Mineralization Age Of Longwei Copper Deposit In Nothwestern Dayaoshan,Guangxi Province

The northwestern Dayaoshan is an important quartz vein copper deposit in Guangxi.Most of them are Quartz vein type copper deposits controlled by SN-trending fault.The Longwei copper mine is selected as the research object.Through field investigation,observation and sample collection,testing,and analysis of quartz veins in the mining area,The crystallization ages of typical chalcopyrite and pyrite were measured by Re-OS isotopic dating method,combined with the characteristics of rocks and minerals,determines the metallogenic age and deposit type of the copper-bearing quartz vein type copper deposit on the northwesten Dayaoshan.The ore of Longwei Copper Mine has a typical metasomatism and fragmentation structure.The pyrite in the deposit mainly exists in the form of metasomatous phenocrysts and fragments.Pyrite was obviously filled with copper-bearing hydrothermal fluid.Fragmentation is common in pyrite,while minerals such as chalcopyrite and quartz that are replaced and filled have no obvious fragmentation.At the same time,the fragmented pyrite has obvious migration and rotation characteristics.It demonstrates that the crystallization of pyrite is obviously earlier than the crystallization of ore-forming hydrothermal fluid and chalcopyrite.The formation of ore has at least experienced several stages of pyrite crystallization →metasomatized pyrite fragmentation → copper-bearing hydrothermal filling and metasomatism → supergene oxidation and alteration.The variation range of Ni/Co in pyrite ores tested in this study was 0 ～ 1.859(unit),with an average of 0.29(unit).The co-Ni distribution of pyrite was mapped and mainly fell into the sedimentary and magmatic genetic classification areas.The content of W(S)/ W(Fe)in pyrite showed that the hydrothermal type was dominant within pyrite,and the addition of sediment was found.Therefore,it is speculated that porphyry pyrite is a complex solution formed by magmatic hydrothermal action in the middle and shallow strata.The average Mo element in chalcopyrite in the study area was 0.65%,lower than the average of 0.933% of pyrite.Most Pb/Zn >,1<Co/Ni<5 in pyrite.Most Pb/Zn in chalcopyrite < 1,Co/Ni > 5.This indicates that chalcopyrite and pyrite are from two different thermal liquid systems,which is consistent with the metasomatic structure characteristics of ores.The formation of metasomatic pyrite is related to magmatism and shallow strata.The crystallization of metallic minerals such as chalcopyrite comes from the metallogenic hydrothermal system whose properties are quite different from those of the previous period.The Re-Os isotopic dating of pyrite shows that the crystallization time of pyrite is 417 ± 25 Ma,and the Re-Os isotopic dating of chalcopyrite shows that the crystallization time of chalcopyrite is 243±18Ma.The Longwei Copper Mine is a reformed superimposed hydrothermal deposit.During the Caledonian magma and hydrothermal process,pyrite crystallized in the SN-hosting fault,which was then broken by brittle structure to form fragmented pyrite plaques.After the formation of the Lower Devonian Lianhuashan Formation,the copper-bearing hydrothermal fluid was poured into the fragmented pyrite faults,and replaced by filling to form a modified superimposed hydrothermal copper deposit.