C S. (main) EXAM, 2009
GEOLOGY

Paper II

Time Allowed Three Hours Maximum Marks 300

INSTRUCTIONS

Each question is printed both in Hindi and in English.

Answers must be written in the medium specified in the Admission Certificate issued to you, which rnust be stated clearly on the cover of the answer-book in the space provided for the purpose. No n1arks will be given for the answers written 1n a medium other than that specified in the Admission Certificate.

Candidates should attempt Question Nos. 1 and 5 which are compulsory, and any three of the remaining questions selecting at least one question from each Section.

Candidates should draw diagrams wherever necessary.

All questions carry equal marks.

Section

1. Attempt any three of the following in 200 words each 3x20=60
Explain how radius ratio (of cation to anion) influences coordination in silicate minerals. Write how an element can have more than one coordination number?
Define the Gibbs phase rule and calculate the variance of the assemblage containmg enstatite forsterite Mg-spinel corundum.
Compare the optical properties of the following mineral patrs, with at least two diagnostic optical properties
quartz and plagioclase
hornblende and diopside
chlorite and muscovite, and
kyanite and sillimanite
Explain how depending on magma compos1- tion, some lavas flow a great distance. while others barely move.

2. With theoretical details, discuss the
opticaJ indicatrix
interference figure and
optic sign determination of uniaxial minerals
With suitable examples. discuss the causes behind and effects of
pleochroism
extinction angles and
birefringence in minerals 2x30=60

3. What are the maJor minerals that constitute carbonate sediments and what physicochemical factors control their precipitation What are the basic cbmponents of Folk's classification of carbonate rocks
By suitable reactions, discuss various mineralogical and mineral chemical changes, that take place during metamorphism of a gabbroic rock at the greenschist-amphibolite facies transition. 2x30=60

4. What are turbidites? With a neat sketch. show different units of a Bouma cycle and flow regimes under which they are formed.
Discuss the role of PH20 in the albite-orthoclase- silica-H20 system. Explain the rarity of rhyolites and preponderance of granites in the rock record. 2x30=60

Section

5. Attempt any three of the following in 200 words each 3x20=60
Explain why ore deposits of Fe and Al are far more common in the rocks compared to those of Ag, Hg and Sb. Add brief notes on tonnage, grade and cut-off grade of an ore.
Enumerate the various corrections that are necessary for reduction of gravity field data in any exploration programme.

Explain how on th.e basis of ionic radius and charge, atomic substitution take place in silicate minerals. What is the effect of electronegativity on the above substitution mechanisms
Discuss the precursor events that might signal the occurrence of an earthquake.

6. Compare the processes that lead to formation of chromite and Ni-Cu sulfide ores in basicultra basic layered rocks.
With suitable cherrticaJ reactions, explain the mineralogical changes that take place, when a Cu suJfide ore body, containing pyrite, undergoes oxidation and supergene enrichment.
2x30=60

7. Enumerate the various natural sources of hydrothermal ore forming fluids and explain how most hydrothermal ore deposits owe their origin to multiple fluid sources.
With suitable examples, define indicator and pathfinder elements in geochemical prospecting. Discuss element mobility, as a result of various processes of dispersion. 2x30=60

8. Discuss the mineralogical (and chemical) compos1t1ons of various meteorites, with a note on how carbonaceous chondrites furnish evidence for planet's composition. 30
Discuss the various causative factors behind different types of mass wasting. 30

Note English version of rhe Instructions is printed on
the front corer of this question paper.