Characteristics And Metallogenic Significance Of Alteration In Shazhou Uranium Deposit,Xiangshan Ore-field

The alteration of Shazhou deposit in Xiangshan uranium ore field was strong and was widely developed in the deposit.According to the spatial morphology,it can be divided into two types:surface alteration and linear alteration,which is the most obvious prospecting mark.A systematic study of the alteration characteristics of the Shazhou deposit can reveal the migration laws of various element components during thealterationprocess.Understandingthephysicochemicalpropertiesof uranium-bearing hydrothermal solution is great theoretical and practical value for the study of metallogeny and characteristics.On the basis of systematic collection and collation of previous research results,combined with field geological survey results,some typical ore-bearing altered sections were selected from the surface of the Shazhou deposit to the middle section of-98m by the systematic sampling method of crosscut ore bodies.The surface and linear alteration samples with different alteration types and alteration intensities are also selected in the deposit.The samples were systematically classified and treated.From the direction of petrography and geochemistry,the geochemical characteristics of the alteration process of the Shazhou uranium deposit were revealed,and the relationship between various alterations and uranium mineralization was discussed.On this basis,single mineral feldspar was selected from the sample by means of microscope observation,chemical composition analysis,electron probe analysis,inclusion study and so on,So as to infer the law of immigration and emigration of various element components in the process of alteration,Physical and chemical properties of uranium-bearing hydrothermal solution and its significance to mineralization.Through the research,we have gained the following knowledge:?1?The main geological body of the Shazhou uranium deposit is coarse-grained porphyritic granite,Generally speaking,the surface alteration types are albitic,hydromicazation,It is found that the phenocryst mainly occurs in albitic and the matrix is mainly hydromicazation.The most common types of linear alteration are zonal distribution of hematitization,fluoritization,carbonatization,pyritization,and chloritization;albitic in width from a few centimeters to several metres,hematitization in width from a few centimeters to 0.2 metres,chloritization usually takes the form of veinlet,fluoritization usually occurs only on both sides of the ore bearing fissure.The alteration types of large area distribution in the Shazhou area can be used as a sign of mineralization.?2?The study of continuous altered ore bearing section found that:With the deepening of alteration degree,the main element content of Fe₂O₃?CaO?MgO?MnO?P₂O₅?SrO?LOI increased gradually;The content of SiO₂?Al₂O₃?Na₂O?K₂O?TiO₂?Ba O decline gradually;Trace elements increase with the intensity of alteration;An increase in the contents of elements such as Ag?Co?Cs?Cu?Mo?Pb?Sn?Sr?Tb?Th?Tl?U?V?W?Zn?Zr;Reduction of the contents of Ba,Rb and Ta elements;With the deepening of alteration intensity,?REE increases,LREE/HREE and LaN/YbN are reduction,The ore shows an obvious negative Eu anomaly.?3?The study of feldspar alteration shows that:The composition of phenocryst feldspar and matrix feldspar is different from surrounding rock to ore.With the increase of the degree of alteration,the molar ratio of each element M?phenocryst/matrix?is also increasing.K₂O in phenocryst feldspar and matrix feldspar has a negative correlation with Na₂O content,The content of potassium in rock decreases during the occurrence of sodium metasomatism,and the content of Na in rock decreases during potassium metasomatism.In the process of potassium,the U moves out,emigration and enrichment of U during sodium process,and the content of U is higher in the matrix.U immigrates from the phenocryst into hydrothermal solution with the process of alteration,and finally accumulates gradually in the ore;The value of the?REE of the phenocryst feldspar is less than that of the matrix feldspar,As the degree of alteration increases,the value of the?REE increases,The difference of LREE between phenocryst feldspar and matrix feldspar.The content of LREE in matrix feldspar is higher.Rare earth elements are more enriched in matrix feldspar.?4?Discussion on the significance of mineralization:Surface alteration usually occurs in the early metallogenic stage,mainly alkaline hydrothermal alteration,that is alkali metasomatism.The initial hydrothermal properties are alkaline and Na⁺is more than K⁺.Due to the influence of early hydrothermal solution,U in the original rock became active,and some structural fracture zones were transformed into areas with metallogenic potential;Linear alteration occurred in the main metallogenic period.The hydrothermal properties changed from alkaline to acidity,and K⁺was more than Na⁺in hydrothermal composition.At this moment,U begins to adsorb and enrich the ore at the site of linear alteration.