Petrogenesis and ore potential of Permian mafic intrusions in the Dacaotan area, eastern Tianshan: Constraints from whole‐rock platinum‐group element contents and Sr–Nd isotopes

Abstract

The eastern Tianshan is an important Ni–Cu mineralization belt that contains several ore‐bearing mafic–ultramafic intrusions. The eastern part of this belt has been well studied, whereas the western part is poorly studied. Here, we present studies of two mafic intrusions (DC3 and DC4) from the Dacaotan area in the western part of the eastern Tianshan. The gabbrosof the DC3 and DC4 intrusions contain plagioclase and clinopyroxene, and are characterized by light rare earth element enrichment, negative Nb anomalies, depleted platinum group element contents, high and variable Cu/Pd ratios, positive εNd (6.0–7.5) values, and low initial 87Sr/86Sr ratios (0.7033–0.7036). The two intrusions have geochemical affinities with intrusions in the Huangshan area, despite mineralogical differences, with orthopyroxene and amphibole being present in the Huangshan intrusions. The two studied mafic intrusions formed from a high‐Mg basaltic magma derived from anhydrous and depleted mantle. Due to the low degree (<8%) of partial melting, the magma was PGE‐depleted and sulphide remained in the mantle source. The PGE contents were further depleted by early magmatic sulphide segregation. Given the limited contamination (<10%) by the upper crust and coeval A‐type granites, these two intrusions have poor potential for Ni–Cu sulphide mineralization.