What is an Ore Pass in Mining?

An ore pass is a mining shaft used to transfer ore and mining waste from the mine. Ore passes are a convenient way to transport and handle materials and minimize hauling distances between levels in a mine.

Considerations for Building an Ore Pass

Ore passes take advantage of gravity to move materials from one level of a mine to another. There are two methods for developing an ore pass: the drill and blast method and the mechanical method.  

The drill and blast method requires miners to drill a hole in the location of the ore pass to then place explosives, blasting a hole for the ore pass. The mechanical method involves using a raise borer, which excavates a circular hole between mine levels.

When building an ore pass, miners consider the following:

• Location. Ore passes should intersect mining levels, making it easy for miners to access hang-ups, or blockages, within the system. Ore pass hang-ups are a common problem in underground mining. Stress conditions and rock type should also be considered when choosing a location. If the ore pass is placed in a location with weak host rock, then the ore pass may be more prone to hang-ups. Ore passes should be located at the opposite end from the mining face in order to maintain the structural integrity of the mine.

• Length. Longer ore passes are more susceptible to degradation and are more costly to build. Typically short ore passes ranging from 10 to 100 meters will be built in mines, but some underground passes can run as long as 300 meters.

• Dimension. Ore pass dimensions are directly influenced by the shape of the opening and the size of materials that will pass through the underground passes.

• Shape. Ore passes can be square, rectangular, or circular. Underground passes that are created using a raise borer are circular. 

• Orientation. Ore passes are either vertical or set on an incline depending on the mine layout, the materials, and the material fragmentation. Vertical ore passes tend to cause more damage to the walls of an ore pass.

• Support. Ore passes can be supported by rebar and liners, like shotcrete.

Watch this video to see footage from Flyability's Elios 2 drone shot inside an ore pass with a hang-up obstructing it:

Types of Ore Pass Systems 

There are two types of ore pass systems in the mining industry: a flow-through ore pass system and a full ore pass system. 

For both systems ore and waste is dumped into the ore pass and ends up at the draw point, or point in which the ore is transported by a loader, conveyor, or rail car to an underground stockpile.

Flow-Through Ore Pass System

In flow-through systems, ore is dumped into the ore pass and then flows down to the draw point.  

This system is used when ore has high levels of fines, or fine particulate, that results in ore pass hang-ups. Because material is flowing at a continual rate, fines don’t settle and hang-ups are less likely to occur. 

Flow-through systems are also used when broken rock is passed through mills—a device that breaks up the ore into smaller pieces—at a rate that exceeds underground ore production in a full system. 

Because of the near constant flow of broken rock through this system, the ore pass is more susceptible to damage that may require reinforcements, maintenance, or even a costly redesign that could prolong downtimes in the mine.

Full Ore Pass System

In full ore pass systems, a certain amount of ore is maintained in the ore pass at all times.

This system is used to prevent degradation of the ore pass, to prevent rock failures, and to prevent mining-related seismic events. However, there is an increased risk of ore pass hang-ups in this system since rock is not consistently flowing through the ore pass. Because of this, fines settle in the underground pass and oxidize, causing these blockages.

In a full ore pass system, the mill is continually fed, making it difficult to maintain overflowing material levels. By increasing draw times from the ore pass, these levels can be better maintained.

A hang-up in an ore pass

Ore Pass Material Control Equipment

The following equipment controls the flow, size, and amount of material moving in and out of an ore pass:

Scalpers

Scalpers are a type of screen used to prevent oversized rock from entering the ore pass. They consist of several rectangular slots made of bars. However, scalpers allow greater amounts of oversize rock to wedge between its bars. These are less effective when screening materials, resulting in miners having to break rock materials through the bars. This can lead to damaged scalpers.

Grizzlies

Grizzlies are the most common type of screen used to prevent oversized rock from entering the ore pass. These screens consist of several square-shaped slots for rock to pass through.

Mantles

Mantles are also a type of screen that are used to prevent oversized rock from entering the ore pass. These screens consist of circular holes for materials to pass through. Mantles require minimal rock breaking but allow larger rocks to pass through, threatening the wall integrity of the ore pass.

Control Chains

Control chains control the flow of material at the bottom of an ore pass to the draw point. These chains hold the ore pass materials in place and can be pulled up to allow for materials to flow into chutes to load rail cars or underground loaders.

Chutes and Feeders

Chutes are used to funnel materials from the ore pass to a rail car or loader for transport to an underground stockpile. Chutes are typically the same size as the ore pass. Chutes are usually used with a control gate.

Feeders are a type of chute set on an incline and are used with control chains. These are less commonly used in ore passes.

Gates

There are several types of gates that are used with chutes, including:

• Bar and chain gates. These gates are not good at controlling fines without hydraulics in place, but are very good for controlling large rock blocks.

• Finger gates. These gates are also not good at controlling fines, but are very good for controlling large rock blocks.

• Undercut arc gates with control chains. These gates are the most commonly used since they are good at controlling fines and blocks with hydraulics in place.

• Underhand guillotine gates. These gates are difficult to control large rocks, but are good for controlling fines. Large rocks will discharge without hydraulics in place.

Ore Pass Monitoring

It’s important to monitor the ore pass in order to preserve the ore pass’s structural integrity, to prevent mining related seismic events, and to prevent overfilling of the ore pass.

Monitoring the material level in an ore pass

The following are monitored and inspected, either manually or by a mine drone, in an underground ore pass:

• Material levels

• Wall quality

• Liner quality

• Material control equipment

Regular ore pass monitoring and inspections can prevent hang-ups and keep the mine safe. Failure to monitor an ore pass could lead to unwanted runs of ore and hang-ups. This can cause equipment damage or failure, can threaten underground structural integrity, and can even cause injuries or fatalities to miners.