Overburden stripping

Blasting

Blasting involves using explosives to detach volumes of fragmented material from the rocky mass in sizes that are suitable for their intended use. The largest size of these irregular blocks may exceed 1 metre.

Three operations :

- Positioning of the holes before drilling: according to the profile of the working face, the holes are positioned in 3D before they are drilled in order to optimise the location of the explosive charges.

- Drilling: refers to the creation of holes in accordance with precise drilling parameters. The diameter of these holes depends on the volume of rock to be blasted and the size of the blocks required.

- Firing: after the explosives have been introduced into the bore holes by pumping and pouring, and methodically primed in accordance with a carefully calculated firing pattern, firing reduces the rock into fragments. It is performed in such a way as to limit the disturbances (vibrations) to surrounding areas.

At both La Noubleau and La Gouraudière, 20,000 to 40,000 tonnes of rock are removed at each firing.

Mucking and Primary Crushing

This is the first stage in the processing of the extracted rock.

- Mucking: the materials are transported from the blasting site (the working face) to the primary crusher. The size of the equipment used is proportionate to the rate of production output. At La Noubleau, the buckets of the mechanical loaders hold up to 20 tonnes of rock and the trucks can carry up to 90 tonnes.

- Primary crushing: the photographs and the animation show how the cone primary crusher at the La Noubleau site is supplied and operates. With a capacity of 1,500 T/hour, it reduces the materials to a maximum size of 250 mm.

The aggregate manufacturing plant

The final phase in the process consists of using additional crushing processes to reduce the size of the materials produced by primary crushing:

- Secondary crushing: starting with the primary 0/250, the 0/30 is screened and the 30/250 is crushed to reduce it to a maximum size of 60 mm.

- Tertiary crushing: The 10/60 is crushed to reduce it to a maximum size of 20 mm.
There may also be a quaternary crushing, carried out by recycling previously crushed materials at the tertiary stage in order to further reduce their size.

- Screening and storage: the material obtained after the various crushing stages is graded using screens that correspond to the required granulometry. The materials are then stored in silos prior to shipping.
This is how the different grades of aggregate are obtained; e.g.: 0/2, 2/4, 4/6, 6/10, 10/14 and 14/20.

Shipping