The conveyance – a skip-over cage – was 5m below the surface platform when it stopped.
The mine’s rescue team was used to evacuate all people. No one was injured.
The friction winder consisted of a solo skip in balance with the skip-over cage.
An inspection revealed one of two 46mm non-rotating balance ropes had broken 25m below the cage.
The broken rope, which weighed several tonnes, fell to the bottom of the shaft some 1000m below, resulting in significant damage.
If the failure had occurred on the solo skip side with the cage conveying the people at the bottom of the shaft, the failed rope could have fallen onto the cage with disastrous consequences.
The 25m portion of the broken balance rope that remained suspended below the cage after the incident was recovered.
The rope was severely corroded immediately adjacent to the break and it appeared the reduction in cross sectional area due to corrosion combined with the self weight of the rope caused the failure.
The corroded section of the rope formed the tail loop at the shaft bottom when the skip-over cage was at the loading stage.
“This section of rope was most exposed to spillage during loading and hence to the corrosion and wear that would result from the entry of fine particles of sulphide ore into the rope structure,” the inspectorate said.
“What could be observed of the remainder of the rope appeared to be relatively free of corrosion although poorly lubricated.
“Non-destructive testing was routinely carried out six monthly. The last test was one month before the incident. No significant loss of area was identified.
“However only those parts of the balance ropes that could be safely accessed from an existing inspection platform were subject to testing.”
The testing did not include the point at which the failure occurred. This was the section that was most prone to corrosion and was the most highly stressed part of the balance rope.
The mines inspectorate has recommended that periodic non-destructive testing and visual inspections covering the full length of the rope be carried out with particular attention being given to inspection and testing of high risk areas, such as the tail loop area on balance ropes.