吉林红旗岭晚三叠世镁铁超镁铁质侵入体矿物化学和岩石地球化学特征:对镍铜成矿的启示

Characteristics of mineral chemistry and geochemistry of the Late Triassic Hongqiling mafic-ultramafic intrusions:Implications for Ni-Cu mineralization

吉林红旗岭镁铁超镁铁质侵入岩群位于中亚造山带东段南缘,由3个北西向岩带(I、II、III)组成,包括30多个小岩株,其中I-岩带的部分岩体伴有铜镍矿化,并且其1和7号岩体分别形成了中型和大型岩浆铜镍硫化物型矿床。矿床主要容矿岩石为辉橄岩、橄辉岩、斜方辉石岩、二辉石岩、苏长岩和辉长岩。主量元素方面,红旗岭岩群具有富镁(w(MgO)=20.7%~31.1%)、低钛(w(TiO_(2))=0.33%~0.79%)、低碱(w(K 2 O+Na 2 O)=0.60%~2.29%)和硅(w(SiO_(2))=40.0%~53.0%)变化范围大的特征;微量元素方面,红旗岭岩群呈现弱富集LREE和LILE(Th)以及亏损HREE和HFSE(Nb-Ta-Ti)。岩相学、地球化学和矿物(橄榄石、斜方辉石、单斜辉石、尖晶石、斜长石和角闪石)主微量元素特征表明,红旗岭岩群明显不同于洋岛型玄武岩、阿拉斯加型环状杂岩和科马提岩,但与岛弧玄武岩以及中亚造山带西段的“黄山西”和“黄山东”铜镍硫化物矿床的容矿超镁铁质岩相似,其母岩浆是一种富Mg、亏损Nb-Ta的岛弧拉斑玄武质熔体,形成于晚三叠世古亚洲洋闭合后伸展环境,演化过程中经历了地壳混染和分离结晶作用,含矿母岩浆可能经历了硫化物的“二次熔离”,最终形成了铂族元素(PGE)亏损型岩浆铜镍硫化物矿床。

The Hongqiling mafic-ultramafic rocks include three belts(I,II and III)and are composed of over 30 small intrusions.They are located in the southern margin of the eastern segment of the Central Asian Orogenic Belt(CAOB).Several intrusions in belt I develop Ni and Cu mineralization,with Nos.1 and 7 intrusions forming medium-and large-sized magmatic Ni-Cu sulfide deposits,respectively.The major host rocks for Ni-Cu ore bodies are harzburgite,lherzolite,orthopyroxenite,websterite,norite and gabbro.These mafic-ultramafic rocks are characterized by high Mg(w(MgO)~20.7%31.1%),moderate Si(w(SiO_(2))~40.03%53.01%)and low Ti(w(TiO_(2))~0.33%0.79%)and alkalis(w(K 2O+Na 2O)~0.60%2.29%)contents.The patterns of trace elements show weak enrichments of LREE(La,Ce,Pr,Nd)and LILE(Th)and depletions of HREE and HFSE(Nb,Ta,Ti).Whole-rock geochemical data and mineral(olivine,orthopyroxene,clinopyroxene,spinel,plagioclase,amphibole)chemistry indicate the Hongqiling mafic-ultramafic intrusions are different from OIB,Alaskan-type complex and komatiite,but similar to arc-type basalt and mafic-ultramafic rocks from the Huangshanxi and Huangshandong Ni-Cu sulfide deposits in the western CAOB.The parental magma for the Hongqiling mafic-ultramafic intrusions is a high-Mg and low Nb-Ta tholeiitic melt which has undergone crustal contamination and fractional crystallization during evolution.Ore-bearing parental magma for the Hongqiling deposit likely experienced“second”separation of sulfide,forming the PGE-depleted Ni-Cu sulfide deposit.