砂岩中自生绢云母的成因及意义——以海拉尔盆地乌尔逊凹陷乌19井为例

形成于中低温条件下的绢云母不仅仅分布于火成岩,变质岩中,而且在盆地砂岩中也有赋存,大量前人文献证实砂岩中绢云母的形成与热流体有关。本文以海拉尔盆地乌尔逊凹陷乌19井南屯组和铜钵庙组砂岩中绢云母为例,选取26个有代表的薄片做岩石学分析,绢云母质量分数介于1%～17%之间,产状主要以充填孔隙为主。与绢云母共生的自生矿物间的共生序列为:菱铁矿、钠长石、方解石、绢云母、白云石。研究发现凹陷内燕山期花岗岩造成盆地内局部高地温梯度异常,为绢云母形成提供热源。结合近几年对绢云母矿及金矿的研究,得出绢云母的形成还与CO2注入有关,是含CO2的水作用于碱铝硅酸盐矿物,在中或中低温条件下形成。

Geological genesis and significance of the sericite in sandstone:a case study from the Well-Wu19, Wuerxun depression of Hailar Basin

Sericite,forming in the middle-low temperature,not only distributes in igneous rocks and metamorphic rocks, but also can be found in sandstone from basin.It has been widely confirmed,by a large number of previous literature,that sericite＇s forming could be associated with thermal fluids.Our research is developed on the basis of sericite in sandstones from Nantun and Tongbomiao Formatioms in Well—Wu19,which deposit in Wuerxun Depression of Hailar Basin.We also picked out 26 thin sections for petrologic analysis and the results are as following：the amount of sericite mineral is between 1%～17%.The main occurrence belongs to filling pore.The sequence among paragenetic minerals,growing simultaneously with sericite mineral,is siderite,albite,calcite,sericite and dolomite.The study indicates that Yanshanian granite led to abnormal high geothermal gradient in part of Hailar Basin and it also provided heat for the formation of sericite.After combining with recent years＇study on sericite and gold deposits,we have come to the conclusion that the formation of sericite was ever connected with CO2 injection also,which means it is the product of the interaction between water with CO2 and alkali aluminum silicate minerals under the middle/middle-low temperature.