Isotope Geochemistry And Metallogenic Model Of Sandaowanzi Gold Deposit And Beidagou Gold Deposit, Heilongjiang Province

Sandaowanzi gold deposit,located in Heilongjiang Province,is the first telluride-gold epithermal deposit in China,and gold mainly occurs in the telluride with a meximum grade of 20,000 g/t.Beidagou deposit,located 5 km to the north of Sandaowanzi deposit,is found by geochemical survey in recent years.So far,the research about the source and evolution of ore-forming fluid and ore-forming material,and genesis in Sandaowanzi deposit is not systematic and insightful.Furthermore,the basic research of Beidagou deposit,for example the mineral assemblage,is very deficient.This paper is designed to analyse the source and evolution of ore-forming fluid and ore-forming material and discuss the genesis of Sandaowanzi and Beidagou deposit by minerallogy and isotope geochemistry method.In addition,the similarities and differences of the above-mentioned deposits are compared comprehensively.The results are as follows:1.The?¹⁸D and?¹⁸O_H2O of Sandaowanzi and Beidagou deposit in the diagram drop near the atmospheric water line,indecate that the atmospheric water is the most important source in the ore-forming fluid.We compare the oxygen isotope of the quartz and calcite which belong to the metallogenic stage and late metallogenic stage respectively with reservoir's oxygen isotope,the result shows that every stage of ore-forming fluid is controlled by atmospheric water.2.The?¹³C_PDB of Sandaowanzi deposit has a very narrow range,and the range is same with mantle,indicates that the carbon of late ore-forming fluid is derived from the mantle.S isotope of pyrite and chalcopyrite which belong to early metallogenic stage and main metallogenic stage and pyrite in Beidagou deposit exhibit smaller positive values and negative values,this characteristic explains that the sulphur of ore-forming fluid comes from mantle.The result of Pb isotope shows that,the lead of monzonitic granite was derived from the earth crust,the trachyandesite and dacite which are the wall rock of Sandaowanzi and Beidagou deposit and ore body come from the mixture of crust and mantle,and the mantle materials occupies a large part,wall rock also provides some ore-forming materials.The lead of granodiorite was derived from the mantle.In conclusion,ore-forming material of Sandaowanzi and Beidagou deposit comes from mantle and crust,and mantle has high proportion.3.Cu isotope of Sandaowanzi deposit was tested in this paper,the result shows that?⁶⁵Cu ranges from-0.06 to 0.86‰,?⁶⁵Cu of chalcopyrite has a very narrow range,the chalcopyrite has the same source.But?⁶⁵Cu of monzonitic granite and trachyandesite is different from the chalcopyrite,and their source was different.The data of this paper enriches the?⁶⁵Cu values of hydrithermal vein deposits.The copper isotope of chalcopyrite shows vertical zonation because of fractionation during magmatic evolutuion process.4.The age of monzonitic granite and trachyandesite is 177.2±1.8Ma and 121.7±1.4Ma respectively,and is the same as other researchers'results.The age of dacite and granodiorite is tested for the first time,the results are 122.0±1.1Ma and 118.7±1.1Ma,respectively.According to the age and space distribution and intercalated relationship of all the geological body,we can confirm that the metallogenic age of Sandaowanzi and Beidagou deposit ranges from 115Ma to 122Ma,and granodiorite has a close relationship with metallogenesis.5.Under the influence of plate subduction,this district was in extensional setting,and large scale valcanic activities happened.Massive mantle fluid which carried tellurium,gold,silver,copper upwell to earth's surface along structural fissures,meteoric water mixed in the ore-forming fluid.Fluid boiling and hydrothermal alteration lead to a series of chemical reaction.Finally,fluid materials such as gold,silver and tellurium precipitate.