Aggregate mapping takes long-term view

Auckland should be nice to its local authority neighbours if it wants to secure long-term rock and sand resources for future growth.

That’s the opinion of GNS Science geologist Matthew Hill who has been involved in a GNS science study to identify where rock and sand resources exist in five major centres.

He hopes the study will lead to a national-scale model of aggregate opportunities, which can be investigated before being allocated to other land uses.

Auckland was one of the five centres included in the study, which showed that the northern area has large areas of hard rock, much of it at or near the surface, providing access to good-quality resources.
Hard rock aggregate opportunities were identified west of Matakana, east and north-east of the Brynderwyns, and east and west of Whangārei.

There were also excellent sand opportunities with extensive sand dune complexes along the west coast and some coastal deposits on the east, which might provide good resources of sand for concrete. On the other hand, gravel opportunities were limited.

Growing need

Each year, Aotearoa New Zealand consumes the equivalent of eight tonnes of aggregate per person across roading, construction and other infrastructure projects, and the need for aggregate is increasing, particularly in high-growth areas such as Auckland.

About 70 per cent of the conservatively estimated 41 million tonnes of rock, sand and gravel produced annually at domestic quarries is used in the North Island. Roading takes about 62 per cent of the quarried material, 27 per cent is used for building, one per cent for reclamation and protection, and 10 per cent for fill.

Hill says efficient use of our aggregate resources is critical to reducing costs and transport emissions.

“A truckload of aggregate roughly doubles in price after 30km, and the further it has to be carted, the greater the road wear costs and carbon emissions. So, the closer that aggregate sources are to where they’ll be used, the better.

“Managing the future demand requirements and planning for aggregate supply is essential,” he says.

Range of factors

When launching the study, Infrastructure Commission chief executive Ross Copland said the maps didn’t just identify quarry resources but looked at a whole range of factors, including an area’s conservation values, biodiversity impacts, local demand, proximity to existing housing, iwi and community concerns, and land with high farming value, before identifying where a rock or sand resource is worth confirming for future use.

“As an industry, we want to identify and secure future potential pockets of high-value quarry resources and secure them, so they aren’t over-taken by urban sprawl.”

Hill believes the study will help councils, iwi and landholders to see what opportunities are one their land.

It can take 10 to 15 years after identifying a quarry site to see it operational, so Hill says there has to be some long-term thinking.

He stresses the study only shows potential opportunities for quarries.

“A lot of additional testing and community engagement is required for any site to be considered a resource and for quarrying to start. Certain geotechnical, regulatory and cultural influences are not included in the modelling so need to be considered as part of follow-up investigation.”

The study sourced data from Land Information NZ, the Department of Conservation, Manaaki Whenua Landcare Research, GNS Science, the Ministry for the Environment, and Statistics NZ.

To view a web map of the results, go to: https://data.gns.cri.nz/tez/index.html?map=Aggregate%20Opportunity