G23: Economic Geology & Resources
The geological resources that sustain modern society: metallic ores, industrial minerals, fossil fuels and water, and how they form.
Economic Geology & Resources
The geological resources that sustain modern society: metallic ores, industrial minerals, fossil fuels and water, and how they form.
Key Fact: An ore is a naturally occurring mineral from which a metal can be economically extracted
Key Fact: Hydrothermal ore deposits: metal-rich hot fluids deposit minerals in veins and fractures (e.g. tin in Cornwall, gold veins)
Key Fact: Placer deposits: heavy minerals concentrated by river or wave action (e.g. gold, diamond placers)
Key Fact: Fossil fuels: coal (from Carboniferous swamp forests), petroleum (from marine microorganisms under heat and pressure)
Key Fact: Evaporite deposits: salt, gypsum and potash formed by evaporation of restricted seawater bodies
Key Fact: Groundwater is stored in aquifers (porous, permeable rocks like sandstone and limestone); it is a vital resource
📋 Key Vocabulary and Concepts
For Economic Geology & Resources, you must know:
- Ore: A naturally occurring mineral deposit from which a metal can be extracted at a profit
- Hydrothermal vein: A mineral deposit formed when hot, metal-rich water flows through rock fractures and precipitates ore minerals as it cools
- Placer deposit: A sedimentary concentration of heavy, resistant minerals accumulated by river or wave sorting
- Aquifer: A porous and permeable rock that stores and transmits groundwater (e.g. sandstone, chalk, limestone)
- Evaporite: A sedimentary deposit formed by evaporation of saline water, producing minerals like halite, gypsum and potash
❓ Practice Questions
Q: How do hydrothermal ore deposits form?
Q: What conditions are needed for petroleum formation?
Q: How do placer deposits form?
Q: What is an aquifer and why is it important?
Q: How do evaporite deposits form?
✅ Answers
- Hot, metal-rich fluids (often from cooling igneous intrusions) circulate through fractures in surrounding rock. As the fluids cool or react with the host rock, dissolved metals precipitate as ore minerals within veins and fractures.
- 1) Source rock: organic-rich sediment buried and heated to produce oil/gas. 2) Reservoir rock: porous sandstone or limestone to store petroleum. 3) Cap/seal rock: impermeable shale or clay to trap petroleum. 4) Trap structure: anticline, fault or salt dome.
- Weathering releases heavy, resistant minerals from bedrock. Rivers transport the material; the heavy minerals (gold, diamond, tin) settle in slower-flowing parts while lighter material is carried further downstream, concentrating the valuable minerals.
- A porous and permeable rock that stores and transmits groundwater. Important aquifers in Britain include the Chalk and Permo-Triassic sandstone, which supply much of the nation's drinking water.
- In warm, arid climates, seawater trapped in restricted basins evaporates. As concentration increases, minerals precipitate in order: first carbonates, then sulfates (gypsum), then halite (salt), and finally potash salts.
🎯 Exam Tips
- Ore = economically extractable mineral deposit
- Hydrothermal veins = cooling igneous fluids precipitate metals in fractures
- Petroleum system: source + reservoir + seal + trap
- Aquifers = porous + permeable rocks storing groundwater
📝 Exam Technique
GCSE Geology Exam Tips — Economic Geology & Resources:
1. For Economic Geology & Resources questions, use correct geological terminology and classify features precisely
2. Reference specific geological time periods and processes
3. When interpreting data, consider the quality and limitations of the evidence
4. Apply your understanding of Economic Geology & Resources to fieldwork observations and map data
5. For evaluation, weigh competing geological theories with evidence
1. For Economic Geology & Resources questions, use correct geological terminology and classify features precisely
2. Reference specific geological time periods and processes
3. When interpreting data, consider the quality and limitations of the evidence
4. Apply your understanding of Economic Geology & Resources to fieldwork observations and map data
5. For evaluation, weigh competing geological theories with evidence
⚠️ Common Errors
✗ All mineral deposits are ores ✓ A mineral deposit is only an ore if the metal can be extracted at a PROFIT; if costs exceed value, it is not currently an ore
✗ Oil forms from dinosaurs ✓ Petroleum forms from microscopic marine organisms (plankton) buried in sediment, not from dinosaurs
✗ All rocks can store groundwater ✓ Only porous AND permeable rocks can be aquifers; shale and clay are porous but impermeable
✍️ Model Answer
Full-Mark Response
Describe how metallic ores and fossil fuels form and explain the geological conditions required for each. [6 marks]
Metallic ores form through several processes. Hydrothermal deposits occur when hot, metal-rich fluids from cooling igneous intrusions circulate through fractures in surrounding rock, precipitating ore minerals as veins when they cool or react with the host rock (e.g. cassiterite in Cornish tin veins). Placer deposits form when weathering releases heavy, resistant minerals that are then concentrated by river or wave sorting (e.g. gold in river gravels). Magmatic segregation deposits form as minerals crystallise and settle from cooling magma. Fossil fuels form from organic material. Coal forms from terrestrial plant material accumulated in waterlogged Carboniferous swamps where oxygen-poor conditions prevented decay; burial compressed and heated the peat into coal. Petroleum forms from marine microorganisms buried in fine sediment. Under increasing temperature and pressure, the organic matter converts to oil (60-120 degrees C) and then gas (>120 degrees C). Petroleum migrates upward through porous reservoir rocks until trapped by impermeable cap rocks above anticline structures, faults or salt domes. The petroleum system requires: a source rock, a porous reservoir rock, an impermeable seal, and a trap structure.
📊 AO Deep Dive
Assessment Objective Analysis
AO1 (Knowledge & Understanding): Demonstrate knowledge and understanding of economic geology & resources, including key geological concepts, observational data and theoretical models relevant to OCR J357.
AO2 (Application of Knowledge): Apply knowledge and understanding of economic geology & resources to both familiar and unfamiliar geological contexts, using field evidence and theoretical principles to explain phenomena.
AO3 (Analysis & Evaluation): Analyse geological data related to economic geology & resources, evaluate evidence from observations and investigations, and construct reasoned arguments using scientific methodology.
📝 Exam Questions by Topic
🎬 Video Resources
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