Geochemical Characteristics And Genesis Of Pb-Zn Deposit In Xiaohe River Of Northeast Yunnan

Based on previous research,combined with regional geological characteristics,geological background and detailed field geological survey,this paper takes Xiaohe lead-zinc deposit as the research object.Aiming at the basic geological characteristics and mineralization alteration in the mining area,the electronic probe analysis of metal sulfide,geochemical analysis of trace rare earth elements,geochemical research of C-O-S isotopes are carried out to explore the source of ore-forming fluid and ore-forming material,and to analyze the genetic mechanism of ore deposits.The main results and understanding are as follows:?1?The rock types of lead-zinc ore-bearing rocks in Xiaohe River were determined.The ore-bearing strata,such as fine-grained dolomite,sandy fine-grained dolomite,siliceous fine-grained dolomite and siliceous rocks,are divided into three types:contact zone type,fault zone type and fracture zone type according to the ore body's origin and occurrence.Alteration-pyrite-sphalerite,silicification-sphalerite-pyrite-weak lead mineralization,silicification-weak dolomite alteration,the longitudinal upper alteration zone is strictly controlled by fracture and shows the characteristics of upper width and lower narrow.?2?The sphalerite can be divided into two phases in the hydrothermal sulfide stage,and the color of the sphalerite changes from reddish brown to light yellow from morning to night.the early stage of sphalerite was enriched Fe,poor Zn?Ge and Cd,late stage was opposite.The Zn/Cd value of sphalerite is 129?575?mean 238?,indicating that the deposit belongs to the mesothermal hydrothermal deposit.The Cd and Zn in sphalerite are positively correlated,and the Cd is negatively correlated with the Fe,which may indicate that the Cd in the study area is mainly replaced by the hom.?3?The isotopic composition range C-O hydrothermal dolomite and hydrothermal calcite is?¹³C_V-PDB-3.6‰?-1.5‰;?the mean value is-2.56‰;?,?¹⁸O_V-SMOWis 7.7‰?20.1‰;?the mean value is 17.26‰?,indicating that the C?O in the fluid mainly comes from the dissolution of the surrounding rock,that is,carbonate rock;the S isotope?34S of metal sulfides is 6.3‰?30.3‰;?the mean value is 22.45‰?,indicating that it is the product of thermal chemical reduction of marine sulfate.C-O-S isotopic characteristics indicate that the ore-forming material of the deposit has shell source characteristics,mainly from metamorphic basement and lamangying formation.?4?According to the results of trace elements,there are mineralized dolomite,siliceous zone dolomite and cataclastic dolomite in the lead-zinc deposit of the River,and the three have similar trace element composition.Rb?Sr?Ba and other large ion oxygen?stone?element content is low;Mn?V?Co?Ni and other iron-friendly elements,the Ni is the most enriched,V?Co?Mn relative losses.There is a weak Ce negative anomaly in the sample,suggesting that the sedimentary diagenesis is in the reduction environment,and the Sr/Cu ratio is all around 5,which reflects that in the late Sinian sedimentary period,the climate of the study area may be between humid and arid.The?REE of rare earths except mudstone is higher,the?REE of rare earths in other surrounding rock is lower,all of them show light rare earth enrichment and heavy rare earth loss,but the differentiation of rare earth elements is different greatly,and there is no good correspondence with the degree of mineralization;several samples with more abnormal rare earth distribution patterns may be jointly affected by hydrothermal action and tectonic movement.?5?Comprehensive studies have shown that the origin of lead-zinc ore in Xiaohe rivers is due to:in the late Indosinian period,the southwestern margin of the Yangtze plate and surrounding land were orogenic events,resulting in a large number of strong thrust nappe structures and erosion folds,causing regional large-scale fluid migration.The deep faults communicate the ore-bearing hydrothermal solution of deep metamorphic basement,which is transported upward along deep faults or secondary faults to the broken zone between laminae groups,reacts with surrounding surrounding rock,and is mixed with brine in the basin containing precipitation and reducing sulfur,resulting in metal mineralization zone and mineralization zone.