UPSC Mains Answer PYQ 2023: Geology Paper 2 (Section- B) | Geology Optional Notes for UPSC PDF Download

Note: These sample answers provide a brief overview of the topic. You may add or reduce information as you see fit, depending on your understanding.

Section - B

Q5: Answer the following questions in about 150 words each : (10x5=50)
(a) Explain the process of manganese nodules formation and give their major occurrences in the world.  
Ans: 
Introduction: 
Manganese nodules, also known as polymetallic nodules, are small, hard lumps of manganese and iron oxides, along with other valuable metals, found on the ocean floor. Their formation is a result of several geological and chemical processes.

Formation Process:

• Accretion of Material: Manganese nodules form by the slow accumulation of metal-rich material on the ocean floor. This material consists of manganese and iron oxides, as well as other metals like nickel, copper, and cobalt.

• Nucleation Sites: Initially, small mineral grains or shell fragments act as nucleation sites for metal deposition. These particles are transported by ocean currents and slowly settle to the seafloor.

• Oxidation: The metal ions dissolved in seawater, such as manganese and iron, oxidize and precipitate onto the nucleation sites in the form of metal oxides.

• Growth Over Time: Over thousands of years, layer by layer of metal oxides is deposited on the nodules, resulting in the growth of the nodules.

Major Occurrences:

• Pacific Ocean: The Clarion-Clipperton Zone in the equatorial Pacific Ocean is one of the most significant areas for manganese nodule deposits. It is estimated to contain vast resources of nodules.

• Indian Ocean: The Central Indian Ocean Basin also hosts manganese nodule fields.

• Atlantic Ocean: Nodules have been found in the Atlantic Ocean, particularly in regions near seamounts and mid-ocean ridges.

Significance: Manganese nodules are of economic interest due to their metal content. They are potential future sources of critical metals and minerals used in various industries, including technology and renewable energy.

(b) Describe the formation of replacement textures in ore minerals and give the criterion of their recognition.
Ans: 
Introduction: 
Replacement textures in ore minerals refer to the alteration of pre-existing minerals by ore-forming processes, leading to the formation of new mineral assemblages. Recognizing replacement textures is essential in ore exploration.

Formation Process:

• Primary Ore Formation: Ore minerals are initially deposited in a host rock through various geological processes, such as hydrothermal deposition, metamorphism, or sedimentation.

• Chemical Alteration: Ore-forming fluids, often hydrothermal in nature, infiltrate the host rock. These fluids may carry ions and elements necessary for mineral replacement.

• Replacement Reactions: The infiltrating fluids react with the primary minerals in the host rock, causing dissolution of the original minerals and precipitation of new ore minerals. This can result in several replacement textures, including pseudomorphs, veining, and alteration halos.

Recognition Criteria:

• Pseudomorphs: Pseudomorphs are mineral shapes that mimic the original minerals but consist of different substances. For example, a quartz pseudomorph after pyrite indicates that pyrite has been replaced by quartz.

• Veins and Fractures: The presence of vein-like structures filled with ore minerals in the host rock is a strong indicator of replacement. These veins often crosscut the original minerals.

• Alteration Halos: Alteration halos are zones of mineralogical change surrounding ore bodies. They result from the chemical alteration of the host rock by ore-forming fluids.

• Texture Contrasts: Visual contrasts in texture between the replaced minerals and the ore minerals can be indicative of replacement. For instance, a fine-grained ore mineral replacing a coarser-grained host mineral is a recognizable contrast.

Example:

• In a copper ore deposit, native copper can replace primary sulfide minerals like chalcopyrite, resulting in pseudomorphs of native copper after chalcopyrite.

Conclusion: 
Recognizing replacement textures is crucial in ore exploration, as it provides insights into the history of ore deposition and aids in the discovery of economically valuable minerals.

(c) Explain the Kriging method for estimating ore reserve.
Ans: 
Introduction: 
Kriging is a geostatistical method used to estimate the spatial distribution of a variable, such as ore grades, based on a set of sample data points. It is widely applied in the mining industry to determine ore reserves.

Process of Kriging for Ore Reserve Estimation:

• Data Collection: Sample data points are collected through drilling, sampling, and assaying. These data include information about the variable of interest (e.g., ore grades).

• Variogram Modeling: A variogram is a mathematical model that describes the spatial variability and correlation of the variable being estimated. It is based on the distance and direction between data points.

• Kriging Estimation: Kriging estimates the variable of interest at unsampled locations by considering both the data values and the variogram model. It uses a weighted linear combination of neighboring data points to make predictions.

• Estimation Variance: Kriging provides not only estimates of the variable but also an estimation variance, which quantifies the uncertainty associated with the predictions.

• Block Kriging: To estimate ore reserves, kriging is often extended to estimate the average grades within blocks of a predefined size. This is essential for mine planning.

Criterion of Recognition:

• The main criterion for the recognition of kriging results is the estimation variance. Lower estimation variances indicate more reliable predictions. The reliability of the estimates can be assessed by comparing the kriged values with additional drilling and sampling.

Example:

• In a gold mining project, kriging is used to estimate the distribution of gold grades within the ore body. The results help determine the quantity and quality of ore reserves, which are crucial for economic feasibility studies.

Conclusion: 
Kriging is a powerful geostatistical method for estimating ore reserves by modeling spatial variability and providing reliable predictions with associated estimation variances. It plays a pivotal role in mine planning and resource management.

(d) Discuss environmental impacts of urbanization and their mitigations with special reference to land and water.
Ans: 
Introduction: 
Urbanization, the process of population concentration in cities and towns, has both positive and negative environmental impacts. Addressing these impacts is crucial for sustainable urban development.

Environmental Impacts:
1. Land Degradation:

• Impact: Urbanization often leads to land degradation due to construction activities, soil sealing, and increased impervious surfaces.
• Mitigation: Implementing green infrastructure, such as urban parks and green belts, helps preserve natural areas and reduce soil sealing.

2. Air Pollution:

• Impact: Increased vehicular traffic and industrial activities in urban areas contribute to air pollution, leading to respiratory issues and environmental damage.
• Mitigation: Encouraging public transportation, promoting electric vehicles, and regulating industrial emissions are effective measures.

3. Water Pollution:

• Impact: Urban runoff containing pollutants like heavy metals, chemicals, and sewage can contaminate water bodies, affecting aquatic ecosystems and human health.
• Mitigation: Implementing stormwater management systems, constructing vegetated swales, and enhancing wastewater treatment facilities help reduce water pollution.

4. Loss of Biodiversity:

• Impact: Urbanization often results in habitat fragmentation and loss, leading to declines in biodiversity and disruption of ecological balance.
• Mitigation: Creating green corridors, protected areas within cities, and promoting urban gardens and green roofs can help conserve biodiversity.

5. Noise Pollution:

• Impact: Urban areas are characterized by high levels of noise pollution, which can lead to stress, hearing impairments, and disturbances to wildlife.
• Mitigation: Implementing noise-reducing measures like sound barriers, green buffers, and zoning regulations can mitigate the effects of noise pollution.

Example:

• The city of Copenhagen, Denmark, has implemented extensive cycling infrastructure, pedestrian-friendly zones, and green spaces to mitigate the environmental impacts of urbanization.

Conclusion: 
Addressing the environmental impacts of urbanization is essential for creating sustainable, livable cities. Implementing a combination of green initiatives, technological solutions, and regulatory measures can help mitigate the negative effects while promoting urban development.

(e) How does coordination number depend on the ratio of ionic radii in a crystal?
Ans: 
Introduction: 
Coordination number refers to the number of neighboring atoms or ions surrounding a central atom or ion in a crystal lattice. It is influenced by the ratio of ionic radii in a crystal.

Relationship Between Coordination Number and Ionic Radii:

• Smaller Ion Radius Ratio: When the ratio of the radii of the cation to anion is small, the coordination number tends to be higher. This is because the smaller ion can fit more closely packed neighbors around it.

• Larger Ion Radius Ratio: When the ratio of the radii is larger, the coordination number tends to be lower. The larger ion requires more space and fewer neighboring ions can be accommodated.

Example:

• In a crystal of sodium chloride (NaCl), the sodium ion (Na⁺) is smaller compared to the chloride ion (Cl^-). The coordination number of sodium ions is 6, indicating that each sodium ion is surrounded by six chloride ions.

Conclusion: 
The coordination number in a crystal is influenced by the ratio of ionic radii. Understanding this relationship is important in crystallography and helps predict the arrangement of ions in a crystal lattice.

Q6:
(a) Describe the formation of Banded Iron Formation (BIF) during Precambrian metallogenic epoch. Write a note on the Indian BIF deposits.    (20 Marks) 
Ans: 
Introduction: 
Banded Iron Formations (BIFs) are distinctive sedimentary rocks composed of alternating layers of iron-rich minerals and chert (microcrystalline quartz). They formed predominantly during the Precambrian era and played a significant role in Earth's early metallogenic history.

Formation Process:

• Early Earth Conditions: BIFs primarily formed between 3.8 to 1.8 billion years ago, during the Precambrian era when Earth's atmosphere lacked free oxygen.

• Abundance of Iron and Silica: The oceans of that time contained high concentrations of dissolved iron (Fe²⁺ ions) and silica (SiO₂).

• Iron Precipitation: The iron-rich waters interacted with oxygen produced by early photosynthetic organisms, causing the iron to oxidize and precipitate as iron oxides (predominantly hematite and magnetite).

• Silica Deposition: Simultaneously, the silica in the seawater combined with dissolved iron to form chert layers.

• Alternating Deposition: The process of iron and silica deposition alternated, resulting in the characteristic banded appearance.

Indian BIF Deposits:

• Singhbhum, Jharkhand: The Singhbhum region in Jharkhand, India, is renowned for its extensive BIF deposits. These are found in areas like Noamundi, Gua, and Barsua.

• Champion, Goa: The Champion deposit in Goa also hosts significant BIF occurrences.

Note: Indian BIF deposits have been crucial in the development of the iron and steel industry in the country.

(b) Discuss the late magmatic ore-forming processes. What are the salient field characters of such ore deposits?    (15 Marks) 
Ans: 
Introduction: 
Late magmatic ore-forming processes involve the emplacement of late-stage magmas enriched in ore-forming elements. These processes contribute to the formation of economically significant ore deposits.

Processes:

• Magmatic Differentiation: Late-stage magmas undergo differentiation, leading to the concentration of ore-forming elements (e.g., Cu, Ni, PGE) in certain portions of the magma chamber.

• Fractional Crystallization: As the magma cools, minerals crystallize at different temperatures, resulting in the segregation of ore minerals from the remaining melt.

• Fluid Immiscibility: Late-stage magmas may release volatile components like sulfur and metals, which can form immiscible fluids. These fluids can migrate and precipitate ore minerals.

Field Characters:

• Mineral Zonation: Ore deposits formed by late magmatic processes often exhibit a zonation pattern, with ore minerals concentrated in specific zones within the host rock.

• Vein and Disseminated Textures: Ore minerals may occur as veins or disseminated grains within the host rock, reflecting the processes of late-stage mineralization.

• Association with Intrusions: Late magmatic ore deposits are typically associated with specific types of intrusions, such as layered mafic intrusions or alkaline complexes.

Example:

• The Noril'sk-Talnakh deposits in Russia are significant examples of late magmatic ore deposits, rich in nickel, copper, and platinum-group elements.

(c) Describe the origin of porphyry copper deposits. Give the geological setup of one porphyry copper deposit of India.    (15 Marks) 
Ans: 
Introduction: 
Porphyry copper deposits are large, low-grade ore bodies associated with intrusions of intermediate to felsic composition. They are an important source of copper worldwide.

Formation Process:

• Intrusion Emplacement: An intrusion of granodiorite or diorite composition is emplaced in the Earth's crust.

• Fluid Migration: Magmatic fluids, rich in metals like copper, gold, and molybdenum, are released from the cooling intrusion.

• Fluid Interaction: These fluids interact with surrounding rocks, altering them and depositing ore minerals, primarily chalcopyrite (copper sulfide).

• Ascending Ore-Bearing Fluids: The ore-bearing fluids ascend through fractures and faults, forming mineralization zones.

• Economic Significance: The large size and tonnage of porphyry deposits make them economically significant sources of copper.

Indian Example:

• Khetri Copper Belt, Rajasthan: The Khetri Copper Belt in Rajasthan, India, hosts several porphyry-type copper deposits. These deposits are associated with the Khetri Group of rocks and are significant contributors to India's copper production.

Conclusion: 
Understanding the formation processes and field characteristics of late magmatic ore deposits and porphyry copper deposits is crucial for exploration and exploitation efforts in the mining industry. These deposits play a vital role in global metal production and economic development.

Q7:
(a) Give an account of external changes in flora due to the presence of anomalous concentration of base metal in a terrain.    (15 Marks) 
Ans: 
Introduction: 
Anomalous concentrations of base metals in a terrain can significantly impact the surrounding flora. Base metals like copper, lead, zinc, and nickel can have both direct and indirect effects on plant communities.

Effects on Flora:

• Phytotoxicity: High concentrations of base metals in soil can be toxic to plants. They can interfere with essential physiological processes, affecting growth and development.

• Nutrient Imbalance: Elevated levels of certain metals can disrupt nutrient uptake by plants. For example, excessive copper can inhibit iron uptake.

• Changes in Plant Physiology: Base metals can alter the physiology of plants, leading to reduced chlorophyll content, stunted growth, and impaired photosynthesis.

• Species Composition Changes: Metal-tolerant species may dominate in areas with high base metal concentrations, displacing sensitive species.

• Bioaccumulation and Biomagnification: Some plants have the ability to accumulate metals in their tissues. This can lead to bioaccumulation in the food chain, potentially affecting herbivores and omnivores.

Example:

• In the Sudbury region of Ontario, Canada, elevated nickel and copper concentrations from mining activities have led to unique flora adaptations. Species like the Sudbury birch have evolved metal-tolerance mechanisms.

Conclusion: 
Anomalous concentrations of base metals in a terrain can have significant and often detrimental effects on the local flora. Understanding these impacts is crucial for environmental management and rehabilitation efforts.

(b) Explain the principle for flotation as a benefication technique. Name various parameters that regulate the flotation process. Explain frothing method giving appropriate examples.    (15 Marks) 
Ans: 
Introduction: 
Flotation is a widely used process in mineral beneficiation for separating valuable minerals from gangue based on their hydrophobicity.

Principle of Flotation:

• The principle of flotation relies on the attachment of air bubbles to hydrophobic particles in a slurry, causing them to rise to the surface and form a froth, while hydrophilic particles remain in the pulp.

Parameters Regulating Flotation:

• Particle Size: The size of the particles in the slurry affects their floatability. Fine particles may not attach to bubbles as effectively as coarser particles.

• Chemical Reagents: Collectors, frothers, and modifiers are used to enhance the hydrophobicity of valuable minerals and stabilize the froth.

• Pulp Density: The concentration of solids in the slurry affects the probability of particle-bubble interaction. An optimal pulp density is required for efficient flotation.

• pH Level: pH influences the surface charge of minerals. Adjusting the pH with pH modifiers can optimize the floatability of specific minerals.

• Agitation and Aeration: Proper mixing and aeration of the slurry are essential for promoting contact between particles and bubbles.

Frothing Method:

• Frothers are added to stabilize the froth and improve its stability. Common frothers include alcohols, glycols, and natural products like pine oil.

Example:

• In sulfide ore flotation, xanthates are commonly used as collectors to enhance the hydrophobicity of minerals like galena (lead sulfide) and chalcopyrite (copper-iron sulfide).

Conclusion: 
Flotation is a versatile and widely used beneficiation technique in the mining industry. It relies on several parameters to achieve efficient separation of valuable minerals from gangue, making it a crucial process in mineral processing operations.

(c) What do you understand by the term ‘industrial minerals? Give examples of any five industrial minerals, their sources, compositions and uses in the industry.    (15 Marks) 
Ans: 
Introduction: 
Industrial minerals are non-metallic minerals that have economic value and are used in various industries for their physical and chemical properties.

Examples of Industrial Minerals:
1. Quartz:

• Source: Quartz is commonly found in igneous, metamorphic, and sedimentary rocks.
• Composition: Silicon dioxide (SiO₂).
• Uses: Used in glassmaking, ceramics, electronics, and as a raw material in the production of silicon.

2. Feldspar:

• Source: Commonly found in granitic and syenitic rocks.
• Composition: A group of minerals comprising aluminum, silicon, and oxygen.
• Uses: Used in ceramics, glassmaking, and as a flux in metallurgical processes.

3. Kaolin (China Clay):

• Source: Derived from the weathering of feldspar-rich rocks.
• Composition: Aluminum silicate.
• Uses: Used in ceramics, paper coating, paint, and as a filler in plastics.

4. Gypsum:

• Source: Often found as evaporite deposits in sedimentary rocks.
• Composition: Hydrous calcium sulfate (CaSO₄·2H₂O).
• Uses: Used in construction materials (e.g., plasterboard), agriculture, and as a soil conditioner.

5. Talc:

• Source: Derived from the alteration of magnesium-rich rocks.
• Composition: Magnesium silicate.
• Uses: Used in cosmetics, ceramics, plastics, and as a lubricant.

Conclusion: 
Industrial minerals play a crucial role in various industries, contributing to economic development and technological advancements. Understanding their sources, compositions, and applications is essential for their sustainable utilization.

Q8:
(a) Discuss the causes of various seismic discontinuities in the upper mantle.    (20 Marks) 
Ans: 
Introduction:
Seismic discontinuities in the upper mantle are boundaries where seismic waves experience abrupt changes in velocity, indicating variations in material properties. These discontinuities provide valuable insights into the composition and behavior of Earth's interior.

Causes of Seismic Discontinuities:
1. Olivine-Spinel Transition (410 km Discontinuity):

• Cause: Occurs due to the phase transition of olivine to a denser mineral, spinel, under high pressure.
• Example: At approximately 410 km depth, olivine undergoes a phase transition to spinel in the upper mantle.

2. Garnet Transition (660 km Discontinuity):

• Cause: Marks the phase transition of pyroxenes to garnet, which is denser, at depths of around 660 km.
• Example: The 660 km discontinuity separates the upper and lower mantle, indicating a change in mineralogy.

3. Majorite Transition (Transition Zone):

• Cause: Majorite, a high-pressure form of garnet, forms in the transition zone (410-660 km depth) due to increased pressure.
• Example: This transition zone provides insights into the presence of water in the mantle.

4. Post-Perovskite Phase (D” Layer):

• Cause: Below 660 km, perovskite undergoes further phase transition, leading to the formation of post-perovskite.
• Example: The D” layer at the core-mantle boundary indicates complex material behavior.

5. Mantle Plumes and Hotspots:

• Cause: Mantle plumes originate from deep within the mantle and can cause localized variations in seismic velocity.
• Example: The Hawaiian hotspot produces distinct seismic features and volcanic activity.

Conclusion: 
Seismic discontinuities in the upper mantle provide crucial information about the composition and dynamics of Earth's interior. Understanding these discontinuities helps geologists interpret seismic data and refine models of mantle behavior.

(b) Discuss the composition, source, types, environmental hazard and utility of fly ash.    (15 Marks) 
Ans: 
Introduction: 
Fly ash is a fine, powdery residue generated from coal combustion in power plants. It is rich in silicate and aluminate minerals and has various environmental and industrial applications.

Composition:

• Fly ash primarily consists of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), along with unburned carbon and trace elements.

Source:

• It is a byproduct of burning pulverized coal in power plants. It is collected from the flue gas by electrostatic precipitators or baghouses.

Types of Fly Ash:
1. Class F Fly Ash:

• Low-calcium fly ash derived from burning anthracite or bituminous coal.
• Predominantly composed of silica, alumina, and iron oxide.

2. Class C Fly Ash:

• High-calcium fly ash derived from burning lignite or sub-bituminous coal.
• Contains higher levels of calcium oxide and is more cementitious.

Environmental Hazard:

• Improper disposal of fly ash can lead to environmental hazards, including air and water pollution. Leaching of trace elements from fly ash can contaminate groundwater.

Utility:

• Construction Industry: Used as a supplementary cementitious material in concrete production, improving durability and reducing carbon emissions.
• Agriculture: Used as a soil amendment to improve fertility and water retention in agricultural fields.
• Mine Reclamation: Used for reclamation and stabilization of mine sites, reducing environmental impact.

Example:

• The Hoover Dam in the United States utilized fly ash in its concrete construction, demonstrating its effectiveness in large-scale infrastructure projects.

Conclusion: 
Fly ash, as a versatile industrial byproduct, finds applications in construction, agriculture, and environmental remediation. Proper management and utilization of fly ash are essential to minimize environmental impacts.

(c) Discuss the hazards in active volcanic terrain during and after eruption.    (15 Marks) 
Ans: 
Introduction: 
Active volcanic terrains are areas where volcanic eruptions have occurred in recent geological history or have the potential for future eruptions. They pose various hazards to surrounding areas.

Hazards during Eruption:

• Pyroclastic Flows: Fast-moving clouds of hot gases, ash, and rock fragments that can travel at high speeds, devastating everything in their path.

• Lahars: Volcanic mudflows consisting of water, volcanic ash, and debris, often triggered by rainfall or the melting of ice during an eruption.

• Ashfall: The deposition of fine volcanic ash over wide areas, which can disrupt transportation, damage infrastructure, and pose respiratory hazards.

• Lava Flows: The slow movement of molten lava, which can destroy structures and vegetation in its path.

Hazards after Eruption:

• Volcanic Gas Emissions: Release of gases like sulfur dioxide, carbon dioxide, and hydrogen sulfide, which can pose health risks and contribute to environmental issues.

• Secondary Lahars: Heavy rainfall following an eruption can remobilize volcanic debris, leading to secondary lahars.

• Ground Deformation: The weight of accumulated lava and magma can lead to ground subsidence, potentially causing sinkholes and infrastructure damage.

Example:

• The eruption of Mount St. Helens in 1980 demonstrated multiple hazards, including pyroclastic flows, lahars, and ashfall, impacting surrounding areas.

Conclusion: 
Understanding and mitigating the hazards associated with active volcanic terrains is crucial for the safety and well-being of communities living near or within these regions. Preparedness, monitoring, and early warning systems are essential components of volcanic risk management.