Geology — Economic Geology, Resource Geology, and Environmental Geology

Economic Geology

Mineral deposit:

A concentration of minerals that can be mined economically
Grade: the mineral content per unit of rock (%)
Economic viability is determined by grade and tonnage together

Types of mineral-deposit formation:

Igneous deposits: magmatic differentiation: chromite and platinum-group metals (Zimbabwe’s Bushveld Complex) pegmatite: lithium, cesium, beryllium, rare earths hydrothermal deposits: precipitated from hot fluids (gold, silver, copper, zinc) porphyry copper deposits: large, low-grade copper (Chile, the United States)
Sedimentary deposits: banded iron formations (BIF): marine precipitates from before the Paleozoic era evaporites: rock salt, gypsum, potash (in arid environments) placer deposits: gold, rutile, ilmenite
Weathering (residual) deposits: residual deposits: bauxite (aluminum from tropical weathering) lateritic nickel
Metamorphic deposits: minerals concentrated during metamorphism

Major metal resources:

Iron (Fe): the most important raw material from BIF · the steel industry Australia’s Pilbara region, Brazil’s Minas Gerais
Copper (Cu): porphyry copper deposits · electrical wiring Chile’s Escondida, the world’s largest
Lithium (Li): pegmatite and salt flats (salars) the “lithium triangle”: Chile, Bolivia, and Argentina a key raw material for EV batteries
Rare earth elements (REE): 17 elements · electronics and advanced industries China produces over 60% · a geopolitical risk factor

Energy resources:

Coal: from deposited plant remains · the coalification process graded as anthracite, bituminous, or lignite
Petroleum and natural gas: converted from marine organic matter migration and accumulation of crude oil (anticline structures) unconventional resources: shale gas, oil sands
Uranium: a nuclear-energy raw material, found in hydrothermal and sedimentary deposits

Mining and the Environment

Acid mine drainage (AMD):

Sulfide minerals (like pyrite) oxidize + water + oxygen 4FeS2 + 15O2 + 14H2O → 4Fe(OH)3 + 8H2SO4
Extremely low pH · heavy-metal leaching (As, Pb, Cd, Zn)
Severe damage to nearby streams and ecosystems
Treatment: limestone neutralization, wetland treatment, bioremediation

Mining methods and environmental impact:

Open-pit mining: large-scale terrain alteration, landscape disruption fugitive dust, noise, vibration
Underground mining: risk of land subsidence, waste leakage
Post-mining reclamation: topsoil preservation, revegetation tunnel stabilization, water treatment

Tailings:

The slurry residue left after crushing ore
Tailings dams: storage facilities dam-failure disasters: Brumadinho, Brazil (2019) heavy-metal contamination, downstream ecosystem destruction
Tailings treatment: filter pressing, dry stacking, submarine disposal (controversial)

Sustainable mining:

Resource efficiency: technology for processing lower-grade ore
The circular economy: a growing share of recycled metal urban mining: gold and rare earths from electronic waste
Social license: community acceptance indigenous rights, environmental-impact assessment

Hydrogeology

The groundwater system:

Vadose zone: from the surface to the water table soil moisture mixed with air
Saturated zone: below the water table all pore space filled with water
Water table: the top of the saturated zone

Aquifer:

A permeable layer that can store and transmit groundwater
Unconfined aquifer: the water table fluctuates freely
Confined aquifer: under pressure between impermeable layers drilling can produce an artesian well
Local aquifer: small scale / regional: basin scale

Groundwater flow:

Darcy’s law: Q = −KA * (dh/dl) Q: flow rate / K: hydraulic conductivity / A: cross-sectional area dh/dl: the hydraulic gradient
Hydraulic conductivity (K): a rock’s permeability gravel and sand: high / clay: very low
Storativity: the volume released per unit change in head

Groundwater contamination:

Point source: landfills, underground storage tanks, direct factory discharge
Nonpoint source: agricultural fertilizer and pesticide runoff, urban surface runoff
Major contaminants: nitrate: agricultural areas, infant methemoglobinemia organic solvents: BTEX, TCE, PCE, dry-cleaning chemicals heavy metals: arsenic, lead, mercury PFAS (fluorinated compounds): persistent contaminants
Contaminant behavior: dissolved contaminants: move as a plume DNAPLs (dense non-aqueous phase liquids): sink vertically

Groundwater development and conservation:

Groundwater depletion: overpumping → the water table falls aquifers in India, California, and Saudi Arabia
Land subsidence: compaction from groundwater extraction parts of Seoul’s Gangnam district, Ho Chi Minh City, Bangkok
Groundwater conservation: artificial recharge zones, enhanced recharge, monitoring

Environmental Geology

Slope stability:

Types of slope failure:
  fall: free fall on a steep slope
  slide: movement along a plane
    translational slide: shallow and planar
    rotational slide: curved and deep
  flow: debris flow, mudflow, avalanche
  spread: movement over a weak layer
→ Factor of safety (FS):
  FS = resisting force / driving force (1 or above = stable)
→ Factors that trigger failure:
  rainfall: increased pore-water pressure
  earthquakes: seismic shaking
  human activity: cutting and loading slopes
→ Mitigation: drainage systems, retaining walls, anchors, vegetation

Soft ground:
→ Cohesive soil, organic soil, reclaimed land, sludge
→ Problems: high compressibility, low shear strength
→ Consolidation settlement: gradual settlement over a long period
→ Ground improvement:
  replacement, compaction, preloading, drainage acceleration (PBDs)
  grouting, pile foundations

Geohazards:
→ Landslides:
  vulnerable areas: steep slopes, weathered granite, high clay content
  vulnerable regions in Korea: the mountains of Gangwon and North Chungcheong Provinces
  early-warning systems: rainfall thresholds, SINMAP analysis
→ Land subsidence:
  underground mining, excessive groundwater extraction, cavity formation
  urban sinkholes in Seoul: aging subway tunnels and sewer pipes
→ Coastal erosion:
  wave energy, sediment transport, sea-level rise
  dune destruction, breakwater effects
  Korea's east coast: accelerating erosion

Geohazard assessment:
→ Hazard maps: GIS-based vulnerability analysis
→ Ground investigation: drilling, the standard penetration test (SPT), the cone penetration test
→ Geotechnical engineering:
  characterizing ground conditions → informs structural design

Frequently Asked Questions

Q. Why does lithium matter so much for the future energy transition, and are there supply concerns? A. Lithium is the key element in the lithium-ion batteries used in electric vehicles, smartphones, and energy storage systems (ESS). It’s light and highly electrochemically active, and there is effectively no substitute. Supply concentration is a serious concern: more than half of the world’s known lithium reserves are concentrated in the salt flats (salars) of Chile, Bolivia, and Argentina, and China controls over 60% of global refining capacity. The reality of supply-shortage worries is nuanced. In the short term, investment in expanded supply struggles to keep pace with rising demand, driving significant price volatility. In the long term, however, known reserves can meet decades of demand, and technological advances — seawater lithium extraction, battery recycling, and solid-state batteries (which use less lithium) — are likely to ease supply pressure. Korea leads the world in EV-battery manufacturing but has no domestic lithium resources, making supply-chain diversification (investment in Australia and South America) and battery-recycling infrastructure strategic priorities.

Q. Why do urban sinkholes form, and how can they be prevented? A. Urban sinkholes generally arise from two causes. First is the formation of underground voids: leaks from aging sewer and water pipes gradually wash away surrounding soil, creating cavities; subway construction and tunnel excavation can also loosen the surrounding ground. Second is insufficient compaction of soft ground: on reclaimed land or loose sand layers, rainwater infiltration or structural loads can trigger sudden settlement. Most sinkholes in Seoul’s downtown have been caused by piping erosion from leaking, aging sewer pipes. Prevention rests on three measures. First, regular inspection of underground facilities, using ground-penetrating radar (GPR) to detect underground cavities — Seoul greatly expanded GPR surveys after the 2014 Seokchon underpass sinkhole incident. Second, replacing aging sewer pipes, prioritizing pipes over 30 years old for replacement or internal lining. Third, monitoring during urban construction, tracking adjacent ground displacement in real time during underground excavation.