Mineralization conditions of Ni-Co in Paleozoic mafic magma in the East Kunlun orogenic belt:Constraints from C-He-Ne-Ar isotopic compositions of ultramafic rocks in the Xiwanggou region
Mineralization conditions of Ni-Co in Paleozoic mafic magma in the East Kunlun orogenic belt:Constraints from C-He-Ne-Ar isotopic compositions of ultramafic rocks in the Xiwanggou region
The Ni-Co metallogenic potentials are significantly different among the Paleozoic mafic magmatism in the East Kunlun orogenic belt,western China.The 406.9Ma and 270.7～264.9Ma two-stage mafic-ultramafic complex and basalts distributed in the Xiwanggou region show different Ni-Co mineralization,and is ideal area for revealing the metallogenic condition of Ni-Co enrichment.The noble gas and carbon isotopes of volatiles in olivine,pyroxene and plagioclase separated minerals from different types of rocks in the Xiwanggou mafic-ultramafic complex have been measured to constraint the difference of metallogenic condition.The δ13C values of CO2 and CH4 vary in a large range,and predominantly plot in the thermogenic and crustal ranges.The δ13C values of CH4 indicated type Ⅰ organic matter.Most of the samples show the normal distribution pattern of carbon isotopic compositions among CH4 to C4H10,and some show the partial reversal distribution pattern.3 He/4 He and 40 Ar/36 Ar values mostly plot along the mixing line of air saturated fluid(ASF)and continental crust(CC).The δ13 C of CO2 and 3 He/4 He show sedimentary organic matter and altered oceanic crust.A negative relationship between the 3He/4He and 4He contents implies accumulation of radiogenic 4He*,and 3He/4He value of 1.8Ra for 406.9Ma Ni-Co ore-bearing intrusion after deducting the radiogenic 4He*reveals a magma source of subcontinental lithospheric mantle(SCLM).The continental crust and sedimentary organic matter could be likely derived from the thermal decomposition components of sedimentary organic matter in country rocks in the existing chamber.The type Ⅰ oceanic sedimentary organic matter,altered oceanic crust and air saturated fluid reveal a recycled oceanic crust and ASF carried by a subducted oceanic crustal plate in the magma mantle source.The Xiwanggou mafic-ultramafic complex has high crustal contamination degree(32％),which could not be a restrict condition of sulfide saturation and segregation for Ni-Co mineralization.The low Ni-Co abundances and low Ni-Co metallogenic potential in the Xiwanggou 270.7～264.9Ma mafic-ultramafic complex could be attributed to the large-scale sulfide segregation in the deep magma chamber.
关键词
岩浆镍钴成矿条件/稀有气体同位素/碳同位素/希望沟镁铁-超镁铁质杂岩体/东昆仑造山带
Key words
Magmatic Ni-Co metallogenic condition/Carbon isotope/Noble gas isotopes/Xiwanggou mafic-ultramafic complex/East Kunlun orogenic belt
维普
万方数据