings are use to backfilled the used parts of the quarry that are eventually returned to farmland. Wheeled equipment stands at one digger (a Cat 320B), one loader (Cat 950G), and two trucks (a Cat 950A and a 936F). The Cat 950 loader is one of the latest, with a command control joystick instead of the conventional steering wheel, which is less fatiguing, says Sands. The loader also has an ‘auto digger’ feature that remembers any particular bucket load and will repeat its actions with a push of a button. “Which effectively means it digs itself, so the operator only has to work the brake and accelerator.” When you are loading a truck from a stockpiling, it means you can consistently pick up a six tonne bucket, he says.
Rock for aggregate is dumped into a large hopper feeding a jaw crusher that is capable of chewing any size rock up to a metre. “Although, we don’t put too much big stuff in there, otherwise it slows the operation down,” comments Sands. It comes out of the jaw crusher at 150mm and different sized screens are used for producing different grades of material to order. Anything small slips onto an elevator and is carted off to the interior crusher, and the rest onto a hammer mill for roading material. On the day of our visit the metal was 25mm. The outside plant is used exclusively for roading aggregate. “We are shifting it all down to the bottom of the quarry where it is closer to the raw material and our stockpiles,” Sands mentioned at the time. The aggregate is trucked by Southern Transport into Invercargill where is stockpiled again at Allied Materials for customers such as Fulton Hogan and South Roads. “It saves the client from having to come all the way down here to collect their aggregate,” says Sands. “Particularly for small jobs where they might just want five tonnes or even small quantities. And sometimes the smaller contracts don’t allow room for large trucks and trailers.”
The 150mm stone is passed through a cone crusher and comes out at 40mm before travelling along a long conveyor belt to a screen where the fines fall through to a dust bin and rest into a 9090 Barmac that has been grinding away since 1995. “We only look at it about once a year,” Sands says, referring to the crusher’s low servicing needs. The 2mm material produced from the Barmac is stored in a loading bin. The fine dust that gets into the air is controlled by a large extractor fan, ducting and a number of sock-like, three metre long, collection bags. Air is shot down these socks to make them vibrate and release the captured dust into a hopper and back into the loading/storage bin. Both crushing plants also employ a mist spraying system to control dust and this is a very carefully controlled operation because the 2mm product won’t go through the screen if it is too moist. The dust is then trucked 18 tonnes at a time from the quarry to the Balance fertilizer works 20 minutes away on the Bluff highway. Around 1000 tonnes are stockpiled at the fertilizer works and another 200 tonne in the quarry bin at any one time.
Production is on demand and the fertilizer works can use up to a 1000 tonne in a week, he says. “That’s a good week’s crushing for us.” The magazine’s visit was over the winter. I imagined the quarry on its exposed coastal location would be a tough workplace when the cruel southerly winds rip into it from the Antarctic? The dust and winter rain also made a fine, grey slurry that stuck to our boots like the proverbial shit to a blanket. Sands is quick to defend his quarry, pointing out that it is not as bad as tramping around in wet material in some other operations. “Because the nature of the rock here, it can absorb quite a bit of water before it goes mushy.” Nor is it dusty in the summer, he adds. “We keep all the roads wet during the summer – it’s not too bad.”
Then there’s the big paua hiding down among the rocks and kelp – calling out to be harvested during one’s lunch hour. “I wouldn’t be in a hurry to leave,” he says. All articles on this website are copyright to Contrafed Publishing Co. Ltd. |
From its location on the peninsula between Invercargill and Bluff, Greenhill Quarry produces a wide range of products from 2mm dust, used in the phosphate industry, to a wide range of roading aggregates, gabion rock and larger rock for flood protection in the region.
The stone resource at Greenhill is extensive, around 250 year’s worth, and very accessible with a just a thin layer of overburden.
There are three permanent staff, including Sands, and others are bought in if things get busy from other operations within the Southern Aggregates family. 
There are two crushing plants; one under cover for producing the powdery 2mm dolomite dust and one outside for the aggregate.
The inside plant is where the ‘dust’ is made for adding to fertilizer. Both the internal and external crushing plants are controlled from a closed off room.
“We can process about 35 tonne an hour of this material and they can cart about 39 tonne every round, 45 minute trip, so we are really going to keep up at times.”
Sands is also quick off the mark to praise his employer. “They look after us very well. We want for nothing in terms of gear and have medical insurance that also covers our families.”