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Breaking of Caprock

After the topsoil, overburden and secondary overburden are removed the caprock is exposed.  The caprock or ‘duricrust’ as it is called by geologists, is a solid concrete-like layer averaging about 1m thick above the friable bauxite layer in the soil profile.  Both the caprock and the friable bauxite are ‘bauxite’ ore and are mined and processed. 
Caprock is formed by thousands of years of weathering processes that dissolve and deposit certain minerals in the soil profile.  To break the caprock, holes are drilled into it.  Explosive slurry is then pumped into the holes and this is wired up with detonators.  When weather conditions indicate that noise levels will not disturb neighbours, the caprock is blasted.  In some instances, when there is likely to be an adverse impact on neighbours, or where the caprock layer is very thin, a large remote controlled bulldozer can be used to rip the caprock.

Undulating surface caprock.

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After Secondary overburden is removed, this hard, undulating surface caprock layer is exposed and ready to be broken up.

The caprock layer is blasted to access the bauxite

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The caprock layer is blasted to access the bauxite beneath it.