At the primary crusher, which is situated below the working level, the rock is broken down by a rotating eccentric vertical column and comes out the other end with maximum dimensions of about 20cm (8") and smaller. The crusher is always well charged with rock in the grinding process, this optimizes the wear on the mechanism which is a problem if under-filled. Each truck dumps a load of 85 tonnes (some trucks have a 50 tonne capacity) in one and half minutes. A total of 12000 tonnes a day.  In this process water from the base of the quarry is pumped to dampen the rock but not to the extent at which the later screening would be affected by blockage from slurry. We were told that the quarry base in winter is flooded to a depth of between 7 - 10 metres, and the point where we were collecting is underwater during that period. From the base of the crushing plant the material is raised to the next stage by conveyor.

The machine that loads the lorries looks like an overgrown bulldozer, the tires cost £12000 each. The front wheels are encased in chains, not for extra grip as with snow chains but to act as chain-mail protection against the rock. Because the trucks descend with their loads to the crushing plant, engine wear is light but brakes are another story! (Swings and Roundabouts). Truck engines are overhauled every 15000 working hours. (An overhaul implies stripping down a replacing worn parts and shouldn't be confused with a simple oil change and other adjustments!)

Quarrying on an industrial scale first started in the mid-nineteenth century. Currently they have an operating license to continue for the next twenty five years and plan to deepen the quarry by another 150m which includes widening the operation to prevent instability with large vertical faces. Some hole!

Back at the site office, there is a small collection of some of the fine Calcite and Analcime mineral specimens this quarry has turned up!

A single crystal about twice the size of the average fist!

Pictured left: Analcime with Iron Oxide, giving a rather appealing colouration

More Analcime plus Les as a pale reflection of the biggest part of himself!

It is impossible to capture the size and depth of this quarry in just a few pictures and words. In many respects I would have preferred to have strolled around the upper parts of the quarry to get a close look at any metamorphic aureole and/or any other localized mineralisation Sadly this was not possible on this occasion.

This site is one for the specialist, at least those of us that appreciate our personal safety and take the proper care. I enjoyed myself by standing back and looking at the rocks, machinery, drilling & blasting technique, and thinking of what was going on some 500Ma ago. For me it was a SUPER DAY in a SUPER QUARRY but I don't collect minerals from this locality.

Many thanks to the Quarry Operators CAMAS for allowing our small group access, we very much appreciated the opportunity.

R Coleman 13 June 2002

Report Archive

Links:
http://www.angelfire.com/ak/qweasd/ A very informative article about Croft, the Village and Quarry!

http://www.cpcayless.fsbusiness.co.uk/croft.htm   Whilst wandering around the bottom I came across some carrion, originally bird, which I thought might have been one of the ducks but the plumage suggested something else. First guess was a Fox did it, but not enough grub down there, second thought was Hawk but all I saw was a couple of seagulls high above and a crow. Perhaps this is the answer but we will have to wait and see!