Lead isotopic composition and genesis of Phanerozoic metal deposits in China |
| |
| Authors: | Yuwei Chen Cunxiao Mao Bingquan Zhu |
| |
| Institution: | 1. Institute of Geochemistry, Academia Sinica, China
|
| |
| Abstract: | Lead isotopic compositions of more than 130 galena specimens from Phanerozoic metal deposits in China have been analyzed with a standard deviation of less than 0.5%. The ranges of isotopic composition are from 17.8 to 19.3 for Pb206/Pb204, 15.2 to 16.0 for Pb207/Pb204 and 37 to 40.8 for Pb208/Pb204. These values overlap those of MORB, pelagic chemical sediments and intra-oceanic arcs of western Pacific in plots of Pb207/Pb204 vs. Pb206/Pb204 and Pb208/Pb204 vs. Pb206/Pb204. This indicates that mixing between mantle and crustal materials due to partial melting of the Pacific subduction slab is the principal mechanism for ore genesis. On the basis of global Precambrian conformable leads, together with that of Guanmenshan, Pengjiapu and Baiyun deposits in China, it is suggested that mantle lead was developed in a single stage with a (U238/Pb204) value of 7.8. If the ages of igneous rocks associated with these deposits are adopted as formation ages, the mean Th/U of the second stage of crust-mantle evolution can be calculated with a lead mixing model. The meanμ value of China continent is 9.98±0.78, which is in agreement with that of global conformable leads, 9.81±0.58. The mean Th/U ratio of 4.27 is distinctly larger than the global value (3.81), indicating that the China continent is rich in Th. Simultaneously, mean formation ages have also been obtained of the continental crusts in various regions, ranging from 3,000 to 3,800 m.y. and from 2,500 to 2,700 m.y., which are comparable with the age distribution of global Archaean cratons. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
