白云鄂博群黑色岩系微量元素地球化学特征及地质意义

Trace Elements Geochemistry of the Black Rock Series from Bayan Obo Group and Their Geological Implications

白云鄂博群位于华北地台北缘,是一套中—新元古代裂谷沉积的产物。尖山组和比鲁特组是其中主要的黑色岩系。对以上两组中的碳质页岩和板岩的Au、Ag、As、Ba、Co、Cu、Hg、Mn、Mo、Ni、P、Pb、V、Zn、U、B、Sb等微量元素和稀土元素进行了较为详细的研究。通过元素含量特征、w(V)/w(V+Ni)、w(Zn)-w(Co)-w(Ni)三元图、稀土配分曲线、w(Ce)/w(La)、Ce和Eu异常、w(La)/w(Yb)-w(Ce)/w(La)和w(La)/w(Yb)-w(ΣREE)图解等方法对其沉积环境特征进行了探讨。微量元素含量分析显示白云鄂博群黑色岩系以富亲铜元素和亲石元素、贫亲铁元素为特征,其中富集Hg、B、As、Mn、Sb、Au、Ag、Pb、P、Ba、U、Mo等多种元素;较高的w(B)反映了黑色岩系沉积于盐度较高的水体中;高的w(V)/w(V+Ni)、w(Ce)/w(La)反映了黑色岩系形成于缺氧的沉积环境中;黑色岩系中Hg、Sb、Ba的富集和w(Zn)-w(Co)-w(Ni)图解中投点大部分靠近热水沉积区域指示了黑色岩系中有热水沉积物的参与;稀土元素配分模式、Ce和Eu异常及w(La)/w(Yb)-w(ΣREE)和w(La)/w(Yb)-w(Ce)/w(La)图解投点在两岩组中的不同特点表明尖山组沉积物以陆源沉积为主,有少量热水沉积物参与;而比鲁特组中热水沉积组分所占比例较大,形成时海水较深。

The Bayan Obo Group of Middle-Upper Proterozoic is co sedimentary rocks distributed in central Inner Mongolia, China. Based on structural characteristics six sedimentary cycles, represented by the Dulahala Formation, the Jianshan Formation, the Halahuogete Formation, the Bilute Formation, the Baiyinbaolage Formation and the Huji＇ertu Formation, can be recognized, in which the Jianshan and Bilute formations are important parts. They contain abundant organic materials and show significant enrichment of a variety of ore-forming elements （ Au, P, Fe, and REEs）. Samples of carbonaceous shale collected from the black rock series were analyzed for trace elements and rare earth elements that were used to demonstrate the paleoenvironmental settings. Remarkable enrichment can be recognized of a variety of trace elements, including Hg, B, As, Mn, Sb, Au, Ag, Pb, P, Ba, U and Mo. The high content of B in the black rock series represents a high-salinity sedimentary condition high V/（ V ＋ Ni） and Ce/La indicate an anoxic sedimentary environment for these shales.The Zn-Co-Ni diagram and the high contents of Ba,As,Sb and B are important indicators of hydrothermal sedimentation.The differences between the Jianshan Formation and Bilute Formation in REE patterns,Ce and Eu anomalies,La/Yb-∑REE and La/Yb-Ce/La diagrams suggest that the Jianshan Formation consists of dominating terrigenous matters with few hydrothermal sediments,while the Bilute Formation formed in a deeper depth contains a higher proportion of hydrothermal sediments than the Jianshan Formation does.