Geology 2022 Paper II 50 marks Explain

Q6

(a) Explain the processes by which sediment hosted Pb-Zn deposits are formed. Describe the geological setting of Agucha and Zawar Pb-Zn deposits in the Aravalli craton. (20 marks) (b) How are diamond bearing kimberlites formed ? Write a note on Majhgawan kimberlite and Wajrakarur kimberlite field. (15 marks) (c) Describe the geological setting and distribution of Tertiary coal deposits in NE India and Lignite deposits in Tamil Nadu. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) उस विधि की व्याख्या कीजिए जिसके द्वारा अवसाद स्थित सीसा-जस्ता निक्षेप बनते हैं । आरावली क्रेटान में अगुचा और जावर सीसा-जस्ता निक्षेपों के भूवैज्ञानिक विन्यास का वर्णन कीजिए । (20 अंक) (b) हीराधारक किम्बरलाइट किस प्रकार बनते हैं ? मझगवां एवं वज्रकरुर किम्बरलाइट क्षेत्र पर टिप्पणी लिखिए । (15 अंक) (c) उत्तर पूर्व भारत में तृतीयकपी कोयला निक्षेपों तथा तामिलनाडु में लिग्नाइट निक्षेपों का भूवैज्ञानिक विन्यास तथा वितरण का उल्लेख कीजिए । (15 अंक)

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Directive word: Explain

This question asks you to explain. 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 'explain' demands clear causal mechanisms and geological processes. Structure: brief introduction on India's economic mineral wealth, then body divided by marks—spend ~40% on part (a) covering SEDEX/MVT models and Aravalli specifics; ~30% each on (b) and (c) covering kimberlite petrogenesis with Indian field examples and Tertiary coal/lignite basins respectively. Conclude with significance for India's mineral security.

Key points expected

  • Part (a): SEDEX (sedimentary exhalative) and MVT (Mississippi Valley Type) genetic models for Pb-Zn; brine expulsion, basin dewatering, and sulfide precipitation mechanisms
  • Part (a): Aravalli craton setting—Proterozoic Delhi Supergroup, carbonate-shale host rocks; Agucha (world-class SEDEX, Bhilwara belt) and Zawar (MVT-type, Udaipur district) specifics
  • Part (b): Kimberlite formation—deep mantle melting (>150 km), CO2-H2O volatile fluxing, rapid ascent as diatremes; diamond preservation in lithospheric mantle xenoliths
  • Part (b): Majhgawan (Panna district, only diamond-producing mine in India, Cretaceous age, pipe structure) and Wajrakarur field (Andhra Pradesh, multiple pipes, lamproite-kimberlite association)
  • Part (c): NE India Tertiary coal—Eocene-Oligocene Barail Series, Assam-Arakan basin, discontinuous belt from Makum to Dilli-Jeypore; high sulfur, oil-prone nature
  • Part (c): Tamil Nadu lignite—Cuddalore Formation, Miocene-Pliocene, Neyveli major deposit (largest in India), Ariyalur-Pondicherry belt; shallow marine-lagoonal environment

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Accurately distinguishes SEDEX vs MVT models for (a); correctly describes kimberlite petrogenesis with depth constraints and diamond stability field for (b); precisely identifies Barail and Cuddalore formations with correct ages for (c); no conceptual errors across all partsBasic genetic concepts stated but models confused (e.g., SEDEX/MVT conflated); kimberlite formation oversimplified; coal/lignite formations named but ages or stratigraphy incorrectMajor errors in genetic mechanisms; incorrect deposit classification; wrong geological formations cited; demonstrates fundamental misunderstanding of ore genesis principles
Diagram / cross-section15%7.5Includes labeled diagrams for at least two parts: e.g., SEDEX brine-cell circulation model for (a), kimberlite pipe structure with crater/diatreme/root zones for (b), or stratigraphic column for (c); diagrams enhance explanation and are properly annotatedOne relevant diagram attempted but poorly labeled or incomplete; OR describes diagrams in text without actual sketch; diagrams do not clearly illustrate key processesNo diagrams despite clear need for visual explanation; OR diagrams entirely wrong (e.g., porphyry copper model for Pb-Zn); messy, unlabeled sketches that confuse rather than clarify
Field evidence20%10Cites specific field evidence: for (a) mentions ore textures (bedded, breccia, replacement), alteration halos, and structural controls; for (b) notes crater facies vs hypabyssal facies at Majhgawan; for (c) describes seam thickness, dip, and quality variations in Makum vs NeyveliGeneral field descriptions without specific evidence; mentions 'ore bodies' or 'coal seams' without texture, structure, or grade details; field relationships implied but not explicitly statedNo field evidence cited; purely theoretical treatment; incorrect field relationships (e.g., kimberlites as lava flows); ignores observable criteria that distinguish deposit types
Quantitative reasoning15%7.5Provides quantitative constraints: depth of kimberlite origin (>150 km, diamond stability field), reserve figures (Agucha: ~150 Mt; Neyveli lignite: ~400 Mt), seam thicknesses, grades (%Pb+Zn, %C), or age dates (Majhgawan ~1075 Ma); uses numbers to support genetic argumentsVague quantitative references (e.g., 'deep origin', 'large reserves'); some numbers cited but without units or context; quantitative data present but not integrated into explanationNo quantitative data; purely qualitative description; incorrect orders of magnitude; confuses reserve and resource figures; numbers appear arbitrary or fabricated
Indian / economic relevance25%12.5Explicitly connects to India's mineral economy: Agucha as largest open-cast Pb-Zn mine; diamond mining history at Panna; Neyveli Lignite Corporation's power generation role; NE coal for regional industry; mentions exploration potential, import substitution, or strategic significanceIndian examples named but economic significance merely stated ('important deposit'); no discussion of production scale, employment, or energy security; economic relevance treated as afterthoughtIndian examples missing or incorrect; treats foreign examples as equivalent; no economic context; fails to demonstrate why these specific Indian deposits matter nationally

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