From the ground up
Britain’s diverse geology means the country has a variety of mineral resources in the ground. Each has unique properties and can be quarried and processed for a wide variety of essential uses.
However, these geological resources are not evenly distributed across the country and must be transported from where they are extracted to where they are needed.
This means that millions of tonnes of mineral products such as aggregates travel around the country by road, rail, river and sea. Transporting mineral products as efficiently as possible to meet the country’s demand is one of the industry’s biggest logistical challenges.
Managed & Monitored
Before any quarrying can begin there’s a long and complex process to identify potential mineral resources and secure the right permissions and licences. This applies whether the mineral is in the ground or beneath the sea. The same applies for proposals for other mineral products activities such as concrete plants, rail depots or recycling facilities.
It’s a process that can take years, but it helps to ensure that the country’s mineral resources are managed and monitored, with full consideration for the environment, local communities and subsequent use of the land after quarrying.
There are more than 2,000 quarries and associated production sites across Great Britain – from quarries and cement works to concrete factories and asphalt plants. Each site is different depending on the type of material, the location of the site, the processes required, the size of the market they supply and many other factors.
Mineral product operations can therefore vary enormously, from a typical ready-mixed concrete plant which can occupy the space less than half a football pitch to a cement works which can cover an area the size of several hundred football pitches. The length of time individual sites work will also be dependent on many factors, ranging from a few years through to many decades.
How Quarrying Works
Broadly speaking, there are two types of quarry – (1) hard rock and (2) sand & gravel:
Hard rock
Hard rock quarries produce aggregates such as limestone and granite. They are usually large and can be very deep – depending on the geology – and the rock will be blasted and dug out at multiple different levels known as ‘benches’.
Sand & gravel
Sand and gravel quarries are shallower than rock quarries because the mineral deposits are usually around 5 metres deep. No blasting is required as the mineral has already been broken down by the action of ice and water over thousands of years.
The key processes in most quarries are as follows:
- Remove surface soils – for new quarry areas, soils are removed and stored in ‘bunds’ around the perimeter. This helps to screen quarrying activities and is used in restoration of the land after mineral extraction ends.
- Drill & blast (hard rock only) – deep holes are drilled down into the rock for explosives. A carefully controlled blast is carried out to break a section of rock away from the face. This is not necessary in a sand and gravel quarry.
- Dig & haul – large excavators scoop up the raw mineral and load it into dump trucks to take to the processing plant which could be up to a mile away. Sometimes a ‘field’ conveyor is used to move material longer distances.
- Crush (hard rock only) – the first part of aggregates processing involves breaking larger rocks down into smaller pieces in a powerful crusher before the material can be washed and screened.
- Wash & screen – the crushed rock or sand and gravel is usually washed to remove silt and unusable finer material, then sieved through a series of giant ‘screens’ to separate the particles out into single sizes, each of which have different uses.
- Stockpile & test – a set of conveyors carries the sorted single-sized aggregates to different stockpiles or storage bays. The products are regularly tested in laboratories to ensure they meet the specification for their use.
- Load & transport – a digger scoops up the single sized aggregates and loads it into waiting tipper lorries which transfer the product to where it is needed in construction or for further processing into other products. In some cases ships, trains or even river barges can be used to transport the processed aggregate.
- Downstream processing – many quarries have on-site facilities for making downstream products such as concrete and asphalt. Such plants also exist in other locations and aggregates are delivered by road or rail.
- Restore quarry – once the mineral has been removed a site can be restored in line with an agreed plan. Most former quarries are returned to agriculture, nature conservation, recreation or leisure.
Planning and permitting
Aggregates are needed for the construction of transport and renewable energy infrastructure, housing and other buildings that are a vital part of the Scottish Government’s infrastructure investment plans for the future.
Adopted in February 2023, the National Planning Framework 4 (NPF4) details the long term planning strategy for Scotland to 2045. However, in order to deliver these plans it is necessary to ensure a suitable supply chain of minerals capable of meeting future demand both in terms of volume of aggregate and also quality of aggregate.
Supply of mineral products cannot be taken for granted; it must be planned, managed, and monitored to ensure demand is met on a secure and sustainable basis.
In Scotland, for many years there has been inadequate replenishment of permitted reserves. Between 2012-2021, of the 30.4 million tonnes of sand and gravel sold, only 16.8 million tonnes of a replacement reserves were permitted – a replenishment rate of just 55%. For crushed rock, over the same period 91.5 million tonnes of sales were replaced with 60.5 million tonnes of new reserves – a replenishment rate of 66%. This replenishment rate is unsustainable, and decisive action is needed to streamline and increase the capacity of the mineral planning system.
There is a planning requirement for a landbank for at least ten years, but this should be considered a minimum, not a target.