Model Answer
0 min readIntroduction
Bauxite, the primary ore of aluminum, is a sedimentary rock formed through intense weathering and leaching of aluminum-rich rocks. India possesses significant bauxite reserves, with a substantial portion concentrated along its East Coast. These deposits are particularly important due to their proximity to ports, facilitating export, and their relatively high alumina content. The East Coast bauxite deposits are largely associated with lateritic formations developed on the Precambrian basement rocks and Tertiary sediments, making their geological understanding crucial for resource management and sustainable exploitation.
Geological Setting of the East Coast
The East Coast of India is characterized by a complex geological history. It’s broadly divisible into three major geological domains:
- Precambrian Basement Rocks: These constitute the oldest rocks, comprising granite, gneiss, and charnockite. They form the foundation upon which younger formations are deposited.
- Gondwana Sedimentary Rocks: Found in pockets, these are Permian-Jurassic in age and represent continental rift-related sedimentation.
- Tertiary Sedimentary Rocks: These are the most widespread younger formations, consisting of sandstones, shales, and laterites, deposited during the Tertiary period.
Formation of East Coast Bauxite Deposits
Bauxite formation along the East Coast is primarily linked to intense tropical weathering and laterization processes. The key steps involved are:
- Source Rock: The primary source rocks are the aluminum-rich Precambrian basement rocks (granites, gneisses) and, to a lesser extent, the Tertiary basalts.
- Weathering: Prolonged and intense chemical weathering, driven by high temperatures and rainfall, leads to the breakdown of aluminosilicate minerals (feldspars, mica) in the source rocks.
- Leaching: Soluble elements like silica, iron, and alkali metals are leached away by percolating rainwater, leaving behind a residual concentration of aluminum hydroxides (gibbsite, boehmite, diaspore).
- Laterization: This process results in the formation of lateritic soils, which, under favorable conditions, evolve into bauxite deposits.
Specific Geological Formations and Deposit Locations
The major bauxite-bearing formations along the East Coast are:
1. Eastern Ghats Mobile Belt (Odisha & Andhra Pradesh)
This region hosts the largest bauxite deposits in India. The bauxite occurs as capping over the Precambrian rocks. The deposits are generally of Tertiary age, formed on weathered khondalite and charnockite rocks. Key locations include:
- Koraput & Rayagada (Odisha): Significant deposits associated with the Eastern Ghats Supergroup.
- Visakhapatnam, Srikakulam & Vizianagaram (Andhra Pradesh): Bauxite occurs as residual deposits on the weathered granites and gneisses.
2. Neyveli Lignite Area (Tamil Nadu)
Bauxite deposits are found as pockets within the Tertiary sediments overlying the Cretaceous formations. These deposits are relatively smaller in size but are important due to their proximity to the Neyveli Lignite Corporation.
3. Coastal Plains of Andhra Pradesh & Tamil Nadu
Smaller, localized bauxite occurrences are found in the coastal plains, associated with Tertiary laterites. These are often found as surface or near-surface deposits.
Mineralogy of East Coast Bauxite
The mineralogical composition of East Coast bauxite varies depending on the geological setting and weathering intensity. Common minerals include:
- Gibbsite (Al(OH)3): The most common aluminum hydroxide mineral, prevalent in intensely weathered bauxites.
- Boehmite (γ-AlO(OH)): Forms under slightly less intense weathering conditions.
- Diaspore (α-AlO(OH)): Indicates higher temperature and pressure conditions during formation.
- Hematite (Fe2O3): An iron oxide commonly associated with bauxite, giving it a reddish color.
- Kaolinite (Al2Si2O5(OH)4): A clay mineral indicating less complete weathering.
| State | Major Bauxite Producing Districts | Geological Formation |
|---|---|---|
| Odisha | Koraput, Rayagada, Kalahandi | Eastern Ghats Supergroup |
| Andhra Pradesh | Visakhapatnam, Srikakulam, Vizianagaram | Precambrian Basement & Tertiary Sediments |
| Tamil Nadu | Cuddalore, Ariyalur | Tertiary Sediments |
Conclusion
The East Coast bauxite deposits of India represent a significant resource for aluminum production. Their formation is intricately linked to the geological history and weathering processes operating along the coast. Understanding the specific geological formations, mineralogy, and weathering conditions is crucial for sustainable exploration, mining, and utilization of these valuable resources. Further research into the genesis of these deposits and the development of environmentally responsible mining practices are essential for ensuring long-term availability.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.