青海东昆仑龙什更铁钴矿成矿时代与成因类型

Metallogenic timing and genesis types of Longshigeng Fe-Co deposit in eastern Kunlun Orogen,Qinghai

为揭示龙什更铁钴矿的形成时代和成因类型,利用锆石U-Pb法定年和岩石地球化学分析对含矿绿泥绢英千枚岩进行了研究。结果表明,该岩石的锆石年龄跨度大((1138±25)~(2791±13)Ma),峰值多,其中最年轻一组的加权平均年龄为(1139±29)Ma,代表其原岩形成时代的下限,同时指示该矿床形成不早于中元古代晚期。岩石的主量元素含量变化较大,具有缓右倾的稀土配分模式和明显的轻重稀土分馏、负铕异常,相对亏损Nb、P、Ti、Ba、Sr和相对富集Th、La、Ce、Nd、Rb和K。经原岩恢复可知其原岩为泥砂质沉积岩,沉积作用占主导同时含少量热水组分,形成于大洋岛弧环境。综合地质、地球化学等特征可知该矿床的成因类型为(热水)沉积型,但热水喷流活动偏弱,形成铁矿体和钴的初始富集,而后期次生富集是形成钴矿体的主要机制。

In order to reveal the metallogenic age and genetic type of the Longshigeng Fe-Co deposit,zircon U-Pb dating and whole-rock geochemical analysis were used to study the ore-hosting chlorite-sericite phyllite in this paper.The analytical results show that zircons from the chlorite-sericite phyllite have a great variation of ^(207) Pb/^(206) Pb age((1138±25)~(2791±13)Ma),and the weighted average age of youngest group is(1139±29)Ma,which represents the lower limit of the formation of its protolith and further indicates that Longshigeng was formed no earlier than the Late Mesoproterozoic.They have varied concentrations of major element,slightly right-leaning REE distribution patterns,significant fractionation between LREE and HREE and negative Eu anomaly.Nb,P,Ti,Ba and Sr are relatively depleted,and Th,La,Ce,Nd,Rb and K are relatively enriched for them.The protophite is likely to be pelitopsammite by protolith reconstruction,which is dominated by sedimentation and contains a small amount of hydrothermal component,and was formed in an oceanic island arc environment.Finally,the Longshigeng Fe-Co deposit is considered to be(hydrothermal)-sedimentary type deposit based on the geology and geochemistry,but the seafloor hydrothermal activity is weak.The formation process of Longshigeng is related to the seafloor hydrothermal activity,resulting the formation of industrial iron ore body and cobalt initial enrichment,but the secondary enrichment is the main mechanism of cobalt ore body formation.