Origin of PGE depletion of Triassic magmatic Cu-Ni sulfide deposits in the central-southern area of Jilin province, NE China

Triassic mafic-ultramafic intrusions are widespread in the central-southern part of Jilin province, northeast China. Many of them are ore-bearing intrusions of considerable economic value. They compose a number of magmatic Cu-Ni sulfide deposits which are characterized by depletion of platinum-group elements (PGEs). In this study, an attempt was made to clarify the relationship between the PGE content of the mafic-ultramafic magmas and the nature and the evolution of their mantle sources. Precise PGE data of some of the typical ore-bearing intrusions are reported and the factors which may affect the PGE content of the intrusions are discussed, such as the presence of PGE in the mantle, the degree of partial melting of the mantle and the evolution of the mantle. In the course of the evolution of the mantle, a large proportion of PGE which are present as fusible components such as sulfides will be extracted, and most of the refractory PGE components such as alloys will be retained in mantle residues. Without further replenishing of PGE, later melts of a residue will contain less PGE. It is because the Triassic mafic-ultramafic intrusions are derived from PGE-depleted mantle that the magmatic Cu-Ni sulfide deposits in the central-southern part of Jilin province are reduced in PGE. We conclude that most of the young mafic-ultramafic intrusions are probably poor in PGEs.