Research On Audio Magnetotelluric Detection Of Zhunuo Porphyry Copper Deposit In Tibet

The Zhunuo porphyry copper deposit is located in Yamu Township,Angren County,Tibet.It is a large-scale porphyry copper deposit in the western section of the Gangdise metallogenic belt with abundant mineral resources.However,due to the harsh natural environment and inconvenient transportation in the mining area,the current level of prospecting and deposit research is still low.In addition,the mining area has experienced complex magmatic activities and weathering and denudation,and lacks reliable deep geophysical data constraints.Therefore,there is considerable controversy over the distribution and extension of ore-forming structures,such as porphyry bodies,fracture zones,and alteration zones in the ground,In exploration and mineralization research.In response to the above problems,this paper carries out inversion modeling of the audio magnetotelluric data covering the Zhunuo mining area,and obtains the underground electrical structure below 1500 meters,so as to provide a more reliable deep geophysical constraint for its exploration and mineralization research.The research content of this paper includes: using Robust estimation,remote reference point processing,and power spectrum editing to perform fine processing on audio magnetotelluric data;performing impedance tensor GB decomposition and phase tensor analysis of audio magnetotelluric data to reveal the research the underground electrical structure of the area has a strong two-dimensionality,and some areas show obvious three-dimensionality.Based on the above analysis results,three sections were selected to perform two-dimensional inversion with topography,and all array data were used to perform three-dimensional inversion to obtain a more detailed electrical structure model underneath the deposit.Finally,combined with other geological structures and geochemistry,drilling data provides comprehensive geological interpretation of electrical models,restricts the underground distribution and extension of porphyry bodies,fractured zones,altered zones and other structures closely related to mineralization in the ground.In addition,it also provides geophysical data for the study of ore prospecting and ore deposit science.The underground electrical model of the Juno mining area has obvious characteristics of“shallow strata are divided horizontally and deep strata are stratified vertically”.According to the distribution characteristics of resistivity,the stratum below 1500 m underground in the Zhunuo mining area can be divided into near-surface high-resistance layer,shallow high-conductivity layer,medium-deep high-resistivity layer and deep high-conductivity layer.Through the geological interpretation,the following new understandings are mainly obtained: there are two obvious high conductivity areas under the main mineralization exposed on the surface,one of which is located near the surface depth and is far from the northwest end of the main two-dimensional profile.About 600?720m,the resistivity value is less than 500?m;the depth of the second layer is about 80?530m,and the distance from the northwest end of the main two-dimensional section is about 100?950m,and the resistivity value is less than 400?m.Therefore,it is inferred that the high-conductor located in the shallow high-conductivity layer may be a reflection of the ore-forming rock mass,and its high conductivity reflects the porphyritic monzonitic granite and monzoni granite porphyry undergoing hydrothermal alteration and mineralization.This high-conductivity area may also be a favorable location for deep magmatic water or atmospheric precipitation enrichment due to the existence of fault zones or rock fracture zones,providing a relatively good place for ore-forming fluids to metasomatize surrounding rocks and copper mineralization.In addition,it is inferred that the transition zone between the shallow high-conductivity layer and the upper and lower high-resistance layers is a bluestone or sericite alteration zone closely related to mineralization,which may be a favorable location for mineralization.Based on this,there are seven prospecting target areas have been circled.