松辽盆地东南部油气、煤层气后生蚀变硫同位素特征

Characteristics of sulfur isotope during the epigenetic alteration of oil-gas and coalbed methane in the southeastern Songliao Basin

对松辽盆地东南部上白垩统泉头组、姚家组和嫩江组岩石中黄铁矿及硫同位素特征研究表明,泉头组、姚家组中后生还原褪色作用形成的灰色、灰绿色砂岩中的黄铁矿及硫同位素均显示出了深部来源的油气、煤层气有机流体作用成分特征。该区原生沉积成岩岩石及黄铁矿中硫同位素的δ34SV-CDT为正值,油气、煤层气有机流体还原作用岩石及黄铁矿中δ34SV-CDT为负值。油气、煤层气还原作用不仅使杂色、紫红色原生氧化砂岩还原为灰色、灰绿色还原性砂岩,还使岩石还原容量大大增强,而且油气、煤层气在有机流体与岩石的相互作用过程中有铀的叠加富集,岩石铀含量普遍增加,局部可形成铀异常、铀矿化。首次在门达地区姚家组含矿砂岩中发现网脉状水云母化,显示铀成矿具有低温热液蚀变特征,铀矿化与低温热流体作用有关。

Through studying the characteristics of pyrite and sulfur isotope in the rock of Upper Cretaceous Quantou Formation, Yaojia Formation and Nenjiang Formation in the southeastern Songliao Basin, occurrence features of pyrite and characteristics of sulfur isotope in gray and grayish-green sandstone produced by epigenetic reducing decoloration of Quantou Formation and Yaojia Formation indicate the characteristics of organic fluid composition in deep-seated oil-gas and coalbed methane. δ^34SV-CDT of sulfur isotope in original sedimentary diagenite is positive, δ^34SV-CDT of organic fluid in oilgas and coalbed methane is negative. Reduction of oil-gas and coalbed methane not only makes mottled and purplish-red original oxidized sandstone reduce to grey and grayish-green reducing sandstone, which makes the reducing capacities of rocks increase greatly, but also uranium is superimposed and enriched during the interaction of rocks with organic fluid of oil-gas and coalbed methane and uranium content increases generally, which results in the forming of uranium anomaly and mineralization in some areas. Stockwork damouritization is discovered in the ore-bearing sandstone of Yaojia Formation in Menda area at the first time, which shows the uranium mineralization is characterized by low temperature hydrothermal alteration and is related with low temperature hydrothermal fluid.