Geological setting for porphyry copper deposits in calc-alkaline rocks: Wadi Rofaiyed area, Sinai, Egypt

Abstract

The close association of copper mineralization with porphyritic quartz diorite and intermediate volcanic rocks, the presence of hydrothermal alteration zones, the disseminated nature of sulfide minerals, and extremely absence of massive lenses and the volcanic arc (orogenic) tectonic situation of ore-bearing rocks are the main geological conditions associated with diorite-type porphyry copper system at Wadi Rofaiyed area, Sinai, Egypt. Chalcopyrite and pyrite are the main sulfide minerals in quartz diorite, whereas chalcopyrite, pyrite, galena, and sphalerite are the main sulfide minerals in Rutig volcanics. Secondary sulfide minerals include chalcocite and covellite. Quartz diorite and Rutig volcanics (intermediate composition) are calc-alkaline, enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). The incompatible trace element patterns favor fractional crystallization of plagioclase and Fe-Ti oxides. Rutig volcanics developed in orogenic arc-type and anorogenic within plate, indicating an eruption in a transitional post-collisional tectonic setting. Two hydrothermal events are thought to take place, which are characterized by zonal pattern composed of a central potassic zone and a peripheral propylitic zone. Both zones are centered over porphyritic intrusive rocks that might be considered the source of hydrothermal solutions. A close relationship of mineralization to pre-Katerina ring dike structures, namely, joints and faults, was revealed. Generally, the gentle dips of bandings in Rutig volcanics and the presence of post-eruption faulting indicate a significant deformation by translational and rotational movement. The average thickness of Rutig volcanics is about 1.4 km, which along with the big masses of intrusive country rocks constitute a considerable volume of mineralized stock. Meanwhile, subsidence of Rutig volcanics which served as capping rocks played, to some extent, an effective role in preserving the mineralization in the underlying country rocks. Multi-scale structural investigations revealed the role of interstitial spaces and fracture network in localizing mineralization. Where two styles of mineralization are recognized, the first is dissemination and the second is fracture filling. The mineralization was formed during a large-scale extensional tectonic event that followed the collisional period.