cage

In a mine shaft, the cage is the platform or framework that carries workers, tools, and broken ore vertically between the surface and the working levels. It is attached to steel rope wound around a drum called a whim (or winch), and as the drum turns, the rope pulls the cage up or lowers it down. The cage itself is constructed from steel or timber, with guard rails and a sturdy floor, and typically accommodates between four and twenty workers depending on the mine's depth and the rope's rated load.

The cage travels inside a vertical shaft that may be several hundred meters deep. Guide rails fixed to the shaft walls keep the cage aligned and prevent it from swinging. As it rises and falls, the cage must be strong enough to withstand repeated shock loads from starting and stopping. Modern cages have safety catches that grip the guide rails if the rope fails, preventing a catastrophic drop.

Two main designs persist in active use

The single deck cage is an open or latticed platform that serves one main purpose, either passenger or ore hoisting, depending on the shift. The double deck cage, or balance cage, has two compartments that move in the same shaft on separate ropes; as one deck rises with loaded ore, the other descends empty, reducing the net load on the drum and saving fuel or power. Balance cages were standard in deep hard rock mines where rope costs and energy consumption were significant.

Wear and failure are constant concerns. The rope deteriorates from metal fatigue and corrosion; the guide rails wear into ruts; the cage floor develops cracks. Most operations carry out detailed rope inspections at fixed intervals, typically every few months or after a set tonnage is hoisted. A slack or frayed rope, or misalignment that causes the cage to bind against the rails, will stop hoisting until repairs are made.

The term cage reflects its fundamental design: a framework that encloses and protects its load, analogous to a birdcage. In some regions and older texts, the hoisting unit is called a skip (a bottomless bucket that tips to dump ore at the surface) or a kibble, but cage remains the standard term for the personnel and general-purpose carrier.