Distribution and genesis of the anomalously high porosity zones in the middle-shallow horizons of the northern Songliao Basin

High-quality reservoirs occur in the middle-shallow horizons of the northern Songliao Basin. The distribution and genesis of their anomalously high porosity zones were studied using measured porosities, examination of ordinary thin sections and blue epoxy resin-impregnated thin sections and by SEM. The results show that there are three anomalously high porosity zones at the depth of 450-900 m, 1,300-1,900 m, 2,050-2,350 m respectively, named zone i, zone ii and zone iii from top to bottom. Horizontally, zone i and zone ii are distributed all over the basin except in the Southeastern Uplift, while zone iii is only distributed in the Central Depression. Zone i was formed by meteoric water leaching as well as organic acid dissolution. Zones ii and iii were dominantly formed by organic acid dissolution. Additionally, clay mineral transformation generating H＋ and hydrocarbon emplacement retarding the cementation of sandstones are also important for the formation of zones ii and iii.

Radiometric and Geophysical Investigations on Exposure Levels and Excess Cancer Risk in Kargi-Kenya

Radiation is considered one of the possible causes of cancer disease with natural background sources including cosmic, terrestrial and internal radiation. A number of cancer disease cases have been reported in Kargi with their causes not properly documented. The present work characterized the radioactivity in soil and water, to find out possible causes of radiation in KARGI-KENYA by studying magnetic intensities, anomalous zones with depth to magnetic sources and delineating subsurface structures. A total of 117 soil and 14 water samples were collected from the entire area and analysed for radionuclides due to 40K, 232Th and 226Ra. Measurement methods of proton magnetometer and gamma spectrometry employing a high purity germanium (HPGe) detector were employed basically to evaluate the magnetic survey and radiological hazard of radioactivities respectively. A total of 51 magnetic field measurements were taken on the eastern part of Kargi, a place suspected to have more concentration of radionuclides. The results showed that there could have been a fractionation during weathering period or metasomatic activity of the radioelements involvement. This study also reveals that the mining activities in the nearby study area could have affected the geologic formation causing more fracturing in rocks and pronounced subsurface structures as a result of mining that could have served as passage for leachates from pollutants as well as the level of radiation in the study area.

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers,NW Pakistan

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan.Two grids covering an area of 10 x18 m2 and 8 x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer.The anomalous zones obtained were plotted on contour maps,2 D and 3 D magnetic intensity maps.Based on the magnetic anomalies,grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis.These zones contain gold concentrations,ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm.Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.

The fine velocity structure of sediment－base－ment layer in the Three－GorgesRegionoftheChangjiangRiver（YangtzeRiver）

In this paper, the study on the fine velocity structure of sedimental and basement layers along 4 deep seismic sounding profiles in the Three Gorges Region of the Changjiang River (Yangtze River) are presented. The velocity of sedimental cover is larger in hills of western Hubei in the western profiles, the total thickness is about 0～0.3 km. However, it becomes thick in southern part of Zigui basin and Zushui river valley, about 5.0 km and 4.0 km thick respectively. The sedimental cover is very thick in Jianghan plains in the eastern profiles, about 5～8 km, and the velocity is lower. The velocity of basemental plane is greater than 6.0 km/s over the whole region. An interface can be divided within the sedimental layer, it is about 3～4 km deep in Jianghan plains, while it approximates to surface in other regions. The profiles are cut by faults in many positions. Where the faults pass, the velocity isopleth varies sharply, and the velocity is obviously low. The basement layer is characterized by high velocity and low gradient, there exist 3 high velocity anomalous zones within the layer, which are located at the west, south and east of Huangling Anticlinorium respectively. They are the upwelling materials of basalt magma with high velocity from deep crust. Perhaps, this process took place before formation of Huangling Anticlinorium. Its action produces the significant variation of basement plane depth and the correspondent development and action of faults.