相山铀矿田地球物理特征及深部地质结构研究

【作者】 陈越；

【导师】 刘庆成； 徐贵来； 邓居智；

【作者基本信息】 核工业北京地质研究院 ， 矿产普查与勘探， 2014， 博士

【摘要】 相山铀矿田位于赣杭构造带火山岩成矿带西段乐安——东乡成矿亚带内的相山火山塌陷盆地中，位于北东向深断裂和北西向断裂带的交汇部位。经过50多年的铀矿勘查，相山盆地已经发展为我国重要的陆相火山岩型铀矿田。近年来，我国在相山铀矿田开展了大量深部找矿工作，对相山火山塌陷盆地的基底构造、富大铀矿成矿规律、控矿因素取得了新认识，发现了“上铀下铅锌”的矿体分布规律，但由于对矿田地球物理特征和深部地质结构认识的缺乏，针对该区的找矿仍主要集中在500米以浅，严重制约了相山铀矿田深部找矿的突破。为研究相山铀矿田地球物理特征和深部地质结构，本文以中国地质调查局“相山火山盆地深部地质调查”项目为依托，开展了以探测主要岩体物性特征，变质基底、大型断裂、岩浆通道的基本格架等主要目标地质体的空间分布为目的的地球物理研究工作。论文相山铀矿田主要岩（矿）石物性特征入手，研究建立相山铀矿田地球物理特征，指导该矿区深部找矿物探方法技术选择和地球物理资料解释，共采集了相山铀矿田1400多块典型标本进行密度、磁化率和电阻率等物性参数测试，绘制了研究区主要岩石单元（流纹英安岩、碎斑熔岩、花岗斑岩和变质岩）的物性频率分布直方图，从图上可以看出四种岩性基本存在单峰正态分布特征，而花岗斑岩的磁化率和电阻率直方图存在双峰正态分布特征，花岗斑岩的电阻率和磁化率交汇图也存在两个明显交汇区域，表明研究区存在两类花岗斑岩,通过岩芯观察，发现高阻、高磁化率为浅肉红色花岗斑岩，低阻、低磁化率为灰色花岗斑岩。为了进一步通过物性测试结果对典型岩石单元进行分类，提出了逆质量磁化率（质量磁化率的倒数，质量磁化率为体积磁化率与密度的比值），通过逆质量磁化率与密度的交汇图更明显的将四种岩性区分开来。区域重磁数据既包括区域异常，又包括局部异常，从叠加异常中提取研究对象产生的异常，必须选择合理异常提取的方法，本文对异常提取方法进行了对比研究。首先收集了相山地区1∶2.5万地面高精度磁法测量和1∶5万重力测量的资料，选择匹配滤波、趋势分析、解析延拓和插值切割等多种数据处理技术对重磁异常进行分离处理，结果表明趋势分析方法划分异常比较单一；匹配滤波方法处理后的结果含有较多的低频成分，高频成分处理过多，使得局部异常包含了过多的深部异常信息，对于局部异常信息的反映相对较少；插值切割方法结果显示近地表的异常场成分较多，使得局部异常结果显得比较复杂，因此结合该研究区的地质资料，解析延拓法能合理的提取该研究区的重磁异常，因此选择解析延拓法作为该研究区的重磁异常提取方法。在异常分离的基础上，对重磁数据进行了三维反演研究，结合主要岩石的物性测试结果和已知的地质情况，对典型的重磁三维反演的图切剖面进行地质－地球物理解译，圈定了典型剖面变质岩、流纹英安岩、碎斑熔岩和花岗斑岩分布情况；通过重磁三维反演结果推测相山地区基底、高密度岩体和火山通道，得出青白口系的变质岩为测区内密度相对较大的岩层，与火山岩系存在一个密度界面，基底岩性的起伏状况与重力值的高低成对应关系，重力值越高，基底埋藏越浅，反之，埋藏越深；高密度体主要出露在盆地的北部和西部，推测高密度岩体为流纹英安岩；低密度体出现在相山盆地的中部、西部和盆地东南角上，总体上能体现了盆地的隆凹，盆地的中部为相山主火山机构，推测出在相山的西部和东南角存在两座侧火山机构。矿集区强电磁干扰严重影响着地球电磁法在深部找矿中的应用效果，为了克服电磁噪声的影响，提高大地电磁数据的质量，本文首先对研究区的噪声特征和噪声源进行分析，噪声根据其时域波形可以分为脉冲噪声、工频谐波噪声、方波噪声、三角波噪声、阶跃噪声、充放电模式噪声等6类；噪声源主要有：矿山干扰、无线通讯干扰、人文干扰、地质噪声等；同时分析这些噪声源对MT数据的影响。在研究区开展了噪声研究，对基于参考道的MT数据去噪技术进行研究，采用了不同参考距离下的本地电参考，本地磁参考，互参考磁道及互参考电道作为参考信号处理数据得出视电阻率相位曲线及信噪比曲线来综合评价不同参考道处理效果。通过对基于形态滤波和基于EMD的阈值去噪方法对研究区的噪声去噪结果进行对比分析，两种方法都适合用于提取该研究区有用信号，达到了信噪分离的目的。论文将电磁去噪研究成果应用于相山铀矿田两条大地电磁法剖面数据处理中，对经去噪后的数据进行了二维反演，反演结果较好圈定了沉积地层、变质岩基底及侵入岩体及断裂构造等深部地质结构。论文研究成果为研究区深部找矿和类似地区深部地质结构探测提供了技术支撑。更多还原

【Abstract】 Xiang-shan uranium ore field is located in collapse basin of Le-an and Dong-xiangmetallogenic belt which belongs to a greater volcano rock tectonic metallogenic belt inGan-hang. The location is in combine zone of North East fracture and North West fracture.Xiang-shan basin already becomes an important continental volcanic type uranium ore fieldin China with more than50years exploration. Recent years, Xiang-shan ore field wasdevoted to much more works for deep mine exploration. New perspectives are gained aboutthe basal structure of collapse basin, mineralization regularity of great uranium deposits, andore controlling factors. The ore body distribution law is that uranium is distributed above thelead zincore. The ore body is mainly distributed500m above. And deep mine exploration isrestricted seriously in the Xiang-shan uranium deposit because without related data aboutgeophysical characteristics and deep geological knowledge in this ore field.In order to investigate the geophysical characteristics and deep geological structure forthe uranium orefield, thisthesis is mainly research the rock physics and spatial distributionof metamorphic rock basement, strikes of great faults and basic framework of magmachannels. This thesis is supported by the Xiang-shan deep geological survey project.For the study of the physical characteristics of the major rock (ore) onxiangshanuranium ore field,establish the geophysical characteristics of xiangshan uraniumorefield,guideto select the deep mining area for mineral exploration method and interpretegeophysical data,collectedand measured more than1400typical rock specimens,and obtaindensity, magnetic susceptibility and resistivity,drew main the histogram of rock unit(porphyroclastic Lava,rhyodacite, granite porphyryand metamorphic rocks),There are singlepeak characteristic from the histogram,but the existence of magnetic susceptibility andresistivity granite porphyry of double peaks phenomenon.There are two obvious connectionregion fromthe intersection chartof the density and magnetic susceptibility of thegraniteanalysis, indicates that there are two types of granite porphyry by analyzing rockcores, high resistance, high susceptibility to light red meat thick spot granite porphyry, lowresistance, low susceptibility to thick grey spot granite porphyry were found.In order tofurther classify the typical rock unit by the test results,the inverse magnetic susceptibility(density/susceptibility) and density crossplot map analysis can be obviously dividedphysical rendezvous regions more obvious, can provide ideas for joint inversion of gravityand magnetic.Regional gravity and magnetic data include both regional anomalies and local anomaly,extractethe abnormal of the research objectfrom the superimposed anomaly, choose a reasonable method of the anomaly extraction,this paper makes a comparative study on theanomaly extraction method.First ground high resolution magnetic data with1:25000andgravity data with1:50000were collected in Xiang-shan district. Gravity and magneticanomalies were separated by use of data processing methods (eg: matched filtering, trendanalysis, analytic continuation and interpolating cut and so on) and the trend analysismethod divide single anomaly successfully.The results of matched filtering method containsmore high frequency components, local anomaly contains much more deep abnormalinformation because the local anomaly information is relatively less. The interpolating cutmethod showed abnormal field components are the surface, the local abnormal results morecomplicated, in combination with geological data of the study area, carries on the contrastanalysis to the separation results extraction, that analytic continuation method canreasonably gravity and magnetic anomaly of the study area.Based on the anomaly separation，three dimensional gravity and magnetic inversionresults were combined with rock physics analysis and geological situation to deduce theunderground parameters distribution. The slice maps of3-D inversion results with typicalanomalieswere used to determine the geology and geophysics phenomena. Through analysis,we delineatethe distribution of metamorphic rocks, rhyodacite, Porphyroclastic Lava andgranite porphyryof the typical section;by the3D inversion of gravity and magneticanomaliessuggests substrate, high density and the volcano, show that this set ofmetamorphic rocks of Qingbaikou system for measuring the area density of rock, theexistence of a density interface and volcano rock series. Fluctuation and the gravitybasement lithology value into a corresponding relation, gravity value higher, basementburied shallower, versus, buried deeper. High density body is mainly exposed in the northernand Western basin,speculate the high density of rock is rhyodacite and low density bodyappear in central area, western and the southeast corner of basin. We deduce that the basinuplift,implemented in the middle of the main volcano in Xiangshan basin. Two volcanoesmaybe existed in the southeast and west of Xiangshan district, respectively.Srong electromagnetic interference effect electromagnetic method application in deepprospecting In the ore district,in order to overcome the influence of electromagneticnoise,andimprove the quality of magnetotelluric data,this paper are analyzed the noisecharacteristics and noise sources on the study area,results show that noise of the study areacan be divided into six types whichcomprise pulse noise, industrial frequency harmonicnoise, square-wavenoise, triangle wave noise, step noise, changed and discharged mode noise. The noise includes mine interference, wireless communication interference, humanbeings disturbance, geological noise etc. We have evaluated the influence of these noises onMT data. Evaluate the quality of MT data by the cross reference,the proposed EMD basedthreshold denoising and morphological filtering denoising method for comparative analysisof the results, two methods are implemented to remove noise, and extract the useful signal,the signal noise separation purposes.The electromagnetic noise research is applied to two magnetotelluric profile dataprocessing on the Xiangshan uranium orefield, the denoised data was conducted2Dinversion, the results delineate sedimentary, metamorphic basement and intrusive rock andfracture structure in deep geological structure better. The research results can providetechnical support for the deep prospectingand deep geological structure of the similar area.更多还原