Study On The Relationship Between Graphite And Uranium Mineralization In Kangding Complex,Datian Area,Panzhihua

Graphite associated with uranium ore has been found in many deposits around the world.For the past few years,extremely high-grade uranium deposits characterized by coarse-grained uraninite have been discovered in the Kangding complex in the south central part of the Kangdian axis.Among them,graphite is closely associated with uranium ore of the Datian uranium-graphite deposit in Panzhihua.Multiple uranium mineralization or abnormal points have been found in some graphite deposits in the same horizon,indicating that uranium mineralization is closely related to graphite in space as well.Geological background,metallogenic geological characteristics and metallogenic regularity of the Datian uranium-graphite deposit have been thoroughly studied by predecessors,but the relationship between graphite and uranium mineralization has not been systematically studied.Graphite is closely associated with uranium ore of the Datian uranium-graphite deposit in Panzhihua,but there are the following problems:(ⅰ)we are not sure whether graphite plays a role in uranium mineralization;(ⅱ)it is uncertain whether graphite acted as a direct reductant,or reacts with the ore-forming hydrothermal fluid to form reducing gas,that caused uraninite precipitation;(ⅲ)it is also unclear whether interaction between ore-forming hydrothermal solution and graphite have left a proof in the graphite that may be used as a uranium mineralisation indicator.Based on the above scientific problems,we take the Datian uranium-graphite deposit,Zhongba graphite deposit,Sandawan graphite deposit and Lazishao graphite occurrence,hosting in Kangding complex,are selected as the research objects,with the geochemical behavior and paragenesis-separation mechanism of uranium and carbon in the whole process of metamorphism as the main line,and the mineral geochemical characteristics and genesis of graphite and uraninite as the core,deeply studied the relationship between graphite and uranium mineralization.The main innovative understanding and results are as following:(1)The petrology,rock geochemistry and carbon isotope of carbonaceous slate,graphite-bearing phyllite,graphite-bearing schist,graphite-bearing gneiss and graphitebearing migmatite occurring in the same stratum(Kangding group)with low to high degree of metamorphism was systematically studied.The restoration result of protolith shows that the five types of metamorphic rocks of Datian area in Panzhihua belong to the same layer and type of sedimentary clayey rocks rich in carbon and uranium.By studying the variation law of uranium and carbon content in rocks with different metamorphic degrees,the geochemical behavior and paragenesis-separation mechanism of uranium and carbon in the whole process from sedimentation to metamorphism are discussed.In the process of sedimentation,the carbonaceous matter mainly adsorbs uranium.In the process of metamorphism,the carbonaceous matter continuously crystallizes to form graphite,which will desorb uranium.The CH4 produced by migmatization and the consumption and alteration of primary graphite under the action of deep high-temperature hydrothermal solution is an important reductant for uranium mineralization.(2)Based on the petrographic study,the crystal morphology and crystallinity of graphite in rocks with different metamorphic degrees are systematically studied by using Laser Raman Spectroscopy,and the formation temperature of graphite is calculated.Combined with carbon isotope analysis,the origin of graphite in the process of metamorphism are discussed.Four different types of graphite are found in the migmatite associated with uranium mineralization and graphite.It is proposed that these four types of graphite were formed by the consumption and alteration of primary graphite under the migmatization and deep-high temperature hydrothermal solution.(3)The mineralogical and geochemical characteristics of uraninite and its paragenetic minerals are studied by using in-situ microanalysis technology.It is found that there are two stages of uranium mineralization in Datian uranium-graphite deposit.The first stage uranium mineralization is magmatic ore-forming related to migmatization,and the spatial distribution of ore bodies is controlled by ductile shear zones and felsic veins.Uraninite is hosted in felsic vein and coexists with ilmenite,monazite and xenotime.Uraninite is formed by crystallization and differentiation from magma formed by low-level partial melting of gneiss rich in uranium and graphite during migmatization.The second stage uranium mineralization is high-temperature hydrothermal ore-forming,and the spatial distribution of ore bodies is controlled by brittle faults and lithologic interfaces.Compared with the first stage uranium oreforming,the most remarkable difference of the second stage uranium metallogenesis is rich in sulfide,and uraninite is symbiotic with pyrite,pyrrhotite and molybdenite.The second stage uranium ore-forming is that during the transformation of tectonic activity from compression to tension in the later stage of migmatization,S-rich and hightemperature hydrothermal solution from deep crust extracted uranium from gneiss and migmatite,or mixed with magmatic vapour-liquid formed by migmatization,to form S-rich and U-rich ore-forming hydrothermal solution.At the same time,graphite is altered by high-temperature hydrothermal solution to produce reducing gas CH4.The mixing and reduction of hydrothermal solutions with different compositions and properties finally formed uranium ore bodies.The second stage uranium ore-forming should be the focus of prospecting and exploration in the future.(4)LA-ICP-MS U-Pb isotope dating method has been used to determine the oreforming ages of two stages of uraninite.The results show that the uranium mineralization age in Datian uranium-graphite deposit is concentrated in841.4±4.0~834.5±4.1 Ma,which is basically consistent with the migmatization age of860~840 Ma obtained by previous studies.Combined with the study of metallogenic geological characteristics and the genesis of uraninite,it is considered that the uraninite,hosting in Kangding complex of Datian area in Panzhihua,is closely related to migmatization caused by Jinningian compression orogeny.(5)The comprehensive study shows that graphite of Datian area in Panzhihua has played an important role in uranium ore-forming.In the sedimentary and diagenetic stage,the adsorption and reduction of uranium by carbonaceous material form carbonous and U-rich rocks,which is the material basis of graphite and uranium mineralization;In the process of metamorphism,carbonaceous material continuously crystallizes to form graphite and desorbs uranium,resulting in the activation,migration and local enrichment of uranium,which is the prelude to uranium ore-forming;Under the migmatization and deep high temperature hydrothermal,reducing gases such as CH4 produced by the consumption and alteration of primary graphite are important reducing agents for second stage uranium mineralization.The research results are helpful to deepen the metallogenic theory of uranium and graphite in the process of metamorphism,and have certain guiding significance for the prospecting and exploration of uranium and graphite deposits in this area.