任家庄井田晚古生代煤系战略性金属元素富集特征

Enrichment characteristics of strategic metal elements in Late Paleozoic coal-bearing sequences in Renjiazhuang Mine Field

煤系是战略性金属矿产增储的重要来源。宁东煤田煤炭资源丰富,部分地区煤中富集战略性金属。以宁东煤田任家庄井田煤系为研究对象,系统采集主煤层剖面煤样、夹矸及顶(底)板样,采用电感耦合等离子体质谱法(ICP-MS)、X-射线荧光光谱(XRF)和X射线衍射(XRD)进行了系统的矿物学和地球化学测试分析,查明常量元素和微量元素分布及富集情况,讨论战略性金属元素富集成因并进行物源分析。结果表明,任家庄井田石炭-二叠纪煤系富集战略性金属矿产,太原组和山西组煤中战略性金属元素整体含量水平较高,以Li-Ga-Zr(Hf)-Nb(Ta)-Th(U)-Pb及REY共富集为特征,且顶底板及夹矸更为富集。其中:5号煤层Li、Ba高度富集,Rb、Zr富集;9号煤层Li高度富集,Zr、Hf、Th富集;9~上煤层微量元素含量整体相对较低,Cr富集。5号煤层和9号煤层战略性金属元素富集程度较9~上煤层更好。5号煤层和9号煤层灰基Li、Ga均达到了开发利用品位,5号煤层灰基REY也达到了开发利用品位,具有良好开发利用前景。基于元素赋存特征、沉积环境、构造演化的综合分析,认为任家庄井田战略性金属元素富集主要受陆源碎屑供给影响,由鄂尔多斯盆地西缘北部阴山古陆与西北部阿拉善地块蚀源区的长英质-中性岩碎屑物质经古水流搬运进入泥炭沼泽,在特定沉积环境及地球化学环境下通过有机质与无机质相互作用而富集,并经多期次构造演化控制形成现今赋存分布状态及富集特征。

Coal-bearing sequences are important source for increasing strategic metal mineral reserves.There are abundant coal resources in Ningdong Coalfield,and strategic metals enrichment have been found in several coal-bearing sequences.The study selected coal-bear-ing sequences of Renjiazhuang Mine Field in Ningdong Coal Field as the research object,the coal samples,gangue,roof and floor plate of the main coal seam section were collected systematically.The mineralogical and geochemical tests were carried out by inductively coupled plasma mass spectrometry(ICP-MS),X-ray fluorescence spectroscopy and X-ray diffraction,and the distribution characteristics of major and trace elements were ascertained.The causes of strategic metal element enrichment and their provenance were analyzed.The results showed that the Permo-Carboniferous coal-bearing of late Paleozoic are the enrichment beds of strategic metal minerals in RenJiazhuang Mine Field.The enrichment of strategic metal elements in coal is common in Taiyuan and Shanxi formations,and the overall content of trace elements is high,which is characterized by Li-Ga-Zr(Hf)-Nb(Ta)-Th(U)-Pb,rare earth element and Yttrium(REY),co-enrichment.Moreover,strategic metal elements are more enriched in coal-bearing near the roof,floor and the gangue.Among them,Li and Ba are highly enriched,Rb and Zr are enriched in No.5 coal seam.Li is highly enriched in No.9 coal seam,while Zr,Hf and Th are enriched.The content of strategic metal elements in upper No.9 coal seam is relatively low and Cr is enriched.The concentration of trace elements in No.5 and No.9 coal is better than that in upper No.9 coal seam.Li and Ga of the ash foundation of No.5 and No.9 coal seam have reached the industrial grade,and REY of the ash foundation of No.5 coal seam has also reached the industrial grade,which presenting a very promising potential for further exploration.Based on the comprehensive analysis of element occurrence characteristics,sedimentary envir-onment and tectonic evolution,it is concluded that the strategic metal element enrichment in Renjiazhuang Mine Field is mainly influ-enced by the clastic supplying of the erosion source area,and the felsitic-neutral rock detrites from the northern Yinshan ancient landthe and the northwestern Alxa block in the western margin of Ordos Basin were transported into the peat swamp by palaeocurrent.It was en-riched through interaction between organic matter and inorganic matter in specific sedimentary environment and geochemical environ-ment,and formed the present distribution state and enrichment characteristics under the control of multi-stage tectonic evolution.