Investigation of opaque minerals (sulfides and oxides) in mafic- ultarmafic igneous complex in Misho, Southwest Marand, NW Iran

Misho mafic and ultramafic complex (pre-Permian) is located in 8km southwest of Marand, East-Azarbaidjan, NW Iran, and has intruded in Proterozoic pelletic rocks of Kahar formation developing contact metamorphism. A reverse fault in the northern portion of the study area brought this complex in contact with a series of gypsiferrous marl and sandstone of Miocene age. Based on field, textural, and structural evidence, the mafic and ultramafic intrusives in Misho are divided into two distinct groups, (1) primary gabbros and (2) secondary gabbros (diabases). Primary gabbros crop out in the form of large, rugged, and massive bodies of rocks covering most of the study area, whereas secondary gabbros appear as small and irregular dikes and sill-like bodies intruding the primary gabbros. Based on silicate mineralogy, texture, and sulfide content, the primary gabbros are further divided into three sub-groups: (1) normal Primary gabbros, (2) sulfide-rich gabbroic patches, and (3) pyroxenite patches, and the secondary gabbros are divided into two subgroups: (1) diabases and (2) sulfide-rich micropyroxenite.Opaque mineral phases (sulfides and oxides) in these rocks principally fill as rounded and bent aggregates the interstitial spaces among silicates and occasionally (in sulfide-rich patches) entirely engulf them. In normal primary gabbros, pyrrhotite and ilmenite are the most abundant sulfide and oxide minerals whose modal values are within the range of 0.5-3% and 0.5-10% respectively. Analytical data shows that the values of Cu, Ni, and Cr in these rocks are <410ppm, <250ppm, and <170ppm respectively. In small Sulfide-rich gabbroic and pyroxenite patches, the modal values of the sulfide and oxide minerals lie within the range of 10-40% and 0.3-3% respectively.Secondary gabbros are mineralogically similar to the primary ones and their opaque phases are mainly ilmenite (3-8%) and pyrrhotite (0.2-2%). The concentration of Cu, Ni, and Cr in these rocks are ~55ppm, ~57ppm, and ~91ppm respectively. Au and Pt values in both Primary and Secondary gabbros are ~5ppb.