The Study On Geological Characteristics And Metallogeny Of Jiling Sodium-metasomatic Uranium Deposit In Longshou Mountain Metallogenic Belt In Gansu Province

Gansu Longshou mountain metallogenic belt is an important Uranium metallogenic belt in Northwest China.There are 5 uranium deposits as follow: Hongshiquan pegmatitic granite type Uranium deposit,Geminggou granite outer contacting zone type uranium deposit,Jinbiansi leaching type uranium deposit,Xinshuijing and Jiling sodic-metasomatism type uranium deposits.Jiling Uranium deposit is one of the infrequent sodic-metasomatism type uranium deposits in China,and it is a typical example of alkaline metasomatite type uranium deposit in North China.Jiling uranium deposit is locating in Jiling Uranium metallogenic region in the middle of Longshou mountain metallogenic belt in Gansu province.It is locating in Southwest of North China Plate,there is Hexi Corridor in south and Chaoshui Basin in north of it.The prospecting of Jiling deposit has been started since 60 s in 20^th century,the exploration is insufficient because of uranium theory and prospecting technology at that time.The study on Jiling uranium deposit was in 60 s and 80 s in last century,mainly on geological characteristics,mineralization,metallogenic regularities,ore controlling factors and prospecting directions,and so on.Because of research condition limiting,there was no great progress in recent tens years,though several experts have been concerning it all the time.This research is based on a new round of uranium resources potential evaluation and prospecting in the Longshou mountain metallogenic belt,which is carried by China Nuclear Industry Geological Survey.It is a great honor for me to preside over the project.Basing on data collecting,sorting,digesting,absorbing,and secondary developing,by detailed field investigating and drill logging,accurate testing and reliable analyzing,deeply and comprehensive researching,I have summarized and researched on deposit geology,ore body characteristics,ore characteristics,metallogenic temperature and material sources,metallogenic regularities,and prospecting potential of Jiling deposit and main invasion units which are closely associated with uranium mineralization.The diorite unit?540 Ma?of Jiling rock mass is generated by northward subduction of the ancient Qilian ocean,it has the characteristics of arc background intrusion,such as rich in aluminum,distinct fractionation of LREE and indistinct fractionation of HREE,relatively depleted of Nb,Ta,Ti and so on.After the closing of Qilian ocean,along with the strong compression and collision,the mountain root of orogenic belt goes deeply into the mantle.Under the effecting of gravity and thermal energy,the mountain root delamination makes slumping and extending between different blocks under orogenic belt.Upwelling mantle goes along the weak structure and forms diabasic dike?485 ma?.Under the post-collision background,the lower crust materials remelting to form granitic magma,and magma emplacing forms porphyritic granite unit?455 ma?in Jiling rock mass.Granitic magma differentiation is relatively mature under the stable environment.There comes alkaline rock,albite rock?443 ma?and uranium bearing hydrothermal with rich in sodium and volatile in the later evolution phase.Jiling sodium metasomatic type uranium deposit is located in altered porphyritice granite,which is contact marble of Longshoushan terrain with a fault structure.The ore bodie shapes of the deposit are like a tubular,a lenticular,a long lenticular or an irregular shape,they are arranged like a line of gooses in alternation belt under Malugou fault.The strike of the alternation is 290 ° 310 °,direction southwest with 60 ° 80 ° angle,the lateral extension of ore bodies is like the strike of Malugou fault.The ore is relatively homogeneous low-grade,its structure is veinlet,vein,disseminated and so on,and its main texture is phorphyritic porphyritic structure,broken porphyritic,fine grained.The main ore mineral is pitchblende which is distributing in fractures or mineral cleavages.In addition to potassium metasomatism and mixing metasomatism of potassium and sodium,there are 7 main alternation zones as follow,from centre to outer of the ore body,vein chloriti zation zone,flake chlorite and pink vein carbonatization zone,snowflake carbonatization zone,hematitization zone,sodium feldspathizationzone,silicification zone,kaolinzation zone,etc.Sodium metasomatic alteration process of porphyritic granite is silicon discharging effect,and is sodium replacing potassium,calcium elimination,reddening,accessory mineral reducing effects too.Compare with normal porphyritic granite,the ?LREE of altered granite is reduced slightly and the ?HREE is increased significantly,the trace elements content are relatively less,such as Rb,Ba,Sc,Bi,Sb,the of Nb and Ta,but V,As,Se,Cs,and Ti are relative increase,the contents changing of Ga,Sr,Zr in inner alteration zone are not obvious,but it in outer zone are reduced distinctly.The chlorites in stringer of Jiling sodic-metasomatism type uranium deposits are brunsvigite,the schistose and granulous chlorites are pycnochlorite,and the pseudo-chlorites are prochlorites.Metallogenic fluid contains a large amount of CH₄,H₂,N₂,H₂S and CO₂,consulting the alter chlorites forming temperature and homogenization temperature of fluid inclusions,the metallogenic fluid's temperature is considered to be 280?³00?.When the Uranium is unloaded from metallogenic fluid,Uranyl carbonate complex([UO₂?CO₃?]^4-)is decomposed,a large amount of CO₂ escaping from fluid leads it's temperature decrease to 240?²60?.The ?¹³CV-PDB and ?¹⁸OV-SMOW features of calcite vein in Jiling Uranium deposit suggest metallogenic fluid is granitic magama water which is rich in HCO₃ and originated from lower crust.The constitutions of metallogenic fluid is changed when it flow through the wall rock,it is rebalanced magama water.Sr,Nd,Pb characteristics of porphyritic granite,albite vein,metallogenic fluid and Uranium are from the same initial origin,they are productions of granitic magama differentiation and evolution in different stage,which are from crust rocks about 2 billion years ago,highly remelted in lower crust at early Paleozoicera.The mineralization and prospecting achievement show that the ore bodies of Jiling sodic-metasomatism type uranium deposit are controlled by the TRINITY of fault structure,lithological interface and sodic-metasomatism altered rock,and albitite vein indicates the hydrothermal activity center.There are great prospecting potentiality in the deep of deposit,southern of fault F105,and mine's periphery ore spots,mineralization spots and abnormal spots and belts.