Structural control on overprinting high-sulfidation epithermal on porphyry mineralization in the Chodarchay deposit, northwestern Iran

Abstract

The Chodarchay high-sulfidation epithermal-porphyry deposit is located in the Tarom volcano-plutonic subzone of Western Alborz structural zone in NW Iran. In addition to Chodarchay, the Tarom subzone hosts several other epithermal deposits. Lithologic units in Chodarchay consist of volcanic-pyroclastic rocks and intrusive bodies. Petrographical studies have identified different rocks which host the mineralization. Mineralization has taken place in both volcanic-pyroclastic units and intrusions. Detailed mineralogical and alteration data gathered from drill cores and thin sections provides support for the hypothesis that the high-sulfidation epithermal mineralization is underlain by a porphyry copper system. This deposit is the first reported porphyry-epithermal mineralization in this subzone. The main structure of the Chodarchay area is a fault zone that formed parallel to the general Tarom NW-SE direction. Based on remote sensing studies, on a wider scale, lineaments generally show NE-SW trends, but the Chodarchay fault zone has a NW-SE strike and is associated with another W-E trending fault zone. These fault zones are correlated with argillic alteration. There are two sets of reverse fault fractures with a strike-slip component, based on slickenlines in the field and core observations. A normal sense of fault movement remains in the NW part of the structural system. These new data sets indicate two main extensional and compressional mechanisms for the fault. The evolution of the fault system from normal to reverse in the deposit characterizes the present day structural system of the Chodarchay area. Plutonism and porphyry mineralization are related to the extensional stage, whereas the epithermal part of the deposit is associated with the compressional stage of fault activation.