Numerical Modeling Of Ore-forming Processes And Three Dimensional Prospectivity Modeling Of The Nanling-Xuancheng Mining District

Mineral exploration of area with thick sedimentary cover sequence is the hot topic in both mineral exploration and prospectivity modeling research.In recent years,new mineral resources such as the Chating large porphyry Cu-Au deposit,the Changshan and the Shuangjing medium-sized skarn Cu-Pb-Zn deposits are discovered in the Nanling-Xuancheng area.In addition,deep margins of the Magushan skarn Cu-Mo deposit and the Qiaomaishan skarn Cu-Wo deposit,two known deposits in this district,are proved prospective.The whole area shows great regional prospective potential and is defined as a new polymetallic mining district in the Middle-Lower Yangtze River Metallogenic Belt(MLYRMB).However,the majority of this area is covered by thick Ouaternary and Cretaceous sediments,with very few outcropping of older rocks.This means field works in this area is very weak.As such,mineral exploration faces a situation where mineralization is hard to recognize and hard to discover,and it’s in desperate need of novel prospecting theory and effective methods.Recently,theories and methods of three-dimensional prospectivity modeling are extensively used in mineral explorations of areas with thick sediments globally.Numerical simulation of ore-forming processes is a computational analysis method combining ore geology,physics,chemisty and computation technology,which is used to simulate ore-forming processes based on finite element method or finite difference method and realize quantitative research of ore-forming processes,quantitative analysis of deposit size,morphology of ore body and distribution of ore grade and the controlling factors and mechanism of them,the duration of ore-forming processes and other questions hard to answer using classic analysis methods.The integration of three dimensional prospectivity modeling and numerical simulation of ore-forming processes could be effective in both theoretical research of ore geology and mineral exploration in area with thick sedimentary cover sequence.This paper collects data of the geological characters of the Nanling-Xuancheng mining district and builds orefield-scale numerical simulation models of the Liqiao-Tongshan and the Xuancheng-Magushan orefields and deposit-scale numerical simulation models of the Chating deposit and the Magushan deposit.This paper also builds two novel workflows for numerical simulation of orefield-scale object based on Flac3 D and numerical simulation of deposit-scale object based on Comsol Multiphysics,respectively.This paper then conducts multi-field coupling numerical simulation on the Liqiao-Tongshan orefield,the Xuancheng-Magushan orefield,the Chating deposit and the Magushan deposit using built workflows in combination with theories of ore geology,especially the metallogenic patterns of porphyry and skarn deposit.Result of numerical simulation of the Chating porphyry deposit shows the distribution of chalcopyrite and temperature match known geological data,which also reveal that the deep margin of the Chating deposit is prospective.Result of numerical simulation of the Magushan skarn deposit shows that the distribution of garnet matches the known Magushan deposit in the southeast limb of the intrusion and the northwest limb also proves to be prospective.On top of that,result of chemical reaction rate implies that the duration of ore-forming processes of the Chating deposit is between 9,600 and 75,000 years,which means the duration of ore-forming processes of porphyry deposit could possibly be less than 100,000 years.This also provides insight into the theoretical research of ore geology.Results of three dimensional numerical simulations of the Liqiao-Tongshan and the Xuancheng-Magushan orefields show that the distribution of the maximum value of volumetric strain increment(VSI)is spatially related with the ore bodies of skarn deposit.25 exploration targets are delineated according to the distribution of VSI,among which 17 are in the Liqiao-Tongshan orefield and 8 are in the Xuancheng-Magushan orefield.Then,targets with high prospective potential are highlighted using regional gravity anomaly data and the result of numerical simulation of the Magushan deposit.In general,this paper combines numerical simulation,three dimensional prospectivity modeling and the classic theory of ore geology and build workflows for numerical simulation of ore-forming processes on multi-scales.Then,this paper conducts researches on the Liqiao-Tongshan and the Xuancheng-Magushan orefields,two orefield-scale objects,and the Chating porphyry deposit and the Magushan skarn deposit,two deposit-scale objects.Results provide insight into the research of ore geology and offer new method for mineral exploration within the Nanling-Xuancheng mining district,which is significant on both theoretical and practical sides.