Geochronology and geochemistry of the five magmatic rocks in the Ningzhen region, China

The Ningzhen region of China is located in the easternmost part of the middle-lower Yangtze River Cu-Fe polymetallic metallogenic belt. From west to east, it comprises five main intermediate-acidic intrusive complexes: the Qilinmen, Anjishan, Xiashu-Gaozi, Shima, and Jianbi complexes. Geochemical investigations show that these five intrusive complexes exhibit high contents of SiO2, at 64.74-73.40 wt%, Al2O3, at 14.15-17.37 wt%, and K2O+Na2O, at 6.49-8.68 wt%. The majority of the samples belong to the high-K calc-alkaline series, with a few samples plotting in the calc-alkaline and tholeiitic series. Trace element analysis shows that the samples are enriched in large ion lithophile elements (LILE) and are depleted in high field strength elements (HFSE). Thechondrite-normalized rare earth element (REE) patterns are characterized by right-inclined curves, showing light rare earth element (LREE) enrichment. In addition, the (La/Yb)(N) ratios are high at 15.02-37.28, with an average of 29.13, and slightly negative or none Eu anomalies are present. In the (La/Yb)(N)-Eu diagram, the samples plot within the crust-mantle type field. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb dating yielded ages of 122.0 +/- 1.0Ma, 106.1 +/- 0.8Ma, 108.7 +/- 1.4Ma, 103.5 +/- 1.9Ma, and 96.8 +/- 1.7Ma for the Qilinmen, Anjishan, Xiashu-Gaozi, Shima, and Jianbi complexes, respectively. On the basis of this research and knowledge of several known metal deposits related to these complexes, we suggest that the Mesozoic large-scale diagenesis and metallogenesis in the Ningzhen region may have ceased at 100Ma or about 95Ma.