Geochemical Characteristics And Metallogenic Mechanism Of Lujing Uranium Ore Field,Se-Hunan,China

Based on the investigation of the regional geological background,the geological characteristics of the ore field and the geological characteristics of the deposit,this paper makes a systematic study on the mineralogy,petrochemistry,chronology,wall rock alteration and the metallogenic mechanism of the typical uranium deposits in Lujing uranium field.The main achievements and understandings are as follows:1.The granite in Lujing uranium orefield is characterized by high silicon,rich alkali,rich potassium,potassium content higher than sodium content,peraluminous and low Ti,Fe,Mg geochemistry,which belongs to typical S-type granite.The rocks show obvious enrichment of Rb,U and Pb,slight enrichment of Th,Nd,Zr,Hf and Sm,obvious depletion of Ba,Sr,Eu and Ti,and slight depletion of Ta,Nb,Ce and P.At the same time,they have higher w(Rb)/w(Sr),w(Rb)/w(Nb)ratio and lower w(Nb)/w(Ta)and w(Zr)/w(Hf)ratio,indicating that the granites are from continental crust with higher maturity.The higher U content and the lower Th/U value of these rocks indicate that they all have the ability to provide sufficient uranium source for uranium mineralization.2.The U-Pb isotopic chronology of SIMS zircon shows that the age distribution of the small bodies in Lujing area and its surrounding areas is between 117 Ma and 155 Ma,all formed in the middle and late Yanshan.3.Uranium elements in ores and mineralized rocks are mainly in the form of independent uranium minerals,and then in the form of isomorphism.The main uranium minerals in the ore are pitchblende,uraninite,uranite,pyrite,chalcopyrite,sphalerite,etc.,while the non-metallic minerals are quartz,fluorite,biotite,chlorite,feldspar,zircon,apatite,rutile,etc.4.The main types of hydrothermal alteration are muscovitization,sericitization,illitization,albitization,silicification,pyritization,hematite,fluoritization and carbonation.From the mineralization center to both sides,the horizontal alteration zones of the ore body are pyritization,hematite,limonitization,silicification ? chloritization,illitization,sericitization ? muscovitization,fluoritization,silicification ? albitization,kaolinzation ? fresh granite.5.In the alteration zone,with the increase of U content,the main elements Fe,Ca,Mg are also increasing.The REE and trace element distribution patterns of the samples in the alteration zone are similar,which shows that LREE is relatively enriched in the right direction.Uranium mineralization makes HREE significantly enriched.Trace elements are characterized by enrichment of Rb,U,Nd,Hf,Ta,and depletion of K,Sr,P,Ti,Eu.With the increase of alteration,trace elements tend to be enriched.6.H-O isotopic test shows that the primary fluid in the formation of the deposit is mainly magmatic water,and atmospheric water is added in the later stage.The ore-forming temperature and pressure indicate that the deposit is a meso-low temperature shallow mineralization.