Using geophysical comprehensive information to study basic geological problems such as deep fault structure and magmatic activity, understand regional metallogenic geological background, and extract concealed structures and magmatic rocks related to mineralization.
(1) fault structure
According to the fault structure characteristics of gravity and magnetic anomalies in the study area (Section III of Chapter III), 16 (hidden fault) is comprehensively determined (see Table 3-3-3 in Chapter III). The inferred fault structure is mainly NE-NNE direction, followed by near EW direction and NW direction.
(2) Magmatic rocks
In this study, there are 58 known and concealed rocks in the * * * delineated area, and some homologous "small" rocks surrounded by multi-center abnormal secondary peaks are not numbered (see Table 3-3-4 in Chapter 3). Among them: ① According to the statistics of rock mass exposure, there are 22 concealed rock masses, 7 partially concealed rock masses and 29 exposed rock masses; ② According to rock types, there are 3 kinds of acid granite and 9 kinds of granite (biotite granite, etc.). ), 42 intermediate-acid granodiorites and 4 intermediate-ultrabasic rock granites. ③ According to the statistics of anomaly interpretation method, there are 47 aeromagnetic anomalies and 47 gravity anomalies 1 1, about half of which have obvious gravity and magnetic anomalies. According to the distribution characteristics and related data of magmatic rocks, this book has the following understanding of its spatial distribution.
① Magmatic activity is obviously controlled by fault structure, and its distribution and occurrence are basically consistent with fault strike. The intermediate-acid rock bodies in Tingxi, Langqiao, Huangshan, yi county and Ehu, Jiangxi Province are controlled by the Langqiao-Lidongkeng fault (F6) and are produced in the northeast direction, and the centers of Yunling-Baocun, Maolin, Langqiao (Sanxi), Jingde and Fuling are obviously arranged in this direction. ② Qingyang-Ningguo rock belt includes intermediate-acid rock bodies such as Houan, Du Hongtian, Maolin, Tingxi, Pancun and Liucun, which are distributed in gravity cascade belt. The overall development is controlled by Qingyang-Ningguo fault (F5, also known as Zhou Wang fault), and the deep occurrence is not obvious. Shitai-Jingde rock belt includes intrusive rocks such as Dali Mountain, Cheng 'an, Huangshan Mountain, Jingde, Fuling, etc., and it is generally arched from east to west to north, and the buried bedrock is intermittently connected. The center of deep acid magma chamber is located in Huangshan-Jingde area. ③ Some intrusive rocks have obvious lithofacies zoning and lithologic differences. For example, the Jingde magnetic anomaly is composed of three groups of interconnected northeast secondary anomaly zones, and their amplitudes are also different, indicating that the content of magnetic minerals in Jingde rock mass is uneven and there are certain lithologic differences; The gravity of the harbor is extremely complete, in the northwest. The abnormal center reflecting the extension of rock mass is located in the harbor, while the magnetic anomaly is only distributed outside the low center of gravity, which also shows the lithologic difference of intrusive rocks in this area.
On the basis of the above regional geophysical anomaly analysis, combined with the geological exposed intrusive rocks and fault structures (including basement fault structures), the concealed or partially concealed intrusive rocks and fault structures related to mineralization inferred from geophysical anomaly interpretation are merged into intrusive rocks and structural layers to form an evaluation and prediction model.
Various gravity and magnetoelectric anomalies discovered in geophysical exploration over the years contain a lot of prospecting information, especially Class A and Class B 1 geophysical anomalies of various working scales. In GIS evaluation of mineral resources, how to extract this kind of information is a problem worthy of further study. First of all, class A geophysical anomalies related to the target minerals should be extracted, and on this basis, any anomalies identified as known deposits (points) should be discarded. Secondly, when geophysical anomalies are within the range of known mineral areas, or the geological environment around the anomalies is conducive to the mineralization of target minerals, geophysical anomalies above Class B 1 should also be evaluated and calculated as variables. According to the above conclusions, 5 1 geophysical anomaly points above1level in southeast Anhui were extracted to form geophysical anomaly layer for evaluation and calculation.
2. Geochemical information
Geochemical information includes geochemical single-element anomalies and multi-element combination anomalies related to mineral resources evaluation (see Chapter 5, Section 3 for their division and determination). How to extract useful information from chemical exploration layers and transform it into computational variables is an urgent problem. Compared with resource evaluation and prediction, single element anomaly can be divided into two types: main element anomaly and indicator element anomaly. The so-called main element refers to the element with the same name directly related to the evaluation (prediction) of the target mineral. For example, the target mineral is copper and the main element is Cu, and so on. Indicator elements refer to elements that have an indicator function relative to the target minerals, and there are generally 2 ~ 5 kinds. For example, in southeastern Anhui, if the target mineral is gold, its related indicator elements are As, Sb and Cd.
Generally speaking, in the GIS evaluation of mineral resources, the "evidence weight" method is to determine the "weight" and "weight" of all geological variables involved in the calculation according to the size of their overlapping area with the ore-bearing grid. If all index elements participate in the calculation according to their own layers, theoretically, their weights are the same as those of the main elements (when the overlapping area of the ore-bearing grid is the same as that of the main elements and related elements), which weakens the contribution of the main elements to the evaluation and prediction results and fails to reflect the role of important related elements. In order to overcome these unfavorable factors, the abnormal layer of geochemical elements is treated as follows.
(1) The main ore-forming elements are taken as independent calculation variables;
(2) If the anomaly of important related elements contains the target deposit (point), the anomaly still exists; If it intersects with other indicator elements abnormally, the anomalies of the overlapping parts are retained.
(3) If two or more elements (including two elements) intersect among other related elements, the overlapping part will remain abnormal.
(4) The reserved important related element anomalies and other overlapping related element anomalies * * * form a related element anomaly layer to participate in the calculation.
3. Remote sensing geological information
According to the interpretation of color infrared aerial photos and TM satellite photos in southeast Anhui, the linear and annular structures are delineated respectively, and the compound annular structures closely related to mineralization, ore control and ore hosting, such as line-ring intersection, ring-ring intersection and ring-ring intersection, are further determined, and extracted from the remote sensing interpretation layer to form geological variables for evaluation and prediction.
4. Natural heavy sand information
Among the natural heavy sand anomalies, the combined mineral element heavy sand anomalies related to the target minerals are the extraction objects of prospecting information, which are extracted according to the evaluation minerals respectively.
5. Catchment basin information
According to the statistical results in Table 6-2-3 ~ 6-2-5, the distribution laws of mineral resources, geochemical exploration and heavy sand anomalies are obvious compared with catchment basins of all levels, and most of them are concentrated in catchment basins of grades 4, 5 and 6, especially the catchment basins of grades 4, 5 and 6 with the most moderate area can be called the basic units of catchment basins, so it is more appropriate to take them as the research object. Therefore, the catchment basins of Grade 4, Grade 5 and Grade 6 can clearly indicate the abnormal sources, which can be extracted from the catchment map layer as evaluation and calculation variables.
Table 6-2-3 Distribution Statistics of Related Geochemical Anomalies in Huishui Basin
Table 6-2-4 Statistics of Abnormal Distribution of Heavy Sand in Huishui Basin
Table 6-2-5 Distribution Table of Mineralization Points in Catchment Basins at Different Levels