Long-wavelength(>500 km)magnetic anomalies originating in the lithosphere were first found in satellite magnetic surveys.Compared to the striking magnetic anomalies around the world,the long-wavelength magnetic ano...Long-wavelength(>500 km)magnetic anomalies originating in the lithosphere were first found in satellite magnetic surveys.Compared to the striking magnetic anomalies around the world,the long-wavelength magnetic anomalies in China and surrounding regions are relatively weak.Specialized research on each of these anomalies has been quite inadequate;their geological origins remain unclear,in particular their connection to tectonic activity in the Chinese and surrounding regions.We focus on six magnetic high anomalies over the(1)Tarim Basin,(2)Sichuan Basin(3)Great Xing’an Range,(4)Barmer Basin,(5)Central Myanmar Basin,and(6)Sunda and Banda Arcs,and a striking magnetic low anomaly along the southern part of the Himalayan-Tibetan Plateau.We have analyzed their geological origins by reviewing related research and by detailed comparison with geological results.The tectonic backgrounds for these anomalies belong to two cases:either ancient basin basement,or subduction-collision zone.However,the geological origins of large-scale regional magnetic anomalies are always subject to dispute,mainly because of limited surface exposure of sources,later tectonic destruction,and superposition of multi-phase events.展开更多
New methods are presented for processing and interpretation of shallow marine differential magnetic data, including constructing maps of offshore total magnetic anomalies with an extremely high reso- lution of up to 1...New methods are presented for processing and interpretation of shallow marine differential magnetic data, including constructing maps of offshore total magnetic anomalies with an extremely high reso- lution of up to 1-2 nT, mapping weak anomalies of 5-10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks, estimating depths to upper and lower boundaries of anom- alous magnetic sources, and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called "seismic gap" region in the central Kuril Arc vary from 10 to 100 km, with typical dimensions of 25-30 km. The area of the "seismic gap" is a zone of intense tectonic activity and recent volcanism. Deep sources causing magnetic anomalies in the area are similar to the "magnetic belt" near Hokkaido. In the southern and central parts of Barents Sea, tectonic blocks with widths of 30-100 kin, and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km are calculated. Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea-Barents Sea paleorift indicate depths to the lower boundary of the layer of 12-30 km. Weak local magnetic anomalies of 2-5 nT in the northern and central Caspian Sea were identified using the new methods, and drilling confirms that the anomalies are related to concentrations of hydrocarbon. Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra. The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30-40 m and 150-200 m.展开更多
Termite mounds are conventionally surmised as one of the best bio-geological indicator for groundwater occurrence in places where they inhibit.Ground magnetic survey was carried out to prove the assumption about termi...Termite mounds are conventionally surmised as one of the best bio-geological indicator for groundwater occurrence in places where they inhibit.Ground magnetic survey was carried out to prove the assumption about termite mounds as an important indicator for groundwater exploration.Occurrences of 18 Termite mounds were mapped using handheld GPS to identify the suitable trend for magnetic survey.After considering all the criteria such as power lines,fences and fracture system,termite mound 2,12 and 18 were selected in the NNE-SSW trend,and the ground magnetic survey was conducted in ESE-WNW direction which is perpendicular to the trend of the termite mounds using Proton Precession Magnetometer.Totally,99 samples were collected with 5 m sampling interval and 50 m profile interval over an area of 22500 sq.m.The magnetic values varied from–7363 nT to 898 nT with the mean of–331 nT.Processed map of reduction to Equator indicates the presence of NNE-SSW and WNW-ESE magnetic breaks.Analytical signal map designated the presence of magnetic low in the WNW-ESE direction which coincides spatially with the magnetic breaks.The magnetic profile lines have also brought to light the structurally weak zones.Causative body depth range was estimated using power spectrum and Euler method which are from 120 m to 40 m and<20 m to>100 m,respectively.The present study appreciably brings out the spatial relationship between the termite mounds and the hydro-fractures.This confirms the assertion with regard to termite mounds as an effective tool for groundwater exploration.展开更多
The geology of Magaoni area is associated with the presence of heavy minerals [1]. Magaoni’s neighbours Maumba and Nguluku where ilmenite was discovered by Tiomin Resource Inc. in 1996, using drilling and chemical an...The geology of Magaoni area is associated with the presence of heavy minerals [1]. Magaoni’s neighbours Maumba and Nguluku where ilmenite was discovered by Tiomin Resource Inc. in 1996, using drilling and chemical analysis [2]. Ilmenite mineral is known to be magnetically weak, but provides observable magnetic response [3]. In this study, ground magnetic survey method was carried out to map magnetic anomalies of established stations, associated with ilmenite bearing formations. The magnetic contour map plotted showed weak and shallow magnetic signatures spread throughout the study area. 2D Euler deconvolution solutions revealed presence of magnetised formations from near surface to a maximum depth of about 450 m at some points. The weak magnetic formations of near surface indicated presence of ilmenite. Energy dispersive X-ray spectroscopy was done on soil samples collected randomly from the study area to determine the percentage of iron and titanium oxides. The results showed elevated values of titanium dioxide, ranging from 1.5% to 13% which is way above the global average of about 0.7% [4]. The percentage of iron oxide was low, ranging from 1.5% to 4%, this being the reason for weak magnetisation of the study area.展开更多
TM Field,located offshore Niger Delta in the Gulf of Guinea(Nigeria),has been evaluated for potential drilling hazards prior to the drilling of a proposed oil well.This is in a region where potential hazards that coul...TM Field,located offshore Niger Delta in the Gulf of Guinea(Nigeria),has been evaluated for potential drilling hazards prior to the drilling of a proposed oil well.This is in a region where potential hazards that could inhibit successful drilling exercise have not been adequately studied.The study adopted the modern technique of offshore geohazard evaluation that relies mainly on suites of geophysical and shallow geological investigations which include ocean bathymetry using multi-beam echo sounder,sidescan sonar,sub-bottom profiler,magnetic,and 2D-high resolution seismic reflection surveys.The results were integrated to draw inferences about the risk potential of the field.From the bathymetric survey,water depths were found to range from 345 m to 650 m LAT,with seabed relief being 305 m.Water depth at the proposed well location was found to be approximately 450 m and the seabed was found to slope in the northwestern direction.Seafloor gradient was computed as 0.05 across the whole area.Two shallow sub-surface stratigraphic units,labelled A and B,were delineated.Unit A was directly beneath the seafloor and seemed to be composed mainly of clayey/silty sand.Its thickness ranged from 6 m to 70 m across the study area.Unit B appeared to be a layer of sand and its total thickness was not fully delineated.Observable kinks and displacements at the flanks of seabed undulations/depressions on subbottom profiler sections suggested that the depressions may be fault-controlled.On the map generated from the marine magnetic data,a magnetic fault was delineated and this appeared to be coincident with the shallower of the two buried faults on the cross-line seismic section cutting through the proposed well-head location.Interpreted seismic reflection data presented this fault as being inactive.Most of the faults mapped,especially the buried ones,appeared to be inactive except a few.Regions with mapped amplitude anomalies are to be avoided during rig-mobilization operations.Though engineering conditions are expected to vary vertically since layers occur as intercalation,significant lateral variation is not expected within uniform layers of bed.Risk of punch-through associated with clayey formation is expected to be low because the geologic layers are not uniformly and entirely clay.The proposed wellhead location was found to be free of potential hazard sources.展开更多
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 w...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 <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra. 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.展开更多
Superconducting quantum interference device(SQUID),with the advantages of ultra⁃high sensitivity,low noise,broad frequency bandwidth,and excellent low⁃frequency response,is widely used in several geophysical methods,s...Superconducting quantum interference device(SQUID),with the advantages of ultra⁃high sensitivity,low noise,broad frequency bandwidth,and excellent low⁃frequency response,is widely used in several geophysical methods,such as vector magnetic survey,electromagnetic method,gravity and gravity gradient measurement.In this paper,the latest technological progress of SQUID and SQUID⁃based geophysical precision measurement technology are described.In addition,the advantages,characteristics,and existing problems of each measurement technology are analyzed.Combined with the requirements of current geophysical technology,the future application prospect is discussed and development suggestions are given.展开更多
The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any groun...The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any ground survey,including magnetic prospecting,difficult and expensive.The current level of geology requires high-precision and large-scale data at the first stages of geological exploration.Since 2012,technologies of aeromagnetic surveying with unmanned aircraft vehicles(UAV)enter the market,but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods.To increase the scale of survey,it is necessary to reduce the altitude and speed of flight,for which the authors develop the methodical and technical solutions described in this article.To obtain data at altitudes of 5 m above the terrain even in a rugged relief,we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions(even a moderate snowfall),and develop a special software to generate flight missions on the basis of digital elevation models.A UAV has special design to reduce magnetic interference of the flight platform;the magnetic sensor is hung below the aircraft.This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016.The results of the comparison between airborne and ground surveys are presented,which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field.An unmanned survey is cheaper and more productive;the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000−1:1000.展开更多
Aeromagnetic interference could not be compensated effectively if the precision of parameters which are solved by the aircraft magnetic field model is low. In order to improve the compensation effect under this condit...Aeromagnetic interference could not be compensated effectively if the precision of parameters which are solved by the aircraft magnetic field model is low. In order to improve the compensation effect under this condition, a method based on small signal model and least mean square(LMS) algorithm is proposed. According to the method, the initial values of adaptive filter's weight vector are calculated with the solved model parameters through small signal model at first,then the small amount of direction cosine and its derivative are set as the input of the filter, and the small amount of the interference is set as the filter's expected vector. After that, the aircraft magnetic interference is compensated by LMS algorithm. Finally, the method is verified by simulation and experiment. The result shows that the compensation effect can be improved obviously by the LMS algorithm when original solved parameters have low precision. The method can further improve the compensation effect even if the solved parameters have high precision.展开更多
基金the National Natural Science Foundation of China(grant numbers 42004051,42274214,41904134).
文摘Long-wavelength(>500 km)magnetic anomalies originating in the lithosphere were first found in satellite magnetic surveys.Compared to the striking magnetic anomalies around the world,the long-wavelength magnetic anomalies in China and surrounding regions are relatively weak.Specialized research on each of these anomalies has been quite inadequate;their geological origins remain unclear,in particular their connection to tectonic activity in the Chinese and surrounding regions.We focus on six magnetic high anomalies over the(1)Tarim Basin,(2)Sichuan Basin(3)Great Xing’an Range,(4)Barmer Basin,(5)Central Myanmar Basin,and(6)Sunda and Banda Arcs,and a striking magnetic low anomaly along the southern part of the Himalayan-Tibetan Plateau.We have analyzed their geological origins by reviewing related research and by detailed comparison with geological results.The tectonic backgrounds for these anomalies belong to two cases:either ancient basin basement,or subduction-collision zone.However,the geological origins of large-scale regional magnetic anomalies are always subject to dispute,mainly because of limited surface exposure of sources,later tectonic destruction,and superposition of multi-phase events.
基金supported by the Russian Fund of Fundamental Research(Grant No.11-05-00280)
文摘New methods are presented for processing and interpretation of shallow marine differential magnetic data, including constructing maps of offshore total magnetic anomalies with an extremely high reso- lution of up to 1-2 nT, mapping weak anomalies of 5-10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks, estimating depths to upper and lower boundaries of anom- alous magnetic sources, and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called "seismic gap" region in the central Kuril Arc vary from 10 to 100 km, with typical dimensions of 25-30 km. The area of the "seismic gap" is a zone of intense tectonic activity and recent volcanism. Deep sources causing magnetic anomalies in the area are similar to the "magnetic belt" near Hokkaido. In the southern and central parts of Barents Sea, tectonic blocks with widths of 30-100 kin, and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km are calculated. Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea-Barents Sea paleorift indicate depths to the lower boundary of the layer of 12-30 km. Weak local magnetic anomalies of 2-5 nT in the northern and central Caspian Sea were identified using the new methods, and drilling confirms that the anomalies are related to concentrations of hydrocarbon. Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra. The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30-40 m and 150-200 m.
文摘Termite mounds are conventionally surmised as one of the best bio-geological indicator for groundwater occurrence in places where they inhibit.Ground magnetic survey was carried out to prove the assumption about termite mounds as an important indicator for groundwater exploration.Occurrences of 18 Termite mounds were mapped using handheld GPS to identify the suitable trend for magnetic survey.After considering all the criteria such as power lines,fences and fracture system,termite mound 2,12 and 18 were selected in the NNE-SSW trend,and the ground magnetic survey was conducted in ESE-WNW direction which is perpendicular to the trend of the termite mounds using Proton Precession Magnetometer.Totally,99 samples were collected with 5 m sampling interval and 50 m profile interval over an area of 22500 sq.m.The magnetic values varied from–7363 nT to 898 nT with the mean of–331 nT.Processed map of reduction to Equator indicates the presence of NNE-SSW and WNW-ESE magnetic breaks.Analytical signal map designated the presence of magnetic low in the WNW-ESE direction which coincides spatially with the magnetic breaks.The magnetic profile lines have also brought to light the structurally weak zones.Causative body depth range was estimated using power spectrum and Euler method which are from 120 m to 40 m and<20 m to>100 m,respectively.The present study appreciably brings out the spatial relationship between the termite mounds and the hydro-fractures.This confirms the assertion with regard to termite mounds as an effective tool for groundwater exploration.
文摘The geology of Magaoni area is associated with the presence of heavy minerals [1]. Magaoni’s neighbours Maumba and Nguluku where ilmenite was discovered by Tiomin Resource Inc. in 1996, using drilling and chemical analysis [2]. Ilmenite mineral is known to be magnetically weak, but provides observable magnetic response [3]. In this study, ground magnetic survey method was carried out to map magnetic anomalies of established stations, associated with ilmenite bearing formations. The magnetic contour map plotted showed weak and shallow magnetic signatures spread throughout the study area. 2D Euler deconvolution solutions revealed presence of magnetised formations from near surface to a maximum depth of about 450 m at some points. The weak magnetic formations of near surface indicated presence of ilmenite. Energy dispersive X-ray spectroscopy was done on soil samples collected randomly from the study area to determine the percentage of iron and titanium oxides. The results showed elevated values of titanium dioxide, ranging from 1.5% to 13% which is way above the global average of about 0.7% [4]. The percentage of iron oxide was low, ranging from 1.5% to 4%, this being the reason for weak magnetisation of the study area.
文摘TM Field,located offshore Niger Delta in the Gulf of Guinea(Nigeria),has been evaluated for potential drilling hazards prior to the drilling of a proposed oil well.This is in a region where potential hazards that could inhibit successful drilling exercise have not been adequately studied.The study adopted the modern technique of offshore geohazard evaluation that relies mainly on suites of geophysical and shallow geological investigations which include ocean bathymetry using multi-beam echo sounder,sidescan sonar,sub-bottom profiler,magnetic,and 2D-high resolution seismic reflection surveys.The results were integrated to draw inferences about the risk potential of the field.From the bathymetric survey,water depths were found to range from 345 m to 650 m LAT,with seabed relief being 305 m.Water depth at the proposed well location was found to be approximately 450 m and the seabed was found to slope in the northwestern direction.Seafloor gradient was computed as 0.05 across the whole area.Two shallow sub-surface stratigraphic units,labelled A and B,were delineated.Unit A was directly beneath the seafloor and seemed to be composed mainly of clayey/silty sand.Its thickness ranged from 6 m to 70 m across the study area.Unit B appeared to be a layer of sand and its total thickness was not fully delineated.Observable kinks and displacements at the flanks of seabed undulations/depressions on subbottom profiler sections suggested that the depressions may be fault-controlled.On the map generated from the marine magnetic data,a magnetic fault was delineated and this appeared to be coincident with the shallower of the two buried faults on the cross-line seismic section cutting through the proposed well-head location.Interpreted seismic reflection data presented this fault as being inactive.Most of the faults mapped,especially the buried ones,appeared to be inactive except a few.Regions with mapped amplitude anomalies are to be avoided during rig-mobilization operations.Though engineering conditions are expected to vary vertically since layers occur as intercalation,significant lateral variation is not expected within uniform layers of bed.Risk of punch-through associated with clayey formation is expected to be low because the geologic layers are not uniformly and entirely clay.The proposed wellhead location was found to be free of potential hazard sources.
文摘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 <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra. 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.
基金National Natural Science Foundation of China(Grant No.41704172)the National Key Research and Development Project(Grant No.2017YFC0602000)the National Key Research and Development Project(Grant No.2016YFC0303000).
文摘Superconducting quantum interference device(SQUID),with the advantages of ultra⁃high sensitivity,low noise,broad frequency bandwidth,and excellent low⁃frequency response,is widely used in several geophysical methods,such as vector magnetic survey,electromagnetic method,gravity and gravity gradient measurement.In this paper,the latest technological progress of SQUID and SQUID⁃based geophysical precision measurement technology are described.In addition,the advantages,characteristics,and existing problems of each measurement technology are analyzed.Combined with the requirements of current geophysical technology,the future application prospect is discussed and development suggestions are given.
基金This work was supported by the Council on grants of the President of the Russian Federation[Grant Number MK-3608.2018.5].
文摘The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any ground survey,including magnetic prospecting,difficult and expensive.The current level of geology requires high-precision and large-scale data at the first stages of geological exploration.Since 2012,technologies of aeromagnetic surveying with unmanned aircraft vehicles(UAV)enter the market,but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods.To increase the scale of survey,it is necessary to reduce the altitude and speed of flight,for which the authors develop the methodical and technical solutions described in this article.To obtain data at altitudes of 5 m above the terrain even in a rugged relief,we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions(even a moderate snowfall),and develop a special software to generate flight missions on the basis of digital elevation models.A UAV has special design to reduce magnetic interference of the flight platform;the magnetic sensor is hung below the aircraft.This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016.The results of the comparison between airborne and ground surveys are presented,which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field.An unmanned survey is cheaper and more productive;the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000−1:1000.
基金co-supported by the National Basic Research Program of China (No. 623125020103)
文摘Aeromagnetic interference could not be compensated effectively if the precision of parameters which are solved by the aircraft magnetic field model is low. In order to improve the compensation effect under this condition, a method based on small signal model and least mean square(LMS) algorithm is proposed. According to the method, the initial values of adaptive filter's weight vector are calculated with the solved model parameters through small signal model at first,then the small amount of direction cosine and its derivative are set as the input of the filter, and the small amount of the interference is set as the filter's expected vector. After that, the aircraft magnetic interference is compensated by LMS algorithm. Finally, the method is verified by simulation and experiment. The result shows that the compensation effect can be improved obviously by the LMS algorithm when original solved parameters have low precision. The method can further improve the compensation effect even if the solved parameters have high precision.