Geology Civil Services Paper 2 Section- B, Questions 5,6_ Solutions
5. (a)- What are the major changes in the process of formation of uranium deposits through geological time?
Answer: The process of formation of uranium deposits has undergone several major changes throughout geological time, resulting in different types of deposits. Here are some of the major changes:
Archean Eon: During the Archean Eon (4.0 to 2.5 billion years ago), uranium deposits were formed through hydrothermal processes, in which hot fluids circulated through fractures and faults in the crust, depositing uranium minerals as they cooled.
Proterozoic Eon: In the Proterozoic Eon (2.5 billion to 541 million years ago), uranium deposits were formed through sedimentary processes, in which uranium-rich minerals were concentrated in sedimentary rocks, such as sandstones or black shales.
Phanerozoic Eon: During the Phanerozoic Eon (541 million years ago to present), uranium deposits were formed through a combination of processes, including hydrothermal and sedimentary processes, as well as in association with granitic intrusions and metamorphic rocks.
Mesozoic Era: In the Mesozoic Era (252 to 66 million years ago), uranium deposits were formed in association with large-scale continental rift systems, such as those that occurred in the western United States.
Cenozoic Era: During the Cenozoic Era (66 million years ago to present), uranium deposits were formed through a combination of processes, including hydrothermal, sedimentary, and weathering processes, as well as in association with volcanic and plutonic rocks.
In summary, the process of formation of uranium deposits has changed over time, depending on the geological setting and the dominant geological processes in play during that time.
5. (b) Describe the geological setting of copper deposits in the Singhbhum shear zone and Khetri copper belt.
Answer: The Singhbhum shear zone and the Khetri copper belt are two significant copper mineralization zones located in India.
The Singhbhum shear zone is a geological feature that runs through the eastern Indian states of Jharkhand and Odisha. It is a zone of intense deformation and metamorphism, resulting from the collision between the Indian and Eurasian plates. The shear zone contains a variety of rock types, including gneisses, granites, amphibolites, and schists, all of which have been subjected to intense deformation and metamorphism. The copper deposits in the Singhbhum shear zone are primarily associated with a series of rocks known as the Singhbhum Copper Belt. This belt comprises a sequence of volcanic and sedimentary rocks that were deposited during the Proterozoic era. The copper deposits in the Singhbhum Copper Belt are mostly stratiform and occur within volcanic and sedimentary rocks.
The Khetri copper belt is located in the state of Rajasthan, in northwestern India. It is a part of the Aravalli mountain range, which was formed as a result of the collision between the Indian and Eurasian plates. The Khetri copper belt is a series of copper deposits that occur within a sequence of rocks known as the Delhi Supergroup. The Delhi Supergroup comprises a variety of sedimentary and volcanic rocks that were deposited during the Proterozoic era. The copper deposits in the Khetri copper belt are primarily associated with a rock known as the Khetri Gneiss, which is a metamorphosed sedimentary rock that contains copper-bearing minerals. The Khetri copper belt also contains significant deposits of other metals, including zinc, lead, and silver.
In both the Singhbhum shear zone and the Khetri copper belt, the copper deposits are associated with intense deformation and metamorphism, which have resulted in the formation of complex mineralized structures. The deposits are also associated with specific rock types that have favorable geological conditions for the formation of copper-bearing minerals.
5. (c) A beneficiation plant processes 12000 tons of copper ore containing 0.8 wt.% Cu in a day and produces ore concentrate containing 25 wt.% Cu. Assuming 80% ore recovery in the beneficiation process, how many tons of ore concentrate will be produced by the plant in a day?
Answer: The amount of copper in the ore can be calculated as follows:
Copper in the ore = 0.008 x 12000 = 96 tons
Assuming 80% ore recovery, the amount of copper in the concentrate can be calculated as follows:
Copper in the concentrate = 0.25 x (0.8 x 96) = 19.2 tons
Therefore, the amount of ore concentrate produced in a day will be:
Ore concentrate produced = (0.8 x 12000) / (1 - 0.8) = 48000 tons
So the plant will produce 48000 tons of ore concentrate containing 19.2 tons of copper.
5. (d) Define equilibrium in a system. What are entropy, enthalpy, and Gibb's free energy
of a system?
Answer: Equilibrium is a state in which a system is balanced and there is no net change in its properties over time. In a thermodynamic sense, equilibrium can refer to thermal equilibrium (when there is no net heat flow between a system and its surroundings), mechanical equilibrium (when there is no net force acting on a system), or chemical equilibrium (when the concentrations of reactants and products in a chemical reaction are constant over time).
Entropy is a measure of the disorder or randomness in a system and is typically denoted by the symbol S. The second law of thermodynamics states that the total entropy of a closed system can never decrease over time, and will tend to increase until the system reaches equilibrium. Entropy is related to the number of possible microscopic arrangements that can give rise to a particular macroscopic state of a system.
Enthalpy is a measure of the total energy of a system, including both its internal energy and any work that it can perform on its surroundings. It is typically denoted by the symbol H. Enthalpy changes are often used to describe the energy changes associated with chemical reactions, and can be used to calculate the amount of heat that is released or absorbed during a reaction.
Gibbs free energy is a measure of the amount of useful work that can be obtained from a system at constant temperature and pressure and is typically denoted by the symbol G. It is related to both the enthalpy and entropy of a system and can be used to predict whether a chemical reaction will be spontaneous or non-spontaneous. If the Gibbs free energy change for a reaction is negative, then the reaction will be spontaneous and can release energy. If the Gibbs free energy change is positive, then the reaction will be non-spontaneous and will require an input of energy to proceed. At equilibrium, the Gibbs free energy change is zero.
5. (e) Discuss environmental hazards caused due to mining.
Answer: Mining is a process of extracting valuable minerals or other geological materials from the earth's surface. While mining has played a significant role in the development of the global economy, it also poses severe environmental hazards. Mining activities can have detrimental effects on the environment, including air, water, and soil pollution, the destruction of natural habitats, and the release of greenhouse gases. In this answer, we will discuss some of the environmental hazards caused by mining:
Soil and water pollution: Mining activities often involve the use of chemicals like cyanide and mercury to extract metals from ore. These chemicals can leach into the soil and water, contaminating them and posing a threat to human health and wildlife. The removal of vegetation and topsoil during mining activities can also lead to soil erosion, which can further contaminate water bodies.
Air pollution: Mining activities can release a large amount of dust and other particulate matter into the air, causing respiratory problems for workers and nearby communities. The use of explosives during mining operations can also release harmful gases like sulfur dioxide, nitrogen oxides, and carbon monoxide into the atmosphere.
Habitat destruction: Mining activities often involve the destruction of natural habitats, including forests, wetlands, and grasslands. This can result in the displacement of wildlife and the loss of biodiversity.
Acid mine drainage: When mining activities expose sulfide-bearing rocks to air and water, they can form sulfuric acid, which can leach into water bodies and cause the water to become acidic. Acid mine drainage can have severe impacts on aquatic life and can also make water unsuitable for human consumption.
Greenhouse gas emissions: Mining activities can release significant amounts of greenhouse gases like carbon dioxide and methane into the atmosphere, contributing to global climate change.
In conclusion, mining activities can have severe environmental consequences. While there are regulations in place to minimize the environmental impact of mining, it is crucial to prioritize sustainable mining practices and invest in the development of technologies that can reduce the environmental hazards associated with mining.
6. (a) Explain the processes by which sediment-hosted Pb-Zn deposits are formed. Describe the geological setting of Agucha and Zawar Pb-Zn deposits in the Aravalli craton.
Answer: Sediment-hosted Pb-Zn deposits are formed through a combination of sedimentary, hydrothermal, and diagenetic processes. These deposits are typically found in sedimentary basins that have undergone deformation, which can cause the expulsion of fluids from sedimentary rocks and the creation of conduits for the flow of mineralizing fluids.
The process begins with the accumulation of sedimentary rocks rich in lead and zinc. These rocks are often deposited in marine environments where the metals are sourced from seawater or hydrothermal fluids. As the sedimentary basin is buried by further sedimentation, compaction and diagenesis occur, causing the sedimentary rocks to become more dense and permeable. This can result in the expulsion of metal-rich fluids, which migrate upwards toward the surface.
In the case of Pb-Zn deposits in the Aravalli craton, the geological setting is characterized by a complex tectonic history involving multiple stages of deformation and metamorphism. The Agucha and Zawar deposits are located in the southern part of the craton, which is dominated by Proterozoic rocks. The rocks in this area are divided into two main groups: the Aravalli Supergroup and the Delhi Supergroup.
The Agucha deposit is located in the Bhilwara district of Rajasthan and is hosted by the Aravalli Supergroup. The deposit is characterized by a series of stratiform lenses of sulfide minerals, including galena, sphalerite, and pyrite. The mineralization is hosted within dolomites and limestones, which have been folded and faulted during the tectonic history of the area. The deposit is thought to have formed during the late Proterozoic through a combination of hydrothermal and diagenetic processes.
The Zawar deposit is located in the Udaipur district of Rajasthan and is hosted by the Delhi Supergroup. The deposit is characterized by multiple orebodies that are hosted within dolomites and quartzites. The mineralization is dominated by sphalerite and galena, with minor amounts of chalcopyrite and pyrite. The deposit is thought to have formed during the late Archean through a combination of sedimentary, hydrothermal, and diagenetic processes.
In summary, sediment-hosted Pb-Zn deposits are formed through a complex interplay of sedimentary, hydrothermal, and diagenetic processes. The geological setting of the Aravalli craton, with its complex tectonic history and diverse sedimentary rocks, has provided an ideal environment for the formation of world-class Pb-Zn deposits such as Agucha and Zawar.
6. (b) How are diamond bearing kimberlites formed? Write a note on Majhgawan
kimberlite and Wajrakarur kimberlite field.
Answer: Diamond-bearing kimberlites are formed deep within the Earth's mantle under high temperature and pressure conditions. Kimberlite magma is generated by the melting of peridotite, which is a rock composed primarily of olivine and pyroxene minerals. The magma rises rapidly to the Earth's surface, carrying with it pieces of mantle rock and diamond crystals that have formed under extreme pressure.
The Majhgawan kimberlite in India is a well-known diamond-bearing kimberlite pipe. It is located in the Panna district of Madhya Pradesh and was discovered in 1967. The kimberlite pipe is oval-shaped, approximately 400 meters long, and 200 meters wide. The depth of the pipe is estimated to be around 200 meters. The kimberlite contains a significant amount of diamonds, with some of them being of gem quality. The Majhgawan kimberlite is considered to be a primary source of diamonds in India.
The Wajrakarur kimberlite field in India is another significant diamond-bearing kimberlite deposit. It is located in the Anantapur district of Andhra Pradesh and was discovered in the early 1970s. The kimberlite field consists of several pipes and dykes, covering an area of approximately 400 square kilometers. The Wajrakarur kimberlite field has been extensively explored, and it is estimated to contain a significant amount of diamonds, with some of them being of gem quality.
In summary, diamond-bearing kimberlites are formed deep within the Earth's mantle, and they bring diamonds and mantle rocks to the Earth's surface. The Majhgawan and Wajrakarur kimberlite deposits in India are important sources of diamonds and have been extensively explored for their commercial value.
6. (c) Describe the geological setting and distribution of Tertiary coal deposits in NE India
and Lignite deposits in Tamil Nadu.
Answer: The Tertiary coal deposits in Northeast India are located in the states of Assam, Arunachal Pradesh, Meghalaya, Nagaland, and Mizoram. These coal deposits are primarily found in the upper parts of the Tertiary rock formations, which are composed of sedimentary rocks such as sandstones, shales, and limestones. The coal seams are generally thin, ranging from a few centimeters to several meters in thickness, and are often interbedded with other sedimentary rocks.
The coal in Northeast India is of sub-bituminous to bituminous quality and is generally low in sulfur and ash content. The coal deposits in this region are believed to have formed during the Paleocene to Eocene epoch, approximately 60 to 40 million years ago when the region was covered by extensive swamps and forests.
On the other hand, lignite deposits in Tamil Nadu are located in the Cuddalore and Ariyalur districts. The lignite in Tamil Nadu is believed to have formed during the Late Oligocene to Early Miocene epoch, approximately 25 to 30 million years ago when the region was covered by shallow seas and extensive mangrove forests.
The lignite deposits in Tamil Nadu are primarily found in the Neyveli Lignite Formation, which is composed of alternating layers of lignite, clay, and sand. The lignite seams in this formation are generally thick, ranging from a few meters to over 30 meters in thickness. The lignite in Tamil Nadu is of low to medium grade and is often used as fuel for thermal power generation.