[short_answer] A mining engineer discovers two deposits of the same mineral — one occurring as a vein within metamorphic rock and the other as a placer deposit in a nearby river valley. Compare these two deposits in terms of (i) how the mineral came to be concentrated in each location, and (ii) the likely method of extraction used for each.
Generated by claude-sonnet-4-6 · 2026-06-26 13:33 · grounding rag
Model Answer
(i) Concentration of Mineral:
- Vein deposit (metamorphic rock): Minerals in liquid/molten or gaseous form were forced upward through cracks and crevices in metamorphic rock. They cooled and solidified, forming veins and lodes. (e.g., copper, tin, zinc)
- Placer deposit (river valley): Minerals resistant to water corrosion were weathered from rocks and transported by water, settling and accumulating in valley floors and bases of hills. (e.g., gold, platinum)
(ii) Method of Extraction:
- Vein deposit: Requires underground shaft mining to access deep-seated mineral veins.
- Placer deposit: Extracted by surface/alluvial methods such as panning or dredging, as minerals lie in loose sand and gravel.
Source: Chapter 5, Mode of Occurrence of Minerals
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Explanation
Examiners look for a clear comparison of both types in both aspects. Key terms to use: veins/lodes, molten/gaseous forms, cool and solidify, alluvial/placer, not corroded by water. The extraction method follows logically from the deposit type — deep veins need underground mining; surface alluvial deposits allow simpler surface extraction. Don't mix up sedimentary beds with veins.