Based on data of magnetic fields, this paper makes an tentative investigation on such aspects of Lop Lake and surrounding areas as characteristics of magne tic fields, properties of basement, and geologic structure at depth, and points out that the central latitudinal rising anomalous belt of Tarim Basin extending to the Lop Lake area has the same basement made up of Lower Proterozoic onArcheozoic strong-magnetic crystalline complexes, thus considering that the Lop Lake area is a part of the Tarim Platform. It is unequivocally indicated in this paper that the eastern boundary of the Tarim Platform is at somewhere near 90°30', without further eastward extension.The paper also demonstrates that the Kuruktag uplift is consistent with So uth Tianshan Mountains but quite different from the Tarim Platform in deep-seated geological structure. During Proterozoic or Lower Paleozoic, it was in a platform-facies sedimentary environment; however, the Hercynian tectonic mo vement caused it to be involved in the movement of Tianshan tectonic belt. Ne vertheless, its ultimate assignment remains to be solved through further investi gation. In this paper, the authors describe the fust delineation of the Lop Lake depression by aeromagnetic survey, and evaluate oil-gas geology, structural con dition and basic prospect of the Lop Lake area in camparison with the neigh bouring areas.

Seismic prospecting has been a traditional means in search for oil-gas reser-voirs; nevertheless, it has such disadvantages as complicated -technology, high cost and less success. The a card measurement test performed in a number of oilfields indicates that ²²²Rn can serve as a pathfinder element for oil-gas re servoirs. Its technique is quite simple and its cost is extremely low. Anomali es are characterized by the phenomenon that the sampling points of low inten sity have nothing to do with the lithologic characters and fall to peripheral areas of the oil-bearing district or over the structure. If the effects of struc tural faults are not considered, the boundary of the oilfield is likely to be indi cated by relatively high 222Rn anomalies. This paper makes a tentative discuss ion on formation mechanism and model of the anomaly and physical prerequi site for a card measurement.

In china, remarkable achievements have already been attained in using radon measurement, especially electrostatic alpha-card method, for groundwater and geothermal prospecting and for engineering geology.weak anomalies of radon usually exist near geological structures containing underground water or geothermal water along fracture zones. The reason is that these structures usually related to some factors affecting the distribution of ra dioactive elements, such as the change of lithologic characters, the rupture of rocks and the high radon content in geothermal water. These structures can therefore be found through detecting the faint radioactive anomalies.The electrostatic alpha-card method invented by the authors is one of the techniques for radon measurement. It has high sensitivity, requires low cost,and is seldom disturbed by topography and other surface features. Hence, it can be used in areas with thick regolith or serious electromagnetic disturbance or noise disturbance, such as cities or town, mountains, factories and mines. The electrostatic alpha-card method serves as an effective and economical method in hy-drogeophysical and engineering geophysical exploration and municipal geophysical exploration.Since 1982, experimental work of electrostatic alpha-card method has been conducted at over 100 places in more than 20 provinces to search for uranium, gold, oil and gas, to detect the leakages of reservoirs, to investigate vein rocks, to delineate boundaries of different rock bodies, and to seek for groundwater and geothermal water. Facts show that this radon-measuring technique yields good geological results snd economic benefits.

Based mainly on gravity data,the present paper deals with spatial distribu tion regularity of brine potash deposits in Qaidam Basin, and makes a predic tion on total potassium chloride reserves in potassium-bearing brine of this ba sin.The potash deposits in Qaidam Basin are mainly brine potash ones, which are strictly confined to the Quaternary depressions and coincide with negative gravity anomalies. The formation and development of the Quaternary depressions are in turn related intimately to the basement properties of the Qaidam massif.It is inferred from the gravity and magnetic anomalies that Qaidam Basin might be divided into eastern part and western part, and from west to east po tash deposits become younger in age and the salt layers get thinner in thick ness.The thickness of the potassium-bearing brine layer shows linear positive coorrelation with intensity of the gravity negative anomaly. On such a basis, we have made a prediction on total potash salt reserves for an area of 50000km² in the west of Qaidam Basin.

This paper deals mainly with the test result of using thermal CO₂-releaing method on carbonaceous-siliceous-argillaceous rock type uranium deposits. Evi dence shows the effectiveness of this method. A preliminary discussion is also given on the mechanism of uranium prospecting by CO₂ method, the sampling procedure, the sample processing and the analytical techniques. It is considered that the soil thermal CO₂-releasing survey is undoubtedly a new effective me thod for uranium prospecting.

Preliminary paleomagnetic studies have been conducted on the Middle-Lo wer Devonian Maoshan sandstone in southern Jiangsu. The result shows: (1) the Yangtze massif was located near the equator during the Early-Middle Devo nian; (2) the Ningzhen mountain range had a clockwise horizontal rotation of 37.5°relative to Wuxi area during the Late Jurassic-Early Cretaceous, while the Maoshan mountain range performed a counterclockwise horizontal rotation of 30.7°relative to Wuxi area in the Late Cretaceous; (3) it seems that the stratigraphic horizon of Maoshan sandstone in Ningzhen and Maoshan areas shou ld be raised somewhat so as to correspond to the middle and lower part of Upper Member of Maoshan sandstone in Wuxi area.

For the purpose of performing a quantitative investigation into the negati ve effect and superpositive (or peak-heightening) effect of IP on horizontal strata, the present paper taking a three-layered section as an example and em ploying "critical resistivity method" and "dilute coefficient method" makes a quite overall and systematic study on the formation condition, scope and intensity of these effects as well as, various factors affecting their existence, and, on such a basis, puts forward some valuable criteria and regularities. In order to demonstrate the objectivity of the IP negative effect and the correct ness of the theoretical analysis, this paper also gives the results of related mo del experimentation.

Aimed at solving the trouble existing in the interpretation of frequency soun ding data in China,this paper puts forward a digital interpretation technique. First of all, the forward calculation of frequency sounding curves using digital filters has been carrried out, whose calculation time is noticeably less than that required by the digital integral method. On such a basis, the automatic inversion interpretation with generalized inverse matrix is developed, resulting in satisfac tory results.

Through theoretical calculation of ρ_s and η_s, anomalies and observational signal on the spheroid, this paper expounds anomalous characteristics of the "bipole-dipole"device, and the main advantages of this device in enhancing obser vational signal and saving electric energy as compared with the "dipole-dipole"device. Besides, the calculation leads to formulating the concept of "criticalAB/MN value", which might serve as theoretical basis for the choice of bipolar distance AB in the practical work.