伊犁盆地南缘有机一无机流体耦合铀成矿作用

The organic-inorganic fluid in the southern coupling uranium mineralization margin of Yili Basin

摘要伊犁盆地是中国西北部重要的产铀盆地，虽然前人对其成矿流体进行过较为系统的研究，但成矿流体的组分、来源等依然存在较大分歧，尤其是该区成矿流体与蚀变特征、铀成矿的内在联系研究较少。利用偏光显微镜、扫描电镜、电子探针等手段对含矿层砂岩蚀变特征进行系统分析，并通过分析流体包裹体特征、流体一围岩相互作用形成的蚀变矿物中稳定同位素的组成特征及该区构造演化特征，对有机一无机流体耦合铀成矿作用进行示踪。研究表明：该区流体包裹体主要含有气烃包裹体、液烃包裹体和盐水包裹体；与砂岩型铀矿有关的蚀变类型主要有黏土化、碳酸盐化、硅化及金属矿化，其中黏土化以高岭石化为主；高岭石δ18Ov-SMOW为11．8‰～13．7‰，δDV.SMOW为-93‰—-48．3‰，与高岭石平衡流体的δ18O（水）V-SMOW为-10．3‰-5．1‰；方解石胶结物δ13Cv-PDB为-18．2‰—-7．2％0，δ18OV-PDB为-14．5‰—5．8‰，δ18OV-SMOW为15．9％0—24．9‰；黄铁矿δ34SV-CDT为-32．21‰-1．2‰。上述特征揭示，伊犁盆地南缘砂岩型铀矿成矿流体是由大气降水性质的地表水（无机）和煤系地层有机质热演化脱羧基作用产生的有机酸及伴生的CH。等还原性气体（有机）两部分组成，铀矿体与蚀变矿物皆是有机一无机流体混合及其与周围砂岩相互作用的结果，且此过程伴有微生物的参与。

The Yili Basin is an important uranium-productive basin in Northwest China, although its metallogenic fluid was studied systematic by predecessor, the problem about its component and source still exist, especially about the internal relation between metallogenic fluid and alteration characteristics and uranium mineralization. In this paper, the methods of polarizing microscope, scanning electron microscope, electronic probe was utilized to analysis alteration characteristics of sandstone in the ore-bearing layer systematically. At the same time, the fluid inclusions in ore-bearing sandstone, the stable isotope about altered mineral which was formed by interaction between fluid and wall rock and the tectonic evolution about Yili basin were utilized to trace the organic-inorganic fluid coupling Uranium mineralization. These studies show that the fluid inclusions in ore-bearing sandstone include gas-hydrocarbon inclusions, liquid-hydrocarbon inclusions and brine-inclusions. The type of alteration which related to sandstone-type uranium deposit mainly include clayzation, carbonation, silication and metal mineralization and the clayzation was first and foremost, the δDV-SMOW and δ18OV-SMOW of kaolinite is varies from -93‰ - -48.3‰, 11.8‰ - 13.7‰ respectively and the δ18OV-SMOW of relevant fluid varies from -10.3‰ -5.1‰; the δ13CV-PDB, δ18OV-PDB and δ18OV-SMOW of the carbonate cement is range between -18.2‰ and -7.2‰, -14.5‰ and -5.8‰, 15.9‰ and 24.9‰; the δ34SV-CDT of pyrite is range from -32.21‰to 1.2‰ respectively. The above characteristics reveal that the metallogenic fluid of sandstone-type uranium deposit in the southern margin area of Yili basin is mixed fluid which consists of surface-water stemming from meteoric waters and organic acid originating from coal measure strata and its concomitant reducing gas （coal-formed gas）. In addition, the uranium ore and altered mineral was the result from reciprocity of organic-inorganic fluid and fluid-rock and microorganism was exist in the mineralization process.