Abstract
The Xinqiao Cu–S–Fe–Au deposit in the Tongling ore district, one of important part of Middle-Lower Yangtze River Valley metallogenic belt in Eastern China, is located along the northern margin of the Yangtze craton. It consists of two major types of mineralization: a more economically significant stratiform orebody with pyrite-bearing quartz veins in its footwall, and the less economically important skarn-type orebodies.An integrated study of zircon U–Pb–Hf and trace elements analysis for the quartz diorite in Xinqiao Jitou stock, Rb–Sr isotope analysis for quartz fluid inclusions from the footwall stockwork mineralization, as well as a systematic S–Pb isotope analysis of sulfides was carried out, all based on detailed field investigations. U–Pb zircon dating of Jitou stock yielded an age of 139.6±1.5Ma (MSWD=0.80), close to the Rb–Sr isotope isochron age (138.0±2.3Ma, MSWD=5.40, an initial 87Sr/86Sr value of 0.71138±0.00014) of quartz fluid inclusions from the footwall stockwork mineralization. The εHf(t) values of zircon grains vary from −15.3 to −8.5 with TDM2 ranging from 2151 to 1729Ma, suggesting that the magma for Jitou stock was probably dominant in crustal-derived magmas with minor mantle material inputs, based on the previous studies on Sr isotope compositions, Nb/Ta ratios and Mg#. The ΔFMQ values (−4.44 to 7.77, average 4.36) suggest that the Jitou stock was derived from the highly oxidized magma and favorable for the Cu mineralization. The systematic S–Pb isotope data and the initial 87Sr/86Sr values demonstrate that the stratiform orebody and the footwall stockwork mineralization were likely to be genetically linked to magmatic-hydrothermal events of Yanshanian (Jurassic – Cretaceous) age, as confirmed by closeness of ages of mineralization and magmatism. Therefore, it is interpreted that the Xinqiao stratiform mineralization may have resulted from Yanshanian magmatic hydrothermal fluids associated with the Jitou stock, as may be the case also for the skarn-type mineralization hosted in the contact between the Yanshanian Jitou stock and the Lower Permian Qixia Formation limestone, based on the basis of ore deposit geology. Generally, the Xinqiao Cu–S–Fe–Au mineralization may have been generated by the Yanshanian tectono-thermal event in Eastern China.
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