Geochemical Characteristics And Petrogenesis Of Magmatic Rocks In Mangchang Orefield,Danchi Metallogenic Belt,guangxi

The Manchang ore field is located in the northern part of the Danchi metallogenic belt on the northern margin of the Huanan fold belt in the Pacific Rim tectonic zone.It is located at the southwestern margin of the Jiangnan paleocontinent,and is located at the junction of the Tethys tectonic domain and the Pacific tectonic domain.It is a famous tin polymetallic metallogenic belt.The Manchang tin polymetallic deposit is a large deposit,and the research work of the predecessors in this area is relatively small.The age of the deposit formation(lack of precise years),the evolution of ore-forming fluids,and-the granite batholith with related mineralization.At present,they are not perfect.The degree of research does not match the large scale of the deposit.In order to find out the diagenesis and mineralization mechanism of the deposit and better guide the production,on the basis of detailed field work,the chronology and geochemistry of granite porphyry and fine-grained muscovite granite closely related to the ore body have been detailedly researched in this paper.Different ore-forming stage fluid inclusions were detailedly studied.At the same time,,the diagenesis and mineralization mechanism of the Manchang ore field was discussed by comparing the diagenesis and ore-forming characteristics of the Dachang ore field.Results and understanding are summarized as following:(1)There are two stages of rock mass in the mining area that the formation age of the early fine-grained muscovite granite is 116.1±7.6Maand the age of the late granite porphyry is 88±2.3Ma,both of which belong to the products of late Yanshanian magmatism..(2)Comparison of two stages of rock mass.fine-grained muscovite granite has high SiO2,low TiO2,high differentiation(DI),ACKN(2.78)>1.1,high potassium calc-alkaline series,stronger peraluminous;trace elements have positive Rb,K,U,Ce,Ta,negative anomalies of Ba,Zr,Ti,Nd,low Nb/Ta ratio,high Rb/Sr ratio characteristics;rare earth elements have obvious "M" type four grouping effect,low light and heavy rare earth ratio,strong enthalpy loss,?Eu0.26<(0.4),low(La/Yb)n ratio,low(La/Sm)N ratio characteristics;oxygen fugacity is significantly better Low(fine-grained muscovite Ce4+/Ce3+=4.28;Granite porphyry Ce4+/Ce3+=238.61),which is a more reduced rock mass.All of the above features show that the fine-grained muscovite granite is more characteristic of tin-forming(polymetallic)rock mass.At the same time,Granite porphyry obviously cut ore body,which indicates that it is later formed by mineralization.Therefore,the fine-grained muscovite granite is considered to be ore-forming rock mass.(3)Granite porphyry and fine-grained muscovite granite,the average value of A/CNK aluminum saturation index is greater than 1.1,with strong aluminum characteristics,rittman index is less than 3.0.Two stage rockmass are characterized by S-type granite.(4)According to the mineral combination of this mining area,the mining area is divided into two metallogenic stages:high temperature and high salinity in the early stage of mineralization and medium and low temperature and low salinity in the late stage.The temperature change of the two stages is not large,but the salinity changes greatly,which indicates that the fluids in the early stage to the late stage are mainly mixed.It is speculated that the later stage mineralization process contains a large amount of atmospheric precipitation mixing;The coexistence of C02,CH4 and S02 in the early inclusions shows a relative reduction environment,while that in the late metallogenic stage is C02 and SO2.the:fluid f evolved from a reducing environment to a relative oxidizing environment from the early metallogenic stage to the late stage mineralization stage.(5)By comparing with the Dachang orefield,the rock mass formation in the two mining areas has a similar tectonic setting,which are the extensional background product of the late Yanshanian Combined with the occurrence of strata,exudation and relationship with the rock mass,etc,there may be a period of ore-forming magmatism about 116.1 Ma in the deep depth of Dachang ore filed,and it may be magmatic activity during the tin-polymetallic ore-forming period.