重力场特征与砂岩型铀矿的关系及地质意义

Correlation of Gravity Field Characteristics with Sandstone-type Uranium Deposit and Its Geological Significance

重力场变化特征能够较好地反映地下地质体信息,砂岩型铀矿分布特征与重力场具有一定联系。我国砂岩型铀矿主要分布在我国布格重力异常场中—西北部区,且砂岩型铀矿床大多位于重力场由高向低变化的梯度带上,但靠近重力场高值区。结合砂岩型铀矿成矿机理,分析中—西北部区主要含铀盆地构造演化、地层结构等特征,认为位于中—西北部区的含铀盆地所经历的"次造山运动"及其后期相对稳定的构造环境有利于砂岩型铀矿成矿。斜坡的适度抬升有利于富铀岩体风化剥蚀,含铀含氧流体运移、断裂等因素控制砂岩型铀矿成矿,斜坡处地形改变形成重力场变化梯度带,地下断裂、岩石组分变化使重力等值线产生同形扭曲或错断现象。因此,重力场变化特征对划定砂岩型铀矿勘探靶区具有一定的借鉴作用,并以松辽盆地西南部钱家店铀矿床为例,探讨其成矿条件与重力场变化特征的关系,体现其实际应用性。

Gravity anomalies can well reflect information of the rock under the ground.There is a close rela-tionship between distribution features of sandstone-type uranium deposit with gravitational field.Sandstone-type uranium deposit is mainly distributed in the second step regions of Bouguer gravity in China.What＇s more,most of sandstone-type uranium deposits lie at the gravity gradient belt,which are close to the high-value gravitational field area.Based on the ore-formation mechanism of sandstone-type uranium deposit,analysis of features of tec-tonic evolution and rock of the major uranium-bearing basins,it is considered that subsequent relatively stable tectonic setting is beneficial to occurrence of sandstone-type uranium deposits in uranium-bearing basins of the second step regions.Orographic uplift benefits the denudation of uranium-bearing rock and migration of ground-water bearing oxygen and uranium,and faults have also played important roles in formation of the sandstone-type uranium deposit.Geographical changes cause the gravity field gradient.Structure fractures and composition changes of formation rock may induce disturbance of gravity anomaly contour lines.Therefore,the variation of gravity can be used to predict target areas of sandstone-type uranium deposit exploration.Taking Qianjiadian uranium deposit in Songliao basin as an example,this study discusses the correlation between gravity field char-acteristics with sandstone-type uranium deposits,reflecting its practical application.