The multipurpose regional geochemical investigation in China revealed the extensive distribution of harmful elements, which has aroused attention among experts. Soil pollution will be harmful to ecological system and human health, and hence the formulation of the soil pollution grade standard is very important. In the National Soil Environment Protection Standard System, the soil pollution grade standard is a quantitative division for the pollution discovered in the investigation, the soil environment quality standard decides the critical value based on the affecting degree of pollution on the environment, and the soil pollution evaluation standard serves as the indexes for scientific researches on the existing problems. A unified grade division standard is adopted for the soil pollution, which divides the grade into national grade, river valley grade, provincial grade and prefecture or city grade. The formulation of the standard has experienced the from-part-to-overall understanding process and the from-overall-to-part policy-making process. It is the authors' leading thought that the soil pollution standard and the division of pollution grade should be first formulated on the basis of multipurpose regional geochemical survey.

In recent years, two remarkable changes have taken place in the concept of oil and gas geochemical exploration, i.e., the oil and gas geochemical exploration has grown from the points (oil and gas reservoirs) to the extensive regions (main oil and gas basins in China), and from the shallow (near-surface) part to the depth (downhole exploration); the oil and gas geochemical exploration has developed from the reconnaissance survey to the four-grade survey stage consisting of general survey, reconnaissance survey, detailed survey and intensive survey. Remarkable advances have been recently made in oil and gas geochemical exploration of China. The method and technology for geochemical exploration have gained development, the basic theoretical researches have made advances, some new test and analysis techniques have been developed, the new data-processing and interpretation-evaluation system has been formulated, and the database of oil and gas geochemical exploration for main oil and gas basins in China has been set up. This paper describes the development trend of oil and gas geochemical exploration in China.

With its special characteristics, the airborne radioactive survey will surely have extensive application prospects in regional environmental radioactive measurement and nuclear accident investigation. Exemplified by some case studies, this paper illustrates the advantages of applying airborne radioactive survey to the investigation of nuclear accidents, and deals with the feasibility of formulating an airborne radioactive emergency early warning plan.

Using about 80,000 km² of 1:200 000 regional geochemical prospecting data, the authors delineated the Ag element geochemical block in west Qinling area, studied the internal geochemical model, traced the probable places of large-superlarge type deposits. With the analogue method of metallogenic rates, the resource quantity was also predicted. The results obtained will play a guiding role in strategic ore resource prognosis and exploration arrangement of this area.

In this paper, with the metallogenic series theory as the guide and the geochemical data as the basis, all lead-zinc ore deposits in the region were classified into two sub-series, i.e., LF type (with low content of iron group elements) and HF type (with high content of iron group elements), and a regional geochemical prognostic model was set up by using the logical information method. The model holds that the metallogenic environment of the LF type is structural reductive space whereas that of the HF type reflects entirely characteristics of sedimentary minerallization, with no evidence of tectonic minerallization. A comparison of the prospecting model of the HF type with the prediction model of the VMS type reveals that their thermal dynamic mechanisms are different: the former is related to basic-ultrabasic rock intrusion, while the latter to acidic rock intrusion.

Based on areal geochemical rock survey in the Qilishan gold ore district,the authors delineated four gold anomalies,of which two are reflections of known ore deposits,whereas the other two are new gold anomalies.Element characteristics of rocks,ores,and anomalies for known gold ore bodies were also studied and,as a result,indicator elements and the element zoning sequence were determined,and the criteria for anomaly appraisal were established.Four gold anomalies were evaluated.Two newly-discovered gold anomalies were considered to be of good prospects,and locations of inspection drill holes were determined.Drilling test at No.4 gold anomaly discovered a rich gold ore body at depth.The geochemical exploration conducted by the authors demonstrate the existence of more concealed ore bodies in this gold mine,and also prove that the application of rock fissure geochemical method to the prospecting for concealed ore bodies in "critical" mines are of great significance.

The ores in the Daijiazhuang Zn-Pb deposit in Tanchang County of Gansu Province are mainly of the oxidation type and the ore bodies are hosted by bioclastic limestone and silicalite formed in shallow-sea facies and biohermal facies. Ore bodies are controlled by NW-trending tenso-shear faults and their subsidiary fractures. The electrical properties of the rocks and ores are obviously different and the determined IP anomalies are distributed along the NW-trending belt. All this is consistent with the results of Pb, Zn, Ag, As, Sb, Au and Hg soil geochemical measurements. Based on geophysical and geochemical studies, the authors found some ore bodies and put up the geological-geophysical-geochemical prospecting criteria.

The Miaoling-Xiaonangou-Zhaoling gold metallogenic belt is a secondary ore-forming belt controlled by Machaoying faulted zone. The authors formulated a geological-geochemical ore-prospecting model for this metallogenic belt on the basis of a systematical summary of the characteristics of the belt, which provides the train of thought for ore-prospecting work in this area.

The Qulong copper porphyry deposit discovered in recent years is likely to develop into a superlarge copper porphyry deposit. The ore district has abundant surface water. There is a malachite precipitation zone several kilometers in length along the lower reach of the main water system in the ore district. This paper has discussed the main factors controlling the accumulation of malachite, the variation of element content in the water system before and after the rainy season and the indication role of hydrogeochemical anomalies in determining the position of the ore deposit and the perspective target area.

In this paper, the authors selected the Wuao Pb-Zn deposit to study the renewing of the earlier geophysical prospecting data, analyze the effects and problems of geophysical prospecting, and summarize more geophysical and geological characteristics of this deposit. On such a basis, the possibility of the peripheral prospecting is discussed.

The distribution and concentration of elements were investigated from the samples collected in vertical profiles over different deposits.The results show that elements are enriched in fine fractions of the samples.In addition,elements tend to be concentrated in cemented silt and clay materials.Sampling of the fine fractions (-160 mesh) from the cemented soil horizon is an effective method for regional exploration.

There are many magnetic anomalies found by aeromagnetic prospecting and ground magnetic exploration in the Qitianling tin-polymetallic ore area in Hunan Province. The right consideration of the relationship between the magnetic anomalies and the ore anomalies will decide the evaluation of the ore-seeking prospects and the arrangement of exploration projects. In the light of the statistic characteristics of the rock magnetic parameters, this paper discusses the problems concerning the application of magnetic exploration.

Starting with the research on the characteristics of frequency spectra of the IP field as well as charging-discharging time and based on experiment results,the authors summed up frequency spectra,time spectra and decay rate characteristics of sulfide mineralized bodies(chalcopyrite) and graphite-bearing dolomitic marble,and detected new parameters for qualitative evaluation of IP anomalies.Practice shows that the application of frequency spectrum characteristics to the evaluation of IP anomalies caused by sulfide mineralized bodies(chalcopyrite) and graphite-bearing dolomitic marble is effective.

Using the results from the fixed point sounding and the traditional sounding methods (symmetric quadrupole sounding and Wenner sounding) in a certain lead-zinc ore district, the authors summed up the results of three different methods. It is held that the fixed point source sounding method is superior to the traditional electrical sounding methods in such aspects as the determination of the central buried depth, geometric shape, and mode of occurrence of the ore body.

Avoiding the influence of the near-surface low-velocity zone and the weathering bed, the inter-well seismic exploration can obtain seismic signals with high resolution and high signal-to-noise ratio. The technique has been put into use in recent years. Three problems concerning the inter-well seismic exploration have been discussed in this paper, namely, the formation mechanism and the attenuation method of the inter-well pipe wave, the method for tomographic imagery and that for XSP-CDP imagery. The inter-well data from Luojia and Ken-71 area were successfully processed, with relatively satisfactory tomographic imagery and reflection wave imagery obtained. These results help us understand the transverse spreading of the inter-well velocity and the existence of small faults.

The quantity of seismic signal data is very large. If merely composite succession FFT algorithm is used to process the seismic signal, the data quantity will be doubled and redoubled, and hence the calculation will become cumbersome. Aimed at the problem of the real succession of the seismic signal, this paper deals with the fast Fourier transform of the real signal. Three fast Fourier transform algorithms for real successions are put forward, a quantitative analysis for reducing the calculation work was made, and the practical seismic data were computed. It can be seen from the analytical and computation results that these three methods can obviously reduce the quantity of calculation and save the storage space of the computer.

The zero-offset (z₀) section is an important achievement in seismic reflection imaging. The differences between the common midpoint (CMP) and the common reflection point (CRP) are discussed on the basis of the dome-like reflector model. In usual seismic data processing, we cannot get the correct z₀ sections if oblique layers are imaged. However, the prestack time migration technique using CRP stacking can help us to obtain the correct z₀ sections. This paper discusses the key steps in the application of such prestack time migration techniques as seismic data preprocessing, construction of migration-velocity field and CRP gather processing after migration. The processing effects are demonstrated with real data.

We introduce the prediction filtering method in f-x-y domain.The prediction filtering method using singular value decomposition in f-x-y domain has been put forward in this paper.The f-x-y prediction filtering can be applied after the SVD filtering.Thus the prediction filtering is carried out in f-x-y domain.Finally we compare the routine prediction filtering method with the prediction filtering method using singular value decomposition.The theoretical modeling results show that the method can more effectively increase the signal/noise ratio than the routine method.And it can maintain the continuity of effective events.

This paper describes the processing result by GPR software. Through reading and displaying data, setting the output parameters and exporting to DXF files, the CAD vectorgraph can be realized. The paper puts up a method for replacing the bitmap by vectorgraph, thus overcoming the troubles such as the GPR bitmap distortion and the difficulty in quoting.

In order to verify the validity of ground-probing radar in search for the fractured zone of bedrock and identify characteristics of its GPR profile, the authors built a fairly good fault zone model by assuming the dielectric constant of the fractured zone which is distributed randomly in a certain spatial range. Using finite-difference time-domain (FDTD) simulation method, the authors obtained the two-dimensional GPR forward profile of the fracture broken belt that can better reveal its features on the GPR profiles. Through simulating different fractured zone models with different crushing degrees or different bedrock dielectric constants, the authors are fully acquainted with their characteristics on GPR profiles. A practical example shows that characteristics of the fractured zone revealed in forward simulation also exist in the practical GPR detection profile. It can thus be concluded that the forward simulation is a practical and reliable means in providing supports for the interpretation of practical GPR profiles.

Based on geological radar penetrating practice for soil and stone dam hidden dangers of reservoirs in northwestern loess areas and from the variations of the disturbance, pore ratios and water contents of the soil bodies in the percolation positions, the authors analyzed the variations of geological waveform characteristics and waveform phase axis continuation, and summed up the graph characteristics of the percolation hidden dangers in different periods.

Based on sampling data from soil of deep and top layers, the authors obtained the standard contents of main heavy metallic elements in soil of a vegetable base in Jiangxi Province, analyzed the distribution and relevant characteristics of five heavy metallic elements in top soil of this base, and probed into the migration features of these elements. According to related laws and decrees issued by the Ministry of Agriculture, this paper preliminarily evaluated the present situation of soil heavy metal pollution in this base and put forward the proposal that the scope of this vegetable base should be reasonably regulated.The research reveals that there exists obvious accumulation of Cd, Hg and Pb in top soil (farming layer) of this vegetable base. Some areas have become "safeless production places" with the Cd, Hg and Pb contents of soil in excess of the Environment Quality Standard for Harmless Food Production Places stipulated by the Ministry of Agriculture. It is found that the original contents of heavy metallic elements in soil are not high, that the accumulation of heavy metallic pollution results mainly from the productive activity of mankind, i.e., from the prolonged unreasonable application of fertilizer and pesticide.

This paper describes the automated Burris metal zero-length spring gravity meter produced by the Zero-Length Spring Corporation,USA,which is an upgrade of LaCoste & Romberg land meters. The new land gravity meter features the UltraGravTM control system, worldwide range with micro-Gal precision, and a fully integrated meter design. This paper also deals with the concept of the zero-length spring and the history of LaCoste & Romberg land meters.