加拿大拉布拉多地槽DSO型铁矿床成矿规律及找矿方法研究

DSO(Direct Shipping Ore)型铁矿床即直运型铁矿床,指加拿大拉布拉多地槽区Fe品位大于50%(w(SiO2)18%)的赤铁矿矿床,因其矿石品位高、经济效益突出而备受关注。对该地区DSO矿床区域成矿背景、典型矿床研究表明:(1)DSO矿体均赋存于苏克曼组含铁建造中;(2)DSO矿体的产出位置主要受构造控制,构造为热液流体的运移提供了通道,也为矿质的重结晶及沉淀提供了空间;(3)软质DSO成因属深部热液-表生改造型,硬质DSO成因则属热液型。根据DSO的成矿特点,可将拉布拉多地槽DSO找矿靶区分为谢弗维尔软质DSO找矿靶区、铁矿湖-阿提卡玛根软质DSO找矿靶区和阿斯特雷—索耶湖硬质DSO找矿靶区。找矿实践中,应通过地质填图、物探等方法对拉布拉多地槽中部地区的岩性和构造进行控制,重点关注NW向大断裂与次级断裂、次级褶皱、玄武岩与含铁建造岩性转换面的叠加处和地球物理低磁高重区。综合地质和地球物理方法优选靶区进行槽探、钻探相结合的快速验证,可有效提高找矿效率,实现拉布拉多地槽区DSO找矿工作的快速突破。     

加拿大拉布拉多地区主要金属矿床地质特征及其时空分布

拉布拉多是加拿大大西洋成矿域中具地质多样性的最大的成矿省,区域成矿地质条件优越,产有Superior型含铁建造、岩浆硫化物、铂族元素、火山成因块状硫化物、铀、稀有稀土等多种金属矿床。文章介绍了拉布拉多铁、铀、稀有稀土、镍多金属等优势金属矿床的成矿背景、成矿特征、矿床(点)分布、典型矿床地质特征及最新勘探成果,分析了区域地质演化作用与区域内主要金属矿床的时空分布。     

Aspects of strain history in folded sediments from the Schefferville Mining District, Labrador Trough, Canada

Preferred orientations of phyllosilicate grains in the shaley rocks of the Labrador Trough were studied using a pole-figure goniometer. Transmitted X-rays permit determination of the basal planes of chlorite and muscovite. From their preferred orientation, strain is calculated according to March's theory. By choosing samples in successively more strongly deformed domains, a strain history can be recognized which started with compaction by loss of pore volume under an overburden and was later followed by an early homogeneous tectonic shortening parallel to bedding and at a right angle to the fold axis. Buckling occurred next, with strain in the limbs becoming different from that in the hinges; the limbs were lengthened parallel to bedding and nearly normal to the fold axis. Continuing appression, finally, led to pervasive shortening normal to the axial plane with concurrent stretching both updip along the axial plane and along the fold axis. This latter stretching may have occurred when variable-plunge basin and dome structures of the Labrador Trough were formed.     

Textural development in sulfide-matrix ore breccias in the Voisey's Bay Ni-Cu-Co deposit,Labrador, Canada

Magmatic Ni-Cu sulfide ores at Voisey’s Bay contain complex assemblages of extremely heterogeneous rocks. These range from polymict breccias, with rock fragments in sulfide-rich and/or sulfide-poor matrices, to heterogeneous “vari-textured” gabbros with rapid short range variations in grain size and content of hydrous phases. Rock fragment populations in the breccias include endogenous olivine gabbros (cumulate and non-cumulate) and cumulate peridotites along with extensively depleted plagioclase-hercynite gneisses interpreted as restites from extensive partial melting of country rock quartzo-feldspathic paragneisses. Using a combination of desk-top microbeam XRF mapping at cm scale and 3D X-ray tomography, we show that both sulfide-poor and sulfide-rich breccias comprise heterolithic assemblages of clasts within a matrix of olivine gabbro. This matrix is characterised by an interconnected 3D framework of plagioclase crystals, highly variable in grain size at mm to cm scale, with interstitial olivine and poikilitic clinopyroxene, and is texturally indistinguishable from clast-free olivine gabbro. Sulfide forms interconnected networks at cm to dm scale and possibly larger. Much of the plagioclase developed by outgrowth from the margins of paragneiss xenoliths when the porosity was occupied by silicate melt. The observed range of textures is explained by a model of percolation of molten sulfide through variably crystalline inter-clast matrix, displacing the silicate melt to leave the refractory plagioclase-olivine or in some cases plagioclase-only component, now entirely within a sulfide matrix. The process is analogous to that believed to have formed interspinifex ore in komatiite-hosted deposits. Biotite rims on plagioclase enclosed in sulfide are interpreted as the result of reaction between plagioclase, olivine and a hydrous component derived from the sulfide melt itself, with a possible component of migrating residual silicate melt wicking along sulfide-silicate contacts. This sulfide infiltration model offers an alternative to the current model for upward emplacement of a slurry of silicate melt, sulfide melt and breccia fragments as a late stage injection into the dyke-sill complex. The preserved range of textures is interpreted as being due to gravity-driven percolation of sulfide liquid through a pre-existing partially molten intrusion breccia. In this model, the breccia serves as a physical trap site, accumulating downward migrating sulfide liquid. However, the invariable close mutual association of sulfide and rock fragments at Voisey’s Bay implies a common derivation.     

Hydrogeochemistry of the permafrost zone in the central part of the Yakutian diamond-bearing province,Russia

The hydrogeochemical characteristics and zonation of the permafrost zone in the central part of the Yakutian diamond-bearing province formed mainly under the influence of cryogenic processes that occurred in the late Cenozoic. On the basis of field and experimental studies, conclusions were formulated that the perennial cryogenesis of the sedimentary cover in this region resulted in increasing the concentration of carbonate and sulfate compounds in groundwaters as well as increasing the concentration of easily soluble compounds (sodium, magnesium, and calcium chlorides).

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Resumen Las características hidrogeoquímicas y la zonación del permafrost existente en el centro de la provincia de Yakutia, rica en diamantes, se formaron fundamentalmente bajo la influencia de procesos criogénicos durante el tramo final del Cenozoico. Con base en estudios de campo y experimentales, se ha concluido que la criogénesis perenne de la cubierta sedimentaria de la región ha provocado un aumento de la concentración de compuestos de carbonato y sulfato en las aguas subterráneas, además de incrementar la concentración de compuestos solubles, como el sodio, magnesio y cloruros de calcio.

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Résumé Les caractéristiques hydrogéochimiques et la zonation de la région de permafrost dans la partie centrale de la province diamantifère de Yakoutie ont été acquises principalement sous l'influence des processus cryogéniques qui existent depuis la fin du Tertiaire. Sur la base d'études expérimentales et de terrain, on conclut que la cryogenèse permanente de la couverture sédimentaire de cette région a provoqué un accroissement de la concentration des composés carbonatés et sulfatés dans les eaux souterraines, en même temps que celui de composés facilement solubles, comme les chlorures de sodium, de magnésium et de calcium.

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On the use of orthogonally stepwise regression discrimination for predicting copper ore deposits of Dongchuan type in central Yunnan, China

In the prediction of ore deposits, a series of geological, geochemical, and geophysical characters are used to describe the model of ore deposits. The problem is how to use the characters of known ore deposits to establish the model and to look for the target areas with similar geological environments. This can be done with a powerful mathematical tool—discriminant analysis. Nevertheless, there generally are too many geological variables to describe a class of ore deposits. Some of them are discrete, and the others are continuous. It is also difficult to know their distributions. A satisfactory method of discrimination has not been developed for such a complicated case. For this reason, we introduce a new method of orthogonally stepwise discrimination. We used this method to predict copper ore deposits of Dongchuan type in central Yunnan, China, with satisfactory results.     

地球物理方法在智利第一大区南部X矿区的应用

智利的区域地质和地球物理勘探的工作程度相对偏低,对矿区的地球物理资料的解释不够,矿床的分布特征了解得不透彻。笔者通过物探地面磁测和电磁法,对智利第一大区X矿区的地质特征与地球物理特征进行了综合分析,认为相对高磁或弱磁低阻异常带及其周围、深部是找矿的地球物理异常标志,本地区构造(破碎带)是下一步成矿规律的研究重点。地球物理方法对实际勘查工作具有指导意义。     

隐伏矿定位预测中探查技术有效性评价——以安徽铜陵凤凰山铜矿南区为例

文章以安徽铜陵凤凰山铜矿南区深边部隐伏矿勘查预测为例，针对研究区矿床和矿体的定位规律和控制因素，采用了构造地球化学、地电化学提取 g 能谱测量、可控源音频大地电磁法、伪随机多频激电探测方法等多种技术方法在靶区开展多方法技术的隐伏矿定位预测，运用因子分析和层次分析法对不同探查方法技术及其组合在综合信息优化集成技术体系中的有效性和有效度进行了研究。通过综合预测，在研究靶区圈定了4个异常带，其中Ⅲ异常已得到工程验证。     

Petrogenesis of the Az Zabirah south zone bauxite ore deposits,central northern Saudi Arabia

Arabian Journal of Geosciences - The bauxite ore deposits are mainly found around the Az Zabirah area in the central northern part of Saudi Arabia. The age of the Az Zabirah bauxites was suggested...     

Iron redistribution during postore stage at uranium deposits of the Khiagda ore field,Vitim district

The localization conditions of mineralization at uranium deposits of the Khiagda ore field related to the economic sandstone type in paleovalleys are considered in this paper. These conditions allow different genetic treatments. Uncertainty in genetic estimates is caused by localization of orebodies in both gray sedimentary rocks at the boundary with bleached rocks and in the bleached rocks themselves. The results of mineralogical and geochemical studies have shown that bleaching is related to iron redistribution at the postore stage. Obvious evidence in favor of this conclusion has been obtained from statistical processing of quantitative soluble iron determinations in various geochemical types of host rocks. The postore bleaching is superposed on earlier oxidized and ore-bearing gray rocks, obliterating the coloration inherent to redox ore-controlling zoning.     

物化探综合方法在天井窝钨多金属找矿中的应用

为了配合九龙脑矿田深部找矿突破,在天井窝钨多金属矿示范区开展面积与剖面测量相结合的物化探综合勘查技术方法,圈定"一带(古亭灰岩与九龙脑复式岩体东西向接触带)三区(Ⅰ、Ⅱ、Ⅲ异常)"为成矿最有利区段.通过钻探工程验证揭露多层厚度1.62~19.37 m似层状、接触带矽卡岩型钨多金属矿体,初步建立起该区矽卡岩型钨多金属矿体物化探综合找矿模式——"二低三高",即低重力、低视电阻率,高强度的ΔT异常、高视极化率ηs异常,并有地球化学W、Sn、Bi、As、Sb、壤中汞气等高异常.区内钨多金属成矿与燕山期岩浆活动关系密切,成矿受地层、岩浆、构造复合控制,因此选区应在反映岩体或隐伏岩体的重力低异常区及断裂构造的壤中汞气异常区.基于以上认识,指出区内南边深部具备地层(古亭灰岩)-构造(F1、F2断裂)-岩浆岩(深部隐伏岩突)成矿有利条件的最佳耦合,深部找矿潜力较大.     

物化探方法在辽宁省西丰县成平钼矿勘查中的应用效果

以辽宁省西丰县成平钼矿的发现为例,详细阐述了化探(水系、土壤)测量在确定本区找矿靶区、成矿类型和寻找矿(化)体的富集地段过程中所发挥的重要作用,以及激电中梯测量在反映本区地下金属硫化物的相对富集程度和花岗岩体内的硅化强弱程度时的应用效果。这说明充分运用物化探方法可以取长补短,减少了异常解释中的多解性,使得异常的解释更加趋于合理,并取得了良好的找矿效果。     

Manganese ore deposits in Koira-Noamundi province of Iron Ore Group, north Orissa, India: In the light of geochemical signature

Several small Mn–Fe oxide and Mn-oxide ore bodies associated with Precambrian Iron Ore Group of rocks are located within Koira-Noamundi province of north Orissa, India. These deposits are classified into in situ (stratiform), remobilized (stratabound) and reworked categories based on their field disposition. Volcaniclastic/terrigenous shale in large geographic extension is associated with these ore bodies.The in situ ore bodies are characterised by cryptomelane-, romanechite- and hematite-dominating minerals, low Mn/Fe ratio (1.1) and relatively lower abundance of trace (1500–2500 ppm) constituents. In such type of deposits the stratigraphic conformity of oxides with the tuffaceous shale suggests precipitation of Mn and Fe at a time of decreased volcaniclastic/terrigenous contribution. The minor and trace elements were removed from solution by adsorption rather than by precipitation. Both Mn and Fe oxides when precipitated adsorb trace elements strongly but the partitioning of elements takes place during diagenesis. The inter-elemental relationship reveals that Cu, Co, Ni, Pb and Zn were adsorbed on precipitating hydrous Mn oxides and form manganates. Some of these elements probably get desorbed from Fe oxide because of their inability to substitute for Fe³⁺ in the lattice of its oxide. However, P, V, As and Mo were less partitioned and retained in Fe-oxide phase. Positive correlation between Al₂O₃ and SiO₂, MgO, Na₂O, TiO₂ and some traces like Li, Nb, Sc, Y, Zr, Th and U points to their contribution through volcaniclastic/terrigenous detritus of both mafic and acidic composition.The remobilized ore bodies are developed in a later stage through dissolution, remobilization and reprecipitation of Mn oxides in favorable structural weak planes under supergene environment. Increase in average Mn/Fe ratio (8) and trace content (5000–8500 ppm) by 5–2.5 orders of magnitude, respectively, or more above its abundance in adjoining/underlying protore is characteristic of these deposits. The newly formed Mn ores constituting lithiophorite, cryptomelane/romanechite and goethite get quantitatively enriched in traces like Cu, Co, Ni, Pb and Zn. Positive correlation between Mn, Li, Co and Zn is due to the formation of mineral of lithiophorite–chalcophanite group during redistribution and reconcentration of Mn oxide. P and V, which were present in Fe oxide, also get dissolved and reprecipitate with Fe oxyhydroxide in these ores. Some other elements like Y, Th and U show positive relation with Fe. This is probably due to leaching of these elements during chemical weathering of associated shale and getting re-adsorbed in Fe-oxyhydroxide phase.However, under oxidizing environment selective cations like Ba, K, etc. resorb from Mn-structure, resulting in the development of pyrolusite (Mn/Fe>20). In such transformation, trace metals from pyrolusitic structure expels out, resulting thereby in a considerable reduction in total trace value (<3000 ppm).The reworked ore bodies are allochthonous in nature and developed through a number of stages during terrain evolution and lateritisation. Secondary processes such as reworking of pre-existing crust; solution and remobilization; precipitation and cementation and transport, etc. are responsible for their development. Such deposits are usually very low in Mn/Fe ratio (3) and trace content (<2000 ppm).     

综合物探方法在广西妙皇隐伏多金属矿勘查中的应用

妙皇多金属矿区位于来宾凹陷东缘与大瑶山隆起西侧交接部位,广西大瑶山及其西侧铅锌成矿带中部成矿条件优越,历年来开展过多种研究和找矿方法,但找矿效果不佳。通过研究妙皇铜铅锌银矿区的地质条件和成矿背景,运用综合物探方法,对区内部分地质问题及矿产特征进行了推断和预测。2012年,依据地质物探综合成果布置了ZK22701号验证孔,取得了突破性的进展。同时,依据物探成果推测了矿区成矿机理和成矿模式,在找矿方向和找矿潜力方面进行了分析探讨,对中深部找矿具有很好的指导意义。     

Pb isotope fingerprinting of mesothermal gold deposits from central Victoria, Australia: implications for ore genesis

New Pb isotope data from three major mesothermal lode gold deposits (Ballarat West, Tarnagulla, Maldon) in central Victoria support a model whereby the metals derived from a large reservoir with a long residence time in the crust below the Palaeozoic Lachlan Fold Belt. The Pb isotopic ratios of least radiogenic samples from these deposits are in close agreement with published Pb signatures for turbidite-hosted gold deposits, and for Devonian granites, elsewhere in the Lachlan Fold Belt. Despite their spatial distribution and variations in the geological setting, the Pb signatures point to the extraction and transport of metals from a crustal source area by long-lasting, large-scale hydrothermal systems, resulting in the prominent homogenisation of Pb isotopic ratios. The enduring interaction between large hydrothermal systems and an extensive crustal source reservoir were a vital pre-requisite in the formation of the Victorian gold province. In this regard, the prospectivity of Victoria is analogous to world-class ore provinces elsewhere, such as the Archaean Yilgarn Block in Western Australia. Received: 10 February 1998 / Accepted: 28 April 1998     

Seismodeformations in Late Holocene estuary deposits in the central part of St. Petersburg

Deformations in a section of layered Late Holocene estuary-flood-plain deposits, found for the first time in the central part of St. Petersburg, are discussed. The discussed reason why this section could have been deformed inside the undeformed stratum is a horizontally directed dynamical shock. The probable causes of deformation are considered, with the most real one being a relatively distant earthquake. An attempt is made to estimate the intensity of this quake for the territory of the city.     

粤中三水盆地构造-岩浆事件与矿集区形成

粤中三水盆地喜山期银矿化粗面质凝灰岩中锆石LA-ICP-MS U-Pb年龄90～3175 Ma.火山岩中锆石主要为其在形成及上升过程中捕获围岩中的碎屑锆石.火山岩中锆石U-Pb年龄表明粤中三水盆地基底含太古宙的残余错石(2489 Ma±30 Ma,3175 Ma±38 Ma),华夏陆块元古宙基底存在与Grenville造山运动相对比的构造岩浆事件(955～1148 Ma)及在新元古代(798 Ma±12 Ma,883 Ma±10 Ma)发生了较强烈的岩浆活动.粤中三水盆地经历了加里东期构造岩浆事件(438.0 Ma±6.8 Ma),之后至少经历了燕山早期(-160 Ma)、燕出境期(98.2Ma±1.1Ma)及喜山期3次构造岩浆事件.三水盆地多期次构造岩浆活动与成矿事件有一定的耦合关系,是控制矿床形成的主要因素.华南褶皱带岩浆活动强烈,经历新生代成矿作用,中新生代盆地边缘是找矿有利靶区.     

综合物探在西藏尼木地区斑岩铜矿找矿中的应用

西藏尼木地区斑岩铜矿是近年发现的大型斑岩型铜矿.在矿产勘查过程中采用综合物探方法进行圈定勘查目标、缩小找矿靶区、确定异常源、推测矿化空间等项工作,取得了较好的勘查效果,说明在西藏尼木县斑岩铜矿区综合运用地面高精度磁测、激电中梯、激电测深等物探勘查方法,能减少物探的多解性,较好地解决具体的地质问题.