An ore pass is a vertical or near-vertical opening, which is created during underground mining operations to transfer materials. It is designed based on the gravitational force between different ground levels, in order to provide a convenient material handling system and reduce haulage distances.
Ore passes are used to drop mined ores into loading points or underground bins. The ores can be hoisted to the surface from the loading points. Unloading of ores from the passes can be carried out using underflow or side discharge chutes.
Ore passes are developed using two conventional methods: the mechanical method, which uses a raised borer, and drill and blast methods.
Alimak is one of the most common ore pass raising and drop-raising techniques. Ore passes need to be properly supported to ensure adequate safety. A number of support systems for ore passes are available, including the resin-grouted short cable bolts and resign-grouted rebar.
In some cases, ore passes require support through shotcrete or steel liners, in addition to the primary reinforcement systems.
There are two major types of ore pass systems: flow-through and full ore pass systems. In both cases, muck is dumped into the ore pass and transferred to an underground stockpile via a secondary transport method, such as a conveyor or rail car.
In a full ore pass system, a certain level of material is maintained within the ore pass at all times. Although there is an increased level of hang-ups risk, seismicity near ore pass walls and the level of ore pass degradation are minimized.
In the flow-through ore pass system, the material is allowed to flow down the pass. As a result, hang-ups are less likely to occur in this system.
The selection of an appropriate ore pass location is critical for the ore pass design process. Ore passes need to be designed to cut across ground levels and sub levels, in order to provide easy access to underground minerals.
The intervals between ore passes should not exceed 500ft, or 150m. Ore pass inclination should be maintained between 45° and 90°, while ore pass length should be in the range of 10m to 300m.