DMS and SO2 at Baring Head, New Zealand: Implications for the Yield of SO2 from DMS

Atmospheric dimethyl sulfide (DMS) and sulfur dioxide (SO₂) concentrations were measured at Baring Head, New Zealandduring February and March 2000. Anti-correlated DMS and SO₂ diurnalcycles, consistent with the photochemical production of SO₂ from DMS, were observed in clean southerly air off the ocean. The data is used to infer a yield of SO₂ from DMS oxidation. The estimated yields are highly dependent on assumptions about the DMS oxidation rate. Fitting the measured data in a photochemical box model using model-generated OH levels and the Hynes et al. (1986) DMS + OH rate constant suggests that theSO₂ yield is 50–100%, similar to current estimates for the tropical Pacific.However, the observed amplitude of the DMS diurnal cycle suggests that the oxidation rate is higher than that used by the model, and therefore, that theSO₂ yield is lower in the range of 20–40%.     

大西洋洋中脊TAG热液区中块状硫化物的Os同位素研究

新测得TAG热液区中5件海底块状硫化物样品的锇含量及其同位素组成,187Os/186Os比值在2.305～7.879之间,均值为5.986,介于现代海水和上部洋壳岩石的锇同位素组成之间,表明该区海底块状硫化物中锇是海水和上部洋壳来源锇混合的产物.在海底热液循环过程中,海水的混入对该区热液流体的Os浓度及其同位素组成产生了明显的影响。     

Tectonic setting and petrogenesis of the Çelebi granitoid, (Kırıkkale-Turkey) and comparison with world skarn granitoids

Many studies have shown systematic correlations between the composition of plutons worldwide and the metal content of associated skarns. This is the first report of similar correlations between the composition of Çelebi granitoid and skarns of the Çelebi district in Central Anatolia, Turkey. The Çelebi district is well known for its polymetallic Fe–W and Cu vein ores. These are hosted by calcic skarn zones. Both exoskarns (pyroxene–garnet) and endoskarns (epidote–pyroxene) occur in the district formed mainly along the granitoid contacts and along the fractures within the marble. Based on mineralogy, petrology and geochemistry, two different igneous rocks were recognized in the Çelebi granitoid, referred to as leucocratic (felsic) and mesocratic (intermediate) Çelebi granitoid. The leucocratic Çelebi occurs as dominant rock type, and is classified as granite. The mesocratic Çelebi is not widespread and is classified as adamellite, tonalite, quartz monzonite and quartz monzodiorite. The mesocratic Çelebi has I-type characteristics, and have subalkaline, calc-alkaline and metaluminous characteristics like most worldwide skarn granitoids.A post-collisional tectonic setting is proposed on the basis of field evidence, the relative timing of intrusions with respect to metamorphic and obducted ophiolitic rocks and trace element geochemistry. The high abundance of La and Ce and the enrichment of V in mafic components suggest that Çelebi granitoids are formed by partial melting of mantle rocks, but have been contaminated by interaction with continental crust involving possible magma mixing processes (i.e. mixing of coexisting felsic and mafic magmas). In the district, the mesocratic type and mafic microgranular enclaves (MME) mainly within leucocratic type represent a mafic underplating magma that was mixed with and/or injected into felsic magma of the leucocratic type.The present study shows that Fe mineralization is associated with mesocratic Çelebi type, whereas W mineralization is associated with leucocratic type. Mesocratic Çelebi granitoid is significantly different from the worldwide average of plutons associated with Fe skarns. In particular, MgO vs. SiO₂, FeOt+CaO+Na₂O/K₂O vs. SiO₂, Fe₂O₃/Fe₂O₃+FeO vs. SiO₂ and V vs. Ni vary from typical values (are lower than values typical for plutons associated with Fe skarns) for plutons associated with Fe skarns. Instead, it resembles the geochemical characteristics of plutons associated with worldwide Cu and possibly Au skarns. This suggests new exploration possibilities for copper and gold in the Çelebi district.     

Iron colloids/organic matter associated transport of major and trace elements in small boreal rivers and their estuaries (NW Russia)

The chemical status of major and trace elements (TE) in various boreal small rivers and watershed has been investigated along a 1500-km transect of NW Russia. Samples were filtered in the field through a progressively decreasing pore size (5, 0.8 and 0.22 μm; 100, 10, and 1 kD) using a frontal filtration technique. All major and trace elements and organic carbon (OC) were measured in filtrates and ultrafiltrates. Most rivers exhibit high concentration of dissolved iron (0.2–4 mg/l), OC (10–30 mg/l) and significant amounts of trace elements usually considered as immobile in weathering processes (Ti, Zr, Th, Al, Ga, Y, REE, V, Pb). In (ultra)filtrates, Fe and OC are poorly correlated: iron concentration gradually decreases upon filtration from 5 μm to 1 kD whereas the major part of OC is concentrated in the <1–10 kD fraction. This reveals the presence of two pools of colloids composed of organic-rich and Fe-rich particles. According to their behavior during filtration and association with these two types of colloids, three groups of elements can be distinguished: (i) species that are not affected by ultrafiltration and are present in the form of true dissolved inorganic species (Ca, Mg, Li, Na, K, Sr, Ba, Rb, Cs, Si, B, As, Sb, Mo) or weak organic complexes (Ca, Mg, Sr, Ba), (ii) elements present in the fraction smaller than 1–10 kD prone to form inorganic or organic complexes (Mn, Co, Ni, Zn, Cu, Cd, and, for some rivers, Pb, Cr, Y, HREE, U), and (iii) elements strongly associated with colloidal iron in all ultrafiltrates (P, Al, Ga, REE, Pb, V, Cr, W, Ti, Ge, Zr, Th, U). Based on size fractionation results and taking into account the nominal pore size for membranes, an estimation of the effective surface area of Fe colloids was performed. Although the total amount of available surface sites on iron colloids (i.e., 1–10 μM) is enough to accommodate the nanomolar concentrations of dissolved trace elements, very poor correlation between TE and surface sites concentrations was observed in filtrates and ultrafiltrates. This strongly suggests a preferential transport of TE as coprecipitates with iron oxy(hydr)oxides. These colloids can be formed on redox boundaries by precipitation of Fe(III) from inflowing Fe(II)/TE-rich anoxic ground waters when they meet well-oxygenated surface waters. Dissolved organic matter stabilizes these colloids and prevents their aggregation and coagulation. Estuarine behavior of several trace elements was studied for two small iron- and organic-rich rivers. While Si, Sr, Ba, Rb, and Cs show a clear conservative behavior during mixing of freshwaters with the White sea, Al, Pb and REE are scavenged with iron during coagulation of Fe hydroxide colloids.     

Cu–Fe Bearing Zinc Sulfide from Laloki Stratabound Massive Sulfide Deposit, Papua New Guinea: Chemical Characterization

Abstract: A strange, unidentified, Cu-Fe bearing zinc sulfide occurs in the Laloki massive sulfide deposit, Papua New Guinea. The mineral is optically uniform in texture but is chemically variable and zoned even within a single grain. Copper contents vary from 0.1 up to 8.85 wt%. Iron reaches 18.31 wt% at maximum and decreases as Cu increases. It is remarkable, however, that the total Fe+Cu remains essentially unchanged between roughly 18 and 20 wt%. Zn and S are least variable, giving 45.85–47.84 wt% and 33.48–34.58 wt%, respectively. Other trace elements such as Cd and Mn are in general less than 0.2 wt%. It is strongly suggested that the mineral in question constitutes a unique Fe-Cu substitutional solid solution series belonging essentially to the Zn–Fe–Cu–S system.
The ideal chemical formula of the solid solution series can well be presented as Zn₁₀(Fe, Cu)₅S₁₅ or Zn₂(Fe, Cu)S₃, where Fe is always greater than Cu. It is intriguing that chalcopyrite blebs are recognizable restrictively only in nearby portions of the Cu-rich end member with the ideal composition close to Zn₁₀Fe₃Cu₂S_15. It has been confirmed by vacuum-sealed heating experiments that this mineral is decomposed to produce chalcopyrite and Fe-bearing normal sphalerite at temperatures below 200C. This would provide another evidence for the existence of such distinct phase as suggested here.     

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.     

阿尔泰可可塔勒铅锌矿床围岩蚀变及成因

可可塔勒铅锌矿床受火山喷发中心和沉积洼地控制，铅锌沉淀于海进阶段的局限还原卤水池中；矿下存在大型蚀变带，构成成矿流体对流循环过程中的水-岩作用带；后期造山挤压过程使地层和矿体倒转，矿床最终定位于麦兹倒转向斜之北东倒转翼的东南近转折部位。指出该矿床属海底火山喷流沉积改造型块状硫化物铅锌矿床。     

Re-Os Age of Cu-Ni Ores from the Huangshandong Cu-Ni Sulfide Deposit in the East Tianshan Mountains and Its Implication for Geodynamic Processes

An isochron age of 282±20 (95% conf. limit) Ma of the sulfide ores in the Huangshandong Cu-Ni sulfide deposit, the East Tianshan Mountains has been obtained through Re-Os isotopic measurement. The age implies that the Cu-Ni sulfide deposit and other related deposits in the same area occurred in a Permian extensional environment of post-collision instead of Devonian-Early Carboniferous ophiolite-related oceanic or island arc environments inferred before. It shares the same ages with the orogenic and epithermal gold deposit systems in the same area. An initial 187Os/188Os ratio of 0.25±0.04 (1σ) and a γos value of 99 on average display the participation of large quantities of crustal components into the rock-forming and ore-forming system during mineralization and magmatic emplacement.     

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.     

中子活化分析在铼—锇法年龄测定中的应用

同位素稀释中子活化分析铼与感耦等离子体质谱法测定锇相结合，应用于辉钼矿及铜＿镍硫化物矿物的铼＿锇年龄测定，取得了满意的结果，扩大了铼＿锇测年法的应用范围。