Underground mining is used to access deep mineral deposits unreachable by surface excavation. This process involves creating vertical shafts and horizontal tunnels to follow and extract ore bodies far beneath the surface. While this technique allows for the recovery of resources like coal, gold, and copper, it introduces challenges affecting human health, the environment, and financial viability. These drawbacks stem directly from working within a confined, high-pressure, and often geologically unstable subterranean environment.
Hazards to Worker Health and Safety
The immediate physical environment exposes personnel to severe acute dangers. Threats involve sudden structural failures, such as rock falls and tunnel collapses, driven by rock pressure and seismic activity. The confined space also makes equipment accidents a persistent risk, as heavy machinery operates in tight, low-visibility conditions.
Explosions are another major hazard, typically caused by the ignition of methane gas (firedamp) or fine, combustible coal dust suspended in the air. Deep tunnels also face the threat of flooding from unexpected water intrusion, which can trap workers and damage life-support systems. These risks necessitate extensive and costly real-time monitoring and ground support measures.
Beyond immediate accidents, long-term occupational health risks are a major concern. Prolonged exposure to respirable crystalline silica and coal dust can lead to lung diseases like silicosis and coal workers’ pneumoconiosis (Black Lung Disease). These conditions involve the scarring and thickening of lung tissue, severely impairing breathing function.
Poor ventilation in deep mines also contributes to health issues by allowing toxic gases, such as carbon monoxide and radon, to accumulate. High temperatures from geothermal heat combined with heavy physical exertion frequently cause heat stress and dehydration. Miners also face chronic exposure to high noise levels and equipment vibration, contributing to long-term hearing loss and musculoskeletal disorders.
Environmental and Surface Impacts
Removing material from the subsurface leads to physical instability on the surface above the mine workings. This phenomenon, known as mine subsidence, occurs when the ground above the excavated voids sinks or collapses. Subsidence can manifest as sinkholes or land troughs, causing significant damage to overlying infrastructure, including roads, buildings, and utility lines.
The shifting of the land surface disrupts natural water flow patterns, altering local drainage and affecting groundwater conditions. The collapse can misdirect streams and disrupt aquifers, impacting regional water supply and natural habitats. This surface damage can occur years, or even decades, after mining operations have ceased, creating long-term liabilities.
Acid Mine Drainage (AMD) is triggered when sulfide minerals, such as pyrite, are exposed to oxygen and water during mining. This reaction produces sulfuric acid, which lowers the water’s pH and dissolves heavy metals like copper, zinc, and lead from the surrounding rock.
This acidic, metal-laden water can leak into groundwater and surface streams, contaminating aquatic ecosystems. The pollution can persist for hundreds or thousands of years after the mine is abandoned, often requiring costly and perpetual water treatment efforts. Managing waste rock and tailings, which contain these sulfide minerals, presents an ongoing challenge to prevent this long-term contamination.
Operational and Economic Constraints
Accessing deep mineral resources involves high financial burdens compared to surface operations. A disadvantage is the high initial capital expenditure required for constructing complex infrastructure, including deep vertical shafts, extensive tunnel networks, and specialized ground support systems. These structures demand continuous, costly maintenance throughout the life of the mine.
Underground mining is less efficient than open-pit methods due to logistical constraints. The confined tunnels limit the size and number of equipment used, making the extraction and haulage of ore slower and more complex. This lower productivity translates into higher operating costs per unit of extracted mineral and slower returns on investment.
A major component of the ongoing operational expense is the high energy demand necessary to maintain a safe working environment. Substantial power is required for constant ventilation to supply fresh air and dilute gases, and for high-capacity pumps to manage groundwater and prevent flooding. The geological complexity of the subterranean environment also creates operational risks, increasing the potential for unexpected geological shifts and delays.