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                      📘 Introduction

Economic Geology is the branch of geology that deals with materials of economic value — mainly minerals, fossil fuels, and rocks used in industry, construction, and metallurgy. It helps mining professionals understand:

• Where valuable minerals occur
• How they form
• How they can be extracted economically

For DGMS and GATE aspirants, Economic Geology forms a core topic, connecting geology, mining economics, and exploration.

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🔍 Definition of Economic Geology “Economic Geology is the scientific study of earth materials that can be used for economic and/or industrial purposes.” It focuses on the mode of occurrence, distribution, classification, and genesis of mineral and energy resources.
The ultimate goal: discovery, development, and sustainable utilization of mineral deposits.

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🧭 Scope and Importance

Economic Geology serves as a bridge between geoscience and mining economics. Its key applications include:

• Identifying new mineral deposits
• Evaluating reserves and ore grades
• Supporting mine planning and feasibility studies
• Promoting resource conservation and sustainability
• Guiding national mineral policies

In DGMS exams, it falls under “Mine Geology and Exploration” with emphasis on ore types, resource classification, and deposit genesis.

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💎 Basic Terms in Economic Geology

Term	Definition	Example
Mineral	Naturally occurring, inorganic solid with definite chemical composition	Quartz, Feldspar
Ore Mineral	Mineral from which metals can be extracted economically	Chalcopyrite (Cu), Galena (Pb), Hematite (Fe)
Gangue	Non-valuable part of the ore	Quartz, Calcite
Tenor / Grade	Metal content of ore or deposit	Cu = 34.65% in Chalcopyrite
Cut-off Grade	Minimum grade for economic mining	Depends on cost vs. metal value
Assaying	Determination of metal concentration	Fire assay for gold

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🧮 Example – Tenor Calculation Mineral: Chalcopyrite (CuFeS₂)

• Atomic weights: Cu = 63.55, Fe = 55.85, S = 32 × 2 = 64
• Molecular weight = 63.55 + 55.85 + 64 = 183.4

Tenor of Cu = (63.55 ÷ 183.4) × 100 = 34.65%
→ Cu content in Chalcopyrite = 34.65%

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⚙️ Classification of Economic Minerals 1️⃣ Metallic Minerals

Type	Examples
Ferrous Metals	Fe, Mn, Cr, Ti
Non-Ferrous Metals	Cu, Pb, Zn, Ni, Sn
Noble Metals	Au, Ag, Pt
Light Metals	Al, Mg, Be, Li
Rare Earths	La–Lu, Sc, Y
Rare & Scarce Metals	W, Mo, Sn, Co, Zr, Nb

2️⃣ Non-Metallic Minerals

Type	Examples
Fossil Fuels	Coal, Petroleum, Natural Gas
Building Materials	Granite, Slate, Gypsum
Ceramics	Clay, Feldspar, Bauxite
Refractories	Magnesite, Graphite
Industrial Minerals	Mica, Talc, Asbestos
Chemicals	Salt, Borates, Nitrates
Abrasives	Corundum, Garnet

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🌋 Genesis of Mineral Deposits

Type	Description	Example
Syngenetic	Formed simultaneously with host rock	Magmatic deposits – Chromite, PGE
Epigenetic	Formed after host rock	Hydrothermal veins – Galena, Chalcopyrite

DGMS Tip:
“SAME = Syngenetic (Same Time)”
“AFTER = Epigenetic (Later Time)”

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📈 Mineral Resource Classification

• Inferred Resource: Based on limited data, least confidence.
• Indicated Resource: Reasonably estimated, moderate confidence.
• Measured Resource: Well-established data, high confidence.
• Proved Reserve: Economically mineable portion verified by feasibility.
• Probable Reserve: Mineable portion verified by prefeasibility.

Formula:
Reserve (Tonnage) = Volume × Specific Gravity

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🧾 DGMS Exam Focus Areas

• Distinction between Mineral, Ore, and Gangue
• Tenor and Grade calculations
• Cut-off grade and its economic importance
• Genesis of Deposits: Syngenetic vs. Epigenetic
• Resource vs. Reserve Classification

💡 DGMS Exam Tip:
Questions like “Define Cut-off Grade” or “Example of Syngenetic Deposit” are frequently asked.

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🏁 Conclusion

Economic Geology forms the foundation of mineral exploration and mining economics.
A solid understanding of ore minerals, grades, genesis, and resource estimation is essential for success in DGMS, GATE, and mining engineering exams.

🧠 25 DGMS MCQs with Answers & Solutions

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Q1. Economic Geology primarily deals with:
A. Fossil discovery
B. Volcano formation
C. Economic minerals and resources
D. Atmospheric studies
E. Oceanography
Answer: C
Solution: Economic Geology focuses on earth materials of commercial value.

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Q2. Ore mineral of lead is:
A. Galena
B. Pyrite
C. Hematite
D. Bauxite
E. Quartz
Answer: A
Solution: Galena (PbS) is the principal ore of lead.

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Q3. The process of determining metal content in ore is called:
A. Sampling
B. Drilling
C. Assaying
D. Logging
E. Sorting
Answer: C
Solution: Assaying determines grade (% of metal).

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Q4. Gangue refers to:
A. Waste rock with ore
B. Metallic mineral
C. Gemstone
D. Fossil remains
E. Radioactive mineral
Answer: A
Solution: Gangue = unwanted material with valuable ore.

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Q5. Mineral from which metal can be extracted profitably is:
A. Rock
B. Ore
C. Fossil
D. Clay
E. Sediment
Answer: B
Solution: Ore = profitable mineral deposit.

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Q6. The term "Tenor" means:
A. Ore size
B. Ore color
C. Metal content in ore
D. Ore shape
E. Mining cost
Answer: C
Solution: Tenor or grade = % of metal in ore.

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Q7. Chalcopyrite is an ore of:
A. Iron
B. Copper
C. Zinc
D. Aluminium
E. Lead
Answer: B
Solution: Chalcopyrite (CuFeS₂) is the main copper ore.

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Q8. The Cu content in Chalcopyrite is approximately:
A. 20%
B. 25%
C. 34.6%
D. 40%
E. 50%
Answer: C
Solution: Calculated using atomic weights = 34.65% Cu.

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Q9. Non-metallic mineral among the following is:
A. Hematite
B. Galena
C. Quartz
D. Chalcopyrite
E. Magnetite
Answer: C
Solution: Quartz is non-metallic and non-conductive.

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Q10. Cut-off grade depends on:
A. Depth
B. Temperature
C. Cost and metal price
D. Ore color
E. Rock type
Answer: C
Solution: Cut-off grade = production cost ÷ metal value.

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Q11. Banded Iron Formation represents which deposit type?
A. Epigenetic
B. Syngenetic
C. Placer
D. Metasomatic
E. Evaporite
Answer: B
Solution: BIFs are syngenetic, formed with host rocks.

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Q12. Epigenetic deposits are formed:
A. After host rock formation
B. Before rock formation
C. During sedimentation
D. Along river channels
E. Only in limestone
Answer: A
Solution: Epigenetic = formed later by hydrothermal activity.

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Q13. The DGMS syllabus includes Economic Geology under:
A. Mine Management
B. Mine Geology
C. Mine Ventilation
D. Mining Machinery
E. Electrical Engineering
Answer: B
Solution: It’s part of Paper-II: Mine Geology.

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Q14. Ore body reserve (tonnage) is calculated by:
A. Volume × Density
B. Volume ÷ Grade
C. Length × Width
D. Area ÷ Price
E. None
Answer: A
Solution: Reserve = Volume × Density.

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Q15. "Measured Resource" indicates:
A. Highest confidence
B. Moderate confidence
C. Low confidence
D. Inferred estimate
E. Random data
Answer: A
Solution: Measured = detailed exploration data.

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Q16. "Proved Reserve" is determined by:
A. Geochemical survey
B. Feasibility study or actual mining
C. Aerial mapping
D. Satellite image
E. Magnetometer
Answer: B
Solution: Proved = confirmed by feasibility or extraction.

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Q17. “Inferred Resource” indicates:
A. Low confidence estimate
B. No geological control
C. Exact tonnage
D. Only chemical data
E. High accuracy
Answer: A
Solution: Inferred = based on limited data.

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Q18. Ore grade influences:
A. Mining method
B. Ventilation rate
C. Power supply
D. Water table
E. None
Answer: A
Solution: High-grade ores allow open-pit or selective mining.

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Q19. Main ore of Aluminium is:
A. Bauxite
B. Galena
C. Pyrolusite
D. Hematite
E. Cassiterite
Answer: A
Solution: Bauxite = Al₂O₃·2H₂O.

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Q20. Ore body with parallel layers is:
A. Bedded deposit
B. Vein deposit
C. Pocket deposit
D. Massive deposit
E. None
Answer: A
Solution: Bedded = stratiform layers formed during sedimentation.

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Q21. DGMS stands for:
A. Directorate General of Mine Safety
B. Directorate Geological Mapping Society
C. District Geological Mapping System
D. Directorate General of Mineral Statistics
E. Directorate of Mining Survey
Answer: A
Solution: DGMS = Directorate General of Mines Safety, Dhanbad.

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Q22. Ore that forms along with host rock is:
A. Syngenetic
B. Epigenetic
C. Hydrothermal
D. Placer
E. Evaporitic
Answer: A
Solution: Syngenetic = same generation as host.

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Q23. Mineral exploration begins with:
A. Geological mapping
B. Extraction
C. Milling
D. Processing
E. Blasting
Answer: A
Solution: Mapping identifies mineralized zones for drilling.

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Q24. Which is a metallic mineral?
A. Limestone
B. Bauxite
C. Galena
D. Graphite
E. Clay
Answer: C
Solution: Galena contains metal (lead).

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Q25. The economic viability of ore depends on:
A. Grade & cost
B. Depth & density
C. Texture & luster
D. Hardness only
E. Rock color
Answer: A
Solution: Higher grade and lower cost improve profitability.

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