The Relationship Between Mineralization And Magmatism In The Muli Antimony Deposit, Southeastern Yunnan, China

The Muli antimony deposit is located at the southwest end of the South China Antimony Belt and is large in scale.The ore body is mainly located in the arc-shaped structural belt sandwiched by the Nawai fault and the Xiaopunong fault.The mineral assemblages are different in different sections of the deposit.The Nadan section is mainly composed of calcite-stibnite type,and the Muli section is dominated by quartz-stibnite-pyrite type.This paper takes the newly discovered diorite in the Muli antimony ore area as a breakthrough and carries out a detailed zircon U-Pb chronology study on it.Methods,the diagenetic and ore-forming age and source of ore-forming fluids of the Muli antimony deposit were studied.The LA-ICP-MS zircon U-Pb dating results show that the diagenetic age of the diorite is 158.5±2.5Ma（MSWD=1.7）,which is within the error range from the previous measured age of the Muli antimony deposit（165Ma）.It is also consistent with the metallogenic age of the antimony deposits in the Yanshanian period in the South China Antimony Belt（160～130Ma）.Correspondinglly,it also matches the large-scale Yanshanian mid-acid magmatic activity in the Cathaysian block,and also consistent with the formation age（160～150Ma）of the W and Sn polymetallic deposits related to the Cathaysian block and granite magma,indicating that the diagenetic age of the diorite is the ore-forming age of the Muli antimony deposit.The Muli antimony deposit and the tungsten-tin mineralization in Cathaysian block have a similar dynamic background,showing the Muli antimony deposit was a product of the early Yanshan Movement.The diorite zircon ¹⁷⁶Hf/¹⁷⁷Hf value is between 0.282600～0.282932,εHf（t）=0.8～2.1,indicating that the magma source area is dominated by newly formed crustal material,which is derived from the young lower crust newly formed from the depleted mantle Partial melting of the substance.The research results of fluid inclusions in the Muli antimony deposit show that gas-liquid two-phase inclusions are mainly developed in quartz and calcite at different metallogenic stages,and the ore-forming fluids are characterized by medium-low temperature（125.2～223.9℃）and low salinity（5.5～11.5wt%）.C-H-O isotope studies show that the fluid source of the metallogenic stage I is mainly magmatic water,and the mineralization stage II and metallogenic stage III are mainly from atmospheric precipitation;the carbon in the metallogenic fluid system is derived from granitic magma.The calcite ⁸⁷Sr/⁸⁶Sr ratio is close to 0.710 during the metallogenic period,showing that it was of crustal origin.By comparing with other typical antimony deposits in the South China Antimony Belt and combining with the above research,it is considered that the Muli antimony deposit belongs to the long-distance post-magmatic antimony deposit.Based on this,the metallogenic model of the deposit is established,which is of great significance to the study on the genesis of the ore deposits in the South China Antimony Belt and the prospecting and exploration.