新疆准东煤田中侏罗统煤系镓元素的分布特征及赋存机理探讨

Discussion on distribution and occurrence mechanism of gallium in the Middle Jurassic coal-bearing strata of the eastern Junggar coalfield,Xinjiang

随着大型煤系稀有金属矿产的发现,煤中伴生微量元素的研究受到广泛关注,但目前对我国西北地区的煤系地层中稀有元素的研究程度较低。选取新疆东北部的准东煤田为研究区,基于煤样的煤质分析和微量元素数据,研究了煤中镓的分布规律、赋存特征及富集成因。研究表明:(1)准东煤田的中侏罗统煤层中镓明显富集。12个矿区煤中镓平均含量在20.78～47.98μg/g,大多高于或接近煤中镓的边界品位(30μg/g)。(2)煤田中镓的分布规律性明显。平面上,盆地周围煤中Ga含量较中部矿区高,特别是东北部和西南部由于分别受克拉美丽山和博格达山物源区的影响,煤中Ga含量异常高,部分区域超过了60μg/g,而中部矿区(ZD10740、ZD10464、ZD10407和ZD10841)的煤中Ga含量表现为从矿区边缘向中心逐渐富集;垂向上,大部分矿区煤中Ga含量从中侏罗统底部向上降低,而受到早燕山运动影响,靠近博格达山的矿区(ZD10740)表现相反。(3)煤中Ga主要以高岭石为载体,部分Ga也存在煤的有机质组分中。镓主要以细粒物质(胶体或有机络合物形式)搬运到沉积盆地,在潮湿覆水沉积条件下发生聚积。

With the discovery of rare metal deposits in large coal measures,wide attention has been paid to the study of trace elements in coal.However,rare element study in the northwest China coal measures is still limited.In this paper,we selected the eastern Junggar coalfield in northeastern Xinjiang as the research object to study the distribution,occurrence and enrichment mechanism of gallium in coal,by analyzing coal quality and trace element data.The results showed：（1）Gallium is obviously enriched in the Middle Jurassic coal seams in the eastern Junggar coalfield,with Ga contents averaged at 20.78-47.98μg/g in twelve coal mines,which are higher than or close to the boundary grade of gallium in coal（30 μg/g）.（2）The distribution regularity of gallium in coal is apparent：on plane,gallium content is higher around the basin rim than in the center;in the northeastern and southwestern coalfields especially,gallium content is abnormally high（partly exceeding 60 μg/g）due to effect of the Kelameili and Bogda Mountains.In contrast,in the central coal mines（ZD10740,ZD10464,ZD10407 and ZD10841）,gallium contents are gradually enriched from the edge to the center.Vertically,gallium contents in most of coal mines studied decrease upward from bottom in the Middle Jurassic coal seams,whereas affected by the early Yanshan movement,ZD10740 near the Bogda Mountain showed the opposite trend.And（3）kaolinite was the main carrier of gallium in coal,and gallium also partly existed in organic matters of coal.Gallium was transported to the sedimentary basin mainly in fine-grained material form（colloid or organic complex）,and accumulated under wet sedimentary conditions.