Underground mining

Also called: Shaft mining · Topic: Primary Activities: Gathering, Pastoralism, Agriculture and Mining · NCERT: Class 12, Ch 4 "Primary Activities"

Meaning

Underground mining (also called shaft mining) is the method used when a mineral lies deep below the surface. Miners sink vertical shafts (deep, straight holes) into the ground. Underground galleries (horizontal tunnels) then branch out from these shafts to reach the mineral.

It matters because it is the only way to reach deep ores. It is also the riskiest form of mining, because of gases, fires, floods and roof collapse. In India it now gives only a small and shrinking share of coal output [4].

Explanation

Why this method is chosen

• The mining method depends on two things: the mode of occurrence (where and how the mineral lies) and the nature of the ore.
• Mode of occurrence is a physical factor of mining, along with size of the deposit and grade of the ore (how much metal the rock holds).
• When the ore lies deep:
• Removing all the rock above it, as open-cast mining does, is not possible.

• So miners have to go down to the ore through shafts.

• Technology (an economic factor) decides how deep miners can go. Better machines make deeper ores reachable.

How it works (process)

• Step 1: sink the shaft. A vertical shaft is dug down to the level of the mineral.
• Step 2: open the galleries. Horizontal tunnels branch out from the shaft into the mineral bed or vein.
• Step 3: break the ore. Drills are used to break the ore at the working face.
• Step 4: haul and lift. Haulage vehicles carry the ore to the shaft. Lifts then raise it to the surface.

What it needs

• Lifts, to move people and ore up and down the shaft.
• Drills, to break the rock and ore.
• Haulage vehicles, to move ore along the galleries.
• Ventilation systems, which pump fresh air in and push dangerous gases out.
• Capital, because all this equipment and safety work makes the method costly.

Risks and harms

• Poisonous gases such as methane and carbon monoxide.
• Fires and explosions.
• Floods, when water suddenly bursts into the mine.
• Caving in of the roof (roof collapse).
• Underground fires can lead to subsidence:
• Coal seams keep burning below the ground for years.
• The ground above loses its support and sinks. This sinking is called subsidence.
• Towns, roads and homes on top are put in danger.

Feature	Underground (shaft)	Open-cast
Depth of mineral	Deep	Near the surface
Cost	High	Low
Output	Smaller, slower	Large, fast
Safety risk	High (gas, fire, flood, roof collapse)	Low
Main harm	Accidents, subsidence, underground fires	Land scarring, people displaced
India's coal share (2023-24)	3.44% [4]	~96.6% [4]

Where it occurs

• India: share of coal output
• The share of underground mining in India's coal output fell every year: 5.54% (2019-20) → 4.50% (2020-21) → 4.26% (2021-22) → 3.90% (2022-23) → 3.44% (2023-24) [4].

• Open-cast mining now gives about 96–97% of Indian coal (2023-24) [4].

• Jharia coalfield (Dhanbad, Jharkhand) is the best-known example of underground coal fires and subsidence.

• Coal seams there have burned underground for decades, and the land above has sunk.
• The Jharia Master Plan (JMP) for fire, subsidence and rehabilitation was approved on 12 August 2009. It cost ₹7,112.11 crore and was meant to run for 10 years, after a 2-year preparation period [3].
• BCCL (Bharat Coking Coal Ltd) ran 27 fire projects. The methods were:
  • surface sealing
  • digging out the burning coal
  • trenching
  • pumping in inert gas (a gas that does not burn)
  • flushing with a sand–bentonite mix [2]
• Surface fire sites fell from 77 to 27. The fire area fell from 17.32 sq km to 1.80 sq km (2023) [2].

• In 2025 the Union Cabinet (CCEA) approved a Revised Jharia Master Plan costing ₹5,940.47 crore. It covers resettlement, a ₹1 lakh livelihood grant, and credit support of up to ₹3 lakh. Families with legal title to their land and families without it both get this support [3].

• Chasnala colliery (near Dhanbad, Jharkhand), 1975: water flooded the mine and drowned the miners working underground. It is one of India's worst mining disasters.

Don't confuse with

• Open-cast (surface) mining: this method removes the overburden (the soil and rock covering the mineral) and digs from an open pit. It is used for minerals near the surface. It is cheap and safe but scars the land. Shaft mining is used for deep ores and is costly and risky.
• Placer mining: this method washes river sand and gravel to separate heavy minerals such as gold, tin and diamonds. It needs no shafts or tunnels.
• Solution mining of brines: at Salar de Atacama (Chile), lithium-rich brine is pumped up from as deep as 30 m and dried in evaporation ponds [5]. No rock is dug, so this is not shaft mining, even though the brine comes from underground.
• Offshore drilling: wells are drilled into the sea floor from oil rigs to get petroleum and gas. This is drilling, not shafts with galleries.

Prelims Hooks

• Shaft mining = vertical shafts + galleries branching out from them. It is used for deep ores. Open-cast = removing the overburden from ores near the surface.
• Risks of underground mining: poisonous gases (methane, carbon monoxide), fires and explosions, floods, roof collapse. Low safety cost is a feature of open-cast mining, not shaft mining, which makes it a common trap.
• India's underground share of coal output was 3.44% in 2023-24. It has fallen every year since 5.54% in 2019-20 [4].
• Jharia (Dhanbad, Jharkhand): underground coal fires. Fire area fell from 17.32 to 1.80 sq km, and fire sites fell from 77 to 27 [2]. The Revised Jharia Master Plan has an outlay of ₹5,940.47 crore [3].
• Chasnala disaster, 1975: the mine flooded, near Dhanbad (Jharkhand). Do not mix it up with Jharia, which is about fire.
• Mode of occurrence, which decides shaft vs open-cast, is a physical factor, like size and grade. Technology and capital are economic factors.

Mains Points

• Open-cast vs underground trade-off (GS-III):
• India mines about 97% of its coal by open-cast because it is cheap and fast [4].
• The cost is scarred land, displaced tribal communities and lost forests.

• Underground mining disturbs much less land on the surface, so it is being promoted again. It needs more capital, technology and safety spending.

• Mine disasters and rehabilitation (GS-III, disaster management):

• Underground fires at Jharia cause subsidence and air pollution, and they put whole towns in danger.
• Scientific fire control (inert gas, sand–bentonite flushing) cut the fire area sharply [2].
• The Revised Jharia Master Plan pairs resettlement with livelihood grants and credit support, which makes it a model response [3].

• Chasnala (1975) shows why ventilation, water control and roof support are basic safety needs.

• Economics of depth (GS-I):

• Whether a deep deposit can be mined is an economic question.
• Higher demand and prices, better technology and more capital can make a deep or low-grade ore worth mining.
• So the mineral map of the world keeps changing, even though the rocks themselves do not.

Related concepts

• Mining
• Factors affecting mining activity
• Open-cast mining
• Mineral-dependent economies
• Katanga-Zambia copper belt

Read more

• Mining: factors and methods