Either because of their rock resource type, or their processing facilities, not all quarries are able to supply ‘premium’ aggregates. Premium aggregates are those used in manufacturing (for example concrete, asphaltic concrete) and as road surfacing, or structural base courses. The rock resource at Hunua is greywacke, which meets the necessary criteria, supplying around 35% of Auckland’s premium market segment.
The transformation of rock from the ground into aggregate products requires firstly the removal of any vegetation, then the stripping of overburden (soils and low quality material) overlying the rock resource. Once the rock resource is exposed it is loosened from the ground and fragmented generally through the use of explosives and heavy machinery. The fragmented rock is excavated from the quarry face or floor and loaded to dump trucks to be hauled, sometimes directly to stockpile storage for sale, or more commonly from the pit to the processing plant. The processing plant comprises a series of crushers, screens (i.e sieves) and conveyors that reduce and sort the excavated rock into various grades and sizes. After resizing and separating the various manufactured aggregates are loaded out to stockpile for sale and transport off site.
The Hunua Quarry operates within a framework of District and Regional Plans defined by the Resource Management Act 1991 and subsequent amendments. This is of course the basic framework at every Winstone Aggregates site, all of which are also operated in accordance with the company’s internal policies. Of these the Environment Policy is particularly relevant in this context, as it underlines an express commitment to environmental management.