初论矿床的成矿系列问题

<正> 一、矿床分类、矿床分带等有关问题的历史回顾 了解矿床的形成过程及其机理,在此基础上划分矿床类型,再结合其区域地质背景和其他有关科技资料的分析,探讨区域成矿的规律性,并进行矿产预测,不仅可以指导一定地区内的普查找矿工作,还具有较大的理论意义。但人们在这方面的工作和取得的认识,有一个积累和发展的过程。     

试论火山岩油气藏成藏机理

全球100多个国家/地区在火山岩内或其周围发现了油气藏或油气显示,展示了火山岩油气藏勘探的广阔前景。火山岩已从油气勘探的"禁区"转变为了"靶区",成为油气勘探的新目标。火山岩储集物性较好,其本身可直接作为储层,各类侵入体与围岩相互作用还可形成与火成岩有关的圈闭。火山岩油气藏的烃源包括有机成因和无机成因两种。火山作用可以明显提高烃源岩内有机质的成熟度,加快烃的产生,促进油气运移,并为无机成因烃提供合成原料(CO_2和H_2等)和运移通道。虽然火山岩在盆地早期尤为发育,约占盆地充填体积的1/4,但是目前火山岩油气储量仅占世界油气探明储量的1%左右,勘探潜力巨大。中国沉积盆地内发育不同时代火山岩,火山岩储层与烃源岩匹配较好,无机成因气来源丰富,火山岩油气藏正在成为我国油气勘探的重要领域之一。     

马达加斯加Antanisoa石墨矿床成因分析

马达加斯加是世界优质大鳞片石墨矿重要产地之一,随着大鳞片石墨在诸多新兴领域发挥着越来越大的作用,对马达加斯加石墨矿床的研究显得越来越重要。矿床成因研究对石墨矿床的找矿勘查具有指导作用,然而目前关于马达加斯加石墨矿床的研究程度较低,人们普遍认为马达加斯加的石墨矿床是沉积变质成因。文章将Antanisoa石墨矿床作为研究对象,通过对矿区内石墨片岩的岩相学研究以及矿物化学特征研究,发现沉积变质成因的说法并不妥当。野外地质调查和岩相学研究显示出较多与流体充填有关的现象,矿物化学特征表明石墨片岩中与石墨共生的云母为金云母,浅色电气石为镁电气石。结合前人对马达加斯加岛地质背景研究结果与认识,认为马达加斯加Antanisoa石墨矿床更有可能与幔源流体充填有关,有待进一步研究。     

试论华北地台中生代超变质作用与地幔热柱作用

本文通过冀西北、胶东等金矿富集区“太古宙”高级变质地体中生代金矿化、变质核杂岩构造、花岗岩、碱性岩等问题的讨论,认为中生代强烈而广泛的混合岩化、花岗岩化、流变“片麻岩”化等超变质作用,是华北地台太古宙高级变质地体变质程度深、同一地质体同位素年龄数据相差悬殊、中生代强烈岩浆活动等异常地质现象的重要原因之一。它既是华北地台活化的重要深部地质作用,亦是深部“去根作用”的具体体现。而中生代地幔热柱作用又是用变质作用、变质核杂岩构造、金矿成矿作用的深部机制,也是华北地台中生代活化的根本原因所在。     

非生物成因天然气(藏)的构造成因类型及其地球化学特征

从大地构造的角度论述了非生物成因天然气的构造成因类型,即伸展构造带非生物成因气（藏）、挤缩构造带非生物成因气（藏）、走滑构造带非生物成因气（藏）、旋转构造带非生物成因气（藏）以及陨击构造带非生物成因气（藏）。重点阐述上述构造作用及其构造带中非生物成因气（藏）的不同类别及其形成环境和条件,从而为非生物成因天然气的理论研究和预测提供一些有益的线索。     

中国东部CO2气地球化学特征及其气藏分布

中国东部CO₂气田(藏)发育广泛,分布复杂。本文对中国东部松辽、渤海湾、苏北、三水、东海、珠江口、莺琼、北部湾等盆地和内蒙古商都地区以及部分现代构造岩浆活动区CO₂气田(藏)和气苗中CO₂的地球化学特征进行了分析和研究,探讨了中国东部CO₂气的成因、来源及分布。中国东部CO₂气的含量主要分布区间为0~10%,其次为90%~100%,呈现典型的U字型。δ¹³C_CO2值则呈现典型的单峰式分布,峰值区间为-6‰~-4‰。CO₂含量、δ¹³C_CO2值和R/Ra值综合表明,中国东部高含CO₂气以幔源无机成因为主,混有部分有机成因气和(或)壳源无机气。中国东部已发现的36个无机成因CO₂气田(藏)在空间分布上与新近纪及第四纪北西西向玄武岩活动带展布一致,深大断裂和岩浆活动是无机成因CO₂富集、运移和分布最重要、最直接的两大主控因素。     

Vein graphite deposits: geological settings,origin, and economic significance

Graphite deposits result from the metamorphism of sedimentary rocks rich in carbonaceous matter or from precipitation from carbon-bearing fluids (or melts). The latter process forms vein deposits which are structurally controlled and usually occur in granulites or igneous rocks. The origin of carbon, the mechanisms of transport, and the factors controlling graphite deposition are discussed in relation to their geological settings. Carbon in granulite-hosted graphite veins derives from sublithospheric sources or from decarbonation reactions of carbonate-bearing lithologies, and it is transported mainly in CO₂-rich fluids from which it can precipitate. Graphite precipitation can occur by cooling, water removal by retrograde hydration reactions, or reduction when the CO₂-rich fluid passes through relatively low-fO₂ rocks. In igneous settings, carbon is derived from assimilation of crustal materials rich in organic matter, which causes immiscibility and the formation of carbon-rich fluids or melts. Carbon in these igneous-hosted deposits is transported as CO₂ and/or CH₄ and eventually precipitates as graphite by cooling and/or by hydration reactions affecting the host rock. Independently of the geological setting, vein graphite is characterized by its high purity and crystallinity, which are required for applications in advanced technologies. In addition, recent discovery of highly crystalline graphite precipitation from carbon-bearing fluids at moderate temperatures in vein deposits might provide an alternative method for the manufacture of synthetic graphite suitable for these new applications.     

东昆仑祁漫塔格地区乌腊德石墨矿床地球化学特征及成矿机制研究

乌腊德石墨矿床是东昆仑祁漫塔格地区新发现的晶质石墨矿床,矿体赋存于古元古代白沙河组条带状大理岩层内,呈带状、似层状,局部呈透镜状产出。对该矿床进行地球化学特征、碳同位素研究,并讨论了其成矿机制。研究结果表明,石墨大理岩主量元素整体表现为低硅、低碱、高钙、高烧失量的特点,微量元素显示Ba、Rb、Th、Sr、P相对富集,K、Zr、Ti相对亏损,稀土总量较低,表现为轻稀土富集、重稀土亏损的特点,具中等负Eu异常,微弱负Ce异常,其成矿原岩为一套浅水环境下沉积的灰岩地层,成岩环境为缺氧的还原环境,沉积时水体介质为咸水。乌腊德矿区大理岩围岩的δ¹³C_PDB为+1.4‰~+3.3‰,与海洋碳酸盐岩的碳同位素分布区间一致,石墨单矿物的δ¹³C_PDB为-5.8‰~-5.4‰。综合研究认为,区内三叠纪石英闪长岩为石墨矿床的形成提供了良好的热力学条件,使得大理岩脱碳反应形成的CO₂与早期变质作用形成的晶质石墨和有机沉积物脱挥发分形成的CH₄发生反应后,沿构造裂隙进一步迁移并集中,形成区域变质-热液改造型石墨矿床。     

新疆东准马依当一带石墨矿地质特征及成矿模式探讨

马依当石墨矿床产出在上志留-下泥盆统红柳沟组中,红柳沟组为一套含碳质绢云母片岩及砂岩;马依当石墨矿床的形成经历了沉积、区域变质及热液变质改造等3个时期。通过对该矿区成矿地质特征、矿体特征等研究,得出了成矿期次、成矿模式及找矿标志;认为马依当一带石墨矿床属沉积变质+热液改造型成因的晶质石墨矿床。     

Engineering geological mapping in terrains of tropical weathering — an example from abuja,nigeria

The importance of engineering geological mapping as a tool in the development planning of civil and mining works has increased in recent years. Its usefulness in the economic development of these works is now widely accepted.The engineering geological mapping of terrains of tropical weathering requires certain techniques. These techniques are the consequence of the special environmental conditions. The general methods of engineering geological mapping as it applies to such terrains is discussed. The use of these methods and specialised techniques in the mapping of a newly planned federal capital city, Abuja, is described. The techniques would find application in similar areas of the world.     

The formation of low-temperature sedimentary pyrite and its relationship with biologically-induced processes

This contribution is an updated review on sedimentary pyrite and on its role in well-consolidated research topics, such as the biogeochemical cycles and the studies on sediment-hosted ore deposit studies, as well as new frontiers of research, such as astrobiology. Textural and compositional information preserved in sedimentary pyrite from sediment-hosted ore deposits has contributed to elucidate their environment of forzmation. In particular, the content of redox-sensitive elements such as Ni, Co, Mo, and V has implications for defining the syn- and post-sedimentary conditions. In addition, the stable isotope compositions are useful indicators of the pathways of both biogenic and abiogenic pyrite formation. Despite the longstanding research on pyrite and the mechanism of its formation, there are still significant gaps in our knowledge. In this nonexhaustive review, we briefly touch on different current aspects of research on sedimentary pyrite, exemplifying how sedimentary pyrite remains relevant to geoscientists, and becomes more and more relevant in understanding some basic aspects of knowledge, such as the origin of life and the search for extraterrestrial life, as well as aspect of classical applied science, such as the implications for ore deposition.     

The first find of biogenic nanosiderite in oxidized ferrous quartzite of the Lebedinsk deposit,Kursk Magnetic Anomaly

The first data on biogenic nanosiderite originally discovered in oxidized Fe-quartzites from the Lebedinsk deposit of the Kursk Magnetic Anomaly (KMA) are reported. Two generations of siderite with radically different morphology and crystal-chemical and physical properties were identified. The biogenic origin is substantiated for the late generation (nanosized siderite particles). We suggest that the early ores were transformed as a result of the evolution of the atmosphere and biosphere in the area of the KMA in the Phanerozoic. Such significant differences in the properties of biogenic nanosiderite and early rhombohedral siderite may provide evidence for their different origins. The early generation of siderite was most likely formed during an abiogenic process.     

Association of manganese ore and phosphorite-bearing facies in sedimentary sequences: Communication 2. Co-occurrence and paragenesis of P and Mn in Lower Paleozoic and Precambrian sediments

The article is dedicated to regularities in the distribution of sedimentary phosphorite and manganese deposits in the Lower Paleozoic and Proterozoic formations. Special attention is paid to co-occurrence of phosphate and manganese ores formed during the Vendian-Cambrian shale formation epoch. It is shown that shale formation in certain epochs of the Precambrian and Phanerozoic was determined by the excess influx of carbon and biogenic elements to seas and marginal parts of the oceans and by enhanced productivity of planktonic organisms in corresponding geological periods.     

Geological comparison of precambrian and early palaeozoic terrains between the Southern West Coast of Africa and the South-East Coast of South America

This paper describes a geological comparison of similar lithostratigraphic sequences of Proterozoic and early Palaeozoic ages between the southern west coast of Africa (Namibia and South Africa) and the south-east coast of South America (Brazil and Uruguay). The oldest terrains present within the compared regions are those comprising the Rio de la Plata and the Richtersveld Provinces of ~ 2000 Ma. Both provinces appear to have evolved from earlier Archaean terrains, i.e., the Guapore Craton in South America and the Kalahari Craton in southern Africa, during the Transamazonic and Eburnian orogenic cycles, respectively. Both the Namaqua Province, affected by the Kibaran orogenesis at ~ 1200 Ma, and the Sinclair Group of 1300 Ma seem to have no comparable geological counterparts in southern Brazil and Uruguay.The late Precambrian—early Palaeozoic successions of the Gariep and Ribeira belts investigated here seem to be remarkably similar and it is suggested that they were parts of the same geological unit, i.e., a mobile belt, developed during the Pan-African-Brasil- iano orogenesis. Geological comparisons are particularly good between the Gariep, Porongos and Lavalleja Groups, and stratigraphic correlations can be successfully at- tempted even between geological formations, i.e., Marica, Piedra de Afilar and Stink- fontein Formations.The lack of detailed geological maps for South America makes it difficult to separate different geological formations from broad lithostratigraphic successions and, consequent- ly, comparisons can only be drawn between subgroups and several geological formations, i.e., Vacacai and Minas Subgroups with Grootderm Holgat and Oranjemund Formations. The extensive magmatic activity generated during the Brasiliano orogenesis and only present in the south-east coast of South America has not affected the southern west coast of Africa. However, two post-tectonic complexes, i.e., the Kuboos—Bremen line of intrusives and the Sierra de Animas Complex appear to be geochronologically analogous and petrologically they seem to have certain similarities. It is also suggested that the Camaqua Group in southern Brazil and the Nama Group could perhaps have certain similarities within their lithological successions and their ages may be also com- parable.The late stages of the geological evolution of the basin, represented by molassic sediments, are only present in south-east Brazil. Finally an interpretation is given of the geological evolution of the Proterozoic—early Palaeozoic terrains compared in this work.     

黑龙江省林口县五义屯石墨矿矿床地质特征及找矿方向

天山—兴蒙造山带是国内晶质石墨矿的主要成矿带,已查明柳毛石墨矿、石场石墨矿等多个大型沉积型石墨矿床,五义屯石墨矿矿床是近年在该带上新探获的一座大型晶质石墨矿床。本文阐述了该矿床的区域地质背景、地球物理特征、矿床地质特征,并分析了矿床成因和找矿方向。结果表明,该矿床是大型沉积变质型石墨矿床,矿体具明显层控特征,主要赋存于中-新元古界麻山岩群余庆岩组中;矿体品位厚度稳定,主要呈大鳞片粒级;矿体与围岩地球物理特征差异明显,具明显低阻高极化特征;本矿床具有成为超大型石墨矿床的潜力,其外围对寻找沉积变质型石墨矿床具有良好的资源远景。     

吉林省集安市马蹄沟晶质石墨矿地质特征及找矿标志

吉林省集安市马蹄沟晶质石墨矿位于吉林省集安市财源乡马蹄沟一带,文章对该矿床地层、构造、岩浆岩等地质特征及矿床成因进行研究,认为赋存于古元古界集安群荒岔沟组的晶质石墨与硼铁建造、含磷透辉石建造、铀-稀土建造等相应矿床均属于海底火山喷发沉积变质、岩浆热液作用的层控矿床,马蹄沟晶质石墨矿成因类型为沉积变质型晶质石墨矿床。总结该地区晶质石墨矿的找矿标志。     

Potential for irradiation of methane to form complex organic molecules in impact craters: Implications for Mars, Titan and Europa

The release of methane from crater sites following meteorite impact is a possible consequence of the thermal alteration of organic matter, or tapping of reservoired gas of biogenic or abiogenic origin. At least the latter is feasible on Mars. Methane and higher hydrocarbons are susceptible to polymerization and precipitation by radioactive minerals. Where such minerals are present in impact target rocks, the craters can be a preferred site for carbon concentration, and the formation of complex organic molecules. On icy bodies, such as Titan and Europa, methane released by impact could be a fuel for prebiotic chemistry involving other forms of irradiation.     

Biogenic laminar calcretes: evidence of calcified root-mat horizons in paleosols

Laminar calcretes are described from the Lower Carboniferous of South Wales, the Upper Jurassic of southern England and the Upper Jurassic-Lower Cretaceous of northern Spain. They are interpreted as calcified root-mats (horizontal root systems) and are compared with other examples in the geological record and with possible modern analogues. All three occurrences consist of virtually identical, centimetre to decimetre-thick, locally organic carbon-rich, laminar micrites containing up to 50% by volume of millimetre-sized typically calcite-filled, tubular fenestrae set in an irregular but very finely laminated matrix. It is suggested that root-mat calcretes are probably very common in the geological record in peritidal, lacustrine margin and floodplain deposits, but owing to their crudely biogenic microstructure, they more closely resemble cryptalgal laminites than do other laminar calcretes. The recognition of such root-mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo-water-tables in certain circumstances.     

前寒武纪沉积岩地球化学特征及其对地壳演化的指示意义

本文介绍了运用前寒武纪沉积岩地球化学特征推断地球早期地壳的组成、增生历史及太古—元古宙界面构造性质突变问题,这已成为国际前寒武纪地质研究的前沿课题,并已相继在世界典型的前寒武纪低级区及部分高级区开展了这一方面的研究工作,取得了一系列重要进展。     

简单分段法及其在地层划分中的应用实例

地层划分中的数学分段法,目前普遍采用的是有序地质量最优分割法,而较简便的简单分段法应用却很少。本文着重对后者进行探讨,提出一些应用意见。