| Taking Xiazhuang uranium ore field as the research object,it analyzes the characteristics of alkaline and acidic altered uranium deposits,including uranium deposits of siliceous vein type,intersection point type,alkaline metasomatic type,cataclastic altered rock type and granite out belt type,summarizes the uranium mineralization distribution characteristics,mineralization differences and ore controlling factors of different uranium deposit,establish the metallogenic model of typical uranium deposit,and identify the prospecting indicator of different uranium deposits.The structure and hydrothermal activity are intensive in Xiazhuang uranium ore field with alkaline alterations in early stage and acidic alterations in late stage,including sodium metasomatism,potassium metasomatism,sericitization,chloritization,silicification,hematitization,pyritization,calcilization,fluoritization,kaolinization etc..Through contrast the ore field alterations can be divided into two phases,alkali alteration in early phase and acidic alteration in late phase.Early alkaline alterations developed in Shituling and Zhushangxia deposits with tourmaline-sericite-uraninite of high temperature alteration in Shituling deposit,and albite-hematite-pitchblende of high temperature alteration in Zhushanxia deposit,and the uranium mineralization is mainly hosted in the contact zone early of Maofeng pluton and Xiazhuang granite controlled by E-W extrusion belt;Late acidic alterations is wide ranging mainly developed in Hope,Xianshi and Xiazhuang deposit with mineral assemblages of microcrystalline quartz-pyrite-pitchblende and purple fluorite-pitchblende in Hope deposit,red siliceous veins-pitchblende and red calcite-pitchblende in Xianshi and Xiazhuang deposit,and the uranium mineralization is mainly hosted in Xiazhuang granite,Maofeng pluton and diabase controlled by the intersection of NE structure and NWW diabase.There are three uranium metallogenic phases in Xiahuang uranium ore field,in which the former two are main mineralization stages,and the third phase is the reconstruction stage of early ore body by late hydrothermal.The first phase is presented by the Shituling and Zhushanxia deposits developed of alkaline alterations controlled by E-W structure,mainly existing in the ductile alteration zone,with uranium metallogenic age of about 138Ma;the second phase is representative by Hope,Xiazhuang,and Zhaixia deposits,developed of acidic alterations controlled by the NE trending extensional tectonic,with metallogenic age of 81~96.4Ma;The third phase is the period of hydrothermal activity due to the activity of North-East ore bearing structure,taking Hope deposit as an example,with the uranium metallogenic age of 61 Ma.The author systematically research on the fluid inclusions of associated minerals in different type of uranium deposit.The results indicated that the metallogenic fluid in different deposit of this ore field has the similar gas phase composition of H2 O,rich CO2?H2,with a small amount of CO and CH4.The fluid has a similar source with strong reducibility,coming from deep mantle.The first metallogenic phase is developed in Shituling and Zhushanxia uranium deposit with high metallogenic temperature of(200? to 330?),high salinity in inclusions bearing daughter mineral up to 40%.The second metallogenic phase developing in Hope,Zhaixia,Xianshi deposit,the metallogenic fluids are similar,and the homogenization temperature and sality are respectively 130?~ 140?,1.57%~4.03% and 270~290?,5.26% to 7.45%;The metallogenic fluid salinity of intersection type uranium deposits-Xia Zhuang and Xianshi are 130~140?,0.58%~4.03% and 270~290?,6.59% ~ 9.21%,with metallogenic mechanism of the mixing of deep fluid and Atmospheric precipitation.At the same time,REE and C,H,O isotopes also indicate that the ore-forming fluids are also from mixed fluids of different source.Through the study of the regional tectonic background,uranium mineralization stages,controlling factors of different uranium deposits and uranium metallogenic mechanism,it establish comprehensive uranium metallogenic model of Xiazhuang ore field,and indicate that the uranium mineralization in the deep is mainly controlled by structure,and tectonic decompression and mixing of mantle fluid with atmospheric precipitation are two main mechanisms for uranium deposit.The deposit developed in ductile shear zone is early,with deep and strong alkali alterations,which is the key parts for deep prospecting;Late uranium mineralization is mainly controlled by the north-east structures,and the uranium ore body are mainly distributed along NE trending,existing in the silicified fracture zone and its secondary structure,in which the uranium minerals coexist with microcrystalline,quartz,hematite,purple black fluorite and red calcite with frequent tectonic activity,long period of uranium mineralization and complex components.Late stage hydrothermal structure activity has a destructive effect on the preservation of ore body,causing the activation of ore bodies,forming late uranium veins and at the same time leading ore dilution.In conclusion,The metallogenic mechanism of different types of uranium deposits in the Xiazhuang Orefield is consistent.Uranium mineralization is a multistage process.The Ore-forming fluid is mixing of mantle source and atmospheric precipitation,with the ore-forming fluid evolving from alkaline to acid,uranium source from uranium rich rock,and mineralization agent from mantle.The location of uranium ore bodies is controlled by virous factors,such as structural properties,surrounding rocks and fluid activities in the later stage of ore deposits.Different types of uranium deposits are the result of unloading minerals in a certain stage under the abrupt change of physical and chemical properties.Early uranium mineralization is medium-high temperature alkaline metasomatic mineralization,and late stage is middle-low temperature acid metasomatic mineralization.Multiple hydrothermal activities may lead to the superimposition of ore bodies,and also may cause reactivation of ore bodies. |
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