Golden Bay Dolomite

The Golden Bay Dolomite Quarry 6km west of Collingwood is this country’s only commercial source of dolomite, a crystalline rock that contains calcium and magnesium carbonates. Ground into a fine powder it can be used in a similar way to conventional lime to raise soil pH and improve soil properties. It is also a source of magnesium, which is deficient in some, possibly many soils. Lack of magnesium in the ruminant diet causes grass staggers and other metabolic problems.

Golden Bay dolomite is BioGro certified for organic use and is particularly prized by biological farmers.

Merv Solly, owner of Solly’s Transport, bought Golden Bay Dolomite in 2007 and is working to build the business. High quality dolomite in powder and chip form is transported around the country by road, barge, and ship. Dolomite with impurities is an attractive rock and used in landscaping.

Dolomite is a mixture of calcium and magnesium carbonates. Golden Bay dolomite has a typical analysis of 39% magnesium carbonate (of which 11% is elemental magnesium) and 57% calcium carbonate (of which 24% is elemental calcium). It may also contain traces of boron 5ppm (parts per million), cobalt 2ppm, copper 1ppm, manganese 173ppm, molybdenum 3ppm, and zinc 10ppm.

Dolomite when topdressed as a fine powder results in rapid increases in pasture plant magnesium, helping to avoid some metabolic problems. It can be used in place of lime (mainly calcium carbonate) as a soil conditioner to raise pH and is said to help make other soil nutrients, notably phosphate, more available. It is often used as a source of magnesium in mixtures with RPR, sulphur super and potash, and as a carrier for selenium, slug baits and other materials.

The Golden Bay Dolomite quarry at Mt Burnett near Collingwood is New Zealand’s only commercial source of high quality dolomite. The existence of the resource has been known for over a century but it has been mined commercially only since the 1940’s. At the turn of this century the Swiss-owned crushing plant had a production capacity of 100,000 tonnes per annum although actual production was less than half of that. By 2007 production had dwindled to about 6000 tpa. In July that year the company was bought by Merv Solly, owner of Solly’s Transport, a large regional trucking company that had for some years been carrying out some of the quarry work and most of the cartage.

The dolomite deposit is huge – estimated to be 50 – 100 million tonnes. It is a very dense rock and has to be blasted from the quarry face. Large chunks may be further broken down by an excavator with a rock breaker attachment. The material is transported 8km to the crushing plant where it is crushed into chips and then goes through one of two mills. One mill makes it into granules of 1.5 – 2mm. This core product goes to a North Island company where it is coated with selenium and shipped around the country. Another core product of slightly different size is used as a carrier for other kinds of materials, such as slug baits. Dolomite is ideal for this as it does not react with the other materials.

A second mill involving a double rotating cage produces a very fine dolomite powder. In this state it is very reactive when topdressed onto land or incorporated into soil. It can also be mixed with other nutrients such as sulphur – the company makes it up to meet farmers’ needs.

Merv Solly says that many farmers see dolomite as a very healthy fertiliser that conditions soil and supplies magnesium.

“They believe it helps keep animal health bills down by reducing metabolic problems like grass staggers that is caused by a lack of magnesium. Intense farming practices mean that the use of dolomite is going to become more and more important to get magnesium back into the soil and forage,” he says.

“Some farmers offer it as a free choice mineral for stock. This is the same fine powder that they spread on the land, and the cows just eat it whenever they feel like it. Horses may also be offered it as part of their diet. It is completely safe for them – they can’t overdo it.”

Golden Bay dolomite is BioGro certified for use on organic properties but there has also been a lot of interest from the biological farming community and it is in this area that sales have increased most in recent years.

“We seem to have had big growth in the Bay of Plenty, Rotorua, Taupo and Northland regions and particularly amongst people who are interested in balancing up base nutrients,” says Merv.

“There is also growth in the garden centre market for both powder and granules, and the impure rock is popular for landscaping.”

Collingwood is an out-of-the-way place, but being a transport operator Merv has got that issue sussed. Dolomite is sent in bulk by barge from the nearby minor port of Tarakohe (site of the old cement works) to Whanganui where it is stored and then distributed. An interest in a coastal ship allows the company to transport bulk dolomite to Northland and other ports, whereas most of the bagged product goes by road to various destinations.

“Each year we have been involved, the amount sold has doubled, and we hope to sell around 40,000 tonnes this year,” says Merv.

“I see steady growth in its use as people change the way they view soil and the fertilisers they use and move towards healthier and more sustainable practices. Many farmers want to get back to good animal health as well as good production figures and less stress for themselves, so the business is becoming more and more interesting every day.”