Taking the 1:200,000 scale Lanping sheet of regional geochemical map (Yunnan Province)as an example, this article compares the effects of different mapping techniques. On this basis,a presentation technique for the 1:200,000 regional geochemical prospecting is suggested.

Asimple, enclosed device for sample dissolution under normal pressure is suggested in this paper. It eliminates the dissolved components of aqua regia produced in the process so as to protect the health of the analysts and to avoid environment pollution. This method has been used in the pilot determination of trace gold in various types of ores and other materials, and the results are compared and proven to be satisfactory.

Tlie a-card method, using a metal or plastic card buried underground for a considerable length of time to collect radon products by adsorption affect, and then using a special instrument to detect the a-radiation, is being increasingly applied to radioactive exploration for discovering very "faint radioactive anomalies. The collection of radon products on precipitators can be enhanced by applying a negative charge, but it complicates the equipment. The a-card method using electrostatic materials as precipitators solves this problem to a large extent. Akind of portable a-scintillator with a large area ZnS (Ag) scin-tillator has been developed by the authors. This method has been prelimina-rily applied in the search for uranium, underground water and cracks of dam. The comparison of it with other geophysical methods shows that it can be conveniently adopted and satisfactory results can be obtained with the advantages of high sensitivity (several times that of a-precipatator method), reliability, simplicity, efficiency and low cost.

It is well-known that the distortion potential is a complicated function of both the terrain angle and the electrode spacing. In this paper polynomes are used to approximate the function, so that the calculation involved becomes quite simple. Afast computer program has been developed for topographic correction in resistivity method (omitted in this paper). Comparing to the results of analytical solution, the mean relative error is less than±0.1%, which meets the needs of field work. By virtue of the simplicity of the formula, calculations can be easily accomplished with a calculator. As a result, it provides a simple and fast technique of topographic correction for prompt and in-situ calculation of large amount of electrical survey data.

Basaed on the interpretation of the regional gravity and magnetic picture of Southern Hunan, the paper presents a general chracterization of regional geophysical and geochemical anomalies of four major polymetal ore fields, namely, the Shuikoushan, Dongpo, Yaoganxian and Huang-shaping, in the light of lithology, regional tectonics, geology at depth, and magnetic activities. It is postulated that the important factor dominating the formation of major ore fields in southern Hunan was the intersection of regional structures cut through by faultings at great depth. It is also noted that the major ore fields are situated close to the zones of "magnetic high", and are often accompanied by characteristic geochemical anomalies with remarkable area! extension, high metal content, and of multielement composition. Various minor magnetic and gravity features, in the meantime, are often indicative of individual local ore deposits.It is evident from the study of the four known ore fields that regional gravi-ty and magnetic data can provide important information regarding the rock and ore-controlling stuctures, as well as other useful information for the metal-logenetic forecasting of the area. Emphasis is given to the close relationship between the west-east running Chengxian-Guiyang zone of magnetic high and the major ore occurrences. Special attention is called to where the zone meets the Lanshan-Lingxian gravity gradient belt, for this is where the major ore fields are centered.It remains an important task for geophysicists to pursue further investigations into the nature of the regional gravity and magnetic anomalies in order to gain still better results in mining geophysical exploration.

This paper is a preliminary summary of an integrated geophysical and geo-chemical survey at a scale of 1:50,000 in Lu-Zong region. After analyzing the regional structure and Moho-isobaths, it is suggested that the background of deep crustal structure is relatively complicated but favorable to the formation of iron, copper and other endogenetic deposits. Results of the survey revealed the unique picture of gravity and magnetic fields and the distinct geochemical features of the volcanic area. On the basis of Bouguer gravity, airborne magnetic, integrated gravity and magnetic, and geochemical anomalies, considerable achievements have been made in understanding the framework of fractures, analyzing the pattern of volcanic depressions, defining the structural outline of pre-xiang-shan group and in delineating the concealed magnetic body, all these have contributed to a better insight into the overall geology of the area geological cognition.The paper concludes that reasonably integrated application of geophysical and geochemical methods has proved to be a. very important approach in regional geological investigation. In addition, the gravity, magnetic and geochemical methods can be used as major tools in₁:50,000 scale integrated geophysical and geochemical survey.

The authors of this article participated in the tra,inning course in the USSR on geophysical prospecting sponsored by the United Nations and the USSR from March to June, 1983.During the course, the authors attended lectares given by the Soviet geophysicists and learned about the state-of-the-art in the USSR. Some of their methods and techniques. might be useful to the geophysical prosp ecting in our Country. This article gives a brief intro-duction of some basic principles as well as the current development of the magnetotelluric method, field establishing method, geoelectrochemical method and piezoeelectrical method in the USSR. The trend of induced polarization method in the USSR is also discussed.