Geology,Geochemistry And Genesis Of Bachagou Ditch Lead-Zinc Deposit In Oroqen Banner,Inner Mongolia

Bachagou lead-zinc deposit is located in Oroqen Autonomous Region of Inner Mongolia Autonomous Region,located in the northern section of the Great Xing'an Mountains.It is a large-sized lead-zinc deposit in the exploration and mining stage,and a skarn deposit.At present,there are few studies on the genesis of the deposit.Based on field geological survey,laboratory observation and analysis,the geological characteristics and metallogenic conditions of the deposit are summarized,and the genesis of the deposit is included.The main deposits in the region are low-temperature hydrothermal deposits,and there are few skarn deposits.The study of this skarn deposit will help to improve the regional metallogenic law and provide theoretical basis for the exploration,evaluation and mining of similar deposits.The Bachagou lead-zinc deposit is located in the outer contact belt between the volcanic rocks of Manketou'ebo Formation and the granites.It is mainly controlled by NE-trending and NW-trending faults.The wall rocks alteration types are skarnization,carbonation,greisenization,silicification,sericitization,chloritization,kaolinization,and the ore minerals are mainly sphalerite,galena and magnetite.The ore structure is irregular massive,massive,brecciary,sparse-dense disseminated,star-scattered and vein-like.ore structures are of medium-fine grain structure,semi-automorphic-heteromorphic granular structure,metasomatic residual structure,metasomatic structure and emulsion droplet solid melt separation structure.The study shows that the Bachagou biotite monzonitic granite rock mass is the ore-forming rock mass of the deposit.According to zircon U-Pb age,the formation age of the rock mass is 141.15±1.1 Ma which belongs to Late Jurassic.The geochemical study of the biotite monzonitic granite shows that it is A-type granite,formed in the orogenic movement related to the closure of the Okhotsk Ocean and in the stage of"collision with each other".The tectonic background of the transition from segment to post-orogenic stage.By studying the minerals of biotite,amphibole and plagioclase in Bachagou biotite monzogranite,it is shown that the granite was formed in the environment of high temperature,low pressure and high oxygen fugacity,and the biotite monzogranite has the characteristics of crust-mantle mixed source.Sr-Nd isotope studies show low(⁸⁷Sr/⁸⁶Sr)_i values and high?Nd?t?values,suggesting that magma originated from newly accreting crustal material from depleted mantle and is a young lower crust with oceanic crust characteristics.The Nd model ages T_2DM is from 721 Ma to 879 Ma,which is Neoproterozoic.Sr-Nd isotope characteristics show that the magmatic source rocks are crustal materials accreting from depleted mantle in Neoproterozoic.Through stable isotope analysis of C-O and S isotope,the stable isotope analysis shows that the value of the calcite?¹³C_V-PDB is between-3.43‰and-2.77‰,the value of?¹⁸O_V-SMOW is-9.34‰¹0.01‰.Pyrite?³⁴S value is 7.17‰⁷.35‰,the lead?³⁴S value is1.85‰³.39‰,sphalerite?³⁴S value is 5.78‰⁷.17‰.The estimated value of?³⁴S_?S in ore-forming fluids is about 4.42‰,indicating that the ore-forming materials are derived from magma.According to galena-sphalerite thermometer,the metallogenic temperature is estimated between 132?and 315?.The study of fluid inclusions shows that the ore-forming hydrothermal fluid has the characteristics of low temperature and low salinity.The homogenization temperature is160.1?²63.4?,the salinity is 7.44¹2.65?wt%NaCI?,which belongs to low and medium salinity,and the fluid density is 0.86¹.0g/cm³.The calculated ore-forming pressure ranges from 18 to 27 MPa,and the ore-forming depth is 1.8 to 2.7km,which belongs to epithermal deposit.In conclusion,Bachagou lead-zinc deposit was formed in the late Jurassic and is a Skarn type lead-zinc deposit with epithermal characteristics.