Genesis of Levikha ores in relation to isotopic composition of their sulfur

Isotopic composition of sulfur was determined in more than 150 samples of sulfides and sulfates from the Levikha ore field. On the basis of the results so obtained, we are discussing the sources of sulfur in the sulfide ores and in sulfates of the ore deposits, physicochemical conditions of their deposition, and their genetic connections with sulfides in the overburden. -- Authors.     

Isotopic composition of pyritic sulfur from the mud volcanic ejecta in Azerbaijan

Geochemical studies of pyrite crystals from the mud volcanic ejecta in Azerbaijan were studied. It is shown that all of them have cubic shape. Determination of the sulfur isotope composition revealed a wide variation range of δ³⁴S values from–27.0 to +26.4‰. Signs of spatial zonation were recorded in the distribution of δ³⁴S values—lower values are confined to the present-day coastline of the Caspian Sea. Appearance of pyrite with a high share of ³⁴S is attributed to sulfate reduction that takes place in an environment with excess organic matter. It is supposed that the isotopically heavy sulfides represent the “neck” facies that are formed at the periphery of mud volcanic conduits at the contact of the hydrocarbon-rich mud volcanic fluids with stratal waters of host sediments.     

四川盆地H2S的硫同位素组成及其成因探讨

四川盆地天然气绝大部分含有硫化氢,部分含量高达15%以上。其中高含硫化氢天然气主要分布在三叠系飞仙关组、雷口坡组和嘉陵江组;震旦系、石炭系、二叠系属于低含硫化氢,上三叠统须家河组和侏罗系属于微含硫化氢或不含硫化氢天然气藏。研究表明,三叠系飞仙关组、雷口坡组和嘉陵江组、震旦系、石炭系储层中发育的膏质岩类为TSR形成硫化氢提供了物质基础;富含有机硫源岩的高温裂解是二叠系低含硫化氢天然气的主要成因。硫同位素组成表明,高含硫化氢天然气的硫同位素比储层硫酸盐硫同位素δ34S亏损7‰～11‰;而低含硫化氢天然气硫同位素分布区间较宽,在0‰～20‰之间,大部分比同期硫酸盐的硫同位素轻15‰左右。四川盆地三叠系膏岩的硫同位素值分布较宽,并呈现阶梯状变化,而硫化氢的硫同位素则呈现出相似的分布规律,表明各气层硫化氢中的硫来自于本层系的硫酸盐,即TSR发生在各自的储集层中;另外四川盆地三叠系TSR发生时各气藏的温度条件相近,即各气藏的硫化氢在大致相同的温度条件下发生;同时也说明TSR过程中硫同位素的分馏过程与硫酸盐本身硫同位素数值的高低无关,而与TSR反应的温度条件和反应程度有关。还建立了运用硫化氢的硫同位素和含量判识硫化氢成因类型的模式。     

Isotopic composition of zinc, copper, and iron in lunar samples

We determined by ICP-MS the concentrations and isotopic ratios of Fe, Cu, and Zn in the Ti-rich lunar basalt 74275, in the lunar orange glass 74220, and in up to 10 lunar soils, namely, 14163, 15231, 64501, 66041, 68841, 69941, 70011, 72501, 75081, and 76501. Two analyses of zinc in lunar basalt 74275 give δ⁶⁶Zn = 0.17‰ and 0.75‰, values within the range of those measured in terrestrial basalts; copper in lunar basalt 74275 has δ⁶⁵Cu  +1.4‰, which is isotopically heavier than values observed in terrestrial basalts. In the orange glass, we measured δ⁵⁶Fe = −0.24‰, δ⁶⁵Cu = −0.42‰, and δ⁶⁶Zn  −3.6‰. These values of δ are more negative than those obtained for 74275 and for typical lunar basalts, but for Cu, comparable to those observed in terrestrial sulfides and meteorites. In lunar soils we found 0.11‰  δ⁵⁶Fe  0.51‰, 2.6‰  δ⁶⁵Cu  4.5‰, and 2.2‰  δ⁶⁶Zn  6.4‰. Insofar as we can generalize from a small sample set, S, Fe, Cu, Zn, and Cd show similar trends in isotopic fractionation on the Moon. Lunar basalts have nearly terrestrial isotopic ratios. Relative to the lunar basalt 74275, the pyroclastic glass 74220 is enriched in the lighter isotopes of Fe, Cu, and Zn, and the soils are enriched in the heavier isotopes of Fe, Cu, and Zn. The patterns in the basalts are likely inherited from the source material; the light-isotope enrichments seen in the orange glass originated during lava fountaining or, less probably, during partial condensation of vapor; and the heavy-isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering. In the orange glass, the light-isotope enrichments (relative to lunar basalts) of Zn are larger than those of Cu. If these enrichments reflect accurately the isotopic composition of the gas, they suggest that Cu is more volatile than Zn in the liquid from which the gas derived. A simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor, predicts heavy-isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm/My. This discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter-scale gardening, or the importance of sputtering.     

Isotope composition of sulfur in Pyrites from North Caucasian copper pyrite deposits

The paper concerns sulfur isotope analysis, predominantly in pyrite, of copper deposits from the North-Caucasus. The deposits studied are Urup and Beskes, both possibly lower Paleozoic, and Ithudes, Lower Carboniferous. The sulfur isotope ratios are compared relative to the physicochemical conditions of formation, the effect of post-ore intrusions and isotope ratios from pyrite in siliceous shales. — M.A. Klugman.     

豫西骆驼山硫多金属矿床纹层状矿石硫化物Rb-Sr定年及S同位素组成对矿床成因的制约

已有研究在骆驼山硫多金属矿床成因方面存在较大争议,争论的焦点在于该矿床是否形成于中—新元古代的喷流沉积成矿作用。纹层状矿石曾被认为是喷流沉积成因矿床的重要证据之一,但也可能为热液交代成因。厘定骆驼山硫多金属矿床纹层状矿石的成矿时代和成矿物质来源是解决争议最为直接有效的途径。通过详细的野外地质观察,该型矿石在空间上主要产于矽卡岩与致密块状硫化物矿石之间,在透辉石长英角岩、矽卡岩及大理岩等围岩中也有分布,这种构造通常由不同金属矿物的纹层相间排列,以及金属矿物纹层与围岩纹层相间排列而成,地质特征表明纹层状矿石交代了矽卡岩。采用硫化物Rb-Sr同位素定年法对9件纹层状构造发育的硫化物样品(6件闪锌矿和3件磁黄铁矿)进行成矿年龄测定,获得闪锌矿和磁黄铁矿的等时线年龄为139.6±2.6Ma,表明骆驼山硫多金属矿床形成于早白垩世。纹层状矿石样品的S和Sr同位素测试结果表明,矿石的δ~(34)S值为+1.7‰~+3.3‰(平均值为+2.44‰),塔式分布特征明显;Sr同位素初始比值(~(87)Sr/~(86)Sr)i介于0.709704~0.709943之间,平均值为0.709823,二者均反映骆驼山硫多金属矿床的成矿物质主要来自下地壳的深源岩浆。综上分析,结合野外地质调查和室内显微镜下观察,认为纹层状矿石是中生代岩浆热液成因,而非中—新元古代喷流沉积成因,进而表明骆驼山硫多金属矿床应属岩浆热液交代成因的矽卡岩型矿床。该结果对于今后在该矿集区乃至整个豫西地区寻找类似的硫多金属矿床具有一定的理论指导意义。     

Hydrogeologic modeling of the genesis of carbonate-hosted lead-zinc ores

 Carbonate-hosted lead–zinc ore deposits in the Mississippi Valley region of North America and in the central midlands region of Ireland provide good examples where ancient groundwater migration controlled ore formation deep within sedimentary basins. Hydrogeologic and geochemical theories for ore genesis are explored in this paper with mathematical models that allow for complex permeability fields in two or three dimensions, hydrothermal flows in fault systems, and coupled effects of geochemical reactions. The hydrogeologic framework of carbonate-hosted ores is analyzed with the aim of developing a quantitative understanding of the necessary and sufficient processes required to form large ore deposits. Numerical simulations of basin-scale hydrodynamics and of deposit-scale reactive flow are presented to demonstrate the processes controlling low-temperature Pb–Zn ore genesis in two world-class ore districts, in southeast Missouri, USA, and central Ireland. The numerical models presented here provide a theoretical basis for the following observations: (1) topography-driven brine migration was the most effective mechanism for forming the large ore districts of the Mississippi Valley, such as the Viburnum Trend of southeast Missouri, during the uplift of the Appalachian–Ouachita mountain belt in late Paleozoic time; (2) three-dimensional flow fields were created by a dolomite facies of the Viburnum Trend, which acted as a giant lens for focusing metal and heat in southeast Missouri to produce the largest known concentration of lead in the Earth's crust; (3) ore-mineralization patterns were controlled locally by basement relief, permeability structure, and sandstone pinchouts, because of their effects on cooling and fluid-flow rates along the Viburnum Trend; (4) both density-driven and topography-driven fluid flow were important for ore genesis in the Irish midlands, where brines moved northward away from the Variscan orogen, leaked into the Hercynian basement, and discharged along normal faults up into the sedimentary cover; and (5) mixed convection within northeast–southwest fault planes elevated heat flow and flow rates that fed ore deposition by fluid mixing, in some cases near the Carboniferous seafloor in Ireland. Received, February 1998 · Revised, July 1998 · Accepted, September 1998     

The sulfur isotopic composition of sulfides from ores and host rocks of the Upper Kolyma region,Magadan Oblast

More than 200 analyses of the sulfur isotopic composition of sulfides from various terrigenous and intrusive host rocks, metasomatically altered wall rocks, and gold lodes of the Upper Kolyma region are presented. In accessory pyrite of the metaterrigenous rocks, δ³⁴S varies from ?23.1 to +5.7‰ δ³⁴S of pyrite and arsenopyrite from gold-quartz mineralization is within the range ?10.6 to ?0.4‰ and is close to the average δ³⁴S of pyrite from the metaterrigenous rocks (?4.4‰). In the intrusive rocks, δ³⁴S of pyrite varies from ?3.8 to +2.6‰ (+0.7‰, on average) and drastically differs from δ³⁴S of arsenopyrite from postmagmatic gold-rare-metal mineralization (?7.9 to ?2.7‰; ?5.2‰, on average). The comparison of the δ³⁴S of accessory sulfides from the host rocks with δ³⁴S of sulfides from the gold deposits suggests that sulfur mobilized from the terrigenous sequences participated in the hydrothermal process. The results obtained are consistent with the metamorphic model of the formation of gold-quartz deposits in the Upper Kolyma region.     

哈图金矿带成矿流体组分、硫同位素分析及矿床成因

哈图金矿带位于新疆西准噶尔地区,是新疆北部最重要的金成矿带之一。哈图金矿带内依次分布有哈图(齐Ⅰ)、齐Ⅱ、齐Ⅲ、齐Ⅳ以及齐Ⅴ五个金矿床(点),其成矿作用和地质特征相似。本文重点对哈图、齐Ⅱ和齐Ⅴ金矿石英脉样品中的石英进行了流体包裹体成分分析,结果显示三者流体包裹体具类似成分特征。气相成分均以H_2O为主,其次是CO_2和CH_4,液相成分为Cl~-+SO_4~(2-)+Na~++K~+组合。按成矿作用从早至晚,流体中H_2O的含量增加,而CO_2含量和Cl~-+SO_4~(2-)+Na~++K~+含量均显著降低。对三个金矿床的矿石样品中的黄铁矿进行了硫同位素分析,δ~(34)S值为-2.0~3.7‰,集中于±0‰附近,表明三者具相同的硫同位素来源,其可能来源于岩浆流体或容矿岩石-玄武岩。哈图金矿带矿床的赋矿围岩、控矿构造、矿石类型和热液蚀变、成矿流体等方面与造山型金矿床相应特征相符,因此认为哈图金矿带中,哈图(齐Ⅰ)、齐Ⅱ和齐Ⅴ金矿均属造山型金矿床。     

Types and genesis of manganese oxide ores in Guangxi, Southwest China

Systematic studies are diven to the genesis and spatial distribution of manganese oxide deposits in Guangxi,Southwest China.The deposits are classified as 3 types and 7 subtypes among which the karst depression type is regionally characteristic an of reat potential.A genetic model is presented for the mineralization on the basis of proto-rock,tectonic background,topographic features and climatic and hydrogeological conditions.     

Isotopic composition of lead from tektites

The isotopic composition of lead in three tektites and Libyan Desert glass is compared with that in known terrestrial and extra-terrestrial sources. The lead contained in the glasses is similar to modern terrestrial lead, particularly lead from modern oceanic sediments. The uranium, thorium and lead concentrations were determined for one of the glasses, an australite. Evidence is given which indicates that within the last tens of millions of years differentiation of uranium, thorium and lead occurred in the parent material of the australite. These results are difficult to explain in terms of any extra-terrestrial origin involving fusion of materials from the moon, meteorites or comets, but they are readily explained if tektites are of terrestrial origin involving fusion of argillaceous sediments in some unspecified way.     

Isotopic composition of silicon in meteorites

Samples of bulk meteorites show only mass-dependent fractionation of silicon isotopes. No isotopic anomalies were found. The variation of the ratios ²⁹Si/²⁸Si and ³⁰Si/²⁸Si over the meteorite classes is small; 1%. per mass unit difference. The average Si isotopic composition for each class of meteorites is identical, within analytical uncertainties. This is quite unlike O, whose anomalous isotopic abundances in bulk samples differentiate among the classes of meteorites. The overlapping abundance ranges of Si isotopes among many classes of meteorites suggest closed-system behavior for this element prior to meteorite accretion and allow calculation of an average solar system Si isotope composition.     

辽宁高家堡子银矿床矿石晶洞构造及其成因机制

高家堡子银矿床是在辽东青城子铅锌矿田内发现的一大型独立银矿床,赋存于辽河群大石桥组第三段以大理岩为主的地层之中,矿体形态及产状受层间破碎带构造控制。矿区矿石分为硅化石英脉型及碎裂大理岩型两类,其中前者为矿区主要的富银矿石。该类矿石晶洞构造极其发育,根据地质及流体包裹体研究成果,认为矿石中的晶洞构造是岩浆来源富CO2流体溶蚀赋矿的大理岩围岩形成的溶洞,被晚期以大气降水为主流体充填形成晶簇状石英。     

High-temperature conductivity of magnetite ores in relation to their genesis and mineral composition (by the example of the Goroblagodatskoe skarn-magnetite deposit)

Samples of magnetite ores of different parageneses and mineral compositions from the Goroblagodatskoe skarn-magnetite deposit were studied by physical and mineralogo-petrographic methods. Electrical-resistance curves were obtained for an ore containing 80–90% magnetite for the temperature range 20–800 ºC. Three groups of samples were recognized according to the pattern of temperature curves and electrical resistance: sulfide-free, sulfide-containing (pyrrhotite), and variolitic ores. The parameters of high-temperature conductivity (activation energy E0 and coefficient of electrical resistance logR0) have been determined. A linear relationship between E0 and logR0 (logR0= a – bE0) has been established for magnetite ores of all mineral types. The coefficient a varies from 1.92 to 4.80 depending on the type and mineral composition of magnetite ores. The coefficient b is nearly constant for all studied samples, 6.65. The figurative points of the samples in the E0–logR0 coordinates lie in the field bounded by the straight lines logR0= 4.80 – 6.65E0 and logR0= 1.92 – 6.65E0. The samples of magnetite ores of the skarn and hydrosilicate paragenesis with visible pyrrhotite inclusions and samples of variolitic ores form an individual group in the above field. Within the group, the ores are also subdivided into garnet-magnetite (skarn paragenesis), epidote-chlorite-magnetite (hydrosilicate paragenesis), pyroxene-magnetite, and orthoclase-magnetite (variolitic ores).     

矿石中铜钴镍的消解方法比对

从实验结果看出,实验采用盐酸-硝酸-氢氟酸-高氯酸酸溶及过氧化钠碱熔分解样品结果大部分元素无显著性差别,建议日常分析采用盐酸-硝酸-氢氟酸-高氯酸分解样品即可,溶液用原子吸收测量。