REE Geochemistry And Its Geological Implications Of Minerals From The Muli Antimony Deposits,Southeastern Yunnan,China

The Muli antimony deposit is located in the Au-Sb polymetallic metallogenic belt in southeastern Yunnan Province,China,belongs to a large ore deposit,the Pojiao(D₁p)formation acts as the main ore-hosting strata and is composed of silexite.The Muli ore section is characterized by a mineral symbiotic association of stibnite,pyrite and quartz,the Nadan ore section is mainly composed of a stibnite and calcite symbiotic association.In this paper,the rare earth elements(REEs),Fe,Mn and other major elements of minerals in Muli antimony deposit are analysed,combined with Field Emission Scanning Electron Microscope(FE-SEM),Focused Ion Beam(FIB),Transmission Electron Microscopy(TEM)and Electron Probe Micro Analyzer,the enrichment regularity of REEs in this deposit and the genetic mechanism and indicative significance of the medium-heavy rare earth element(M-HREE)enriched calcite have been studied in this paper.The analysis of trace elements shows that:in the Muli ore section,quartz and pyrite in the metallogenic period show enrichment with light rare earth element(LREE),the wall rock shows LREE enrichment similar to quartz and pyrite in ore-forming period,the REE distribution of quartz and calcite in the late ore-forming stage appeared the"W"shaped tetrad effect,the calcite in the post-metallogenic shows LREE enriched.There is a typical medium-heavy rare earth element(M-HREE)enrichment type in calcite during the ore-forming period in the Nadan ore section.The characteristics of REE indicate that the early stage of ore formation in Muli ore section may be related to the formation of meteoric leaching of surrounding rock strata,while the late stage may have the participation of fluids from hidden magmatic rocks.The ore-forming fluids in the Nadan ore section are mainly derived from concealed magmatic rocks.Fe and Mn element analysis feature display that the content of the Fe and Mn elements of the calcite in the ore-forming period is obviously higher than that of the calcite after the ore-forming period,and the correlation between the content of the LREE/HREE and the Fe and Mn elements shows that the REE fractionation of the calcite has a certain correlation with the content of the Fe and Mn.Eu and Ce anomalies of different types of minerals indicate that the temperature and fo₂ are constantly changing during mineralization,and the temperature of the main ore-stage is more than 200? in an oxidized state.Based on the microanalysis of Fe,Mn phase in M-HREE enriched calcite,it is found that Fe,Mn mainly occurs in the Fe,Mn dolomite crystallites inside calcite crystals.The fractionation of REE may be related to the Fe,Mn dolomite crystallite.It is believed that M-HREE enriched calcite is probably an important record of the hydrothermal fluids evolved from concealed magmatic rocks,which is of great significance to the study of the genesis of Au,Sb deposits in the large-scale low-temperature epithermal metallogenic domain in southwest China.