| With the development of mineral resources exploration and mining,easy-identifying ore, surface ore, shallow ore has been decreasing, and the mineral exploration work is searching for the direction change of the indiscernible,concealedand deep-seated ore.Meantime, the State Council "prospecting breakthrough strategic action outline" clearly put forward to "rely on scientific and technological innovation, and let the metallogenic theory and prospecting model to play the guide role inthe ore-prospecting work;focus on deep prospecting and complex area prospecting technology, importing the advanced prospecting methods from abroad,organizing independent research and development, promotinga demo application, to improve the overall level of mineral exploration." The comprehensive geophysical prospecting model based on the metallogenic theory and geophysical exploration practice accumulation can effectively overcome the unification of geological observation and multiple solutions of geophysical exploration,it is easy to form an integrated exploration technology advantages with multi-method,multi-parameters and multi-scale.The gold mine, located in the southern tip of Lijiang fold belt on the western margin of the Yangtze platform,Beiyabelong to south-central segment of NW-SE trending eastern Tibet-western Yunnan alkaline porphyry polymetallic metallogenic belt. With the special tectonic location and sophisticated crust evolution,excellent metallogenic conditions, abundant mineral resources, diversity of mineralization and complex type of deposit, this area has a great potentialfor looking expensive,scarce or rare mineral resource.For now, the gold mine, explored the resources of Au with 300 tons and Fe with 25 million tons, is the largest gold deposit in Yunnan province.But there are some current situations such as complex geological structure,low degree of geological studiedness, inconvenient traffic, tough working environment, and the short annual effective working time.Therefore, we select the typical deposit in Beiya gold mine, from the perspective of the metallogenic prediction, based on comprehensivelyanalyzethe metallogenic model,metallogenic regularity andprospecting marks, to establish a suitable comprehensive geophysical prospecting model for Beiya mine and the surrounding area, to provide scientific exploration methods and exploration mode of fast and effective prospecting evaluation for Beiya gold deposit in Northwest Yunnan.Theoretically, it will perfect of the ore-prospecting technology and method system, the practice,it will provide a direction for ore-prospecting in the mining and surroundingarea.Both of them provide technical support and exploration demonstration for the rapid breakthrough of mineral exploration in the southwestern China,meet the strategic requirements of the country and the local demand for ore prospecting.This article is mainly focus on geophysical exploration methods used in Beiya areato carry out a comprehensive study. The main research work from the following aspects will be conducted in order to obtain a more comprehensive and systematic understanding.1、On the basis of the information collectionin this region, through analysis and research metallogenic regularity and metallogenic model of Beiya area,discuss the ore-prospecting signs(geology signs, physical signs, prospecting mechanism), to providethe effective and clear target detection and corresponding geological evidence for geophysical exploration.2、According to the mineralize characteristics and general rules of Beiya gold polymetallic ore deposit,through statistical analys of physical parameters combined with known geological conditions,numerical modeling of geophysical model structure,ore body, and make the comprehensive analysis and research on the corresponding simulation results. Forward modeling is a bridge to the metallogenic model and geophysical prospecting model. Forward modeling results can be used to predict whether the geophysical prospecting method is effective or not.Carry out comprehensive study of geophysical prospecting technology mechanism and prospecting model, including comprehensive electrical prospecting directly for ore and indirect geophysical exploration model through the gravity and magnetic data searching for structure or porphyry. Establishing a research system of metallogenic model-forward modeling- geophysical exploration model.Through statistical analys of physical parameters combined with known geological conditions,numerical modeling of geophysical model structure, ore body,and make the comprehensive analysis and research on the corresponding simulation results. The forward modeling results show that the resistivity of the parameters to carry out magnetotelluric sounding for structure and deep strata distribution; gravityanomaly can reveal the porphyry body excluding the topographic effects;Polarization and magnetic prospecting with polarization and magnetization rate parameters can directly find ore body to carry out prospecting prediction.Starting from the mineralization types and characteristics of Beiya area, we study the role and laws of alkali-rich porphyry mineralization, and carry out 3-D Gravity Inversion Research, according to the geological model and physical characteristics,combined with 3-D density structure, to analyze the porphyry’s deep features of extension; based on the linear signal enhancement and extraction of the gravity anomaly, combined with boundary information of regional magnetic source, to discuss the mineralization and influence caused by regional tectonic.The theoretical simulation and known test results show that the 3D gravity density inversion combined with linear signal enhancement and extraction can obtain more accurate linear structure and can effectively detect the deep 3D extension of alkali-rich porphyry body.It played a very good effect for prospecting in Beiya area through geophysical prospecting model of indirect information.According to the principle of magnetic prospecting, and mineralization characteristics of gold ore associated with iron ore, we suggest that by using high precision magnetic survey can directly searchfor high magnetic anomaly produced by magnetite orebodies which closely related to gold mine,according to the size and boundary of the known ore body,we put forward the EMD method, using this method to process the magnetic anomaly can keeps the multi-resolution of wavelet and overcome the difficulties with wavelet basis function selection,can achieve multi-scale signal decomposition and improve the abnormal screen resolution, also can enhance the identification resolution of abnormal boundary.We designed the electrical modelbased on the numerical simulation, and conducted the comparative study of AMT,CSAMT inversion, selected the best magnetotelluric method Beiyatoanalyze the general rules of data analysis and interpretationin area.According to the regional tectonic structure and local structure which control the Beiya mineralization, we suggestto use the CSAMT for exploration in mineralization favorable areas, using the traditional Occam inversion largely to determine the geoelectric section, using the inversion method named smoothness constrained least-squares to highlight the high resistance body and the interfaces between high and low resistivity layer. This optimization inversion method can form a more suitable geoelectric model from resistance aspect.According to the characteristics of the sulfide deposit induced polarization inBeiya mine area, we built the orebody model which imaginary induced polarization current based on the actual geological structure,Optimization of the working parameters of induced polarization method by two times field voltage and measured value stability test under different power of supply voltage,preferred high power direct current IP method, puts forward using IP exploration in prospective area,choose IP anomaly peak to carry out IP sounding measurements to get induced polarization anomalies, and longitudinal extension feature of polarization body, and contrast with plane anomaly,corrected plane anomaly position, formed “effective high polarization anomalies”, thus infer correspondence between planar anomaly and deep mineralization, inferred mineralization favorable accumulation position.3、We also conducted the experimental research on comprehensive geophysical exploration modelin the known mining area and the surroundings,summed up the application of exploration methods and techniques. We choose the typical Hongnitang section, to study regional geological background, take the geological information as a constraint, to infer hidden porphyry extension feature on the 3D inversion of gravity,according to CSAMT inversion of resistivity structure model, we delineated the Hongnitang and Dashadiconcealed rock body and the contact between the porphyryand surrounding rock, established the stratigraphic interpretation model;Combinedwith the magnetic information constraints,we identified the potential contact zone for finding skarn-type iron deposit; established the ore body interpretation model according to the structure model of polarizability, and builtthe geophysical exploration model and method of exploration technology of the skarn type gold mine using multiple constraints.We delineatedthe ore-prospecting area using 1:50000 regional geochemical and geophysical data; comprehensively used the gravity, magnetic,induced polarization,CSAMT, drilling and other method in prospective areas, combined the interpretation method of multi-parameter and multi physical property, to locate and predict the concealed ore-body, to validate and improve the deep prospecting geophysical model in Beiya area.4 、 Finally, we proposed the comprehensive geophysical prospecting model through testing in the known and the prospective areas: regional geological background analysis is carried out for the geological basis of geophysical work,according to the geophysical characteristics of rocks and ores, select the corresponding geophysical methods. Using gravity exploration as the forerunner to obtain roughly block tectonic division, using in linear signal to identify the regionalfaults,using 3D density inversion to divide the favorable areas of mineralization;using high precision magnetic survey directly to search the high magnetic anomaly produced by magnetite orebodies which closely related to gold mine; and using CSAMT to test and control the deep ore structure and lithologic interface; In prospective areas, using IP exploration, choose IP anomaly peak to carry out IP sounding measurements to get induced polarization anomalies, and longitudinal extension feature of polarization body, and contrast with plane anomaly, to correct plane anomaly position; to determine the different levels of prospecting space; and to achieve comprehensive detection of multi method, multi parameter, multi scale and multi angle; Finally, to verify the validity and feasibility of the geophysical exploration model by drilling. |
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