Geology 2021 Paper II 50 marks 150 words Compulsory Calculate

Q5

Answer the following questions in about 150 words each: (a) Lead (Pb) mineralization zone is drawn in the given diagram with nomenclature. The related data is also provided in the table. Calculate the average grade of lead (Pb) in percentage. Scale : 1"=10' Sample No. | Zone of Influence, L (ft) | Width, W (ft) | W × L (ft²) | % Pb S-1 | 6·0 | 3·5 | 21·00 | 7·1 S-2 | 7·5 | 2·5 | 18·75 | 7·5 S-3 | 10·0 | 3·0 | 30·00 | 6·9 S-4 | 12·5 | 3·5 | 43·75 | 8·9 (b) Describe the geological nature of coal deposits of Jharia (Jharkhand) and comment on their economic potential. (c) What are geophysical methods of exploration? How is gravity method useful in mapping the metallic ores? (d) Define 'trace element'. Discuss the possible ways that a trace element can enter into a mineral structure. (e) State the sea level changes in Late Pleistocene period with possible causes. Add a note on anthropogenic causes occurred in last two centuries.

हिंदी में प्रश्न पढ़ें

निम्नलिखित प्रश्नों में से प्रत्येक का लगभग 150 शब्दों में उत्तर दीजिए : (a) नामकरण के साथ दिए गए आरेख में सीसा (Pb) खनिजीभवन क्षेत्र दर्शाया गया है। इससे सम्बन्धित आँकड़े भी तालिका में दिए गए हैं। प्रतिशत में सीसे (Pb) के औसत ग्रेड की गणना कीजिए। पैमाना : 1"=10' नमूना संख्या | प्रभाव-क्षेत्र, L (ft) | चौड़ाई, W (ft) | W × L (ft²) | सीसा % S-1 | 6·0 | 3·5 | 21·00 | 7·1 S-2 | 7·5 | 2·5 | 18·75 | 7·5 S-3 | 10·0 | 3·0 | 30·00 | 6·9 S-4 | 12·5 | 3·5 | 43·75 | 8·9 (b) झरिया (झारखण्ड) के कोयला निष्क्षेपों की भूवैज्ञानिक प्रकृति का वर्णन कीजिए तथा उनकी आर्थिक क्षमता पर टिप्पणी कीजिए। (c) अन्वेषण की भूभौतिक विधियाँ क्या हैं? धात्विक अयस्कों के मानचित्रण में गुरुत्वाकर्षण विधि किस प्रकार उपयोगी है? (d) 'सूक्ष्मात्रिक तत्व' को परिभाषित कीजिए। उन सम्भावित तरीकों पर चर्चा कीजिए, जिनसे एक सूक्ष्मात्रिक तत्व खनिज संरचना में प्रवेश कर सकता है। (e) प्लीस्टोसीन काल के अन्त में समुद्र की सतह में होने वाले परिवर्तनों को सम्भावित कारणों सहित समझाइए। पिछली दो शताब्दियों में मानवजनित कारणों पर टिप्पणी कीजिए।

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Directive word: Calculate

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

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How this answer will be evaluated

Approach

This multi-part question requires precise time allocation: spend ~25% on (a) for correct weighted average calculation using area-weighted grade formula; ~20% each on (b)-(e) for concise 150-word responses. For (a), apply Σ(W×L×%Pb)/Σ(W×L); for (b), emphasize Gondwana stratigraphy and coking coal significance; for (c), contrast gravity with magnetic/electrical methods; for (d), explain substitution vs. interstitial entry; for (e), link Milankovitch cycles to eustatic changes and industrial-era thermal expansion.

Key points expected

(a) Correct application of weighted average formula: Σ(W×L×%Pb)/Σ(W×L) = (21×7.1 + 18.75×7.5 + 30×6.9 + 43.75×8.9)/(21+18.75+30+43.75) = 7.73% Pb
(b) Jharia coal: Lower Gondwana (Barakar Formation), bituminous rank, high volatile matter, premier coking coal reserve of India, challenges of coal fires and subsidence
(c) Geophysical methods: gravity, magnetic, seismic, electrical; gravity detects density contrasts for massive sulphide bodies, chromite, and iron ore deposits
(d) Trace element definition (<0.1%): substitution (diadochy, coupled substitution), interstitial sites, surface adsorption, fluid inclusions
(e) Late Pleistocene: 120m lower at LGM (~20 ka), Milankovitch forcing, ice-volume equivalent sea level; anthropogenic rise 3.3mm/yr post-industrial, thermal expansion + glacier melt

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	25%	12.5	Precisely defines weighted average grade calculation for (a); accurately identifies Barakar Formation and coking coal petrography for (b); correctly distinguishes active vs. passive geophysical methods and gravity anomaly principles for (c); rigorously defines trace element thresholds and crystal-chemical substitution mechanisms for (d); accurately describes eustatic vs. isostatic mechanisms and Milankovitch cyclicity for (e)	Partially correct calculations with minor errors; basic Gondwana identification without stratigraphic precision; lists geophysical methods without gravity-specific application; vague substitution concepts; general sea level trend without causal mechanisms	Incorrect formula application or arithmetic errors; confuses Jharia with Raniganj or Tertiary coals; conflates gravity with magnetic method; fails to define trace element or conflates with rare earth elements; no distinction between natural and anthropogenic causes
Diagram / cross-section	10%	5	Reproduces the Pb mineralization zone diagram with proper nomenclature (S-1 to S-4 positions), scale bar, and sample locations; sketches Gondwana basin cross-section showing Barakar-Damuda sequence; illustrates gravity anomaly profile over ore body	Mentions diagram without clear reproduction; basic stratigraphic column without structural detail; generic geophysical schematic	No diagram reference despite question requirement; missing all visual elements; incorrect or irrelevant sketches
Field evidence	15%	7.5	Cites specific GSI reserve estimates for Jharia (>35 billion tonnes); references known Pb-Zn deposits like Zawar or Sindesar Khurd for analogous mineralization; mentions Bouguer anomaly values from Dharwar or Singhbhum craton surveys; cites coral terrace or oxygen isotope evidence for sea level reconstruction	General reserve figures without attribution; generic mention of Aravalli or Cuddapah metallogeny; standard gravity survey references; textbook sea level curves without data source	No field data or empirical evidence; purely theoretical responses; invented statistics or incorrect localities
Quantitative reasoning	25%	12.5	Correct weighted average calculation yielding 7.73% Pb with proper unit handling (ft² conversion implicit); precise arithmetic showing intermediate steps; for (e), quantifies LGM sea level at -120±5m and current rise rate at 3.3±0.4 mm/yr with uncertainty awareness	Correct formula but arithmetic errors; simple arithmetic mean (7.6%) instead of weighted; rounded figures without precision; qualitative sea level description	Incorrect formula (unweighted average, or sum of grades/4); unit confusion between feet and meters; no calculations where required; order-of-magnitude errors in sea level change
Indian / economic relevance	25%	12.5	Emphasizes Jharia's critical role in India's steel industry (90%+ prime coking coal); links Pb exploration to HZL's Rampura-Agucha operations; connects gravity surveys to NGRI/AMD programs in Dharwar, Bastar and Singhbhum cratons; discusses climate vulnerability of Indian coastal cities (Mumbai, Chennai, Kolkata) to anthropogenic sea level rise	Mentions Indian coal reserves without sectoral significance; generic exploration context; basic coastal impact statement	No Indian examples; Western-centric case studies; ignores economic implications entirely; no climate policy relevance

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