Joint inversion of gravity and magnetic data for a two-layer model

Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose a joint gravity and magnetic inversion methodfor two-layer models by concentrating on the relationship between the change of thicknessI and position of the middle layer and anomaly and discuss the effects of the key parameters. Model tests and application to field data show the validity of this method.

3D inversion modeling of joint gravity and magnetic data based on a sinusoidal correlation constraint

Joint inversion based on a correlation constraint utilizes a linear correlation function as a structural constraint.The linear correlation function contains a denominator,which may result in a singularity as the objective function is optimized,leading to an unstable inversion calculation.To improve the robustness of this calculation,this paper proposes a new method in which a sinusoidal correlation function is employed as the structural constraint for joint inversion instead of the conventional linear correlation function.This structural constraint does not contain a denominator,thereby preventing a singularity.Compared with the joint inversion method based on a cross-gradient constraint,the joint inversion method based on a sinusoidal correlation constraint exhibits good performance.An application to actual data demonstrates that this method can process real data.

Monazite Recovery by Magnetic and Gravity Separation of Medium Grade Zircon Concentrate from Senegalese Heavy Mineral Sands Deposit

Gravity, magnetic and electrostatic separation methods allowed to obtain different titanium oxide concentrates (ilmenite, leucoxene, rutile) and different varieties of zircon concentrates (premium zircon, standard zircon, medium grade zircon standard) from Senegal’s heavy mineral sands. During mining separation, monazite, which is a paramagnetic mineral, was found in a non-negligible concentration of 0.57 wt% on average in the medium grade zircon standard which also contains 37.96 wt% zircon and 44.46 wt% titanium oxides. Magnetic and gravity separation tests were carried out on the Medium grade zircon standard (MGZS) to produce a monazite concentrate at Eramet Ideas laboratory. Magnetic separation at 1.5 teslas intensity resulted in the recovery of 94.8% of the monazite from the MGZS. Gravity separation also recovered 76.6% of the monazite from the MGZS. The combination of these two treatment methods can thus produce three concentrates from MGZS (a monazite concentrate, a zircon concentrate, and a titanium oxide concentrate).

Fast 3D joint inversion of gravity and magnetic data based on cross gradient constraint

The gravity and magnetic data can be adopted to interpret the internal structure of the Earth.To improve the calculation efficiency during the inversion process and the accuracy and reliability of the reconstructed physical property models,the triple strategy is adopted in this paper to develop a fast cross-gradient joint inversion for gravity and magnetic data.The cross-gradient constraint contains solving the gradients of the physical property models and performing the cross-product calculation of their gradients.The sparse matrices are first obtained by calculating the gradients of the physical property models derived from the first-order finite difference.Then,the triple method is applied to optimize the storages and the calculations related to the gradients of the physical property models.Therefore,the storage compression amount of the calculations related to the gradients of the physical property models and the cross-gradient constraint are reduced to one-fold of the number of grid cells at least,and the compression ratio increases with the increase of the number of grid cells.The test results from the synthetic data and field data prove that the structural coupling is achieved by using the fast cross-gradient joint inversion method to effectively reduce the multiplicity of solutions and improve the computing efficiency.

Simultaneous Structure-Coupled Joint Inversion of Gravity and Magnetic Data Based on a Damped Least-Squares Technique

The structure-coupled joint inversion method of gravity and magnetic data is a powerful tool for?developing improved physical property models with high resolution and compatible features;?however, the conventional procedure is inefficient due to the truncated singular values decomposition?(SVD) process at each iteration. To improve the algorithm, a technique using damped leastsquares?is adopted to calculate the structural term of model updates, instead of the truncated SVD. This?produces structural coupled density and magnetization images with high efficiency. A so-called?coupling factor is introduced to regulate the tuning of the desired final structural similarity level.?Synthetic examples show that the joint inversion results are internally consistent and achieve?higher?resolution than separated. The acceptable runtime performance of the damped least squares?technique used in joint inversion indicates that it is more suitable for practical use than the truncated SVD method.

A MATLAB-Based Numerical and GUI Implementation of Cross-Gradients Joint Inversion of Gravity and Magnetic Data

The cross-gradients joint inversion technique has been applied to multiple geophysical data with a significant improvement on compatibility, but its numerical implementation for practical use is rarely discussed in the literature. We present a MATLAB-based three-dimensional cross-gradients joint inversion program with application to gravity and magnetic data. The input and output information was examined with care to create a rational, independent design of a graphical user interface (GUI) and computing kernel. For 3D visualization and data file operations, UBC-GIF tools are invoked using a series of I/O functions. Some key issues regarding the iterative joint inversion algorithm are also discussed: for instance, the forward difference of cross gradients, and matrix pseudo inverse computation. A synthetic example is employed to illustrate the whole process. Joint and separate inversions can be performed flexibly by switching the inversion mode. The resulting density model and susceptibility model demonstrate the correctness of the proposed program.

COMPREHENSIVE INTEGRATION METHODS AND APPLICATION OF GRAVITY-MAGNETIC DATA IMAGE

the technique of image processing and analysis of gravity and magnetic data is one of themost effective ways to extract geological information from gravity and msanetic data. The presentpaper investigates, from an angle of generalized joint inversion, thc methods and procedures ofcomprehensive processing of multi-source geological image , and a specific example in Huai Nan coalfield is given here as well.

Characterization and processing of talc-magnesite from the Zinelbulak deposit

The characteristics of talc-magnesite from the Zinelbulak deposit(Uzbekistan) were investigated via X-ray diffraction, differential thermal analysis,infrared spectroscopy and optical microscopy.The mineralogical composition of the Zinelbulak talc-magnesite consists of 52 wt.%talc,43 wt.%carbonates and 5 wt.%of the iron-containing minerals magnetite,siderite and chlorite.Petrographic analysis confirmed the presence of carbonates in two forms:magnesite and breunnerite.Grindability tests revealed that talc and magnesite particles are completely separated after a grinding process carried out for 10～12 min.The distribution of the yield of talc and magnesite,as a function of the particle size,shows an irregular feature in that a comparatively coarser sample(>0.1 mm) is richer in magnesite and poor in talc while a comparatively finer sample(<0.1 mm) has a composition poorer in magnesite.The dressability of the Zinelbulak talc-magnesite was tested using conventional gravity concentration,flotation and electromagnetic separation.Gravity concentration was found to be the most economic initial process for the complete separation of magnesium carbonate and talc.Subsequent flotation and magnetic separation techniques could further increase the yield of high quality magnesite and talc.Refractory samples prepared by heating the separated magnesite at 1600℃for 2 h met the State Standards for refractory materials.

Deep structural research of the South China Sea: Progresses and directions

The South China Sea(SCS)is the hotspot of geological scientific research and nature resource exploration and development due to the potential for enormous hydrocarbon resource development and a complex formation and evolution process.The SCS has experienced complex geological processes including continental lithospheric breakup,seafloor spreading and oceanic crust subduction,which leads debates for decades.However,there are still no clear answers regarding to the following aspects:the crustal and Moho structure,the structure of the continent-ocean transition zone,the formation and evolution process and geodynamic mechanism,and deep processes and their coupling relationships with the petroliferous basins in the SCS.Under the guidance of the“Deep-Earth”science and technology innovation strategy of the Ministry of Natural Resources,deep structural and comprehensive geological research are carried out in the SCS.Geophysical investigations such as long array-large volume deep reflection seismic,gravity,magnetism and ocean bottom seismometer are carried out.The authors proposed that joint gravitymagnetic-seismic inversion should be used to obtain deep crustal information in the SCS and construct high resolution deep structural sections in different regions of the SCS.This paper systematically interpreted the formation and evolution of the SCS and explored the coupling relationship between deep structure and evolution of Mesozoic-Cenozoic basins in the SCS.It is of great significance for promoting the geosystem scientific research and resource exploration of the SCS.

Study on Scandium Separation from Rare Earth Ore in Yunnan Province

Chemical components, main mineral content and mineral composition of rare earth ore in Yunnan Province was measurated by the analysis of the spectrum and the chemical components. The study shows that main metals mineral in the rare earth ore are magnetite, tatanomagnetite, limonite; less metals mineral are ilmenite, hematite; some minim minerals were iron pyrites, zircon, scheelite, and so on. Main nonmetals mineral are quartz, feldspar(plagioclase, K-feldspar); less nonmetals mineral are hopfnerite, biotite, titanite; some minim minerals are kaolinite and dolomite. Ilmenite has the highest content of Sc as 175 g·t -1, next is titanite as 81.2 g·t -1. Based on this result, A new method of extracting Sc is put forward. The technological flowsheet of separating Sc of low-intensity magnetic separation,tabing, gravity concentrate, high-gradient magnetic separation, and electrostatic separation was prepared. Amplified experiment obtained Sc concentrate with Sc content of 148.54 g·t -1, the yield of 7.92%,recovery of 69.20%, at the same time, a Fe concentrate with the grade of 63.88% and the yield of 5.91% is obtained.

Experimental study on separation of valuable refractory aggregate from investment casting ceramic shell waste

In the present study, a processing technique for recycling investment casting ceramic shell waste was proposed to separate valuable refractory aggregate zircon sand. The microstructure and phase constituents of the shell waste and separation process were investigated. The results show that the characteristics of microstructure and phase constituents of the shell waste can meet the conditions for preferential y separating zircon sand, and zircon sand can be separated by gravity separation on a shaking table. The separated zircon sand has good shape and high purity, and can be used for the production of castings and other applications.

THREE-DIMENSIONAL GRAVITY-MAGNETIC CROSS-GRADIENT JOINT INVERSION BASED ON STRUCTURAL COUPLING AND A FAST GRADIENT METHOD

In order to effectively solve the low precision problem of the single gravity density inversion and the magnetic susceptibility inversion,and the limitation of the gravity?magnetic joint inversion method based on the petrophysical parameter constraint,this paper studies the three-dimensional gravity?magnetic cross-gradient joint inversion based on the structural coupling and the fast optimization algorithm.Based on the forward and inversion modeling of three-dimensional gravity density and three-dimensional magnetic susceptibility using the same underground grid,along with cross-gradient coupling as the structural cons train t,we propose a new gravit y?magnetic joint inversion objective function including the data fitting term,the total variation regularization constraint term and the crossgradient term induced by the structural coupling?The depth weighted constraint and the data weighting constraint are included into the objective function,which requires different physical property models to minimize their respective data residuals.At the same time,the cross-gradient term tends to zero,so that the structure of the gravity and magne ic models tends to be consistent.In realization,we address a fast and efficient gradient algorithm to iteratively solve the objective function.We apply this new joint inversion algorithm to the 3D gravity-magnetic model inversion test and compare it with the results of a single inversion algorithm.The experimental tests of synthetic data indicate that the gravity-magnetic cross-gradient joint inversion method can effectively improve the accuracy of the anomaly position and numerical accuracy of the inverted anomaly physical parameters compared with the single physical inversion method.

高精度重磁方法寻找隐伏矽卡岩型铁矿

位于华北克拉通东部的鲁中莱芜地区是矽卡岩型富铁矿重要产区,矿床主要产于矿山岩体与中奥陶统碳酸盐岩地层的接触带中。本文利用最新重磁测量成果,对矿山岩体外围西部石家泉—刘家庙一带重磁异常特征进行了细致研究,结合区内已知铁矿重磁场特征,圈定了深部找矿靶区。在成矿有利地段布设了大比例尺重磁剖面,以已知钻孔为约束条件,利用2.5D重磁联合反演技术,对重磁异常进行了定性及定量解释。解释结果为后续钻孔位置布设及深度预测提供了依据,该钻孔揭露了15.8 m厚的富铁矿,找矿效果显著,为今后本区进一步寻找矽卡岩型铁矿提供了重要指示依据。

乌干达某铁铌多金属矿石中铌与重晶石的回收试验

乌干达某铌多金属矿原矿风化严重,矿石性质复杂,属极难选多金属矿,矿石TFe品位为39.78%,REO品位为1.79%,Nb_(2)O_(5)品位为0.62%,BaO品位为7.68%;主要脉石矿物为石英、长石和高岭石等。为了高效回收利用该矿石资源中伴生的铌和重晶石,以现场磁选铁尾矿为对象,采用重磁联合预富集、反浮选分离铌与重晶石的工艺流程进行了选矿试验。试验结果表明:现场磁选铁尾矿采用1次摇床重选、1次弱磁选、1粗4精1精扫2扫闭路浮选流程处理,最终可获得Nb_(2)O_(5)品位7.33%、回收率41.94%的铌精矿,BaSO_(4)品位94.23%、回收率50.98%的重晶石精矿。研究结果可作为现场开展伴生铌和重晶石回收工艺改造的依据。

面向深部矿产资源勘探的井中重磁三维交叉梯度联合反演

单一井中重磁方法解决问题有限,其三维反演具有严重的多解性。开展面向深部矿产资源勘探的井中重磁三维交叉梯度联合反演,采用交叉梯度函数对密度和磁化率进行耦合,综合井中重磁多参数信息进行联合反演,减少反解的多解性,提高深部矿体识别的准确性。通过理论模型和实际资料进行反演分析。结果表明:井中重磁交叉梯度联合反演具有较高的纵向分辨能力,可以显著提高深部矿体识别的准确性,特别是能有效识别深部隐伏矿体。

国内某低品位风化型钛矿选矿试验研究

文章对国内某低品位风化型钛矿进行了工艺矿物学研究,采用化学分析、物相分析、岩矿鉴定、矿物解离分析仪(MLA)等手段查明了矿石中矿物组成、有用有害元素赋存状态和解离程度等特性。为了合理开发该钛铁矿资源,对其进行了选矿工艺研究,最终确定采用磨矿—湿式弱磁选—湿式强磁选—摇床试验的工艺流程。当原矿中的TiO_(2)品位为5.32%时,通过该试验流程,获得TiO_(2)品位46.70%,钛回收率50.94%的钛精矿,可以达到冶金用钛精矿工业指标要求。试验研究结果为后续的工艺流程设计提供了依据。

磁-重联合工艺从钽铌尾矿中分选钽的实验研究

钽铌矿组分结构复杂,嵌布粒度细,品位较低,选矿工艺比较复杂。针对宜春钽铌尾矿中钽铌含量少,难以回收利用的问题,采用高梯度磁选机和摇床对钽铌尾矿进行分选。针对Ta_(2)O_(5)品位0.0134%、Nb_(2)O_(5)品位0.0078%的钽铌尾矿,采用“磁选-重选”联合工艺流程对其进行富集,分别得到Ta_(2)O_(5)品位为11.286%、回收率为40.74%、Nb_(2)O_(5)品位为6.633%、回收率为40.74%的钽铌精矿产品,试验指标良好。Ta_(2)O_(5)、Nb_(2)O_(5)得到了较好的综合回收,证明了“磁选-重选”联合工艺的可行性,并且该工艺提供了环保绿色的回收钽铌矿的方法,为钽铌矿及同类资源的综合回收提供了的技术支持。

我国铌矿资源概况及选矿技术进展

我国铌矿资源储量丰富,但矿石品位低,且共伴生有多种有价金属,可供经济开采的铌矿资源稀缺,对外依存度超过90%。分析了全球铌资源概况及供需关系,简要阐述了铌的性质、用途、分布特征以及矿床类型,归纳总结了重选工艺、磁选工艺、浮选工艺、焙烧—浸出工艺以及联合工艺等铌矿选矿工艺研究进展,并对其进行了对比分析。最后,展望了选铌工艺的研究方向,并提出了保障我国铌资源稳定供应的对策。