A venerable stone

They were hacking limestone rocks out of North Otago’s rolling hills as early as 1862 and, as HUGH DE LACY finds, demand remains undiminished for the milky-coloured stone that is synonymous with Oamaru.

Over its 102 years of operation, Parkside Limestone Quarry has seen many neighbours on its stoney turf come and go and even gobbled up a few of the stayers, but this year it could be welcoming a new neighbour in the form of a $200 million cement plant.

Though no final decision will be made until mid-year on whether the new Holcim plant will go ahead, it looks likely to become the latest in a long line of businesses that have harvested the massive resources of limestone beneath the pastures surrounding North Otago’s principal town of Oamaru.

Holcim, which won interim resource consent for its plant in November 2007, looks set to add a new dimension to the range of applications for Oamaru lime: unlike Parkside’s building and agricultural uses, Holcim will burn the lime to make Portland cement. Assuming the cement works goes ahead, the company will occupy a 120 hectare farm adjacent to Parkside, which itself began operations as a farm, albeit with two quarries within its boundaries. 

Parkside farm comprises 300 hecares and the quarries have been operating almost as long as the farm has, but the size of the mineral resource is such that even after all these years the quarries have left only a small footprint.

Each quarry occupies about four hectares each and they are just a couple of kilometres apart, but the seam they exploit is a monstrous 40-50 metres deep – unusually big for lime – and extends far beyond the farm boundaries.

Parkside’s rock quarry is today the sole commercial supplier of the milky white stone that features in Oamaru’s priceless inventory of imposing colonial buildings.

By no means all the stone for such buildings in the town’s business centre and at its wharfside precinct came from Parkside, but Oamaru stone has been quarried as building product by a succession of businesses for nearly 150 years.

Oamaru stone started its commercial life rather humbly as a substitute for the Tasmanian sandstone that was being imported for civic and commercial buildings in Auckland, Wellington, Christchurch and Dunedin from the early 1860s.

The Tasmanian stone enjoyed the advantages of getting a free ride across the Tasman Sea as ships’ ballast, and of colonial architects being more familiar with that type of rock than they were with limestone.

Oamaru stone also found its way overseas to Melbourne as ballast, but the overall traffic was heavily in the opposite direction, with even many of Dunedin’s colonial finest being built of Tasmanian sandstone rather than the white rock available just up the road at Oamaru.

While Tasmanian stone was used to build Auckland’s Union Bank and Bank of New Zealand in 1864 and 1867 respectively, construction of the Queen City’s first Oamaru stone building, the Church of St Matthew in the City, did not begin until 1902.

Limestone blocks were used for farm buildings from the earliest days of the Otago settlement, and there were as many as a dozen rock quarries near Oamaru in the second half of the nineteenth century, but Parkside Quarries was not founded until 1905.

It began its life as Gay’s Oamaru Stone Company on land bought in the 1870s by one Henry Mitchell, part of a farm he named Parkside after a hotel he used to own in Caversham, Dunedin.

Originally of 440 hectara, Parkside farm passed down to Henry’s sons James and Joseph in 1891, then in 1933 to Joseph’s son Ivan, and thence to his sons Joe and Derek in 1964.

Derek subsequently sold out to Joe who went on to make his mark as a farmer by introducing the first bulk-handling combine harvester and grain-drying machines to North Otago.

In 1974 Joe Mitchell bought the stone quarry from the prominent local diversified company G.T. Gillies, which had acquired it from Gay’s in 1945. It was by that time the sole remaining rock quarry in the Oamaru area, Gay’s having bought out and shut down all the competition.

Seventeen years later Mitchell also bought out Taylor’s Lime whose quarry, like Gillies’, was situated within the Parkside farm boundaries.

Today, at 75, Joe Mitchell continues as managing director of the two Parkside quarries which, between them, harvest close to 80,000 tonnes of lime a year.

By far the bulk of it – 50-60,000 tonne – is agricultural lime, some of it ground extra-fine for application by helicopter and fixed-wing aircraft, and the rest with a small lump in it for application by truck.

The stone quarry produces up to 5500 1.5 tonne pallets a year of 100mm thick building veneer ranging in height from 40mm to 500mm, and in a standard length of 650mm.

Parkside’s Oamaru stone veneer is direct-marketed throughout the country, but the builders aren’t the rocks’ only buyer.

There’s a small but high-profile niche among the country’s sculptors for the stone, with artists like Sam Genet, Llew Summers and Bon Souter having made their names working in it.

The 2.5 tonne blocks they specify are typically 1.4 metres by 1.2 metres by 700mm, and every second year a sculptors’ symposium is held in Oamaru, attracting up to 200 visitors a time.

Cutting the blocks out of the quarry used to be done with an electric chainsaw operated by one man working full-time, and with the pieces broken out with wedges and hammers, but in 2004 this system was replaced by diggers with three metre diameter circular saw-blades on booms. One of Parkside’s such machines is a 22-tonner with a single blade, while the other weighs 33 tonne and has two blades in parallel cutting vertically.

Once the cuts have been made, the block is levered out of the main body of stone by a tracked loader with tungsten-hardened spikes on its front bucket. The blocks are then carted to the on-site factory to be cut to size, much as with timber, by a series of four break-down saws.

Nothing from the stone quarry is wasted: chips and off-cuts are alike carted over to the lime quarry – nowadays by the new Caterpillar truck (cover story in the December 07-January issue) with its 40 tonne capacity – where they’re ground up for agricultural application by a bar-mill crusher.

While Joe Mitchell continues to oversee the operations of the two Parkside quarries, Bob Wilson serves as both manager and director, and he has his work cut out meeting demand for the building stone.

“We don’t want to increase the factory size in the foreseeable future, but we’re three to four months behind meeting demand, and it’s a struggle to keep up at times,” Wilson told Q&M magazine.

Virtually all production is sold onto the domestic market, though a small amount gets exported. Wilson said that Oamaru stone’s reputation has long since stepped out of the shadow of the Tasmanian sandstone that was once preferred over it. No better evidence of this is the Oamaru District Council’s recent decision to spend $9.5 million refurbishing the first local building to be made out of Parkside stone, the 1906 Opera House which is now known as the Municipal Building.

“For a town of only 14,000 people to spend that much on doing up a building shows the value it puts on the local stone,” Wilson says.

And with the resource seemingly unlimited, it’s likely that Oamaru stone’s reputation, and its uptake by the New Zealand building industry, will alike grow indefinitely.