Petrogenesis of the Gold Bearing Zarrin Granite

Zarrin granite intrusion is located in the Central Iran, to west of Chapedoni and Posht-e-Badam faults. It consists of three separate outcrops situated at the northern end of a long mountain range, which is comprised of Mesozoic rocks. Lithologically the intrusion contains granites as well as, gneisses (?) and aplites. Petrographic and geochemical evidence strongly suggest that they are cogenetic. High aluminum contents and other characteristics of these rocks, as well as petrographic evidence, indicate that the granite is ²S-type². Moreover, on the basis of geochemical evidence it is suggested that this granite intrusion may be classified as a Post-Orogenic Granite (POG) and Within Plate Granite (WPG). It is also suggested that the intrusion occurred in a relatively quietperiod of the final stage of an orogeny.Lamprophyric dykes cutting Zarrin granite have similar orientations and are parallel to the major faults zone. It appears that their genesis is related to the deep faults, which extend down to the upper mantle. Due to the activities of these faults, the upper mantle melted and consequently caused, the crustal rocks melt at a higher level earlier than expected, and formed granite magma which moved upward along these faults.Gold mineralization occurred in the north eastern part of the intrusion. The mineralization is most frequent, where lamprophyric dykes are greater in number. It appears that hydrothermal fluids, which developed after lamprophyre intrusion, has leached the gold present in dykes and emplaced it in the surrounding rocks.