Geochronology of the diorite porphyrites in Ning-Wu basin and their metallogenic significances

Ning-Wu basin is the important parts of the Middle-Lower Yangtze River Valley metallogenic belt, where there are widespread porphyry-like type ( magnetite-apatite type) iron deposits. However, the researches on precise ore-forming and magmatic activity epoch and tectonic setting are very weak. Based on detailed field geological work, we carried out systematic geochronological study of diorite porphyrite plutons related to porphyry-like type iron deposits in the basin. LA-ICP-MS zircon U-Pb dating for seven diorite porphyrite plutons such as Washan, Taocun, Heshangqiao, Dongshan, Baixiangshan, Hemushan and Gushan intrusions, has been carried out. LA-ICP-MS zircon U-Pb dating yield the ages of 130.2 ± 2.O Ma, 130.7 ± 1.8 Ma, 131.1 ± 1.5 Ma, 131.1 ± 3.1 Ma, 130.0 ± 1.4 Ma, 131.1 ± 1.9 Ma and 129.2 ± 1.7 Ma for intrusions respectively. The dating result indicates that different diorite porphyrite plutons in Ning-Wu volcanic basin are all formed in the early stage of Early Cretaceous about 130Ma, which can nearly represent the metallogenetic epoch of the porphyry-like type iron deposits. There are three periods (145-136 Ma, 135-127 Ma, 126-123 Ma) of ore-forming and magmatic activity in the Middle-Lower Yangtze River Valley metallogenic belt. The diorite porphyrite plutons in Ning-Wu basin were the products of the second period magmatic activity and obviously later than the 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 diorite porphyrite plutons in Ning-Wu volcanic basin were thought to be formed under regional lithospheric and thinning environment.