skip

A skip is a robust steel container that rides up and down a vertical or near-vertical shaft in a mine, carrying broken ore, waste rock (mullock), or occasionally personnel. It is suspended from wire rope and connected to a winding engine at the surface; the operator lowers and raises it by controlling the engine. Skips are fundamental to underground extraction: they are the primary method of moving bulk material from the working level to surface, then to the mill or waste dump.

Skips vary in size and design according to the mine's layout and throughput. A small mine may use a skip holding 1 to 2 tonnes; large operations run skips of 5, 10, or more tonnes. The container is typically open at the top and may have a flat or slightly tapered bottom. Many skips feature a bottom discharge gate or quick-release trap that tips the load once the skip is positioned over a grizzly, bin, or crusher at surface. The rope attachment point must handle tensile loads several times the skip's own weight plus its load.

Shaft and rope systems

Most shafts accommodate two skips in a single compartment, one ascending while the other descends, to balance load and minimize winding time. Each skip has its own guide rails or ropes to keep it centred and prevent it from swinging. The wire rope itself, typically 16 to 32 mm diameter steel, must be regularly inspected for wear, corrosion, and broken strands; rope breakage during a hoist is catastrophic. Rope life depends on the number of cycles, shock loads, and environmental conditions in the shaft.

Safety systems surround skip operation. Mechanical catches or safety clamps on the rope will arrest a falling skip if the main rope fails. Depth indicators show the winder operator where the skip is in the shaft. Overload protection limits the amount of material loaded into each skip. The shaft itself must have a sturdy timber or steel collar at the top to catch a skip if it rides past its normal position.

The term 'skip' is British and Commonwealth industrial usage; in North America the same vessel is often called a 'cage' or 'bucket'. Underground coal mines use skips routinely, as do hard-rock mines extracting base metals, gold, and other ores. The skip's position at the centre of the mine's material-handling system makes it one of the most critical pieces of infrastructure below surface. A jammed skip or rope fault can halt all production until repairs are completed.