Logan Point Quarry
Geology
The Logan Point quarry is based on a series of phonolite domex deposited 13 millions years ago and characteristic of the Dunedin Volcanics.
At present, the quarry is working down to 60 metres below sea level. Since the rock is relatively impermeable, water is not a major problem with pumps only working intermittently. At times of heavy rain, however, the pit does flood but that is only 3 - 4 times a year and is usually pumped dry in less than a week.
Quarrying
All rock is won by drill and blast method with a hydraulic drill rig, drilling 89mm holes with a 2.8m burden and spacing on a 10m face. Electronic detantors and bulk explosives are used to blast the rock. The electronic detonators allow us to control vibration and improve fracture of the rock. Any oversize is broken using a Terminator rock breaker on our excavators. Loading at the face is performed by a 30 tonne excavator with a 20 tonne wheel loader used for different jobs around the face. Two dump trucks are used to cart the rock to the primary crusher each taking around 20 tonne per trip.
Sales
All sales from the stockpile area with no customer trucks under the bin. The quarry bin trucks supply a concrete plant and asphalt plant on the quarry site but all outside deliveries are done by independent carriers. A 20 tonne loader takes care of all loading from stockpiles with all sales going over a computerised weighbridge.
Processing
The rock trucks tip into a 50 tonne hopper with an apron feeder supply on Allis 1208 jaw crusher at up to 200 tonned for hour. The -30mm is taken off to clean the rock of clay fines and the +30mm goes into a 1000 tonne surge pile. A variable speed feeder under the surge piles feeds an Allis H4000 hrdrocone crusher which crushes down to 55mm. Roadbases are take off at this stage. Any oversize is circulated through a Barmax 9600 Duopactor until it passes the 16mm sieve and becomes a sealing chip, concrete aggregate or asphalt dust. All products are stockpiled using two bin trucks.
Environment
The Logan Point Quarry is located within 2km of the centre of Dundein hence environmental considerations are very important. A regime of sampling and testing is performed on water discharges, dust deposited at the boundary and vibration from blasting. With the current quarrying operation 60 metres below sea level, water has to be pumped out. This water is used in clean sealing chips & concrete aggregate and in turn is cleaned through a water treatment plant before being discharged. Dust suppression is a priority with water sprays throughout the plant and use of water on trucks on all quarry roads. Modern blasting techniques minimise noise and vibration outside the quarry boundary. The Logan Point Quarry has environment systems audited to NZ's 14001/
Health & safety
Being in an industry with large stationary and mobile equipment, blasting operations and an ever changing environment, Health and Safety is a major focus of the company.
An externally audited health and safety system is in place to NZ's 4801 with all staff taking responsibility for safety on the site.
Quality
Logan Point is the largest supplier of quality aggregates in the Dunedin area, the quarry supplies around 30 different products to suit customer needs. Blackhead Quarries have an externally audited Quality Assurance system in place to ISO 9001.200 and on site materials testing laboratory.