Analysis Of Geological Characteristics And Genetic Mechanism Of Miaoan Gold Deposit In The Northern Section Of Taihang Mountains

Miaoan gold deposit is located in Laiyuan County,Hebei Province,and its geotectonic location is in the north central part of the North China Craton.The deposit is mainly controlled by faults and folds.The ore bodies are in the outer contact zone between the carbonate rocks of the Gaoyuzhuang Formation of the Mesoproterozoic and the Laiyuan complex of the Mesozoic era.Pyrite is the main gold bearing mineral.Combined with field geological exploration and laboratory analysis,this paper comprehensively studies the geological characteristics of miao'an gold deposit,analyzes trace elements of whole rock and pyrite,carbon and oxygen isotopic composition of whole rock and pyrite,sulfur isotope composition of pyrite,discusses the source of ore-forming material and fluid,analyzes the genetic mechanism of the deposit,and establishes the metallogenic model of the deposit.The study of trace elements shows that pyrite and ore are rich in sulfophilic elements,including copper,zinc,cobalt and lead,and lack of HFSE,such as Cu,Zn,Co,Pb,etc.The ratios of Nb/Ta,Zr/HF,Y/Ho varies greatly,instructing that the ore forming hydrothermal system may be superimposed or metasomatized by multiple hydrothermal activities.The Y/Ho ratio of pyrite is between 26.7 and 35.8,which is consistent with the mantle ratio and the continental crust ratio in eastern China.It shows that the ore-forming material source has the characteristics of crust mantle mixed source.The Th/La and Nb/La ratios of pyrite are less than 1,which indicates that the ore forming hydrothermal system of Miaoan gold deposit is mainly rich in Cl.The Co/Ni ratio of pyrite is between 1.50 and 23.4,with an average of 10.9,which is close to volcanic origin,indicating that the pyrite has experienced a medium high temperature medium low temperature mineralization process.LREE are enriched in the whole rock and pyrite,The REE parameters the?Eu values range from 0.180 to 0.900,and the?Ce values range from 0.790 to 1.13,indicating that the ore-forming system is in a relatively reduced physical and chemical environment,and the ore-forming temperature changes greatly.The sulfur isotopic composition of pyrite shows that the?³⁴S value ranges from-5.5‰to+1.6‰,indicating that the ore-forming material is derived from the deep magma of the earth,which is basically consistent with the?³⁴S value of gold and polymetallic deposits in the middle and northern part of Taihang Mountains.According to the analysis of carbon and oxygen isotopic composition,?¹³C_V-PDBvalue ranges from-4.2‰to-1.0‰,?¹⁸O_V-SMOWvalue ranges from 9.3‰to 24.1‰.indicating that the source of ore-forming materials should be related to mantle exhalation or magma,and the ore-forming hydrothermal fluid should be related to the devolatilization or degassing process of magma cooling.Miaoan gold deposit was formed in the late Mesozoic extensional tectonic environment.In the early Cretaceous,Taihang mountain area was in a strong extensional tectonic environment,experienced huge magmatic activities,and accompanied by a large amount of lithosphere delamination,asthenosphere material upwelling,the crust and the mantle interact,the crust mantle mixed hydrothermal solution was formed,and the ore-forming hydrothermal solution in the process of continuous migration produced water rock reaction with the surrounding rock The decrease of gold content leads to the precipitation of gold element and enrichment of ore in favorable structural fractures.