Jet bore mining is an underground mining method that uses high pressure water to enlarge caverns and cut material (usually ore) into transportable pieces. Jet bore mining is an in situ, remote controlled process, meaning that the personnel generally stay above ground, decreasing the costs of removing overburden and increases the safety of the operation. This process is also referred to as borehole mining, hydraulic or water jet borehole mining, water jet mining, underground or subsurface hydraulic mining, or jet reaming.
In this process, a borehole is dug using a conventional drill. Tools are then lowered into the borehole. A high pressure hydraulic jet is used to carve or cut out the desired area or cavern. The loose material is then removed from the cavern, either as dry material or as part of a slurry (a mix of the loose material and water) to make it easier to pump out.
Jet bore mining is used for a few different applications that include: ore mining (uranium, diamonds, tin, gold, and coal being the most common); enlarging flow ways for water or oil and gas wells; and environmental reclamation, particularly areas of deep contamination where underground soils need to be removed but the overlying layers are uncontaminated.
The initial steps of the jet bore mining process for uranium is a bit different than for other materials. A very cold brine is circulated under ground in order to freeze the ore and surrounding rocks in order to provide safe operation. A shaft below the ore deposit is dug, encased in concrete to provide secure mining. A drill digs a hole into the deposit above, in which a high pressured water nozzle is input, which rotates through the deposit spraying it with water. The water cuts loose the ore, allowing it to fall into collecting vehicles below. The vehicles take it to underground processing, where the ore is mixed into a slurry and pumped to the surface. See uranium mining for other methods of attaining uranium.
The video below (from Cameco, a uranium mining company) shows how jet bore mining is used for uranium extraction.