Demand for ornamental blue limestone also drives Carrieres du Hainaut's production of 2.2million tonnes of aggregates each year
While the focus for many quarries is to produce high quality aggregates, for some the aggregates are a by-product of the quest to produce higher value materials. For Belgium-based
The quarry - 13km north east of Mons in the Walloon region of Belgium - has been operating for 120 years and was opened to extract the blue limestone that is highly sought after for its decorative qualities. Today the quarry produces 200,000m3 of the material a year from the 450,000m2 quarry and the Pierre Bleu is shipped to customers up to 250km away.
Carrieres du Hainaut operates eight benches within the Pierre Bleu with four extractive faces being worked at the same time. Material is extracted using a trencher and cable diamond saws.
Overlying the blue limestone is a 50m thick deposit known as râches - a black limestone - which Carrieres du Hainaut extracts to access the limestone and then processes for road construction aggregates. The quarry currently extracts 2.2million tonnes of this material each year but production is expected to ramp up to 2.75million tonnes by 2013 as the company strips more overburden to access the blue limestone.
The aggregate feed stock is extracted by drill and blast with two blasts carried out every week to extract 5000tonnes at a time. Blasts generally use 100g of explosives per tonne of rock but close to the boundary with the blue limestone, the quantity is reduced to 10g per tonne in order to avoid fracturing the ornamental stone deposits below.
The quarry operator has to strip 20m of overburden to reach the black limestone and usually moves 300,000m3 of material each year. The râches aggregates are generally sold for just €1 per tonne but, according to Carrieres du Hainaut project engineer Alexandra Ciuch Pilette, the value of the ornamental stone makes the operation financially viable.
