Geochronology,Petrogeochemistry And Tectonic Setting Of Mandong Cu-Ni Sulfide Deposit In North Guangxi

The Baotan area in northern Guangxi is located in the southeastern margin of the Yangtze block-the western section of the Jiangnan orogenic belt.The stratified basic ultrabasic intrusive rock is developed in the Sibao Group in the Neoproterozoic Era,and the Cu-Ni sulfide deposit is produced at the bottom of the rock mass with good crystallization differentiation.At present,there is still controversy about the metallogenic epoch,metallogenic model and tectonic setting of the Baotan Cu-Ni sulfide deposit in northern Guangxi.This paper focuses on the rock mass of the ground Disu mine in the Mandong mining area.Through the detailed field survey and core observation,the testing methods of the lithofacies analysis,zircon geochronology,all rock geochemistry and sulphur and sulfur isotopes are used,the metallogenic epoch is determined,crystallization differentiation of ore bearing basic ultrabasic rock is revealed,sulfide detachment is revealed,and metallogenic tectonic background of the rock mass is discussed.The main understanding of this article is as follows:(1)The zircon U-Pb age of the diorite at the top of the Disu ultramafic-mafic-neutral complex rock mass is 857±7Ma,and the metallogenic epoch of the copper nickel sulfide deposit in the Baotan area of Northern Guangxi is the early Neoproterozoic.(2)There is a negative correlation between Al₂O₃,CaO and MgO of the eclogite,pyroxenite and gabbro in the di Su rock body.There is a positive Eu anomaly fo the gabbro(?Eu=1.58).The La/Sm ratio(2.19-4.22) is relatively low and the Mg^# value(Mg^#=72?80) is higher.The simulation results of(Th/Nb)N-(Th/Yb)N of the mantle derived magma and surrounding rock four clastic rocks show that the degree of mixed dyeing is only 10?20%,indicating that the rock mass is exposed to a low degree of contamination of the continental crust.The ?³⁴S value of ore is between 2.3?3.8‰and slightly higher than that of MORB mantle(-1.57 to+0.60‰),indicating the existence of crustal sulfur.The results of rock geochemistry and sulfur isotopes indicate that the contamination of crustal material and the differentiation of magma crystallization are the main factors contributing to the sulphur saturation and the sulfide melting in the Baotan area of Northern Guangxi.(3)The content of PGE in the Disu ore rock mass has a strong loss relative to Ni and Cu,and the content of the PGE content of the disseminated ore is even lower than that of the original mantle,and the content is only 1.17?14.38ppb.The lump ore Cu/Pd is 746?1830×10³,the mineralized pyroxenite and the olivite are 10?294×10³,and the ore free rock is212?376×10³,which is far greater than the original mantle value(6500),Jinchuan(50000)and Lima River(37100).This indicates that there is deep detachment in the primary magma of the Su Su,so it is obviously depleted in PGE.And there is potential for deep buried PGE deposits.(4)The geochemistry of the basic-ultrabasic rock is characterized by enrichment of light rare earth and large ionic stone elements(Rb,Th,U),relatively high field and strong elements(Nb,Ta,Ti),and relatively high Th/Yb ratio(1.9?2.4).In the Nb/Yb-Th/Yb diagram,the input points are obviously deviated from the MORB-OIB evolution line,suggesting that the source area is bright.The influence of subduction component shows that the Cu-Ni sulfide deposit in Baotan area,Northern Guangxi is formed in the subduction environment.