鄂尔多斯盆地砂岩型铀矿碳酸盐岩碳氧同位素及其天然气-水混合流体作用特征

Characteristics of natural gas-water mixed fluid and carbon oxygen isotopes of carbonatitein the sandstone uranium deposits,Ordos Basin

【研究目的】本文以杭锦旗—大营铀矿为研究区,研究了矿床的碳酸盐化类型、期次和原位微区碳氧同位素特征,为该区砂岩型铀矿的形成及成因认识提供了新的信息和依据。【研究方法】采用野外调研、工业孔含矿层位岩芯采集、高倍显微镜观察、电子探针图像分析等方法,区分不同期次的碳酸盐化(主要是方解石),在此基础上运用SHRIMP稳定同位素示踪技术进行C-O同位素测试,为更加精确示踪砂岩铀矿形成过程提供了合理的途径。【研究结果】利用原位微区碳氧同位素示踪技术分析了铀成矿期及成矿期后流体特征,显示具有有机质来源的特点,其中方解石的氧同位素显示流体具有大气水作用的特点,认为天然气向北部运移耗散与地下水形成的低温混合热液流体为它们提供了碳质来源。本区“钙化木”状碳酸盐化的方解石多显示沿晶洞分布或沿裂隙贯穿,明显为成矿期后天然气沿裂隙充填的结果;因此,天然气-水混合流体作用从成矿期可一直延至成矿期后,具有叠加富集及保矿作用。【结论】采用电子探针和镜下观察相结合的方法,在区分不同期次方解石的基础上,原位微区稳定同位素示踪技术为精细研究砂岩型铀矿成矿流体特征提供了有效的技术支撑。

This paper is the result of oil and gas exploration engineering[Objective]This paper takes Hangjinqi-Daying Uranium deposit as the research area,and we studied the carbonation type、period and the characteristics of in-situ micro-zone carbon and oxygen isotopes,providing a new information and basis for the formation and cause of sandstone uranium deposits in this area.[Methods]By using the field observation,rock core collection of industrial hole in ore-bearing horizon,high power microscope observation,electron probe analysis,we distinguished the different stages of Carbonation(Mainly calcite).The C-O isotope test was carried out by using the SHRIMP stable isotope tracer technology,which provides a reasonable and more accurate way to tracing the formation process of sandstone uranium deposit.[Results]Both the mineralization period and post mineralization period of fluid have the source of genetic characteristics by using in-situ micro-area C-O isotopes testing method,and the oxygen isotope of calcite shows that the fluid has the characteristics of atmospheric water.it is believed that the natural gas moved to the north together with the groundwater forming the low-temperature hydrothermal fluid provided the carbon source.The"calcified wood"-like carbonated calcite in this area is mostly distributed along crystal caves or penetrated along cracks,and it is obviously the result of natural gas filling along the cracks in post mineralization period.Therefore,the natural gas-water mixed fluid effect can be extended to post mineralization period,which has the effect of superimposed enrichment and mineral preservation.[Conclusions]The application of electron probe,SHRIMP stable isotope tracing and other methods provide the core technical guarantee for in-situ micro-area stable isotope tracing,and provide an effective test method for the fine study of the characteristics of ore-forming fluids.