Introduction > Types of Mines

Types of Mines

There are two mining techniques used for extracting ore from buried potash deposits – conventional mechanized underground mining and solution mining. Both are under consideration in the Holbrook Basin, but the emphasis at this time is on underground mining.

Underground Mining

Worldwide, most potash is mined using conventional underground mining methods. The mines in Canada, the world’s largest potash producing country, are largely underground mines, as are the mines in the leading potash–producing region in United States, near Carlsbad, New Mexico.
Mine Shaft

Typically, a mine has at least two shafts from the ground surface to the level of the potash deposit. The service shaft is for moving people, materials, and machinery. The production shaft is for moving ore to the ground surface. The shafts are generally four to six meters in diameter. In cases with shallow deposits (like the deposits in the Holbrook Basin), a declining ramp may be used instead of mine shafts.

Underground potash mines typically are constructed using the room–and–pillar method, where large “pillars” are left intact to support the roof of the mine, while ore is extracted from
Continuous Miner
“rooms". Ore is mined by blasting or using continuous boring machines, called “continuous miners.” Ore is transported by conveyor to the mine shaft or ramp, where it is loaded and transported to the ground surface.

Once at the ground surface, the ore is moved to a mill for processing. While the technologies used vary from one mill to the next, processing involves a series of steps, such as: crushing and grinding to separate the minerals in the ore; desliming and separation to remove the waste minerals and other by–products; drying, compaction and granulation; and disposal of wastes, including brines (salty water), fines and salt tailings.

Brines that are not reused are retained in surface ponds with fines for solar evaporation. Salt tailings are typically piled on the land surface in a tailings management area. The finished product is raw material for fertilizer that is shipped out in rail cars or trucks.

Major activities involved in constructing an underground mine include: building production and service shafts or a declining ramp; developing a service area and main entry way; lowering and assembling machinery; connecting power and piping; and constructing and lowering conveyor systems. Construction of surface facilities involves building the mill and administrative, maintenance, warehouse and storage buildings, load–out facilities and rail yard, and completing infrastructure for power gas and water supplies, roads and a rail spur.

Solution Mining

In solution mining, fluid is injected into the ore body through injection wells to dissolve potassium, and then the potassium–rich fluid is pumped to the ground surface. Once at the ground surface, potassium is separated from the fluid either in solar evaporation ponds, or through processing at a mill.

Mine Conversion

Sometimes underground mines are converted to solution mines after the potential for economic extraction of ore using conventional methods has
Intrepid Potash Solution Mine
Moab, Utah
been exhausted, or because it is no longer economic to operate the mine due to water infiltration. In other cases, solution mines are constructed where there is no pre–existing mine.

Conversion of an underground mine to a solution mine involves installation of wells for injection into the mines' rooms and extraction of potash–rich brine. The injection wells are connected to water sources and the extraction wells are connected to solar evaporation ponds or to the mill through networks of pipelines and pumping stations. Conversion may also involve re–tooling of old mill facilities, or construction of a new mill.

During the initial phase of operations the underground rooms are flooded with brine (salty water), either heated or not, and brine use is intensive. In the next phase, brine in the rooms is kept at a steady state, with injected brine balancing extracted brine, and brine use is less intense. In the third phase, brine is extracted from the rooms and not replaced.

The ore dissolution process works by selectively dissolving and leaching potassium salts from the floors, pillar walls, and ceiling of the former underground mine. Where the potassium chloride in the surfaces is exposed to injected brine, the sodium ions in the brine are exchanged for potassium ions and the brine becomes potassium–rich, while sodium lines the mine surfaces.

In some cases, hydraulic fracturing—or “fracking”—is used to build pressure in flooded rooms to get old mine walls to crack, increasing the exposure of brine to potassium and increasing yield. This type of fracking does not involve chemicals. The primary safety issues surround the integrity of the well bore, and the ability to predict and manage the location and extent of fracturing.

Greenfield Solution Mines

When a solution mine is built where there is no existing underground mine, the initial phase involves development of underground caverns,
Intrepid Potash Solar Evaporation Ponds
Moab, Utah
sometimes using directional–drilling technology. The caverns are constructed by injecting fresh water or heated brine into the ore body to dissolve the potash bed. Once the caverns have reached the desired shape and size, operations are modified for the purpose of dissolving only potassium from the walls, ceilings and floors of the caverns. During this phase, brine is injected to selectively dissolve potassium, exchanging potassium ions for sodium ions on the surfaces of the cavern. Potassium–rich brine is pumped to the land surface and the potassium is extracted either through solar evaporation or by recrystallization in the mill.

Major construction activities include: establishment of drilling pads; directional drilling of wells; sump development; lateral cavern connection and roof development; site preparation on the surface; installation of pipeline networks for transporting water and brine; and construction of above ground buildings, infrastructure, a mill, and waste and tailings management areas. For mines that use solar evaporation, a series of solar evaporation ponds is constructed.

For More Information

Environmental Aspects of Phosphate and Potash Mining

Potash Processing in Saskatchewan: A Review of Process Technologies

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