高精度重、磁测量在大兴安岭找矿工作中的应用

根据以往的经验,在找矿勘查中,通常应用高精度磁法和电法,很少应用重力方法.本文通过小面积的大比例尺高精度重力工作,展示了重力工作在找矿勘查中所起的作用.尤其是在高纬度覆盖区,地表地质不甚明了、电法工作比较困难的情况下,可以发挥重力工作受环境干扰小的优势,寻找高密度地质体.在本矿区中,重力工作作为高精度磁测工作的重要补充,有利于更准确地确定矿体的位置和平面形态特征.由于高精度磁测方法寻找的是有磁性矿物,当矿体无磁性时,磁异常不能反映矿体的位置和形态.本文根据重力方法和磁测方法的原理,对矿区的地球物理场进行研究,给出本矿区识别矿体异常的原则,根据磁性矿物与铅锌矿伴生的特点,结合磁异常,如果重磁异常中心吻合较好,重磁异常幅值和梯度也较大,表明矿体异常的可靠性很大;当然,对磁异常表现为负磁异常的高频重力高异常也不能忽视,有可能是埋藏浅的无磁性金属矿的反映.所以,需要密切关注幅值大、梯度大的高频重力高异常.     

空地磁残差计算在平原厚覆盖区找矿应用

磁法是寻找隐伏磁铁矿最有效的地球物理方法,但是厚覆盖层下方铁矿体产生的磁异常较弱,有必要综合空地磁场数据突出铁矿弱异常信息.为有效利用已有的空地磁场数据及在山东齐河平原厚覆盖区实现深部找矿新突破,本文介绍了区域磁场及深部铁矿磁场特征,以不同高度磁场变化规律为依据,设计理论模型获取了不同高度正演磁场,通过计算空地磁残差,突出深部铁矿引起的弱异常.为了验证方法的实际效果,利用近年在该地区实测航空及地面磁场数据计算磁残差,结合推断的地质构造,分析找矿有利部位,确定钻探验证位置.     

鲁西莱芜地区地球物理特征及 富铁矿床勘查模型建立

鲁西莱芜地区是国内重要的富铁矿基地之一,是典型的与中基性侵入岩有关的矽卡岩型铁矿,矿石品位高、储量大。该区铁矿找矿采用地面磁测、航空磁测和重力测量作为主要方法,在区内圈定多个物探异常,累计探明大中小型富铁矿床40余个。在此基础上总结分析该区富铁矿成矿规律,介绍张家洼典型矿床磁异常特征,建立莱芜地区富铁矿地质-地球物理综合勘查模型,得到以下认识:①航磁、重力异常圈定隐伏岩体效果好;②地质、物探密切配合是正确评价异常的关键;③研究低缓异常必须高精度;④要注重研究磁场的局部特征变化;⑤突破乱磁场区可能取得找矿实践。     

黄土覆盖区钼矿综合地球物理找矿技术组合:以沙坡岭钼矿为例

覆盖区寻找隐伏矿成为当前找矿工作的热点问题,为了能在地表地质信息少的黄土覆盖区,寻找隐伏的有经济价值的矿床,本文以沙坡岭钼矿为例,综合应用r能谱、高精度磁法、高密度电法三种地球物理方法进行找矿勘探,辅以偏提取化探法对地球物理异常进行约束,结合地质资料进行解译,预测了有利的成矿区域,通过钻探得到了有效验证,初步建立了黄土覆盖区钼矿的综合地球物理找矿模式,为下一步的综合勘探打下了基础.     

新疆西天山东段航磁异常特征及找矿效果

介绍了高精度航磁调查在西天山东段的应用效果.在高精度航磁图上,展现出多个不同磁场背景及磁异常特征区,它们是不同构造、岩浆活动、地层及岩性分布的综合反映.该区不仅区域磁场特征明显,而且局部异常信息也极为丰富.在最新的高精度航磁图上,已知铁矿异常特征明显,为矿区外围勘探和同类地区寻找新的铁矿提供了依据.利用高精度航磁资料,新发现了五十余处铁矿异常,在2007年进行了地面查证的5处异常中,有4处见矿.这些新的铁矿异常的成功发现不仅带来了巨大的经济效益,也为今后利用高精度航磁测量在类似地区进行找矿积累了经验.     

物探方法在青海哈得尔甘南地区寻找矽卡岩型铁多金属矿中的应用效果

哈得尔甘南地区位于柴达木盆地西南缘,所处大地构造位置在区域上隶属东昆仑岩浆弧带祁漫塔格造山亚带,具有良好的找矿前景.已发现矿体与区域成矿格局和物化探异常不甚相符,经对该区物性资料的分析,结合区域成矿规律,提出了在该区寻找矽卡岩型铁多金属矿的找矿标志和物探工作方法.通过高精度扫面圈定磁异常,在磁异常处布设激电中梯剖面进一步确定异常源,结合磁电异常特征,能够快速圈定铁及多金属矿体在地表的投影位置.对利用物探方法预测的成矿靶区进行深部验证,发现多个矿体,为该区今后的找矿工作提供经验.     

有限元-无限元耦合法在复杂金属矿体电阻率/极化率正演模拟中的应用——以庐枞盆地泥河铁矿床为例

金属矿电法勘探由于受限于探测深度和复杂矿体形态的解释,在深部矿产资源勘探中难受重视.安徽庐江泥河铁矿床是长江中下游成矿带中最主要的矿床类型之一,矿区复杂的地质结构和矿体形态以及矿体的大深度赋存状态给地球物理勘探特别是电法勘探带来了很大的挑战.为了研究电阻率/极化率法在大深度复杂金属矿体探测中的应用效果,本文以泥河铁矿某勘探剖面为例,在实际矿区的地质模型基础上通过简化建立了相应的地球物理模型,采用偶极-偶极装置及二极装置,对矿区进行直流电阻率/极化率数值模拟.提出采用有限元-无限元耦合法以解决传统有限元法截断边界所引起的问题.理论和计算结果表明:有限元-无限元耦合法相比传统有限元法,能显著提高计算的效率和精度.偶极-偶极装置的视电阻率断面图较二极装置能更好的区分不同地层及磁铁矿异常,而根据铁矿高极化特性,探测深度相对较大的二极装置的视极化率断面图能够更好的反映出异常体位置及范围.     

老挝波乔省某磁铁矿区磁法勘探

勘查区位于老挝西北部之波乔省,地表风化严重、浮土掩盖厚、深林茂密、基岩露头少,虽然局部地段出露有大量的铁帽,但不敢判断该区是否有大规模的磁铁矿.为此,我们采用1∶10000地面高精度磁法测量以了解磁铁矿的有无、范围、延伸、规模.后期勘探阶段开展2.5D人机交互正反演工作以了解深部磁铁矿的有无.结果表明,在老挝西北部地质勘查程度低的地区开展高精度磁测扫面工作是寻找磁铁矿产行之有效的方法,能够解决基础地质问题,矿山勘查问题,后期运用2.5D人机交互正反演能够解决一定的矿层预测工作.     

综合电磁法在矿区深部成矿机制中的应用研究——以皖南乌溪多金属矿区为例

乌溪矿区介于长江中下游多金属成矿带与华南成矿带之间,是江南造山带上的一个找矿新区.本文在这一找矿新区开展了有效的电磁方法综合勘探,试图对该区深部成矿机制进行研究.我们收集了该区的地质地球化学资料,从地质地球化学资料中分析了区域成矿背景;我们还采集了区域出露的主要岩石类型,在实验室开展物性测定,在此基础上选择了三种电磁方法开展研究区的野外测量.通过地面高精度磁测、激发极化法和可控源音频大地电磁法(CSAMT)三种地球物理方法,开展了研究区的磁化率、极化率和电阻率的分布特征研究.深入分析了地质、地球化学和地球物理三种资料与成矿的关系,相互约束,探讨成矿模型、成矿机制和成矿的可能性,推测可能的矿体赋存位置和深度范围.在地球物理研究结果基础上,结合地质和地球化学背景资料,构建了研究区的成矿动力学模型,推测了研究区成矿机制,揭示了矿区的成矿潜力.综合所得结果布设了钻孔,钻探结果揭示了研究区深部存在强烈矿化蚀变和强蚀变斑岩,初步确认为斑岩型矿床,与CSAMT剖面的解释结果基本一致,也与推测的测区内深部成矿机制相吻合.钻孔结果和地球物理结果的一致性以及对已构建的成矿动力学模型的支持,充分证明了综合电磁方法在斑岩型多金属矿床的发现和预测中的重要作用,同时斑岩型矿床的确认进一步印证了华南成矿带与俯冲作用形成的成矿带的相似性,从而推动整个华南地区的成矿地质研究.     

先验地质信息约束下的三维重磁反演建模研究 ——以安徽泥河铁矿为例

安徽泥河铁(硫)矿床是近年发现的大深度隐伏矿床,它的发现再次引发了庐枞地区深部找矿的热潮.建立矿区的三维精细地质模型,对寻找深、边部隐伏矿体,深入认识深部成矿、控矿规律意义重大.本文以泥河矿区为实例,开展先验地质信息约束的三维重磁建模研究,获得了矿区面积5.6 km²(2.8 km×2.0 km)、深度1.2 km内的三维地质模型.在三维可视化平台上对该模型进行了地质解释,全面分析了矿体、地层与次火山岩之间的空间分布及对应关系,发现铁矿主要赋存于闪长玢岩与砖桥组火山岩之间,且在玢岩穹窿地段矿体厚大,这对认识"玢岩型"铁矿的成矿模式具有重要的实际意义;三维模型的重磁正演响应基本拟合了实际重磁异常,说明在建模区域内已没有新的矿体;本文提出的三维地质建模流程可为其它地区开展类似工作提供借鉴,同时研究表明地质信息约束下的三维重磁建模研究在深、边部找矿和重磁异常的精细解剖等方面具有潜在的价值和广阔的应用前景.     

河南遂平石寨铺铁矿区地球物理特征及找矿远景

遂平石寨铺铁矿区位于河南省隧平县境内,属于沉积变质型铁矿,含铁层位是太古界太华岩群。依据地球物理特征及物探高精度磁法工作结果,与舞阳铁矿成矿条件对比,预测西北部找矿远景较好。     

老挝铁矿资源与成矿预测

经资料整理与实地调研：老挝已发现铁矿床（点）42处。重要矿床为万象省（P．Vientiane）万荣（Vang—viang）铁矿、川圹省（P．Xiangkhouang）富诺安（Phou．Nhouan）铁矿、万象省（P．Vientiane）帕莱（PhaLek）铁矿、甘蒙省（P．Khammouan）班农洛（BanNonglao）铁矿。重要矿床的矿体呈似层状、脉状产出,矿石质量较好,矿床属接触交代矿床、热液矿床。据地层条件、岩浆岩条件、构造条件、铁矿床（点）的分布情况,老挝划分出琅勃拉邦（Louangphabang）、孟佩（MuangPek）、桑怒（Xam—Nua）3个成矿预测区。     

低场理论及有利找矿标志

找铀矿要到放射性高异场中去找,这似乎已成为一种习惯,因而也影响找矿效果．实践表明,约有80％的矿是位于低异常场及与之相邻的离异常场附近,特别是面积为几十平方公里的小高异常场中通过对国内外上千个矿田、矿床和矿点的统计研究,提出在自然界中存在着呈“萝卜型”分布的异常（矿床或矿体）为核心的低场理论、探讨了低异场产生的机制,总结了低场中的10种有利找矿标志．对两个地区今后的勘查进行了有益的讨论     

安徽省霍山县东溪-南关岭金矿地质特征与成矿条件

东溪-南关岭金矿为北淮阳东段发现的第一个原生金矿,产于磨子潭-晓天中生代火山盆地边缘,容矿围岩为安山质-英安质火山岩,矿化和蚀变受桐柏-桐城深大断裂带的次级构造带控制。该金矿发育陡倾斜的脉状矿体和缓倾斜的似层状矿体,成因类型为冰长石-绢云母型浅成低温热液金矿。火山岩盆地之下的变质基底可能起到了初始矿源层作用,桐柏-桐城断裂带及其次级构造破碎带为重要的导岩导矿构造,早白垩世强烈的岩浆活动提供了热源、动力源和部分矿源。参照国内外类似金矿的特征,认为本区成矿地质条件良好,有可能隐伏着与石英正长岩体有关的细脉浸染型矿化,晓天火山盆地具有良好的找矿前景。     

乌拉嘎金矿主要控矿因素与激电法找金效果

乌拉嘎金矿主要控矿因素是构造破碎带及裂隙带、斜长花岗斑岩体和老基底变质杂岩.其中构造破碎带是最主要控矿因素.矿化富集与含金玉髓状石英细脉或细网脉、黄铁一白铁矿脉和碳酸盐脉的发育程度密切相关.含金热液脉体的形态产状受构造破碎带和裂隙带控制，经过多期次叠加，往往造成矿化的进一步富集.矿体呈脉状、复脉状、扁豆状等形态.上述特点为该区电法找金提供了先决条件.金矿石是本区主要极化体.在乌拉嘎金矿区的张才沟靶区获得低阻高极化和高阻高极化异常，可望找到含金石英脉及含矿破碎带.     

Summary of technology for a comprehensive geophysical exploration of gold mine in North China Craton

The North China Craton is the oldest continental block, and has suffered from large-scale lithospheric thinning and destruction, which in turn led to gold deposits in northern China. The decratonic gold deposits in the North China Craton became the most important gold deposits in China, and geophysical methods are key means to detect and discover gold deposits there. In this paper, based on the geological and petrophysical characteristics of the North China Craton, the geological model of the decratonic gold deposits is transformed into a geophysical model. At present, two methods of geophysical exploration of decratonic gold deposits are in use: rapid and efficient exploration on the scale of the ore concentration area, and large depth exploration on the scale of the deposit area. In detail, the airborne electromagnetic,magnetic and gravity methods are used to detect the shallow(1,500 m) anomaly area on the scale of the ore concentration area.Through the ground-controlled source electromagnetic and ground magnetotelluric methods, explorations for targets at significant depth(5,000 m) are carried out in the mining area. Then, taking the Liaodong ore concentration area as an example,geophysical methods are used to discover two prospecting areas around the Jianshanzi Fault in the Qingchengzi ore concentration area, Baiyun-Xiaotongjiapuzi deep prospecting area, and Qingchengzi deep prospecting area. Next, three prospecting areas are delineated around the Jixingou Fault in the Wulong mining area, Wulong deep prospecting area, Weishagou deep prospecting area, and Chang'an deep prospecting area. The anomalies in the ore concentration area and mining area are revealed by means of three-dimensional exploration methods, thereby providing technical support for the exploration of metal minerals such as decratonic gold deposits.     

Characteristics of the genetic mineralogy of pyrite and its significance for prospecting in the Denggezhuang gold deposit,Jiaodong Peninsula,China

This paper reports the variation rules for the typomorphic parameters of the pyrite and the gold enrichment rules of the Denggezhuang quartz vein gold deposit at a large-depth scale,providing the mineral signs for deep prospecting prediction through detailed study of the characteristics of crystal' habits,chemical composition,the thermoelectricity of pyrites,and mineralogical mapping.This paper primarily discusses the correlation between the mineralization intensity and the space-time evolution of the mineralogical parameters,clarifies the physicochemical conditions during gold mineralization,and provides information useful for deep mineralization prediction.We demonstrate that the crystal habits of the pyrites are very complex,primarily occurring as {100},{210},and their combinate form.{210} and {100}+{210} have positive correlations with gold mineralization,and {100}+{210} therefore can be useful for locating rich ore segments.The composition of pyrites is characteristically poor in S and rich in As.Their typical trace elements are composed of Mo,As,Pb,Cu,Bi,Zn,Au,Co,Se,Sb,Ag,Ni,Cr,and Te.The average contents of trace elements in pyrites from various stages show that the crystallizing temperature gradually decreased from an early stage to the metallogenic episodes.The precipitation and accumulation of Au and Ag occur primarily in the quartz-pyrite stage(III) and the polymetal minerals stage(IV).The occurrence rate of P-type pyrites(P(%)) is 83.52%.There is a larger dispersion of the thermoelectrical coefficient of pyrite(α) in the Denggezhuang gold deposit than in other deposits in the Jiaodong Peninsula.The electrical conductivity assemblage of pyrites from I to V is characterized by P≥N→PN→PN→PN→P≥N,which is usually considered beneficial for mineralization.The relative contents of As+Sb+Se+Te and Co+Ni are closely correlated to P-type and N-type average values and their occurrence rates.According to the crystallizing temperature of pyrite,the mineralization intensity,and the denudation degree,the mineralization temperature of the Denggezhuang gold deposit is in the range of 150–322℃ and is of a medium-low temperature.The orebody has already become denuded to the top-middle of the orebody,and the size of the orebody is larger than 900 m.Based on the vertical zoning of the thermoelectrical coefficients of pyrites and P-type pyrite mapping,it is suggested that the segment between ?425 and ?800 m may have exploration potential to the northeast of line 94 of the No.I2-2 orebody.     

New insights from legacy seismic data: reprocessing of legacy 2D seismic data for imaging of iron-oxide mineralization near Sishen Mine,South Africa

Two overlapping legacy seismic profiles, 130 km long end to end, were shot in the 1990s over the Kuruman Hills on the western margin of the Kaapvaal Craton in southern Africa. The 6-s profiles were aimed at investigating the crustal structure of the western Kaapvaal Craton as well as to locate potential continuation of the Witwatersrand gold-bearing horizons beneath the cover rocks, the latter of which was unsuccessful. In this study, the legacy seismic data are reprocessed and used to image the iron-oxide (mainly haematite) mineralization found in the Kuruman Formation of the Griqualand-West Supergroup, which outcrops along the two seismic profiles. The seismic profiles are located close to the Sishen open pit iron mine, where one of the world's largest iron ore concentrations (986 Mt) is mined. The reprocessed and merged seismic data are combined with magnetic, magnetotelluric, borehole and outcrop data to constrain the interpretation, and all indicate the mineralization host rocks to have ∼500 m thickness and 950 m depth. The seismic data further reveal seismic reflections associated with multiple iron ore horizons, which are affected by a first-order scale syncline and numerous near-vertically dipping (∼65–80°) normal and reverse faults of various orientations and throws, thus providing insight into the structurally controlled iron ore mineralization in the area. Seismic tomography and magnetotellurics characterize the sediments to have a velocity ranging between 5000 and 6000 m/s and a resistivity of <10 Ωm. The seismic imaging of the syncline and associated structural disruptions is important for future mining purposes and plans in the area as these structures might have preserved iron-oxide mineralization from erosion. The reprocessed data thus provide information that could be incorporated in potential future underground mine planning in the area, improving the resource evaluation of the iron-oxide deposit. Legacy seismic data are thus shown to hold intrinsic quality and possible untapped potential that can be realized via data reprocessing.