河北省奥陶纪马家沟组顶部古风化壳中三稀元素赋存状态及富集机制

Occurrence state and enrichment mechanism of rare earth, rare metal and rare dispersed elements in paleo-weathering crust of Ordovician Majiagou Formation, Hebei

河北省奥陶纪马家沟组与晚石炭世本溪组之间发育一套古风化壳层,岩性主要为铁质黏土岩、铝质黏土岩和铝土岩,剖面从顶到底具典型的“煤-铝-铁”结构。地球化学分析结果显示,冀东石岭和冀南同义岭古风化壳样品的轻稀土元素氧化物总质量分数分别达0.0893%和0.0717%,均超过了古风化壳型轻稀土矿边界品位,冀北煤窑山古风化壳样品的轻稀土元素总质量分数为0.0504%,也具明显富集特征。古风化壳中部分样品稀有元素Li含量也超过了伴生边界品位。通过元素逐级分离试验定量分析出古风化壳中的三稀元素主要以矿物相存在,再通过X射线衍射分析、电子探针分析进一步确定三稀元素主要以类质同象赋存于伊利石、高岭石等黏土矿物中,少量以化合态存在于独立的稀土矿物中。综合分析认为,古风化壳中三稀元素的矿化富集依次经历了风化壳形成阶段、铝质岩系形成阶段及沉积压实阶段的多阶段演化。

The paleo-weathering crust, which is composed of iron claystone, aluminum claystone and allite, is generally developed between Ordovician Majiagou Formation and Late Carboniferous Benxi Formation in Hebei Province, and it has a typical coal-bauxite-iron structure from top to bottom. The LREE of samples from the paleo-weathering crust of Shiling profile in eastern Hebei is 0.0893%, while Tongyiling profile in southern Hebei is 0.0717%, which are both exceed the cutoff grade of paleo-weathering crust type LREE ore. The LREE of samples from the paleo-weathering crust of Meiyaoshan profile in northern Hebei is 0.0504%, also shows obvious enrichment characteristics. In addition, the content of Li in paleo-weathering crust exceeds the associated cutoff grade.It is quantitatively analyzed that the mineral facies is the main occurrence state of rare earth, rare metal, and rare dispersed elements in the paleo-weathering crust through separation test of elements, it is further confirmed that those elements exist in clay minerals such as illite and kaolinite in the form of isomorphism, and minor amount exist in independent minerals by XRD and EPMA. It can be concluded that the mineralization enrichment of those elements have undergone multiple stages of evolution, including the formation stage of weathering crust,the formation stage of aluminous rock series and the sedimentary compaction stage.