Geological Processes, Mineral Deposits, and Geohazards

Posted on Nov 7, 2025 in Geology

Mineral Deposits and Formation Processes

Mineral deposits are concentrations of materials linked to geological processes, requiring sufficient concentration factors to be economically viable.

Geological Processes

These are categorized into two main types:

  • Exogenous Processes: External processes (e.g., weathering, sedimentation).
  • Endogenous Processes: Internal processes (e.g., volcanism, tectonics).

Endogenous Mineralization

Associated with volcanic construction at plate boundaries (active margins, destructive margins, interplate zones, hot spots).

Magmatic Deposits

These result from the consolidation and crystallization of magmas (igneous rocks).

  • Volcanic Deposits: Formed by sublimation or gases associated with volcanic processes.
  • Plutonic Deposits (Ortomagmatic): Result from the crystallization of deep magmas. Formation mechanisms include:
    • Mineral segregation (heavy metals).
    • Dissemination (crystals included within the magma body).
    • Injection (forming deep veins).
  • Pegmatitic Deposits: Formed by the precipitation of minerals from residual liquid waste (magmatic fluids) as it cools, resulting in pegmatites.

Hydrothermal Deposits

Formed by precipitation from hot water solutions (hydrothermal veins). These are classified based on temperature and depth (e.g., epithermal, mesothermal, hypothermal).

Metamorphic Deposits

Formed when rocks change state (solid) due to factors like temperature, pressure, or fluids (metamorphism).

  • Hydrothermal Metamorphic Deposits: Related to fluid circulation during metamorphism.
  • Contact Metamorphic Deposits: High-temperature processes produced by magmatic masses interacting with surrounding rocks, often involving the replacement of chemical elements in the crystal lattice.

Nuclear Energy and Radioactive Contamination

Nuclear Reactor Components

The reactor core is where the nuclear reaction occurs and heat is generated. Key components include:

  • Fuel: Typically enriched uranium, housed in the core.
  • Moderator: Introduced between the fuel elements; it absorbs neutrons and reduces their energy (speed).
  • Control Rods: Absorb neutrons to control the speed and rate of the reaction.
  • Coolant Fluid: Extracts heat, often through pressurized water circuits.

Radioactive Contamination and Waste

Contamination is caused by radioactive particles emitting alpha or beta radiation, which are particularly dangerous.

Sources of Contamination:

  • Mineral extraction and dispersion into the environment.
  • Transport of radioactive materials.
  • Operation of nuclear power plants.

Radioactive Waste: This is material that is no longer useful but emits particles or radiation at concentrations higher than permitted limits. Disposal sites are often referred to as nuclear waste repositories.

Geothermal Energy Sources

Geothermal energy utilizes the Earth’s internal heat source to obtain hot water and steam. Extraction requires controlled drilling points. While generally renewable, specific reservoirs may not be sustainable (not perpetual).

Types of Geothermal Resources

  1. Hot Springs and Geysers: Water heated naturally through contact with hot rocks near the surface.
  2. Deep Hot Groundwater: Hot water extracted from deep aquifers, often requiring excavation.
  3. Hot Dry Rock (HDR): Accessible hot rock (e.g., batholiths) where water is injected and then extracted as steam or hot water.

Geothermal energy can be used directly for heating or converted into electricity. Typically, two wells are required: one for extraction and one for injection (to replenish the reservoir).

Metasomatism

Metasomatism is a geological process involving the substitution of one mineral for another, driven by the interaction with hydrothermal fluids (e.g., dolomitization).

Geological Risks: External Geodynamic Processes

External geodynamic processes involve the movement of materials on slopes, primarily driven by gravity.

Types of Slope Movements

  • Rockfalls (Detachment): Movement of rock masses leaping through the air. A few falls constitute a rockfall; numerous falls constitute an avalanche.
  • Gliding (Sliding): Movements of rock masses along a defined failure surface. These can be translational (parallel to the surface) or rotational (curved failure surface).
  • Creep: Very slow, continuous downslope movement of the alteration mantle (soil/regolith). Displacement occurs through cycles of expansion and shrinkage.
  • Flows: Movements of unconsolidated material saturated with water, such as gelifluction or mudflows.

Landslides and Ground Subsidence

Landslides involve vertical movements caused by the closing of rock pores, which can be natural or anthropogenic.

Two main types of vertical movement:

  • Subsidence: Slow, progressive sinking of the ground.
  • Collapse: Sudden sinking of the ground.

Factors Contributing to Ground Movement:

  • Hydrocompaction: Loss of cohesion due to water saturation.
  • Liquefaction: Loss of soil strength, often triggered by earthquakes.
  • Karstic Processes: Dissolution of soluble rocks (e.g., limestone, salt, and gypsum).
  • Contraction: Ground loss due to moisture reduction (drying).
  • Compaction: Caused by human constructions or former mineral exploitation creating large underground voids.

Avalanches (Snow)

Rapid movement of large amounts of snow on steep slopes. While small avalanches in uninhabited areas pose little risk, the danger increases significantly due to human activity.

Factors Increasing Avalanche Risk:

  • Increased snow accumulation.
  • Temperature changes or rain (especially during thaw periods).
  • Steep slope angle.
  • Lack of stabilizing vegetation.
  • Natural or human-induced vibration.

Clay Expandability

Certain clays absorb and lose water easily, causing significant volume changes (expansion and shrinkage). This process lifts and moves the soil, posing a geological risk where pressure affects roads or buildings.

Causes: Natural (e.g., droughts or heavy rain) or induced (e.g., overexploitation of aquifers).

Shifting Sand Dunes

Movement of sand masses driven by wind in arid and coastal areas. While often localized, they pose risks such as burying structures and favoring seawater penetration along the coast.

Sedimentation and Diagenesis

Sedimentation is the process where geological agents deposit materials, resulting in both unchanged and processed sediments. Deposits near the bedrock often undergo alteration.

Types of Sedimentary Rocks

  • Detrital: Formed by the accumulation of rock debris (clasts), undergoing little or only partial chemical change.
  • Chemical: Formed by the precipitation of substances dissolved in water.
  • Biochemical and Organic: Formed from the remains of living organisms and organic matter.

Diagenesis: Transformation of Sediments

Diagenesis is the physical and chemical transformation of sediments into sedimentary rocks. Key processes include:

  • Compaction: Reduction of volume as sediments accumulate under pressure.
  • Cementation: Particles are joined together by a cementing agent (e.g., silica, calcite, or clay).
  • Neoformation: Formation of new, diagenetic minerals due to changing physical and chemical conditions.