Small Amount Of Sulfide Research Articles

A contribution to the understanding of the origin of the Ginebra Gold District mineralizations, Colombia

Ginebra´s gold mineralization is hosted by the Ginebra Ophiolitic Massif and the Buga Batholith, in the western flank of the Central Cordillera of Colombia. Gold occurs as disseminations, quartz-carbonate stockwork veinlets and quartz lodes with a strong structural control and are composed by small amounts of sulfides, mostly pyrite, with galena, sphalerite and chalcopyrite in at least two different deposition events and related to strong sericite-chlorite-epidote haloes, indicative of near-neutral and reduced fluids. Petrography and Raman spectroscopy allowed to identify two main fluid inclusions assemblages primary to pseudo-secondary in origin, both of them aqueous and CO2-rich, with variable N2. Microthermometric analysis indicates the hydrothermal fluids associated with the gold were low saline (0.75-6.22 wt% NaCl equiv.) and presented a minimum trapping temperature ranging from 237.4 to 301.6°C. Petrography and microthermometric results suggest an isothermal fluid mixing and/or H2S loss as the main mechanisms related to gold bi-sulfide/thio-sulfide complexes destabilization and precipitation. Sulfur isotopes indicates a close to zero range (-8.2-+4.8‰), suggesting a restricted fluid circulation through the magmatic rocks of the Buga Batholith and the Ginebra Ophiolitic Massif. Besides, the oxygen and deuterium isotopes from hydrothermal sericite and chlorite accompanying to gold events, indicates a metamorphic origin for the hydrothermal fluids. 40Ar-39Ar dating of the hydrothermal alteration haloes, from El Retiro and La Esperanza, indicates a late Cretaceous-Paleocene age, between 67 and 65 Ma, contemporaneous with a regional strong dextral transpressive deformation related to subduction to obduction and exotic terrane accretion against the north-western part of the South American Plate. Although the hydrothermal fluid characteristics of the Ginebra Gold Disctrict are compatible with both the Intrusion-Related and Orogenic Gold deposit types, the metamorphic nature of the hydrothermal fluids and the tectonic regime at the time of mineralization event, allow us to propose they are compatible with an Orogenic Gold deposit.

Process optimization and mechanism for removal of high-concentration chlorine from municipal solid waste incineration fly ash washing wastewater by Friedel's salt

Waterwashing is an important pretreatment method for the reuse of municipal solid waste incineration (MSWI) fly ash. However, the presence of high levels of chlorides and small amounts of sulfides in the waterwashing solution makes it difficult to treat and reuse. Therefore, in this study, a calcium sulfate- Friedel's salt precipitation method was used to dechlorinate and desulfurize in the MSWI fly ash washing solution. This paper mainly focused on the chloride removal, and the effects of factors such as reagent ratios, temperature, and reaction time on chloride removal rate and the two-stage dechlorination and desulfurization process were optimized. The experimental results indicated that when the ratio in the first stage was n(Ca):n(Al):n(Cl) = 3:1.5:1, and in the second stage, n(Ca):n(Al):n(Cl) = 8:4:1, a chloride removal rate of up to 90.5% and a sulfide removal rate of over 99.88% could be obtained. The deposited particles were analyzed by using FE-SEM, XRD, and FTIR to investigate their size, morphology, phase composition, and functional groups. The study revealed that excessively high or low reagent ratios could reduce the interlayer spacing of Friedel's salt. Additionally, high temperatures led to the decomposition of Friedel's salt, and the dechlorination efficiency was affected.

Lower Talnakh Type Intrusions of the Norilsk Ore Region

Troctolites, olivine and picrite gabbrodolerites account for up to 75% of the Lower Talnakh type intrusions in places of their increased thickness whereas reduced thickness sections consist of olivine-free and olivine-bearing gabbrodolerites. Differentiation is not obvious within these high-Mg cumulates, although the content of TiO2 and alkalis increases towards the upper endocontacts. The transitions between the rock types are gradational, and the composition of low Ni olivine in different rocks (Fo70–83, 0.01–0.2 wt % NiO) overlap significantly. Clinopyroxene (Fs7–13, Mg# 68–89) is characterized by both the lowest contents and variation ranges of Cr2O3 (0.01–0.5 wt %) and TiO2 (0.05–1.0 wt %) among all types of the intrusions of the Norilsk complex that is consistent with the Cr-depleted (0.002–0.051 wt % Cr2O3) bulk rock compositions. Later orthopyroxene (Fs15–30) is crystallised by the reaction of the residual melt with early olivine. Plagioclase forms porphyritic phenocrysts and their intergrowths along with ophitic laths as well as dominates in schlieren and fragments of leucocratic rocks in taxitic and picritic gabbrodolerites with a poorly sorted layered texture. In olivine-rich rocks, sulfides are represented by the association of troilite ± hexagonal pyrrhotite + Fe- and Co-rich pentlandite + Fe-enriched chalcopyrite (± putoranite, talnakhite) ± cubanite. In the upper and lower parts of the intrusions, the association of hexagonal pyrrhotite + chalcopyrite + pentlandite occurs, while monoclinic pyrrhotite + chalcopyrite + Ni-enriched pentlandite are formed in the endo- and exocontacts. The concentration of base (0.077–0.21 wt % Ni, 0.05–0.38 wt % Cu) and platinum metals (0.03–0.26 to 0.40 g/t total PGE) in mineralized rocks is very low. Upon small amounts of sulfides and extremely low base and platinum metal tenors, the heterogeneous S isotopic composition of Lower Talnakh type sulfides (mainly 3.8–8.6‰, but up to 11.8%) most likely reflects the achievement of repeated sulfide saturation during the assimilation of sulfate S by magma that has previously experienced loss of chalcophile metals into a coexisting sulfide fluid at depth. The Sr-Nd isotopic compositions of the Lower Talnakh intrusions (Sri – from 0.7073 to 0.7087 and εNd(Т) from –1.8 at –5.9 recalculated to 250 Ma) show the predominant contamination with Proterozoic material, in contrast to the ore-bearing intrusions, which Sr-Nd isotope compositions indicate contamination with upper crustal sedimentary matter of the Paleozoic age.

El Álamo district (Baja California, México): A hint of a new Cordilleran orogenic gold belt?

The El Álamo is one of the most important historic gold mining districts in the Peninsular Ranges batholith. Gold mineralizations at El Álamo consist in fault-fill laminated quartz veins with small amounts of sulfides and oxides, and lesser amounts of gold. Veins are mainly emplaced along compressional brittle-plastic shear zones within the El Álamo quartz diorite (146.6 ± 1.6 Ma, U–Pb zircon), which is intruded by the San Marcos dike swarm (126.8 ± 1.7 Ma, U–Pb zircon). Several lines of evidence indicate that the dike swarm is older than quartz veins, and the formation of the later is related to the Peninsular Ranges orogeny (∼110−98 Ma). Gold bearing quartz veins formed during regional prograde metamorphism (greenschist facies), and the veins subsequently underwent plastic deformation, dynamic recrystallization and metamorphism. Gold remobilization and concentration seems to have been largely enhanced by metamorphism, probably accounting for very high grade, albeit sporadic, bonanza ores, typical of the district. 40Ar/39Ar dating of hydrothermal white micas from the auriferous veins yielded ages of 97.86 ± 0.17 Ma at the Ulises mine and 97.46 ± 0.17 Ma at the La Americana mine. These ages are interpreted as the minimum age of the regional metamorphism in the area. Based on their primary characteristics, the gold deposits from El Álamo district can be ascribed to the orogenic gold type. These deposits are similar to other known deposits in the same orogenic context (e.g., Julian district; southern California), and they probably conform a new Cordilleran orogenic gold belt that could extend over much of the exhumed axis of the Peninsular Ranges batholith.

The role of early sulfide saturation in the formation of the Yulong porphyry Cu-Mo deposit: Evidence from mineralogy of sulfide melt inclusions and platinum-group element geochemistry

Sulfide melt inclusions enclosed in silicate minerals have been observed in many oxidized Cu-bearing porphyries. The origin of such sulfide melt inclusions could bear critical information of metal enrichment or depletion during magma evolution of porphyry systems. The giant Yulong porphyry Cu-Mo deposit in eastern Tibetan Plateau consists of a series of felsic intrusions, among which the mineralized Yulong intrusion emplaced at a late stage of the magmatic activity. This study reports detailed texture and composition of sulfide melt inclusions from barren and mineralized intrusions, as well as platinum-group elements of these intrusions, to evaluate potential role of early sulfide saturation in the porphyry mineralization system. These sulfide melt inclusions, occurring as globules or droplets, are preserved in zircon, amphibole and quartz grains. Most of them are composed of a major phase of pyrrhotite and minor pyrite, chalcopyrite and pentlandite. Smooth boundaries between these phases suggest the origin of fractionation from sulfide melt upon cooling. Small amounts of Cu and Ni are heterogeneously distributed in the pyrrhotite. The sulfide melt inclusions could be observed in both the pre- and syn-mineralization intrusions at Yulong, indicating that sulfide saturation had commonly occurred during magma evolution. Magnetite mineral inclusions could be observed in zircon and amphibole grains as well. The mineral assemblage of magnetite + pyrrhotite + pyrite of the mineral inclusions constrains the Yulong magmatic system to redox conditions near the magnetite-pyrite/pyrrhotite buffer and above the fayalite/ magnetite-quartz buffer (FMQ). High Eu/Eu* values (0.56–0.78) of the hosting zircons and high calculated ΔNNO values (>0.5) of the hosting amphibole indicate highly oxidized nature of the parental magma.Both pre- and syn-mineralization intrusions have low PGE contents (Pt = 0.04 to 0.17 ppb, Pd = 0.19–0.60 ppb) with compositions plotting in the Au-poor porphyry Cu fields in discriminating diagrams. Early sulfide saturation may have been reached and small amounts of sulfides have been segregated from magma. Most PGEs and Au but little Cu have been removed from the evolved magma because the partition coefficient of Cu between sulfide and silicate melt is about two orders of magnitude lower than PGE or Au. As a consequence, the evolved magma would have high Cu but very low PGE and Au, resulting in the Au-poor porphyry Cu mineralization at Yulong.

Mineral chemistry and genesis of the Permian Cihai and Cinan magnetite deposits, Beishan, NW China

Cihai and Cinan are Permian magnetite deposits related to mafic-ultramafic intrusions in the Beishan region, Xinjiang, NW China. The Cihai mafic intrusion is dominantly composed of dolerite, gabbro and fine-grained massive magnetite ore, while gabbro, pyrrhotite+pyrite-bearing clinopyroxenite and magnetite ore comprise the major units in Cinan. Clinopyroxene occurs in both deposits as 0.1–2mm in diameter subhedral to anhedral grains in dolerite, gabbro and clinopyroxenite. High FeO contents (11.7–28.9wt%), low SiO2 (43.6–54.3wt%) and Al2O3 contents (0.15–6.08wt%), and low total REE and trace element contents of clinopyroxene in the Cinan clinopyroxenite imply crystallization early, at high pressure. This clinopyroxene is FeO-rich and Si and Ti-poor, consistent with the clinopyroxene component of large-scale Cu-Ni sulfide deposits in the Eastern Tianshan and Panxi ares, as well as Tarim mafic intrusion and basalt, implying the Cinan mafic intrusion and sulfide is related to tectonic activity in the Tarim LIP. The similar mineral chemistry of clinopyroxene, apatite and magnetite in the Cihai and Cinan gabbros (e.g., depleted LREE, negative Zr, Hf, Nb and Ta anomalies in clinopyroxene, lack of Eu anomaly in apatite and similarity of oxygen fugacity as indicated by V in magnetite), indicate similar parental magmatic characteristics. Mineral compositions suggest a crystallization sequence of clinopyroxenite/with a small amount of sulfide – gabbro – magnetite ore in the Cinan deposit, and magnetite ore – gabbro – dolerite in Cihai. The basaltic magma was emplaced at depth, with magnetite segregation (and formation of the Cinan magnetite ores) occurring in relatively low fO2 conditions, after clinopyroxenite and gabbro fractional crystallization. The evolved Fe-rich basaltic magma rapidly rose to intermediate or shallow depths, forming an immiscible Fe-Ti oxide magma as fO2 increased and leaving a Fe-poor residual magma in the chamber. The residual magmas was emplaced at different levels in the crust, forming the Cihai gabbro and dolerite, respectively. Finally, the immiscible Fe-Ti oxide magma was emplaced into the earlier formed dolerite because of late magma pulse uplift, resulting in a distinct boundary between the magnetite ores and dolerite.

Mineralogical changes upon heating in the Millbillillie meteorite: Implications for paleointensity determination in Apollo samples

Measuring the intensity of the Moon's ancient magnetic field is an important goal of lunar sample analysis. Paleointensity estimates using thermal methods (Thellier–Thellier) raise the problem of sample alteration, especially for lunar samples carrying sulfides. To address this problem, we made real-time measurements of sample magnetization during heating with a three-axis vibrating sample magnetometer (the Triaxe, LeGoff and Gallet, 2004), in the hope that rapid heating would minimize alteration (Coe et al., 2014). We studied the Millbillillie meteorite, which has a lunar-like mineralogy. We find that after repeated heating phases to ∼600°C, we form pyrrhotite, magnetite, and magnetic phases with low (200–270°C) Curie temperatures. These low-temperature phases appear after pyrrhotite has apparently been destroyed by subsequent heating phases, and their mineralogy is unknown. These results have implications for the paleomagnetic study of any extraterrestrial samples with even small amounts of sulfides, and further experiments are required to understand them.

A Study of Organic Sulfur Analysis in Coal Using Non-destructive Techniques

The Xinyu coal under study was received from Shanxi province, China. Raw coal and its extracted coals were investigated for distribution of various forms of organic sulfur and effects of solvent polarity on extraction organic sulfur from the coal during continuous extraction by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with chemical analysis. The distribution and primary existent forms of organic sulfur in Xinyu coal is mercaptan/thioether (44.9%), thiophene (24.4%), sulfones sulfur (30.7%), and a small amount of sulfide. Carbon disulfide (CS2), dichloromethane (CH2Cl2), and propylalcohol (CH3CH2CH2OH) was applied to explore the applicability for the removal of sulfur compounds. The experimental results show that the CH3CH2CH2OH removal of mercaptan/thioether ability (51.1% → 35.8%) is markedly higher than others. CS2 has a higher selectivity of removing thiophene (24.4% → 19.6%) and sulfones sulfur (30.7% → 26.6%). CH2Cl2 has the extraction abilities for the sulfones and mercaptan, but the effect is not obvious. The results have guiding significance for the selection of the appropriate extractants using the gas chromatography technique coupled extraction to identify organic sulfur compounds species. Continuous extraction provides a way of non-destructive depth profilings with X-ray photoelectron spectroscopy, which can improve the reliability and comprehensiveness of the X-ray photoelectron spectroscopy analysis.

Area specific resistance of the scale formed on Crofer 22APU ferritic steel in atmospheres containing SO2

The effect of the presence of sulfide in scales grown on the Crofer 22APU steel in the air+1% SO2 gas mixture at 1073K on their area specific resistance has been investigated. Three types of samples were studied: “non-pre-oxidized” steel exposed to oxidation in the gas mixture of air+1% SO2 for 300h, “pre-oxidized” steel oxidized in air for 200h and then for 100h in the gas mixture of air+1% SO2, and steel oxidized in pure air for 300h at 1073K as reference. The structure and microstructure of the scales were characterized by means of XRD, SEM-EDS and TEM-EDX. Electrochemical impedance spectroscopy (EIS) and dc 2-probe methods were used to determine electrical resistance. TEM-EDX analyses indicate that the scales grown in the mixture of air+1% SO2 are two-layered and consist of an outer MnCr2O4 spinel containing a small amount of sulfide, probably in the form of MnS, and an inner chromium oxide layer, which is the main oxidation product formed on the Crofer 22APU steel. Since the thickness of both scales is approximately equal, the ASR difference may be attributed to the manganese sulfide content in the studied scales. The reference scale formed on the studied steel in pure air after 300h of oxidation at 1073K is thinner than the above scales, and subsequently exhibits a lower resistance. The long-term test of ASR for scales formed on the Crofer 22APU steel in the atmosphere containing SO2 showed that they meet the requirements set for interconnect materials in SOFCs.

Recovery of cobalt from converter slag of Chambishi Copper Smelter using reduction smelting process

The reduction smelting process for cobalt recovery from converter slag of the Chambishi Copper Smelter in Zambia was studied. The effects of reducing agent dosage, smelting temperature and time and the addition of slag modifiers (CaO and TiO 2) were investigated. In addition, the depleted slag and cobalt-bearing alloy were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Under the determined conditions, 94.02% Co, 95.76% Cu and less than 18% Fe in the converter slag were recovered. It was found that the main phases of depleted slag were fayalite and hercynite; and the cobalt-bearing alloy mainly contained metallic copper, Fe-Co-Cu alloys and a small amount of sulfide.

Trace elements in recent groundwater of an artesian flow system and comparison with snow: enrichments, depletions, and chemical evolution of the water

Snow samples collected from hand-dug pits at two sites in Simcoe County, Ontario, Canada were analysed for major and trace elements using the clean lab methods established for polar ice. Potentially toxic, chalcophile elements are highly enriched in snow, relative to their natural abundance in crustal rocks, with enrichment factor (EF) values (calculated using Sc) in the range 107 to 1081 for Ag, As, Bi, Cd, Cu, Mo, Pb, Sb, Te, and Zn. Relative to M/Sc ratios in snow, water samples collected at two artesian flows in this area are significantly depleted in Ag, Al, Be, Bi, Cd, Cr, Cu, Ni, Pb, Sb, Tl, V, and Zn at both sites, and in Co, Th and Tl at one of the sites. The removal from the waters of these elements is presumably due to such processes as physical retention (filtration) of metal-bearing atmospheric aerosols by organic and mineral soil components as well as adsorption and surface complexation of ionic species onto organic, metal oxyhydroxide and clay mineral surfaces. In the case of Pb, the removal processes are so effective that apparently "natural" ratios of Pb to Sc are found in the groundwaters. Tritium measurements show that the groundwater at one of the sites is modern (ie not more than 30 years old) meaning that the inputs of Pb and other trace elements to the groundwaters may originally have been much higher than they are today; the M/Sc ratios measured in the groundwaters today, therefore, represent a conservative estimate of the extent of metal removal along the flow path.Lithogenic elements significantly enriched in the groundwaters at both sites include Ba, Ca, Li, Mg, Mn, Na, Rb, S, Si, Sr, and Ti. The abundance of these elements can largely be explained in terms of weathering of the dominant silicate (plagioclase, potassium feldspar, amphibole and biotite) and carbonate minerals (calcite, dolomite and ankerite) in the soils and sediments of the watershed. Arsenic, Mo, Te, and especially U are also highly enriched in the groundwaters, due to chemical weathering: these could easily be explained if there are small amounts of sulfides (As, Mo, Te) and apatite (U) in the soils of the source area. Elements neither significantly enriched nor depleted at both sites include Fe, Ga, Ge, and P.

Ferrihydrite-dependent growth of Sulfurospirillum deleyianum through electron transfer via sulfur cycling.

Observations in enrichment cultures of ferric iron-reducing bacteria indicated that ferrihydrite was reduced to ferrous iron minerals via sulfur cycling with sulfide as the reductant. Ferric iron reduction via sulfur cycling was investigated in more detail with Sulfurospirillum deleyianum, which can utilize sulfur or thiosulfate as an electron acceptor. In the presence of cysteine (0.5 or 2 mM) as the sole sulfur source, no (microbial) reduction of ferrihydrite or ferric citrate was observed, indicating that S. deleyianum is unable to use ferric iron as an immediate electron acceptor. However, with thiosulfate at a low concentration (0.05 mM), growth with ferrihydrite (6 mM) was possible and sulfur was cycled up to 60 times. Also, spatially distant ferrihydrite in agar cultures was reduced via diffusible sulfur species. Due to the low concentrations of thiosulfate, S. deleyianum produced only small amounts of sulfide. Obviously, sulfide delivered electrons to ferrihydrite with no or only little precipitation of black iron sulfides. Ferrous iron and oxidized sulfur species were produced instead, and the latter served again as the electron acceptor. These oxidized sulfur species have not yet been identified. However, sulfate and sulfite cannot be major products of ferrihydrite-dependent sulfide oxidation, since neither compound can serve as an electron acceptor for S. deleyianum. Instead, sulfur (elemental S or polysulfides) and/or thiosulfate as oxidized products could complete a sulfur cycle-mediated reduction of ferrihydrite.

Corrosion Behavior of Fe–25Cr in a N2–0.1% SO2 Atmosphere at 973 K Under Mechanical Loading

The corrosion behavior of an Fe-25Cr alloy was investigated in a N2-0.1 vol.% SO2 atmosphere at 973 K with and without stress. Without stress, the surface scale formed at the very initial stage consisting of Cr oxides and sulfides, which later changed to a Cr2O3-rich scale with the initially formed sulfides remaining. Under relatively low constant stress, +15 and +20 MPa, as well as cyclic stress of ±30 or ±40 MPa, the total strain for 36 ks was less than 0.1% and there was little cracking of the external scale, which consisted of Cr2O3 and (Fe, Cr)3O4 with small amounts of sulfide, growing faster. The external scale here was poorly adhesive. Under high stress, +25 and +35 MPa, cracks formed in the external scale and both oxides and Fe sulfide grew rapidly through the cracks to form nodules. The nodules consisted of an FeS-rich core surrounded by Fe3O4. With increasing strain, the preformed Cr2O3-rich scale changed drastically to a multilayered scale with an alternating oxide layer-sulfide layer structure.

On the role of microbes in the alteration of submarine basaltic glass: a TEM study

The alteration of submarine basaltic glass that has been attributed to microbial activity was investigated via transmission electron microscopy in order to document glass alteration and to understand the chemical reactions that bacteria could utilize. The features that were examined occur within fresh glass at the alteration front and consist of 0.1–2.3 μm patches or tubes of phyllosilicates rimmed by 0.1–0.3 μm wide zones of altered glass. The altered glass has lost significant Mg, Fe, Ca and Na, slight amounts of Al and Mn, and exhibits an order of magnitude increase of K. This incongruent dissolution occurred at neutral to acid pH and temperatures <90°C. Phyllosilicates consist of montmorillonite–saponite with berthierine interlayers, plus a mica component. The phyllosilicates directly replace altered glass along the perimeters of the phyllosilicate areas, but the centers of many of these areas may be filled pore space formerly occupied by microbes that facilitated glass alteration. If so, the sizes of the bacteria ranged to less than 0.1 μm and into the range of nano-organisms. Iron in secondary products is essentially all ferrous, and is most likely mobilized from glass as the ferrous ion, possibly with the reduction of minor primary ferric iron in the glass. Small amounts of sulfide in secondary pyrite associated with altered glass may be derived from microbial reactions or from the glass itself. Net bulk chemical changes for altered glass plus phyllosilicates include losses of Si, Al, Fe, Mn, Ca and Na, plus possible slight losses of Ti. This material is redistributed into fracture-filling smectite along with significant K and Mg from seawater. The uptake of K requires the circulation of large amounts of seawater through fractures in the glass (>100 fracture volumes), which may be important for the supply of nutrients for microbial activity.

Simple methods for preparation of a well-defined 4-pyridinethiol modified surface on Au(111) electrodes for cytochrome c electrochemistry

A very small amount of sulfide impurity in 4-pyridinethiol (4-PySH) modifier solution was found to interfere with the proper formation of the 4-PySH modified surface for cytochrome c electrochemistry on an Au(111) electrode. When the modification was conducted in an alkaline (e.g. 0.1 M KOH) solution, in aqueous solutions under applying a potential more positive than 0.3 V vs. Ag/AgCl, or at a low modifier concentration (e.g. 20 μM), the proper 4-PySH modified surface was obtained even using 4-PySH as received, which contained a small amount of sulfide. The selective adsorption of 4-PySH in the presence of a small amount of sulfide under these conditions was due to the rapid formation of proper 4-PySH modified surface, which prevented the sulfide from reacting with the electrode surface.

Physical and chemical constraints on platinum-group element behavior during crystallization of a basaltic komatiite liquid; example of the Proterozoic Delta Sill, New Quebec, Canada

The Delta sill, located in the southern part of the 2.03 to 1.92 Ga Cape Smith fold belt, northern Quebec, is composed of a peridotite, pyroxenite, gabbronorite, and anorthosite suite derived from a basaltic komatiite parental magma (MgO = 13.58-15.66%). Despite its rather limited thickness (215-275 m), it contains three platinum-group elements (PGE) horizons, two slightly enriched horizons, one in the peridotite and one in the lower gabbronorite, and a strongly PGE-enriched horizon (forming a reef) in the upper gabbronorite. The high PGE content in the reef implies a system with an R factor (volume of immiscible sulfide liquid/ volume of silicated magma) of 100 to 1.000. However, the small volume of magma involved suggests that several other processes controlled the PGE behavior. Some experimental works have shown that the CaO and FeO contents in parental magmas influence the sulfide capacity and consequently the sulfur fugacity. The last parameter, as well as the oxygen fugacity, have been previously recognized as having a fundamental influence on the PGE enrichment processes. Because of the relatively high CaO contents (7.21-11.26%) of parental magma and the existence of PGE enrichment, the Delta sill provides an opportunity to test the effects of varying sulfur and oxygen fugacities on the processes of PGE enrichment. Thus, the PGE concentration profiles observed in the two sections transecting the sill are in good agreement with the experimentally determined behavior of these elements in silicate melts as a function of oxygen and sulfur fugacities. First, the relatively high Ca content of the initial magma induced a high sulfide capacity in the liquid. Second, decreasing sulfide capacity (and correlatively, an increase in sulfur fugacity) produced by the precipitation of, calcic phases--notably clinopyroxene and plagioclase--account for the PGE anomalies as well as the late-stage crystallization of sulfides in the reef. In the lowermost PGE anomaly, Ir and Ru enrichment within the peridotitic layer can be clearly related to early ferrochromite crystallization due to increasing oxygen fugacity, whereas subsequent Pt enrichment can be related to the formation of an isoferroplatinum phase (Pt 3 Fe) associated with ferrochromite. In the second PGE anomaly, located in the lower gabbronorite, synchronous Ir and Ru, Rh, Pt, and Pd, and S enrichments are due to the precipitation of small amounts of sulfides under low oxygen fugacity. Both the Ir and Ru and the Rh, Pt, and Pd, left over from the first chromite-forming stage, are complexed by sulfur when the sulfide capacity increases, consequent to CaO removal from the melt by plagioclase fractionation. Finally, the third anomaly in the PGE reef, appears to record the crystallization of a differentiated Fe- and Ti-rich residual liquid containing fluid phases and sulfur. It reflects the migration of an S-bearing liquid following the important lowering of sulfide capacity in the liquid due to the increase of SiO 2 and TiO 2 in the liquid and to the precipitation of Ca-bearing minerals.

Composition of Copper Tarnish Products Formed in Moist Air with Trace Levels of Pollutant Gas: Sulfur Dioxide and Sulfur Dioxide/Nitrogen Dioxide

The objective of the work reported here was to characterize the tarnish products formed on copper during the early stages of exposure to moist air with trace levels of pollutant gas, in particular, sulfur dioxide and sulfur dioxide/nitrogen dioxide. A mixed‐flowing‐gas chamber was used to control part per billion (ppb) gas concentrations, relative humidity, temperature, and flow conditions. Two analytical techniques, x‐ray photoelectron spectroscopy and coulometric reduction (chronopotentiometry), were utilized to study the tarnish products. The exposure of copper to 75 ppb sulfur dioxide at 23°C and 70% relative humidity produced a tarnish product layer containing a small amount of sulfide. Exposure of copper to 75 ppb sulfur dioxide and 120 ppb nitrogen dioxide at 23 and 70% relative humidity produced cupric species, and, in addition to . Trace amounts of sulfide and oxy‐sulfur species were also detected.

Geochemical characteristics of Jinwozi gold deposit, Xinjiang

The Jinwozi gold deposit consists of gold-bearing quartz veins in a biotite granodiorite of Hercynian age (zircon U-Pb age ≈ 335.7 Ma). Ore mineralogy is simple. In addition to native gold, there are only small amounts of sulfides, mainly pyrite and minor sphalerite, chalcopyrite and galena. δ34S values average 6.69‰, and δ18O 13.99‰ Abundant CO2 is contained in fluid inclusions from quartz. Homogenization temperatures of fluid inclusions are between 186 and 262 °C. REE distribution patterns indicate that the igneous mass may have been derived from a common initial material of calcareous-argillaceous sediments and alkali basalts as the country rocks. In other words, the Jinwozi granodiorite is of remelting origin from crustal material. Isotopic evidence of S, O and Pb shows that the ore-forming material is genetically related to magmatic hydrothermal activity.

The geology and geochemistry of the Waterfall Gorge section of the Insizwa Complex with particular reference to the origin of the nickel sulfide deposits

The Jurassic-aged mafic rocks from the Waterfall Gorge section of the Insizwa layered complex, Transkei, range in composition from olivine gabbro and picrite (Basal zone), through a series of gabbros (Central zone), to monzonites (Roof zone). The compositional data for the mineral phases (olivine, plagioclase, bronzite, and augite) show significant features: in the basal gabbro the trend in compositional variation is the reverse of that seen in the Central zone of the intrusion; and olivines from the picrite unit are the most forsteritic in the intrusion, but they are depleted in Ni compared to olivines from the basal gabbro and Central zone. The data for olivines from the picrite unit at Tabankulu exhibit a similar but more significant degree of depletion.Mineral compositional and whole-rock geochemical data for the basal olivine gabbro suggest that olivine control is primarily responsible for the compositional variation in this unit at Insizwa, however, to account for the upward increase in the forsterite content of the cumulus olivine at the base, the intrusion of successively less-fractionated batches of a low MgO magma is suggested.We suggest that the depletion of the olivines in Ni can be attributed to the equilibration of the parent magma with sulfide and we show that these data are consistent with experimental distribution coefficient data for Ni between olivine and sulfide, permitting broad constraints to be placed on the grade, as well as the tonnage and location of the ore. Extrapolation of these conclusions to the Tabankulu intrusion suggest that the highly Ni-depleted olivines of the picrite have equilibrated with a magma from which a particularly high proportion of sulfide has segregated. Geophysical data fail to detect a massive orebody at the base of the intrusion, though several small bodies may exist. It is suggested that saturation may have occurred at depth, and only a small amount of sulfide has been transported to the surface in the picrite and concentrated in depressions at the base of the intrusion.Massive and disseminated magmatic Ni sulfide mineralization is confined to the lower Basal zone and shows a consistent fractionation into pyrrhotite-pentlandite-rich ore at the base and chalcopyrite-rich ore at the top (in both massive sheets and globular ore).The cause of sulfur saturation cannot be attributed to the reduction of the solubility of sulfur in the magma by increasing the SiO 2 concentration (contamination), despite the close association of the ore with granophyric segregations in the basal olivine gabbro. Indeed, the major and trace element data argue strongly against wholesale assimilation of crust at any stage in the production of the basal gabbro.

The platiniferous dunite pipes of the eastern Bushveld

The platinum-group mineralogy of the platinum pipes has been well documented in recent years. The same, however, cannot be said for their silicate and oxide constituents. A microscopic study of mineralized and unmineralized dunites, hortonolite dunites, and dunite-bronzitites from the Onverwacht, Mooihoek, and Driekop pipes revealed the presence of one-phase and polyphase spinels.The results of more than 300 microprobe analyses show that pipe deposit-type spinels do not plot within the field of stratiform deposit-type spinels from the chromitite layers of the Bushyeld Complex, because they are characterized by lower Cr-Fe and Mg and, occasionally, higher Ti. There are, however, certain similarities with spinels from the Merensky Reef. Polyphase spinels comprise up to four constituent phases, with increasing reflectance and Fe contents corresponding to decreasing Cr, Al, and Mg. They are interpreted as products of complex postmagmatic processes.Graphite occurs in dunties as globules, as intergranular films between olivine grains, and on fractures in Cr-Ti spinel. Small amounts of sulfides and platinum-group minerals are also found in these locations.Accelerator mass spectrometry of dunites and chromitite reveals extremely low Pt (0.03-38.0 ppb) values. The results suggest that the actual platinum-group element content of the silicates is low, with the platinum-group elements contained in sulfides or platinum-group minerals.Microprobe data and the presence of graphite in the dunites support the concept of metasomatic pipe formation from Fe-rich, late and postmagmatic solutions, with some of the platinum-group elements possibly transported as organometallic compounds. Pegmatoid features, spinel compositions, and graphite encountered in both the pipes and the Merensky Reef suggest a common genetic denominator.