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3D Gravity And Magnetic Inversion Modeling Constrained By Geological Information

Posted on:2014-02-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:G QiFull Text:PDF
GTID:1220330395496560Subject:Earth Exploration and Information Technology
Abstract/Summary:PDF Full Text Request
3D gravity and magnetic inversion modeling is an efficient way to obtain subsurfacestructures.Due to the inherent nonuniqueness of gravity and magnetic methods, traditionalinversion method is very difficult to obtain consistent results with the actual geologicalsituation, a priori information and constraints are essential for successful inversions.Combined with geologic knowledge and additional independent data sets, these data canlead to distinct and robust interpretations.At present, there are many different2D/3D gravity and magnetic inversion method, andthere is its own advantages and disadvantages in each method. The method adopted in thisstudy can well reflect geological information, and also make the fitting error smaller. Thebiggest advantage of this method is easy to integrate all prior geologic information, such asdip direction, fault and mineralized bodies, and so on. And the method can join thegeologists’ knowledge of the region.A gravity and magnetic inversion project has been carried out in the study area whichcontain Tongling area and Nihe ore deposit in order to verify and demonstrate the feasibilityof the gravity and magnetic inversion method. The main contents are as follows: First of all,after the collection of field data, it has been disposed properly, and the results have beenevaluated and preliminary analysis. And then,3D geological and geophysical models havebeen constructed by gravity and magnetic inversions, which integrate all prior geologicinformation and geologists’ knowledge of the region. Finally, the structure of study areas,internal structure, interface of strata, the spatial distribution of rock and ore bodies wereanalysised and researched combining with the geological data.A pilot3D geologic model of Tongling area, covering an area of160km2and extendsto a depth of3km, has been constructed by the method adopted in the study. The majoroutcomes of the study are as follows:(1) The structural architecture of the study areaconsists of two northeast-trending anticlines(Tongguanshan anticline and Qingshananticline): Tongguanshan anticline is an asymmetrical structure with a steeply dipping southeast limb, whereas the Qingshan anticline is a symmetrical one with two moderatelydipping limbs;(2) The3D model show detailed characterization of the distribution ofSilurian to Triassic strata in3D, in particular, the spatial variation of the major ore-bearingstrata;(3) detailed definition of the3D extent of the intrusions has been identified. Severalconcealed intrusions were modeled in the southwest of the study area, which provideimportant clues for future discovery;(4) two deep targets have been identified for futureexploration in the mapping area.In the mean time, the Nihe ore deposit3D geologic model, covering an area of5.6km2and extends to a depth of1.2km, has been constructed by the method adopted in the study.The major outcomes of the study are as follows:(1)Nihe ore deposits mainly occurred in thetop of diorite-porphyrite and volcanic of Zhuanqiao formation, and only a small part of thepyrite mainly occurred in the upper Zhuanqiao formation, which distribution is layered;(2)diorite-porphyrite is the main parent rock of the Nihe ore deposit, the ore bodies werecontrolled by domal uplift structure.(3) Contrast the theory and observed anomalies, showthat there is no new ore bodies at the edge of the study area, and the probalbility that thereare new ore bodies in the depth of2km is low.This study shows that the research of geologic constrained3D gravity and magneticmodeling has potential value and broad application prospect. The flow work in this studycan provide reference for similar work in other areas, and also has important applicationvalue.
Keywords/Search Tags:Gravity and magnetic inversion, geological and geophysical model, Tongling area, Nihe ore deposit, potential field modeling, deep mineral exploration
PDF Full Text Request
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