Studies Of Petrology And Geochemistry On The Limahe Mafic-Ultramafic Intrusion In Panxi District, SW China

In Panxi district (SW China), there are a series of world-famous giant V-Ti magnetite deposits, however Cu-Ni-(PGE) sulfide deposit is relatively small. The study on the origin of Limahe mafic-ultramafic intrusion, a typical one hosting Cu-Ni sulfide deposit in this district, is important not only to understand the genesis of Cu-Ni-(PGE) sulfide deposits but also to the mineral exploration in this district. Based on the petrology, we would reveal formation of the Limahe intrusion and provide important constraint on ore genesis of Cu-Ni-(PGE) sulfide deposits by geochemical study. The Limahe intrusion is composed of ultramafic unit and mafic unit. Geochemical characteristics of Limahe intrusion imply the genetic relation with Emeishan basalt, and they have similar source, produced by relatively low degree of partial melting of garnet peridotite. The primary magma should be a picrite with 14.1% MgO and 14.6% FeO by use olivine - melt equilibrium. The phase equilibria relation suggests that the gabbros of the Limahe intrusion and high-Ti basalts are possibly linked by crystal fractionation, and it also implies that the Limahe peridotites, picrites and low- Ti basalts could be co-magmatie, which suggests that mafic and ultramafic unit have their own source. Remarkably negative Nb, Ta anomalies exist on the primitive mantle -normalized patterns, characterizing crustal contamination. The negativeεNd(t) value, high O isotope value and orthopyroxene in ultramafic unit also support the above conclusion. The good correlations between MgO and major element oxides suggest dominant olivine fractionation/accumulation in the ultramafic unit, and fractionation of a gabbroic assemblage in the mafic units. Consequently, crustal contamination could play a significant role in the generation of the Limahe Cu–Ni sulfide deposit. Thus, it can be inferred that the difference of the geological settings between the Emeishan and Siberian LIPs might be a key factor for their different mineralization features.