新疆北部后碰撞与幔源岩浆有关的成矿谱系

Metanogenic spectrum related to post-collisional mantle-derived magma in north Xinjiang.

新疆北部与后碰撞幔源岩浆作用有关的矿床主要有四类:铜镍硫化物矿床、钒钛磁铁矿矿床、钛铁矿-铜镍硫化物复合矿床和玄武岩型自然铜矿床。上述四类矿床成矿时代相近(主成矿期为二叠纪),空间相邻,跨构造单元分布,彼此之间可出现过渡或复合矿床类型,构成了独特的后碰撞与幔源岩浆作用有关的成矿谱系,也是中亚型造山后碰撞阶段颇具特色的成矿组合。依据其成矿专属性的不同,新疆北部与幔源岩浆有关的矿床可分为两个系列:钛铁系列和铜镍系列。钛铁系列以尾亚矿床为代表,以高钛富碱为特征,为碱性系列,REE总量高,LREE富集,ε_(Nd)(t)近0值,其含矿岩体的地球化学特征与峨嵋大火成岩省钒钛磁铁矿含矿岩体特征一致,推测其含矿岩浆来源与地幔柱活动有关;而以黄山、喀拉通克为代表的铜镍矿床成矿岩体,以相对富镁为特征,属钙碱系列和拉斑玄武岩系列,REE总量较低,模式曲线呈LREE略富集的平缓型分布,ε_(Nd)(t)为明显的正值,可能来自亏损岩石圈地幔的部分熔融。新疆北部后碰撞阶段除发育了与幔源岩浆有关的成矿谱系外,还发育了与造山带有关的构造-岩浆-成矿体系。这种既有地幔柱成矿又有造山带成矿的双重特性,可能是二叠纪地幔柱活动与造山(后碰撞)作用叠加的结果。

Four types of deposits related to post-eollisional mantle-derived magma： copper-nickel sulfide （CNS）, vanadie titianomagnetite （VTM）, ilmenite-CNS composite deposit and native copper （NC） deposits, developed in north Xinjiang. These deposits distribute in spanning tectonic units with close metallogenic epoch （peak in Permian）. The transitional and/or composite mineralization can be recognized between two end-members. They constitute a metallogenic spectrum related to mantle-derived magma formed in post-collisional setting, which is also a distinctive metallogenic assemblage owned by Central Asia metallogenic province. The deposits related to mantle-derived magma in north Xinjiang are classified into two series： Ti-Fe series and Cu-Ni series. The Ti-Fe series represented by Weiya VTM deposit is alkalic rock series ,and characterized by higher Ti, alkali, and REE contents, and around- zero εNd （t） value. The data suggest that the magma might derive from mantle-plume activity, in accordance with the VTM deposits in the Emeishan LIP. The host rocks of the Cu-Ni series, represented by Huangshan and Kalatongke deposits, is calc-alkalic and tholeiite rock series, characterized by Mg-rieh, lower REE contents with smooth REE pattern and higher positive εNd （t） value. These suggest that the magma of Cu-Ni series might derive from partial melting of depleted lithospherie mantle. Besides of the metallogenie spectrum related to mantle-derived magma, the mineralization system related to orogeny is also developed in the post-eollisional stage of north Xinjiang, The Characteristics with both mantle-plume and orogeny associated mineralization possibly results from superimposition of Permian mantle-plume activity and post-eollisional orogenesis.