GEOL 101 Study Notes

GEOL 101: Sedimentary Rocks and Coal Formation

Types of Sedimentary Rocks

Optimal Characteristics for Specific Rock Roles

  • Source Rock:

    • Best type: Organic-rich shales (often black shale).

    • Rationale: High organic content allows for potential hydrocarbon generation after undergoing fracturing to release organic material.

    • In rare cases, limestones can preserve sufficient organic material, qualifying as potential source rocks.

  • Reservoir Rock:

    • Best types: Rocks with high porosity and/or high permeability.

    • Porosity: Number of holes (pores) within the rock.

    • Permeability: Ease of fluid flow through the pores, often enhanced by fractures.

    • Specific examples:

    • Sandstones and conglomerates: High primary porosity.

    • Fractured shale: May exhibit significant permeability and secondary porosity (porosity gained post-formation).

    • Dissolved limestones: Possessing secondary porosity as well.

  • Seal Rock:

    • Best types: Impermeable rocks, such as shales and slates, along with non-fractured crystalline igneous rocks.

Overview of Hydrocarbon Reserves

  • Key Factors:

    • Porosity: Indicates storage capacity for hydrocarbons.

    • Permeability: Determines the ability for hydrocarbons to flow through reservoir rocks.

    • Seal, Source, and Reservoir Rocks: Essential components in the formation and retention of hydrocarbons.

Coal

Coal Formation and Types (Section 14.6)

Formation Process

  • Stages of Coal Formation:

    1. Peat: Initial accumulation of plant material.

    2. Lignite: Formed at temperatures of less than 100ext°C100^ ext{°C} during burial.

    3. Bituminous Coal: Formed at temperatures between 100ext°C100^ ext{°C} and 200ext°C200^ ext{°C} during burial.

    4. Anthracite ('hard coal'): Formed at temperatures between 201ext°C201^ ext{°C} and 300ext°C300^ ext{°C} during burial.

Coal Rank

  • Coal rank categorization based on carbon content:

    • Low rank: 60-70% carbon.

    • Intermediate rank: 70-80% carbon.

    • High rank: Approximately 90% carbon.

Coal Mining Methods

Methods Overview

  • Coal can be mined using two primary techniques:

    1. Strip Mining:

    • Involves removing the overburden (surface layer) to expose the coal seam.

    • Advantages include ease of access and cost-effectiveness.

    • Process includes:

      • Use of machinery like draglines (shown in figures) for efficient excavation.

      • The area is eventually reclaimed after coal extraction.

    1. Underground Mining:

    • Coal is extracted deep underground without exposure to the surface air (as shown in figures).

    • Techniques involve tunneling and may utilize sophisticated ventilation systems.

Mineral Resources Overview

Overview and Learning Objectives

  • Main Focus:

    • Understand ore formation, particularly in relation to environmental concerns associated with mining practices.

    • Discuss the interrelationship between renewable energy, rare earth elements (REEs), and non-renewable resources.

Formation of Ore Minerals

Definition of Ores

  • Ores: Naturally occurring rocks, metals, or minerals that can be economically processed to extract valuable metals.

Formation Processes of Ores

  1. Crystallization in a Melt (Magmatic Deposits):

    • As magma cools, sulfide minerals crystallize at higher temperatures and accumulate, forming magmatic deposits with concentrated sulfide minerals.

  2. Hydrothermal Activity (Precipitation from Hot Water):

    • Circulation of hot aqueous solutions, often through magma or surrounding rocks, dissolves metal ions.

    • As conditions shift (temperature, pressure), metals precipitate out of solution, leading to hydrothermal deposits.

  3. Accumulation in Sediment:

    • Banded iron formations (BIF):

      • Resulting from the precipitation of iron oxide minerals as atmospheric oxygen increased between 2.5 billion and 1.8 billion years ago.

      • Composed of alternate layers of gray iron oxides (magnetite or hematite) and chert (jasper).

  4. Accumulation as Nodules:

    • In certain marine environments, manganese oxide minerals form lumpy deposits called manganese nodules on the ocean floor.

    • These nodules are estimated to contain a significant supply of copper and manganese, with ongoing exploration for mining technologies.

  5. Interaction with Groundwater:

    • Groundwater can alter ore-bearing rocks, dissolving minerals and carrying ions to new locations, resulting in the precipitation of ore minerals in higher concentrations.

Environmental Concerns Related to Mining

Negative Effects of Mining on Environment

  • Acid Mine Runoff:

    • Mining can lead to heavy metal concentration in surface waters, resulting in acidification, harmful alterations in pH, affecting aquatic ecosystems.

  • Acid Rain:

    • Produced as a byproduct of smelting and refining processes, these gases can lead to environmental damage due to the leaching of soil nutrients and negative effects on water bodies.

Summary of Environmental Concerns

  • Key issues include:

    • Landscape degradation

    • Unequal mineral deposit distribution

    • Acid mine runoff

    • Acid rain impacts on soil and ecosystems.

Rare Earth Elements (REEs)

Characteristics and Importance

  • Nature of REEs:

    • Rare Earth Elements are not actually 'rare', but their extraction poses significant challenges.

    • Typically found in low concentrations and rarely exist in pure forms.

Applications of REEs

  • Common uses in technology and renewable energy:

    • LEDs, TVs, lasers, batteries, fuel cells, superconductors, magnets, wind turbines, hybrid vehicles, mobile phones, and more.

Overview of REE Production

  • World Distribution (2019):

    • Notable outputs by country:

    • Australia: 21,000 tonnes

    • China: 132,000 tonnes

    • United States: 26,000 tonnes

    • Other countries contribute smaller quantities, e.g., India (3,000), Russia (2,700).

  • REEs are crucial for renewable technologies yet are finite resources with geographic disparities in mining.

Summary of Mineral Resources Overview

  • REEs are vital for modern technologies, particularly in renewable energy applications. Despite their label, they are not 'rare', but their availability is limited, presenting challenges for sustainability and resource management.