Fluid Inclusions Evidences For The Mineralization Of The Organic Fluid In The Nanmushu Pb-Zn Deposit, Mayuan, Shaanxi, China

Most of the MVT lead-zinc deposits in world are inseparable from organic matter.The lead-zinc deposits in the Ma Yuan area belong to the MVT-type lead-zinc deposit,and a large amount of asphalt is present in the ore deposit.The inclusions in the sphalerite are rich in organic matter.The origin of organic matter in the deposit and the role of organic matter in the process of mineralization play the role of actors in recent years to become the focus of geological scholars.On the basis of clarifying the geological characteristics and metallogenic stage of the deposit,the paper studies the inclusions of the system,analyzes the characteristics of the ore-forming fluid,tries to explain how the organic matter participates in the metal mineralization process from the perspective of mineral inclusions,and obtains the following understanding:The Nanmushu lead-zinc deposit is located in the northern margin of the Sichuan Basin,and the tectonic location is in the range of regional oil and gas reservoirs,and there is a certain degree of superposition in the space,and the ore-forming age of the deposit is similar to that of the first phase,Both show a strong correlation.The main ore-controlling structure of the deposit is the monument dam dome,which is not affected by the magmatic activity.The lead-zinc ore body is produced in the Sinian Dengying Formation,and the brecciated dolomite in the formation is the main ore-bearing rock,so the brecciated ore is the main ore type of the ore deposit.Affected by the formation,ore body mostly layered,like layered.The ore-forming period is divided into sedimentary period,hydrothermal period,oxidation period and hydrothermal period.It is divided into asphalt-dolomite stage,sphalerite-galena-barite stage?main metal metallogenic stage?,late asphalt stage.Mineral minerals are mainly sphalerite,galena and a small amount of pyrite,gangue minerals are mainly dolomite,barite,quartz,natural asphalt and calcite.In the main metallogenic stage,asphalt and metal minerals can be seen in close symbiotic,and in this stage there are a large number of organic inclusions and inorganic inclusions,the two are closely symbiotic,the morphology is mainly negative crystal type,micro-temperature display Its uniform temperature is also a small difference.Among them,inorganic inclusions mainly H₂O inclusions,organic inclusions often contain hydrocarbon-H₂O inclusions,hydrocarbon inclusions two types.According to the analysis of single inclusions laser Raman,organic inclusions contain:CH4,C2H6,H2S,CO2 and so on.Organic inclusions appear in the main metal metallogenic stage,showing that organic matter and metal mineralization are closely related.The temperature range of ore-forming fluids is 110?²50?,and the salinity is between 3¹6 wt%NaCl.And the ore-forming fluid density is 0.89¹.02g/cm³,lead-zinc mineralization pressure in the range of 12.5³3.4MPa,which estimates the mineralization depth of 371.1¹264.3m.These results indicate that the ore-forming fluids of the Nanmushu lead-zinc deposit belong to the medium-low temperature,medium and low salinity and high density fluid.The fluid system belongs to the NaCl-H₂O system in general,and has similar characteristics with the typical MVT type lead-zinc deposit,Ore-forming fluids may be in shallow mineralization.The hydrothermal isotopic study shows that the mineralization hydrothermal fluid has the characteristics of mixing water with seawater,while the helium and argon isotopic studies show that the ore-forming fluid properties are between atmospheric saturated water and crustal fluid.Mixed fluid;and inclusions contained methane,hydrogen sulfide,organic carbon isotopes show that organic matter may come from ancient reservoirs,can determine the ore-forming fluid is a strong reducing fluid mixture;In summary,that Phoebe lead Zinc Deposits The ore-forming fluids are not composed of a single fluid and are a mixture of fluids of different natures,including basin brine and organic fluids.The basal rock system has a very high abundance of lead and zinc metal elements,and the basins from the Sinian sedimentary strata are infiltrated into the basal rock and the metal ions such as lead and zinc are extracted to form a fluid rich in metal complexes.The movement not only accelerates the metal-rich fluid along the fissures,the fracture moves upwards,and the heat it provides also increases the temperature of the basin.The first stage of the reservoir is thermally cracked due to the rising temperature,The Cambrian marine sulphate undergoes a TSR reaction that evolves to form an organic fluid rich in H₂S and other gases,accompanied by the formation of the first stage of the asphalt;when the lead-zinc basin brine meets the organic fluid in the lamellar breccia and mixes,Lead-zinc metal ions in the mixed fluid react with the H₂S precipitation,the formation of lead-zinc deposit.