First discovery of the Late Triassic syenite and coeval epigenetic Cu mineralization in the Jianglang Dome, eastern Tibetan Plateau, China

Abstract

The Jianglang Dome has integral tectonostratigraphic units and contains a suite of high-grade stratiform Cu deposits. However, the formation mechanism of this dome and genetic model of Cu mineralization remain a matter of debate. The resolution of these problems hinges on the presence of magmatic intrusions in the core. Here, we report bulk geochemical and zircon U-Pb data of a newly discovered syenite intrusion as well as chalcopyrite Re-Os dating results. We aim to explore genesis of the Jianglang Dome, genetic model of the stratiform Cu deposits, and rare metal mineralization potential of the syenite intrusion. The dated syenite sample yields an emplacement age of 207.1 ± 2.0 Ma, which matches post-collisional extension in the Songpan-Ganze Orogen. The syenite rocks have average high (Zr + Nb + Ce + Y) concentrations of 512 ppm, 10000×Ga/Al ratios of 3.97, and crystallization temperatures of 827 °C, together with low Mg# values of 1.73; they fit the A-type granitoid definition and a crustal origin. Chalcopyrite separates yield a Re-Os isochron age of 207.1 ± 5.3 Ma, which markedly postdates the formation age of their ore-hosting rocks (the Liwu Group, ca. 553 Ma). Our new age determination, together with previous chalcopyrite Re–Os isochron age of ca. 151.1 Ma and sulfide sulfur isotope (δ³⁴S_V-CDT = 8.7‰–5.6‰) and tourmaline boron isotope (δ¹¹B = − 15.47‰ to  − 5.91‰) data, confirms multistage epigenetic Cu mineralization related to magmatic-hydrothermal fluids. Compared with regional ca. 209–207 Ma fertile granitoids, the studied syenite intrusion shows unevolved and barren affinities and negligible rare metal mineralization potential. Combined with residual gravity low anomalies in the core of the Jianglang Dome, which suggest a large deep-seated granitic batholith, we prefer thermal doming resulting from magma-induced uplift for the nature of this dome.