Step 2. Mining
Mining can take place through open cut or underground mining methods. At Griffin Coal’s Collie mines open cut mining methods are used. The mining process involves the removal of overburden and extraction of coal but can be considered as four distinct operations:
Topsoil is removed ahead of mining and either spread directly on shaped rehabilitation areas or stockpiled for later use. This operation is performed using dozers, front end loaders and trucks.
The cap rock (up to 2 metres thick) is either ‘ripped’ by dozers or blasted and recovered for use as road surfacing material.
All overburden apart from the ‘Nakina Formation’ is drilled with rotary ‘blast hole’ drilling rigs and charged with bulk explosive, typically a mixture of ammonium nitrate and fuel oil (ANFO).
After blasting, overburden is loaded by hydraulic excavator or front end loader into rear dump trucks and placed in overburden dumps. Initially these had to be placed out of the pit in order to create a large enough hole to work in. The worked over areas of the pit are now filled in, a process known as backfilling.
When the mine gets to the back firing stage, the hole gets bigger and moves slowly across the deposit. Then overburden materials are removed from the operating faces and dumped into backfill on the other side of the mine.
In its operations, Griffin Coal places all overburden into mined out areas and focuses on the rehabilitation of the newly created final land surface.
When overburden has been removed from the coal seam, the roof of the seam is cleaned using bulldozers. The coal seam is then drilled and blasted. Bulldozers clean down to the floor of the coal seam and front end loaders and coal trucks transport coal to either the Ewington Crushing Facility or direct to Muja Power Station.
In some areas, coal can be loaded directly into trucks using a large backhoe, without need for bulldozing. Once the coal has been extracted it is then processed.
Click Here to find out more about processing coal.
Click Here to find out more about open cut and underground mining methods.