福建梅仙铅锌矿田磁铁矿成因类型与指示意义

梅仙铅锌矿田为闽中地区的大型铅锌矿集区,矿床成矿年代与成因类型尚有争议。梅仙铅锌矿石中普遍发育磁铁矿,通过电子探针分析磁铁矿成分特征,判别其成因类型,对矿床成矿过程进行约束。研究表明,铅锌矿石中磁铁矿成矿可分为3个阶段,不同阶段磁铁矿主量与微量元素含量差异明显;微量元素地球化学特征指示第一阶段磁铁矿属于喷流沉积成因,第二、三阶段磁铁矿为矽卡岩型;不同阶段磁铁矿的成因类型反映了梅仙矿田多期次岩浆活动与成矿作用的特征。     

从磁铁矿特征论铜厂铁矿床的成因——前寒武纪一个特殊的铁矿类型

矿床成因类型的建立是成因分类的基础,也是矿床学研究的重要内容之一.笔者试图从磁铁矿的成因方面讨论一个产于闪长岩体附近蛇纹岩中,但不属于接触交代和岩浆成因的特殊铁矿类型——铜厂式铁矿,即与元古界(钙)镁硅酸盐岩有关的火山沉积受变质型矿床.一、     

四川木里县长枪穹窿超贫易选磁铁矿地质特征及找矿方向

近年来,在长枪穹窿志留系通化组二段地层中发现的超低品位磁铁矿床,具有浅部易采、易选,铁精矿品位高的特点;虽然矿石品位低,但矿床位于攀西地区,距离攀钢较近,具有一定经济价值。作者通过对该类矿床地质特征、控矿因素、矿床成因及选矿技术的探讨,认为该区磁铁矿赋存于志留系通化组二段区域变质海相火山～碎屑沉积建造内,磁铁矿主要受地层、岩性控制;通过对该类型矿床成矿地质条件及找矿标志的总结,为实现该类矿床的找矿突破指明了方向,在区域上具有一定的指示意义。     

与镁铁－超镁铁质岩石有关的矿床类型

本文综述了近年来的研究成果,介绍了与镁铁质-超镁铁质岩有关的矿床类型和成矿作用。重点讨论的矿种有钒钛磁铁矿、铜-镍、铬铁矿、磁铁矿、铂族、钴、金、镁、磷灰石、金刚石、石棉、蛭石、宝玉石等,涉及的矿床成因类型主要有:岩浆型(包括岩浆熔离、贯入、分异和爆发型)、热液型、矽卡岩型、变质型、火山喷溢型、风化型(包括风化壳和砂矿)以及复合型等。从勘查找矿考虑,可从含矿镁铁-超镁铁质岩石类型入手,结合矿床成因类型和产出构造环境因素,将矿床分为与深成岩、浅成岩和喷出岩有关的三大类和若干亚类矿床,并详细介绍了各类的主要矿床类型、成矿地质特征、成因特点和矿床实例。在此基础上,对与镁铁-超镁铁质岩有关的成矿作用进行了4个层次讨论,包括单一矿床的复合成矿作用、杂岩体本身的不同矿床类型和矿种的组合、不同镁铁-超镁铁质岩套之间的伴生,以及与非超镁铁质岩套的共生与组合。     

云南沉积及沉积变质鉄矿的找矿方向

云南省的鉄矿种类很多,从矿物成分上看,有磁铁矿,赤铁矿,镜铁矿,褐铁矿,沼铁矿等;从矿床成因上看,有岩漿分異矿床,热液交代矿床,沉积变質矿床,沉积矿床,风化壳类型矿床等。但多为中、小型,目前还未找到大型的矿床,正当全国大跃进之     

滇中武定迤纳厂铁铜矿床磁铁矿元素地球化学特征及其成矿意义

武定迤纳厂矿床位于我国云南省中部,在大地位置上处于扬子板块西缘,康滇地轴云南段,是滇中具有代表性的元古代铁-铜-金-稀土矿床.其矿化作用分为岩浆气液期、交代成矿期、热液成矿期和成矿后热液期4个期次,其中前3个期次是铁成矿的主要期次,分别以角砾状磁铁矿、浸染状磁铁矿和粗粒脉状磁铁矿为代表.各类磁铁矿含有一定量的SiO2、Cr2O3、Al2O3、MgO等,角砾状磁铁矿石的主元素成分与铁成分比值最高,其次为浸染状磁铁矿,最低为脉状磁铁矿.不同类型的磁铁矿微量元素变化很大,浸染状磁铁矿稀土配分具四重效应,角砾状磁铁矿和粗粒脉状磁铁矿稀土配分为右倾型.成矿早期磁铁矿的形成受岩浆作用影响强烈,含铁的岩浆导致围岩碎裂,形成了早期角砾状矿石;交代成矿期的铁质主要源于岩浆演化晚期分异形成的富铁流体,富铁流体与围岩发生强烈的物质交换,导致大量铁质沉淀;随着矿化作用的进行,热液作用逐渐增强,加之外界流体的逐渐加入,对之前形成的磁铁矿进行改造,使其具有热液成因的表象特征.从矿物成分体现出的矿床成因上看,该矿床属于岩浆隐爆-交代型成因,与世界知名的IOCG型矿床有相似之处.     

福建李家坊金矿床磁铁矿成因及其对金矿化过程的指示

福建泰宁李家坊金矿床位于武夷山成矿带中段,为闽西北何宝山矿田内新发现的一个中型金矿床,成因类型尚未明确。磁铁矿是该矿床中常见的氧化物,文章应用磁铁矿微量元素特征对李家坊金矿床成矿过程与成因类型进行约束。基于野外地质踏勘和钻孔岩芯编录,结合室内详细的岩相学观察,依据磁铁矿的结构和矿物共生组合,文章将其分为4种类型（Mt1a、Mt1b、Mt2和Mt3）。其中,Mt1a位于铜金矿脉边缘,呈板柱状,与绿泥石共生; Mt1b位于铜金矿脉边缘,呈自形-半自形粒状,与绿泥石-赤铁矿共生; Mt2位于铜金矿脉中,呈脉状产出,穿插早阶段的石英-黄铁矿脉,与绿泥石-绿帘石共生; Mt3位于铜金矿脉中,呈半自形-他形粒状,与绿帘石-赤铁矿共生,被后阶段黄铜矿包裹、交代。金主要以自然金和银金矿的形式赋存于Mt3中。原位微区分析结果表明,李家坊金矿不同类型磁铁矿均属于热液型磁铁矿。此外,从Mt1a型到Mt3型磁铁矿,w（Ti）呈逐渐降低的趋势,指示热液流体逐渐向低温条件演化; w（V）表现出先降低后升高再降低的变化规律,暗示热液流体的氧逸度有明显波动,但总体呈升高趋势。磁铁矿的显微结构和化学组成具矽卡岩型矿化特征,是判断矿床成因类型的证据。其中,Mt3型磁铁矿与Au矿化密切相关,其矿物组合与微量元素特征可指示金在低温高氧逸度的环境下沉淀。     

青海虎头崖多金属矿床矿石矿物标型特征与成因

虎头崖矿床是青海祁漫塔格地区重要的铅锌多金属矿床之一,该区岩浆活动强烈,具有Fe、Cu、Mo、Pb、Zn等多金属成矿元素组合.本文在前人研究成果的基础上,通过分析虎头崖矿床不同矿脉黄铜矿、闪锌矿、磁铁矿、磁黄铁矿、方铅矿和毒砂6种主要矿石矿物的标型特征,探讨其对于矿床成矿作用的指示意义.通过分析虎头崖矿床2号矿脉、6号矿脉、7号矿脉闪锌矿中Zn/Fe比值(平均值分别为19.62、32.71、24.91)、Zn/Cd比值(均值分别为179.39、148.00、182.33)、Fe含量和FeS含量,以及黄铜矿中S元素含量、(Fe+Cu)/S比值(平均值分别为1.97、1.90、1.86),认为虎头崖矿床大致形成于中温环境,成矿温度自主岩体沿断层接触带向围岩逐渐降低,且7号脉闪锌矿成矿温度表现出从第1世代到第3世代逐渐降低的特点.根据磁铁矿中TiO2、A12O3、MgO、MnO和闪锌矿中Fe、Mn、Cd、Zn等化学成分特征,结合矿床地质特征和前人研究成果,认为虎头崖矿床成因类型为矽卡岩型矿床.     

新疆塔什库尔干地区“帕米尔式”铁矿床的发现及其地质意义

新疆塔什库尔干地区近年来发现了一系列规模较大的铁矿床,如老并铁矿床、乔普卡里莫铁矿床、叶里克铁矿床、吉尔铁克沟铁矿床等。由于这些矿床具有较为独特的矿床地质特征和成矿时代特点而有别于世界上已知的铁矿床,因而将其命名为“帕米尔式”铁矿床。以老并铁矿床为例对“帕米尔式”铁矿床的地质特征、成矿年代、矿床成因等进行了初步研究。研究表明,“帕米尔式”铁矿床主要赋存于布伦阔勒岩群黑云石英片岩岩性段内,该岩性段磁铁矿化现象较为普遍,普遍发育磁铁矿、黄铁矿、石膏、硬石膏的矿物同生组合,为一种特殊的膏铁建造;LA-ICP-MS碎屑锆石U-Pb同位素测年表明,含铁建造布伦阔勒岩群的形成时代为早古生代;矿床成因类型为海相火山沉积型磁铁矿矿床,后期受到一定的区域变质作用的叠加改造。该类型矿床的发现,对于丰富世界铁矿床的类型和同类型铁矿床的找矿工作都具有重要的借鉴意义。     

新疆塔什库尔干地区“帕米尔式”铁矿床的发现及其地质意义

新疆塔什库尔干地区近年来发现了一系列规模较大的铁矿床,如老并铁矿床、乔普卡里莫铁矿床、叶里克铁矿床、吉尔铁克沟铁矿床等。由于这些矿床具有较为独特的矿床地质特征和成矿时代特点而有别于世界上已知的铁矿床,因而将其命名为"帕米尔式"铁矿床。以老并铁矿床为例对"帕米尔式"铁矿床的地质特征、成矿年代、矿床成因等进行了初步研究。研究表明,"帕米尔式"铁矿床主要赋存于布伦阔勒岩群黑云石英片岩岩性段内,该岩性段磁铁矿化现象较为普遍,普遍发育磁铁矿、黄铁矿、石膏、硬石膏的矿物同生组合,为一种特殊的膏铁建造;LA-ICP-MS碎屑锆石U-Pb同位素测年表明,含铁建造布伦阔勒岩群的形成时代为早古生代;矿床成因类型为海相火山沉积型磁铁矿矿床,后期受到一定的区域变质作用的叠加改造。该类型矿床的发现,对于丰富世界铁矿床的类型和同类型铁矿床的找矿工作都具有重要的借鉴意义。     

Partial least squares-discriminant analysis of trace element compositions of magnetite from various VMS deposit subtypes: Application to mineral exploration

The petrography and mineral chemistry of magnetite from fifteen volcanogenic massive sulfide (VMS) deposits in Canada, and the Lasail VMS deposit in Oman, as well as from two VMS-associated banded iron formations (BIF), Austin Brook (New Brunswick, Canada) and Izok Lake (Nunavut, Canada), were investigated using optical microscopy, electron probe micro-analyzer (EPMA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The method of robust estimation for compositional data (robCompositions) was applied to investigate geochemical censored data. Among thirty-seven elements analyzed by EPMA and/or LA-ICP-MS in magnetite from the studied deposits/bedrock lithologies, only the results for Si, Ca, Zr, Al, Mg, Ti, Zn, Co and Ni contain < 40% censored values, and thus could be imputed using robCompositions. Imputed censored data were transformed using centered log-ratios to overcome the closure effect on compositional data. Transformed data were classified by partial least squares-discriminant analysis (PLS-DA) to identify different compositional characteristics of magnetite from VMS deposits and BIFs. The integration of petrography and mineral chemistry identifies three types of magnetite in VMS settings: magmatic, hydrothermal, and metamorphic. Magmatic magnetite in VMS deposit host bedrocks is characterized by ilmenite exsolution and may be overprinted by metamorphism. Some VMS deposits contain hydrothermal magnetite, which is intergrown with sulfides, and shows a metamorphic overprint as it is partly replaced by common metamorphic minerals including chlorite, sericite, anthophyllite, and/or actinolite, whereas the majority of the deposits are characterized by metamorphic magnetite formed by replacing pre-existing sulfides and/or silicates, and is intergrown with metamorphic minerals. Among VMS deposits of the Noranda mining district, the West Ansil deposit is characterized by hydrothermal-metamorphic magnetite zoned by inclusion-free cores and Si- and Mg-rich rims. Magnetite from the studied VMS-associated BIFs is also metamorphic in origin. Aluminum, Ti and Zn contents of magnetite can separate BIF from the other mineralized and un-mineralized bedrock lithologies in the studied VMS settings.PLS-DA shows that variable compositions of magnetite slightly discriminate different studied deposits/bedrock lithologies. The geochemical observations suggest that the variation in magnetite chemistry from different VMS settings might be sourced from differences in: 1) the composition and temperature of parental magmas or hydrothermal fluids, 2) the composition of host bedrocks, 3) the composition of co-forming minerals, and 4) oxygen fugacity. PLS-DA distinguishes magnetite compositions from the studied VMS deposits and BIFs from that of the other ore deposit types including Ni–Cu, porphyry Cu-Mo-Au, iron oxide-copper- gold, iron oxide-apatite, and the Bayan Obo REE-Fe-Nb deposit. Magnetite from the VMS settings on average contains lower concentrations of Si, Zr, Al, Mg, Ti, Zn, Co and Ni relative to that from the other mineral deposit types. PLS-DA of magnetite data from VMS deposits and BIFs of the Bathurst mining camp as well as PLS-DA of magnetite compositions from various mineral deposit types yield discrimination models for application to mineral exploration for VMS deposits using indicator minerals in Quaternary lithified sedimentary rocks.     

内蒙古陈巴尔虎旗八大关铜钼矿岩石地球化学特征及U-Pb、Re-Os年龄

得尔布干成矿带是中国东北地区中、俄、蒙毗邻区域一条重要的铜、钼、金、铅锌多金属成矿带,控制产出大量多金属矿床。满洲里—陈巴尔虎旗一线集中产出铜钼矿,如乌奴格吐山铜钼矿、八大关铜钼矿、八八一铜钼矿。然而与相邻俄罗斯额尔古纳—上黑龙江—岗仁成矿带中的铜钼矿产出现状对比,无论数量还是规模均相差甚远,显示仍存在较大找矿空间。在近年来大量野外地质工作及矿床实际考察基础上,阐述了八大关铜钼矿矿床地质特征。通过岩石地球化学特征研究、LA-ICPMS锆石U-Pb及辉钼矿Re-Os年龄测试,确定八大关铜钼矿为形成于印支晚期(205.8±3.4Ma),受八大关短轴背斜及NE-SN向断裂控制的造山带斑岩型铜钼矿。与乌奴格吐山铜钼矿对比,八大关矿区形成于燕山早期的花岗质斑岩体极有可能是新的铜钼赋矿体。     

Discrimination of Pb-Zn deposit types using sphalerite geochemistry: New insights from machine learning algorithm

Due to the combined influences such as ore-forming temperature, fluid and metal sources, sphalerite tends to incorporate diverse contents of trace elements during the formation of different types of Lead-zinc (Pb-Zn) deposits. Therefore, trace elements in sphalerite have long been utilized to distinguish Pb-Zn deposit types. However, previous discriminant diagrams usually contain two or three dimensions, which are limited to revealing the complicated interrelations between trace elements of sphalerite and the types of Pb-Zn deposits. In this study, we aim to prove that the sphalerite trace elements can be used to classify the Pb-Zn deposit types and extract key factors from sphalerite trace elements that can discriminate Pb-Zn deposit types using machine learning algorithms. A dataset of nearly 3600 sphalerite spot analyses from 95 Pb-Zn deposits worldwide determined by LA-ICP-MS was compiled from peer-reviewed publications, containing 12 elements (Mn, Fe, Co, Cu, Ga, Ge, Ag, Cd, In, Sn, Sb, and Pb) from 5 types, including Sedimentary Exhalative (SEDEX), Mississippi Valley Type (MVT), Volcanic Massive Sulfide (VMS), skarn, and epithermal deposits. Random Forests (RF) is applied to the data processing and the results show that trace elements of sphalerite can successfully discriminate different types of Pb-Zn deposits except for VMS deposits, most of which are falsely distinguished as skarn and epithermal types. To further discriminate VMS deposits, future studies could focus on enlarging the capacity of VMS deposits in datasets and applying other geological factors along with sphalerite trace elements when constructing the classification model. RF’s feature importance and permutation feature importance were adopted to evaluate the element significance for classification. Besides, a visualized tool, t-distributed stochastic neighbor embedding (t-SNE), was used to verify the results of both classification and evaluation. The results presented here show that Mn, Co, and Ge display significant impacts on classification of Pb-Zn deposits and In, Ga, Sn, Cd, and Fe also have relatively important effects compared to the rest elements, confirming that Pb-Zn deposits discrimination is mainly controlled by multi-elements in sphalerite. Our study hence shows that machine learning algorithm can provide new insights into conventional geochemical analyses, inspiring future research on constructing classification models of mineral deposits using mineral geochemistry data.     

吉林放牛沟硫铁多金属矿床矿物地球化学及矿床成因

本文总结了黄铁矿、闪锌矿的成因地球化学标志;阐明了黄铁矿中元素在空间上的分带规律和在成矿过程中时间上的演化规律;建立了反映上述分带规律的回归方程组;论证了本矿床矿石中黄铁矿与磁黄铁矿间、矿石矿物与花岗岩副矿物磁铁矿间的成因联系;类比了国内外铅锌矿床上述矿物的地球化学特征。由此得出结论:放牛沟硫铁多金属矿床系岩浆热液成因,其成矿物质主要来自后庙岭花岗岩深部岩浆源。铅锌矿主要在中温条件下形成,接触带矿体与外接触带矿体属同一成矿系列。放牛沟矿床与后庙岭花岗岩系同一岩浆—热液系统的产物。     

山东齐河—禹城地区李屯富铁矿床地球化学特征及地质意义

李屯铁矿为近年在山东省齐河—禹城地区发现的隐伏富磁铁矿床,为空白区地质找矿新发现。本文通过详细野外调查、室内镜下观察及地球化学分析测试,对矿床地质、地球化学特征进行了系统研究,初步揭示矿床成因。磁铁矿体赋存于李屯岩体与石炭纪—二叠纪地层接触带附近的砂泥岩地层内。李屯铁矿中岩体微量元素分配模式具有较好的一致性,均不同程度地富集Rb、Ba、Sr等大离子亲石元素,亏损Zr、Nb、Ta等高场强元素,磁铁矿石中富集大离子亲石元素Sr,亏损K;高场强元素富集U、P、Hf、Ta,亏损Nb、Ti。岩体与磁铁矿石稀土元素均表现出轻稀土富集、重稀土亏损的右倾型配分模式。李屯铁矿形成于岩石圈大规模快速减薄期,成矿构造背景应为板块伸展扩张环境。李屯岩体的岩浆来源为壳幔混源,尖晶石相二辉橄榄岩发生部分熔融产生的的岩浆熔体;成矿物质来源于深源岩浆及其形成的岩浆岩。磁铁矿成矿与李屯岩体关系密切,矿床成因类型应是接触交代型矽卡岩铁矿床。     

LA-ICP-MS Analysis of Magnetite and Application in Genesis of Mineral Deposit

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is well characterized by the in-situ, real time, lower limit of detection and high space resolution, etc. Therefore, it is more excellent in the analysis of trace element for varied minerals in comparison to other micro-zone analysis technologies. Magnetite as a common mineral from different deposits and rocks has been focused on chemical compositions by researchers worldwide. In fact, as the insignificant matrix effect for most elements in magnetite, analysis results could be calculated effectively against Fe-rich silicate glass as the reference material. Therefore, researches on trace element distribution of magnetite have been developed rapidly in recent years, and it has a wide application prospect in reflecting the condition of ore-forming, discriminating different deposit types and indicating prospecting exploration. Comparing varied previous discrimination diagrams about magnetite via collecting trace element data from available literatures based on 25 deposits, we found that there was an urgent need for further detailing and reexamining the boundary of fields representing different genetic types, and it was vital for interpreting the data through carefully petrographical observation before analysis. In addition, we discussed several complex physicochemical factors, which would influence the element concentration of magmatite in igneous and hydrothermal processes, such as melt/fluid composition, temperature, cooling rate, pressure, oxygen fugacity, sulfur fugacity and silica activity. In magma stage, Magnetite’s components are closely related to melts composition and differentiation, while fluid features would also significantly change magnetie's components. Furthermore, there is serious interference for discriminating the genesis of magnetite because of late stage fluids and equilibrium again in subsolidus condition. This paper reviewed the developments of trace elements analysis by LA-ICP-MS and important applications about magnetite in mineral deposit so that unique thoughts for the research on mineralization and ore-forming processes could be obtained.     

激光剥蚀电感耦合等离子体质谱-电子探针分析白山堂铜矿中的黄铁矿成分

通过激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）获得被测物相中痕量元素的丰度值是目前原位分析矿物物相的技术之一。黄铁矿作为斑岩铜矿中的重要矿物,其主量、微量元素的特征能为成矿过程提供重要信息。本文建立了应用LA-ICP-MS测定黄铁矿微区微量元素组成、电子探针（EMPA）测定主量元素的方法,并将该方法应用到白山堂斑岩铜矿区。LA-ICP-MS实验采用60 μm的激光束对分析样品进行斑点式剥蚀,以氦气作载气,重复频率5 Hz,激光能量约6 J/cm2;单点分析时间60 s,分析数据以Fe作内标,用MASS-1黄铁矿标样进行校正,多数元素分析精度好于10%。针对黄铁矿与毒砂光学性质相似,容易混淆的问题,可以利用二者物理性质的差异进行区分。测试结果显示：矿区黄铁矿的主量元素呈亏硫高铁的特征,指示其为热液成因;微量元素特征表明其形成深度为中部,属与火山作用有关的中低温热液型黄铁矿。此结论对白山堂铜矿的成因类型、成矿流体来源等提供了相应的证据,对矿区的勘查具有理论指导意义。     

Magnetite geochemistry of the Longqiao and Tieshan Fe–(Cu) deposits in the Middle-Lower Yangtze River Belt: Implications for deposit type and ore genesis

Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong ore district) and Tieshan Fe–(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China.Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe–(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate).Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid–rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO₂, may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO₂, but lower fluid–rock interactions and ore-forming temperature than the Longqiao deposit. The TiO₂–Al₂O₃–(MgO + MnO) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe–(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed.