3D Quantitative Metallogenic Prediction Of Lannigou Gold Deposit In Guizhou Province

As a globally important strategic mineral resource,gold plays an irreplaceable role in maintaining national economic and financial security and ensuring the steady growth of national wealth.As an important part of the Yunnan-Guizhou-Guangxi"Golden Triangle"metallogenic area in China,the southwestern Guizhou region is the second largest concentration of Carlin-type gold deposits after Nevada,USA,with a gold resource of over 900 tons.As a proven super-large gold deposit in the area,the search for deeper ores and difficult-to-identify hidden ores has become the focus of the search in recent years as surface,shallow and easily identifiable ores continue to be depleted.In the face of the new situation in the development of ore prospecting prediction,3D metallogenic prediction has become a hot spot in the research of mineral resource prediction in recent years,and it has brought new challenges to the study of metallogenic laws and the innovation of metallogenic prediction methods.Previous studies on the Lannigou gold deposit mostly focused on the genesis of deposits,ore-forming chronology,and the source of metallogenic materials.There are still many deficiencies in the research on ore-forming prediction,especially the lack of research on three-dimensional quantitative metallogenic prediction,and the 3D quantitative prediction of mineral resources is an important study direction to cater to the research of national strategic resources.Based on this,this paper systematically carried out a 3D quantitative metallogenic prediction study of the Lannigou gold deposit in Guizhou with multidisciplinary methods such as geomechanics,geostatistics,and fractal theory.The main results obtained are as follows:(1)The rock matrix in the study area is rich in siliceous minerals,among which quartz is the main brittle mineral,and the main component of clay minerals is illite,which also contains minerals such as feldspar and pyrite;The rock pore types are mainly intragranular pores,intergranular pores and organic matter pores,and the intragranular pores mainly come from the pores of mineral particle dissolution;The ore has the highest quartz content,ranging from 34.9%to 71.2%,with an average content of 58.9%,followed by calcite,pyrite,plagioclase and siderite;The morphology and structural characteristics of mineral particles are relatively diverse.The pyrite content is generally between 2-5%,and the crystal particle size is uneven,generally between 0.01-0.5mm,mostly euhedral-semi-autohedral granular distribution,with star point and sparsely disseminated basal distribution as the main ones;The content of arsenopyrite is generally less than 1%,and the distribution is mostly uneven and segregated,the crystal grain size is generally between 0.03-0.30mm,and the distribution is euhedral-semi-euhedral-heteromorphic needle columnar;Quartz is vein-like segregated distribution,crystal size<0.03-0.50mm,euhedral-semi-euhedral-other-shaped granular crystals;Quartz and pyrite form a fragmented structure due to crushing under force.(2)Through the systematic analysis and processing of geological data in the study area,a multi-information comprehensive database was constructed,and a 3D geological model of the study area was established based on the GOCAD 3D geological software platform.Convert GOCAD 3D geological model to midas GTS geometric model through 3D point cloud reverse engineering,the geological features such as the real contact relationship of different strata and the spatial coupling relationship between structure and different strata are completely converted into the midas GTS calculation model,which realizes the accurate description of the geometric model of the study area.Based on the analysis of regional tectonic evolution history,geological interpretation,rock mechanics experiments and paleo-tectonic stress test results,the finite element method(FEM)was used to invert the paleo-stress field considering multi-stage structural superposition.The results show that the maximum principal stress in the superimposed study area is mainly distributed between 153.85 MPa and 189.53 MPa,and the maximum shear stress is distributed between 83.53 MPa and 98.42 MPa,and its distribution characteristics are mainly affected by the spatial distribution of faults.Different degrees of stress concentration occurred at the intersection of the faults,at the ends of the faults,and near the fault zone,the stress level is relatively high,while the stress value between the faults is relatively low.(3)Based on the inversion results of the paleo-tectonic stress field,combined with the rock fracture criterion,a comprehensive fracture rate parameter(I_z)was introduced to predict the distribution of fracture development in the study area.The results show that the fracture development area(I_z>1.2)is mainly distributed in the interior of the fault zone,the intersection of different fault zones and the turning point of the fault zone;The areas with relatively developed fractures(0.8<I_z<1.2)are mainly distributed in the fault zone and the edge of the intersection of the fault zone;The areas with slight fracture development(0.4<I_z<0.8)are mainly distributed in the deep central and western parts of the study area and the shallow areas in the northeastern part of the study area.The underdeveloped fracture area(I_z<0.4)is mainly distributed in the transition area of adjacent fault zones.The distribution of fractures and the degree of fracture development are controlled by the main faults,it is recommended to select the fracture development area and the relatively developed area for the key prospecting areas in the next study area.Using the combined modeling technique of GOCAD and midas GTS to realize the conversion from 3D geological model to geomechanical model,a set of comprehensive fracture distribution prediction technique for the superposition of multi-stage tectonic stress fields of mineral deposits in complex tectonic areas has been formed,and provide a reference for the prediction of fracture distribution in similar complex structural areas.(4)According to the principle of rescaled range analysis and fractal correlation integration,a multi-fractal dimension calculation system was independently developed based on the MATLAB platform.Based on this system,the fractal study of the gold grade data in the boreholes in the study area was carried out,the relationship between the fractal dimension and the spatial distribution of the gold mineralization process was revealed,and the favorable mineralization area was determined.The results show that the distribution of gold grade(g/t)in the vertical direction of all drill holes has a fractal structure,indicating that the mineralization has scale invariance within a certain spatial range,the persistence of gold mineralized veins throughout the drill hole means that these gold-rich areas are the main targets of gold exploration,and the results obtained by rescaled range analysis can be used to describe the behavior of drill holes passing through gold-bearing veins;The high-grade gold deposits are mainly located on steep fractal gradients,and the obtained fractal dimension values can be used to better constrain possible ore-bearing fluid flow paths,and the fractal dimension gradient plays an important role in locating potential economic gold deposits as a spatial proxy;The relationship between the fractal characteristics of the ore-forming elements and the mineralization intensity in the mining area has been systematically studied,and the influence of the structural environment on the distribution characteristics of the ore-forming elements in the Carlin-type gold deposit has been ascertained,the discrepancy and aggregation mechanism and the spatio-temporal distribution pattern of ore-forming elements during the formation and evolution of the metallogenic system are revealed,which is of great scientific significance for the understanding and understanding of the complex phenomena and formation mechanism of the ultra-large Carlin-type gold deposit system.(5)Through the comprehensive analysis and sorting out of the ore-forming geological background,genetic type,ore-forming conditions and metallogenic laws in the study area,various favorable factors for ore-forming are summarized,and based on the actual data,a prospecting geological model suitable for the Lannigou gold deposit is constructed;On the basis of the 3D geological model of the study area,the statistical analysis of the ore body and each metallogenic element was carried out,using mathematical geological algorithms,the advantageous and beneficial intervals of favorable metallogenic elements were quantitatively extracted,and 3D spatial reconstruction was carried out to establish a 3D quantitative prediction model for the study area;The comprehensive delineation method of combining the amount of prospecting information and 3D evidence weight was used to predict the mineralization of the study area,effectively reducing the uncertainty of the prediction results.Finally,three Class A target areas,two Class B target areas,and one Class C target area were delineated.