东昆仑古生代镁铁质岩浆镍钴成矿条件——希望沟地区超镁铁质岩C-He-Ne-Ar同位素制约  

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

作　　者：李思奥 包亚文 梁慨慷 高旭 许瑶 张铭杰 李立武 李中平 LI SiAo;BAO YaWen;LIANG KaiKang;GAO Xu;XU Yao;ZHANG MingJie;LI LiWu;LI ZhongPing(School of Earth Sciences,MNR Key Lab of Strategic Mineral Resources of the Upper Yellow River,Lanzhou University,Lanzhou 730000,China;Key Laboratory of Petroleum Resources(Gansu Province),Northwest Institute of Eco-Environment and Resources,CAS,Lanzhou 730000,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,自然资源部黄河上游战略性矿产资源重点实验室,兰州730000 [2]中国科学院西北生态环境资源研究院,甘肃省油气资源研究重点实验室,兰州730000

出　　处：《岩石学报》2024年第7期2153-2168,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42272069、91962212、41872075);国家重点研发计划项目(2022YFC2903504)联合资助。

摘　　要：东昆仑造山带广泛发育古生代以来的镁铁质岩浆作用,不同的镁铁质岩浆在镍钴关键金属成矿潜力方面存在显著差异,希望沟地区出露的玄武岩及406.9Ma和270.7~264.9Ma两期镁铁-超镁铁质岩的Ni-Co成矿规模不同,是对比认识镍钴富集成矿条件差异的理想地区。本文测定了超镁铁质岩单矿物中流体挥发份的稀有气体和碳同位素组成,橄榄石、辉石和斜长石释出CO _(2)和CH4的δ^(13)C值变化范围大,δ^(13)CCO _(2)和δ^(13)C_(CH4)位于有机质热裂解成因及地壳值的范围内,δ^(13)C_(CH4)值具有I型有机质来源特征,CH4同系物的碳同位素组成随碳数呈正序及局部反序的分布特征,3He/4He与40Ar/36Ar指示大气饱和流体与大陆地壳端元,3He/4He与δ^(13)CCO _(2)揭示Ⅰ型沉积有机质与蚀变洋壳。3He/4He与4He含量负相关表明放射性成因4He~*的大量积聚,扣除掉4He~*后含镍钴成矿的406.9Ma岩体的3He/4He值达1.8Ra,揭示岩浆来源于岩石圈地幔。大陆地壳和沉积有机质可能来自围岩的沉积有机质热裂解组分,Ⅰ型沉积有机质、蚀变洋壳及大气饱和流体揭示岩浆地幔源区的俯冲洋壳板片携带再循环地壳组分。希望沟镁铁-超镁铁质杂岩体的地壳混染比例(32%)高于夏日哈木矿床,不是制约硫化物饱和熔离镍钴成矿的条件,270.7~264.9Ma岩体低的Ni-Co含量及成矿规模可能与深部岩浆房硫化物的熔离有关。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.Theδ^(13)C values of CO _(2) and CH_(4) vary in a large range,and predominantly plot in the thermogenic and crustal ranges.Theδ^(13)C values of CH_(4) indicated typeⅠorganic matter.Most of the samples show the normal distribution pattern of carbon isotopic compositions among CH_(4) to C 4H 10,and some show the partial reversal distribution pattern.3He/4He and 40 Ar/36 Ar values mostly plot along the mixing line of air saturated fluid(ASF)and continental crust(CC).Theδ^(13)C of CO _(2) and 3He/4He 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 typeⅠoceanic 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

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 

分 类 号：P618.63[天文地球—矿床学] P618.62[天文地球—地质学]