Magmatic Evolution And Metallogenetic Potential Of Basic And Ultrabasic Rock Intrusions, East Kunlun Mountain, Xinjiang

The Dalaku’an rock intrusions, located in the west of the South Belt of the East Kunlun area and the southern margin of the Altyn fault, are typical bodies of ferro-peridotite series in the South Apa basic and ultrabasic rock belt with the complex geological structure, frequent volcanic and magmatic activities and Cu, Ni, Au, Ag, Zn, and other metal deposits or mineralized points. The Dalaku’an rock intrusions, composed of No. I, No. II basic- ultrabasic intrusions and twenty gabbroic bodies, have undergone sufficient crystallization differentiation, and rich rock type and obvious mineralization phenomenon. This paper chooses the Dalaku’an rock intrusions for study, systematically discusses the fractional crystallization, assimilation and contamination, the nature of primary magma, the source region, the degree of partial melting, tectonic environment in terms of their chronology, petrology, geochemistry, mineral crystal chemistry. In addition, we further study the sulfur content at sulfide saturation in primary magma and magmatic immiscibility, and analysis and evaluate the mineralization potential. The results are as follows:1. The Dalaku’an rock intrusions are located in the Kalamilan Neopaleozoic trench-arc system, and emplaced into the mid-Variscan granodiorte. The main rock types include wehrlite, Olivine Clinopyroxenite, Clinopyroxenite, plagioclase-bearing pyroxenite, mela-grabbro, grabbro. Thereinto, taxitic and nodular primary sulfides occur in the clinopyroxenite, which also have dense disseminated texture locally. The main ore minerals are pentlandite, pyrrhotite, chalcopyrite and pyrite.2. The zircon U-Pb dating yields 245.5±0.5Ma for the grabbro of the Dalaku’an NO.II intrusion, which belongs to Early Triassic Olenekian. Regional data suggests the Early Triassic Olenekian is a stage when the Paleo Tethys ocean subducted northward. Geochronology, mineral crystal chemistry and petrochemistry all show that the intrusions possess arc magmatic characteristics.3. The primary magma of the Dalaku’an intrusions is water-bearing picritic magma with liquidus and solidus 1364℃, 990 ℃respectively, whose Mg O content is 17.17% and formation depth is 56.6km, as a result of 30% partial melting of spinel lherzolite. The equivalent of primary magma is plagioclase-bearing olivine websterite, which has 15.5%Ol+43.5%Cpx+18.62%Opx+ 6.18%Plag+13.65% Melts. The magma experienced fractional crystallization of olivine and clinopyroxene. The crystal temperatures of clinopyroxene, orthopyroxene and plagioclase are 1160℃, 1040℃, 1010℃, respectively.4. The ratio of magma to sulfide(the R factor) of the Dalaku’an rock intrusions is 122, similar to the R factor of the Xiarihamu nickel deposit and below that of Jinchuan deposit. The crystal chemistry of olivine deduces the primary magma experienced about 0.86% segregated sulfide. And the main cause of sulfide saturation and segregation could be the sufficient crystallization differentiation and the addition of the crustal materials into the magma.5. In view of the rock types, ore texture/ structure, immiscible separation of metal sulfide and mass balance, the Dalaku’an intrusions possess a favorable condition for magmatic Ni-Cu sulfide deposit and a large deep prospecting potential.