Geochronology and geochemistry of mineralized and barren intrusive rocks in the Yemaquan polymetallic skarn deposit, northern Qinghai-Tibet Plateau: A zircon perspective

The Yemaquan polymetallic skarn deposit is located in the Qimantagh metallogenic belt (QMB), northern Qinghai-Tibet Plateau, China, with total ore resources of 82.7 million metric tons at 29.46 percent Fe, 0.40% Cu, 2.08% Pb and 1.77% Zn. In this study, new trace element composition of zircon in tandem with LA-ICP-MS U-Pb geochronology are provided for mineralized and barren intrusive rocks occurring within two magnetic anomaly areas (M1 and M13) at the Yemaquan deposit. These data, combined with whole rock major and trace element compositions, allow to constrain the geochronological framework and magmatic processes for different types of intrusive rocks within the district. The zircon U-Pb ages reveal that the polymetallic mineralization in the M1 and M13 anomaly areas results from two temporally distinct intrusive centers. Different to the M13 area where only the mineralized Devonian intrusions are recorded, both mineralized and barren intrusive rocks in the M1 area were emplaced in the Late Triassic. Whole rock major and trace elements indicate that both Triassic mineralized and barren rocks underwent significant fractional crystallization, with the Triassic barren rocks displaying much stronger plagioclase fractionation. In contrast, the limited whole rock silica range and high Eu/Eu* of Devonian mineralized intrusions indicate that they did not experience evident fractionation. Zircon trace elements show that the two mineralized groups at Yemaquan display similar, high zircon Ce/Ce* but distinguishable Eu/Eu* ratios, which suggest a consistent, high magmatic oxidation state but different water content. The magmatic water content of Devonian mineralized rocks higher than that of their Triassic counterparts probably suggests that the former are more Cu-fertile. This study confirms that both Devonian and Triassic intrusive activities are responsible for skarn Fe-Cu-Pb-Zn mineralization at the Yemaquan deposit. Meanwhile, in view of the general feature of Yemaquan in the context of skarn deposits from the QMB, we thus suggest that in future mineral exploration great attention should be paid to both the Triassic and Devonian intrusive rocks.