Application Of Regional Geophysical And Geochemical Data To Geological Survey In Shallow Overlay Area

Regional geological surveys are the basis and first step of geological exploration. The method is affected by geological landscape area. The coverage area without bedrock outcrop in our country accounts for about 1 / 3 of the mainland, a considerable part of which is shallow coverage area. Medium-scale geological mapping relies mainly on float, local scattered outcrops or limited project exposure. Deep geological conditions such as blind rocks, stratigraphy, tectonics, mineral(ize) cannot be directly observed. Prospecting techniques in geological research, can exert methods advantages, extract useful geological information, and meet the objective needs of development. In addition, our country has a national coverage of basic geophysical and geochemical data, which can provide useful basic information for the geological mapping of shallow coverage area or for the geological studies. That's of great practical significance.In the aspect of rock inversion with regional geophysical data, the material magnetic, mineral magnetic and rock magnetic, as well as the determinant factors of the density of rock and classic rock density were analyzed in turn, and the magnetic field characteristics of rock mass with different types and the determinant factors of gravity anomalies with different levels were summarized. Then, the conventional treatments of gravity and magnetic data were divided into abnormal enhancement method and field separation method according to different purposes of data processing. Abnormal enhancement methods are mainly pole transform method, directional derivative method and extension method; Field separation method is mainly the matched filtering of wave number domain methods and the curve fitting of interpolation cutting methods. In order to carry out a comprehensive analysis of gravity and magnetic data, the correspondence analysis methods were discussed. In addition to analysis and comments of various data processing methods, a new idea that identifying shallow geological body with the magnetic distribution and difference of shallow rock based on an interpolation cutting method was tested.In the aspect of rock inversion with regional geophysical data, the elements content and combination change in the process of rock decaying to soil in north Greater Hinggan Mountain as well as the results of the analysis of influencing factors were first studied in the article. The results showed that elements experienced two different causes of "homogenization" in the process of rock decaying to soil and in the process of stream sediment forming, leading to information extraction and recognition difficult of bedrock. However, there was no significant change in the combinations of main rock-forming oxides (elements), which provided a theoretical foundation for geochemical bedrock data inversion. The results also showed that the grain size and organic matter had a certain impact on the results of the analysis. In the above foundation, geochemical bedrock inversion methods were studied. Two bedrock inversion methods using regional geochemical data, namely "inversion method without standard rock samples to monitor" and "inversion method with standard rock samples to monitor ", were respectively put forward under the two circumstances that there are regional rock data and regional stream sediment data and there are typical geological body and its corresponding chemical composition of stream sediment.Through the summation of geophysical and geochemical bedrock inversion theories and methods, it's considered that the two methods should display their own strengths, combine with each other, and complement each other. The types of geologic body should mainly determined by geochemical interpretation inference. The geological boundaries were synthetically determined by the change band of geophysical field characteristics, the boundaries of geochemistry zoning and the types of petrochemistry.In the aspect of structure Inference, the theory of regional geochemical methods is that geologic bodies on both sides of faults move horizontally or vertically as a result of crustal movement, resulting in differences in both sides of the rock to form the chemical composition differences. Based on this, two methods were proposed. Using the geometrical shape of contact border of geochemical zoning and the spatial distribution patterns of mineralizer elements (As, Sb, Hg, etc.) combinations to determine fracture, and using the boundary shapes of different units and their mutual relationship to identify faults. However, due to restrictions on the sampling density, the plane location of the fault inferred and interpreted by regional geochemical methods has a great error, and it reflects only the surface information. Differently, there are mature theoretical approaches of identifying structure with gravity and magnetic methods, with big sampling density and high precision. Therefore, this paper argues that the identification of construction should first use gravity and magnetic methods, and combine geochemical exploration properly as supplement and validation.Taking Tahe area, Heilongjiang province as an example, the methods were tested.The characteristics of rock density, rock magnetic, gravity field and magnetic field of the study area were analyzed detailedly. Then, the geophysical field in the area was explained. The Results show that a simple gravity method is difficult to distinguish between intrusive rocks, volcanic rocks, metamorphic rocks and sedimentary rocks which have the same rock density and different chemical composition, but it can reflect deep information well. Magnetic methods can give out a clear explanation of shallow information. But the same-magnetic body is not geological mapping unit. When different geologic bodies have the same or similar magnetic properties, it need for other information to support due to the "multiple solutions". Geochemical information can be processed to have a very good reflection on the main geologic bodies. Practice has proved that the geochemical method can effectively determine rock types, but the inference accuracy of rock boundaries is restricted by the sampling density of rock, and it need to refer to the interpretation results of geophysical information.