Final exam. Of ore petrology and applied sedimentology for 4th year geology student
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. ( ´ ).
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 (´ ).
D- Layered chromite deposits are formed in tectonically unstable environments while podiform ones are formed in tectonically stable conditions. ( ´ ).
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 ores 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 exsolution.
C- Experimental work showed that chalcopyrite disease is not an exsolution, so it is most propably to be epitaxial intergrowth.
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