Mining for solids uses different techniques. They are divided into four main types of mining. Click on their names below.
surface (or opencast) underground fluid marine.
Petroleum, natural gas and water are all drilled.
Click here to learn about drilling.
Click on the photos to see larger images.
Surface Mining
© Don Baccus
When the mineral is pretty
close to the surface, there are many ways to mine it, after you get all of the
waste material out of the way. The easiest way to get the mineral is a process
called open pit. The open pit is getting to the mineral by just digging deeper
and deeper into a pit, removing more and more material.
Most places are hard to dig, so
they are broken up by explosives that are put into the ground. To get explosives
in the ground, miners use rotary or percussion drills to drill holes in the
ground.
Strip mining is used when the mineral layer is thin, but
extends for some distance beneath the surface. The layer is reached by using
bulldozers and scrapers. Then, the mineral is broken up, stripped, and removed
from the ground. Sometimes when a layer of mineral is covered thickly by ground,
they are removed by augers, which are large screws with a cutting head that
rotates into the layer to a depth of 200 feet.
Underground Mining
Schullsburg Mine photos
ice stalagmites and stalactites
Schullsburg Mine photos
When the waste material is up to
100 feet thick, underground mining can be used, but when the material to be
mined is even deeper, underground mining methods must be used. Drift mine is the
simplest type of underground mining. Drift mine is a process of driving the side
of a hill to follow an outcropping layer, that often slopes down as it follows
the layer. Tunnels called adits could be driven horizontally to reach a layer,
and they are usually used to provide water drainage from the workings. More
frequent than that, a vertical shaft is sunk into the ground with galleries that
are dug out at levels, where mineral deposits are mined.
Underground mines can have large depths. Some of the
South African gold mines have depths up to more than 12,000 feet! Such huge
depths like these have raised temperatures from the Earth's heat that can
reach over 122F in the mine tunnels! Cooling systems are used in these situations so the miners don't die of heat.
Digging out levels can be made in two main ways: room
and pillar, and longwall. In the room and pillar system, parallel inclines
are driven into the layer from the main galleries. Then, the ore is dug
up from a few working areas mined between a pair of roads. Pillars of ore that
are unmined, can be left between the rooms to support the roof, or it can be
mined out to let the roof to fall. The longwall system is the main mining method
used for coal mining in Europe. It's a method of carrying extraction on a
face, up to 600 feet or more long, between two roads. The face is moved
forward in a line, while all of the material is removed. The longwall system is
used in deeper mines, so they won't be interrupted by surface mining.
When the material to mine is hard, miners use
explosives to break it away. Explosive charges are put into holes
usually 1 to 2 inches in diameter, and have depths of 6 to 10 feet.
Fluid Mining
Drilling boreholes from the surface into the ground to get the material is used in fluid mining. A process of mining sulfur is when they pump boiling water into pipes installed in the borehole, then the water melts the sulfur, and the sulfur is taken up as a liquid. This process is called the Frasch process.
Bucket wheel, grab or suction cup dredgers are used to get lots of different minerals from the sea floor. Systems of marine mining can go to a depth of more than 200 feet to get minerals. There has been political arguments about the ownership of economic mining going to a depth of 12,000 feet deep under the ocean, for mineral use.
At first, Cable-Tool drilling was done, where a huge chisel was raised and dropped until stone was broken up. But, it took a long time, because the crushed rock would have to be removed, as well as any water that was in the way. And because the well was dry and there was nothing to stop the Petroleum from coming out, when the miners hit gas or liquid Petroleum, they would end up with a "gusher", wasting a lot before the well could be capped. Then Rotary drilling replaced this method.
Rotary Drilling is what it sounds like...the drill bit turns around all the time instead of being dropped. But, in this method they use a weighted liquid inside the drilling area called Drilling Mud. It does three things, stops water from getting into the Petroleum or Gas, stops the "Gushers" from happening, and carries all the crushed rock away from the drill bit. This makes non-stop drilling possible.