Quarrying & Mining Magazine

Quarrying unique schist

Quarrying Unique Schist

Central Otago has a rapidly expanding economy that has triggered a building boom right across the region, which has opened the way for new aggregate operations. By PETER OWENS.

The Otago region has been renowned since the gold rush days of the mid-19th century for the quality of its schist rock as a building material. It was the only local building material available in those heady times and today it is a popular cladding and pavement material around the country.

Ernst Jonker on the Cluden Steinex guillotine
Ernst Jonker on the Cluden Steinex guillotine.

There are about 10 schist quarries in the Upper Clutha area supplying stone to Wanaka, Queenstown and further afield.

One of these is Cluden Stone Quarry which has been operating near Tarras for over 25 years. It is owned by Grant and Lucy Middendorf who bought it two years ago and it is now producing about 500 tonnes of cut schist annually. The couple arrived just after the building boom began and they have been inundated with orders from the local construction industry.

In order to keep up with demand, the Middendorfs have bought a new $100,000 Italian designed and manufactured guillotine for cutting rock. When the guillotine blade drops the table on which the block of schist sits also drops down and another set of teeth below the rock come into operation. These 24 tungsten-tipped teeth adjust to the shape of the rock so that it exerts 120 tonnes of pressure evenly over the rock surface. Stonemasons prefer schist cut to widths of 150mm for use as cladding.

Around half of the processed schist is bought by the local building industry and the rest is sent further north.

Otago schist formed around 200 million years ago during the Jurassic period when plate tectonics forced sandstone and volcanic materials to be buried deep in the earth. High temperatures melted some minerals and realigned them into the linear and platy schist rock that became a distinctive part of the Otago region. The distinctive earthy shades of grey and brown have formed through the separation of different minerals into layers creating colourful variations in tone and shade unique to Wanaka schist.

Uplift and erosion have removed the softest rocks, leaving hard and stable rock in place for quarrying. Having already survived millions of years in the harsh Otago climate Wanaka schist will last longer than almost all other materials used in building or landscaping.

Steinex guillotine
Steinex guillotine.

Grant Middendorf grew up in Queenstown and spent over 10 years in the Army Engineers Corp (RNZE). During this time he trained and earned his initial quarry manager and explosives licences. Since then Grant has accumulated over 20 years of experience drilling, blasting and operating heavy machinery in quarries and mines around New Zealand, Australia and the Pacific.

Lucy Middendorf, a qualified geologist, has worked for over 10 years in our mining industry and spent a number of years working in Australia, Armenia, and the Philippines. Although the couple have been living at Lake Hawea for about nine years, they have been flying in and out of New Zealand for much of that time. Now the Middendorfs say they are very pleased to be able to settle down and work in the one place.

At present the only rock mined at Cluden is schist as there is no other local hard rock. The couple have a total of 69 hectares of permitted land in the Cluden Creek area and are planning to develop another area.

Featured image shows Cluden Quarry staff 2015: (from left) Ernst Jonker, Rodney Wallbank, Lucy Middendorf and Grant Middendorf.

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