东天山含铜镍-钛铁复合矿化松杉岩体的发现及地质意义

The discovery and geological significance of Cu-Ni-Ti-Fe composite mineralized Songshan intrusion in eastern Tianshan

中文关键词:铜镍-钛铁复合矿化岩体  岩浆演化过程  找矿潜力  东天山  松杉杂岩体

keywords:Cu-Ni-Ti-Fe mineralized complex  Magmatic evolution processes  mineral prospecting potential  eastern Tianshan  Songshan complex

中文摘要:东天山是中国重要的岩浆型铜镍和钛铁矿床的聚集区，松杉杂岩体是继香山西杂岩体后发现的又一个岩浆型铜镍-钛铁复合矿化的岩体。然而，岩浆型铜镍-钛铁复合矿化岩体的成因机制及东天山地区该类复合矿化的找矿潜力仍缺乏研究。文章首次测定了松杉橄榄辉长岩和辉长岩的成岩年龄，分别为（280.94±0.82）Ma和（279.30±0.84）Ma，均形成于早二叠世。松杉杂岩体主微量元素特征具有过渡性，碱金属含量（Na₂O+K₂O）、镁铁比值（m/f）及稀土元素总量（ΣREE）等均介于典型岩浆型铜镍硫化物矿床和典型岩浆型钛铁氧化物矿床。Th/Yb vs. Ba/La和(Th/Nb)_PM vs. (Sm/Yb)_PM图解结合极低的Th含量、La/Sm和Nb/La比值以及Ce、Nb、Ta的负异常，表明松杉岩体的原始岩浆可能起源于软流圈上涌驱动的受交代岩石圈地幔的共同熔融。SiO₂与MgO的负相关、MgO与相容元素（Co、Ni和Sc）、TiO₂与FeO_T和V与FeO_T的正或弱正相关性，表明岩浆在演化过程中主要经历了橄榄石、单斜辉石和斜长石的分离结晶，并伴随着铜镍硫化物的熔离及铁氧化物的结晶。松杉岩体富集大离子亲石元素、轻稀土元素且亏损高场强元素，Th/Nb、La/Nb和Zr/Nb比值有所升高且Ce/Pb比值有所降低，暗示了岩浆经历了地壳混染作用。松杉岩体的地质、地球化学特征与区域上赋存铜镍和铜镍-钛铁复合的镁铁-超镁铁质岩体具有可比性，具有良好的找矿潜力。东天山镁铁质岩体是未来寻找铜镍-钛铁复合矿床的良好对象。

Abstract:The eastern Tianshan in China is a significant concentration area for magmatic Cu-Ni and Ti-Fe deposits. The Songshan complex represents another magmatic Cu-Ni-Ti-Fe mineralized body discovered following the Xiangshanxi complex. However, the genetic mechanism and mineral prospecting potential of magmatic Cu-Ni-Ti-Fe mineralized body in eastern Tianshan remain poorly understood. This study is the first to report the emplacement ages for the Songshan olivine gabbro (280.94±0.82 Ma) and gabbro (279.30±0.84 Ma), indicating formation during the Early Permian. Geochemically, the Songshan complex displays signatures transitional between typical magmatic Cu-Ni sulfide deposits and typical magmatic Ti-Fe oxide deposits, as evidenced by alkali content (Na₂O+K₂O), mafic ratio (m/f), and total rare earth element abundance (ΣREE). Geochemical indicators—including Th/Yb vs. Ba/La and (Th/Nb)_PM vs. (Sm/Yb)_PM illustrations, coupled with very low Th contents, La/Sm and Nb/La ratios, and negative anomalies of Ce, Nb and Ta —collectively suggest the Songshan complex's parental magma originated from co-melting of metasomatized lithospheric mantle driven by asthenospheric upwelling. Negative correlations between SiO₂ and MgO, positive to weak positive correlations between MgO and compatible elements (Co, Ni, Sc), TiO₂ and FeO_T and V and FeO_T indicate fractional crystallization dominated by olivine, clinopyroxene, and plagioclase, accompanied by Cu-Ni sulfide segregation and Fe-oxide crystallization, during magma evolution. The Songshan complex exhibits LILEs and LREEs enrichment with HFSEs depletion, along with diagnostic ratios—elevated Th/Nb, La/Nb, and Zr/Nb alongside decreased Ce/Pb—demonstrate significant crustal contamination. These geological and geochemical signatures align closely with regional mineralized mafic-ultramafic intrusions hosting Cu-Ni or Cu-Ni-Ti-Fe deposits, confirming favorable mineral prospecting potential. The mafic intrusions in eastern Tianshan are good targets for future exploration of magmatic Cu-Ni and Ti-Fe deposits.