Mine Features and Hazards

Common features found in and around mines:

Drifts are horizontal passages within a mine.  A drift with an opening to the outside (called a portal) is an adit.  Drifts that intersect the ore vein are called crosscuts.  Drifts with portals at each end are tunnels.  Within a drift, the roof is called the back and the side walls are called the rib.  The floor may sometimes be referred to as the sill.

Headframes are wood or steel structures constructed over a mine shaft or winze to support pulleys used with cables and hoists for haulage and access.  Headframes often have attached or nearby ore bins for storing and sorting ore and waste rock.

Shafts are vertical or inclined passages which connect the underground workings of the mine with the surface.  The top of a shaft is called the collar.  Shafts are primarily used for haulage and personnel access.  A secondary shaft which has been driven down from within the mine is called a winze.  A secondary shaft which has been driven upwards from within the mine is called a raise.  Winzes and raises are mainly used as air shafts, ore chutes, manways or for exploratory purposes.

Stopes are areas of the mine where ore was removed.  They usually follow the ore vein closely and are often at steep angles to the horizontal.  Stopes may be huge caverns or narrow convoluted passageways with systematic or random timbering called stulls.  Many stopes have large drops or confined spaces and often contain an abundance of loose rock.  The roof of a stope is called the hanging wall and the floor is the footwall.

Timbering consists of wood supports inside the mine workings to prevent collapse or rock falls from the rib or back.  Timbering can be made from finished, rough cut or raw wood.  Types of timbering include cribbing (timbers laid at right angles to each other log cabin style and sometimes backfilled with rock debris) and square set (timbers laid in boxes which can be stacked on top of each other or side by side).

Mines were generally constructed and maintained to be safe while they were operational.  After they are abandoned, workings may decay to a point where they could become dangerous.  For instance, some support structures may have been removed before abandonment for re-use elsewhere or supporting pillars may have been quarried away, leaving the chamber unstable.  Ventilation and water pumping systems that once maintained safe working conditions have been removed.

There are a number of potential hazards that mine explorers face:

  • Bad Air:  Abandoned mine workings may contain areas with low oxygen levels due to displacing gases (blackdamp) or areas with poisonous gases.  Concentrations of carbon dioxide, carbon monoxide, hydrogen sulfide or methane can poison someone outright or cause asphyxiation from low oxygen concentrations.  Some of these gases can also pose an explosion hazard.  Unventilated areas of a mine with extensive rust or rotted timbers can have depleted oxygen levels due to the oxidation process involved.  Standing water can absorb carbon dioxide or hydrogen sulfide which might be liberated into the atmosphere when disturbed.

  • Collapse:  The effects of blasting, weathering, and earthquakes destabilize once-strong bedrock through time.  Portals and collars in particular are affected but ribs and backs can also destabilize.  Support timbers, ladders and other similar structures may appear safe but could have degraded from water rot, dry rot or termites.  Similarly, waste rock dumped or backfilled into chambers may be unstable and rockslides can occur.

  • Darkness:  As with most underground places, the darkness in a mine is total.  Without a strong light source it may be difficult or impossible to exit a mine.

  • Explosives:  Explosives such as dynamite, black powder and blasting caps may be present in abandoned mines.  Many explosives become increasingly unstable with age and could be detonated by the slightest movement or even the vibrations from explorers themselves.

  • Falls:  Falling down vertical openings is the most common cause of death and injury in abandoned mines.  The ground around abandoned mine shafts and open pits may be weak and could cave-in without warning.  Undergrowth may hide shafts while timber used for capping may have rotted to a point where it will collapse if weight is put on it.  Even scarier are eroded "ant-trap" shafts where loose earth around the collar crumbles away over time leaving a funnel-shaped drop-off.  If a curious person attempts to look down the shaft, he or she could begin sliding into it with nothing to stop the fall.  Inside the mine, winzes may be located at any place, even right in the center of a drift.  False floors may be unstable and collapse when walked on.  False floors may also be present in substantial lengths of tunnel where the floor level has been worked (understoped).  Such floors may be supported by rotten wood but surfaced with rock and not clearly distinguishable from a solid floor.

  • Hazardous chemicals:  Mines dug in wet areas give underground water a path to percolate through rock and exit via the tunnel systems.  In some areas, the mine water can contain various types of heavy metals.  Bacterial action can create acids and other compounds that are hazardous to humans.  In addition, mills and other processing areas may contain traces of cyanide and mercury compounds that were once used to separate precious metals from the ore.

  • Remoteness:  Most mines are located in remote areas and are far from medical assistance or even mobile phone coverage.  Depending on the circumstances, simply getting an injured explorer to the portal of a mine can be difficult and challenging prospect, let alone seeking outside help.

  • Water:  Water in mines is often deep and can be dangerously cold.  If it fills an area with steep sides it may not be easy to climb out.  Seemingly shallow water can conceal sharp objects, drop-offs, winzes and other hazards.  Disturbed water may release poisonous or displacing gases.  In addition, a wet mine can rot or rust timbers, shoring and ladders making conditions hazardous.  Desert mines tend to be dry and therefore relatively safe in this regard, however, dry rot or termites can weaken wood even in dry mines.
  • Wildlife:  Snakes, coyotes, bobcats, mountain lions and bats often call a mine and the area around it home.  Injury from venom, bites and claws plus possible diseases carried by these animals is a serious concern.


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