Geochemical Characteristics Of Sphalerite And Zn Isotope Study In Tongkeng Tin Polymetallic Deposit,Dachang,Guangxi

The Tongkeng tin polymetallic deposit is a super-large deposit with the most typical ore-forming characteristics in the Dachang ore field in Guangxi.It is also the main object of the previous research on the large-scale tin mine,especially the cause of controversy.On the basis of the predecessors,this paper systematically carried out trace elements of sphalerite in different types(upper tin polymetallic ore,deep zinc-copper ore)and different occurrences ore bodies(like layered,vein-like),ore rare earth element,Zn isotope study.The study further explored the source of ore-forming fluids and the genesis of the ore deposits in the area,and achieved the following results and understanding:(1)The trace element characteristics of sphalerite show that whether it is the upper tin polymetallic ore or the deep zinc-copper ore,the sphalerite is rich in Cd,Mn and Ni,but the sphalerite in the tin polymetallic ore is rich in In.?Sn?Ga,lean Cu,zinc ore in the deep zinc-copper ore body rich in Cu?Co?In?Sn indicating that there are some differences in the trace elements of the sphalerite.Compared with the typical types of typical deposits in South China,it is found that the ore-forming materials of tin polymetallics may have both the initial enrichment of early submarine jets and the superposition transformation of magmatic hydrothermal fluids in late Yanshan period,while the mineralization of zinc-copper deposits mainly comes from magmatic hydrothermal fluid.(2)Comparing the rare earth characteristics of the upper tin polymetallic ore,deep zinc-copper ore and the dragon box cover rock mass in Tongkeng,it can be seen that the rare earth distribution curves of the three have similarities and differences,and all three are"V"Type,but the ore sample has a more obvious Ce loss than the rock mass,while the rock sample has a significant loss of Eu,indicating that the ore forming material in the area is related to the rock mass but not entirely from the rock mass.In addition,the Y/Ho value of the ore rare earth is 28.3-38.8,which is higher than the Y/Ho value of the rock box cover rock mass(average 27.8),which falls into the range of modern seabed hydrothermal fluid(25?50),indicating that the ore-forming materials in the area are not only From magma,there may be early involvement of the Devonian submarine hydrothermal fluid.(3)The S isotope thermodynamic calculation shows that the S isotope of the sulfide in the layered tin polymetallic ore body in the upper part of the Tongkeng does not reach equilibrium,generally has a large negative value,and the variation range is large,indicating that the source of S is diverse,and it is the mixture of sulfur from strata and magma;The S isotope of the sulfide in the veined tin polymetallic ore has reached the fractional equilibrium,and the ore-forming fluid ?34?s/‰ is calculated as-10.2?0.2,indicating that the source of S is stable,indicating that the source of S is mainly mixed,and some formation sulfur is magma.The S isotope of sulfide in the deep zinc-copper ore body is balanced,and the ore-forming fluid ?34S?s/‰ is-0.8?4.7,which indicates that the source of deep zinc-copper ore S is mainly magma sulfur,mixed with a small amount of formation sulfur.(4)Zn isotope data indicate that the Zn isotope values of different types of ore bodies(tin polymetallic ore,zinc-copper ore)and different colors(brown black,black)and different occurrences(vein,layered)are basically consistent within the error range,?66Zn‰=0.22?0.34,??66Zn‰?0.10,indicating that the Zn isotope in the region may have the same source,and the fluid is stable during the migration and precipitation in the hydrothermal system,making sphalerite grew up in a relatively balanced Zn isotope in the system.The fluid Zn isotope composition calculated from sulfides is 0.42?0.54‰,which is basically consistent with the Longxianggai Rock Mass(0.41?0.55‰).The magma in the indicated area provides the main source of Zn in the sulfide.(5)The comprehensive research shows that the metallogenic material source of the tin polymetallic deposits in Tongkeng deposit is more complicated than that of deep zinc-copper ore.However,the main body of ore-forming materials from tin polymetallic or zinc-copper ore comes from magma.The initial enrichment of the Devonian submarine jet deposition may occur during the formation of the Tongkeng tin polymetallic deposit,but the main body of the ore-forming is related to the superimposition of the Cretaceous magmatic hydrothermal.