This paper reports an integrated study of in situ U-Pb geochronology and elemental geochemistry of zircons from the Xianglushan iron-polymetallic deposit in western Guizhou Province, Southwest China. Genetic relationship between this new type of deposit and unroofing of the Emeishan large igneous province(ELIP) is focused. Along with the zoning pattern in spatial distribution of diverse weathering-related deposits along the southern and southeastern margins of the ELIP, it is suggested that the genesis of the iron-polymetallic deposit was specialized by factors of coastal paleogeography in hot-humid climate, where iron-enriched laterites formed, and repetitive marine transgression-regression occurred during the Late Permian.
MENG ChangZhongCHEN YangZHANG YingHuaWU HuiLING WenLiZHANG HaiLIU Jun
Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic（~800 Ma） Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of ？Ce（t） variation but limited ？Nd（t） range, which cause a deviation from the ＂crustal array＂ and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce＊ ratios but broadly proximate εCe（t） values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe（t） and Ce/Ce＊ is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies（TCe） for the intermediate-mafic samples infers that the alteration events took place 〉350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.
