Geochemistry Characteristics And Genesis Of Hydrothermal Gold Deposits In West Qinling

West Qinling region is the most important gold and polymetallic metallogenic belt in our country.In addition to part of placer gold and associated gold of copper nickel sulfide deposits,all gold deposit belongs to hydrothermal gold deposit.At present,there were few systematic study about hydrothermal gold deposit in the area.This paper based on the ore deposits,geochemical,late tectonic theory and ecessors geochemical data,according to the carlin and orogenic type gold deposits in different metallogenic belt of west Qnling as guidance,to analyze the geological tectonic hydrothermal gold deposits,metallogenic epoch,metallogenic material source and characteristics of ore-forming fluid in the area,and respectively from the angles of time and space to explore its causes.By collecting and analyzing chronology data of hydrothermal gold deposits in west Q inling,combined with tectonic evolution history in the region,this paper will divide the hydrothermal gold deposits metallogenic epoc h into three stages:gold enrichment stage(250?225Ma),superposition of main ore-forming period(220?170Ma)and the late superposition stage(140?110Ma).To analysis the physical and chemical parameters of the fluid inclusion in quartz,the ore-forming fluid has the characteristics of the low pressure,low temperature and low salinity;To collect and analysis the stable isotope such as H,O,C,S in pyrite and gangue minerals,the hydrothermal gold mineralization fluid in this area generally is a mixture of meteoric water,magmatic water and metamorphic water.The ore forming material is the mixed source of deep material and sedimentary material dominated by carbonate rocks.West Q inling hydrothermal gold deposit ore-forming epochage is long,source of ore-forming fluid and material has the feature of multiple source,cause relatively complex.To conclusion regular:To discuss by space,three metallogenic belt in the area of ore-forming fluid and the source material has the feature of obvious zonality.Songpan metallogenic belt is given priority to with deep magma source,and organic matter in the surrounding rock,the ore-forming hydrothermal thermodynamic driven by deep and structure.South Qinling belt ore-forming fluid of atmospheric precipitation in mineralization,has the feature of mixing source,analogy carlin gold deposit in the United States,formation mechanism and atmospheric precipitation of surrounding rock and leaching effect of regional strata;To discuss by time,the hydrothermal gold mineralization in the area are both long-term and intermittent,cyclicity characteristics,combined with the west Q inling orogenic belt evolution history,west Q inling hydrothermal gold deposits in three metallogenic stages are related to plate subduction and collisio n,collision and subduction depth determines the ore-forming fluid of metamorphic hydrothermal,magmatic hydrothermal and hydrothermal modification to participate in the degree of mineralization.Daqiao gold depsit is a large hydrothermal gold mine in west Q inling area newly discovered,the research work is still in its infancy,has a high potential mineral resources development value.This article through in the ore S and Re-Os isotope testing work,based on the predecessors'primary fluid inclusions and s iliceous breccia,trace element research materials,discussing its metallogenic model hydrothermal gold deposit characteristics in the west Q inling,Dianqiangui and Nevada,in order to the hydrothermal gold deposit in the west Q inling mountain area geological prospecting work to provide theoretical foundation and basis.Daqiao gold deposit in this paper has made the following points:(1)The Re measured pyrite content is 2559ppt to 32905ppt,content of Os are 60.4ppt to 299.5ppt,model 54.3Ma to 74.7Ma age range,the initial ¹⁸⁷Os/¹⁸⁸ Os ratio was1.333±0.069,fitting isochron age of 56±3.3Ma.Daqiao gold deposit mineralization in early stage of Cenozoic,corresponding to the west Q inling Himalayan stage hydrothermal activity stage,its metallogenic by Himalayan period,the west Q inling tectonic activation and Eocene crustal stretching influence;(2)To combined with this paper and previous pyrite mine the delta?³⁴S content between-3.6 to 3.6‰,and mainly concentrated in the near 0‰and 4?10‰two interval,explain the source of sulfur are two:one for mantle source or crust source and formation of mixed material,the other is metamorphic source;Combined with the initial ¹⁸⁷Os/¹⁸⁸Os ratio,the value is greater than the mantle ¹⁸⁷Os/¹⁸⁸Os ratio,between the source mantle source and shell.Indicating mineralization and magmatic emplacement to join a large number of the earth's crust in the process of metallogenic system,the shell source as the main elements involved in mineralization.Daqiao gold deposit is located in the south Q inling metallogenic belt,the belt gold ore-forming fluid is mainly on atmospheric precipitation.Contrast,the gold metallogenic material source and the south Q inling belt and Carlin-type gold deposit of dianqiangui area-the kind of card forest gold sulfur source broadly similar,for the earth's crust and mantle magma mixed with sedimentary strata source;(3)Daqiao gold deposit belong to Carlin-type gold deposit.The early stage of Himalayan movement,intense intracontinental orogeny caused lower crust mantle magmatic intrusion,and the melt carry mantle source material into the earth's crust to form mixed fluid,move up and ore-forming fluid extraction with the argillaceous rocks formation;Since the Eocene,crustal stretch,ore-forming fluid up into lively sex strong formation,with the surrounding rock to mud,the carbonation effect,lead to surrounding rock sulfide;At the end of the day,reducing the ore-forming fluid diluted by atmospheric precipitation,mixing,cooling,gold all to microscopic particles occurrence in the precipitation of pyrite.