Vertical Variation Of Physical And Chemical Conditions Of Ore-Forming Fluids In Maoping Germanium-Rich Lead-Zinc Deposit,Northeastern Yunnan

Maoping germanium-rich lead-zinc deposit is located in the northeastern Yunnan ore concentration area,is one of the famous large-super large lead-zinc deposits.Based on data collection and comprehensive analysis,and on the basis of field geological survey,this paper studies and summarizes the geological characteristics of the deposit.In view of the weak links in the study of physical and chemical conditions of ore-forming fluids and mineral assemblage types in different stages,large-scale fluid mapping and fluid geochemistry studies of typical veins in different middle sections of the mining area are carried out through fluid geochemistry studies.The differences in fluid properties in different middle sections are compared,and the characteristics of ore-forming fluids in different ore sections and their vertical variation laws are summarized.The control mechanism of vertical variation of ore-forming fluid properties in the deposit is revealed.The main achievements and understandings are as follows:（1）The petrographic study of fluid inclusions found that the fluid inclusions in the deposit can be divided into six categories:pure gas inclusions,liquid-rich gas-liquid two-phase inclusions,gas-rich gas-liquid two-phase inclusions,pure liquid inclusions,multi-phase inclusions daughter minerals and three-phase inclusions containing CO₂.（2）The microscopic temperature measurement of fluid inclusions shows that the uniform temperature range of fluid inclusions in the deposit is 120～420°C,with an average of 257.6°C.The peak temperature in the first stage was 290～340°C,with an average of 324°C;the peak temperature in the second stage was 230～298°C,with an average of 253°C;the peak temperature of stage III was 170～250°C,with an average of 193°C;the peak temperature of stage IV is 130-190°C,with an average of167°C.the salinity range was 2.24～25.95 wt.%Na Cleq.,with an average of 11.69wt.%Na Cleq.;the density ranged from 0.68 to 1.05 g/cm³,with an average of 0.913g/cm³.The pressure range is 112.5～606.9×10⁵pa,with an average of 248.5×10⁵pa.The metallogenic depth range is 298～1669.7 m.（3）The stable isotope studies show that theδ¹³C_v-PDB of the deposit is between-5.4‰and-0.2‰,with an average value of-3.5‰,and theδ¹⁸O_v-PDB is between-17.8‰and-9.3‰,with an average value of-11.4‰,indicating that the carbon is mainly derived from marine carbonate rocks,and deep fluid carbon sources are added.TheδD_v-SMOW ranges from-47.7‰to-78.7‰with an average of-65.8‰,and theδ¹⁸O_v-H2O ranges from 4.2‰to 11.6‰with an average of 8.1‰,indicating that the ore-forming fluids are mainly basin fluids and deep fluids.（4）The vertical variation of ore-forming fluid properties shows that from deep to shallow,the uniform temperature gradually decreases,the fluid pressure gradually decreases,the fluid salinity gradually decreases,the fluid density gradually increases,and the distribution range of various physical parameters gradually narrows.The evolution law of ore-forming fluid is high temperature–medium high salinity→medium high temperature–medium salinity→medium temperature–medium low salinity→medium low temperature–low salinity→low temperature–low salinity.（5）Large-scale ore-forming fluid mapping shows that:t The homogenization temperature and pressure of ore-forming fluid in Hexi section of the same middle section are always higher than those in Hedong section;multiple ore bodies have the characteristics of enechelon and equidistant distribution in the vertical direction,and the uniform temperature and pressure of ore-forming fluid in the vertical direction also have this feature.The temperature field of No.I-6 ore body,No.I-10 ore body and No.VI ore body were analyzed,and the metallogenic centers of each ore body were determined.The migration direction of ore-forming fluid is SW-NE along NE structure in the mining area,and SE-NW along interlayer structure and favorable lithology in the same stratum.（6）The controlling mechanism of vertical variation of ore-forming fluid properties and fluid metallogenic model are as follows:the deep medium-high temperature acidic fluid（p H:1.8～3.2）migrates from deep to shallow driven by tectonic dynamics,lead and zinc exist in the form of chloride complexes and extract continuously in large quantities,and the fluid density increases gradually.The deep fluid penetrates along the fault-fold structural belt,and is subjected to decompression boiling（’fault valve’control,fluid pressure decreases suddenly）,resulting in further enrichment of gas-liquid separation.The water-rock interaction increases the p H of the fluid,and the hydrolysis of lead and zinc causes the enrichment of ore-forming materials again,and the fluid density continues to increase.When the circulating reducing fluid in the basin infiltrates into the metallogenic structure,the two types of fluids are mixed and the temperature is reduced,resulting in the precipitation and mineralization of metal sulfides.