Identification and significance of the Sc-rich regolith on Early Paleozoic mafic-ultramafic intrusions in the southeastern Wuyi-Yunkai Orogenic Belt,South China
This paper reports the discovery of scandium(Sc)-rich regolith of the Lanpai mafic-ultramafic intrusion in the southeastern Wuyi-Yunkai orogenic belt,South China.Preliminary estimates yield a potential Sc resource of 524 to 566 tonnes which makes the regolith a potentially large-size Sc deposit.The Early Paleozoic Lanpai mafic-ultramafic intrusion,which intruded into the Yonghe dioritic pluton,consists of peridotite,pyroxenite and gabbro.The pyroxenite has a zircon U-Pb age of 428.3±2.0 Ma(MSWD=0.92).Rocks from this intrusion have total w(Fe2O3)contents ranging from 12.1％to 18.7％.Pyroxenites contain Sc contents varying from 44×10-6 to 97×10-6 which are generally higher than those of peridotites(20×10-6 to 89×10-6)and gabbro(28×10-6 to 48×10-6).The Sc-rich rock association of the Lanpai intrusion differs significantly from carbonatite-alkaline rock complexes and Alaskan-type complexes which are thought to be rich in Sc.It may represent a new type of source rocks for the regolith-hosted Sc deposit.It is inferred that the Sc-rich Lanpai intrusion was formed by the magma produced from the partial melting of the Sc-enriched mantle source in a locally induced extensional part of the post-collisional setting.The well-developed weathering profile includes a pedolith zone and saprolith zone overlying on bedrocks of the mafic-ultramafic intrusion.The upper part of the pedolith is rich in iron(hydro)oxides(magnetite,hematite,and goethite),whereas the middle and lower parts of the pedolith are predominantly composed of clay minerals such as kaolinite.The saprolith is composed of major clay minerals including montmorillonite,with minor Fe-Ti-oxides and silicates including pyroxene or related alteration minerals.The regolith samples in the Lanpai area contain 21×10-6-304×10-6 of Sc,which are 2 to 3-times higher than those of corresponding bedrocks.Especially,a sample containing the highest Sc concentration was collected from a layer,which is mostly enriched in Fe-oxides and dominantly contains over 100×10-6 of Sc,in the upper part of the pedolith.The positive correlation between Sc contents and indexes of lateritization(IOL)of the regolith samples indicates that the lateritization process had significant influence on the Sc enrichment of the regolith.A preliminary study suggests that Sc was enriched in the regolith through a process of multiple stages of activation-migration-precipitation during the lateritization of regolith.In the early stage of weathering,Sc was incorporated into clay minerals such as montmorillonite through isostructural substitution.In the middle to late stages of weathering,Sc occurred mianly in Fe(hydro)oxides resulted from the decomposition of magnetite and montmorillonite.In the late stage of weathering,a part of Sc was migrated downward into a certain layer due to the dissolution of Fe-(hydro)oxides in the surficial part of regolith.The discovery of Sc-rich regolith of the Lanpai mafic-ultramafic intrusion demonstrates the potential of high-grade Sc ores of regolith-hosted Sc deposits in China,enricates the types of ore-forming parent rocks of regolith-hosted Sc deposits,and thus provides a new perspective for the theoretical study of early Paleozoic mineralization and the exploration of strategic minerals in South China.
regolith-hosted Sc depositWuyi-Yunkai orogenic beltmafic-ultramafic complexlateritization index
NETL
NSTL
万方数据
