Abstract:

The Balkhash metallogenic zone in Kazakhstan is an important porphyry Cu-Mo metallogenic belt in the Central Asia metallogenic domain. In this paper, zircon SHRIMP U-Pb dating, major, rare earth and trace elemental geochemistry, and Sr and Nd isotope tracing of porphyry granitoids from Kounrad, Borly and Aktogai large and super-large porphyry Cu deposits, provide important informations on porphyry Cu metallogenic time and tectonic environment of the zone. Two stages of metallogenesis, one at ~327 Ma with the formation of Kounrad and Aktogai deposits, and the other at ~316 Ma with Borly deposit, are determined. The porphyry granitoids from this zone are mainly high K calc-alkaline series volcanic arc granite, some of them are adakite-like in trace element geochemistry. ε_Sr(t) and ε_Nd(t) of granitoids from three deposits are in the ranges of -6.35-34.03 and -0.46-5.53, respectively. Their Sr-Nd isotopic signatures indicate that porphyry granitoids from Kounrad and Borly were derived from a mixing source between the depleted mantle and the ancient continental crust, whereas that from Aktogai were derived from the depleted mantle directly. Via comparison of the Balkhash metallogenic zone and Junggar metallogenic zone, they are considered to be formed in the same Late Paleozoic Balkhash-Junggar porphyry Cu-Mo Metallogenic zone.

Key words: porphyry copper deposit, geochronology, geochemistry, Balkhash metallogenic zone, Central Asia metallogenic domain