This paper makes a brief review on the history of geophysical exploration work conducted by MGMR in the past 10 years, during which the geophysical work has experienced three stages, i. e., early pioneering stage, development and expansion stage and all-round development stage, with the number of geo physical workers expanded to more than 40000 people. The methods have increased from three types (including four sorts) of basic methods to six types (including over forty sorts) of common ones, some of which have reached the advanced world levels. With geophysical exploration, we have delineated hundreds of oil-gas structures and oil-fields, detected thousands of metallic and nonmeta-llic ore occurrences, accomplished tens of thousands of geophysical exploration projects on water sources and engineering environments, put forward new under standing on lots of problems concerning basic geology and deep geology, located prospective oil-gas areas in four offshore fields, and undertaken geotectonic investigation into pelagic fields. In the aspect of geophysical explorationl technology, we have established in the past 40 years 2nd generation aerogeophysical technical system, regional gravity investigation technical system, petroleiim seismic exploration technical system, deep geophysical prospecting method series for solid ore resources, hydrologic, geothermal, engineering and environmental geophysical exploration method series, borehole geophysical prospecting Imethod series, logging series for oil-gas, coal fields, saline deposits and hydrogeology, marine geophysical technical system, deep geophysical investigation method series and system, and computer application system. At present, our ministry owns a contingent of geophysical workers who are able to conduct aerial, surface, underground and marine geophysical survey with a complete set of methods and techniques and are well qualified to tackle focal tasks before us, i. e, ensuring the performance of regional geophysical exploration, strengthening geophysical reconnaissance for ore resources that are urgently wanted, widening the fields of hydrologic, engineering and environmental geophysical exploration, promoting technical progress and developing technical markets.

The development of geochemical exploration since the establishment of the Ministry of Geology and Mineral Resources 40 years ago is briefly reviewed in this paper. The Geochemical Prospecting Division under MGMR was set up in 1952. Since then, geochemical prospecting has experienced several stages; first, there was the early starting stage; from 1960 s, the levels of methods a.nd techniques for geochemical prospecting were steadily raised, and the contingent of technicians was expanded year after year; since 1978, geochemical prospe cting has entered a stage of all-round and rapid development, and this is espe cially obvious in such aspects as regional geochemical prospecting, geochemicalprospecting for gold deposits, geochemical rock survey, mercurometric survey and analytical methods and techniques. In the past ten years, regional geoche mical prospecting has covered an area of 4010000 km2 in China, geochemical prospcting has gained conspicuous ore-prospecting effects in search for ore resources of noble metals and nonferrous metals, and geochemical methods and techniques have ascended to a new height: relatively advanced world levels have been reached In such fields as working methods for geochemical prospe cting (especially the working method for geochemical prospecting in special landscape units), the analytical techniques of samples and quality monitoring, the preparation of standard samples, the application of computers to geochemi cal prospecting, and the development of instruments for geochemical prospe cting. Looking forward to the future, the geochemical prospecting work of MGMR has clear and definite objectives and arduous tasks, and is bound to play an increasingly important role in geological ore-prospecting as well as in environmental and agricultural studies.

In the field where nuclear survey is comparatively extensively applied, many valuable anomalies detected by field radiometric survey are weak or low-value anomalies. For these low-value anomalies, the authors suggest the utiliza tion of high-precision radiometric survey. In order to raise the reliability oi the determination of these low-value anomalies, the paper points out that impor tance should be attached to the measures for raising the precision of field survey (mainly the surface total gamma amount and gamma spectrometry), which include, for example, the selection of proper instruments and time of measurement, and the control and reduction of interference factors in field survey. Besides, the data-processing is the key-link in the interpretation of weak anomalies. The paper describes briefly some currently-used common methods for determining weak radioactive anomalies and the data-processing method in search for nonradioactive elements by means of data from gamma spectrometry. The third part of the paper outlines the application of field radio-metric technique to the prospecting for gold, petroleum, groundwater sources and other important metallic ore resources and to the solution of problems in the aspect of engineering geology.

The axial orientation of the aeromagnetic anomaly is one of the important characteristics of the magnetic field. With practical examples, this paper gives an account of the statistical methods for axial azimuths of anomalies, mean square errors of azimuths and densities of axial lines, and discusses the geological and ore-prospecting significance of these characteristic essential elements.

The axial orientation of the aeromagnetic anomaly is one of the important characteristics of the magnetic field. With practical example, this paper gives an account of the statistical methods for axial azimuths of anomalies, mean square errors of azimuths and densities of axial lines, and discusses the geological and ore-prospecting significance of these characteristic essential elements.

We should know not only the distribution pattern of the geomagnetic field but also the distribution pattern of the geomagnetic field gradient. Based on the Gauss theory and the spherical harmonic model of the geomagnetic field, this paper has calculated the horizontal gradient (in SN and EW directi ons) and vertical gradient of the total geomagnetic intensity for China and its neighboring areas, drawn the corresponding contour map and analysed the distribution pattern of the total intensity gradient.The horizontal gradient and vertical gradient of the total geomagnetic intensity vary mainly with the latitude and have little to do with the longitude. It is worth noticing that the horizontal gradient value of the total geomagnetic intensity is highest in the central part of China.

In frequency spectrum IP method, the application of residual electroma gnetic effect to the study of the distribution of underground electricity has aroused much interest. Based on an analysis of numerical calculations, this paper points out that, when the high frequency f_G is properly chosen, the phaseφ_s(f_G) of apparent complex resistivity is observed by dipole device, and it is normalized by the phase theoretical valueφ_s⁰(f_G) of the apparent complex resistivity of uniform ground under the corresponding condition, then the ratio φ_s(f_G)/φ_s⁰(f_G) obtained is the ideal parameter representing residual electroma gnetic effect. Combining numerical calculations with field data, the paper also makes an analysis of the anomalous character of this parameter and its effect in the prospecting for oil and gas.

Geochemical survey is an effective and important method in prospecting for geothermal systems. As geothermal reservoirs are closely related to structu res, it is essential for us to. investigate the structures contiolling the geothermal water in the process of geothermal field exploration.This paper summarizes the geochemical methods available for detecting faults in the geothermal system, with special attention paid to some testing results of gas geochemical survey performed in the last few years for faults in geothermal fields. It is shown that such methods as mercury vapor in soil, ²¹⁰Po, Alpha-card and in-situ goil-gas CO₂ accumulative determination are all effective mneas for detecting faults in the geotheraml area. Our study has also proved that the multi-parameter survey is much more effective and reliable than the single-parameter survey. The geochemical survey can be used not only to find faults but also to disclose concealed structures in the geothermal system.