Sohag University
Faculty of Science
Dept of Geology
Final exam in Applied Sedimentology and ore Petrology for 4th year geology students
January 2013 2 hours
A- Applied Sedimentology
Answer the following illustrating your words whenever possible.
1- ” Weathering processes have a great economic importance” , discuss this statement concentrating on the following points:
a – Weathering products ( 6 marks)
b – Super gene enrichment (6 marks)
c – Roll-front uranium ore (6 marks)
2- Tick the true statement and put (x) by the false one. (12 marks)
a – Placer deposits usually found in the up-stream end of point pars
b – Meander fluvial deposits usually form giant hydrocarbon reservoirs
c – galena is one of the most dangerous minerals
d – Grain size parameters control the suitability of a sediment for use in industrial purposes.
e – The Libyan Augla oil field is an example of hydrocarbon reservoirs in granite wash.
f – All porous rocks are permeable.
3 – Finish the following : (12marks)
a – Fluvial deposits are of very economic importance because:
i – …………………………………………………………….
i ………………………………………………………………
i …………………………………………………..
b- The permeability of rocks is controlled by :
i – ………………………………………………………….
ii …………………………………………………………
iii – …………………………………………………
4 – The petroleum geologist examining thin section usually feel happy when he see dolomite rhombs, why? (3 marks)
B – Ore Petrology
1- Complete the missing parts in the following statements (15 marks):
A- Experimental work proved that the relationship between chalcopyrite and ……….. (chalcopyrite disease) is not …………, so it is most propably to be epitaxial growth or ……………….
B- In the Fe-Ti oxide deposits, exsolution lamellae of ……….. in magnetite are sharp & equal in width , those of hematite in ilmenite are ………….., while the ………. fabric in titaniferous magnetite results from fine exsolution lamellae of ulvöspinel (along 100) & ilmenite (along 111).
C) In the ………….. deposits, tetrahedrite whose formula is …………… is usually present as small rounded blebs within or along the margins of ………
D– Movement along fractures produces ……… in the less steeply dipping parts and dilatant zones (open spaces or cavities) in … …, leading to formation of…………….. structure.
E)- The exsolution type in which structures of both phases are completely different across …………. between phases is called ………. that is best represented by the case of ………..
2-Choose the correct answer (5 marks)
a- Inversion is the transformation of a mineral into another of (the same structure but with a different composition – the same composition but with a different structure – different structure and composition).
b- Oxide minerals in lavas develop in the form of (euhedral to subhedral crystals – round droplets – skeletal crystals).
c- The tubular disconcordant orebodies are characterized by (pinch and swell structure – stockworks – branching and anastomosing).
d- Nickel occurs in podiform chromite deposits in the form of (pentlandite and gersdorffite – solid solution in olivine – interstitial to ore crystals).
e- Inversion of argentite to acanthite results from transformation of crystal structure from (orthorhombic to monoclinic – cubic to monoclinic – monoclinic to cubic).
3- Put (Ö) after the true statement and (×) after the false one in the following: (5 marks)
A- Inversion of marcasite into pyrite comprises 30 % volume reduction leaving characteristic pore spaces.
B- Rounding-off of wall-rock surfaces on both sides of a mineral deposit within a fracture indicates its formation by open space deposition.
C- stratiform orebodies are restricted to a particular part of the stratigraphic column, regardless whether the orebody is concordant or discordant.
D- Metamorphic fluids are produced by break down of hydrous silicate and carbonate minerals at the transition from greenscist to amphipolite facies.
E- Layered chromite deposits are formed in tectonically unstable environments while podiform ones are formed in tectonically stable conditions.
4- Do the following (20 marks):
a- How does the exsolution process take place? what does this process kinetically depend on? what controls exsolution? How can we differentiate between replacement and exsolution?
b- Compare between layered and podiform chromite deposits.
c- Explain with illustrations the ore petrology of Fe-Ti oxide deposits.
d- How and where do the Fe-Cu-Ni sulfide deposits occur? and what are their essential, minor and secondary minerals?
Good luck Dr. Abdel Aziz El Haddad
Dr. Ahmed Abdel Rasheed