晚二叠世峨眉山地幔柱岩浆成矿作用

晚二叠世峨眉山地幔柱岩浆作用同时形成了Cu-Ni-PGE硫化物矿床和V-Ti-Fe氧化物矿床等不同类型的岩浆矿床。从硫化物矿床的PGE富集型、Cu-Ni-PGE富集型到Cu-Ni富集型,再到钒钛磁铁矿矿床,成矿基性-超基性岩体中基性岩石比例逐渐增加,PGE含量降低。铜镍铂族硫化物矿床具Nb和Ta负异常,岩浆流体组分含量较高,含有较高的H₂;而钒钛磁铁矿矿床具Nb、Ta和Ti正异常,Zr和Hf负异常,岩浆流体组分含量较低,含有较高的H₂O、CO₂和H₂。两类矿床强不相容元素和轻稀土元素(LREE)富集,Sr-Nd同位素组成与峨眉山玄武岩的演化趋势一致。Sr-Nd-Os-C-He同位素组成揭示岩浆上升过程中经历了不同程度的地壳混染,高钛玄武岩和钒钛磁铁矿矿床成矿岩体的地壳混染程度较低,部分低钛玄武岩和铜镍硫化物矿床存在明显的地壳混染。这两类岩浆矿床的形成与峨眉山地幔柱玄武岩浆有关,岩浆介质环境中H₂含量较高,V-Ti-Fe 氧化物矿床的形成与分离结晶、高含量的水和氧逸度的升高有关,Cu-Ni-(PGE)硫化物矿床的形成与还原性流体介质、结晶分异和地壳混染作用有关。

The magmatic ore-forming system of late-Permian Emeishan mantle plume

Different types of magmatic deposits, such as Cu-Ni-PGE sulfide deposits and V-Ti-Fe oxide deposits, have been formed in the late-Permian Emeishan mantle plume magmatic system. They show the trends of increase of basic rock proportion and the decrease of PGE content from PGE-rich, Cu-Ni-PGE, through Cu-Ni-rich sulfide deposits, to V-Ti-Fe oxide deposits. Cu-Ni-PGE sulfide deposits are characterized by negative anomalies of Nb and Ta, relatively high contents of H₂ and magmatic volatiles, whereas V-Ti-Fe oxide deposits are characterized by positive anomalies of Nb, Ta and Ti, and negative anomalies of Zr and Hf, as well as higher contents of H₂O, CO₂ and H₂, and lower contents of magmatic volatiles. They both are enriched in strongly incompatible elements and light REE. Sr-Nd isotopic compositions of whole rocks from these deposits are similar to those of Emeishan basalts. Sr, Nd, Os, C and He isotopic compositions indicate different degrees of crustal contamination. High Ti basalts and V-Ti-Fe oxide deposits show low degrees of crustal contamination, whereas some low Ti basalts and Cu-Ni-PGE sulfide deposits display high degrees of crustal contamination during magmatic evolution. These data suggest that the formation of these magmatic deposits might have been related to the Emeishan basaltic system. The formation of oxide deposits was probably related to fractional crystallization, high contents of H₂O and elevated oxygen fugacity, whereas sulfide mineralization might have been formed in reduced magmatic media by fractionation and crustal contamination during the magmatic evolution.