苗儿山地区中生代酸性脉岩地球化学特征及其成因

Geochemical characteristics and genesis of Mesozoic acid dikes in Miaoershan area

苗儿山地区中生代酸性脉岩主要为细粒白云母花岗岩和花岗斑岩,具有较高的Al2O3、K2O、Na2O含量和较低的TiO2、MgO含量,微量元素以富集Rb、Th、U、Ta而亏损Ba、Sr为特征,稀土元素总量偏低,轻稀土富集,Eu亏损强烈。在CaO/Na2O-Al2O3/TiO2和Rb/Sr-Rb/Ba图解上,酸性脉岩具有上地壳富黏土质泥岩的特征。这些特征与豆乍山、香草坪等岩体的地球化学特征相似,表明酸性脉岩与岩体的物质来源相同,即早期酸性花岗岩体的母岩浆滞留于地下深部,经一定程度分离结晶和固结后,晚期熔体沿花岗岩体内外接触带及断裂构造上升形成脉岩。强烈的分离结晶作用可以导致铀等成矿元素在残余熔体中的高度富集,为铀矿床的形成提供必要的物质基础。

There are two types of Mesozoic acid dikes in Miaoershan area,granite-porphyry and fine-grained muscovite granite.The acid dikes are characterized with relatively higher content of Al2O3,K2O,Na2O,slightly lower content of TiO2,MgO,the enrichment of Rb,Th,U and Ta,depletion of Ba,Sr in trace elements,relatively low total REEs and enrichment in LREE with strong Eu depletion.In the CaO/Na2O-Al2O3/TiO2 and Rb/Sr-Rb/Ba diagram,the Mesozoic acid dikes belong to crust sourced type granite which is similar to Douzhashan granite and Xiangcaoping granite.The study result suggests that the acid dikes and granite come from the same deep sources and formed by the raising melt part along the fault and the contact zone.The intense cristalization and differentiation may cause the enrichment of uranium in the residual melt and provide material source for uranium mineralization.