Geology 2025 Paper II 50 marks Discuss

Q6

(a) Give an account of geology, mode of occurrence, genesis and distribution of Pb-Zn deposits of Aravalli region. (15 marks) (b) Give the distribution of petroliferous basins of India. Discuss the geology of Cambay Basin. (15 marks) (c) Give a brief account on the volcanogenic massive sulphide (VMS) deposit. Cite suitable Indian examples. (20 marks)

हिंदी में प्रश्न पढ़ें

(a) अरावली क्षेत्र में पाए जाने वाले सीसा-जस्ता (Pb-Zn) भंडारों के भूविज्ञान, उपस्थिति शैली, उत्पत्ति तथा वितरण का वर्णन कीजिए। (15 अंक) (b) भारत के पेट्रोलियमधारित क्रोड़ियों का वितरण बताइए। खम्भात (कैम्बे) क्रोड़ी के भूविज्ञान पर चर्चा कीजिए। (15 अंक) (c) ज्वालामुखीय स्थूल सल्फाइड (वी० एम० एस०) निक्षेप का एक संक्षिप्त विवरण दीजिए। भारत से समुचित उदाहरण उद्धृत कीजिए। (20 अंक)

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Directive word: Discuss

This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'discuss' demands a comprehensive, analytical treatment with balanced coverage across all three sub-parts. Allocate approximately 30% time/words to part (a) on Aravalli Pb-Zn deposits, 30% to part (b) on Cambay Basin geology, and 40% to part (c) on VMS deposits given its higher mark weightage. Structure with brief introductions for each part, systematic body covering geology, genesis and distribution, and conclude with integrated remarks on India's metallogenic and petroliferous provinces.

Key points expected

  • Part (a): Aravalli Pb-Zn deposits — stratiform nature in Precambrian metasediments, Rampura-Agucha and Rajpura-Dariba as type examples, syngenetic-diagenetic to epigenetic genetic models, Zawar belt distribution
  • Part (b): Petroliferous basins — Mumbai Offshore, Krishna-Godavari, Cauvery, Assam-Arakan, Cambay Basin; Cambay Basin geology — Tertiary rift basin, Olpad Formation volcanics, Cambay Shale source rock, Kalol and Ankleshwar reservoirs
  • Part (c): VMS deposits — Cyprus/Kuroko/Besshi types, seafloor hydrothermal systems, bimodal volcanics association; Indian examples — Ambaji-Deri belt (Aravalli), Sargipalli (Singhbhum), Betul belt
  • Genetic comparisons across deposit types — contrasting sediment-hosted (Aravalli) vs. volcanogenic (VMS) vs. biogenic/thermogenic (petroleum) systems
  • Economic significance — India's Zn-Pb self-sufficiency, petroleum import dependency, critical mineral potential of VMS Cu-Zn
  • Temporal evolution — Archaean VMS, Proterozoic SEDEX/Aravalli type, Tertiary petroleum systems

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precisely distinguishes SEDEX vs. VMS genetic models for (a) and (c); correctly identifies Cambay as Tertiary rift basin with Deccan Trap basement for (b); uses accurate stratigraphic nomenclature (Delhi Supergroup, Olpad Formation, etc.)Basic genetic concepts stated but conflates SEDEX-VMS or misidentifies basin type; minor stratigraphic errorsFundamental confusion between syngenetic/epigenetic, rift/shelf basin, or volcanic-exhalative processes
Diagram / cross-section20%10Includes at least two quality diagrams: schematic cross-section of Aravalli Pb-Zn stratiform ore body showing host rock relationships, and Cambay Basin structural-stratigraphic column; labels essential features (ore lenses, shale source, reservoir sands)One adequate diagram with partial labeling; or two rough sketches lacking geological detailNo diagrams, or irrelevant/incorrect sketches that misrepresent structural or stratigraphic relationships
Field evidence20%10Cites specific field observations: Rampura-Agucha massive sulphide bands, Zawar manto-type ore geometry, Cambay Basin well data (Cambay-3, etc.), VMS stockwork zones at Ambaji; mentions exploration indicators (gossans, gravity anomalies)Generic field descriptions without specific localities; mentions major mines but lacks observational detailNo field evidence cited; purely theoretical treatment without connection to actual deposits or basins
Quantitative reasoning15%7.5Provides reserve/production data: Rampura-Agucha ~75 Mt ore, Cambay Basin ~25% of Indian oil production; mentions depth ranges (Cambay Shale ~1500-3000m), grade values (Zn 10-15% at Zawar); uses comparative statistics across basinsApproximate figures for one or two deposits; order-of-magnitude estimates without precisionNo quantitative data; or significantly incorrect figures that undermine credibility
Indian / economic relevance20%10Integrates strategic significance: HZL's dominance in Zn-Pn production, India's petroleum security through Cambay-Mumbai-KG basins, VMS potential for Cu import reduction; mentions NMET, critical minerals policy, or exploration initiativesLists economic importance without integration; mentions companies or policies superficiallyNo economic context; treats deposits as academic exercises without national resource implications

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