准噶尔盆地西北缘深部烃类流体与表生氧化流体叠合铀成矿作用

Superimposed Uranium Metallogenesis Between DeepHydrocarbon Fluid and Supergene Oxidation Fluid in the Northwestern Margin of Junggar Basin

为查明准噶尔盆地西北缘中、下侏罗统砂岩铀矿化成因及其与烃类流体间的关系。通过对目的层油砂提取物碳同位素和Re-Os同位素测试,得出目的层中的烃类主要是深部油气藏在晚侏罗世-早白垩世时期(155±51 Ma)遭受构造破坏逸散后充注的,初始来源于玛湖坳陷下二叠统风城组烃源岩。结合野外地质调查、岩心宏观及镜下微观鉴定,得出目的层砂岩在烃类流体充注前后分别遭受过后生氧化作用。前期古氧化作用程度强,发育赤铁矿化,成矿潜力大;而后期氧化为近现代氧化,强度偏弱,以褐铁矿化为主,时代新,成矿规模小。最终,建立了该区中、下侏罗统砂岩烃类流体还原与后生氧化耦合的四阶段铀成矿模式:(1)八道湾组-西山窑组期间为原生还原性含矿建造形成期;(2)头屯河组-齐古组期间为古层间氧化带及其古铀矿床形成期;(3)齐古组晚期-新近纪末为烃类流体充注还原与泥岩超覆掩盖期;(4)第四纪以来为近现代层间氧化带及其铀矿体形成期。该模式的提出对含油气盆地内砂岩型铀矿找矿具有指导意义。

To understand the genesis of uranium mineralization within the Middle-Lower Jurassic sandstone and its relationship with hydrocarbon fluids in the northwestern margin of Junggar basin,this study carried out an analysis of carbon isotope and Re-Os isotope.Carbon isotope and Re-Os testing of the oil-sand extract indicate that the hydrocarbon initially originated from source rock of the Lower Permian Fengcheng Formationreservoir during late Jurassic to early Cretaceous period.Field geological survey,core macroscopic and microscopic identification suggest that the sandstone were subjected to two-stage epigenetic oxidization before and after hydrocarbon injection.The intensive early oxidation resulted in great potential for hematite mineralization.While weak later oxidation gave rise to the widespread ferritization and possible a small-scale metallogenic process.At last,a four-stage uranium metallogenic model was established for reduction and epigenetic oxidation of hydrocarbon fluids within the middle-lower Jurassic sandstone.The primary reductive ore-bearing formation formed in the early-middle Jurassic.（2）The paleo interlayer oxidation type uranium deposits formed during the middle-late Jurassic.（3）The hydrocarbon filling and the upper mudstone cover from Cretaceous to Neogene.（4）The modern interlayer oxidation zone and uranium mineralization formed since Quaternary.The proposed model is of significance for sandstone-type uranium deposits prospecting in petroliferous basins.