巴音戈壁盆地塔木素铀矿床成矿作用新认识:热水白云石化-渗出叠加-渗入改造模式

Hydrothermal Dolomitization-exudation Superposition-infiltration Transformation Model for Uranium Metallogenesis of Tamusu Deposit in Bayin Gobi Basin

为了解释巴音戈壁盆地塔木素铀矿床矿体多层性、高品位成因,提炼新的关键控矿要素,重建塔木素铀矿床成矿模式,进而指导矿床外围和深部乃至类似地区铀矿找矿。文章基于因格井凹陷构造演化史、沉积充填史和生排烃史特征,通过塔木素铀矿床构造、建造、蚀变、铀矿化、铀成矿时代分析,详细阐述了矿床矿石矿物、矿石元素地球化学、矿石包裹体特征,确认本铀矿床含矿目的层为下白垩统巴音戈壁组上段,受扇三角洲沉积体系、20%~70%含砂率、20%~60%灰砂率、深切箕状凹陷、断裂、白云石化-渗出还原-渗入氧化蚀变等要素控制;认为铀矿化与同沉积热水白云石化程度呈正比,全岩白云石含量达12%以上,以富含Ca、Fe、P_(2)O_(5),低SiO_(2)含量为特征,并富含Co、Ni、Pb、Zn等深源元素;铀矿床成矿年龄多样,可分为三期,第一期为全岩年龄113.3~109.7 Ma,与沉积成岩期相当;第二期为富矿石沥青铀矿年龄70.9 Ma、69.6 Ma,与油气大规模渗出时间相吻合;第三期为富矿石沥青铀矿年龄45.4 Ma、34.7 Ma和20.6 Ma,与区内挤压快速抬升蚀剥时间相符;建立了塔木素砂岩铀矿床渗出复成因型铀成矿模式,认为在沉积成岩阶段发育与白云石化有关的热液铀成矿作用,形成品位于小于0.05%铀矿化;在80~65 Ma,发育渗出还原叠加铀成矿作用;65 Ma以来,发育渗入氧化铀活化再富集铀成矿作用,形成品位大于0.2%的富矿化。

In order to explain the multi-layer and high-grade genesis of Tamusu uranium deposit in Bayin Gobi Basin,new metallogenic model is need to be studied by extracting key ore-controlling factors and guide the uranium prospecting in the periphery of the deposit and similar areas.Based on the characteristics of tectonic evolution history,sedimentary filling history and hydrocarbon generation and expulsion history in Yingejing sag,this paper expounded the characteristics of ore minerals,ore element geochemistry and ore inclusions in detail by analyzing the structure,construction,alteration,uranium mineralization and uranium mineralization age of Tamusu uranium deposit.The results showed that the ore-bearing target layer is the upper member of Bayingebi Formation of Lower Cretaceous,which was the sediment of fan delta sedimentary system comprised by 20%~70% sand stone,20%~60% lime sandstone and controlled by deep half-graben depression,fracture and the dolomitization-exudation reduction-infiltration oxidation.It was believed that uranium mineralization is proportional to the degree of dolomitization of synsedimentary hot water.The whole rock thickness,the dolomite is over 12%,which is characterized by the high Ca,Fe,P_(2)O_(5),content and low SiO2 content,and rich in deep source elements such as Co,Ni,Pb and Zn.The metallogenic age of uranium deposits is diversity and can be divided into three stages.The first stage was 109.7~113.3 Ma of whole rock,which is equivalent to the sedimentary diagenesis stage.The second stage is 70.9 Ma and 69.6 Ma of the pitchblende in the rich ore,which is consistent with the large-scale oil and gas seepage age.The third stage is 45.4 Ma,34.7 Ma and 20.6 Ma pitchblende from the rich ore,which was consistent with the time of rapid uplift and denudation in the area.A exudative polygenetic uranium metallogenic model of Tamusu sandstone uranium deposit was established.It was concluded that the hydrothermal uranium mineralization related to dolomitization was formed in the sedimentary diagenesis stage and resulted in the uranium mineralization with grade less than 0.05%.In 80~65 Ma,the exudative reduction superimposed uranium mineralization developed.Since 65 Ma,the activation and reaccumulation of uranium by infiltration oxidation developed,forming a rich mineralization with a grade of more than 0.2%.