Q1. [3] deep thorough-understanding
India's vast alluvial plains of north India are described as almost devoid of economic minerals, whereas the peninsular rocks are mineral-rich. Using your understanding of how minerals form in different rock types, explain why the alluvial plains are so poor in mineral deposits.
Generated by claude-sonnet-4-6 · 2026-06-26 13:33 · grounding rag
Model Answer
The alluvial plains of north India are formed by deposition of sediments carried by rivers from the Himalayas. These plains lack the igneous and metamorphic rock formations where metallic minerals (like copper, zinc, tin) occur in veins and lodes through cooling of molten magma. They also lack the ancient peninsular rock systems where minerals concentrate over geological time. The loose alluvial sediments do not support the heat, pressure, or chemical processes needed to form economic mineral deposits, making the region almost devoid of minerals.
Source: Chapter 5 – Minerals and Energy Resources, Mode of Occurrence of Minerals
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Explanation
- The key is linking rock type → mineral formation process:
- Igneous/metamorphic rocks → veins and lodes (metallic minerals)
- Peninsular rocks → ancient, subjected to heat and pressure over millions of years
- Alluvial plains → recent sediment deposits, no such geological processes
- Examiners want you to explicitly state why alluvial regions lack minerals, not just that they lack them.
- Quote or closely paraphrase: "These variations exist largely because of the differences in the geological structure, processes and time involved in the formation of minerals."
- Do not list minerals found elsewhere — focus on the formation logic for the plains.