Q1. [4] medium exam-ready
Read the following passage and answer the questions that follow:
The distribution of minerals across India is highly uneven and is closely linked to the geological history of different regions. The Peninsular plateau, underlain by ancient crystalline rocks, is the storehouse of most of India's metallic minerals. In contrast, the vast alluvial plains of northern India, though agriculturally rich, are almost devoid of economic mineral deposits. Some minerals are concentrated in specific geological structures such as cracks, joints, and faults, while others are spread through sedimentary strata or found in residual deposits left by weathering. The type of geological structure also determines the method and cost of extraction.
(i) Why are the alluvial plains of northern India largely deficient in mineral resources? [1]
(ii) Name two major metallic minerals obtained from veins and lodes in igneous and metamorphic rocks. [1]
(iii) What are placer deposits? Name two minerals commonly found in them. [2]
Generated by claude-sonnet-4-6 · 2026-06-26 13:34 · grounding rag
Model Answer
(i) The alluvial plains of northern India are largely deficient in mineral resources because they are underlain by alluvium deposited by rivers, not by ancient crystalline or hard rocks. Economic minerals are formed in igneous, metamorphic, or sedimentary rocks through geological processes, which are absent in alluvial plains.
(ii) Two major metallic minerals obtained from veins and lodes in igneous and metamorphic rocks are copper and tin.
(iii) Placer deposits are alluvial deposits found in sands of valley floors and the base of hills. They generally contain minerals that are not corroded by water. Two minerals commonly found in placer deposits are gold and platinum.
Source: Chapter 5 – Minerals and Energy Resources, Mode of Occurrence of Minerals
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Explanation
- (i) Key reason: alluvial plains lack the rock formations (igneous/metamorphic/sedimentary) needed for mineral formation. The textbook directly states they are "almost devoid of economic minerals" due to differences in geological structure.
- (ii) The passage lists tin, copper, zinc, and lead — any two are acceptable. Copper + tin is a safe, commonly expected pair.
- (iii) Definition must mention "alluvial deposits," "valley floors/base of hills," and "not corroded by water." Gold and platinum are the most important examples from the textbook. Tin and silver are also acceptable.