柴达木盆地西北缘新近系上油砂山组烃类流体特征与铀成矿的关系

Hydrocarbon Fluid Feature of the Shangyoushashan Formation Sandstone in the Northwest Qaidam Basin and its Relationship to Uranium Mineralization

通过对柴达木盆地西北缘新近系上油砂山组18个样品的酸解烃分析,探讨了酸解烃中烃类气体组成特征、成因及来源,并结合该区铀矿地质特征初步分析了烃类流体与砂岩型铀成矿关系。酸解烃的分析结果表明,新近系上油砂山组砂岩层中烃类气体为有机成因的油型气和煤型气的混合气。烃类气主要处于成熟—高成熟阶段,是原油裂解气与原油伴生气的混合气,主要来源于路乐河组和下干柴沟组湖相腐泥型烃源岩。这些原油裂解气和原油伴生气的混合气主要沿断裂、微裂缝等通道向上运移到上油砂山组砂岩中,上油砂山组灰绿色砂岩即是烃类气体对红色砂岩还原的产物。研究区砂岩型铀矿成矿作用为原生红色—后生还原灰绿色的氧化还原作用过程,找矿标志为灰绿色含砾砂岩、砂砾岩,灰绿色砂岩层的古迎水面为该地区的找矿方向。

Based on the analysis of acidolysis hydrocarbon from 18 samples of Shangyoushashan formation in the northwestern Qaidam basin, the characteristics, genesis and sources of acidolysis hydrocarbon were discussed, and the relationship between acidolysis hydrocarbon and sandston-type uranium mineralization was preliminarily analyzed based on the geological characteristics of uranium deposits in this area. The characteristic parameters of acidolysis hydrocarbon show that hydrocarbon gas within the sandstone of the Neogene Shangyoushashan formation is characterized by organic origin,with the gas at the stage of maturity to high maturity,and should be mixed gas consisting of cracked crude oil gas and associated gases. Based on the characteristics,it can be inferred that gas,developed in sandstone of lower Section of Shangyoushashan formation may derive from sapropelic source rock of Lulehe formation and Xiaganchaigou formation. The mixture of cracking gas from crude oil and associated gas from crude oil mainly migrated upward to the sandstones of the Shangyoushashan formation along the migration channels such as faults and micro-fractures. The grey-green sandstones of the Shangyoushashan formation are the products of the reduction of red sandstones by hydrocarbon gases. Mineralization of sandstone-type uranium deposits in the study area is an oxidation-reduction process of primary red-epigenetic reduction to grey-green. Gray-green sandstone is the indicator for deposit, and the upstream face of gray-green sandstone is the direction of ore prospecting in this area.