羌塘盆地中生代钾盐矿成矿预测

Metallogenic Prediction of Mesozoic Potash Deposits in Qiangtang Basin

中文关键词:  羌塘盆地  钾盐  成矿预测  沉积相  青藏高原

英文关键词:Qiangtang Basin  Potassium  Metallogenic prediction  Sedimentary facies  Qinghai-Tibet Plateau

中文摘要:

      位于青藏高原腹地的羌塘盆地是我国最大的中生代海相含油气盆地,盆地发育多套生储盖组合,其中蒸发岩的膏盐层往往作为油气藏研究的盖层。但盆地内蒸发岩大多只达到硫酸盐沉积阶段,盆地内是否存在古钾盐矿？最佳的钾盐矿成矿有利区域具体位于何处？保存的远景资源量有多少？通过青藏高原形成过程中微地块的碰撞和拼合历史。研究羌塘盆地中生代沉积和演化过程,厘清羌塘盆地钾盐主要富集在中生代侏罗系的局限台地相区域。结合地震勘探和构造演化史恢复,阐明只有在逆冲推覆构造之下的区域才可能保存钾盐矿。根据羌塘盆地侏罗系夏里组沉积相带分布范围,推测保存钾盐矿的两个有利区主要位于安多县北西方向,面积约8 000 km²。综合地表膏盐层分布和地球物理勘探推断的羌塘盆地中侏罗统石膏层厚度分布图,根据海水中析出石膏和钾盐的比例,结合推覆构造对侏罗系夏里组的保存比例,推测羌塘盆地保存的钾盐资源量约为11亿吨。该研究为进一步勘查古钾盐矿提供了明确的范围和方向。

英文摘要:

      Qiangtang Basin, located in the hinterland of the Qinghai-Tibet Plateau, is the largest Mesozoic marine petroliferic basin in China. However, most of the evaporites in the basin only reach the stage of sulphate deposition. Is there an ancient potash deposit in the basin? Where is the best favorable area for sylvite mineralization? How many prospective resources are saved? Based on the collision and splicing history of microblocks during the formation of the Qinghai-Tibetan Plateau, this paper studies the Mesozoic sedimentation and evolution of the Qiangtang Basin, and shows that the potassium salts in the Qiangtang Basin are mainly concentrated in the restricted platform facies of the Jurassic in the Mesozoic. Combined with seismic exploration and tectonic evolution history restoration, it is shown that only the area under the thrust nappe structure can be preserved. According to the distribution of sedimentary facies zone of Jurassic Xiali Formation in Qiangtang Basin, it is speculated that the two favorable areas for the possible preservation of potash deposits are mainly located in the northwest direction of Anduo county, covering an area of about 8 000 km². Based on the distribution of gypsum and salt layers on the surface and the thickness distribution map of middle Jurassic gypsum layer inferred from geophysical exploration, according to the ratio of gypsum and potassium salt precipitated in seawater and the preservation ratio of Jurassic Xiali Formation by nappe structure, it is estimated that the preserved potassium salt resources in the Qiangtang Basin are about 1.1 billion tons. This study provides a clear scope and direction for further exploration of paleosylvite deposits.