Two magma series and associated ore deposit types in the Permian Emeishan large igneous province, SW China

Abstract

The Late Middle Permian (∼ 260 Ma) Emeishan large igneous province in SW China contains two magmatic series, one comprising high-Ti basalts and Fe-rich gabbroic and syenitic intrusions, the other low-Ti basalts and mafic-ultramafic intrusions. The Fe-rich gabbros are spatially and temporally associated with syenites. Each series is associated with a distinctive type of mineralization, the first with giant Fe-Ti-V oxide ore deposits such as Panzhihua and Baima, the second with Ni-Cu-(PGE) sulfide deposits such as Jinbaoshan, Limahe and Zhubu. New SHRIMP zircon U-Pb isotopic data yielded 263 ± 3 Ma for the Limahe intrusion, 261 ± 2 Ma for the Zhubu intrusion and 262 ± 2 Ma for a syenitic intrusion. These new age dates, together with previously reported SHRIMP zircon U-Pb ages, suggest that all these intrusions are contemporaneous with the Emeishan flood basalts and formed during a major igneous event at ca. 260 Ma. The oxide-bearing intrusions have higher Al 2O 3, FeO (as total iron) and total alkalis (Na 2O + K 2O) but lower MgO than the sulfide-bearing intrusions. All intrusions are variably enriched in LREE relative to HREE. The oxide-bearing intrusions display positive Nb- and Ti-anomalies and in certain cases negative Zr-Hf anomalies, whereas the sulfide-bearing intrusions have obvious negative Nb- and Ti-anomalies, a feature of crustal contamination. Individual intrusions have relatively small ranges of e{open}Nd(t) values. All the intrusions, however, have e{open}Nd(t) values ranging from - 3.9 to + 4.6, and initial 87Sr/ 86Sr ratios from 0.7039 to 0.7105. The syenites have very low MgO (< 2 wt.%) but highly variable Fe 2O 3 (2.5 to 13 wt.%) with initial 87Sr/ 86Sr ratios ranging from 0.7039 to 0.7089. Magmas from both series could have derived by melting of a heterogeneous mantle plume: the high-Ti series from a Fe-rich, more fertile source and the low-Ti series from a Fe-poor, more refractory source. In addition, the low-Ti series underwent significant crustal contamination. The two magma series evolved along different paths that led to distinct mineralization styles. © 2007 Elsevier B.V. All rights reserved.