Zircon LA-ICP-MS U-Pb dating of ore-bearing pyroxene-trachyandesite porphyry and its geological significance in Luohe-Nihe iron ore field in Luzong basin, southern Anhui, China.

here is a Luohe-Nihe iron ore field in Luzong volcanic basin on the Lower Yangtze region ,and an important role for the porphyry iron deposits is closely related to magmatism of Yanshanian. Based on the study of petrographic thin section and chemical analysis of four ore-bearing porphyry samples in Luohe-Nihe iron ore field, the results shows that these ultra-hypabyssal mgmatites are neutral-basic pyroxene-trachyandesite porphyry. Zircon LA-ICP-MS U-Pb dating for three porphyry samples yielded weighted mean age of 133.3±0.6 Ma, 133.2±1.1Ma, 132.8±2.6Ma, suggests the crystallization age is about 133 Ma. This age is between Longmenyuan-Zhuanqiao and Shuangmiao-Fushan volcanic eruption period, indicating the igneous rocks intruded followed the Longmenyuan-Zhuanqiao paroxysmal eruption. On the basis of this analysis and combined with the basic geological characteristic, we suggest that the mineralization age of the porphyrite iron ore field was between ~133 Ma and ~131Ma, which were coupled with the extensional geodynamical event during the later stage of tectonic system transformation occurring at about 140 Ma and the lithosphere large-scale detachment at about ~130 Ma in East China.