Structure cristalline d'une ménéghinite naturelle pauvre en cuivre,Cu0,58Pb12,72(Sb7,04Bi0,24)S24Crystal structure of a Cu-poor natural meneghinite,Cu0.58Pb12.72(Sb7.04Bi0.24)S24

Cu-poor meneghinite from La Lauzière Massif (Savoy, France) has the composition (electron microprobe) (in wt%): Pb 59.50, Sb 20.33, Bi 1.19, Cu 0.87, Ag 0.05, Fe 0.03, S 17.62, Se 0.05, Total 99.64. Its crystal structure (X-ray on a single crystal) was solved with R1=0.0506, wR2=0.1026, with an orthorhombic symmetry, space group Pnma, and a=24.080(5) Å, b=4.1276(8) Å, c=11.369(2) Å, V=1130.0(4) Å³, Z=4. Relatively to the model of Euler and Hellner (1960), this structure shows a significantly lower site occupancy factor for the tetrahedral Cu site (0.146 against 0.25). Among the five other metallic sites, Bi appears in the one with predominant Sb. Developed structural formula: Cu_0.15Pb₂(Pb_0.53Sb_0.47)(Pb_0.46Sb_0.54)(Sb_0.75Pb_0.19Bi_0.06)S₆; the reduced one: Cu_0.58Pb_12.72(Sb_7.04Bi_0.24)S₂₄. The formation of such a Cu-poor variety seems to be related to specific paragenetic conditions (absence of coexisting galena), or to crystallochemical constraints (minor Bi). To cite this article: Y. Moëlo et al., C. R. Geoscience 334 (2002) 529–536.     

略阳煎茶岭铜镍硫化物矿床Re—Os同位素年龄及其地质意义

采用矿石Re-Os同位素方法对陕西省煎茶岭硫化镍矿床矿石进行了成矿年代学研究,获得了878士27 Ma(1σ)的等时线年龄,首次厘定了该矿床成矿时代为新元古代,成岩成矿基本同时.通过对878 Ma硫化镍矿石初始Re-Os同位素体系的γOs计算和Re/Os值分析表明,其yOs和Re/Os值变化范围大,深部条带状矿石的Re/Os值仅为0.05,yOs为-6.70;块状矿石的Re/Os值范围为4.24～24.43,γOs为-15.37～+280.65,说明成矿过程中有壳源物质的混染;两件样品的γOs为负值(-15.37,-6.70),可能指示其超镁铁质岩浆来源于Re亏损地幔.煎茶岭超基性岩体年龄及其镍矿石的Re-Os等时线年龄与扬子克拉通北缘火山岩浆活动时间相对应,它们是扬子克拉通西北缘晋宁期构造岩浆成矿作用的产物.     

内蒙古镁铁质-超镁铁质岩型铜镍矿床成矿条件与找矿远景分析

按构造环境控岩控矿特点,划分区内铜镍型矿成矿(岩)带,分析成矿条件,研究了与该类矿床成矿有关的镁铁质岩、超镁铁质岩分布规律及铜镍硫化物成矿特征,提出了找矿方向和建议.     

Improved Platinum-Group Element Extraction by NiS Fire Assay from Chromitite Ore Samples Using a Flux Containing Sodium Metaphosphate

Many chromite-rich rocks contain relatively high concentrations of the platinum-group elements (PGE). In many cases, the phases carrying PGE occur as either platinum-group minerals (PGM) or as base metal sulfides in solid solution in sulfides. In some cases, such as the UG-2 unit of the Bushveld Complex, the PGM are occluded inside chromite grains. Chromites are notably difficult to dissolve in most fluxes and if the chromite contains some PGM the possibility exists that not all the PGE will be recovered during fusion. In this work, shortcomings in published methods of analysis based on the nickel sulfide fire assay procedure were investigated and a new procedure developed based on the addition of sodium metaphosphate to the fusion mixture. Optimum composition of the fusion mixture was found to be 10 g sodium metaphosphate and 9 g silica to 10 g sample, 15 g sodium carbonate, 30 g lithium tetraborate, 7.5 g nickel and 4.5 g sulfur to achieve complete dissolution of chromite grains. The new flux mixture was evaluated by the analysis of reference material CHR-Pt+ (which is known to contain PGM inside chromite grains) and no undissolved chromite grains were found in the glassy slag. Analysis of the nickel sulfide beads from this fire assay using neutron activation analysis showed similar results for Rh and Ru when compared with published conventional true (or accepted) values, while Au, Ir, Os, Pd and Pt values determined here were 10 to 30% higher than the corresponding published conventional true values. It was concluded that the addition of sodium metaphosphate improved chromite dissolution in the flux and appears to improve PGE recovery.     

含硫化物镁铁质-超镁铁质侵入体中橄榄石Mg、Ni含量的制约:原理、模式及Voisey's Bay侵入体样品研究

镁铁质-超镁铁质岩浆结晶分离早期形成镁铁矿物,镁铁矿物中的Ni和Mg是相容元素。随着结晶分离作用的进行,Ni、Mg在硅酸盐岩浆及后形成的硅酸盐物质中的丰度下降。橄榄石中Ni含量及硅酸盐物质MgO/FeO比值都与母岩浆的相关值相关,据此可推断母岩浆的信息,它们之间可由实验测得的系数相联系。当岩浆饱和硫化物时,在结晶分离过程中硫化物珠滴会与镁铁硅酸盐物质一道析出,同时,与硫化物非饱和岩浆相比,过多的Ni会随之析出。这也反映在Ni、Mg含量比无硫化物分离时有更迅速的降低上。Ni、Mg含量变化值可以在VoiseysBay侵入体的模式曲线上反映出,加拿大Labrador的这一侵入体赋存了一个世界级的Ni-Cu-Co硫化物矿床。过去的作法是将侵入体中橄榄石的Ni、Mg含量与Simkin和Smith得出的各种火成岩中橄榄石的Ni、Mg含量相比较以确定Ni亏损,进而假定橄榄石来自硫化物饱和、有经济价值的岩浆。现在的研究显示这种简单的对比会导致错误。将样品数据与模式曲线对比并反映出侵入体矿物结晶堆积特征是重要的方法。使用这一方法,样品数据能很好地被模式曲线拟合。以在VoiseysBay的研究为例,当硫化物液相与硅酸盐矿物被去除后,硫化物非饱和的分离作用期就会显现出来,随后是硅酸盐结晶作用期。     

中国西北地区岩浆铜镍矿床地质特点与找矿潜力

西北地区是中国岩浆铜镍硫化物矿床最为发育的地区,主要有3个重要成矿期,其地质特点、成矿条件、形成标志等存在明显不同.笔者梳理了 目前诸多学者对岩浆铜镍硫化物矿床的研究工作,并结合野外实际,发现大陆裂谷是形成巨型-超大型岩浆铜镍硫化物矿床的构造背景条件,铁质系列的镁铁-超镁铁质岩体才可能形成有经济价值的岩浆铜镍硫化物矿体...     

Metasomatism and sulfide mobility in lithospheric mantle beneath eastern Australia: Implications for mantle Re–Os chronology

Spinel lherzolite xenoliths from Tertiary basaltic host magmas at Allyn River, eastern Australia reveal two distinct petrographic and geochemical types. One group is distinguished by xenoliths with undeformed, equilibrated microstructures and interstitial melt patches; The second group shows deformation and contains abundant fluid inclusions but no melt patches. Trace-element signatures of clinopyroxene in these xenoliths provide evidence for metasomatism by a silicate agent with hydrous component and by a carbonate-rich agent respectively.

Melt patches in the undeformed xenoliths contain secondary minerals including clinopyroxene, olivine, feldspar, Mg- and Ca-rich carbonate, apatite, ilmenite and spinel. They are interpreted to represent volatile-rich melt captured shortly prior to entrainment in the host basalt. Sulfide globules, now recrystallised to discrete sulfide phases but inferred to be molten at lithospheric mantle T and P, are closely associated with the melt patches. The close association between sulfide and highly mobile, volatile-bearing fluid has important implications for the mobility of Re and Os, the use of their isotopes in dating mantle events, and the possible effect of volatile-bearing metasomatic agents on their composition.     

白垩纪中期异常地质事件与全球变化

白垩纪中期(125~90 Ma)是地质历史中一个极端温室时期,集中出现一系列异常事件。异常事件是地球系统内各圈层相互耦合的产物,事件相互之间不是孤立的,单个事件引起的全球变化对其他事件起着明显的正/负反馈机制作用。文中基于对白垩纪中期异常事件的深入解剖和分析,包括大规模海底火山事件、大洋缺氧事件、生物异常更替与绝灭、白垩纪超静磁带、大洋红层出现等,在探讨白垩纪中期各个事件特征基础上,重点阐述异常事件所引起的全球变化及其对海洋、气候的影响;提出异常事件之间的相互关联与反馈机制。研究发现,大规模海底火山作用是引起白垩纪中期异常海洋和气候的最根本原因,直接促进大洋缺氧事件、生物绝灭与更替、沉积记录的转变等事件的发生。     

Hydrogen sulfide measurements in air by passive/diffusive samplers and high-frequency analyzer: A critical comparison

In this study, hydrogen sulfide (H₂S) measurements in air carried out using (a) passive/diffusive samplers (Radiello^® traps) and (b) a high-frequency (60 s) real-time analyzer (Thermo^® 450i) were compared in order to evaluate advantages and limitations of the two techniques. Four different sites in urban environments (Florence, Italy) and two volcanic areas characterized by intense degassing of H₂S-rich fluids (Campi Flegrei and Vulcano Island, Italy) were selected for such measurements. The concentrations of H₂S generally varied over 5 orders of magnitude (from 10⁻¹–10³ μg/m³), the H₂S values measured with the Radiello^® traps (H₂S_R) being significantly higher than the average values measured by the Thermo^® 450i during the trap exposure (H₂S_Ta), especially when H₂S was <30 μg/m³. To test the reproducibility of the Radiello^® traps, 8 passive/diffusive samplers were contemporaneously deployed within an 0.2 m² area in an H₂S-contaminated site at Mt. Amiata (Tuscany, Italy), revealing that the precision of the H₂S_R values was ±49%. This large uncertainty, whose cause was not recognizable, is to be added to that related to the environmental conditions (wind speed and direction, humidity, temperature), which are known to strongly affect passive measurements. The Thermo^® 450i analyzer measurements highlighted the occurrence of short-term temporal variations of the H₂S concentrations, with peak values (up to 5732 μg/m³) potentially harmful to the human health. The Radiello^® traps were not able to detect such temporal variability due to their large exposure time. The disagreement between the H₂S_R and H₂S_Ta values poses severe concerns for the selection of an appropriate methodological approach aimed to provide an accurate measurement of this highly toxic air pollutant in compliance with the WHO air quality guidelines. Although passive samplers may offer the opportunity to carry out low-cost preliminary surveys, the use of the high-frequency H₂S analyzer is preferred when an accurate assessment of air quality is required. In fact, the latter provides precise real-time measurements for a reliable estimation of the effective exposure to hazardous H₂S concentrations, giving insights into the mechanisms regulating the dispersion of this air pollutant in relation to the meteorological parameters.     

金川铜镍矿床中新生代抬升冷却过程：来自裂变径迹的证据

本文基于热年代学理论,利用锆石和磷灰石裂变径迹测年数据及对磷灰石热史的模拟,分析探讨金川铜镍矿床在中新生代的抬升冷却过程,认为金川超基性岩体自中生代以来一直处于持续的冷却抬升阶段,且在中侏罗世和晚白垩世早期经历了两期快速的抬升冷却事件,推断此事件与青藏高原后期活动时间相对应,证明金川岩体受到该事件的远程效应波及,致使该矿床遭受了一定的改造。