New data on the age and geodynamic position of copper-porphyry mineralization in the Main Uralian fault zone (South Urals)

Abstract

1317 In this communication, we discuss new data on the radiological age and composition of parental rocks of the Voznesenskoe deposit and Karagaikul occurrence of the copper-porphyry type localized in the melange zone of the Main Uralian fault in the northwestern part of the Magnitogorsk megazone of the South Urals (Fig. 1). The Main Uralian fault zone represents here a system of steep eastwarddipping tectonic slices, which include serpentinites, serpentinite melange, pyroxenites, gabbrods, and blocks of volcanogenic, volcanosedimentary, and sedimentary (siliceous shales, limestones) variousage rocks deformed into synand antiform folds (7). The Voznesenskoe copper-porphyry deposit is located in a dikeshaped massif of diorite-quartz diorites steeply westwarddipping and extending in the NNE direction for a distance of 2.5 km. Its stringer-dis� seminated sulfide mineralization is developed in the northeastern endocontact of the massif being mostly confined to plagiogranite-porphyry dikes that intrude diorites parallel to their contact with host ser� pentinites (10). We have investigated the microelemental composi� tion of diorites and plagiogranite-porphyries with variable degrees of metasomatic alterations and have conducted U-Pb dating of zircons from quartz dior� ites. The Sm-Nd method was used for dating altered plagiogranite-porphyries. The microelemental composition of rocks from the productive intrusive body (Fig. 2) indicates all the ana� lyzed rock varieties belong to island arc calcalkaline magmatites. This is evident from negative Nb and Zr and positive Sr anomalies, low TiO 2 concentrations (0.03-0.16%), and plots illustrating the REE distribu� tion (Fig. 2b). By the distribution patterns and con� centrations of trace elements, REE included, plagiog� ranite-porphyries are similar to diorites from the Voznesenka massif. This implies their common origin and that they belong to different phases of formation of the massif.