Numerical Simulation Of Metallogenic Process Of Pulang Copper Deposit In Yunnan Province And Its Enlightenment To Mineral Prospecting

In recent years,the demand for copper resources in China’s economic development has been rising.However,the dependence on foreign copper resources has remained high for a long time,which has seriously affected China’s resource security and sustainable development of the economic society.Therefore,it is necessary to strengthen the prospecting and exploration of strategic mineral resources such as copper based on the dometic situation,improving the protection of domestic resources.The giant Pulang copper polymetallic deposit is located in the southern segment of the Yidun arc in the middle segment of the Sanjiang metallogenic belt in southwest China.It is the largest porphyry copper polymetallic deposit formed in indosinian period discovered so far in China.Great achievements have made in geological research and exploration of this deposit.However,the understanding of the metallogenic process and deep prospecting potential of the deposit is still insufficient,and the deep edges of some ore bodies have not been engineering controlling.In consequence,it is of great theoretical and practical significance to consider Pulang copper deposit as the research object to carry out numerical simulation of mineralization process.It is well-known that the numerical simulation of mineralization processes is based on the relevant physical and chemical equations,geological models and numerical simulation models.Then,the Finite Different Method or Finite Element Method are used to simulate the physical and chemical processes,such as rock stress or strain,ore-forming fluid migration,ore-forming material migration,temperature change and heat transfer,and chemical reaction,and further quantitatively analyze the influence of various geological factors on the metallogenic system.In this thesis,firstly,relevant geological exploration and analytical data accumulated by previous studies of Pulang copper deposit are collecting and further sorting out.Secondly,on the basis of geological work such as field geological survey,borehole core cataloging,indoor microscopic identification,the previous research results and existing problems in the mineralization process of Pulang copper deposit are summarized.Finally,the numerical simulation model of this deposit are established after necessary abstraction and simplification,the initial conditions,boundary conditions and thermodynamic parameters of the model are set according to previous research.The numerical simulation software Comsol Multiphysics is used to quantitatively simulate five physical and chemical processes involved in post-magma hydrothermal mineralization,including heat transfer,pressure,fluid-flow,chemical reaction,and material migration.The key factors controlling the formation of the deposit and its enlightenment to the prospecting work are discussed.The main achievements and conclusions of the thesis are as follows:（1）Numerical simulation results show that the hydrothermal convergence and heat conduction are the key factors restricting the complex mineralization process of Pulang copper deposit.Among them,one of the key factors affecting the formation of deposits is the conververgent migration of hydrothermal solution rich in ore-forming elements such as Cu and volatile components.The precipitation and enrichment of chalcopyrite in hydrothermal solution are greatly affected by the change of temperature field and the concentration of Cu ore-forming solution.（2）Combined with the mineralization rate of chalcopyrite obtained by numerical simulation and the average grade of copper ore in Pulang deposit,it is possible to estimate the duration of ore-formation in the study area,suggested that the chalcopyrite within the Pulang deposit was deposited to be approximately 1.51～1.87Ma.This method makes up for the deficiency that isotope chronology can accurately determine the mineralization age but is difficult to describe the duration of mineralization,which provides a new idea for ore geology research.（3）The influence of shape and dip angle of quartz monzonite porphyry on mineralization is analyzed and discussed by using numerical simulation method.Among them,the shape of hypabyssal porphyry body affects the location of Cu enrichment center in hydrothermal solution.The inclination angle of hypabyssal porphyry body affects the location of chalcopyrite precipitation in the process of hydrothermal intrusion,thus further controlling the spatial distribution of copper ore bodies.By fitting the data of the cumulative area of chalcopyrite and the inclution angle of porphyry in the numerical simulation result,it is found that there is a multifractal relationship between them.（4）The uncertainty of metallogenic thermodynamic parameters and initial conditions in the process of numerical simulation is analyzed.The simulation results show that the initial inlet size,initial velocity and initial Cu²⁺concentration of metallogenic hydrothermal solution needs to be controlled in a proper range to be more favorable for the formation of porphyry copper ore bodies,and the thermal expansion coefficient of rock is positively correlated with chalcopyrite enrichment.By fitting the data of fluid inflow size and cumulative area of chalcopyrite,it is found that there is a fractal relationship.（5）Through the numerical simulation of mineralization process,it can be found that on the one hand,this method can not only provide more intuitive“process reproduction”of temperature and pressure changes,hydrothermal migration and metallogenic material precipitation enrichment,and help to improve the understanding of metallogenic mechanism and metallogenic model.On the other hand,basd on the results of this numerical simulation study,it is found that the“multi-factor coupling”part of the lower section of the model can be used to guide deep prospecting work.