Geochronology of the Nihe deposit and in the Lu-Zong basin and its metallogenic significances

The Lu-Zong basin is one of the important parts of the Middle-Lower Yangtze River Valley metallogenic belt, where there are widespread iron deposits. The volcanic and intrusive plutons occur widely in Lu-Zong basin, including four formations of volcanic rocks, such as Longmenyuan Formation, Zhuanqiao Formation, Shuangmiao Formation and Fushan Formation and 34 intrusive plutons. Nihe deposit located in the northwest part of Lu-Zong basin, which is a new found large iron deposit. However, the precise ore-forming and magmatic activity epoch study about Nihe deposit are still very weak. Based on detailed field geological work, we carried out systematic geochronological study of Nihe iron deposits. LA ICP-MS U-Pb zircon dating of pyroxene diorite porphyrite, syenite porphyry and trachyandensite is 132. 4 ± 1. 5Ma, 129. 4 ±2. OMa and 134. 3 ± 1. 2Ma, respectively; ⁴⁰Ar/³⁹ Ar dating of phlogopite is 130. 9 ± 2. 6Ma. Geological characteristics of ore deposit indicate that syenite porphyry formed after the deposit and trachyandensite formed before the mineralization, coinciding with the dating result. The Nihe deposit are formed in early stage of Early Cretaceous about 130Ma, which can nearly represent the metallogenetic epoch of the porphyry-like type iron deposits in the basin. The Nihe deposit in the Lu-Zong basin were the product of the second period magmatic activity and obviously later than high-K calc-alkaline intrusions related to skarn-porphyry Cu-Au deposits in uplift areas in the Middle-Lower Yangtze River Valley metallogenic belt. The pyroxene diorite porphyrite in Lu-Zong volcanic basin were thought to be important metallogenetic potentiality.