Hill, M.P.; Chilton, M.O. 2024 Aggregate opportunity modelling for the northern Auckland area of New Zealand. Lower Hutt, NZ: GNS Science. GNS Science report 2024/11. 23 p.; doi: 10.21420/DS28-ZG73
Abstract
Efficient utilisation of aggregate resources is important to supporting infrastructure development and reducing operational and transport costs related to extraction of raw materials. To understand the spatial distribution of future resources, aggregate opportunity in the northern Auckland area (central Auckland to Whangarei) has been mapped. Modelling of geological, land-use, infrastructure and cultural digital data has been used to map where future resources are located, facilitating prioritisation over less-critical land uses to support our growing economy. Aggregate opportunity areas are places that have overlapping spatial data classes favourable for extractive activities. These indicate where there is a good possibility that an aggregate resource could be developed; however, follow-up investigation of unmapped geotechnical data; non-spatial factors, such as community and iwi values; and the local council plan and policies need to be considered. A spatial modelling approach has been used to identify places with opportunity for future hard rock, gravel and sand extraction in the northern Auckland area. The modelling process involves three levels: classification of source data into mappable criteria layers, combination of criteria layers into predictive components and development of aggregate opportunity models. Geographic information system (GIS) software has been used to build 19 maps of the essential components of aggregate opportunity: source rocks, land use, feasibility and cultural sensitivity to extractive activities. The maps are then combined using fuzzy logic expert-weighted spatial modelling to qualitatively rank aggregate resource opportunities in the region, identifying high-value areas for aggregate exploration. The resulting maps and their accompanying GIS datasets of sand, gravel and hard rock aggregate opportunity can be used to manage aggregate resources; generate targets for exploration activities; and provide insight into future resources, ensuring that they are not unavailable in the future due to other land use. The project identifies constraints such as regulatory and cultural considerations, emphasising the importance of comprehensive data integration and stakeholder engagement in resource management. Despite challenges such as incomplete data and regulatory complexities, the modelling approach provides valuable insights into aggregate resource distribution and potential extraction sites. Results for the region show large areas of opportunity for sandstone hard rock resources west of Matakana, in the ranges northeast of Brynderwyn, and east of Whangarei. Opportunity for basalt, andesite and dacite volcanic rocks occurs east of Brynderwyn and west of Whangarei. Gravel opportunity is limited in northern Auckland; however, there is excellent sand aggregate opportunity. Extensive sand dune complexes that extend for several kilometres inland along the western coast and some deposits at east coast beaches may provide good resources of sand for concrete. Offshore sand deposits are not within scope of this project. This project’s findings facilitate informed decision-making for sustainable resource utilisation and infrastructure development in the northern Auckland area (auths)
