地学前缘 ›› 2015, Vol. 22 ›› Issue (3): 368-381.DOI: 10.13745/j.esf.2015.03.032

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鄂尔多斯盆地杭锦旗地区砂岩型铀矿流体作用与成矿

张龙, 刘池洋, 赵中平, 王飞飞, 宋子升   

  1. 西北大学 地质学系; 大陆动力学国家重点实验室, 陕西 西安 710069
  • 收稿日期:2014-01-02 修回日期:2014-04-15 出版日期:2015-05-15 发布日期:2015-05-15
  • 作者简介:张龙(1988—)，男，博士研究生，矿产普查与勘探专业。E-mail：longz_1988@126.com
  • 基金资助:

    国家自然科学重点基金项目(41330315)

Fluid evolution and mineralization of Hangjinqi sandstonetype uranium deposit, Ordos Basin.

 ZHANG  Long, LIU  Che-Xiang, DIAO  Zhong-Beng, WANG  Fei-Fei, SONG  Zi-Sheng   

  • Received:2014-01-02 Revised:2014-04-15 Online:2015-05-15 Published:2015-05-15

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摘要：

鄂尔多斯盆地北部中侏罗统直罗组富铀砂岩成岩过程复杂，铀成矿并非典型的层间氧化带模式。通过对盆地北部杭锦旗地区矿化砂岩成岩矿物、方解石碳氧同位素、流体包裹体的综合分析，探讨了杭锦旗砂岩型铀矿的流体作用特征与铀成矿过程。结果表明：矿区砂岩遭受碱性渗入水、烃类降解酸性水、碱性热液3种类型流体作用；碱性热液为最晚期的流体活动，亮晶方解石捕获的原生流体包裹体均一温度峰值为140~160 ℃，盐度为8.00%~16.34%，方解石δ13C明显偏负(-7.1‰~-18.3‰)，为有机来源碳参与的高盐度碱性热流体。前人证实盆地北部砂岩型铀矿具有生物成因特征，与热液活动相悖；结合铀元素迁移特征，认为热液活动与微生物还原作用并不矛盾，碱性热液改变了矿区砂岩流体的物理化学环境，稳定络合物的形成对铀元素具有萃取再富集作用；热液活动是富矿流体形成的关键事件，微生物活动在热液活动停止后直接参与铀还原成矿。

关键词: 流体作用, 碱性热液, 砂岩型铀矿, 鄂尔多斯盆地

Abstract:

Uraniumbearing sandstone diagenesis is a complicated process in the Middle Jurassic Zhiluo Formation, north of Ordos Basin, and mineralization is inconsistent with typical interlayer redox model. On the basis of the study of diagenetic minerals, stable isotope composition (δ13C and δ18O) of calcite cements and fluid inclusions in Hangjinqi uranium deposit, north of Ordos Basin, we discussed the features of fluid activities and the process of uranium mineralization. The result shows that three fluid types were identified in the uraniumbearing sandstone: oxidizing meteoric water, acidic fluid generated by biodegradation of hydrocarbon, and alkaline hydrothermal fluid. The peak homogenization temperatures of primary aqueous inclusions trapped in sparry calcite are 140160 ℃, with the salinities ranging from 8.00% to 16.34%. The sparry calcite in sandstone has negative values of δ13C between -7.1‰ to -18.3‰(PDB). These data indicate that hightemperature, highsalinity and hydrocarbon related fluid occurred at the late stage of fluid evolution history. Previous studies have proved bacterial activity caused the uranium reduction in Zhiluo Formation sandstonehosted deposit, north of Ordos basin. However, such bacterial activity cannot occur in the hightemperature environment. Considering the uranium mobility characteristics in groundwater, we concluded that hydrothermal fluid activity was not contradictory with the microbial reduction of uranium. Hightemperature alkaline fluid changed the physicochemical condition of fluid environment, which facilitated the formation of stable CaU(VI)CO3 complex, enriching the concentration of soluble uranium in solution. Bacteria exerted the reduction of the uranium after the hydrothermal fluidrock interaction.

Key words: fluid rock interaction, alkaline hydrothermal fluid, sandstonetype uranium deposit, Ordos Basin

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