The Ore-Forming Geochemical Mechanism Of The Zhaoiikou Epithermal Pb-Zn Ore Deposit,Anhui Province

Geochemical exploration has been playing a very important role in the field of mineral resouces prospecting and evaluation.At present,the mining industry has a clear demand that the study of geochemical exploration should return to the focus of the basic theory.The multi-dimesional anomaly system(MAS)is one of Chinese respondences in this regarding.MAS means that anomalies of many attributes which formed in different ways during a specific ore-forming period co-exist sequentienlly in space and indicate the ore bodies/deposits progressively.The spacial structure and formation processes of multi-attribute anomaly in MAS are the foundation to study ore-forming geochemical mchenism and prospect new ore bodies/deposits.Meanwhile,it is also the cutting edge of exploration geochemistry.In this dissertation,we selected the Zhaojikou epithermal Pb-Zn ore deposit,Anhui Province,as the object of study.First of all,the method of mass-transfer balance was used to study the elemental mobilities in the ore-forming process,to construct an ore-forming anomaly model,and to reveal the ore-forming geochemical mechanism.Then,the distributions of elements of interest in different levels were visullized to show the ore prospecting direction in the deep.Finally,fractal model and PCA and factor analysis based on the compositional theory were uesd to study the distributions,anomalies,and controlling factors of elements of interst in the surface to help the geochemical exploration projects in the periphery of the Zhaojikou District.The results show that the average mass-transfer rate of the ore-forming mass system is a.4%,indicating that the ore-forming system was open,external substances participated in the ore-forming process,and the total mass of the ore-forming system increased.The average mass-transfer rate of Qingbaikou System is a.-18%,indicating that its total mass lost.The average mass-transfer rate of the fracture,ore-body,and Jixin System are a.14%,23%,and 8%,respectively,indicating that the total mass of these three parts gained.As major elements,SiO2,Fe2O3,MgO,CaO,Na2O,and K2O were lost in Qingbaikou System and gained in the ore-body.Lead,Zn,Cu,Au,Ag,Mo(as ore-forming elements,),As,Bi,Sb,Se(as associated elements),and S(as mineralizing agent)were gained increasingly from the walls to ore-body.Barium,Be,Sr,Nb,and P(as lithophile elements)were lost in the Qingbaikou System and gained in the ore-bearing areas and Jixian System.Manganese,Cr,Sc,V,and Ni(as siderophile elements)were gained in the whole ore-forming systems.The REEs were lost in the Qingbaikou System.There are system mass-transfer ? anomaly,negative Na2O anomaly(as major element),positive S anomaly(as mineralizing agent),the correlation of S-Fe-Pb+Zn,and positive Pb,Zn,Cu,Ag,As,and Sb anomalies in the ore-forming sytem of the Zhaojikou Pb-Zn ore deposit.These anomalies show multi-attribute charachteristics.The multi-attribute aomaly charachteristics mean that not only ore-forming elements(e.g.,Pb,Zn,Cu,Ag,As,and Sb),but also mineralzing agents(i.e.,S)and major elements(e.g.,Na2O)are anomalous,emphasizing positive anomaly,negative anomaly,and correlation among differernt elements.The multi-attribute anomaly results in the element migration during ore-forming processes.Considering the REEs,we proposed the ore-forming geochemical mechanism of the Zhaojikou epithermal Pb-Zn ore deposit.The Zhaojikou epithermal Pb-Zn ore deposit was formed by regional metamorphism,structural movement,and fluid activity.The heat resulted from regional metamorphism and/or structural movement reacitived some elements in the strata.These reacitived elements moved for the fractures,and precipitated there.The sequentional co-existence of multi-attibute in space formed the ore-forming anomaly structure model.The known ore-body lies in the center wehre,?,Na2O,S,Pb,Zn,Cu,Ag,As,and Sb anomalies overlap.The negative Na2O anomaly covers the broadest area,overlapping all the ore-bearing areas and Pb,Zn,Cu,Ag,As,and Sb anomalies areas.The correlation of S-Fe-Pb+Zn exists in the S anomaly area.There is little/no ore in the high concentration of FeO area.Lead,Zn,Cu,Ag,As,and Sb anomalies occur in the place of S anomaly area where FeO is low.The mass gained 30%in the ore-bearing zones.According to the ore-forming anomaly structure model,there is possibility to find new ores in the deep along Dongzhi Fault,especially in the foot wall.The multi-attribute anaomaly structure is inherited in the elemental anomalies in the surface.The surficial inheritance of the multi-attribute anomaly structure provides the geochemical exploration project with theoretical bases.The results of fractal,PCA,and FA showed that the distribution of elements of interest in the surface was jointly controlled by the original contents in the rock,weathering,and ore-forming processes.Alumilum oxide,K20,Rb,Ba,TFe2O3,Sr,Na2O,CaO,MgO,Si02 were mainly affected by the original contents and weathering processes.The negative anomalous feature of Na2O,was formed in the ore-forming processes and enhanced by weathering,and is of ore prospecting function.Whereas Pb,Zn,Ag,Cu,Cd,W,Sb,and As were mainly affected by ore-forming processes.Hafnium and Zr were controlled by both weathering and ore-forming processes.Sodium oxide was depleted in both weathering and ore-forming processes.The depletion feature was enhanced by weathering.The distribution of elements of interest in the surface inherited the anomaly features which formed during mineralization and plays as geochemical signals of ore prospecting in the periphery of Zhaojikou District.