Final exam. Of ore petrology and applied sedimentology for 4th year geology students
First semester ( January 2011) Time allowed 2 hours
A- Applied sedimentology
Answer the following questions illustrating your word whenever possible:
1- The roll-front uranium ore is controlled by weathering process and environment of deposition, explain this and give an example from the geological record for this type of ore. (20 marks)
2- Tick the correct statement and put (x) by the false one: (15 marks)
a- Cinnabar mineral is one of the most dangerous mineral.
b- Eolian sand is suitable for making concrete.
c- Placers can accumulate on the lee side of sand dunes.
d- Granite wash serve as good oil reservoir.
e- All porous rocks are permeable.
3- Complete the following sentences: (10 marks)
a- Limestone is very important sedimentary rocks. Several important industries depend on it as 1- ………..,2-…………. 3-
b- Fluvial deposits are very important because 1…………. 2———— 3——–
c- Weathering products may be solids which remain in situ as residual deposits as …………, ……….and …………….or go in solution as ………and ……..
B- Ore Petrology
1- Explain briefly (with illustrations):
A) The petrological interrelationships of ore minerals in the following ore deposits: (15 marks)
1) Fe-Ti oxide deposits.
2) Fe- Cu-Ni sulfide deposits.
3) Alpine-type chromite deposits.
B) The method of Sharpe et al (1985) of arsenopyrite geothermometry. (5 marks)
2-Choose the correct answer (10 marks)
a- Growth of sulfide minerals in lavas takes place in the form of (skeletal crystals – round droplets – euhedral to subhedral crystals).
b- The tubular disconcordant orebodies are characterized by (pinch and swell structure – branching and anastomosing – stockworks).
c- (Stratiform – Starabound – Disseminated) deposits show a considerable development parallel to bedding and a limited development perpendicular to it.
d- Diamond deposits in kimberlite represent (concordant orebodies- discordant orebodies- residual orebodies).
e- Replacement of magnetite by martite is carried out through (change in oxidation state – change in anions – selective remove of one cation).
4- Put (Ö) after the true statement and (X) after the false one in the following: (10 marks)
A-Rounding-off of wall-rock surfaces on both sides of a mineral deposit within a fracture indicates its formation by open space deposition. (X).
B- Starabound orebodies are restricted to a particular part of the stratigraphic column, regardless whether the orebody is concordant or discordant. (Ö ).
C-“Pinch and swell structure” results from later replacement of fracture walls (X).
D- Layered chromite deposits are formed in tectonically unstable environments while podiform ones are formed in tectonically stable conditions. (X).
E- Metamorphic fluids are produced by break down of hydrous silicate and carbonate minerals at the transition from greenscist to amphipolite facies. (Ö ).
5- Complete the missing parts in the following statements (5 marks):
A) Breccia ore results from deformation of crustified veins during or after ore formation.
B)- The exsolution type in which structures of both phases are completely different or without crystallographic continuity across the interface between phases is called incoherent exsolution.
C- Experimental work showed that chalcopyrite disease is not an exsolution, so it is most propably to be epitaxial growth or replacement by Cu-rich fluids (any or both).
D– VMS deposits are generally stratiform lenticular or sheetlike orebodies developed at interfaces or horizons of pauses in volcanism or change from volcanism to sedimentation.
E- In Ag-Bi-Co-Ni-As vein deposits, native silver is petrologically found in dendritic patterns that are surrounded by rosettes of colloform arsenides.
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Good luck __________________________ Dr. Abdel Aziz El Haddad
Dr. Ahmed Abdelrasheed