The newly discovered Dongyang low‐sulphidation epithermal Au deposit is located in central‐eastern Fujian Province, coastal SE China. Ore bodies occur in Late Jurassic rhyolite porphyry, rhyolite, and dacitic crystal tuff lava. In this study, rhyolite and dacitic crystal tuff lava are dated to 151.9 ± 0.4 Ma and 158.3 ± 0.4 Ma, respectively, and belong to the second member of the Nanyuan Formation. They are high in K2O (6.91–3.81 wt%) and Na2O/K2O (0.55–0.02), strongly peraluminous (A/CNK = 2.11–1.67) and high‐K calc‐alkaline or shoshonitic. They contain low ∑REEs (248–125 ppm), are enriched in Rb, K, Au, and depleted in Ba, Sr, P, Zr, Hf, and have slightly negative Eu anomalies (δEu = 0.94–0.56), suggesting that they are weakly fractionated felsic volcanic rocks. The zirconεHf(t) values (−11.2 to −5.4; two‐stage model ages = 2,650–2,128 Ma) suggest that they were mainly derived from Palaeoproterozoic crust. Lead isotope compositions also imply a dominantly lower crustal source. Detailed geological characteristics and elemental and isotopic data suggest that the oxidizing and weakly fractionated nature of the Dongyang high‐K felsic magma may have played a key role in Au mineralization. Integrating new and published data on the tectonic evolution, we suggest that the Late Jurassic Au mineralization and its causative magmatism actually extended to the SE China coastal area. The Dongyang rhyolite and dacitic crystal tuff lava may have been generated from partial melting of the crust caused by underplating of mantle‐derived magmas in an extensional environment. Regional extension may have been related to the NW‐directed roll‐back of the Palaeo‐Pacific Plate beneath the South China Block.
Kaoshan medium-and fine-grained syenogranites emplaced along the Yitong-Shulan Fault Zone in the southern part the Zhangguangcai Range, central Jilin Province, intruded Middle Triassic granitoids and Carboniferous-Devonian intrusive rocks. They have medium-and fine-grained textures and contain K-feldspar, quartz, plagioclase, and biotite. They are peraluminous (A/CNK = 1.13-1.20) and have high values of SiO 2 (74.60-75.82 wt%), total alkalis (Na 2 O + K 2 O = 8.28-9.18 wt%), light rare earth elements (20.89-56.14 ppm), large-ion lithophile elements, and FeO/ MgO = 2.78-5.93. In contrast, they feature low values of CaO (0.40-0.49 wt%), TiO 2 (0.05-0.14 wt%), P 2 O 5 (0.02-0.04 wt%), Sr (24.20-62.59 ppm), heavy rare earth elements (5.14-11.80 ppm), high-field-strength elements, and δEu (0.41-0.76), and the calculated zircon saturation temperatures (T zr ) range from 804 to 870 C, all of which are similar to the geochemical signatures of anorogenic A 1 -type granites. Zircon U-Pb geochronology analyses from the medium-and fine-grained syenogranites yield concordia ages of 193.18 ± 0.95 Ma (MSWD = 6.7, n = 18) and 190.29 ± 0.92 Ma (MSWD = 8.7, n = 17), respectively, and belong to the Early Jurassic Sinemurian stage. In situ Hf isotope analyses of dated zircons yield ε Hf (t) values ranging from +17.0 to +9.7 and Hf model ages (T DM C ) of 225-614 Ma. Their whole-rock ( 87 Sr/ 86 Sr) i (0.704740-0.704133) and ε Nd (t) values (+2.8 to +0.2) are similar to those of many coeval A 2 -type granites in this region, and they form an Atype granite assemblage. Consequently, the Kaoshan medium-and fine-grained syenogranites were probably derived from partial melting of juvenile lower crust and might be related to the subduction of the Palaeo-Pacific Plate.
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