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.
