Geochemistry of the Kalatongke layered intrusion, Xinjiang NW China: Implications for the genesis of a magmatic Cu-Ni sulfide deposit

Abstract

The Kalatongke mafic-ultramafic intrusions that hosts large Cu-Ni sulfide deposit is located in the Junggar Variscan orogenic belt. Four intrusive types are recognized, which from top to bottom of the intrusive complex, include biotite diorite, biotite-hornblende norite, biotite-hornblende-olivine norite and biotite hornblendegabbro-dolerite. The low (⁸⁷Sr/⁸⁶Sr)_t ratios of the intrusions (0.70375 to 0.70504), and high (ε_Nd)t from (+6.3 to +8.2), the strong enrichment of lithophile elements, and the low Nb and Ta abundance and the high δ¹⁸O values of separated clinopyroxene (mostly>6‰) suggest that the primary magmas were derivedfrom MORB-type mantle source involved in previously subducted oceanic crust, which released aqueous liquid that promoted partial melting. The intrusions were generated by fractional crystallization in situ accompanying assimilation of upper crust at the upper part of the intrusions within high-level magma chamber. The distinct boundaries between masive ores and disseminated ores suggest that the massive ores were formed by immiscible sulfide liquid formed within deep-seated crust chamber following physicochemical change, which was transported upwards to their present locations. In contrast, the gradual change relationship between disseminated ores and barren wallrocks were formed by crystal fractionation of the settling of sulfides in situ within high-level magma chamber.