Blackhead Quarry
Quarrying started at Blackhead in the 1950's and is now producing around 120,000 tonnes per year. Products range from general AP materials to high quality M4 roadbases, concrete aggregate, blasting sand, sealing chips and railway ballast.
Geology
Blackhead is a promontory of black basalt situated on the coast approximately 5km south east of Dunedin City's St Clair Beach. Composed of volcanic basalt it was formed about 10 million years ago during the third eruptive phase of the Dunedin volcanic complex. Columnar jointing on the basalt was formed during this cooling and this produced regular sided columns helping the crushing process.
Quality
The high quality resource is used to produce top end products i.e. M4 roadbase, concrete aggregates and sealing chips. To assure anything produced at the Blackhead Quarry meets specification there is an on site laboratory. The entire operation is externally audited for quality assurance to ISO 9001-2000.
Environment
Blackhead Quarry has a covenant; put in place in 1990, to protect unique rock formations at sea level. Blackhead has 0.7 hectares of settling ponds for water treatment. Dust is controlled throughout the plant by the use of water sprays and dust deposited at the boundary is monitored monthly.
The quarry was the winner of the 1995 Nissan Diesel Environmental Award and the 1996 winner of the Winstone Safety Award.
Quarrying
Rock is won by drill and blast with a pattern of 2.7m x 3.3m x 10m bench heights. A 30 tonne excavator is used to load a 10 cubic metre rock truck to transport rock to the primary crusher. A 20 tonne loader is also used on the face for general tidyup, road maintenance and load out duties.
Quarried rock is tipped into a 70 tonne hopper and fed to a Nordberg 40 x 30 single toggle jaw crusher which feeds to a 6000 tonne surge pile. An Allis H4000 cone crusher then crushes the rock to 65mm with a screen taking out roadbases, the oversize then feeds a No. I Kumbee for railway ballast production. Any overrun goes to a surgepile to feed a Barmac 9600 duopactor used to produce sealing chips, concrete aggregates and sand. The plant is highly mechanised with video monitoring from the weighbridge. A 20 tonne front end loader handles sales from the stock pile with everything sold over a 13m computerised weighbridge.