Ore Petrology
1- Explain briefly (with illustrations) :……………………………(20 marks)
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 () 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 ( ).
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.
5- Complete the missing parts in the following statements (5 marks):
a- ………… 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………………..
c- Experimental work showed that chalcopyrite disease is not an exsolution, so it is most propably to be…………………
d- ………. 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, …………is petrologically found in dendritic patterns that are surrounded by rosettes of colloform arsenides.