Mining commenced in 1965 with underground access being provided by the driving of the No.1 Drift, which heads inland in a northerly direction. The drift is 330 metres in length at a decline of 1 in 5 gradient, with salt being first encountered at 70 metres below surface. Workings now extend to an area of over 350 hectares, at a current depth of over 400 metres below surface.
The salt extraction at Kilroot is carried out by conventional room and pillar methods. Unmined pillars of rock salt are left in place for support. The reserve is mined with an extraction ratio of between 40-60%. The current development area uses pillars of 30-50 metres square to create rooms of up to 10 metres high by 15 metres wide.
In 2011 the company was granted a further extension area of 280 hectares, which on current extraction rates will extend the life of the mine to beyond 2040.
In June 2015 ISME completed a second driveable access into the mine, known as the No.2 DQ Drift. At a length of 1151 metres, a gradient of 1 in 8.6 and a diameter of 7.2 metres, it is wide enough to allow for 2 way traffic to pass, cut down on travel time to the working areas and provides enhanced ventilation for future development.