成岩温度的判别标志

“沉积物沉积之后,在没有受到高压和岩浆热力影响时所经历的一切物理的和化学的变化”,Walther(1894)称之为成岩作用。这一定义包括了我们所谓的准同生作用、成岩作用和表生作用等阶段,即广义的成岩作用。成岩作用的主要控制因素是主岩成分、温度、压力和孔隙流体性质。其中温度是最关键的因素,人们也主要是根据温度来划分成岩作用和后生作用的界限。一般把浊沸石稳定的上     

礁型层控硫化金属矿床的沉积特征及成因探讨

文章通过广西南丹大厂中泥盆世北流期礁型铅锌矿床及滇东元古界昆阳群落雪组陆缘迭层藻礁型铜矿床的沉积环境分析,总结了层控硫化金属矿床生物礁沉积特点。用生物地球化学成因观点,对该类矿床的成矿物质来源、矿床形成的必要条件及分布规律等进行了探讨,提出了礁型层控硫化金属矿床成矿模式,分析了成矿作用在沉积阶段、成岩阶段及成岩后生阶段的生物化学作用过程。最后对滇黔桂地区寻找礁型层控金属矿床指出了有利沉积相带和远景地区。     

滇中地区层控菱铁矿成因机制探讨

阐述了云南滇中地区层控菱铁矿的矿床类型、原生沉积成矿作用特征、区域动力改造成矿作用特征及表生改造成矿作用特征。研究认为,该区菱铁矿的富集成因机制具有多阶段成矿的特点,可分为三个成矿阶段,即:原生沉积-成岩阶段,发生于1600~1500M a之间,是形成菱铁矿矿源层的重要阶段;区域动力改造阶段,发生于800~650M a之间,是菱铁矿的主要富集成矿阶段;表生改造阶段,主要发生在第三纪,是菱铁矿床形成垂直分带并再次产生改造加富作用的阶段。     

鲕粒的结构变化与成岩作用性质和强度的关系

成岩作用是沉积物转化为变质岩之前的一系列重要作用的总合,成岩作用的性质和强度控制了岩石的总特征,因而研究成岩作用具有重要的理论和实际意义。关于成岩作用的定义和成岩阶段的划分等问题,多年来存在着很大的分歧。综合国内外常见术语和划分方案可将成岩作用划分为同生和准同生作用、成岩作用、后生作用和表生作用等五个阶段。通过岩石的组构类型和某些颗粒的结构特征及变化研究成岩作用,不失为一种常用而有效的方法。     

陕西大西沟喷流沉积型菱铁矿矿床地质特征及矿床成因

陕西大西沟铁矿床位于秦岭造山带山-柞盆地西北部,与银洞子大型银铅矿床毗邻。矿体主要赋存在泥盆系青石垭组中上段,容矿岩石为一套海相复理石碎屑岩和碳酸盐岩建造。矿床的金属矿物主要有菱铁矿、磁铁矿、黄铁矿,其次为黄铜矿、磁黄铁矿等;非金属矿物主要是重晶石、石英、铁白云石,其次为方解石、绢云母、绿泥石、黑云母、斜长石、钠长石、堇青石等,局部地段由于表生氧化和次生富集作用而形成针铁矿、赤铁矿、蓝辉铜矿等。与矿化有关的围岩蚀变较弱,主要有硅化、绢云母化、绿泥石化和碳酸盐化。基于野外地质观察、矿物共生组合和矿石结构构造的系统研究,将大西沟铁矿床的形成划分为3期6阶段,分别是:①喷流沉积期:硅质岩-黄铁矿-菱铁矿阶段(Ⅰ)、重晶石-磁铁矿阶段(Ⅱ);②热液改造期:堇青石-黄铁矿-磁铁矿阶段(Ⅲ)、石英-碳酸盐阶段(Ⅳ)、碳酸盐-硫化物-磁铁矿阶段(Ⅴ);③表生氧化期(Ⅵ)。流体包裹体显微测温结果表明,喷流沉积期Ⅰ阶段菱铁矿完全均一温度和盐度w(NaCl_(eq))峰值区间分别为230～270℃和13%～14.5%,Ⅱ阶段重晶石中流体包裹体的完全均一温度和盐度w(NaCl_(eq))峰值区间分别为220～290℃和9%～13%;热液改造期Ⅳ阶段菱铁矿和石英中气液两相包裹体均一温度峰值区间为240～300℃,盐度w(NaCl_(eq))为2.6%～15.7%;热液改造期Ⅴ阶段菱铁矿与石英中流体包裹体,除大量气液两相包裹体外,还发育有含子矿物多相包裹体,其中,气液两相包裹体均一温度峰值区间为290～340℃,盐度w(NaCl_(eq))为5.1%～13.4%,含子矿物多相包裹体均一温度峰值区间为380～440℃,盐度w(NaCl_(eq))为40.6%～59.7%。含子晶流体包裹体可能是流体不混溶或/和高盐度流体加入的反映。矿区内不同产状碳酸盐矿物的C、O同位素组成比较均一,δ~(13)C_(PDB)值集中在-3.58‰～-1.15‰之间,δ~(18)O_(SMOW)值为21.22‰～21.82‰,均表现出海相碳酸盐或海底喷流热液溶解海相碳酸盐的特征。大西沟矿床的地质、矿化和流体特征与海底热液喷流沉积型矿床一致,可能属于典型的喷流沉积型菱铁矿床,但后期受到秦岭造山作用的影响及热液叠加改造并形成磁铁矿和少量硫化物。大西沟菱铁矿矿床与邻近的银洞子铅锌矿组成一个较完整的喷流沉积成矿系统,两者可能分别代表了喷流沉积的边缘相和中心相。     

层控矿床的控矿构造类型

层控矿床一般具有多种成因、多阶段形成的特点,它一开始在火山作用参与下(或没有参与)形成同生沉积非工业矿化层(胚胎矿),其后在成岩作用、后生作用、变质作用和各种成因热水溶液的作用下发生原生成矿物质的重新组合,并生成了更富集的假后生矿床。因而它既不同于后生矿床,也不完全等同于同生矿床,一般具有迭生(Diplogenetic)矿床的特点。这类矿床不仅受地层、岩性控制和古基底的构造控制,另因迭生成矿作用和再造成矿作用均与构造活动密切相关,故这类矿床受构造的控制也极为明显。其不仅具有其他类型矿田与矿床构造的某些特点,而且还有其固有的控矿构造类型。     

沉积岩分散有机质变质程度的初步研究

沉积岩中蕴藏着丰富的矿产资源。据统计,沉积成因的矿产占整个世界矿产资源的75～80%。沉积成因矿床的形成与岩石的成岩阶段、后生变化,以及有机质的作用有着密切的关系。但国内外以前在研究沉积岩的成岩阶段和后生变化方面。偏重于无机矿物的研     

牟定郝家河铜矿床的沉积-改造成因

关于牟定郝家河矿床的成因,前人主要有沉积同生说、沉积成岩说和后生成矿说等论点。笔者根据近年来研究获得的新资料,认为矿床为沉积-改造(?)成因。早白垩世晚期—晚白垩世早期,来自东部古陆的富铜岩石和铜矿床长期风化形成的富铜风化产物,在高能氧化辫状河环境形成紫色矿源层。喜马拉雅早期褶皱运动,形成了矿区构造,矿源层中Cu活化迁移到背斜鞍部附近等低压空间浅色层中沉淀,从而形成了工业矿体。     

华南晚古生代碳酸盐岩建造中层控铀矿床的地质和成因探讨

矿床多出现于晚古生代海盆边缘凹陷中。矿床的产出和分布受泻湖相潮坪碳酸盐沉积所控制。矿体呈似层状、透镜状,与上下围岩整合-准整合接触,沿层分布。矿石即为含铀不纯碳酸盐岩,其特征是色较深,含泥碳质及星散黄铁矿。矿石成分、结构构造、微量元素含量、δ~(14)S、δ(18)O值与围岩近于一致,唯矿石中铀含量高,达工业采冶要求。近矿围岩蚀变微弱。沥青铀矿U-Pb年龄测定多为57—96Ma,主要反映矿石的后生改造年龄,但部分沥青铀矿年龄(380Ma)与所在地层时代(D_1)相近,表明成岩成矿期矿石仍有存在。且后生改造、叠加富集作用主要发生在原有矿层内,使矿体(层)仍保留原地-准原地特征,因而,应属沉积成岩成矿为主兼有后生改造的层控铀矿床。矿床的形成经历了沉积、成岩成矿和改造富化三个阶段。     

青海尕龙格玛铜多金属矿床矿物学特征对成因的指示意义

为了探究尕龙格玛铜多金属矿床成因,选取金属硫化物为研究对象,通过电子探针进行矿物学分析研究。结合矿床地质特征,为该矿床成因提供依据。结果表明:该矿床成矿阶段可划分为火山沉积热液期和中温热液硫化物期,并进一步细分为热水沉积-黄铁矿阶段、石英-黄铁矿阶段、碳酸盐阶段、铜铅锌-硫化物阶段和闪锌矿-碳酸盐阶段等五阶段。不同成矿阶段的黄铁矿标型特征表明其分别具有火山喷流沉积、火山热液改造和岩浆热液等不同成因。该矿床经历了早期火山喷流沉积,形成火山沉积(热液)矿化;中期受较大范围的火山热液充填交代;后期中酸性岩浆侵入引起的中温岩浆热液矿化,沿着断裂构造上侵,在前期矿化体中叠加成矿。     

庐枞盆地龙桥铁矿床中菱铁矿的地质特征和成因意义

龙桥铁矿床是庐枞火山岩盆地中的一个大型的铁矿床,多年来对其矿床成因的认识存在较大的争论.文章在野外地质研究工作的基础上,通过对矿床中菱铁矿的岩矿分析鉴定和电子探针测试,确定了矿床纹层状矿石中的菱铁矿为沉积成因.通过对菱铁矿的产出特征分析,并结合龙桥铁矿床的部分地质地球化学研究成果,认为在该矿床形成过程中,早期沉积形成了纹层状的菱铁矿层,在燕山期的岩浆热事件中,部分沉积菱铁矿被交代形成了磁铁矿和具有残余骸晶结构等一系列矿石交代组构特征的矿物.纹层状矿石既具有沉积特征,也具有热液改造特征,证实了矿床的形成存在早期(三叠纪)的沉积成矿(菱铁矿)作用和晚期(燕山期)的热液成矿(磁铁矿)作用.菱铁矿的研究为进一步确定龙桥铁矿床的成因提供了新的佐证.     

万山汞矿区汞质沉积成因研究

万山汞矿是典型的层控矿床,属沉积改造成因。矿质主要来自围岩。从寒武纪初至寒武纪末,形成了一个完整的沉积成矿系列,即形成磷、镍、钒、银、钾、汞、铅、锌、金等的沉积或沉积改造矿床。不仅在沉积岩中,而且在一些典型的沉积矿物、生物化石、生物礁中都有高丰度的汞、铅、锌、砷、锑,在三叶虫化石中含汞最高达100ppm。从矿物的结构构造特征方面也可找到沉积汞的证据,典型的沉积辰砂与热液辰砂大有区别,并发现极少数微粒辰砂赋存在透镜状褐铁矿结核的中心。各方面的资料说明,沉积岩中分散状态的汞质是沉积成因的。     

Problems of Siderite Formation and Iron Ore Epochs: Communication 1. Types of Siderite-Bearing Iron Ore Deposits

It is shown that siderite is unstable during sedimentation, diagenesis, and metamorphism of sedimentary and volcanosedimentary rocks. Regularities in the distribution of siderite in Precambrian jaspilites (iron formations), metasomatic ores of the Bakal type, continental–marine coaliferous formations, and oolitic iron ores are discussed. The genesis of the Precambrian iron formations and Riphean–Lower Paleozoic elisional–hydrothermal deposits is considered. The genetic relation of nodular siderites from coaliferous formations and oolitic iron ores with lowmoor coal-forming peat deposits is noted.     

The Nuheting deposit,Erlian Basin,NE China: Synsedimentary to diagenetic uranium mineralization

Sedimentary units deposited during the post-rift stage of the Erlian Basin located in northeast China present an alternation of sandstone and mudstone layers. This sedimentological architecture is at the origin of confined permeable reservoirs hosting sandstone-type uranium deposits. The study of the Nuheting deposit offered the opportunity to identify synsedimentary/early diagenetic uranium concentrations and diagenetic mineralization hosted in mudstone-dominated layers of the Erlian Formation, indicating that a stock of uranium was present in the basin prior to the genesis of sandstone-hosted uranium deposits. Therefore, this pre-existing stock may constitute a significant source of uranium for the formation of roll front deposits present in other parts of the Erlian Basin.Detailed petrographic and geochemical study of drill-core samples from the Nuheting deposit led to the characterization of different stages related to the formation of the uranium ore bodies and allowed to propose a new metallogenic model. Uranium mineralization of the Nuheting deposit is mainly hosted in dark gray silty mudstone of wetland depositional environment of the Late Cretaceous Erlian Formation. Petrographic observations and EMP analyses evidenced that a significant amount of uranium was associated with clay minerals (interstratified clays, smectite, chlorite, palygorskyte, illite and kaolinite), either adsorbed on mineral surfaces as U (VI) ions or reduced mainly as UO₂ nano to microcrystals disseminated in the clayey matrix, which corresponds to synsedimentary/early diagenetic concentrations. Trace elements on pyrite analyzed by LA-ICPMS, petrographic observations and whole-rock geochemical data led to the characterization of a diagenetic uranium mineralization. High As (1–50 ppm), Mo (10–500 ppm) and Se concentrations in the whole rock and the incorporation of these elements in pyrite highlight reducing conditions within the host-rocks during the diagenesis of the Erlian Formation. During the early diagenetic stage, uranium was either desorbed from clay minerals and organic materials to be reduced or directly reduced and precipitated as P-rich coffinite and pitchblende on pyrite crystals. During the late diagenetic stage, uranium was redistributed in situ and locally deposited mainly as coffinite on pyrites. Finally, an epigenetic stage of cementation was identified with sulfate and carbonate minerals, which may enclose some uranium minerals. This epigenetic stage of fluid circulation may be responsible for a minor uranium remobilization. Therefore, the Nuheting deposit experienced three main stages: (i) a synsedimentary/early diagenetic uranium concentration and mineralization, (ii) a late diagenetic in situ uranium remobilization and deposition on pyrite and (iii) an epigenetic cementation. Rock-Eval pyrolysis indicates that the organic matter contained in host-rocks of the Nuheting deposit is of type IV, inherited from land plant, and do not contain free hydrocarbons (very low S1). Therefore, our results do not support that migrated hydrocarbons were involved as a reducing agent for uranium mineralization.     

The Multiple Factors and Multiple Stages Involved in Sedimentary Ore Genesis

Sedimentary mineral deposits cannot be formed by any kind of simple chemical reactions,but are products of a complex multi-episodic process depending on multiple factors,The whole process is governed by a combination of sedimentary,geochemical,biogeochemical,organic geochemical,paleoclimatical,mechanical agents as well as by the properties of relevant earth crust segment and its structural making up and tectonic mobility A Sedimentary ore deposit is nothing but a special kind of sedimentary facies,characterized by definite sedimentary assemblages,Different genetic types of ore deposit and different ore associations characterize different sedimentary assemblages in different ore-forming belts.Crustal movement,including orogenic,epeirogenic and,oparticularly eustatic events,controls the formation and distribution of all kinds of sedimentary mineral deposits,most of which occur within the transgression front in the lower part of marine transpressive series.Mineral deposits of economic importance cannot be precipitated directly from sea water,but are products of terrestrial imbibition,biological enrichment and pore water concentration instead,Deposits formed above the wave base in the inner continental shelf under strong dynamic condition of sea water are often large and predominantly clastic in texture with commercial grade.Below the wave base in the outer continental shelf environment,where it is more or less dynamically stagnant and oxygen-deficient,the resulted in dustrial ore deposits are mostly of diagenetic or strata-bound type,formed through deep-burying diagenesis.The theory of multi-factor and multi-episodic metallogenesis includes three major aspects:the ore-forming process,the sedimentary environment and the geological background.The study of the forma tion process itself and the sources of ore-forming elements would provide useful clues to further prospectiong Whereas,invstigations of the sedimentary environments should shed light on the spacial distribution of deposits and the analysis of geological background would contribute a lot to our knowledge of the temporal evolution of sedimentary metallogenesis.     

Diagenetic pyrite from the lead-zinc deposits of Zawar,India

Pyrite from the Precambrian lead-zinc deposits of Zawar, West India, shows excellent sedimentary features, viz., composite bedding, lenticular bedding, flame structure etc. which are attributed to turbidites. Early diagenetic pyrite occurs as framboids and isolated euhedral as well as subhedral grains. Most of the isolated grains are probably derived from the breaking of unconsolidated framboids. Diagenetic crystallization of pyrite became operative during an early stage of deposition and continued to modify the initial sedimentary fabrics.     

沉积、成岩与铀成矿:中国砂岩型铀矿研究的创新发现与认知挑战

21世纪,中国在砂岩型铀矿勘查领域获得了前所未有的辉煌成就.砂岩型铀矿产出于沉积盆地,铀矿的形成必须经历由沉积埋藏到抬升成矿两个重要的演化阶段.其中,在抬升成矿阶段,大气降水和氧化-还原作用的参与和约束是最显著的成矿特征.显然,这是一种典型的表生成岩作用的产物,是铀储层复杂成岩序列中的重要一环,隶属于“外生成矿”的范畴.虽然,砂岩型铀矿的成矿作用遵循氧化还原与铀变价的普遍机理,但是特殊的沉积背景却导致了铀成矿作用的多样性和地区的专属性.一些由沉积作用、沉积环境和古气候造就的关键控矿要素,能够从“基因”上直接影响表生成岩阶段的铀成矿作用,由沉积、成岩到铀成矿是一个具有成因联系的地质过程,而盆山耦合机制始终是其最根本的原始驱动力.随着对铀成矿作用细节行为研究的深入,一些创新发现不断地冲击着以往固有的认识,诸如碳质碎屑与铀成矿的相互作用、黄铁矿复杂而有序的演化习性、碳酸盐胶结物与铀成矿的共生叠置、敏感矿物的流体示踪、铀储层非均质性制约下的铀成矿机理、双重还原介质制矿模型、铀成矿的复合地球化学障等.还有一些研究对传统地质学理论提出了认知挑战,诸如,铀储层开放成岩环境中碳质碎屑的“碳化作用机理”、黄铁矿溶蚀或者生长界面上的铀沉淀化学动力机制、干旱沉积背景的铀成矿机理等.同时,铀成矿机理和普遍规律的研究,也为砂岩型铀矿的衰变地质效应研究和盆地铀资源的系统探索奠定了良好的地质基础.相信,针对沉积盆地整装的系统的成矿机理与成因联系研究,必将释放巨大的盆地铀资源潜力和矿床产能,在进一步丰富铀成矿理论的同时助力实现“双碳目标”.      

滇黔桂典型锰矿床矿相学特征及其对成矿过程的指示

滇黔桂地区代表性锰矿包括贵州松桃大塘坡锰矿、广西大新下雷锰矿、遵义铜锣井锰矿和云南砚山斗南锰矿.本文利用显微镜、X衍射仪、扫描电镜等仪器,通过研究滇黔桂地区典型锰矿矿相学特征,结合碳酸盐岩研究方法,查明产于南华系大塘坡组第一段(Nh1d1)贵州松桃大塘坡锰矿矿物组合包括菱锰矿、钙菱锰矿、锰白云石、锰方解石、石英、伊利石,微相为SMF2、沉积相FZ1(盆地相),形成于沉积环境伸展阶段;产于上泥盆统五指山组(D3w)广西大新下雷锰矿矿物组合包括褐锰矿、锰钾矿、菱锰矿、钙菱锰矿、蔷薇辉石、透闪石、石英,微相为SMF2和SMF15-M、沉积相FZ7(台地相),形成于沉积环境伸展阶段;产于中二叠统茅口组第二段(P2m2)遵义铜锣井锰矿矿物组合包括菱锰矿、钙菱锰矿、锰方解石、锰白云石、硫锰矿、黄铁矿、闪锌矿、高岭石、伊利石、菱铁矿,微相为SMF15-C和SMF17、沉积相FZ7(台地相),形成于沉积环境收缩阶段;产于中三叠统法郎组(T2f)其矿物成分包括云南砚山斗南锰矿矿物组合包括褐锰矿、水锰矿、钙菱锰矿、含锰方解石、方解石、石英,微相为SMF4和SMF13、沉积相FZ4(斜坡相),形成于沉积环境伸展阶段.     

秦岭凤太矿田层控铅锌(铜)矿床的氧化硅产出特征及其硅质来源

秦岭凤太矿田的所有铅锌(铜)矿床中都含有大量的氧化硅，前人资料中往往以沉积或蚀变单一形成方式论其成因，非此即彼。本文提出氧化硅有三种产出类型，以同生沉积型为主，其次为成岩后生阶段交代灰岩者，第三类为造山期形成的脉体。三类氧化硅的产出特征有许多不同，但硅质来源一致，即均来自深部地层和岩石中循环的含矿热液。对矿床中氧化硅的研究不仅有助于深入探讨矿床的成因，而且对于该类矿床的勘查有较重要的意义。     

Ironstones in the Upper Oxfordian of southern England

The Upper Calcareous Grit, the last of the four upward shallowing cycles that comprise the Corallian Beds of southern England, is relatively enriched in iron minerals, having local developments of chamosite oolite mudstone and much more widespread deposits of sand and mud containing variable amounts of siderite and disseminated chamosite. The chamosite oolite mudstones have a restricted fauna dominated by oysters and probably accumulated in slightly hyposaline lagoons where the ooids formed from mixed iron-, alumina- and silica-bearing gels. Siderite was produced during diagenesis from iron carried on the surface of clay minerals. This intimate association with the terrigenous clay fraction means that siderite occurs in sediments deposited in a variety of environments ranging from offshore shelf to lagoonal. The most important factor responsible for ironstone development was a very low rate of clastic supply throughout Upper Calcareous Grit times. The iron was probably derived by normal processes of weathering and erosion of sedimentary rocks exposed around the basin margin, but this cannot be conclusively proved and quite different iron sources may have been involved.