A Study On The Role Of Ore-forming Fluids In The Granite-type Uranium Deposits In The Yangtze River Area Of Southern Zhuguang

Hydrothermal type uranium deposit is the main industrial type of uranium deposit in China.Granite type uranium deposit is one important type of hydrothermal type uranium deposit.Zhuguangshan uranium ore field is one of the important granite type uranium ore fields in South China.The Changjiang area as an important part of the Zhuguangshan ore fields,In the past,a large number of studies only focused on a single deposit,and the study and comparison of various deposits in the region are insufficient.The study of ore-forming fluid has always been one of the core issues in the study of hydrothermal type uranium deposits.The systematic study of ore-fluid interaction on hydrothermal type uranium deposits in south Zhuguang Changjiang area can perfect and supplement the metallogenic mechanism of uranium deposits in this area.The main uranium deposits in the Changjiang area are distributed in the north-south structures whitch are held hostage by the main structure such as Mianhuakeng,Lizhou,Huuangxishui and Youdong fault.Uranium mineralized minerals are mainly pitchblende,associated metal minerals are pyrite,galena,sphalerite,chalcopyrite,etc.Gangue minerals are mainly quartz,fluorite,illite,calcite,etc.According to the actual mineralization of each uranium deposit,uranium mineralization can be divided into three stages,that is,the early stage of mineralization,the early stage of mineralization and the late stage of mineralization.The early mineralization stage is characterized by red microcrystalline quartz,the main mineralization stage is mainly white microcrystalline quartz or colorless quartz vein and purple fluorite,while the late mineralization stage is accompanied by the development of light fluorite,calcite and comb quartz.The ore-forming fluid in The Mianhuakeng deposit gradually evolved from low salinity(6.15wt%Na Cleqv)and medium-high temperature(308?)Na CL-KCl-Ca SO₄-H₂O system to simple Na Cl-Ca SO₄-H₂O system with low salinity(3.00wt%Na Cleqv)and low temperature(147?)in the late mineralization stage.The early ore-forming fluids were mainly Ca²⁺rich fluids.The composition and properties of ore-forming fluids:the ore-forming fluid system of the uranium deposit in Changpai area(No.1 ore body of The GUSD)in early stage of mineralization is characterized by Na Cl(F)-KCl(F)-Ca SO₄-H₂O with high sulfur and low salinity(10.77wt%Na Cleqv),high density and high temperature(291?).At the later stage of mineralization,it was transformed into low temperature(152?),low salinity(3.9wt%Na Cleqv),high density and low sulfur Na Cl(F)-KCl(F)-Ca SO₄-H₂O system.The ore-forming fluid is relatively rich in Ca²⁺,and oxygen is the main component of the encapsulated gas phase in quartz during the ore-forming period.The ore-forming fluid in Shulouqiu deposit is transformed from low-salinity(5.4wt%Na Cleqv),medium-high temperature(284?)and medium-density fluid in the ore-forming period to low-salinity(189?),low-salinity(4.9wt%Na Cleqv)and high-density fluid in the later period.The fluid in the late ore-forming period of shuishi deposit is characterized by low salinity(3.87wt%Na Cleqv),medium high density and low temperature(157?).The geochemical study of altered rocks shows that the uranium ore-forming fluid is alkaline earth-rich element(Ca O),large ion transition element(Co,Cr,Mo),and ore-forming fluid is rich in heavy rare earth elements(U),volatile elements(F,SO₄^2-),and ore-forming fluid is reductive fluid.The source of ore-forming fluid is magmatic hydrothermal fluid and the characteristics of deep source mantle fluid,is applied to the deep magmatic hydrothermal circulation of groundwater along the tectonic upwelling and rock mass effect of extraction of uranium ore-forming materials production,and in the process of migration and mineralization has been filled by atmospheric precipitation,late stage on the evening of mineralization and metallogenic is gradually increasing the proportion of atmospheric precipitation,and becomes the primary area of illite fluid source.In terms of the evolution of ore-forming fluid,the ore-forming fluid evolved from alkaline and reductive high temperature and high pressure and sulfur fluid containing mantle-derived components to oxidizing and acidic fluid with the characteristics of atmospheric precipitation from early to late mineralization stage and then to late mineralization stage.Under the action of Mesozoic continental hot spots,uranium mineralization in the Changjiang Area is caused by the continuous interaction of fluids from deep crust and mantle with uranium-rich rock mass along the deep faults in the region,enriching U element and gradually unloading uranium ore after mixing with atmospheric precipitation in the shallow part.The deep uranium mineralization in Changjiang No.1 indicates that the area has good metallogenic potential in the deep.