Discrimination between productive and non-productive granitoid intrusions in Kerman porphyry copper belt: Results of preliminary petrographic and mineralogical studies


Department of Geology, Faculty of Sciences, University of Golestan, Gorgan, Iran


Petrographic study on least altered and unaltered samples of porphyritic granitoids in Kerman porphyry copper belt indicated granodioritic composition for productive intrusions and quartzdioritic or dioritic compositions for non-productive intrusions. Texturally, the groundmass and size of phenocrysts in productive intrusions varied from coarse to medium, whereas non-productive intrusions contained fine-grained groundmass and small phenocrysts. The phenocryst/groundmass ratio in Productive intrusions varied between 1:1 and 2:1, whereas this ratio in sub-to-non-productive intrusions was smaller in Productive intrusions. The present study indicated that productive intrusions have 5-10 wt% hornblende and 3-5 wt% biotite, whereas sub-to-non-productive intrusions contained more amount of biotite in regard to hornblende. Also, plagioclase of productive intrusions was mainly oligoclase (An=10-30), and it was andesine (An=30-50) in sub-to-non-productive intrusions. Rock-composition and textural-mineralogical characteristics of productive intrusions can reflect suitable conditions for parent magma of these intrusions for porphyry copper mineralization. These characteristics were consistent with water super-saturation of parent magmas due to lesser crystallization of mafic-hydrous minerals but much more duration of crystallization and much amount of felsic minerals because of much differentiation of these magmas.  


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