Natural remanent magnetization (NRM) is the part of rock magnetism, which leads to more complex magnetic data inversion and interpretation. The conventional inversion methods focus on reducing the influence of the remanent magnetization and recovering the depth and shape of magnetic sources, while the remanent magnetization is an important parameter to understand the mineralization /geological process. The remanent magnetization can not only reflect the geological structure and mineral composition, but also contain the geomagnetic field record of each geological period. We study to obtain the geological information involved with the remanent magnetization. In the case of Daye iron-ore deposit in Hubei province, we calculate the direction and intensity of remanent magnetization based on the prior information of Königbergs ratio, the direction and intensity of the total magnetization. In the Yeshan region, we use the IDQ curve to estimate the direction of the remanent magnetization. The results show that the remanent magnetization direction, extracted from magnetic anomaly, can not only indicate the information of local geological activities, but also be used to classify the lithologies of the sub-anomalies.
Magnetization vector inversion has been developed since it can increase inversion accuracy due to the unknown magnetization direction caused by remanence. However, the three components of total magnetizations vector are simultaneously inverted and then synthesized into the magnetization magnitude and direction, which increases the inherent non-uniqueness of the inversion. The positions of the three components of the magnetization vector are originally consistent. If there is a lack of constraints between them during the inversion process, they may be misaligned, resulting in a large deviation between the synthesized vector model and the ground truth. To address this issue and at the same time increase the accuracy of the edges of the inversion models, this paper proposes a magnetization vector inversion scheme with model and its gradients’ constraints by sparse Lp norm functions based on the amplitude of the three components of the magnetization vector instead of a single component to improve the accuracy of the inversion result. To evaluate the inversion accuracy performance, an improved evaluation index is also proposed in this paper, which can better evaluate the accuracy of the shape, position and magnetization amplitude of the inversion model. The proposed inversion method can recover the models with higher accuracy compared with traditional methods, indicated by the inverted model and the evaluation indexes. Simulation results based on the open-source SimPEG software and inversion on actual measured Galinge iron ore deposit (China) data verified the effectiveness and advantages of the proposed method.
SUMMARY Magnetic susceptibility and natural remanent magnetization of rocks are useful parameters to study geological structures and geodynamic processes. Traditional widely used algorithms for the inversion of magnetic data can recover the distribution of the apparent susceptibility or total magnetization intensity, but do not provide information on the remanent magnetization. In this paper, we propose a framework to directly invert for the magnetic susceptibility and the natural remanent magnetization vector using surface or airborne magnetic data, assuming that the Köenigsberger ratio of the rock is known or approximately deducible. The susceptibility and remanence are computed using two different approaches: (1) the susceptibility, intensity, and direction of the remanent magnetization are continuously recovered for each discretized cell and (2) the remanence direction is assumed to be uniform in each subzone and is iteratively computed as discrete values. Both processes are implemented using the preconditioned conjugate gradient algorithm. The method is tested on three synthetic models and one field data set from the Zaohuohexi iron-ore deposit, Qinghai Province, northwest China. The results of the continuous inversion show the trend of the remanent magnetization directions, while the discrete inversion yields more specific values. This inversion framework can determine the source bodies’ geometry and position, and also provide superposed and comprehensive information on the natural remanent magnetization, which may be useful to investigate geological bodies bearing stable primary remanent magnetization.
Farmland and grassland are the main land utilization pattern in the western China.For resource sustainable development and utilization,it is urgent to strengthen the protection and construction of farmland and grassland resource.Comprehensive analysis on the status of farmland and grassland show that the resource of farmland and grassland are rich,but low productivity and deteriorative environment have been a serious drawback for the development of western China.The farmland and grassland is not only a guarantee of food safety,but also an important barrier for environment protection.Strengthen law construction and capital inputting,increasing technique and carrying out long term monitoring and evaluation of farmland and grassland in the western China are the main ways for the protection and construction of farmland and grassland resource.
Abstract: The Zhou'an PGE‐Cu‐Ni deposit was recently discovered in the Qinling orogenic belt bound by the Yangtze and the North China Cratons. It is a blind deposit thoroughly covered by the Cenozoic alluvial sediments in the Nanyang Basin. As the first large PGE‐Cu‐Ni deposit discovered in the Qinling‐Dabie‐Sulu orogenic belt, its geological and geochemical characteristic, isotope age, genesis and tectonic setting are of wide concern in both scientific studies and ore exploration. In this contribution, we report the results obtained from a pioneering study. The Zhou'an ultramafic complex is ferruginous, with m/f = 4.79–5.08, and shows the nature of tholeiite series. It is rich in light rare earth elements, Rb, Th, U, La, Sm, Zr and Hf, and poor in heavy rare earth elements, Nd and Ta, suggesting an intraplate setting. It has high 87 Sr/ 86 Sr and low 143 Nd/ 144 Nd ratios. The ratios of Zr/Nb, La/Nb, Ba/Nb, Rb/Nb, Th/Nb, Th/La and Ba/La, suggest the magma originated from lithosphere mantle. The Fo values of olivine and Pd/Ir‐Ni/Cu diagram suggest primary magma was High Mg basalt. The laser ablation inductively coupled plasma atomic emission spectroscopy zircon U‐Pb age is 641.5 ± 3.7 Ma.
Many scholars in China introduced the theory of sequence stratigraphy,applying to Chinese continental fault depression lake, they have made a lot of achievements in scientific research. However, there are still a lot of controversy according to the establishment in Shahezi group of sequence stratigraphic framework in Xujiaweizi fault depression.Sequence boundary identification method in this paper is based on the “instruction of Vail’s sequence stratigraphy theory, identification of seismic unconformity, verification by using logging methords”. And, following the principle of isochronous ,sequence stratigraphic framework of this region is established clearly. The southern Xujiaweizi fault depression in Shahezi group is divided into 1 second grade sequence, in the interior distributed SQ1-SQ4 4 third grade sequences from the bottom. Developmental stages at the bottom of SQ1 and the top of SQ4, basin is small and water is shallow. However, Developmental stages in SQ2 and SQ3,water enters the lake basin continuously, formed a sedimentary background of “wide basin and deep water”. In addition, each of the three grade sequence has split structure, the lake transgressive domain and lake regression domain two system tracts. Besides, the reversed order para-sequence sets caused by the lake regression and progradation set on the positive para-sequence sets caused by the lake transgression and retrogradation. On the basis of sequence stratigraphic division and correlation, conbined with the regional construction and the supply of provenance ,the sedimentary sequence framework of evolution characteristics are studied.That fan delta,braided river delta, lacustrine are the main facies types in study area. Characteristics of sedimentary evolution there are like this: the characteristics of sedimentation evolution show framework controls sand, succession of evolution, separated-source sedimentary, contiguously distribution.
Abstract Gravity prospecting is an important geophysical method for mineral resource exploration and investigating crustal structures. Based on the importance of this method, we propose a novel method that takes advantage of rock data, using a supervised deep fully convolutional neural network, that generates a sparse subsurface distribution from gravity data. During the data preparation phase, we used the random walk to synthesize diverse geological models, in which each model element has only two choices. During network training, we feed the geological model as labels and their corresponding forward modeling of gravity data as the input, after which the network parameters are learned using the Dice coefficient. During network testing, six general types of 3D models were developed, and corresponding gravity data was entered into a trained network to achieve the prediction results in less time. The statistical analysis of two evaluation metrics showed that our network was highly effective using our proposed data set, wherein the recovered models were characterized by distinct boundaries. Furthermore, our approach was validated using real data obtained from the San Nicolas deposit in central Mexico.
Natural remanent magnetization and self-demagnetization on high-susceptibility bodies are two important factors affecting magnetic data inversion. We propose a framework for the inversion and interpretation of magnetic anomalies, in which significant remanent magnetization and self-demagnetization are present simultaneously. The framework is based on the assumptions that the external applied field and internal self-demagnetization field are uniform and the deflection of self-demagnetization in the total magnetization direction is negligible. First, the magnetization vector distributions are obtained from magnetic data by estimating the magnetization direction, then inverting for the magnetization intensity distribution, using the inferred magnetization direction as a constraint. Based on a priori information about the Koenigsberger ratio derived from petrophysical measurements, the direction and intensity of the remanent magnetization are obtained. The self-demagnetization factor is then computed using the finite volume method. Finally, the true-susceptibility distribution is achieved by correcting for the self-demagnetization effect. The method is first applied to synthetic magnetic data produced by a prism-shaped source model that has significant remanent magnetization and high susceptibility. In a case study of the Daye iron-ore deposit, Hubei province, China, the true susceptibility and remanent magnetization are reconstructed. The remanence direction information reveals that local geological activities such as synclines and faults lead to changes in the remanence directions at different local deposits.
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