Characteristics of Platinum Group Element in Neoproterozoic Mafic Intrusions in the Northern Margin of the Yangtze and Exploration Implications

Multiple layered mafic intrusions occur along the northern margin of the Yangtze Block, SW China. The Neoproterozoic Bijigou and Wangjiangshan mafic intrusions are two of the best exposed intrusions in the region. The Bijigou and Wangjiangshan mafic intrusions are thought to be generated by 10% to 20% of partial melting of a depleted mantle source. Uniformly high Cu/Pd (3.52×10⁴～3.97×10⁵ for the Bijigou samples and 1.78×10⁴～1.61×10⁶ for the Wangjiangshan samples) indicate that the parental magma of these intrusions experienced prior sulfide segregation before their intrusions into the shallow crust. Positive correlation between IPGE with whole–rock Ni, and negative correlation between Cu/Ir and Ni/Pd illustrate that the distribution of PGE is mainly controlled by the accumulation of olivine under an S–unsaturated condition. In comparison no linearly correlation between PGE and whole–rock Ni, V and TiO₂, and positive correlation between Cu/Ir and Ni/Pd illustrate that the PGE in the Wangjiangshan intrusion is controlled by the second-stage sulfide saturation. The general lack of parallel alignment of tabular minerals in the Bijigou and Wangjiangshan intrusions, combined the PGE depletions in the Wangjiangshan second segregated sulfides, indicates that these intrusions probably intruded and cooled under a single episode of magma replenishment, rather than a dynamic magma conduit system. Therefore the shallow part may not have the conditions to host large deposits and future prospecting work should focus on the deeper part.