Rock quarries usually operate for at least 30 years and are developed in distinct benches or steps. A controlled explosion is normally used to release the rock from the working face. It is then transported by truck or conveyor to a crusher, where it goes through a series of crushing and screening stages to produce a range of final sizes to suit customers’ needs. Just enough explosive is used in blasting to break the rock from the face. A powerful excavator loads the rock into dump trucks for delivery to the primary crusher.
Powerful hammers or metal jaws within the primary crusher break the rock down. Rock passes through a series of screens that sift it into different sizes. It may also pass through further crushing stages. Dry stone is delivered by road or rail from the quarry.
Sand and gravel quarries are much shallower than rock quarries and are usually worked and restored in progressive phases. This minimizes the area exposed for quarrying at any time, and limits the period the land is out of use for other productive purposes.
Sand and gravel quarries are pumped to allow them to be worked dry or operated as lakes with extraction below water.
A conveyor draws raw material into the processing plant, where it is washed to remove unwanted clay and to separate sand. Sand separated during processing is de-watered and stockpiled. Gravel then passes over a series of screens that sift the material into different sizes.
Processing separates the gravel into stockpiles in a range of sizes for delivery by truck.
A significant proportion of the demand for aggregates is satisfied from river, lake, and sea beds. Our marine resources are an increasingly important alternative source of aggregates. Marine aggregates play an important role in replenishing beaches and protecting coastlines from erosion.
Satellite navigation may be used to position vessels precisely within licensed dredging areas. Vessels trail a pipe along the marine floor at speeds approaching 1.5 knots and use powerful suction pumps to draw sand and gravel into the cargo hold.
Dredged material is discharged at wharves and other marine facilities, where it is processed, screened, and washed as required.