Geophysical Characteristics And Deep Mineralization Prediction Of Jinchuan Cu-Ni Sulfide Deposit

Strengthening mineral resources reserve is an important guarantee for the sustained and stable growth of national economy,and exploring deep resources is an important direction to achieve resource security.Jinchuan Cu-Ni sulfide deposit is the largest copper-nickel production base in China.Deep exploration in this area is of great significance to increase resource reserve.Geological research is the basic condition for deep exploration.Geophysics can be used to explore minerals according to the difference of physical properties of underground media.It is an important scientific and technological support condition with multiple methods,large exploration depth and high resolution.On the basis of geological research,through processing and interpreting the data of geophysical potential field exploration and electrical prospecting with complementary resolution,this paper infers the potential favorable metallogenic locations in the depth of Jinchuan Cu-Ni sulfide deposit.1.Through the systematic collection and analysis of previous data,field survey,rocks and minerals identifications and physical property parameters tests,the following knowledge is obtained:(1)Jinchuan Cu-Ni sulfide deposit is located in the north-west direction of the region on the gradient belt of gravity and magnetic anomalies,at the junction of North China plate and Qilian block,corresponding to the known Longshoushan continental margin belt,which shows that its formation is related to the development of deep faults.The result of interface inversion shows that Longshou mountain is located in the steep change zone of crustal thickness,with the crustal thickness of about 55 km.The crustal thickness change of North China plate in the NE direction is relatively small,which reflects the attribute of its stable block.The crust thickness of Qilian block in the southwest is relatively large and uneven,which indicates that the tectonic movement in this area is complex and has been strongly pushed and squeezed,resulting in uneven deformation.(2)The occurrence of Cu-Ni deposit is closely related to strata,structures and magmatic rocks.The ore bearing rock body is mainly intruded into the stratum of baijiazuizi formation of the Changcheng system,trending to the northwest,tending to the southwest,with a large dip angle.It is most closely related to the northwest structures.The Northwest faults often control the ore,and the folds often play a role of transformation and enrichment.The ultramafic rock bodies in the mining area are the ore-forming parent rocks,also the surrounding rocks,and the ore bodies often occur in the lower part of the rock masses.The genesises of the deposits are different,and the main ore-forming process is deep fusion and penetration.The ore minerals are mainly composed of orpyrite,pentlandite,chalcopyrite,olivine,pyroxene,etc.The complete mineral crystal shape is less,the mineral fracture is developed,and it often has obvious alteration phenomenon,which indicates that the ore bodies’ formation has the characteristics of multi-stage,and they had been strongly reformed in the later stage.(3)Based on the characteristics of density,magnetism and resistivity,the rocks and ores in the mining area can be roughly divided into three types.The first type is copper-nickel ore,which shows the characteristics of high density,high magnetism and low resistivity;the second type is ultrabasic rock mass,which has the characteristics of high density,strong magnetism and medium resistivity;the third type is the surrounding rock of ultrabasic rock mass,which has the characteristics of low density,weak magnetism and high resistivity.The differences of these physical characteristics provide a precondition for the exploration of geophysics in the study area.2.In order to obtain more abundant information related to ore,the methods of data processing of potential field are studied.(1)The traditional separation methods of potential field data often emphasize the regional field and local field,or the multi-scale separation methods have the phenomenon of mode overlapping.In order to better extract more effective potential field data information of different scales,one-dimensional and two-dimensional dual-tree complex wavelets are introduced into the processing of potential field data for the first time.This method has the characteristics of approximate translation invariance,more direction selectivity,and limitation of data redundancy.Model test shows that this method has advantages over wavelet analysis,and can achieve better separation of information at different scales of multi-frequency aliasing signals.In addition,based on the basic operators of mathematical morphology,by adjusting the morphological structural elements of different sizes,morphological operators for multi-scale decomposition of one-dimensional and two-dimensional signals are proposed.Model tests show that the operators can separate signals of different scales well and have higher computational efficiency.(2)Aiming at the problems of ambiguous output boundary,poor anti-noise ability,unbalanced strong and weak anomalies or false boundaries in the results when both positive and negative anomalies exist of traditional edge detection methods,a new edge detection operator MMA is constructed based on the good performance in edge detecting and noise eliminating of mathematical morphology.The operator can effectively recognize the edges of potential field data by using its maximum.In order to make it have the ability of balancing strong and weak anomalies,two balanced boundary recognition filters,MMAT and MMAZ,are proposed.The model tests results show that compared with the tilt angle method,the total horizontal derivative of tilt angle,Theta map method and other traditional methods,the operator can effectively identify the edges of potential field data.The two filters can not only balance the anomalies of different amplitudes,but also obtain more sharper edges,at the same time,there are no false additional boundaries when the positive and negative anomalies coexist at the same time,in addition they have good anti-noise ability.(3)Inversion is an important method to locate anomalous geological bodies in spatial location,physical parameters estimation and underground structures inference in data processing and interpretation of potential field,which is of great significance to deep mineral exploration.In order to overcome the shortcomings of multi-solution,low precision and low computational efficiency in inversion of potential field data,the smooth L0 norm compact support focusing method and GPU parallel computation are adopted to quickly obtain the inversion accurate and quick results of potential field data with high accuracy.The effectiveness of the method is verified by the model of two geological bodies with different buried depths.3.These potential field processing methods are used to process the aeromagnetic anomaly data of the mining area.The results of boundaries identification show that the NW structures are the most developed in the mining area,followed by the NE structures;the boundaries of known ore bearing rock masses and positive aeromagnetic anomalies in the South extension area of the mining area are determined.The results of potential field separation and inversion show that the deep part of the mining area has a good prospecting prospect.4.In order to better understand the deep exploration abilities of different geophysical methods and establish prospecting model,the potential anomaly characteristics of deep anomalous bodies and prospecting indicators of CSAMT inversion results are studied and summarized through gravity and magnetic simulation of multiple models and inversion results of previous actual CSAMT data in mining areas.It is concretely recognized that for deep prospecting,attention should be paid to the low positive aeromagnetic anomaly area with large horizontal range in the study area,but the low positive anomaly large horizontal range may not necessarily reflect the deep ultrabasic rock mass,but may also be a mixed rock belt or some metamorphic rocks with several times magnetic difference from the ultrabasic rock mass,et al.This is because for the same scale anomalous body,the difference of magnetic anomaly caused by different effective magnetization intensity is more obvious in the shallow part,the difference is larger,but in the deep part,the difference is smaller.In addition,in view of the large dip angle of rocks and ore bodies in the study area(50 ~80°),the influence of dip angle of rocks and ore bodies can be neglected.In different areas with the same anomaly amplitude,if the horizontal distance of positive anomaly is larger,the buried target body may have larger depth and scale.The magnetic anomalies with similar characteristics may be caused by complex magnetic anomalies.For deep prospecting,it is necessary to understand and combine abundant comprehensive information such as known geology,drilling and so on,so as to give a more reasonable prospecting position for deep prospecting.For deep prospecting,gravity and magnetic methods basically show similar anomalous characteristics.Fractured zones reflected by resistivity differences are also important prospecting indicators.Combined with geology,geochemistry,remote sensing and other prospecting indicators,a prospecting model mainly based on geology and geophysics is established.5.According to the prospecting model,combined with the processing and interpretation results of the actual gravity,magnetic and electrical profile data in the mining area,six favorable ore-forming target areas in the deep,edge and periphery of the mining area are delineated.As for the large-scale high magnetic anomaly area(Dongwan exploration area)in the eastern part of the main mining area,no favorable prospecting location has been found in its deep part.