The present paper discusses the effectiveness of geochemical prospecting forgold and silver resources and some problems which are likely to occur in utili-zation of this technique.Abrief description is made in this paper on the results achieved in geoche-mical prospecting for gold and silver deposits from 1980 to 1985: 59 ore depositsor occurrences were detected during this period. It is indicated that, in search foroldg and silver deposits under the geographical and geological conditions ofChina, small-scale regional geochemical prospecting should first be carried out inorder that the target area can be reduced as soon as possible and the promisingarea wil1 be delineated. It is only on such a base that the reconnaissanceand detailed exploration will attain satisfactory ore-searching results and thereduction of ore prospecting period and expenses will be achieved. It alsodeals with the tasks assigned to various stages of geochemical prospecting suchas regional survey, reconnaissance and detailed exploration. At the stages of1:200, 000 regional survey and 1:50, 000 reconnaissance, stream sediment surveyis the main method to use; during the large-scale detailed exploration, however,the soi1 survey or rock survey shou1d be adopted. Adiscussion is given on tech-niques for combining samples during the reconnaissance and detailed exploration.In addition, this paper points out that it is essential for the geological partyresponsible for gold and silver prospecting to master the analytical technique oftrace gold and to form its own independent working capabilities.

Based on geological and aeromagnetic surveying data, this paper deals syste-matically with some problems concerning geotectonic regionalization and crustalstructure of the Sino-Korean paraplatform, indicating that this paraplatform shouldbe divided into three portions, i. e., North China massif, Baoyin massif and Jiao-liao massif. Adetailed description is made on geological structure of the NorthChina massif with the properties of its two marginal crustal fractures illustrated.It is pointed out for the first time that the Pingdingshan-/wybabsga mega-fracture zone is a mantle-derived ultradeep structure whose eastern and westernsegments are briefly described in such aspecta as their characteristics and theirrole in the evolution of geotectonics and crustal structures.

Results of mercury survey test conducted over three nonanticlinal confinedtype oil and gas fields are reported in this paper. The oil-bearing reservoirs areusually buried 1200-3000m below the surface, pertaining respectively to oil andgas field of lithological confinement, that of fault block confinement and that oflithological-faulting confinement. The techniques employed include such means asdetermining gaseous mercury in soil all by negative pressure method and accu-mulative adsorption method, total mercury content in soil, adsorbed mercury insoil and mercury in water. The test results indicate that the methods used alldisplay distinct anomalies over the oil and gas fields, with their characteristicsanalogous to those of mercury vapour anomalies over metallic ore deposits. Theshape and spatial distribution of these anomalies depend largely on properties ofvapour-leading structures.The mercury vapour anomaly and electrical anomaly are contrasted relativeto oil and gas accumulations. These two sorts of anomalies sometimes coincidewith, and sometimes respectiely have some distance from, the projection of theoil and gas accumulation. This further demonstrates the effects of structural con-figuration on the anomalies.In addition,it is inferred that the location of oil andgas accumulation might be approached and determined on the basis of characte-ristics of mercury vapour aomalies and electrical anomalies.

Conventional analyses of exploration geochemical data assume that the bank-ground is a constant or slowly changing value, equivalent to a plane or smoothlycurved surface. Nevertheless, It is better to regard the geochemical backgroundas a rugged surface, varying with changes in geology and environment. Thisregged surface can be estimated from observed geological, geochemical, andenvironmental properties by using robust multivariate statistics.Ametbod of background adjustment was developed and applied to ground-water and stream sediment reconnaissance data collected from the Black Hillsarea, South Dakota, U. S. A. The Iithology of source rocks seems to be a dominantfactor determining chemical composition of groundwater or stream sadiments. Themost efficacious adjustment procedure is to regress uranium comcentration on sele-cted geochemical and environmental variables for each lithologic unit, and thento delineate anomalies of the combined residuals. This is called the "methed ofunit-wise adjustment of geochemical background". Robust versions of regressionand RQ-mode principal components analyds rather than ordinary techniques wereused to guard against distortion caused by outliers. Anomalies delineated by thisbackground adjustment procedure correspond with uranium prospects much betterthan anomalies delineated by conventional procedures do. The procedure should beapplicable to geochemical exploration for other metals at different scales, andthe adoption of this procedure may result in a revolution in geochemical dataanalyses.

Of various parameters of depths related to ore resources,the basicity mightreflect the differences in components or average chemical composition of theearth's crust. Amethod for calculating apparent basicity of the crust by usinggravity data is proposed in this paper with a discussion on some relativelydecisive parameters. Atechnique for dividing the crust and calculating thedepths of interfaces within the crust is also presented on the basis of apparentbasicity together with a description of its application in southeastern Hubei.

The five-pole central array is one of the focusing techniques. The presentpaper mainly describes the basic principle of this device. By varying parame-ters of some regular geometric bodies, the authors have also conducted ditchand resistive network modeling, with the results of the simulation contrastedgraphically with those obtained by conventional devices.

In practical work, the relative position between the blind orebody and thetwo power-supply electrodes of the intermediate-gradient facility not distant fromthe orebody frequently makes the blind orebody somewhat under the conditionof non-horizontal uniform polarization. This causes the obtained η_s curve and theconnections of the η_s curve formed by movement of the power-supply electrodesto be distorted to some extent.Through simulating the usually-adopted IPintermediate-gradient facilityand taking volume polarization as an example,the present paper makes an ana-lysis and discussion on the above-mentioned distortion by calculating the inter-mediate-gradient η_s curve and its connections with the formula of point powersource. In addition, it mentions some problems that are worth noticing in proces-sing observed intermediate-gradient η_s data and gives some viewe on IP η_s full-field measurement technique that deserves popularization.