The Zhireken Porphyry Mo‐Cu Deposit, Eastern Transbaikalia, Russia: Isotope Geochemistry, Geochronology and Implications for Magma Sources

The Late Mesozoic Mo-Cu porphyry Zhireken deposit is located within the eastern segment of the Central Asian Orogenic Belt, bordering the northern margin of the Mongol-Okhotsk suture zone (Fig. 1). The Zhireken deposit was formed in the intraplate setting resulted from the closure of the Mongolo-Okhotsk ocean and collision between the Siberian and Mongolia-North China continents. Collision of the Siberian and Mongolia North China plates and the complete closure of Mongol-Okhotsk Ocean in its western part (in the territory of present Transbaikalia) happened at the Lower-Middle Jurassic boundary (Zorin et al., 1997). The deposit includes rocks of two magmatic complexes: the precursor plutonic Amanan and the ore-bearing Porphyry complexes. SHRIMP U–Pb zircon dating yielded ages of 162.6±1.4 Ma for the Amanan granites, while the Porphyry complex showed ages of 159.0±1.6 and 157.5±2.0 for the fine-grained leucogranites and monzonite porphyries, respectively. Mineralization is temporally and spatially associated with granitic porphyry stocks (Porphyry complex), which intruded J2 granitoids of the Amanan complex. The Amanan and Porphyry complexes at Zhireken are represented by a series of high-K calc-alkaline rocks similar in composition. The Amanan complex is dominated by coarse-grained biotite granites and finegrained leucogranites, with rare gabbro. The subvolcanic Porphyry complex is mainly consists of granite porphyries with subordinate monzoniteand quartz monzonite porphyries. Mafic rocks are rare and occur mainly as remnants among granitoid rocks. Both Amanan and Porphyry complexes include adakite-like rocks with geochemical characteristics of K-adakites associated with high-K calc-alkaline granitoids with typical arc-type characteristics. Recent studies on geology and geotectonics of Eastern Transbaikalia (Yarmolyuk et al., 2000; Zorin et al., 2001) together with geochronological data (Ponomarchuk et al., 2004; this study) are consistent with the emplacement of the Amanan complex at the final stages of the collisional regime in the region; the formation of the Porphyry complex may have overlapped with a transition to extension. In general, the Zhireken deposit is similar in many respects to porphyry Cu-Mo deposits from the Tibet–Himalayas and North-Chinese craton–Yangtze collisional zones.