The Zhireken porphyry Mo ore-magmatic system (eastern Transbaikalia): U–Pb age, sources, and geodynamic setting

Abstract

Two intrusive complexes are recognized in the Zhireken deposit: Amanan and ore-bearing porphyry. According to the ages obtained by U-Pb zircon dating (Amanan complex-162.6 ± 1.4 Ma, granites and monzonite-porphyry of the ore-bearing complex-159.0 ± 1.6 and 157.5 ± 2.9 Ma), the Amanan complex formed at the end of collision, and the ore-bearing porphyry complex, during the change of the geodynamic regime by the postcollisional (rift) one. The rocks of two complexes have high contents of LILE and LREE and low contents of HFSE and HREE. The ( 87 Sr/ 86 Sr) 0 ratio in the gabbro and granites of the Amanan complex is 0.70501 and 0.70534, respectively, and that in the rocks of the porphyry complex is within 0.70451-0.70633. The Amanan gabbro, gabbro-diorites, and granites are characterized by ε Nd (T) = -1.4, -1.8, and -10.3, respectively, and the rocks of the ore-bearing complex, by ε Nd (T) = -3.7 to +1.0. The model T Nd (DM) age of the Amanan granites is 1.5 Ga, and that of the granites and porphyry of the ore-bearing complex is 1.0-0.8 Ga. The Pb isotope ratios in the rocks of the Amanan and porphyry complexes are: 206 Pb/ 204 Pb = 18. . The results of geological, geochemical, and isotope studies admit that magmas were generated from juvenile and ancient crusts. Melts probably ascended from a depth of no less than 55 km during the melting of crust thickened as a result of tectonic deformations (in the upper horizons) and during the basic-magma supply (in the lower horizons). Juvenile mafic crust is considered to be the major source of fluid components and metals. Favorable conditions for the ore generation in the magmatic system during the formation of the porphyry complex arose at the previous stage, during the formation of the Amanan complex, which we regard as a preparatory stage in the evolution of the long-living ore-magmatic system.

Paleozoic–Mesozoic Porphyry Cu(Mo) and Mo(Cu) Deposits within the Southern Margin of the Siberian Craton: Geochemistry, Geochronology, and Petrogenesis (a Review)

“…The data were processed with Ludwig SQUID1.0 and ISOPLOT programs. Instrumental conditions and analytical details were as described in [52,60]. Geological features [90,91] and geochronological data [47,60,94] show that the Shakhtama pluton was intruded synchronously with the final stage of the collisional tectonics in the region.…”

“…Strontium isotopic analyses were performed on an MI 1201AT solid mass spectrometer at the Analytical Centre of the Institute of Geology and Mineralogy, Novosibirsk, Russia, using analytical procedures as described in [52]. Samarium and neodymium isotope analyses were performed at the Laboratory of Geochronology, Geological Institute of Kola Scientific Center of the Russian Academy of Sciences (Apatity) on a multi-collector Finnigan MAT-262 (RPQ) thermal ionization mass spectrometer, operating in static mode.…”

“…The precision for Sm, Nd, and 147 Sm/ 144 Nd was ±0.2% (2σ). The details of the analytical procedures were as described in [52].…”

“…The data were processed with Ludwig SQUID1.0 and ISOPLOT programs. Instrumental conditions and analytical details were as described in [52,60]. 40 Ar/ 39 Ar dating.…”

“…SHRIMP U-Pb zircon dating yielded ages of 164-161 Ma for the intrusion of Zhireken pluton, while the porphyry complex showed ages of 161 ± 1.6 and 157.5 ± 2.0 [52]. The Re-Os dating of molybdenite of three different samples from Zhireken deposit are 162 ± 1, 163 ± 1, and 163 ± 1 Ma [94].…”