sink

A sink is a vertical or near-vertical excavation driven downward into rock or ore, typically 20 to 100 meters deep, with the specific purpose of exploration or access rather than primary extraction. Unlike a shaft, which connects surface to an operating mine and carries ore, personnel, and services in both directions, a sink serves as a dead end: it goes down to investigate geology, test ore quality, or reach a lower working level, but does not continue to the surface on the other side.

Sinks are sunk, meaning driven downward from existing levels or from surface, through various methods depending on rock type and urgency. Hard rock sinks use drill and blast: holes are drilled in a pattern, loaded with explosive, fired to break the rock, and the rubble is mucked out by hand loader or conveyor. Softer ground may be sunk by mechanical digger or even manual pick and shovel work. Temporary support comes from timber cribbing or steel sets; deeper sinks require continuous wall support as ground becomes less stable and water pressure increases.

The chief difference from a shaft lies in purpose and design. A shaft is a permanent, heavily engineered structure with steel frames, permanent hoisting equipment, and defined service lines. A sink may be temporary, lasting months or a few years, and often requires only basic ventilation and ladder access. Many sinks are abandoned once their geological purpose is fulfilled; others are converted to permanent use if ore is found. Sinking a shaft is capital-intensive; sinking a test hole is reconnaissance work.

Sinks generate characteristic problems: water inflow is common below the water table, requiring pumping; loose ground can slump and trap equipment; and ventilation is difficult in a dead-end hole, creating air quality and methane hazards in coal mining. Escape routes must be redundant, and ladder shafts are often sunk alongside working sinks for safety. In deep mining, sinks driven from lower levels to upper levels explore the limits of ore bodies and identify new ore zones before major development.

The term appears in both hard rock mining and coal mining, though its use has declined with modern exploration methods. Reverse circulation and percussion drilling from surface have reduced the need for exploratory sinks in greenfield work. However, in active underground mines, sinking remains a standard technique for accessing new ore and opening new levels of operation.