According to abundant case histories concerning discovery of various sortsof ore deposits using geochemical prospecting methods provided recently bybureau of geology and mineral resources of various provinces, MGMR, the pres-ent paper deals with the topic of rational procedure in geochemical explorati-on. From summarization of these case histories, the author has drawn four ty-pes of procedures for geochemical exploration, with a discussion given on theitrespective characteristics. While emphasizing the necessity that the geochemi-cal reconnaissance and detailed exploration in an ore prospect area should bebased on previous geochemical prospecting data, the author points out that theexploration procedure is not unchangeable, and that the optimum explorationprocedure should de designed and fixed on the basis of varied factors such asrequirements for an exploration project, funds available and anomaly examination.

The hydroelectrochemical method was tentatively used for the first timein the Jincheng ore district in western part of east Shandong. This techniqueis based on the following principle: Around the orebody there exist an ionichalo; under the action of external electric field, metallic ions in the ionic halowill concentrate towards the cathode where they will be absorbed by selectiveadsorbents; the contents of metallic ions in adsorbents may therefore be usedto evaluate ore prospects.During the test, distinct gold anomalies were discovered in the gold oredistrict and some new anomalies were detected in the surrounding areas. Theexamination of a certain proportion of anomalies suggests that gold anomaliesare mainly related to primary gold mineralization and placer gold. In addition,two new gold occurrences and some new anomalies of ore-prospecting signific-ance were found, which provide new targets for gold-survey in this area.This hydroelectrochemical method might concentrate the metallic ions inwater to the maximum, extend the depth of geochemical expolration, lower therequirements for analytical sensitivity, check the seasonal variation of metallicions in water, and thus supply the survey of concealed placer ore depositswith a new effective means.

The Lianyungang-Linyi-Sishui sounding profile runs across the middie partof the Tanlu paleorift belt in eastern China. In 1983, the authors made interpre-tation using one-dimensional vertical non-uniform crustal velocity model, and.in combination of such geologic-ge sical data as gravity and magnetism,performed comprehensive analysis. On the bssis of this work, dynamic beamtracing techique and crustal velocity model for two-dimensional non-uniformmedia were employed to further investigate characteristics of crustal texture inthe middle part of the Tanlu paleorift, with the preliminary achievements illus-trated in this paper. ln dealing with the deep-seated crustal texture and struc-ture as well as their evolution along the Tanlu paleorift, the authors have alsomade a prediction for ore potential in the middle part of this paleorift.

Researches on paleomagnetism and physical properties of rocks were carri-ed out along the Libixia profile in Hechuan area of Sichuan Province, withmore than 500 samples collected from Triassic Xujiahe Formation, LeikoupoFormation, Jialingjiang Formation and Feixianguan Formation. Remanent mag-netization and orientation, magnetic susceptibility and density were determinedfor 2200 samples. Heat demagnetization and alternation demagnetization wereperformed for all samples,and microscopic identification was conducted for partof the samples, indicating that magnetic minerals in major sedimentary rocksof this area axe magnetite and small amounts of pyrrhotite.The paleomagnetic measurements show that during Triassic the SichuanBasin continued to drift from south to north far away from the equator. AtEarly Triassic it was near 18.70°of Northern Latitude, and then reached26.68°, with the latter having a clockwise rotation of 30°relative to the form-er. It is noticed that vertical movement also took place during this period. Allthese data demonstrate that this area in Triassic lay in middle or low latituderegion favourable for formation of saline deposits, thus indicating an encouragingprospect for saline prediction in this area. In addition, strata in this area weredivided according to comprehensive data on physical properties of rocks.It is evident from the research work along the Hechuan profile that thestudy of paleomagnetism and physical properties of rocks is a very effectivemeans in the investigation of formation environment of saline deposits and incorrelation of strata, thus deserving of extensive application.

This paper gives some examples of applying shallow-layer high-resolutionseismic reflection survey to municipal basic engineering geologic exploration. Itdeals emphatically with the trouble met in recording reflected waves tens ofmeters in depth on the background of the city's high noise and the technicalmeasures employed. It is demonstrated by comparison that the selection ofproper parameters in computer processing of data and the migration stack ofwave equation will help to raise the resolving power for faults with small dis-placement.Drilling has evidently shown that this techniques is effective in the inves-tigation into buried depth of foundation of a large building and in finding outconditions of faults and fracture zones. It should therefore be looked upon as animportant method in municipal geophysical prospecting.

Field practice shows that apparent time constant (τ_s) of IP spectrum hasrelatively low dilution, and the differences in time constants between variousrocks and minerals may lead to the discovery of anomalies from orebodies ormineralizations at depth which are unlikely to be detected by parameters ofIP intensities (η_sρ_sm_s orψ_s). Using τ_s as the main parameter and also tak-ing into account all the other parameters of IP spectrum, one might distingu-ish between characteristics of IP anomalies arising from different shallow sour-ces.

Taking magnetic prospecting in the Jurassic coalfield of northern Shaanxias an example, this paper describes techniques and geological effects of magne-tic prospecting in the fire area. The Jurassic coalfield in northern Shaanxi ischaracterized by gently-dipping strata, and has a great abundance of sideriteand pyrite nudules in the overlying rocks. The burnt rock formed by sponta-neous ignition of the coal hed has relatively strong magnetism, whose measuredcurves are complex in shape and show indistinct regularity. Through a compa-rison and analysis of △T anomaly curves along the profile of known outcropsand the exploration peofile, combined with diagnostic points of magnetic mea-surement curves, the present paper delimits the boundary of fire area of thecoalbed. Drilling demonstrates that the boundary of fire area inferred by thismethod has rather high precision and satisfactory geological effects.

Some errors of gravity and magnetic anomalies calculated in terms of Fou-rier transformation are caused by discretizating and truncating of their spectra.The authors have evaluated the folding and wrinkle of the calculated anoma-lies and sugest that a convolution and folding be needed before anti-Fouriertransformation to get rid of such errors. The paper also deals with the singula-rity problem of the spectrum function.

DDC-2 electronic automatic compensater is still being used in hydrogeolo-gical and engineering geological work. Nevertheless, this instrument is pondero-us and has low observation precision and little Tesistance to interference. The DWD-1 type microcomputer electrical sounding instrument designed and produ-ced by Beijing Geological Instruments Factory has attained the advanced levelin China. Its working principle, properties and test result in the field are descri-bed in this paper.