The vector transformation and pole reduction from the total-field anomaly are signifi cant for the interpretation.We examined these industry-standard processing procedures in the Fourier domain.We propose a novel iter...The vector transformation and pole reduction from the total-field anomaly are signifi cant for the interpretation.We examined these industry-standard processing procedures in the Fourier domain.We propose a novel iteration algorithm for regional magnetic anomalies transformations to derive the vertical-component data from the total-field measurements with the variation in the core-fi eld direction over the region.Additionally,we use the same algorithm to convert the calculated vertical-component data into the corresponding data at the pole and realize the processing of diff erential reduction to the pole(DRTP).Unlike Arkani-Hamed’s DRTP method,the two types of iterative algorithms have the same forms,and DRTP is realized by implementing this algorithm twice.The synthetic model’s calculation results show that the method has high accuracy,and the fi eld data processing confi rms its practicality.展开更多
A magnetic survey was carried out to find out the possibilities of demarcating a phosphate deposit from the surrounding country rocks. It is a well-established fact that the magnetic mapping can be utilised to investi...A magnetic survey was carried out to find out the possibilities of demarcating a phosphate deposit from the surrounding country rocks. It is a well-established fact that the magnetic mapping can be utilised to investigate the subsurface objects, materials or different rock types based on their magnetic properties. Those rocks with ferro-magnetic minerals such as magnetite generate magnetic anomalies which in turn help to investigate the subsurface occurrence of mineral deposits. An economic phosphate deposit in Sri Lanka, known as Eppawala Phosphate deposit was selected for this study. The deposit was formed as an accumulation of secondary products of an apatite-rich carbonatite. Due to weathering of iron-rich carbonatite, magnetite and its derivatives are intimately bound with the said deposit. Therefore, the magnetic signature of the phosphate body is different to that of the surrounding country rocks. Despite some studies on different aspects of the deposit, subsurface extents of the ore body are so far not adequately studied. Therefore, this study was conducted to identify the boundaries of the phosphate body. The study was carried over an area of 12 km2 5 km north from the current mining site and survey was conducted. GSM-19 Overhouser system with integrated GPS was used to collect field data. Magnetic anomalies were plotted using a predefined grid. The maximum positive and negative anomalies encountered in the survey area are 690 nT and 829 nT respectively. This study showed that magnetite is not distributed evenly in the area and the deposit extended along the north south direction. Further, processing of analytical signal using the anomalies showed that the carbonatite occurs as a continuous body trending in North South direction. Low magnetic latitudes magnetic data interpretation is difficult because the vector nature of the magnetic field. Therefore, “reduction to pole” concept and “analytical signal concept” were used for the data analysis. Reduction to pole map and analytical signal map are comparatively similar and the change of declination value has no significant effect on the map of reduction to pole.展开更多
基金supported by the National Key R&D Program of China (No. 2017YFC0602000)the China Geological Survey Project (Nos. DD20191001 and DD20189410)。
文摘The vector transformation and pole reduction from the total-field anomaly are signifi cant for the interpretation.We examined these industry-standard processing procedures in the Fourier domain.We propose a novel iteration algorithm for regional magnetic anomalies transformations to derive the vertical-component data from the total-field measurements with the variation in the core-fi eld direction over the region.Additionally,we use the same algorithm to convert the calculated vertical-component data into the corresponding data at the pole and realize the processing of diff erential reduction to the pole(DRTP).Unlike Arkani-Hamed’s DRTP method,the two types of iterative algorithms have the same forms,and DRTP is realized by implementing this algorithm twice.The synthetic model’s calculation results show that the method has high accuracy,and the fi eld data processing confi rms its practicality.
文摘A magnetic survey was carried out to find out the possibilities of demarcating a phosphate deposit from the surrounding country rocks. It is a well-established fact that the magnetic mapping can be utilised to investigate the subsurface objects, materials or different rock types based on their magnetic properties. Those rocks with ferro-magnetic minerals such as magnetite generate magnetic anomalies which in turn help to investigate the subsurface occurrence of mineral deposits. An economic phosphate deposit in Sri Lanka, known as Eppawala Phosphate deposit was selected for this study. The deposit was formed as an accumulation of secondary products of an apatite-rich carbonatite. Due to weathering of iron-rich carbonatite, magnetite and its derivatives are intimately bound with the said deposit. Therefore, the magnetic signature of the phosphate body is different to that of the surrounding country rocks. Despite some studies on different aspects of the deposit, subsurface extents of the ore body are so far not adequately studied. Therefore, this study was conducted to identify the boundaries of the phosphate body. The study was carried over an area of 12 km2 5 km north from the current mining site and survey was conducted. GSM-19 Overhouser system with integrated GPS was used to collect field data. Magnetic anomalies were plotted using a predefined grid. The maximum positive and negative anomalies encountered in the survey area are 690 nT and 829 nT respectively. This study showed that magnetite is not distributed evenly in the area and the deposit extended along the north south direction. Further, processing of analytical signal using the anomalies showed that the carbonatite occurs as a continuous body trending in North South direction. Low magnetic latitudes magnetic data interpretation is difficult because the vector nature of the magnetic field. Therefore, “reduction to pole” concept and “analytical signal concept” were used for the data analysis. Reduction to pole map and analytical signal map are comparatively similar and the change of declination value has no significant effect on the map of reduction to pole.
