与花岗岩有关锡矿成岩成矿作用研究若干问题讨论

文章基于近年来大量典型锡矿床和成矿区带成岩成矿作用及高温高压实验研究成果,对锡矿成矿年代学、成矿花岗岩类型、物质来源、源区物质的熔融条件及锡在岩浆中的存在形式、熔体-流体相间分配行为及热液流体中的存在形式等方面的研究进展及存在问题进行了系统综述,指出:①锡石原位U-Pb测年已成为直接测定锡成矿年龄的有效手段,近年来发展起来的多种矿石矿物U-Pb测年方法与传统蚀变矿物测年方法的结合,将为研究锡多金属矿床多期次成矿作用叠加、矿集区内不同类型矿床成因联系及区域矿床组合模型的建立提供关键的年代学依据;②锡的富集成矿不仅与花岗质岩浆的高程度的结晶分异密切相关,而且受源区组成及部分熔融条件的制约;③全球锡多金属矿床的不均匀分布、与准铝质花岗岩有关锡矿的富集成矿机制以及各类复杂的锡-钨-铜-钼-铅-锌银多金属矿种组合差异及其金属元素富集机制亟待查明;④已有的关于锡在花岗质熔体、热液流体相中的存在形式及两相间的分配行为的高温高压实验结果受锡与贵金属容器间合金效应的影响,人工合成流体包裹体等新的实验方法的开发及XAS同步辐射和激光拉曼等原位分析技术的应用,将为研究花岗岩浆-热液过程锡的迁移、富集及沉淀成矿机制提供更为直接、可靠的实验依据。     

Origin of polyhalite deposits in the Zechstein (Upper Permian) Zdrada platform (northern Poland)

Polyhalite deposits in the Zechstein (Upper Permian) of northern Poland occur in the Lower Werra Anhydrite. In the Zdrada Sulphate Platform, the polyhalite appears to be a very early replacement of anhydrite. The replacement was caused by the halite-precipitating brines which contained potassium and magnesium ions. The formation of polyhalite was preceded by the syndepositional anhydritization of the original gypsum deposit which has often preserved its primary textures. This anhydritization on the platform and its slopes was a reaction of the precipitated gypsum in a hydrologically open evaporite basin, with brines of salt basins adjacent to the sulphate platform. These brines, when nearly saturated with respect to halite, and potassium and magnesium rich, reacted with anhydrite to precipitate polyhalite along the slopes of the Zdrada Platform. The oxygen and sulphur isotopic compositions of sulphate evaporites indicate that marine solutions were the only source of sulphate ions supplied to the Zechstein basin, and that anhydrite was transformed to polyhalite by reaction with marine brines more concentrated than those that precipitated precursor calcium sulphate minerals.     

Pyrite deformation in stratiform lead-zinc deposits of the Canadian Cordillera

Pyrite textures in five stratiform lead-zinc deposits from lower to upper greenschist facies environment of the Canadian Cordillera are described and discussed in terms of deposition/early diagenesis, deformation, metamorphism and hydrothermal alteration processes. Overgrowth is an important process during both diagenesis and deformation. Diagenetic and deformational overgrowths can be distinguished. Diffusive mass transfer, involving pressure solution and oriented overgrowth of pyrite is the main deformation mechanism in pyrite deposits at low metamorphic grades. Although diffusive mass transfer favours fine-grained mineral aggregates, its effect on coarse pyrite grains has also been identified. Ore minerals dissolved by pressure solution may be transported, with the assistance of pore fluids within fractures and grain boundaries, over distances significantly greater than the scale of individual grains to give a range of pressure solution/overgrowth textures. The textural modification of pyritic ores from the early stages of diagnesis, through metamorphism and deformation, to post deformation thermal annealing, has important implications for the distribution of trace elements and isotopic compositions in pyritic ores.     

Carboniferous deposits in the basement of the southwestern West Siberian geosyneclise (Kurgan Region)

The ⁴⁰Ar/³⁹Ar age of volcanics from the sections of core boreholes in the northern Tyumen’-Kostanai trough (Kurgan Region) has been determined. The geologic structure of the northern part of the trough has been refined. The paleogeographic environments and geodynamic settings of formation of Carboniferous deposits have been established by sedimentological, petrological, and geochemical studies of the sections. In the Visean, marine environments with maximum basin depths were predominant. In the Kachar epoch (C1v3-s), the submarine relief of the basin became more complicated; blocks of older rocks appeared in the deposits. The geochemical indicator characteristics of the volcanics—contents of HFSE (Ti, Nb, Ta, Th, and Hf)—are close to those of andesitoids of island arcs and Andean-type active continental margins, as well as present-day andesites from the Kurile-Kamchatka zone. They are an order of magnitude lower than those in similar continental-rift volcanics, among which are volcanics of the Valer’yanovka zone (according to some researchers). The contents of Ni, Co, and V are similar to those in island-arc andesites, including rocks of the Kurile-Kamchatka zone. The Ba/Ta and Ba/La ratios and the proportions of Th, Hf, and Ta in andesitoids of the Valer’yanovka and Kachar Groups are close to the indicator characteristics of island-arc and active-continental-margin volcanics. The Kachar Group siliceous rocks are similar in the Rb/Zr-Nb, Fe-Nb, and Rb-(Y + Nb) correlations to rocks of mature island arcs and active continental margins. The incompatible-element and REE patterns for the Valer’yanovka and Kachar volcanics are typical of island-arc volcanics, including rocks from the Kurile-Kamchatka zone. The indicator geochemical features and petrology of the volcanics and the sedimentologic features of the deposits testify to their formation on an Andean-type active continental margin (western margin of the Kazakhstan paleocontinent) in the Early-Middle Carboniferous.     

南岭锡钨多金属矿区碱长花岗岩的厘定及其意义

南岭地区锡钨多金属矿成矿作用主要与燕山早期花岗岩岩浆活动有关,这些花岗岩一直被认为是黑云母花岗岩、二长花岗岩、细粒二长花岗岩等,少量矿区岩体顶部出现钠长石花岗岩。通过对湖南瑶岗仙钨矿岩体的深入解剖,以及对杮竹园、黄沙坪、锡田、邓阜仙、栗木、梅子窝等矿区花岗岩全面的岩矿鉴定和电子探针分析,确定钨矿区致矿花岗岩的长石主要为碱性长石,其中绝大部分样品中钠长石An<5,因此确定这些花岗岩均属于碱长花岗岩。与成矿有关的由浆液过渡态流体形成的云英岩包体中的钠长石更加富Na,An<3。碱长花岗岩的成分以及钠长石成分在岩体顶部约1 000 m深度范围内无明显垂向变化。致矿花岗岩体中部分早期花岗岩包体、晚期花岗斑岩,部分花岗岩基以及印支期花岗岩、加里东期花岗闪长岩等,钠(斜)长石An值明显高,很多属更长石、中长石甚至基性长石。这种包含有两种碱性长石的碱长花岗岩由富挥发分的岩浆形成,在岩体顶部附近广泛发生液态不混溶作用,是导致锡钨多金属矿富集成矿的主要分异方式。钨锡矿区碱长花岗岩钠长石An值明显低于区域大花岗岩基或不致矿花岗岩,可作为花岗岩的钨锡成矿评价标志之一。     

Dike-filled extensional structures in Cenozoic deposits of the Kleszczów Graben (Central Poland)

The origin and development of the Cenozoic Kleszczów Graben were strongly influenced by a pre-existing fault pattern within the Permian–Mesozoic bedrock. Dike-filled fractures penetrating Neogene/Quaternary deposits, analysed in the opencast Bełchatów browncoal mine, follow extensional structural patterns parallel to the axes of the local anticlinal forms established (or rejuvenated) in the Quaternary. These structures are particularly well developed along the fold crests. The spacing and structural features of the fractures and normal faults are explained in terms of the tensile stress operating in beds subjected to folding. The main localities of the Quaternary folds precisely align with segments of two deep-seated reverse faults: the Kleszczów–Kodrąb Fault and the Gomunice–Piaski Fault. Both are NW–SE orientated dislocations along a hinge zone of the Laramide Łękińsko Anticline, subcropping the Cenozoic graben infill in the open mine. The origin of the Quaternary folds as fault-overlying folds is attributed to a young block uplift on the Łękińsko Anticline area, which is well recorded by a strong reduction in thickness of the Cenozoic sediments; the Quaternary succession is reduced in thickness twice as much as the Neogene. The successive stages of Quaternary reactivation of the Łękińsko Anticline (during the Cromerian through the Late Saalian), with diminishing intensity, are believed to be correlatable with the sequence of glacial rebound events coupled with mobility of the deep-rooted fault zone.     

滇西锡矿的花岗岩类及其成矿作用

滇西锡矿是三江锡矿域的主体。本文论述了三江锡矿域与东南亚锡矿域各带的对比,指出滇西锡矿受特提斯构造演化的控制。腾冲一梁河地区花岗岩类首次划出3个岩群、8个超单元、28个单元和若干侵入体。对滇西原生锡矿床类型、成矿系列和成矿特征进行了较详细的研究。     

Pre-metamorphic folded chromite deposits of stratiform type in the early Precambrian of West Greenland

The low-grade chromite deposits at Fiskenaesset, West Greenland, occur in 0,5–20 m wide horizons in anorthosites which represent the main component of an original layered intrusion, the Fiskenaesset complex. An exposed length of 125 km of this has been mapped, forming conformable stratigraphic horizons in the early Precambrian gneiss basement. The pre-metamorphic chromite deposits have been affected by at least two major phases of folding and metamorphism, but magmatic features are still recognizable. Mineralogical data on the chromite are given together with the petrography of the chromitite. The primary magmatic and secondary metamorphic features of the Fiskenaesset deposits are described and discussed in relation with similar chromite deposits of stratiform type elsewhere in the world.

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Zusammenfassung Im Gebiet von Fiskenaesset, Westgrönland, treten 0,5–20 m mächtige Chromit-Bänder in anorthositischen Gesteinen auf. Die Anorthosite liegen in alt-präkambrischen Gneisen (basement) und stellen den Hauptanteil des intrusiven Fiskenaesset-Komplexes dar. Dieser Komplex konnte bisher auf eine streichende Länge von 125 km nachgewiesen werden. Er liegt als konforme stratigraphische Einheit in den Gneisen. Der Komplex mit seinen schichtgebundenen Chromit-Vorkommen wurde während mehrerer Deformationsperioden stark beansprucht und dabei hochmetamorph überprägt. Anhand von mineralogischen und petrographischen Untersuchungen werden die primären, magmatischen Merkmale im Verhältnis zu den sekundären, metamorphen Merkmalen der Chromite besprochen. Es werden Vergleiche zu ähnlichen Chromit-Lagerstätten gezogen.

     

New data about the kilo-moto gold deposits (Zaïre)

Petrological studies based on core drillings have shown that two main factors have contributed to the gold mineralization in the district of Mongbwalu: 1) Plutonic activity of a granitic or a dioritic magma, resulting in a first concentration of the metal originally dispersed in some of the intruded Kibalian rocks. 2) Development of shear zones with important quartz mobilizations resulting in a second concentration of the metal in their zone of influence.

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Résumé Des études pétrologiques basées sur des sondages carottés ont montré que deux facteurs ont joué en ordre principal dans la genèse de la minéralisation aurifère du district de Mongbwalu: 1) L'activité plutonique d'un magma granitique ou dioritique provoquant une première concentration de l'or qui se trouvait originellement à l'état dispersé dans certaines roches kibaliennes intrudées par ce magma. 2) Le développement d'un système de failles cisaillantes accompagné d'importantes mobilisations de quartz, qui ont assuré une concentration locale de l'or dans leurs zones d'influence.

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Publication authorized by the General Manager, Office des Mines d'Or de Kilo-Moto.     

Fractional crystallization and the origin of tin deposits in granitoids

A comparison between tin-bearing granitoids in an anorogenic setting (Bushveld Complex) and an orogenic setting (Blue Tier Batholith, Tasmania) reveals a number of genetically important similarities. These include: in situ fractional crystallization characterised by marked decrease in Ba and Sr and increase in Rb; the accumulation of late melt in a sheet-like form near the roof zone; the association of barren pegmatites overlying the ore; and of aplites; and the occurrence of conformable tin-bearing sheets, often exhibiting greisenization. These features allow the formulation of the following genetic model. A crustally-derived granitoid magma is emplaced and undergoes fractional crystallization from the margins inwards, with bottom crystallization dominating. Disruption of earlier formed solids by rest liquid commonly occurs. Continued fractional crystallization causes enrichment in volatiles and incompatible elements in the late rest melts, which have a sheet-like habit. The efficiency of enrichment of incompatible elements is critically dependant on the degree of separation of melt from solids throughout crystallization. An early, tin-poor vapour may separate after initial water-saturation of the magma is achieved, and this collects under the roof, commonly forming an impermeable barrier to later tin-bearing fluids. Continued fractional crystallization on the floor further enriches incompatible elements, and at a very late stage a Sn-rich vapour separates within the intercumulus phase and becomes concentrated by progressive crystallization of the intercumulus melt. At a late stage of solidification, this vapour loses equilibrium with the earlier formed feldspars and greisenization ensues, accompanied by the crystallization of cassiterite and other ore minerals. The nature of the mineralization changes if through-going fractures tap the late fluids. This model predicts systematic changes in trace element geochemistry with crystallization which provide useful tools for assessing the tin potential of a granitoid, and for indicating the direction of crystallization of the magma, and hence the location of possible ore.     

Influence of arsenic-bearing gold deposits on water quality in Zloty Stok mining area (SW Poland)

 The Sudety Mountains contain polymetallic deposits which have been exploited since the Middle Ages. Distinct concentrations of As, Hg, F, Cr in surface water near Zloty Stok suggested that groundwater in the area could also contain elevated metal concentrations. Water samples from 15 locations including Zloty Stream, mine adit discharges, and selected springs generally show low levels of dissolved components and near-neutral pH. However, arsenic concentrations range from 0.99 mg/l to 26.16 mg/l at all 15 sample locations. Mercury concentrations were locally as high as 0.011 mg/l. These high arsenic and mercury concentrations significantly exceed water quality standards and raise concerns for using Zloty Stream for potable water. Recieved: 21 December 1998 · Accepted: 8 June 1999     

论新疆伊犁浅成低温热液型金矿与斑岩型铜（钼金）矿的相随相伴规律

中亚成矿域中的斑岩型铜（钼金）矿,有别于滨太平洋区的斑岩铜矿,它们大部分是形成于大洋消亡之后,与A型俯冲或后碰撞阶段的构造岩浆作用有关,并非都形成于岛弧发展阶段,且常与浅成低温热液型金矿（产于陆相-亚陆相火山岩内）时间相随、空间相伴,两者属于一个统一的岩浆系统;浅部是浅成低温热液型金矿,深部是高温斑岩型铜（钼金）矿,其成矿特点表现出两者元素组合连续、过渡与转化,两者类型相随相伴。     

Tournaisian age of granitoids from the Odra Fault Zone (southwestern Poland): equivalent of the Mid-German Crystalline High?

The Odra Fault Zone of southwestern Poland is a NW-trending horst marked by gravimetric and magnetic anomalies and composed of high- to low-grade metamorphic and igneous rocks which are only known from boreholes. This zone embraces a concealed border between Variscan internides and externides. It also contains an array of several I-type, metaluminous to peraluminous, high potassic granitoid bodies which intruded earlier metamorphosed rocks. Except for one case, they remain unfoliated and undeformed, and presumably play a role of stitching plutons at the suture between two obliquely colliding terranes. U–Pb TIMS dating of single zircons from one foliated and one unfoliated granitoid samples yielded identical concordant ages of 344±1 Ma (Tournaisian). They resemble a Pb–Pb age of 350±5 Ma obtained for S-type granitoids from the Luckau area further west in Germany, which is generally regarded as an eastern segment of the Mid-German Crystalline High. Carboniferous granitic intrusions in the high are generally younger (340–290 Ma). Correlations of the the Odra Fault Zone with the Mid-German Crystalline High appear plausible, but by no means certain and require further confirmation.     

赞比亚砂（页）岩型铜矿成矿年龄及其成因意义

砂(页)岩型铜矿床是全球第二重要的铜矿类型,重要性仅次于斑岩型铜矿,具有巨大的资源量和找矿潜力。本文总结了砂(页)岩型铜矿床的时空分布特点,然后选取该类矿床的典型——赞比亚砂(页)岩型铜矿床来探讨大型砂(页)岩型铜矿的控矿因素。本文系统论述了赞比亚砂(页)岩型矿床的地质背景,报道了赞比亚铜带省典型矿床卢安夏矿床黄铜矿Rb-Sr放射性同位素等时线年龄为501±19 Ma,Sm-Nd等时线年龄为499.1±38 Ma,总结了赞比亚砂(页)岩型矿床的分布规律,探讨了其成矿物质来源,认为赞比亚砂(页)岩型矿床为岩浆期后热液充填矿床。     

冀东兴隆一带层状黄铁矿—铅锌矿床的地质特征及其成因

冀东兴隆一带中元古界高于庄组中有一些层状黄铁矿-铅锌矿床,如杨树庄、高板河、杨树台、黄土梁、梓木林、椴木峪和沙窝店(关堂子)等,分布在近东西向长六七十千米的一条线上,它们的地质特征很相似。矿床的成因有争议。一派认为是后生热液交代矿床,选择性交代使矿体依岩层成假象;     

Two-brine model of the genesis of strata-bound Zechstein deposits (Kupferschiefer type), Poland

These Kupferschiefer deposits were probably formed as a result of a mixing of two brines. The upper cold brine (UCB) is an unmineralized brine rich in Na, Ca, Cl and SO₄, with a pH>7 and originating from evaporites overlying the metal-bearing Zechstein rocks. The lower hot brine (LHB) rich in Mg, K, Cl, SO₄ and CO₃ with a pH<=7 formed in sediments in the central part of the Zechstein basin at a depth of 7,000 m. This brine was subjected to heating and upward convection toward the Fore-Sudetic monocline along the bottom of the Z₁ carbonates. During its migration, it caused albitization, serpentinization and leaching of the primary metal deposits in rocks underlying the Zechstein becoming enriched in heavy metals. The mineralization process, being a result of the mixing of the two brines (UCB and LHB), and catalytic oxidation of the organic matter of the black shale were initiated at shallow depths in the area of the Fore-Sudetic monocline. The boundary of the two brines generally overlapped the strike of the black shale.Parts of the deposit with shale-free host rock suggest that the action of two brines alone was capable of producing economic concentrations of Cu, Pb and Zn. Where the boundary of the two brines overlaps the autooxidation zone (the black shale bottom) and also coincides with radiation of thucholite, concentrations of noble metals result.The characteristic vertical distribution of the triplet CuPbZn from the bottom upward is universal in the Kupferschiefer environment.     

密西西比河谷型(MVT)铅锌矿床:认识与进展

MVT铅锌矿床作为一种重要的沉积型铅锌矿床类型一直受到人们的重视,近年来取得了许多重要进展,主要体现在6个方面:①MVT铅锌矿床研究范围逐渐扩大,在全世界发现了诸多相关矿床,多归为其亚类;②提出该类矿床主要分布在造山带的前陆盆地、逆冲推覆带等构造挤压环境,少数产于陆内伸展环境,改变了MVT矿床与板块构造无关的观点;③放射性同位素测年和古地磁测年技术广泛应用,获得了大量成矿年龄数据,表明MVT矿床主要形成在显生宙石炭纪—早三叠纪和白垩纪—第三纪两个时期,与地球演化史上全球尺度的板块会聚时间密切相关;④流体包裹体研究揭示了成矿流体温度主要为90~150℃,盐度w(NaCleq)为10%~30%,成矿流体具有盆地卤水特征,卤水源自近地表蒸发海水或围岩蒸发盐,同位素资料反映Pb来自地壳岩石,S来自地壳岩石或沉积物中残留的硫酸盐。成矿流体驱动机制包括构造挤压和重力驱动两种;⑤古地磁和生物化学标志物判定,单期热液活动可能持续几千到几万年,而整个矿床形成可能持续几个到十几个百万年;⑥矿质沉淀机制主要有3种:流体混合、硫酸盐还原和还原硫机制,不同成矿环境可能受不同机制控制。     

Ore mineralization of the Amur stratiform zinc deposit (Southern Urals)

This paper deals with the geological structure of the Amur zinc deposit. The host shaly-carbonaceous flysch sediments are evaluated from the point of view of their precious metal, tungsten, and molybdenum potential. It is shown that the rare-metal mineralization is superimposed on a primarily sedimentary precious-metal mineralization and stratiform zinc ores. The discussed data permit us to look at these carbonaceous sediments as highly prospective for rare metal and precious metal mineralization.